Article

Microsedimentological characterization using image analysis and μ-XRF as indicators of sedimentary processes and climate changes during Lateglacial at Laguna Potrok Aike, Santa Cruz, Argentina

July 2013
Quaternary Science Reviews 71:191–204

July 2013
71:191–204

DOI:10.1016/j.quascirev.2012.06.003

Authors:

Guillaume Jouve

Exail

Pierre Francus

Institut National de la Recherche Scientifique

Scott F. Lamoureux

Queen's University

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A multi-proxy μ-XRF inferred lake sediment record of environmental change spanning the last ca. 2230 years from Lake Kanono, Northland, New Zealand

Article

Oct 2019
QUATERNARY SCI REV

Reliable interpretation of annual-resolution climate proxies for wind, precipitation, and detrital influx are required for identifying the onset and periodicities of climatic events. In particular, this is essential for the evaluation of inter-annual, decadal, and centennial trends driven by shifting positions of the Southern Westerly Winds (SWW) and subsequent storm belts associated with the Southern Annular Mode (SAM) and El Niño Southern Oscillation (ENSO). Here we present a quasi-annual data set of μ-XRF time series spanning ca. 2230 years from lake sediment cores from Lake Kanono, Northland, New Zealand. The μ-XRF time series were interpreted using a combination of principal component analysis (PCA) and cluster analysis, then verified with comparison to regionally averaged empirical rainfall and wind climate station data. Our results show that the wavelet patterns align with the PCA results allowing the μ-XRF time series to be classified into: Group I (detrital) and Group II (biological productivity and normalized climate proxies). The normalized Group II μ-XRF time series wavelet analyses displayed periodicities in the 2–16 year frequency, likely associated with ENSO, from ca. 237 BCE – 1330 CE. The data show clear evidence of both Polynesian and European settlement phases in this part of northern New Zealand, and that Polynesian settlement impact was coeval with changes in ENSO intensity and a phase shift in SAM ca. 1350 CE. The Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) appear in the μ-XRF time series data as separate clusters. This data suggests that the MCA is associated with windy/dry conditions with intermittent storminess. During the LIA, the 2–16 year periodicity associated with ENSO decreased and centennial to multi-decadal length periodicities increase, which may be an indication of an underlying SAM signal within the data. European settlement also had a direct impact on the lake basin via increased detrital influx, likely from farming activities and intensification of local forestry operations.

Past human populations and landscapes in the Fuegian Archipelago, southernmost South America

Article

Full-text available

Apr 2019

This contribution discusses possible relationships between human populations and Holocene environmental deterioration phenomena (cold/arid pulses and volcanic eruptions) in the Fuegian Archipelago (South America), based on summed probability distributions of archaeological dates, paleoenvironmental information, geospatial data, and archaeological evidence. During the first millennia after peopling, only the Hudson (ca. 7700 cal yr BP) and the first Monte Burney (ca. 8600 cal yr BP) eruptions might have played a role in human dispersion. Particularly, a more intense human occupation around the Beagle Channel and long-distance interactions are proposed as risk-buffer strategies related to the Hudson eruption. A cooling phase and a demographic growth at ca. 5500 cal yr BP might have favored more dispersed spatial occupations and a subsistence diversification in the Beagle Channel. In the northern steppes, the second Monte Burney eruption (ca. 4300 cal yr BP) and an arid episode (ca. 2600 cal yr BP) are proposed as the main triggers for changes in land-use patterns, long-network interactions, and subsistence strategies. Even though occupation changes in the Fuegian Archipelago coexist with environmental deterioration episodes after 1500 cal yr BP, demographic processes and the European colonization most likely explain this trend. Similarities between the steppe/ecotone and forest occupation curves suggest common behavioral patterns across the Holocene.

Climatic influence of the latest Antarctic isotope maximum of the last glacial period (AIM4) on Southern Patagonia

Article

Feb 2017
PALAEOGEOGR PALAEOCL

This paper presents the first detailed paleoclimate reconstruction of the latest Antarctic isotope maximum (AIM4, ~ 33–29 ka cal. BP) at 52°S in continental southeastern Argentine Patagonia. High-resolution sedimentological and geochemical analyses of sediments from the maar lake Potrok Aike (PTA) reveal a decrease in the thickness of flood-induced turbidites and a series of wind burst deposits during AIM4, both pointing to increasingly drier conditions. This interpretation is also supported by a significant amount of runoff-driven micropumices incorporated within the sediments that suggests a lower lake level with canyons incising thick tephra deposits around the lake. Increased gustiness and/or dust availability in southeast Patagonia, together with intensified Antarctic circumpolar circulation in the Drake Passage, dust deposition in the Scotia Sea and in Antarctica ice shelf, are consistent with a southward shift of the Southern Westerly Winds (SWW) during the AIM4. In contrast to other warmer AIMs, the SWW during the AIM4 did not migrate far enough south to generate upwelling in the Southern Ocean and they did not reach 52°S in SE Patagonia, as revealed by unchanged values of the rock-magnetic proxy of wind intensity obtained from the same PTA core. Nevertheless, the SWW displacement during AIM4 imposed drier conditions at 52°S in southeast Patagonia likely by blocking precipitation from the Atlantic Ocean, in a way similar to modern seasonal variations and the other Antarctic warm events.

Late Glacial and Holocene Palaeolake History of the Última Esperanza Region of Southern Patagonia

Preprint

Full-text available

Mar 2022

We undertook multiproxy analyses on two sediment cores from Lago Pato, a small lake basin at 51°S topographically separated from Lago del Toro in Torres del Paine (TdP), to provide insights into glacier dynamics and lake level change in the TdP and Última Esperanza region over the last ~30,000 cal a BP (30 ka). Lago Pato is situated in a region overridden by the Southern Patagonian Icefield during the Last Glacial and in a transitional climatic zone of Southern Patagonia sensitive to seasonal- to millennial-scale changes in the Southern Hemisphere Westerly winds (SWW). Results show that a deep ice dammed and enlarged palaeolake encompassed Lago del Toro and Lago Pato c. 30–20 ka, after ice had retreated from local-Last Glacial Maximum (l-LGM) limits at c. 48–34 ka, and during the build-up to the global-Last Glacial Maximum (g-LGM), c. 26–19 ka. Gaps in both sediment records between c. 20–13.4 ka and c. 20–10 ka suggest hiatuses in sediment accumulation during the g-LGM and Antarctic Cold Reversal (ACR) readvances and/or removal by lake lowering or flushing during the Late glacial–early Holocene. The palaeolake level dropped from >100 m a.s.l. to ~40–50 m a.s.l. towards the end of the ACR c. 13.4–13.0 ka, creating a shallower glaciolacustrine environment dammed by an ice tongue in the Estancia Puerto Consuelo–Última Esperanza fjord. Further lowering of the enlarged palaeolake level occurred when the ice thinned to <40 m a.s.l., eventually isolating Lago Pato from Lago del Toro and glaciogenic sediment input at c. 11.7 ka. After isolation, the ecology and water levels in Lago Pato became sensitive to regional climate shifts. The shallow, stable, and highly anoxic environment that developed after c. 11.7 ka is associated with weaker (or poleward shifted) SWW at 51°S and was replaced at c. 10 ka by an increasingly productive shallow-littoral lake with a variable lake-level and periodic shifts in anoxic-oxic bottom water conditions and ratios of benthic-planktonic diatoms. A more open Nothofagus forest, established at c. 8.6–7.5 ka, and more arid conditions c. 7.5–5.7 cal ka BP are linked to another phase of weaker (or poleward shifted) SWW at 51°S. More persistently wet conditions from c. 5.7 ka, with extensive closed Nothofagus forests and planktonic diatoms dominant, are associated with stronger (or equatorward shifted) SWW over 51°S. The abrupt return of benthic-to-tychoplanktonic diatoms after c. 3 ka reflects enhanced SWW at 51°S. Increasingly stable lacustrine and littoral wetland conditions established in the last ~500 years reflect weaker SWW and lasted until recent decades.

Micro-XRF-inferred depositional history of the Orakei maar lake sediment sequence, Auckland, New Zealand

Article

Full-text available

Apr 2022
J PALEOLIMNOL

Lake sediment records offer insights into past climate and environmental changes. There are, however, few continuous lake sediment records from the Southern Hemisphere mid-latitudes that span the last glacial interval (LGI) and have the requisite chronological control and sampling resolution. Orakei maar paleolake in the Auckland Volcanic Field, New Zealand, is an exception, as it contains a high-resolution record of continuous lacustrine sedimentation from its formative phreatomagmatic eruption ~ 130 ka, until post-glacial sea-level rise breached the crater tuff rim and connected the lake to the sea ~ 9 ka. We used micro-XRF core scanning, dry bulk density, loss-on-ignition and visual facies descriptions to investigate the depositional history of Orakei maar lake as a response to regional and global drivers of climate change, and to erosional events in the lake catchment. The climate history of the lake was divided into six depositional phases: (I) Earlywarming with frequent in-wash events, followed by climate fluctuations coeval with marine isotope stages (MIS) 5e to mid-5c, (II) Warm, quiescent depositional conditions during mid-MIS 5c to 5a, (III) A colder, windier interval during MIS 4, (IV) Warmer conditions with dominantly autochthonous sedimentation during MIS 3, (V) Cold conditions followed by a slow temperature increase and the onset of sealevel rise during late MIS 2, (VI) Warm conditions that culminated in formation of a peat unit at the top of the Orakei lacustrine sediment sequence, which was terminated by an influx of massive marine muds into the basin at 9.75 ka. Comparison of the inferred climate evolution at Orakei with climate inferences from the global marine benthic MIS record during LGI shows general agreement, though inferred climate changes consistently occur earlier at Orakei than in the MIS. There is also general agreement in temperature changes inferred from the Orakei record and from other regional lake sediment records, but more detailed comparison requires additional proxy climate data such as pollen, organic geochemistry and biomarkers, to better understand discrepancies between some records. This study demonstrated the great potential of the Orakei record for paleoclimate inference and the applicability of micro-XRF core scanning data for addressing questions about paleoclimate and paleoenvironment. It also highlighted past intervals that require further study.

High-resolution geochemical (μXRF) and palynological analyses for climatic and environmental changes in lake sediments from Sultansazlığı Marsh (Central Anatolia) during the last 14.5 kyr

Article

Sep 2021
QUATERN INT

Multi-proxy analyses of Sultansazlığı Marsh sedimentary sequence covering the last ∼14.5 kyr documents climatic and environmental changes in Central Anatolia (Turkey) and can be correlated with Holocene Rapid Climate Changes (RCCs). Well-correlated geochemical compositions (μXRF), pollen and lithological analyses, together with an age-depth model, were used to determine the time intervals of cold, dry, warm, and wet conditions in Sultansazlığı. Geochemical and pollen data including Younger Dryas (YD) revealed 9 arid periods RCCs; 11.1 ka, 10.3 ka, 9.3 ka, 8.2 ka, 7.3 ka (for this study), 6.5 ka (for this study), 5.9 ka, 4.2 ka, and 2.8 ka. The analysis of glacial advance during the Lateglacial suggests that the climate was cold and wet. YD and two more hiatuses have been accurately determined from the μXRF geochemical proxies. However, YD cold period does not show severe conditions like in other areas in the world. Moreover, the other two hiatuses were clearly determined between Early- Middle and inside the Middle Holocene. In general, the period after 9.8 ka indicates warming conditions towards the recent with some fluctuations compared to an overall trend of the climate.

Phacotus lenticularis content in carbonate sediments and epilimnion in four German hard water lakes

Article

Full-text available

Apr 2020

Autochthonous calcite precipitation is an important process for C-fixation in hard-water lakes, which is mainly induced by the photosynthesis of planktonic microorganisms. Among these, the widespread calcifying green alga Phacotus lenticularis (Ehrenberg) Diesing contributes to biogenic calcite precipitation in temperate regions. Its role in carbonate precipitation needs to be investigated, because there are no studies dedicated to the quantitative contribution of Phacotus shells to long term carbonate sequestration in hard-water lake sediments. In order to fill this gap, the Phacotus shell content in the sediments of four German hard-water lakes was determined and compared to the fraction of Phacotus shells in the total suspended autochthonous calcite of the euphotic zone. It was found that the Phacotus shells contributed at least 10% to the autochthonous carbonate precipitation in the upper water column in three investigated lakes. During a Phacotus mass occurrence with a cell density of 1.8 × 106 Ind L-1 in Lake Hopfensee, even 59% of the 3.6 mg L-1 total carbonate concentration consisted of Phacotus shells. In contrast to this high amount, the topmost basinal sediment contained a Phacotus shell content between 80 and 36,252 individuals per mg dry sediment, representing only 0.02% to 2.28% of the total carbonate sediment content. In a gravity core from Lake Grosser Ostersee, dating back ~150 years, the Phacotus shell content was continuously below 0.24% whereas the shell diameters remained equal to those of living individuals found in the water column proving that Phacotus shells are capable to persist in the sediment after deposition. A main reason for the large discrepancy between Phacotus shell abundance in the euphotic zone and in sediment was found to be the gross authigenic carbonate precipitation, which dilutes the sedimenting Phacotus shells that accumulate exclusively during short and intensive population peaks in summer. Additionally, dissolution of the carbonate shells during sedimentation was proven to be a relevant factor in Lake Igelsbachsee by means of reducing the number of Phacotus shells reaching the lake bottom. These facts explain that short-term high Phacotus carbonate contents of the total suspended carbonate in the water column do not mirror the contribution of Phacotus shells in the sedimentary record.

Climates of the last three interglacials in subtropical eastern Australia inferred from wetland sediment geochemistry

Preprint

Full-text available

Nov 2019

Records of Australian climate during Marine Isotope Stages 5 and 7 (130-71 and 243-191 ka) are rare, preventing detailed assessments of long-term climate, drivers and ecological responses across the continent over glacial-interglacial timescales. This study presents a geochemistry-based palaeoclimate record from Fern Gully Lagoon on North Stradbroke Island (also known as Minjerribah) in subtropical eastern Australia, which records climates in MIS 7a-c, MIS 5 and much of the Holocene, in addition to MIS 4 (71-57 ka), and parts of MIS 6, MIS 3 and MIS 2 (191-130, 57-29 and 29-14 ka). Indicators of inorganic sedimentation from a 9.5 m sediment core-focussed on high-resolution estimates of sediment geochemistry supported by x-radiography, inorganic content and magnetic susceptibility-were combined with a chronology consisting of six radiocarbon (14 C) and thirteen single-grain optically stimulated luminescence (OSL) ages. Hiatuses occurred at ~178-153 ka, ~36-21 ka and ~7-2 ka and likely result from the wetland drying. Low values of locally sourced aeolian materials indicate a wet MIS 7a-c and early MIS 6 before a relatively dry MIS 5. Inorganic flux during the Holocene was up to four times greater than during MIS 5, consistent with long-term interglacial drying observed in other regions, most notably in central Australia. This study highlights the importance of employing a combination of multiple dating approaches and calibrated geochemical proxies to derive climate reconstructions and to identify depositional complexities in organic-rich wetland records.

Climates of the last three interglacials in subtropical eastern Australia inferred from wetland sediment geochemistry

Article

Full-text available

Nov 2019
PALAEOGEOGR PALAEOCL

Records of Australian climate during Marine Isotope Stages 5 and 7 (130–71 and 243–191 ka) are rare, preventing detailed assessments of long-term climate, drivers and ecological responses across the continent over glacial-interglacial timescales. This study presents a geochemistry-based palaeoclimate record from Fern Gully Lagoon on North Stradbroke Island (also known as Minjerribah) in subtropical eastern Australia, which records climates in MIS 7a–c, MIS 5 and much of the Holocene, in addition to MIS 4 (71–57 ka), and parts of MIS 6, MIS 3 and MIS 2 (191–130, 57–29 and 29–14 ka). Indicators of inorganic sedimentation from a 9.5 m sediment core – focussed on high-resolution estimates of sediment geochemistry supported by x-radiography, inorganic content and magnetic susceptibility – were combined with a chronology consisting of six radiocarbon (14C) and thirteen single-grain optically stimulated luminescence (OSL) ages. Hiatuses occurred at ~178–153 ka, ~36–21 ka and ~7–2 ka and likely result from the wetland drying. Low values of locally sourced aeolian materials indicate a wet MIS 7a–c and early MIS 6 before a relatively dry MIS 5. Inorganic flux during the Holocene was up to four times greater than during MIS 5, consistent with long-term interglacial drying observed in other regions, most notably in central Australia. This study highlights the importance of employing a combination of multiple dating approaches and calibrated geochemical proxies to derive climate reconstructions and to identify depositional complexities in organic-rich wetland records.

A 4000-year record of hydrologic variability from the Olympic Mountains, Washington, USA

Article

Full-text available

May 2019

Sedimentological and geochemical analyses of gravity and piston cores retrieved from Lake Quinault, Washington, reveal an ~4000-year flood-dominated depositional record. Individual flood event layers are identified by combining core stratigraphy, sedimentology, and the ratio of incoherent to coherently scattered x-ray radiation (inc/coh) from µXRF (x-ray fluorescence) core scans. The inc/coh time series is used as a proxy for sediment grain size and, in combination with radiocarbon-anchored core age–depth models, enables the reconstruction of late-Holocene hydrologic variability for the Quinault River catchment. Decadal to centennial variability in inc/coh is interpreted to reflect trends in ocean-atmosphere teleconnections favorable for the formation of land-falling atmospheric rivers along the Pacific Ocean flank of the Olympic Mountains. Such processes likely modulate the rate of flooding and may explain notable increases in the frequency of flood event layers observed during the periods 2350–2450 cal. yr BP and the most recent century (AD 1910–2010). Understanding past hydrologic variability has important implications for the landscape and ecosystem response of Olympic Mountain catchments to future climate warming.

Recent hydrological variability of the Moroccan Middle Atlas Mountains inferred from microscale sedimentological and geochemical analyses of lake sediments

Article

Dec 2018

Study of the hydro-sedimentary dynamics of lakes provides key information on hydrological changes. In this work, we investigate Lake Azigza in the Moroccan Middle Atlas, a region that suffers from a scarcity of observational hydrological data necessary for a coherent management of water resources. Sedimentary deposits of Lake Azigza (32°58′N, 5°26′W, 1,550 m above sea level) were dated and analyzed by combining geochemical and mineralogical measurements coupled with microfacies characterization for the last 134 yr. The detrital component derived from X-ray fluorescence elemental composition and microstructures analysis of the lake sediments provided proxies of runoff activity and lake-level changes, respectively. These proxies were calibrated with regional hydro-climatic and instrumental measurements available over the last 50 yr and used to reconstruct past hydrological changes on inter-annual to decadal time scales between 1879 and 2013. Since 1879, lake level and runoff proxies responded in phase to regional inter-annual precipitation variations. We also show that after the major lake-level drop observed in 2008, the response of the runoff proxy to variable precipitation regime is enhanced. Such an approach emphasizes the potential of these hydro-climate-sensitive sedimentary archives to assess the impact of climate change in the Mediterranean region.

Correlation of abiotic proxies in Holocene lacustrine sediments of the peri-Atlantic Arctic

Thesis

Aug 2017

Matěj Roman

Holocene climate and environmental variability in NE Germany inferred from annually laminated lake sediments

Thesis

Feb 2017

Nadine Dräger

Understanding the role of natural climate variability under the pressure of human induced changes of climate and landscapes, is crucial to improve future projections and adaption strategies. This doctoral thesis aims to reconstruct Holocene climate and environmental changes in NE Germany based on annually laminated lake sediments. The work contributes to the ICLEA project (Integrated CLimate and Landscape Evolution Analyses). ICLEA intends to compare multiple high-resolution proxy records with independent chronologies from the N central European lowlands, in order to disentangle the impact of climate change and human land use on landscape development during the Lateglacial and Holocene. In this respect, two study sites in NE Germany are investigated in this doctoral project, Lake Tiefer See and palaeolake Wukenfurche. While both sediment records are studied with a combination of high-resolution sediment microfacies and geochemical analyses (e.g. µ-XRF, carbon geochemistry and stable isotopes), detailed proxy understanding mainly focused on the continuous 7.7 m long sediment core from Lake Tiefer See covering the last ~6000 years. Three main objectives are pursued at Lake Tiefer See: (1) to perform a reliable and independent chronology, (2) to establish microfacies and geochemical proxies as indicators for climate and environmental changes, and (3) to trace the effects of climate variability and human activity on sediment deposition. Addressing the first aim, a reliable chronology of Lake Tiefer See is compiled by using a multiple-dating concept. Varve counting and tephra findings form the chronological framework for the last ~6000 years. The good agreement with independent radiocarbon dates of terrestrial plant remains verifies the robustness of the age model. The resulting reliable and independent chronology of Lake Tiefer See and, additionally, the identification of nine tephras provide a valuable base for detailed comparison and synchronization of the Lake Tiefer See data set with other climate records. The sediment profile of Lake Tiefer See exhibits striking alternations between well-varved and non-varved sediment intervals. The combination of microfacies, geochemical and microfossil (i.e. Cladocera and diatom) analyses indicates that these changes of varve preservation are caused by variations of lake circulation in Lake Tiefer See. An exception is the well-varved sediment deposited since AD 1924, which is mainly influenced by human-induced lake eutrophication. Well-varved intervals before the 20th century are considered to reflect phases of reduced lake circulation and, consequently, stronger anoxic conditions. Instead, non-varved intervals indicate increased lake circulation in Lake Tiefer See, leading to more oxygenated conditions at the lake ground. Furthermore, lake circulation is not only influencing sediment deposition, but also geochemical processes in the lake. As, for example, the proxy meaning of δ13COM varies in time in response to changes of the oxygen regime in the lake hypolinion. During reduced lake circulation and stronger anoxic conditions δ13COM is influenced by microbial carbon cycling. In contrast, organic matter degradation controls δ13COM during phases of intensified lake circulation and more oxygenated conditions. The varve preservation indicates an increasing trend of lake circulation at Lake Tiefer See after ~4000 cal a BP. This trend is superimposed by decadal to centennial scale variability of lake circulation intensity. Comparison to other records in Central Europe suggests that the long-term trend is probably related to gradual changes in Northern Hemisphere orbital forcing, which induced colder and windier conditions in Central Europe and, therefore, reinforced lake circulation. Decadal to centennial scale periods of increased lake circulation coincide with settlement phases at Lake Tiefer See, as inferred from pollen data of the same sediment record. Deforestation reduced the wind shelter of the lake, which probably increased the sensitivity of lake circulation to wind stress. However, results of this thesis also suggest that several of these phases of increased lake circulation are additionally reinforced by climate changes. A first indication is provided by the comparison to the Baltic Sea record, which shows striking correspondence between major non-varved intervals at Lake Tiefer See and bioturbated sediments in the Baltic Sea. Furthermore, a preliminary comparison to the ICLEA study site Lake Czechowskie (N central Poland) shows a coincidence of at least three phases of increased lake circulation in both lakes, which concur with periods of known climate changes (2.8 ka event, ’Migration Period’ and ’Little Ice Age’). These results suggest an additional over-regional climate forcing also on short term increased of lake circulation in Lake Tiefer See. In summary, the results of this thesis suggest that lake circulation at Lake Tiefer See is driven by a combination of long-term and short-term climate changes as well as of anthropogenic deforestation phases. Furthermore, the lake circulation drives geochemical cycles in the lake affecting the meaning of proxy data. Therefore, the work presented here expands the knowledge of climate and environmental variability in NE Germany. Furthermore, the integration of the Lake Tiefer See multi-proxy record in a regional comparison with another ICLEA side, Lake Czechowskie, enabled to better decipher climate changes and human impact on the lake system. These first results suggest a huge potential for further detailed regional comparisons to better understand palaeoclimate dynamics in N central Europe.

Varve microfacies and varve preservation record of climate change and human impact for the last 6000 years at Lake Tiefer See (NE Germany)

Article

Full-text available

Mar 2017

The Holocene sediment record of Lake Tiefer See exhibits striking alternations between well-varved and non-varved intervals. Here, we present a high-resolution multi-proxy record for the past ~6000 years and discuss possible causes for the observed sediment variability. This approach comprises microfacies, geochemical and microfossil analyses and a multiple dating concept including varve counting, tephrochronology and radiocarbon dating. Four periods of predominantly well-varved sediment were identified at 6000–3950, 3100–2850 and 2100–750 cal. a BP and AD 1924–present. Except of sub-recent varve formation, these periods are considered to reflect reduced lake circulation and consequently, stronger anoxic bottom water conditions. In contrast, intercalated intervals of poor varve preservation or even extensively mixed non-varved sediments indicate strengthened lake circulation. Sub-recent varve formation since AD 1924 is, in addition to natural forcing, influenced by enhanced lake productivity due to modern anthropogenic eutrophication. The general increase in periods of intensified lake circulation in Lake Tiefer See since ~4000 cal. a BP presumably is caused by gradual changes in the northern hemisphere orbital forcing, leading to cooler and windier conditions in Central Europe. Superimposed decadal- to centennial- scale variability of the lake circulation regime is likely the result of additional human-induced changes of the catchment vegetation. The coincidence of major non-varved periods at Lake Tiefer See and intervals of bioturbated sediments in the Baltic Sea implies a broader regional significance of our findings.

Aridity and saharian input in alpine lake sediments during the Holocene (Sierra Nevada, Spain)

Article

Sep 2012

Orbital modulation of an intensified hydrological cycle during the Paleocene-Eocene Thermal Maximum

Article

Full-text available

Apr 2024
EARTH PLANET SC LETT

The Paleocene-Eocene Thermal Maximum (PETM, ∼56 Ma) was an abrupt global warming event linked to massive carbon release into the ocean-atmosphere system. As such, it is considered a potentially useful analogue for present and future climate change. Consequently, deciphering its impact on the hydroclimate is important for predicting future changes under high pCO2 and temperature conditions, especially in East Asia where more than a quarter of the world's population lives. Here, we use magnetic and geochemical data obtained through a thick lacustrine record of the PETM from China to demonstrate a large-scale increase in weathering and precipitation coeval with the PETM. Moreover, we show that precipitation variations through the PETM were strongly controlled by eccentricity, precession and half-precession climate cycles. Our results show that orbital forcing of low-latitude insolation played a key role in driving hydroclimate fluctuations and multi-phase changes in precipitation during the PETM, emphasizing the sensitivity of East Asian hydroclimate to subtle changes in insolation under conditions of high temperature and pCO2, perhaps similar to those expected in the future.

Disentangling the impact of anthropogenic and natural processes on the environment in a subtropical subalpine lake catchment in northeastern Taiwan over the past 150 years

Article

Dec 2022
SCI TOTAL ENVIRON

Human activities impose significant changes on sedimentation processes and vegetation cover within lake catchments. However, the needed time for an anthropogenically disturbed natural state to be reversed back to its natural state by environmental protection programs is still ambiguous. Here we employ a multi-proxy approach to delineate major environmental disturbances such as logging and forest fires on the catchment in Cueifong Lake, a subtropical subalpine lake in northeastern Taiwan. X-ray Fluorescence (XRF) core scanning, bulk total organic carbon (TOC), bulk total nitrogen (TN), stable carbon isotope (δ13Corg) analysis, and macro-charcoal counting were utilized to reconstruct changes in the catchment environment based on a sediment core from Cueifong Lake. The results show that the element content changed distinctly around 1975 CE, which coincided with the onset of profound deforestation in the lake vicinity recorded in historical documents and aerial photos. After the cessation of the logging event, the detrital input increased, accompanied by decreasing C/N ratios and increasing δ13Corg values. This suggests that increased terrestrial nutrient input promoted algae growth. After the deforestation phase, our results imply a gradual recovery of elemental composition in the catchment environment. By extrapolating the XRF element records, we suggest that it might take >50 years for the sedimentary regime to reach its pre-logging baseline. In contrast to the depositional system, the C/N and δ13Corg shifted significantly - potentially irreversibly - towards an algae-dominant environment instead of recovering to the pre-logging condition. This could be due to both 1) the changes in the different vegetation species used for reforestation and/or 2) anthropogenically introduced fishes in the 1980s. This study proposes the first assessment of the needed recovery time for subtropical Asian subalpine forests after large-scale logging activity and thus provides an apparent reference for policy decisions on natural resource development and environmental protection.

Southern HemisphereWesterlyWinds have modulated the formation of laminations in sediments in Lago Fagnano (Tierra del Fuego, Argentina) over the past 6.3 ka

Article

Full-text available

Sep 2022
BOREAS

Tierra del Fuego in Argentina is a unique location to examine past Holocene wind variability since it intersects the core of the Southern HemisphereWesterlyWinds (SHWW). TheSHWWare the most powerful prevailing winds on Earth. Their variation plays a role in regulating atmospheric CO2 levels and rainfall amounts and distribution, both today and in the past. We obtained a piston core (LF06-PC8) from Bahía Grande, a protected sub-basin at the southern margin of Lago Fagnano, the largest lake in Tierra del Fuego. This article focuses on the uppermost 185 cm of this core, corresponding to laminated sediment from the last ~6.3 ka. Laminations consist of millimetrescale paired dark and light layers. Previous studies and new geochemical analysis show that the dark and light layers are characterized by differing concentrations of Mn and Fe.We attribute the distribution of Mn and Fe to episodic hypolimnic oxic–anoxic variations. The age model suggests an approximately bidecadal timescale for the formation of each layer pair. We propose a new model of these redox changes with the SHWW variations. The most likely phenomenon to produce complete water-column mixing is thermobaric instability, which occurs in colder winters with low-intensity SHWW (El Niño-like conditions). In contrast, windier winters are characterized by highertemperatures and reduced mixing in the water column, facilitating a decline in oxygen concentration. Laminations, and the inferred presence of periodic hypolimnion redox changes, are common features of the past ~6.3 ka. Geochemical proxy variability is compatible with an intensification of El Niño/Southern Oscillation activity during the past ~2 ka

Abrupt climate changes and extreme events in two different varved lake sediment records

Thesis

Full-text available

Aug 2022

Daniela J. M. Müller

Different lake systems might reflect different climate elements of climate changes, while the responses of lake systems are also divers, and are not completely understood so far. Therefore, a comparison of lakes in different climate zones, during the high-amplitude and abrupt climate fluctuations of the Last Glacial to Holocene transition provides an exceptional opportunity to investigate distinct natural lake system responses to different abrupt climate changes. The aim of this doctoral thesis was to reconstruct climatic and environmental fluctuations down to (sub-) annual resolution from two different lake systems during the Last Glacial-Interglacial transition (~17 and 11 ka). Lake Gościąż, situated in the temperate central Poland, developed in the Allerød after recession of the Last Glacial ice sheets. The Dead Sea is located in the Levant (eastern Mediterranean) within a steep gradient from sub-humid to hyper-arid climate, and formed in the mid-Miocene. Despite their differences in sedimentation processes, both lakes form annual laminations (varves), which are crucial for studies of abrupt climate fluctuations. This doctoral thesis was carried out within the DFG project PALEX-II (Paleohydrology and Extreme Floods from the Dead Sea ICDP Core) that investigates extreme hydro-meteorological events in the ICDP core in relation to climate changes, and ICLEA (Virtual Institute of Integrated Climate and Landscape Evolution Analyses) that intends to better the understanding of climate dynamics and landscape evolutions in north-central Europe since the Last Glacial. Further, it contributes to the Helmholtz Climate Initiative REKLIM (Regional Climate Change and Humans) Research Theme 3 “Extreme events across temporal and spatial scales” that investigates extreme events using climate data, paleo-records and model-based simulations. The three main aims were to (1) establish robust chronologies of the lakes, (2) investigate how major and abrupt climate changes affect the lake systems, and (3) to compare the responses of the two varved lakes to these hemispheric-scale climate changes. Robust chronologies are a prerequisite for high-resolved climate and environmental reconstructions, as well as for archive comparisons. Thus, addressing the first aim, the novel chronology of Lake Gościąż was established by microscopic varve counting and Bayesian age-depth modelling in Bacon for a non-varved section, and was corroborated by independent age constrains from 137Cs activity concentration measurements, AMS radiocarbon dating and pollen analysis. The varve chronology reaches from the late Allerød until AD 2015, revealing more Holocene varves than a previous study of Lake Gościąż suggested. Varve formation throughout the complete Younger Dryas (YD) even allowed the identification of annually- to decadal-resolved leads and lags in proxy responses at the YD transitions. The lateglacial chronology of the Dead Sea (DS) was thus far mainly based on radiocarbon and U/Th-dating. In the unique ICDP core from the deep lake centre, continuous search for cryptotephra has been carried out in lateglacial sediments between two prominent gypsum deposits – the Upper and Additional Gypsum Units (UGU and AGU, respectively). Two cryptotephras were identified with glass analyses that correlate with tephra deposits from the Süphan and Nemrut volcanoes indicating that the AGU is ~1000 years younger than previously assumed, shifting it into the YD, and the underlying varved interval into the Bølling/Allerød, contradicting previous assumptions. Using microfacies analyses, stable isotopes and temperature reconstructions, the second aim was achieved at Lake Gościąż. The YD lake system was dynamic, characterized by higher aquatic bioproductivity, more re-suspended material and less anoxia than during the Allerød and Early Holocene, mainly influenced by stronger water circulation and catchment erosion due to stronger westerly winds and less lake sheltering. Cooling at the YD onset was ~100 years longer than the final warming, while environmental proxies lagged the onset of cooling by ~90 years, but occurred contemporaneously during the termination of the YD. Chironomid-based temperature reconstructions support recent studies indicating mild YD summer temperatures. Such a comparison of annually-resolved proxy responses to both abrupt YD transitions is rare, because most European lake archives do not preserve varves during the YD. To accomplish the second aim at the DS, microfacies analyses were performed between the UGU (~17 ka) and Holocene onset (~11 ka) in shallow- (Masada) and deep-water (ICDP core) environments. This time interval is marked by a huge but fluctuating lake level drop and therefore the complete transition into the Holocene is only recorded in the deep-basin ICDP core. In this thesis, this transition was investigated for the first time continuously and in detail. The final two pronounced lake level drops recorded by deposition of the UGU and AGU, were interrupted by one millennium of relative depositional stability and a positive water budget as recorded by aragonite varve deposition interrupted by only a few event layers. Further, intercalation of aragonite varves between the gypsum beds of the UGU and AGU shows that these generally dry intervals were also marked by decadal- to centennial-long rises in lake level. While continuous aragonite varves indicate decadal-long stable phases, the occurrence of thicker and more frequent event layers suggests general more instability during the gypsum units. These results suggest a pattern of complex and variable hydroclimate at different time scales during the Lateglacial at the DS. The third aim was accomplished based on the individual studies above that jointly provide an integrated picture of different lake responses to different climate elements of hemispheric-scale abrupt climate changes during the Last Glacial-Interglacial transition. In general, climatically-driven facies changes are more dramatic in the DS than at Lake Gościąż. Further, Lake Gościąż is characterized by continuous varve formation nearly throughout the complete profile, whereas the DS record is widely characterized by extreme event layers, hampering the establishment of a continuous varve chronology. The lateglacial sedimentation in Lake Gościąż is mainly influenced by westerly winds and minor by changes in catchment vegetation, whereas the DS is primarily influenced by changes in winter precipitation, which are caused by temperature variations in the Mediterranean. Interestingly, sedimentation in both archives is more stable during the Bølling/Allerød and more dynamic during the YD, even when sedimentation processes are different. In summary, this doctoral thesis presents seasonally-resolved records from two lake archives during the Lateglacial (ca 17-11 ka) to investigate the impact of abrupt climate changes in different lake systems. New age constrains from the identification of volcanic glass shards in the lateglacial sediments of the DS allowed the first lithology-based interpretation of the YD in the DS record and its comparison to Lake Gościąż. This highlights the importance of the construction of a robust chronology, and provides a first step for synchronization of the DS with other eastern Mediterranean archives. Further, climate reconstructions from the lake sediments showed variability on different time scales in the different archives, i.e. decadal- to millennial fluctuations in the lateglacial DS, and even annual variations and sub-decadal leads and lags in proxy responses during the rapid YD transitions in Lake Gościąż. This showed the importance of a comparison of different lake archives to better understand the regional and local impacts of hemispheric-scale climate variability. An unprecedented example is demonstrated here of how different lake systems show different lake responses and also react to different climate elements of abrupt climate changes. This further highlights the importance of the understanding of the respective lake system for climate reconstructions.

Multi-análisis del esqueleto postcraneal del rumiante basal Nanotragulus (Artiodactyla:Hipertragulidae) del Oligoceno Temprano en Santiago Yolomécatl, Oaxaca, México

Thesis

Feb 2022

Perla Guadalupe Butrón Xancopinca

Los elementos postcraneales de Nanotragulus se han recolectado de sedimentos fluvio-lacustres del Oligoceno temprano en Santiago Yolomécatl, al noroeste de Oaxaca. La fauna del sitio ha recibido el nombre de la Fauna local Iniyoo, y se localiza en el margen de un cuerpo de agua lacustre que frecuentemente recibía aporte sedimentario de lugares cercanos. Los elementos postcraneales incluyen vértebras, radio-ulnas, huesos radiales, metapodiales, un húmero, tibias, calcáneos, astrágalos, falanges y costillas fragmentadas, los cuales mostraron diferencia de tamaño y sugirieron la presencia de dos morfotipos en la muestra. A través de análisis univariados y multivariados, los astrágalos rechazaron la posibilidad de un solo morfotipo de Nanotragulus, demostrando que el cambio de tamaño está relacionado a la preferencia de hábitat. Se sugiere que el morfotipo más grande estuvo mejor adaptado a zonas abiertas mientras que el pequeño prefería zonas cerradas. Los resultados de los análisis mineralógicos junto con la fauna asociada, permitieron inferir dos hábitats que cubren desde áreas abiertas en su mayoría representadas por árboles y arbustos y el otro representado por áreas boscosas cerradas con dominio de árboles. El clima era semi-árido y subhúmedo con lapsos de sequía e inundación. Los análisis tafonómicos sugieren que existieron etapas de inundación donde los restos fueron dispersados y transportados a corta distancia por flujos hidráulicos de baja energía hacia su sitio de entierro final. El transporte se considera escaso y de baja energía debido a la excelente conservación de los fósiles, en gran parte debido a la estructura resistente e impermeable de la montmorillonita. Las modificaciones físicas incluyeron agrietamientos, descamación, fragmentación, hoyos y perforaciones, óxido de manganeso, marcas en forma de “V” por arrastre, marcas de raíces de plantas, reemplazamiento por cristales de calcita y digestión. En menor cantidad, las modificaciones biológicas incluyen mordeduras de roedor, decoloración ósea, intemperismo, fracturas por pisoteo y abrasión. En cuanto a la comparación en el tamaño con especímenes de Estados Unidos, Nanotragulus de la Fauna Local Iniyoo era mucho más grande que sus contemporáneos. Además, su distribución geográfica se expande 1,400 km al sur constituyendo el registro más sureño del género en Norteamérica.

PALEOENVIRONMENTAL ANALYSIS OF A LOWER CRETACEOUS PALEOLAKE FROM THE IGUATU BASIN BASED ON ITS OSTRACOD FAUNA AND XRF DATA

Article

Dec 2021

This paper presents the results of a paleoenvironmental study of two Hauterivian–Aptian adjacent sections (Transnordestina A/B) of the Iguatu Basin using ostracods and aided by X-ray fluorescence (XRF), total organic carbon (TOC), total sulfur (S), and spectral analyses. Cluster analysis divided the 10 genera found into two main groups: one composed of Alicenula-Pattersoncypris?-Brasacypris-Hastacypris-Ilyocypris?, and the second composed of Cypridea-Looneyellopsis-Rhinocypris?. The first group is interpreted as representing paleoenvironments with permanent waterbodies, such as lakes, and the second as being indicative of ephemeral settings, such as temporary pools in an inundation plain. XRF analysis using the positive peaks of Ca/Ti and Ca/ΣTi, Fe, Al ratios show a few dry periods, particularly in the lower and middle part of Transnordestina A, between 0 to 175 m and 385 to 475 m, which also display a small number of ostracods. Total S shows several high peaks which might be indicative of gypsum deposition during droughts. Spectral analysis of molar Ti/Al ratio shows two intervals with different sedimentation rates, between 0 and 233 m, and 233 to 836 m. For the first interval, six 100 ka eccentricity cycles were identified; the low number of ostracods for the interval and highly variable Ca/Ti and Ca/ΣTi, Fe, Al values indicate a different sedimentation rate in a drier environment. For the second interval, ten 405 ka cycles were identified; its higher ostracod count and more stable Ca/Ti and Ca/ΣTi, Fe, Al values could be indicative of increasing humidity.

Hydroclimate change in the Garhwal Himalaya, India at 4200 yr BP coincident with the contraction of the Indus civilization

Article

Full-text available

Nov 2021

High-resolution analysis of a 3.80 m sediment core recovered from Deoria Tal, a mid-elevation lake located at 2393 m a.s.l. in the Garhwal Himalaya, documents long-term and abrupt hydroclimate fluctuations in northern India during the mid- to late Holocene. The sediment chronology, based on ten 14C dates, indicates the core spans 5200 years. Non-destructive, radiological imaging approaches (X-ray fluorescence (XRF), X-ray imaging, and CT scans) were used to assess the response of the lake system to changing hydroclimatic conditions. Variations in elemental concentrations and sediment density evidenced notable hydroclimate change episodes centered at 4850, 4200, and 3100 cal yr BP. Elevated detrital input, greater sediment density, decreased lake ventilation, and lower autochthonous productivity reflects lake deepening between 4350 and 4200 cal yr BP. An abrupt shift in elemental concentrations and sediment density indicated the onset of lake drawdown at 4200 cal yr BP and a negative hydroclimate anomaly between 4200 and 4050 cal yr BP. Lower detrital flux, decreased sediment density, increased oxygenation, and higher autochthonous productivity, reflects a reduction in lake volume between 3200 and 3100 cal yr BP. The potential link between abrupt climate change at 4200 cal yr BP and the contraction of the Indus civilization is explored.

A multi-proxy record of environmental change through the last 53,000 years recorded in the sediments of Lake Kanono, Northland, New Zealand

Article

Oct 2021

Lake sediment archives from Southern Hemisphere mid-latitude regions provide invaluable records of late Quaternary environmental change. Here, changes in depositional environment over the past ca. 53,000 years were reconstructed using a range of physical, sedimentological, geochemical, and μ-XRF elemental proxy datasets analyzed from lake sediment cores obtained from Lake Kanono, Northland, New Zealand. The Lake Kanono stratigraphy displays a terrestrial peat environment (ca. 53,700–6,670 cal yr BP), followed by a trend of increased influx of detrital sediment during the Late Glacial–Interglacial Transition (LGIT) at ca. 14,000 cal yr BP with a peak from ca. 12,000 to 9,000 cal yr BP driven by increasingly dry conditions. The increase in sediment influx continued during the early to mid-Holocene, leading to dune reactivation which altered the catchment dynamics of the region, leading to the inception of a shallow lake basin at ca. 6,670 cal yr BP. The timing of the formation of this lake basin can be associated with changes in intensity of the Southern Westerly Winds (SWW) and the appearance and increase in intensity of the El Niño Southern Oscillation (ENSO) after ca. 7,500–7,000 cal yr BP (Moy et al. 2002; Moreno et al. 2018). Drier conditions peaked from ca. 4,000 to 2,400 cal yr BP, possibly culminating in decreased lake levels that persisted from ca. 2,400 to 2,210 cal yr BP, renewed dune accumulation, and blocked stream outlets, resulting in a deep lake basin with thermal stratification that persisted to the present. Cluster analysis of the μ-XRF data demonstrates that the most prominent change in chemistry is near the onset of the Last Glacial Maximum (LGM) at ca. 26,700 cal yr BP associated with a transition to a drier, windier climate. The second most prominent change in the μ-XRF data is during the Polynesian phase of human settlement at ca. 612–575 cal yr BP (1338– 1375 CE). Hence, we can demonstrate the utility and power of a multi-proxy approach coupled with μ-XRF element data to interpret changing sediment sources to a lake basin. Such an approach allows rapid and reliable evaluation of catchment processes influenced by climate events and land-use changes at a resolution not available using other approaches.

A high-resolution paleoclimate record from SE Iran reveals extreme sensitivity of West Asia to temperature changes since the Little Ice Age

Conference Paper

Sep 2021

The dearth of high-resolution climate records for the past millennium has largely limited our understanding of the impacts of natural (e.g., the Little Ice Age: LIA) and anthropogenic climate perturbations (i.e., the ongoing global warming) on the arid regions of West Asia (also referred to as the Middle East). Here, we present multiproxy records including compound-specific δ13C signature of leaf-wax-derived n-alkanes (δ13Cn-C29), elemental and mineralogical compositions, total organic and inorganic carbon contents, C/N ratio, biogenic silica content and magnetic susceptibility of a 550 cm-long lacustrine sediment core retrieved from Sardarya Lake, SE Iran, spanning the period 1450-2017 AD. In our archive, n-alkane C29 is the dominant homologue and primarily derived from Artemisia herba-alba shrubs—a C3 plant prevailing on the slopes overlooking the lake. Compound-specific δ13Cn-C29 values fluctuate in the range of C3 plants (-29.4 to -32.1‰ VPDB) with enriched (depleted) values corresponding to episodes of decreased (increased) lake levels reconstructed using the Rb/Sr ratio, as well as with the significant presence of evaporitic minerals such as aragonite, gypsum and calcite, corroborating the applicability of δ13Cn-C29 as a proxy for plant water use efficiency (i.e., water stress). Our proxy data reveal three distinct climate intervals: (I) arid LIA (1450-1830 AD), (II) wet post-LIA (1830-1990 AD), and (III) arid recent decades (1990-2017 AD). The increased climate aridity during the LIA shows a link to the decrease in solar activity with the driest conditions being synchronous with the Maunder Minimum (1645-1715 AD), which is thought to be the coldest part of the LIA. On the contrary, the recent dry decades, which appear as severe as those during the LIA, coincide with the climax of human-caused global warming. Thus, our findings reveal an extreme sensitivity and vulnerability of the arid regions of West Asia to rather small natural and anthropogenic temperature changes. This highlights the need for forward-looking collaborative policies to mitigate future impacts of the ongoing global warming and to lessen the risk of droughts as a potential exacerbating factor for social upheavals in West Asia.

Holocene high-resolution forest-steppe and environmental dynamics in the Tarvagatai Mountains, north-central Mongolia, over the last 9570 cal yr BP

Article

Aug 2021
QUATERNARY SCI REV

The Tarvagatai Nuruu National Park, situated in the northern Khangai Mountains in central Mongolia, is dominated by a forest-steppe ecosystem. An extreme continental and semi-arid climate is characteristic for forest-steppe ecosystems in Central Asia and their vegetation is very sensitive to climatic changes and human impacts by pastoralism and tree-logging. In the selected study area, nowadays human impact is exceptionally low, and it has potentially also been in the past. The focus of this paper was to reconstruct vegetation variability, climate dynamics, intensity of human impact and fire dynamics by applying a broad multi-proxy approach on a lacustrine sediment core from a small closed lake in the study area. The analyses include reconstructions of pollen, spores, non-pollen palynomorphs, and charcoal distribution as well as XRF-scanning. Overall, the radiocarbon-dated lacustrine sediment core reveals stable, long-term environmental conditions since the early Holocene (9570 cal yr BP). Palynological results indicate that vegetation varies on a comparably low level. We assume that nomadic pastoralism played a tangential role on the vegetation changes in the study area. Higher values of coprophilous fungi between 9570 and 8350 cal yr BP suggest the highest wildlife activity during the early Holocene. Hence, our multi-proxy data reveal a surprisingly stable vegetation composition and only slight climatic changes in north-central Mongolia for the entire Holocene. An initial moist and warm period from 9570 to 4180 cal yr BP was followed by a period of slightly drier and potentially cooler conditions from 4180 until 430 cal yr BP. The latest period from 430 cal yr BP to present was moist and warm. Fires were in general relatively rare except from a strong phase of fire activity between 3550 and 2960 cal yr BP.

Living environment of the early Jehol Biota: A case study from the Lower Cretaceous Dabeigou Formation, Luanping Basin (North China)

Article

Mar 2021

The Jehol Biota of northern China provides a new and unmatched window for the reconstruction and understanding of Early Cretaceous terrestrial ecosystems. Previous studies on the paleoenvironmental and paleoclimatic background of the Jehol Biota have mainly focused on middle–late evolutionary stages while the less diverse and more narrowly distributed early Jehol Biota remains less understood. The Lower Cretaceous (Valanginian–Hauterivian) Dabeigou Formation in the Luanping Basin (North China), preserves the early stages of the Jehol Biota and can be subdivided into three members. To reconstruct the living environment of the early Jehol Biota, we explored the geochemistry, bulk mineralogy, total organic carbon, sedimentology, and paleoecology of the Dabeigou Formation from the Yushuxia section of the Luanping Basin. Decreased volcanic activity during the deposition of the Dabeigou Formation resulted in changes in its source material from felsic to mafic. The Luanping palaeolake reached its deepest water depth during deposition of the Member 2, and generally exhibited low salinity, while a short time of high salinity occurred during deposition of the Member 3. Analysis on the paleoweathering indices and other evidences, indicate that the Luanping area was generally in cold and humid climate conditions during deposition of the members 1 and 2 (correlated to the Weissert Event), but changed to warm climate conditions during deposition of the Member 3, which coincides with an increasing trend of biotic diversity. Consequently, our results suggest that the increasingly warm paleoclimate and lacustrine productivity, associated with decreasingly volcanic activity in North China, have contributed to the early evolution of the Jehol Biota.

Varve microfacies and chronology from a new sediment record of Lake Gościąż (Poland)

Article

Jan 2021
QUATERNARY SCI REV

The varved sediment of Lake Gościąż (Central Poland) is one of the most detailed and complete climate archives of the Late Glacial and the Holocene in Central Europe. Here, we present microfacies analyses in combination with μXRF core scanning and a detailed varve chronology of a new and continuous GOS18 sediment record. This record presents six lithozones that mark the most prominent depositional and geochemical changes during the Holocene and Late Glacial. Varve boundaries and five main varve microfacies types were distinguished under petrographic microscope. Analysis provides detailed insights into depositional processes and its changes since the Late Glacial. Microfacies components were used to interpret processes leading to varve formation. A new and independent chronology is obtained by triple varve counting on petrographic thin sections that is complemented by ¹³⁷Cs measurements and ¹⁴C AMS dating of terrestrial plant remains. The age-depth model consists of three parts: (1) the upper part (0–520 cm) that is primarily based on varve counting, (2) the middle part (520–758 cm) obtained through age-depth modelling and (3) the lower part (758–1897 cm) developed by varve counting. The bottom of the composite profile coincides with the onset of lacustrine sedimentation in the late Allerød at 12,834 +134/-233 varve yr BP. The largest shift in geochemistry, expressed by log(Ca/Ti) and log(Si/Ti) ratios show a rapid increase of calcite precipitation and primary productivity at 7940 +112/-168 varve yr BP. Possible triggers for this include local changes in hydrology as the formation of “Na Jazach” system due to the Ruda River development and fluctuations of lake water level.

A multiproxy analysis of extreme wave deposits in a tropical coastal lagoon in Jamaica, West Indies

Article

Full-text available

Dec 2020
NAT HAZARDS

The Small Island Developing States (SIDS) of the Caribbean Region are vulnerable to natural hazards including earthquakes, tsunamis and tropical cyclones that can cause widespread devastation. Sedimentary archives of these hazards are often well-preserved in coastal lagoons; however, few studies in the Caribbean have adopted a multiproxy approach to their reconstruction. Here, we present a 1200-year multiproxy record of extreme washover events deposited within a coastal mangrove lagoon on the south coast of Jamaica. Manatee Bay lagoon is a permanent fresh-brackish-water mangrove lagoon separated from the Caribbean Sea by a low-elevation carbonate beach. Fifteen sediment cores recovered along five shore-normal transects contain ostracod-rich authigenic carbonate lake muds interspersed with beds of organic lake mud and mangrove peat. The cores contain evidence of multiple palaeo-washover deposits that are readily distinguished by their sedimentology, geochemistry and microfossil assemblages. Hypersaline conditions dominated the early part of the record (~ 800 to 900 CE), and we infer a freshening of lagoonal waters and the subsequent expansion of the mangrove community following an extreme wave event that occurred some time before ~ 1290 to 1400 CE. We constrain the primary historical-washover deposit to 1810–1924 CE (2σ; 71% probability), a period characterised by extreme tectonic and meteorological events, which include the Great Kingston Earthquake of 1907 and a local episode of enhanced hurricane activity. Whilst the balance of circumstantial evidence indicates that the deposit was probably emplaced during the tsunami generated by the 1907 earthquake, we are currently unable to differentiate between tectonically and meteorologically driven washover events based on their sedimentological characteristics.

Ostracoda (Crustacea) as indicators of subaqueous mass movements: An example from the large brackish lake Tangra Yumco on the southern Tibetan Plateau, China

Article

Sep 2015

Lailah Gifty Akita

A multi-proxy paleoenvironmental interpretation spanning the last glacial cycle (ca. 117 – 8.5 ka BP) from a lake sediment stratigraphy from Lake Kai Iwi, Northland, New Zealand

Article

Full-text available

Jan 2021
J PALEOLIMNOL

A 9.3-m-long lake sediment core from dune-impounded Lake Kai Iwi in Northland, New Zealand provides a nearly continuous record of environmental changes from multi-proxy organic, physical index, and l-XRF elemental data sets. The chronology for the upper 3 m of the core was established by 210Pb, 14C and tephrochronology and includes Marine Isotope Stage (MIS) 1 (Holocene), MIS 2 and late MIS 3. From this well-dated section of the core stratigraphy we were able to infer the environmental proxies that respond to wind and/or precipitation during cool periods (MIS 2 and 4) and with the warm periods (MIS 1 and 5). Principal component analysis (PCA) and cluster analysis were performed on the l-XRF elemental data set including elements common in lake sediments (P, S, Fe, Ti, K, Ca, and Si) and five ratios (Sr/Ca, Br/Cl, Mn/Fe, Ti/K, and Inc/coh) to identify patterns in the l-XRF proxy data associated with environmental change manifesting as changes in precipitation and wind deposition. The PCA indicates that Component (PC)-1 represents detrital versus organic deposition, and PC-2 is associated with nutrient influx versus anoxic conditions in the lake. The cool periods of MIS 2 and 4 are apparentin the l-XRF data as having increased detrital influx in the form of Sr/Ca from marine derived sediments from the exposed continental shelf during low sea level indicating cool and dry conditions. Warmer and wetter periods (MIS 1 and 5) are identified by increased Ti/K influx from precipitation runoff and increased organic productivity as shown by Inc/coh and total organic carbon. The Holocene warm equivalent conditions of MIS 5e are not represented in the lower part of the Lake Kai Iwi core stratigraphy consistent with an extrapolated basal age of 117 ± 8.5 ka BP.

Late Holocene paleoenvironmental records in Eastern Bangladesh from lake sediments: A multi-proxy approach

Article

Full-text available

Aug 2020
QUATERN INT

Lacustrine sediments in a poorly documented region regarding to lake sedimentation and paleo-environments (Bangladesh) were investigated using a multiproxy approach. Pukurpara Lake is located in eastern Bangladesh at an elevation of 360 m above sea level with a maximum water depth of 28 m. An age-depth model allowed us to investigate the changes in sedimentation that occurred since 850 CE. The high resolution multielement analyses by micro-X fluorescence scanning (μXRF) showed multiple variations over short increments. Variation in the abundance of elements with depth as well the ratios of the abundance of some elements (Fe/Ti and Zr/Rb) suggested both rapid and long-term changes in the origin of the material deposited, which, in turn, suggested changes in weather conditions. Principal Components Analysis (PCAs) mixing μXRF and Magnetic Susceptibility data allow identifying changes in geochemical redox processes between the Medieval Warm Period (MWP) and Little Ice Age (LIA). The drastic changes in the different proxies (magnetic susceptibility, diatom assemblages, fresh water/marine water diatom ratios, abundance of Fe and S, and the Fe/Ti ratio) were interpreted to be the result of climate change before and after the MWP-LIA transition period, the Little Ice Age period being relatively wet.

2,100 years of human adaptation to climate change in the High Andes

Article

Full-text available

Jan 2020
Nat. Ecol. Evol.

Humid montane forests are challenging environments for human habitation. We used high-resolution fossil pollen, charcoal, diatom and sediment chemistry data from the iconic archaeological setting of Laguna de los Condores, Peru to reconstruct changing land uses and climates in a forested Andean valley. Forest clearance and maize cultivation were initiated during periods of drought, with periods of forest recovery occurring during wetter conditions. Between ad 800 and 1000 forest regrowth was evident, but this trend was reversed between ad 1000 and 1200 as drier conditions coincided with renewed land clearance, the establishment of a permanent village and the use of cliffs overlooking the lake as a burial site. By ad 1230 forests had regrown in the valley and maize cultivation was greatly reduced. An elevational transect investigating regional patterns showed a parallel, but earlier, history of reduced maize cultivation and forest regeneration at mid-elevation. However, a lowland site showed continuous maize agriculture until European conquest but very little subsequent change in forest cover. Divergent, climate-sensitive landscape histories do not support categorical assessments that forest regrowth and peak carbon sequestration coincided with European arrival. Multi-proxy palaeoecological methods reconstruct phases of land clearance, maize cultivation and forest regrowth in the High Andes centuries before European incursion, and do not support the idea that forest regrowth and peak carbon sequestration were coincident with European arrival.

Abrupt changes in Indian summer monsoon strength during the last deglaciation and early Holocene based on stable isotope evidence from Lake Chenghai, southwest China

Article

Aug 2019
QUATERNARY SCI REV

Identifying variability and the mechanisms driving variability in the Indian summer monsoon (ISM) since the last deglaciation is critical for understanding past hydroclimatic change. In this study, we present an accelerator mass spectrometry radiocarbon dated record of δ¹⁸O variations in authigenic carbonates derived from Lake Chenghai in southwest China, a region that receives moisture mainly from the Indian Ocean. The δ¹⁸O values vary from −11.9 to +0.1‰, providing a detailed record of variations in ISM precipitation δ¹⁸O values, and lake hydrological balance. The record shows that the ISM generally strengthened in the post-glacial between 15.6 and 8.8 cal ka BP, but that three centennial to millennial-scale drought events were superimposed on the long-term trend. Drought events, as indicated by substantial positive shifts in δ¹⁸O value, occurred from 15.6 ± 0.2 to 14.4 ± 0.2, 12.5 ± 0.2 to 11.7 ± 0.2 and 10.1 ± 0.1 to 10.0 ± 0.1 cal ka BP, corresponding to the Heinrich 1, Younger Dryas, and Bond 7 cold events in the North Atlantic region, respectively. The timings of these droughts are suggested to be related to meltwater discharge into the North Atlantic. The weakened Atlantic Meridional Overturning circulation, which leads in turn to the southward migration of the intertropical convergence zone and cooling in the tropical Indian Ocean.

Tracing lake mixing and oxygenation regime using the Fe/Mn ratio in varved sediments: 2000 year-long record of human-induced changes from Lake Żabińskie (NE Poland)

Article

Dec 2018
SCI TOTAL ENVIRON

This study explores the long-term drivers of changes in lake mixing regime and the causes of lacustrine anoxia in the 2000 year-long, varved sediment record from Lake Żabińskie in northeastern Poland. Annually resolved geochemical data (μXRF and CNS) and pollen data were used to find links between changes in catchment land use and lake mixing regime. Furthermore, we tested the applicability of the Fe/Mn ratio for the reconstruction of past water ventilation. Multivariate statistical analyses show that Fe and Mn were mostly independent of terrestrial inputs and lake trophy, meaning that the Fe/Mn ratio mainly responded to changes in redox potential in hypolimnetic waters. Characteristic changes of the Fe/Mn ratio corresponded to transformations of woodland cover in the catchment as registered by changes of the arboreal/non-arboreal pollen ratio. Six main phases of different lake mixing intensity were distinguished. The local landscape was more open during phases of intensified human impact and catchment deforestation, leading to the intensification of lake mixing. At times of negligible human impact, the catchment was mostly wooded, and thus the lake was well sheltered from intense wind-driven mixing. This led to periods of prolonged anoxia. The Fe/Mn record accurately traced past changes in lake mixing intensity and related shifts in water column oxygenation. During the last two millennia, the mixing regime of Lake Żabińskie mostly depended on human activity in the catchment and landscape openness, while long periods of anoxia were not exclusive to only the most recent sediments.

Reconstrucción paleoambiental de la subcuenca de Xochimilco, centro de México, entre 18000 y 5000 años antes del presente

Article

Full-text available

Nov 2018

Presentamos un registro de las oscilaciones de escala milenaria de un sitio en la cuenca de Xochimilco (parte central de México) entre ca. 18000 y 5000 años cal AP, derivado de indicadores de mineralogía magnética, contenido de elementos mayores y asociación de diatomeas. La edad de la secuencia sedimentaria analizada está definida por el reconocimiento de dos marcadores estratigráficos ampliamente usados en esta región: la Pómez Tutti Frutti del Popocatépetl (ca. 17070 años cal AP) y la Pómez Toluca Superior del Nevado de Toluca (ca. 12320 años cal AP). Adicionalmente, se dispone de una edad de 14C de un concentrado de ostrácodos. Las variaciones temporales en susceptibilidad magnética (χ), abundancia de óxidos y oxihidróxidos de Fe (hematita y goethita), minerales magnéticos ultrafinos, titanio, carbón orgánico e inorgánico, así como las relaciones hierro/titanio, calcio/titanio, carbono orgánico/nitrógeno, silicio/titanio y contenido de diatomeas, indican variaciones en la erosión, origen de los minerales de Fe, salinidad, productividad y origen de la materia orgánica. Estas variaciones responden a oscilaciones climáticas de escalas milenarias. Durante la deglaciación (18000 y 11700 años cal AP), ocurrió una actividad volcánica intensa y este periodo está caracterizado por la dominancia de sedimentación clástica en un lago somero de agua dulce. Los eventos Heinich 1 (frío), Bølling/Allerød (cálido) y Younger Dryas (frío) se documentan con variaciones en la erosión, el contenido de materia orgánica y la precipitación de carbonatos. Durante el Holoceno temprano (11700–8200 años cal AP), se registraron las condiciones más secas de toda la secuencia. El Holoceno medio (8200–5000 años cal AP) registró un retorno a condiciones húmedas y el establecimiento de un lago de agua dulce, que probablemente favorecieron el desarrollo de comunidades en la ribera del lago.

Middle to late Holocene palaeoenvironmental study of Gialova Lagoon, SW Peloponnese, Greece

Article

Full-text available

Mar 2018
QUATERN INT

The coastal areas of Eastern Mediterranean have long been the subject of research, due to their rapid geomorphological changes, but also because of their archaeological interest. Our study is focused on a shallow coastal lagoon of Peloponnese, Gialova Lagoon, which for several years has attracted the scientific interest of archaeologists, geomorphologists as well as sedimentologists. Gialova lagoon is located near the ancient city of Pylos, the kingdom of king Nestor during the Mycenaean period (1600–1100 BC). The objectives of this study are: (a) to reconstruct the middle to late Holocene depositional environments of the lagoon and (b) to correlate our data to already existing publications, in order to shed new light on the Holocene evolution of the lagoon and the associated coastal palaeoenvironmental changes. An 8 m deep vibracore was drilled and a multi proxy analysis was carried out on the sediment sequence, including sedimentological (grain size analysis and moment measures, total organic carbon – TOC, total nitrogen – TN and total phosphorus – TP), high resolution geochemical (XRF-scanning) and palaeontological (micro- and macro faunal) analysis. The chronological framework is based on five ¹⁴C datings forming the basis for an age depth model, calculated using the OxCal software. The radiocarbon dates from previous studies (6 cores, ∼20 dates) were also taken into account. The data synthesis and interpretation provided robust and coherent indications regarding the palaeoenvironment, shoreline changes and the rate of geomorphological changes of the coastal area of Gialova Lagoon, as well as useful information about the palaeonvironmental and palaeoclimatic conditions that prevailed during the Mycenaean period. The interpretation, reveal a transition from a shallow marine environment (6500-5800 yr B.P.) to a brackish/lagoonal (5800-3300 yr B.P.), followed by a shift towards a freshwater/marsh environment (3300 yr B.P. to present).

A multiproxy palaeolimnological reconstruction of the nature and timing of climatic changes in the Northern Isles from the end of the last glaciation through the early Holocene

Thesis

Jun 2017

Melanie Kingsbury

Holocene paleohydrological reconstruction of Lake Strzeszyńskie (western Poland) and its implications for the central European climatic transition zone

Article

Full-text available

Apr 2018
J PALEOLIMNOL

Western Poland is located in the central European climatic transition zone, which separates the mild and humid Atlantic climate of Western Europe and the East European continental climate. This region is sensitive to lateral shifts of the European climate zones and is particularly suitable for reconstructing Holocene climate variability. This paper presents detailed analyses of the sedimentary record from Lake Strzeszyńskie since the Late Pleistocene. These include smear-slide and thin-section observations, X-ray fluorescence core scanning, magnetic susceptibility measurements, pollen analyses, and radiocarbon dating. The sediment record reveals three distinct sedimentary units consisting of: (1) an alternation of sand layers and laminated silt and clay deposits accumulated prior to 14,600 cal yr BP; (2) faintly laminated calcareous sediments intercalated with organic matter-rich layers deposited between 14,600 and 10,200 cal yr BP; and (3) massive calcareous mud deposited after 10,200 cal yr BP. The Holocene period is marked by nine phases of organic-rich sedimentation and enhanced Fe deposition, which occurred at ca. 10.1, 9.3, 6.4–6.1, 5.5–5.1, 4.7–4.5, 2.7–2.4, 1.3–1.2, 0.8–0.6, 0.4–0.2 kyr cal BP. These phases are associated with high lake levels and correspond with wet periods recognized in several other records from Poland and central Europe. These phases partly coincide with North Atlantic cold periods, which may suggest that high lake levels are triggered by an ocean-continent linking mechanism.

Geochemical characterization of the middle and late Pleistocene alluvial fan-dominated infill of the northern part of the Weihe Basin, Central China

Article

May 2017
PALAEOGEOGR PALAEOCL

Major reorganizations in climate and tectonic regime occurred in East Asia during the Pleistocene, resulting in large-scale environmental changes. In this paper a detailed geochemical and mineralogical record of these changes is presented from a distal alluvial fan sedimentary sequence in the northern Weihe Basin. Established that, in addition to glacial-interglacial variation, there are three distinctly different units deposited over the past 1 m.y. These units are the result of variations in the overall tectonic regime in the northern Weihe Basin.

Timing of the late-glacial climate reversal in Southern Hemisphere: update using high-resolution Bayesian age modeling (Bpeat) at Kaipo bog, New Zealand

Article

Jan 2007
QUATERN INT

A multiproxy (micro-XRF, pollen, chironomid and stable isotope) lake sediment record for the Lateglacial to Holocene transition from Thomastown Bog, Ireland

Article

Full-text available

Jul 2015
J QUATERNARY SCI

A multiproxy Lateglacial environmental record is presented for a ca. 3.5-m lacustrine sequence retrieved from a small basin (ca. 2 km2) at Thomastown Bog in County Meath, Ireland. Sediment chemistry, pollen, chironomid and stable isotope data provide a detailed picture of catchment and lake system changes from the end of the last glacial (GS-2a) to the early Holocene that correspond closely to existing local and regional models of climate change. Concomitant adjustments in independent proxy records are matched to the NGRIP oxygen isotope curve giving 12 event-episodes ranging from major climatic shifts to lower amplitude, centennial- to sub-centennial-scale adjustments, including a previously unreported regressive period of landscape instability during the north-west European ‘Rammelbeek Phase’. The study emphasizes the potential of palaeoenvironmental reconstruction from sediment chemistry where the sediment mixing system reflects autochthonous versus allochthonous inputs. The investigation also indicates problems of interpreting isotope data derived from bulk marl due to possible lag effects controlling the delivery of soil and groundwater and multiple sources of HCO3– (aq.). These research findings have implications for core site selection and for studies attempting to use stable isotopes for correlation purposes.

Growth responses of the calcite-loricated freshwater phytoflagellate Phacotus lenticularis (Chlorophyta) to the CaCO3 saturation state and meteorological changes

Article

Full-text available

May 2014

The pelagic phytoflagellate Phacotus lenticularis creates a shell of highly symmetrical calcite crystals at its outer extracellular layer and thereby constitutes a significant source of calcite in temperate alkaline lakes worldwide. Responses of P. lenticularis to a changing lake environment therefore have potential implications for the calcium carbonate flux in lakes. How meteorological variability in interaction with the CaCO3 saturation state may influence the abundance and phenology of P. lenticularis has not been investigated so far. We measured, biweekly to daily, algal abundance, CaCO3 saturation, pH, water temperature and nutrient status in three hard-water lakes that varied in lake morphology and wind exposure. Our data provide evidence that increasing supersaturation of CaCO3 mediates the onset of P. lenticularis exponential growth and stimulates seasonal peak development. However, total cell concentration in the lake water appears to be independent of the CaCO3 saturation state and was the highest in the most wind exposed lake. Phacotus lenticularis abundance and epilimnetic CaCO3 supersaturation were significantly positively correlated at a time lag of about 1 day. Wind caused an immediate decline in epilimnetic pH followed by a decline in CaCO3 saturation about 2 days later. Solar irradiance positively affected both pH and water temperature, but water temperature changes were insufficient to produce a significant CaCO3 saturation response. We conclude that the CaCO3 saturation state is a determinant factor driving the timing of P. lenticularis peaks in alkaline lakes.

The potential for palaeoseismic and palaeoclimatic reconstructions from Lake Tennyson, North Canterbury, New Zealand

Article

May 2023

Varied sediment archive of Fe and Mn contents under changing reservoir mixing patterns, oxygenation regimes, and runoff inputs

Article

Mar 2023
ECOL INDIC

Water hypoxia intensification in lakes and reservoirs has become a global problem under global warming. The Mn/Fe ratio is frequently employed to reconstruct historical redox conditions, but interpretation of this ratio may be problematic when the accumulation of Fe and Mn is governed by factors in addition to redox processes. We tested the Fe and Mn contents and bacterial diversity of a 250 cm sediment column in a monomictic reservoir. The deposition time frame and sedimentary rate (approximately 60 cm/y) were determined by integrating the Fe and Mn contents with the hydrological time series, providing a sufficient archive to reconstruct the intra-year variation in water qualities. The inapplicability of the Mn/Fe ratio observed because redox processes, mixing patterns, and biological activity jointly affected the net accumulation of Fe and Mn in the sediment. The causes of the vertical variations in the sediment Fe and Mn contents are discussed, considering the runoff sediment input, hydrodynamic and thermodynamic characteristics of this reservoir, and bacterial distributions in the sediment column. High-speed deposition intensively occurred in summer and autumn; thus, during this period, fluvial sediment was the main source of Fe and Mn. Another source was biochemical sedimentation due to mixing and oxygenation in this reservoir, which played a larger role in spring and winter. Our study showed that the easily accessible current hydrological data of the reservoir provide a reference time frame for identifying historical environmental events and that the use of the Fe/Mn ratio alone is inconclusive for interpreting the historic oxygenation regimes of reservoirs. Future applications of this method should consider the individual reservoir characteristics that impact the mobility and net accumulation of Fe and Mn in the sediment.

Environmental change inferred from multiple proxies from an 18 cal ka BP sediment record, Lake Barrine, NE Australia

Article

Sep 2022
QUATERNARY SCI REV

Available online xxx Handling Editor: P Rioual Keywords: Paleoclimate change Northeastern Australia Bulk organic geochemistry m-XRF Maar lake sediment Deglacial Carbon isotope a b s t r a c t Lake Barrine (17.25 S, 145.64 E), on the Atherton Tablelands in tropical northeast Australia, was formed as a maar lake in the late Pleistocene. The 65 m-deep stratified lake provides a detailed sediment record of climate and environmental change on the Tablelands. We reconstruct hydroclimate and vegetation change over the last~18,000 years from a 7.2 m long sediment core at 20-year resolution using multiple paleoenvironmental proxies (m-XRF elements, d 13 C TOC , TOC and C:N ratio). The data series are supported by a chronology based on 22 accelerator mass spectrometer (AMS) radiocarbon dates. The results suggest a distinct period of intense but highly seasonal rainfall coincident with the Antarctic Cold Reversal (14.7 e13.0 cal ka BP). This period was followed by a trend into the early Holocene toward wetter, less seasonal conditions that allowed the progressive establishment of tropical forest in the catchment. The catchment was completely covered by closed forest by 7.3 cal ka BP. The inferred precipitation changes at Lake Barrine are consistent with other records on the Tablelands and in phase with the changes in tropical SE Africa, NW Australia and anti-phase with the East Asian summer monsoon region in the Holocene but not before that. This result supports previous conclusions that precipitation variations correlate (in phase or anti-phased) in these regions. This correlation results from a dynamic balance among intertropical convergence zone (ITCZ), the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO).

A Multi-Proxy Holocene Palaeoenvironmental Record of Climate Change and Prehistoric Human Activity from Lough Cullin, southeast Ireland

Article

Nov 2021
HOLOCENE

A multiproxy (pollen, microcharcoal, loss-on-ignition, magnetic susceptibility and geochemistry) sequence from Lough Cullin, southeast Ireland, supported by a high-resolution radiocarbon chronology, modelled using Bayesian approaches, provides a record of environmental change for much of the Holocene. Following the establishment of mixed deciduous woodland, climatic deterioration was likely responsible for pronounced vegetation change and erosion, 7615–6500 cal. BC to 6245–5575 cal. BC, evidence for the ‘8.2 Kyr’ BP climate event. The so-called ‘elm decline’ is dated to 4220–3980 cal. BC and whilst there are possible indications of an anthropogenic cause, clear evidence of woodland clearance with cereal pollen is recorded at 3900–3700 cal. BC, 3790–3580 cal. BC and 3760–3650 cal. BC, during a period of clearance and farming of 320–450 years duration. A reduction in farming/settlement and woodland regeneration during the Middle Neolithic parallels the archaeological record, with low levels of activity during the Late Neolithic/Chalcolithic after 2960–2525 cal. BC, prior to increases during the Bronze Age then woodland clearance and agriculture between 1500–1410 and 1275–1000 cal. BC, corresponding with the archaeological evidence. A subsequent ‘step-wise’ reduction in human activity follows, from the latter date to 815–685 cal. BC, and a brief but pronounced cessation at 690–535 cal. BC. Renewed woodland clearance and agriculture commenced until 415–250 cal. BC. From the latter date until cal. AD 390–540, the Late Iron Age/Early Medieval period, a phase of woodland recovery is attested, followed by renewed landscape disturbance and arable agriculture in particular, continuing to the close of the record at cal. AD 780–1035.

Climate driven declines in terrestrial input over the middle and late Holocene of perched boreal lakes in northeast Ontario (Canada) and teleconnections to the North Atlantic

Article

Jul 2021
QUATERNARY SCI REV

The landscape of northeast Ontario, Canada, is dominated by glacial and postglacial landforms including numerous boreal lakes that formed following the retreat of the Laurentide Ice Sheet (LIS) and Glacial Lake Ojibway. This study uses micro-X-Ray Fluorescence elemental analysis to examine changes in sediment cores from two boreal lakes from northeast Ontario with the goal of inferring changes in terrestrial inputs and redox status of these lakes over the middle to late Holocene. These headwater lakes were selected as they have small watersheds that minimizes the complexity of hydrological responses, and as they are relatively proximal (∼130 km distance between lakes) to allow the detection of regional signals related to changes in climate over the Holocene. Strong correlations between Si, K, Ca, and Ti in Hogback Lake and Green Lake cores suggest that these elements represent proxies of terrestrial input. Standardized composite trends of these elements were very similar between the two lakes and were combined to represent a regional signal, with the highest terrestrial inputs between ∼6000 and ∼4000 cal yr BP, that subsequently declined through the Holocene. These results suggest that regional patterns in terrestrial input are linked to changes in hydroclimate and likely increased terrestrial stability over the middle to late Holocene. These composite trends are compared to similar geochemical composite trends from Iceland suggesting climate teleconnections between northeast North America and the North Atlantic. Cool conditions in the North Atlantic result in increased soil erosion in Iceland and correspond to cool and dry conditions in boreal northeast Ontario with corresponding low inputs of terrestrial material, and vice versa, over multidecadal time scales over the middle to late Holocene.

Lake-Level Changes and Their Paleo-Climatic Implications at the MIS12 Lower Paleolithic (Middle Pleistocene) Site Marathousa 1, Greece

Article

Full-text available

Jul 2021

Lithics and cut-marked mammal bones, excavated from the paleo-lake Marathousa 1 (MAR-1) sediments in the Megalopolis Basin, southern Greece, indicate traces of hominin activity occurring along a paleo-shoreline ca. 444,000 years (444 ka) ago. However, the local environment and climatic conditions promoting hominin activity in the area during the MIS12 glacial remain largely unknown. In order to reconstruct the paleo-environment including paleo-lake levels and governing paleo-climatic factors on a high temporal resolution, we analyzed a 6-meter-long sediment sequence from the archeological site MAR-1 and a Bayesian age model was computed for a better age constrain of the different sedimentary units. A multiproxy approach was applied using ostracods, sponge spicules, diatoms, grain sizes, total organic carbon, total inorganic carbon and conventional X-ray fluorescence analysis. The results from the site represent a protected region surrounded by high mountains under the constant influence of water, either as a shallow partly anoxic water body surrounded by reed belts (>463-457 ka, <434-427 ka), a riverine-lake deltaic system (∼457-448 ka), a floodplain (∼448-444 ka) or a seasonal freshwater pond (∼444-436 ka). The local changes of water levels resemble large trends and rhythms of regional records from the Mediterranean and appear to directly respond to sea surface temperature (SST) changes of the North Atlantic. In particular, when the SSTs are high, more moisture reaches the study area and vice versa. Additional water reaches MAR-1 through melting of the surrounding glaciers after brief warm phases during MIS12 in the Mediterranean realm, which leads to the formation of smaller fresh water ponds, where also the horizon of the excavated remains is placed. Such ponds, rich in ostracods and other microorganisms, provided mammals and humans valuable resources, such as potable water, a wide range of plant species and hunting opportunities. These deposits therefore bear a high archeological potential. The results from our study suggest that the Megalopolis Basin could have served as a refugium for hominins and other organisms due to its capacity to retain freshwater bodies during glacial and interglacial periods.

Patterns of aeolian deposition in subtropical Australia through the last glacial and deglacial periods

Article

Feb 2021

Debate about the nature of climate and the magnitude of ecological change across Australia during the last glacial maximum (LGM; 26.5–19 ka) persists despite considerable research into the late Pleistocene. This is partly due to a lack of detailed paleoenvironmental records and reliable chronological frameworks. Geochemical and geochronological analyses of a 60 ka sedimentary record from Brown Lake, subtropical Queensland, are presented and considered in the context of climate-controlled environmental change. Optically stimulated luminescence dating of dune crests adjacent to prominent wetlands across North Stradbroke Island (Minjerribah) returned a mean age of 119.9 ± 10.6 ka; indicating relative dune stability soon after formation in Marine Isotope Stage 5. Synthesis of wetland sediment geochemistry across the island was used to identify dust accumulation and applied as an aridification proxy over the last glacial-interglacial cycle. A positive trend of dust deposition from ca. 50 ka was found with highest influx occurring leading into the LGM. Complexities of comparing sedimentary records and the need for robust age models are highlighted with local variation influencing the accumulation of exogenic material. An inter-site comparison suggests enhanced moisture stress regionally during the last glaciation and throughout the LGM, returning to a more positive moisture balance ca. 8 ka.

Micro-XRF Core Scanning in Palaeolimnology: Recent Developments

Chapter

Full-text available

Aug 2015

Within the last ten years, micro-XRF (µXRF) core scanning has become an important addition to the suite of techniques for investigating lacustrine sediments. Most studies to date have focused on records of detrital material. These have typically used elements such as Si, K, Ca, Ti, Fe, Rb, Sr and Zr as single element profiles or ratios. Inferences are made about changing catchment dynamics such as glacier advance and retreat, variations in run-off and soil erosion, weathering rates and processes and grain-size fluctuations. These can be linked, depending on the context of the individual basin, to factors such as climatic variability, meteorological events, seismic activity, tephra deposition or anthropogenic disturbance such as agriculture or deforestation. Studies of in-lake dynamics focus on elements affected by redox changes (e.g., Fe, Mn) or those which can be produced authigenically either as a result of evaporative concentration or biological processes (e.g., Ca). Here, we review the use of µXRF core scanning on lake sediments and summarise the range of elements and ratios that have been applied as a reference point for users. We consider some of the challenges involved in interpreting elemental data, given the wide variety of internal and external factors that can affect lake sediment composition.

The Laguna Potrok Aike Scientific Drilling Project PASADO (ICDP Expedition 5022)

Article

Full-text available

Sep 2009

No abstract available. doi:10.2204/iodp.sd.8.04.2009

The last deglaciation: timing the bipolar seesaw

Article

Full-text available

Jun 2011

Precise information on the relative timing of north-south climate variations is a key to resolving questions concerning the mechanisms that force and couple climate changes between the hemispheres. We present a new composite record made from five well-resolved Antarctic ice core records that robustly represents the timing of regional Antarctic climate change during the last deglaciation. Using fast variations in global methane gas concentrations as time markers, the Antarctic composite is directly compared to Greenland ice core records, allowing a detailed mapping of the inter-hemispheric sequence of climate changes. Consistent with prior studies the synchronized records show that warming (and cooling) trends in Antarctica closely match cold (and warm) periods in Greenland on millennial timescales. For the first time, we also identify a sub-millennial component to the inter-hemispheric coupling. Within the Antarctic Cold Reversal the strongest Antarctic cooling occurs during the pronounced northern warmth of the Bølling. Warming then resumes in Antarctica, potentially as early as the Intra-Allerød Cold Period, but with dating uncertainty that could place it as late as the onset of the Younger Dryas stadial. There is little-to-no time lag between climate transitions in Greenland and opposing changes in Antarctica. Our results lend support to fast acting inter-hemispheric coupling mechanisms, including recently proposed bipolar atmospheric teleconnections and/or rapid bipolar ocean teleconnections.

Late Pleistocene dust deposition in the Patagonian steppe - extending and refining the paleoenvironmental and tephrochronological record from Laguna Potrok Aike back to 55 ka

Article

Full-text available

Dec 2009

Paleoenvironmental records extending well into the last glacial period are scarce in the steppe regions of southern South America. Here, we present a continuous record for the past 55 ka from the maar lake Laguna Potrok Aike (51°58′ S, 70°23′ W, southern Patagonia, Argentina). Previous studies on a sedimentary core from a lake level terrace near the northern margin of the lake covered parts of Oxygen Isotope Stage (OIS) 3 (59–29 ka) whereas a second core from the centre of the basin comprised the last 16 ka. Tephrostratigraphical constraints and OSL ages from a third core located below the lake level terrace provide the crucial piece to close the gap between the previous coring sites. High-resolution XRF and magnetic susceptibility as well as grain size data indicate a positive hydrological balance alongside with relatively high aeolian activity during the glacial which is contemporaneous with increased dust fluxes in Antarctica. This is therefore the first evidence for contemporaneity of aeolian deposition in both the target area (Antarctica) and in the major source area of Patagonia. During the Holocene climatic conditions driving sediment deposition seem to have been more variable and less dominated by wind compared to glacial times. The identification of a minor lake level lowering at approximately 4 cal ka BP allows to refine earlier paleoenvironmental reconstructions for the Holocene. Within error margins the OSL ages are consistent with published radiocarbon-dated records offering hence a valuable tool for further studies of the sediments from Laguna Potrok Aike. The new chronology confirms the age of three tephra layers up to now only found in Laguna Potrok Aike sediments and ascribed to OIS 3.

Deep Drilling at Laguna Potrok Aike, Argentina: Recovery of a Paleoclimate Record for the Last Glacial from the Southern Hemisphere

Article

Full-text available

Jan 2009

Laguna Potrok Aike, located in the South-Patagonian province of Santa Cruz (52°58'S, 70°23'W), was formed 770 ka ago by a volcanic (maar) eruption. Within the framework of the ICDP-funded project PASADO two sites were drilled from September to November 2008 using the GLAD800 drilling platform. A total of 513 m of lacustrine sediments were recovered from the central deep basin by an international team. The sediments hold a unique record of paleoclimatic and paleoecological variability from a region sensitive to variations in southern hemispheric wind and pressure systems and thus significant for the understanding of the global climate system. Moreover, Laguna Potrok Aike is close to many active volcanoes allowing a better understanding of the history of volcanism in the Pali Aike Volcanic Field and in the nearby Andean mountain chain. These challenging scientific themes need to be tackled in a global context as both are of increasing socio-economic relevance. On-site core logging based on magnetic susceptibility data documents an excellent correlation between the quadruplicate holes drilled at Site 1 and between the triplicate holes recovered from Site 2. Also, correlation between both sites located 700 m apart from each other is feasible. After splitting the cores in the lab, a reference profile was established down to a composite depth of 107 m for the replicate cores from Site 2. Sediments consist of laminated and sand-layered lacustrine silts with an increasing number of turbidites and homogenites with depth. Below 80 m composite depth two mass movement deposits (10 m and 5 m in thickness) are recorded. These deposits show tilted and distorted layers as well as nodules of fine grained sediments and randomly distributed gravel. Such features indicate an increased slump activity probably related to lake level fluctuations or seismicity. Also with depth coarse gravel layers are present and point to changes in hydrological conditions in the catchment area. Intercalated throughout the record are 24 macroscopic volcanic ash layers that document the regional volcanic history and open the possibility to establish an independent time control through tephrochronology. These isochrones potentially act as links to marine sediment records from the South Atlantic and to Antarctic ice cores. Preliminary interpretation of all available data and extrapolation of sedimentation rates determined for the upper 16 ka indicate that the record may go back in time to oxygen isotope stage 5a and covers approximately the last 80 ka.

On the occurrence of Phacotus lenticularis (Chlorophyta) in lakes of different trophic state

Article

Full-text available

May 1998
HYDROBIOLOGIA

The occurrence of the calcite-loricated chlamydophycean alga Phacotus lenticularis was investigated in relation to the trophic state of inland waters. The Phytoflagellate was observed in deep, stratified dimictic lakes, in shallow polymictic lakes, oxbow-lakes and ponds. Habitats of Phacotus are rich in lime and vary from oligo- to hypertrophic. Mass developments with cell numbers of 500,000–5.5 x 106 individuals l-1 were found in lakes with properties in the ranges: TP 34–484 µg l-1, SRP 2–88 µg l-1, NO2-0–32 µg 1-1, NO3-0–820 µg l-1 and NH4 + 10–740 µg l-1. The most consistently co-incidental site factors were water temperature and pH values. High abundances were observed at temperatures between 15.8 and 24.7 °C and at pH values from 8.3 to 9.6. The results are discussed in the context of numerous records of Phacotus published in the literature. The morphometric and ecological data come mainly from the main investigated waters of the Baltic Lake District of northeastern Germany.

Weather Observations Across the Southern Andes at 53°S

Article

Full-text available

Mar 2003

Regional variations of weather pattern were analyzed along a west-to-east profile across the Southern Andes (53°S), one of the most pronounced climate-divides in the world. For the first time we present a meteorological record from an array of three automatic weather stations (AWS), operated by the authors, for the central part of the climate divide which, together with previously existing Chilean weather stations, complete the transect. These data cover a time period of 3 yr. from October 1999 until September 2002. Air temperatures along the profile are highly correlated. Annual precipitation drops from between 6000 mm and 7000 mm at sea level along the main divide of the mountains to only about 1000 mm at the eastern slopes of the Andes and to as little as 430 mm at Punta Arenas. The variations of rainfall with wind direction and synoptic weather types are markedly different between the central part of the Andes and Punta Arenas. At the center of the climate divide precipitation correlates positively with wind speed from the west, whereas at Punta Arenas, east of the Andes, higher rainfall rates occur with easterly air flow. It is assumed that this reflects the barrier effect of the mountain range of the Andes. The results indicate that in order to make references about present or past climatic variations in Patagonia, it is essential to consider the effect of changes in circulation patterns.

Digital Scanning of Thin Sections and Peels

Article

Full-text available

Jul 1999

Thomas De Keyser

Digital film scanners allow direct capture of high-resolution digital images of entire petrographic thin sections or acetate peels, a capability not available using standard petrographic microscopes. Using a small-format, 35 mm film scanner as an example, this article describes a means of directly scanning, at high resolution, standard petrographic thin sections, larger (2 x 3 in.; 5.08 x 7.62 cm) thin sections, and portions of acetate peels and saving them as digital images. Such images fall into the range of macrophotography and bridge the gap between standard photography and photomicrography. Because no film is used and the light passes through no distorting lenses, the images obtained are of exceptional quality and can be processed and printed immediately. By sandwiching the thin section between sheet polarizing filters, scanned images through cross-polarized light can be obtained, simulating crossed nicols. The images of acetate peels far exceed the quality of equivalent photographs. Other film scanners and scanning film backs are available in large format and can be mounted directly on microscopes for digital imaging at higher magnification and can eliminate the need for conventional film in petrographic studies.

29 Holocene palaeoclimates of southern 30 Patagonia: limnological and 31 environmental history of Lago Cardiel

Article

Full-text available

Multiproxy palaeoenvironmental and palaeolimnological analyses of two Holocene-age sediment cores from the margin of Lago Cardiel, a 76 m deep, closed-basin lake in southern Patagonia (latitude 49°S), provide information on lake-level changes that can be related to regional palaeoclimate scenarios. Sedimentol- ogic (magnetic susceptibility, organic and inorganic carbon content) and environmental indicators (pollen, dia- toms, ostracodes and stable isotopes on ostracodes) show lake levels markedly higher than today during the early Holocene, following a rapid lake-level rise after a desiccation phase prior to 11 000 BP. After about 6000 BP, lake levels were generally lower, but underwent repeated fluctuations. These inferred changes support the previously proposed view that the southern westerly stormtracks were focused (zonal) north of latitude 50°S during the early Holocene, allowing for Antarctic cold fronts to bring easterly moisture to southern Patagonia, whereas during the late Holocene the stormtracks shifted seasonally, with an overall more meridional behaviour, resulting in less and more variable moisture at these latitudes.

Ikaite pseudomorphs in the Zaire deep-sea fan: An intermediate between calcite and porous calcite

Article

Full-text available

Mar 1987
GEOLOGY

Translucent brown aggregates of calcium-carbonate crystals have been found in cores from the Zaire deep-sea fan (west equatorial Africa). The aggregates are well preserved but very friable. Upon storage they become yellowish white and cloudy and release water. Chemical, mineralogical (XRD), petrographical, crystal-morphological, and stable-isotope data demonstrate that the crystals have passed through three phases: (1) an authigenic carbonate phase, probably calcium carbonate, which is represented by the external habit of the present crystals; (2) a translucent brown ikaite phase (CaCO3·6H2O), unstable at temperatures above 5 °C; and (3) a phase consisting of calcite microcrystals that are poorly cemented and form a porous mass within the crystal form of the morphologically unchanged first phase. The transformation from the first phase into ikaite was probably a kinetic replacement. The transformation from ikaite into the third phase occurred because of storage at room temperature. The presence of ikaite is indicative of a low-temperature, anaerobic, organic-carbon-rich marine environment. Ikaite is probably the precursor of a great number of porous calcite pseudomorphs, and possibly also of many marine authigenic microcrystalline carbonate nodules.

Faulting and Fracturing of Nonwelded Bishop Tuff, Eastern California: Deformation Mechanisms in Very Porous Materials in the Vadose Zone

Article

Full-text available

May 2004
VADOSE ZONE J

Field and microstructural studies were conducted on the basal, nonwelded and partially welded portions of the rhyolite Bishop Tuff in eastern California to examine the nature and processes of brittle deformation in these units. The nonwelded tuff consists of a variable sequence of finely laminated to massive pumice-rich deposits, finegrained ash, and pyroclastic glass erupted from the Long Valley Cal-dera. The deposits are experiencing east-west extension in the hanging wall of the White Mountain fault, and small-displacement faults and fractures cut the tuff. Deformation in the Bishop Tuff occurred by fracturing associated with faults, and by slip along narrow faults with smooth, often mineralized surfaces. Localization of fracturing appears to be a function of welding. Units with a greater degree of welding have a greater abundance of fractures associated with faults, whereas nonwelded portions typically have a narrow deformation band-type faults with littleornoassociated damage. Microstructural observations show that transgranular fractures lie along grain boundaries of pumice and feldspar phenocrysts, and these fractures are often filled with calcite. These deposits appear to have behaved as an open-cell foam with a low strength, but with a cohesion that allowed the support of a differential stress to failure that resulted in \1vertical open fractures and faults. These results demonstrate how brittle deformation may be manifested in nonwelded deposits in the vadose zone, and impart an anisotropy in which flow would be enhanced vertically and impeded horizontally. The Bishop Tuff is analogous to other nonwelded tuffs in the western USA. Thus, these results have implications for understanding deformation and flow in a variety of arid regions.

Paleoclimate studies of minerogenic sediments using annually resolved textural parameters

Article

Full-text available

Oct 2002

We obtained quantitative multivariate data from each varve of a minerogenic lacustrine sequence from the Canadian High Arctic, using an image analysis technique applied to thin-sections. The information on each varve from the uppermost core section was compared with a 35 yr meteorological dataset. Snowmelt intensity, which is an index reflecting the energy available for sediment transport, correlates well with the median grain-size measured for each varve, as well as with the weight of the 10-20 and 20-60 mum fractions. The proportion of fine silt also correlates with low intensity summer precipitation. This methodology allows us to decipher the climatic control on sedimentary processes and yield a new perspective for constructing models which link climate to sediments that contain few biological remains. This model can then be used to infer paleoclimate with annual resolution from the downcore grain-size analysis.

Climate induced changes in the content of carbonaceous and organic matter of sediments from Laguna Potrok Aike (Argentina) during the past 50 ka inferred from infrared spectroscopy

Article

Full-text available

Jan 2012
QUATERNARY SCI REV

Dust and sea salt variability in central East Antarctica (Dome C) over the last 45 Krys and its implications for southern high-latitude climate

Article

Full-text available

Oct 2002

A detailed record of non-sea-salt calcium, a proxy for dust, and sea-salt sodium, a proxy for sea salt, covering the last 45 kyr is presented. It shows that in the first part of the transition from the last glacial period to the Holocene (18-15 kyr BP), the changes in dust flux mainly reflect changes at the dust source, namely vegetation cover and local climate. The changes in the later part of the transition (12-11 kyr BP) are similar in extent to the changes seen in sea salt and most likely reflect a reorganization of the atmospheric circulation. During the last glacial period, considerable variation of dust but not of sea salt is observed, pointing to climatic changes in Patagonia, the main dust source for Dome C. A comparison of the glacial records from Dome C and Taylor Dome suggests that similar influences controlled aerosol input at both sites during this period.

Influence of Patagonian glaciers on Antarctic dust deposition during the last glacial period

Article

Full-text available

Mar 2009

Ice cores provide a record of changes in dust flux to Antarctica, which is thought to reflect changes in atmospheric circulation and environmental conditions in dust source areas. Isotopic tracers suggest that South America is the dominant source of the dust, but it is unclear what led to the variable deposition of dust at concentrations 20-50 times higher than present in glacial-aged ice. Here we characterize the age and composition of Patagonian glacial outwash sediments, to assess the relationship between the Antarctic dust record from DomeC (refs9,13) and Patagonian glacial fluctuations for the past 80,000 years. We show that dust peaks in Antarctica coincide with periods in Patagonia when rivers of glacial meltwater deposited sediment directly onto easily mobilized outwash plains. No dust peaks were noted when the glaciers instead terminated directly into pro-glacial lakes. We thus propose that the variable sediment supply resulting from Patagonian glacial fluctuations may have acted as an on/off switch for Antarctic dust deposition. At the last glacial termination, Patagonian glaciers quickly retreated into lakes, which may help explain why the deglacial decline in Antarctic dust concentrations preceded the main phase of warming, sea-level rise and reduction in Southern Hemisphere sea-ice extent.

Paleolimnology: The History and Evolution of Lake SystemsThe History and Evolution of Lake Systems

Book

May 2003

Andrew S. Cohen

Image Analysis, Sediments and Paleoenvironments

Book

Jan 2004

Pierre Francus

Klimatische Aspekte der Weidedegradation in Ost-Patagonien

Article

Jan 1993

Wilfried R Endlicher

Lacustrine environment

Article

Jan 1983

Freshwater Carbonate Sedimentation

Chapter

Jan 1978

Carbonate minerals are a common constituent of lacustrine sediments. The great variability with respect to geological setting, climatic environment, water chemistry, and biological activity limits generalizations about mechanisms of carbonate sedimentation. On the whole, in constrast to an oceanic environment, the bulk of primary lacustrine carbonates are inorganic chemical precipitates. Two distinctly different geological settings can be recognized: (1) carbonate and evaporite deposition in brine lakes or on playas in arid regions (see Chap. 8, this volume), and (2) carbonate sedimentation in fresh- and brackish-water lakes in humid regions. Occurrences of lacustrine chalks and marls in young geological formations of temperate regions have been described since the time of Lyell (1830). In northern America and Europe, Late Quaternary chalks were found near still existing lakes and their genesis was related to a postglacial period of climatic amelioration (e.g., Heim, 1919). Typically, these deposits are fine grained, either rhythmically laminated or massive, white to dull-yellowish gray chalks to marls. This distinction is qualitative based on a bulk carbonate content boundary around 60%. The dominant mineral is calcite. Similar varve-like carbonate or marl sediments were found in older lacustrine deposits (e.g., Bradley, 1929). Nipkow (1920) described recent analogies to laminated lacustrine carbonates in Lake Zurich; the light laminae are rich in CaCO3. Forel (1901) early recognized a biological role, but Minder (1922, 1926) developed the concept of inorganic, biogenically induced calcite precipitation. Meanwhile lacustrine marls in regions of Quaternary glaciation around the Great Lakes in North America were studied (e.g., Davis, 1901; Pollock, 1918). Calcite precipitation in those biologically active hardwater lakes (e.g., Halbfass, 1923; Ruttner, 1962; Pia, 1933; Ohle, 1952; Hutchinson, 1957; Wetzel, 1975) was soon related to extraction of Co2 during photosynthesis by algae.

Geología, petrología, quimismo y origen de los volcanes del área de Pali-Aike, Magallanes, Chile

Article

Jan 1978

Alexandra Skewes

Diagenesis of manganese in Lake Michigan sediments

Article

May 1975

The authors have attempted to develop a theoretical treatment of manganese diagenesis applicable to dissolved manganese profiles in Lake Michigan sediments. It is shown that the observed distribution of sedimentary and dissolved manganese can be described quantitatively in terms of steady-state diagenesis without specific reference to changes in geochemistry of the sediments which may have been caused by man. Conceivably the approach developed below may be applied to the distributions of other elements. Refs.

Towards a Late Quaternary tephrochronological framework for the southernmost part of South America−the Laguna Potrok Aike tephra record

Article

Jul 2013

A total of 18 tephra samples have been analysed from the composite sediment sequence from Site 2 of the Laguna Potrok Aike ICDP expedition 5022 from southern Patagonia, Argentina, which extends back to ca 51 ka cal BP. Analyses of the volcanic glass show that all layers but one are rhyolitic in composition, with SiO2 contents ranging between ca 74.5 and 78 wt% and suggest an origin in the Austral Andean Volcanic Zone (AVZ; 49–55°S). Nonetheless, two main data clusters occur, one group with K2O contents between ca 1.5 and 2.0 wt%, indicating an origin in the Mt. Burney volcanic area, and one group with K2O contents between ca 2.7 and 3.9 wt%, tentatively correlated with Viedma/Lautaro and the Aguilera volcanoes in the northern part of the AVZ. The early Holocene Tephra, MB1 and the late Pleistocene Reclus R1 tephra occur in the upper part of the sequence. Periods with significant tephra deposition occurred between ca 51–44 ka cal BP, and ca 31–25 ka cal BP, with a decrease in tephra layer frequency between these two periods.

Lithology, radiocarbon chronology and sedimentological interpretation of the lacustrine record from Laguna Potrok Aike, southern Patagonia

Article

Jul 2013

The 106 m long composite profile from site 2 of ICDP expedition 5022 (PASADO) at Laguna Potrok Aike documents a distinct change in sedimentation patterns from pelagic sediments at the top to dominating mass movement deposits at its base. The main lithological units correspond to the Holocene, to the Lateglacial and to the last glacial period and can be interpreted as the result of distinct environmental variations. Overflow conditions might have been achieved during the last glacial period, while signs of desiccation are absent in the studied sediment record. Altogether, 58 radiocarbon dates were used to establish a consistent age-depth model by applying the mixed-effect regression procedure which results in a basal age of 51.2 cal. ka BP. Radiocarbon dates show a considerable increase in scatter with depth which is related to the high amount of reworking. Validation of the obtained chronology was achieved with geomagnetic relative paleointensity data and tephra correlation.

Ikaite precipitation in a lacustrine environment – implications for palaeoclimatic studies using carbonates from Laguna Potrok Aike (Patagonia, Argentina)

Article

Jul 2013

The monoclinic mineral ikaite (CaCO3 · 6H2O) and its pseudomorphs are potentially important archives for palaeoenvironmental reconstructions. Natural ikaite occurs in a small temperature range near freezing point and is reported mainly from marine and only rarely from continental aquatic environments. Ikaite transforms to more stable anhydrous forms of CaCO3 after an increase in temperature or when exposed to atmospheric conditions. The knowledge about conditions for natural ikaite formation, its stable isotope fractionation factors and isotopic changes during transformation to calcite is very restricted. Here, for the first time, primary precipitation of idiomorphic ikaite and its calcite pseudomorphs are reported from a subsaline lake, Laguna Potrok Aike, in southern Argentina. The calculated stable oxygen isotope fractionation factor between lake water and ikaite-derived calcite (αPAI = 1.0324 at a temperature of 4.1 °C) is close to but differs from that of primarily inorganically precipitated calcite. Pseudomorphs after ikaite rapidly disintegrate into calcite powder that is indistinguishable from μm-sized calcite crystals in the sediment record of Laguna Potrok Aike suggesting an ikaite origin of sedimentary calcites. Therefore, the Holocene carbonates of Laguna Potrok Aike have the potential to serve as a recorder of past hydrological variation.

Atmospheric simulations of southern South America's climate since the Last Glacial maximum

Article

Jul 2013

This study investigates the simulated present and past climate of southern South America through the use of the PSU/NCAR MM5 mesoscale model forced by Princeton GFDL global atmosphere-ocean model data. This approach is taken to obtain climate data with sufficiently high resolution to resolve the steep mountain ranges of the southern Andes, which generate large amounts of orographic precipitation. Results indicated that the region experienced northward shifted low level westerlies at and before 9000 years before present and shifts in upper level winds associated with the midlatitude jet culminated about 9000 years ago. A simple energy balance model indicates that the lower equilibrium line altitudes in the southern Andes during the Last Glacial maximum persisted into the early Holocene, resulting in an expansion of the area receiving net snow accumulation, particularly in eastern parts of the Andes mountains. Changes in simulated winds and precipitation in the lee of the southern Andes are consistent with Laguna Potrok Aike climate proxies.

Climate induced changes as registered in inorganic and organic sediment components from Laguna Potrok Aike (Argentina) during the past 51 ka

Article

Jul 2013

Authigenic, detrital and diagenetic minerals in the Laguna Potrok Aike sediment sequence

Article

Jul 2013

The ∼100 m-long Laguna Potrok Aike sediment sequence yielded a record spanning the Last Glacial period to the Holocene. This paper presents and discusses two aspects of the mineralogy of the lake. The first aspect is based on a semi-quantitative X-ray diffraction analysis of bulk and clay mineralogical assemblages. Minor mineralogical changes are observed throughout the glacial section suggesting relatively uniform sediment sources. The transition into the Holocene is characterized by increasing fluxes of endogenic calcite thought to relate to lower lake levels. The second aspect is based on analysis of uranium-series disequilibria in diagenetic vivianite from the glacial section. U-series ages were expected to yield minimum ages for the host-sediment. Unfortunately, very little authigenic U is present in vivianite grains. The low primary productivity of the lake and thus low organic carbon fluxes might have prevented the development of strong redox gradients at the water-sediment interface and thus reduced diagenetic U-uptake into the sediment. One vivianite sample, at a 56.9 m composite depth, yielded enough authigenic uranium to calculate a 230Th-age of 29.4 ± 5.9 ka (±2σ). This age is younger than the one indicated by the radiocarbon chronology. It is thus concluded that a relatively late diagenetic evolution of the U–Th system characterizes the recovered vivianite minerals. The authigenic U displays a very high excess in 234U (over 238U) with an activity ratio of 4.58 ± 0.58 (±2σ). It suggests that it originates from the transfer of highly fractionated U from surrounding detrital minerals through very low U-content pore waters.

The Pali Aike Volcanic Field, Patagonia: Slab-window magmatism near the tip of South America

Article

Jun 2000
TECTONOPHYSICS

The Pali Aike Volcanic Field (PAVF) represents the southernmost occurrence of the Cenozoic back-arc Patagonian Plateau Lavas. Its activity (Pliocene–Recent) started forming tabular lavas followed by the growth of about 470 essentially monogenetic volcanic centers (tuff-rings, maars, spatter and scoria cones). Azimuths of cone alignment, cone elongation and morphologic lineations show prevailing ENE–WSW and NW–SE trends. Erupted products consist mainly of alkaline basalt and basanite, with minor olivine basalt. PAVF rocks are quite primitive in composition (average Mg#=66, Ni=220 ppm and Cr=313 ppm) with relatively high TiO2 (average 3.0 wt.%). Ultramafic garnet- and/or spinel-bearing xenoliths are found within PAVF volcanics. Chondrite-normalized REE patterns are significantly LREE-enriched and almost rectilinear [(La/Yb)N=10.9–21.0]. Primordial mantle-normalized distributions of incompatible trace elements, as well as Sr and Nd isotope ratios (87Sr/86Sr=0.70317–0.70339, 143Nd/144Nd=0.51290–0.51294), show values typical of intra-plate basalts, despite the fact that these rocks occur only 200 km east of the Andean Cordillera. Primary magmas were generated from a fertile garnet-bearing asthenospheric source at P=1.9–2.9 GPa and T=1420–1470°C.The data suggest a geodynamic model that implies sub-slab asthenosphere flow through a slab window, which started opening below this sector of South America 14 m.y. ago as a consequence of the collision of the Chile Ridge with the Chile Trench. The trailing edge of the Nazca Plate crossed below the Pali Aike area at 9–10 Ma, that is 6–5 m.y. before the onset of the volcanic activity. We hypothesize that this time delay resulted from changes in the kinematics of the South America–Scotia transform plate boundary which only allowed the Pali Aike magmas to rise after about 4 m.y.

LM- oder REM-Beobachtungen an Phacotus sphaericus (Wislouch) Giering nov. stat. (Chlamydophyceae, Phacotaceae)

Article

Dec 1990

A green flagellate of the genus Phacotus with a spherical calcite-lorica was found in field collections from limerich waters in the Baltic Lake District of the G.D.R. LM observations showed wide coincidence with Phacotus lenticularis (EHRENBERG) STEIN var. sphaerica WISLOUCH, described from Poland. SEM examinations demonstrated the autonomous character of this taxon for which the new status Phacotus sphaericus (WISLOUCH) GIERING is suggested.

ITRAX: Description and Evaluation of a New Multi-Function X-ray Core Scanner

Article

Jan 2006

A new automated multi-function core scanning instrument, named ITRAX, has been developed that records optical, radiographic and elemental variations from sediment half cores up to 1.8 m long at a resolution as fine as 200 μm. An intense micro-X-ray beam focused through a flat capillary waveguide is used to irradiate samples to enable both X-radiography and X-ray fluorescence (XRF) analysis. Data are acquired incrementally by advancing a split core, via a programmable stepped motor drive, through the flat, rectangular-section X-ray beam. Traditional XRF determination of element composition in sediments provides high-quality data, but it takes a considerable time and normally consumes grain quantities of material that is often only available in limited quantities. The ITRAX core scanner non-destructively collects optical and X-radiographic images, and provides high-resolution elemental profiles that are invaluable for guiding sample selection for further (destructive) detailed sampling. This paper presents a description of the construction, characteristics and capabilities of the ITRAX system. Higb-resolution ITRAX data obtained from sediment cores are also presented and compared with results from traditional wavelength-dispersive XRF analysis at lower resolution. Finally, some recent technical developments linked to the second-generation ITRAX are presented.

The Potential of Ikaite to Record the Oceanic Evolution of ?18O

Article

Dec 2005

Despite the importance of sea level for understanding past climates, paleoceanographers struggle to construct a continuous and definitive record of oceanic delta18O over millennial timescales. Here, we explore the possibility that ikaite, a hydrated form of calcium carbonate which forms monoclinic crystals made of CaCO3.6H2O units linked together by hydrogen bonds, may record the delta18O of the water from which it precipitates. Naturally occurring samples of ikaite have been found in the Ikka Fjord in Greenland where the crystals grow into huge chimneys around cold water springs at a temperature of 3°C, and ephemeral occurrences are also noted in alkaline lakes such as Mono Lake, California. The stability field of ikaite suggests that it should not exist at normal ocean temperatures and pressures. Nonetheless, the presence of ikaite has been recognised increasingly in areas such as the Bransfield Strait, Sea of Okhotsk, the Laptev Sea and the Lower Zaire Deep Sea fan, where sediments rich in organic carbon are characterised by high alkalinity and the presence of sulphate or phosphate which inhibits calcite precipitation. Whilst the presence and isotopic composition of glendonite, a pseudomorph of ikaite has been used as a key environmental indicator in the geological record, ikaite from recent ocean sediments has never been preserved for geochemical analysis. We have performed a series of laboratory growth experiments of ikaite under controlled conditions of alkalinity and temperature, from waters with a range of delta18O. Our results demonstrate that, in accordance with theory, the crystal bound waters in ikaite are isotopically heavier than the ambient water. Further a simple linear relationship with a non-zero intercept exists between the delta18O of the hydration waters of ikaite, and the waters from which the crystal precipitated. These data provide a firm foundation for application of this methodology to reconstruct oceanic delta18O from ikaite in Pleistocene sediments.

Paleolimnology: The History and Evolution of Lake Systems

Article

Apr 2004

Elizabeth Gierlowski-Kordesch

Late Pleistocene sea level variations derived from the Argentine Shelf

Article

Dec 2000
GEOCHEM GEOPHY GEOSY

Neritic-littoral marine sedimentary deposits from the Argentine Shelf provide a record of late Pleistocene sea level variation. Sediments interpreted to reflect the last glacial maximum low-stand are ˜150 m below present. Using a simple Airy isostatic model for hydroisostatic compensation and correcting for a minor tectonic component yields a local eustatic sea level lowering of ˜105 m at the last glacial maximum. The deglacial sea level curve records two rapid sea level rises consistent with MWP1-A and 1-B as documented by the Barbados coral-based sea level curve. Comparison with relative sea level variations predicted by the ICE4G VM2 viscoelastic model have highlighted a deficiency in the model's predicted sea level history for this region. Detailed data-model comparisons of late Pleistocene sea level variations are necessary in the face of climate change induced sea level perturbations to determine regional and or systematic biases in the treatment of lithosphere viscosity and accurate predictions of future sea level.

Activation Spectrometry in Chemical Analysis, Vol. 119 in Chemical Analysis: A Series of Monographs on Analytical Chemistry and its Applications

Article

Jun 1992
ANAL CHIM ACTA

R DAMS

Subsampling unconsolidated sediments: a solution for the preparation of undisturbed thin-sections from clay-rich sediments

Article

Using the principle of electro-osmosis, a sub-sampling technique for clay-rich sediments is introduced that pro- duces undisturbed thin-sections from sediment cores. The fragile sample remains in the same disposable box through- out the process, preventing collapse of its structure during sub-sampling, manipulation and impregnation, as well as other potential problems. Note

Lacustrine Environments

Article

Jul 2009

In the second half of the 20th century, the famous Swedish limnologist Forel has defined lake as a mass of stagnant water located in a trough of the ground and has no direct contact with the sea. It can be geologically considered as a temporary water mass, appearing or disappearing within a short time period.

Origin and Paleoenvironmental Significance of Calcite Pseudomorphs after Ikaite in the Oligocene Creede Formation, Colorado

Article

Jan 1994

Daniel Larsen

Pseudomorphs of calcite are present in lacustrine strata and travertine of the Oligocene Creede Formation, the sedimentary moat fill of the Creede caldera in the Tertiary San Juan volcanic field. The pseudomorphs, previously thought to have formed after gaylussite (Ca-CO[sub 3]Na[sub 2]CO[sub 3] [center dot] 5H[sub 2]O), are interpreted to have formed after ikaite (CaCO[sub 3] [center dot] 6H[sub 2]O) on the basis of their modes of occurrence, pseudomorph morphology, and textural and chemical aspects of the calcite replacement. The extent of their exposure and degree of preservation in the Creede Formation allow elucidation of the depositional conditions in which the ikaite formed and was subsequently pseudomorphically replaced. The revised paleoenvironmental interpretation of the Creede Formation also has implications for understanding of the late Oligocene climate of the southwestern US. Formation of ikaite requires water temperatures of 0--3 C, supersaturation with respect to calcite, and the presence of a chemical inhibitor, such as dissolved phosphate, to prevent growth of calcite or aragonite (Shearman and Smith 1985). Geochemical calculations and hydrogeologic considerations suggest that waters with dissolved phosphate contents sufficient to inhibit calcite growth and stabilize ikaite could have developed in the Creede moat lake, although a chemical remnant of high phosphate content is not observed in the strata. The granular texture of the Creede pseudomorphs is common to calcite pseudomorphs after ikaite from many localities. A model is proposed in which slow pseudomorphic replacement (over a period of a day or more) results in sand-size calcite grains formed directly from the ikaite. This model has important implications for the interpretation of isotopic and chemical data obtained from pseudomorphs (and thinolitic tufa).

Ikaite, CaCO3⋅6H2O, precursor of the thinolites in the Quaternary tufas and tufa mounds of the Lahontan and Mono Lake Basins, western United States

Article

Jul 1989

The thinolites in the Quaternary tufas and tufa mounds of the Lahontan and Mono Lake basins are identified as being pseudomorphous after crystals of the mineral ikaite, a metastable mineral. The likely implication is that the thinolites record ice-cold episodes during deposition of the tufas. -from Authors

A Scale of Grade and Class Terms of Clastic Sediments

Article

Jan 1922

C.K.A. Wentworth

Freshwater carbonate sedimentation in Lakes-Chemistry

Article

K. Kelts

Destructive and non-destructive density determination: Method comparison and evaluation from the Laguna Potrok Aike sedimentary record

Article

Jul 2013
QUATERNARY SCI REV

Lithology, radiocarbon dating and sedimentological interpretation of the 51 ka BP lacustrine record from Laguna Potrok Aike, southern Patagonia

Data

Jan 2013

Potential of ikaite to record the evolution of oceanic δ18O

Article

Jun 2006
GEOLOGY

A challenge in the quest to understand the sensitivity of the climate system is the separation of the competing effects of ice volume or sea level, salinity, and temperature on foraminiferal sigma O-18. We present precipitation experiments on the mineral ikaite, a hydrated form of calcium carbonate found in organic carbon-rich deep-marine sediments, that show that the hydration waters within the ikaite crystal capture the delta O-18 of seawater (delta O-18(sw).) with a fractionation factor of 1.0029 (+/- 0.0002). The delta O-18(sw) measures the volume of continental ice, with an overprint of local salinity. Isolation of delta O-18(sw) by analysis of the hydration waters of sedimentary ikaite preserved at temperatures < 4 degrees C could be exploited to create a record of sea level during the Pleistocene. Preliminary data of delta O-18(sw) from hydration waters of ikaite at the Last Glacial Maximum agree with estimates from modeling of pore waters that Antarctic Bottom Water was +1.4 parts per thousand +/- 0.2 parts per thousand heavier.

Vostok Ice Core: A Continuous Isotope Temperature Record over the Last Climate Cycle (160,000 Years)

Article

Sep 1987

A continuous deuterium record along the Vostok ice core has been obtained and is interpreted in terms of local surface temperature changes over the past 160 kyr. The record is dominated by the large glacial-interglacial signal occurring at about 100 kyr with a total temperature amplitude of about 11 C. It is confirmed that the warmest part of the Last Interglacial Period was about 2 C warmer than the Holocene. This climatic record is the awaited terrestrial complement of the deep-sea records supporting the existence of a relation between the Pleistocene climate and orbital forcing.

Changements abrupts dans un monde glaciaire

Article

Jun 2004
CR GEOSCI

The most characteristic records of the millennial variability of climate during the last glacial period may be separated into two classes of signals: Greenland and Antarctic. The Greenland type is found over the whole North American and Euro-Asian continental blocks. Continental cooling associated with the maximum ice sheet extension, and resulting surges on the marine margins have affected the whole latitude range, with a probable strong albedo feedback due to winter snow cover. At the opposite, the surface temperature of tropical oceans did not change as much, which created large seasonal meandering of the Intertropical Convergence Zone (ITCZ), and facilitated meridional atmospheric vapour transport towards cold continents, and heat transfer in particular to the southern hemisphere. The rapid growth of ice sheets facilitated periodic surges and decreases in meridional overturning circulation. We propose that the major difference in the characteristics of the ‘Greenland’ and ‘Antarctic’ classes of climate variability result mostly from the difference in continent/ocean distribution in both hemispheres. To cite this article: L. Labeyrie et al., C. R. Geoscience 336 (2004).

Stratigraphy and Sedimentation

Article

May 1951
SOIL SCI

Renewed glacial activity during the Antarctic cold reversal and persistence of cold conditions until 11.5 ka in southwestern Patagonia

Article

Mar 2009
GEOLOGY

Resolving the timing, direction, and magnitude of paleoclimate changes in the southern midlatitudes is a prerequisite for determining the mechanisms underlying abrupt and widespread climate changes between the hemispheres during the Last Glacial-Interglacial transition (LGIT). This issue is still debated, with previous studies producing apparently discordant findings. Here we show evidence for a glacial readvance and a cold episode between ca. 14.8 and 12.6 ka in southwestern Patagonia (50 degrees S), contemporaneous with the Antarctic cold reversal. This was followed by ice recession under cold but relatively milder conditions until ca. 11.5 ka, when paleovegetation records indicate the onset of warm interglacial conditions. These findings differ from those reported in northern Patagonia (similar to 40 degrees S), where deteriorating conditions before 13.5 ka were followed by the coldest part of the LGIT that lasted until ca. 11.5 ka. We interpret the apparent blend of Greenlandic and Antarctic cold phases as evidence for their co-occurrence in the southern middle latitudes in Patagonia, and hypothesize that the position of the Antarctic Polar Front modulated the strength of these cold events in regions to the north or south of it.

Major lake level fluctuations and climate changes for the past 16,000 years as reflected by diatoms and chironomids preserved in the sediment of Laguna Potrok Aike, southern Patagonia

Article

Aug 2012
QUATERNARY SCI REV

High-resolution paleomagnetic secular variations and relative paleointensity since the Late Pleistocene in southern South America

Article

May 2012

a b s t r a c t Paleomagnetic inclination, declination and relative paleointensity were reconstructed from the sedi-ments of Laguna Potrok Aike in the framework of the International Continental scientific Drilling Program (ICDP) Potrok Aike maar lake Sediment Archive Drilling prOject (PASADO). Here we present the u-channel-based full vector paleomagnetic field reconstruction since 51.2 ka cal BP. The relative paleo-intensity proxy (RPI) was built by normalising the natural remanent magnetisation with the anhysteretic remanent magnetisation using the average ratio at 4 demagnetisation steps part of the ChRM interval (NRM/ARM 10e40 mT). A grain size influence on the RPI was removed using a correction based on the linear relationship between the RPI and the median destructive field of the natural remanent magnetisation (MDF NRM). The new record is compared with other lacustrine and marine records and stacks from the mid-to high-latitudes of the Southern Hemisphere, revealing consistent millennial-scale variability, the identification of the Laschamp and possibly the Mono Lake geomagnetic excursions, and a direction swing possibly associated to the Hilina Pali excursion at 20 ka cal BP. Nonetheless, a global-scale comparison with other high-resolution records located on the opposite side of the Earth and with various dipole field references hint at a different behaviour of the geomagnetic field around southern South America at 46 ka cal BP.

The occurrence of calcified planktonic green algae in freshwater carbonates

Article

Jan 1981
SEDIMENTOLOGY

Phacotus and Coccomonas, two carbonate-secreting, non-marine, planktonic chlorophyte genera, are important sediment contributors mainly in hard water lakes. The calcite loricae of these flagellate algae exhibit characteristic features easily recognizable under the microscope, making Phacotus and Coccomonas important facies fossils for the recognition of ancient non-marine environments. The fossil record of Phacotus can be traced back to the Miocene and it is probable that further research could extend this record into pre-Tertiary periods.