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Millennial-scale climate variability in the eastern Mediterranean region during Marine Isotope Stages 8 and 9 a-c (240 to 310 ka)

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1] A 50 kyr-long exceptionally well-dated and highly resolved stalagmite oxygen (d 18 O) and carbon (d 13 C) isotope record from Sofular Cave in northwestern Turkey helps to further improve the dating of Greenland Interstadials (GI) 1, and 3 – 12. Timing of most GI in the Sofular record is consistent within ±10 to 300 years with the ''iconic'' Hulu Cave record. Larger divergences (>500 years) between Sofular and Hulu are only observed for GI 4 and 7. The Sofular record differs from the most recent NGRIP chronology by up to several centuries, whereas age offsets do not increase systematically with depth. The Sofular record also reveals a rapid and sensitive climate and ecosystem response in the eastern Mediterranean to GI, whereas a phase lag of $100 years between climate and full ecosystem response is evident. Finally, results of spectral analyses of the Sofular isotope records do not support a 1,470-year pacing of GI. Citation: Fleitmann, D., et al. (2009), Timing and climatic impact of Greenland interstadials recorded in stalagmites from northern Turkey, Geophys. Res. Lett., 36, L19707, doi:10.1029/ 2009GL040050.
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ODP Sites 1055–1062 on the Blake-Bahama Outer Ridge (BBOR) are characterized by high sedimentation rates, which allow high-resolution analyses to reconstruct the behavior of the Deep Western Boundary Current (DWBC) as a function of depth along the BBOR. The ODP sites provide an intermediate and deep water transect from 1800 to 4760 m water depths. We focused on the time interval from 350 to 250 ka (marine isotope stages (MIS) 10.2–8.3). Grain size and magnetic properties were analyzed with centennial- to millennial-scale time resolution. Integrating the results of grain size analyses, lightness, and magnetic properties, the changes in the vertical position and the intensity of the DWBC core were inferred. During glacial periods (MIS 10.2 and 8.4–8.3) the DWBC core was located at around 2200 m water depth, whereas it deepened to 3000 m or more during warm periods (interglacial stage 9.3 and interstadial 8.5). Between these periods, the DWBC core moved to shallower depth (2500–3000 m) and its intensity increased, which generally provided coarser sediments to a broad depth range from 2100 to 4800 m. Furthermore, the magnetic properties imply that the DWBC supplied carbonate material other than terrigenous sediments to the deeper sites during MIS 9. The depositional processes at Site 1062 are characterized by sudden influxes of fine carbonate-rich sediments, which gradually decreased with time. Paleocurrent directions inferred from the direction of the great axis of the magnetic fabric are consistent with the modern topography at Sites 1055, 1056, 1058 and 1060 during the relatively warm period, from stages 9.3 to 8.5. At Site 1062, the deepest site, which exhibits a mud-wave field, the inferred flow direction is parallel to the bathymetric contours during warm periods, while the nearly cross-wave direction seemingly dominated during the other periods. It appears that topographic position may have affected the scattering of azimuth plots. Moreover, there is a possibility that the changes in flow direction correlate with climate changes.
Article
Large areas of Montenegro were glaciated during the Pleistocene. This paper presents evidence from the massifs of central Montenegro, including Durmitor and Sinjajevina, Moračke Planine, Maganik, Prekornica and Vojnik. Glacial deposits have been subdivided on the basis of morphostratigraphy and soil weathering and 31 U-series ages from cemented tills provided a geochronological framework. The largest glaciation occurred before 350 ka when a series of conjoined ice caps over the massifs of central Montenegro covered a total area of nearly 1500 km2. These formed during MIS 12 and correspond with the largest Skamnellian Stage glaciations in Greece to the south. Later Middle Pleistocene glaciations occurred during the penultimate glacial cycle correlating with the Vlasian Stage in Greece (MIS 6) when ice caps covered an area of 720 km2 over central Montenegro. There is also geochronological evidence of glacial deposits dating from the interval between MIS 12 and MIS 6, before the interglacial complex of MIS 7. This glaciation appears to have been very similar in extent to that which occurred during MIS 6. The last glacial cycle in central Montenegro was characterised by valley and cirque glaciers covering a total area of 49 km2. It is very likely that glaciers have been present in the mountains of central Montenegro during every glacial cycle since a small glacier still survives today. The smaller glaciers of the last glacial cycle are likely to have been associated with summer temperatures that were warmer than those of earlier cold stages. The striking contrast in the extent and thickness of ice cover during the cold stages of the Pleistocene has an important bearing on the geomorphological and biological evolution of the Balkans.
Article
Multiproxy data from North Atlantic deep-sea sediment core NEAP18K provide a detailed record of climate through oxygen isotope stage (OIS) 5. Seven distinct, large-scale episodes of ice rafting (C25 C19) were identified between 126 and 70 ka. Global ice-volume reconstructions, based on high-resolution benthic δ18O records, indicate that major ice-rafting events were not confined to ice-volume maxima at OIS 5d and 5b, but also occurred during periods of ice-sheet growth and disintegration. However, iceberg discharges were restricted to times when sea levels were 40 65 m below present values. Ice-rafting episode C25, the first large-scale cooling of mid-Atlantic surface waters after the last interglacial, occurred during the gradual buildup of continental ice sheets at the OIS 5e-5d transition. Major ice-sheet collapses allied to ice-rafting events C24 and C21 were associated with rapid sea-level increases of 20 and 40 m, respectively. Suborbital climatic fluctuations in the NEAP18K sedimentary record, denoted by prominent 7.5, 4.5, and 3 k.y. cyclicities, appear to correlate with both Greenland atmospheric temperatures and changes in thermohaline circulation patterns, inferred from benthic δ13C values, and hence provide clear evidence of a highly interconnected North Atlantic climatic regime during OIS 5.
Article
During the last glacial period, iceberg discharges into the North Atlantic led to a disruption of the Atlantic Meridional Overturning Circulation (AMOC), a cooling of the Northern Hemisphere, and a warming of Antarctica. This asymmetric response has been explained in terms of a bipolar seesaw mechanism, whereby changes in the strength of the AMOC result in changes in interhemispheric heat transport. However, it remains unclear to what extent the response of the AMOC and the operation of the bipolar seesaw may depend on background climate conditions, or the magnitude/delivery of freshwater flux to the North Atlantic. Here we present foraminiferal isotope and pollen records from the Portuguese margin from the last and penultimate glacial periods. A comparison of our records with temperature reconstructions from Antarctica indicates that the bipolar seesaw was a characteristic feature of both glacial periods. However, our comparison also underlines the dependence of the bipolar seesaw on background climate as well as the magnitude of iceberg discharge. Our results suggest that an intensified hydrological cycle may lead to a weaker overturning circulation with a smaller disruption threshold and extended North Atlantic stadial durations.
Article
A core recovered on the Iberian margin off southern Portugal can be correlated with Greenland ice cores using oxygen isotope variability in planktonic foraminifera which closely matches the ice core records of temperature over Greenland. Our age model identifies the base of every interstadial between 64,000 and 24,000 years ago and uses the Greenland Ice Core Project (GRIP) timescale. The oxygen isotope signal in benthic foraminifera (on this GRIP-based timescale) is quite different from the planktonic record and resembles the temperature record over Antarctica when this is synchronized with Greenland using the record of methane in the atmospheric air in the polar ice cores. We interpret the benthic record as indicating significant fluctuations in ice volume during millennial events, and we suggest that Antarctic temperature changed as a function of ice volume.
Article
Core Vema 28-238 preserves an excellent oxygen isotope and magnetic stratigraphy and is shown to contain undisturbed sediments deposited continuously through the past 870,000 yr. Detailed correlation with sequences described by Emiliani in the Caribbean and Atlantic Ocean is demonstrated. The boundaries of 22 stages representing alternating times of high and low Northern Hemisphere ice volume are recognized and dated. The record is interpreted in terms of Northern Hemisphere ice accumulation, and is used to estimate the range of temperature variation in the Caribbean.
Article
The sediments of Lake Fimon, N-Italy, contain the first continuous archive of the Late Pleistocene environmental and climate history of the southern Alpine foreland. We present here the detailed palynological record of the interval between Termination II and the Last Glacial Maximum. The age–depth model is obtained by radiocarbon dating in the uppermost part of the record. Downward, we correlated major forest expansion and contraction events to isotopic events in the Greenland Ice core records, via a stepping-stone approach involving intermediate correlation to isotopic events dated by TIMS U/Th in Alpine and Apennine stalagmites, and to pollen records from marine cores of the Iberian margin. Modelled ages obtained by Bayesian analysis of deposition are thoroughly consistent with actual ages, with maximum offset of ±1700 years. Sharp expansion of broad-leaved temperate forest and of sudden water table rise mark the onset of the Last Interglacial after a treeless steppe phase at the end of penultimate glaciation. This event is actually a two-step process which matches the two-step rise observed in the isotopic record of the nearby Antro del Corchia stalagmite, respectively dated to 132.5±2.5 and 129±1.5ka. At the interglacial decline mixed oak forests were replaced by oceanic mixed forests, the latter persisting further for 7ka till the end of the Eemian succession. Warm-temperate woody species are still abundant at the Eemian end, corroborating a steep gradient between central Europe and the Alpine divide at the inception of the last glacial. After a stadial phase marked by moderate forest decline, a new expansion of warm broad-leaved forests, interrupted by minor events and followed by mixed oceanic forests, can be identified with the north-alpine Saint Germain I. The spread of beech during the oceanic phase is a valuable circumalpine marker. The subsequent stadial–interstadial succession, lacking the telocratic oceanic phase, is also consistent with the evidence at the north-alpine foreland. The Middle Würmian (full glacial) is marked by persistence of mixed forests dominated by conifers but with significant lime and other broad-leaved species. A major Arboreal Pollen decrease is observed at modelled age of 38.7±0.5ka (larch expansion and last occurrence of lime), which has been related to Heinrich Event 4. The evidence of afforestation persisting south of the Alps throughout most of MIS 3 contrasts with a boreal and continental landscape known for the northern alpine foreland, pointing to a sharp rainfall boundary at the Alpine divide and to southern air circulation. This is in agreement with the Alpine paleoglaciological record and is supported by the pressure and rainfall patterns designed by mesoscale paleoclimate simulations. Strenghtening the continental high pressure during the full glacial triggered cyclogenesis in the middle latitude eastern Europe and orographic rainfall in the eastern Alps and the Balkanic mountains, thus allowing forests development at current sea-level altitudes.
Article
Continental polar outbreaks into the Levant and eastern Mediterranean regions originate in vast continental regions over Asia and Europe, causing respective unique weather conditions - cold, dry, and stable. These north-easterly winds have important environmental implications for agriculture, cold stress, and air pollution, which were the motivation for this study. They are exemplified here by statistical and synoptic study of such events over Israel. Seventy-two days of such outbreaks were observed during 6 years (1983-1988), all of them between October-May associated with different synoptic patterns. The typical duration of these events was of two categories: short events of 1-2 days, and long events of 4-5 days. The latter are the result of quasi- stationary systems whereas the short ones are due to the passage of disturbances over the eastern Mediterranean. The highest frequency is in December, with 28 days (between 1983 and 1988), compared with 13 days in January and 8 days in February. The decrease in frequency towards February can be attributed to changes in the cyclone's trajectories, and to pressure gradient magnitude between the anticyclone over Asia and Turkey and the lower barometric pressure over the Mediterranean. These events have a typical course of pressure increase preceding the outbreak and during its first 2 days, and then a pressure decrease that is mostly accompanied with temperature increase.
Article
Abstract Global vegetation changes at the time-scale of the Earth’s orbital variations (104–105 years) have been interpreted as a direct effect of consequential climatic changes, especially temperature. At mid- and high latitudes, the evidence from fossil data and general circulation models (GCMs) supporting this hypothesis is strong, but at low latitudes there is a major discrepancy. GCMs predict temperature changes that are less than those inferred from palaeoclimatic data, including the plant fossil record. However, changes in atmospheric CO2 concentrations can account for a high proportion of the low-latitude vegetation change hitherto attributed to temperature change, and may thus explain the discrepancy. The implications of this finding are considerable for understanding patterns of macroevolution and ecosystem development throughout the geological record.
Article
A high-resolution palynological and stratigraphical record of a marine deep-sea core in the Adriatic sea documents marine and continental palaeoenvironmental changes in the basin during the last deglaciation and early Holocene. A chronology is derived from the oxygen isotope stratigraphy. Three periods of aridity, marked by the development of a semi-desert rich in Artemisia, occurred between 18.5 and 16kyr, between 14.4 and 12.7kyr and between 11.1 and 9.7kyr, consistent with the Last Glacial Maximum, the Oldest Dryas and the Younger Dryas. They are correlated with increases in productivity and intensification of the Levantine water formation in the Eastern Mediterranean basin. During the warmer Bölling/Alleröd (12.7–11.1kyr), the presence of the cold temperate dinocyst Bitectatodinium tepikiense is interpreted as indicating the establishment of a strong seasonal thermal gradient, probably linked to seasonal cold freshwater runoff from the Pô river, attested by the unique presence of pollen of freshwater plants. The expansion of forest and the development of the warmer dinocysts start with Termination IB. During the Holocene, three tree phases are recognized and are contemporaneous with the Preboreal, Boreal and Atlantic chronozones of Europe. The two phases of sapropel deposition are marked by higher pollen and dinocyst concentrations and a high representation of Brigantedinium spp which indicate higher preservation of organic material and/or freshwater runoff of the Pô River.
Article
Tsiripidis, I. & Athanasiadis, N.: Contribution to the knowledge of the vascular flora of NE Greece: Floristic composition of the beech (Fagus sylvatica L.) forests in the Greek Rodopi. - Willdenowia 33: 273-297. - ISSN 0511-9618; © 2003 BGBM Berlin-Dahlem. The first floristic inventory of the beech forests in the Greek Rodopi is presented. The investigation in- cluded pure beech (Fagus sylvatica L. s.l.) stands as well as mixed stands of beech with Pinus syl- vestris, P. nigra, Picea abies, Abies ×borisii-regis, Quercus petraea subsp. medwediewii and Q. frainetto. The floristic catalogue is based on the floristic data of 584 phytosociological beech forests relevés and on a supplementary floristic inventory. Published information of records from inside beech forests has also been taken into account. For each taxon information is given about its spatial and altitudinal distribution and constancy in the Greek Rodopi as well as about its ecological preferences. The floristic catalogue is divided in two parts. The first part includes the taxa that constitute the beech forest community. The second part includes taxa that appear randomly in the beech forests. Three spe- cies, Hieracium praecurrens, Pyrola media and Verbascum lanatum, are recorded for the first time from Greece.
Article
A new high-resolution Last Interglacial pollen record from the Tenaghi Philippon peatland, northeast Greece, documents variability in forest composition and cover, which we attribute to changes in temperature and moisture availability. The declining stage of the interglacial was marked by a stepwise decrease in temperate tree populations and culminated in the complete collapse of forest at the onset of the ensuing stadial. The coincidence of the onset of the stepwise declining trend with the increased prominence of North Atlantic ice-rafting events suggests that ecological thresholds in southern Europe were only crossed once ice rafting events intensified, and implies that changes in North Atlantic ocean circulation were an important contributing factor to the declining temperate forest cover in southern Europe. Our results provide evidence for intra-interglacial variability in the low mid latitudes and suggest a coupling between the high northern latitudes and the northeast Mediterranean during this interval. Copyright © 2013 John Wiley & Sons, Ltd.
Article
This paper presents the outcome of a workshop, held in Berlin in February 2009, concerned with current research on the glacial history of northern Europe, including the British Isles. The methodologies presently used to resolve this topic are outlined. Particular attention is given to new analytical methods deriving from high resolution remote imaging of glacial terrain both on land and on the sea-bed, key new stratigraphic sections, higher resolution results from conventional geochronological methods like radiocarbon and more recently developed technologies such as luminescence and cosmogenic radionuclide dating. The relationships between the results derived from these two methods are discussed in further detail along with possible explanations for these differences. An outline of a ‘most likely’ glacial history of the Scandinavian and British and Irish Ice Sheets is presented along with possible links to global climate change as represented by the marine isotope (MIS) record. Tentative evidence for glaciation is identified in MIS 22, 16, 12, 10, 8, 6, 4 and 2 and correlations of ‘phases’ within the Last Glaciation are also explored for both the Scandinavian and British and Irish Ice Sheets. The results show that the character and extent of glaciation in different parts of the region are not synchronous and much more geochronological work is required before regional correlations can be established with confidence.
Article
The change from a glacial to an interglacial climate is paced by variations in Earth's orbit. However, the detailed sequence of events that leads to a glacial termination remains controversial. It is particularly unclear whether the northern or southern hemisphere leads the termination. Here we present a hypothesis for the beginning and continuation of glacial terminations, which relies on the observation that the initial stages of terminations are indistinguishable from the warming stage of events in Antarctica known as Antarctic Isotopic Maxima, which occur frequently during glacial periods. Such warmings in Antarctica generally begin to reverse with the onset of a warm Dansgaard-Oeschger event in the northern hemisphere. However, in the early stages of a termination, Antarctic warming is not followed by any abrupt warming in the north. We propose that the lack of an Antarctic climate reversal enables southern warming and the associated atmospheric carbon dioxide rise to reach a point at which full deglaciation becomes inevitable. In our view, glacial terminations, in common with other warmings that do not lead to termination, are led from the southern hemisphere, but only specific conditions in the northern hemisphere enable the climate state to complete its shift to interglacial conditions.
Article
Terrestrial and marine proxies (pollen, planktic and benthic foraminiferal oxygen isotopes, alkenone-and foraminifer-derived sea-surface temperatures (SSTs), ice-rafted debris) from IMAGES deep-sea cores MD95-2042 and SU81-18 (371N, 101W), MD99-2331 and MD03-2697 (421N, 91W), and MD04-2845 (451N, 51W) show that western European and offshore environments were strongly affected by Dansgaard–Oeschger (D–O) and Heinrich (H) events. We concentrate here on latitudinal variability in the forest cover extent and composition of western Europe during the succession of D–O events, showing new pollen records for core MD04-2845 and for marine isotopic stages (MIS) 3 and 4 of core MD99-2331. In general, cold SSTs characteristic of Greenland stadials were contemporaneous with the expansion of semi-desert or steppic vegetation while Greenland interstadials were synchronous with the expansion of forest. Our data reveal that the amplitude of Atlantic and Mediterranean forest expansions differs for any given D–O warming during the glacial period (74–18 ka). In the western Mediterranean, D–O 16–17 and D–O 8 and 7 (corresponding to minima in precession) were associated with strong expansion of forest cover contrasting with weak expansion of forest cover during D–O 14 and 12; the opposite pattern is revealed at the Atlantic sites. Further north, the strongest Greenland warmings are recorded for D–O 19, 11 and 8. This contrasting latitudinal climatic scenario is compared with other northern hemisphere records, revealing similarities between the Mediterranean climate and the Asian monsoon regime, which may relate to a summer atmospheric teleconnection between the two regions comparable to the present-day situation. Parallels between Mediterranean climate enhance-ment and peaks in global methane (CH 4) during the last glacial period suggest a significant role of monsoon activity in determining CH 4 emission from wetlands.
Article
The biostratigraphical classification of long pollen sequences in relation to the definition of pollen assemblage biozones according to the International Stratigraphic Guide is examined. To facilitate the description and organization of pollen stratigraphical data the concept of a ‘pollen assemblage superzone’ is introduced. A hierarchical approach relying on superzones, zones and subzones appears to be better suited to the different levels of variation encountered in long pollen sequences and is here applied to a recored from the loannina basin, northwest Greece.
Article
We present evidence of a recent drying in the eastern Mediterranean, based on weather and tree-ring data for Samos, an island of the eastern Aegean Sea. Rainfall declined rapidly after the late 1970s following trends for the entire Mediterranean and was associated with reduced tree-ring width in Pinus brutia. The most recent decline led to the lowest annual radial stem increment after the last 100 years (as far as records reach). As moisture availability decreased best correlations of tree growth with rainfall were obtained for progressively longer integration periods (1–2 years in moister periods, 5–6 years during the severe dryness of 20th century's last decades), suggesting increasing dependency in deep soil water. Such long-term integration periods of tree-growth responses to precipitation have not been reported before. They may reflect a tree-rooting pattern adapted to cope with even several successive dry years. In late summer 2000, moisture reserves became exhausted, however, and a substantial fraction of low altitude pines died, including some 80-year-old trees, which underlines the exceptional extent this trend had reached. Our findings provide empirical support for Intergovernmental Panel on Climate Change projections derived from global circulation models that the Mediterranean, its eastern basin in particular, should become drier as temperature rises, as was the case in the recent past.
Article
The Middle Pleistocene palaeoclimate and palaeoenvironment evolution of the Las Tablas de Daimiel wetlands is described using a combination of sedimentology, pollen and δ13C and δ18O isotopic records of Unit B of core LT-199906. This unit mostly contains fluvial and palustrine sediments. U/Th and amino acid racemization (AAR) dating and a comparison of the δ18O curve of Unit B with oceanic records suggests that Unit B spans the period from the end of Marine Isotope Stage (MIS) 10 (340 ka) to the first stages of MIS 7 (ca. 210 ka). MIS 9 was characterised by a regional vegetation dominated by Cupressaceae, with Pinus as a tree element. The water level was high and temperatures were very probably higher than during the Holocene. MIS 8 and the first substages of MIS 7 (7e, 7d and 7c) were dominated by xerophilous steppe vegetation in lowlands (elevations around 610 m above sea level) near to the wetland. At higher altitudes, far away from the wetland, there were fewer Pinus than in MIS 9, and a greater presence of warm, temperate and cool climate tree elements. The aquatic system in MIS 9 became shallower, with eutrophication and the accumulation of organic matter occurring; temperatures were similar to or lower than those of the Holocene. Copyright © 2011 John Wiley & Sons, Ltd.
Article
A 46-m core of lake sediments, obtained from the center of the explosion crater of Praclaux (Haute-Loire, Velay, France), was studied on the basis of 368 pollen spectra. Five temperate forest episodes alternating with phases indicative of glacial climates are recorded. Two of these episodes show vegetation successions representative of full interglaciations; the oldest is contemporaneous with the Holsteinian interglaciation. A thick trachytic tephra permits correlation to be established with the pollen sequence from Lac du Bouchet. This comparison indicates the presence of two complete interglaciations between the Holsteinian and the Eemian that are the equivalents of marine isotope stages 7 and 9. The Holsteinian therefore corresponds to isotope stage 11.
Article
1] The simplest possible model is proposed to explain a large fraction of the millennial climate variability measured in the isotopic composition of Antarctic ice cores. The model results from the classic bipolar seesaw by coupling it to a heat reservoir. In this ''thermal bipolar seesaw'' the heat reservoir convolves northern time signals with a characteristic timescale. Applying the model to the data of GRIP and Byrd, we demonstrate that maximum correlation can be obtained using a timescale of about 1000–1500 years. Higher correlations are obtained by first filtering out the long-term variability which is due to astronomical and greenhouse gas forcing and not part of the thermal bipolar seesaw. The model resolves the apparent confusion whether northern and southern climate records are in or out of phase, synchronous, or time lagged. INDEX TERMS: 1620 Global Change: Climate dynamics (3309); 1635 Global Change: Oceans (4203); 4267 Oceanography: General: Paleoceanography; KEYWORDS: bipolar seesaw, synchronization of Antarctic and Greenland ice cores, Dansgaard-Oeschger events, north-south connection Citation: Stocker, T. F., and S. J. Johnsen, A minimum thermodynamic model for the bipolar seesaw, Paleoceanography, 18(4), 1087, doi:10.1029/2003PA000920, 2003.