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Holocene glacier history of the Lago Argentino basin, Southern Patagonian Icefield
Abstract
We present new geomorphic, stratigraphic, and chronologic data for Holocene glacier fluctuations in the Lago Argentino basin on the eastern side of the southern Patagonian Andes. Chronologic control is based on 14C and surface-exposure 10Be dating. After the Lateglacial maximum at 13,000 cal yrs BP, the large ice lobes that filled the eastern reaches of Lago Argentino retreated and separated into individual outlet glaciers; this recession was interrupted only by a stillstand or minor readvance at 12,200 cal yrs BP. The eight largest of these individual outlet glaciers are, from north to south: Upsala, Agassiz, Onelli, Spegazzini, Mayo, Ameghino, Perito Moreno, and Grande (formerly Frías). Holocene recession of Upsala Glacier exposed Brazo Cristina more than 10,115 ± 100 cal yrs BP, and reached inboard of the Holocene moraines in Agassiz Este Valley by 9205 ± 85 cal yrs BP; ice remained in an inboard position until 7730 ± 50 cal yrs BP. Several subsequent glacier readvances are well documented for the Upsala and Frías glaciers. The Upsala Glacier readvanced at least seven times, the first being a relatively minor expansion – documented only in stratigraphic sections – between 7730 ± 50 and 7210 ± 45 cal yrs BP. The most extensive Holocene advances of Upsala Glacier resulted in the deposition of the Pearson 1 moraines and related landforms, which are divided into three systems. The Pearson 1a advance occurred about 6000–5000 cal yrs BP and was followed by the slightly less-extensive Pearson 1b and 1c advances dated to 2500–2000 and 1500–1100 cal yrs BP, respectively. Subsequent advances of Upsala Glacier resulted in deposition of the Pearson 2 moraines and corresponding landforms, also separated into three systems, Pearson 2a, 2b, and 2c, constructed respectively at ∼700, >400, and <300 cal yrs BP to the early 20th century. Similar advances are also recorded by moraine systems in front of Grande Glacier and herein separated into the Frías 1 and Frías 2a, 2b, and 2c. The Onelli and Ameghino glacier valleys also preserve older Holocene moraines. In the Agassiz, Spegazzini, and Mayo valleys, ice of the late-Holocene advances appears to have overridden landforms equivalent in age to Pearson 1. Perito Moreno Glacier is an extreme case in which ice of historical (Pearson 2c) advances overrode all older Holocene moraines. Based on the distribution and number of moraines preserved, we infer that the response to climate differed among the Lago Argentino outlet glaciers during the Holocene. This led us to examine the effects of climatic and non-climatic factors on individual glaciers. As a consequence, we detected an important effect of the valley geometry (hypsometry) on the timing and magnitude of glacier response to climate change. These results indicate that caution is needed in correlating moraines among glacier forefields without firm morpho-stratigraphic and age control. Finally, we note important similarities and differences between the overall moraine chronology in the Lago Argentino basin and that in other areas of southern South America and elsewhere in the Southern Hemisphere.
... The lake has received and preserved sediment delivered by the waxing and waning of the former Argentino Glacier for ≤20,000 years, and represents an almost perfect trap for the sediments eroded in the upland catchments, thereby minimizing stratigraphic and sedimentary incompleteness. The region offers a radiocarbon and cosmogenic nuclide-rich geomorphological record of Pleistocene and Holocene climate changes (e.g., Kaplan et al., 2016;Strelin et al., 2011Strelin et al., , 2014Romero et al., 2024, and others) that constrain the time of deposition of subaqueous sediments. We estimate basin-wide erosion rates over 10 0 -10 4 yr timescales using high resolution seismic reflection data imaging the glacial and glaciolacustrine sedimentary sequences. ...
... The study area preserves a system of moraines exposed on land ( Figure 1) from which the evolution of the former Argentino Glacier, the paleo-glacier that carved Lago Argentino and the surrounding region, has been reconstructed. The moraines have been extensively mapped (Ackert et al., 2008;Aniya & Sato, 1995;Glasser et al., 2008;Kaplan et al., 2011;Mercer, 1965Mercer, , 1976Strelin et al., 2011;Strelin & Malagnino, 2000) and dated using 14 C and 10 Be dating techniques (e.g., Kaplan et al., 2011Kaplan et al., , 2016Strelin et al., 2011Strelin et al., , 2014, and show that Lago Argentino was covered by ice during the LGM (∼35-18 ka in Patagonia; Clark et al., 2009;Davies et al., 2020;McCulloch et al., 2000;Rabassa & Clapperton, 1990), and only afterward opened to sedimentation. Subsequently, the Argentino Glacier underwent several readvances during the Late glacial (∼18-10 ka; Rabassa et al., 2022;Strelin et al., 2011) and the Neoglacial (mid-to late Holocene Porter, 2000;Strelin et al., 2014), which culminated during the Little Ice Age (LIA, ∼1550-1800 AD; Meyer & Wagner, 2008, 2009Von Storch et al., 2004). ...
... The moraines have been extensively mapped (Ackert et al., 2008;Aniya & Sato, 1995;Glasser et al., 2008;Kaplan et al., 2011;Mercer, 1965Mercer, , 1976Strelin et al., 2011;Strelin & Malagnino, 2000) and dated using 14 C and 10 Be dating techniques (e.g., Kaplan et al., 2011Kaplan et al., , 2016Strelin et al., 2011Strelin et al., , 2014, and show that Lago Argentino was covered by ice during the LGM (∼35-18 ka in Patagonia; Clark et al., 2009;Davies et al., 2020;McCulloch et al., 2000;Rabassa & Clapperton, 1990), and only afterward opened to sedimentation. Subsequently, the Argentino Glacier underwent several readvances during the Late glacial (∼18-10 ka; Rabassa et al., 2022;Strelin et al., 2011) and the Neoglacial (mid-to late Holocene Porter, 2000;Strelin et al., 2014), which culminated during the Little Ice Age (LIA, ∼1550-1800 AD; Meyer & Wagner, 2008, 2009Von Storch et al., 2004). As the ice retreated and readvanced across the region, the main lake, Brazo Norte, and other brazos evolved from ice-contact/ice-proximal to ice-distal depositional settings (and vice versa). ...
Recovering the patterns of glacial erosion over time is key to understanding feedbacks between climate and tectonic processes. Glacial erosion rates have been shown to systematically increase worldwide toward the present since the late Cenozoic, a behavior interpreted as the response of glaciers to a cooling and increasingly variable climate. However, the validity of this signal has been questioned, and suggested to be affected by the incompleteness of the sedimentary record, which can introduce a time dependent bias in the time averaged rates. In this study, we present new glacial erosion rates estimated from sediment accumulations in Lago Argentino, Patagonia, a proglacial basin with a nearly complete preserved sedimentary record. The erosion rates are estimated through the past 20,000 years and averaged over time intervals ranging from sub‐decadal to millennial, allowing us to explore erosion rate variability through time and within a glacial cycle. The data show that erosion rates have varied substantially, from 0.43 ± 0.12 to 82.38 ± 17.58 mm/yr, with no systematic increase (or decrease) through time. Rather, erosion occurs during discrete, intense events separated by times of quiescence. In addition, we find that glacial erosion rates have comparable magnitudes when averaged over similar time intervals. Our data show a power‐law increase in glacial erosion rates with decreasing averaging time interval, consistent with other observations globally. Given our observed intermittent character of glacial erosion, we attribute this increase to a time averaging bias, rather than to an escalation in magnitude of erosional pulses toward the present.
... ka BP in Potter Cove followed by a glacier readvance at <7.0 cal. ka BP on Potter Peninsula (Strelin et al., 2014) (Figures 3, 5a, 6a and 7e-g). ...
... The Stage 3 readvance was broadly synchronous with two phases of glacier expansion and the reformation of ice shelves on the north-eastern AP (Figure 5f), and in Southern South America between c. 1.5 and 1.1 cal. ka BP (Balco and Schaefer, 2013;Kaplan et al., 2020;Moreno et al., 2018;Strelin et al., 2014) and occurred when a colder conditions existed on the north-eastern AP (Figure 5g) (Mulvaney et al., 2012), but also when composite ice core records from elsewhere in Antarctica show a predominantly warmer phase (Masson et al., 2000). ...
... ka BP which coincided with the transition to colder and more negative SAMlike conditions as the SHW migrated marginally equatorward (Figure 7a-c and g). Glacier readvance(s) on KGI are regionally coherent with readvances on the eastern AP (Kaplan et al., 2020;Figure 5f) and in Patagonia at c. 7 ka (Reynhout et al., 2019;Strelin et al., 2014), implying a common forcing mechanism. ...
To provide insights into glacier-climate dynamics of the South Shetland Islands (SSI), NW Antarctic Peninsula, we present a new deglaciation and readvance model for the Bellingshausen Ice Cap (BIC) on Fildes Peninsula and for King George Island/Isla 25 de Mayo (KGI) ~62°S. Deglaciation on KGI began after c. 15 cal. ka BP and had progressed to within present-day limits on the Fildes Peninsula, its largest ice-free peninsula, by c. 6.6–5.3 cal. ka BP. Probability density phase analysis of chronological data constraining Holocene glacier advances on KGI revealed up to eight 95% probability ‘gaps’ during which readvances could have occurred. These are grouped into four stages – Stage 1: a readvance and marine transgression, well-constrained by field data, between c. 7.4 and 6.6 cal. ka BP; Stage 2: four probability ‘gaps’, less well-constrained by field data, between c. 5.3 and 2.2 cal. ka BP; Stage 3: a well-constrained but restricted ‘readvance’ between c. 1.7 and 1.5 cal. ka BP; Stage 4: two further minor ‘readvances’, one less well-constrained by field data between c. 1.3 and 0.7 cal. ka BP (68% probability), and a ‘final’ well-constrained ‘readvance’ after <0.7 cal. ka BP. The Stage 1 readvance occurred as colder and more negative Southern Annular Mode (SAM)-like conditions developed, and marginally stronger/poleward shifted westerly winds led to more storms and precipitation on the SSI. Readvances after c. 5.3 cal. ka BP were possibly more frequent, driven by reducing spring/summer insolation at 62°S and negative SAM-like conditions, but weaker (equatorward shifted) Westerlies over the SSI led to reduced storminess, restricting readvances within or close to present day limits. Late Holocene readvances were anti-phased with subaquatic freshwater moss layers in lake records unaffected by glaciofluvial inputs. Retreat from ‘Neoglacial’ glacier limits and the recolonisation of lakes by subaquatic freshwater moss after 1950 CE is associated with recent warming/more positive SAM-like conditions.
... Glaciers are sensitive to climatic variations, and glacial landforms indirectly preserve information about past climate (Leger et al., 2021). Many Patagonian glaciers record multiple past advances through frontal moraines (Davies et al., 2020;Kaplan et al., 2016;Reynhout et al., 2019;Strelin et al., 2014), corresponding to times of higher precipitation or lower temperatures. Numerical modeling of past glacier extents under a suite of different climatic scenarios has been used to quantitatively constrain past precipitation and temperature ranges (Leger et al., 2021), although qualitative correlations between glacier extent and climatic conditions are more common (Kaplan et al., 2016;Strelin et al., 2014;Warren, 1993). ...
... Many Patagonian glaciers record multiple past advances through frontal moraines (Davies et al., 2020;Kaplan et al., 2016;Reynhout et al., 2019;Strelin et al., 2014), corresponding to times of higher precipitation or lower temperatures. Numerical modeling of past glacier extents under a suite of different climatic scenarios has been used to quantitatively constrain past precipitation and temperature ranges (Leger et al., 2021), although qualitative correlations between glacier extent and climatic conditions are more common (Kaplan et al., 2016;Strelin et al., 2014;Warren, 1993). Reynhout et al. (2019) proposed that variations in SAM phase have paced Holocene glacier fluctuations in Patagonia by controlling the local precipitation and temperature. ...
... Studies with both a high temporal resolution and temporal coverage greater than 1000 years (Abram et al., 2014;Elbert et al., 2012;Lara et al., 2020;Moreno et al., 2014) show limited agreement, and are too spatially far apart for a consensus Patagonian paleoclimate reconstruction. Our best understanding of past SAM changes comes from an agreement between Southern Patagonian pollen assemblage changes (Moreno et al., 2014) and glacial fluctuations (Kaplan et al., 2016;Reynhout et al., 2019;Strelin et al., 2014), which suggest an approximately 200-year duration of SAM-positive phases. ...
... On the eastern, leeward, side of the SPI, terrestrial archives of glacier variability are abundant (Davies et al., 2020) and numerous moraine systems have been dated through lichenometry (Garibotti and Villalba, 2009), dendrochronology (Masiokas et al., 2009a), radiocarbon (Mercer, 1968;Moreno et al., 2009;Strelin et al., 2014Strelin et al., , 2011, or cosmogenic nuclide exposure-age dating (Kaplan et al., 2016;Moreno et al., 2009;Reynhout et al., 2019;Strelin et al., 2014). As a result, postglacial fluctuations along the eastern side of the icefield are relatively well constrained. ...
... On the eastern, leeward, side of the SPI, terrestrial archives of glacier variability are abundant (Davies et al., 2020) and numerous moraine systems have been dated through lichenometry (Garibotti and Villalba, 2009), dendrochronology (Masiokas et al., 2009a), radiocarbon (Mercer, 1968;Moreno et al., 2009;Strelin et al., 2014Strelin et al., , 2011, or cosmogenic nuclide exposure-age dating (Kaplan et al., 2016;Moreno et al., 2009;Reynhout et al., 2019;Strelin et al., 2014). As a result, postglacial fluctuations along the eastern side of the icefield are relatively well constrained. ...
... (b) Overview map of the Southern Patagonian Icefield (SPI) and the adjacent fjord region. Glaciers investigated in this study are indicated in red (# 8e10), those investigated by Mercer (1970) in gray (# 3e6), by Reynhout et al. (2019) in yellow (#7), and by Kaplan et al. (2016) and Strelin et al. (2014) in dark blue (# 11e18). The western limits of the Patagonian Ice Sheet during the local LGM (orange line) and of the SPI at 13 kyr BP (dotted white line) are from Davies et al. (2020). ...
Postglacial fluctuations of Southern Patagonian Icefield (SPI) glaciers are well constrained on the leeward side of the Andes, but they remain mostly unknown on the windward side of the icefield, where most glaciers are marine-terminating. Here, we reconstruct the postglacial fluctuations of the HPS19, Penguin, and Europa glaciers along the hyperhumid western side of the SPI using a multi-proxy sedimentological and geochemical analysis of a 12.2 m long sediment core from Wide Channel (50°S). Results show that the glaciers retreated into Penguin and Europa fjords by 11.2 cal kyr BP and that they were relatively stable and marine-terminating between 11.2 and 5.8 cal kyr BP. Thereafter, they fluctuated rapidly, with four marked episodes of glacier shrinkage at 5.8-4.8, 3.9-2.4, 1.0-0.2 cal kyr BP, and during the 20th century. Although the HPS19, Penguin, and Europa glaciers were calving into Penguin and Europa fjords during most of the Holocene, our data suggest that they retreated to land-based positions between 5.8 and 4.8 cal kyr BP. The comparison of our sediment record with geological archives from both sides of the Patagonian icefields (46-56°S) suggests synchronous glacier variability on multi-centennial timescales during the Neoglacial period, which is particularly clear after 2.5 cal kyr BP. We conclude that western SPI outlet glaciers remained relatively stable during the first half of the Holocene but fluctuated considerably during the Neoglacial period, and that they retreated to locations further inland than today during the first retreat of the Neoglacial period between 5.8 and 4.8 cal kyr BP.
... Our understanding of the climatic evolution of the southern mid-latitudes during and since the last ice age has benefited from a flurry of paleoclimate research in southern Patagonia and Tierra del Fuego (49 -55 S) over the last decades (Borromei and Quattrocchio, 2008;Borromei et al., 2010;Candel et al., 2020;Coronato et al., 2022;Fern andez et al., 2013Kaplan et al., 2016;Kilian et al., 2007;Kilian and Lamy, 2012;Lamy et al., 2010;Laprida et al., 2021;Markgraf and Huber, 2010;Mancini, 2009;Mansilla et al., 2016Mansilla et al., , 2018Mayr et al., 2007;McCulloch et al., 2019McCulloch et al., , 2020McCulloch et al., , 2021Moreno et al., 2009Moreno et al., , 2010Moreno et al., , 2012Moreno et al., , 2018aMoreno et al., , 2018bMoreno et al., , 2021aMoy et al., 2011;Quade and Kaplan, 2017;Recasens et al., 2015;Sagredo et al., 2011;Strelin et al., 2011Strelin et al., , 2014Sch€ abitz et al., 2013;Tonello et al., 2009;Unkel et al., 2010;Villa-Martínez and Moreno, 2007;Waldmann et al., 2010;Wille and Sch€ abitz, 2009;Zolitschka et al., 2013). Although major advances have shed light on the functioning of the terrestrial and marine paleoenvironments, some subjects remain elusive and, in some instances, compounded by unconstrained geological and ecological assumptions among diverse depositional environments (Kilian and Lamy, 2012;Moreno et al., 2018a). ...
... (d) Lago Cipreses principal component 1 (PC1) score with positive (negative) anomalies in light blue (red) shading (this study). (e) 10 Be cosmogenic dates from Glaciar Torre (i; Reynhout et al., 2019), 14 C and 10 Be dates from Lago Argentino (ii and iii, respectively; Strelin et al., 2014;Kaplan et al., 2016), along with the recalibrated chronology of Cipreses Cycles using SHcal20 (iv; Moreno et al., 2018b). For (i) and (iii), we show the arithmetic mean (red line) with 1s uncertainty (light blue box) crossed by the peak age (blue line) and median age (green line). ...
... In total, the first two phases revealed by the diatom record in L. Cipreses are directly compatible with the pan-Patagonian Early Holocene Westerly Minimum (EHWM) reported by Moreno et al. (2021a) and opposite to the SWW early Holocene maximum inferred from sites near Gran Campo Nevado ( Fig. 1; Lamy et al., 2010). Consistent with this triphasic structure, exposure-age chronologies from Glaciar Torres (Reynhout et al., 2019) and other glaciers adjacent to Lago Argentino (Strelin et al., 2014) provide evidence for glacier advances during the precursor and exit phases but largely absent during the acute phase (Fig. 9e). Furthermore, recent palynological evidence from the Cerro Benítez site, located~35 km southeast of L. Cipreses, indicates forest opening and low bog surface wetness between~8.7-7.2 cal. ...
Conflicting, even opposite interpretations on the evolution of the Southern Westerly Winds (SWW) are evident in paleoenvironmental records from southwestern Patagonia since the last ice age. These divergences call for new approaches utilizing different, ideally independent indicators of paleoenvironmental/paleoclimatic change from sensitive sites in climatically relevant locations. Here we present a multidecadally resolved diatom record from Lago Cipreses (51S), a small closed-basin lake located in a bedrock depression along the eastern foothills of the southern Patagonian Andes. The hydrological balance evolution of this isolated lake affords a direct tie with SWW intensity in a mountainous sector where zonal wind strength and local precipitation are highly correlated. We detect cold-tolerant diatoms (small fragilarioids) between ~14-11.9 cal. ka BP followed by a shift to planktonic assemblages (Discostella pseudostelligera, Aulacoseira spp.) under warmer Holocene conditions. Diatom assemblages indicative of stratified water-column conditions (Discostella pseudostelligera, Achnanthidium aff tepidaricola, Achnanthidium sieminskae) reached their maximum stability between ~9.1-7.4 cal. ka BP. Stronger water-column mixing is evident by an abrupt species turnover to Aulacoseira spp. between ~7.4-3.1 cal. ka BP, superimposed on centennial-scale alternations between assemblages since ~6.1 cal. ka BP. Cold-tolerant diatoms resurge at ~3.1 cal. ka BP and persist until the present. Our record offers assemblage-based evidence we interpret as sub-centennial to multimillennial scale changes in hydroclimate indicative of: (i) strong SWW influence between ~14-11.9 cal. ka BP, (ii) a transition between ~11.9-11.3 cal. ka BP to weak SWW influence between ~11.3-6.5 cal. ka BP, with a SWW minimum between ~9.1-7.4 cal. ka BP, and (iii) strong SWW influence since ~6.5 cal. ka BP, with a Holocene SWW maximum since ~3.1 cal. ka BP. We posit that enhanced hydroclimate variability since ~6.1 cal. ka BP attests to the onset of Southern Annular Mode-like changes at centennial-to sub-centennial timescales. We detect a remarkably coherent and synchronous response of terrestrial and aquatic ecosystems at local scale since ~14 cal. ka BP, highlighting the overriding importance of variations in SWW influence in terrestrial and aquatic environments at multiple timescales.
... However, the beginning of the late Holocene is marked by a global cooling trend (Neoglacial) leading to glacier advances and sea surface temperature decrease in different places in the world (e.g., Jerardino, 1995;Sepúlveda et al., 2009;Aniya et al., 2013;Solomina et al., 2015). SST estimates in the SJG records indicate a slight cooling after 4 cal ka BP, but the onset of the cooling dates from 7 cal ka BP, which is consistent with previous study based on glacier history showing that the onset of cooling has started much earlier, at about 7730 cal BP in Patagonia, marking the beginning of successive glacier advances ( Fig. 7; Strelin et al., 2014;Kaplan et al., 2016). ...
... The marine records of Pacific and Atlantic oceans at high southern latitudes show drastic changes with a cooling trend during this period (Fig. 10, Bianchi and Gersonde, 2004;Kaiser et al., 2005). Indeed, this interval corresponds to the Antarctic and Younger Dryas cold reversals that led to glacier advances in the Southern Hemisphere (Bianchi and Gersonde, 2004;Kaiser et al., 2005;Strelin et al., 2014;Quade and Kaplan, 2017), probably as a result of northward shift of the SWWB. ...
... The SWWB shift in the middle Holocene is consistent with reduced moisture over southern Patagonian and the interruption of the wind driven-upwellings in the high latitudes of the South Atlantic sector (Anderson et al., 2009;Lamy et al., 2010). Such northward migration of the core of the SWWB might have led to the onset of cold conditions in Southern South America, which caused glacier advances after 7730 cal ka BP (Strelin et al., 2014;Kaplan et al., 2016). ...
We use pollen and dinocyst assemblages from three sedimentary sequences of the San Jorge Gulf (SJG) to document the vegetation history of the extra-Andean/eastern Patagonia (Argentina), and the latitudinal variations of the Southern Westerly Wind Belt (SWWB) in relation with ocean changes during the Late Pleistocene and Holocene. Our results suggest that prior to 14 cal ka BP, the vegetation of the SJG was dominated by halophytic taxa probably related to arid conditions in coastal environments. After 14 cal ka BP, pollen data suggest the development of shrub and herb vegetation in the Patagonian steppe then characterized by semi-arid conditions. The 14 cal ka BP transition is marked by increasing Nothofagus pollen abundances, suggesting strong westerlies at the onset of the Antarctic Cold Reversal (ACR). This transition is also marked by the occurrence of marine palynomorphs (dinocysts, organic linings of foraminifers), which relate to sea-level rise. The dinocyst assemblages allowed us to quantitatively estimates changes in summer sea-surface temperature (SST) and annual net primary productivity. Between 14 and 10.8 cal ka BP, which encompasses the glacial termination and the early Holocene, dinocyst assemblages are dominated by Operculodinium centrocarpum (∼82%) and Spiniferites mirabilis (∼8%) that suggest warmer conditions than at present. The transition from early to middle Holocene was marked by high SWWB intensity as suggested by pollen assemblages, and an increase of heterotrophic taxa such as Brigantedinium spp., Echinidinium sp., Dubridinium sp., and the cysts of Polykrikos kofoidii, suggesting increased primary productivity and gradual cooling of surface water. After 4 cal ka BP, pollen data suggest a decrease in the SWWB intensity that correlates with glacier advances in Patagonia and a further decrease in summer SST in the SJG.
... Un problema que ha tenido especial relevancia en la discusión de dichas etapas, ha sido el abandono o uso discontinuo de ciertas zonas y el reposicionamiento de los grupos humanos en función de los cambios climáticos registrados durante el Holoceno medio-tardío (Borrero & Franco, 2000;Franco et al. 2004;Franco et al. 2018). Para dichos momentos se ha registrado una relación inversa de las precipitaciones entre la zona ubicada al este del área y la zona cercana a los Andes (Mancini, 2002;Tonello et al. 2009en Franco et al. 2018Mancini et al. 2013;Ohlendorf et al. 2014;Strelin et al. 2014). En consecuencia, se ha sugerido que el cambio ambiental influyó en la movilidad y los tipos de asentamientos al oeste y al este del Lago Argentino (Franco et al. 2016(Franco et al. , 2018. ...
... Sin embargo, para el momento en que RB1 registra evidencias humanas -hace ca. 350 años AP nuevamente se registran condiciones más áridas en la estepa (Tabla 1), (Aniya, 2013y Strelin et al. 2014en Franco et al. 2018. ...
... 450 años cal. AP, el cual se reflejó en un aumento de la humedad en los Andes, acompañado de condiciones más áridas en la estepa (Aniya, 2013;Strelin et al. 2014en Franco et al. 2018. ...
ln this paper we perform an exploratory study of the formation processes involved in the case of RB1 site, based on the analysis of the zooarchaeological record of stratified layers dated between ca. 4.200 and 350 years BP. To do that, we evaluated the degree of intervention of different agents and studied the preservation and the integrity of the zooarchaeological record in relation to changes in site morphology, to be able to discuss the human role in the formation of assemblages. The results indicate that humans were the main accumulator agent, and their actions have varied throughout the analyzed sequence. The zooarchaeological record suggests changes in the preservation of bone remains, which, according to the results are closely related to environmental variations in the area.
... Un problema que ha tenido especial relevancia en la discusión de dichas etapas, ha sido el abandono o uso discontinuo de ciertas zonas y el reposicionamiento de los grupos humanos en función de los cambios climáticos registrados durante el Holoceno medio-tardío (Borrero & Franco, 2000;Franco et al. 2004;Franco et al. 2018). Para dichos momentos se ha registrado una relación inversa de las precipitaciones entre la zona ubicada al este del área y la zona cercana a los Andes (Mancini, 2002;Tonello et al. 2009en Franco et al. 2018Mancini et al. 2013;Ohlendorf et al. 2014;Strelin et al. 2014). En consecuencia, se ha sugerido que el cambio ambiental influyó en la movilidad y los tipos de asentamientos al oeste y al este del Lago Argentino (Franco et al. 2016(Franco et al. , 2018. ...
... Sin embargo, para el momento en que RB1 registra evidencias humanas -hace ca. 350 años AP nuevamente se registran condiciones más áridas en la estepa (Tabla 1), (Aniya, 2013y Strelin et al. 2014en Franco et al. 2018. ...
... 450 años cal. AP, el cual se reflejó en un aumento de la humedad en los Andes, acompañado de condiciones más áridas en la estepa (Aniya, 2013;Strelin et al. 2014en Franco et al. 2018. ...
En este trabajo realizamos un estudio exploratorio de los procesos de formación del sitio RB1, a partir del análisis del registro zooarqueológico comprendido en capas estratificadas entre ca. 4.200 y 350 años AP. Para ello evaluamos el grado de intervención de diferentes agentes y estudiamos la preservación e integridad del registro en relación con los cambios en la morfología del sitio para discutir el rol humano en la formación de los conjuntos. Los resultados indican que el ser humano habría sido el principal agente acumulador y que su accionar habría variado a lo largo de la secuencia analizada. A su vez, el registro faunístico sugiere cambios en la preservación de los restos óseos, los cuales se encuentran en estrecha relación con las variaciones ambientales del área.
... The eastern margin of the SPI consisted of four main ice lobes, which are constrained chronostratigraphically. In the studied area, the Lago Argentino Lobe is one of them (Kaplan et al., 2016;Strelin et al., 2011Strelin et al., , 2014. ...
... There is extensive work on the Puerto Bandera moraines which constrains late-glacial recession (Strelin and Malagnino, 2000;Strelin et al., 2011). The ice dynamics during Holocene times are dated on the Herminita Peninsula, around Lago Pearson and around Lago Frías ( Fig. 1; Strelin et al., 2014;Kaplan et al., 2016). ...
... The history of deglaciations in the southern arms of Lago Argentino during the late-glacial is presented by Strelin et al. (2011Strelin et al. ( , 2014 and Kaplan et al. (2011). The oldest minimum limiting age of 12,660 cal yrs BP corresponds to the plant colonization of spillways "M" and "A" of Brazo Rico (sector 3 in Strelin et al., 2011), located in the eastern margin of the Brazo Rico (Fig. 4). ...
Lago Argentino hosts various calving glaciers, including the most famous Perito Moreno. Although the onland late-glacial glacier dynamics is rather well constrained, its submerged evidences remains largely unknown. A detailed analysis of high-resolution seismic reflection profiles acquired in the southern arms of Lago Argentino has allowed the identification of several unconformities within the lacustrine sedimentary infill. Four seismostratigraphic sequences have been identified in Brazo Rico and three in Brazo Sur. These sequences are separated by three erosive unconformities in Brazo Rico and two in Brazo Sur, and reflect the sedimentation of a pre-Holocene deep basin in a proglacial lake. The older unconformities were developed as consequence of mass movements, possibly triggered by seismicity in the area. The younger erosive unconformities were correlated with the “Pearson 1a/Frias 1 advance”, the major glacier advance in the mid-Holocene. This study highlights the importance of the glaciolacustrine sediments, representing decisive records of the glacial history and palaeoclimate, which could help unveiling the origin of the different behavior of the glacier Perito Moreno, which in a warming climate is relatively stable.
... Historical records and remotely sensed data have allowed monitoring the magnitude of such changes throughout the twentieth and twentyfirst centuries, and reveal both high and accelerating ice loss in the Lago Argentino basin (Abdel Jaber et al., 2019;Van Wyk de Vries et al., 2023c). Geologic data retrieved from moraines (Strelin et al., 2014;Kaplan et al., 2016) and tree rings (Mercer, 1968;Aniya, 1996;Masiokas et al., 2009) in the Lago Argentino region provide a broader and longer term context of glacial and climatic fluctuations in the pre-observational era. ...
... The two possible sources for the sandy sediments in 33A-3 are Perito Moreno Glacier and Ameghino Glacier. However, a subaqueous moraine associated with the late Herminita glacial advance of Perito Moreno Glacier (Kaplan et al., 2011(Kaplan et al., , 2016Strelin et al., 2011Strelin et al., , 2014Lodolo et al., 2020) could topographically inhibit the supply of coarse sediments to the 33A site. On the other hand, Ameghino Glacier retreated from its subaerial moraine during the mid-twentieth century (Masiokas et al. 2009), leading to the formation of Laguna Ameghino and isolating its coarse sediment supply from the 33A site. ...
Lake sediment provides a valuable record of past environmental change. However, the controls on sedimentation in proglacial lakes and their relation to glacier retreat remain poorly understood. In this study we analyze glaciolacustrine sediment production and deposition in Canal de los Témpanos, Lago Argentino, Argentine Patagonia. We associate temporal changes in the sedimentologic and geochemical characteristics analyzed from Lago Argentino cores with Late Holocene fluctuations of the Perito Moreno and Ameghino glaciers. We show that the dominant sediment source at our study site switched from Ameghino to Perito Moreno Glacier after the recession of Ameghino Glacier and the formation of the marginal ice-contact lake into which it currently calves. Spectacular ice-dam rupture events generated by Perito Moreno Glacier redistribute large volumes of water through the lake system but do not leave a significant sedimentary signature. Our results demonstrate that a detailed analysis of sedimentologic, petrophysical, and geochemical changes in lake cores can provide insight into regional glacial dynamics and sedimentary processes even in complex systems with multiple competing glacial sources and that changing glacier geometries during retreat can provide insights into the provenience of the sediments.
... Evidence of the Stage 1 readvance and a marine transgression, when relative sea-level was ~15 m a.s.l. after 7.5-7.0 ka cal BP in Potter Cove (Strelin et al., 2014) Data constraining RSL from the SSI are more complex than other locations across Antarctica, and several different RSL curves have been suggested for the SSI (Pallàs et al., 1997;Bentley et al., 2005;Hall, 2010;Roberts et al., 2011;Watcham et al., 2011;Simms et al., 2012;2021;Johnson et al., 2021). Bentley et al. (2005) initially proposed that RSL declined from an undated early-mid Holocene marine limit of ~16-18 m above present sea-level (henceforth, m a.s.l.) in a discontinuous manner, interrupted at 14.5-16 m a.s.l. by a redavance between 5.8-3.0 ka cal BP). ...
... The Stage 3 readvance was broadly synchronous with two minor phases of glacier expansion on the north-eastern AP (Kaplan et al., 2020) (Figure 5E), in Southern South America between c. 1.5 and 1.1. ka cal BP (Strelin et al., 2014;Moreno et al., 2018), and a predominantly warmer phase in composite ice core records from elsewhere in Antarctica (Masson et al., 2000). ...
The timing of mid–late Holocene deglaciation and glacier readvances on the South Shetland Islands, northern Antarctic Peninsula has been long debated. We used a combined geomorphological, chronological, and palaeolimnological approach to develop a new readvance model for the Bellingshausen Ice Cap (BIC) on the Fildes Peninsula, King George Island/Isla 25 de Mayo, South Shetland Islands, NW Antarctic Peninsula. Results show that retreat to within present-day limits occurred by c. 6 ka, as spring/summer insolation at 62 °S peaked. Probability density analysis of new and previously published chronological data (n=80) from across Fildes Peninsula and King George Island identified up to eight probability ‘gaps’ when glacier readvances might have occurred: 1) a well-defined readvance (with a marine transgression) between c. 7.4–6.6 ka cal BP; 2–5) four possible readvances between c. 5.3–4.8 ka cal BP, 4.5–3.9 ka cal BP, 3.3–3.0 ka cal BP and/or 2.6–2.2 ka cal BP; 6) a well-defined readvance at 1.7–1.3 ka; 7–8) well-defined readvances between c. 1.3–0.7 and after <0.7 ka cal BP. Mid-late Holocene readvances of the BIC on the Fildes Peninsula were limited to within or around the current ice margin. Prior to c. 5 ka cal BP, readvances were initiated during phases of reduced global solar irradiance, with colder and more humid negative Southern Annular Mode (SAM)-like conditions. After c. 5 ka, a declining trend in insolation at 62 °S led to persistently colder/ wetter and more negative SAM-like conditions that likely drove late Holocene readvances.
... Extensive on October 23, 2020 http://advances.sciencemag.org/ Downloaded from glacier advances occurred at a similar latitude in Patagonia between 6.0 to 4.0 ka BP (38)(39)(40). These recent well-dated chronologies revise the timing of neoglacial cooling in the region to 6.0 ka BP, approximately 1000 years before previous interpretations (41). ...
... The potential faunal shift indicated by the change in the bio-element assemblage at ~2.0 ka BP (Fig. 2, A to F) occurred after a 2°C warming of February SSTs at 50°S in the South Atlantic Ocean (37) and enhanced SWW over Tierra Del Fuego at 1.75 ka BP (30). It also coincides with west Antarctic Peninsula SST warming (50), a highly variable ENSO state, a longer duration of sea ice presence in the eastern South Atlantic (37), and regional cooling (38,51). Without knowing species compositions, it is difficult to identify a causal mechanism for the apparent turnover, but it may reflect poleward range shifts in seabird species as ocean temperatures warmed. ...
The coastal tussac (Poa flabellata) grasslands of the Falkland Islands are a critical seabird breeding habitat but have been drastically reduced by grazing and erosion. Meanwhile, the sensitivity of seabirds and tussac to climate change is unknown because of a lack of long-term records in the South Atlantic. Our 14,000-year multiproxy record reveals an ecosystem state shift following seabird establishment 5000 years ago, as marine-derived nutrients from guano facilitated tussac establishment, peat productivity, and increased fire. Seabird arrival coincided with regional cooling, suggesting that the Falkland Islands are a cold-climate refugium. Conservation efforts focusing on tussac restoration should include this terrestrial-marine linkage, although a warming Southern Ocean calls into question the long-term viability of the Falkland Islands as habitat for low-latitude seabirds.
... In general, calculated temperatures for the Late Holocene showed significant differences when compared to the modern shell, which showed lower mean temperatures when compared to the modern shell (~18-19 °C and ~ 21 °C, respectively). Even if those values coincide with the cooler temperature pulses interpreted by other authors in Patagonia during the Late Holocene (Schäbitz, 1994;Villalba, 1994;Meyer and Wagner, 2008;Boretto et al., 2013;Strelin et al., 2014) we would be very careful to derive such an interpretation from single shell specimens each representing a slice of a few years, within an interval of a few hundred years. It however very much justifies future studies focussing in more detail at specific time intervals in the past using A. purpurata as an archive. ...
... A more detailed look into the stable isotope analyses in Holocene shells will then be needed in order to distinguish if environmental changes are more likely to occur due to local variations or global climate changes and which time scale these changes occur. Some environmental events during the Late Holocene, such as temperature variability, were reported for Patagonia: Neoglacial pulses, the Medieval Warm Period and the Little Ice Age (Schäbitz, 1994;Villalba, 1994;Iriondo and Garcia, 1993;Cioccale, 1999;Prevosti et al., 2004;Meyer and Wagner, 2008;Boretto et al., 2013;Strelin et al., 2014;among others). All these climatic changes registered by different archives (pollen, tree-rings, glacial records, aeolian deposits, fossil soils, biogeographic records, etc.) were interpreted as variations in temperature, humidity as well as rainfall frequency. ...
Amiantis purpurata is a common warm-temperate water bivalve species distributed from southern Brazil to northern Patagonia, Argentina, which has a rich and well preserved fossil record in the San Matías Gulf (SMG) dating back to the late Quaternary. This study aims to establish A. purpurata shells as a new palaeoarchive of past marine conditions in South America. We compared the stable oxygen and carbon profiles (δ 18 O shell ; δ 13 C shell) of eleven specimens of A. purpurata from different geological times (modern, Late Holocene and interglacial Late Pleistocene), and additionally present in situ oxygen isotope values of seawater within SMG (δ 18 O water). Using both sets of information, we calculated and reconstructed palaeowater temperatures for the Late Holocene and compared them to modern water temperatures. Our findings indicate that A. purpurata records past environmental parameters such as water temperatures on a seasonal scale and can therefore be considered a suitable candidate for future palaeoenvironmental reconstructions in Northern Patagonia. This study is the first step towards further stable isotope analyses on fossil A. purpurata shells, which will show whether and if so, to what extent, important global climate events such as the Neoglacial (Early Holocene), the Hypsithermal (Middle Holocene) and the Little Ice Age (Late Holocene) occurred in South America.
... The dating of moraines (1500 -1100 cal yr (Schaefer et al., 2009), (c) glaciogenic input in a Chilean fjord based on MS variability (Bertrand et al., 2011), (d) composite of glacier advances from the SPI (Masiokas et al., 2009), (e) a δ 18 O Pisidium-based record of lake water evaporation and inferred wind (SHW) intensities in southern Patagonia (Moy et al., 2008), (f) standardised glacier records from the South Georgia Field (van der Bilt et al., 2017;Oppedal et al., 2018;Bakke et al., 2021), and (g) ensemble proxy-and simulation-based temperature reconstruction for the SH (Neukom et al., 2014). BP) of east-facing outlet glaciers (~50 • S) from the southern Patagonian Icefield (SPI) -and comparison with previous research in the region revealed synchronous advances during this period (Strelin et al., 2014). At the Ema Glacier valley further south (54 • S, 71 • W) -moraine formation is dated to 1200 cal yr BP based on 14 C dated glacially abraded tree trunks incorporated in the moraine (Strelin et al., 2008) and Oppedal et al. (2018) reported increasing glaciogenic input in Lake Diamond (54 • S, 36 • W) on South Georgia at approximately 1170 cal yr BP based on a standardised MS record. ...
Southern Ocean (SO) climate is rapidly changing because of global warming and regional climate feedback loops
like shifts of the Southern Hemisphere (SH) westerly winds (SHW) and related Southern Annular Mode (SAM).
Over the past decades, the former has been persistently positive, shifting the latter southwards: the ensuing
changes in temperature and precipitation are linked to the rapid retreat of mid-latitude mountain glaciers.
Beyond the short instrumental period, the long-term impact of this coupled SHW-SAM system on regional glaciers remains poorly constrained. To help close this gap, we reconstruct glacier advances from an outlet glacier
on the sub-Antarctic Kerguelen (49◦S, 69◦E), an archipelago that is strategically located in an under-investigated
region of the SHW core belt. Based on alternations between relatively organic and minerogenic mud detected
using a multiproxy approach on a 1200-year-long sediment record from a glacial threshold basin, we document
glacier advances between 1150 and 850, 820–620, 500–250 and 160–90 cal yr BP. Coincident glacier advances
in adjacent regions like sub-Antarctic South Georgia and southern Patagonia, suggest that SO glaciers responded
symmetrically to climate forcings during the past 1200 years. We attribute this synchronicity to shifting SAM-like
conditions and associated temperature changes. We suggest that cold and negative SAM-like conditions,
favourable for glacier growth on the Kerguelen and other SO land masses, dominated during much of this period.
Furthermore, the findings presented here support the growing consensus for a two-phased regional expression of
the Little Ice Age (LIA).
... According to a glacier inventory of the Southern Patagonia Icefield performed with remote sensing images, only two glaciers (Frías and Bravo) are not calving in the last years (Aniya et al., 1996). The Perito Moreno Glacier had several readvances during the Holocene (Strelin et al., 2014). Based on photographs from glaciers and runoff records during the XX century (period 1912-2002) drier and warmer trends were suggested for northwestern Patagonia (Masiokas et al., 2007). ...
Patagonia and Tierra del Fuego are the only places to analyse climate changes at high latitudes in the Southern (Oceanic) Hemisphere. This region is totally dominated by westerly winds, although the altitude of the Andes Cordillera —transverse to these winds— modifies their effects. According to short meteorological records, air temperature is increasing slightly while precipitations are diminishing. Hydrologic records are longer; their trends are biased by geomorphological changes in the watersheds by fluvial andglacier captures. The discharges of the Negro, Chubut, Senguerr, Deseado, Santa Cruz and Gallegos rivers have decrease although some of them are not significantly modified by dams. The Santa Cruz River is the only example that is increasing the discharges due to significant variations at the upper watershed.
... L as expansiones d e l os glaciares durante la Pequeña Edad de Hielo se han registrado en diferentes regiones del mundo, pero no demuestran un comportamiento homogéneo (Solomina et al. 2016). Para la región patagónica, estudios recientes en áreas proglaciales de los glaciares Torre (49,3°S/73,0°O, Monte Fitz Roy) (Reynhoult et al., 2019), Marinelli (54,5°S/69,5°O, Cordillera Darwin) (Hall et al., 2019), Tyndall, Pingo y Zapata (51°S/73,3ºO, Torres del Paine; TDP) (García et al., 2020) y Upsala y Frías (50°S/72,2°O, cuenca del Lago Argentino) (Strelin et al., 2014;Kaplan et al., 2016) sugieren que los máximos glaciales durante el último milenio habrían oscilado entre los siglos XIV y XV. Lo expuesto anteriormente, deja en evidencia que la cronología presentada en Masiokas et al. (2009b) es aún parte de un debate abierto, el que, sin ir más allá, ha dificultado el entendimiento del clima del último milenio. ...
En los Andes Patagónicos aún es materia de debate cuándo los glaciares alcanzaron su máxima expansión durante el último milenio. En este trabajo analizamos las fluctuaciones del Glaciar Tenerife (51°S), un pequeño glaciar de montaña ubicado inmediatamente al sur de los Campos de Hielos Patagónicos. Un análisis detallado de las geoformas glacia-les del valle nos permitió identificar tres sistemas de morrenas, en la parte sur-central, suroccidental y septentrional del valle del Monte Tenerife, respectivamente. Mediante las edades obtenidas a través del conteo de anillos de árboles (Nothofagus pumilio) y medi-das del diámetro de líquenes de Placopsis cf. gelida (L.) Linds, estimamos que el Glaciar Tenerife retrocedió de su máxima expansión de los últimos mil años inmediatamente des-pués de 1742-1765 AD. La máxima expansión del Glaciar Tenerife durante el último milenio coincide con las máximas expansiones de los glaciares Schiaparelli (54°S) y Stoppani (55°S). Sin embargo, otros glaciares alcanzaron su límite máximo glacial más temprana-mente y muestran una asincronía temporal en cuando ellos alcanzaron su extensión más grande. Esto sugiere una variabilidad temporal en la máxima expansión de los glaciares durante el último milenio en Patagonia sur (49° y 55°S).
ABSTRACT. In the Patagonian Andes it is still under debate when the glaciers reached their maximum expansion during the last millennium. In this work we analyze the fluctuations of Tenerife Glacier (51°), a small mountain glacier located immediately to the south of the Patagonian Ice Fields. A detailed analysis of the glacial landforms of the valley allowed us to identify three moraine systems, in the south-central, southwestern, and northern parts of the Monte Tenerife valley, respectively. Based on ages obtained by count tree rings (Nothofagus pumilio) and Placopsis cf. gelida (L.) Linds lichens diameter measurements , we estimated that the Tenerife Glacier receded from its maximum extent in the last thousand years immediately after 1742-1765 AD.
... 8000 and ca. 100 a (Reynhout et al., 2019;Davies et al., 2020), evidenced today by different series of moraines in the Andean landscape all over the region. Previous studies have documented several glacier advances at Lago Argentino (Strelin et al., 2014;Kaplan et al., 2016), Lago Pearson (Kaplan et al., 2016) and in the Torre glacier valley (Reynhout et al., 2019). Neoglacial advances have been related to changes in the intensity of summer insolation and precipitation associated with the Southern Annular Mode-like (SAM-like) phases throughout the Holocene (Reynhout et al., 2019). ...
Southeastern Patagonia's (49° S) post‐glacial history inferred from high Andean lake sediments provides new insights regarding Late Pleistocene and Holocene vegetation dynamics at the eastern margin of the Southern Patagonian Icefield. The fossil records of pollen, charcoal and geochemical data from tephra layers from Laguna Chiquita and Laguna Gemelas Este were analysed to reveal past landscape dynamics related to vegetation changes, fire and volcanic events from ca . 15 200 cal a bp to the present. Nothofagus forest expanded over shrubland communities sometime between 15 200 and 4600 cal a bp , along with at least three disturbance sources related to the volcanic eruptions of Lautaro, Aguilera and Hudson, important local fire episodes, and neoglacial advances. Major charcoal deposition reveals moderate fire activity during the Late Pleistocene related to an open landscape characterised by a grass/shrub steppe. Local glacier advances may have affected the Laguna Gemelas Este sedimentation. Tephra deposition events do not correlate to vegetation changes inferred from the Laguna Gemelas Este and Laguna Chiquita pollen records. Late Holocene eastern Andean forest changes and fire activity at 49° S match other southern palaeoenvironmental records (50–52° S) suggesting that changes in the Southern Westerly Wind latitudinal position and intensity drove major palaeovegetation and fire dynamics before the European settlement. In the last centuries, fire and vegetation changes have been closely related to an increase in local ignition sources and the introduction of alien species.
... kyr BP) and may have exhibited variability on centennial timescales (van der Bilt et al., 2017;Berg et al., 2019). Covariance of Patagonian and South Georgian glacier fluctuations may indicate a shared regional climate forcing (Strelin et al., 2014). One such forcing is changes in the southern westerly winds (SWWs), which have a major impact on precipitation rates and temperature (Mayr et al., 2007;Lamy et al., 2010;Perren et al., 2020;Fletcher et al., 2021;Zwier et al., 2021;Spoth et al., 2023). ...
The subantarctic islands of South Georgia are located in the Southern Ocean, and they may be sensitive to future climate warming. However, due to a lack of well-dated subantarctic palaeoclimate archives, there is still uncertainty about South Georgia's response to past climate change. Here, we reconstruct primary productivity changes and infer Holocene glacial evolution by analysing two marine gravity cores: one near Cumberland Bay on the inner South Georgia shelf (GC673: ca. 9.5 to 0.3 cal. kyr BP) and one offshore of Royal Bay on the mid-shelf (GC666: ca. 15.2 cal. kyr BP to present). We identify three distinct benthic foraminiferal assemblages characterised by the dominance of Miliammina earlandi, Fursenkoina fusiformis, and Cassidulinoides parkerianus that are considered alongside foraminiferal stable isotopes and the organic carbon and biogenic silica accumulation rates of the host sediment. The M. earlandi assemblage is prevalent during intervals of dissolution in GC666 and reduced productivity in GC673. The F. fusiformis assemblage coincides with enhanced productivity in both cores. Our multiproxy analysis provides evidence that the latest Pleistocene to earliest Holocene (ca. 15.2 to 10.5 cal. kyr BP) was a period of high productivity associated with increased glacial meltwater discharge. The mid–late Holocene (ca. 8 to 1 cal. kyr BP), coinciding with a fall in sedimentation rates and lower productivity, was likely a period of reduced glacial extent but with several short-lived episodes of increased productivity from minor glacial readvances. The latest Holocene (from ca. 1 cal. kyr BP) saw an increase in productivity and glacial advance associated with cooling temperatures and increased precipitation which may have been influenced by changes in the southwesterly winds over South Georgia. We interpret the elevated relative abundance of F. fusiformis as a proxy for increased primary productivity which, at proximal site GC673, was forced by terrestrial runoff associated with the spring–summer melting of glaciers in Cumberland Bay. Our study refines the glacial history of South Georgia and provides a more complete record of mid–late Holocene glacial readvances with robust chronology. Our results suggest that South Georgia glaciers were sensitive to modest climate changes within the Holocene.
... Our ages (10.8 and 3.6 ka) coincide with warm and dry intervals recorded by changes in pollen assemblages retrieved from Lago Cipreses (Moreno et al., 2018), which is located less than 100 km south 415 of Lago Argentino. Additionally, no evidence for glacial advances is available from southern Patagonia during these periods (Strelin et al., 2014;Kaplan et al., 2016;Reynhout et al., 2019). ...
Determining the timing and extent of Quaternary glaciations around the globe is critical to understanding the drivers behind climate change and glacier fluctuations. Despite synchronous ice-volume and extent change across hemispheres, evidence from the southern mid-latitudes indicates that local glacial maxima occurred earlier in the glacial cycle, preceding the global Last Glacial Maximum (LGM), implying that feedbacks in the climate system or ice dynamics played a role beyond the underlying orbital parameters. To shed light on these processes, we investigated the glacial landforms shaped by the Lago Argentino glacier (50° S), an outlet lobe of the former Patagonian Ice Sheet in southern Argentina, during the last two glacial cycles. We mapped geomorphological features on the landscape and dated moraine boulders and outwash sediments using 10Be cosmogenic nuclides and feldspar infrared stimulated luminescence (IRSL) to constrain the chronology of glacial advance and retreat. We, therefore, provide the first published age constraints on the middle-to-late Pleistocene glaciations at Lago Argentino, and report that this outlet lobe expanded during Marine Isotope Stage 6, at 153.0 ± 14.7 ka, and during Marine Isotope Stage 3, culminating at 44.5 ± 8.0 ka and at 36.6 ± 1.0 ka. Our results indicate that the most recent was its most extensive advance during the last glacial period, and hypothesize that this was a result of longer and colder winters, as well as increased precipitation delivered by a northward migration of the Southern Westerly Winds belt, highlighting the role of local and regional climate feedbacks in driving ice mass changes in the southern mid-latitudes.
... Following the rivers downstream, the vegetation is dominated by Nothofagus antarctic (Ñire). Towards the west, Nothofagus pumilio (Lenga) and Nothofagus betuloides (Coihue) are the dominant species, as the area is wetter, especially near the lakes (Strelin et al., 2014). In all the high mountain slopes and valleys of the area, Nothofagus pumilio acts as a slope support when the soils are saturated (Moragues et al., 2021b). ...
... The lake level decline in L. Lepué between ~11-7.9 ka was coeval with recession of valley glaciers in the north Patagonian Andes (Moreno et al., 2021b;Sagredo et al., 2018;Soteres et al., 2022a), and peak temperatures in marine core MD07-3088 between ~11.1-7.5 ka in (Haddam et al., 2018) (Fig. 6). A transgressive lake phase ensued at ~7.9 ka suggesting stronger SWW influence, in agreement with a decline in fire activity at regional scale (Moreno et al., 2022 and renewed glacier activity in the Patagonian Andes (Kaplan et al., 2016;Reynhout et al., 2019;Sagredo et al., 2021;Strelin et al., 2014). SST cooling in MD07-3088 began at ~7.5 ka and intensified at ~2.7 ka and ~0.6 ka, culminating in a SST minimum during the 20 th century (Weighted Mean: 11.6 • C) (Haddam et al., 2018) (Fig. 6). ...
We report a fossil diatom record from small closed-basin Lago Lepué (43 • S) to examine past changes in freshwater ecosystems and hydrologic balance in northwestern Patagonia since ~18 ka. The record starts with abundant staurosiroids and the heavily silicified Aulacoseira granulata suggesting deep turbulent mixing during a low lake level stand between ~18-16.4 ka. A. distans increased shortly after ~16.4 ka and achieved maximum abundance between ~15.4-13.6 ka, while A. granulata disappeared at ~15.8 ka and A. alpigena rose at ~14.9 ka to its maximum between ~13-12 ka. We infer turbulent, cold, and circumneutral to slightly acid lake conditions contemporaneous with a steady lake level rise that started at ~16.4 ka and culminated between ~13-12 ka. These trends reversed between ~11-7.8 ka with the dominance of Discostella stelligera and staurosiroids, suggesting warmer lake conditions and shallower mixing. Subsequent changes include increases of A. distans with D. stelligera between ~7.8-5.8 ka, dominance of the former between ~5.8-3.3 ka, a rapid increase in A. perglabra at ~3.3 ka, and ensuing diversification of benthic acidophilous species. We infer a rapid lake-level decline between ~11-7.8 ka, with subsequent rising pulses at ~7.8 ka and ~5.8 ka, a multimillennial-scale lake acidifi-cation trend, and overall high lake levels with centennial-scale reversals between ~6-0 ka. Coherent variations in terrestrial and aquatic ecosystem changes recorded in the same core suggest negative hydrologic balance between ~18-16.4 ka and ~11-7.8 ka, positive balance between ~14.9-12 ka and ~6-0 ka, with transitional conditions in the interim, overprinted by millennial-scale changes and enhanced variability since ~6 ka. Covariation with paleoclimate records at regional, pan-Patagonian, and hemispheric scale suggests millennial to centennial-scale variability superimposed upon a multi-millennial pacing of Southern Westerly Wind evolution since ~18 ka.
... Demonstrating this at Lago Argentino is challenging, as it exhibits strong spatial variability and a non-unique relationship between the proxy and climatic variables of interest. In particular the distance between any given location and the glacier fronts has evolved through time due to glacier advance and retreat (Strelin et al. 2014;Kaplan et al. 2016) and the local conditions have fluctuated on centennial timescales due to large-scale climatic systems (Van Wyk de Vries et al. 2023). The strong spatial variability in Lago Argentino is best illustrated by the correlation between DJF wind speed and red PxI in cores 41A and 42A, located within 3 km of each other in a region where the lake is at its narrowest. ...
The quantity and characteristics of sediment deposited in lakes are affected by climate to varying extents. As sediment is deposited, it provides a record of past climatic or environmental conditions. However, determining a direct relationship between specific climatic variables and measurable sediment properties, for instance between temperature and sediment optical reflectance, is complex. In this study, we investigate the suitability of sediment reflectance, recorded as sediment pixel intensity (PxI), as a paleoclimate proxy at a large ice-contact lake in southern Patagonia, Lago Argentino. We also evaluate whether sediment PxI can be used to investigate the present-day climatic drivers of sedimentation across Lago Argentino. First, we show that sediment PxIs relate to underlying sediment composition, and are significantly correlated with XRF-derived major element composition. Secondly, we find that PxIs correlate with both austral summer temperatures and wind speeds, but not with precipitation. PxI timeseries reach the p <0.1 correlation significance threshold for use as a paleo-wind proxy in as many as 6 cores and a paleo-temperature proxy in up to 4 cores. However, high spatial variability and the non-unique relationship between PxI and both temperature and wind speed challenges the necessary assumption of stationarity at Lago Argentino. While not suitable as a paleoclimatic proxy, correlations between PxI and instrumental climate data do chronicle current climatic controls on sediment deposition at Lago Argentino: high summer temperatures enhance settling of coarse, optically dark grains across the lake basin by promoting ice melt and lake stratification, while high wind speeds reduce the settling of fine, optically bright grains in the ice-proximal regions by transporting sediment-rich waters away from the glacier fronts. The assumptions required for quantitative paleoclimatic reconstruction must be carefully evaluated in complex lacustrine environments, but records unsuitable for use as proxies might nevertheless yield valuable information about the drivers of modern sedimentary transport and deposition.
... Following the rivers downstream, the vegetation is dominated by Nothofagus antarctic (Ñire). Towards the west, Nothofagus pumilio (Lenga) and Nothofagus betuloides (Coihue) are the dominant species, as the area is wetter, especially near the lakes (Strelin et al., 2014). In all the high mountain slopes and valleys of the area, Nothofagus pumilio acts as a slope support when the soils are saturated (Moragues et al., 2021b). ...
... This environmental situation is contemporaneous with the generation of moraines in Argentino lake basin before 400 and after 300 cal yrs. BP (Strelin et al., 2014) or around 360-240 cal yrs. BP (Kaplan et al., 2016, Fig. 12 A). ...
Environmental changes were reconstructed from a multiproxy synthesis of over 30 localities from the Isla Grande de Tierra del Fuego and Isla de los Estados, southernmost South America. At a local scale, the results from the mountain forest and gently undulating steppe areas were integrated as well as those from the marine environments of the Beagle Channel and the Atlantic coasts. At a regional scale, the results were integrated with those published for the southernmost Andean and Extra-Andean Patagonia and the Antarctic Peninsula. This study focuses on the environmental evolution during the Late Glacial-Holocene transition, the Middle to Late Holocene transgressive-regressive hemicycle and wet-dry oscillations, the Medieval Climate Anomaly, the Little Ice Age, the tephra inputs from the Patagonian Andes, and the recent climatic warming. Most paleoenvironmental changes are related to variations in the latitudinal position and intensity of the Southern Westerly Winds (SWW) while others are associated with astronomical or endogenous forcings. At a strong intensity of the SWW, a greater contribution of humidity to the forest areas and an increase in the rainfall gradient create windy and arid conditions in the steppe. At a weak intensity of the SWW, lower humidity input in the forest areas and the advection of air masses from the Atlantic Ocean promoted humid and slightly windy conditions in the steppe. Similar environmental trends are observed between terrestrial and marine environments in the center and south of Tierra del Fuego, Isla de los Estados and the Antarctic Peninsula, and between the Fuegian steppe and Extra-Andean Patagonia. The paleoclimatic evidence reveal high environmental variability in the last 10,000 years for this sector of the Southern Hemisphere.
... (b) Seismic profiles tracks (magenta lines) within the southern arms of Lago Argentino. Cyan dots correspond to the Puerto Banderas moraine and dated spots from Strelin, Denton, Vandergoes, Ninnemann, and Putnam (2011);Strelin, Kaplan, Vandergoes, Denton, and Schaefer (2014) and Kaplan et al. (2011). (c) Close-up of Lago Roca. ...
Lago Roca is a NE–SW elongated lacustrine body located to the south of Lago Argentino, the largest lake of the UNESCO ‘Los Glaciares’ National Park. An extensive high‐resolution seismic survey carried out within the Lago Roca, integrated with geological information gathered in the area, have allowed to produce: (a) a complete bathymetric map of the lake; (b) a basement topography map and a structural map; and (c) an analysis of the geometry, distribution, and thickness of the sedimentary infill. Two sub‐basins were recognized in Lago Roca, separated by a central basement high that shows a pop‐up structure. The northern and southern margins of the lake basement are bounded by NE–SW trending strike‐slip faults that constitute subsidiary faults strands of the regional structural lineament known as the ‘Lago Argentino transfer fault’. The shallow, low magnitude seismicity recorded in the area supports the interpretation that this fault segment is active at the present. The relative motion along the fault led to the deformation of the sedimentary infill of the lake, which was also affected by several subsidiary normal faults oriented parallel to the Lago Argentino transfer fault. Data show the peculiar asymmetry in the sedimentary filling of Lago Roca, typical of those of pull‐apart basins generated along transform margins. A simplified model for the evolution of Lago Roca is also here proposed, based on the analysed data and the regional tectonic background. A high‐resolution seismic survey carried out within Lago Roca has allowed to produce a bathymetric map of the lake, a basement topography map, and a structural map. Two sub‐basins were recognized separated by a central basement high. Northern and southern margins of the lake basement are bounded by NE–SW trending strike‐slip faults that constitute subsidiary faults strands of the regional structural lineament known as ‘Lago Argentino transfer fault’.
... This decrease in marine influence might have resulted from a combination of decelerated global sea-level rise (Lambeck et al., 2014) and accelerated glacial isostatic uplift in response to glacier recession from their Neoglacial maxima (Fig. 8;Aniya, 2013;Davies et al., 2020). More specifically, this acceleration seems to have mostly occurred after Neoglaciation III (2780 e 1910 cal yr BP; ages calibrated from Aniya, 2013 using SHCal20), and may therefore represent isostatic uplift due to the recession of glaciers on both the Northern and Southern Patagonian Icefields after this particularly extended Neoglacial advance (Bertrand et al., 2012a;Harrison et al., 2008;Mercer, 1982;Siani et al., 2010;Strelin et al., 2014). This paleoenvironmental reconstruction implies that (1) during most of the last 9.1 kyr glacial isostatic adjustment was relatively slow, and (2) that glacial isostatic adjustment accelerated during the late Holocene in response to Neoglacial ice load changes. ...
Our understanding of glacial isostatic rebound across Patagonia is highly limited, despite its importance to constrain past ice volume estimates and better comprehend relative sea-level variations. With this in mind, our research objective is to reconstruct the magnitude and rate of Late Glacial and Holocene glacial isostatic adjustment near the center of the former Patagonian Ice Sheet. We focus on Larenas Bay (48°S; 1.26 km2), which is connected to Baker Channel through a shallow (7.4 m) and narrow (ca. 150 m across) inlet, and hence has the potential to record periods of basin isolation and marine ingression. The pale-oenvironmental evolution of the bay was investigated through a sedimentological analysis of a 9.2 m long radiocarbon-dated sediment core covering the last 16.8 kyr. Salinity indicators, including diatom paleoecology, alkenone concentrations and CaCO3 content, were used to reconstruct the bay's connec-tivity to the fjord. Results indicate that Larenas Bay was a marine environment before 16.5 cal kyr BP and after 9.1 cal kyr BP, but that it was disconnected from Baker Channel in-between. We infer that the postglacial rebound started before 16.5 cal kyr BP and that it outpaced global sea-level rise until slightly before 9.1 cal kyr BP. During the Late Glacial and early Holocene, the center of the former Patagonian Ice Sheet experienced an absolute uplift of ca. 96 m, at an average rate of 1.3 cm/yr. During the remainder of the Holocene, glacial isostatic adjustment continued (ca. 20 m), but at a slower average pace of 0.2 cm/yr. Comparisons between multi-millennial variations in the salinity indicators and existing records of global sea-level rise suggest that the glacial isostatic adjustment rate also fluctuated within these time intervals, likely in response to glacier dynamics. More specifically, most of the glacial isostatic adjustment registered between 16.5 - 9.1 cal kyr BP seems to have occurred before meltwater pulse 1A (14.5 - 14.0 kyr BP). Likewise, it appears that the highest glacial isostatic rebound rates of the last 9.1 kyr occurred during the late Holocene, most likely in response to glacier recession from their Neoglacial maxima. This implies a relatively rapid response of the local solid earth to ice unloading, which agrees with independent modelling studies investigating contemporary uplift. We conclude that the center of the former Pata-gonian Ice Sheet experienced a glacial isostatic adjustment of ca. 116 m over the last 16.5 kyr, and that >80% occurred during the Late Glacial and early Holocene.
... La conexión de la cuenca con el CHPS determinó que los avances neoglaciares aumentaran las condiciones de estacionalidad habituales hacia el oeste (menores temperaturas y mayor carga nival) de los campos de invernada y que se haya generado mayor aridización (Strelin et al. 2014;Kaplan et al. 2016). Eso se tradujo en condiciones de estrés invernal más rigurosas. ...
Luis Alberto Borrero changed the way of producing archaeological knowledge in Patagonia and Tierra del Fuego (as well as beyond). The interrelationship between distributional archaeology and regional taphonomy-two research programs introduced by him 30 years ago-highlights the importance of three analytical units: the region, the artifact and the element (bone). Combined with an epistemology centered on falsifiability, this is the structure for formulating broad questions mostly related to Holocene hunter-gatherer landscape use. Building on this legacy, the article presents a case study of the winter grounds on the north shore of Lake Viedma. It integrates the taphonomic results of guanaco (Lama guanicoe) with those of artifact distribution. Furthermore, we present new radiocarbon dates that frame the analysis of fauna from several archaeological sites located in the deflation hollows of coastal sand dunes. The identification of a similar set of environmental and archaeological conditions to that proposed by Borrero in 1988 in the trampling model he used for guanacos in Tierra del Fuego demonstrates the latter’s relevance to the Viedma Lake region.
... At the head of Lago Argentino, the Upsala glacier at Lago Pearson may have been expanded until close to 1000 yr ago, given one sample age of ∼960 ± 30 (Kaplan et al., 2016). Regardless, in general, Patagonian glaciers reached their maximum Holocene positions earlier, during the middle or early Holocene (Aniya, 2013;Kaplan et al., 2016;Reynhout et al., 2019); the advances of the last millennium started around or after ∼700 yr ago (Strelin et al., 2014;García et al., 2020). ...
In the Cordillera Darwin, southernmost South America, we used ¹⁰ Be and ¹⁴ C dating, dendrochronology, and historical observations to reconstruct the glacial history of the Dalla Vedova valley from deglacial time to the present. After deglacial recession into northeastern Darwin and Dalla Vedova, by ~16 ka, evidence indicates a glacial advance at ~13 ka coeval with the Antarctic Cold Reversal. The next robustly dated glacial expansion occurred at 870 ± 60 calendar yr ago (approximately AD 1150), followed by less-extensive dendrochronologically constrained advances from shortly before AD 1836 to the mid-twentieth century. Our record is consistent with most studies within the Cordillera Darwin that show that the Holocene glacial maximum occurred during the last millennium. This pattern contrasts with the extensive early- and mid-Holocene glacier expansions farther north in Patagonia; furthermore, an advance at 870 ± 60 yr ago may suggest out-of-phase glacial advances occurred within the Cordillera Darwin relative to Patagonia. We speculate that a southward shift of westerlies and associated climate regimes toward the southernmost tip of the continent, about 900–800 yr ago, provides a mechanism by which some glaciers advanced in the Cordillera Darwin during what is generally considered a warm and dry period to the north in Patagonia.
... In order to evaluate the ability of countMYvarves to resolve very fine scale laminations, we use an example from Lago Argentino, a large proglacial lake in southern Patagonia, Argentina (Skvarca and Naruse, 1997;Pasquini and Depetris, 2011;Richter et al., 2016). Three large outlets of the Southern Patagonian Icefield (Glaciar Upsala, Spegazzini and Perito-Moreno) calve directly into this lake, resulting in a large influx of freshly eroded glacial flour (Skvarca et al., 2002(Skvarca et al., , 2003Pasquini and Depetris, 2011;Strelin et al., 2014). The main basin of the lake is separated from these actively calving glaciers by a network of glacial fjords nearly 50 km long, and sedimentation rate in the main basin is dominated by gradual fallout of fine silt to mud-scale particles. ...
Annual resolution sediment layers, known as varves, can provide continuous and high-resolution chronologies of sedimentary sequences. In addition, varve counting is not burdened with the high laboratory costs of geochronological analyses. Despite a more than 100-year history of use, many existing varve counting techniques are time consuming and difficult to reproduce. We present countMYvarves, a varve counting toolbox which uses sliding-window autocorrelation to count the number of repeated patterns in core scans or outcrop photos. The toolbox is used to build an annually-resolved record of sedimentation rates, which are depth-integrated to provide ages. We validate the model with repeated manual counts of a high sedimentation rate lake with biogenic varves (Herd Lake, USA) and a low sedimentation rate glacial lake (Lago Argentino, Argentina). In both cases, countMYvarves is consistent with manual counts and provides additional sedimentation rate data. The toolbox performs multiple simultaneous varve counts, enabling uncertainty to be quantified and propagated into the resulting age-depth model. The toolbox also includes modules to automatically exclude non-varved portions of sediment and interpolate over missing or disrupted sediment. CountMYvarves is open source, runs through a graphical user interface, and is available online for download for use on Windows, macOS or Linux at https://doi.org/10.5281/zenodo.4031811 .
... Se registraron avances neoglaciares a lo largo de los últimos 4500 años (Wenzens & Wenzens, 1998) que generaron una mayor estacionalidad en el extremo occidental del lago (Kaplan et al., 2016;Strelin et al., 2014). Esto probablemente causó el uso intermitente o el abandono de este sector de la cuenca. ...
Se presentan los resultados de nuevos trabajos en el bosque de Nothofagus en la localidad de El Chaltén, lindante con el Campo de Hielo Patagónico Sur. El ambiente es marcadamente estacional y el espacio configura un callejón sin salida. Las excavaciones de sitios en bloques La Lagunita-La Fisura, Alero 1 y Alero 2 brindan información sobre tecnología lítica y arqueofaunas que fue complementada con relevamientos de motivos rupestres y el registro de hallazgos aislados. El registro arqueológico muestra baja intensidad de uso y el desarrollo de actividades focalizadas en el mantenimiento de artefactos, mientras que la arqueofauna evidencia procesamiento intensivo. Los tres sitios poseen motivos rupestres zoomorfos que no sugieren diferencias importantes en sus momentos de ejecución. Se propone el uso marginal del bosque por parte de partidas logísticas con individuos equipados. Dos dataciones radiocarbónicas circa 400 años AP muestran la integración tardía de este ambiente a los sistemas cazadores recolectores de la margen Norte del lago Viedma. Una primera comparación en torno al uso del bosque en la margen sur del lago y en cuencas vecinas (lagos San Martín y Argentino) indicaría la existencia de distintos umbrales de marginalidad.
... The Southern Patagonian Icefield (SPI), extending between 48.2 • and 51.6 • S along the Southern Patagonian Andes, responds very sensitively to climatic changes (Mercer, 1976;Strelin et al., 2011Strelin et al., , 2014Glasser et al., 2011;Meier et al., 2018;Lodolo et al., 2020). At present, it is subject to rapid ice-mass loss (Malz et al., 2018;Braun et al., 2019;Richter et al., 2019;Dussaillant et al., 2019;Abdel Jaber et al., 2019). ...
The Southern Patagonian Icefield is located in an area with a complex tectonic-rheological structure and is affected by intense glacial-isostatic adjustment and rapid ice retreat. Geodetic observations of loading effects provide information on earth structure. Perito Moreno Glacier repeatedly dams the Brazo Rico and Brazo Sur branches of Lago Argentino. The rupture of the ice dam applies an intense hydrological load signal which results in an elastic response of the solid earth. We present a modelling procedure to predict loading effects in response to water-level changes in Brazo Rico. The output is compared with site displacements observed by GNSS during the 2016 rupture event. Our results show that water-level changes in Brazo Rico exceeding 5 m produce vertical deformations detectable with GNSS observations. A geodetic observation of loading effects at magnitudes similar to those of the maximum historic event in 1956 could provide meaningful constraints on elastic earth models. We discuss consequences for the determination of accurate deformation rates, implications for our understanding of the intense uplift observed at the Southern Patagonian Icefield, and requirements and prospects for obtaining geodetic observations of the loading effects of future rupture events.
Determining the timing and extent of Quaternary glaciations around the globe is critical to understanding the drivers behind climate change and glacier fluctuations. Evidence from the southern mid-latitudes indicates that local glacial maxima preceded the global Last Glacial Maximum (LGM), implying that feedbacks in the climate system or ice dynamics played a role beyond the underlying orbital forcings. To shed light on these processes, we investigated the glacial landforms shaped and deposited by the Lago Argentino glacier (50° S), an outlet lobe of the former Patagonian Ice Sheet, in southern Argentina. We mapped geomorphological features on the landscape and dated moraine boulders and outwash sediments using 10Be cosmogenic nuclides and feldspar infrared stimulated luminescence (IRSL) to constrain the chronology of glacial advance and retreat. We report that the Lago Argentino glacier lobe reached more extensive limits prior to the global LGM, advancing during the middle to late Pleistocene between 243–132 ka and during Marine Isotope Stage 3 (MIS 3), culminating at 44.5 ± 8.0 and at 36.6 ± 1.0 ka. Our results indicate that the most extensive advance of the last glacial cycle occurred during MIS 3, and we hypothesize that this was a result of longer and colder winters, as well as increased precipitation delivered by a latitudinal migration of the Southern Westerly Winds belt, highlighting the role of local and regional climate feedbacks in modulating ice mass changes in the southern mid-latitudes.
Holocene environmental changes in Patagonia were mostly shaped by fluctuating ice cover recession. Consequently, environmental reconstructions are largely based on discontinuous moraine chronologies from valley deposits. Here, we present a 3 m long continuous sediment record recovered from Laguna Meseta (LME), a lake located on Meseta Chile Chico. Its altitude and location relative to the North Patagonian Icefield provide a unique opportunity to reconstruct the glacial history and related environmental dynamics.
Our radiocarbon chronology constrains sedimentation to the last ∼10000 years and provides a minimum age for postglacial ice-free lacustrine conditions, due to a westward retreat of the ice cap. Lacustrine productivity reached its maximum at the start of the lake phase and decreased afterwards. Between 5500 and 4600 cal yr BP, a major shift towards allochthonous sediment accumulation occurred, caused by an abrupt increase in clastic deposition from basaltic lithologies of the Meseta Chile Chico. This episode correlates with the precipitation-driven Mid-Holocene glacier advance of Patagonian glaciers and suggests that conditions were colder and/or wetter on Meseta Chile Chico at that time. After 4600 cal yr BP, these conditions continued to supply LME with clastic sediments until a stepped decrease around 900 cal yr BP. Thereupon, lacustrine productivity distinctly increased and stabilized around 300 cal yr BP.
Our findings indicate that changes in sedimentation on Meseta Chile Chico were mainly controlled by regional variability in the precipitation. Furthermore, strong correlation between our records and available proxies for oscillations of the Southern Hemisphere Westerly Winds suggest a pronounced climatic control by this prominent wind system for central west Patagonia during the last 10 000 years.
An asthenospheric window underneath much of the South American continent increases the heat flow in the southern Patagonian Andes where glacial–interglacial cycles drive the building and melting of the Patagonian Icefields since the latest Miocene. The Last Glacial Maximum (LGM) was reached ∼26000 yr BP (years before present). Significant deglaciation onsets between 21 000 and 17 000 yr BP were subject to an acceleration since the Little Ice Age (LIA), which was ∼400 yr BP. Fast uplift rates of up to 41±3 mm yr-1 are measured by global navigation satellite system (GNSS) around the Southern Patagonian Icefield and are currently ascribed to post-LIA lithospheric rebound, but the possible longer-term post-LGM rebound is poorly constrained. These uplift rates, in addition, are 1 order of magnitude higher than those measured on other glaciated orogens (e.g. the European Alps), which raises questions about the role of the asthenospheric window in affecting the vertical surface displacement rates. Here, we perform geodynamic thermo-mechanical numerical modelling to estimate the surface uplift rates induced by post-LIA and post-LGM deglaciation, accounting for temperature-dependent rheologies and different thermal regimes in the asthenosphere. Our modelled maximum post-glacial rebound matches the observed uplift rate budget only when both post-LIA and post-LGM deglaciation are accounted for and only if a standard continental asthenospheric mantle potential temperature is increased by 150–200 °C. The asthenospheric window thus plays a key role in controlling the magnitude of presently observed uplift rates in the southern Patagonian Andes.
Holocene environmental changes in Patagonia were mostly shaped by unsteady ice-cover recession. Consequently, environmental reconstructions are largely based on discontinuous moraine chronologies from valley deposits. Here, we present a 3 m-long continuous sediment record recovered from Laguna Meseta (LME), a lake located on Meseta Chile Chico. Its altitude and location relative to the North Patagonian Icefield provide a unique opportunity to reconstruct the glacial history and the related environmental dynamics.
Our radiocarbon chronology constrains sedimentation to the last ~10,000 years and provides a minimum age for postglacial ice-free lacustrine conditions due to a westward retreat of the ice cap. Lacustrine productivity reached its maximum at the start of sedimentation and decreased afterwards. Between 5,500 and 4,600 cal yr BP, a major shift towards allochthonous sediment accumulation occurred, caused by an abrupt increase in clastic deposition from basaltic lithologies of the Meseta Chile Chico. This episode correlates with the precipitation-driven mid-Holocene glacier advance of Patagonian glaciers and suggests that conditions were colder/wetter on the Meseta Chile Chico at that time. After 4,600 cal yr BP these conditions continued to supply LME with clastic sediments until a stepped decrease around 900 cal yr BP. Thereupon, lacustrine productivity distinctly increased and stabilized around 300 cal yr BP. Our findings indicate that environmental conditions on Meseta Chile Chico were mainly controlled by precipitation variability during regional oscillations of the Southern Hemisphere Westerly Winds over the last 10 ka.
In order to understand the paleogeographic evolution of Viedma Lake (252 masl) sedimentary sequences with glaciolacustrine and lacustrine strata between 307 masl and 266 masl and bathymetric fluctuations between 27 ka. and 2.4 ka. were identified. The paleoenvironmental interpretation of the stratigraphic profiles was carried out based on the analysis of facies and their associations. The oldest age was recorded at 301 masl (27 ka) and the youngest corresponds to 266 masl (2.4 ka). The record of 27 ka was compared with another dated record of the Tar-San Martin Lakes basin showing that Viedma – Tar-San Martín Lakes were formed at similar ages. Taking into account that the deposits of Bahía Túnel are located at 266 masl and that the level of the lake would be above this height, it is proposed that this lake level would have restricted the movement of hunter-gatherer populations along the coast and to the west. From 2.4 ka on a new space started to be available for these populations broadening the wintering grounds (≤400 masl). The chronology of the archaeological record found in this new space fits the proposed paleogeographic evolution. This paper complements the research on the evolution of lacustrine systems in the Patagonian Mountain range and broadens the discussion of human mobility in the Viedma Lake basin during the Holocene.
The Patagonian Andes were affected by a range of geophysical drivers of landscape incision during the Last Glacial Interglacial Transition and Early Holocene. Deciphering drivers of river system response during this period is complex, and magnitudes and timescales of landscape change are poorly constrained. Herein, a remotely sensed time series of modern terrace formation is investigated from the Laguna del Viedma valley as a modern analogue of Late Quaternary landscape evolution in Patagonia. The aim of the research was to constrain the timing of terrace formation following lake level fall of the Laguna del Viedma over a 35 year period from 1985-2019. The objectives were to: 1) use satellite imagery from 1985-2019 to document glacier and lake changes in the study area; 2) map landforms of the Laguna del Viedma valley; and 3) analyse terrace elevations. In total seven terrace surfaces were distinguished, with the oldest four pre-dating the ALOS PALSAR DEM (February 2000) used. Landform evidence shows the highest, and vegetated, T1 terrace surface (+40-75 m) grades to the highest lake level and was likely the elevation of the valley floor during Holocene neoglacials. Viedma glacier recession then led to a phase of lake regressions/transgressions with an overall trend of lake level fall. The DEM shows ~20 m incision from the 1985 floodplain level (T3) to the T4 level floodplain by 2000. This constrains a minimum rate of incision of 1.33 m/yr, however, the satellite time series demonstrates rapid T3 terrace formation, with evidence for mass movements contributing to lateral terrace erosion by 1986. The implications of the data-are discussed within the context of the Late Quaternary palaeohydrology of Patagonia where lake level falls of 10s to 100s of metres occurred within many large river systems of the Patagonian Andes from 42-52⁰ S. The data herein demonstrate that base level falls from sudden lake drainage events were likely a major driver of rapid landscape change in Patagonia during deglaciation.
The Patagonian glaciations developed since the latest Miocene (ca. 6 Ma) in multiple events, of varied duration and intensity. Most of the present glacial landscape is the outcome of the glacial modelling during the Pleistocene, since the Great Patagonian Glaciation (GPG; ca. 1 Ma). The Patagonian Andes were covered by a continuous mountain ice sheet, from 37º S to Cape Horn (56º S) in at least five major glaciations for more than 15 cold events in the last million years. The present drainage network was developed after the Last Glacial Maximum (LGM; ca. 24 cal. ka BP), particularly those cases with drainage reversal, when the glaciers began to melt due to global climatic changes. The environmental impact of Pleistocene glaciations extended all over Patagonia. The knowledge about the Last Glaciation, the Late Glacial and Holocene glaciations is very important because the human settling of the Patagonian landscape as we know it took place during this period. Moreover, the human colonization of Patagonia took place sometime after the Last Glacial Maximum and during the Late Glacial (ca. 18,000 to 10,000 years ago) and it was completed along the entire Early Holocene.
We map the glacial geomorphology of the former Patagonian Ice Sheet between 44°S and 46°S. Building on previous work, our map covers a ∼50,000 km² region of west-central Patagonia. The study area includes the eastward-flowing Río Pico, Río Caceres, Río Cisnes, Lago Plata-Fontana, El Toqui, Lago Coyt/Río Ñirehuao, Simpson/Paso Coyhaique, and Balmaceda palaeo-outlet glaciers, adjacent valleys, and the Andean Cordillera. The inventory contains >70,000 individual landforms mapped from remotely-sensed imagery and field surveys. Mapping was classified into ice-marginal (e.g. moraine ridges, trimlines), subglacial (e.g. glacial lineations, flutes), glaciolacustrine (e.g. palaeolake shorelines, perched deltas), glaciofluvial (e.g. proglacial outwash plains, meltwater channels), and non-glacial (e.g. palaeochannels, landslides or slumps) landform groups. The new map will inform future interpretations of regional glacier dynamics, and the development of robust geochronological datasets that test the timing of glaciation and deglaciation.
Geological climate archives from the Holocene Epoch provide baseline information concerning natural climate variability. Temperate mountain glacier extent is sensitive to summer air temperature, thus geological records of past glacier length changes are a useful proxy for this climatic variable. Here we present a new cosmogenic ¹⁰Be chronology of glacier length changes at Dart Glacier in the Southern Alps, New Zealand. Prominent moraines deposited 321 ± 44 yr ago (n = 11) and 7.8 ± 0.3 ka (n = 5) show glaciers during the Little Ice Age were less extensive than during the early Holocene. This pattern of net Holocene glacier retreat is consistent with emerging data from other catchments in New Zealand and across the southern mid-latitudes. Using the physical framework of a transient global climate model simulation, we suggest that cool summers in the early Holocene were promoted by the local summer insolation minimum, together with low atmospheric greenhouse gas concentrations, causing an early Holocene austral glacial maximum. An insolation-driven reduction in seasonality at southern mid-latitudes may reconcile differences between early Holocene temperature reconstructions where climate proxies have different seasonal sensitivities. We suggest that rising greenhouse gas concentrations after 7 ka caused regional-scale glacier retreat and appear to be the dominant driver of multi-millennial summer temperature trends in the southern mid-latitudes during the present interglacial.
The aim of this paper is to describe and discuss the strategies and technology implemented by Late Holocene hunter-gatherers to hunt their most prominent animal resources, guanaco (Lama guanicoe) and choique (Rhea pennata pennata), in different settings in the north margin of Lake Viedma (Santa Cruz province, Argentina). In order to do that, we use archaeological distributional data from different altitudinal levels, namely lakeshore dunes (255–275 m.a.s.l), mid-altitude plains or pampas (276–900 m.a.s.l.), and Del Tobiano basaltic plateau (≥900 m a.s.l.). The pampas, particularly the grounds below 400 m.a.s.l., may have been used by both species as their wintering grounds (although their permanence in this environment could have occurred throughout the year), while the mid-altitude plains and the plateau seem to have been primarily used by the guanaco as grazing and calving grounds from late spring to early fall, the months in which most of its surface is free of snow. Likely, differences in seasonality, topography and use of these environments by the guanaco and choique social groups may have forced people to adopt different hunting strategies, tactics and weaponry. Frequency variations in the presence of projectile points and bolas at different altitudinal levels have been observed. In the pampas, evidence suggests that guanaco hunting was aided by the use of bow and arrows and/or throwing weapons, such as spears and bolas, the latter likely also used in the hunting of choique. In the plateau, on the other hand, guanaco hunting tactics involved the use of blinds either by individuals or small groups of hunters who were mainly equipped with throwing weapons and/or bow and arrows. The archeological record of the plateau shows a logistic hunting-oriented strategy as well as a residential use during summer months. Artifact density and variety at lakeshore dunes suggest a greater intensity of occupation of these grounds, probably linked to a more residential use—either seasonal (fall/winter) or year-round—made possible by the availability, although in variable density throughout the year, of guanaco and choique. Consequently, the regional archeological landscape exhibits evidence of integration and complementarity of the different altitudinal levels in the northern margin of the Lake Viedma, at least during the Late Holocene.
Perito Moreno is the most famous calving glacier of the South Patagonia Icefield, the largest temperate glacier system of the Southern Hemisphere. Unlike most of the glaciers in the region that have strongly retreated in recent decades, the position of perito Moreno glacier front remained relatively unchanged in the last century. However, earliest photographic documents show that, at the end of the nineteenth century, the front was ca. 800 m behind the current position. There is no reliable information about the positions of the perito Moreno front in earlier times. Here we show evidence of two subaqueous moraine systems both in the canal de Los témpanos and in the Brazo Rico, the two arms of Lago Argentino along which Perito Moreno glacier has flowed over time. These moraines, identified for the first time in the Canal de Los Témpanos from bathymetric and high-resolution seismic profiles, mark the position of the largest glacier advance, tentatively correlated with the moraines of the "Herminita advance" identified and dated onland. We interpret these bedforms as the evidence of the most pronounced advance of Perito Moreno glacier during the mid-Holocene cooling event that characterized this sector of the Southern Hemisphere. this study highlights the importance of subaqueous glacial bedforms, representing decisive records of the glacial history and palaeoclimate, which could help unveiling the origin of the different behavior of glaciers like Perito Moreno that in a warming climate are relatively stable.
A simple equation is derived relating the net mass-balance and hypsometric curves of a steady-state valley glacier. It is used to examine how valley shape is linked to disparate extents and responses of glaciers subjected to similar climatic conditions. Examples are given which show that area-based indices (e.g. AAR) for estimating the equilibrium line altitude (ELA) may be subject to a substantial built-in variance because they implicitly rely upon similarity of glacier shape and regimen over a region. If accurate topographic maps are available, the equation may be used to infer the regimen of modern glaciers in the form of a dimensionless ratio of net mass-balance gradients. Alternatively, if similar information is available concerning regional glacier regimen, disparate extents and responses may be collectively utilized to estimate values of ELA or to infer climatic influence, taking glacier hypsometry into account.
A survey of some relict and active landforms in the Lachman and Rink Crags areas of NW James Ross Island on the Antarctic Peninsula has yielded new evidence that provides a better understanding of the Holocene morphoclimatic evolution of this currently deglaciated sector of James Ross Island. Six Holocene (mainly land-grounded) glacial advances were delimited by these morphological and stratigraphic studies, dated at 6700–6400, 4900–4400, and shortly after 3900 14C yr B.P., with three more recent advances, dated by regional correlations, that occurred between the Holocene regional climatic optimum (3900–3000 14C yr B.P.) and the Little Ice Age (ca. 300 14C yr B.P.). In some cases, ice-cored rock glacier formation followed the younger glacier advances. In recent decades, the significant climatic warming recorded in the NE region of James Ross Island has produced a number of changes in the periglacial and glacial landforms. Stone-banked terraces and lobes have developed in the Rink Crags, and protalus rampart formation has ceased in favor of protalus lobe development in the Cerro Triple area. Conical depressions filled with water have also increased in area over the surface of the Lachman II ice-cored rock glacier, threatening to destroy this landform.
The Patagonian icefields are the largest mid-latitude ice masses and yet few glaciological data exist for them. The presence of the Andes lying athwart the westerlies makes for a dynamic glacial system with steep balance gradients and west-east equilibrium-line altitude gradients. The overall trend during the 20th century has been glacier retreat. However, whereas most eastern outlets retreated consistently from the beginning of the century, recession on the west began later, has been interrupted by readvances, and most recently has accelerated markedly, reaching higher mean rates of retreat than those on the east. This contrast may result from a predominantly precipitation-controlled mass-balance regime in the west and a dominant temperature control in the east. Superimposed on these contrasts is the anomalous behavior of certain calving glaciers, the oscillations of which contrast in magnitude, timing and sign with each other and with noncalving glaciers, and which in many cases do not relate directly to climate change. Two large calving outlets are at or near their Neoglacial maxima. The tantalizing fragments of information that exist suggest that there is a rich glaciological source to be mined in Patagonia yielding insights into glacioclimatic interactions, calving dynamics, Holocene climate change and the role of topography in controlling glacier behavior. 118 refs., 13 figs., 2 tabs.
The timing and magnitude of postglacial climatic changes around the globe provide insights into the underlying drivers of natural climate change. Using geomorphologic mapping of moraines, ¹⁰Be surface-exposure dating, snowline reconstructions, and numerical modeling, we quantified glacier behavior during Late Glacial (15–11.5 ka) and Holocene (the past ∼11.5 k.y.) time in the Ben Ohau Range, New Zealand. Glaciers were more extensive during the Antarctic Cold Reversal (ACR), than subsequently, and the margins underwent a punctuated net withdrawal over the Holocene. Numerical modeling experiments that achieve the best fit to the moraines suggest that air temperature during the ACR was between 1.8 °C and 2.6 °C cooler than today, with similar (±20%) prescribed precipitation. After the ACR, a net snowline rise of ∼100 m through the Younger Dryas stadial (12.9–11.7 ka) was succeeded by a further “long-term,” or net, rise of ∼100 m between ∼11 k.y. and ∼500 yr ago. Glacier snowline records in New Zealand show generally coherent Late Glacial and Holocene climate trends. However, the paleoclimate record in the southwest Pacific region shows important differences from that in the Northern Hemisphere.
The melting of mountain glaciers and ice caps is expected to contribute significantly to sea-level rise in the twenty-first century, although the magnitude of this contribution is not fully constrained. Glaciers in the Patagonian Icefields of South America are thought to have contributed about 10% of the total sea-level rise attributable to mountain glaciers in the past 50 years. However, it is unclear whether recent rates of glacier recession in Patagonia are unusual relative to the past few centuries. Here we reconstruct the recession of these glaciers using remote sensing and field determinations of trimline and terminal moraine location. We estimate that the North Patagonian Icefield has lost 103+/-20.7km3 of ice since its late Holocene peak extent in AD 1870 and that the South Patagonian Icefield has lost 503+/-101.1km3 since its peak in AD 1650. This equates to a sea-level contribution of 0.0018+/-0.0004mmyr-1 since 1870 from the north and 0.0034+/-0.0007mmyr-1 since 1650 from the south. The centennial rates of sea-level contribution we derive are one order of magnitude lower than estimates of melting over the past 50 years, even when we account for possible thinning above the trimline. We conclude that the melt rate and sea-level contribution of the Patagonian Icefields increased markedly in the twentieth century.
The Southern Patagonia Icefield (SPA) is located at mid-latitudes in southern South America, which is dominated by the westerly regime and frontal systems. This results in a high frequency of cloudy days (more than 70% of the time) and precipitation events. Analysis of air temperature and precipitation data from southern meteorological stations for the past century indicate and overall warming and decrease in precipitation until the mid-80´s, but not significant changes are observed afterwards. In fact, the coastal stations show an increase in precipitation after the 1980´s. The mid-term behavior of the atmospheric variables introduces uncertanties in predicting the consequences of future climate change in southern South America.
Glacial geologic evidence indicates that glaciers throughout the Andes and Antarctica fluctuated during the Holocene. Radiocarbon dating and other age determinations suggest that glaciers readvanced significantly only during the last 5 ka, reaching positions from several 100 m to a few kilometres beyond their present limits. In South America tenuous evidence from radiocarbon dates, with dendrochronological data and environmental interpretations from pollen analyses indicate four main periods of Neoglacial advance, culminating 5000-4000 BP, 3000-2000 BP, 1300-1000 BP, and 15th-late 19th centuries; smaller advances may have occurred at ca. 8400 BP, ca. 7500 BP, and ca. 6300 BP. The meagre data are consistent in indicating broad synchrony throughout the Andes during the last 5 ka, suggesting response to global climatic changes. Anomalies exist in Patagonia where some tide-water glaciers reached their maximal Holocene limits recently this century.
Investigations carried out in the Ema Glacier valley, Tierra del Fuego, on the eastern side of Monte Sarmiento Massif, enable the recognition of five Holocene glacial events. The oldest glacial advance deposited the so-called external moraines of Ema Glacier, with a probable occurrence between 6000 and 5000 14 C y BP without discarding the potential for these deposits to be from Lateglacial time. The remaining four readvances built up a complex inner moraine system named informally internal moraines of Ema Glacier. The oldest recognized till unit that constitutes this proximal moraine system was deposited shortly before 3135 14 C y BP, when glaciolacustrine sedimentation took place during glacier recession. Subsequent glacial advances accumulated till at about 1288 14 C y, shortly after 695 14 C y, and between 379 14 C y and 60 y BP. This chronology of Holocene glacier events coincides with and is well complemented by the one established by other authors for Fiordo Pía at Cordillera Darwin, 75 km to the east. The Ema-Pía chronology is used to calibrate tentatively a series of moraine belts previously identified in the mountain ranges adjacent to Ushuaia, 150 km SE of the surveyed region. A comparative chart shows that the chronological data obtained for the neoglacial readvances in Tierra del Fuego are in accordance with those for the southern Patagonian Andes further north. It follows that the Holocene behavior of the glaciers in the Andean region of Tierra del Fuego and southern Patagonia is essentially a response to the same regional climate change.
This paper presents the evidence for Late Pleistocene and Holocene palaeoclimate and glacier fluctuations of the two major icefields in Patagonia, the Hielo Patagónico Norte (47°00′S, 73°39′W) and the Hielo Patagónico Sur (between 48°50′S and 51°30′S). The palaeoenvironmental evidence suggests that glaciers still covered large areas of Patagonia at approximately 14,600 14C years BP. Uniform and rapid warming took place after 13,000 14C years BP, with no unequivocal evidence for climate fluctuations equivalent to those of the Northern Hemisphere Younger Dryas cooling event (the Younger Dryas Chronozone, dated to 11,000–10,000 14C years BP (12,700–11,500 cal. years BP). During the early Holocene (10,000–5000 14C years BP) atmospheric temperatures east of the Andes were about 2 °C above modern values in the period 8500–6500 14C years BP. The period between 6000 and 3600 14C years BP appears to have been colder and wetter than present, followed by an arid phase from 3600 to 3000 14C years BP. From 3000 14C years BP to the present, there is evidence of a cold phase, with relatively high precipitation. West of the Andes, the available evidence points to periods of drier than present conditions between 9400–6300 and 2400–1600 14C years BP. Holocene glacier advances in Patagonia began around 5000 14C years BP, coincident with a strong climatic cooling around this time (the Neoglacial interval). Glacier advances can be assigned to one of three time periods following a ‘Mercer-type’ chronology, or one of four time periods following an ‘Aniya-type’ chronology. The ‘Mercer-type’ chronology has glacier advances 4700–4200 14C years BP; 2700–2000 14C years BP and during the Little Ice Age. The ‘Aniya-type’ chronology has glacier advances at 3600 14C years BP, 2300 14C years BP, 1600–1400 14C years BP and during the Little Ice Age. These chronologies are best regarded as broad regional trends, since there are also dated examples of glacier advances outside these time periods. Possible explanations for the observed patterns of glacier fluctuations in Patagonia include changes related to the internal characteristics of the icefields, changes in the extent of Antarctic sea-ice cover, atmospheric/oceanic coupling-induced climate variability, systematic changes in synoptic conditions and short-term variations in atmospheric temperature and precipitation.
This paper presents an updated, extensive review of glacier fluctuations during the past 1000 years in the extratropical Andes of South America between ca. 17° and 55°S. Given the variety of environmental conditions and evidence available for glacier fluctuations across this wide latitudinal range, regional accounts are given for the Desert Andes (∼ 17°–31°S), the Andes of central Chile and Argentina (31°–36°S), and the North (36°–45°S) and South (45°–55°S) Patagonian Andes. The techniques, dating limitations, and interpretations of the glacier records along this transect are also discussed. Information on glacier fluctuations in the Desert Andes is limited to the 20th century. Documentation on past glacier variations is more abundant in the Central Chilean-Argentinean Andes, but the number of chronologies dealing with glacier fluctuations prior to the 1900s is also limited. Most records indicate that glaciers were generally more extensive prior to the 20th century, with dates of maximum expansion ranging from the 16th to the 19th centuries. The number and extent of glaciers increase significantly in the Patagonian region, where the evidence available for dating glacier variations during the past centuries is more abundant and the dating control for glacier events is generally better than in the northern parts of the study area. For some Patagonian glaciers, maximum Little Ice Age (LIA) or post-LIA advances have been precisely dated by dendro-geomorphological determinations or in situ measurements. However, for most sites, the evidence available is still preliminary and there is considerable variability in the extent and timing of events related to the maximum LIA expansion identified in most areas between the 16th and 19th centuries. Evidence is starting to appear at a growing number of sites for glacier advances during the first half of the past millennium. These events were generally less extensive than the LIA maximum pulses. Despite the occurrence of several post-LIA readvances over the past 100–110 years, most areas in the Andes of extratropical South America have experienced a general pattern of glacier recession and significant ice mass losses. The differences in the glacier histories observed at local and regional scales probably reflect the inherent limitations associated with the glacier records and/or the dating techniques used in each case together with the varying dominance of precipitation, temperature and other climatic and non-climatic factors on glacier mass balance and glacier dynamics. These differences indicate that the late Holocene glacier history of southern South America is more complex than commonly assumed. The evidence discussed in this study highlights not only the immense potential for glaciological studies of this region but also a significant need for an increased number of detailed, well-dated records of glacier fluctuations.
Recent measurements on dendrochronologically-dated wood from the Southern Hemisphere have shown that there are differences between the structural form of the radiocarbon calibration curves from each hemisphere. Thus, it is desirable, when possible, to use calibration data obtained from secure dendrochronologically-dated wood from the corresponding hemisphere. In this paper, we outline the recent work and point the reader to the internationally recommended data set that should be used for future calibration of Southern Hemisphere ¹⁴C dates. This article has been published in the journal: Radiocarbon. © 2004 by the Arizona Board of Regents on behalf of the University of Arizona. Used with permission.
Vive La Différence
How closely do climate changes in the Northern and Southern Hemispheres resemble each other? Much discussion has concentrated on the Holocene, the warm period of the past 11,500 years in which we now live, which represents a baseline to which contemporary climate change can be compared. Schaefer et al. (p. 622 ; see the Perspective by Balco ) present a chronology of glacial movement over the last 7000 years in New Zealand, which they compare to similar records from the Northern Hemisphere. Clear differences are observed between the histories of glaciers in the opposing hemispheres, which may be owing to regional controls. Thus, neither of two popular arguments—that the hemispheres change in-phase or that they change in an anti-phased manner—appear to be correct.
Digital elevation models of the Northern and Southern Patagonia Icefields of South America generated from the 2000 Shuttle
Radar Topography Mission were compared with earlier cartography to estimate the volume change of the largest 63 glaciers.
During the period 1968/1975–2000, these glaciers lost ice at a rate equivalent to a sea level rise of 0.042 ± 0.002 millimeters
per year. In the more recent years 1995–2000, average ice thinning rates have more than doubled to an equivalent sea level
rise of 0.105 ± 0.011 millimeters per year. The glaciers are thinning more quickly than can be explained by warmer air temperatures
and decreased precipitation, and their contribution to sea level per unit area is larger than that of Alaska glaciers.
We present here a review of the current glaciological knowledge of the Southern Patagonia Icefield (SPI). With an area of 13,000 km2 and 48 major glaciers, the SPI is the largest ice mass in the Southern Hemisphere outside of Antarctica. The glacier inventory and recent glacier variations are presented, as well as ice thickness data and its variations, ice velocity, ablation, accumulation, hydrological characteristics, climate changes and implications for sea level rise. Most of the glaciers have been retreating, with a few in a state of equilibrium and advance. Glacier retreat is interpreted primarily as a response to regional atmospheric warming and to a lesser extent, to precipitation decrease observed during the last century in this region. The general retreat of SPI has resulted in an estimated contribution of 6% to the global rise in sea level due to melting of small glaciers and ice caps. Many glaciological characteristics of the SPI, in particular its mass balance, need to be determined more precisely.
The last major glacial readvance in southern S America occurred no later than 13 000 yr BP. The deglaciation that followed was rapid. By 12 500 yr BP the ice had withdrawn into the mountains, opening ice-free corridors through which former ice-dammed lakes east of the Cordillera drained westward to the Pacific Ocean. Recession continued and by 11 000 yr BP, the ice had withdrawn to within its present borders, implying the start of the local Hypisthermal Interval. No readvance during the Younger Dryas chron has been detected. Neoglaciation began after 6800 yr BP. During the present century most glaciers have receded, to a much greater extent on the east side of the mountains than on the west. -from Author
A simple equation is derived relating the net mass-balance and hypsometric curves of a steady-state valley glacier. It is used to examine how valley shape is linked to disparate extents and responses of glaciers subjected to similar climatic conditions. Examples are given which show that area-based indices (e.g. AAR) for estimating the equilibrium line altitude (ELA) may be subject to a substantial built-in variance because they implicitly rely upon similarity of glacier shape and regimen over a region. If accurate topographic maps are available, the equation may be used to infer the regimen of modern glaciers in the form of a dimensionless ratio of net mass-balance gradients. Alternatively, if similar information is available concerning regional glacier regimen, disparate extents and responses may be collectively utilized to estimate values of ELA or to infer climatic influence, taking glacier hypsometry into account.
After a late-glacial readvance, the glaciers in Argentine Patagonia receded quickly, and by 10,000 B.P. at least one glacier was little larger than it is today. Three episodes of postglacial readvance followed, the first culminating about 4600 B.P. during early Sub-Boreal time, the second about 2000 B.P. during the Sub-Atlantic, and the third during recent centuries. In contrast to most other parts of the world, no glacier, so far as is known, reached its maximum postglacial extent in recent centuries.
The Hielo Patagónico (Patagonia Icefield), South America, is the largest temperate ice body in the Southern Hemisphere with more than 70 major outlet glaciers and a total area of ca. 17,200 kn2. For the Hielo Patagónico, two major schemes for the Holocene glaciations (Neoglaciations) have been proposed. Mercer first proposed three Neoglaciations, I at 4500-4000 years before the present (yr BP), II at 2700-2000 yr BP and III at the 17-19th centuries. Aniya later postulated a scheme of four Neoglaciations, I at ca. 3600 yr BP, 11 at 2400-2200 yr BP, III at 1600-900 yr BP. and IV at the 17-19th centuries, which is congruent with other regions of the Andes. The main differences are the age of Neoglaciation 1 and the existence of a Neoglaciation at 1600-900 yr BP. After examining the dates given by other studies, although scanty, I propose a new scheme of five Neoglaciations, I at 4500-4000 yr BP, II at 3600-3300 yr BP, III at 2700-2000 yr BP, IV at 1600-900 yr BP and V at 17-19th centuries, that is, the Little Ice Ace (LIA). In addition, there were two earlier Holocene glaciations, probably at 5700-5000 yr BP and 8100-6800 (or 7500) yr BP. Two older ages, 8800-8500 yr BP and 9700-9100 yr BP. are uncertain.
An account of field work in Argentina in 1975. The section on narrative and glacial geology is by Mercer and that on vegetational history by Ager. The main glacial results have already been published. More than 700 plant specimens were collected, surface pollen spectra measured, cores collected from peat bogs and pollen diagrams constructed, one of which is illustrated here. There is also a table of 13 radiocarbon dates. -K.Clayton
The last decade has seen a global surge in the number and resolution of well-dated geomorphological reconstructions of mountain glacier fluctuations and former ice sheet extents. This has been facilitated by the widespread deployment of large samples of terrestrial cosmogenic nuclide dating (TCND) allowing more sophisticated probability analyses for reducing the statistical uncertainty of moraine ages, and testing of correlations at local, regional and hemispheric scales. Geochronological advances in the field, laboratory and on model calibration have taken place in parallel with modelling of palaeoclimate based on glacier reconstructions, and of glacier sensitivity to temperature and precipitation forcing. In spite of these advances, basic conceptual issues remain. This review questions whether the technical leap forward in dating has encouraged us to over-reach our interpretive limits, particularly in terms of the concept and practice of correlation. We propose that to enable reliable correlation, glacier chronologies should first be examined for their climatic integrity, spatial coherence, and chronological robustness. Even with excellent dating, interpretive complexity remains due to complex climate signals and glacier response characteristics, and to erosion censoring of the landform record. All are issues which must be addressed to avoid either spurious “lumping” (correlation) or “splitting” (differentiation) of glacier chronologies, and thus misinterpretation of the climatic significance of reconstructed glacier advances. We suggest that the reliability of correlation is no better than the weakest link in the chain of reasoning which connects climatic fluctuations with dated landforms and sediments. Improved dating means that poor chronological resolution is less likely to be the limiting factor for correlation, but shifts the focus onto other less quantifiable sources of uncertainty. These conceptual statements are exemplified with reference to Holocene glacial chronologies of contrasting mid-latitude environments in southern Norway, Iceland and New Zealand.
When calculated with the commonly accepted average Northern Hemisphere production rate, 10 Be dates of surface boulders on moraines in the Lago Argentino area of Patagonia are younger than minimum-limiting 14 C ages for the same landforms. This disagreement could result from the lack of a regional 10 Be production-rate calibration site. To assess this possibility, we here present high-precision measurements of 10 Be in samples collected from surface boulders on the Herminita and Puerto Bandera moraine complexes deposited alongside Lago Argentino on the eastern flank of the Andes at 50°S in Patagonia. Together with maximum- and minimum-limiting 14 C ages for the two moraine systems, these measurements confine the local 10 Be production rate to between 3.60 and 3.82 atoms/g/yr (midpoint = 3.71 ± 0.11 atoms/g/yr) when using a time-dependent scaling method that incorporates a high-resolution geomagnetic model. This range includes upper and lower error bounds of acceptable production rates derived from both the Herminita and the Puerto Bandera sites. The upper limit of this range is more than 12% below the average Northern Hemisphere production rate, as calculated using the same scaling method, given in Balco et al. [Quat. Geochron 3 (2008) 174-195]. Other scaling models yield production rates with similarly large offsets from the Balco et al. (2008) rate. On the other hand, the range of acceptable production rate values determined from Patagonia overlaps at 1sigma with, and encompasses, the production rate recently derived in Macaulay valley in the Southern Alps of New Zealand [A. Putnam et al., Quat. Geochron. 5 (2010a) 392-409]. Within uncertainties (i.e., overlap at 1 sigma) this Patagonian production rate range also agrees with a recently determined production rate from low-elevation sites in northeastern North America and northern Norway. When the Macaulay production rate is used to calculate Patagonian exposure dates, 14 C and 10 Be chronologies are mutually compatible for late-glacial moraine systems. Both chronologies then indicate that outlet glaciers of the Southern Patagonian Icefield achieved a late-glacial maximum in the western reaches of Lago Argentino at 13,000 cal. yr BP at the end of the Antarctic Cold Reversal (14,500-12,900 cal. yr BP). Outlet glaciers subsequently receded to near present-day ice margins during the Younger Dryas stadial (12,900-11,700 cal. yr BP). This general retreat was interrupted about 12,200 cal. yr BP when Upsala Glacier constructed an interlobate complex of moraine ridges on Herminita Peninsula. Mountain glaciers in Patagonia and New Zealand, on both sides of the South Pacific Ocean, exhibited a coherent pattern of late-glacial ice-margin fluctuations.
Radiocarbon dates of incorporated moss indicate advance of the Collins Ice Cap on Fildes Peninsula (King George Island) after ~650 cal. yr BP (~AD 1300), broadly contemporaneous with the `Little Ice Age', as defined in Europe. During that time, the glacier extended less than 400—500 m beyond its present-day margin. Moreover, radiocarbon data indicate that this was the most extensive advance of the last 3500 cal. years. Prior to ~650 cal. yr BP, the ice must have been at or behind its present position. Furthermore, the data indicate that climate conditions prior to the late-Holocene advance may have been similar to (or possibly warmer than) today.