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This paper systematically reviews the geomorphological and geochronological evidence of the last glacial cycle (∼115-11.7 ka) south of 52°S in southernmost Patagonia. We review the extent and timing of glaciation, compile geochronometric data from published studies into an open-access database and present an updated empirical reconstruction of ice-sheet evolution. The extent and timing of the local Last Glacial Maximum is ambiguous and we review the data that indicate that the local Last Glacial Maximum occurred during Marine Isotope Stage (MIS) 3/MIS 4 versus during MIS 2 at the time of the global Last Glacial Maximum. These contrasting scenarios differ by ∼100 km in lateral ice extent and 10s of thousands of years in timing, implying drastically different past environmental conditions, and therefore drivers. All of the major ice lobes were extensive until at least 18 ka and the onset of deglaciation occurred at ∼18-17 ka. The southernmost Patagonian Ice Sheet rapidly collapsed to the Fuegian fjords in <1000 years, likely due to the lower altitude of the Andes in this region, lower slopes of the glacier surfaces and through ice calving within the deep fjords into which the ice sheet retreated. During the Antarctic Cold Reversal (∼14.7-13 ka), glaciers readvanced only a few kilometres, restricted to the Fuegian fjords, and not ∼100 km to a 'Stage E' moraine, as previously hypothesised. This review highlights the disparity of dating constraints across southernmost Patagonia and suggests possible approaches for further study. More work is required to understand and resolve the discrepancy in the geochronological data and to determine a robust empirical reconstruction for the maximum last glacial extent in southernmost Patagonia, which is imperative for making climate inferences and comparing to numerical ice-sheet models. • New integrated review of the last glacial cycle for the southernmost PIS. • We collate dating constraints for the region and present new schematic figures. • It is unclear whether the local LGM was during the global LGM (MIS 2) or MIS 3/4. • Rapid PIS collapse initiated at 18-17 ka, retreating >100 km to the Fuegian fjords. • We present an updated ice-sheet reconstruction for southernmost Patagonia. [ABSTRACT FROM AUTHOR]

Abstract Erosion rates offer insight on landscape development and the relative importance of chemical and physical processes of weathering. Minimal chemical weathering makes Antarctica an ideal location in which to compare the physical weathering of carbonate rocks to other lithologies. Here we report the first cosmogenic nuclide-derived erosion rates for carbonate rocks in Antarctica. Carbonate samples collected in the southernmost Ellsworth Mountains reflect a 36Cl erosion rate of 0.22 ± 0.02 mm/ka. This erosion rate is consistent with other reported Antarctic erosion rates, but is lower than 36Cl erosion rates derived from other arid regions in the world. These results are integrated with a continent-wide reanalysis of 28 cosmogenic nuclide erosion rate studies (>200 measurements), which comprise numerous rock types and multiple cosmogenic nuclides. By combining cosmogenic nuclide-derived erosion rates across studies, the larger trends provide insight into factors (e.g. lithology, glacial history, and availability of abrasive material) affecting subaerial erosion rates in Antarctica. Statistical analysis of the compiled data set shows differences based on lithology, with sandstone having the largest range of erosion rates. The compiled data also reveals higher erosion rates in areas with a large potential sediment supply, like the Dry Valleys. Samples collected from boulders yield lower erosion rates than those collected from bedrock, likely due to a combination of physical processes that affect boulders and bedrock differently, and glacial history, which can affect the apparent cosmogenic-nuclide derived erosion rate. Highlights • Low cosmogenic 36Cl erosion rates from carbonate bedrock in Antarctica. • Statistical analysis of compiled Antarctic erosion studies shows lithologic dependence. • Boulder erosion rates are lower than bedrock erosion rates. • Higher erosion in the Dry Valleys is likely due to sediment supply. • Consistent, low erosion rates support the dominance of mechanical processes. [ABSTRACT FROM AUTHOR]

The timing, structure and termination of the last southern mountain glaciation and its forcing remains unclear. Most studies have focused on the global Last Glacial Maximum (LGM; 26.5–19 ka) time period, which is just part of the extensive time-frame within the last glacial period, including Marine Isotope Stages 3 and 4. Understanding the glacial fluctuations throughout the glacial period is a prerequisite for uncovering the cause and climate mechanism driving southern glaciation and the interhemispheric linkages of climate change. Here, we present an extensive (n = 65) cosmogenic 10 Be glacier chronology derived from moraine belts marking the pre-global LGM extent of the former Patagonian Ice Sheet in southernmost South America. Our results show the mountain ice sheet reached its maximum extent at 48.0 ± 1.8 ka during the local LGM, but attained just half this extent at 21.5 ± 1.8 ka during the global LGM. This finding, supported by nearby glacier chronologies, indicates that at orbital time scales, the southern mid-latitude glaciers fluctuated out-of-phase with northern hemisphere ice sheets. At millennial time-scales, our data suggest that Patagonian and New Zealand glaciers advanced in unison with cold Antarctic stadials and reductions in Southern Ocean sea surface temperatures. This implies a southern middle latitudes-wide millennial rhythm of climate change throughout the last glacial period linked to the north Atlantic by the bipolar seesaw. We suggest that winter insolation, acting alongside other drivers such as the strength and/or position of the southern westerlies, controlled the extents of major southern mountain glaciers such as those in southernmost South America. [ABSTRACT FROM AUTHOR]

An elevated erosional trimline in the heart of West Antarctica in the Ellsworth Mountains tells of thicker ice in the past and represents an important yet ambiguous stage in the evolution of the Antarctic Ice Sheet. Here we analyse the geomorphology of massifs in the southernmost Heritage Range where the surfaces associated with the trimline are overlain by surficial deposits that have the potential to be dated through cosmogenic nuclide analysis. Analysis of 100 rock samples reveals that some clasts have been exposed on glacially moulded surfaces for 1.4 Ma and perhaps more than 3.5 Ma, while others reflect fluctuations in thickness during Quaternary glacial cycles. Modelling the age of the glacially moulded bedrock surface based on cosmogenic 10 Be, 26 Al and 21 Ne concentrations from a depth-profile indicates a minimum exposure age of 2.1–2.6 Ma. We conclude that the glacially eroded surfaces adjacent to the trimline predate the Last Glacial Maximum and indeed the Quaternary. Since erosion was by warm-based ice near an ice-sheet upper margin, we suggest it first occurred during the early glaciations of Antarctica before the stepped cooling of the mid-Miocene at ∼14 Ma. This was a time when the interior Antarctic continent had summers warm enough for tundra vegetation to grow and for mountain glaciers to consist of ice at the pressure melting point. During these milder conditions, and subsequently, erosion of glacial troughs is likely to have lowered the ice-sheet surface in relation to the mountains. This means that the range of orbitally induced cyclic fluctuations in ice thickness have progressively been confined to lower elevations. [ABSTRACT FROM AUTHOR]

Southern South America contains a glacial geomorphological record that spans the past million years and has the potential to provide palaeoclimate information for several glacial periods in Earth's history. In central Patagonia, two major outlet glaciers of the former Patagonian Ice Sheet carved deep basins ∼50 km wide and extending over 100 km into the Andean plain east of the mountain front. A succession of nested glacial moraines offers the possibility of determining when the ice lobes advanced and whether such advances occurred synchronously. The existing chronology, which was obtained using different methods in each valley, indicates the penultimate moraines differ in age by a full glacial cycle. Here, we test this hypothesis further using a uniform methodology that combines cosmogenic nuclide ages from moraine boulders, moraine cobbles and outwash cobbles. 10 Be concentrations in eighteen outwash cobbles from the Moreno outwash terrace in the Lago Buenos Aires valley yield surface exposure ages of 169–269 ka. We find 10 Be inheritance is low and therefore use the oldest surface cobbles to date the deposit at 260–270 ka, which is indistinguishable from the age obtained in the neighbouring Lago Pueyrredón valley. This suggests a regionally significant glaciation during Marine Isotope Stage 8, and broad interhemispheric synchrony of glacial maxima during the mid to late Pleistocene. Finally, we find the dated outwash terrace is 70–100 ka older than the associated moraines. On the basis of geomorphological observations, we suggest this difference can be explained by exhumation of moraine boulders. [ABSTRACT FROM AUTHOR]

Abstract: This paper evaluates the chronology of the last glacial cycle and deglaciation in the Lago Pueyrredón valley of central Patagonia, 47.5° S, Argentina. The valley was a major outlet of the former Patagonian Ice Sheet and the moraines that record its fluctuations are an important proxy record of climate change in southern South America. Such moraines are well-preserved in the Lago Pueyrredón valley owing in part to the semi-arid environment east of the mountain front. Here, we provide the first direct chronology for the age of the “Rio Blanco” moraine system by utilizing cosmogenic-nuclide surface exposure ages. Boulders on the moraines give 10Be exposure ages that indicate the Last Glacial Maximum (LGM) maximum extent occurred by 27–25ka. Subsequent advances occurred at 23–22ka, 20–18ka, and ca. 18–17ka. Initial deglaciation began after ca. 18–17ka and was interrupted as evidenced by the Lago Columna moraines up-valley. Subsequently the outlet glaciers occupying both the Lago Pueyrredón basin (Chilean name: Lago Cochrane) and the Lago Buenos Aires basin (Chilean name: Lago General Carrera) to the north, rapidly retreated more than 80km at around 16.5–15ka. The timing of the LGM maximum extent and the onset of deglaciation occurred broadly synchronously throughout Patagonia. Deglaciation resulted in a series of interconnected glacier-dammed lakes in the region that initially drained toward the Atlantic Ocean and later drained to the Pacific Ocean as a consequence of disintegrating ice in the Andes. [Copyright &y& Elsevier]

Abstract: In southern South America, the maximum areal extent of ice during the Quaternary Period, the Greatest Patagonian Glaciation (GPG, [Mercer, J.H., 1983. Cenozoic glaciation in the southern hemisphere. Annual Reviews of Earth and Planetary Science 11, 99–132.]), occurred at 1.1 Ma and subsequent glaciations were overall less extensive. The GPG preceded global minimum temperatures and maximal volume of ice, which occurred in the last ~800 kyr, as recorded in the marine δ 18O record. Significant modification of the drainage morphology of the southern Andes from a non-glaciated to glaciated landscape occurred throughout the Quaternary Period. We infer a non-climatic relationship between glacial modification of the mountains and the decreasing extent of ice and we discuss processes of landscape development that could have caused the trend. Specifically, these include modification of valleys, such as development from a V- to a U-shape, and lowering of mass-accumulation areas. Such changes would strongly affect glacial dynamics, the mass balance profile and mass-flux during succeeding glaciations, especially for low-gradient outlet glaciers occupying low areas. Other areas around Earth (at least where ice has been warm-based) also may exhibit a non-random trend of decreasing extent of ice with time, ultimately because of glacial erosion in the Quaternary Period. [Copyright &y& Elsevier]

In southern South America, well-dated glacial geomorphological records constrain the last glacial cycle across much of the former Patagonian Ice Sheet, but its northeastern sector remains comparatively understudied and unconstrained. This knowledge gap inhibits our understanding of the timing of maximum glacier extent, the duration of the glacial maximum, the onset of deglaciation, and whether asynchronies exist in the behaviour of the former ice sheet with latitude, or with location (east or west) relative to the ice divide. Robust glacial reconstructions from this region are thus required to comprehend the mechanisms driving Quaternary glaciations at the southern mid-latitudes. We here present 10 Be surface exposure ages from five moraine sets along with Bayesian age modelling to reconstruct a detailed chronology of Last Glacial Maximum expansions of the Río Corcovado glacier, a major former ice conduit of northern Patagonia. We find that the outlet glacier reached maximum expansion of the last glacial cycle during the global Last Glacial Maximum at ∼26.5–26 ka, and that at least four subsequent advances/stillstands occurred over a 2–3 ka period, at ∼22.5–22 ka, ∼22–21.5 ka, ∼21–20.5 ka and 20–19.5 ka. The onset of local ice sheet deglaciation likely occurred between 20 and 19 ka. Contrary to several other Patagonian outlet glaciers, including from similar latitudes on the western side of the Andes, we find no evidence for MIS 3/4 advances. Exposure dating of palaeo-shoreline cobbles reconstructing the timing of proglacial lake formation and drainage shifts in the studied region indicate three glaciolacustrine phases characterised by Atlantic-directed drainage. Phase one occurred from 26.4 ± 1.4 ka, phase two between ∼21 and ∼19 ka and phase three between ∼19 ka and ∼16.3 ka. Exposure dating of ice-moulded bedrock in the interior of the cordillera indicates local disintegration of the Patagonian Ice Sheet and the Atlantic-Pacific drainage reversal had occurred by ∼16.3 ka. We find that local Last Glacial Maximum glacier expansions were coeval with Antarctic and southern mid-latitude atmospheric and oceanic cooling signals, but out of phase with local summer insolation intensity. Our results indicate that local Patagonian Ice Sheet deglaciation occurred 1–2 ka earlier than northwestern, central eastern and southeastern Patagonian outlet glaciers, which could indicate high regional Patagonian Ice Sheet sensitivity to warming and drying during the Varas interstade (∼22.5–19.5 ka). • The Río Corcovado glacier experienced five advances during the Last Glacial Maximum. • These advances occurred over a 6–7 ka period, during Marine Isotope Stage 2. • We find no evidence for more extensive local Marine Isotope Stage 3/4 advances. • Local Patagonian Ice Sheet deglaciation started at ∼19–20 ka. • Local Atlantic/Pacific reversal of proglacial lake waters occurred at ∼16.3 ± 0.3 ka. [ABSTRACT FROM AUTHOR]

The spatial-temporal footprint of millennial-scale climate events during the last glacial-interglacial transition can yield insights into the underlying drivers of climate change, but remains poorly resolved in Patagonia. Here, we assess the glacier response to abrupt cold events and palaeolake evolution using geomorphological mapping along with 10 B e ages and optically stimulated luminescence ages from near Lago Belgrano (47.9° S) on the eastern side of Monte San Lorenzo. The former Belgrano glacier was sustained by a climatically sensitive ice cap, making the site ideal for investigating the glacier response to abrupt cold reversals. Our data reveal an extensive re-advance at 13.1 ± 0.6 ka, consistent with cooling and increased precipitation during the Antarctic Cold Reversal (ACR). Subsequently, ice retreated by at least 10 km and created an ice-dammed proglacial lake in the Belgrano valley. Rapid recession was punctuated by smaller advances/still-stands sufficient to maintain an ice-dam for the palaeolake and deposit a lateral moraine dated at 12.4 ± 0.3 ka during the Younger Dryas (YD). The final withdrawal of glaciers to the mountains allowed the palaeolake to drain and resulted in an Atlantic/Pacific drainage reversal. This marks the final separation of the Patagonian Ice Sheet into the individual ice fields at the YD-Holocene transition. Our data demonstrate the dominant ACR climate signal in central Patagonia, but also reveals a co-occurrence of the northern hemisphere YD signal, albeit of smaller magnitude. The ACR re-advance was primarily climatically controlled, but its relative magnitude was likely a consequence of ice divide migration and ice flow re-routing during the break-up of the Patagonian Ice Sheet. • Our 10Be data reveal an extensive re-advance at 13.1 ± 0.6 ka coeval the Antarctic Cold Reversal. • Subsequently ice retreated rapidly and an ice-dammed proglacial lake formed, which persisted for up to a millennium. • Together with a lateral moraine dated at 12.4 ± 0.4 ka, this indicates smaller advances/still-stands during the Younger Dryas. • The subsequent withdrawal of glaciers to the mountains allowed the proglacial lake to drain. • This marks the final break-up of the Patagonian Ice Sheet at the Younger Dryas - Holocene transition. [ABSTRACT FROM AUTHOR]

The timing and magnitude of glacial advances throughout a glacial cycle can give insight on the underlying drivers of climate change. Our knowledge of glacial activity early in a glacial cycle, however, is limited by incomplete preservation of the geomorphological record. Here, we present a B 10 e -dated glacial chronology from early in the last glacial cycle from the Belgrano valley, east of Monte San Lorenzo in central Patagonia. Our chronology reveals the most extensive glacial advance of the last glacial cycle occurred at ∼ 75 ka, at the end of Marine Isotope Stage 5. A second, less-extensive advance occurred at ∼ 25 ka during the global Last Glacial Maximum. The topographic setting is such that ice growth would have initiated on and around the San Lorenzo massif at the start of the glacial cycle. We suggest reduced southern hemisphere summer insolation at the time played a significant role in driving this early advance. The comparatively smaller glacier extent during the global Last Glacial Maximum is likely a consequence of the build-up of the full Patagonian Ice Sheet, which would have caused ice-divide migration, ice-flow re-routing, and increased aridity on its lee side. Image 1 • We present a new 10Be chronology from the Lago Belgrano valley on the eastern side of Monte San Lorenzo, central Patagonia. • The maximum advance of the last glacial cycle culminated at the end of Marine Isotope Stage 5. • The San Lorenzo likely supported an independent ice cap early in the last glacial cycle. • Last glaciation of the Patagonian Andes was likely triggered by reduced southern hemisphere summer insolation. • Build-up of the Patagonian Ice Sheet caused ice-divide shift and snow starvation over San Lorenzo during the global LGM. [ABSTRACT FROM AUTHOR]

Raised shorelines and associated lacustrine sediments in the central Estrecho de Magallanes (Strait of Magellan) have been interpreted as products of cordilleran glaciers impounding a large proglacial lake and preventing drainage to the South Pacific and Southern Ocean during the Late glacial between c. 15.0 and 12.0 cal ka BP. However, a growing body of glacial geological evidence points towards an earlier retreat of the Magellan cordilleran ice dome, insufficient to dam lakes at that time. We critically re-evaluate the extant evidence for the c. 15.0–12.0 cal ka BP lake, here named 'Lago Kawésqar', and provide further sedimentological and chronological evidence for its existence. We also provide new cosmogenic surface nuclide dating of erratic and bedrock samples collected from extensive field campaigns that confirm the rapid and widespread retreat of the Magellan ice fields to the inner fjords of the Fuegian archipelago by c. 16.0 ka. To resolve the apparent paradox between these two lines of evidence we propose that glacial isostatic adjustment led to a topographic barrier to lake drainage rather than an ice dam. We use Glacial Isostatic Adjustment modelling to demonstrate that rapid isostatic recovery following the early deglaciation after c. 17.0 cal ka BP likely led to elevation of the present shallow south-western coastal margin of the Fuegian archipelago. Final drainage of Lago Kawésqar was probably caused by neotectonic subsidence of the same margin along the boundary of the South American – Scotia tectonic plates at c. 12.0 cal ka BP. • Evidence for a large Late glacial lake in the Strait of Magellan is confirmed. • New ages for deglaciation of the Magellan ice dome after the LGM are presented. • An alternative theory for the damming of the Late glacial Magellan lake is discussed. • Glacial isostatic adjustment modelling supports bedrock uplift damming the lake. • A neotectonic event likely led to final drainage of the Magellan lake. [ABSTRACT FROM AUTHOR]

Sub-Antarctic glacier chronologies can provide valuable information about the past variability of climate dynamics in the Southern Ocean region. The Kerguelen Archipelago (49°S) is advantageously located under the influence of the Southern Hemisphere's westerly wind belt, thus fluctuations of climate-sensitive glaciers on Kerguelen can provide a baseline for understanding the behavior of this atmospheric regime in response to climatic forcings. We present 17 36Cl exposure ages of moraine and erratic boulders to provide chronological constraints to paleoglacier extents of the Guynemer cirque glacier, located just north of the Cook Ice Cap. Erratic boulders show ice thinning in the Guynemer region started to occur in the Late Glacial by 13.5 ka and continued past 12.4 ka. Ice retreat was punctuated by the formation of two moraine stages, the outermost at 11.5 ± 0.4 ka followed by another at 10.4 ± 1.2 ka, which are indicative of Early Holocene glacier advances/standstills. A glacial advance occurred at 1.4 ± 0.3 ka, which corroborates other Late Holocene re-advances elsewhere on the archipelago. Finally, three undated moraine stages are found between 1.4 ka and the 1960s. The lack of moraines after 10.4 ka and through the Mid-Holocene suggests that the Guynemer glacier was significantly smaller during this extended period of the Holocene compared to its Early Holocene as well as its Late Holocene limits. The Guynemer glacier history provides unique evidence of Early Holocene moraines on Kerguelen, which have not been discovered thus far on the archipelago. Similar to glaciers in Patagonia, New Zealand and South Georgia, the Guynemer glacier was at its largest Holocene extent in the Early Holocene. However, while other southern mid-latitude glacier chronologies show progressively smaller glacial extents throughout the Mid- to Late Holocene, the Late Holocene re-advance of the Guynemer glacier, like other Kerguelen glaciers, likely exceeded its Mid-Holocene extent. • We present 17 new 36Cl surface exposure ages from the Kerguelen Archipelago. • 36Cl ages range from 13.5 ± 0.3 ka to 1.2 ± 0.2 ka. • First early Holocene-dated moraines on Kerguelen. • Glacial readvance occurred in late Holocene. • Holocene glacial evolution on Kerguelen differs from other sub-Antarctic glaciers. [ABSTRACT FROM AUTHOR]

The Weddell Sea sector is one of the main formation sites for Antarctic Bottom Water and an outlet for about one fifth of Antarctica's continental ice volume. Over the last few decades, studies on glacial–geological records in this sector have provided conflicting reconstructions of changes in ice-sheet extent and ice-sheet thickness since the Last Glacial Maximum (LGM at ca 23–19 calibrated kiloyears before present, cal ka BP). Terrestrial geomorphological records and exposure ages obtained from rocks in the hinterland of the Weddell Sea, ice-sheet thickness constraints from ice cores and some radiocarbon dates on offshore sediments were interpreted to indicate no significant ice thickening and locally restricted grounding-line advance at the LGM. Other marine geological and geophysical studies concluded that subglacial bedforms mapped on the Weddell Sea continental shelf, subglacial deposits and sediments over-compacted by overriding ice recovered in cores, and the few available radiocarbon ages from marine sediments are consistent with major ice-sheet advance at the LGM. Reflecting the geological interpretations, different ice-sheet models have reconstructed conflicting LGM ice-sheet configurations for the Weddell Sea sector. Consequently, the estimated contributions of ice-sheet build-up in the Weddell Sea sector to the LGM sea-level low-stand of ∼130 m vary considerably. In this paper, we summarise and review the geological records of past ice-sheet margins and past ice-sheet elevations in the Weddell Sea sector. We compile marine and terrestrial chronological data constraining former ice-sheet size, thereby highlighting different levels of certainty, and present two alternative scenarios of the LGM ice-sheet configuration, including time-slice reconstructions for post-LGM grounding-line retreat. Moreover, we discuss consistencies and possible reasons for inconsistencies between the various reconstructions and propose objectives for future research. The aim of our study is to provide two alternative interpretations of glacial–geological datasets on Antarctic Ice-Sheet History for the Weddell Sea sector, which can be utilised to test and improve numerical ice-sheet models. [ABSTRACT FROM AUTHOR]