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

Current consensus places a Southern Hemisphere post-glacial cooling episode earlier than the Younger Dryas in the Northern Hemisphere. New Zealand sequences of glacial moraines and speleothem isotopic data are generally interpreted as supporting the absence of a Southern Hemisphere Younger Dryas. Radiocarbon age series of habitat specialist moa (Aves: Dinornithiformes) show, however, that a sudden return to glacial climate in central New Zealand contemporary with the Younger Dryas. The cooling followed significant warming, not cooling, during the period of the Antarctic Cold Reversal. In addition, the moa sequence chronology also shows that the Oruanui (New Zealand) and Mt Takahe (Antarctica) volcanic eruptions were contemporary with abrupt cooling events in New Zealand. The independent high spatial and temporal resolution climate chronology reported here is contrary to an inter-hemispheric post-glacial climate see-saw model.

Inter-hemispheric asynchrony of climate change through the last deglaciation has been theoretically linked to latitudinal shifts in the southern westerlies via their influence over CO2 out-gassing from the Southern Ocean. Proxy-based reconstructions disagree on the behaviour of the westerlies through this interval. The last deglaciation was interrupted in the Southern Hemisphere by the Antarctic Cold Reversal (ACR; 14.7 to 13.0 ka BP (thousand years Before Present)), a millennial-scale cooling event that coincided with the Bolling–Allerod warm phase in the North Atlantic (BA; 14.7 to 12.7 ka BP). We present terrestrial proxy palaeoclimate data that demonstrate a migration of the westerlies during the last deglaciation. We support the hypothesis that wind-driven out-gassing of old CO2 from the Southern Ocean drove the deglacial rise in atmospheric CO2.

International audience; L’archipel des Kerguelen constitue un observatoire unique pour l’étude des paléoglaciers. Il s’agit, en effet, de la plus grande surface de terres englacées de la zone subantarctique de l’océan Indien, où de nombreuses formations glacio-géomorphologiques peuvent y être datées. Toutefois, nos connaissances des fluctuations glaciaires sur l’archipel pendant le Tardiglaciaire et l’Holocène restent limitées. C’est pourquoi des échantillons issus de ces morphologies glaciaires ont été collectés dans les vallées glaciaires du glacier Arago, du Val Travers et du glacier Ampère. Les nouveaux âges 36Cl et 10Be de durée d’exposition au rayonnement cosmique présentés dans cette étude permettent de mieux contraindre la chronologie glaciaire existante au cours des derniers 17000 ans. Une avancée glaciaire a pu être mise en évidence durant le Tardiglaciaire il y a 14.4 ka sur le site du Val Travers, probablement liée à l’événement froid de l’Antarctic Cold Reversal. Ces résultats sont cohérents avec ceux précédemment obtenus sur l’archipel et plus généralement dans la zone subantarctique, suggérant que tous les glaciers à cette latitude ont été globalement sensibles à ce signal climatique. L’évolution des glaciers à Kerguelen pendant l’Holocène reste en revanche encore largement méconnue. Des datations radiocarbone d’éléments tourbeux sur le site du glacier Ampère suggèrent que les glaciers étaient certainement moins étendus au début de l’Holocène qu’à la fin de l’Holocène. En outre, aucune avancée du début et du milieu de l’Holocène n’a pu être démontrée jusqu’à présent. Enfin, les glaciers semblent avoir réavancé uniquement lors de la fin de l’Holocène. La comparaison de ce nouveau jeu de données avec des âges 10Be disponibles provenant d’autres régions subantarctiques a permis d’identifier 3 différents schémas possibles d’évolution des glaciers pendant l’Holocène. Parmi ces schémas, l’oscillation des glaciers observée à Kerguelen semble particulièrement originale. Nous discuterons enfin des facteurs climatiques pouvant rendre compte de l’évolution des glaciers à Kerguelen (température, précipitations).

Funding was provided by an Antarctic Bursary awarded to J.A.S., ERC and NERC grants awarded to L.F.R. (278705, NE/S001743/1, NE/R005117/1) and L.F.R. and J.W.B.R. (NE/N003861/1). The Antarctic Cold Reversal (ACR; 14.7 to 13 thousand years ago; ka) phase of the last deglaciation saw a pause in the rise of atmospheric CO2 and Antarctic temperature, that contrasted with warming in the North. A re-expansion of sea ice and a northward shift in the position of the westerly winds in the Southern Ocean are well-documented, but the response of deep-sea biota and the primary drivers of habitat viability remain unclear. Here we present a new perspective on ecological changes in the deglacial Southern Ocean, including multi-faunal benthic assemblage (foraminifera and cold-water corals) and coral geochemical data (Ba/Ca and δ11B) from the Drake Passage. Our records show that, during the ACR, peak abundances of thick-walled benthic foraminifera Uvigerina bifurcata and corals are observed at shallow depths in the sub-Antarctic (∼300 m), while coral populations at greater depths and further south diminished. Our ecological and geochemical data indicate that habitat shifts were dictated by (i) a northward migration of food supply (primary production) into the Subantarctic Zone and (ii) poorly oxygenated seawater at depth during this Antarctic cooling interval. Publisher PDF

Millennial‐scale climate anomalies punctuating the last deglaciation were expressed differently in the Northern and Southern Hemispheres. While changes in oceanic meridional overturning circulation have been invoked to explain these disparities, the nearly synchronous onset of such events requires atmospheric mediation. Yet the extent and structure of atmospheric reorganization on millennial timescales remains unclear. In particular, the role of the Southern Hemisphere westerly winds (SHWW) and associated storm tracks is poorly constrained, largely due to the paucity of accessible archives of wind behavior. Here we present a new paleohydrologic record from a Lake Hayes, New Zealand (45° S) sediment core from ~17‐9 ka. Using two independent proxies for lake hydrology (Ca/Ti in sediments and δD values of aquatic plant biomarkers), we find evidence for a wetter Antarctic Cold Reversal (ACR, 14.7‐13.0 ka) and a drying trend during the Younger Dryas (YD, 12.9‐11.6 ka) and early Holocene (11.7 ka onward in this record). Comparisons of the Lake Hayes record with other Southern Hemisphere sites indicate coherent atmospheric shifts during the ACR and YD, whereby the former is wetter/cooler and the latter is drier/warmer. The wet/cool phase is associated with a northward shift and/or strengthening of the SHWW, whereas the drier/warmer phase indicates weaker mid‐latitude winds. These climatic trends are opposite to the Northern Hemisphere. There is a decoupling of climatic trends between Southern Hemisphere low‐ and mid‐latitude climates in the early Holocene, which could be explained by several mechanisms, such as the retreat of Antarctic sea ice.

The geomorphological record in glaciated landscapes can provide important information for the study of the response of glaciers to rapid climate change. This study presents a new reconstruction of the glacial history of the northern Monte San Lorenzo ice cap, southern South America, during a period of accelerated warming and deglaciation following the Antarctic Cold Reversal (14.5–12.8 ka). We present a detailed geomorphological map of the valleys to the north of Monte San Lorenzo. Sediment-landform assemblages identified include lateral and terminal moraine ridges, flutes, deltas, ice-contact fans, palaeoshorelines, kame terraces and outwash plains. We map 14 primary ice-limits, 7 of which are newly identified, and 7 of which are from previous studies, mapped here in greater detail. We devise landsystem models to formalise and document spatial and temporal changes in glacial processes and environments. Our new geomorphological mapping and landsystem reconstructions provide an important insight into the response of temperate Patagonian glaciers to rapidly-warming climate.

International audience; The small ice caps distributed across the Antarctic Peninsula region have undergone large ice volume changes since the Last Glacial Cycle, in line with most of the Antarctic continent. While the surface extent of glacial shrinking is relatively well known, the timing of glacial oscillations and the magnitude of ice thinning remain little investigated. Cosmic-Ray Exposure (CRE) dating applied on ice-free vertical sequences can provide insights about the temporal framework of glacial oscillations. However, the potential occurrence of nuclide inheritance may overestimate the real timing of the last glacial retreat. This problem has been observed in many areas in Continental Antarctica, but similar studies have not yet been conducted in environments of the Maritime Antarctica, such as the South Shetland Islands (SSI). This research focuses on the Hurd Peninsula ice cap (HPIC, ca. 60 degrees 22' W, 62 degrees 40' S), located in the SW of Livingston Island, SSI. Past climate oscillations since the Last Glacial Cycle have determined the amount of ice stored in the ice cap. Today, this polythermal ice cap is surrounded by several nunataks standing out above the ice. Three of them have been selected to explore their deglaciation history and to test the potential occurrence of nuclide inheritance in deglaciated bedrocks associated with polythermal glaciers. We present a new dataset with 10 Be-10 exposure dates. Some of them were found to be anomalously old, evidencing that nuclide inheritance is present in bedrocks associated with polythermal ice caps and suggesting complex glacial exposure histories. We attribute this to limited erosion, given the gentle slope of the nunatak margins and the cold-based character of the surrounding ice. The remaining samples allowed to approach local surface-elevation changes of the HPIC. Our results suggest that ice thinning started during the Last Glacial Maximum (LGM) at similar to 22 ka but intense glacial shrinking occurred from similar to 18 to similar to 13 ka, when the nunataks became exposed, being particularly intense at the end of this period (similar to 14-13 ka) coinciding with the time of the meltwater pulse 1a (MWP-1a) and the end of the Antarctic Cold Reversal (ACR).

The accelerated melting of ice on the Antarctic Peninsula and islands in the sub-Antarctic suggests that the cryosphere is edging towards an irreversible tipping point. How unusual is this trend of ice loss within the frame of natural variability, and to what extent can it be explained by underlying climate dynamics? Here, we present new high-resolution reconstructions of long-term changes in the extents of three glaciers on the island of South Georgia (54°S, 36°W), combining detailed analyses of glacial-derived sediments deposited in distal glacier-fed lakes and cosmogenic exposure dating of moraines. We document that the glaciers of South Georgia have gradually retracted since the Antarctic cold reversal (ACR, 14.5–12.8 ka), culminating in the disappearance of at least one of the reconstructed glaciers. The glacier retreat pattern observed in South Georgia suggests a persistent link to summer insolation at 55°S, which intensified during the period from the ACR to approximately 2 ka. It also reveals multi-decadal to centennial climate shifts superimposed on this long-term trend that have resulted in at least nine glacier readvances during the last 10.5 ka. Accompanying meridional changes in the Southern Hemisphere westerlies and their interconnection with local topography may explain these glacier readvances.

The dynamics of the Late Glacial have been demonstrated by numerous records from the Northern Hemisphere and far fewer from the Southern Hemisphere (SH). SH paleoclimate records reveal a general warming trend, interrupted by a deglaciation pause Antarctic Cold Reversal (ACR; similar to 14,700-13,000 cal BP). Here, we present decadal tree-ring stable isotope chronologies (delta O-18, delta C-13) from New Zealand (NZ) subfossil kauri trees (n = 6) covering the post-ACR millennium from 13,020 to 11,850 cal BP. We find a distinct, simultaneous downturn (similar to 12,625-12,375 cal BP) in all tree-ring proxies paralleling regional tree growth declines, suggesting a widespread climate deterioration. This downturn was characterized by sustained high precipitation, low temperatures, and high relative humidity in NZ with incoming weather fronts from the South Ocean. Despite these promising results, questions remain about what drove the Kauri Downturn and how the hydroclimatic conditions were altered during this time period.

ASTER Team: Georges Aumaître, Didier L. Bourlès and Karim Keddadouche; International audience; Debris-covered glaciers constitute a large part of the world's cryosphere. However, little is known about their long-term response to multi-millennial climate variability, in particular in the Southern Hemisphere. Here, we provide first insights into the response of a debris-covered glacier to multi-millennial climate variability in the sub-Antarctic Kerguelen Archipelago, which can be compared to that of recently investigated debris-free glaciers. We focus on the Gentil Glacier and present thirteen new 36 Cl cosmic-ray exposure ages from moraine boulders. The Gentil Glacier experienced at least two glacial advancesthe first one during the Late Glacial (19.0-11.6 ka) at ~14.3 ka and the second one during the Late Holocene at ~2.6 ka. Both debris-covered and debris-free glaciers advanced broadly synchronously during the Late Glacial, most probably during the Antarctic Cold Reversal event (14.5-12.9 ka). This suggests that both glacier types at Kerguelen were sensitive to abrupt temperature changes recorded in Antarctic ice cores, associated with increased moisture. However, during the late Holocene, the advance at about ~2.6 ka was not observed in other glaciers and seems to be an original feature of the debris-covered Gentil Glacier, either related to distinct dynamics or distinct sensitivity to precipitation changes.

International audience; The respective impacts of Northern and Southern Hemispheric climatic changes on the Tropics during the last deglaciation remain poorly understood. In the High Tropical Andes, the Antarctic Cold Reversal (ACR, 14.3-12.9 ka BP) is better represented among morainic records than the Younger Dryas (12.9-11.7 ka BP). However, in the Altiplano basin (Bolivia), two cold periods of the Northern Hemisphere (Heinrich Stadial 1a, 16.5-14.5 ka BP, and the Younger Dryas) are synchronous with (i) major advances or standstills of paleoglaciers and (ii) the highstands of giant paleolakes Tauca and Coipasa. Here, we present new cosmic ray exposure (CRE) ages from glacial landforms of the Bolivian Andes that formed during the last deglaciation (Termination 1). We reconstruct the equilibrium line altitudes (ELA) associated with each moraine and use them in an inverse algorithm combining paleoglaciers and paleolake budgets to derive temperature and precipitation during the last deglaciation. Our temperature reconstruction (ΔT relative to present day) yields a consistent regional trend of progressive warming from ΔT = −5 to −2.5°C during 17-14.5 ka BP, followed by a return to colder conditions around −4°C during the ACR (14.5-12.9 ka BP). The Coipasa highstand (12.9-11.8 ka BP) is coeval with another warming trend followed by ΔT stabilization at the onset of the Holocene (ca. 10 ka BP), around −3°C. Our results suggest that, during the last deglaciation (20-10 ka BP) atmospheric temperatures in the Tropical Andes mimicked Antarctic variability, whereas precipitation over the Altiplano was driven by changes in the Northern Hemisphere.

The Southern Ocean occupies 14% of the Earth’s surface and plays a fundamental role in the global carbon cycle and climate. It provides a direct connection to the deep ocean carbon reservoir through biogeochemical processes that include surface primary productivity, remineralization at depth and the upwelling of carbon-rich water masses. However, the role of these different processes in modulating past and future air–sea carbon flux remains poorly understood. A key period in this regard is the Antarctic Cold Reversal (ACR, 14.6–12.7 kyr bp), when mid- to high-latitude Southern Hemisphere cooling coincided with a sustained plateau in the global deglacial increase in atmospheric CO2. Here we reconstruct high-latitude Southern Ocean surface productivity from marine-derived aerosols captured in a highly resolved horizontal ice core. Our multiproxy reconstruction reveals a sustained signal of enhanced marine productivity across the ACR. Transient climate modelling indicates this period coincided with maximum seasonal variability in sea-ice extent, implying that sea-ice biological feedbacks enhanced CO2 sequestration and created a substantial regional marine carbon sink, which contributed to the plateau in CO2 during the ACR. Our results highlight the role Antarctic sea ice plays in controlling global CO2, and demonstrate the need to incorporate such feedbacks into climate–carbon models.

Financial support to DJW, TS, and TvdF was provided by the Natural Environment Research Council (NE/N001141/1), the Leverhulme Trust (RPG-398), the Grantham Institute for Climate Change and the Environment, and a Marie Curie Reintegration grant (IRG 230828). LFR acknowledges support from the Natural Environment Research Council (NE/N003861/1) and the European Research Council (278705). The sequence of deep ocean circulation changes between the Last Glacial Maximum and the Holocene provides important insights for understanding deglacial climate change and the role of the deep ocean in the global carbon cycle. Although it is known that significant amounts of carbon were sequestered in a deep overturning cell during glacial periods and released during deglaciation, the driving mechanisms for these changes remain unresolved. Southern Ocean sea-ice has recently been proposed to play a critical role in setting the global deep ocean stratification and circulation, and hence carbon storage, but testing such conceptual and modelling studies requires data constraining past circulation changes. To this end, we present the first deglacial dataset of neodymium (Nd) isotopes measured on absolute-dated deep-sea corals from modern Lower Circumpolar Deep Water depths in the Drake Passage. Our record demonstrates deglacial variability of 2.5 εNd units, with radiogenic values of up to during the Last Glacial Maximum providing evidence for a stratified glacial circulation mode with restricted incorporation of Nd from North Atlantic Deep Water in the lower cell. During the deglaciation, a renewed Atlantic influence in the deep Southern Ocean is recorded early in Heinrich Stadial 1, coincident with Antarctic sea-ice retreat, and is followed by a brief return to more Pacific-like values during the Antarctic Cold Reversal. These changes demonstrate a strong influence of Southern Ocean processes in setting deep ocean circulation and support the proposed sea-ice control on deep ocean structure. Furthermore, by constraining the Nd isotopic composition of Lower Circumpolar Deep Water in the Southern Ocean, our new data are important for interpreting deglacial circulation changes in other ocean basins and support a spatially asynchronous return of North Atlantic Deep Water to the deep southeast and southwest Atlantic Ocean. Postprint Postprint

We present PATICE, a GIS database of Patagonian glacial geomorphology and recalibrated chronological data. PATICE includes 58,823 landforms and 1,669 geochronological ages, and extends from 38°S to 55°S in southern South America. We use these data to generate new empirical reconstructions of the Patagonian Ice Sheet (PIS) and subsequent ice masses and ice-dammed palaeolakes at 35 ka, 30 ka, 25 ka, 20 ka, 15 ka, 13 ka (synchronous with the Antarctic Cold Reversal), 10 ka, 5 ka, 0.2 ka and 2011 AD. At 35 ka, the PIS covered of 492.6 x103 km2, had a sea level equivalent of ~1,496 mm, was 350 km wide and 2090 km long, and was grounded on the Pacific continental shelf edge. Outlet glacier lobes remained topographically confined and the largest generated the suites of subglacial streamlined bedforms characteristic of ice streams. The PIS reached its maximum extent by 33 – 28 ka from 38°S to 48°S, and earlier, around 47 ka from 48°S southwards. Net retreat from maximum positions began by 25 ka, with ice-marginal stabilisation then at 21 – 18 ka, which was then followed by rapid, irreversible deglaciation. By 15 ka, the PIS had separated into disparate ice masses, draining into large ice-dammed lakes along the eastern margin, which strongly influenced rates of recession. Glacial readvances or stabilisations occurred at least at 14 – 13 ka, 11 ka, 6 – 5 ka, 2 – 1 ka, and 0.5 – 0.2 ka. We suggest that 20th century glacial recession (% a-1) is occurring faster than at any time documented during the Holocene.

Constraining Antarctica's climate evolution since the end of the Last Glacial Maximum (∼18 ka) remains a key challenge, but is important for accurately projecting future changes in Antarctic ice sheet mass balance. Here we perform a spatial and temporal analysis of two transient deglacial climate simulations, one using a fully coupled GCM (TraCE-21ka) and one using an intermediate complexity model (LOVECLIM DGns), to determine regional differences in deglacial climate evolution and identify the main strengths and limitations of the models in terms of climate variables that impact ice sheet mass balance. The greatest continental surface warming is observed over the continental margins in both models, with strong correlations between surface albedo, sea ice coverage, and surface air temperature along the coasts, as well as regions with the greatest decrease in ice surface elevation in TraCE-21ka. Accumulation–temperature scaling relationships are fairly linear and constant in the continental interior, but exhibit higher variability in the early to mid-Holocene over coastal regions. Circum-Antarctic coastal ocean temperatures at grounding line depths are highly sensitive to the meltwater forcings prescribed in each simulation, which are applied in different ways due to limited paleo-constraints. Meltwater forcing associated with the Meltwater Pulse 1A (MWP1A) event results in subsurface warming that is most pronounced in the Amundsen and Bellingshausen Sea sector in both models. Although modelled centennial-scale rates of temperature and accumulation change are reasonable, clear model–proxy mismatches are observed with regard to the timing and duration of the Antarctic Cold Reversal (ACR) and Younger Dryas–early Holocene warming, which may suggest model bias in large-scale ocean circulation, biases in temperature reconstructions from proxy records, or that the MWP1A and 1B events are inadequately represented in these simulations. The incorporation of dynamic ice sheet models in future transient climate simulations could aid in improving meltwater forcing representation, and thus model–proxy agreement, through this time interval.

This paper reviews current understanding of deglaciation in North, Central and South America from the Last Glacial Maximum to the beginning of the Holocene. Together with paleoclimatic and paleoceanographic data, we compare and contrast the pace of deglaciation and the response of glaciers to major climate events. During the Global Last Glacial Maximum (GLGM, 26.5-19 ka), average temperatures decreased 4° to 8°C in the Americas, but precipitation varied strongly throughout this large region. Many glaciers in North and Central America achieved their maximum extent during the GLGM, whereas others advanced even farther during the subsequent Heinrich Stadial 1 (HS-1). Glaciers in the Andes also expanded during the GLGM, but that advance was not the largest, except on Tierra del Fuego. HS-1 (17.5-14.6 ka) was a time of general glacier thickening and advance throughout most of North and Central America, and in the tropical Andes; however, glaciers in the temperate and subpolar Andes thinned and retreated during this period. During the Bølling-Allerød interstadial (B-A, 14.6-12.9 ka), glaciers retreated throughout North and Central America and, in some cases, completely disappeared. Many glaciers advanced during the Antarctic Cold Reversal (ACR, 14.6-12.9 ka) in the tropical Andes and Patagonia. There were small advances of glaciers in North America, Central America and in northern South America (Venezuela) during the Younger Dryas (12.9-11.7 ka), but glaciers in central and southern South America retreated during this period, except on the Altiplano where advances were driven by an increase in precipitation. Taken together, we suggest that there was a climate compensation effect, or ‘seesaw’, between the hemispheres, which affected not only marine currents and atmospheric circulation, but also the behavior of glaciers. This seesaw is consistent with the opposing behavior of many glaciers in the Northern and Southern Hemispheres.

We present 14 new 10Be cosmogenic nuclide exposure ages quantifying asynchronous readvances during the Antarctic Cold Reversal from glaciers in the Baker Valley region of central Patagonia. We constrain glacier and ice-dammed palaeolake dynamics using a landsystems approach, concentrating on outlet glaciers from the eastern Northern Patagonian Icefield (NPI) and Monte San Lorenzo (MSL). Soler Glacier (NPI) produced lateral moraines above Lago Bertrand from 15.1 ± 0.7 to 14.0 ± 0.6 ka, when it dammed the drainage of Lago General Carrera/Buenos Aires through Rio Baker at a bedrock pinning point. At this time, Soler Glacier terminated into the 400 m “Deseado” level of the ice-dammed palaeolake. Later, Calluqueo Glacier (MSL) deposited subaerial and subaqueous moraines in the Salto Valley near Cochrane at 13.0 ± 0.6 ka. These moraines were deposited in an ice-dammed palaeolake unified through the Baker Valley (Lago Chalenko; 350 m asl). The Salto Valley glaciolacustrine landsystem includes subaqueous morainal banks, ice-scoured bedrock, glacial diamicton plastered onto valley sides, perched delta terraces, kame terraces, ice-contact fans, palaeoshorelines and subaerial push and lateral moraines. Boulders from the subaqueous Salto Moraine became exposed at 12.1 ± 0.6 years, indicating palaeolake drainage. These data show an asynchronous advance of outlet glaciers from the Northern Patagonian Icefield and Monte San Lorenzo during the Antarctic Cold Reversal. These advances occurred during a period of regional climatic cooling, but differential moraine extent and timing of advance was controlled by topography and calving processes.

A new Late glacial-Holocene palaeoenvironmental record from near Lago Lynch (53°54′S, 69°26′W), Tierra del Fuego is presented. The record was sampled from a mire located within the deciduous Nothofagus forest-steppe ecotone and pollen and spore analysis suggest a high degree of vulnerability of past vegetation to changes in effective moisture. AMS radiocarbon dating supplemented by the application of tephrochronology including the geochemical fingerprinting of six visible and cryptotephra layers provides robust age constraint. The Lago Lynch record commences at c.15.6 ka. The sequence of vegetation changes between c.15.6 and 14.4 ka reflect a gradual increase in temperature and humidity followed by a colder interval between c.14.4 and 13.3 ka, which is broadly coeval with the Antarctic Cold Reversal. After c.13.3 ka patches of Nothofagus forest appeared, suggesting more mesic-temperate conditions leading gradually to the establishment of an open-canopy Nothofagus forest by c.12.5 ka which marks the start of the Holocene. Moderate to strong effective moisture levels dominated during the early Holocene until c.11.0 ka, followed by a sustained period (c.11.0–6.5 ka) of drier climatic conditions, particularly two arid phases at c.10.5–10.0 ka and 8.5–6.5 ka. An eastwards expansion of the forest margin after c.6.5 ka at the site suggests a return to more humid conditions during the late Holocene. We argue that the periods of increased moisture and aridity inferred from Lago Lynch closely reflect the extent to which the southern westerly winds (SWWs) push eastwards to the drier regions of Fuego-Patagonia during the Holocene. The longitudinal variations in moisture are driven by the nature and timing of latitudinal shifts in the SWWs. More significantly the vulnerability of the forest-steppe ecotone to moisture changes amplifies the ecological impact of relatively small-scale shifts in the SWWs.

We present a high-resolution precisely dated terrestrial paleovegetation/paleoclimate record from Lago Pichilaguna, northwestern Patagonia (40°–44°S), which spans continuously from the Last Glacial Maximum (LGM) to the present. We find abundant and continuous presence of arboreal pollen (chiefly Nothofagus) during the LGM, accompanied by other trees, shrubs, and alpine herbs. These results suggest Subantarctic parkland and/or scattered woodlands under a cold and hyperhumid climate during the LGM (∼25,000–17,800 cal. yr BP) with expansion of Nothofagus under relatively warm interstadial conditions between 25,000 and 19,200 cal. yr BP. This was followed by cooling and a precipitation increase between 19,200 and 17,800 cal. yr BP, which was contemporaneous with the youngest LGM advance of Andean glaciers in the region and maximum influence of the Southern Westerly Wind (SWW). The Last Glacial Termination (T1) started at 17,800 cal. yr BP and featured the spread of thermophilous trees and ferns characteristic of North Patagonian rainforests, along with lake level lowering. These results suggest a warm pulse and southward shift of the SWW, concurrent with a rapid collapse of Andean glacier lobes. Subsequent changes led to the establishment of closed-canopy rainforests under peak interstadial warmth between ∼16,000 and 15,000 cal. yr BP. We detect a shift to cold/wet conditions during the Antarctic Cold Reversal (14,800–12,700 cal. yr BP) and a precipitation decline during Younger Dryas time, followed by maximum temperature, relatively lower lake level and minimum SWW influence between 11,300 and 7700 cal. yr BP. Precipitation then rose punctuated by centennial-scale variations since 6200 cal. yr BP. Chilean-European deforestation and spread of invasive exotic species started at ∼350 cal. yr BP aided by fire. We conclude that temperate rainforests have persisted with little interruption since T1, with major changes in floristic composition driven by climate change and fires. Rainforest composition and heterogeneity declined in response to Chilean/European disturbance during the 1600s and intensified since the 1800s. These events constitute the fastest/largest-magnitude vegetation changes of the last ∼25,000 years.

We studied the pollen content of a well-preserved coprolite of a Late-Glacial giant ground sloth (Mylodon darwinii) from the Mylodon Cave, province Última Esperanza, southern Chile. The specimen was obtained in 1909 and has been stored in a museum in the Netherlands since. It was radiocarbon dated to 13,140 ± 55 BP (15,927–15,522 cal BP), which fits with other radiocarbon dates showing the early Late-Glacial presence of M. darwinii in the province Última Esperanza. Contemporaneous oxygen isotope data from Antarctic EPICA Dome C indicates that our Mylodon specimen lived during a warming phase of the Late-Glacial, ca. 1000 years before the start of the Antarctic Cold Reversal. We compared our pollen data with pollen records showing contemporaneous regional vegetation and discuss the uncertainties in the interpretation of pollen spectra from faeces. To expand on the pollen data, we tested ancient DNA preservation in the sample; we sequenced ~ 9.4 million DNA reads and found that the concentration of ancient plant DNA is below detectable levels. Pollen analysis confirms earlier findings that the Mylodon was a grazer, but the discovery of large amounts of Fragaria and Azorella pollen in the faeces may indicate that Mylodon was also able to select and consume specific plants, and therefore could also be regarded as a selective feeder.

In this study, we examine glacier retreat and associated processes in the Lejiamayu valley, central Cordillera Blanca, Peru (9.27°S; 77.48°W) since the Last Glacial Maximum (LGM). Based on detailed mapping of well-preserved moraines, we reconstruct glacier extent during the LGM, the Antarctic Cold Reversal (ACR) and the Little Ice Age (LIA), being 21.34 km2 (LGM), 13.68 km2 (ACR) and 6.84 km2 (LIA). We document that glacier extent decreased to 2,86 km2 since the end of the LIA in this catchment (ice loss 58%). In addition, we explore the colonization and growth of lichens and Schmidt-hammer rock test R-values over the deglaciated surfaces, suggesting a relationship to possible evironmental controls rather than to the timing of the exposure. Further, we use empirical glacier velocity-based equation to estimate maximum potential future volume of the new glacial lake forming in the upper part of the valley (4725 m a.s.l.; 2.2 Mm3). We conclude that previous estimates of future lake volume might have been underestimated and that the sufficiency of the glacial lake outburst flood (GLOF) mitigation measures implemented at downstream located Lake Lejiacocha (4628 m a.s.l.) should be revised in future.

The tropical Andes of Peru and Bolivia are important for preserving geomorphic evidence of multiple glaciations, allowing for refinements of chronology to aid in understanding climate dynamics at a key location between hemispheres. This review focuses on the deglaciation from Late-Pleistocene maximum positions near the global Last Glacial Maximum (LGM). We synthesize the results of the most recent published glacial geologic studies from 12 mountain ranges or regions within Peru and Bolivia where glacial moraines and drift are dated with terrestrial cosmogenic nuclides (TCN), as well as maximum and minimum limiting ages based on radiocarbon in proximal sediments. Special consideration is given to document paleoglacier valley localities with topographic information given the strong vertical mass balance sensitivity of tropical glaciers. Specific valley localities show variable and heterogeneous sequences ages and extensions of paleoglaciers, but conform to a generally cogent regional sequence revealed by more continuous lake sedimentary records. There are clear distributions of stratigraphically older and younger moraine ages that we group and discuss chronologically. The timing of the local LGM based on average TCN ages of moraine groups is 25.1 ka, but there are large uncertainties (up to 7 ka) making the relative timing with the global LGM elusive. There are a significant number of post-LGM moraines that date to 18.9 (± 0.5) ka. During the Oldest Dryas (18.0 to 14.6 ka), moraine boulders date to 16.1 (± 1.1) ka, suggesting that glaciers either experienced stillstands or readvances during this interval. The Antarctic Cold Reversal (ACR; 14.6 to 12.6 ka) is another phase of stillstanding or readvancing glaciers with moraine groups dating to 13.7 (± 0.8) ka, followed by retreating ice margins through most of the Younger Dryas (YD; 12.9 to 11.8 ka). During the early Holocene, groups of moraines in multiple valleys date to 11.0 (± 0.4) ka, marking a period when glaciers either readvanced or paused from the overall trend of deglaciation. The pattern of glacial variability during the Late Glacial after ~14.6 ka appears to be more synchronous with periods of cooling in the southern high latitudes, and out-of-phase with the overall deglacial trend in the Northern Hemisphere. While insolation and CO2 forcing likely drove the general pattern of deglaciation in the southern tropical Andes, regional ocean-atmospheric and hypsometric controls must have contributed to the full pattern of glacial variability.

This paper reviews published geochronological data on glacier fluctuations and environmental changes in central Patagonia (44° S - 49° S) from the Last Glacial Maximum (LGM) through to the Holocene. Well-dated glacial chronologies from the southern mid-latitudes can inform on the synchronicity of glacial advances worldwide and provide insight on the drivers of southern hemisphere glaciations. In central Patagonia, two large outlet lobes of the former Patagonian Ice Sheet advanced in broad synchrony with the global LGM. In contrast to other parts of Patagonia, there is no convincing evidence for a more extensive local LGM advance during Marine Isotope Stage 3. Deglaciation initiated at ca. 19 ka, earlier than in other parts of Patagonia and regionally in the Southern Hemisphere, and rapid deglaciation saw ice margins retreat in places by at least 80-120 km within a few millennia. The Lateglacial glacier margins are poorly constrained, but an ice mass substantial enough to maintain a large regional proglacial lake must have persisted at this time. The timing of lake drainage and opening of the Río Baker drainage route to the Pacific Ocean is debated; the only directly dated shoreline suggests this occurred at the end of the Antarctic Cold Reversal at 12.7 ka. Palaeoecological evidence for cooling during the Antarctic Cold Reversal or Younger Dryas remains equivocal, which may reflect both the eurythermic nature of Patagonian vegetation and shifting Southern Westerly Winds. Eastern outlet glaciers appear to have advanced or stabilised at the Lateglacial/Holocene transition when palaeoenvironmental records indicate warmer and drier conditions, but the reason for this is unclear. Our review reveals both spatial and temporal gaps in available data that provide avenues for future research.

This work presents a summary of all contributions included in this Special Issue on the deglaciation of America. It analyses the differences and coincidences between the phases of glacial evolution and their chronology in each of the regions studied, and seeks a possible explanation for asynchronies, according to the opinions of the authors of the contributions. Most of the papers show significant diversity within each region due to local factors and different approaches to their study. Often, local differences are even more important than differences with other regions. In North and Central America glacial evolution appears quite uniform, in line with the evolution of the temperature in the North Atlantic. The differences found between some regions may be due to slight variations in the impact of the temperature of the Atlantic in each region, and to differences in approaching their study. The glacial evolution of the Andes presents a greater diversity, probably due to the existence of arid areas along most of the mountain range, which show a greater sensitivity to the reception of humidity than to temperature in their glacial balance. In general, researchers have detected an attenuation of the influence of the temperature of the North Atlantic towards the south, and of the Antarctic Cold Reversal towards the north.

The sensitivity of tropical glaciers to paleoclimatic conditions that prevailed during the Antarctic cold reversal (ACR, ca. 14.5-12.9 ka) has been the subject of a wide debate. In 2014 a paper suggested that tropical glaciers responded very sensitively to the changing climate during the ACR (Jomelli et al., 2014). In this study, we reexamine the conclusions from this study by recalculating previous chronologies based on 226 10Be and 14 3He ages respectively, and using the most up-to date production rates for these cosmogenic nuclides in the Tropical Andes. 53 moraines from 25 glaciers were selected from the previous analysis provided by Jomelli et al. (2014) located in Colombia, Peru and Bolivia. We then focused on two distinct calculations. First we considered the oldest moraine and its uncertainty for every glacier representing the preserved evidence of the maximum glacier extents during the last deglaciation period, and binned the results into 5 distinct periods encompassing the Antarctic cold reversal and Younger Dryas (YD) chronozones: pre-ACR, ACR, ACR-YD, YD and post-YD respectively. Results revealed a predominance of pre-ACR and ACR ages, accounting for 60% of the glaciers. Second we counted the number of moraines per glacier according to the different groups. 21 moraines (40%) of the selected glaciers belong to the pre-ACR-ACR chronozones while 3 moraines only (5%) were dated to the YD and YD-Holocene groups. The rest was assigned to the ACR-YD. These results suggest that moraine records are a very good proxy to document the ACR signal in the Tropical Andes.