Global LGM Research Articles

Equilibrium line altitudes of alpine glaciers in Alaska suggest Last Glacial Maximum summer temperature was 2–5 °C lower than during the pre-industrial

Abstract. The lack of continental ice sheets in Alaska during the Last Glacial Maximum (LGM; 26–19 ka) has long been attributed to extensive aridity in the western Arctic. More recently, climate model outputs, a few isolated paleoclimate studies, and global paleoclimate synthesis products show mild summer temperature depressions in Alaska compared to much of the high northern latitudes. This suggests the importance of limited summer temperature depressions in controlling the relatively limited glacier growth during the LGM. To explore this further, we present a new statewide map of LGM alpine glacier equilibrium line altitudes (ELAs), LGM ΔELAs (LGM ELA anomalies relative to the Little Ice Age, LIA), and ΔELA-based estimates of temperature depressions across Alaska to assess paleoclimate conditions. We reconstructed paleoglacier surfaces in ArcGIS to calculate ELAs using an accumulation area ratio (AAR) of 0.58 and an area–altitude balance ratio (AABR) of 1.56. We calculated LGM ELAs (n= 480) in glaciated massifs in the state, excluding areas in southern Alaska that were covered by the Cordilleran Ice Sheet. The data show a trend of increasing ELAs from the southwest to the northeast during both the LGM and the LIA, indicating a consistent southern Bering Sea and northernmost Pacific Ocean precipitation source. Our LGM–LIA ΔELAs from the Alaska Range, supported with limited LGM–LIA ΔELAs from the Brooks Range and the Kigluaik Mountains, average to −355 ± 176 m. This value is much greater than the global LGM average of ca. −1000 m. Using a range of atmospheric lapse rates, LGM–LIA ΔELAs in Alaska translate to summer cooling of < 2–5 ∘C. Our results are consistent with a growing number of local climate proxy reconstructions and global data assimilation syntheses that indicate mild summer temperature across Beringia during the LGM. Limited LGM summer temperature depressions could be explained by the influence of Northern Hemisphere ice sheets on atmospheric circulation.

Rapid deglaciation of the La Vega gorge (Sierra de Gredos, Iberian Peninsula) at the end of the global Last Glacial Maximum

AbstractPrevious studies from the Iberian Central System and other mountains of the Iberian Peninsula and Europe suggest that deglaciation in this area occurred at the end or immediately after the global Last Glacial Maximum (LGM, 26.5–19 ka). In this research, we investigate the timing and speed of deglaciation of the palaeoglacier in La Vega gorge (Iberian Central system) since the global LGM, dating the outer moraines, glacially polished bedrock and glaciofluvial deposits by means of in situ cosmogenic 10Be and optically stimulated luminescence. The results show that one intermediate arc located at the outer frontal moraine system has an age of ~21 ka, being consistent with the global LGM. Deglaciation began at ~21–19 ka, speeding up at ~19 ka. We estimate that around 4–5 km of the palaeoglacier receded in ~1–2 kyrs since ~19 ka, leaving La Vega gorge probably ice‐free at ~18 ka. Therefore, our data confirm that deglaciation in Sierra de Gredos began at the end of the global LGM, characterised by a rapid and massive retreat of glaciers.

Geomorphological Processes in the Central Kamchatka Depression (the Kamchatka Peninsula, Ne Pacific) During the Last 30 Ka

The paper presents a reconstruction of geomorphological processes in the Central Kamchatka Depression (CKD) since 30 ka, including the global LGM time. Major geomorphological processes of this period included the evolution of volcanic edifices accompanied by steady tectonic submergence. Glaciers that originated from volcanic edifices were greatly affected by both climatic forcing and the eruptive history of their host volcanoes.
 The most prominent geomorphological feature of the studied time was a giant paleolake filled the CKD. The reassessed extent and timing of glaciation and volcanism provided the possible lake fill and discharge model due to the evolution of a piedmont glacier originating from the Old Shiveluch Volcano edifice. The lake discharge likely was gradual and started some 19 ka during the cold settings of LGM, and therefore did not have a climatic origin. The most possible trigger of the discharge is the change in ice supply from the highly active Shiveluch Volcano due to large sector collapses. During the Holocene, the ongoing tectonic submergence of the CKD have been preventing the complete drainage of this paleolake. Even now, an enormously wide floodplain of the Kamchatka River hosts a lacustrine system with a total area of water surface comparable to the largest lakes of the peninsula.

A Modeling Perspective on the Lingering Glacial Sea Surface Temperature Conundrum

AbstractThe strong cooling during the Last Glacial Maximum (LGM, 21 ka BP) provides a rigorous test of climate models' ability to simulate past and future climate changes. We force an atmospheric general circulation model with two recent global LGM sea surface temperature (SST) reconstructions, one suggesting a weak and the other a more pronounced cooling, and compare the simulated land surface temperatures (LSTs) to reconstructed data. Our results do not confirm either SST reconstruction. The cold SST data set leads to good agreement between simulated and observed LSTs at low latitudes, but is systematically too cold at mid‐latitudes. The opposite is true for the warm SST data set. Differences between the simulated LSTs are caused by varying land surface albedos, which is lower for the warmer SST reconstruction. The inconsistency between reconstructed and simulated climate points to a potentially significant bias in the proxy reconstructions and/or the climate sensitivity of current climate models.

Quaternary ice thinning of David Glacier in the Terra Nova Bay region, Antarctica

Understanding the history of Antarctic glaciation is important for interpreting paleoclimatic changes and estimating the changes in climate, sea level, and ice volume in the future. Ice core studies of the East Antarctic Ice Sheet (EAIS) and marine sediment cores from the entire Ross Sea have employed numerous proxies to reconstruct the glacial history of the Antarctic region. However, the ice and marine core records can be biased because of their specific locations, such as the uppermost accumulation zone or the terminus of the ablation zone, thereby introducing significant uncertainties in ice modeling. In this study, we analyzed 34 new 10 Be and 26 Al samples from four benches that were glaciated in the past by David glacier and incorporate the present ice-free flat surfaces. We suggest that the David glacier experienced monotonic and stepwise vertical lowering along the flanks of Mt. Priestley since the early Pleistocene. The uppermost bedrock benches on Mt. Priestley were exposed at 1.77 ± 0.32 Ma, with no evidence of subsequent overriding by readvancing ice. At Mt. Priestley, the David glacier has been characterized by a cold-based regime since 1.77 Ma, with a denudation rate of only ∼16 cm/Ma, corresponding to the regional transition from warm to cold-based glaciation at 3.5 Ma. Simple exposure ages from two lower benches date to Marine Isotope Stage (MIS) 7 (234.1 ± 13.1 ka; 545 m asl) and MIS 4 (64.8 ± 13.7 ka; 222 m asl), suggesting that, since MIS 8, the overall lowering of glaciers has remained monotonic. The upper bench marks the lower limit of the MIS 8 glacial period and the upper limit of Penultimate Glacial Maximum (MIS 6), while the lower landform defines the upper limit of the last glacial period (MIS 4–2). The magnitude of Quaternary ice thinning at the David glacier was the highest (∼990 m) in the present terminal area (i.e., the most sensitive ablation zone), in contrast to the other outlet glaciers draining into the Terra Nova Bay, which experienced less ice lowering. The combination of the terrestrial (in situ 10 Be and 26 Al) and previous marine (authigenic 10 Be) cosmogenic data used in our study document the history of lowering of the David glacier driven by climatic changes during the Pleistocene. Both deglaciation and glaciation were limited during the mid-Pleistocene transition (MPT) and prior to the mid-Bruhnes event (MBE), due to the prevailing cold and arid climate, whereas deglaciation was dominant during other warm periods. • 10 Be & 26 Al, in combination with previous authigenic 10 Beelucidate the glacial history of David glacier during the entire Quaternary period. • Experienced monotonic terrestrial vertical lowering with complex and multiple cycles of horizontal retreat–advance at its marine margin. • The greatest ice lowering along David glacier during the Quaternary (∼990 m) occurred at its present terminal region. • The ice surface elevation of the East Antarctic Ice Sheet was greater during the Pliocene than the Pleistocene. • Ice thickness was greater in MIS 8 than MIS 6 and the Global LGM.

Early glacial maximum and deglaciation at sub-Antarctic Marion Island from cosmogenic 36Cl exposure dating

Southern Hemisphere glacial chronologies can provide valuable insights into interactions between glaciation and past climate changes, but are not well constrained on most sub-Antarctic islands. We present the first cosmogenic 36Cl exposure ages of deglaciated bedrock surfaces and moraine deposits from sub-Antarctic Marion Island in the southern Indian Ocean. Results show that the ice reached a local Last Glacial Maximum before 34 ka and retreated, with no re-advances, but possibly minor stand stills, until ∼17 ka. This early deglaciation left island surfaces below 850 m a.s.l. ice-free after ∼19 ka, and any subsequent advances during the Antarctic Cold Reversal or Holocene cooling periods would have been restricted to the interior. This glacial chronology is similar to that of some other sub-Antarctic Islands (e.g. the Kerguelen archipelago, Auckland and Campbell islands, and possibly South Georgia) and a number of other Southern Hemisphere glaciers (e.g. in Patagonia and New Zealand) and adds to evidence that suggest the Southern Hemisphere was in a glacial maxima earlier than the global LGM. We suggest a combination of declining temperatures, a northward migration of oceanic fronts and the Southern Hemisphere westerly winds (causing precipitation changes), as well as the physiography of Marion Island, created optimal conditions for glacier growth during Marine Isotope Stage (MIS) 3 instead of MIS 2. Our findings redefine the glacial history of Marion Island, and have implications for future investigations on post-glacial landscape development and ecological succession.

Late Quaternary glaciations and cosmogenic 36Cl geochronology of Mount Dedegöl, south‐west Turkey

ABSTRACTWe present details on the timing of glaciations during the late Quaternary in the western Taurus Mountain Range of Turkey. Twenty‐five boulders from prominent moraines in three northern glacial valleys of Mount Dedegöl (37.40°N, 31.17°E, 2992 m above sea level, ∼15 km west of Lake Beyşehir) were dated based on cosmogenic 36Cl surface exposure. The geomorphological mapping of the N‐NE‐trending Sayacak, Kisbe and Karagöl valleys and their in situ produced 36Cl glacial chronology revealed several glacial episodes during the late Quaternary from (pre‐Last Glacial Maximum (pre‐LGM) to early Holocene. Pre‐LGM glaciations are represented by a push‐hummocky moraine complex in the northern Sayacak Valley and dated to 29.7 ± 2.9 ka. The ages obtained from these hummocky moraines give substantial evidence regarding ice accumulation before the global LGM. In the same valley, glaciers reached their maximum positions at the LGM and deposited lateral moraines at 19.7 ± 1.6 ka. Lateglacial moraines were dated to between 16.4 ± 0.7 and 12.0 ± 1.0 ka in the nearby east‐facing Karagöl valley. The youngest glacial stages occurred during the Younger Dryas stadial (11.5 ± 0.8 ka) and early Holocene (9.8 ± 1.4 ka) in Mount Dedegöl.

Constraining the age of superimposed glacial records in mountain environments with multiple dating methods (Cantabrian Mountains, Iberian Peninsula)

Numerous cases of timing differences between glacier advances recorded in mountain environments have been documented over the last decade, usually suggesting potential age conflicts between the different dating techniques. The frequent use of a single technique to date numerically a given glacial sequence makes it difficult to address to what extent age differences can be an artifact related to biased numerical age results or a paleoclimate signature. Here we present a new set of 43 numerical ages based on three dating techniques —10Be surface exposure dating; radiocarbon; and optically stimulated luminescence— that complement the chronology of Pleistocene glacial advances in the Porma valley, in the central Cantabrian Mountains of Spain. Results compliment previous chronologies in the area, supporting an important glacial advance during Marine Isotope Stage 3 (Stage IIa: ∼56 ka) that culminated with the Last Glacial Maximum advance (Stage IIb: ∼33–24 ka) of MIS 2 in response to increased rainfall and solar insolation minima. Glacier fronts reached elevations as low as 1130 m a.s.l. possibly without overriding evidence related to the previous Pleistocene glacial maximum extent. Glacier recession in the Cantabrian Mountains started at 21–20 ka ago, after the global LGM. We suggest that the recession was initiated by increased insolation followed by hyper-cool and dry conditions during Heinrich Stadial 1 in response to meltwater discharges in the North Atlantic.

Last Glacial Maximum and Lateglacial in the Polish High Tatra Mountains - Revised deglaciation chronology based on the 10Be exposure age dating

Deglaciation chronology of the Polish High Tatra Mountains has been reconstructed based on 10Be exposure age dating. Fifty-seven rock samples were collected from boulders located on the terminal and lateral moraines that limit the horizontal extent of the LGM and the Lateglacial glaciers in the Biała Woda and Sucha Woda catchments. The uncertainty-weighted mean age of 21.5 ± 2.5 ka obtained for the maximum terminal moraine in the Sucha Woda Valley indicates that the oldest preserved moraines were formed during the global LGM. The age population ranges between 15.1 ± 1.0 and 28.3 ± 2.0 ka, and suggests that glaciers reached their maximum position (LGM I) as early as 28–25 ka and the final stabilization of the form occurred much later possibly after melting of buried dead ice. The younger glacial oscillation (LGM II) occurred no later than 20.5 ka and is represented by well-preserved termino-lateral moraine systems in the Pańszczyca Valley. The first Lateglacial stage (LG1) in the study area is documented in the Rybi Potok Valley at the RP1 moraine (1300 m a.s.l.), which was stable at around 16.6 ± 0.3 ka. The younger LG2 stage has no defined absolute age, however, it is constrained between 16.5 and 15.5 ka by the timing of the LG3 stage. This cold event is represented by well-formed moraines in the Roztoka/Pięć Stawów Polskich, Rybi Potok and Pańszczyca valleys of which exposure age indicates their deposition between 15.0 ± 0.5 and 15.6 ± 0.1 ka. The LG1, LG2 and LG3 stages likely occurred during the Oldest Dryas cold stage (Greenland Stadial 2.1a) related to the North Atlantic cooling Heinrich Event 1. The youngest glacial oscillation is evidenced by moraines in the Pusta and Pańszczyca valleys. These moraines are composed of very large granitic blocks of which exposure ages often exhibit isotope inheritance. This is reflected by the youngest P3 moraine in the Pańszczyca Valley with a mean age of deposition close to the LGM. The R4 moraine system in the Pusta Valley, however, indicates two oscillations phases that occurred at around 13 ka and correlates well with the timing of RP5 moraine formation in the Za Mnichem Valley. The LG4 stage is related to the climate cooling during the Younger Dryas (Greenland Stadial 1).LGM ELAs reconstructed for the Biała Woda and Sucha Woda/Pańszczyca glaciers were located at 1460–1480 m a.s.l. During the Oldest Dryas stages, the ELA in the High Tatras rose from 1600 to 1650 m a.s.l. in the Rybi Potok Valley and from 1700 to 1800 m a.s.l. in the Roztoka/Pięć Stawów Polskich Valley. The Younger Dryas ELA, depending on glacier's exposition, was located between 1950 and 2000 m a.s.l. Climate modelling results show that the LGM glaciers (maximum advance) could have advanced in the High Tatras when the mean annual temperature was lower than today by 11–12 °C and precipitation was reduced by 40–60%. During the Lateglacial stages the temperature decrease in the study area changed from 10 °C during the Oldest Dryas to 6 °C during the Younger Dryas and precipitation lowering decreased from −50% to −30% or even −10%, respectively compare to modern conditions.

The MIS 3 maximum of the Torres del Paine and Última Esperanza ice lobes in Patagonia and the pacing of southern mountain glaciation

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 10Be 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.

Cosmogenic evidence for limited local LGM glacial expansion, Denton Hills, Antarctica

The geomorphology of the Denton Hills provides insight into the timing and magnitude of glacial retreats in a region of Antarctica isolated from the influence of the East Antarctic ice sheet. We present 26 Beryllium-10 surface exposure ages from a variety of glacial and lacustrine features in the Garwood and Miers valleys to document the glacial history of the area from 10 to 286 ka. Our data show that the cold-based Miers, Joyce and Garwood glaciers retreated little since their maximum positions at 37.2 ± 6.9 (1σ n = 4), 35.1 ± 1.5 (1σ, n = 3) and 35.6 ± 10.1 (1σ, n = 6) ka respectively. The similar timing of advance of all three glaciers and the lack of a significant glacial expansion during the global LGM suggests a local LGM for the Denton Hills between ca. 26 and 51 ka, with a mean age of 36.0 ± 7.5 (1σ, n = 13) ka.A second cohort of exposure ages provides constraints to the behaviour of Glacial Lake Trowbridge that formerly occupied Miers Valley in the late Pleistocene. These data show active modification of the landscape from ∼20 ka until the withdrawal of ice from the valley mouths, and deposition of Ross Sea Drift, at 10–14 ka.

Late Pleistocene glacial fluctuations in Cordillera Oriental, subtropical Andes

The behavior of subtropical glaciers during Middle to Late Pleistocene global glacial maxima and abrupt climate change events, specifically in Earth's most arid low-latitude regions, remains an outstanding problem in paleoclimatology. The present-day climate of Cordillera Oriental, in arid northwestern Argentina, is influenced by shifts in subtropical climate systems, including the South American Summer Monsoon. To understand better past glacier-subtropical climates during the global Last Glacial Maximum (LGM, 26.5–19 ka) and other time periods, we combined geomorphic features with forty-two precise 10Be ages on moraine boulders and reconstructed paleo-equilibrium line altitudes (ELA) at Nevado de Chañi (24°S) in the arid subtropical Andes. We found a major glacial expansion at ∼23 ± 1.6 ka, that is, during the global LGM. Additional glacial expansions are observed before the global LGM (at ∼52–39 ka), and after, at 15 ± 0.5 and 12 ± 0.6 ka. The ∼15 ka glacial event was found on both sides of Chañi and the ∼12 ka event is only recorded on the east side. Reconstructed ELAs of the former glaciers exhibit a rise from east to west that resembles the present subtropical climate trajectory from the Atlantic side of the continent; hence, we infer that this climate pattern must have been present in the past. Based on comparison with other low-latitude paleoclimate records, such as those from lakes and caves, we infer that both temperature and precipitation influenced past glacial occurrence in this sector of the arid Andes. Our findings also imply that abrupt deglacial climate events associated with the North Atlantic, specifically curtailed meridional overturning circulation and regional cooling, may have had attendant impacts on low subtropical Southern Hemisphere latitudes, including the climate systems that affect glacial activity around Nevado de Chañi.

Did Pyrenean glaciers dance to the beat of global climatic events? Evidence from the Würmian sequence stratigraphy of an ice-dammed palaeolake depocentre in Andorra

Abstract The ice-marginal depositional sequence of La Massana provides a chronostratigraphic benchmark for reconstructing the Würmian glacial evolution of the Valira catchment in Andorra, SE Pyrenees. The sedimentary record of Andorra confirms the asynchronous chronology of glacier fluctuations in different parts of the Pyrenean mountain range. A major ice recession occurred at the end of Marine Isotope Stage (MIS) 4. High magnitude valley-glacier fluctuations during MIS 3 constitute another important finding. Major readvances occurred toward the end of MIS 3, whereas MIS 2 (in particular, the global Last Glacial Maximum, or LGM) featured sharp contrasts in ice recession rates between Pyrenean valleys. Substantial distances separated MIS 4 glacier fronts (the Würmian maximum ice extent, or MIE) from those reached during the global LGM, in contrast to situations in the eastern Pyrenees, where Würmian MIE and global LGM ice fronts nearly coincided. Overall, the Valira glaciers reveal patterns that are more similar to those recorded elsewhere in the western and central Pyrenees than in the eastern Pyrenees. The rapid fluctuations recorded by Andorran glaciers during the second half of the Würm also suggest a response to global forcing events such as Heinrich events in the North Atlantic.

The last maximum ice extent and subsequent deglaciation of the Pyrenees: an overview of recent research

This paper reviews data currently available on the glacial fluctuations that occurred in the Pyrenees between the Würmian Maximum Ice Extent (MIE) and the beginning of the Holocene. It puts the studies published since the end of the 19th century in a historical perspective and focuses on how the methods of investigation used by successive generations of authors led them to paleogeographic and chronologic conclusions that for a time were antagonistic and later became complementary. The inventory and mapping of the ice-marginal deposits has allowed several glacial stades to be identified, and the successive ice boundaries to be outlined. Meanwhile, the weathering grade of moraines and glaciofluvial deposits has allowed Würmian glacial deposits to be distinguished from pre-Würmian ones, and has thus allowed the Würmian Maximum Ice Extent (MIE) –i.e. the starting point of the last deglaciation– to be clearly located. During the 1980s, 14C dating of glaciolacustrine sequences began to indirectly document the timing of the glacial stades responsible for the adjacent frontal or lateral moraines. Over the last decade, in situ-produced cosmogenic nuclides (10Be and 36Cl) have been documenting the deglaciation process more directly because the data are obtained from glacial landforms or deposits such as boulders embedded in frontal or lateral moraines, or ice-polished rock surfaces. On that basis, it is now accepted that (i) the Würmian MIE occurred in the Pyrenees during MIS 4 and not the Global LGM; and that (ii) a major glacial readvance took place during the Global LGM. This ice readvance reached a position close to the MIS 4 icefield boundary in the Eastern part of the range, but apparently not in the west. (iii) Soon after the Global LGM, the Pyrenean ice margin went into major and rapid recession. Even before the beginning of the Lateglacial, the main trunk glaciers had already retreated to the upper parts of the valleys. (iv) The paleogeography of the Pyrenean icefield during the Last Glacial-Interglacial Transition (LGIT) is still partially unknown but all available data indicate that glaciers during the Oldest Dryas (GS-2a) were substantially smaller than during the Global LGM. During the Bølling-Allerød interstadial, the Pyrenean ice margins retreated substantially, and glaciers locally vanished definitively. The Younger Dryas cooling event generated either a short readvance of existing cirque glaciers or the development of rock glaciers.

The human occupation of the northwestern Pyrenees in the Late Glacial: New data from the Arudy basin, lower Ossau valley

Excavated since the 1860s, the Arudy basin has yielded a number of rich Magdalenian sites that enable us to address the question of the human reoccupation of the lower Pyrenean valleys at the end of the Last Glacial Maximum. Until the 1990s, it was considered that at Arudy this reoccupation started ca. 16,000 cal BP in the Middle Magdalenian and continued into the Upper Magdalenian until ca. 14,000 cal BP. However, since the mid-2000 s, this picture has been modified through a series of new analyses, excavations (caves of Laa 2 and Tastet), 14C dates and reassessment of ancient collections. Evidence of human occupation ca. 20,000–19,000 cal BP, although limited, has been identified at Laa 2 and Tastet, consistent with numerous data obtained at Pyrenean scale showing a deglaciation of the north Pyrenean foothills as early as the end of the global LGM. The number of sites with evidence of Magdalenian has increased, showing that human presence in the basin was more intensive than previously thought. The Middle and Upper Magdalenian occupations have been redated to at least 18,000–17,500 cal BP to 15,000–14,500 cal BP, with the transition between the two phases probably occurring ca. 16,600–16,200 cal BP. The faunal records of these sites document an emphasis on horse hunting, which is not common in the northern Pyrenees, but also witness an evolution over time in the range of species hunted. Furthermore, the Pyrenean affinities of the Arudy groups and their relations with neighboring regions, such as Spain and the northern part of the Aquitaine basin, can be addressed through new evidence: in particular lithic and osseous raw materials and specific types of projectile tips. These results significantly change our view of the nature, rhythm and chronology of the Late Glacial settlement in this area.

Glacier advances in northeastern Turkey before and during the global Last Glacial Maximum

Our study in the Başyayla Valley in northeastern Anatolia showed evidence of four glacier advances that built terminal and lateral moraines. Surface exposure dating of boulders on these moraines showed that the Maximum Ice Extent (MIE) was asynchronous with the global Last Glacial Maximum (LGM; 22.1 ± 4.3 thousand years; ka). The local MIE took place at least 57.0 ± 3.5 ka ago. The extent of the Başyayla Glacier during this advance is not known exactly because the boulders are only preserved on a lateral moraine. The next advance was prior to 41.5 ± 2.5 ka, and it descended down the valley to approximately 2320 m above sea level (m a.s.l.), with a glacier length of 5.3 km. During the early global LGM, the Başyayla Glacier extended for a distance of 4.9 km down to approx. 2430 m a.s.l. The last recorded advance occurred during the global LGM. This extension was 0.7 km smaller than the local MIE and its terminus reached 2490 m a.s.l. only. The exposure ages of boulders in a retreat position at an altitude of approx. 3045 m a.s.l. indicate that the valley has remained ice-free since the Lateglacial period. Therefore, the Lateglacial extent was limited to the cirque system in the uppermost part of the catchment. Furthermore, Holocene glacier oscillations seem to be either absent or restricted to solifluction in the whole catchment and to rock glacier movements in the southern tributary of the Başyayla Valley system.

Paleoglaciation of the Tibetan Plateau and surrounding mountains based on exposure ages and ELA depression estimates

The Tibetan Plateau holds an ample record of past glaciations, and there is an extensive set of glacial deposits dated by exposure dating. Here a compilation is presented of 10Be exposure ages from 485 glacial deposits with 1855 individual samples on the Tibetan Plateau, and ELA depression estimates for the glacial deposits based on a simple toe to headwall ratio approach. To recalculate the Tibetan Plateau exposure ages, 10Be production rates from 24 calibration sites across the world are compiled and recalibrated yielding an updated global reference 10Be production rate. The recalculated exposure ages from the Tibetan Plateau glacial deposits are then divided into three groups based on exposure age clustering, to discriminate good (well-clustered) from poor (scattered) deglaciation ages. A major part of the glacial deposits have exposure ages affected by prior or incomplete exposure, complicating exposure age interpretations. The well-clustered deglaciation ages are primarily from mountain ranges along the margins of the Tibetan Plateau with a main peak between 10 and 30 ka, indicating glacial advances during the global LGM. A large number of deglaciation ages older than 30 ka indicates maximum glaciation predating the LGM, but the exposure age scatter generally prohibits accurate definition of the glacial chronology. The ELA depression estimates scatter significantly, but the main part is remarkably low. Average ELA depressions of 337 ± 197 m for the LGM and 494 ± 280 m for the pre-LGM indicate restricted glacier expansion.

Progressive glacial retreat in the Southern Altiplano (Uturuncu volcano, 22°S) between 65 and 14 ka constrained by cosmogenic 3He dating

This work presents the first reconstruction of late Pleistocene glacier fluctuations on Uturuncu volcano, in the Southern Tropical Andes. Cosmogenic 3He dating of glacial landforms provides constraints on ancient glacier position between 65 and 14ka. Despite important scatter in the exposure ages on the oldest moraines, probably resulting from pre-exposure, these 3He data constrain the timing of the moraine deposits and subsequent glacier recessions: the Uturuncu glacier may have reached its maximum extent much before the global LGM, maybe as early as 65ka, with an equilibrium line altitude (ELA) at 5280m. Then, the glacier remained close to its maximum position, with a main stillstand identified around 40ka, and another one between 35 and 17ka, followed by a limited recession at 17ka. Then, another glacial stillstand is identified upstream during the late glacial period, probably between 16 and 14ka, with an ELA standing at 5350m. This stillstand is synchronous with the paleolake Tauca highstand. This result indicates that this regionally wet and cold episode, during the Heinrich 1 event, also impacted the Southern Altiplano. The ELA rose above 5450m after 14ka, synchronously with the Bolling–Allerod.

Paleoglaciation of Shaluli Shan, southeastern Tibetan Plateau

Reconstructing the paleoglaciation of the Tibetan Plateau is critical to understanding linkages between regional climate changes and global climate changes, and here we focus on the glacial history of the Shaluli Shan, an area of the southeastern Tibetan Plateau that receives much of its precipitation from monsoon flow. Based on field investigation, geomorphological mapping, and 10Be exposure dating of moraines, we identify glacial deposits from the Late Glacial, with minimum ages at 13.0 ± 1.2 –17.1 ± 1.6 ka, global Last Glacial Maximum (gLGM) at 21.6 ± 2.0 ka, and pre-gLGM at 102.3 ± 10.0–183.6 ± 17.0 ka. These ages are consistent with and significantly extend the known range from most prior chronological work using terrestrial cosmogenic nuclides in this area, and include a set of dates for the Kuzhaori moraine that raise questions about prior chronologies based on the electron spin resonance technique. Ice caps about 4000 km2 in size covered the Haizishan Plateau and the Xinlong Plateau during the global LGM, with large glaciers extending far down outlet valleys. The presence of ice cap glaciation, here, contrasts strongly to glaciation elsewhere in the Shaluli Shan and more central regions of the Tibetan Plateau where ice expansion remained constricted to valleys. This work provides important insights into the paleoclimate pattern and monsoon evolution of the Tibetan Plateau over past glacial cycles and indicates that the Shaluli Shan has a glacial chronology more consistent with the Northern Hemisphere paleo-ice sheets than other areas of the Tibetan Plateau.

Palaeocirculation across New Zealand during the last glacial maximum at ∼21 ka

What circulation pattern drove Southern Alps glacial advances at ∼21 ka? Late 20th century glacial advances in New Zealand are commonly attributed to a dual precipitation increase and cooler than normal temperatures associated with enhanced westerly flow that occur under synoptic pressure patterns termed ‘zonal’ regimes (Kidson, 2000). But was the circulation pattern that supported major Southern Alps glacial advances during the global LGM similar to the modern analog? Here, a Regional Climate Regime Classification (RCRC) time slice was used to infer past circulation for New Zealand during the LGM at ∼21 ka. Palaeoclimate information that supported the construction of the ∼21 ka time slice was derived from the NZ-INTIMATE Climate Event Stratigraphy (CES), one new Auckland maar proxy record, and additional low-resolution data sourced from the literature.The terrestrial evidence at ∼21 ka implicates several possibilities for past circulation, depending on how interpretations for some proxies are made. The interpretation considered most tenable for the LGM, based on the agreement between terrestrial evidence, marine reconstructions and palaeoclimate model results is an ‘anticyclonic/zonal’ circulation regime characterized by increased influences from blocking ‘highs’ over the South Island during winter and an increase in zonal and trough synoptic types (with southerly to westerly quarter wind flow) during summer. These seasonal circulation traits would have generated lower mean annual temperatures, cooler than normal summer temperatures, and overall lower mean annual precipitation for New Zealand (particularly in the western South Island) at ∼21 ka.The anticyclonic/zonal time slice reconstruction presented in this study has different spatial traits than the late 20th Century and the early Little Ice Age signatures, suggesting more than one type of regional circulation pattern can drive Southern Alps glacial activity. This finding lends support to the hypothesis that temperature over precipitation change is more important as the primary modulator of Southern Alps ice advances. The RCRC approach also demonstrates some subtle advantages of integrating multi-proxy data within a palaeocirculation context for New Zealand, notably because this reconstruction technique enables direct comparisons to coarsely resolved palaeoclimate model outputs that do not have downscaled information.