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We present 40 new 10Be exposure ages of moraines and other glacial deposits left behind by the southeastern sector of the Laurentide Ice Sheet (LIS) in southern New England and New York, summarize the regional moraine record, and interpret the dataset in the context of previously published deglaciation chronologies. The regional moraine record spans the Last Glacial Maximum (LGM), with the outermost ridge of the terminal complex dating to ~26–25 ka, the innermost ridge of the terminal complex dating to ~22 ka, and a series of smaller recessional limits within ~50 km of the terminal complex dating to ~21–20.5 ka. The chronology generally agrees with independent age constraints from radiocarbon and glacial varves. A few inconsistencies among ages from cosmogenic-nuclide measurements and those from other dating methods are explained by geologic scatter where several bedrock samples and boulders from the outer terminal moraine exhibit nuclide inheritance, while exposure ages on large moraines are likely affected by postdepositional disturbance. The exposure-age chronology places the southeastern sector of the LIS at or near its maximum extent from ~26 to 21 ka, which is broadly consistent with the LGM sea-level lowstand, local and regional temperature indicators, and local summer insolation. The net change in LIS extent represented by this chronology occurred more slowly (<5 to 25 m yr-1) than retreat through the rest of New England, consistent with a slow general rise in insolation and modeled summer temperature. We conclude that the major pulse of LIS deglaciation and accelerated recession, recorded by dated glacial deposits north of the moraines discussed here, did not begin until after atmospheric CO2 increased at ~18 ka, marking the onset of Termination 1. [ABSTRACT FROM AUTHOR]

Millennial-scale cold reversals in the high latitudes of both hemispheres interrupted the last transition from full glacial to interglacial climate conditions. The presence of the Younger Dryas stadial (~12.9 to ~11.7kyr ago) is established throughout much of the Northern Hemisphere, but the global timing, nature and extent of the event are not well established. Evidence in mid to low latitudes of the Southern Hemisphere, in particular, has remained perplexing [1-6]. The debate has in part focused on the behaviour of mountain glaciers in New Zealand, where previous research has found equivocal evidence for the precise timing of increased or reduced ice extent [1-3]. The interhemispheric behaviour of the climate system during the Younger Dryas thus remains an open question, fundamentally limiting our ability to formulate realistic models of global climate dynamics for this time period. Here we show that New Zealand's glaciers retreated after ~13 kyr bp, at the onset of the Younger Dryas, and in general over the subsequent ~1.5-kyr period. Our evidence is based on detailed landform mapping, a high-precision [sup.10]Be chronology [7] and reconstruction of former ice extents and snow lines from well-preserved cirque moraines. Our late-glacial glacier chronology matches climatic trends in Antarctica, Southern Ocean behaviour and variations in atmospheric C[O.sub.2]. The evidence points to a distinct warming of the southern mid-latitude atmosphere during the Younger Dryas and a close coupling between New Zealand's cryosphere and southern high-latitude climate. These findings support the hypothesis that extensive winter sea ice and curtailed meridional ocean overturning in the North Atlantic led to a strong interhemispheric thermal gradient [8] during late-glacial times, in turn leading to increased upwelling and C[O.sub.2] release from the Southern Ocean9, thereby triggering Southern Hemisphere warming during the northern Younger Dryas., The transition of Earth's climate from the last ice age to the warm conditions of the Holocene epoch (the past ~11.5 kyr) is not yet fully explained. Polar ice-core records [...]

The terrestrial glacial record reflects past snowline variability and atmospheric temperature changes. When combined with secure chronologies, these data can be used to test models of ice-age climate. We present new in situ cosmogenic [sup.10]Be, [sup.26]Al, and [sup.3]He exposure ages, supported by limiting [sup.4]Ar/[sup.39]Ar and [sup.14]C ages, for seven of the youngest moraines east of Lago Buenos Aires, Argentina, 46.5[degrees]S, that were deposited by a large outlet glacier of the Patagonian Ice Cap. Following a major glaciation that deposited extensive moraines prior to 109 ka, paired [sup.1]Be-[sup.26]Al ages indicate that the next youngest complex of moraines was deposited from 23.0 [+ or -] 1.2 to 15.6 [+ or -] 1.1 ka (1 [sigma]). During the last glaciation, ice was at its maximum extent prior to 22 ka and at least five moraines were deposited in less than 10 k.y. These data are in good agreement with three [sup.14]C ages of ca. 16 ka from varved sediment banked on top of the youngest of these five moraines and limiting [sup.3]He ages, which range from ca. 33 to 19 ka. The most extensive ice marginal deposits preserved within the last 109 k.y. were formed during marine oxygen isotope stage 2; no moraines dating to stage 4 were found. For stage 2, the distribution of ages at Lago Buenos Aires is similar to cosmogenic nuclide-based glacial chronologies from western North America. In fact, the structure of the last mid-latitude South American ice age--specifically, the overall timing, a maximum ice extent prior to 22 ka, and deglaciation after 16 ka--is indistinguishable from that of the last major glaciation in the Northern Hemisphere, despite a maximum in Southern Hemisphere insolation during this period. The similar mid-latitude glacial history in both hemispheres implies that a global climate forcing mechanism, such as atmospheric cooling, as opposed to oceanic redistribution of heat, synchronizes the ice age climate on orbital time scales. Keywords: South America, ice ages, glacial maximum, last, exposure age, paleoclimatology, and geochronology.

Radiocarbon, cosmogenic surface exposure, and relative sea-level data are used to examine deglaciation and glacioisostatic adjustment of Cumberland Sound and Cumberland Peninsula, and southeastern Baffin Island, in the context of a new model for the glacial history of the eastern Canadian Arctic. Over the last decade, a multidisciplinary effort on easternmost Baffin Island has documented far greater ice expansion during the last glacial maximum than previously believed, including low gradient glaciation in marine embayments coexisting with ice free or thin cold-based ice on adjacent upland crystalline terrain. This study documents that the Cumberland Sound region underwent about twice as much glacioisostatic movement during the last glacial maximum as shown in previous reconstructions. However, the loading impact of the Laurentide Ice Sheet and local glaciation on adjacent Cumberland Peninsula was limited; the mapped zero isoline on emergence shows that postglacial eustatic rise exceeded glacial isostatic uplift for much of the eastern peninsula, a finding that is consistent with that of prior studies. The center of loading and the major source of glacial ice for the entire Cumberland Sound region were Foxe Basin and western Baffin Island. Strandlines dated 10,500 and 8500 [sup.14]C yr B.P. show that slow deglaciation of Cumberland Sound was punctuated by at least two periods of faster grounding line retreat. Coastal southeastern Cumberland Peninsula was deglaciated before 9400 [sup.14]C yr B.P., and other areas surrounding Cumberland Sound were deglaciated after ca. 9000 [sup.14]C yr B.P.; these land areas experienced relatively slow glacial retreat and restrained rebound. Cosmogenic surface exposure ages on glacially-scoured bedrock support the [sup.14]C-based inferred timing for deglaciation of the sound, although inheritance of nuclides from prior exposure is evident in samples, indicating limited bedrock erosion in many areas. For central Cumberland Sound, a rapid rise of relative sealevel of ~4-5 m/100 [sup.14]C yr (4-6 m/100 yr) and a half life for crustal response of Keywords: Arctic, Baffin Island, exposure age, glacial geology, isostatic rebound, Laurentide ice sheet.

In the Cordillera Darwin, southernmost South America, we used 10Be and 14C dating, dendrochronology, and historical observations to reconstruct the glacial history of the Dalla Vedova valley from deglacial time to the present. After deglacial recession into northeastern Darwin and Dalla Vedova, by ~16 ka, evidence indicates a glacial advance at ~13 ka coeval with the Antarctic Cold Reversal. The next robustly dated glacial expansion occurred at 870 ± 60 calendar yr ago (approximately AD 1150), followed by less-extensive dendrochronologically constrained advances from shortly before AD 1836 to the mid-twentieth century. Our record is consistent with most studies within the Cordillera Darwin that show that the Holocene glacial maximum occurred during the last millennium. This pattern contrasts with the extensive early- and mid-Holocene glacier expansions farther north in Patagonia; furthermore, an advance at 870 ± 60 yr ago may suggest out-of-phase glacial advances occurred within the Cordillera Darwin relative to Patagonia. We speculate that a southward shift of westerlies and associated climate regimes toward the southernmost tip of the continent, about 900–800 yr ago, provides a mechanism by which some glaciers advanced in the Cordillera Darwin during what is generally considered a warm and dry period to the north in Patagonia. [ABSTRACT FROM AUTHOR]

An expansion of alpine glaciers during the latest Pleistocene produced an extraordinarily well defined end moraine system in the Ahklun Mountains, southwestern Alaska. These moraines, deposited during the Mount Waskey advance, are several kilometers beyond modern glacier termini, and ~80 km upvalley of the late Wisconsin Ahklun Mountains ice cap terminal moraine. Eleven cosmogenic [sup.10]Be and [sup.26]Al exposure ages on moraine boulders, combined with radiocarbon ages from a lake core upvalley of a moraine deposited during the Mount Waskey advance, suggest that the advance culminated between 12.4 and 11.0 ka, sometime during, or shortly following, the Younger Dryas event (ca. 12.9-11.6 ka). We believe that the Mount Waskey advance was a consequence of cooling during the Younger Dryas. These data further strengthen emerging evidence for Younger Dryas-age cooling of the North Pacific region. Keywords: Alaska, cosmogenic exposure dating, glaciers, Younger Dryas, late glacial.

Ice-margin retreat, glacial processes, and associated marine environmental conditions were investigated along a tidewater margin of the Laurentide ice sheet in eastern coastal Maine. The ubiquitous presence of recessional moraines that typically show crosscutting relationships indicates that numerous stillstands and readvances interrupted net ice-margin retreat. Commonly, moraines exhibit changes in orientation associated with elevation changes, suggesting topographic control on retreat. Till, glaciofluvial facies, and glaciomarine sediment are the dominant components of the moraines. These sediments show that the ice terminated in the sea and that glacial meltwater played a key role in their deposition. The most continuous landforms in the study area are the Pond Ridge moraine and Pineo Ridge moraine system. Both landforms crosscut older moraines and contain ice-shove features, and crosscutting of moraines exists within the Pineo Ridge moraine system, indicating that the ice sheet readvanced during their formation. The Pond Ridge moraine and Pineo Ridge moraine system are straighter across elevation changes, compared to other moraines in the area, implying that during their formation, topography had less of a destabilizing influence on ice-margin dynamics. Foraminifera, Ostracode, and mollusk species in ice-proximal and ice-distal glaciomarine sediments indicate that arctic to subarctic climate conditions existed during deglaciation. Despite the persistence of a cold environment, 20 km of net ice-margin retreat occurred between ca. 14000 and 13000 (super.14)C yr B.P., mostly in contact with the sea.