Radiocarbon chronology of the late-glacial Puerto Bandera moraines,Southern Patagonian Icefield,Argentina

We report radiocarbon dates that constrain the timing of the deposition of the late-glacial Puerto Bandera moraine system alongside the western reaches of Lago Argentino adjacent to the Southern Patagonian Icefield. Close maximum-limiting radiocarbon ages (n = 11) for glacier advance into the outer moraines, with a mean value of 11,100 ± 60 ¹⁴C yrs BP (12,990 ± 80 cal yrs BP), were obtained from wood in deformation (soft) till exposed beneath flow and lodgment till in Bahía del Quemado on the northeast side of Brazo Norte (North Branch) of western Lago Argentino. Other exposures of this basal deformation till in Bahía del Quemado reveal incorporated clasts of peat, along with larger inclusions of deformed glaciofluvial and lacustrine deposits. Radiocarbon dates of wood included in these reworked peat clasts range from 11,450 ± 45 ¹⁴C yrs BP to 13,450 ± 150 ¹⁴C yrs BP (13,315 ± 60 to 16,440 ± 340 cal yrs BP). The implication is that, during this interval, glacier fronts were situated inboard of the Puerto Bandera moraines, with the peat clasts and larger proglacial deposits being eroded and then included in the basal till during the Puerto Bandera advance.Minimum-limiting radiocarbon ages for ice retreat come from basal peat in cores sampled in spillways and depressions generated during abandonment of the Puerto Bandera moraines. Glacier recession and subsequent plant colonization were initiated close behind different frontal sectors of these moraines prior to: 10,750 ± 75 ¹⁴C yrs BP (12,660 ± 70 cal yrs BP) east of Brazo Rico, 10,550 ± 55 ¹⁴C yrs BP (12,490 ± 80 cal yrs BP) in Peninsula Avellaneda, and 10,400 ± 50 ¹⁴C yrs BP (12,280 ± 110 cal yrs BP) in Bahía Catalana. In addition, a radiocarbon date indicates that by 10,350 ± 45 ¹⁴C yrs BP (12,220 ± 110 cal yrs BP), the Brazo Norte lobe (or former Upsala Glacier) had receded well up the northern branch of Lago Argentino, to a position behind the Herminita moraines. Furthermore, glacier termini had receded to just outboard of the outer Holocene moraines at Lago Frías and Lago Pearson (Anita) prior to 10,400 ± 40 ¹⁴C yrs BP (12,270 ± 100 cal yrs BP) and 9040 ± 45 ¹⁴C yrs BP (10,210 ± 50 cal yrs BP), respectively. The most extensive recession registered during the early Holocene was in Agassiz Este Valley, where the Upsala Glacier had pulled back behind the outer Holocene moraine, reaching close to the present-day glacier terminus before 8290 ± 40 ¹⁴C yrs BP (9300 ± 80 cal yrs BP).The radiocarbon-dated fluctuations of the Lago Argentino glacier in late-glacial time, given here, are in accord with changes in ocean mixed layer properties, predominately temperature, derived from the isotopic record given here of ODP Core 1233, taken a short distance off shore of the Chilean Lake District. It also matches recently published chronologies of late-glacial moraines in the Southern Alps of New Zealand on the opposite side of the Pacific Ocean from Lago Argentino. Finally, the timing of the late-glacial reversal of the Lago Argentino glacier fits the most recent chronology for the culmination of the Antarctic Cold Reversal (ACR) in the deuterium record of the EPICA Dome C ice core from high on the East Antarctic Plateau. Therefore, we conclude that the climate signature of the ACR was widespread in both the ocean and the atmosphere over at least the southern quarter of the globe.     

Greenland ice sheet history since the last glaciation

The position of the Inland Ice margin during the late Wisconsin-Würm glaciation (ca. 15,000 yr BP) is probably marked by offshore banks (submarine moraines?) in the Davis Strait. The history of the Inland Ice since the late Wisconsin-Würm can be divided into four principal phases: (1) Relatively slow retreat from the offshore banks occurred at an average rate of approximately 1 km/100 yr until ca. 10,000 yr BP (Younger Dryas?) when the Taserqat moraine system was formed by a readvance. (2) At ca. 9500 yr BP, the rate of retreat increased markedly to about 3 km/100 yr, and although nearly 100 km of retreat occurred by ca. 6500 yr BP, it was punctuated by frequent regional reexpansions of the Inland Ice that formed extensive moraine systems at ca. 8800-8700 yr BP (Avatdleq-Sarfartôq moraines), 8400-8100 yr BP (Angujârtorfik-Fjord moraines), 7300 yr BP (Umîvît moraines), and 7200-6500 yr BP (Keglen-Mt, Keglen moraines). (3) Between 6500 and 700 yr BP, discontinous ice-margin deposits and ice-disintegration features were formed during retreat, which may have continued until the ice margin was near or behind its present position by ca. 6000 yr BP. Most of the discontinuous ice-margin deposits occur within 5–10 km of the present ice margin, and may have been formed by two main phases of readvance at ca. 4800-4000 yr BP and 2500-2000 yr BP. (4) Since a readvance at ca. 700 yr BP, the Inland Ice margin has undergone several minor retreats and readvances resulting in deposition of numerous closely spaced moraines within about 3 km of the present ice margin. The young moraines are diffieulto to correlate regionally, but several individual moraines have the following approximate ages: A.D. 1650, 1750, and 1880–1920.Inland Ice fluctuations in West Greenland were very closely paralleled by Holocene glacial events in East Greenland and the eastern Canadian Aretic. Such similarity of glacier behavior over a large area strongly suggests that widespread climatic change was the direct cause of Holocene glacial fluctuations. Moreover, historical advances of the Inland Ice margin followed slight temperature decreases by no more than a few decades, and ¹⁸O data from Greenland ice cores show that slight temperature decreases occurred frequently throughout the Holocene. Therefore, we conclude that construction of the major Holocene moraine systems in West Greenland was caused by slight temperature decreases, which decreased rates of ablation and thereby produced practically immediate advances of the ice sheet margin, but did not necessarily affect the long-term equilibrium of the ice sheet.     

Fluctuations of the South Patagonian Ice-field during the last glaciation and the Holocene

Mapping along a transect from the southeastern margin of the South Patagonian Ice-field in Torres del Paine National Park (Chile) to the limits of fresh moraines of the last glacial cycle indentified eight glacier advances. The four younger ones have been dated by dendrochronology, tephrochronology and radiocarbon dating. Although the bases of 10 m deep bogs were sampled, close limiting radiocarbon dates were not obtained because bog formation in this rain-shadow area appears not to have commenced until ca.12000 yr ago. The outermost Little Ice Age moraine formed during the seventeenth century and three inner ones were deposited around ad 1805, 1845 and after 1890. Densely vegetated older moraines contiguous with Little Ice Age deposits are possibly of late Holocene age. Tephra from the eruption of Reclus volcano at ca. 11 880 yr BP was incorporated by a readvance that deposited large multiple moraines 10–16 km from the modern ice-front; the oldest basal peat found inside the moraine has been dated to ca. 9200 yr BP. These bracketing dates indicate that some eastern outlet glaciers of the ice-field advanced at a time when some western tidewater outlet glaciers terminated inside their modern limits. This questions the view of J. H. Mercer and other that Patagonian glaciers did not readvance during the late-glacial interval. A stadial event also occurred when the glaciers were some 18–20 km from their modern positions and is closely dated to ca. 11880 yr BP because Reclus pumice flushed down-glacier forms thick upper beds in outwash deltas deposited in proglacial lakes. The four older moraines pre-date the late-glacial eruption of Reclus but are not dated closely. Comparison of their spatial extent with well-dated moraines in the Chilean Lakes Region suggests that they may mark advances culminating at ca. 14000 yr BP, ca. 20000 yr BP and earlier.     

Cosmogenic nuclide exposure ages for moraines in the Lago San Martin Valley, Argentina

At several times during the Quaternary, a major eastward-flowing outlet glacier of the former Patagonian Ice Sheet occupied the Lago San Martin Valley in Argentina (49°S, 72°W). We present a glacial chronology for the valley based on geomorphological mapping and cosmogenic nuclide (¹⁰Be) exposure ages (n = 10) of boulders on moraines and lake shorelines. There are five prominent moraine belts in the Lago San Martin Valley, associated with extensive sandar (glaciofluvial outwash plains) and former lake shorelines. Cosmogenic nuclide exposure ages for boulders on these moraines indicate that they formed at 14.3 ± 1.7 ka, 22.4 ± 2.3 ka, 34.4 ± 3.4 ka to 37.6 ± 3.4 ka (and possibly 60 ± 3.5 ka), and 99 ± 11 ka (1σ). These dated glacier advances differ from published chronologies from the Lago San Martin Valley based on ¹⁴C age determinations from organic sediments and molluscs in meltwater channels directly in front of moraines or in kettleholes within end moraine ridges. The moraine boulder ages also point to possible pre-LGM glacial advances during the last glacial cycle and a key observation from our data is that the LGM glaciers were probably less extensive in the Lago San Martin Valley than previously thought.     

Pleistocene glaciation in the southern Lake District of Chile

Relative-age criteria permit deposits of successive Andean glacier advances in the southern Lake District of Chile to be divided into four mappable drift sheets, the oldest two of which overlie Tertiary bedrock along the eastern flank of the Cordillera de la Costa. Only the youngest drift (Llanquihue) is datable by radiocarbon. During the most extensive ice advance of the last glaciation the Lago Llanquihue glacier was about 95 km long and reached an estimated maximum thickness of between 1000 and 1300 m. Glacier equilibrium lines at that time lay about 1000 m below their present level and rose eastward with a gradient of about 5 m/km. Successive ice advances in the Lago Llanquihue basin, which resulted in construction of end moraines and associated outwash plains beyond the lake margin, culminated sometime before about 20,000 yr ago and between 20,000 and 19,000 yr ago. A later readvance, inferred from the sedimentary record of lake-level fluctuations in the basin, had begun by about 15,000 yr ago and culminated shortly after 13,000 yr ago. A comparable, but less-closely dated, record of ice advances is found northwest of Seno Reloncaví and on Isla Chiloé. Deglaciation following the latest advance is likely to have been rapid, for the major glacier lobes fronted on deep water bodies that would have promoted extensive calving.     

Late-glacial ice advances in the western Italian Alps

The extent of ice on the south side of the Mont Blanc massif during two late-glacial readvances is known primarily from the distribution of crystalline erratics on sedimentary and metasedimentary terrain, and from the distribution of end moraines and outwash remants. Similar dual moraine complexes are found elsewhere in upper Val d'Aosta and indicate that the pattern is regional in character. During the earlier readvance equilibrium-line altitudes were ca. 450 ± 50m lower than at present, whereas during the later readvance they were ca. 350 ± 50 m lower. The moraines, not yet closely dated, were deposited sometime after 14,200 ¹⁴C Years ago by which time Lago'd Alice near the margin of the würm moraine system at Ivrea had been deglaciated, and before 8400 years ago, at which time Rutor Glacier in upper Val d'Aosta was no larger than at present. The younger moraines are believed to correlate with Egesen moraines on the north side of the Alps, whereas the older set may either correlate with an early phase of the Egesen or with Daun advance.     

Evidence for Heinrich event 1 in the British Isles

In the north Irish Sea basin (ISB), sedimentary successions constrained by AMS ¹⁴C dates obtained from marine microfaunas record three major palaeoenvironmental shifts during the last deglacial cycle. (i) Marine muds (Cooley Point Interstadial) dated to between 16.7 and 14.7 ¹⁴C kyr BP record a major deglaciation of the ISB following the Late Glacial Maximum (LGM). (ii) Terminal outwash and ice-contact landforms (Killard Point Stadial) were deposited during an extensive ice readvance, which occurred after 14.7 ¹⁴C kyr BP and reached a maximum extent at ca.14 ¹⁴C kyr BP. At this time the lowlands surrounding the north ISB were drumlinised. Coeval flowlines reconstructed from these bedforms end at prominent moraines (Killard Point, Bride, St Bees) and indicate contemporaneity of drumlinisation from separate ice dispersal centres, substrate erosion by fast ice flow, and subglacial sediment transfer to ice-sheet margins. In north central Ireland bed reorganisation associated with this fast ice-flow phase involved overprinting and drumlinisation of earlier transverse ridges (Rogen-type moraines) by headward erosion along ice streams that exited through tidewater ice margins. This is the first direct terrestrial evidence that the British Ice Sheet (BIS) participated in Heinrich event 1 (H1). (iii) Regional mud drapes, directly overlying drumlins, record high relative sea-level (RSL) with stagnation zone retreat after 13.7 ¹⁴C kyr BP (Rough Island Interstadial). Elsewhere in lowland areas of northern Britain ice-marginal sediments and morainic belts record millennial-scale oscillations of the BIS, which post-date the LGM advance on to the continental shelf, and pre-date the Loch Lomond Stadial (Younger Dryas) advance in the highlands of western Scotland (ca. 11–10 ¹⁴C kyr BP). In western, northwestern and northern Ireland, Killard Point Stadial (H1) ice limits are reconstructed from ice-flow lines that are coeval with those in the north ISB and end at prominent moraines. On the Scottish continental shelf possible H1-age ice limits are reconstructed from dated marine muds and associated ice marginal moraines. It is argued that the last major offshore ice expansion from the Scottish mountains post-dated ca. 15 ¹⁴C kyr BP and is therefore part of the H1 event. In eastern England the stratigraphic significance of the Dimlington silts is re-evaluated because evidence shows that there was only one major ice oscillation post-dating ca.18 ¹⁴C kyr BP in these lowlands. In a wider context the sequence of deglacial events in the ISB (widespread deglaciation of southern part of the BIS → major readvance during H1 → ice sheet collapse) is similar to records of ice sheet variability from the southern margins of the Laurentide Ice Sheet (LIS). Well-dated ice-marginal records, however, show that during the Killard Point readvance the BIS was at its maximum position when retreat of the LIS was well underway. This phasing relationship supports the idea that the BIS readvance was a response to North Atlantic cooling induced by collapse of the LIS. © 1998 John Wiley & Sons, Ltd.     

Late Pleistocene and Holocene glaciation of the Fish Lake valley,northeastern Alaska Range,Alaska

We reconstructed a chronology of glaciation spanning from the Late Pleistocene through the late Holocene for Fish Lake valley in the north‐eastern Alaska Range using ¹⁰Be surface exposure dating and lichenometry. After it attained its maximum late Wisconsin extent, the Fish Lake valley glacier began to retreat ca. 16.5 ka, and then experienced a readvance or standstill at 11.6 ± 0.3 ka. Evidence of the earliest Holocene glacial activity in the valley is a moraine immediately in front of Little Ice Age (LIA) moraines and is dated to 3.3–3.0 ka. A subsequent advance culminated at ca. AD 610–900 and several LIA moraine crests date to AD 1290, 1640, 1860 and 1910. Our results indicate that ¹⁰Be dating from high‐elevation sites can be used to help constrain late Holocene glacial histories in Alaska, even when other dating techniques are unavailable. Close agreement between ¹⁰Be and lichenometric ages reveal that ¹⁰Be ages on late Holocene moraines may be as accurate as other dating methods. Copyright © 2009 John Wiley & Sons, Ltd.     

Lateglacial and early Holocene dynamics of adjacent valley glaciers in the Western Swiss Alps

The Alps play a pivotal role for glacier and climate reconstructions within Europe. Detailed glacial chronologies provide important insights into mechanisms of glaciation and climate change. We present 26 ¹⁰Be exposure dates of glacially transported boulders situated on moraines and ice‐moulded bedrock samples at the Belalp cirque and the Great Aletsch valley, Switzerland. Weighted mean ages of ～10.9, 11.1, 11.0 and 9.6 ka for the Belalp, on up to six individual moraine ridges, constrain these moraines to the Egesen, Kartell and Schams stadials during Lateglacial to early Holocene times. The weighted mean age of ～12.5 ka for the right‐lateral moraine of the Great Aletsch correlates with the Egesen stadial related to the Younger Dryas cooling. These data indicate that during the early Holocene between ～11.7 and ～9.2 ka, glaciers in the Swiss Alps seem to have been significantly affected by cold climatic conditions initiated during the Younger Dryas and the Preboreal Oscillation. These conditions resulted in glacier margin oscillations relating to climatic fluctuations during the second phase of the Younger Dryas – and continuing into Boreal times – as supported by correlation of the innermost moraine of the Belalp Cirque to the Schams (early) Holocene stage. Copyright © 2011 John Wiley & Sons, Ltd.     

Itkillik Glaciation in the Brooks Range,northern Alaska

During the Itkillik Glaciation the Brooks Range supported an extensive mountain-glacier complex that extended for 750 km between 141° and 158°W longitude. Individual ice streams and piedmont lobes flowed as much as 50 km beyond the north and south margins of the range. Glaciers in the southern Brooks Range were longer than those farther north because of a southerly precipitation source, whereas those in the central and eastern part of the range were larger than glaciers at the extremities of the mountain system because of higher and more-extensive accumulation areas. Glacier equilibrium-line altitudes (ELAs) at the time of greatest advance were depressed 600 ± 100 m below present levels, whereas during a less-extensive late-glacial readvance (Alapah Mountain) ELA depression was about 300 ± 30 m. Radiocarbon dates indicate that Itkillik drift correlates with Late Wisconsin drift along the southern margin of the Laurentide Ice Sheet and with drift of Cordilleran glaciers in southern Alaska and the western conterminous United States deposited during the last glaciation. Itkillik I moraines represent the maximum ice advance under cold full-glacial conditions between about 24,000 and 17,000 ¹⁴C y. a. Itkillik II sediments, probably deposited close to 14,000 y. a., are characterized by abundant outwash and ice-contact stratified drift implying a milder climate than that of the Itkillik I phase. Alapah Mountain moraines at the heads of valleys draining high-altitude (≥1800 m) source areas record a possible late Itkillik readvance that is not yet closely dated. Itkillik glaciers may have largely disappeared from Brooks Range valleys by the beginning of the Holocene.     

Cosmogenic nuclide chronology of pre-last glacial maximum moraines at Lago Buenos Aires, 46°S, Argentina

At Lago Buenos Aires, Argentina, ¹⁰Be, ²⁶Al, and ⁴⁰Ar/³⁹Ar ages range from 190,000 to 109,000 yr for two moraines deposited prior to the last glaciation, 23,000–16,000 yr ago. Two approaches, maximum boulder ages assuming no erosion, and the average age of all boulders and an erosion rate of 1.4 mm/10³ yr, both yield a common estimate age of 150,000–140,000 yr for the two moraines. The erosion rate estimate derives from ¹⁰Be and ²⁶Al concentrations in old erratics, deposited on moraines that are >760,000 yr old on the basis of interbedded ⁴⁰Ar/³⁹Ar dated lavas. The new cosmogenic ages indicate that a major glaciation during marine oxygen isotope stage 6 occurred in the mid-latitude Andes. The next five youngest moraines correspond to stage 2. There is no preserved record of a glacial advance during stage 4. The distribution of dated boulders and their ages suggest that at least one major glaciation occurred between 760,000 and >200,000 yr ago. The mid-latitude Patagonian glacial record, which is well preserved because of low erosion rates, indicates that during the last two glacial cycles major glaciations in the southern Andes have been in phase with growth and decay of Northern Hemisphere ice sheets, especially at the 100,000 yr periodicity. Thus, glacial maxima are global in nature and are ultimately paced by small changes in Northern Hemisphere insolation.     

Upper Wisconsinan submarine end moraines off Cape Ann,Massachusetts

Seismic profiles across the southwest end of Jeffreys Ledge, a bathymetric high north of Cape Ann, Massachusetts, reveal two end moraines. The moraines overlie upper Wisconsinan glacialmarine silty clay and are composed mostly of subaqueous ice-contact deposits and outwash. They were formed below sea level in water depths of as much as 120 m during fluctuations of a calving ice front. The moraines are late Wisconsinan in age and were formed after the Cambridge readvance, about 14,000 yr B.P., and before the Kennebunk readvance, about 13,000 yr B.P. They represent fluctuations of the ice front during overall retreat of Laurentide ice from the Gulf of Maine and New England.     

Late quaternary glacial history of George VI Sound area, West Antarctica

During the last glacial maximum in West Antarctica separate ice caps developed on Alexander Island and on Palmer Land, became confluent in George VI Sound, and discharged northward from latitude 72° S. Radiocarbon (>32,000 yr) and amino acid (approximately 120,000 yr) age determinations on shell fragments (Hiatella solida) found in basal till suggest a Wisconsin age for the glaciation that incorporated them. The pattern of ice flow differed from that deduced for this area in the CLIMAP reconstruction. Following the maximum stage, there was a stadial event when outlet valley glaciers flowed from smaller ice caps into George VI Sound. More widespread recession permitted the George VI ice shelf to deposit Palmer Land erratics on eastern Alexander Island before isostatic recovery raised them to final elevations of about 82 m. The ice shelf may have been absent at about 6500 yr B.P., when large barnacles (Bathylasma corolliforme) were living in the sound. Small glaciers readvanced to form at least two terminal moraines before the ice shelf re-formed and incorporated the barnacle shells into its moraine on Alexander Island. The shells gave a ¹⁴C age (corrected for Antarctic conditions) of about 6500 yr B.P. and an amino acid ratio consistent with a Holocene age. Valley glaciers readvanced over the ice-shelf moraine before oscillations of both valley glaciers and the ice shelf led to the formation of the present sequence of contiguous ice-cored moraines, probably during the Little Ice Age. Such oscillations may represent a climatic control not yet observed in the dry valleys of Victoria Land, the only other part of Antarctica studied in detail for glacier fluctuations.     

Lateglacial and early Holocene palaeoclimatic reconstruction based on glacier fluctuations and equilibrium‐line altitudes at northern Folgefonna,Hardanger, western Norway

Northern Folgefonna (c. 23 km²), is a nearly circular maritime ice cap located on the Folgefonna Peninsula in Hardanger, western Norway. By combining the position of marginal moraines with AMS radiocarbon dated glacier‐meltwater induced sediments in proglacial lakes draining northern Folgefonna, a continuous high‐resolution record of variations in glacier size and equilibrium‐line altitudes (ELAs) during the Lateglacial and early Holocene has been obtained. After the termination of the Younger Dryas (c. 11 500 cal. yr BP), a short‐lived (100–150 years) climatically induced glacier readvance termed the ‘Jondal Event 1’ occurred within the ‘Preboreal Oscillation’ (PBO) c. 11 100 cal. yr BP. Bracketed to 10 550–10 450 cal. yr BP, a second glacier readvance is named the ‘Jondal Event 2’. A third readvance occurred about 10 000 cal. yr BP and corresponds with the ‘Erdalen Event 1’ recorded at Jostedalsbreen. An exponential relationship between mean solid winter precipitation and ablation‐season temperature at the ELA of Norwegian glaciers is used to reconstruct former variations in winter precipitation based on the corresponding ELA and an independent proxy for summer temperature. Compared to the present, the Younger Dryas was much colder and drier, the ‘Jondal Event 1’/PBO was colder and somewhat drier, and the ‘Jondal Event 2’ was much wetter. The ‘Erdalen Event 1’ started as rather dry and terminated as somewhat wetter. Variations in glacier magnitude/ELAs and corresponding palaeoclimatic reconstructions at northern Folgefonna suggest that low‐altitude cirque glaciers (lowest altitude of marginal moraines 290 m) in the area existed for the last time during the Younger Dryas. These low‐altitude cirque glaciers of suggested Younger Dryas age do not fit into the previous reconstructions of the Younger Dryas ice sheet in Hardanger. Copyright © 2005 John Wiley & Sons, Ltd.     

The Late Quaternary sedimentary record in Scoresby Sund, East Greenland

Until recently, little was known about the Quaternary marine sedimentary record in East Greenland. Geophysical and geological investigations in Scoresby Sund were undertaken to characterize the nature and chronology of this record. Seismic records show that almost 70% of the outer fjord system is covered by about 10 m of unlithified sediments, making direct correlation with the Quaternary records on land and the adjacent continental margin difficult. These acoustically unstratified sediments are scoured by icebergs above 550 m water depth. Almost 90% of core material is massive diamicton of Holocene age, deposited mainly from iceberg rafting and turbid meltwater. Sedimentation rates are 0.1 -0.3 m 1000 yr-¹. Thicker accumulations of unlithified Quaternary sediments in Scoresby Sund occur as sediment ridges and in two other major depocentres. A low sediment ridge runs across the mouth of Scoresby Sund, and is interpreted as an end moraine of Late Weichselian Flakkerhuk stadial age. The very restricted sediment thickness suggests that grounded ice filled the fjord during the Flakkerhuk and an ice shelf was not present. High inputs of ice rafted debris to the continental margin at about 18 000 BP indicate this as a probable age for the moraine. During the Allerød Interstadial, ice probably retreated from the outer fjord system, since massive diamictons similar to those of Holocene age are present at the base of most cores. A major depocentre of acoustically stratified sediments at the head of Hall Bredning is interpreted to represent ice proximal deposits from a glacier margin extending across the fjord. It is adjacent to dated moraines on land and is inferred to be of Milne Land stadial age (about 10 000 BP). A similar age is interpreted for acoustically laminated sediments and a moraine at the entrance of Vikingebugt, on the south side of Scoresby Sund. Dated kame terraces in the inner fjord system indicate that ice retreated to its present position 6–7000 years ago.     

Exposure ages from relict lateral moraines overridden by the Fennoscandian ice sheet

Lateral moraines constructed along west to east sloping outlet glaciers from mountain centred, pre-last glacial maximum (LGM) ice fields of limited extent remain largely preserved in the northern Swedish landscape despite overriding by continental ice sheets, most recently during the last glacial. From field evidence, including geomorphological relationships and a detailed weathering profile including a buried soil, we have identified seven such lateral moraines that were overridden by the expansion and growth of the Fennoscandian ice sheet. Cosmogenic ¹⁰Be and ²⁶Al exposure ages of 19 boulders from the crests of these moraines, combined with the field evidence, are correlated to episodes of moraine stabilisation, Pleistocene surface weathering, and glacial overriding. The last deglaciation event dominates the exposure ages, with ¹⁰Be and ²⁶Al data derived from 15 moraine boulders indicating regional deglaciation 9600 ± 200 yr ago. This is the most robust numerical age for the final deglaciation of the Fennoscandian ice sheet. The older apparent exposure ages of the remaining boulders (14,600-26,400 yr) can be explained by cosmogenic nuclide inheritance from previous exposure of the moraine crests during the last glacial cycle. Their potential exposure history, based on local glacial chronologies, indicates that the current moraine morphologies formed at the latest during marine oxygen isotope stage 5. Although numerous deglaciation ages were obtained, this study demonstrates that numerical ages need to be treated with caution and assessed in light of the geomorphological evidence indicating moraines are not necessarily formed by the event that dominates the cosmogenic nuclide data.     

Glacial geomorphology and chronology of deglaciation,South Georgia,sub-Antarctic

We mapped and dated the glacial geomorphology of north-east South Georgia, in the maritime sub-Antarctic. The aim was to examine the timing of deglaciation of the island in the context of inter-hemispheric phasing of climate change. Former glacier limits are restricted to the inner fjords, and our detailed mapping of them has demonstrated a consistent geomorphological pattern that is similar across several different glacier types and sizes. The pattern comprises three suites of moraines (categories “a–c”), not all of which are represented at every site because the outer suite is often overridden by younger suites. Category “a” is an outer wide, low amplitude moraine ridge, category “b” comprises 2–4 sharp-crested, bouldery moraines that are often located close to or even over-riding “a”, and category “c” is a series of lower amplitude moraines with overprinted streamlined landforms such as flutings. Analysis of in situ cosmogenic ¹⁰Be in boulders on these moraines has allowed us to determine a deglacial chronology for the older two moraine groups. The age of the inner (youngest) group has been estimated from soil development. The cosmogenic nuclide ages show that the outermost moraine was deposited ca 12.2±1.5 ka BP, but that a subsequent readvance in the mid-Holocene (ca 3.6±1.1 ka BP) reached and, in places, over-rode this earlier moraine. This latter advance coincides with the “Mid Holocene Hypsithermal”. A final Late Holocene advance reached closely similar limits to the previous two fluctuations and is estimated from soil data to have an age of ca 1.1 ka BP. We suggest that the close concordance of Late-Glacial and interglacial limits (in this case associated with warming) can be explained by a change in dominant forcing. During glacials, extensive sea-ice limits precipitation availability and so glaciers are restricted to the inner fjords. During interglacials precipitation is not limited in the same way by sea-ice cover and so during warming precipitation increases and tidewater glaciers on the island have responded by advancing. This study emphasises the importance of a clear understanding of geomorphology in order to interpret chronological information.     

The Ledsjö end moraine—a subaquatic push moraine composed of glaciomarine clay in central Sweden

During the Younger Dryas cold event, the Scandinavian ice sheet readvanced in southwest Sweden and formed the Middle Swedish end-moraine zone (MSEMZ). Recent highway construction near Skara has created an exposure through the prominent ridge at Ledsjö. Through sketching and measurement of structural information, we have documented the internal character of the Ledsjö moraine. The moraine consists predominantly of clay with numerous sand pods and lenses, which show undeformed, brittle deformed, or fluidized structures. Based on geomorphology and structural geology, it is clear the moraine was made during two advances. As ice advanced, proglacial marine clay was subglacially mobilized by the ice and extruded at the ice margin forming a ramp of debris-flow sediment. Contemporaneously, subglacial meltwater transported sand to the margin, where the meltwater became a buoyant plume, and sand was deposited near the ice margin by currents moving away from as well as toward the ice margin. These processes resulted in interbedded sand and clay. Continued advance of the ice margin deformed this package and further pushed the assemblage into a ridge form with gravity sliding of portions of the ridge. Prior to the second advance, sand was deposited on the proximal side of the initial ridge. During readvance, this sand was thrust faulted and intruded by mobilized clay. Up ice of the intruded sands, subglacial, extensional deformation created a complex shear zone of faulted sand and clay. The Ledsjö moraine represents a subaerial example of submarine push moraines like the submerged moraines recently documented in Svalbard.     

Submarine and onshore end moraines in southern Newfoundland: implications for the history of late Wisconsinan ice retreat

Recessional positions of the Newfoundland ice sheet 14-9 ka BP are represented by fjord-mouth submarine moraines, fjord-head emerged ice-contact marine deltas, and inland moraine belts. The arcuate submarine moraines have steep frontal ramparts and comprise up to 80 m of acoustically incoherent ice-contact sediment (or till) interfingered distally with glaciomarine sediment that began to be deposited c. 14.2 ka BP. The moraines formed by stabilization of ice that calved rapidly back along troughs on the continental shelf. The ice front retreated to fjord-heads and stabilized to form ice-contact delta terraces declining in elevation westward from +26 m to just below present sea level. Stratified glaciomarine sediments accumulated in fjords, while currents outside fjords eroded the upper part of the glaciomarine deposits, forming an unconformity bracketed by dates of 12.8 and 8.5 ka BP. The delta terraces are broadly correlated with the 12.7 ka BP Robinson's Head readvance west of the area. The ice front retreated inland, pausing three or four times to form lines of small bouldery stillstand moraines, heads of outwash, sidehill meltwater channels, and beaded eskers. Lake-sediment cores across this belt yield dated pollen evidence of three climatic reversals to which the moraines are equated: the Killarney Oscillation c. 11.2 ka BP, the Younger Dryas chronozone 11.0-10.4 ka BP, and an unnamed cold event c. 9.7 ka BP. Relative sea level fell in the early Holocene because of crustal rebound, so that outwash and other alluvium accumulated in deltas now submerged due to relative sea-level rise.     

In situ cosmogenic exposure ages from the Isle of Skye,northwest Scotland: implications for the timing of deglaciation and readvance from 15 to 11 ka

We present 10 in situ cosmogenic exposure ages from two moraines on the Isle of Skye. The Strollamus medial moraine was deposited during deglaciation of the Devensian ice sheet and yields a mean exposure age from five samples of 14.3 ± 0.9 ka. The moraine age indicates that a significant ice mass existed on Skye at the time of a regional readvance recorded in Wester Ross, northwest Scotland. Taken at face value the ages suggest that deglaciation did not occur until well into Greenland Interstade 1. The Slapin moraine represents the local limit of the Loch Lomond Readvance (LLR) and yields a mean exposure age from five samples of 11.5 ± 0.7 ka, which is consistent with deposition relating to the LLR. These ages suggest that the maximum extent may have been reached late in the stadial and that some glaciers may have remained active until after the climatic amelioration that marks its end. This scenario is considered unlikely given the nature of the climate during this period, which leads us to call for a locally calibrated production rate. Copyright © 2011 John Wiley & Sons, Ltd.