Ice Readvance Research Articles

Discussion on a revised model for the last deglaciation of eastern Scotland Journal , Vol. 164, 2007, 313–316

J. D. Peacock, M. Armstrong, M. A. E. Browne, N. R. Golledge & M. S. Stoker write: We are unable to support the view of McCabe et al . (2007) that there were significant readvances of the Scottish Ice-sheet at Lunan Bay and near Perth. The authors provide no criteria for readvances of glaciers such as terminal moraines, a second till and/or deforming bed, and rafting and overriding of marine sediments. However, we believe that the four new 14C dates in their table 1 are useful additions to knowledge. The supposed Perth Readvance in the type area . We agree that the till at the base of the Almondbank was produced by advancing ice. However, because such till is widespread in eastern Scotland, its occurrence does not of itself support the concept of a readvance, and none of the criteria noted above are satisfied. Indeed, the only indication of a possible very local readvance in the Perth area is near Moneydie, where a section formerly exposed two tills and highly deformed lacustrine silts (Paterson 1974). This we could attribute to the expected readjustment of ice-streams during retreat. Menzies & Van Der Meer (1998) concluded that the evidence here did not support a major readvance, but rather represented ‘a single winter event’. The package of sediments was described as ‘part of a tectonised, sub-glacial, deforming bed sequence’. In the upper Forth Estuary, near Grangemouth, Sissons & Smith (1965) showed that the Main Perth Shoreline is associated with the eastern limit of a stillstand or readvance of ice, which they correlated with the ‘Perth Readvance’. However, in the Tay–Earn area, the marine limit above the Main Perth Shoreline can be followed almost to Crieff, some 25 km west of Perth, where there are fluvial terraces relating to a sea level at …

Radiocarbon constraints on readvances of the British–Irish Ice Sheet in the northern Irish Sea Basin during the last deglaciation

Moraines deposited by the Dundalk Bay ice lobe record two readvances of the Irish Ice Sheet into the northern Irish Sea Basin during the last deglaciation. These readvances overrode and incorporated fossiliferous marine muds from the floor of Dundalk Bay. AMS 14C dates from monospecific microfaunas obtained from these muds indicate that the earlier (Clogher Head) readvance occurred sometime between 15.0 and 14.2 14C ka BP, thus identifying a previously unrecognized ice-margin fluctuation in the Irish Sea Basin that is correlative with a readvance in northwest Ireland. The younger readvance occurred after 14.2 14C ka BP and is equivalent to the Killard Point readvance identified elsewhere in the Irish Sea Basin. These readvances occurred during the Oldest Dryas cold interval and bracket Heinrich event 1. Raised marine muds that were deposited between ice readvances require that a substantial ice sheet remained on Ireland throughout much of the last deglaciation, with attendant isostatic depression of at least 110 m.

Re-advance of the Fennoscandian Ice Sheet during Heinrich Event 1

Five sediment cores, bathymetric and 2D seismic reflection data from Vestfjorden, northern Norway, were studied in order to constrain the timing and extent of a major ice stream draining the northwestern Fennoscandian Ice Sheet during the last deglaciation (15–10 14C ka B.P.). The bathymetric and seismic data indicate that Vestfjorden/Trænadjupet was covered by grounded ice reaching the shelf break during the Last Glacial Maximum (LGM). After the LGM break-up and recession towards outer inner Vestfjorden at ∼ 13.6 14C ka B.P., the ice re-advanced towards the outer part of Vestfjorden prior to 13.1 14C ka B.P. This is inferred from glaciomarine sediments overlain by diamicton at the base of the sediment cores interpreted as basal tills and associated contemporaneous build-up of grounding zone wedges in the central Vestfjorden. This sequence of events is coherent with the late Weichselian ice sheet dynamics both along the western Norwegian continental shelf and in the Barents Sea, possibly indicating a direct response to meltwater injection and accompanied cooling during disruption of the thermohaline circulation associated with Heinrich Event 1. Enhanced supply of suspension load resulted in deposition of laminated sediments at ∼ 13 14C ka B.P. reflecting the retreat of the ice stream towards the inner fjord in response to global climate amelioration and increased Atlantic water inflow. Two additional ice re-advances towards the Norwegian coastline are inferred from distinct input of ice-rafted debris (IRD) with a typical mineralogical fingerprint derived from Neoproterozoic–Early Silurian calcite and dolomite marbles in the ice sheet catchment area. Thus, the re-advances may be concurrent with the Older Dryas (∼ 12.2 14C ka B.P., Skarpnes) and Younger Dryas (∼ 10.7 14C ka B.P., Tromsø Lyngen) cooling events.

The paradox of the global standard Late Ordovician–Early Silurian sea level curve: Evidence from conodont community analysis from both Canadian Arctic and Appalachian margins

Relative sea level fluctuations in the Late Ordovician–Early Silurian were largely driven by Gondwana deglaciation, three possible short-lived ice readvances, and the closure of the Iapetus Ocean. This study establishes and compares sea level events on the Canadian Arctic and Appalachian margins of Laurentia based on the pattern of conodont communities, and demonstrates that sea level events were not synchronous on the two margins. Conodont data were compared for a) the Arctic margin from the Cape Phillips Formation (Richmondian, Upper Ordovician through lower Sheinwoodian, Lower Silurian), Cornwallis Island, Canadian Arctic Islands, and b) the Appalachian margin from the upper Ellis Bay, Becscie, Merrimack, Gun River, Jupiter and Chicotte formations (Richmondian, Upper Ordovician, Rhuddanian, Aeronian, and most of Telychian, Lower Silurian), Anticosti Island, Quebec. The pattern of Late Ordovician–Early Silurian conodont communities is established based on three cluster analyses on conodonts from Cornwallis Island (4967 specimens representing 54 species from 77 samples, Cape Phillips Formation) and Anticosti Island (1980 specimens representing 21 species from 25 samples, upper Ellis Bay Formation; 24,839 specimens representing 42 species from 123 samples, Becscie, Merrimack, Gun River, Jupiter and Chicotte formations). Overall, the sea level curves inferred from the distribution of the conodont communities from Cornwallis and Anticosti exhibit gradual and rapid oscillating patterns, respectively. Specifically, during the time interval of the latest Ordovician and the Early Silurian (Rhuddanian), the sea level behaved differently in these two regions: 1) during the latest Ordovician, conodont community changes show the different patterns in the two regions, which reflects a transgression on Cornwallis, but a regression on Anticosti; 2) during the earliest Rhuddanian, similar conodont communities arose in both regions, but they indicate a regression on Cornwallis and a transgression on Anticosti; 3) in the early Rhuddanian, these communities were replaced by a deeper water community on Cornwallis and a shallower water community on Anticosti, which suggest a transgression on Cornwallis and a regression on Anticosti; 4) a highstand drove out almost all conodonts from Anticosti by the end of Rhuddanian, which is not seen on Cornwallis; 5) a deep-water conodont community remained almost unchanged on Cornwallis from the late Rhuddanian to the early Aeronian, whereas a shallow water conodont community returned to Anticosti in the early Aeronian. However, the sea level dropped on both Cornwallis and Anticosti during the late Telychian, and the sea level curves show a similar pattern. The difference in the sea level pattern during the late Richmondian, Rhuddanian and Aeronian on both the northern and southern margins of Laurentia reflected by conodont communities is supported by the studies on Quaternary glaciation/deglaciation events, where the melting of an ice sheet was accompanied by sea level change but with variable regional isostatic effects that do not generate a uniform global eustatic signal.

A glacial stage spanning the antarctic cold reversal in torres del paine (51°s), chile, based on preliminary cosmogenic exposure ages

ABSTRACT. Initial cosmogenic 10Be results from a former ice limit in Torres del Paine indicate a shortlived stillstand or readvance of Patagonian ice culminating at 12–15 kyr BP with a mean age of 13.2 ± 0.8 kyr BP. The glacier extended some 40 km beyond the present ice margin and was within 15 km of the presumed Last Glacial Maximum limits. The timing of the glacier stage spans the cooling event recorded in Antarctic ice cores, termed the Antarctic Cold Reversal (14.5–12.9 kyr BP). This result implies that glaciers at these latitudes were out of phase with those in the northern hemisphere; instead they mirrored the climate structure of Antarctica during the last glacial to interglacial transition.

Deglacial chronology from County Donegal, Ireland: implications for deglaciation of the British–Irish ice sheet

In the north of Ireland ice advanced northwards onto the continental shelf from inland centres of dispersion at the last glacial maximum. We constrain the timing of three subsequent events by accelerator mass spectrometry 14 C dating of marine microfaunas from muds at Corvish, County Donegal. Early and rapid deglaciation of the continental shelf off northwestern Ireland occurred before 17.1 k 14 C years bp when marine muds formed in Trawbreaga Bay. Ice subsequently readvanced into the bay some time between 15.0 and 14.0 k 14 C years bp and compressed contemporary sea stacks and beach cobbles into a ridge at Ballycrampsey. Early deglacial muds were deformed during this ice readvance and redeposited with stratigraphically inverted 14 C ages between 16.0 and 15.2 k 14 C years bp. The deformed mud is overlain by undeformed laminae deposited during the final deglaciation of the area after 14.1 k 14 C years bp. The early deglaciation in the north at c . 17 k 14 C years bp is correlative with deglaciation recorded in the Irish Sea Basin, western Ireland and northeastern Scotland, indicating a response of the entire British–Irish ice sheet to early warming of the North Atlantic Ocean that resulted in a loss of up to two-thirds of its mass. Subsequent ice-sheet readvance between 15.0 and 14.1 k 14 C years bp in the north is part of a widespread response of the British–Irish ice sheet to Heinrich event 1 during the Killard Point Stadial. High relative sea levels that accompanied deglaciation at 17 k 14 C years bp and again at 14.1 k 14 C years bp indicate substantial loading and attendant isostatic depression by the British–Irish ice sheet.

Late Devensian marine deposits (Errol Clay Formation) at the Gallowflat Claypit, eastern Scotland: new evidence for the timing of ice recession in the Tay Estuary

Synopsis The Late Devensian arctic marine deposits (Errol Clay Formation) at the Gallowflat Claypit between Perth and Dundee are correlated with the type succession at nearby Inchcoonans, but include an expanded basal glaciomarine unit with rhythms interpreted as symmict varves. Laminated silt–clay couplets are thought to be tidal. Conditions were fully marine by 13.8 ka bp (based on new radiocarbon dates and a 400 a reservoir age). Following recession of the Tay–Forth glacier from its advanced Late Devensian position at the Wee Bankie Terminal Moraine, it is inferred that deglaciation of the middle Tay estuary some 100 km to the west took place between 14.5 and 14 ka bp . The possibility that there was a readvance of ice in the Tay and Forth estuaries during or close to the Heinrich iceberg discharge event H1 is briefly discussed.

Late Wisconsinan stratigraphy and chronology of southern St. George's Bay, Newfoundland: a re-appraisal: Discussion

A sedimentological model has been presented by Bell et al. (2001) to explain the stratigraphy and chronology of glacigenic sediments at localities in southern St. George’s Bay, west Newfoundland. These authors claim that this model succeeds earlier interpretations of the sediments at these localities made by MacClintock and Twenhofel (1940) and Brookes (1969, 1974, 1977 a ), and, by implication, find fault with the history of late-glacial relative sea level for these localities and the wider area presented in Brookes (1974, 1977 a ) and, with some revision, in Forbes et al. (1993). This note draws attention to two points of difference I have with Bell et al. (2001) at the local and regional scales, namely the applicability of the adopted sedimentological model and the relation of the sediments concerned to late-glacial sea level. MacClintock and Twenhofel (1940) presented an inventory and interpretation of glacial and associated sediments exposed in tens of kilometres of coastal cliffs around St. George’s Bay (well portrayed in Bell et al. 2001, fig. 4). They divided the sediments into ( i ) a compact basal till, low in the cliffs, overlain in places by kame gravels — named “St. George’s River Drift,” ( ii ) an overlying marine sequence, comprising lower muds and higher deltaic sands and gravels, in places underlying a delta surface — named “Bay St. George Delta,” and ( iii ) in a few places, an upper unit of till and kame gravel, with morainic topography — named “Robinsons Head Drift.” The sequence was interpreted to have resulted from an ice advance beyond the present coast of the bay, followed by ice retreat and local stagnation at the present coast, then by marine submergence, and, finally, an ice readvance in several lobes across the present coastline into the sea and sediments previously deposited in it. Brookes (1969, 1974, 1977 …

Bedform patterns, subglacial meltwater events, and Late Devensian ice sheet dynamics in north-central Ireland

Glacial bedform patterns and sediments deposited by the temperate and polythermal Late Devensian ice sheet in north-central Ireland record changes in the processes, location, and magnitude of subglacial meltwater throughout the last full glacial cycle (∼21–14 14C kyear BP). Meltwater characteristics are related directly to basal ice thermal regime and ice dynamics, including ice velocity and shifts in the location of ice centres. Therefore, reconstructed meltwater characteristics may provide insight into wider controls on dynamic ice behaviour. A range of meltwater-related features are present across north-central Ireland. These include tunnel valleys, drumlin leeside sequences, eskers, and boulder lags. Other bedforms including Rogen moraines were modified by meltwater activity along ice streams. Meltwater was stored subglacially in two contrasting regions located beneath or near ice centres in north-central Ireland. (1) The Lough Erne Basin is developed in a lowland depression occupied partly by subglacial Rogen moraine ridges which were formed around the time of the last glacial maximum. Meltwater was stored between Rogen ridge crests and released by hydraulic jacking associated with drumlinisation (∼16.6 14C kyear BP) and ice streaming (∼13.8 14C kyear BP). (2) The Lough Neagh Basin occupies a similar lowland depression and was the location of an ice sheet centre throughout the last glacial cycle. No bedforms are present beneath or immediately surrounding Lough Neagh. A larger, more continuous meltwater lake existed in the Lough Neagh depression, probably sealed by a region of cold-based ice outside lake margins. Water escaped through regional-scale tunnel valleys, particularly the Poyntzpass channel which was active during the Carlingford ice readvance (Killard Stadial, correlated with Heinrich event 1 at ∼14.5 14C kyear BP). Overall, reconstructed subglacial lake characteristics and drainage mechanisms are related closely to basal ice thermal regime and substrate relief (controlling lake geometry), and provide insight into controls on overall ice sheet dynamics.

Late Paleozoic glaciotectonic structures in northern Paraná Basin, Brazil

Fluviatile–deltaic sediments containing thin coal layers, and glaciofluvial sediments of the Itararé Subgroup (late Paleozoic) cropping out near Cerquilho, northern Paraná Basin, exhibit post-depositional deformation such as recumbent and drag folds, shear fractures, faults and shear lamination. The deformation occurs in an interval of 3–4 m thick and is confined between horizontal strata. The deformed strata are directly overlain along a horizontal erosional/tectonic contact surface by a silty–sandy, massive, 1 m thick, clast-poor tillite. Deformation shows a consistent geometry indicating a predominant vergence toward the SSW having been developed under a horizontal stress oriented from NNE to SSW. The deformation is interpreted to be of glaciotectonic origin associated with an ice readvance in the area. The glacier moved toward the SSW on relatively soft, deformable sediments, depositing the subglacial till on top of them. The tillite shows parallel, upglacier-dipping shear fractures at its base and wedge-like intrusions into the underlying sandstone, probably formed during its subglacial deposition. The tillite is overlain by cyclic (braided stream) fluviatile, sandstone beds. The top of these shows deformations (small recumbent folds and reverse faults) below another clast-poor, silty–sandy tillite. This could represent another glacial readvance with subglacial deposition of till. Occurrence of glaciotectonic deformation overlain by subglacially deposited tillites in the Cerquilho area indicates glacier readvances and permanence of the glacial influence in the upper part of the Itararé Subgroup. Absence of incorporated material from the underlying deformed sediments in the tillite and the style of the deformations suggest an unfrozen, water-saturated, mostly unconsolidated substratum. These conditions may have generated instability and fast ice flow of the glacier. They also suggest that the sediment may have most likely failed in this manner under rapidly applied stresses associated with a surging behavior of the retreating glacier.

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.

Sedimentological and micromorphological examination of a Late Devensian multiple diamicton sequence near Moneydie, Perthshire, east-central Scotland

Synopsis Re-investigation of a site at Shochie Burn near Moneydie in east-central Scotland suggests that earlier interpretations need to be modified. At this site, in the past, two tills were recognized as indicative of two separate ice advances. Previously, this site was known as a stratotype for the Perth Readvance in eastern Scotland. The evidence for a regional readvance is no longer accepted but the two-till problem remains unexplained. Present investigations suggest that the two tills are part of a large package of sediments deposited as stacked layers of a subglacial deforming bed that have been tectonized by a very short and local ice readvance perhaps of the type that occurs as a winter readvance. Sedimentological and micromorphological evidence points to the tills as not being separate but of the same depositional phase undergoing subglacial deformation and/or local marginal tectonization following subglacial transport in a deforming bed environment resulting in the incorporation of proximal outwash sediments. The till at Shochie Burn exhibits evidence, both at the macro- and microscale, of intense deformation under high porewater pressures that are attributable to the strong plasmic microstructures, fold structures, shear zones, Riedel shears, and of possible submarginal freezing conditions resulting in localized brecciation and foliation structure development. This is the first site in this area to indicate the presence of subglacial deforming bed conditions followed by marginal glaciotectonism, therefore continued research is necessary to establish this modified view of subglacial conditions in this part of Scotland.

The Preboreal oscillation around the Nordic Seas: terrestrial and lacustrine responses

The occurrence of an early Preboreal climatic cooling/oscillation (PBO) in lacustrine and glacial records from northwest Europe, Iceland and Greenland is reviewed and documented. The often subtle response of the proxy records to this oscillation, in combination with its short duration, make it difficult to detect. Owing to its chronostratigraphic position between the 10000–9900 and 9600–9500 14C plateaux (c. 11300–11150 calendar yr BP) it is also difficult to 14C date with precision. We find that the vegetation response to the PBO varies between sites and regions. In contrast to the pioneer vegetation in Iceland and southern Sweden, the expanding birch–pine forest in Germany–Denmark was more susceptible to deteriorating growing conditions. The combined lacustrine, tree-ring and glacial records imply that the PBO was characterised by cool and humid conditions throughout northwestern and central Europe. This is documented by vegetation changes, decreased aquatic production, increased soil erosion, increased 2H and 13C content in tree-rings, readvances or stillstands of the ice sheet in Norway and Finland, and ingression of brackish water into the Baltic. Icelandic proxy records from lake sediments and glacial moraines imply cooler conditions than during the previous Preboreal period, but not as extreme as during the Younger Dryas. Greenland records suggest that the early Preboreal was characterised by ice readvances, as an effect of cool climate and increased precipitation (in relation to the Younger Dryas). It was not until the end of the PBO that climate was warm enough to melt the land-based ice sheet. This Preboreal oscillation, found on both sides of the Nordic Seas, is interpreted as an effect of increased freshwater forcing on the thermohaline circulation in the Nordic Seas, which is implied by a simultaneous and distinct rise in the atmospheric 14C/12C ratio. A slow-down of the thermohaline circulation may temporarily have pushed the Polar Front further south. © 1997 John Wiley & Sons, Ltd.

The Preboreal oscillation around theNordic Seas: terrestrial and lacustrine responses

The occurrence of an early Preboreal climatic cooling/oscillation (PBO) in lacustrine and glacial records from northwest Europe, Iceland and Greenland is reviewed and documented. The often subtle response of the proxy records to this oscillation, in combination with its short duration, make it difficult to detect. Owing to its chronostratigraphic position between the 10000–9900 and 9600–9500 14C plateaux (c. 11300–11150 calendar yr BP) it is also difficult to 14C date with precision. We find that the vegetation response to the PBO varies between sites and regions. In contrast to the pioneer vegetation in Iceland and southern Sweden, the expanding birch–pine forest in Germany–Denmark was more susceptible to deteriorating growing conditions. The combined lacustrine, tree-ring and glacial records imply that the PBO was characterised by cool and humid conditions throughout northwestern and central Europe. This is documented by vegetation changes, decreased aquatic production, increased soil erosion, increased 2H and 13C content in tree-rings, readvances or stillstands of the ice sheet in Norway and Finland, and ingression of brackish water into the Baltic. Icelandic proxy records from lake sediments and glacial moraines imply cooler conditions than during the previous Preboreal period, but not as extreme as during the Younger Dryas. Greenland records suggest that the early Preboreal was characterised by ice readvances, as an effect of cool climate and increased precipitation (in relation to the Younger Dryas). It was not until the end of the PBO that climate was warm enough to melt the land-based ice sheet. This Preboreal oscillation, found on both sides of the Nordic Seas, is interpreted as an effect of increased freshwater forcing on the thermohaline circulation in the Nordic Seas, which is implied by a simultaneous and distinct rise in the atmospheric 14C/12C ratio. A slow-down of the thermohaline circulation may temporarily have pushed the Polar Front further south. © 1997 John Wiley & Sons, Ltd.

Drumlin evolution and ice sheet oscillations along the NE Atlantic margin, Donegal Bay, western Ireland

Satellite imagery of Donegal Bay, northwestern Ireland, reveals two streamlined subglacial bedform sets produced during the late Devensian glaciation (ca. 22,000–15,000 yrs B.P.). The first bedform set trends northeast-southwest and records fast ice flow from inland ice domes onto the eastern Atlantic continental shelf. The second bedform set, trending east-west, crosscuts and partially reorientates the first. Morphological and sedimentary evidence show that the second set corresponds to the last phase of fast ice flow (drumlinization) in northwestern Ireland. Morphological characteristics of the Donegal Bay drumlin field, and sedimentary characteristics of the Mullinasole drumlin, Donegal Bay, support a two-stage interpretation of drumlin evolution. These are the following. (1) Deposition of glaciomarine mud and diamict facies at a tidewater glacier margin. Stratified diamicts record debris flow events and sediment reworking. This facies sequence is erosionally truncated. (2) Deposition of subglacial diamict and sand facies recording ice readvance and drumlinization. Drumlinization (sediment streamlining) reflects ice mass-balance destabilization, episodic: fast ice flow and ice-marginal oscillation, and may be correlated with millennial-time scale climate changes in the circum-North Atlantic.

Abrupt changes in marine conditions, Sunneshine Fiord, eastern Baffin Island, NWT during the last deglacial transition: Younger Dryas and H-0 events

Abstract Sunneshine Fiord is a shallow fiord that lies at the easternmost tip of Baffin Island, NWT, c . 66°33′ N on the western end of Davis Strait, a 600 m deep sill that links Baffin Bay to the north with the Labrador Sea and the North Atlantic in the south. Offshore surface circulation today consists principally of the southward transport of Polar Water in the Baffinland Current. Raised marine deposits in the outer part of the fiord are radiocarbon dated at >57 ka and can be associated with large lateral moraines on both walls of the fiord; Holocene raised marine sediments appear to be absent. A gravity and piston core together (HU82-031-SU5) sample about 8.5 m of the sediment fill. Nine AMS 14 C dates on marine shells and foraminifera indicate that the coring recovered sediments that span around 14 calibrated (cal) of record. Seismic surveys indicate that the upper sediment is acoustically transparent and overlies acoustically stratified materials. There is a major reflector towards the base of the cored section. Analyses of physical properties, lithofacies and biofacies indicate that there is a very sharp break in the record at around 12.4 cal ka, which is interpreted as a change from relatively ice-distal conditions to one characterized by a dramatic increase in cold, ice-proximal foraminiferal benthic species, notably Elphidium excavata forma clavata . At the same time, there was an extremely abrupt increase in detrital carbonate, most of which is dolomite. Because there is no known local source of detrital carbonate within the fiord, this abrupt event signals an increase in the transport of detrital carbonate derived from icebergs and/or meltwater from sources further north in Baffin Bay, or immediately to the south from Cumberland Sound. The onset of this event at 12. 4 cal ka is synchronous with evidence for an abrupt increase in detrital calcitic carbonate emanating from an ice re-advance within and probably across Hudson Strait. These events are the probable source of detrital calcitic carbonate in the northwestern North Atlantic associated with the Younger Dryas cold period and iceberg rafting event, H-0.

Glacial geological evidence for the medieval warm period

It is hypothesised that the Medieval Warm Period was preceded and followed by periods of moraine deposition associated with glacier expansion. Improvements in the methodology of radiocarbon calibration make it possible to convert radiocarbon ages to calendar dates with greater precision than was previously possible. Dating of organic material closely associated with moraines in many montane regions has reached the point where it is possible to survey available information concerning the timing of the medieval warm period. The results suggest that it was a global event occurring between about 900 and 1250 A.D., possibly interrupted by a minor readvance of ice between about 1050 and 1150 A.D.

A reinterpretation of Scottish ‘hummocky moraine’ and its significance for the deglaciation of the Scottish Highlands during the Younger Dryas or Loch Lomond Stadial

AbstractThe aim of this paper is to demonstrate that much of the ‘hummocky moraine’ present within the northern part of the LochLomond Readvance ice cap formerly situated in the North West Scottish Highlands may be interpreted as suites of ice-front moraines deposited during active decay. These landforms can be used to reconstruct ice cap decay, whichleads to important insights into the shrinking form of the ice cap and associated environmental conditions. Evidence has been collected from 10803 airphotographs and from detailed field survey. It is presented at three spatial scales.

Younger Dryas‐age readvance of Laurentide ice into the Champlain Sea

Occurrences of Balanus hameri‐bearing diamicts described in this paper and pertinent (Balanus plates and pelecypods shells) 14C dates suggest that there was glacial activity in the Champlain Sea basin between 11,000 BP and 10,400 BP and that this activity can be ascribed to a climatic cooling episode correlative with the Younger Dryas of the late‐glacial sequence of northeastern Europe.

Seismic architecture and sedimentation in northwest Spitsbergen fjords

Acoustic records from several Spitsbergern fjords yield a characteristic sedimentary architecture. Subaqueous fans (1–3° surface slope), fed by tidewater glacier-derived sediments, are particularly well developed. An upper fan has been built on an underlying fan in response to a shift in the position of the tidewater glacier sediment source. The sequence of tidewater glacier fluctuations and sedimentation since the Late Weichselian, interpreted from seismic records, comprises the following: (1) Deposition of an acoustically transparent unit, interpreted as either basal till deposited during Late Weichselian glaciation or a glacimarine unit formed during early, rapid ice retreat. (2) Ice retreat up fjords by about 9000–10,000 yrs B.P. (3) Deposition of a lower fan complex over several thousand years, and slow infilling of bedrock-controlled basins in more ice distal locations. (4) Ice readvance to 2–3 km beyond modern ice margins, linked to Little Ice Age climatic deterioration from the 13–14th century. Overriding of part of the lower fan complex, inducing deformation. (5) Deposition of Little Ice Age submarine terminal moraines and basal till by readvancing glaciers. Deposition of the upper fan during 500 yr Little Ice Age ice advance. (6) Retreat of tidewater glacier termini to their present positions since Little Ice Age termination at the end of the 19th century. Deposition of a thin veneer of sediment inside the Little Ice Age submarine moraines as glacier retreat takes place.