scholarly journals The implications of the Pineo Ridge readvance in Maine

2011 ◽  
Vol 31 (3-4) ◽  
pp. 203-206 ◽  
Author(s):  
Harold W. Borns ◽  
Terence J. Hughes
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Bay Of Fundy ◽  
Great Lakes Region ◽  
Ice Streams ◽  
Ice Caps ◽  
Major Consequence ◽  
Ice Cap ◽  
The North

Much of the Laurentide ice sheet in Maine, Atlantic Provinces, and southern Quebec was a "marine ice sheet," that is it was grounded below the prevailing sea level. When proper conditions prevailed, calving bays progressed into the ice sheet along ice streams partitioning it, leaving those portions grounded above sea level as residual ice caps. At least by 12,800 yrs. BP a calving bay had progressed up the St. Lawrence Lowland at least to Ottawa while a similar, but less extensive calving bay developed in Central Maine at approximately the same time. Concurrently, ice draining north into the St. Lawrence and south into the Central Maine calving bays rapidly lowered the surface of the intervening ice sheet until it eventually divided over the NE-SW trending Boundary and Longfellow Mountains and probably over other highland areas as well. A major consequence of these nearly simultaneous processes was the separation of an initial large ice cap over part of Maine, New Brunswick, and Québec which was bounded on the west by the calving bay in Central Maine, to the north by the calving bay in the St. Lawrence Lowland, to the south by the Bay of Fundy, and to the east by the Gulf of St. Lawrence. In coastal Maine, east of the calving bay, the margin of the ice cap receded above the marine limit at least 40 km and subsequently read-vanced terminating at Pineo Ridge moraine approximately 12,700 yrs. BP. These events are the stratigraphie and chronologic equivalent of the Cary-Pt. Huron recession/Pt. Huron readvance of the Great Lakes region.

scholarly journals Late Pleistocene and Holocene glaciation and deglaciation of Melville Peninsula, Northern Laurentide Ice Sheet

2004 ◽  
Vol 55 (2) ◽  
pp. 159-170 ◽  
Author(s):  
Lynda A. Dredge
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
North Coast ◽  
Baffin Island ◽  
Ice Flow ◽  
Ice Caps ◽  
The North ◽  
Northern Areas ◽  
Controlled Flow

Abstract Melville Peninsula lies within the Foxe/Baffin Sector of the Laurentide Ice Sheet. Pre-Foxe/Pre-Wisconsin ice may have covered the entire peninsula. Preserved regolith in uplands indicates a subsequent weathering interval. Striations and till types indicate that, during the last (Foxe) glaciation, a local ice sheet (Melville Ice) initially developed on plateaus, but was later subsumed by the regional Foxe ice sheet. Ice from the central Foxe dome flowed across northern areas and Rae Isthmus, while ice from a subsidiary divide controlled flow on southern uplands. Ice remained cold-based and non-erosive on some plateaus, but changed from cold- to warm-based under other parts of the subsidiary ice divide, and was warm-based elsewhere. Ice streaming, generating carbonate till plumes, was prevalent during deglaciation. A late, quartzite-bearing southwestward ice flow from Baffin Island crossed onto the north coast. A marine incursion began in Committee Bay about 14 ka and advanced southwards to Wales Island by 8.6 ka. The marine-based ice centre in Foxe Basin broke up about 6.9 ka. Northern Melville Peninsula and Rae Isthmus were deglaciated rapidly, but remnant ice caps remained active and advanced into some areas. The ice caps began to retreat from coastal areas ~6.4 to 6.1 ka, by which time sea level had fallen from 150-180 m to 100 m.

scholarly journals The Dynamics of Marine Ice Sheets

1979 ◽  
Vol 24 (90) ◽  
pp. 167-177 ◽  
Author(s):  
Robert H. Thomas
Keyword(s):  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Shelves ◽  
The North ◽  
West Antarctic ◽  
Grounding Line ◽  
Ice Sheet Dynamics

AbstractMarine ice sheets rest on land that, for the most part, is below sea-level. Ice that flows across the grounding line, where the ice sheet becomes afloat, either calves into icebergs or forms a floating ice shelf joined to the ice sheet. At the grounding line there is a transition from ice-sheet dynamics to ice-shelf dynamics, and the creep-thinning rate in this region is very sensitive to sea depth; rising sea-level causes increased thinning-rates and grounding-line retreat, falling sea-level has the reverse effect. If the bedrock slopes down towards the centre of the ice sheet there may be only two stable modes: a freely-floating ice shelf or a marine ice sheet that extends to the edge of the continental shelf. Once started, collapse of such an ice sheet to form an ice shelf may take place extremely rapidly. Ice shelves which form in embayments of a marine ice sheet, or which are partially grounded, have a stabilizing influence since ice flowing across the grounding line has to push the ice shelf past its sides. Retreat of the grounding line tends to enlarge the ice shelf, which ultimately may become large enough to prevent excessive outflow from the ice sheet so that a new equilibrium grounding line is established; removal of the ice shelf would allow retreat to continue. During the late-Wisconsin glacial maximum there may have been marine ice sheets in the northern hemisphere but the only current example is the West Antarctic ice sheet. This is buttressed by the Ross and Ronne Ice Shelves, and if climatic warming were to prohibit the existence of these ice shelves then the ice sheet would collapse. Field observations suggest that, at present, the ice sheet may be advancing into parts of the Ross Ice Shelf. Such advance, however, would not ensure the security of the ice sheet since ice streams that drain to the north appear to flow directly into the sea with little or no ice shelf to buttress them. If these ice streams do not flow over a sufficiently high bedrock sill then they provide the most likely avenues for ice-sheet retreat.

scholarly journals The Dynamics of Marine Ice Sheets

1979 ◽  
Vol 24 (90) ◽  
pp. 167-177 ◽  
Author(s):  
Robert H. Thomas
Keyword(s):  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Shelves ◽  
The North ◽  
West Antarctic ◽  
Grounding Line ◽  
Ice Sheet Dynamics

AbstractMarine ice sheets rest on land that, for the most part, is below sea-level. Ice that flows across the grounding line, where the ice sheet becomes afloat, either calves into icebergs or forms a floating ice shelf joined to the ice sheet. At the grounding line there is a transition from ice-sheet dynamics to ice-shelf dynamics, and the creep-thinning rate in this region is very sensitive to sea depth; rising sea-level causes increased thinning-rates and grounding-line retreat, falling sea-level has the reverse effect. If the bedrock slopes down towards the centre of the ice sheet there may be only two stable modes: a freely-floating ice shelf or a marine ice sheet that extends to the edge of the continental shelf. Once started, collapse of such an ice sheet to form an ice shelf may take place extremely rapidly. Ice shelves which form in embayments of a marine ice sheet, or which are partially grounded, have a stabilizing influence since ice flowing across the grounding line has to push the ice shelf past its sides. Retreat of the grounding line tends to enlarge the ice shelf, which ultimately may become large enough to prevent excessive outflow from the ice sheet so that a new equilibrium grounding line is established; removal of the ice shelf would allow retreat to continue. During the late-Wisconsin glacial maximum there may have been marine ice sheets in the northern hemisphere but the only current example is the West Antarctic ice sheet. This is buttressed by the Ross and Ronne Ice Shelves, and if climatic warming were to prohibit the existence of these ice shelves then the ice sheet would collapse. Field observations suggest that, at present, the ice sheet may be advancing into parts of the Ross Ice Shelf. Such advance, however, would not ensure the security of the ice sheet since ice streams that drain to the north appear to flow directly into the sea with little or no ice shelf to buttress them. If these ice streams do not flow over a sufficiently high bedrock sill then they provide the most likely avenues for ice-sheet retreat.

Late Wisconsinan glaciation of Amund and Ellef Ringnes islands, Nunavut: evidence for the configuration, dynamics, and deglacial chronology of the northwest sector of the Innuitian Ice Sheet

2003 ◽  
Vol 40 (3) ◽  
pp. 351-363 ◽  
Author(s):  
Nigel Atkinson
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Marine Fauna ◽  
Ice Flow ◽  
Ice Caps ◽  
Ice Cap ◽  
Sequential Entry ◽  
Data Record ◽  
Late Wisconsinan ◽  
Glacial Landforms

Geomorphic and chronologic evidence from Amund and Ellef Ringnes islands documents the configuration, dynamics, and collapse of the northwest sector of the Innuitian Ice Sheet. These data record the inundation of the Ringnes Islands by northwestward-flowing ice from divides spanning the alpine and lowland sectors of the Innuitian Ice Sheet. Ice-flow indicators and granite dispersal along eastern Amund Ringnes Island suggest Massey Sound was filled by an ice stream discharging coalescent alpine and lowland ice from Norwegian Bay. In contrast, the interior of Amund Ringnes Island was overridden by predominantly non-erosive, granite-free ice from a divide in the lowland sector of the ice sheet. Glacial landforms on Ellef Ringnes Island record coverage by largely non-erosive ice, but it remains uncertain whether these features relate to northward-flowing lowland ice or a cold-based local ice cap. Deglaciation of the Ringnes Islands commenced ~10 000 14C years ago. Deglacial dates between 9.7 and 9.2 ka BP record the sequential entry of marine fauna along Massey and Hassel sounds, concomitant with the southward retreat of trunk ice towards Norwegian Bay. These data suggest marine-based trunk glaciers were vulnerable to calving during pre-Holocene eustatic sea-level rise. However, deglacial dates from inner embayments indicate that residual ice caps persisted on Amund and Ellef Ringnes islands for 800 to 1400 14C years after retreat of trunk ice from the adjacent marine channels. Lateral meltwater channels record the subsequent retreat of these ice caps, which became increasingly confined within upland valleys after 8.6 ka BP.

scholarly journals The Last Scottish Ice Sheet

2018 ◽  
Vol 110 (1-2) ◽  
pp. 93-131 ◽  
Author(s):  
Colin K. BALLANTYNE ◽  
David SMALL
Keyword(s):  
North Sea ◽  
Ice Sheet ◽  
Irish Sea ◽  
Ice Streams ◽  
East Anglia ◽  
Ice Cap ◽  
The North ◽  
Outer Hebrides ◽  
Moray Firth ◽  
The North Sea

ABSTRACTThe last Scottish Ice Sheet (SIS) expanded from a pre-existing ice cap after ∼35 ka. Highland ice dominated, with subsequent build-up of a Southern Uplands ice mass. The Outer Hebrides, Skye, Mull, the Cairngorms and Shetland supported persistent independent ice centres. Expansion was accompanied by ice-divide migration and switching flow directions. Ice nourished in Scotland reached the Atlantic Shelf break in some sectors but only mid-shelf in others, was confluent with the Fennoscandian Ice Sheet (FIS) in the North Sea Basin, extended into northern England, and fed the Irish Sea Ice Stream and a lobe that reached East Anglia. The timing of maximum extent was diachronous, from ∼30–27 ka on the Atlantic Shelf to ∼22–21 ka in Yorkshire. The SIS buried all mountains, but experienced periods of thickening alternating with drawdown driven by ice streams such as the Minch, the Hebrides and the Moray Firth Ice Streams. Submarine moraine banks indicate oscillating retreat and progressive decoupling of Highland ice from Orkney–Shetland ice. The pattern and timing of separation of the SIS and FIS in the North Sea Basin remain uncertain. Available evidence suggests that by ∼17 ka, much of the Sea of the Hebrides, the Outer Hebrides, Caithness and the coasts of E Scotland were deglaciated. By ∼16 ka, the Solway lowlands, Orkney and Shetland were deglaciated, the SIS and Irish Ice Sheet had separated, the ice margin lay along the western seaboard, nunataks had emerged in Wester Ross, the ice margin lay N of the Cairngorms and the sea had invaded the Tay and Forth estuaries. By ∼15 ka, most of the Southern Uplands, the Firth of Clyde, the Midland Valley and the upper Spey valley were deglaciated, and in NW Scotland ice was retreating from fjords and valleys. By the onset of rapid warming at ∼14.7 ka, much of the remnant SIS was confined within the limits of Younger Dryas glaciation. The SIS, therefore, lost most of its mass during the Dimlington Stade. It is uncertain whether fragments of the SIS persisted on high ground throughout the Lateglacial Interstade.

scholarly journals Deglaciation of the Laurentide Ice Sheet from the Last Glacial Maximum

2017 ◽  
Vol 43 (2) ◽  
pp. 377 ◽  
Author(s):  
Ch.R. Stokes
Keyword(s):  
Sea Level ◽  
Last Glacial Maximum ◽  
Ice Sheet ◽  
Glacial Maximum ◽  
Laurentide Ice Sheet ◽  
Boreal Summer ◽  
Last Deglaciation ◽  
Ice Streams ◽  
Surface Mass ◽  
Last Glacial

The last deglaciation of the Laurentide Ice Sheet (LIS) was associated with major reorganisations in the ocean-climate system and its retreat also represents a valuable analogue for understanding the rates and mechanisms of ice sheet collapse. This paper reviews the characteristics of the LIS at its Last Glacial Maximum (LGM) and its subsequent deglaciation, with particular emphasis on the pattern and timing of ice margin recession and the driving mechanisms of retreat. The LIS initiated over the eastern Canadian Arctic ~116-110 ka (MIS 5d), but its growth towards the LGM was highly non-linear and punctuated by several episodes of expansion (~65 ka: MIS 4) and retreat (~50-40 ka: MIS 3). It attained its maximum position around 26-25 ka (MIS 2) and existed for several thousand years as an extensive ice sheet with major domes over Keewatin, Foxe Basin and northern Quebec/Labrador. It extended to the edge of the continental shelf at its marine margins and likely stored a sea-level equivalent of around 50 m and with a maximum ice surface ~3,000 m above present sea-level. Retreat from its maximum was triggered by an increase in boreal summer insolation, but areal shrinkage was initially slow and the net surface mass balance was positive, indicating that ice streams likely played an important role in reducing the ice sheet volume, if not its extent, via calving at marine margins. Between ~16 and ~13 ka, the ice sheet margin retreated more rapidly, particularly in the south and west, whereas the north and east underwent only minimal recession. The overall rate of retreat decreased during the Younger Dryas (YD), when several localised readvances occurred. Following the YD, the ice sheet retreated two to five times faster than previously, and this was primarily driven by enhanced surface melting while ice streams reduced in effectiveness. Final deglaciation of the Keewatin and Foxe Domes, left a remnant Labrador Dome that disappeared ~6.7 ka.

Early and Middle Pleistocene environments, landforms and sediments in Scotland

2018 ◽  
Vol 110 (1-2) ◽  
pp. 5-37 ◽  
Author(s):  
Adrian M. HALL ◽  
Jon W. MERRITT ◽  
E. Rodger CONNELL ◽  
Alun HUBBARD
Keyword(s):  
Sea Level ◽  
Chemical Weathering ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Early Pleistocene ◽  
Middle Pleistocene ◽  
Glacial Erosion ◽  
Glacial Sediments ◽  
Ice Caps ◽  
The North

ABSTRACTThis paper reviews the changing environments, developing landforms and terrestrial stratigraphy during the Early and Middle Pleistocene stages in Scotland. Cold stages after 2.7 Ma brought mountain ice caps and lowland permafrost, but larger ice sheets were short-lived. The late Early and Middle Pleistocene sedimentary record found offshore indicates more than 10 advances of ice sheets from Scotland into the North Sea but only 4–5 advances have been identified from the terrestrial stratigraphy. Two primary modes of glaciation, mountain ice cap and full ice sheet modes, can be recognised. Different zones of glacial erosion in Scotland reflect this bimodal glaciation and the spatially and temporally variable dynamics at glacier beds. Depths of glacial erosion vary from almost zero in Buchan to hundreds of metres in glens in the western Highlands and in basins both onshore and offshore. The presence of tors and blockfields indicates repeated development of patches of cold-based, non-erosive glacier ice on summits and plateaux. In lowlands, chemical weathering continued to operate during interglacials, but gruss-type saprolites are mainly of Pliocene to Early Pleistocene age. The Middle Pleistocene terrestrial stratigraphic record in Scotland, whilst fragmentary and poorly dated, provides important and accessible evidence of changing glacial, periglacial and interglacial environments over at least three stadial–interstadial–interglacial cycles. The distributions of blockfields and tors and the erratic contents of glacial sediments indicate that the configuration, thermal regime and pattern of ice flow during MIS 6 were broadly comparable to those of the last ice sheet. Improved control over the ages of Early and Middle Pleistocene sediments, soils and saprolites and on long-term rates of weathering and erosion, combined with information on palaeoenvironments, ice extent and sea level, will in future allow development and testing of new models of Pleistocene tectonics, isostasy, sea-level change and ice sheet dynamics in Scotland.

Observations of postglacial uplift at Churchill, Manitoba

1992 ◽  
Vol 29 (11) ◽  
pp. 2418-2425 ◽  
Author(s):  
A. Mark Tushingham
Keyword(s):  
Sea Level ◽  
Tide Gauge ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Glacial Isostatic Adjustment ◽  
Tide Gauge Record ◽  
Isostatic Adjustment ◽  
Absolute Gravimetry ◽  
The Earth ◽  
Level Data

Churchill, Manitoba, is located near the centre of postglacial uplift caused by the Earth's recovery from the melting of the Laurentide Ice Sheet. The value of present-day uplift at Churchill has important implications in the study of postglacial uplift in that it can aid in constraining the thickness of the ice sheet and the rheology of the Earth. The tide-gauge record at Churchill since 1940 is examined, along with nearby Holocene relative sea-level data, geodetic measurements, and recent absolute gravimetry measurements, and a present-day rate of uplift of 8–9 mm/a is estimated. Glacial isostatic adjustment models yield similar estimates for the rate of uplift at Churchill. The effects of the tide-gauge record of the diversion of the Churchill River during the mid-1970's are discussed.

scholarly journals Objective Reconstructions of the Late Wisconsinan Laurentide Ice Sheet and the Significance of Deformable Beds

2007 ◽  
Vol 39 (3) ◽  
pp. 229-238 ◽  
Author(s):  
D. A. Fisher ◽  
N. Reeh ◽  
K. Langley
Keyword(s):  
Yield Stress ◽  
Flow Direction ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Hudson Bay ◽  
Ice Streams ◽  
Ice Flow ◽  
Surface Slopes ◽  
Late Wisconsinan

ABSTRACT A three dimensional steady state plastic ice model; the present surface topography (on a 50 km grid); a recent concensus of the Late Wisconsinan maximum margin (PREST, 1984); and a simple map of ice yield stress are used to model the Laurentide Ice Sheet. A multi-domed, asymmetric reconstruction is computed without prior assumptions about flow lines. The effects of possible deforming beds are modelled by using the very low yield stress values suggested by MATHEWS (1974). Because of low yield stress (deforming beds) the model generates thin ice on the Prairies, Great Lakes area and, in one case, over Hudson Bay. Introduction of low yield stress (deformabie) regions also produces low surface slopes and abrupt ice flow direction changes. In certain circumstances large ice streams are generated along the boundaries between normal yield stress (non-deformable beds) and low yield stress ice (deformabie beds). Computer models are discussed in reference to the geologically-based reconstructions of SHILTS (1980) and DYKE ef al. (1982).

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