scholarly journals Site information and initial results from deep ice drilling on Law Dome, Antarctica

1997 ◽  
Vol 43 (143) ◽  
pp. 3-10 ◽  
Author(s):  
V.I. Morgan ◽  
C.W. Wookey ◽  
J. Li ◽  
T.D. van Ommen ◽  
W. Skinner ◽  
...  
Keyword(s):  
Ice Core ◽  
Ice Sheet ◽  
High Accumulation ◽  
Ice Flow ◽  
Ice Cap ◽  
Basal Ice ◽  
Inland Ice ◽  
The Last Glacial Maximum ◽  
Initial Results ◽  
The Last Glacial

AbstractThe aim of deep ice drilling on Law Dome, Antarctica, has been to exploit the special characteristics of Law Dome summit, i.e. low temperature and high accumulation near an ice divide, to obtain a high-resolution ice core for climatic/environmental studies of the Holocene and the Last Glacial Maximum (LGM). Drilling was completed in February 1993, when basal ice containing small fragments of rock was reached at a depth of 1196 m. Accurate ice dating, obtained by counting annual layers revealed by fine-detail δ18О, peroxide and electrical-conductivity measurements, is continuous down to 399 m, corresponding to a date of AD 1304. Sulphate concentration measurements, made around depths where conductivity tracing indicates volcanic fallout, allow confirmation of the dating (for Agung in 1963 and Tambora in 1815) or estimates of the eruption date from the ice dating (for the Kuwae, Vanuatu, eruption ~1457). The lower part of the core is dated by extrapolating the layer-counting using a simple model of the ice flow. At the LGM, ice-fabric measurements show a large decrease (250 to 14 mm2) in crystal size and a narrow maximum in c-axis vertically. The main zone of strong single-pole fabrics however, is located higher up in a broad zone around 900 m. Oxygen-isotope (δ18O) measurements show Holocene ice down to 1113 m, the LGM at 1133 m and warm (δ18O) about the same as Holocene) ice near the base of the ice sheet. The LGM/Holocene δ18O shift of 7.0‰, only ~1‰ larger than for Vostok, indicates that Law Dome remained an independent ice cap and was not overridden by the inland ice sheet in the Glacial.

scholarly journals Site information and initial results from deep ice drilling on Law Dome, Antarctica

1997 ◽  
Vol 43 (143) ◽  
pp. 3-10 ◽  
Author(s):  
V.I. Morgan ◽  
C.W. Wookey ◽  
J. Li ◽  
T.D. van Ommen ◽  
W. Skinner ◽  
...  
Keyword(s):  
Ice Core ◽  
Ice Sheet ◽  
High Accumulation ◽  
Ice Flow ◽  
Ice Cap ◽  
Basal Ice ◽  
Inland Ice ◽  
The Last Glacial Maximum ◽  
Initial Results ◽  
The Last Glacial

Abstract The aim of deep ice drilling on Law Dome, Antarctica, has been to exploit the special characteristics of Law Dome summit, i.e. low temperature and high accumulation near an ice divide, to obtain a high-resolution ice core for climatic/environmental studies of the Holocene and the Last Glacial Maximum (LGM). Drilling was completed in February 1993, when basal ice containing small fragments of rock was reached at a depth of 1196 m. Accurate ice dating, obtained by counting annual layers revealed by fine-detail δ18 О, peroxide and electrical-conductivity measurements, is continuous down to 399 m, corresponding to a date of AD 1304. Sulphate concentration measurements, made around depths where conductivity tracing indicates volcanic fallout, allow confirmation of the dating (for Agung in 1963 and Tambora in 1815) or estimates of the eruption date from the ice dating (for the Kuwae, Vanuatu, eruption ~1457). The lower part of the core is dated by extrapolating the layer-counting using a simple model of the ice flow. At the LGM, ice-fabric measurements show a large decrease (250 to 14 mm2) in crystal size and a narrow maximum in c-axis vertically. The main zone of strong single-pole fabrics however, is located higher up in a broad zone around 900 m. Oxygen-isotope (δ18O) measurements show Holocene ice down to 1113 m, the LGM at 1133 m and warm (δ18O) about the same as Holocene) ice near the base of the ice sheet. The LGM/Holocene δ18O shift of 7.0‰, only ~1‰ larger than for Vostok, indicates that Law Dome remained an independent ice cap and was not overridden by the inland ice sheet in the Glacial.

scholarly journals Towards a GIS assessment of numerical ice-sheet model performance using geomorphological data

2007 ◽  
Vol 53 (180) ◽  
pp. 71-83 ◽  
Author(s):  
Jacob Napieralski ◽  
Alun Hubbard ◽  
Yingkui Li ◽  
Jon Harbor ◽  
Arjen P. Stroeven ◽  
...  
Keyword(s):  
Flow Direction ◽  
Ice Sheet ◽  
Model Performance ◽  
Initial Step ◽  
Ice Flow ◽  
Flow Models ◽  
Flow Directions ◽  
The Last Glacial Maximum ◽  
Basal Flow ◽  
The Last Glacial

AbstractA major difficulty in assimilating geomorphological information with ice-sheet models is the lack of a consistent methodology to systematically compare model output and field data. As an initial step in establishing a quantitative comparison methodology, automated proximity and conformity analysis (APCA) and automated flow direction analysis (AFDA) have been developed to assess the level of correspondence between modelled ice extent and ice-marginal features such as end moraines, as well as between modelled basal flow directions and palaeo-flow direction indicators, such as glacial lineations. To illustrate the potential of such an approach, an ensemble suite of 40 numerical simulations of the Fennoscandian ice sheet were compared to end moraines of the Last Glacial Maximum and the Younger Dryas and to glacial lineations in northern Sweden using APCA and AFDA. Model experiments evaluated in this manner were ranked according to level of correspondence. Such an approach holds considerable promise for optimizing the parameter space and coherence of ice-flow models by automated, quantitative assessment of multiple ensemble experiments against a database of geological or glaciological evidence.

scholarly journals Ice Flow Along an I.A.G.P. Flow Line and Interpretation of Data From an Ice Core in Terre Adélie, Antarctica

1979 ◽  
Vol 24 (90) ◽  
pp. 103-115 ◽  
Author(s):  
D. Raynaud ◽  
C. Lorius ◽  
W. F. Budd ◽  
N. W. Young
Keyword(s):  
Flow Line ◽  
Ice Core ◽  
Ice Sheet ◽  
Sheet Thickness ◽  
Gas Content ◽  
Ice Flow ◽  
The Core ◽  
The Past ◽  
Terre Adélie ◽  
Inland Ice

AbstractAn ice core has been obtained to the bedrock about 300 m deep in Terre Adélie, 5 km inland from the coast. Stable isotopes and gas content have been measured over the length of the core. The results have been interpreted in terms of the temperature and elevation of origin of the ice further inland on the ice sheet from the data obtained along an 800 km traverse towards Dome “C”, and from Dome “C”, at an elevation of about 3 200 m. The flow of the ice from Dome “C“ to the coast has been modelled to determine the ages and particle trajectories of the ice for present conditions.It has been found that the upper isotope and gas-content values in the core can be matched with the present regime using a base for ice flow above the present bed which is suggested by moraine in the ice core. The ice in the layer from the 200 m depth, where the age is apparently more than 5 000 years, to the 250 m depth, appears to have originated from conditions which differ substantially from those existing on the present inland ice-sheet surface. The results give an indication of a colder climate and greater ice-sheet thickness in the past.

The deglacial history of NW Alexander Island, Antarctica, from surface exposure dating

2012 ◽  
Vol 77 (2) ◽  
pp. 273-280 ◽  
Author(s):  
Joanne S. Johnson ◽  
Jeremy D. Everest ◽  
Philip T. Leat ◽  
Nicholas R. Golledge ◽  
Dylan H. Rood ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Antarctic Peninsula ◽  
Ice Sheet ◽  
Glacial Maximum ◽  
Ice Shelf ◽  
Last Glacial ◽  
Ice Cap ◽  
The Antarctic ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Recent changes along the margins of the Antarctic Peninsula, such as the collapse of the Wilkins Ice Shelf, have highlighted the effects of climatic warming on the Antarctic Peninsula Ice Sheet (APIS). However, such changes must be viewed in a long-term (millennial-scale) context if we are to understand their significance for future stability of the Antarctic ice sheets. To address this, we present nine new cosmogenic 10Be exposure ages from sites on NW Alexander Island and Rothschild Island (adjacent to the Wilkins Ice Shelf) that provide constraints on the timing of thinning of the Alexander Island ice cap since the last glacial maximum. All but one of the 10Be ages are in the range 10.2–21.7 ka, showing a general trend of progressive ice-sheet thinning since at least 22 ka until 10 ka. The data also provide a minimum estimate (490 m) for ice-cap thickness on NW Alexander Island at the last glacial maximum. Cosmogenic 3He ages from a rare occurrence of mantle xenoliths on Rothschild Island yield variable ages up to 46 ka, probably reflecting exhumation by periglacial processes.

Implications for Deglaciation Chronology from New AMS Age Determinations in Central West Greenland

1996 ◽  
Vol 45 (3) ◽  
pp. 245-253 ◽  
Author(s):  
Frank G. M. van Tatenhove ◽  
Jaap J. M. van der Meer ◽  
Eduard A. Koster
Keyword(s):  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
New Age ◽  
Time Frame ◽  
West Greenland ◽  
System A ◽  
New Evidence ◽  
The Last Glacial Maximum ◽  
The Last Glacial

AbstractNew evidence has been obtained for the age of the Umı̂vı̂t/Keglen and Ørkendalen moraine systems close to the present ice sheet margin in central West Greenland. The Umı̂vı̂t/Keglen moraine system is dated at 7500 to 6500 14C yr B.P., which is older than the previously assumed date of 7300 to 6000 14C yr B.P. The Ørkendalen system is now dated at 6200 to 5600 14C yr B.P. against earlier estimates of 300 to 700 14C yr B.P. The new age is based on AMS radiocarbon-dated organic material within depressions between morainic ridges belonging to the Ørkendalen system. A major implication of the new age is that ice margin positions prevailed for about 6000 years behind the present ice sheet margin. The retreat behind the present margin could be substantial, and in the light of deglaciation rates prior to the Ørkendalen phase, may be ca. 10's of kilometers rather than kilometers. Circumstantial evidence is found for the retreat of the ice sheet margin behind its present position during the Holocene climatic optimum. The results, placed into a time frame of deglaciation since the last glacial maximum, enable comparison with Greenland ice sheet models and ice core records.

scholarly journals Deglacial and Holocene changes in accumulation at Law Dome, East Antarctica

2004 ◽  
Vol 39 ◽  
pp. 359-365 ◽  
Author(s):  
Tas D. Van Ommen ◽  
Vin Morgan ◽  
Mark A. J. Curran
Keyword(s):  
Accumulation Rate ◽  
Absolute Humidity ◽  
Large Change ◽  
East Antarctica ◽  
Early Holocene ◽  
High Accumulation ◽  
Ice Flow ◽  
Atmospheric Moisture Content ◽  
The Last Glacial Maximum ◽  
The Last Glacial

AbstractDating constraints have been combined with an ice-flow model to estimate surface accumulation rates at Law Dome, East Antarctica, to approximately 80 kyr BP. Results indicate that the present high-accumulation regime (~0.7ma–1 ice equivalent) was established some time after ~7 kyr BP, following an increase of approximately 80% from early to mid-Holocene. The accumulation rate at the Last Glacial Maximum is estimated at less than ~10% of the modern value. The record reveals an approximately linear dependence between temperature (inferred from isotope ratio) and accumulation rate through the glacial period. This dependence breaks down in the early Holocene, and this is interpreted as a change to a mode in which moisture-transport changes have a stronger influence on accumulation than temperature (via absolute humidity). The changes in accumulation, including the large change in the early to mid-Holocene, are accompanied by changes in sea-salt concentrations which support the hypothesis that Law Dome climate has shifted from a glacial climate, more like that of the present-day Antarctic Plateau, to its current Antarctic maritime climate. The change between these two modes occurred progressively through the early Holocene, possibly reflecting insolation-driven changes in atmospheric moisture content and circulation.

Former southwesterly ice flows in the Abitibi–Timiskaming region: implications for the configuration of the late Wisconsinan ice sheet

1986 ◽  
Vol 23 (11) ◽  
pp. 1724-1741 ◽  
Author(s):  
J. J. Veillette
Keyword(s):  
Flow Direction ◽  
Ice Sheet ◽  
Ice Flow ◽  
Almost Everywhere ◽  
Ice Flows ◽  
Show Evidence ◽  
The Cross ◽  
Late Wisconsinan ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Measurements at some 300 cross-striated sites in the Abitibi–Timiskaming area of Quebec and Ontario revealed two former directions of ice flow: an older west-southwest one (230–270°) in the extreme western part of the area, and a younger, widespread south-southwest one (180–220°) in the region west of the Harricana – Lake McConnell glaciofluvial complex. These sets of older striae, whether one or both on the same outcrop, are almost everywhere crossed by marks of a younger ubiquitous flow to the south-southeast (130–170°). On the basis of striae directions measured below an older till and of three dates obtained from intertill (below the surficial till) nonglacial sediments in the Timmins and Matheson areas in Ontario and the Selbaie mine area in Quebec, the oldest west-southwest (230–270°) striae are tentatively associated with the west-southwest flow that deposited this lowermost till in early to mid-Wisconsinan time or earlier.The Harricana – Lake McConnell glaciofluvial system extends from James Bay to the vicinity of North Bay Ontario and probably continues farther south to the Lake Simcoe area. It is strictly an interlobate deglaciation feature and does not result from the converging flows of two coalescing glaciers. At the last glacial maximum the dominant ice-flow direction in the area was probably toward the southwest, across the space occupied by this glaciofluvial system, confirming the flow lines shown by most models of the late Wisconsinan ice sheet. Because none of the cross-striated outcrops showing marks of the former south-southwest (180–220°) and of the last south-southeast (130–170°) movements show evidence of differential weathering and because glacial transport was due to the former southwest movement at several locations, it is proposed that the cross-striations result from the same ice mass subjected to (1) a general change in flow direction from the southwest to the southeast and (2) a complete scission that led ultimately to the deposition of the Harricana – Lake McConnell glaciofluvial system in the interlobate position.

scholarly journals Quaternary glaciation history and glaciology of Jakobshavn Isbræ and the Disko Bugt region, West Greenland: a review

2007 ◽  
Vol 14 ◽  
pp. 1-78 ◽  
Author(s):  
Anker Weidick ◽  
Ole Bennike
Keyword(s):  
Sea Level ◽  
Last Glacial Maximum ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Early Holocene ◽  
Ice Streams ◽  
Last Glacial ◽  
Inland Ice ◽  
The Last Glacial Maximum ◽  
The Last Glacial

The Disko Bugt region in central West Greenland is characterised by permanent ice streams, of which Jakobshavn Isbræ is by far the most important. The first thorough studies on the glaciology of the region were conducted over 150 years ago by H.J. Rink, who introduced the terms 'ice streams' and 'Inland Ice'. Rink's work inspired new field work, which has continued to the present, and the long series of observations are unique for an Arctic region. Cooling during the Cenozoic led to ice-sheet growth in Greenland. A number of interglacial occurrences have been reported from the Disko Bugt region, and during the penultimate glacial stage, the Greenland ice-sheet margin extended to the shelf break. During the last glacial maximum, the ice margin probably extended only to the inner part of the banks on the continental shelf, and large floating glaciers may have been present at this time. During the Younger Dryas cold period, the ice margin may have been located at a marked basalt escarpment west of Disko Bugt. Disko Bugt was deglaciated rapidly in the early Holocene, around 10 500–10 000 years before present (10.5–10 ka B.P.), but when the ice margin reached the eastern shore of the bay, recession paused, and major moraine systems were formed. With renewed recession, the present ice-margin position was attained around 8–6 ka B.P., and by c. 5 ka B.P. the ice margin was located east of its present position. The subsequent Neoglacial readvance generally reached a maximum during the Little Ice Age, around AD 1850. This was followed by recession that has continued to the present day. The relative sea-level history shows a rapid sea-level fall in the early Holocene, and a slow rise in the late Holocene. This development mainly reflects a direct isostatic response to the ice-margin history. Jakobshavn Isbræ is the main outlet from the Greenland ice sheet. It drains c. 6.5% of the present Inland Ice, and produces c. 35–50 km3 of icebergs per year, corresponding to more than 10% of the total output of icebergs from the Inland Ice. The velocity of the central part of the ice stream at the front has been around 7 km/year since records began, but has nearly doubled in recent years. Other calf-ice producing glacier outlets in Disko Bugt produce c. 18 km3 per year. The large calf-ice production of Jakobshavn Isbræ may have been initiated at about 8 ka B.P. when the glacier front receded from the iceberg bank (Isfjeldsbanken) near Ilulissat. Ice streams in inner and outer Egedesminde Dyb may have been active during the early Holocene and during the last glacial maximum.

scholarly journals Influx of meltwater to subglacial Lake Concordia, East Antarctica

2005 ◽  
Vol 51 (172) ◽  
pp. 96-104 ◽  
Author(s):  
Anahita A. Tikku ◽  
Robin E. Bell ◽  
Michael Studinger ◽  
Garry K. C. Clarke ◽  
Ignazio Tabacco ◽  
...  
Keyword(s):  
Ice Core ◽  
Ice Sheet ◽  
East Antarctica ◽  
Lake Ecosystems ◽  
Subglacial Lake ◽  
Lake Volume ◽  
Hydrological System ◽  
Strain Heating ◽  
The Last Glacial Maximum ◽  
The Last Glacial

AbstractWe present evidence for melting at the base of the ice that overlies Lake Concordia, an 800 km2 subglacial lake near Dome Concordia, East Antarctica, via a combination of glaciohydraulic melting (associated with the tilted ice ceiling and its influence on lake circulation/melting temperature) and melting by extreme strain heating (where the ice sheet is grounded). An influx of water is necessary to provide nutrients, material and biota to support subglacial lake ecosystems but has not been detected previously. Freezing is the dominant observed basal process at over 60% of the surface area above the lake. The total volume of accreted ice above the lake surface is estimated as 50-60 km3, roughly 25-30% of the 200 ± 40 km3 estimated lake volume. Estimated rates of melting and freezing are very similar, ±2-6 mm a-1. The apparent net freezing may reflect the present-day response of Lake Concordia to cooling associated with the Last Glacial Maximum, or a large influx of water either via a subglacial hydrological system or from additional melting of the ice sheet. Lake Concordia is an excellent candidate for subglacial exploration given active basal processes, proximity to the Dome Concordia ice core and traverse resupply route.

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