Evidence from 40Ar/39Ar Ages of Individual Hornblende Grains for Varying Laurentide Sources of Iceberg Discharges 22,000 to 10,500 yr B.P.

2000 ◽  
Vol 54 (3) ◽  
pp. 372-383 ◽  
Author(s):  
Sidney R. Hemming ◽  
Gerard C. Bond ◽  
Wallace S. Broecker ◽  
Warren D. Sharp ◽  
Mieczyslawa Klas-Mendelson
Keyword(s):  
North Atlantic ◽  
Sediment Cores ◽  
Ice Sheet ◽  
Ice Cores ◽  
Laurentide Ice Sheet ◽  
Baffin Island ◽  
Relative Timing ◽  
Shelf Slope ◽  
Iceberg Calving ◽  
Different Sources

The abundance and lithic content of ice rafted detritus in glacial North Atlantic sediment cores vary abruptly on millennial time scales that have been correlated to Dansgaard-Oeschger cycles in the Greenland ice cores. There is growing evidence that various ice sheet outlets contributed increased iceberg fluxes at multiple discrete intervals, and the relative timing of iceberg discharges from different sources is important for understanding interactions between oceans and ice sheets. We present a provenance study based on 40Ar/39Ar dates of individual hornblende grains from 20 samples taken at 600 to 700 yr spacing between 10,500 and 22,000 yr B.P., from Orphan Knoll core EW9303-GGC31. Heinrich layers are characterized by a dominant Paleoproterozoic hornblende provenance consistent with published studies. A change in provenance between Heinrich events H2 and H1 indicates contributions of iceberg calving from the Newfoundland and southern Labrador margins. Between H1 and the Younger Dryas interval, Paleoproterozoic ice rafted grains remained dominant. The dominance of Baffin Island (or Greenland?) sources to the ice rafted detritus is ascribed to the retreat of the southern Laurentide ice sheet at about the time of H1—a retreat that isolated Newfoundland and southern Labrador ice from the shelf-slope boundary.

scholarly journals An ice-marginal δ18O record from Barnes Ice Cap, Baffin Island, Canada

2002 ◽  
Vol 35 ◽  
pp. 145-149 ◽  
Author(s):  
Christian M. Zdanowicz ◽  
David A. Fisher ◽  
Ian Clark ◽  
Denis Lacelle
Keyword(s):  
Ice Sheet ◽  
Ice Cores ◽  
Late Glacial ◽  
Laurentide Ice Sheet ◽  
Baffin Island ◽  
Last Glacial ◽  
Ice Cap ◽  
White Band ◽  
Arctic Ice ◽  
The Last Glacial

AbstractBarnes Ice Cap, Baffin Island, Canada, is a remnant of the Laurentide ice sheet that separated from it about 8500 years ago. Owing to recession of the ice cap during the Holocene, Pleistocene-age ice is now exposed along the margin in a distinctive bubble-rich white band. δ18O variations across the white ice resemble those in Canadian Arctic ice cores, suggesting that Barnes Ice Cap preserves a climatic record through the last glacial period, possibly reaching back into the previous (Sangamon) interglacial. the δ18O shift at the Wisconsin–Holocene transition (15‰) exceeds that in other Canadian and Greenland records and cannot be explained solely in climatic terms. A steady-state model reconstruction of the Laurentide ice sheet during the Last Glacial Maximum suggests that Late-glacial strata in Barnes Ice Cap originated high up (>2400ma.s.l.) and far “inland” on the ice sheet, along a ridge that extended between the ancestral Foxe and Keewatin ice domes.

Correlated Millennial-Scale Changes in Surface Hydrography and Terrigenous Sediment Yield Inferred from Last-Glacial Marine Deposits off Northeastern Brazil

1998 ◽  
Vol 50 (2) ◽  
pp. 157-166 ◽  
Author(s):  
Helge W. Arz ◽  
Jürgen Pätzold ◽  
Gerold Wefer
Keyword(s):  
North Atlantic ◽  
Isotope Composition ◽  
Sediment Cores ◽  
Ice Cores ◽  
Northeastern Brazil ◽  
Salt Flux ◽  
Terrigenous Sediment ◽  
The North ◽  
North Brazil ◽  
The North Atlantic

The stable isotope composition of planktonic foraminifera correlates with evidence for pulses of terrigenous sediment in a sediment core from the upper continental slope off northeastern Brazil. Stable oxygen isotope records of the planktonic foraminiferal species Globigerinoides sacculiferand Globigerinoides ruber(pink) reveal sub-Milankovitch changes in sea-surface hydrography during the last 85,000 yr. Warming of the surface water coincided with terrigenous sedimentation pulses that are inferred from high XRF intensities of Ti and Fe, and which suggest humid conditions in northeast Brazil. These tropical signals correlate with climatic oscillations recorded in Greenland ice cores (Dansgaard-Oeschger cycles) and in sediment cores from the North Atlantic (Heinrich events). Trade winds may have caused changes in the North Brazil Current that altered heat and salt flux into the North Atlantic, thus affecting the growth and decay of the large glacial ice sheets.

scholarly journals Holocene lowering of the Laurentide ice sheet affects North Atlantic gyre circulation and climate

2018 ◽  
Vol 51 (9-10) ◽  
pp. 3797-3813 ◽  
Author(s):  
Lauren J. Gregoire ◽  
Ruza F. Ivanovic ◽  
Amanda C. Maycock ◽  
Paul J. Valdes ◽  
Samantha Stevenson
Keyword(s):  
North Atlantic ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Gyre Circulation

scholarly journals Numerical simulations of the Cordilleran ice sheet through the last glacial cycle

2016 ◽  
Vol 10 (2) ◽  
pp. 639-664 ◽  
Author(s):  
Julien Seguinot ◽  
Irina Rogozhina ◽  
Arjen P. Stroeven ◽  
Martin Margold ◽  
Johan Kleman
Keyword(s):  
Sediment Cores ◽  
Ice Sheet ◽  
Ice Cores ◽  
High Mountain ◽  
Glacial Cycle ◽  
Mountain Areas ◽  
Last Glacial ◽  
Proxy Records ◽  
Cordilleran Ice Sheet ◽  
The Last Glacial

Abstract. After more than a century of geological research, the Cordilleran ice sheet of North America remains among the least understood in terms of its former extent, volume, and dynamics. Because of the mountainous topography on which the ice sheet formed, geological studies have often had only local or regional relevance and shown such a complexity that ice-sheet-wide spatial reconstructions of advance and retreat patterns are lacking. Here we use a numerical ice sheet model calibrated against field-based evidence to attempt a quantitative reconstruction of the Cordilleran ice sheet history through the last glacial cycle. A series of simulations is driven by time-dependent temperature offsets from six proxy records located around the globe. Although this approach reveals large variations in model response to evolving climate forcing, all simulations produce two major glaciations during marine oxygen isotope stages 4 (62.2–56.9 ka) and 2 (23.2–16.9 ka). The timing of glaciation is better reproduced using temperature reconstructions from Greenland and Antarctic ice cores than from regional oceanic sediment cores. During most of the last glacial cycle, the modelled ice cover is discontinuous and restricted to high mountain areas. However, widespread precipitation over the Skeena Mountains favours the persistence of a central ice dome throughout the glacial cycle. It acts as a nucleation centre before the Last Glacial Maximum and hosts the last remains of Cordilleran ice until the middle Holocene (6.7 ka).

scholarly journals GIS analyses of ice-sheet erosional impacts on the exposed shield of Baffin Island, eastern Canadian Arctic

2015 ◽  
Vol 52 (11) ◽  
pp. 966-979 ◽  
Author(s):  
Karin Ebert
Keyword(s):  
Ice Sheet ◽  
Canadian Arctic ◽  
Laurentide Ice Sheet ◽  
Baffin Island ◽  
Glacial Erosion ◽  
Ice Sheet Erosion ◽  
The Impact ◽  
Exposure Ages ◽  
Eastern Canadian Arctic ◽  
Sheet Erosion

The erosional impacts of former ice sheets on the low-relief bedrock surfaces of Northern Hemisphere shields are not well understood. This paper assesses the variable impacts of glacial erosion on a portion of Baffin Island, eastern Canadian Arctic, between 68° and 72°N and 66° and 80°W. This tilted shield block was covered repeatedly by the Laurentide Ice Sheet during the late Cenozoic. The impact of ice-sheet erosion is examined with GIS analyses using two geomorphic parameters: lake density and terrain ruggedness. The resulting patterns generally conform to published data from other remote sensing studies, geological observations, cosmogenic exposure ages, and the distribution of the chemical index of alteration for tills. Lake density and terrain ruggedness are thereby demonstrated to be useful quantitative indicators of variable ice-sheet erosional impacts across Baffin Island. Ice-sheet erosion was most effective in the lower western parts of the lowlands, in a west–east-oriented band at around 350–400 m a.s.l., and in fjord-onset zones in the uplifted eastern region. Above the 350–400 m a.s.l. band and between the fjord-onset zones, ice-sheet erosion was not sufficient to create extensive ice-roughened or streamlined bedrock surfaces. The exception — where lake density and terrain ruggedness indicate that ice-sheet erosion had a scouring effect all across the study area — was in an area from Foxe Basin to Home Bay with elevations <400 m a.s.l. These morphological contrasts link to former ice-sheet basal thermal regimes during the Pleistocene. The zone of low glacial erosion surrounding the cold-based Barnes Ice Cap probably represents the ice cap’s greater extent during successive Pleistocene cold stages. Inter-fjord plateaus with few ice-sheet bedforms remained cold-based throughout multiple Pleistocene glaciations. In contrast, zones of high lake density and high terrain ruggedness are a result of the repeated development of fast-flowing, erosive ice in warm-based zones beneath the Laurentide Ice Sheet. These zones are linked to greater ice thickness over western lowland Baffin Island. However, adjacent lowland surfaces with similar elevations of non-eroded, weakly eroded, and ice-scoured shield bedrock indicate that—even in areas of high lake density and terrain ruggedness—the total depth of ice sheet erosion did not exceed 50 m.

scholarly journals Ice-sheet modelling characteristics in sea-level-based temperature reconstructions over the last glacial cycle

2006 ◽  
Vol 52 (176) ◽  
pp. 149-158 ◽  
Author(s):  
Frank Wilschut ◽  
Richard Bintanja ◽  
Roderik S.W. Van De Wal
Keyword(s):  
Sea Level ◽  
Sediment Cores ◽  
Ice Sheet ◽  
Ice Cores ◽  
Glacial Cycle ◽  
Deep Sea Sediment ◽  
Last Glacial ◽  
Proxy Records ◽  
Temperature Reconstructions ◽  
The Last Glacial

AbstractA widely used method for investigating palaeotemperatures is to analyze local proxy records (e.g. ice cores or deep-sea sediment cores). The interpretation of these records is often not straightforward, and global or hemispheric means cannot be deduced from local estimates because of large spatial variability. Using a different approach, temperature changes over the last glacial cycle can be estimated from sea-level observations by applying an inverse method to an ice-sheet model. In order to understand the underlying physical mechanisms, we used a 1-D ice-sheet model and a 3-D coupled thermodynamic ice-sheet–ice-shelf–bedrock model to investigate the importance of several physical processes for the inverse temperature reconstructions. Results show that (i) temperature reconstructions are sensitive to the employed formulation of mass balance, (ii) excluding thermodynamics in the ice sheet leads to a smaller temperature amplitude in the reconstruction and (iii) hysteresis in the non-linear relation between sea level and temperature occurs as a consequence of ice redistribution in the process of merging and separation of ice sheets. The ice redistribution does not occur if the geometry does not support the formation of a relatively flat dome, which tends to be preserved in warming conditions.

Late Quaternary (Stage 2 and 3) Meltwater and Heinrich Events, Northwest Labrador Sea

1994 ◽  
Vol 41 (1) ◽  
pp. 26-34 ◽  
Author(s):  
John T. Andrews ◽  
Helmut Erlenkeuser ◽  
Katherine Tedesco ◽  
Ali E. Aksu ◽  
A.J.Timothy Jull
Keyword(s):  
North Atlantic ◽  
Late Quaternary ◽  
Planktonic Foraminifera ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Labrador Sea ◽  
Near Surface ◽  
Heinrich Events ◽  
Eastern Margin ◽  
Detrital Carbonate

AbstractTwo major meltwater events are documented in cores from the NW Labrador Sea. One occurred ca. 20,000 14C yr B.P. in association with deposition of a major detrital carbonate unit. Both prior to and after this event, δ18O values of near-surface planktonic foraminifera were 4.5%, indicating fully enriched glacial values. A younger event (ca. 14,000 14 C yr B.P.) is characterized by a dramatic change in δ18O from 4.5 to 2.0% and coincided with the retreat of ice from the outer SE Baffin Shelf, possibly into Hudson Strait. These meltwater events coincide with Heinrich (H) layers 1 and 2 from North Atlantic sediments. The 14,000 14C yr B.P. meltwater event indicates that the eastern margin of the Laurentide Ice Sheet also underwent rapid retreat at approximately the same time as other ice sheet margins around the NE North Atlantic. A third major detrital carbonate event at the base of HU87-033-009, possibly correlative with Heinrich layer 3, occurred ca. 33,960 ± 675 14 C yr B.P.; however, this is older than the accepted date for H-3 of 27,000 14C yr B.P. and may be H-4.

Oceanic Evidence for the Mechanism of Rapid Northern Hemisphere Glaciation

1980 ◽  
Vol 13 (1) ◽  
pp. 33-64 ◽  
Author(s):  
W. F. Ruddiman ◽  
A. McIntyre ◽  
V. Niebler-Hunt ◽  
J. T. Durazzi
Keyword(s):  
Northern Hemisphere ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Local Source ◽  
The North ◽  
Land Mass ◽  
Oxygen Isotopic ◽  
The North Atlantic

AbstractThe oxygen isotopic stage 5/4 boundary in deep-sea sediments marks a prominent interval of northern hemisphere ice-sheet growth that lasted about 10,000 yr. During much of this rapid ice growth, the North Atlantic Ocean from at least 40°N to 60°N maintained warm sea-surface temperatures, within 1° to 2°C of today's subpolar ocean. This oceanic warmth provided a local source of moisture for ice-sheet accretion on the adjacent continents. The unusually strong thermal gradient off the east coast of North America (an “interglacial” ocean alongside a “glacial” land mass) also should have directed low-pressure storms from warm southern latitudes north-ward toward the Laurentide Ice Sheet. In addition, minimal calving of ice into the North Atlantic occurred during most of the stage 5/4 transition, indicative of ice retention within the continents. Diminished summer and autumn insolation, a warm subpolar ocean, and minimal calving of ice are conducive to rapid and extensive episodes of northern hemisphere ice-sheet growth.

Subglacially precipitated carbonates record geochemical interactions and pollen preservation at the base of the Laurentide Ice Sheet on central Baffin Island, eastern Canadian Arctic

2014 ◽  
Vol 81 (1) ◽  
pp. 94-105 ◽  
Author(s):  
Kurt A. Refsnider ◽  
Gifford H. Miller ◽  
Marilyn L. Fogel ◽  
Bianca Fréchette ◽  
Roxane Bowden ◽  
...  
Keyword(s):  
Chemical Weathering ◽  
Ice Sheet ◽  
The Arctic ◽  
Laurentide Ice Sheet ◽  
Geochemical Data ◽  
Baffin Island ◽  
Columnar Crystal ◽  
Ice Cap ◽  
Basal Ice ◽  
Isotopic Analyses

AbstractThe mineralogy and isotopic compositions of subglacially precipitated carbonate crusts (SPCCs) provide information on conditions and processes beneath former glaciers and ice sheets. Here we describe SPCCs formed on gneissic bedrock at the bed of the Laurentide Ice Sheet (LIS) during the last glacial maximum on central Baffin Island. Geochemical data indicate that the Ca in the crusts was likely derived from the subglacial chemical weathering Ca-bearing minerals in the local bedrock. C and Sr isotopic analyses reveal that the C in the calcite was derived predominantly from older plant debris. The δ18O values of the SPCCs suggest that these crusts formed in isotopic equilibrium with basal ice LIS preserved in the Barnes Ice Cap (BIC). Columnar crystal fabric and the predominance of sparite over micrite in the SPCCs are indicative of carbonate precipitation under open-system conditions. However, the mean δ18O value of the calcite crusts is ~ 10‰ higher than those of primary LIS ice preserved in the BIC, demonstrating that SPCCs record the isotopic composition of only basal ice. Palynomorph assemblages preserved within the calcite and basal BIC ice include species last endemic to the Arctic in the early Tertiary. The source of these palynomorphs remains enigmatic.

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