CGRG Bibliography of Canadian Geomorphology
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Author : Barber, D.C.; Jennings, A.E.; and Andrews, J.T.
Date : 1996
Title : Iceberg flux from Hudson Strait during Heinrich event 2: data from NW Labrador Sea sediments.
Publication : 26th International Arctic Workshop: Arctic and Alpine Environments, Past and Present - Abstracts , Institute for Arctic and Alpine Research, University of Colorado, Boulder,
Issue :
Page(s) : 11
Abstract
The series of foraminifera-poor, ice-rafted debris (IRD)-rich Heinrich (H-) layers observed in late Pleistocene North Atlantic sediments result from increased iceberg flux from the region's ice sheets. Much of this iceberg flux originated at marine calving margins of the northeastern Laurentide Ice Sheet, principally in the vicinity of Hudson Strait. In an effort to describe the mode and timing of the Laurentide iceberg discharges, we are studying detrital carbonate (DC) layers in cores from the northwest Labrador Sea. Two of the Labrador Sea DC layers (DC-1 and -2) have been established as proximal correlatives to H-1 and H-2, with ages = 14,000 and 20,500 C-14 years before present, respectively (Andrews and Tedesco, 1992). The timing of deposition for the 50-cm thick H-2 layer in core HU87033-009 (NW Labrador Sea slope) is bracketed by reservoir-corrected C-14 dates of 20,330 +/- 260 yrs immediately above the layer and 20,620 +/- 220 directly below. Therefore, the time for deposition of H-2 ranges between instantaneous (dates overlap within 1 standard deviation) and 770 years (maximum age difference within 1 standard deviation). These dates are from peaks in planktonic foraminifera per gram, and are considered quite reliable. Taking the dates at face value, deposition of the 50 cm layer in 290 years represents a sedimentation rate 10X that prior to the event and 8X that following the event. The increased amount of detrital carbonate (40%) and the calcite/dolomite ratio (4) are nearly constant within the H-2 layer, at values consistent with a Hudson Strait source. The grain-size fines upward through the H-2 layer from 20% sand near the base to 5% sand in upper part of the layer, possibly indicating that the calving ice margin retreats during the Heinrich event, back to a position inside the mouth of Hudson Strait. The duration of H-2 calculated from our observations is consistent with glaciologic models that simulate ice-streaming and rapid, massive iceberg calving from Hudson Strait (e.g., MacAyeal, 1993). Dowdeswell and others (1995) assume ranges of IRD-flux-per-iceberg-volume and use the observed IRD layer thickness to calculate the total iceberg volume for H-2. Dividing this volume by the duration of H-2 (290 yr) yields a rate of freshwater input to the North Atlantic of approximately 0.025 Sv (Sv = 1 million cubic meters per second). Thus as the Hudson Strait icebergs melted, freshwater was contributed at a rate close to the 0.03 Sv threshold value that Rahmstorf (1995) determined is necessary to shut down Labrador Sea Deep Water production under present boundary conditions. Labrador Sea Deep Water is a key contributor to the global thermohaline circulation, therefore our result underscores the potential impact of Heinrich events on thermohaline circulation and the global climate system.
Bibliography of Canadian Geomorphology