Abstract
We examine variations in the ice-rafted sources for sediments in the Iceland/East Greenland offshore marine archives by utilizing a sediment unmixing model and link the results to a coupled iceberg-ocean model. Surface samples from around Iceland and along the E/NE Greenland shelf are used to define potential sediment sources, and these are examined within the context of the down-core variations in mineralogy in the <2 mm sediment fraction from a transect of cores across Denmark Strait. A sediment unmixing model is used to estimate the fraction of sediment <2 mm off NW and N Iceland exported across Denmark Strait; this averaged between 10 and 20%. Both the sediment unmixing model and the coupled iceberg-ocean model are consistent in finding that the fraction of “far-travelled” sediments in the Denmark Strait environs is overwhelmingly of local, mid-East Greenland, provenance, and therefore with a significant cross-channel component to their travel. The Holocene record of ice-rafted sediments denotes a three-part division of the Holocene in terms of iceberg sediment transport with a notable increase in the process starting ca 4000 cal yr BP. This latter increase may represent the re-advance during the Neoglacial period of land-terminating glaciers on the Geikie Plateau to become marine-terminating. The contrast in spectral signals between these cores and the 1500-yr cycle at VM28-14, just south of the Denmark Strait, combined with the coupled iceberg-model results, leads us to speculate that the signal at VM28-14 reflects pulses in overflow waters, rather than an ice-rafted signal.
Highlights
Starting in 1988, research cruises have been undertaken by the Institute of Arctic and Alpine Research (INSTAAR) and international colleagues on both the Greenland and Iceland continental margins of the Denmark Strait (e.g. Mienert et al, 1992; Helgadóttir, 1997; Labeyrie et al, 2003) with a goal of establishing the late Quaternary history of this critical area
The eastward transport of sediment from glaciated Greenland is illustrated by the contrast in mineralogy between ice-rafted debris (IRD) Icelandic basalt and Icelandic seafloor sediments (Fig. 3E and D). 2) What fraction of the sediment on the North Iceland shelf is derived from E/NE Greenland? The SedUnMix modelling indicates that downcore variations in mineral composition are well explained by local sources plus a combination of sediments derived from the “felsic” Kangerlussuaq Fjord and the more mafic outcrops of the Geikie Plateau
Counts of IRD clasts do not delimit source areas, but we show the quantitative Xray diffraction (qXRD) analyses can be used to characterize the fraction of sediment contributed from specific areas (Fig. 6) and to document long-term changes in these sources (Fig. 5)
Summary
Icelandic tidewater glaciers ceased to deliver ice-rafted debris (IRD > 2 mm) to the shelf ca 10,000 cal yr BP (Castaneda et al, 2004), whereas there are numerous tidewater glaciers across Denmark Strait along the E/NE Greenland margin (Nuttall, 1993; Bigg, 1999; Seale et al, 2011). In our area of interest this includes the Kangerlussuaq ice stream (Dwyer, 1995; Joughin et al, 2008), 19 tidewater glaciers that debouche to sea level from the Geikie Plateau (Nuttall, 1993), and several large outlets in Scoresby Sund and fjords to the north (Reeh, 1994; Bigg, 1999; Reeh et al, 2001; Seale et al, 2011). The contributions from specific sediment sources (tidewater glaciers in fjords, or from sea ice from the Arctic Ocean) are expected to decrease in influence along the ice transport path
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