Holocene sediment properties of the East Greenland and Iceland continental shelves bordering Denmark Strait (64-68°N), North Atlantic

摘要

The oceanographic Polar Front separates the East Greenland and Iceland margins. Surface water temperatures across Denmark Strait vary by 8-12 ℃ and represent one of the steepest oceanographic gradients on earth. The East Greenland margin is a polar environment, with extensive sea-ice cover and calving glacier margins; in contrast, the Iceland shelf is much more temperate, and freshwater run-off is a key component in land-ocean sediment transfers. Average sediment properties from these two contrasting climate and oceanographic continental shelf environments are compared in the spatial domain at 13 sites; the data represent the last 10 000 radiocarbon years of 'normal' marine sedimentation for the two regions. The two regions have similar average rates of sediment accumulation (around 43·5 cm kyr~(-1)), so that this key variable is factored out in explaining any differences in sediment properties. Dry sediment density, moisture content, hygroscopic moisture, total organic carbon and carbonate contents, mass magnetic susceptibility and the percentages of sand and silt are compared focusing on: (1) median values for sediment properties; and (2) downcore variability, measured by the coefficient of variation (CV). There are significant differences in all but one (hygroscopic moisture) of the sediment properties between Iceland and East Greenland; in four cases, the sense of the differences was not as predicted. In terms of downcore variation (CV), no difference was found between the two regions, nor between the 13 sites, whereas there are some significant differences between the variables. Carbonate and mass magnetic susceptibility have the largest spreads, and moisture content and dry sediment density are the least variable. Protocols are developed to identify the 'type core' in a regional series of sites. The results indicate a need to develop a regional perspective on sediment properties, both as inputs to models of sedimentary processes in different polar/arctic environments, and as an indication of which sediment properties might be best suited for palaeoenvironmental downcore time series.