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MIDDLE HOLOCENE PALEOCEANOGRAPHY IN THE DENMARK STRAIT REGION

JENNINGS, ANNE E  Univ. of Colorado.
Stoner, Joe  Univ. of Colorado.
Hall, Ian  Univ. of Cardif.
Kristjansdottir, Greta  Univ. of Colorado.

Large shifts in paleoceanographic parameters including IRD, biogenic carbonate, stable isotopes, and foraminiferal assemblages, occur in Holocene sediments from shelf troughs in the Denmark Strait area. These shifts are well documented in two cores, MD99-2269 from the northern Iceland shelf, and MD99-2322 from the southeast Greenland shelf. A combined age model for these two cores was constructed after paleomagnetic depth correlations were made, allowing for very well constrained age control in these cores. The carbonate records of the two cores are very similar, although the Iceland shelf core has higher carbonate contents. A striking aspect of the carbonate records is an interval of high carbonate content between 6,200 and 2000 cal yrs. BP. Coccolith analyses on MD99-2269 (Giraudeau et al., submitted) have shown that production of Coccolithus pelagicus, a cold-water species, generated much of the carbonate in this interval of MD99-2269. The percentage distributions of Cassidulina neoteretis in MD99-2269, parallel the carbonate record of MD99-2269, supporting an interpretation of a stratified water column on the northern Iceland shelf, with Atlantic Water carried in the Irminger Current submerging beneath fresher Arctic or Polar waters as it rounded the Northwest Peninsula of Iceland. The closely parallel carbonate record of MD99-2322 suggests that the Kangerlussuaq Trough also was affected by Irminger Intermediate Water in the middle Holocene, and that this influence was strongest between 6200 and 2000 cal yrs. BP. In MD99-2322, delta 18-O data on planktic foraminifers shows isotopic depletions generally associated with relative low carbonate intervals as well as IRD spikes. These depletions likely represent strong Polar Water outflows in the East Greenland Current. The IRD content of MD99-2322 shows frequent spikes after 3300 cal yrs BP. To the north of Denmark Strait, on the East Greenland Shelf, core MD99-2317 has an almost identical IRD record to MD99-2322, suggesting cooling and/or thickening of the surface Polar Water, finally leading to a decline in the carbonate production on the shelves after 2000 cal yrs BP. MD99-2317 has very low carbonate content. However, the Atlantic Intermediate Water indicator species, C. neoteretis, shows large, abrupt percentage variations beginning at 6200 cal yrs BP, coincident with the rise in carbonate in the other two cores. The large percentage spikes in C. neoteretis give way to an almost fully agglutinated fauna by 2800 cal yrs BP. We anticipate that the variations in carbonate content and foraminiferal faunas reflect hydrographic and climatic conditions that relate to intermediate convection in the Iceland and possibly the Greenland seas. To explore this idea we make preliminary comparisons between these parameters and the sortable silt (mean of the 10-63 micron size fraction) in core MD99-2246, which is interpreted to reflect the flow strength of the DSOW.

REFERENCES
Giraudeau, J., Jennings, A.E., and Andrews, J.T., subm., Timing and mechanisms of surface and intermediate water circulation changes in the Nordic Seas over the last 10,000 cal. years: a view from the North Iceland Shelf. Quaternary Science Reviews.


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