The High Northern Latitudes are key areas for understanding the global climate system and its change through time. The deep-water exchange between the Arctic and Atlantic Oceans, for instance, is a major driver of the global thermohaline circulation controlling global heat transfer
and climate. The permanent Arctic sea-ice cover with its strong seasonal variations in the marginal areas has a strong influence on the earth´s albedo, marine ecosystem, and oceanic circulation, which are also all major mechanisms affecting the global climate. Despite the importance of the Arctic Ocean and its marginal seas for the global climate system, its exploration remained relatively small in comparison to the other world ocean areas.
In order to study the paleoceanographic and tectonic history in the Arctic Gateway region in more detail, drilling was performed at seven sites on the Iceland Plateau (Site 907), in the Fram Strait (Sites 908 and 909), on the southern Yermak Plateau (Sites 910 - 912), and at the East Greenland Continental Margin (Site 913) during Ocean Drilling Program Leg 151. At the different locations, sedimentary sequences (200 to 1040 m thick) of Quaternary to middle Eocene age were recovered (Myhre et al., 1994).
In this study we investigated organic carbon content and composition of the sediments to quantifiy the flux of marine and terrigenous organic matter, its change through time, and its relationship to changes in sea-ice distribution, oceanic currents, paleoclimate etc. For comparison, organic carbon data of surface and short core sediments, recovered during RV "Polarstern"-cruise ARCTIC ´91 are shown in this poster.
Very different processes must have controlled organic carbon deposition on the Yermak Plateau and in the Fram Strait area in comparison to the Greenland Sea and Iceland Plateau areas (Myhre et al., 1994), as indicated by the distinct differences in flux and composition of the organic carbon fractions. The very high flux of marine and terrigenous organic carbon at the northern Sites 909 and 911 requires (paleo-) oceanographic conditions different from the "normal open-ocean" ones. Because the Yermak Plateau and Fram Strait sites are in the area strongly influenced by the warm Westspitsbergen Current and the sea-ice cover, the interaction between both and the variations through time may be a dominant mechanism controlling the organic carbon deposition. Increased surface-water productivity near the ice-edge might have caused increased marine organic carbon supply. Due to strong sea-ice melting, major amounts of terrigenous particles (i.e., organic as well as siliciclastic) are released from the ice and settled to the sea floor. This may explain the high flux rate of terrigenous organic carbon, but also the high flux rates of bulk sediment (which is mainly of terrigenous origin).
The flux of organic carbon decreased significantly
from the late Pliocene to the Quaternary. The average accumulation rate of (marine) organic carbon on the Yermak Plateau prior to the major expansion of Northern Hemisphere glaciation at 2.6 Ma, was by a factor of 3 - 4 higher than the middle to late Quaternary rate. These drastic changes very probably reflect changes in sea-ice cover and Westspitsbergen Current intensity due to the extension of major northern hemisphere glaciation. A more closed sea-ice cover would certainly result in a decrease in surface-water productivity.
It appears to be possible to correlate long-term changes in organic carbon deposition during Miocene and Oligocene/ Eocene times between the record of Site 909 to similar records at other ODP sites. The middle Miocene organic carbon maximum (as well as the mid-Pliocene decrease) in organic carbon contents recorded at Site 909 also occur at Site 645 (ODP-Leg 105, Baffin Bay) (Stein, 1991).
Myhre, A. M., Thiede, J., Firth, J. V., et al., Proc. ODP, Init. Repts., 151, 925 (1994).
Stein, R., Lecture Notes in Earth Sciences 34, 217 (Springer, 1991).