Seasonal Transport Dynamics along Siberian Continental Margins
Final Report Abstract
The overall purpose of the project was to investigate transport mechanisms and shelf-basin exchange processes in Siberian shelf/margin regimes. To better understand the shelf-basin exchange of suspended particulate matter (SPM), salt and heat, one-year monitoring data as well as summer process studies from the Laptev Sea shelf and margin area were examined. SPM concentration was derived directly from filtered water samples and indirectly from optical and acoustic backscatter measurements. On the basis of 2002-2009 cross-slope (NABOS cruises), margin region measurements (TRANSDRIFT expeditions) and historical hydrographic data (1932-2008) the interannual variability of suspended particulate matter (SPM) dynamics, heat and salt exchange was examined. It could be shown that the interannual variability of the transport dynamics at the Laptev Sea shelf margin strongly correlates with the prevailing atmospheric circulation patterns over the adjacent Arctic Ocean and the associated distribution of the freshwater plume of the River Lena over the Laptev Sea shelf: during years with predominantly shoreward-directed winds on the shelf region (cyclonic circulation), on the eastern outer Laptev Sea shelf and continental margin region, the entire water column is assumed to be less stratified and vertical mixing is taking place. Thus, bottom material is resuspended and the bottom transport is increased, leading to increased potential export of SPM as well as of Laptev Sea shelf bottom waters into the deep Arctic Ocean. During years with northward winds (anticyclonic circulation) the water column on the eastern outer shelf and continental margin region is stratified due to the relatively far northward cross-shelf transport of the freshwater plume of the River Lena. Vertical mixing is limited to the upper water column and bottom transport is diminished. Export of SPM and Laptev Sea bottom shelf waters appear to be very small, even partly shut down. The data provided not only insight into offshelf transport processes but as well evidence for upwards transport of heat in the outer shelf margins, mainly during winter. The upwards transport seems to be associated with increased resuspension of bottom material in the polynya region. During the last two decades there is a positive trend in mean cyclone depth and radius over the Eurasian Basin, inducing cyclonic circulation patterns and increased transport dynamics on the outer shelf region. A continuation of this trend might not only impact the sediment budget but could also have negative consequences for the sensitive ecosystem due to changes in nutrient availability and light penetration.
Publications
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(2009). Eurasian Arctic shelf hydrography: Exchange and residence time of southern Laptev Sea waters. Continental Shelf Research
Bauch, D., Dmitrenko, I.A., Kirillov, S.A., Wegner, C., Hölemann, J., Pivovarov, S., Timokhov, L.A., Kassens, H.
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(2009). Exchange of Laptev Sea and Arctic Ocean halocline waters in response to atmospheric forcing. Journal of Geophysical Research, 114, C05008
Bauch, D., Dmitrenko, I.A., Wegner, C., Hölemann, J., Kirillov, S.A., Timokhov, L.A., Kassens, H.
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(2010). Impact of the Arctic Ocean Atlantic water layer on Siberian shelf hydrography, Journal of Geophysical Research, 115, C08010
Dmitrenko, I. A., Kirillov, S.A., Tremblay, L.B., Bauch, D., Hölemann, J.A., Krumpen, T., Kassens, H., Wegner, C., Heinemann, G., and Schröder, D.
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(2013). Interannual variability of surface and bottom sediment transport on the Lpatev Sea shelf during summer. Biogeosciences, 10, 1117-1129
Wegner, C., Bauch, D., Hölemann, J.A., Hölemann, Janout, M.A., Heim, B., Novikhin, A., Kassens, H., Timokhov, L.
