The Baltic Sea Bottom Currents and Contourite Drifts: an Analogue of the Deep-Sea Along-Slope Contouritic Processes

Abstract:

It was suggested by Sivkov et al. (2002) that muddy contourite drifts are formed not only in the deep ocean but also in the shallow Baltic Sea. Such drifts are formed in southern and central subbasins of the Baltic Sea where so-called “major inflows” of the relatively saline water from the northeast Atlantic (North Sea) penetrate. Today, major inflows occur sporadically (every few years) and circulate mainly as along-slope geostrophic (contour) currents. Here we present new evidence of elongated mounded drift which have been recognized in the central part of the Baltic Sea (the Gotland Deep), hereafter, the Gotland Drift. Elongation is generally parallel to the margin, but progradation leads to the drift being extended almost perpendicular to the margin. The Gotland Drift spans several 10s of kilometers with width about 10 km. The main feature of the drift is that it composed of the highly gas-saturated contourite sediments. This is manifested in large numbers of pockmarks on the drift surface. Non-depositional (not erosional!) discontinuities in the Gotland Drift typically result from a non-depositional period reflecting decreased bottom current intensity. Each period of intensified bottom current is linked to hydrological events (transgressions). Such events can have either climatic (variations in ocean/sea level) or tectonic origin. For example, the bathymetric conditions at sills and gateways that control bottom water exchange between ocean and the Baltic Sea. A total of 4 possible transgressions which occurred during the last 8 ka, i.e. since the Danish straits became open, linking the ocean with European Seas, are established. The similarity between the Baltic Sea and deep-sea contourite drifts allow to use the shallow Baltic Sea as “natural laboratory” to study of along-slope contouritic processes in the oceans.

This work was supported by Russian Scientific Fund (grant No. 14-37-00047).