Helene Bergsten

Biostratigraphic and sedimentological evidence of hydrographic changes in the Kattegat during the later part of the Holocene

Abstract Detailed sedimentological and micropaleontological investigations complemented with 14 C analyses were made in a large number of cores from the Kattegat. In general, the Holocene in the Kattegat is represented by sediments deposited since 4000 yrs B.P., resting directly upon glacial sediments. Sediments formed between the Younger Dryas and 4000 yrs B.P. are found in restricted areas near the coast, at present-day water depths of less than 20–25 m. The cores yield evidence of one pronounced hydrographic shift at 4000 yrs B.P. and two minor changes at 2000 and at about 300 yrs B.P. These three hydrographic shifts are, in addition to sedimentological changes, also characterized by the following biostratigraphic markers: (1) At 4000 yrs B.P. the benthic foraminifers, Nonion labradoricum , a different variety of Ammonia batavus and a benthic microforaminiferal fauna became established, (2) at 2000 yrs B.P. a pronounced appearance of an algal cyst occurred, called here Varia type A, and (3) at about 300 yrs B.P. Varia type A peaked and subsequently vanished. The hydrographic shifts are attributed to changes in the inflow—outflow regime between the North Sea and the Skagerrak—Kattegat—Baltic and tentatively to changes in the large-scale circulation patterns of the North Atlantic.

Recent benthic foraminifera of a transect from the North Pole to the Yermak Plateau, eastern central Arctic Ocean

The Recent distribution of living and dead benthic foraminifera of the Arctic Ocean proper has been examined in surface sediments that were sampled during the International Arctic Ocean Expedition 1991 (Arctic 91). The samples represent the Amundsen and Nansen Basins, the Morris Jesup Rise, and the Yermak Plateau from 90°N to 79°42.4′N, 05°15.6′E. Due to the technical difficulties of deep-sea drilling in the Arctic Ocean these areas have, until now, been investigated only in very low density sampling. The Arctic 91 sites of this study cover a water depth range between 552 and 4375 m and represent three sites which are seasonally ice-free, although not yearly, while the other sites are characterized by permanent sea-ice. There is a Recent production of benthic foraminifera in the whole investigation area and all surface samples contain both benthic and planktonic foraminifera. Abyssal assemblages are recorded in the Amundsen and Nansen Basins where Stetsonia arctica dominates with high abundances. It is, however, also possible to distinguish these two basins by the use of diagnostic species. At intermediate water depths (500 to 2000–2500 m) the faunas show higher diversities and higher abundances of Atlantic species than the deep-sea sites. Mixing of North Atlantic water down to approximately 2500 m, is suggested to explain the influx of Atlantic species on the Yermak Plateau and the Morris Jesup Rise. The foraminiferal tests are well preserved within the investigation area and dissolution does not seem to be very obvious in the deeper areas. There is no evidence from the Recent foraminiferal faunas that the bottom waters of the eastern, central Arctic Ocean are undersaturated with respect to calcium carbonate and the deep-sea areas appear, therefore, to lie above the present CCD.

An ice-margin oscillation during the Late Weichselian in the Lake Vänern area, SW Sweden

Abstract A Late Weichselian ice-margin oscillation close to the Levene moraine, SW Sweden, has been detected by means of detailed litho- and biostratigraphic investigations, complemented with geotechnical data. The two localities investigated, Tyskahagen and Satenas, are situated a few hundred metres, respectively south and north, from the Levene moraine. A varying sediment composition with fine-grained sediments, layers of friction material, boulders/boulder-clay and a strongly over-consolidated clay is assumed to be a result of at least one distinct ice-margin readvance at the locality Satenas. The readvance took place over previously deposited sediments. The result is compressed sediment sequences and stratigraphic disturbances of a very local nature. The event discussed took place in a glacio-marine depositional environment in the Lake Vanern estuary, with water depths of about 40–80 m.