Clay minerals in the Norwegian Sea and Fram Strait, investigation from sediment traps and cores

The grain size distribution and clay mineral composition of lithogenic particles of ice-rafted material, sinking matter, surface sediments, as well as from deep-sea cores are analysed. The samples were collected in the Fram Strait, the Arctic Ocean, and the Norwegian Sea during several expeditions with the research vessels "Polarstern", "Meteor" and "Poseidon", and Norwegian rearch vessels. Sinking matter was caught with sediment traps, fitted with timer-controlled sample changers, which had been deployde in the sea for usually one year.

Physical oceanography during POLARSTERN cruise ARK-XVIII/1a

In spite of the lack of bottom reaching convection in the Greenland Sea since the 1980s, convection continues to ventilate the Greenland Gyre down to intermediate depth. The variability of this ventilation activity is determined here annually for eight winters according to a multiple criteria catalogue, applied to annual summer conductivity-temperature-depth transects along 75°N. The comparison of the ventilation depths with the meteorological forcing, the ice cover, and the stratification of the water column shows the decisive influence of the hydrographic structure in the upper and intermediate layers. Ice, on the other hand, is not necessary for convection to occur. Ice formation does not even lead to particularly deep convection. A stability maximum, which currently dominates the vertical structure of the water column at medium depth, limits the ventilation depths effectively.

Biogeochemistry of the Eastern Weddell Gyre

The Southern Ocean (SO) plays a key role in modulating atmospheric CO2 via physical and biological processes. However, over much of the SO, biological activity is iron-limited. New in situ data from the Antarctic zone south of Africa in a region centered at -20°E - 25°E reveal a previously overlooked region of high primary production, comparable in size to the northwest African upwelling region. Here, sea ice together with enclosed icebergs is channeled by prevailing winds to the eastern boundary of the Weddell Gyre, where a sharp transition to warmer waters causes melting. This cumulative melting provides a steady source of iron, fuelling an intense phytoplankton bloom that is not fully captured by monthly satellite production estimates. These findings imply that future changes in sea-ice cover and dynamics could have a significant effect on carbon sequestration in the SO.