229 resultados para 080-1


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With the examination of multinet catches (63 µm mesh size), the present study analyzes the distribution of planktonic foraminifera in Polar regions: the Labrador Sea, Greenland Sea at 75°N and Fram Strait at 80°N. The community of the planktonic foraminifera, which in the study area mainly consists of six species: left and right-coiling N. pachyderma, T. quinqueloba, G. bulloides, G. glutinata and G. uvula, is primarily controlled by the temperature in the different water masses. Besides hydrographic parameters, the changes in the horizontal and vertical distribution of N. pachyderma (s.) and T. quinqueloba as well as their shell size distribution in the study area are primarily influenced by the synchrone reproduction, which is coupled to the lunar cycle. Detailed examinations of the isotope signal in dependency on the shell size and weight for N. pachyderma (s.) and T. quinqueloba from plankton tows, indicated the weight or degree of calcification to not be the primary factor controlling the isotope signal of encrusted specimens.The d18O vital effect is primarily caused by the thermal stratification of the water column, whereas the d13C vital effect mainly results from the ontogenetic development.

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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.

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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.