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Abstract

Comparison of T and S values in areas 1, 2, and 3 in the Bransfield Strait and Admiralty Bay (Fig. 1) shows that the warmest waters are found in area 1, while the coldest in area 3. Surface salinity is the lowest in area 2 as a result of water outflow from land. In area 3 vertical salinity variations are the lowest, with the maximum occurring at the surface. At 500 m depth the highest salinity is recorded in area 1. The most homogeneous distribution of temperature and salinity is observed in area 3. In Admiralty Bay, in the annual cycle of 1995 water temperatures at 4 m, 10 m and 100 m are similar to those in 1979 except in the winter, when they are lower.
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Abstract

A year-round (3 March 1994 - 28 February 1995) phytoplankton study in Admiralty Bay revealed nanoplankton flagellates (< 20 μm) to be the major algae of the plankton, both in terms of cell numbers and carbon biomass. Their quantities fluctuated widely thoroughly the year showing several peaks, in May, April, December and January. Summer maximum of the group in December was mainly due to Cryptophyceae (4.9 x 106 cells l-1; 98.0 μg C 1-1) and Prasinophyceae (7.3 x 105 cells -1; 33.5 μg C -1). Diatoms were usually scarce (max. 6.8 x 105 cells -1; 7.82 p:g C 1-1) and were dominated by small species of Thalassiosira and by Nitzschia spp. (Pseudonitzschia); the domination structure somewhat differed from that observed in Admiralty Bay in the summer of 1977/78. Algal peaks were related to the surface water (4 m depth) temperature rise from +0.16 to +1.71˚C. Summer phytoplankton maxima were about 5-fold greater than those recorded in the summer of 1977/78.
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Abstract

Net phytoplankton cell numbers in 50 m water column of Admiralty Bay ranged between 0.2 x 10 5 x m-2 on 24 August 1990 and 2.3 x 10 7 x m-2 on 15 November 1990. Cluster analysis has confirmed the presence of two groups of samples: spring and summer ones (October to April), rich in cells and in species, and, on the other hand, winter samples (June to August) impoverished in algae. Spring and summer fluctuations of diatoms were mainly due to Corethron criophilum, Rhizosolenia alata and its varieties, R. hebetata f. semispina, Thalassiosira spp., Chaetoceros spp., and Nitzschia spp. (Fragilariopsis and Pseudonitzschia groups). The abundance and succession of species in Admiralty Bay reflect seasonal differences in diatom growth; they also reflect mixed populations of the Weddell and Bellingshausen seas entering Admiralty Bay via Bransfield Strait. Striking poverty of algae in some summer samples can most likely be attributed to zooplankton grazing.
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