Abstract
Abstract. During the austral summer of 2008, we carried out a high resolution survey of the microplankton communities along a south to north transect covering a range of environments across the Scotia Sea, Southern Ocean; high and low productivity, sea-ice to open water conditions, and over a number of oceanographic fronts and bathymetric features. Cluster analysis revealed five distinct communities that were geographically constrained by physical features of bathymetry and fronts. From south to north the communities were: (1) the South Orkney group, a mixed community of naked dinoflagellates and heavily silicified diatoms, (2) southern Scotia Sea, a mixed community of cyptophytes and naked dinoflagellates, (3) central Scotia Sea, dominated by naked dinoflagellates, (4) southwest of the island of South Georgia, lightly silicified diatoms and naked dinoflagellates (5) northwest of South Georgia, dominated by diatoms. Data from a previous summer cruise (2003) to the Scotia Sea followed a similar pattern of community distribution. MODIS images, Chlorophyll a and macronutrient deficits revealed dense phytoplankton blooms occurred around the island of South Georgia, were absent near the ice edge and in the central Scotia Sea and were moderate in the southern Scotia Sea. Using these environmental factors, together with community composition, we propose that south of the Southern Antarctic Circumpolar Current Front, biogenic silica is preferentially exported and north of the front, in the vicinity of South Georgia, carbon is exported to depth.
Highlights
The Scotia Sea, in the south Atlantic sector of the Southern Ocean, is a region of complex bathymetry with numerous seamounts and oceanic islands
Ocean colour images have shown these topographic features support extensive blooms which stand in stark contrast to the high-nutrient, low chlorophyll (HNLC) conditions characterising much of the open Southern Ocean (Comiso et al, 1993; Arrigo et al, 1998; Holm-Hansen et al, 2004a; Korb et al, 2004; Tyrrell et al, 2005)
Oceanographic surveys have demonstrated the patchiness of blooms in the region, with areas of very high biomass and productivity adjacent to patches of HNLC-like water (Holm-Hansen et al, 2004b; Korb et al, 2005)
Summary
The Scotia Sea, in the south Atlantic sector of the Southern Ocean, is a region of complex bathymetry with numerous seamounts and oceanic islands. Blooms at South Georgia, on the northern Scotia Ridge, are generally dominated by diatoms but can contain significant numbers of heterotrophic dinoflagellates (Korb et al, 2008; Korb and Whitehouse, 2004). Such a food web could have important implications for carbon export in this region with diatoms as potential carbon sinks vs carbon recycling by heterotrophic dinoflagellates (Archer et al, 1996; Smetacek et al, 2004). We relate the patterns of community composition to environmental conditions and discuss our results in terms of potential carbon export during the austral summer
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