Regional relationships between biological and hydrographical properties in the Weddell Gyre in late austral winter 1989

Abstract

The surface layer properties of the Weddell Gyre were measured during a cruise of the R/V “Polarstern” in September and October 1989 on a transect between the tip of the Antarctic Peninsula (northwestern Weddell Sea) and Cape Norvegia (southeastern Weddell Sea). Sea ice cover, hydrography, and the distribution of inorganic nutrients and dissolved oxygen represented late winter conditions: a quasi-homogeneous Winter Water layer with near-freezing temperatures, high salinities and high levels of nitrate, and undersaturated with dissolved oxygen. The area investigated could be divided into three regions based on the physical, chemical and biological patterns: the western and eastern flanks and the gyre interior. In all areas, autotrophic biomass in sea ice was high in comparison with the underlying water column. Within the sea ice mainly diatoms and dinoflagellates were present, but the dominant autotrophic organisms in the water column were nanoflagellates. Ammonium values were relatively high in the Winter Water layer in the central region, indicating heterotrophic activity. Mesozooplankton was dominated by copepods, which can in turn be divided into two groups: overwintering, inactive Calanus acutus were found in the Warm Deep Water, whereas actively feeding Calanus propinquus were most abundant in the upper 120 m of the water column under the sea ice in the central region. These spatial differences may influence development of the respective summer pelagic communities.