Fronts and habitat zones in the Scotia Sea

The fronts in the Antarctic Circumpolar Current (ACC) comprise the Southern ACC Front (SACCF), the Polar Front (PF) and Sub-Antarctic Front (SAF), which, together with the Southern Boundary (SB), separate zones with distinct water mass properties in the Southern Ocean. They are important for describing habitat ranges of oceanic species over the range of trophic levels and are also key habitat zones in their own right for a variety of species. Frontal positions were studied along a transect running S to N across the Scotia Sea during three hydrographic cruises in spring 2006, summer 2008 and autumn 2009. Subsurface data from these cruises and Argo data are here combined with Aviso satellite absolute dynamic topography data to locate these fronts, facilitating study of their ecological significance within the Scotia Sea. Northern and southern dynamic height limits are found for each front, as opposed to the more usual one dimensional line. Thus the SB was found between −132 to −116 dyn cm, the SACCF between −115 to −99 dyn cm and the PF between −71 to −45 dyn cm. Argo data allow the sensitivity of the dynamic heights found to be tested against seasonal, interannual and longitudinal effects and each is found to be small. Although the SAF lay beyond the northern extent of the transect we sampled along, Argo profiles allowed us to determine its limits as lying between −5 and +29 dyn cm. The dynamic height limits found are thus suitable for assessing the location, in relation to fronts, of any sample or tracked animal within this area. The chlorophyll distribution across the Scotia Sea is assessed relative to frontal positions and known iron sources. The physical conditions (sea surface temperature, sea ice and mixed layer depth) along the sampling transect are also presented, allowing the oceanographic conditions of the stations occupied across the Scotia Sea to be assessed.

Details