Retention of phytoplankton by an eddy

A patch of high phytoplankton biomass, approximately 109 m2 in area, remained apparently stationary off King George Island, South Shetland Islands, over a period of at least 11 days. The patch was centred on an eddy at the apex of a tight meander formed by water passing round the eastern end of King George Island and being turned back immediately by the strong northeastern flow of water within the Bransfield Strait. Chlorophyll a biomass approached 1 g m2 and was concentrated within the top 50–75 m of water. The community consisted mainly of diatoms, which were growing actively. Growth in situ might have been sufficient to generate the observed high biomass from the general concentration of phytoplankton observed locally but only if all production had been retained within the patch. However, elevated biomass downcurrent of the patch suggested that physical retention was only about 50% efficient. It is concluded that the patch was derived from a pulse of high biomass which had been transported into the area and partially retained by the horizontal recirculation of water within the eddy. Dominant diatom species, Odontella weissflogii, Proboscia ‘alata’, Chaetoceros curvisetum and Thalassiosira tumida, were also predominant in a phytoplankton maximum off Brabant Island, upcurrent of the study site. This may have provided the seed population for the patch off King George Island. Vertical migration may have prevented krill accumulation within the eddy and it is concluded that some shallow eddies may partially insulate phytoplankton communities from heavy grazing pressure.


Publication status:
Authors: Heywood, R.B., Priddle, J.

1 August, 1987
Continental Shelf Research / 7
Link to published article: