PARENT SESSION

Symposium S2D Marine photosynthesis and production
Monday August 30th, 2004 2:40 PM-4:40 PM Room 510B
Chair: John Raven
Co-Chair: Doug Campbell

Impacts of eddies and mixing on plankton community structure and primary productivity in the sargasso sea. Thomas Bibby^*,1, Max Gorbunov¹, Paul Falkowski¹, ¹ Institute of Marine and Coastal Sciences, New Brunsiwck, New Jersey, USA

ABSTRACT- Estimates of new production in the oligotrophic waters of the main subtropical gyres are in excess of what has been predicted by traditional mechanisms of nutrient supply. Recent evidence suggests that nutrients induced into the euphotic zone by isopycynal displacements resulting from mesoscale eddies can result in an accumulation of chlorophyll in surface waters; potentially stimulating new primary productivity that could account for the observed discrepancy. Presented here are the results of the first stage of a two-year project (summer 2004, summer 2005) that sets out to characterise the physical, chemical and biological characteristics of an eddy-induced nutrient-upwelling events in the Sargasso Sea. Relatively few direct observations of this process are available, owing to the spatial and temporal intermittency of the events which drive it. Here, satellite based altimetry has been used to locate eddy-induced upwelling-events in the Sargasso Sea which then guided ship based analysis of the phytoplankton physiological response and changes in community structure. The use of continuous measurements obtained by a Fast Repetition Rate Fluoromerty (FRRF) has allowed the photosynthetic parameters of the changing phytoplankton community to be monitored in real time, in addition a range of nutrient-enrichment incubation experiments has been employed to identify the limiting nutrients preceding the Eddy event and the effect that their reintroduction has on photosynthetic parameters and the species assemblage of phytoplankton. The data here is planned to be incorporated into basin-scale eddy-resolving models of the North Atlantic in order to investigate the impacts of this coupled physical-biological dynamic on large scale biogeochemical dynamics.

KEY WORDS: primary productivity, eddy, FRRF