Burkill, P. CCMS Plymouth Marine Laboratory, p.burkill@pml.ac.uk
Edwards, E. CCMS Plymouth Marine Laboratory, e.edwards@pml.ac.uk

The conventional view on biological response to upwelling is that diatoms outcompete other phytoplankton groups and come to dominate the phytoplankton. During the German JGOFS programme in the Arabian Sea in 1997, we ran a 17-day drift experiment during the upswing of the summer monsoon. We were surprised to find few diatoms in surface waters and those present, particularly Dactyliosolen phukensis & Lauderia annulata, declined. At the same time photosynthetic and heterotrotrophic bacteria, including Synechococcus, increased. Such a response is more characteristic of a 'recycling' community rather than one fueled by 'new' production considered more typical of upwelling zones. During the drift experiment, upwelling was vigorous and surface nitrate concentrations raised from 8 to 14 ÁM. Microzooplankton populations were low, their herbivory decreased in parallel with the loss of diatoms and did not increase with the rise in picoplankton. This may be a key to what is forcing the system. The paper will elaborate on this and conclude that we now need to reappraise our views on biological response to upwelling and the factors that control production in such systems.
Day: Friday, Feb. 5
Time: 12:00 - 12:15pm
Location: Sweeney Center
Code: CS55FR1200S