Martin, Adrian P., and Paula McLeod

Southampton Oceanography Centre, Empress Dock, Southampton, SO14 3ZH, UK, Tel: 00 44 (0)23 80596342/80596631, Fax: 00 44 (0)23 80596197, E-mail: apm1@soc.soton.ac.uk

Impact of mesoscale and sub-mesoscale physics on phytoplankton distribution and production

Ocean circulation exerts a very strong influence on phytoplankton ecology. This is especially true at the mesoscale and sub-mesoscale (1-500km) where there are high vertical velocities, large horizontal shear and strong dynamical features such as eddies and fronts. Work is presented illustrating three aspects of this interaction.

1. FILAMENTATION OF PHYTOPLANKTON DISTRIBUTIONS

The presence of streaks and filaments in phytoplankton distributions is a ubiquitous feature of satellite images of ocean colour. The role of the physical flow and biological processes in controlling the evolution and width of such filaments are quantified. The difficulties in observing and interpreting such filamentous fields by ship are also highlighted and addressed.

2. PATCHY PRIMARY PRODUCTIVITY

It is demonstrated that the new primary production in a region with heterogeneous but strong upwelling, such as that observed at the periphery of eddies and in frontal regions, is strongly influenced by horizontal mixing. In particular, the relationship between upwelling regions and eddies is shown to have a key role in controlling regional primary production.

3. EFFICIENCY OF EDDY-PUMPING

“Eddy-pumping” provides large intermittent pulses of nitrate to the euphotic zone. If all such upwelled nitrate can be converted to phytoplankton biomass (100% efficiency) then this phenomenon may close the problematic nitrate budget of the Sargasso Sea (N. Atlantic western sub-tropical gyre). The efficiency of this process is investigated using a variety of models. The resulting implications for the Sargasso Sea nitrate budget are subsequently discussed.