Hydrological Features Of A Warm Core Eddy And Their Biological Implications

The. Advanced Research Inst i tute (ARI) on Dynamic Processes in the Chemistry of the Upper OCean had its origins in discussions by the NATO Special Programme Panel on Marine Sciences during 1978 when a wide range of topics for future ARIs was being considered. What was then envisaged was a workshop on chemical aspects of the oceanic mixed layer, at which consider ation would be given to the inputs, cycling and removal of material, and the problems involved in the quantitative assessment of fluxes. It was realised that any attempt to model chemical processes would need the active collaboration of workers from other fields, especially physical oceano graphers concerned with air-sea interaction and turbulence, and biological oceano~raphers with expertise in primary productivity and the cycling of particulate and dissolved organic material. As plans for the ARI developed further a somewhat different emphasis emerged, focused on the question as to how chemists should set about observing an environment as variable and dynamic as the upper ocean and selecting the appropriate scales for the framework of measurements to study a particular process, especially in the light of current knowledge of physical processes of transport and mixing. It was plain that the capabil ity of physical oceanographic methods to resolve differences on small spatial and temporal scales is considerably ahead of the capabilities of biologists and chemists who rely upon discrete sampling and complex lab oratory manipulations in order to obtain most of their data.

It is now well known that the mid-ocean flow is almost everywhere domi nated by so-called synoptic or meso-scale eddies, rotating about nearly vertical axes and extending throughout the water column. A typical mid ocean horizontal scale is 100 km and a time scale is 100 days: these meso scale eddies have swirl speeds of order 10 cm s -1 which are usually con siderably greater than the long-term average flow. Many types of eddies with somewhat different scales and characteristics have been identified. The existence of such eddies was suspected by navigators more than a century ago and confirmed by the world of C. O'D. Iselin and V. B. Stock man in the 1930's. Measurements from RIV Aries in 1959/60, using the then newly developed neutrally buoyant floats, indicated the main char acteristics of the eddies in the deep ocean of the NW Atlantic while a se ries of Soviet moored current-meter arrays culminated, in POLYGON- 1970, in the explicit mapping of an energetic anticyclonic eddy in the tropical NE Atlantic. In 1973 a large collaborative (mainly U. S. , U. K. ) program, MODE-I, produced synoptic charts for an area of the NW At lantic and confirmed the existence of an open ocean eddy field and es tablished its characteristics. Meso-scale eddies are now known to be of interest and importance to marine chemists and biologists as well as to physical oceanographers and meteorologists.