BIOLOGICAL AND CHEMICAL OCEANOGRAPHIC PROCESSES IN SHALLOW NORTH WEST SHELF WATERS SURROUNDING THE HARRIET A PRODUCTION PLATFORM

Abstract

A diverse range of biological and chemical oceanographic properties and processes were measured in shallow NW shelf waters surrounding the Harriet A production platform in September 1995. Shelf waters were characterised by low plankton biomass levels, very low dissolved nutrient concentrations, relatively high water column primary and bacterial production rates, rapid nutrient uptake rates and rapid rates of water column particle turnover. While concentrations of dissolved organic carbon (DOC) and P04 in PFW were elevated ca. 100-fold relative to ambient concentrations in shelf waters, daily discharge fluxes are small relative to local water column stocks. In contrast, PFW discharges of NH4 were very large relative to regional water column stocks. Because local plankton are strongly N-limited, this NH4−N was very rapidly taken up (depletion times <1 hr) in the immediate vicinity of the platform. Water column particulate matter, largely derived from resuspended sediments appears to turn over on time scales of one day or less, rapidly stripping particle-associating PFW constituents from the water column. Production by local water column bacteria, but not phytoplankton was inhibited by additions of Harriet PFW. Toluene also inhibited phytoplankton and bacterial production to varying degree, but not isopropanol or NH4. The Harriet A PFW outfall discharges into a dynamic and productive pelagic ecosystem and at present discharge levels, appears to have relatively little effect on regional water column biological processes.