Biological and physical controls on dissolved dimethylsulfide over the north-eastern continental shelf of New Zealand

Data presented in this paper are part of an extensive investigation of the physics of cross-shelf water mass exchange in the north-east of New Zealand and its effect on biological processes. Levels of dissolved dimethylsulfid e (DMS) were quantified in relation to physical processes and phytoplankton biomass. Measurements were made at three main sites over the north-east co ntinental shelf of New Zealand's North Island during a current-driven upwel ling event in late spring 1996 (October) and an oceanic surface water intru sion event in summer 1997 (January). DMS concentrations in the euphotic zon e ranged between 0.4 and 12.9 nmol dm(-3). Integrated water column DMS conc entrations ranged from 33 to 173 mu mol m(-2) in late spring during the hig her biomass (15-62 Chl-a mg m(-2)) month of October, and from 25 to 38 mu m ol m(-2) in summer during the generally lower biomass (16-42 Chl-a mg m(-2) ) month of January. We observed high levels of DMS in the surface waters at an Inner Shelf site in association with a Noctiluca scintillans bloom whic h is likely to have enhanced lysis of DMSP-producing algal cells during pha gotrophy. Integrated DMS concentrations increased three-fold at a Mid Shelf site over a period of a week in conjunction with a doubling of algal bioma ss. A high correlation (r(2) = 0.911, significant <0.001) of integrated DMS and chlorophyll-a concentrations for compiled data from all stations indic ated that chlorophyll-a biomass may be a reasonable predictor of DMS in thi s region, even under highly variable hydrographic conditions. Integrated ba cterial production was inversely correlated to DMS production, indicating a ctive bacterial consumption of DMS and/or its precursor. (C) 2000 Elsevier Science B.V. All rights reserved.