Distributions and photosynthesis of phototrophs in sea-surface films

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Abstract
An automatic sampler was used to collect water from the sea-surface microlayer and from 10 cm below the surface during repeated transects in the Damariscotta estuary, Maine, USA. The fluorescence of chlorophyll a, ultraviolet absorbance, temperature and conductivity were measured continuously. Discrete samples were taken for measurements of chlorophyll concentration, in vivo fluorescence, and photosynthesis vs irradiance (P-I). Patterns observed during the transects were in substantial agreement with a previous study of surface films in the Damariscotta estuary, but the spatial resolution was vastly better. Dissolved organic matter, as indicated by ultraviolet absorbance, and photosynthetic cells (in vivo fluorescence) showed similar patterns of enrichment in slicks. Chlorophyll concentrations were highest in slicks, with enhancements in some of 5 times or more over subsurface water. In clean regions, however, chlorophyll in the surface layer was often slightly depleted as compared to subsurface water. The photoautotrophs in surface films were photosynthetically competent and physiologically similar to those from 10 cm below the surface, with P-I curves quite typical for healthy phytoplankton. It is possible that photosynthesis in sea surface films was mildly inhibited by solar radiation, but severe stress from exposure to bright light was evident neither in fresh samples nor in those held in bottles at the surface for several hours.