Determination of Bio-optical Provinces in the North Atlantic Ocean: A Collaboration between JGOFS and WOCE

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*** 9618722 Marra The last series of WOCE Hydrographic Program (WHP) cruises will begin the North Atlantic in summer, 1997. For JGOFS, the collaboration with the WHP has been for a CO2 survey, and for bio-optics and pigments, in order to obtain a spatially extensive data set on upper ocean properties. For the WHP section A20 (roughly along 55 W from the Grand Banks to Trinidad), data on bio-optical (spectral irradiance, fluorescence, beam attenuation, chlorophyll-a) and physical (temperature, salinity) properties in near- surface waters will be collected at a station spacing of no more than 100 km. The objective of this observational program is to determine whether the biogeochemical provinces that have been described for the western North Atlantic have a big-optical basis. The descriptions of the provinces rely on currents, water-column stability, temperature, proximity to land, etc., but are only semi-quantitative. The hypothesis to be tested is whether these provinces exist in a big-optical sense, the null hypothesis being that there are no big-optical differences along the transect beyond the distinction of Case- 1 and Case-2 waters. Since the cruise will occur in summer, with surface temperature differences at a minimum, the data collected will be a stronger test of the alternative hypothesis (that bio- optical provinces exist) than otherwise. Once collated and organized, the data will be made available to all investigators via the World-Wide Web. If biogeochemical provinces can be shown to exist as big-optical entities, it will allow greater precision in the calculation of primary production from satellite imagery, and also prove useful in helping to classify ocean areas with respect to their plankton ecology. Biogeochemical provinces are thus a means or organizing the study of the mechanistic basis of plankton processes. It is expected that the WHP cruises will occur after the launch (now scheduled for February, 1997) of the new ocean color sensor, SeaW iFS, and thus this observational program may assist in providing sea-truth for the satellite data.