Aquatic Sciences Meeting, Albuquerque 2001

SS02 Photochemical Reactions In Surface Waters: A Major Issue in the 21st Century? (Environmental Connections)

Date: Friday, February 16, 2001, Time: 11:00:00 AM

Location: San Miguel

Nelson, N, B, ICESS, University of California, Santa Barbara, USA, norm@icess.ucsb.edu

Scott, A, J, Bermuda Biological Station for Research, St. George's, Bermuda, ascott@bbsr.edu

LIGHT ENERGY AVAILABILITY FOR PHOTOCHEMISTRY IN THE SARGASSO SEA ON SECONDS TO SEASONS TIME SCALES

An interdisciplinary study of the cycling of short-lived photochemically-produced species was carried out in the Sargasso Sea near the BATS time-series site (near 31N, 64W) in August of 1999 (summer) and March 2000 (spring). Above-surface spectral irradiance (325-555 nm in 7 discrete bands) was measured continuously during each of the ca.10 day studies. Underwater spectroradiometer profiles (2-3 per day) were performed to determine the diffuse attenuation coefficient spectrum. Absorption spectra of colored dissolved organic matter (CDOM) from discrete water samples were also measured. We combined these three sets of measurements to prepare a time-depth-wavelength data set describing light energy availability (i.e. quanta absorbed and capable of initiating photochemistry). From a preliminary analysis of the data we suggest that the effect of greater light availability in the summer is mostly offset by decreased surface CDOM (a consequence of bleaching in stratified waters), leading to similar areal photochemical reaction rates year-round. The impact of shorter term processes impacting light availability (e.g. cloudiness) and other competing processes (light absorption by phytoplankton and other particulate matter) will also be discussed.

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Aquatic Sciences Meeting, Albuquerque 2001

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