Lohrenz, S. E.. University of Southern Mississippi, steven.lohrenz@usm.edu
Schofield, O. E.. Rutgers Unversity, oscar@ahab.rutgers.edu
Fahnenstiel, G. L.. NOAA, fahnenstiel@glerl.noaa.gov
Millie, D. F.. USDA, dmillie@nola.srrc.usda.gov

A diatom bloom is a consistent feature of southern Lake Michigan during the spring isothermal period, which typically coincides with a recurrent coastal turbidity plume (RCP). Although light availability is believed to be important in regulating the bloom, the impact of the RCP is unclear. The recurrent coastal turbidity plume was particularly intense during the 1998 season with peak activity occurring in mid-March. Inherent and apparent optical properties of the RCP and adjacent waters were characterized using a combination of in situ instrumentation and in vitro spectrophotometric methods. Data were used to evaluate the hypothesis that spatial and temporal variations in photosynthesis and growth of phytoplankton were related to optical properties. Optical profiles included spectral measurements of downwelling irradiance, upwelling radiance, beam attenuation and absorption. Mean irradiance in the plume was <30% of that outside the plume. In the RCP, attenuation was 2-3 times higher, largely due to increased absorption. In contrast, scattering was only slightly higher within the RCP. Spectrophotometric analyses revealed that absorption was dominated by non-pigmented suspended particles and chromophoric dissolved organic matter. The intense RCP event was apparently responsible for a reduced intensity and altered composition of the spring diatom bloom (see Millie et al.).
Day: Thursday, Feb. 4
Time: 02:30 - 02:45pm
Location: Eldorado Hotel
Code: SS52TH0230E