Gustafson, A. B. University of Maryland CES/Horn Point Labs, abgust@hpl.umces.edu
Fisher, T. B. University of Maryland-CES/Horn Point Laboratory, fisher@hpl.umces.edu
Haas, L. W. Virginia Institute of Marine Sciences, lhaas@vims.edu
Walstad, L. University of Maryland-CES/Horn Point Laboratory, walstad@hpl.umces.edu

 
THE SURFACE MIXED LAYER OF CHESAPEAKE BAY, USA
 
TS profiles and Secchi depths at 16 stations were obtained from the CBP database for 1990-1996. We computed density and surface mixed layer depth (Zm), using a threshhold density gradient of 0.4 kg m-4 to define the top of the pycnocline. We also computed the ratio of Zm to Secchi depth (S) as a dimensionless indicator of light limitation of phytoplankton growth. Down the axis of the Bay, both Zm and S generally increased from 3-10 m and 1-4 m, respectively. Secchi varied within narrow ranges at each station, but Zm varied seasonally, increasing from a spring minimum to a fall maximum. Occasional deep mixing also resulted from winter storms. Zm/S ranged over 2-8 and followed the seasonal and spatial variations in Zm. In tributaries, both Zm and S were shallower at mesohaline stations than at adjacent bay stations, and Zm/S was higher (3-10). At tidal fresh stations, Zm was usually defined by the bottom, but S was shallower, resulting in the greatest values of Zm/S (20-40) at stations where light limitation was common. These data suggest that Zm/S may be a simple indicator of light limitation in estuaries, similar to that proposed by Wofsy as Zm*kz.
 
Day: Friday, Feb. 5
Time: 09:00 - 09:15am
Location: Eldorado Hotel
 
Code: CS57FR0900E