Abstract
Dramatic changes in plankton productivity, abundance, vertical distribution, and relative sensitivity to added copper occurred during an 8-day station within the Gulf Loop Intrusion in February 1981. Passage of an atmospheric front associated with a continental high temporarily deepened the mixed layer from 20–40 m to 110–120 m but did not measurably increase inorganic nutrients within it. Primary productivity increased from 14 to 62 mg C m −2 h −1 and bacterioplanktoon increased from 4.3 × 10 13 to 6.1 × 10 13 cells m −2. Vertical redistribution of biomass may have decoupled zooplankton grazing from primary production contributing to increases in phytoplankton and bacterioplankton standing stocks. Satellite thermal imagery indicated that the position was well removed from the active field of the Loop Current, but detailed analysis of hydrographic data revealed that wind-induced mixing had been superimposed upon an advective event—the passage of a warm, low-salinity lens. Phytoplankton in the low-salinity lens were remarkably insensitive to added copper (4 × 10 −8 M) due to unusually high sequestering of added copper by qualitatively distinct marine humus. The observations were in marked contrast to previous ones at the same general location.
Published Version
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