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Free Content Subsurface chlorophyll maximum and hydrodynamics of the water column

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The vertical distributions of chlorophyll a (in vivo fluorescence) and hydrodynamic properties were monitored in the Gulf of St. Lawrence (Canada) from 6 to 10 August 1983, using an automatic yo-yo profiling system and a chain of 4 current meters. Spectral analyses of temperature and in vivo fluorescence series showed that dominant frequencies were associated with internal waves (∼16 h inertial frequency). A subsurface chlorophyll maximum was continuously observed in the lower part of the 20 m thick photic layer, at a depth corresponding with maximum vertical stability of the water column, just above the nutricline.

The depth of maximum phytoplankton production, at least on sunny days, corresponded to that of the subsurface chlorophyll maximum and of the maximum in vertical stability. This close association persisted despite strong horizontal advection and vertical movements caused by internal waves. Photosynthetic adjustment did occur in the water column: higher vertical stability at depth favored shade adaptation of the phytoplankton in the layer of maximum stability, as compared to the more light-adapted cells of the upper well-mixed layer. At our sampling station, vertical turbulent diffusion seemed to be high enough to replenish nutrients in the photic layer, so that they never became completely exhausted, even in surface waters. Therefore, the observed subsurface chlorophyll maximum not only resulted from environmental conditions more favorable for phytoplankton accumulation and growth, but it also involved active photosynthetic responses of phytoplankton.

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Document Type: Research Article

Publication date: May 1, 1987

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  • The Journal of Marine Research, one of the oldest journals in American marine science, publishes peer-reviewed research articles covering a broad array of topics in physical, biological and chemical oceanography. Articles that deal with processes, as well as those that report significant observations, are welcome. Biological studies involving coupling between ecological and physical processes are preferred over those that report systematics. The editors strive always to serve authors and readers in the academic oceanographic community by publishing papers vital to the marine research in the long and rich tradition of the Sears Foundation for Marine Research. We welcome you to the Journal of Marine Research.
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