Phytoplankton in wind-mixed layers

Phytoplankton are known to adapt to varying irradiance. In a wind-mixed surface layer, this photoresponse can change the integrated productivity of the water column. To explore this phenomenon, Dr. John Marra of the Lamont-Doherty Earth Observatory and I developed a new formulation for the phytoplankton photoresponse. We then incorporated this model into a wind-driven mixed-layer model.

The mixing model showed that the modelled photoresponse could increase the integrated production under certain conditions of wind forcing and diffuse attenuation of irradiance.

• Time response of phytoplankton photosynethesis under constant irradiance. Data for plots from Marra (1978a, b)
• Time response of phytoplankton photosynethesis (solid line, dots) under varying irradiance (dashed line).
• Time response of phytoplankton photosynethesis (solid line, dots) under fluctuating irradiance (dashed line).
• Vertical distribution of instantaneous photosynthetic rate of 2000 cells in a wind-driven mixed layer at 4 times during the day. Solid line is no wind mixing
• Vertical distribution of Pmax of the same cells. Solid line is no wind mixing.
• Animation of photosynthetic rate of 2000 cells in wind-mixed layer
• Animation of Pmax of cells from above animation

This work was funded in part by U.S. GLOBEC

Franks, P.J.S. and J. Marra. 1994. A simple new formulation for phytoplankton
     photoresponse and an application in a wind-driven mixed-layer model.
     Marine Ecology Progress Series 111:143-153.

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