Ocean color and sun-stimulated phytoplankton fluorescence

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The surface expression of the WHOTS mooring. Four downward-looking spectroradiometers on this buoy monitors water-leaving radiance in four directions, and an upward looking spectroradiometer  monitors incoming solar irradiance.

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View of the Air-Sea Interaction Tower (ASIT) at the WHOI Martha's Vineyard Coastal Observatory. The location of the radiometers is indicated by an arrow.


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A closeup view of the radiometer system on the ASIT. Two radiometers (left) measure the radiance emitted by the ocean at two angles from the solar plane. Another radiometer (right) measures the incident irradiance at the same seven wavelengths of the two radiometers. Data are transmitted in real time by an Ethernet link to computers in our shore laboratory where they are logged, processed, and quality-controlled.


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An example of one day of radiometer data from the SAS system on the ASIT tower. Diurnal incident PAR and spectral irradiance (top two plots) indicate a cloud-free day. Water-leaving spectral radiances (bottom two plots) contain variability due not only to the incident solar radiation but also physiological factors in the photosynthetic apparatus of phytoplankton, optical properties of the water column, geometrical issues with the observations, and sea state. Separating these various controls on sun-stimulated fluorescence is extremely difficult without making these measurements in conjunction with other ocean properties currently monitored by instrumentation on the ASIT.


Sun-stimulated fluorescence on ocean moorings


Collaborators:
Dr. Robert Weller, WHOI Physical Oceanography Department
Dr. Al Plueddemann, WHOI Physical Oceanography Department

I received a 2009 NASA New Investigator award to begin long-term, ocean color radiometric time series on open ocean moorings. My main interest in this is to better unerstand short-term and seasonal variability in the diurnal pattern of sun-stimulated phytoplankton fluorescence. An abovewater, five-radiometer sensor suite is being integrated into the WHOTS8 mooring to be deployed at Station ALOHA off Oahu in fall 2011. This suite will record spectral water-leaving radiance as well as incident spectral irradiance, and telemeter these data to shore using an Iridium link. In addition, three underwater on the mooring will measure chlorophyl lfluorescence at three depths in the euphotic zone, to assess diurnal variability in fluorescence quenching.


Sun-stimulated fluorescence from fixed platforms


Collaborators:
Dr. Heidi Sosik, WHOI Biology Department
Dr. Ricardo Letelier, College of Oceanic & Atmospheric Sciences, Oregon State University

Starting December 2007 we began collecting continuous measurements of the sun-stimulated chlorophyll fluorescence of phytoplankton at the Air-Sea Interactions Tower (ASIT) in WHOI's Martha's Vineyard Coastal Observatory (MVCO). Tower-mounted radiometers measure sun-stimulated fluorescence from the ocean as well as incident irradiance at seven wavelengths in the visible with high temporal variability (6 Hz). These radiometric data are combined with the broad array of other biological and physical ocean properties also measured by in-water and surface instruments on the ASIT, making it possible to begin developing robust models for understanding how different environmental factors contribute to variability in sun-stimulated fluorescence.


 

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Last updated April 17, 2011
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