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Primary Productivity

Primary productivity in the ocean is the rate of carbon fixation as a direct result of photosynthesis (measured in mg C/m2/day), and plays an essential role in the global carbon cycle. Although marine photosynthetic organisms are almost entirely single-celled phytoplankton that comprise less than 1 percent of the the total global plant biomass, they account for about 40 percent of total global carbon fixation.
 

WET Labs sensors allow you to monitoring chlorophyll in situ to derive primary production proxy in various environments such as a coastal estuary.

Washington State Dept. of Ecology deployed moored WETStars and CT meters at four locations in Willapa Bay WA from 1998 through 2000. The goals of this study were to evaluate watershed vs. oceanic influence on the estuary and to assess controls on primary production. Chlorophyll fluorescence was measured at a 15-minute resolution for over three years in the turbid, productive and physically dynamic estuary, severely testing the performance of the sensors.

Transmissometers are effective in monitoring diel cycles in the particle load. Optical instrumentation can provide crucial data for biogeochemical studies. In the open ocean, the particle field is dominated by phytoplankton and biologically derived particles such as empty tests and plant material.
 
With a well designed sampling scheme, optical instruments can capture the variability in biological systems driven by physical forcing functions such as the light field and vertical mixing. In the Equatorial Pacific, beam attenuation profiles taken with a 650 nm transmissiometer showed diel cycles in the particle load in the photic zone. The daily change in the total particle load for three days during which profiles were taken every three hours can be represented by a sine curve. Taking the peak-to-trough difference and dividing by the trough value yields a dimensionless growth rate (mu) that can be compared to traditional methods of estimating phytoplankton productivity, such as labled CO2 uptake and physiological modeling.
 
 The beam attenuation coefficient in the red wavelengths can be well correlated with the both the total particle load and the particulate organic carbon concentration. The transmissometer data set can then be used to calculate integrated production and test models of production. Spectral attenuation and absorption instruments (ac-s) expand the available data sets by constraining the dissolved organic carbon pool, the particle size spectra and the particle composition
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