Variability in satellite algorithms for regional assessments of pCO₂

Steven E. Lohrenz, The University of Southern Mississippi, steven.lohrenz@usm.edu (Presenting)
Wei-Jun Cai, University of Georgia - Athens, wcai@uga.edu
Xiaogang Chen, The University of Southern Mississippi, xiaogang.chen@usm.edu
Feizhou Chen, University of Georgia - Athens, fchen@uga.edu
Merritt Tuel, The University of Southern Mississippi, merritt.tuel@usm.edu
Sumit Chakraborty, The University of Southern Mississippi, sumit.chakraborty@usm.edu

A major objective of the U.S. Global Change Research Program Climate Change Science Program Strategic Plan and the North American Carbon Program is the application of satellite ocean color to characterize the spatial variability of air-sea CO₂ flux in the oceans adjacent to the North American continent. Recent studies in the northern Gulf of Mexico and elsewhere demonstrate that enhanced biological production in large river plumes may strongly influence surface pCO₂ levels. We have used a combination of satellite and ship-based observations to examine variability in surface pCO₂ and air-sea flux of CO₂ in the outflow region of the Mississippi River. Our findings suggest that late spring and early summer is a period of lower surface pCO₂ corresponding to a strong biological pump and autotrophic fixation of inorganic carbon. Other key environmental drivers appear to be seasonal variations in temperature and freshwater discharge. A key question will be the degree to which satellite imagery can be used to provide regional assessments of carbon system properties over seasonal time scales. This will depend on whether algorithms can be extended beyond periods for which in situ observations are available for validation and tuning. We examined this question by comparing principal component loadings and regression coefficients for four different periods. In all cases for the low salinity data sets, negative relationships to salinity were consistent with the observed decrease in surface pCO₂ in relationship to increasing salinity as seen in the underway survey data. Negative coefficients related to chlorophyll could be explained by decreasing pCO₂ in relationship to increasing chlorophyll as light availability increased along the river-ocean mixing gradient. Efforts to improve performance of algorithms and extend their applicability will require a better understanding of underlying processes driving variations in carbon system properties coupled with more sustained and extensive in situ data.

NASA Carbon Cycle & Ecosystems Active Awards Represented by this Poster:

• Award: NNG05GD22G