Reducing uncertainty in the marine carbon cycle by coupling satellite and in-water robotic measurements

            This is a regional study that provides critical insight into reducing major uncertainties about the global carbon cycle. We propose a coupled satellite-data - robotic underwater glider study of the spring bloom in the Gulf of Maine. Our goal through underwater measurements is to improve accuracy in quantification of key biogeochemical stocks and input variables for satellite-based productivity models in mid-latitude coastal ecosystems and provide objective estimates of both their precision and the sensitivity of that precision to subsurface processes. Key estimates from in-water measurements are of high-frequency variation aliased by satellites, small-scale horizontal variations below satellite pixel resolution and depth variations impossible to resolve from the net water-leaving radiance. We target those areas where current productivity models show greatest disagreement, i.e., areas of high productivity and waters colder than 10C. The expected outcomes of this study are a reduction in uncertainty in productivity estimates on the local level and a demonstration of how the coupled use of satellites and in-water robotic gliders can be best used to reduce specific components of uncertainty.

            Four major challenges to accurate space-based assessment of marine productivity that can be addressed today with existing underwater glider technology are: 1) verification of derived products within different bio-optical regimes; 2) determination of key biogeochemical stocks in the entire euphotic zone; 3) actual measurement of input variables for productivity models; 4) continuity of stock measurements during periods of cloudiness.

            The project includes a two-year field campaign to study the spring bloom in the Gulf of Maine, from mid-March to mid-May. Satellite ocean color and sea-surface temperature will be collected and analyzed for water-leaving radiance, standard pigment products, optical backscattering coefficients, colored dissolved and particulate detrital concentrations, and sea-surface temperature. Two-optically instrumented gliders will be deployed within a defined box to measure chlorophyll and colored dissolved material fluorescence, optical backscattering coefficients, spectral upwelling and downwelling (ir)radiance, as well as temperature, salinity, and oxygen. Stratification indices will be determined during the evolution of the bloom. Additional optical and chemical measurements (i.e., particulate and dissolved organic carbon, pigments, CDOM and particulate detrital absorption) will be measured on the glider deployment / retrieval cruises to validate the optical proxies for carbon-cycle components.