Development and application of ocean color algorithms for estimating particulate organic carbon in the Southern Ocean from satellite observations
- Author(s): Allison, David Benjamin;
- et al.
Empirical algorithms have been developed for estimating surface concentration of particulate organic carbon (POC) from remotely-sensed ocean color in the Southern Ocean using field data POC, spectral remote-sensing reflectance, R/rs[lambda], and the inherent optical properties (IOPs) of seawater. Several algorithm formulations have been considered. The best algorithm performance was obtained for the power function fit POC (mg m⁻³) = 189.29 [R/ rs(443)/R/rs(555)]⁻⁰·⁸⁷ with mean bias of 3%, normalized mean square error 7%, and determination coefficient 0.93. Analysis of match-up comparisons between satellite-derived and in situ POC support application of this algorithm in the Southern Ocean. The bio-optical relationships on which the POC algorithms are based exhibit significant variability mainly due to differing particulate assemblages. To quantify the sources of this variability, Mie scattering modeling and empirical data were used to calculate IOPs, POC, and chlorophyll-a content for 21 representative classes of particles. These classes represent colloids, organic detritus, minerals, and various plankton species. By using this reductionist approach, 38 different bulk models of seawater were constructed and analyzed. The utility of this approach in advancing an understanding of variability in the POC algorithms is shown; for example, the relationship between POC and particulate backscattering is investigated. The POC retrieval algorithm based on the reflectance band ratio was applied to SeaWiFS satellite data to demonstrate seasonal and interannual variability in POC in the Southern Ocean (south of 35°S) from 1997 through 2007. Typically the surface POC concentrations range from 30 to 120 mg mg m⁻³ while the monthly means range from 70-80 mg m⁻³. The seasonal maximum stock of POC (0.6 Pg) integrated within the top 100 m of the ocean occurs in December. The seasonal range of area-normalized POC is 5.5 - 6.6 g m⁻². The region south of 55°S provides a dominant contribution to the accumulation of POC during the productive period of the season. During the austral spring, the area-normalized POC accumulates in these high-latitude waters at rates from about 0.2 to 0.7 g m⁻² month⁻¹. The comparison of these rates with large-scale satellite-based estimates of net primary production indicates that only a small fraction (<10%) of production accumulates as POC