Particulate optical scattering coefficients along an Atlantic Meridional Transect

The particulate optical backscattering coefficient (b(bp)) is a fundamental optical property that allows monitoring of marine suspended particles both in situ and from space. Backscattering measurements in the open ocean are still scarce, however, especially in oligotrophic regions. Consequently, uncertainties remain in b(bp) parameterizations as well as in satellite estimates of b(bp). In an effort to reduce these uncertainties, we present and analyze a dataset collected in surface waters during the 19th Atlantic Meridional Transect. Results show that the relationship between particulate beam-attenuation coefficient (c(p)) and chlorophyll-a concentration was consistent with published bio-optical models. In contrast, the particulate backscattering per unit of chlorophyll-a and per unit of c(p) were higher than in previous studies employing the same sampling methodology. These anomalies could be due to a bias smaller than the current uncertainties in b(bp). If that was the case, then the AMT19 dataset would confirm that b(bp):c(p) is remarkably constant over the surface open ocean. A second-order decoupling between b(bp) and c(p) was, however, evident in the spectral slopes of these coefficients, as well as during diel cycles. Overall, these results emphasize the current difficulties in obtaining accurate b(bp) measurements in the oligotrophic ocean and suggest that, to first order, b(bp) and c(p) are coupled in the surface open ocean, but they are also affected by other geographical and temporal variations. (C) 2012 Optical Society of America