Bio-optical characteristics of the western Arctic Ocean: implications for ocean color algorithms

Global ocean color algorithms designed to estimate chlorophyll a concentration (chla) are not accurate at high latitudes. Although a regional Arctic OC4L algorithm was designed to be applicable to high northern latitudes, its applicability remains uncertain. To examine these issues, we investigated the light absorption coefficients of phytoplankton, non-algal particles (NAP), and colored dissolved organic matter (CDOM) and remote sensing reflectance, R-rs(lambda), covering most of the western Arctic Ocean. A higher pigment packaging effect was identified relative to that at lower latitudes. The CDOM absorption dominated and accounted for 76% of the total non-water absorption at 443 nm and did not covary with variations in chla. This absorption is significantly higher than those in other marine environments. We also examined the backscattering coefficient of particles obtained from the inversion of R-rs(lambda) and found that it covaried well with variation in NAP absorption. Our evaluation shows that when turbid waters (R-rs(670) > 0.00042 sr(-1)) are excluded, the performance of the OC4L is good and much better than that of the sea-viewing wide field-of-view sensor (SeaWiFS) OC4V4 and the moderate-resolution imaging spectroradiometer (MODIS) OC3M (root mean square error (RMSE) of 0.13, 0.21, and 0.22, respectively). The reason why the OC4L performs well despite strong CDOM absorption is discussed.