554 / 2024-09-18 12:15:47

Revisiting the ocean color algorithms for particulate organic carbon and chlorophyll-a concentrations in the Ross Sea

ocean color,Ross Sea,POC,chl

The Ross Sea is the most productive marginal sea in the Southern Ocean and plays an important role in carbon cycling. However, limited sampling of Chlorophyll-a (Chl) and particulate organic carbon (POC) concentrations from research expeditions constrains our understanding of the biogeochemical processes there. Satellites provide a useful tool for synoptic mapping of surface water properties on regional and global scales, yet the general applicability of the published algorithms in the Ross Sea are poorly known. Based on data collected from 18 cruises in the past 20 years, we analyzed both the NASA standard and locally-developed Chl and POC algorithms applicable to the Ross Sea. Our results show the Chl and POC are markedly underestimated using the NASA standard algorithms, with mean bias (MB) of -3.48 mg m^-3 and -159.1 mg m^-3, for a wide range of Chl (0.42-16.3 mg m^-3) and POC (46.8-812 mg m^-3). Similar poor performances were also found for other algorithms applicable in the Ross Sea. We locally tuned both Chl and POC algorithms, and found the Rrs667-based approach showed the most robust performances in retrieving both Chl and POC with  limited biases. Our results show that, the algal bloom signals in the Ross Sea in terms of Chl and POC are significantly greater than previously determined. More field observations will further constrain the locally-tuned algorithms.