Status and prospects of biogeochemical Argo observations of chlorophyll-a in the northwest Pacific

Biogeochemical Argo (BGC-Argo) floats are autonomous marine observing platforms that monitor chlorophyll-a and other indicators of ocean ecosystem health globally. Since 2018, there has been an increase in the number of chlorophyll-a observations in the northwest Pacific due to the deployment of BGC-Argo floats. Such progress offers an unprecedented opportunity to develop a skillful operational ocean biogeochemical model. Here, we assess the performance of BGC-Argo floats in measuring chlorophyll-a concentrations and their spatiotemporal structures via comparison with satellite and shipboard data. Results show a good correlation (r = 0.61) between the float and satellite observations and an excellent correlation (r = 0.87) between the satellite and shipboard observations of sea surface concentrations. The float data have a bias of about 0.04 mg m−3 or 59 % with respect to the satellite observations. Rare matchups between the float and shipboard observations of winter and summer profiles in the upper 200 m reveal an excellent correlation (r = 0.86), demonstrating the reliability of the vertical structure obtained from these floats. Concurrent two-year time series from five BGC-Argo floats reveal the prevalence of subsurface chlorophyll-a maxima in the subtropical northwest Pacific that can persist throughout the year. These findings stress the importance of subsurface monitoring to better quantify biological productivity and carbon export. We discuss the status of BGC-Argo floats in the northwest Pacific and recommend possible directions for modelling work and deployment efforts in achieving the proposed global array of 1000 floats in this decade, which has significant potential to improve predictability.