Presenter: Ahlem Jemai (University of Oldenburg)

Description:
Observational coverage from Argo floats far exceeds that of conventional observation methods (e.g., ships, aircraft) continuous, rapid, and depth-resolved measurements that enable historical analysis. The addition of bio-optical sensors (BGC-Argo) facilitates biogeochemical and climate research. BGC-Argo has recently been extended to marginal seas and optically complex inland waters and provides estimates of water-quality parameters including chlorophyll-a (chl-a), colored dissolved organic matter (CDOM), and total suspended matter (TSM), challenging standard ocean color approaches aimed at optically simple water types. Investigation of optically complex biogeochemical provinces was hindered by the sparsity of in situ observations, as well as the unknown seasonal influence. Over 1600 BGC-Argo floats had been deployed by September 2021, providing an on-demand capability for long-term observation of larger regions, e.g. the Baltic Sea. However, advanced bio-optical studies are limited by the spectral capabilities of the current sensors (multispectral radiometry). Therefore, ongoing studies in the Baltic Sea are evaluating the addition of hyperspectral radiometers to BGC-Argo, which measure downward irradiance from the ultraviolet (280nm) to the end of the visible range (720nm), along with the legacy BGC-Argo parameters. We exploit this dataset to refine empirical and semi-analytical approaches by regional tuning. Retrievals of biogeochemical variables, e.g., CDOM, will be investigated in the Baltic Sea. Our main objective is to analyze continuous, synchronized bio-optical profiles of chl-a, CDOM, and TSM (which vary across short spatio-temporal scales) using one sensor, and compare with hyperspectral radiometry and satellite matchups. We present an example that exploits hyperspectral information and Argo data to devise local or global algorithms that constrain the spatial and seasonal patterns of bio-optical properties, in order to observe optically complex regions.