Remote sensing monitoring of the spatio-temporal dynamics of the marine carbon polls of the global coastal ocean over the two last decades

• DOI: 10.5194/oos2025-577
• Publication Date: 2025-03-26T01:20:54Z
• Authors: Hubert Loisel; Roy El Hourany; Vincent Vantrepotte; Daniel S.F. Jorge; Marie monterro; Lucile Duforet-Ga...; Marine Bretagnon; Philippe Bryère; Antoine Mangin

The increase of atmospheric CO2 levels by as much as about 10% since the beginning of 21st century and its impact on the Earth’s climate and the biosphere represent a major concern. Based on a compilation of in situ data extrapolated over the global coastal ocean, previous studies indicate that the world’s coastal shelves absorb about 0.25 Pg C/year (~17% of oceanic CO2 influx), although these areas represent only 7% of the oceanic surface area. However, large uncertainties in coastal carbon fluxes and stocks exists due to their under sampling in both space and time. Moreover, all of the methods used to assess the land carbon sink rely upon accurate estimate of oceanic carbon as a key constraint or input. In this context, satellite remote sensing of ocean colour play a central role, as this Essential Climate Variables is currently the only ones for monitoring coastal and open ocean waters globally and systematically, at high spatial and temporal resolutions. Based on the development of recent algorithms performed in the frame of several research projects funded by CNES, EUMETSAT, ANR, and the COPERNICUS marine service, we present and discuss the first global vision of key aquatic carbon components over the global coastal ocean at high spatial resolution. The different algorithms developed to assess the particulate organic carbon, POC, dissolved organic carbon, DOC, and the in-water partial pressure of CO2, pCO2w, from ocean colour remote sensing will be presented with their quantified uncertainties. Theses algorithms will then be applied to the remote sensing reflectances obtained from the ESA Data User Element Project GlobColour to assess the spatio-temporal patterns of POC, DOC, and pCO2w over the global coastal waters from 1998 to 2024. The main temporal patterns will be presented and discussed and the global coastal carbon hot spots of long-term significative changes will be identified.