Using ocean color satellite data to examine spatial and temporal coastal CO2 dynamics in the North Sea

The coastal ocean is a key component of the global carbon cycle, transferring carbon from land to the open ocean and supporting blue carbon accounting and climate change mitigation efforts. Coastal carbon dynamics remain however poorly constrained. This results from the complex biological and physio-chemical processes that occur in coastal seas which drive the spatial and temporal variability of the exchange of carbon dioxide (FCO₂) between the coastal seas and the atmosphere. To address this knowledge gap, region-specific and highly resolved analyses in time and space are required.

The dense network of in-situ measurements of seawater partial pressure of CO₂ (pCO₂) obtained from e.g. buoys and research vessels in the North Sea offers a unique opportunity to study coastal FCO₂ dynamics. Here, we combine high-resolution satellite observations of ocean colour (ESA Ocean Colour Climate Change Initiative, OC-CCI) and sea surface temperature with all available in situ pCO₂ observations (Surface Ocean CO₂ Atlas, SOCAT) to study the spatial and temporal variability of pCO₂  in the North Sea over the past decade. Using regionally optimized retrieval algorithms, we estimate key biogeochemical drivers of pCO₂ dynamics, including chlorophyll-a, suspended particulate matter and particulate organic carbon. Our findings suggest the presence of distinct biogeochemical regions within the North Sea, detectable from remote sensing data, shaped by primary productivity, riverine plume inputs, and sediment dynamics. These processes have varying impacts on regional pCO₂ dynamics, from locally enhancing the CO₂ uptake to degassing CO₂. Overall, this study advances our understanding of the complex processes driving coastal carbon dynamics and demonstrates a framework that can be applied beyond the North Sea in coastal regions globally.