Distribution of Transparent Exopolymer Particles (TEP) and TEP-Carbon content in the North Sea in summer

Gianfranco Anastasi1,2, Naomi Greenwood2, Gill Malin1, Dorothee C E Bakker1, Luca Polimene3 and Martin Johnson1,2, (1)University of East Anglia, School of Environmental Sciences, Norwich, United Kingdom, (2)Centre for Environment, Fisheries & Aquaculture Science (Cefas), Lowestoft, United Kingdom, (3)Plymouth Marine Laboratory, Plymouth, United Kingdom
A key requirement for the quantitative assessment of the global marine carbon cycle is to improve understanding of the regulation of dissolved organic carbon (DOC) concentrations. Continental shelf seas make an important contribution to sequestration of CO2 from the atmosphere, through physical and biological processes, ie. the Continental Shelf Pump (CSP). The role of organic matter dynamics in the CSP is poorly understood. Decoupling the carbon to nitrogen stoichiometry of organic matter production from that of the primary producers can lead to excess uptake of dissolved carbon relative to nitrogen, allowing for ‘overconsumption’ of carbon and increased biological pump efficiency. This process could be particularly effective if carbon-rich material such as gel-like transparent exopolymer particles (TEP) are formed as these can sink out of the surface layer. The aim of this project is to understand the role of dissolved organic matter (DOM) and TEP production in carbon overconsumption in shelf seas. To this end, a combined experimental-modelling approach was used. TEP samples collected in the North Sea in August 2014 were analysed to obtain a detailed snapshot of TEP distribution in summer. A new parameterisation was derived for the representation of TEP-C in the the European Regional Seas Ecosystem Model (ERSEM) in order to investigate the mechanism governing the production and sinking of TEP. Our results show concentrations of TEP-C close to the value for overconsumption of dissolved inorganic carbon (DIC) predicted by Prowe at al. (2009) for the North Sea in summer. A clear relationship between TEP-C and chlorophyll was observed. ERSEM was able to quantitatively reproduce the observed TEP-C concentrations and simulate the seasonal cycle at a North Sea site, along with a likely sinking pattern of TEP-C. These results suggest that qualitative or quantitative changes in TEP production could have considerable influence on the efficiency of the CSP and carbon export.