Observations and modelling of transparent exopolymer particles (TEP) and their role in carbon cycling in shelf seas

• Main Author: Anastasi, Gianfranco
• Published: University of East Anglia 2018
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.768444

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, i.e. the Continental Shelf Pump (CSP). However, 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. This research investigated the role played by TEP in carbon cycling in NW European shelf seas by using a combination of field observations and modelling approaches. Results show that shelf sea systems with higher primary production (PP) lead to a higher TEP concentrations. In shelf seas TEP can be produced as a by-product of primary production, in coastal areas or during periods of nutrient limitation via overflow production of carbon-rich TEP precursors in seasonally stratified areas. A clear relationship between TEP and chlorophyll a observed in this study reinforces the evidence that phytoplankton is the main driver of TEP production. Results from the modelling work indicate that TEP can change the partitioning of the exported carbon, leading to an increase of the benthic respiration of ~ 30 %. This result improves our understanding of TEP dynamics and demonstrates that TEP can play a potentially significant role in carbon cycling and export in shelf seas, where its concentration is disproportionately high relative to the open ocean.