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Marine POC, DOC and DIC interactions traced by radiocarbon content (14C) and molecular signatures

Atmospheric pCO2 is highly responsive to changes in surface ocean dissolved inorganic carbon (DIC) content due to the rapid exchange of CO2 between the ocean’s surface and the atmosphere. The processes controlling distribution and fluxes of DIC are described by the “carbon pump” model (Sarmiento and Gruber, 2006). Briefly, DIC is removed in surface waters by photosynthesis and is fixed as particulate organic carbon (POC) and dissolved organic carbon (DOC). POC and DOC are intensely recycled in the photic zone (remineralized to DIC), but small amounts of POC escape surface waters by forming sinking particles via coagulation, aggregation, and adsorption. The carbon pump directly controls surface ocean pCO2 and thus influence the global short-term carbon cycle (Hansell and Carlson, 2015). However, little is known about the cycling, carbon partitioning potential and interactions between the three C pools (DIC, POC, and especially DOC) and how they influence the strength of the carbon pump. A better understanding of these processes is needed to make justified predictions on how climate change will alter the current state of the global carbon pump.

Aims of this Project:

  • Trace interactions of oceanic C phases using their specific radiocarbon isotope (14C) content.
  • Identify key C phase transition processes by molecular composition changes.

A detailed understanding of the interaction between DIC, DOC and POC requires the application of state-of-the-art analytical equipment and methodology. The first phase of the project focuses on establishing laboratory procedures utilizing the MICADAS AMS at AWI Bremerhaven to precisely and reliably determine the radiocarbon (14C) content of the three co-existing C phases. Here we work on samples collected from the Centre of Excellence key study site off Cape Blanc, where we aim to produce high-resolution 14C spatial distribution maps of the three C phases for varying seasons. Ultimately, the isotopic information will be paired with C phase specific molecular information to identify key processes involved in C phase transitions.

References

Hansell, D.A., Carlson, C.A., 2015. Biogeochemistry of marine dissolved organic matter, Second edi. ed. Elsevier.

Sarmiento, J.L., Gruber, N., 2006. Ocean Biogeochemical Dynamics. Princeton University Press, Princeton, NJ.