Ocean-atmosphere exchange of organic carbon and CO<sub>2</sub> in the Antarctic Peninsula – physical and biological controls

Abstract. Exchangeable organic carbon (OC) dynamics and CO2 fluxes in the Antarctic Peninsula region during austral summer are highly variable. By stations, the region is a weak source of CO2 to the atmosphere, however, continuous records of CO2 revealed this area as a weak sink. OC fluxes are also in both directions but generally towards the ocean and much higher than CO2 fluxes, sometimes by a factor of 10. Surface exchangeable dissolved organic carbon (EDOC) measurements had a 43 ± 3 μmol C L−1 overall mean, while the gaseous organic carbon equilibrated in water as given by the Henry's Law constant (H') resulted in (GOC H'−1) concentrations of 46 ± 3 μmol C L−1. EDOC represents around 66% of surface dissolved organic carbon (DOC) in Antarctic waters. There is a tendency towards low partial pressures of CO2 in waters with high Chlorophyll a (Chl a) content and high fCO2 in areas with high krill densities. However, such relationships were not found for EDOC. Depth profiles of EDOC were also quite variable and followed Chl a profiles, but only in some instances, while diel cycles of EDOC revealed two distinct peaks around midday and middle of the short austral dark period concurrent with solar radiation maxima and krill night migration patterns. However, there was no evident diel pattern for GOC H'−1. The pool of exchangeable OC reveals itself as an important compartment of the carbon budget in the Antarctic Peninsula and adds to previous studies highlighting its importance in the redistribution of carbon in marine environments.