Interannual variability of air-sea CO₂ fluxes and carbon system in the East Siberian Sea

Abstract. Over the past couple of decades it has become apparent that air-land-sea interactions in the Arctic have a substantial impact on the composition of the overlying atmosphere (ACIA, 2004). The Arctic Ocean is small (only ~4 % of the total World Ocean), but it is surrounded by offshore and onshore permafrost which is thawing at increasing rates under warming conditions, releasing carbon dioxide (CO₂) into the water and atmosphere. The Arctic Ocean shelf where the most intensive biogeochemical processes have occurred occupies 1/3 of the ocean. The East Siberian Sea (ESS) shelf is the shallowest and widest shelf among the Arctic seas, and the least studied. The objective of this study was to highlight the importance of different factors that impact the carbon system (CS) as well as the CO₂ flux dynamics in the ESS. CS variables were measured in the ESS in September 2003 and, 2004 and in late August–September 2008. It was shown that the western part of the ESS represents a river- and coastal-erosion-dominated heterotrophic ocean margin that is a source for atmospheric CO₂. The eastern part of the ESS is a Pacific-water-dominated autotrophic area, which acts as a sink for atmospheric CO₂.

Our results indicate that the year-to-year dynamics of the partial pressure of CO₂ in the surface water as well as the air-sea flux of CO₂ varies substantially. In one year the ESS shelf was mainly heterotrophic and served as a moderate summertime source of CO₂ (year 2004). In another year gross primary production exceeded community respiration in a relatively large part of the ESS and the ESS shelf was only a weak source of CO₂ into the atmosphere (year 2008). It was shown that many factors impact the CS and CO₂ flux dynamics (such as river runoff, coastal erosion, primary production/respiration, etc.), but they were mainly determined by the interplay and distribution of water masses that are basically influenced by the atmospheric circulation. In this contribution the air-sea CO₂ fluxes were evaluated in the ESS based on measured CS characteristics, and summertime fluxes were estimated. It was shown that the total ESS shelf is a net source of CO₂ for the atmosphere in a range of 0.4 × 10¹² to 2.3 × 10¹² g C.