Variations in the isotopic composition of particulate organic carbon and their relation with carbon dynamics in the western Arctic Ocean

Abstract The relation between the dissolved carbon dioxide (CO 2 ) and the stable isotopic composition of particulate organic matter in the water column has not been well quantified, but this information could help provide a better understanding of carbon dynamics in a warmer Arctic Ocean. The stable carbon isotopic composition of suspended particulate organic carbon (δ 13 C POC ) in the surface waters of the western Arctic Ocean was measured during July–September 2003, to evaluate the spatial variability of δ 13 C POC and its key controlling factors. Values of δ 13 C POC fell within the range of −28.5‰ to −21.1‰, with an average of −24.5±2.3‰. The spatial variability of δ 13 C POC showed a general decreasing trend from shallow waters in the continental shelf toward the deeper, colder waters in the basin. A negative correlation between δ 13 C POC and the dissolved CO 2 concentration in surface waters was observed, indicating that carbon isotopic fractionation during photosynthesis was largely dependent on the dissolved CO 2 concentration. Compared to the solubility pump, biological processes may play a more important role in determining the distribution and variation of δ 13 C POC in the western Arctic Ocean during summer. The coupled relationship between CO 2 concentration and stable isotopic composition of particulate organic matter has the potential to be used for reconstruction of sea-surface CO 2 changes in the past, provided a quantitative relationship of δ 13 C between POC and sediments can be established.