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

The relation between the dissolved carbon dioxide (CO2) 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 (δ13CPOC) in the surface waters of the western Arctic Ocean was measured during July–September 2003, to evaluate the spatial variability of δ13CPOC and its key controlling factors. Values of δ13CPOC fell within the range of −28.5‰ to −21.1‰, with an average of −24.5±2.3‰. The spatial variability of δ13CPOC showed a general decreasing trend from shallow waters in the continental shelf toward the deeper, colder waters in the basin. A negative correlation between δ13CPOC and the dissolved CO2 concentration in surface waters was observed, indicating that carbon isotopic fractionation during photosynthesis was largely dependent on the dissolved CO2 concentration. Compared to the solubility pump, biological processes may play a more important role in determining the distribution and variation of δ13CPOC in the western Arctic Ocean during summer. The coupled relationship between CO2 concentration and stable isotopic composition of particulate organic matter has the potential to be used for reconstruction of sea-surface CO2 changes in the past, provided a quantitative relationship of δ13C between POC and sediments can be established.