A baseline for the vertical distribution of the stable carbon isotopes of dissolved inorganic carbon (δ13CDIC) in the Arctic Ocean

Abstract

Stable carbon isotopes of dissolved inorganic carbon (δ13CDIC) in the ocean are generally not well understood as they are governed by a complex interplay of biological processes and air–sea exchange. In the Arctic Ocean, δ13CDIC values are prone to change in the near future with rapidly changing climate conditions. This study provides a baseline to assess the δ13CDIC of the Arctic Ocean with a focus on upper to intermediate waters (to ~500 m). Measured δ13CDIC values in the Arctic Ocean range from ~−0.6 to +2.2 ‰. In the Eurasian Basin, the δ13CDIC values lie between ~1 and 1.5 ‰ and exhibit little variation within the upper layers. In the Canada Basin, δ13CDIC values reach 2 ‰ in the surface layer, with lowest values of ~−0.6 ‰ found at ~200 m water depth. At greater depth, δ13CDIC values range from ~1 to 1.5 ‰ within both basins. In the Canada Basin, nutrient levels are higher than in the Eurasian Basin and associated variations in δ13CDIC are clearly related to biological processes. However, low δ13CDIC values in the Canada Basin are also strongly influenced by non-equilibrium air–sea exchange processes. The different δ13CDIC patterns between the Canada Basin and the Eurasian Basin appear to be linked to differences in transport processes within the Arctic Ocean halocline. The upper layers in the Canada basins have direct contributions of waters from the Laptev, East Siberian and Chukchi shelves, which contain elevated fractions of river waters and sea-ice related brines, whereas their counterparts, in the Eurasian Basin, are mostly formed by halocline waters from the Barents and Kara seas. River waters have low δ13CDIC of ~−8 ‰ on average, but in the Arctic basins this signal is mostly lost and δ13CDIC values show only a weak correlation to river water fractions contained in the water mass. No relation between δ13CDIC and sea-ice related brine contribution is apparent.