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 (d 13 C DIC ) 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, d 13 C DIC values are prone to change in the near future with rapidly changing climate conditions. This study provides a baseline to assess the d 13 C DIC of the Arctic Ocean with a focus on upper to intermediate waters (to *500 m). Measured d 13 C DIC values in the Arctic Ocean range from *-0.6 to ?2.2 %. In the Eurasian Basin, the d 13 C DIC values lie between *1 and 1.5 % and exhibit little variation within the upper layers. In the Canada Basin, d 13 C DIC values reach 2 % in the surface layer, with lowest values of *-0.6 % found at *200 m water depth. At greater depth, d 13 C DIC 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 d 13 C DIC are clearly related to biological processes. However, low d 13 C DIC values in the Canada Basin are also strongly influenced by non-equilibrium air-sea exchange processes. The different d 13 C DIC 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 d 13 C DIC of *-8 % on average, but in the Arctic basins this signal is mostly lost and d 13 C DIC values show only a weak correlation to river water fractions contained in the water mass. No relation between d 13 C DIC and sea-ice related brine contribution is apparent.

Epibenthos Dynamics and Environmental Fluctuations in Two Contrasting Polar Carbonate Factories (Mosselbukta and Bjørnøy-Banken, Svalbard)

“…Lynch-Stieglitz et al, 1995) at greater depth in Mosselbukta and at Bjørnøy-Banken instead may result from brine rejection during sea-ice formation and a relatively strong invasion of atmospheric CO 2 associated with sinking cold water, respectively. This is consistent with low δ 13 C as on Arctic shelf areas, mainly reflecting the invasion of isotopically light atmospheric CO 2 under non-equilibrium conditions (Bauch et al, 2015).…”

“…. The detailed study by Bauch et al (2015) showed that air-sea exchange processes in the entire Arctic Ocean and shelf regions are far from being at equilibrium, implying that at high latitudes diffusion of CO 2 from the atmosphere into the oceanic system leads to a decrease in δ 13 C DIC and δ 13 C as (Lynch-Stieglitz et al, 1995). This is also consistently identifiable in the present relationship between pCO 2 and δ 13 C as values ( Figure 10C).…”

“…This method subtracts the δ 13 C values predicted from biological activity alone from the actual δ 13 C DIC assuming that all non-biotic factors are related to air-sea exchange processes. This approach is based on ideal biological processes with a constant fractionation and constant Redfield nutrient ratio (Lynch-Stieglitz et al, 1995;Bauch et al, 2015). We are aware that this approach is not adjusted to local Arctic conditions (see Table 2 for the observed variation in N:P), but it nevertheless gives an indication to what degree air-sea exchange processes control the δ 13 C DIC distribution around Spitsbergen.…”

Sea‐air exchange patterns along the central and outer East Siberian Arctic Shelf as inferred from continuous CO2, stable isotope, and bulk chemistry measurements

“…Whereas the δ 13 C CO2 value is influenced by short-term physical (sea-air exchange) and biological processes (primary production and respiration) on the order of days (biological processes) to weeks (sea-air exchange), the exchange of the DIC pool and related δ 13 C DIC signature takes decades in a coastal water body with the volume comparable to the LS [Zeebe et al, 1999]. The assumed outer end-member in our isotope mixing model of 1‰ for open waters appears also rather robust, since Shelf Break waters and ArcO are pretty stable in δ 13 C DIC [Bauch et al, 2015]. These authors also conclude that ice melting-that had already occurred in the LS during the SWERUS cruise-has a negligible effect on δ 13 C DIC signatures.…”

Temporal and spatial trends in marine carbon isotopes in the Arctic Ocean and implications for food web studies

“…To relate the temporal trend in δ 13 C‐POC water values to the predicted decline of δ 13 C‐DIC and δ 13 C‐CO 2 values, a compilation of data on δ 13 C‐DIC values was extracted from three publications (Bauch, Polyak, & Ortiz, ; Schmittner et al, ; Young et al, ) and two databases (Becker et al, ; Key et al, ). δ 13 C‐CO 2 values were determined from the δ 13 C‐DIC values and absolute temperature following the Equation (1) (Rau, Riebesell, & Wolf‐Gladrow, ).…”