Anthropogenic increase of oceanic pCO2 in the Barents Sea surface water

Abstract

We evaluate the change of surface water CO2 partial pressure ( pCO2 sw) in the Barents Sea (BS) between 1967 and 2000–2001. We use temperature (T) data collected during a survey in the BS in 1967 and a relationship between surface water CO2 mole fraction and T identified by Kelley [1970] to estimate the 1967 pCO2 sw. On the basis of data of total inorganic carbon, alkalinity, T, and salinity (S) collected during two recent surveys in the BS, we compute pCO2 sw of 2000–2001. In order to be able to account for natural variations of pCO2 sw we develop an empirical predictive equation for pCO2 sw through multivariable linear regression with the 2000–2001 data of T, S, and apparent oxygen utilization (AOU). This relationship is applied to the 1967 T, S, and AOU data, and the output is compared to the 1967 estimates of pCO2 sw. The difference is ascribed to net uptake of excess CO2. The computations show a pCO2 sw increase of 42 ± 31 matm between 1967 and 2000–2001, which is due to uptake of excess CO2. The pCO2 increase was uniformly distributed in the BS, suggesting that the uptake of the excess carbon from the atmosphere took place outside the BS rather than across the sea-air interface within the BS. Moreover, the computed increase was comparable to the increase in atmospheric pCO2 (~47 matm), and thus the pCO2 gradient across the sea-air interface has remained nearly unchanged relative to 1967.