Spatiotemporal variability of air-sea CO _2 fluxes in the Barents Sea, as determined from empirical relationships and modeled hydrography

摘要

Shelf seas play a major role in the global carbon cycle, but estimates of regional oceanic CO _2 uptake are limited in time and space due to scarcity of observed carbon parameters. Here, air-sea CO _2 fluxes in the Barents Sea and the dominant drivers of variability during the period 2000-2007 are investigated using a carbon system model based on hydrography coupled to a hydrodynamic model. The strong thermohaline control on the surface ocean CO _2 system allows for estimates of alkalinity and partial pressure of CO _2 (pCO _2) based on simulated temperature and salinity. Biological drawdown of CO _2 is calculated from changes in total inorganic carbon based on prescribed values of carbon to nitrate uptake ratio and a prescribed seasonal cycle of nitrate. Compared to available measurements the use of temperature and salinity data to reconstruct spatial and temporal variability of carbon system variables in the Barents Sea is shown to be reasonable. This allows, for the first time, an estimate of the spatiotemporal variability of air-sea CO _2 exchange for the whole Barents Sea. Our analysis indicates that the Barents Sea is a sink for atmospheric CO _2 throughout the year during the study period. The mean annual air-sea flux is 40±5g Cm ~(-2), corresponding to an ocean uptake of 0.061±0.007Gt Cyr ~(-1). Higher fluxes are found in the Atlantic southern Barents Sea (45±5g Cm ~(-2)), whereas less gas exchange takes place in the seasonally ice covered northern Barents Sea (33±4g Cm ~(-2)). Due to the combined effect of large concentration gradients across the air-sea interface (δpCO _2) and high wind speeds, the largest CO _2 uptake occurs in September and October. Interannually, the fluxes vary by ±12% of the mean oceanic uptake, mostly driven by variations in wind speed.