Distribution of sea-air co 2 fluxes in the patagonian sea: seasonal, biological and thermal effects

Abstract

Sea-air CO 2 fluxes (FCO 2 ) in the Patagonian Sea (PS) were studied using observations collected in 2000–2006. Based on the PS frontal structures and the thermal and biological contributions to FCO 2 we present a regional subdivision between distinct regimes that provide new insights on the processes that control these fluxes. The coastal regime (CR) is a net source of atmospheric CO 2 (4.9 × 10 -3 mol m -2 d -1 ) while the open shelf regime (SHR) is a net CO 2 sink (-6.0 × 10 -3 mol m -2 d -1 ). The interface between these two regions closely follows the location of along-shore fronts. In addition, based on the nature of the processes that drive the FCO 2 , the PS is subdivided between northern (NR) and southern (SR) regions. Both, NR and SR are CO 2 sinks, but the CO 2 uptake is significantly higher in NR (-6.4 × 10 -3 mol m -2 d -1 ) than in SR (-0.5 × 10 -3 mol m -2 d -1 ). The data reveal a strong seasonality in FCO 2 . The mean CO 2 capture throughout the PS in austral spring is -5.8 × 10 -3 mol m -2 d -1 , reaching values lower than -50 × 10 -3 mol m -2 d -1 ) in NR, while in winter FCO 2 is close to equilibrium in SR. The analysis of the biological and thermal effects (BE and TE, respectively) on seasonal pCO 2 variability indicates that regions of CO 2 emission are dominated by the TE while regions of CO 2 uptake are dominated by the BE. Our results indicate that the biological pump is the dominant process determining the sea-air CO 2 flux in the PS. Highlights: Near-shore regions outgas CO 2 to the atmosphere while offshore regions uptake CO 2 . Thermal effects dominate the CO 2 variability in the near-shore region. Biological effects dominate the CO 2 variability in the offshore region.