Anthropogenic and natural CO<sub>2</sub> exchange through the Strait of Gibraltar

Abstract

Abstract. The exchange of both anthropogenic and natural inorganic carbon between the Atlantic Ocean and the Mediterranean Sea through Strait of Gibraltar was studied for a period of two years under the frame of the CARBOOCEAN project. A comprehensive sampling program was conducted, which was design to collect samples at eight fixed stations located in the Strait in successive cruises periodically distributed through the year in order to ensure a good spatial and temporal coverage. As a result of this monitoring, a time series namely GIFT (GIbraltar Fixed Time series) has been established, allowing the generation of an extensive data set of the carbon system parameters in the area. Data acquired during the development of nine campaigns were analyzed in this work. Total inorganic carbon concentration (C T ) was calculated from alkalinity-pH T pairs and appropriate thermodynamic relationships, with the concentration of anthropogenic carbon (C ANT ) being also computed using two methods, the C* and the TrOCA approach. Applying a two-layer model of water mass exchange through the Strait and using a value of −0.85 Sv for the average transport of the outflowing Mediterranean water recorded in situ during the considered period, a net export of inorganic carbon from the Mediterranean Sea to the Atlantic was obtained, which amounted to 25±0.6 Tg C yr −1 . A net alkalinity output of 16±0.6 Tg C yr −1 was also observed to occur through the Strait. In contrast, the Atlantic water was found to contain a higher concentration of anthropogenic carbon than the Mediterranean water, resulting in a net flux of C ANT towards Correspondence to: I. E. Huertas

Physical forcing and physical/biochemical variability of the Mediterranean Sea: a review of unresolved issues and directions for future research

“…Lateral exchanges of carbon to surrounding seas are significant (e.g., Ait-Ameur and Goyet, 2006;Huertas et al, 2009;Schneider et al, 2010;Flecha et al, 2012) well constrained, similar to different methods for calculating C ant in the Mediterranean Overflow Water (MOW), which lead to different magnitudes and even direction of the net flux through the Strait of Gibraltar. In particular, it seems that the TrOCA method overestimates the C ant concentration in the MOW, leading to too large an export of C ant from the Mediterranean to the Atlantic.…”

Spatiotemporal variability of alkalinity in the Mediterranean Sea

“…A Newtonian dumping term regulates the Atlantic buffer zone that is outside the Strait of Gibraltar (atl in Fig. 1), where the alkalinity and DIC concentrations are relaxed to the mean profiles derived from the data published by Huertas et al (2009) andDafner et al (2001).…”

“…In addition, regressions based on local areas exist (SantanaCasiano et al, 2002;Huertas et al, 2009), some of which indicate a negative correlation between alkalinity and salinity in regions of freshwater (river) input (Luchetta et al, 2010). Few data, however, are available for the Mediterranean Sea, and as such, in this important basin the statistical spatial interpolation and extrapolation of existing information are critical.…”

A model-based assessment of the TrOCA approach for estimating anthropogenic carbon in the ocean

“…Sabine and Tanhua (2010) compared the pros and cons of the different methods, but did not venture into making a full assessment. Studying CO 2 exchange through the Strait of Gibraltar, Huertas et al (2009) compared C * and TrOCA estimates of C ant , and found large differences with TrOCA estimating increases with depth. Reasoning from Mediterranean circulation patterns and dissolved CFC concentrations, they concluded that the TrOCA parameter values optimised in Touratier et al (2007) should be adapted for this location.…”