Carbon fluxes in the mixed layer of the Mediterranean Sea in the 1980s and the 2000s

Mixed-layer CO2 fluxes in the 1980s (1979–1983) and the 2000s (1998–2001) are assessed in the Mediterranean Sea. The analysis uses an array of one-dimensional physical–biological–chemical coupled models covering all areas where depth is greater than 300 m. These models are driven by surface heat fluxes and wind stress, and surface chlorophyll concentrations. This approach provides estimations of basin-scale oceanic CO2 levels over two time periods separated by a 14-year gap and allows characterizing differences between these two periods. The results indicate that the Mediterranean Sea was more biologically productive (by about 16 gC m−2 y−1) during the 2000s, with an increase of carbon export to deep layers by about 7 gC m−2 y−1 as compared to the 1980s. The consecutive modification of CO2 fluxes toward deep layers did not, however, strongly modify the oceanic CO2 levels, which differ by only ∼5–10 μatm between the two periods. The reason is the increase of atmospheric CO2 levels by 30 μatm between the two periods, which led to an increase of the CO2 flux from the atmosphere to the ocean. The Mediterranean Sea was a CO2 source to the atmosphere in the 1980s (about 1.5×1012 molC y−1). It is close to equilibrium with the atmosphere in the 2000s (slight sink of about −0.2×1012 molC y−1).

► Upper mixed-layer CO2 fluxes in the 80s and 2000s are assessed in the Mediterranean.
► The basin has become more productive and carbon export to deep layers has increased.
► The basin was a CO2 source to the atmosphere, it is close to equilibrium in the 2000s.