Regional differences in modelled net production and shallow remineralization in the North Atlantic subtropical gyre

Abstract. We used 5-yr concomitant data of tracer distribution from the BATS (Bermuda Time-series Study) and ESTOC (European Station for Time-Series in the Ocean, Canary Islands) sites to build a 1-D tracer model conservation including horizontal advection, and then compute net production and shallow remineralization rates for both sites. Our main goal was to verify if differences in these rates are consistent with the lower export rates of particulate organic carbon observed at ESTOC. Net production rates computed below the mixed layer to 110 m from April to December for oxygen, dissolved inorganic carbon and nitrate at BATS (1.34±0.79 mol O₂ m⁻², −1.73±0.52 mol C m⁻² and −125±36 mmol N m⁻²) were slightly higher for oxygen and carbon compared to ESTOC (1.03±0.62 mol O₂ m⁻², −1.42±0.30 mol C m⁻² and −213±56 mmol N m⁻²), although the differences were not statistically significant. Shallow remineralization rates between 110 and 250 m computed at ESTOC (−3.9±1.0 mol O₂ m⁻², 1.53±0.43 mol C m⁻² and 38±155 mmol N m⁻²) were statistically higher for oxygen compared to BATS (−1.81±0.37 mol O₂ m⁻², 1.52±0.30 mol C m⁻² and 147±43 mmol N m⁻²). The lateral advective flux divergence of tracers, which was more significant at ESTOC, was responsible for the differences in estimated oxygen remineralization rates between both stations. According to these results, the differences in net production and shallow remineralization cannot fully explain the differences in the flux of sinking organic matter observed between both stations, suggesting an additional consumption of non-sinking organic matter at ESTOC.