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

Abstract

We used 5-year concomitant data of tracers 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 compute net production and shallow remineralization rates at both sites. 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 O<sub>2</sub> m<sup>−2</sup>, −1.73 ± 0.52 mol C m<sup>−2</sup> and −125 ± 36 mmol N m<sup>−2</sup>) showed no statistically significant differences compared to ESTOC (1.03 ± 0.62 mol O<sub>2</sub> m<sup>−2</sup>, −1.42 ± 0.30 mol C m<sup>−2</sup> and −213 ± 56 mmol N m<sup>−2</sup>). Shallow remineralization rates between 110 and 250 m computed at ESTOC (−3.9 ± 1.0 mol O<sub>2</sub> m<sup>−2</sup>, 1.53 ± 0.43 mol C m<sup>−2</sup> and 38 ± 155 mmol N m<sup>−2</sup>) were statistically higher for oxygen compared to BATS (−1.81 ± 0.37 mol O<sub>2</sub> m<sup>−2</sup>, 1.52 ± 0.30 mol C m<sup>−2</sup> and 147 ± 43 mmol N m<sup>−2</sup>). Lateral advection, which was more significant at ESTOC, was responsible for the differences in estimated oxygen remineralization rates between both stations. Due to the relevance of the horizontal transport at ESTOC, we cannot assert that the differences in shallow remineralization rates computed for both stations can explain the observed descrepancies in the flux of sinking organic matter

Non-redfieldian mesopelagic nutrient remineralization in the eastern North Atlantic subtropical gyre

“…Our results indicate that, although our study was carried out over an area of presumably significant influence of allochthonous carbon inputs, they do not shift the metabolic state of the upper-ocean ecosystem towards net heterotrophy, at least in the time scales associated with the renewal time of the surface layer of the box (∼ 1 year). On the other hand, our results are in good agreement with biogeochemical estimates and ecosystem models, arguing for the prevalence of net autotrophy (González-Dávila et al, 2007, Fernández-Castro et al, 2012, Emerson, 2014, Letscher and Moore, 2017, Lovecchio et al, 2017. Very recently, Letscher and Moore (2017) evaluated the metabolic state of the oligotrophic ocean at a global scale using a 3D ecosystem model.…”

High sensitivity of ultra‐oligotrophic marine ecosystems to atmospheric nitrogen deposition

“…Higher simulated C:N ratios at NASE are consistent with indications of carbon overconsumption in the mixed layer available just to the north of NASE [Koeve, 2006], excess carbon export at ESTOC , and C:N ratios of particulate export fluxes close to Redfield ratios measured at BATS [Schnetzer and Steinberg, 2002]. A recent study reporting the comparison of net production and shallow remineralisation rates at BATS and ESTOC estimated from a 1D tracer budget approach for oxygen, DIC and nitrate suggests a C:N ratio for shallow remineralisation of 40 AE 162 at ESTOC and 10.2 AE 3.6 at BATS [Fernández-Castro et al, 2011]. The only time-series of vertical export fluxes available at NASE derives from the sediment traps deployed at ESTOC, which is close to the high end of productivity inside the NASE region [Mouriño-Carballido and Neuer, 2008].…”