Latitudinal patterns in the concentrations of biologically utilised elements in the surface ocean

Abstract. Understanding of controls on the spatial distributions of chemical elements in the surface ocean has improved over time. Macronutrients were understood first, followed by dissolved inorganic carbon and alkalinity. Utilising data collected in the Atlantic by the ongoing GEOTRACES programme, controls can now start to be investigated for other elements. Here we investigate the generality of the rule that, in surface waters, higher concentrations occur at higher latitudes. Our analyses of Atlantic GEOTRACES data show that, after salinity normalisation, all biologically utilised elements except iron follow this rule (ρ ≥ 0.45). Most elements (nitrate, phosphate, cadmium, barium, and nickel) are even more strongly correlated (ρ > 0.6) with latitude. We attribute this pattern to upwelling and/or entrainment of deep water at high latitudes. Although only Atlantic data was analysed here, we predict that this rule will be found to hold true for all oceans in which surface and deep waters exchange more readily at high latitudes. The rule does not hold in the central western Arctic Ocean, where a year-round strong halocline prevents exchange of surface and deep waters.