Constraining The Global Ocean Cu Cycle With A Data-Assimilated Diagnostic Model

Copper (Cu) is a biologically important trace metal for marine plankton, but it is also toxic at high concentrations. Understanding the global distribution of Cu and the processes controlling its cycling in the ocean is important for understanding how the distribution of this important element can respond to climate change. Here, we use available observations of dissolved copper, an artificial neural network, and an ocean circulation inverse model, to derive a global estimate of the three-dimensional distribution and cycling of dissolved Cu in the ocean. We find that there is net removal by bio-assimilation and/or scavenging of dissolved Cu in the surface ocean at a rate of similar to 1.7 Gmol yr(-1) and that both the concentration and export of dissolved Cu are highest in the Southern Ocean. In the subsurface above the near-sediment layer, dissolved Cu is removed at a net rate of similar to 2.4 Gmol yr(-1), consistent with scavenging onto sinking particles, contributing to an increase in the flux of particulate Cu with depth. This removal of Cu by scavenging in the interior ocean is balanced by a net near-sediment source of dissolved Cu, which sustains a gradual increase in the concentration of dissolved Cu with depth. Globally, this net near-sediment source is estimated at similar to 2.6 Gmol yr(-1) in the deep ocean and similar to 0.8 Gmol yr(-1) along continental shelves and slopes. Our results suggest an active oceanic dissolved Cu cycle with a mean internal ocean residence time of similar to 530 years, highlighting the potential for climate-driven changes in the marine Cu cycle.