Abstract
AbstractUpwelling ocean currents associated with oxygen minimum zones (OMZs) supply nutrients fuelling intense marine productivity. Perturbations in the extent and intensity of OMZs are projected in the future, but it is currently uncertain how this will impact fluxes of redox‐sensitive trace metal micronutrients to the surface ocean. Here we report seawater concentrations of Fe, Mn, Co, Cd, and Ni alongside the redox indicator iodide/iodate in the Peruvian OMZ during the 2015 El Niño event. The El Niño drove atypical upwelling of oxygen‐enriched water over the Peruvian Shelf, resulting in oxidized iodine and strongly depleted Fe (II), total dissolved Fe, and reactive particulate Fe concentrations relative to non‐El Niño conditions. Observations of Fe were matched by the redox‐sensitive micronutrients Co and Mn, but not by non‐redox‐sensitive Cd and Ni. These observations demonstrate that oxygenation of OMZs significantly reduces water column inventories of redox‐sensitive micronutrients, with potential impacts on ocean productivity.
Highlights
Coastal waters associated with eastern boundary currents receive high inputs of macronutrients (N, P, and Si) and bioessential trace elements (Fe, Mn, Co, Zn, and Cd) as deeper waters upwell to the surface (Bruland et al, 2005; Lohan & Bruland, 2008)
These observations demonstrate that oxygenation of oxygen minimum zones (OMZs) significantly reduces water column inventories of redox‐sensitive micronutrients, with potential impacts on ocean productivity
In our study we found that concentrations of other redox‐sensitive trace metals (TMs), dCo and dMn, were elevated in this part of the water column, while non‐redox‐sensitive TMs dCd and dNi remained unchanged, instead exhibiting profiles resembling macronutrients (Figures 3 and 4)
Summary
Coastal waters associated with eastern boundary currents receive high inputs of macronutrients (N, P, and Si) and bioessential trace elements (Fe, Mn, Co, Zn, and Cd) as deeper waters upwell to the surface (Bruland et al, 2005; Lohan & Bruland, 2008). During off shelf transport of surface waters, phytoplankton growth can deplete Fe to limiting levels, leading to sharp reductions in phytoplankton productivity (Browning et al, 2017, 2018; Hutchins et al, 2002; Moore et al, 2013). Constraining the factors that determine Fe supply in eastern boundary currents is critical for projecting biogeochemical feedback to physical‐chemical perturbations in these systems (Capone & Hutchins, 2013)
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