SUBPROJECT - B10
Pelagic transfer of iron and nutrients in the Peruvian oxygen minimum zone
This subproject will focus on the transfer of nutrients (Fe, N, P) from the bottom boundary layer of the Peruvian oxygen minimum zone (OMZ) to the surface ocean and off shore. These nutrients play a key role in ocean primary productivity, di-nitrogen fixation, microbial community structure and carbon cycling. There are uncertainties about the fluxes of total dissolved P and N in OMZs, largely related to the magnitude of the organic fractions (dissolved organic phosphorous (DOP) and dissolved organic nitrogen (DON)) which form important nutrient sources to microbial communities in the off shore oligotrophic ocean gyre.
In addition, the fluxes and mechanisms stabilizing and removing Fe in OMZs are not well known and quantified. As a result of increasing intensity and expanding geographical extent of OMZs, the P and Fe source strengths are expected to increase in future. This process may enhance di-nitrogen fixation and carbon export in the immediate vicinity of OMZs and thereby provide a positive feedback to OMZ expansion. In addition, changes in Fe, P, N concentrations, and nutrient ratios (in particular N/P), in waters advected from OMZs may influence primary productivity and di-nitrogen fixation on ocean basin scales.
The overall aim of this project is to determine the Fe, P, N fluxes, and processes affecting Fe behaviour in the Peruvian shelf region, with an emphasis on the effects of spatial and temporal variations in redox conditions in the water column. The observational work will be placed in context by use of geochemical tracers for flux quantification (Ra, Co, Mn, CF3SF5), redox conditions (I-/IO3-) and DOP and DON degradation (phosphomonesters/amino acids), in addition to physical observations (advective and turbulent mixing) and modelling efforts, in strong collaboration with A3, B9, A2, B1, B5 and B6. B10 will provide crucial data to A2 and B1 (N, P, Fe to validate biogeochemical models), A5 (Fe status for Si utilization by diatoms), A6 (Mo levels and fluxes), B5 (pelagic Fe, P, N transfer), B6 (I-/IO3-, DOP/DON in benthic chambers), B7 (I-/IO3- in bottom/porewaters), B9 (Fe in sinking particles). The Fe and P work in B10 will be done in strong collaboration with B2, who will focus on mesocosm experiments. We will also investigate Fe, P and N cycling during sporadic hydrogen sulfide releases from anoxic sediments. The work will build upon previous observations made as part of SFB 754 in the Peruvian and Mauritanian OMZs, and deal with outstanding questions on DOP, DON and Fe transport, and Fe stabilization, removal and recycling along and across redox gradients.
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