Impact of Suboxia on Sinking Particles: Non-Redfield Diagenesis and its Potential Role in C fluxes and N Cycling

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The diagenesis of sinking particulate organic matter in suboxic water columns may be less efficient compared with the degradation rate that is observed in oxic water columns throughout the world's ocean. An alternative to differential degradation due to low oxygen concentration is that significant dust inputs in these same regimes might lead to enhanced organic carbon:mineral (ballast) fluxes. To test these ideas, a researcher from the University of Washington will participate in a cruise to the Arabian Sea aboard the R/V Revelle. To study whether degradation is less efficient, settling particles will be collected using drifting net traps and a series of ship-board experiments will be performed. Settling material will be incubated under oxic and suboxic conditions and the degradation rates and residual organic matter compositions of bulk settling material and specific organic components (proteins) will be measured. To evaluate the role of mineral ballast in generating enhanced fluxes, two approaches will be used; a) dust will be added to some trap incubations to probe whether adding mineral results in decreased organic matter diagenesis and thus enhanced carbon:mass ratios at the end of incubations, and b) trap and incubation samples will be probed for ballast types, mineral surface areas, and organic:mineral interactions using a combination of density fractionation, X-ray photoelectron spectroscopy, mineralogical and organic analyses.After the Arabian Sea cruise, the PI will visit the oxic, suboxic and anoxic basins of Nootka Sound, British Columbia to conduct a series of comparative experiments to the Arabian Sea. Nootka Sound is an ideal locale to compare with the Arabian Sea because unlike the Arabian Sea, Nootka Sound has inlets with deep water of varying redox conditions, making natural controlled experiments feasible. In addition to the broader impact arising from training a graduate student, this proposal will leverage an undergraduate mentoring program, the Apprenticeship Learning Program, where undergraduate researchers are mentored by two faculty members and receive multidisciplinary research training.