Aquatic Organic Geochemistry

Oh, the glory of collecting tiny sinking dead things.  We are evaluating the impact of suboxia and anoxia on sinking particles. There is a basic need to understand processes influencing carbon and nitrogen cycling in suboxic waters because these areas, and their impinged sediments, act as disproportionally important sink terms for both carbon (via preservation) and fixed nitrogen (via denitrification or anammox). This research provides quantified ‘rate and fate’ information on carbon and nitrogen cycling of sinking particles in oxic, anoxic and suboxic waters.

The diagenesis of sinking particulate organic matter in suboxic water columns may be different (less efficient and non-Redfield) compared with the degradation that is observed in oxic water columns throughout the world’s ocean. To test whether degradation is less efficient, settling particles in the Arabian Sea were collected in fall 2007 using drifting net traps and a series of ship-board experiments were 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) were measured.  To evaluate whether suboxic conditions might preferentially liberate nitrogen for use in either denitrification or anamox, the flux of protein amino acid carbon and nitrogen will be monitored. Differentiation between complete C and N remineralization to their oxidized forms versus selective deamination without concomitant carbon oxidation will help in understanding the degradative processes occurring in suboxic waters, and might help in defining the processes contributing to nitrogen deficits in suboxic waters.

An alternative to differential degradation in suboxic zones is that dust inputs might lead to enhanced organic carbon:mineral (ballast) fluxes in the Arabian Sea. To evaluate the role of mineral ballast in generating enhanced fluxes, two approaches will be used; a) dust was 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 are being 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 (e.g. amino acids, cupric oxide oxidation products, etherlipids).

Arabian Sea particle compositions are being compared with sinking particles that have been and will be collected within the oxic, suboxic and anoxic basins of Clayoquot and Nootka Sounds. Incubation experiments using particles from these local environments will be conducted and compared with those from the Arabian Sea.