Date

2018-02-12

Author

Yücel, Mustafa
Salihoğlu, Barış
Arkın, Sinan
Fach Salihoğlu, Bettina Andrea
Akoğlu, Ekin
Özkan, Korhan
Tezcan, Devrim
Gazihan, Ayşe
Tuğrul, Süleyman

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Existing marine oxic-anoxic interfaces are expanding and new redox gradients are establishing themselves higher up in the water column in productive oceans and restricted marine basins. The feedback from these interfaces to euphotic zone can be diverse and can include higher internal loading of phosphorus and ammonium, as well as amplified oxygen consumption in cases of excessive hydrogen sulfide formation. There will be no single recipe to parametrize redox processes across these interfaces in next generation biogeochemical models, therefore, both existing and newly forming redox gradients need to be analyzed in a comparative fashion. Here we present the latest observations in two interconnected, but altogether restricted marine basins: Black Sea and Marmara Sea. Using latest water column and sediment microsensor biogeochemical profiles, we show that the Black Sea’s suboxic zone is likely to be sustained by high metal (manganese and iron) fluxes from especially southwestern shelf. The onset of sulfide in the Black Sea has not significantly changed, underpinning the likelihood that the control on the sulfide onset may not short-term physical forcing but a geochemical control sustained by benthic reactive metal stocks. Just to the south of Western Black Sea, connected by Bosporus, is the Marmara Sea (max. depth 1200 m) that is undergoing deoxygenation due to a number of poorly constrained anthropogenic and natural influences. Latest expeditions with R/V Bilim-2 revealed a thin (<40 m) oxic layer with a sharp oxycline. Trace levels (<10 microM) re-appear around 600-800 m in the water column. Biogeochemical profiles indicate that the sub-oxycline water column hypoxic region is dominated by respiratory processes using nitrate as electron acceptor. Only in the very eastern sub-basin of Marmara (Cinarcik Basin), beyond 1000 m depth, we have measured micromolar levels of hydrogen sulfide, indicating that a basin-wide switch to sulfate-reduction in deep Marmara can be likely within the near future. As will be demonstrated in this presentation, seas hosting dynamic redox interfaces will have their uniquely interacting processes and therefore response of each system to anthropogenic and natural forcing will be correspondingly distinct, posing a challenge to ecosystem modeling and subsequent management efforts.

URI

https://hdl.handle.net/11511/79433
https://agu.confex.com/agu/os18/meetingapp.cgi/Paper/315848

Collections

Graduate School of Marine Sciences, Conference / Seminar