Feedbacks in the cycles of N and P in anoxic waters - negative or positive?.

Kähler, Paul and Koeve, Wolfgang (2015) Feedbacks in the cycles of N and P in anoxic waters - negative or positive?. [Talk] In: ASLO Aquatic Sciences Meeting 2015. , 22.-27.02.2015, Granada, Spain .

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Abstract

In marine environments, negative and positive feedbacks associated with anoxic conditions have been described for nitrate (removal by denitrification) and phosphate (liberation from iron oxides as they are reduced), respectively. In both feedbacks, the supply of organic matter to deep water from surface production, controlled by the respective element, is essential for establishing or maintaining deep-water anoxia. The Baltic and Black Seas, both with large anoxic deep-water bodies are examined for the existence of these feedbacks using extensive datasets collected during the past decades. For both the Baltic Sea with its deep water alternating between oxic and anoxic conditions, and the Black Sea with permanently anoxic deep water, these feedbacks are shown to be not important. The removal of nitrate by denitrification, which requires the absence of oxygen depends also on the presence of nitrate, which itself requires oxygen to form. In the Baltic Sea, the overwhelming share of denitrification occurs in sediments where nitrate - and thus indirectly oxygen - availability limits denitrification. The liberation of phosphate from iron oxides being reduced can significantly increase deep water phosphate concentration, but not necessarily that in surface water, which would be necessary for the proposed feedback loop. On the contrary, surface phosphate concentrations are especially low in the Black Sea. This is most likely due to the re-precipitation of metal oxides, their re-adsorption of phosphate and subsequent sinking from surface water. In oceanic oxygen minimum zones (OMZ) N and P feedbacks work differently since there sediments are involved to a much lesser degree.

Document Type: Conference or Workshop Item (Talk)
Research affiliation: OceanRep > SFB 754 > A2
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BM Biogeochemical Modeling
OceanRep > SFB 754 > A4
OceanRep > SFB 754
Projects: SFB754
Date Deposited: 16 Dec 2015 08:46
Last Modified: 16 Dec 2015 08:46
URI: http://oceanrep.geomar.de/id/eprint/30599

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