Causes and Effects
Anoxic conditions result from several factors; for example, stagnation conditions, density stratification, inputs of organic material, and strong thermoclines. The bacterial production of sulfide starts in the sediments, where the bacteria find suitable substrates, and then expands into the water column.
When oxygen is depleted in a basin, bacteria first turn to the second-best electron acceptor, which in sea water, is nitrate. Denitrification occurs, and the nitrate will be consumed rather rapidly. After reducing some other minor elements, the bacteria will turn to reducing sulfate. If anoxic sea water becomes reoxygenized, sulfides will be oxidized to sulfate according to the chemical equation:
- HS− + 2 O2 → HSO4−
In the Baltic Sea, the slowed rate of decomposition under anoxic conditions has left remarkably preserved fossils retaining impressions of soft body parts, in Lagerstätten.
Read more about this topic: Anoxic Waters
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