Describe how the chemical composition of pore waters in marine sediments reflects the oxidation of organic carbon during diagenesis?

What is diagenesis?

Diagenesis is the compaction of sediments through chemical, biological and physical means. Changes also occur in chemical, biological and physical means.

What happens when organic carbon is oxidised?

When oxygen interacts with the different forms of organic carbon, many substances are released by the breakdown of organic carbon, methane, organic acids, organic matter and carbon dioxide.

What occurs in the upper sediment layers when oxidation is occuring?

There is an acceleration in aerobic and microbial degradation, which releases co2 into the water and therefore increases the acidity of pore waters.

What happens as a result of increasing acidity in the pore waters?

As there is more H+ and hco3 2 -, there is more anaerobic degradation which leads to calcifying organisms dying because of the inability to use carbonate to build their shells.

What is the consequence of organisms not being able to build shells and sinking to the lower layers?

There is more methanogenesis as these dead organisms decay on the deep sea sediments in anaerobic conditions.

Consequence of methanogenesis?

methane release in the deep ocean and pore waters cause further acidification of pore waters and ocean waters.

How does nutrient cycling relate to the oxidation of organic carbon?

In anaerobic pore waters, usually in the deep sediment layers, nitrite and nitrate act as electron acceptors and microorganisms participate in denitrification as a result and convert nitrite and nitrate into nitrogen gas, contributing to nitrogen cycling within the sediments.