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The University of Southampton
Ocean and Earth Science, National Oceanography Centre Southampton

Research project: Marine sediment tephra

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These tephra layers are the result of deposition of volcanic ash in the oceans. Their physical and geochemical composition can be used to study the evolution of the volcano from which they were derived. They are also highly reactive and exert important impacts on the biogeochemistry of the background marine sediments around them.

Preservation of organic carbon in marine sediments plays a major role in defining ocean-atmosphere CO2 levels, Earth climate, and the generation of hydrocarbons. Important controls over sedimentary organic carbon preservation include; biological productivity, isolation from oxidants (mainly dissolved O2) in the overlying water column and sediments, and mineral association in sediments. Deposition of the products of explosive volcanism (tephra) in the oceans directly enhances organic carbon burial through all these mechanisms, and indirectly through enhanced formation of authigenic carbonate derived from sedimentary organic carbon. In the modern oceans, it is suggested that tephra deposition may account for 5–10% of the organic carbon burial flux and 10–40% of the authigenic burial flux. However, during certain periods in Earth's history, extensive explosive volcanism may have led to enhanced authigenic carbon precipitation on a sufficiently large scale to influence the global ocean-atmosphere carbon cycle. Changes in tephra-related organic carbon preservation may also have played a role in increasing preservation rates in local marine basins, at the oxic-anoxic boundary and enhanced the generation of hydrocarbon deposits in these settings.

Tephra role preserving organic carbon

The role of tephra in enhancing the preservation of organic carbon in marine sediments. 1) Fe fertilization; 2) O2 depletion; 3) reactive Fe complexation; 4) authigenic carbonate formation

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