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Durham University

Durham Geochemistry Centre

Chemical oceanography and paleoceanography

The chemistry of the modern oceans largely reflects a balance of inputs from continental weathering (via rivers, groundwaters and aeolian input) and hydrothermal exchange at mid-ocean ridges. Marine sedimentary archives potentially preserve a record of changes in the balance of those inputs over geological time, and such isotope and elemental records may serve as proxies for changes in ocean temperature and salinity, ocean circulation the flux of elements and alkalinity from continental weathering, ocean anoxia and ocean and atmospheric CO2. Research in this area is aimed at quantifying the balance of inputs (and outputs) to the oceans for key isotope systems at the present–day, and the retrieval of past seawater compositions on both short (millennial) and long (million year) timescales to elucidate the relationship between ocean chemistry and the biological response of the ocean, to climatic and tectonic change.

Current areas of research include:

Modern ocean chemistry.

Measurement of both conventional radiogenic and non-traditional stable isotopes, and elements, in the modern oceans, to constrain the sources of input, and elemental and isotope behaviour in seawater.

Weathering and ocean circulation records.

Retrieval of marine sedimentary records to determine changes in erosional input (from continental weathering) accompanying climate change and subsequent dispersal through ocean circulation, using tracers with a range of residence times to determine both the local and global response. Retrieval of records of ocean circulation and their relationship to key tectonic events and the opening and closing of oceanic gateways.

Redox records.

Retrieval of isotope records from organic-rich sediments and carbonates to provide information on the extent of ocean anoxia (regional or global) accompanying oceanic anoxic events (OAEs). Linking records of oceanic redox, continental weathering and productivity to determine the controls on OAEs. Using the same redox and paleoproductivity proxies to trace the presence of hydrocarbon source rocks in sedimentary basins.

Carbonate sedimentation and burial.

Tracing variations in carbonate sedimentation using stable isotopes. Combining records of deep-ocean carbonate ion [CO32-] with weathering proxies to determine the controls on oceanic [CO32-], and atmospheric CO2, and the relationship to climate change – on both millennial and Cenozoic timescales.

Experiments.

Involving the culturing of biogenic carbonate and silicate to quantify the temperature, pH and growth rate dependence of elemental incorporation and isotope fractionation in these microorganisms, and the role that these factors play in the retrieval of proxy records.

We are also interested in using redox and paleoproductivity proxies to trace the presence of hydrocarbon source rocks in sedimentary basins.