MGGD Research Areas


Marine geochemistry and global biogeochemical cycles

Ocean acidification thumbnail image. Within the Marine Geology and Geochemistry Division, observational, experimental and theoretical studies are conducted that cover a broad spectrum of research in the areas of marine geochemistry and global biogeochemical cycles. This includes sediment geochemistry and sediment diagenesis as well as the biogeochemistry and physics of the benthic boundary layer and permeable sediments. Many of our endeavors in this area require a sound knowledge of the kinetics and thermodynamics of mineral-water reactions and of isotope geochemistry. Members of the division also study the interaction of seawater with the oceanic crust, which includes the hydrothermal circulation through mid-ocean ridge flanks and associated exchanges of heat and chemical elements, and formation and dispersion of hydrothermal plumes in the deep ocean. A related topic is the interaction of seawater with lava. Among other implications, upper ocean volcanism constitutes a source of both toxic and nutrient elements to the surrounding ocean. Another focus within the Marine Geology and Geochemistry Division is trace element and rare earth element chemistry. For example, iron (an essential micronutrient) is found in seawater only in trace concentrations, which limits marine productivity in large areas of the ocean. Rare earth element concentrations in seawater hold promise as tracers for water mass distribution and origin. The Division also has expertise in the area of seawater carbonate chemistry — knowledge that is vital to understanding natural and human-induced changes in atmospheric carbon dioxide. Further efforts of the Division include investigation of particle dynamics and the role of aggregates in material transport. One example here is the study of ascending particle fluxes from hydrothermal plumes and their biogeochemical linkages with the upper water column.

Divisional research also encompasses the investigation of biogeochemical cycling of elements such as carbon, nitrogen, phosphorus, sulfur, and iron << what else? >> . Several of these elements are of particular importance for our understanding of climate change because of their role in carbon cycle-climate system interactions. Another theme of divisional research focuses on anthropogenic and marine aerosols and their significance for global pollution, biogeochemical cycles, and climate. Studies of dust deposition to the ocean elucidate the role of aeolian sources of elements such as iron, which is critical for carbon and nutrient cycling in the marine environment. Biogeochemical research in the division also includes microbial-chemical interactions in redox transition zones. Furthermore, members of the Division use natural and anthropogenic tracers to understand transport processes in atmosphere, oceans, lakes, rivers and groundwater. We also investigate the effects of invasion of anthropogenic carbon dioxide in the world's ocean, termed ocean acidification.

CO2-C- flux thumbnail image.

Historical and projected magnitudes of the anthropogenic fluxes of CO2 and their sinks in the atmosphere, ocean, and on land. The future role of the land vegetation and soils as a source or sink of anthropogenic CO2 is controversial but it is very likely the sink strength of the ocean will decrease, leading to a positive feedback to increasing atmospheric CO2 concentrations and hence global warming.

Foram thumbnail image.

Information on Earth's climate in the past can be extracted from fossil CaCO3 shells of foraminifera (photo shows a living specimen). This requires proper translation and interpretation of their shell chemistry and isotopic composition in terms of past climatic and environmental conditions.

Ice core trends thumbnail image.

Historical trends in Antarctica Ice Core parameters. Notice especially that present greenhouse gas concentrations are higher than those of the past and that the rise and fall of atmospheric CO2 is closely tracked by temperature in the 630,000 long year record.

[ ABOVE ] A large portion of the carbon dioxide that is currently released by humans is taken up by the ocean, which makes seawater less basic, or more acidic. As a consequence, the oceanís saturation state for minerals such as calcite is decreasing. This affects the ability of marine calcifying organisms to build their carbonate shells and skeletons.

Nitrite deficit thumbnail image.

dN (nitrate deficit by partial nitrification; µmol/kg) and O2 contours in a latitude-depth space for the cruise i07n data. (from: Li, Y.H., Menviel, L., Peng, T.H., 2006. Nitrate deficits by nitrification and denitrification processes in the Indian Ocean. Deep-Sea Res. I, 53, 94-110.)

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