Geochemistry

Geochemistry is a powerful tool for investigating a wide variety of geosystems in the ocean basins. Current topics of study include sediment biogeochemistry, submarine hydrothermal systems and the origin of mineral deposits on the seafloor, melt generation and flow in the earth's mantle, crustal magmatic systems, and seafloor volcanic processes.

Research spans the globe and uses combinations of field studies, both on land and at sea (some using deep submergence facilities), and analytical, experimental and theoretical approaches. The WHOI-MIT community offers a spectrum of analytical facilities to Joint Program students.

The MIT EAPS faculty and the WHOI Geology and Geophysics staff have close ties with other WHOI departments (Biology, Marine Chemistry and Geochemistry, Applied Ocean Physics and Engineering) to facilitate cross-disciplinary approaches to a number of these problems.

Areas of specialty include:

• Formation of the earth's crust—Investigating processes that form the earth's crust has been the central focus of igneous petrology for over a century. Systematic chemical variation in the igneous ocean crust is observed at many scales, from meters to hundreds of kilometers. The exact nature and origin of this variation is not completely understood. Current projects address the igneous stratigraphy and structure of the ocean crust, magma mixing, and chemical differentiation of the crust.
• Mantle geochemistry—Convective flow within the mantle drives the processes that contribute to the chemical evolution of the earth. Researchers use natural tracers (such as isotopic compositions, and distribution patters of major and trace elements) determined in constituent minerals and bulk rock samples to understand processes within the mantle, such as partial melting, melt extraction, and melt migration. These studies are closely linked to work being conducted in geophysics and fluid dynamics.
• Seafloor hydrothermal systems—Seafloor hydrothermal systems are an integral part of processes occurring along the mid-ocean ridges, and they transfer energy and mass from the lithosphere to the hydrosphere. Convection of seawater through the crust results in a chemical exchange that plays a role in controlling the chemistry of seawater, modifies the composition of the oceanic lithosphere, and leads to the formation of massive sulfide deposits. Current geochemical projects include water-rock reactions, the formation and growth of mineral deposits, and mineral-microbe interactions.
• Sedimentary biogeochemistry—Sediments are recorders of environmental conditions in the past, and they are also home to single-celled organisms that play important roles in the biogeochemical cycles of C, O, S, N, P, etc. Some geochemists use chemical tracers to reconstruct paleoclimate, paleoceanography, and paleoecology, while others extract those chemical signals specifically linked to microbially driven processes from sediments to investigate their role in cycles of biologically relevant elements.

Faculty: Anne Cohen (G&G), Henry Dick (G&G), Glenn Gaetani (G&G), Tim Grove (EAPS, MIT), Susan Humphris (G&G), Mark Kurz (MCG), Bernhard Peucker-Ehrenbrink (MCG), Roger Summons (EAPS, MIT), Maurice Tivey (G&G), Weifu Guo (G&G), Sune Nielsen (G&G), Forrest Horton (G&G)