Sea salt is composed of hundreds of chemical species that show a great diversity in their behavior and distribution. While seemingly benign, the question of "Why is the ocean salty?" is a dynamic and evolving area of research. For instance, we measure the isotopic composition of iron in the ocean to probe how this "micronutrient" limits the productivity of marine plants. Our investigation of the oceanic sulfur cycle tries to constrain this element's important role in preserving organic matter in marine sediments, ultimately leading to the formation of oil and the accumulation of oxygen in the atmosphere.
The ocean circulation influences the Earth's climate through its vast capacity to store heat, its exchange of trace gases with the atmosphere and its impact on marine ecosystems. The distribution of ocean properties depends on both broad, basin-wide currents that transport water masses between the equator and poles as well as smaller features, such as eddies and fronts, that control air-sea interactions. We address key dynamical questions, such as the formation and export of deep water masses around Antarctica and heat and tracer transport by ocean eddies. Methods include theoretical and modeling studies of water mass formation and circulation of the Southern Ocean, as well as field work using ocean gliders to obtain high temporal and spatial resolution data of ocean fronts and currents.
How has the earth's climate varied in the past? We know from ice core records that the CO2 content of the atmosphere is correlated with climate variations. These records also tell us that global climate has many timescales of variability, from one hundred thousand to tens of years. We use records from deep-sea corals and ocean sediments to understand the ocean's role in these processes. We mine the information in tropical cave deposits to constrain the relative roles of low-latitude processes like El Niño, and high-latitude processes like deep ocean circulation, in setting past climate change. Models ranging from simple reservoir exchanges in the carbon system to fully dynamic ocean circulation examples help us interpret the data from these climate archives. Our goal is to understand why there are glacial cycles in the past, and the rapid changes associated with them, with the hope of better understanding our climate future.
Providing researchers with an important baseline of environmental data, the EAC houses sophisticated instrumentation to examine pollutants in groundwater, date prehistoric fossils, and analyze the composition of smog.
Measurements of trace metals in the environment and precise dating of corals and cave deposits all require extremely clean conditions for processing samples. The clean room, custom designed for this purpose, is unlike any built earlier. It has air cleansed of almost all particles and has been constructed entirely from non-metallic materials. Measurements of corals and stalagmites in it reveal how climate has varied in Earth's past and how carbon cycles between the biosphere, the atmosphere, and the oceans.
The instrument lab houses three inductively coupled plasma mass spectrometers (ICP-MS). They are used to measure metal isotope ratios and Uranium-Thorium (U-Th) dates of samples that have been chemically processed in the clean room. They are also used to measure sulfur isotopes in the modern ocean and in ancient rocks to develop a quantitative understanding of how oxygen levels in the atmosphere have evolved over Earth's history.
We have coupled two disparate techniques, growing corals in controlled cultures and nanoscale analysis of metals and isotopes via Secondary Ion Mass Spectrometry (nanoSIMS), to probe the way corals make their skeletons. Our goal is to understand how chemical tracers are incorporated into living coral hard parts to better understand how to read them for the record of past climate change in the oceans. In addition, as ocean acidification is a certain outcome of burning fossil fuels, we hope to understand how corals will react to their future environment, perhaps even finding the telltale signals of stress in the trace metal chemistry of their skeletons.
The Geological and Planetary Sciences' supercomputing facility is used in computational modeling studies to interpret and explain data obtained in the laboratory and in field campaigns and to investigate computationally how the climate system responds to perturbations such as those owing to anthropogenic emissions of greenhouse gases and pollutants.
Underwater ocean gliders are autonomous vehicles that achieve low-power propulsion through the use of wings and buoyancy changes to convert vertical motion to horizontal. This allows gliders to sample water properties, such as temperature and salinity, for periods of months while being "piloted" remotely through satellite communications. Glider networks are proving invaluable in providing high spatial and temporal resolution observations of sub-surface ocean dynamics.