Pore Fluid GeochemistryA motivating question for my research is “How do geophysical processes influence sediment-seawater geochemistry on convergent margins?” At convergent margins, such as the Chile Margin, geophysical processes (e.g., tectonism, diffusion, and advection) can: (1) enhance ion exchange processes or in situ geochemical reactions (e.g., illitization and marine silicate weathering), which constitute major sources or sinks of CO2 and elements in the ocean; (2) intensify pore fluid advection through accreted sediment, carrying deep geochemical signals to the shallow sediment and disproportionately influencing sedimentary/oceanic geochemical budgets; and (3) modify the zonation of geological reservoirs of carbon such as gas hydrates.
Pore fluid chlorinity is commonly used to elucidate mechanisms driving sedimentary processes; however, different mechanisms (hydrate dissociation, meteoric fluids, and geochemical reactions) can have the same effect on a chlorinity, leading to misinterpretations. I use a range of geochemical proxies (oxygen, hydrogen, and strontium isotopes, as well as major and minor ions) in deep sea pore fluids to understand physical and chemical processes driving the regional system. Projects:
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Geological Carbon and Climate ChangeGeological carbon sources include hydrothermal vents and gas hydrates. My research focuses on how these systems operate, whether we can record them with novel paleoceanographic proxies, and whether they have contributed to climate change in the past.
Hydrothermal Vents It has been hypothesized that hydrothermal vents serve as a source of geological carbon on glacial-interglacial timescales. Changes in sea level can regulate the pressure on tectonic plates, which in turn can influence the rate of seafloor volcanism. I examined the boron-calcium ratio (B/Ca) of benthic foraminifer shells from a sediment core taken at the Juan de Fuca Ridge (NE Pacific Ocean) to understand the influence of hydrothermal activity on the deep ocean carbonate chemistry, and the diagenetic effects on the B/Ca proxy itself. Gas Hydrates Today, gas hydrates store 2-3 times as much carbon as the atmosphere at relatively shallow depths in the sediment. Most of this is in the form of methane, which is a potent greenhouse gas. It has been hypothesized that global hydrate destabilization and release of this methane has impacted climate in the past, potentially driving mass extinctions during the Permian, rapid climate changes during the PETM, or even abrupt warming during the last 70,000 years. I am using a suite of paleoceanographic proxies (stable isotopes, trace elements, radioisotopes, organic biomarkers, and pore fluids) to study the Chile Margin gas hydrates system in the modern sediment and whether it has contributed to climate in the past. This project is being completed at Rutgers University. Projects:
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SedimentologySediment cores acquired via ocean drilling provides us with a window into the past. Instrumental scanning of cores yields ultra high-resolution details of the sediment. In some cases, this allows me to examine Earth system processes on decadal or annual timescales. For example, X-ray Fluorescence (XRF; <1 mm precision) reveals the elemental composition of the sediment, which can be used to reconstruct dust fluxes (Fe), terrestrial runoff (Ti/Al), and primary productivity (Ca). The color of the sediment also reveals many interesting things. Red-Green-Blue (RGB) values can be extracted from a core image scan at <1 cm precision. Changes in the value of individual colors (e.g., Red) or ratios of the colors (G/B) can reflect changes in sediment or oceanic processes.
For my research, I pair sediment geochemistry with the sediment properties—such as lithology, density, color, and magnetic susceptibility—to study changes in (1) oceanic and biogeochemical processes and (2) land-sea interactions over time. Projects:
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Global Ocean CirculationInteractions between the ocean and atmosphere have helped sequester a significant amount of the excess heat and carbon dioxide (CO₂) from anthropogenic forcing. Global circulation patterns transport heat, CO₂ throughout the world oceans, regulating both regional and global climates. Moreover, ocean circulation distributes nutrients, which help drive much of the life in the marine ecosystem; this too plays a part in Earth's climate. These processes all converge in the Southern Ocean, which connects each major ocean basin and serves as a key regions of water mass formation, biogeochemical activity, and air-sea exchange. However, warming is changing Southern Ocean circulation patterns, which could have global consequences. Given limited observational data, we can look to the past to provide context for how global ocean circulation responds to warming.
My research focuses on how Southern Ocean circulation has changed over time, with emphasis on intervals of abrupt (10-1,000 year) climate warming. I use ocean sediment cores to study how changes in ocean circulation affect ocean heat content, nutrient distribution, and the ability of the ocean to serve as a source/sink of CO₂. Projects:
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Changes in Oceanic Carbon StorageCarbon dioxide (CO2) is a greenhouse gas that acts as an atmospheric blanket by trapping heat radiated from Earth. Over the past 200 years, CO2 concentrations in the atmosphere have increased by over 50 percent as a result of human consumption of fossil fuels (~410 ppm as of Spring 2018). This perturbation is largely driving the documented increase in global average temperatures. But did you know that there is roughly 50 times more carbon stored in the ocean interior than the atmosphere? The amount of CO2 stored in the ocean changes on centennial to millennial timescales (or longer) due to variations in global ocean circulation patterns, biological activity in the surface ocean, and ocean chemistry, and these changes in carbon storage can drive changes in Earth's climate. Understanding how and why this reservoir changes over time can help us prepare for future climate changes.
Through my research, I seek to provide a better understanding of the carbon system, and how and why it has changed throughout the geologic past. While I primarily focus on the South Pacific and Southern Ocean, where deep waters rise to the surface and release CO2 into the atmosphere, I am interested in global processes. Projects:
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