Research
Isotope geochemistry is a profoundly powerful tool through space and time.
Current projects
Yucatan groundwater trace metals
The Yucatan Peninsula is a sub-tropical karst platform with abundant caves full of groundwater. When seasonal rainfall lands on the peninsula, it immediately percolates into these caves and steadily flows toward the coasts where it discharges as coastal springs full of natural trace metals (strontium and barium, among others) from the carbonate rock. Marine organisms known as foraminifera that live at the coast near these springs incorporate these metals into their shells. Over time the generations of foraminifera record these metal fluxes, and their shells become part of the coastal lagoon sediments. It is possibly to reconstruct the groundwater discharge, and thus amount of rainfall, from the trace metals in their shells. This project looks at how rainfall variability over a 5,000 year record with the goal of understanding how widespread drought events occur that may impact current societies living on the Yucatan, as is thought to have happened to the Mayans.
Boron isotopes
Boron isotopes are incorporated into the carbonate shells of marine organisms, and they reflect the pH at the time of incorporation. These isotopes are providing new insights into past ocean acidification and show promise at reconstructing past atmospheric carbon dioxide conditions. We still have much to learn about these isotopes in natural environments. This study looks at the boron isotopes of foraminifera near low-pH springs of the Yucatan at field sites that allow correlation with multiple concurrent processes like photosynthesis and rainfall changes. Boron isotope work requires the cleanest of clean labs, and this work was conducted with collaborators in Taiwan.
Foraminifera paleoecology
Coastal lagoon systems can provide climate records only if the lagoon geomorphology is known. A coastal lagoon that builds sand bars and restricts spring water would locally elevate trace metal concentrations, giving the appearance of increased spring flux. The community of shelled organisms like foraminifera respond to restricted lagoon circulation, as well, and the abundance and type of species present can indicate if a lagoon system has significantly changed. This project makes extensive use of count statistics of more than 25 species of foraminifera and ordination methods to trace lagoon paleoecology through time.
Mangrove carbon sequestration
Blue carbon is carbon stored by coastal ecosystems including wetlands, marshes, and lagoons. These systems play an outside role in removing carbon from the carbon cycle, and with sea level rise and continued coastal development, such systems are at risk of degradation, exacerbating our carbon problem. Mangrove forests cover much of the tropical coastlines, and while studies are quantifying how much current systems sequester, it is unclear how carbon sequestration changes over time and how climate impacts mangrove forest dynamics. In conjunction with the trace metal and paleocological studies above, this project seeks to quantify long-term (5,000 year) carbon storage by mangroves of the Yucatan.
Past projects
Cattle grazing nutrient runoff
Land use and resource management greatly impact the quality and behavior of water across landscapes. Bacteriological monitoring, including E. coli, is a tool used to determine and mitigate the impact of cattle grazing on public lands. This project worked with the US Forest Service and Central Valley Regional Water Quality Control Board to find economically feasible methods of monitoring the rough, remote terrain of Lassen National Forest. Nutrient data and E. coli abundance suggest the lower-most reaches of streams at forest boundaries may be suitable sites for the fate and transport of E. coli into REC-1 contact waters.
Heavy metals in Red Sea beaches
Heavy metals are a concern where the public may contact contaminants. the Gulf of Aqaba between Israel and Jordan on the Red Sea is a popular tourist destination for warm waters, thriving corals, and sandy beaches. Working with Tariq Al-Najjar, director of the Marine Science Station in Aqaba, Jordan, we measured some of the first heavy metal concentrations in foraminifera and seagrasses along the Jordanian stretch of coastline. Preliminary results suggest that copper, lead, and chromium are elevated near public beaches, possibly due to hotel plumbing systems or frequent mixing of deeper sediments from public swimming and activity. We are aiming to make the Gulf safer for the public and industry.
Antarctic isoscapes
An isoscape is like a contour map, but rather than elevation, the contours represent isotope values measured in a system. This allows mapping of processes that affect isotope geochemistry rather than mapping physical features, though the two are often related. In oceanography, phytoplankton and other primary producers use nitrate and other nutrients throughout the productive season. They draw down local reservoirs, causing an isotope signature that can change with the seasons. The polar regions of earth have dramatic seasonal changes that include plankton blooms, and this study mapped the season change in isotopes around Antarctica. Such detailed studies are useful for monitoring long-term change to sensitive polar regions and for future conservation efforts.
Antarctic bioturbation
Antarctica has had ice caps for a long time, and the growth and collapse of these sheets with climate change leaves records of debris in surrounding coastal environments. A key aspect of polar oceanography is the presence of sea ice - frozen ocean that seasonally melts and is unrelated to the floating ice shelves, ice bergs, or ice sheets. Sea ice greatly enhances albedo to reflect ocean energy and prevent it from absorbing into dark ocean waters, so it is important to know how these environments have changed with past climate. Ice does not stick around in the geologic record, but sediments do, and it appears that sea ice is prone to creating quiet environments where abundant scallops and brittle stars can mix the sediments. The sedimentary fabric left behind may be indicative of past sea ice extent, and this knowledge can help improve models that reconstruct climate dynamics around Antarctica.