Visiting Assistant Professor of Geology Maria Prokopenko has received a three-year $126,000 research grant from the National Science Foundation’s (NSF) program on chemical oceanography to study the distribution of a nitrogen isotope over the life cycle and skeletal afterlife of cold-water corals. The collaborative study “Refining the use of scleractinian cold-water coral skeleton-bound δ15N as a proxy for marine N cycling” will be completed with colleagues from the University of Connecticut and St. Olaf College.
It takes a multidisciplinary approach to study the ocean. Prokopenko is perfectly suited for this approach: She earned her undergraduate degree in geology at Moscow State University, her Ph.D. in earth science from University of Southern California and she has held postdoctoral positions in geochemistry and oceanography.
Prokopenko’s research is driven by questions of how the processes occurring in the ocean are shaped by interactions between the three major components of the Earth system: the biological, hydrological and geological.
For this NSF grant, the team of researchers will study the Balanophyllia spp., a cold-water coral that is fairly common in the Pacific Ocean and can be found in great depths as well as close to the surface. These corals, along with several other cold-water species, act as natural “sediment traps,” catching organic matter from the surface and incorporating the chemical signatures of the surface conditions into their mineral skeletons, made of aragonite, as they grow.
The goal of this project is to understand how faithfully the corals record the ratio of nitrogen isotopes (15N/14N ratio) that they receive as food from the ocean surface. Juvenile coral specimens have already been collected live by Prokopenko’s colleague, Anne Gothmann at St. Olaf College, where they have been growing in Gothmann’s laboratory under controlled conditions.
Once the coral specimens are large enough, they will be harvested and sent to Pomona, where Prokopenko’s team will prepare their skeletons for nitrogen isotope analyses. This is a demanding process: The cold-water corals grow slowly and only tiny amounts of their aragonitic skeletons will be available for analysis. The high risk of external contamination for these tiny samples requires rigorous laboratory protocols, which Prokopenko’s lab has developed and implemented.
The chemically cleaned and processed samples will be finally sent to another project collaborator, Julie Granger at the University of Connecticut, to be analyzed for the isotope ratio with a highly sensitive method which reliably determines 15N/14N ratios on samples as small as three to five nanomoles.
In addition to lab experiments, sampling and measurement of live corals, the project also includes the analysis of archived skeletal material from different ocean regions and depth horizons, to further evaluate the fidelity of coral-bound nitrogen as an archive for the oceanic 15N/14N history.
“The study will provide critical insight into the reliability of corals as sensitive archives of oceanic conditions, including currents and nutrient supply, and ultimately, rates of the plankton growth, to help scientists understand the cycling of elements, central for life as we know it—carbon, nitrogen and oxygen—through ancient and modern seas,” says Prokopenko.
“The circulation of ocean currents along with nutrient-controlled growth of marine plankton, regulate atmospheric carbon dioxide and planetary climate on time scales of hundreds to hundreds of thousands of years. Knowledge of nitrogen cycling can help build a high-resolution history of paleoenvironmental change, illuminating the drivers of past climate change and potentially helping us adjust to and mitigate the consequences of ongoing change.”
The nitrogen cycle is linked to the cycling of other environmentally and climatically important elements (carbon and oxygen), such that records of nitrogen cycle variability can offer a valuable window into paleoenvironmental change. Cold-water corals are of particular interest as archives of past marine nitrogen cycling because they can provide high-resolution records in time, have a broad geographic distribution and can be precisely dated radiometrically.
The research at Pomona led by Prokopenko will be conducted primarily by teams of geology students. In addition, there were plans for summer research assistants from nearby Mt. San Antonio College, one of the largest two-year community colleges in California, to be involved in the project. This may have to be readjusted or delayed given the coronavirus (COVID-19) outbreak, but Prokopenko is currently looking into ways of involving some students, though a smaller number, into the aspects of this research remotely. Specifically, they could work at managing the existing databases of coral 15N/14N ratios collected by Prokopenko over the last several years at 鶹ý.