Maria G. Prokopenko
University of Southern California
Department of Earth Sciences
3651 Trousdale Parkway
Los Angeles, CA 90089-0740
Office: 223c Zumberge Hall
email: prokopen (at) usc * edu
Benthic nitrogen cycling in anoxic environments
One of the predicted consequences of the global warming is areal growth and intensification of oxygen-deficient zones (ODZ) in the oceans. The oceaninc ODZs are the regions where denitrification, or loss of nitrate from the oceans, occurs. Beginning with my Ph.D work, I have been applying nitrogen isotopes to understand and quantify processes contributing to fixed nitrogen losses in the sediments of anoxic and suboxic regions of the ocean.
Development of a new proxy for reconstructing deep ocean circulation through time
Biologically available, 'fixed' nitrogen (N) is a major nutrient for marine primary production. Through its interactions with the global carbon cycle, N can influence concentrations of greenhouse gases, CO2 and N2O and, as consequence, global climate. Downcore oscillations in d15N of organic nitrogen (Norg) reported from globally distributed locations indicate that regional and global N cycles underwent substantial restructuring at the same time as global climate change. However, our mechanistic understanding of the links between the N cycle and global climate is hampered by two factors: lack of 1) direct information on d15N of oceanic nitrate in the past and, 2) records with high enough temporal resolution. Considering the short residence time of N in the ocean, it is likely that reorganization of N cycle may have occurred on a time scale ~1000 year, which is not easily resolved in a sedimentary record, thus a better time-resolved proxy is needed. I am currently developing a new proxy for d15N of oceanic nitrate, Carbonate Associated Nitrate (CAN) in deep sea corals, which have been proven to be important high-resolution archives for the evolution of ocean chemistry through time.
Consequences of climate change for the biological production in the marginal ice zones: using O2/Ar ratios and oxygen isotopes to quantify marine primary production
The eastern shelf of the Bering Sea is the grounds for the most productive US fisheries, and provides subsistence food for the indigenous communities in the region. However, located in the marginal ice zone, the Bering Sea ecosystem is particularly sensitive to the global warming. Observed in the recent decades profound changes in the Bering Sea ecosystem have been correlated with climatically induced shifts in regional hydrography. These observations require better understanding of oceanographic factors, influencing the magnitude of primary productivity, the basis of the ecosystem, on the eastern Bering Sea shelf. Participating in a large multi-PI NSF-funded study (BEST), I apply O2/Ar and triple oxygen isotope methods to quantify primary production during spring blooms in the Bering Sea. The results of my work will contribute to our understanding of the consequence of the inevitable climate change for the primary production in the region, and provide recommendations for better management of the Bering Sea natural resources.
Figures for Manuscript:
Primary Production from O2/Ar ratios and triple oxygen isotopes in a marginal ice
vernal bloom on the eastern Bering Sea shelf, 2007
Prokopenko, M.G., Granger J., Mordy, C., DiFiore, P., Cassar, Bender, M., Shull, D.,
Kachel, N., Kachel, D., Cockelet, E., Sambrotto, R., Sigman, D., Moran, B. ( to be
submitted to JGR)