Roman de Jesus
Scripps Institution of Oceanography
Geosciences Research Division
9500 Gilman Drive
La Jolla, CA 92093-0208
email: rdejesus (at) ucsd (dot) edu
phone: 858-534-5770
CV:
Marine dissolved organic carbon (DOC) has the potential to play a significant role in the global carbon cycle. The average radiocarbon (14C) age of DOC in the ocean is around 6000 years indicating that DOC accumulates in the ocean over long timescales. The ability of DOC to accumulate in the ocean provides the ocean with the potential to act as a carbon capacitor. This may be an important factor in the carbon cycle as global warming increases due to the rising concentrations of CO2 in the atmosphere. However, little is known about the origin, age, and specific compounds that compose DOC. DOC is presumably derived from marine primary productivity, but some studies have shown that terrestrial DOC is likely present as well. Furthermore, with an average age of 6000 years, DOC must harbor some chemical structure that is resistant to microbial or abiotic degradation.
My thesis work focuses on addressing the relationship between the chemical structure of organic compounds within DOC and their residence time in seawater. I've been developing methods to isolate and fractionate DOC and analyzing the fractions for radiocarbon content in the Southern California Bight. At LLNL-CAMS, I've analyzed the 14C content of samples from 4 different CalCOFI cruises during 2003 and 2004. A clear trend of enriched 14C content was observed with the polar fractions consistent with previous studies. We observed temporal variations in radiocarbon content between the spring and fall seasons. Different fractions showed varying degrees of 14C changes indicate that some compounds accumulate and/or are removed at different rates. These preliminary results suggest that there is a distinct relationship between chemical composition and residence time in seawater.
I am also working on isolating individual compounds (from these 5 classes) for radiocarbon measurements. Using different organic chemistry techniques including chromatography I expect to isolated neutral sugars, lignin phenols, and lipids. The 14C analyses of these compounds will give us more information on the sources, cycling, and residence times of these classes of compounds in the ocean.
Another project that I am working on is a collaboration with Orjan Gustaffson and Chris Reddy investigating the chemical structure and isotope values of halogenated compounds in DOM. Based on the isotope values of organohalogen compounds we hope to determine whether the compounds are formed enzymatically or abiotically in the marine environment.
