PRINCIPAL 



INVESTIGATOR(S) Larry K. Benninger 



Department of Geology 



University of North Carolina - Chapel Hill 



Chapel Hill, NC 27599 



PROJECT TITLE CARBON CYCLING ON THE CONTINENTAL MARGIN: 



EVIDENCE FROM SEDIMENT 14-C AND NUTRIENT 

 ELEMENTS 



AMOUNT OF FUNDING FY 1994: $119 K 



SUMMARY OF GOALS 



a. Identification of sites of deposition of modern organic carbon from estuaries to the continental 

 rise. Our tracer for modern carbon is bomb 14-C, manifest as either future, or anomalously 

 young, age in surface sediments. We will use fallout radionuclides (Pu; 137-Cs if present) and 

 natural 210-Pb as indices of modern particle accumulation or mixing. 



b. Modern rates of carbon burial. In environments of rapid modern sediment accumulation 

 (probably > ~3 mm/year) fallout nuclides and 210-Pb will be used to estimate rates of sediment 

 accumulation. Together with carbon concentrations, the accumulation rates will yield carbon 

 burial rates. Since burial of carbonate-C and organic-C affect atmospheric C0 2 in opposite 

 senses, we will quantify both carbonate carbon and organic carbon. 



c. Nutrient-to-organic-carbon ratios in modern sediments. Nitrogen and phosphorus will be 

 determined in modern sediments so that we can quantify nutrient/carbon ratios in deposition and 

 burial. If organic carbon burial on the continental margin is to significantly affect atmospheric 

 C0 2 , nutrients must escape burial through preferential recycling. 



d. 14-C signal in modern organic production. Analysis of plankton and Sargassum samples will 

 directly characterize the carbon-isotopic signature of present-day primary production. When 

 available in sufficient quantity for analysis, benthic macroinvertebrates will reflect the 

 carbon-isotopic composition of organics reaching the benthic food web. 



e. Long-term trends in carbon and nutrient burial. Carbon, carbon isotopes, and nutrients in long 

 cores (> 1 m) will be used to quantify burial rates over hundreds - thousands of years. Deeper 

 profiles will also aid in interpretation of near- interface, modern phenomena of deposition and 

 burial. 



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