Background
The authors write that "black carbon (BC) is a highly condensed, refractory and polymerized residue of combustion (Hammes et al., 2007) ranging from char to smaller-sized soot aerosols ~1 µm in diameter (Palmer and Cullis, 1965)," and that "because of its slow microbial oxidation rates (Hamer et al., 2004), BC represents a pool of carbon that may be sequestered into the geosphere over geological timescales."

What was done
Based on data obtained from a Chesapeake Bay sediment core collected just east of the Potomac River confluence, Mitra et al. compared down-core BC, non-BC organic carbon (OC) and polycyclic aromatic hydrocarbon (PAH) concentrations to identify large-scale combustion events that they compared to historical climate proxies "in order to examine the influence of climate on carbon sequestration in the coastal zone."

What was learned
The five researchers discovered what they call "the first evidence of climate-controlled centennial- and millennial-scale oscillations in the sequestration of both BC and OC in the coastal zone."

What it means
Mitra et al. concluded that "while the increased incidence of wildfires that may occur with climate change could release additional CO2 to the atmosphere (Wiednmyer and Neff, 2007), this could be countered over the long term by increased soil or sediment sequestration of BC," and they say that "this sink for atmospheric CO2 into an estuarine environment would represent a negative climate feedback and may play a regulatory role in centennial and millennial-scale climate variability."

References
Hamer, U., Marschner, B., Brodowski, S. and Amelung, W. 2004. Interactive priming of black carbon and glucose mineralization. Organic Geochemistry 35: 823-830.

Hammes, K., Schmidt, M.W.I., Smernik, R.J., Currie, L.A., Ball, W.P., Nguyen, T.H., Louchouarn, P., Houel, S., Gustafsson, O., Elmquist, M., Cornelissen, G., Skjemstad, J.O., Masiello, C.A., Song, J., Peng, P., Mitra, S., Dunn, J.C., Hatcher, P.G., Hockaday, W.C., Smith, D.M., Hartkopf-Fröder, C., Böhmer, A., Lüer, B., Huebert, B.J., Amelung, W., Brodowski, S., Huang, L., Zhang, W., Gschwend, P.M., Flores-Cervantes, D.X., Largeau, C., Rouzaud, J., Rumpel, C., Guggenberger, G., Kaiser, K., Rodionov, A., Gonzalez-Vila, F.J., Gonzalez-Perez, J.A., de la Rosa, J.M., Manning, D.A.C., López-Capél, E. and Ding, L. 2007. Comparison of quantification methods to measure fire-derived (black/elemental) carbon in soils and sediments using reference materials from soil, water, sediment and the atmosphere. Global Biogeochemical Cycles 21: 10.1029/2006GB002914.

Palmer, H.B. and Cullis, C.F. 1965. The formation of carbon from gases. In: Walker Jr., P.L. et al. (Eds.) Chemistry and Physics of Carbon - A Series of Advances, Marcel Dekker, New York, NY, USA, pp. 266-319.

Wiedinmyer, C. and Neff, J.C. 2007. Estimates of CO2 from fires in the United States: Implications for carbon management. Carbon Balance Management 2: 10.1186/1750-0680-2-10.