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Understanding the Ocean Carbon and Sulfur Cycles in the Context of a Variable Ocean: A Study of Anthropogenic Carbon Storage and Dimethysulfide Production in the Atlantic Ocean

Naomi M. Levine, Ph.D., 2010
Scott Doney and Dierdre Toole, Advisors

The impact of interannual variability on the detection of anthropogenic carbon (anthro) and the storage of Canthro is analyzed using a three-dimensional ocean model. Several regions are identified where empirical methods used to estimating Canthro are not able to correct for natural variability in the ocean carbon system. This variability is also shown to bias estimates of long term trends made from hydrographic observations. Finally, the storage of Canthro in North Atlantic mode waters is shown to be strongly influenced by water mass transformation.

The primary mechanisms responsible for seasonal variability in dimethylsulfoniopropionate (DMSP) degradation and dimethylsulfide (DMS) production in the oligotrophic North Atlantic are investigated using potential enzyme activity and gene expression and abundance data. Vertical mixing and UV radiative stress appear to be the dominant mechanisms behind seasonal variability in DMS production. This thesis demonstrates the importance of and dynamics of bacterial communities responsible for DMSP degradation and DMS production in oligotrophic waters. These findings suggest that modifications to current numerical models of the upper ocean sulfur cycle may be needed. Specifically, current static parameterizations of bacterial DMSP cycling should be replaced with a dynamic bacterial component including DMSP degradation and DMS production.