Kent A. Fanning Ph.D.

Marine nutrients like dissolved nitrate or silica are the focus of our research. Our main emphasis concerns inorganic nutrients in upper ocean waters, where most oceanic photosynthesis occurs even though nutrient concentrations are often very low. The challenge is to detect changes in those concentrations as precisely as possible and then try to find explanations for the changes. We conduct detailed surface surveys with highly sensitive nutrient measurements in patches of coastal surface waters labeled with tracers. Nutrient concentrations in these waters are usually well down into the nanomolar range. Principal nutrients under investigation are nitrate, nitrite, and ammonium ion. Initial findings are that nitrate and nitrite in these coastal surface waters show only slight variations from the averages over an annual cycle, but that, in sharp contrast, ammonium ion concentrations can vary up to many-fold times higher than what appears to be normal background ammonium levels. We are currently investigating likely causes for this vastly different behavior of ammonium ion relative to the other main nitrogen-bearing inorganic nutrients. A major part of the fieldwork is to develop a version of our high-sensitivity nutrient sensor that will function in an autonomous underwater vehicle. It will allow us to determine the lateral shapes of patches of coastal water with ammonium enrichments, among other things. The AUV will greatly help the search for explanations. The other part of our research concerns comparisons of and temporal trends in nutrient concentrations within permanently anoxic ocean waters. Multi-year trends are being measured in the Cariaco Basin along the Venezuelan continental margin, and those results are compared to nutrient data from the Black Sea and other anoxic regions in the ocean. The objective of this work is to understand the pathways by which anoxia can alter chemical processes in the sea.