(Invited Presentation) Fifty years at the skin of the ocean; Understanding the air-sea exchange of trace elements on Bermuda under the Duce legacy
Our Bermuda studies were initiated in the eighties under the auspices of the WATOX, AEROCE and FeAST projects in order to understand the atmospheric source, deposition and fate of trace elements at the surface ocean. These elements span those dominated by the seasonal invasion of lithogenic dust, to those that have both natural and anthropogenic emissions from sources surrounding the North Atlantic. A prime example is the abundant evidence of Pb from gasoline additives during the earlier records. Using stable isotopes it is possible to identify the continental source of Pb and associated trace elements, and upon deposition to the sea surface to trace its oceanic circulation. Similarly Bi data, including that from the early Duce records, suggests a primary source from coal combustion and a potential tracer. Somewhat surprising is the soluble nature of non-lithogenic Fe, a required micro-nutrient for important biological processes such as nitrogen fixation in the Sargasso Sea. Here a marked signature associated with Ni and V indicates residual oil combustion and implicates background emissions from the transit of ocean vessels. Similar emission sources of micro-nutrients may contribute to either nutrition or toxicity in the case of Cu, or a limiting growth vitamin in the in the case of Co. The surface micro-layer was early identified by Duce as an important phase for enrichment and recycling by sea salt aerosol as confirmed at Bermuda. Lastly, there is the unequivocal role of methylation processes at the sea surface for elements such as Se, Te and Po that through vapor phase transfer contribute to their enrichment in the marine atmosphere. Without the Bob Duce legacy, many of these studies on Bermuda and elsewhere would have not come to fruition.