Tracing Upper Arctic Circulation Via Barium, Oxygen Isotopesand DOM Fluorescence

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Approximately ten percent of the world's total river discharge flows into the Arctic Ocean, strongly influencing its physical and chemical properties. Determining the fate of river waters flowing into the Arctic is necessary for understanding oceanic circulation in the Arctic and its links to global climate, and for assessing the transport of radioactive and industrial wastes dumped into the rivers and shallow marginal seas of the Arctic. A variety of physical and chemical tracers, including temperature, salinity, alkalinity, 3He, tritium, halocarbons, nutrients, and oxygen isotopes, have been applied to investigations of Arctic circulation. These tracers have been successfully used with simple linear mixing models to distinguish the riverine component from sea-ice meltwater, Pacific, and Atlantic components of Arctic Ocean waters. None of these tracers, however, are able to distinguish between waters from different rivers within the Arctic. Past work has shown the utility of dissolved barium (Ba) as a naturally occurring geochemical tracer that can offer new insights into oceanic circulation in the Arctic, particularly with regards to its riverine component. Ba concentrations are highly elevated in the Mackenzie River (the only major North American river flowing directly into the Arctic) relative to any of the Eurasian Arctic rivers (i.e. the other nine of the ten largest rivers flowing directly into the Arctic). The investigators will analyze water samples collected from 1993 to 1996 to verify that the geographical distribution of Ba in the surface waters of the Arctic Ocean reflect the significant difference between Ba concentrations in the Mackenzie and Eurasian Arctic rivers, and that Ba can be used to distinguish between North American and Eurasian sources of river discharge to the Arctic and thus provide information not available from other tracers of oceanic circulation in the Arctic. Ba data will also be combined with other tracer fields obtained over the same period of ti me to quantitatively map freshwater contributions throughout the upper Arctic. Using this background information, the investigators will examine continuous UV-fluorescence records generated from sensors mounted on the hull of the nuclear submarine USS Pogy in 1996 during the SCICEX96 expedition throughout the Arctic interior. These data will provide information about the distributions of both marine and terrestrial derived dissolved organic matter (DOM). Terrestrial DOM may prove useful as a tracer of riverine discharge to the Arctic Ocean and the simultaneous, continuous records of both components will improve our knowledge of carbon cycling within the Arctic.