Role of the Southern Ocean Meridional Overturning Circulation in the Oceanic Distributions of N2O

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Nitrous oxide, N2O, is a trace atmospheric gas whose natural concentrations are being affected by the activities of man. Its atmospheric concentrations have increased at the rate of approximately 0.7 parts per billion (ppb) per year from pre-industrial levels of 270 ppb to over 325 ppb at present. This trace gas both acts as a greenhouse gas and contributes to the depletion of ozone in the upper atmosphere. The ocean is a significant source of N2O to the atmosphere – contributing nearly ¼ of the annual global input to the atmosphere. N2O is produced within the ocean by the biologically-mediated processes that affect the oceanic distribution of this compound. However, measurements of the concentrations of N2O in the world oceans are relatively sparse. In order to better model how the N2O concentrations may change in response to changes in the climate, it is important to monitor the current distributions of this trace gas in the ocean and to determine the rates at which the concentrations are changing. Over the past decade, an analytical method for measuring the N2O concentrations from seawater samples collected for measurement of the anthropogenic tracers (i.e. CFC-11, CFC-12, and SF6) has been developed. Preliminary measurements of N2O concentrations have been made on several GO-SHIP hydrographic sections. One component of this proposal is to finalize these data sets by ensuring they are reported on the same calibration scale and that they have undergone the same steps in the final processing of the data. These N2O data will then be merged with the hydrographic data and made available for the broader scientific community via the Climate and Carbon Hydrographic Data Office. This research will specifically focus on Southern Ocean, where only a few previous measurements of N2O has been made but is an important region for setting the concentrations of trace gases within the deep and bottom waters of the ocean. We propose to analyze dissolved N2O from five surveys into and within the Southern Ocean. This will allow the Southern Ocean influence of air-sea exchange and of in-situ production of N2O to be characterized, and will allow the N2O of Southern Ocean water masses to be quantified. These will provide critical endmember information on the production rate estimates in the adjoining basins, thus improving our understanding and monitoring of the ocean’s likely changing N2O cycleThis award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.