Trace Gas Distributions and Correlations Observed In The Southern Ocean Atmosphere During the ORCAS Mission

The biologically productive waters of the Southern Ocean are potentially a significant source and sink for trace gases that impact atmospheric chemistry and climate. However, relatively little is known about the variations and atmospheric vertical structures of trace gases in this region. During January/February, 2016, we participated in the O2/N2 Ratio and CO2 Airborne Southern Ocean (ORCAS) Study, an airborne mission that included the measurement of a wide range of trace gases. This presentation will focus on a selection of gases measured from the Whole Air Sampler and from an in-situ GC/MS system (TOGA). The gases measured by these instruments included a range of reactive halocarbons produced by marine organisms in the surface ocean (e.g., dimethyl sulfide, bromoform, methyl iodide), produced from marine surface photochemistry (e.g., methyl nitrate), and introduced to the region from long-range transport (e.g., chlorinated solvents, CFCs and HCFCs, non-methane hydrocarbons). Distributions of these gases should reflect the biological productivity of the region, the surface flux rates, and the rates of atmospheric transport and mixing. The concentrations of biogenic trace gases that we measured in the marine boundary layer showed significant regional differences in concentrations and different seasonal changes over the course of the experiment. Vertical profiles of biogenic trace gases could be related to the surface sources, exchange with the free troposphere, and the photochemical lifetime of the different gases. Because of the potential relationship of biogenic trace gases to biological productivity in the surface ocean, the measurements will be compared to distributions of chlorophyll a, as observed remotely from the GV aircraft and from satellites. For trace gases with a large interhemispheric gradient and primarily northern hemisphere source (e.g. mainly anthropogenic sources), atmospheric vertical profiles showed an average increase in mixing ratio with altitude that reflected the large-scale transport pathways from northern to southern hemisphere and photochemical processing during transport. Relationship of the various trace gases we measured to O2 and to carbon cycle gases (CO2, CO, CH4) will also be discussed in terms of potential sources, sinks, and biogeochemical processes.