Surface seawater and boundary layer atmospheric samples were collected on the FS Polarstern during cruise ARKXX in the North Atlantic and Arctic Ocean in 2004. Samples were analyzed for persistent organic pollutants (POPs), with a focus on organochlorine pesticides, including hexachlorocyclohexanes (HCHs), chlordanes, DDTs, hexachlorobenzene (HCB), and polycyclic aromatic hydrocarbons. In addition, the enantiomer fractions (EFs) of pesticides, notably alpha-HCH and cis-chlordane (CC), were determined. Concentrations of dissolved HCB increased from near Europe (approximately 1-2 pg/L) toward the high Arctic (4-10 pg/L). For dissolved HCB, strongest correlations were obtained with the average air or water temperature during sampling, not latitude. In the western Arctic Ocean, surface waters with elevated concentrations of HCB (5-10 pg/ L) were flowing out of the Arctic Ocean as part of the East Greenland current In contrast to dissolved compounds, atmospheric POPs did not display trends with temperature. Air-water exchange gradients suggested net deposition for all compounds, though HCB was closest to air-water equilibrium. EFs for alpha-HCH in seawater ranged from 0.43 to 0.50, except for two samples from 75 degrees N in the East Greenland Sea, with EFs of 0.31 and 0.37. Lowest EF (0.47) for CC were also at 75 degrees N, other samples had EFs from 0.49 to 0.52. It is suggested that samples from around 75 degrees N in the Greenland Gyre represented a combination of surface and older/deeper Arctic water.

Polyethylene passive samplers (PEs) were deployed in a vertical array (bottom water, surface water, near-surface air) to study the cycling of active polychlorinated biphenyls (PCBs) between reservoirs in an urban estuary (Narragansett Bay, RI), from May to November 2006. Performance reference compounds were used to account for nonequilibrium of PCBs in PEs. Activity gradients were established from direct comparisons of temperature, salt, and nonequilibrium corrected PE concentrations. The uncertainty of determining air-water gradients was < 70%, and < 50% within the water column. Except during the height of summer, PCB activities were up to 30 times higher in the air than in the surface water, but closer to equilibrium in the water column. Surface waters became depleted in PCBs during periods of highest temperature and stratification, leading to the uptake of gaseous PCBs. Our results demonstrate that passive samplers are powerful tools to determine the flux directions of organic contaminants in the environment.

Passive polyethylene (PE) samplers were deployed at six locations within Narragansett Bay (RI, USA) to determine sources and trends of freely dissolved and gas-phase polycyclic aromatic hydrocarbons (PAHs) from May to November 2006. Freely dissolved aqueous concentrations of PAHs were dominated by fluoranthene, pyrene, and phenanthrene, at concentrations ranging from tens to thousands of pg/L. These were also the dominant PAHs in the gas phase, at hundreds to thousands of pg/m3. All stations mostly followed the same temporal trends, with highest concentrations (up to 7300 pg/L for sum PAHs) during the second of 11 deployments, coinciding with a major rainstorm. Strong correlations of sum PAHs with river flows and wastewater treatment plant discharges highlighted the importance of rainfall in mobilizing PAHs from a combination of runoff and atmospheric washout. PAH concentrations declined through consecutive deployments III to V, which could be explained by an exponential decay due to flushing with cleaner ocean water during tides. The estimated residence time (tres) of the PAH pulse was 24 days, close to an earlier estimate of tres of 26 days for freshwater in the Bay. Air-water exchange gradients indicated net volatilization of most PAHs closest to Providence. Further south in the Bay, gradients had changed to mostly net uptake of the more volatile PAHs, but net volatilization for the less volatile PAHs. Based on characteristic PAH ratios, freely dissolved PAHs at most sites originated from the combustion of fossil fuels; only two sites were at times affected by fuel spill-derived PAHs.

Up in the air Understanding ocean-atmospheric carbon dioxide (CO 2 ) fluxes in the Southern Ocean is necessary for quantifying the global CO 2 budget, but measurements in the harsh conditions there make collecting good data difficult, so a quantitative picture still is out of reach. Long et al . present measurements of atmospheric CO 2 concentrations made by aircraft and show that the annual net flux of carbon into the ocean south of 45°S is large, with stronger summertime uptake and less wintertime outgassing than other recent observations have indicated. —HJS

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This article provides an overview of the NASA Atmospheric Tomography (ATom) mission and a summary of selected scientific findings to date. ATom was an airborne measurements and modeling campaign aimed at characterizing the composition and chemistry of the troposphere over the most remote regions of the Pacific, Southern, Atlantic, and Arctic Oceans, and examining the impact of anthropogenic and natural emissions on a global scale. These remote regions dominate global chemical reactivity and are exceptionally important for global air quality and climate. ATom data provide the in situ measurements needed to understand the range of chemical species and their reactions, and to test satellite remote sensing observations and global models over large regions of the remote atmosphere. Lack of data in these regions, particularly over the oceans, has limited our understanding of how atmospheric composition is changing in response to shifting anthropogenic emissions and physical climate change. ATom was designed as a global-scale tomographic sampling mission with extensive geographic and seasonal coverage, tropospheric vertical profiling, and detailed speciation of reactive compounds and pollution tracers. ATom flew the NASA DC-8 research aircraft over four seasons to collect a comprehensive suite of measurements of gases, aerosols, and radical species from the remote troposphere and lower stratosphere on four global circuits from 2016 to 2018. Flights maintained near-continuous vertical profiling of 0.15–13-km altitudes on long meridional transects of the Pacific and Atlantic Ocean basins. Analysis and modeling of ATom data have led to the significant early findings highlighted here.

A s the primary conduit for CO 2 and heat exchange between the atmosphere and the deep ocean, the Southern Ocean is an important part of the climate system. Approximately 40% of the ocean's inventory of anthropogenic carbon entered through the air-sea interface south of 40°S (Khatiwala et al. 2009), and the region will continue to serve as an important carbon sink into the future (Ito et al. 2015). Despite its importance, the processes controlling air-sea gas exchange in the Southern Ocean are poorly represented by models. This was highlighted in a recent comparison of models from phase 5 of the Coupled Model Intercomparison Project (CMIP5), wherein the simulated seasonal cycles of air-sea CO 2 exchange with the Southern Ocean were widely divergent and in poor agreement with observational estimates (Anav et al. 2013;Jiang et al. 2014), suggesting possible model biases in the timing, spatial A recent Southern Ocean airborne campaign collected continuous, discrete, and remote sensing measurements to investigate biogeochemical and physical processes driving air-sea exchange of CO 2 , O 2 , and reactive biogenic gases.

Abstract.A new coastal background site has been established for observations of greenhouse gases (GHGs) in the central Namib Desert at Gobabeb, Namibia. The location of the site was chosen to provide observations for a datapoor region in the global sampling network for GHGs. Semi-automated continuous measurements of carbon dioxide, methane, nitrous oxide, carbon monoxide, atmospheric oxygen, and basic meteorology are made at a height of 21 m a.g.l., 50 km from the coast at the northern border of the Namib Sand Sea. Atmospheric oxygen is measured with a differential fuel cell analyzer (DFCA). Carbon dioxide and methane are measured with an early-model cavity ring-down spectrometer (CRDS); nitrous oxide and carbon monoxide are measured with an off-axis integrated cavity output spectrometer (OA-ICOS). Instrument-specific water corrections are employed for both the CRDS and OA-ICOS instruments in lieu of drying. The performance and measurement uncertainties are discussed in detail. As the station is located in a remote desert environment, there are some particular challenges, namely fine dust, high diurnal temperature variability, and minimal infrastructure. The gas handling system and calibration scheme were tailored to best fit the conditions of the site. The CRDS and DFCA provide data of acceptable quality when base requirements for operation are met, specifically adequate temperature control in the laboratory and regular supply of electricity. In the case of the OA-ICOS instrument, performance is significantly improved through the implementation of a drift correction through frequent measurements of a reference cylinder.