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The flux of gases between the atmosphere and the oceans can be calculated from the product of the concentration difference across the sea surface and a kinetic term, often called a transfer velocity. The transfer velocity is frequently parameterized in terms of wind speed, although the actual exchange process is also affected by waves, bubbles, wind fetch, and less certainly by surfactants and chemical reactivity. There is currently an uncertainty of about a factor of two in using the wind speed parameterization. In view of the windiness of the Southern Ocean, transfer velocities will often be high, although there are few published in situ measurements of transfer rates made in the region. Data for gas concentration fields in the Southern Ocean are generally sparse compared to other better studied oceanic areas. In this paper we discuss what is known for the region for carbon dioxide, including the oceanic sink for man-made inputs to the atmosphere; dimethyl sulphide, where there appears to be a substantial source, which has the potential for a significant climatic effect due to the low particulate loading in the region; and organo-halogen and alkyl nitrate gases, where marine emissions may play an important role in controlling the oxidation capacity of the Antarctic atmosphere.

It is well known that iron fertilization can increase primary production and hence CO 2 drawdown over a significant fraction of the oceans. What is less well established is the extent to which this leads to long-term sequestration of carbon to the deep oceans, and to feedbacks to the atmosphere arising from increased biological activity. In this note results for changes in trace gas concentrations during an iron addition experiment in the Southern Ocean are presented. They demonstrate that a complex situation exists; some gases (DMS, CH 3 I, CHBr 2 Cl) show increases in concentration following fertilization with iron while others show no change (CH 3 ONO 2 , CH 2 ClI) or even a decrease (CHBr 3 ). The concomitant effects on air–sea fluxes of these gases are potentially important for climate and atmospheric composition. DOI: 10.1111/j.1600-0889.2005.00141.x

Sea-to-air emissions of bromocarbon gases are known to play an important role in atmospheric ozone depletion. In this study, seawater concentrations of bromoform (CHBr3) and dibromomethane (CH2Br2) were measured regularly between February 2005 and March 2007 at the Rothera Oceanographic and Biological Time Series (RaTS) site located in Marguerite Bay on the Antarctic Peninsula. Strong seasonality in CHBr3 and CH2Br2 concentrations was observed. The highest bromocarbon concentrations (up to 276.4 +/- 13.0 pmol CHBr3 L-1 and 30.0 +/- 0.4 pmol CH2Br2 L-1) were found to coincide with the annual microalgal bloom during the austral summer, with lower concentrations (up to 39.5 pmol CHBr3 L-1 and 9.6 +/- 0.6 pmol CH2Br2 L-1) measured under the winter fast ice. The timing of the initial increase in bromocarbon concentrations was related to the sea-ice retreat and onset of the microalgal bloom. Observed seasonal variability in CH2Br2/CHBr3 suggests that this relationship may be of use in resolving bromocarbon source regions. Mainly positive saturation anomalies calculated for both the 2005/2006 and 2006/2007 summers suggest that the bay was a source of CHBr3 and CH2Br2 to the atmosphere. Estimates of bromocarbon sea-to-air flux rates from Marguerite Bay during ice-free periods are 84 (-13 to 275) CHBr3 nmol m(-2) d(-1) and 21 (2 to 70) nmol CH2Br2 m(-2) d(-1). If these flux rates are representative of the seasonal ice edge zone bloom which occurs each year over large areas of the Southern Ocean during the austral summer, sea-to-air bromocarbon emissions could have an important impact on the chemistry of the Antarctic atmosphere.

[1] Surface seawater and atmospheric concentrations of methyl iodide, chloroiodomethane, bromoform, dichlorobromomethane, and chlorodibromethane were measured during three open ocean cruises in the Atlantic and Southern oceans. The measurements spanned a longitudinal range of 115°, between 50°N and 65°S. The saturation anomalies and the instantaneous air-sea fluxes of the gases during one of these cruises (ANT XVIII/1) are presented and discussed. Methyl iodide and chloroiodomethane were highly supersaturated (>1000%) throughout the temperate and tropical regions, with calculated mean fluxes of 15 and 5.5 nmol m−2 d−1, respectively. The oceanic emissions of the brominated compounds were less substantial, and a significant area of the temperate Atlantic Ocean was found to be a sink for bromoform. Correlation analyses have been used to investigate possible controls on the concentrations of these gases. In particular, the relationship of CH3I with sea surface temperature and light is discussed, with the tentative conclusion that this compound may be formed abiotically.

[1] During a west to east crossing of the tropical Atlantic Ocean in October–November 2002 on R/V Meteor (M55), carbon monoxide (CO) and ozone were continuously monitored, and pressurized air samples were collected and later analyzed in the laboratory for various volatile organic compounds. A sequence of alternating CO and propane rich events were observed over the east Atlantic, the events of enhanced carbon monoxide being out of phase with those observed for propane. A combined study of air mass origin (back trajectories and backward emission sensitivity calculations) and source region distribution comparison (CO satellite data from MOPITT and propane emission data from the EDGAR database) showed that the CO events were due to African biomass burning emissions, whereas the propane events were due to industrial emissions from areas of northern Africa. Both events were associated with elevated ozone. A comparison of the measured concentrations of CO and propane with those simulated by the global Model of Atmospheric Transport and Chemistry-Max Planck Institute for Chemistry (MATCH-MPIC) shows that the model reproduces the general longitudinal gradient observed for both compounds and simulates elevated CO concentrations during the pollution events. However, it systematically overestimates the CO mixing ratios. It is suggested that the northern African biomass burning emissions used in the model are not distributed correctly (incorrect timing) and, in particular, that too high emissions from the region “northern Sudan-Sahel” are used for this period. The model does not capture the influence from industrial emissions from northern Africa, which may be caused by too strong diffusion of the plume.

Alkyl nitrates are a significant component of the “odd nitrogen” reservoir and play an important role in regulating tropospheric ozone levels in remote marine regions. Measurements of methyl and ethyl nitrate in seawater and air samples along two Atlantic Ocean transects provide the first direct evidence for an oceanic source of these compounds. Equatorial surface waters were highly supersaturated (up to 800%) in both species, with the waters in the temperate regions generally being closer to equilibrium. A simple box model calculation suggests that the equatorial source could be a major component of the local atmospheric alkyl nitrate budget.

Environmental Context. The alkyl nitrates are a group of organic compounds that are known to be produced naturally in seawater. The sea-to-air flux of alkyl nitrates is believed to contribute significantly to the ‘odd nitrogen’ reservoir of the atmosphere and to play an important role in regulating tropospheric ozone levels in remote marine regions. Here we expand our knowledge of alkyl nitrate concentration distributions and saturation anomalies to Southern Ocean waters. Abstract. We report the first coupled atmosphere and seawater alkyl nitrate measurements for the Southern Ocean in the area bounded by 36–65°S, 30–70°W (November/December, 2004). Methyl and ethyl nitrate concentrations in seawater were 3.1–194.9 and 0.3–71.8 pmol L–1, respectively. Atmospheric mixing ratios ranged from 1.0 to 71.5 ppt for methyl nitrate and 0.6 to 16.6 ppt for ethyl nitrate. No correlations between alkyl nitrate distributions, and sea surface temperature, windspeed or chlorophyll a were observed. However, methyl and ethyl nitrate were well correlated in both the air and seawater, which suggests a common source. Calculations based on these observations estimate median saturation anomalies of –40% (–95 to 220%) for methyl nitrate and –11% (–98 to 174%) for ethyl nitrate. Positive saturation anomalies were spatially patchy, which suggests that some methyl and ethyl nitrate production was taking place in isolated areas of the study region. Overall our negative median saturation anomaly values suggest that during late austral spring (2004) the region of the Southern Ocean in which our measurements were made was not a net source of methyl or ethyl nitrate to the atmosphere. These results reinforce previous findings which suggest that whilst the equatorial ocean is a major source of methyl and ethyl nitrates to the atmosphere, higher latitude waters are generally at equilibrium or under-saturated. More measurements are required to assess how representative our results are of other areas of the Southern Ocean.