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Glycine betaine (GBT) is a nitrogenous osmolyte ubiquitous throughout the marine environment. Despite its widespread occurrence and significance in microbial cycling, knowledge of the seasonality of this compound is lacking. Here, we present a seasonal dataset of GBT concentrations in marine suspended particulate material. Analysing coastal waters in the Western English Channel, GBT peaked in summer and autumn but did not follow the observed maxima in total phytoplankton biomass or chlorophyll a. Instead, we found evidence that GBT concentrations were associated with specific phytoplankton groups or species, particularly in the summer when GBT correlated with dinoflagellate biomass. In contrast, autumn maxima corresponded with a period of rapidly changing salinity and nutrient availability, with potential contributions from some phytoplankton species and Harpacticoid copepods. This suggests distinct environmental drivers for different periods of the GBT seasonality. Building on evidence that GBT and dinoflagellate biomass peak in summer, concomitantly with low nutrients, we propose that GBT positively affects dinoflagellate fitness, allowing them to outcompete other plankton when inorganic nutrients are depleted. By using this assumption, we improved the performance of a marine ecosystem model to reproduce the observed increase in dinoflagellates biomass in the transition from spring to summer. This work sheds light on the interplay between phytoplankton succession, competitive advantage and changing environmental factors relevant to climate change. It paves the way for future multidisciplinary research aiming to understand the importance of dinoflagellates in key coastal ecosystems and their potential significance for methylamine production, compounds relevant for particle growth in atmospheric chemistry.

Choline and glycine betaine (GBT) are utilized as osmolytes to counteract osmotic stress, but also constitute important nutrient sources for many marine microbes. Bacterial catabolism of these substrates can then lead to the production of climate active trace gases such as methylamine and methane. Using radiotracers, we investigated prokaryotic choline/GBT uptake and determined biotic and abiotic factors driving these processes in the Western English Channel, UK. Kinetic uptake parameters indicated high affinity (nM range) for both osmolytes and showed a seasonal pattern for choline uptake. Generalized linear modeling of uptake parameters suggested a significant influence of sea surface temperature and salinity on prokaryotic uptake of both osmolytes. The presence of diatoms significantly influenced prokaryotic choline/GBT uptake dynamics. Choline uptake was further related to the occurrence of Phaeocystis spp., which were highly abundant in the phytoplankton community during spring, and dinoflagellates abundance during summer. While Rhodobacteraceae were the most important bacterial drivers for prokaryotic choline uptake, prokaryotic GBT uptake was associated with various groups such as SAR11 (Pelagibacterales) and Gammaproteobacteria, suggesting a wider capacity for GBT catabolism than previously recognized. Furthermore, using a newly developed approach we determined the first available data for dissolved GBT concentrations in seawater and found both osmolytes to be at the sub-nanomolar range. Together, this study improves our understanding of the biogeochemical cycling of these environmentally important osmolytes and highlights how their cycles may be affected by a changing climate.\ud \ud

9 pages, supporting information https://dx.doi.org/10.1021/acsearthspacechem.9b00028, Measurements of alkylamines from seawater and atmospheric samples collected simultaneously across the Antarctic Peninsula, South Orkney and South Georgia Islands are reported. Concentrations of mono-, di-, and trimethylamine (MMA, DMA, and TMA, respectively), and their precursors, the quarternary amines glycine betaine and choline, were enhanced in sympagic seawater samples relative to ice-devoid pelagic ones, suggesting the microbiota of sea ice and sea ice-influenced ocean is a major source of these compounds. Primary sea-spray aerosol particles artificially generated by bubbling seawater samples were investigated by aerosol time-of-flight mass spectrometry (ATOFMS) of single particles; their mixing state indicated that alkylamines were aerosolized with sea spray from dissolved and particulate organic nitrogen pools. Despite this unequivocal sea spray-associated source of alkylamines, ATOFMS analyses of ambient aerosols in the sympagic region indicated that the majority (75-89%) of aerosol alkylamines were of secondary origin, that is, incorporated into the aerosol after gaseous air-sea exchange. These findings show that sympagic seawater properties are a source of alkylamines influencing the biogenic aerosol fluxed from the ocean into the boundary layer; these organic nitrogen compounds should be considered when assessing secondary aerosol formation processes in Antarctica, The study was supported by the Spanish Ministry of Economy through project BIOeNUC (CGL2013-49020-R), PI-ICE (CTM2017-89117-R) and the Ramon y Cajal fellowship (RYC-2012-11922), and by the EU though the FP7-PEOPLE-2013-IOF programme (Project number 624680, MANU - Marine Aerosol NUcleations), all to MD, and PEGASO (CTM2012-37615) to RS

We report the first measurements of surfactant activity (SA) in the sea surface microlayer (SML) and in sub-surface waters (SSW) at the ocean basin scale, for two Atlantic Meridional Transects (AMT) from 50°N to 50°S during 2014 and 2015. Northern hemisphere (NH) SA was significantly higher than southern hemisphere (SH) SA in the SML and in the SSW. SA enrichment factors (EF = SASML/SASSW) were also higher in the NH, for wind speeds up to ~13 m s-1, questioning a prior assertion that Atlantic Ocean wind speeds > 12 m s-1 poleward of 30°N and 30°S would preclude high EFs and showing the SML to be self-sustaining with respect to SA. Our results imply that surfactants exert a control on air-sea CO2 exchange across the whole North Atlantic CO2 sink region and that the contribution made by high wind, high latitude oceans to air-sea gas exchange globally should be re-examined.

We performed an annual study of oxygenated volatile organic compound (OVOC) seawater concentrations at a site off Plymouth, UK in the Western English Channel over the period of February 2011–March 2012. Acetone concentrations ranged from 2–10 nM (nanomole/L) in surface waters with a maximum observed in summer. Concentrations correlated positively with net shortwave radiation and UV light, suggestive of photochemically linked acetone production. We observed a clear decline in acetone concentrations below the mixed layer. Acetaldehyde varied between 4–37 nM in surface waters with higher values observed in autumn and winter. Surface concentrations of methanol ranged from 16–78 nM, but no clear annual cycle was observed. Methanol concentrations exhibited considerable inter-annual variability. We estimate consistent deposition to the sea surface for acetone and methanol but that the direction of the acetaldehyde flux varies during the year.

We present air–sea fluxes of oxygenated volatile organics compounds (OVOCs) quantified by eddy covariance (EC) during the Atlantic Meridional Transect cruise in 2012. Measurements of acetone, acetaldehyde, and methanol in air as well as in water were made in several different oceanic provinces and over a wide range of wind speeds (1–18 m s−1). The ocean appears to be a net sink for acetone in the higher latitudes of the North Atlantic but a source in the subtropics. In the South Atlantic, seawater acetone was near saturation relative to the atmosphere, resulting in essentially zero net flux. For acetaldehyde, the two-layer model predicts a small oceanic emission, which was not well resolved by the EC method. Chemical enhancement of air–sea acetaldehyde exchange due to aqueous hydration appears to be minor. The deposition velocity of methanol correlates linearly with the transfer velocity of sensible heat, confirming predominant airside control. We examine the relationships between the OVOC concentrations in air as well as in water, and quantify the gross emission and deposition fluxes of these gases.

[1] Oceanic methanol, acetaldehyde, and acetone concentrations were measured during an Atlantic Meridional Transect (AMT) cruise from the UK to Chile (49°N to 39°S) in 2009. Methanol (48–361 nM) and acetone (2–24 nM) varied over the track with enrichment in the oligotrophic Northern Atlantic Gyre. Acetaldehyde showed less variability (3–9 nM) over the full extent of the transect. These oxygenated volatile organic compounds (OVOCs) were also measured subsurface, with methanol and acetaldehyde mostly showing homogeneity throughout the water column. Acetone displayed a reduction below the mixed layer. OVOC concentrations did not consistently correlate with primary production or chlorophyll-a levels in the surface Atlantic Ocean. However, we did find a novel and significant negative relationship between acetone concentration and bacterial leucine incorporation, suggesting that acetone might be removed by marine bacteria as a source of carbon. Microbial turnover of both acetone and acetaldehyde was confirmed. Modeled atmospheric data are used to estimate the likely air-side OVOC concentrations. The direction and magnitude of air-sea fluxes vary for all three OVOCs depending on location. We present evidence that the ocean may exhibit regions of acetaldehyde under-saturation. Extrapolation suggests that the Atlantic Ocean represents an overall source of these OVOCs to the atmosphere at 3, 3, and 1 Tg yr−1 for methanol, acetaldehyde, and acetone, respectively.

[1] The biogeochemistry of oxygenated volatile organic compounds (OVOCs) like methanol, acetaldehyde, and acetone in marine waters is poorly understood. We report the first in situ gross production rates for methanol, acetaldehyde, and acetone of 49–103, 25–98, and 2–26 nmol L−1 d−1 over contrasting areas of marine productivity, including oligotrophic gyres and eutrophic upwellings. Photochemical production estimates are mostly negligible for methanol, up to 68% for acetaldehyde and up to 100% of gross production rates for acetone. Microbial surface OVOC oxidation to CO2 accounts for between 10–50% and 0.5–13% of the methanol and acetone losses, respectively, but largely control acetaldehyde concentrations (49–100%). Biological lifetimes in a coastal upwelling vary between ≤1 day for acetaldehyde, to approximately 7 days for methanol and up to ~80 days for acetone. In open oceanic environments, the lifetime of acetaldehyde ranges between 2 and 5 h, compared to 10–26 days for methanol and 5–55 days for acetone.

We present here vertical fluxes of oxygenated volatile organic compounds (OVOCs) measured with eddy covariance (EC) during the period of March to July 2012 near the southwest coast of the United Kingdom. The performance of the proton-transfer-reaction mass spectrometer (PTR-MS) for flux measurement is characterized, with additional considerations given to the homogeneity and stationarity assumptions required by EC. Observed mixing ratios and fluxes of OVOCs (specifically methanol, acetaldehyde, and acetone) vary significantly with time of day and wind direction. Higher mixing ratios and fluxes of acetaldehyde and acetone are found in the daytime and from the direction of a forested park, most likely due to light-driven emissions from terrestrial plants. Methanol mixing ratio and flux do not demonstrate consistent diel variability, suggesting sources in addition to plants. We estimate air–sea exchange and photochemical rates of these compounds, which are compared to measured vertical fluxes. For acetaldehyde, the mean (1σ) mixing ratio of 0.13 (0.02) ppb at night may be maintained by oceanic emission, while photochemical destruction outpaces production during the day. Air–sea exchange and photochemistry are probably net sinks of methanol and acetone in this region. Their nighttime mixing ratios of 0.46 (0.20) and 0.39 (0.08) ppb appear to be affected more by terrestrial emissions and long-distance transport, respectively.

Oxygenated volatile organic compounds (OVOCs) in the atmosphere are precursors to peroxy acetyl nitrate (PAN), affect the tropospheric ozone budget, and in the remote marine environment represent a significant sink of the hydroxyl radical (OH). The sparse observational database for these compounds, particularly in the tropics, contributes to a high uncertainty in their emissions and atmospheric significance. Here, we show measurements of acetone, methanol, and acetaldehyde in the tropical remote marine boundary layer made between October 2006 and September 2011 at the Cape Verde Atmospheric Observatory (CVAO) (16.85° N, 24.87° W). Mean mixing ratios of acetone, methanol, and acetaldehyde were 546 ± 295 pptv, 742 ± 419 pptv, and 428 ± 190 pptv, respectively, averaged from approximately hourly values over this five-year period. The CAM-Chem global chemical transport model reproduced annual average acetone concentrations well (21% overestimation) but underestimated levels by a factor of 2 in autumn and overestimated concentrations in winter. Annual average concentrations of acetaldehyde were underestimated by a factor of 10, rising to a factor of 40 in summer, and methanol was underestimated on average by a factor of 2, peaking to over a factor of 4 in spring. The model predicted summer minima in acetaldehyde and acetone, which were not apparent in the observations. CAM-Chem was adapted to include a two-way sea-air flux parametrization based on seawater measurements made in the Atlantic Ocean, and the resultant fluxes suggest that the tropical Atlantic region is a net sink for acetone but a net source for methanol and acetaldehyde. Inclusion of the ocean fluxes resulted in good model simulations of monthly averaged methanol levels although still with a 3-fold underestimation in acetaldehyde. Wintertime acetone levels were better simulated, but the observed autumn levels were more severely underestimated than in the standard model. We suggest that the latter may be caused by underestimated terrestrial biogenic African primary and/or secondary OVOC sources by the model. The model underestimation of acetaldehyde concentrations all year round implies a consistent significant missing source, potentially from secondary chemistry of higher alkanes produced biogenically from plants or from the ocean. We estimate that low model bias in OVOC abundances in the remote tropical marine atmosphere may result in up to 8% underestimation of the global methane lifetime due to missing model OH reactivity. Underestimation of acetaldehyde concentrations is responsible for the bulk (∼70%) of this missing reactivity.

The role of the ocean in the cycling of oxygenated volatile organic compounds (OVOCs) remains largely unanswered due to a paucity of datasets. We describe the method development of a membrane inlet-proton transfer reaction/mass spectrometer (MI-PTR/MS) as an efficient method of analysing methanol, acetaldehyde and acetone in seawater. Validation of the technique with water standards shows that the optimised responses are linear and reproducible. Limits of detection are 27 nM for methanol, 0.7 nM for acetaldehyde and 0.3 nM for acetone. Acetone and acetaldehyde concentrations generated by MI-PTR/MS are compared to a second, independent method based on purge and trap-gas chromatography/flame ionisation detection (P&T-GC/FID) and show excellent agreement. Chromatographic separation of isomeric species acetone and propanal permits correction to mass 59 signal generated by the PTR/MS and overcomes a known uncertainty in reporting acetone concentrations via mass spectrometry. A third bioassay technique using radiolabelled acetone further supported the result generated by this method. We present the development and optimisation of the MI-PTR/MS technique as a reliable and convenient tool for analysing seawater samples for these trace gases. We compare this method with other analytical techniques and discuss its potential use in improving the current understanding of the cycling of oceanic OVOCs.

Methanol is the second most abundant organic gas in the atmosphere after methane, and is ubiquitous in the troposphere. It plays a significant role in atmospheric oxidant chemistry and is biogeochemically active. Large uncertainties exist about whether the oceans are a source or sink of methanol to the atmosphere. Even less is understood about what reactions in seawater determine its concentration, and hence flux across the sea surface interface. We report here concentrations of methanol between 151–296 nM in parts of the oligotrophic North Atlantic, with corresponding microbial uptake rates between 2–146 nM d−1, suggesting turnover times as low as 1 day (1–25 days) in surface waters of the oligotrophic tropical North East Atlantic. Methanol is mainly (≥97%) used by microbes for obtaining energy in oligotrophic regions, which contrasts with shelf and coastal areas where between 20–50% can be used for cell growth. Comparisons of microbial methanol oxidation rates with parallel determinations of bacterial leucine uptake suggest that methanol contributes on average 13% to bacterial carbon demand in the central northern Atlantic gyre (maximum of 54%). In addition, the contribution that methanol makes to bacterial carbon demand varies as a power function of chlorophyll a concentrations; suggesting for concentrations −1 that methanol can make a significant contribution to bacterial carbon demand. However, our low air to sea methanol flux estimates of 7.2–13 μmol m−2 d−1 suggest that the atmosphere is not a major methanol source. We conclude that there must be a major, as yet unidentified, in situ oceanic methanol source in these latitudes which we suggest is sunlight driven decomposition of organic matter.

This document is a supplement to “Physical Exchanges at the Air–Sea Interface: UK–SOLAS Field Measurements,” by Ian M. Brooks, Margaret J. Yelland, Robert C. Upstill-Goddard, Philip D. Nightingale, Steve Archer, Eric d’Asaro, Rachael Beale, Cory Beatty, Byron Blomquist, A. Anthony Bloom, Barbara J. Brooks, John Cluderay, David Coles, John Dacey, Michael DeGrandpre, Jo Dixon, William M. Drennan, Joseph Gabriele, Laura Goldson, Nick Hardman-Mountford, Martin K. Hill, Matt Horn, Ping-Chang Hsueh, Barry Huebert, Gerrit de Leeuw, Timothy G. Leighton, Malcolm Liddicoat, Justin J. N. Lingard, Craig McNeil, James B. McQuaid, Ben I. Moat, Gerald Moore, Craig Neill, Sarah J. Norris, Simon O’Doherty, Robin W. Pascal, John Prytherch, Mike Rebozo, Erik Sahlee, Matt Salter, Ute Schuster, Ingunn Skjelvan, Hans Slagter, Michael H. Smith, Paul D. Smith, Meric Srokosz, John A. Stephens, Peter K. Taylor, Maciej Telszewski, Roisin Walsh, Brian Ward, David K. Woolf, Dickon Young, and Henk Zemmelink (Bull. Amer. Meteor. Soc., 90, 629–644) • ©2009 American Meteorological Society • Corresponding author: Ian M. Brooks, Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom • E-mail: i.brooks@see.leeds.ac.uk • DOI:10.1175/2008BAMS2578.2

Acetone is an important oxygenated volatile organic compound in the troposphere where it influences the oxidising capacity of the atmosphere. However, the air-sea flux is not well quantified, in part due to a lack of knowledge regarding which processes control oceanic concentrations, and, specifically whether microbial oxidation to CO2 represents a significant loss process. We demonstrate that 14C labelled acetone can be used to determine microbial oxidation to 14CO2. Linear microbial rates of acetone oxidation to CO2 were observed for between 0.75-3.5 hours at a seasonally eutrophic coastal station located in the western English Channel (L4). A kinetic experiment in summer at station L4 gave a Vmax of 4.1 pmol L-1 h-1, with a Km constant of 54 pM. We then used this technique to obtain microbial acetone loss rates ranging between 1.2-42 pmol L-1 h-1 (monthly averages) over an annual cycle at L4, with maximum rates observed during winter months. The biological turnover time of acetone (in situ concentration divided by microbial oxidation rate) in surface waters varied from ~3 days in February 2011, when in situ concentrations were 3 ± 1 nM, to >240 days in June 2011, when concentrations were more than 2 fold higher at 7.5 ± 0.7 nM. These relatively low marine microbial acetone oxidation rates, when normalised to in situ concentrations, suggest that marine microbes preferentially utilise other oxygenated volatile organic compounds such as methanol and acetaldehyde.

Many of the reactive trace gases detected in the atmosphere are both emitted from and deposited to the global oceans via exchange across the air–sea interface. The resistance to transfer through both air and water phases is highly sensitive to physical drivers (waves, bubbles, films, etc.), which can either enhance or suppress the rate of diffusion. In addition to outlining the fundamental processes controlling the air–sea gas exchange, the authors discuss these drivers, describe the existing parameterizations used to predict transfer velocities, and summarize the novel techniques for measuring in situ exchange rates. They review trace gases that influence climate via radiative forcing (greenhouse gases), those that can alter the oxidative capacity of the atmosphere (nitrogen- and sulfur-containing gases), and those that impact ozone levels (organohalogens), both in the troposphere and stratosphere. They review the known biological and chemical routes of production and destruction within the water column for these gases, whether the ocean acts as a source or sink, and whether temporal and spatial variations in saturation anomalies are observed. A current estimate of the marine contribution to the total atmospheric flux of these gases, which often highlights the significance of the oceans in biogeochemical cycling of trace gases, is provided, and how air–sea gas fluxes may change in the future is briefly assessed.

In the troposphere, methanol (CH3OH) is present ubiquitously and second in abundance among organic gases after methane. In the surface ocean, methanol represents a supply of energy and carbon for marine microbes. Here we report direct measurements of air–sea methanol transfer along a ∼10,000-km north–south transect of the Atlantic. The flux of methanol was consistently from the atmosphere to the ocean. Constrained by the aerodynamic limit and measured rate of air–sea sensible heat exchange, methanol transfer resembles a one-way depositional process, which suggests dissolved methanol concentrations near the water surface that are lower than what were measured at ∼5 m depth, for reasons currently unknown. We estimate the global oceanic uptake of methanol and examine the lifetimes of this compound in the lower atmosphere and upper ocean with respect to gas exchange. We also constrain the molecular diffusional resistance above the ocean surface—an important term for improving air–sea gas exchange models.

We present here vertical fluxes of methanol, acetaldehyde, and acetone measured directly with eddy covariance (EC) during March to July 2012 near the southwest coast of the UK. The performance of the proton-transfer reaction mass spectrometer (PTR-MS) for flux measurement is characterized, with additional considerations given to the homogeneity and stationarity assumptions required by EC. Concentrations and fluxes of these compounds vary significantly with time of day and wind direction. Higher values of acetaldehyde and acetone are usually observed in the daytime and from the direction of a forested park, most likely due to light-driven emissions from terrestrial plants. Methanol concentration and flux do not demonstrate clear diel variability, suggesting sources in addition to plants. We estimate air–sea exchange and photochemical rates of these compounds, which are compared to measured vertical fluxes. For acetaldehyde, the mean (1σ) concentration of 0.13 (0.02) ppb at night may be maintained by oceanic emission, while photochemical destruction outpaces production during the day. Air-sea exchange and photochemistry are probably net sinks of methanol and acetone in this region. Their nighttime concentrations of 0.46 (0.20) and 0.39 (0.08) ppb appear to be affected more by terrestrial emissions and long distance transport, respectively.

The oceans contribute significantly to the global emissions of a number of atmospherically important volatile gases, notably those containing sulfur, nitrogen and halogens. Such gases play critical roles not only in global biogeochemical cycling but also in a wide range of atmospheric processes including marine aerosol formation and modification, tropospheric ozone formation and destruction, photooxidant cycling and stratospheric ozone loss. A number of marine emissions are greenhouse gases, others influence the Earth's radiative budget indirectly through aerosol formation and/or by modifying oxidant levels and thus changing the atmospheric lifetime of gases such as methane. In this article we review current literature concerning the physical, chemical and biological controls on the sea-air emissions of a wide range of gases including dimethyl sulphide (DMS), halocarbons, nitrogen-containing gases including ammonia (NH3), amines (including dimethylamine, DMA, and diethylamine, DEA), alkyl nitrates (RONO2) and nitrous oxide (N2O), non-methane hydrocarbons (NMHC) including isoprene and oxygenated (O)VOCs, methane (CH4) and carbon monoxide (CO). Where possible we review the current global emission budgets of these gases as well as known mechanisms for their formation and loss in the surface ocean.

[1] The role of the ocean in the cycling of ethanol and propanol remains unanswered due to a total lack of data on their concentrations in seawater. We report the first measurements of these low molecular mass alcohols made during two field experiments in the Atlantic Ocean. Ethanol concentrations ranged from 2–33 nM. Our analytical technique allowed the separation of the two propanol isomers and concentrations of 1- and 2-propanol varied between 2–22 nM and 1–19 nM respectively. Global extrapolation of the sea - air fluxes indicate that the ocean may be an important source for these compounds to the atmosphere and suggest that the magnitude of the fluxes may be enhanced in natural upwelling regions.

Methanol is the predominant oxygenated volatile organic compound in the troposphere, where it can significantly influence the oxidising capacity of the atmosphere. However, we do not understand which processes control oceanic concentrations, and hence, whether the oceans are a source or a sink to the atmosphere. We report the first methanol loss rates in seawater by demonstrating that (14)C-labelled methanol can be used to determine microbial uptake into particulate biomass, and oxidation to (14)CO(2). We have found that methanol is used predominantly as a microbial energy source, but also demonstrated its use as a carbon source. We report biological methanol oxidation rates between 2.1 and 8.4 nmol l(-1) day(-1) in surface seawater of the northeast Atlantic. Kinetic experiments predict a V(max) of up to 29 nmol l(-1) day(-1), with a high affinity K(m) constant of 9.3 nM in more productive coastal waters. We report surface concentrations of methanol in the western English channel of 97±8 nM (n=4) between May and June 2010, and for the wider temperate North Atlantic waters of 70±13 nM (n=6). The biological turnover time of methanol has been estimated between 7 and 33 days, although kinetic experiments suggest a 7-day turnover in more productive shelf waters. Methanol uptake rates into microbial particles significantly correlated with bacterial and phytoplankton parameters, suggesting that it could be used as a carbon source by some bacteria and possibly some mixotrophic eukaryotes. Our results provide the first methanol loss rates from seawater, which will improve the understanding of the global methanol budget.

As part of the U. K. contribution to the international Surface Ocean-Lower Atmosphere Study, a series of three related projects-DOGEE, SEASAW, and HiWASE-undertook experimental studies of the processes controlling the physical exchange of gases and sea spray aerosol at the sea surface. The studies share a common goal: to reduce the high degree of uncertainty in current parameterization schemes. The wide variety of measurements made during the studies, which incorporated tracer and surfactant release experiments, included direct eddy correlation fluxes, detailed wave spectra, wind history, photographic retrievals of whitecap fraction, aerosol-size spectra and composition, surfactant concentration, and bubble populations in the ocean mixed layer. Measurements were made during three cruises in the northeast Atlantic on the RRS Discovery during 2006 and 2007; a fourth campaign has been making continuous measurements on the Norwegian weather ship Polarfront since September 2006. This paper provides an overview of the three projects and some of the highlights of the measurement campaigns.

The oceans contribute significantly to the global emissions of a number of atmospherically important volatile gases, notably those containing sulfur, nitrogen and halogens. Such gases play critical roles not only in global biogeochemical cycling but also in a wide range of atmospheric processes including marine aerosol formation and modification, tropospheric ozone formation and destruction, photooxidant cycling and stratospheric ozone loss. A number of marine emissions are greenhouse gases, others influence the Earth's radiative budget indirectly through aerosol formation and/or by modifying oxidant levels and thus changing the atmospheric lifetime of gases such as methane. In this article we review current literature concerning the physical, chemical and biological controls on the sea-air emissions of a wide range of gases including dimethyl sulphide (DMS), halocarbons, nitrogen-containing gases including ammonia (NH(3)), amines (including dimethylamine, DMA, and diethylamine, DEA), alkyl nitrates (RONO(2)) and nitrous oxide (N(2)O), non-methane hydrocarbons (NMHC) including isoprene and oxygenated (O)VOCs, methane (CH(4)) and carbon monoxide (CO). Where possible we review the current global emission budgets of these gases as well as known mechanisms for their formation and loss in the surface ocean.