Abstract. The size of phytoplankton is a key metric that influences organic carbon production in the ocean and its transfer efficiency through marine food webs. There is evidence that the size structure of phytoplankton in Antarctic waters differs markedly from that in tropical oceans. However, logistical challenges have left many Antarctic regions poorly sampled. Here, we explore a dataset collected during an austral summer research cruise to the rarely sampled northwestern Weddell Sea continental shelf and open waters near the eastern Antarctic Peninsula. The dataset includes discrete measurements of size-fractionated chlorophyll-a concentration (pico- <2 μm, nano- 2–20 μm, and microphytoplankton >20 μm) obtained using in vitro fluorescence and sequential size-fractionated filtration (SFF), phytoplankton pigments measured by high-performance liquid chromatography (HPLC), and in situ radiometric (ocean-colour) observations. We find broad agreement between HPLC-based (using diagnostic pigment analysis) and SFF-based estimates of total and size-fractionated chlorophyll-a, but with systematic differences for some size classes depending on the technique used. Ocean-colour chlorophyll-a algorithms developed in other regions of the Southern Ocean perform well in the northwestern Weddell Sea and outperform standard global algorithms, which systematically underestimate chlorophyll-a. SFF measurements indicate that medium-sized phytoplankton (nanophytoplankton) dominate both shelf and open waters of the northwestern Weddell Sea. We fitted a simple three-component model to the SFF data describing the partitioning of chlorophyll-a among the three size classes as a function of total chlorophyll-a. Model parameters were similar to those derived from an independent dataset from the western Antarctic Peninsula, supporting the broader dominance of nanophytoplankton around the entire Antarctic Peninsula, but differed markedly from parameters derived from lower-latitude tropical and subtropical (50° N to 50° S) Atlantic waters, where picophytoplankton dominate. Finally, we combined satellite-derived estimates of total chlorophyll-a during the cruise period with the tuned model parameters to map the spatial distribution of phytoplankton size classes across the broader northwestern Weddell Sea region, which confirmed the widespread dominance of nanophytoplankton. These datasets provide a valuable baseline for quantifying the rate and fate of organic carbon production in this rapidly changing region.

The central Arctic Ocean (CAO) plays an important role in the global carbon cycle, but the current and future exchange of the climate-forcing trace gases methane (CH4) and carbon dioxide (CO2) between the CAO and the atmosphere is highly uncertain. In particular, there are very few observations of near-surface gas concentrations or direct air–sea CO2 flux estimates and no previously reported direct air–sea CH4 flux estimates from the CAO. Furthermore, the effect of sea ice on the exchange is not well understood. We present direct measurements of the air–sea flux of CH4 and CO2, as well as air–snow fluxes of CO2 in the summertime CAO north of 82.5∘ N from the Synoptic Arctic Survey (SAS) expedition carried out on the Swedish icebreaker Oden in 2021. Measurements of air–sea CH4 and CO2 flux were made using floating chambers deployed in leads accessed from sea ice and from the side of Oden, and air–snow fluxes were determined from chambers deployed on sea ice. Gas transfer velocities determined from fluxes and surface-water-dissolved gas concentrations exhibited a weaker wind speed dependence than existing parameterisations, with a median sea-ice lead gas transfer rate of 2.5 cm h−1 applicable over the observed 10 m wind speed range (1–11 m s−1). The average observed air–sea CO2 flux was −7.6 mmolm-2d-1, and the average air–snow CO2 flux was −1.1 mmolm-2d-1. Extrapolating these fluxes and the corresponding sea-ice concentrations gives an August and September flux for the CAO of −1.75 mmolm-2d-1, within the range of previous indirect estimates. The average observed air–sea CH4 flux of 3.5 µmolm-2d-1, accounting for sea-ice concentration, equates to an August and September CAO flux of 0.35 µmolm-2d-1, lower than previous estimates and implying that the CAO is a very small (≪ 1 %) contributor to the Arctic flux of CH4 to the atmosphere.

The ocean annually absorbs about a quarter of all anthropogenic carbon dioxide (CO2) emissions. Global estimates of air-sea CO2 fluxes are typically based on bulk measurements of CO2 in air and seawater and neglect the effects of vertical temperature gradients near the ocean surface. Theoretical and laboratory observations indicate that these gradients alter air-sea CO2 fluxes, because the air-sea CO2 concentration difference is highly temperature sensitive. However, in situ field evidence supporting their effect is so far lacking. Here we present independent direct air-sea CO2 fluxes alongside indirect bulk fluxes collected along repeat transects in the Atlantic Ocean (50° N to 50° S) in 2018 and 2019. We find that accounting for vertical temperature gradients reduces the difference between direct and indirect fluxes from 0.19 mmol m-2 d-1 to 0.08 mmol m-2 d-1 (N = 148). This implies an increase in the Atlantic CO2 sink of ~0.03 PgC yr-1 (~7% of the Atlantic Ocean sink). These field results validate theoretical, modelling and observational-based efforts, all of which predicted that accounting for near-surface temperature gradients would increase estimates of global ocean CO2 uptake. Accounting for this increased ocean uptake will probably require some revision to how global carbon budgets are quantified.

The Western Channel Observatory (WCO) comprises a series of pelagic, benthic and atmospheric sampling sites within 40 km of Plymouth, UK, that have been sampled by the Plymouth institutes on a regular basis since 1903. This longevity of recording and the high frequency of observations provide a unique combination of data; for example temperature data were first collected in 1903, and the reference station L4, where nearly 400 planktonic taxa have been enumerated, has been sampled on a weekly basis since 1988. While the component datasets have been archived, here we provide the first summary database bringing together a wide suite of the observations. This provides monthly average values of some of the key pelagic and benthic measurements for the inshore site L4 (50∘15.00′ N, 4∘13.02′ W; approx. depth 55 m), the offshore site E1 (50∘02.00′ N, 4∘22.00′ W; approx. depth 75 m) and the intermediate L5 site (50∘10.80′ N, 4∘18.00′ W; approx. depth 58 m). In brief, these data include the following: water temperature (from 1903); macronutrients (from 1934); dissolved inorganic carbon and total alkalinity (from 2008); methane and nitrous oxide (from 2011); chlorophyll a (from 1992); high-performance liquid chromatography (HPLC)-derived pigments (from 1999); <20 µm plankton by flow cytometry, including bacteria (8 functional groups from 2007); phytoplankton by microscopy (6 functional groups from 1992); microplankton and mesozooplankton from FlowCam (6 groups from 2012); Noctiluca sp. dinoflagellate (from 1997); mesozooplankton by microscopy (8 groups from 1988); Calanus helgolandicus egg production rates (from 1992); fish larvae from the Young Fish Trawl survey (4 groups from 1924); benthic macrofauna (4 groups from 2008); demersal fish (19 families from 2008); blue shark, Prionace glauca (from 1958); and 16S alpha diversity for sediment and water column (from 2012). These data have varying coverage with respect to time and depth resolution. The metadata tables describe each dataset and provide pointers to the source data and other related Western Channel Observatory datasets and outputs not compiled here. We provide summaries of the main trends in seasonality and some major climate-related shifts that have been revealed over the last century. The data are available from the Data Archive for Seabed Species and Habitats (DASSH): https://doi.org/10.17031/645110fb81749 (McEvoy and Atkinson, 2023). Making these data fully accessible and including units of both abundance and biomass will stimulate a variety of uptakes. These may include uses as an educational resource for projects, for models and budgets, for the analysis of seasonality and long-term change in a coupled benthic–pelagic system, or for supporting UK and north-eastern Atlantic policy and management.

The Central Arctic Ocean’s (CAO) current and future role in the exchange of climate-forcing trace gases with the atmosphere is highly uncertain due to sparse observations of dissolved gas concentrations and sea-air fluxes the poorly understood role of sea ice in the exchange, and the rapidly reducing sea-ice cover. The highest rates of gas exchange in pack ice regions occur through open water areas such as leads. These appear on scales from < 1m to > 10km, but are highly variable in form, size, and existence.Estimates of polar region trace gas fluxes are highly dependent on the choice of gas transfer parameterisation. Differences in Arctic Ocean CO2 uptake estimates resulting from this choice may be as large as 50 Tg C yr-1, ~30 % of the total (Yasunaka et al., 2018). Direct gas exchange observations suggest that gas transfer rates will be reduced in the presence of sea ice (Prytherch and Yelland, 2021).There are no previously reported direct sea-air methane flux estimates from the CAO. Indirect flux rates estimated from water column measurements of dissolved methane are variable but low, typically < 10 mol m-2 day-1. Much higher fluxes, 125 mol m-2 day-1, have been derived from aircraft-based atmospheric profile measurements (Kort et al., 2012). Sea-air CO2 fluxes determined from direct, eddy covariance measurements in areas adjacent to ice or from lead water surfaces in both central and outlying areas of the Arctic Ocean are on the order of 10 mmol m-2 day-1 (Prytherch and Yelland, 2021).Here we present direct measurements of the sea-air flux of CH4 and CO2, as well as ice-air fluxes of CO2 in the summertime CAO, obtained during the Synoptic Arctic Survey (SAS) expedition carried out on the Swedish icebreaker Oden in 2021. Measurements of sea-air CH4 and CO2 flux were made using floating chambers deployed in leads accessed from sea ice and from the side of Oden. Fluxes and dissolved gas concentrations from surface water were used to determine gas transfer velocities. The dependence of the exchange on wind speed, buoyancy, lead width and ice condition was investigated in order to develop improved parameterisations of polar sea-air gas exchange. The directly measured fluxes provide an improved constraint on the regional sea-air exchange of CH4 and CO2, and in particular show that CH4 emissions in the summertime CAO are substantially lower than suggested by previous estimates. Kort, E. A. et al: Atmospheric observations of Arctic Ocean methane emissions up to 82° north, Nature Geosci, 5, 318–321, https://doi.org/10.1038/ngeo1452, 2012.Prytherch, J. and Yelland, M. J.: Wind, Convection and Fetch Dependence of Gas Transfer Velocity in an Arctic Sea‐Ice Lead Determined From Eddy Covariance CO2 Flux Measurements, Global Biogeochem Cycles, 35, https://doi.org/10.1029/2020gb006633, 2021.Yasunaka, S., et al: Arctic Ocean CO2 uptake: an improved multiyear estimate of the air–sea CO2 flux incorporating chlorophyll a concentrations, Biogeosciences, 15, 1643–1661, https://doi.org/10.5194/bg-15-1643-2018, 2018.

An automated system was developed using commercially available Cavity Ring-Down Spectroscopy (CRDS) technology (Picarro LTD., G2508) which was interfaced to a custom-made system which automated the equilibration and analysis of seawater dissolved nitrous oxide (N2O) and methane (CH4). The combined system was deployed during two research cruises in the Atlantic Ocean, which combined covered 16,500 kms, one on a west to east transect between the United States and Europe at approximately 24°N, the second was a north to south transect which covered approximately 70° of latitude between the Tropic of Cancer and the Southern Ocean. Semi-continuous measurements using the CRDS (Approx. 73,000) were compared to discretely collected samples (n=156) which were analysed using gas chromatography (GC) with flame ionisation detection for CH4 and electron capture detection for N2O. Excellent agreement between the two approaches, though with an increase in analytical precision offered by CRDS compared to GC gives great confidence in the applicability of the CRDS system, whilst the significant (2 to 3 orders of magnitude) increase in measurement frequency offer an opportunity to greatly increase the number of dissolved N2O and CH4 data that are currently available. Whilst identifying a number of small-scale features, deployment during this study showed that whilst the surface of large areas of the Atlantic Ocean were in-balance with the overlying atmosphere with respect to N2O, the most of this region was offering a source of atmospheric CH4.

Estuaries receive and process a large amount of particulate organic carbon (POC) prior to its export into coastal waters. Studying the origin of this POC is key to understanding the fate of POC and the role of estuaries in the global carbon cycle. Here, we evaluated the concentrations of POC, as well as particulate organic nitrogen (PON), and used stable carbon and nitrogen isotopes to assess their sources across 13 contrasting British estuaries during five different sampling campaigns over 1 year. We found a high variability in POC and PON concentrations across the salinity gradient, reflecting inputs, and losses of organic material within the estuaries. Catchment land cover appeared to influence the contribution of POC to the total organic carbon flux from the estuary to coastal waters, with POC contributions >36% in estuaries draining catchments with a high percentage of urban/suburban land, and <11% in estuaries draining catchments with a high peatland cover. There was no seasonal pattern in the isotopic composition of POC and PON, suggesting similar sources for each estuary over time. Carbon isotopic ratios were depleted (−26.7 ± 0.42‰, average ± sd) at the lowest salinity waters, indicating mainly terrigenous POC (TPOC). Applying a two‐source mixing model, we observed high variability in the contribution of TPOC at the highest salinity waters between estuaries, with a median value of 57%. Our results indicate a large transport of terrigenous organic carbon into coastal waters, where it may be buried, remineralized, or transported offshore.

The flux of CO2 between the atmosphere and the ocean is often estimated as the air–sea gas concentration difference multiplied by the gas transfer velocity (K660). The first order driver for K660 over the ocean is wind through its influence on near surface hydrodynamics. However, field observations have shown substantial variability in the wind speed dependencies of K660. During a ~ 11,000 km long Southern Ocean transect, we measured K660 with the eddy covariance technique. In parallel, we made a novel measurement of the gas transfer efficiency (GTE) based on partial equilibration of CO2 using a Segmented Flow Coil Equilibrator system. GTE varied by 20% during the transect, was distinct in different water masses, and related to K660. At a moderate wind speed of 7 m s−1, K660 associated with high GTE exceeded K660 with low GTE by 30% in the mean. The sensitivity of K660 towards GTE was stronger at lower wind speeds and weaker at higher wind speeds. Naturally-occurring organics in seawater, some of which are surface active, are likely the cause of the variability in GTE and in K660. To investigate this further, we perform further laboratory experiments to assess the effects of surfactant concentration and water temperature on GTE.

Human activities are changing the Arctic environment at an unprecedented rate resulting in rapid warming, freshening, sea ice retreat and ocean acidification of the Arctic Ocean. Trace gases such as nitrous oxide (N 2 O) and methane (CH 4 ) play important roles in both the atmospheric reactivity and radiative budget of the Arctic and thus have a high potential to influence the region’s climate. However, little is known about how these rapid physical and chemical changes will impact the emissions of major climate-relevant trace gases from the Arctic Ocean. The combined consequences of these stressors present a complex combination of environmental changes which might impact on trace gas production and their subsequent release to the Arctic atmosphere. Here we present our current understanding of nitrous oxide and methane cycling in the Arctic Ocean and its relevance for regional and global atmosphere and climate and offer our thoughts on how this might change over coming decades.

Surface ocean carbon dioxide (CO2) measurements are used to compute the oceanic air–sea CO2 flux. The CO2 flux component from rivers and estuaries is uncertain due to the high spatial and seasonal heterogeneity of CO2 in coastal waters. Existing high-quality CO2 instrumentation predominantly utilises showerhead and percolating style equilibrators optimised for open-ocean observations. The intervals between measurements made with such instrumentation make it difficult to resolve the fine-scale spatial variability of surface water CO2 at timescales relevant to the high frequency variability in estuarine and coastal environments. Here we present a novel dataset with unprecedented frequency and spatial resolution transects made at the Western Channel Observatory in the south-west of the UK from June to September 2016, using a fast-response seawater CO2 system. Novel observations were made along the estuarine–coastal continuum at different stages of the tide and reveal distinct spatial patterns in the surface water CO2 fugacity (fCO2) at different stages of the tidal cycle. Changes in salinity and fCO2 were closely correlated at all stages of the tidal cycle and suggest that the mixing of oceanic and riverine endmembers partially determines the variations in fCO2. The correlation between salinity and fCO2 was different in Cawsand Bay, which could be due to enhanced gas exchange or to enhanced biological activity in the region. The observations demonstrate the complex dynamics determining spatial and temporal patterns of salinity and fCO2 in the region. Spatial variations in observed surface salinity were used to validate the output of a regional high-resolution hydrodynamic model. The model enables a novel estimate of the air–sea CO2 flux in the estuarine–coastal zone. Air–sea CO2 flux variability in the estuarine–coastal boundary region is influenced by the state of the tide because of strong CO2 outgassing from the river plume. The observations and model output demonstrate that undersampling the complex tidal and mixing processes characteristic of estuarine and coastal environment biases quantification of air–sea CO2 fluxes in coastal waters. The results provide a mechanism to support critical national and regional policy implementation by reducing uncertainty in carbon budgets.

Uncertainty in the CO2 gas transfer velocity (K660) severely limits the accuracy of air-sea CO2 flux calculations and hence hinders our ability to produce realistic climate projections. Recent field observations have suggested substantial variability in K660, especially at low and high wind speeds. Laboratory experiments have shown that naturally occurring surface active organic materials, or surfactants, can suppress gas transfer. Here we provide direct open ocean evidence of gas transfer suppression due to surfactants from a ~11,000 km long research expedition by making measurements of the gas transfer efficiency (GTE) along with direct observation of K660. GTE varied by 20% during the Southern Ocean transect and was distinct in different watermasses. Furthermore GTE correlated with and can explain about 9% of the scatter in K660, suggesting that surfactants exert a measurable influence on air-sea CO2 flux. Relative gas transfer suppression due to surfactants was ~30% at a global mean wind speed of 7 m s-1 and was more important at lower wind speeds. Neglecting surfactant suppression may result in substantial spatial and temporal biases in the computed air-sea CO2 fluxes.

The flux of terrigenous organic carbon through estuaries is an important and changing, yet poorly understood, component of the global carbon cycle. Using dissolved organic carbon (DOC) and fluorescence data from 13 British estuaries draining catchments with highly variable land uses, we show that land use strongly influences the fate of DOC across the land ocean transition via its influence on the composition and lability of the constituent dissolved organic matter (DOM). In estuaries draining peatland‐dominated catchments, DOC was highly correlated with biologically refractory “humic‐like” terrigenous material which tended to be conservatively transported along the salinity gradient. In contrast, there was a weaker correlation between DOC and DOM components within estuaries draining catchments with a high degree of human impact, that is, relatively larger percentage of arable and (sub)urban land uses. These arable and (sub)urban estuaries contain a high fraction of bioavailable “protein‐like” material that behaved nonconservatively, with both DOC removals and additions occurring. In general, estuaries draining catchments with a high percentage of peatland (≥18%) have higher area‐specific estuarine exports of DOC (>13 g C m−2 yr−1) compared to those estuaries draining catchments with a high percentage (≥46%) of arable and (sub)urban land uses (<2.1 g C m−2 yr−1). Our data indicate that these arable and (sub)urban estuaries tend to export, on average, ∼50% more DOC to coastal areas than they receive from rivers due to net anthropogenic derived organic matter inputs within the estuary.

Air‐sea carbon dioxide (CO 2 ) flux is generally estimated by the bulk method using upper ocean CO 2 fugacity measurements. In the summertime Arctic, sea‐ice melt results in stratification within the upper ocean (top ∼10 m), which can bias bulk CO 2 flux estimates when the seawater CO 2 fugacity is taken from a ship's seawater inlet at ∼6 m depth ( f CO 2w_bulk ). Direct flux measurements by eddy covariance are unaffected by near‐surface stratification. We use eddy covariance CO 2 flux measurements to infer sea surface CO 2 fugacity ( f CO 2w_surface ) in the Arctic Ocean. In sea‐ice melt regions, f CO 2w_surface values are consistently lower than f CO 2w_bulk by an average of 39 μatm. Lower f CO 2w_surface can be partially accounted for by fresher (≥27%) and colder (17%) melt waters. A back‐of‐the‐envelope calculation shows that neglecting the summertime sea‐ice melt could lead to a 6%–17% underestimate of the annual Arctic Ocean CO 2 uptake.

The flux of CO2 between the atmosphere and the ocean is often estimated as the air–sea gas concentration difference multiplied by the gas transfer velocity (K660). The first order driver for K660 over the ocean is wind through its influence on near surface hydrodynamics. However, field observations have shown substantial variability in the wind speed dependencies of K660. In this study we measured K660 with the eddy covariance technique during a ~ 11,000 km long Southern Ocean transect. In parallel, we made a novel measurement of the gas transfer efficiency (GTE) based on partial equilibration of CO2 using a Segmented Flow Coil Equilibrator system. GTE varied by 20% during the transect, was distinct in different water masses, and related to K660. At a moderate wind speed of 7 m s−1, K660 associated with high GTE exceeded K660 with low GTE by 30% in the mean. The sensitivity of K660 towards GTE was stronger at lower wind speeds and weaker at higher wind speeds. Naturally-occurring organics in seawater, some of which are surface active, may be the cause of the variability in GTE and in K660. Neglecting these variations could result in biases in the computed air–sea CO2 fluxes.

Dimethyl sulphide (DMS) and carbon monoxide (CO) are climate-relevant trace gases that play key roles in the radiative budget of the Arctic atmosphere. Under global warming, Arctic sea ice retreats at an unprecedented rate, altering light penetration and biological communities, and potentially affect DMS and CO cycling in the Arctic Ocean. This could have socio-economic implications in and beyond the Arctic region. However, little is known about CO production pathways and emissions in this region and the future development of DMS and CO cycling. Here we summarize the current understanding and assess potential future changes of DMS and CO cycling in relation to changes in sea ice coverage, light penetration, bacterial and microalgal communities, pH and physical properties. We suggest that production of DMS and CO might increase with ice melting, increasing light availability and shifting phytoplankton community. Among others, policy measures should facilitate large-scale process studies, coordinated long term observations and modelling efforts to improve our current understanding of the cycling and emissions of DMS and CO in the Arctic Ocean and of global consequences.

Nitrous oxide (N 2 O) is important to the global radiative budget of the atmosphere and contributes to the depletion of stratospheric ozone. Globally the ocean represents a large net flux of N 2 O to the atmosphere but the direction of this flux varies regionally. Our understanding of N 2 O production and consumption processes in the ocean remains incomplete. Traditional understanding tells us that anaerobic denitrification, the reduction of NO 3 − to N 2 with N 2 O as an intermediate step, is the sole biological means of reducing N 2 O, a process known to occur in anoxic environments only. Here we present experimental evidence of N 2 O removal under fully oxygenated conditions, coupled with observations of bacterial communities with novel, atypical gene sequences for N 2 O reduction. The focus of this work was on the high latitude Atlantic Ocean where we show bacterial consumption sufficient to account for oceanic N 2 O depletion and the occurrence of regional sinks for atmospheric N 2 O.

Estimates of oceanic emissions of nitrous oxide (N2O) are surrounded by a considerable degree of uncertainty, particularly regarding the contribution of productive shelf regions, where assessments are based on limited observations. In this paper, we have applied a coupled hydrodynamic‐biogeochemical model resolving N2O dynamics to estimate N2O emissions within the northwest European continental shelf. Based on 10‐year average distributions (2006–2015), dominant seasonal patterns of N2O air‐sea exchange were identified. Within the southwest region of the shelf and deep parts of the North Sea, emissions are highest during winter. Peak emissions during late autumn are typical for the northwest part of the shelf and central North Sea, while in the western English Channel, Irish Sea and western North Sea peak outflux shifts toward early autumn. Within these regions, most N2O production occurs below the seasonal pycnocline, and duration and intensity of stratification defines the timing and rate of its subsequent release to the atmosphere. In contrast, within the southeast North Sea and most of the coastal areas, lack of stratification allows the excess N2O to outgas as soon as it is produced, driven by ammonium availability, resulting in peak emissions in summer. We estimate that N2O emissions from the northwest European shelf contribute 0.02224 Tg N to the atmosphere annually, that is, between 3.3–6.8% of total emissions from European shelves and estuaries.

Dimethyl sulfide and volatile organic compounds (VOCs) are important for atmospheric chemistry. The emissions of biogenically derived organic gases, including dimethyl sulfide and especially isoprene, are not well constrained in the Southern Ocean. Due to a paucity of measurements, the role of the ocean in the atmospheric budgets of atmospheric methanol, acetone, and acetaldehyde is even more poorly known. In order to quantify the air–sea fluxes of these gases, we measured their seawater concentrations and air mixing ratios in the Atlantic sector of the Southern Ocean, along a ∼ 11 000 km long transect at approximately 60∘ S in February–April 2019. Concentrations, oceanic saturations, and estimated fluxes of five simultaneously sampled gases (dimethyl sulfide, isoprene, methanol, acetone, and acetaldehyde) are presented here. Campaign mean (±1σ) surface water concentrations of dimethyl sulfide, isoprene, methanol, acetone, and acetaldehyde were 2.60 (±3.94), 0.0133 (±0.0063), 67 (±35), 5.5 (±2.5), and 2.6 (±2.7) nmol dm−3 respectively. In this dataset, seawater isoprene and methanol concentrations correlated positively. Furthermore, seawater acetone, methanol, and isoprene concentrations were found to correlate negatively with the fugacity of carbon dioxide, possibly due to a common biological origin. Campaign mean (±1σ) air mixing ratios of dimethyl sulfide, isoprene, methanol, acetone, and acetaldehyde were 0.17 (±0.09), 0.053 (±0.034), 0.17 (±0.08), 0.081 (±0.031), and 0.049 (±0.040) ppbv. We observed diel changes in averaged acetaldehyde concentrations in seawater and ambient air (and to a lesser degree also for acetone and isoprene), which suggest light-driven production. Campaign mean (±1σ) fluxes of 4.3 (±7.4) µmol m−2 d−1 DMS and 0.028 (±0.021) µmol m−2 d−1 isoprene are determined where a positive flux indicates from the ocean to the atmosphere. Methanol was largely undersaturated in the surface ocean with a mean (±1σ) net flux of −2.4 (±4.7) µmol m−2 d−1, but it also had a few occasional episodes of outgassing. This section of the Southern Ocean was found to be a source and a sink for acetone and acetaldehyde this time of the year, depending on location, resulting in a mean net flux of −0.55 (±1.14) µmol m−2 d−1 for acetone and −0.28 (±1.22) µmol m−2 d−1 for acetaldehyde. The data collected here will be important for constraining the air–sea exchange, cycling, and atmospheric impact of these gases, especially over the Southern Ocean.