Abstract. Sulfur-containing volatile organic compounds (VOCs) such as dimethyl sulfide (DMS) and methanethiol (MeSH) are are of particular interest among oceanic VOCs emitted by the ocean, both for their central role in the marine sulfur cycle and as potential precursors to secondary aerosol formation. However, the quantification of DMS and MeSH emissions as a function of biological components of the ocean under variable environmental factors are still too scarce for reliable future predictions. In this study we report on measurements of DMS, MeSH and nanoparticle concentrations in the headspace of two on-deck Air-Sea Interface Tanks (ASITs). The cover of one ASIT prevented the transmission of UV light below 380 nm in wavelength and we report on the effect of UV light on fluxes and concentrations. These measurements were carried out near the Antarctic Peninsula during the POLAR-CHANGE campaign in summer 2023. Air-sea fluxes inside the ASITs were always positive, i.e. degassing from seawater to air, with DMS and MeSH fluxes averaging 3.03 pmol·m⁻²·s⁻¹ (FASIT-DMS) and 0.64 pmol·m⁻²·s⁻¹ (FASIT-MeSH), respectively. DMS emission did not vary significantly between day and night, but the ratio FASIT-MeSH/(FASIT-DMS + FASIT-MeSH) showed a clear maximum at night and a decrease over daytime. Calculated aqueous DMS concentrations showed maxima in the open Southern Ocean north of the Antarctic Peninsula (2.5–3 nM), minima in the Marginal Ice Zone (MIZ) in the Weddell Sea (1 nM) and moderate values along the western coast of the peninsula (around 1.5–2 nM). Cryptophytes, nanophytoplankton, and bacterial concentrations showed positive correlations with calculated aqueous DMS and MeSH concentrations during two experiments when seawater was held in the ASITs for two days. Removal of UV light increased DMS fluxes by 24 % and MeSH fluxes by 58 %. New particle formation occurred only in the absence of UV-light. Interestingly, the highest impact of UV removal, especially on increased MeSH emission, was seen during the night suggesting a lag period between the exposure and the physiological response of the cells. UV light caused slight phytoplankton light stress at noon, which negatively affected the short-term growth of nanophytoplankton in the ASIT, especially in open Southern Ocean waters.

New particle formation is an important source of Arctic atmospheric particles and cloud condensation nuclei, yet their precursor sources and molecular-level mechanisms remain poorly understood. Here we report comprehensive ship-based observations from 19 May to 26 June 2022 from southeastern to western Greenland and into the Davis Strait's marginal ice zone to investigate sources and processes controlling atmospheric particles and cloud condensation nuclei. Our observations provide field evidence of frequent nucleation events driven by the multicomponent iodine oxoacid and sulfuric acid mechanism recently identified in laboratory studies. Newly formed particles grew rapidly beyond 20 nm on 8 out of 13 nucleation days, mainly driven by oxygenated organic molecules from aldehyde and monoterpene oxidation. We also report a previously unobserved class of iodine-containing oxygenated organic molecules that contributed to particle growth and enhanced cloud condensation nuclei formation. We show that marginal sea ice zone produces precursors that drive rapid new particle formation and enhance cloud condensation nuclei concentrations by up to 50-fold. Our findings demonstrate that Arctic iodine, sulfur and organic precursors can enhance cloud condensation nuclei abundance through new particle formation, highlighting a potential but unquantified pathway for influencing cloud cover, radiative balance and the hydrological cycle.

The Antarctic coastal zones are among the most biologically productive areas on Earth. The effect of marine microbiota on the emissions of sea spray particles, a critical factor for global climate and clouds, remains an open and actively researched question. Here, by means of in situ ship-borne bubble-bursting SSA production experiments at multiple locations around the Antarctic Peninsula, we show a 2-fold variability in the 10-500 nm size-resolved SSA number concentrations. We observed that the organic chemical composition of seawater (SW) and surface microlayers (SML) clearly impacts SSA number concentrations. SW and SML samples with saccharides, proteins, and N-osmolytes were less efficient at emitting SSA compared with waters rich in biotic material originating from lipids, such as fatty acids and polyols. We found that the dissolved organic carbon (DOC) fraction containing lipid degradation products and polyols indicates higher SSA production. Our results indicate that low concentration organic components, rather than the most abundant classes of biomolecules, influence the ability to be aerosolized, with strong chemical selectivity affecting SSA production.

The formation of cloud condensation nuclei is a critical but uncertain factor in Arctic climate dynamics. A major nuclei contributor is new particle formation, yet the geographical variations in activity and the factors driving it remain poorly understood. Here, we present a nine-year (2010–2018) analysis of atmospheric particle number size distributions from Tiksi, Russia, integrated with air mass trajectory modelling and ocean remote sensing. We show that aerosol formation rates are significantly enhanced—particle formation rates increase by 300

The Arctic is warming at more than twice the global average rate, a phenomenon known as Arctic amplification (Rantanen et al., 2022). In addition to greenhouse gases, short-lived climate forcers play a critical role in modulating Arctic climate through their impacts on radiation, cloud properties, and the surface energy balance (e.g. AMAP, 2015, 2021). Among these forcers, elemental carbon (EC) is of particular importance due to its strong light-absorbing properties and its ability to reduce surface albedo when deposited on snow and ice. Furthermore, aged EC particles transported to the Arctic can act as cloud condensation nuclei, influencing cloud microphysical processes and thereby modifying Arctic radiative forcing and climate feedbacks.In this study, we investigate long-term trends in EC concentrations and their potential drivers in the high Arctic using 16 years of continuous EC measurements from the Villum Research Station in northeast Greenland. We combine in situ observations with Lagrangian transport modelling and back-trajectory analyses to assess the relative contributions of changes in source-region emissions, transport pathway variability, and wet scavenging processes to the observed EC trends. Robust non-parametric statistical methods are applied to assess monotonic trends over the full observational period and before 2020, enabling a systematic comparison between the declining and stagnating phases. This integrated observational–modelling framework provides new constraints on the processes controlling EC variability in the Arctic and advances our understanding of how anthropogenic emission reductions are reflected in Arctic atmospheric composition under a rapidly evolving climate.

Carbohydrates are important components of marine organic aerosol particles and may influence Arctic cloud formation and properties, yet their sources and atmospheric fate remain poorly understood. We present the first year-round measurements of combined and dissolved carbohydrates (CCHOaer; DFCHOaer) in aerosol particles collected throughout the annual cycle of the MOSAiC expedition in 2019-2020. CCHOaer were detected in all seasons (0.5-17 ng m⁻³), and contributed between 0.03 and 2.2% (mean 0.3%) to the particulate mass. Their molecular composition was relatively stable and dominated by glucose, xylose, and galactose, with additional presence of uronic acids in summer. Both, CCHOaer and DFCHOaer showed pronounced summer maxima and seasonal variability that partially aligned with chlorophyll-a, nanophytoplankton, and heterotrophic microorganisms, indicating enhanced biological contributions after sea ice melt. The summer increase in DFCHOaer also coincided with warmer temperatures and higher humidity. In winter, the presence of carbohydrates may be sustained by microbial degradation or viral lysis of organic material in under-ice environments. CCHOaer and DFCHOaer concentrations showed no direct correlation to wind speed or air mass origins instead displaying a high variability in summer. The seasonal behavior of CCHOaer in Arctic aerosol particles differed from primary marine tracers like sodium that was associated with direct oceanic sources in summer and blowing snow in winter. This contrast suggests that carbohydrates, while possibly originated from marine biological sources, undergo significant atmospheric modification that overlay direct source signatures. Strong correlations between CCHOaer and low-molecular-weight organic acids further point to photochemical oxidation as an additional driver of secondary carbohydrate processing. CCHOaer displayed seasonal trends similar to warm-temperature ice-nucleating particles and hyper-fluorescent aerosol particles, supporting their role within a broader Arctic bioaerosol particle population. Overall, our results indicate that marine ecosystems provide a continuous source of atmospheric carbohydrates, but their composition is strongly modified by both biotic and abiotic processes, particularly in summer.Acknowledgement: This work was supported by the DFG funded Transregio-project TRR 172 “Arctic Amplification (AC)3“.

Among the wide variety of VOCs emitted by the oceans, sulfur-containing compounds such as dimethyl sulfide (DMS) and methanethiol (MeSH) can be particularly important due to their prominent role in the marine sulfur cycle and their fate as secondary aerosol precursors. However the quantification of DMS and MeSH emissions as a function of biological components of the ocean under variable environmental factors are still too scarce for reliable future predictions. In this study we report on measurements of natural DMS, MeSH and nanoparticle concentrations within the deckborne Air-Sea Interfacial Tanks (ASITs) and the effect of UV light on their fluxes and concentrations. These measurements were carried out near the Antarctic Peninsula during the PolarChange campaign in 2023. DMS dissolved concentrations showed maxima in the open Southern Ocean north of the peninsula (2.5-3 nM), minima in the Marginal Ice Zone (MIZ) (1 nM) and moderate along the western coast of the peninsula (around 1.5-2 nM). Fluxes measured inside the ASITs were always positive, i.e. degassing from seawater to air, with equivalent 2 m·s-1 wind speed fluxes averaged from 3.03 pmol·m⁻²·s⁻¹ for DMS to 0.64 pmol·m⁻²·s⁻¹ for MeSH. DMS emissions did not vary significantly between day/night conditions, however the ratio of MeSH to DMS did have a clear maximum at night and a decrease around midday. Cryptophytes, nanophytoplankton, and bacterial concentrations showed positive links with dissolved DMS and MeSH concentrations during the experiments. A clear negative impact of UV light on DMS and MeSH fluxes was observed with DMS net fluxes 24% higher and MeSH net fluxes 58% higher in UV light filtered ASIT, and on new particle formation that surprisingly occurred only in the absence of UV light. Interestingly, the highest impact of UV, especially on MeSH emissions, was seen during the night. UV light had also a negative impact on the development of nanophytoplankton especially in Open Southern Ocean waters, and a slight increase in phytoplankton stress at noon .

Black carbon (BC) is an important short-lived climate forcer that contributes to Arctic warming, yet observations of BC in the Arctic marine boundary layer remain sparse. Here, we report shipborne measurements of refractory BC (rBC) mass and particle mixing state during a cruise from southeast to west Greenland in May-June 2022. Using a single-particle soot photometer (SP2XR) and transmission electron microscopy (TEM), we characterize both rBC concentrations and individual-particle morphology, representing one of the first ship-based SP2XR data sets in the Arctic marine boundary layer. rBC concentrations were highest in the Greenland coastal region (2.4 ng m-3), compared with the open ocean (1.7 ng m-3) and the marginal ice zone (0.6 ng m-3). Mixing-state analysis shows that 54% of soot particles in coastal air masses were externally mixed, consistent with relatively fresh emissions, whereas most soot particles over the open sea and sea-ice regions were internally mixed, indicative of aged, transported aerosol. FLEXPART modeling suggests BC enhancements along the Greenland coast. Our data indicate that Greenland acts as a regional source of BC to the Arctic marine boundary layer in late spring and early summer, when midlatitude transport is weak.

Melt ponds are a common feature of the Arctic sea-ice environment during summer, and they play an important role in the exchange of heat and water vapor between the ocean and the atmosphere. We report the results of a time-series study of the CO2 dynamics within melt ponds (and nearby lead) and related fluxes with the atmosphere during the summer-to-autumn transition in the central Arctic Ocean during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. In late summer 2020, low-salinity meltwater was distributed throughout the melt ponds, and undersaturation of pCO2 in the meltwater drove a net influx of CO2 from the atmosphere. The meltwater layer subsequently thinned due to seawater influx, and a strong gradient in salinity and low-pCO2 water was observed at the interface between meltwater and seawater at the beginning of September. Mixing between meltwater and underlying seawater drives a significant drawdown of pCO2 as a result of the non-linearities in carbonate chemistry. By the middle of September, the strong stratification within the meltwater had dissipated. Subsequent freezing then began, and cooling and wind-induced drifting of ice floes caused mixing and an influx of seawater through the bottom of the melt pond. The pCO2 in the melt pond reached 300 µatm as a result of exchanging melt pond water with the underlying seawater. However, gas exchange was impeded by the formation of impermeable freshwater ice on the surface of the melt pond, and the net flux of CO2 was nearly zero into the pond, which was no longer a sink for atmospheric CO2. Overall, the melt ponds in this Arctic sea-ice area (both melt ponds and lead water) act as moderate sinks for atmospheric CO2.

The rapidly changing Arctic has led to evolving natural aerosol emissions, which have strong feedback effects on its climate system. Sea spray aerosol (SSA) particles are a main source of aerosols; they influence cloud formation and cloud properties. Ocean microbiota potentially have an impact on SSA production and flux, but our understanding of the mechanisms is still limited. The potential impact of ocean microbiota on SSA fluxes is still a matter of active research. In this multidisciplinary study conducted in the central Arctic during The Multidisciplinary Drifting Observatory for the Study of Arctic Climate expedition, air-sea interactions were measured by means of in situ bubble-bursting experiments. For the first time, we studied the effect of zooplankton grazing on aerosol production. We found that surface water subjected to zooplankton grazing had a 2-fold increase in SSA production relative to controls without zooplankton. Our biogeochemical results suggest that fresh organic material-possibly dissolved organic carbon and dissolved organic nitrogen from humic-like substances-influences aerosol production. We find a strong chemical-selective process affecting SSA production, with humic-like substances much enriched (40%-280%) relative to protein-like material in the aerosol relative to the water. Our results point to a complex relationship between specific low-concentration organic components in the water phase and its relative capability of being aerosolized, with strong chemically selective processes affecting SSA production. We provide evidence for the role of zooplankton, implying a complex microbial loop that may be regulating the organic component of the SSA production. This study underlines the role of zooplankton in biogeochemical cycles, due to their large biomass and transformation of organic matter during feeding and digestion. Similar processes may occur in other regions with high zooplankton grazing impact, for example, in productive parts of the Southern Ocean and in upwelling regions.

The loss of Arctic Sea ice enlarges the ocean water surface exposed to wind speed, increasing the emissions of sea spray aerosols (SSAs). Given the unique evolution of upper ocean salinity waters and ice-associated ecosystems, it is crucial to improve Arctic-specific SSA parametrizations to represent the currently poorly understood feedback processes. Here, by using Arctic ship-borne in situ aerosol tank laboratory experiments, we study SSA produced from open ocean, open leads, and melt ponds. We find a complex nonlinear, yet unresolved variation in SSA production associated with salinity and organic composition. Specifically, we find that melt ponds drastically reduce SSA production, whereas ice algal microgels may enhance it. During the summer 2017 cruise (research vessel Araon), we also carried out aerosol ambient measurements across the Chukchi and East Siberian Seas. Size resolved ambient particle number concentrations reveal at least 17% and 42% of ambient number aerosol concentrations (N10-300 nm and N100-300 nm, respectively) are possibly attributable to SSA. Our results may help modeling experiments using SSA parametrization currently suffering from large uncertainty for constraining the sea spray emission fluxes from leads, melt ponds, and salinity gradients encountered in the Arctic Ocean.

Alkylamines, volatile organic nitrogen compounds with low molecular weight, are present in the surface ocean and participate in the marine biogeochemical nitrogen cycle, atmospheric chemistry and cloud formation. Alkylamines have been detected in polar regions, suggesting that these areas constitute emission hotspots of these compounds. However, knowledge of the sea surface distribution patterns and factors modulating alkylamines remain limited due to their high reactivity and low concentrations, which hamper accurate measurements. We investigated the presence and distribution of alkylamines in seawaters around the Antarctic Peninsula and the northern Weddell Sea during the late austral summer and explored their potential links to marine microbiota. Alkylamines were ubiquitous in all analysed samples, accounting for ∼ 2 % of the dissolved and particulate organic nitrogen pool. The only particulate form found was trimethylamine (TMA), detected for the first time in Antarctic waters at concentrations of 9.7 ± 4.6 nM. We efficiently measured dissolved trimethylamine (TMA, 20.9 ± 15.2 nM), dimethylamine (DMA, 32.3 ± 32.7 nM) and diethylamine (DEA, 7.2 ± 1.7 nM) across the surveyed area, while dissolved monomethylamine (MMA, 12.7 ± 0.1 nM) remained below the detection limit in most samples. Variations in alkylamine concentrations did not align with the overall phytoplankton biomass but with specific biological components. TMA was predominantly associated with, and released from, nanophytoplankton. DMA was likely produced by the degradation of TMA or trimethylamine oxide by nanophytoplankton cells or associated heterotrophic bacteria. The sources of DEA remain unclear but were suggestive of a distinct biogeochemical pathway from those of TMA and DMA. MMA is thought to primarily originate from bacterial degradation of nitrogen-based osmolytes or amino acids, but detection in too few samples precluded any robust association with microbiota. This study reveals that volatile alkylamines are widespread in Antarctic surface waters, where they are primarily sourced from nanophytoplankton cells and associated heterotrophic bacteria and protists.

A major natural route of dispersal to Antarctica is often assumed to be atmospheric transport, although few studies have documented this in detail. Aerial dispersal to Antarctica is very challenging as the continent is geographically remote from other land areas and is isolated by the atmospheric circumpolar vortex. Detailed information about aerial routes by which microorganisms arrive and circulate in Antarctica is generally lacking, as few aerobiological studies have focused on eukaryotes and those that have predominantly relied on traditional morphological identification. Recent advances in molecular biology, such as DNA metabarcoding by high throughput sequencing (HTS), have provided a powerful new tool for the study of atmospheric biological diversity and can retrieve levels of diversity an order of magnitude higher than traditional methods. In this study, we used HTS to investigate the diversity of non-fungal eukaryotes present in the atmosphere and freshly precipitated snow on Livingston Island. In a total of 740 m3 of air and 3.76 L of snow sampled, representatives of four kingdoms (Protozoa, Chromista, Viridiplantae and Animalia) and five phyla (Ciliophora, Ochrophyta, Chlorophyta, Magnoliophyta and Porifera) were found. The most diverse phylum was Chlorophyta, represented in our samples by 10 taxa, with Trebouxia asymmetrica Friedl & Gärtner the most abundant representative.

During the late Austral summer of 2023, we carried out three surveys in the West Antarctic Peninsula (WAP) from Horseshoe Island (67° 514 south) to the Northern tip of the Peninsula to document the distribution of CH4 in surface waters. We observed a striking feature in Dodman Island in the Grand Didier Channel with a marked supersaturation of methane (up to 400%) in the bay of the island, whereas saturation (maximum of 260%) was observed elsewhere. Our main hypothesis is that this supersaturation is linked to meltwater from the glacier on the island, which acts as a source of methane in the water column. This hypothesis is supported by vertical profiles of CH4 concentration, field observations of sub-glacial water flowing to the surface of the water column, as well as by variations in salinity showing a freshwater inflow. This phenomenon has already been suggested in the Arctic (Lamarche-Gagnon et al., 2019) but does not yet seem to have been demonstrated in the Antarctic. These data show that it would be worthwhile investigating areas with active glaciers to determine whether melting glaciers can be a source of methane for the Antarctic water column.

Measurements of pre-industrial conditions are of paramount importance for understanding historical climate change. The Southern Ocean and Antarctic continent are some of the least polluted environments on planet Earth. Alkylamines can rapidly partition into aerosols, increasing their mass, as well as form new particles altogether. We demonstrate the importance of pelagic “open ocean” (OO) and sympagic “sea ice” (SI) regions in supplying distinct organic nitrogen aerosol components. In the aerosol phase, dimethylamine (DMA) and trimethylamine (TMA) are both secondary, though DMA likely originates mainly from pelagic regions, while TMA is associated mainly with sympagic regions. Parallel measurements in ice and surface waters reveal that melting sea ice contains a factor of four more TMA than coastal Antarctic Peninsula waters; and seventeen times more TMA than OO regions - suggesting additional coastal Antarctic sources. To better interpret future climate change, we recommend employing regional atmospheric chemistry models to understand these diverse aerosol sources.

We present data on ice nucleating particles (INPs) from three Antarctic locations, a region for which INP measurements are still rare: the German Neumayer research station, contributing 2 years of data; the Belgian Princess Elisabeth station (PES) with samples from two austral summer seasons; and the region of the Antarctic Peninsula, adding data from a research cruise and subsequent land-based sampling. While often land masses are INP sources, we found especially low INP concentrations for the two stations furthest south, Neumayer and Princess Elisabeth. At Neumayer no clear annual cycle could be identified. No strong signal from biological particles, as known to occur for example, in the summertime Arctic, was observed. Our findings suggest that Antarctica lacks INP sources, especially from the biosphere, which exist elsewhere, even in the Arctic. Furthermore, a simple INP parameterization was derived, based on the Neumayer data set and tested for data from PES.

Marine microorganisms play a crucial role in biogeochemical cycles, especially in the surface microlayer (SML), which differs from adjacent subsurface waters (SSW). In this study, we sampled the SML and SSW at 20 sites along the western Antarctic Peninsula during the summers of 2015 and 2019, examining microbial, viral and environmental differences. We focused on phototrophic protists, specifically Phaeocystis-like species, known for their high dimethylsulphoniopropionate (DMSP) contents, which can be released through viral lysis. DMSP is a precursor to dimethylsulphide (DMS), a gas influencing Earth's climate. We hypothesized a significant relationship between Phaeocystis-like abundance and DMSP concentration, with strong interactions with their specific viruses (V4) in the SML. Most biotic variables showed higher mean values in the SML, although these differences often were not statistically significant. DMSP concentrations correlated with Phaeocystis-like species abundance in both layers (R 2 = 0.482, P <= 0.01; R 2 = 0.532, P <= 0.01, respectively), whereas V4 abundance significantly correlated with Phaeocystis-like species only in the SML (R 2 = 0.572, P <= 0.01). These results suggest stronger interactions between viruses and DMSP-rich hosts in the SML, potentially increasing DMS emissions to the atmosphere and impacting climate regulation.

In order to reduce the uncertainty of aerosol radiative forcing in global climate models, we need to better understand natural aerosol sources which are important to constrain the current and pre-industrial climate. Here, we analyse particle number size distributions (PNSDs) collected during a year (2015) across four coastal and inland Antarctic research bases (Halley, Marambio, Dome C and King Sejong). We utilise k-means cluster analysis to separate the PNSD data into six main categories. “Nucleation” and “bursting” PNSDs occur 28 %–48 % of the time between sites, most commonly at the coastal sites of Marambio and King Sejong where air masses mostly come from the west and travel over extensive regions of sea ice, marginal ice and open ocean and likely arise from new particle formation. “Aitken high”, “Aitken low” and “bimodal” PNSDs occur 37 %–68 % of the time, most commonly at Dome C on the Antarctic Plateau, and likely arise from atmospheric transport and ageing from aerosol originating likely in both the coastal boundary layer and free troposphere. “Pristine” PNSDs with low aerosol concentrations occur 12 %–45 % of the time, most commonly at Halley, located at low altitudes and far from the coastal melting ice and influenced by air masses from the west. Not only the sea spray primary aerosols and gas to particle secondary aerosol sources, but also the different air masses impacting the research stations should be kept in mind when deliberating upon different aerosol precursor sources across research stations. We infer that both primary and secondary components from pelagic and sympagic regions strongly contribute to the annual seasonal cycle of Antarctic aerosols. Our simultaneous aerosol measurements stress the importance of the variation in atmospheric biogeochemistry across the Antarctic region.