The session focuses on new research in several areas which include: air-sea fluxes of climate-active trace gases (CO2, CH4, N2O) mediated by the atmospheric boundary layer above the oceans and in polar regions; regional emission and vertical mixing of aerosol, such as cloud-forming particles (CCN/INP) and their precursors (including dimethyl sulfide (DMS), marine organic compounds and halogenated species) and their impacts on atmospheric composition and climate; atmospheric deposition of nutrients (e.g., nitrogen, phosphorus, iron) and its impact on ocean biological systems; and biogeochemistry-climate feedback loops in the ocean-atmosphere system. We also welcome studies on how these surface fluxes may change in response to climate warming, as well as the local to large-scale influences on these exchanges. An adequate understanding and quantification of these processes is necessary to improve modeling and prediction of future changes above the oceans and in the polar regions, their teleconnections with mid-latitude weather and climate (including meridional transport of heat, moisture, chemical trace species, aerosols and isotopic tracers), and the coupling between local and large-scale dynamics.
The session has strong links to the Surface Ocean ̶ Lower Atmosphere Study (SOLAS) and the GESAMP Working Group 38 on atmospheric input of chemicals to the ocean. Submissions are encouraged from all areas covered by these programs, using a range of analysis approaches including field measurements, remote sensing, laboratory studies, and atmospheric and oceanic numerical models.
This year we particularly welcome studies on the impact of extreme events on air-sea gas exchange of climate-relevant compounds in marine systems. Here we invite contributions addressing physical drivers such as marine heatwaves, storms and tropical cyclones, circulation anomalies or sea ice changes; biogeochemical drivers such as hypoxic or anoxic conditions and acidification pulses; biological drivers such as harmful algal blooms; or compound events. Relevant studies may address impacts in all oceanic domains; e.g., open ocean, shelf waters and shallow (< 20 m depth) coastal ecosystems. The reporting on progress as well as critical knowledge gaps in polar regions will help define upcoming research programmes as part of Antarctica InSync and the International Polar Year 2032-33.
The gas transfer velocity k for the air-sea exchange of CO2 is often parameterized as a function of wind speed alone, as wind speed fundamentally controls turbulence at the air-sea interface and thus the flux across it. However, numerous other processes affect the air-sea gas exchange, such as the presence of surface-active substances (surfactants) directly at the interface, the so-called sea surface microlayer (SML). These processes are not explicitly accounted for in the wind speed-only parameterizations. Surfactants in the SML likely reduce k, potentially due to two effects. Firstly, the surfactants represent a physicochemical barrier at the interface, and secondly, they dampen the turbulence at the interface. Consequently, the presence of surfactants leads to lower gas transfer velocities than estimated from the wind speed-only parameterizations of k, especially since the SML can be stable up to medium high wind speeds. The mechanisms that control how exactly surfactants in the SML affect the air-sea gas exchange are, however, not yet fully understood. Therefore, it is important to measure air-sea gas exchange under various surfactant conditions to potentially include the SML effects in future parameterizations of k. During a research cruise to the Gotland Basin in the early summer of 2025, the direct air-sea flux of CO2 was measured using the eddy covariance method. This method is particularly well-suited to study the influence of surface processes on gas exchange, as it can determine k on timescales of 10 minutes and is therefore likely to resolve the variability in different surfactant states. In addition to the direct CO2 flux measurements, a range of other parameters influencing air-sea flux were also measured. In particular, the surfactants in the SML were sampled and analysed during the research cruise. Consequently, we investigate the behaviour of k under not only varying wind speeds, but now also under various surfactant states, including the presence of a surface slick.
How to cite: Scheidereit, L., Dong, Y., Lange, L., Arévalo-Martínez, D. L., Bange, H., Klöss, A., Karnatz, J., Barthelmeß, T., Engel, A., and Marandino, C.: Eddy covariance CO2 air-sea fluxes under variable surfactant conditions in the Baltic Sea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9820, https://doi.org/10.5194/egusphere-egu26-9820, 2026.
The ATL2MED mission (October 2019–July 2020) investigated air–sea CO₂ exchange across the Eastern Atlantic Ocean and the Mediterranean Sea using high-resolution measurements from Saildrone autonomous surface vehicles (SDs), complemented by fixed stations, gliders, and research vessels. Operating under diverse environmental conditions, the SDs provided detailed observations of seawater CO₂ and hydrographic parameters, although sensor drift and biofouling affected data quality during the long deployment. Dedicated data correction and validation procedures were applied: salinity was corrected using model products and validated against independent observations. Dissolved oxygen was adjusted using the Argo oxygen correction. These efforts compensated for limited discrete sampling during COVID-19 restrictions. The corrected data revealed strong regional contrasts in CO₂ dynamics driven by physical and biogeochemical processes. Intense outgassing occurred in the upwelling regions off northwest Africa, while the western Mediterranean Sea acted as a CO₂ sink during the spring bloom. The Adriatic Sea showed recurrent outgassing episodes linked to stratification, river plumes, and coastal upwelling. The SDs captured sub-mesoscale and short-term variability often missed by traditional platforms and model simulations. The study highlights the importance of high-frequency, multi-platform measurements to resolve the highly variable air–sea CO₂ fluxes occurring at short temporal scales.
How to cite: Martellucci, R., Dentico, C., Coppola, L., Skjelvan, I., Giani, M., Cantoni, C., Pensieri, S., Cardin, V., Fourrier, M., Bozzano, R., Paulsen, M., and Mauri, E.: High-resolution air–sea CO₂ observations during the ATL2MED mission: data correction and process variability across the Eastern Atlantic Ocean and the Mediterranean Sea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18714, https://doi.org/10.5194/egusphere-egu26-18714, 2026.
Arctic shelf seas are important sites for global carbon and sulfur cycling, yet their biogeochemical feedbacks are rapidly changing due to climate change. This study characterizes Dimethylsulfoniopropionate (DMSP) and hydrocarbon signatures in surface sediments (0–1 cm) along a six-station transect in the Kara Sea, from the Yenisey River estuary to Novaya Zemlya (from approx. 71°31' to 77°00' N).
The transect spans a distinct environmental gradient from coastal stations dominated by land-fast ice to open-shelf waters characterized by first-year ice or free from ice. By coupling DMSP concentrations with hydrocarbon biomarkers, we differentiate between terrestrial riverine inputs and autochthonous marine production as drivers of the benthic reservoir. DMSP production is low in riverine regions (~2 nmol g-1) but higher in all marine regions (40-80 nmol g-1) with metagenomic analysis suggesting production is primarily from bacteria. Other bacteria contain DMSP catalysis genes encoding proteins converting DMSP to dimethylsulfide (DMS), a global cooling gas. This suggests that production of DMSP and DMS in the Russian Arctic is widespread and large-scale.
Our findings reveal how specific sea-ice regimes and river discharge regulate organic matter provenance and sulfur biochemistry. These baseline data are essential for predicting how Arctic biogeochemical feedbacks — specifically sediment-atmosphere chemical fluxes — will respond to projected declines in sea ice extent and increased river runoff.
How to cite: Pedentchouk, N., Sun, K., Pearce, D., Todd, J. D., and Lea-Smith, D. J.: Controls on Benthic Sulfur and Carbon Reservoirs in the Kara Sea: Tracing DMSP and Hydrocarbons across an Ice-Regime Gradient, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22600, https://doi.org/10.5194/egusphere-egu26-22600, 2026.
Methanethiol (MeSH), a reduced sulfur compound, has received far less attention than dimethyl sulfide (DMS) despite its potential importance for atmospheric sulfur cycling and climate-relevant aerosol processes. Compared with DMS, gas-phase oxidation of MeSH yields more SO2 and has a shorter atmospheric lifetime, suggesting a disproportionate influence on new particle formation, aerosol growth, and cloud condensation nuclei (CCN) abundance in the marine atmosphere. Current global estimates of marine MeSH emissions have relied on scaling DMS concentration climatologies using empirical MeSH:DMS ratios, implicitly assuming co-variability between the two compounds.
Here, we present global monthly marine MeSH emissions derived using a machine-learning framework constrained by 27 years of satellite observations, ocean reanalysis products, and shipboard measurements. Key satellite predictors include chlorophyll-a (Chl-a), phytoplankton functional types (PFTs), phytoplankton size classes (PSCs), and photosynthetically active radiation (PAR). Our approach directly predicts MeSH concentrations from environmental drivers, independent of DMS distributions. The regression models were trained and validated using MeSH sea-surface concentration measurements from multiple oceanographic field campaigns.
We estimate a global annual marine MeSH emission of 5.06 Tg S yr-1. Regional emissions were analyzed by dividing the global ocean into nine Longhurst biomes. The largest contributions originate from the Southern Westerlies (29.05%), Pacific Trades (15.22%), and Coastal Ocean regions (14.03%). Both seawater MeSH concentrations and emissions exhibit pronounced seasonal variability, with peak global emissions occurring in October and a minimum in June. These results provide a satellite-based global climatology of marine MeSH emissions and establish a basis for assessing its impacts on atmospheric chemistry and global climate.
How to cite: Zhang, W.: A Global Marine Methanethiol Climatology Estimated Using Machine Learning, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9950, https://doi.org/10.5194/egusphere-egu26-9950, 2026.
Black carbon (BC) is a strong short-lived climate forcer and an important pathway for atmospheric carbon input to the ocean. Although the Northern Indian Ocean (NIO) receives a strong outflow from the Indian subcontinent (high BC emission region), quantitative estimates of its wet deposition to the oceans which is a dominant atmospheric removal mechanism remains largely unavailable for the Bay of Bengal (BoB) and the Arabian Sea (AS). This study provides the first long-term, basin-scale assessment of BC wet deposition fluxes over the NIO for the period 2002–2022, focusing on their seasonal variability and inter annual trends.
BC wet deposition fluxes were estimated using a parameterized approach in which the flux is defined as the product of BC concentration, an empirical particle washout ratio, and the precipitation rate. Near-surface aerosol mass concentration was derived by normalizing MODIS/Aqua Level-2 MYD04_3K (Collection 6.1) derived columnar mass concentration with boundary layer height from ERA5 reanalysis. These near surface mass concentration is corrected by density followed by hygroscopic growth factor. Surface BC mass concentration is estimated by applying a black carbon mass fraction (f_BC) to the hygroscopicity-corrected near-surface aerosol mass concentrations, which is further used to compute the BC wet deposition fluxes.
Results show strong seasonal variability in BC wet deposition over the NIO, with flux maxima during the southwest monsoon driven mainly by enhanced precipitation. Inter annual variability in BC wet deposition correlates to precipitation variability, confirming rainfall as the dominant controlling factor for BC removal over the region. Basin-scale contrasts show higher wet deposition over the BoB than AS, reflecting closer proximity to major continental emission sources. Spatially, BC wet deposition is enhanced over coastal and nearshore regions compared to the open ocean, reflecting a sharp gradient from the coast toward the open ocean and highlighting a strong influence of meteorology and source proximity in BC deposition across the NIO. These results provide the constrained, long-term estimate of BC wet deposition to the BoB and AS, offering inputs for regional climate modeling and improved understanding of aerosol–monsoon–ocean interactions.
How to cite: K. Singh, S. and Tiwari, S.: Estimation of Black Carbon Wet Deposition Fluxes from the Marine Atmospheric Column over the Northern Indian Ocean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5069, https://doi.org/10.5194/egusphere-egu26-5069, 2026.
A low-cost project recorded unexpected surges of acidity in UK rainfall events over eight summer weeks. With hindsight we now convert the pH values to xH, thereby showing that these rain events typically have at least one acid spike-and-decay sequence. We compared the acid decay curves with that in a solution of carbon dioxide (CO2) exposed to a blustery atmosphere, and have separately recorded similar spikes using CO2 spectrometry in the headspace above incoming rainwater. For one rain event a suite of twelve ion analyses was made at three intervals showing no other significant acid anhydride, again indicating the identity of the acidic agent as CO2.
In our most complete week, a frequency analysis showed that 8,840 of the 10,080 records had acidity of less than 3µmols [H+] per mol H2O, representing the local equilibrium state in the sample well between rain events. The remaining 1240 records show active rainfall with acidity averaging 31.3 µmols [H+] per mol water. Adopting the conversion curve established by Butler (1982), this would represent dissolved CO2 ten times the measured local equilibrium state, i.e. ten times supersaturated, while including three spikes exceeding thirty-five times supersaturated.
This kinetic behaviour in dissolved CO2 seems to have escaped scientific notice. If occurring over an ocean such surges would contribute to acidification, defined as `reduction in the pH of the ocean over an extended period of time, caused by uptake of CO2 from the atmosphere’ (NOAA accessed 2/11/2025). This process is monitored on a three-hourly cycle by Global Ocean Acidification Observing Network, and we have therefore downloaded CO2 measurements for tethered buoys WHOTS and SOTS in case CO2 spikes coincide with lowered salinity as an indicator of local rainfall.
In speculating a concentrating mechanism for CO2 within the precipitating atmosphere we review 20th-century arguments for the capture of anionsby cloud ice against a 21st-century thermodynamic model of the formation of CO2 gas hydrate.
How to cite: Durham, B. and Pfrang, C.: Surges of acidity in UK rainwater: implications for ocean acidification?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7048, https://doi.org/10.5194/egusphere-egu26-7048, 2026.
With the acceleration of global economic development and urbanization, the impacts of anthropogenic emissions on the Earth system have intensified. East Asia, as one of the most densely populated and economically active regions in the world, emits substantial amounts of particulate matter into the atmosphere. Influenced by the prevailing westerlies and the East Asian monsoon, these particles are transported downwind to the Northwest Pacific, exerting significant effects on marine atmospheric composition and ocean ecosystems in this region.
Focusing on key marine atmospheric nutrients including iron (Fe) and nitrogen (N), this study employs a multi-platform approach encompassing satellite remote sensing, in situ Argo floats, shipborne observations, and atmospheric chemical transport modeling to investigate the contribution of East Asian continental aerosol outflow to nutrient supply and the subsequent ocean response. A central highlight of this work is quantifying anthropogenic contributions to atmospheric Fe and N over the Northwest Pacific in recent years.
First, by integrating shipborne online measurements (2021–2022) of multiple atmospheric metals with a positive matrix factorization (PMF) model, we developed a high-time-resolution source apportionment framework for marine atmospheric metals including Fe. This approach provides the first observation-based quantification of contributions from several anthropogenic sources to marine atmospheric Fe and soluble Fe at hourly resolution. The results showed land anthropogenic emissions contributed substantially to atmospheric soluble Fe, accounting for 57% in the open Northwest Pacific during spring and increasing to 62% in summer. These results were further cross-validated against advanced Fe isotope–based source apportionment, yielding strong agreement (R2 = 0.94).
Second, for atmospheric nitrogen, shipborne sampling combined with nitrogen isotope analysis revealed sharp spatial gradients in atmospheric nitrate concentrations and sources from the Chinese marginal seas to the open Northwest Pacific. Coupled with an atmospheric chemical transport model, we further quantified the flux and temporal variability of multiple nitrogen species transported from East Asia to the Northwest Pacific during 2005–2019 and assessed the response of marine atmospheric nitrogen deposition to emission reductions in recent years in East Asia. These findings provide novel insights into the important impacts of land-derived emissions on ocean ecosystems, particularly anthropogenic sources, in shaping biogeochemical processes in downwind oceanic regions and advance our understanding of land–ocean interactions under anthropogenic perturbations.
How to cite: Zhang, T., Zhu, B., Zhang, L., Wang, Y., Chai, F., and Zheng, M.: Influence of East Asian Continental Emissions on Marine Atmospheric Chemistry and Ocean Ecosystems in the Northwest Pacific, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11536, https://doi.org/10.5194/egusphere-egu26-11536, 2026.
Elongated cracks in the Arctic sea-ice cover, so-called leads, expose the cold atmosphere to the relatively warm ocean, and are thus critical to the Arctic energy budget. Here, high-resolution large-eddy simulations (LES) are used to examine the impact of Arctic sea-ice leads on the wintertime lower atmosphere. Fourteen simulated cases representing various realistic atmospheric states are studied based on MOSAiC campaign data, expanding on previous LES studies of leads, which often utilize single idealized conditions. Control runs are contrasted against perturbed runs containing a 1.2 km wide idealized lead, which evolves through a prescribed open–refrozen–closed life cycle. Impacts on the moist static energy budget of the lower atmosphere are then investigated, also in the context of the well-known bimodal state in the surface energy budget in the Arctic. During the lead-open phase, all simulations show large increases in the turbulent heat fluxes, with a slight reversed effect after lead closure. These fluxes are well-predictable from bulk theory applied to a given control atmospheric state. The atmospheric response depends strongly on the initial atmospheric conditions. Cloudy cases remain in a cloudy state, featuring a small increase in near-surface long wave net radiation. The response of clear-sky cases, however, critically depends on initial relative humidity. Moist clear-sky cases can transition to a cloudy state when condensed plumes form, becoming radiatively active and acting as efficient “radiator fins”. Here, energy is efficiently removed from the atmosphere, a surprising behavior argued to have implications for sea-ice melt. In contrast, dry clear-sky cases produce little condensation, and radiative effects remain minimal.
How to cite: Schnierstein, N. and Neggers, R.: Lead Impacts on the Moist Static Energy Budget of the Low-Level Arctic Atmosphere in Large-Eddy Simulations based on MOSAiC Data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13657, https://doi.org/10.5194/egusphere-egu26-13657, 2026.
Precipitation is an essential component of the Arctic climate system as part of the hydrological cycle, linking the atmosphere and cryosphere. Much of the Arctic precipitation sublimates or evaporates before it reaches the ground due to dry sub-cloud layers. The processes are thus controlling the input of the surface mass balance.
We use long-term atmospheric observations at Ny-Ålesund, Svalbard, with vertically-pointing cloud radars and backscattering lidars to identify and quantify atmospheric sublimation/evaporation. Radar observation-based sub-cloud precipitation profiles are studied by employing a virga detection tool, the so-called Virga-Sniffer (Kalesse-Los et al., 2023). The quantification of the sublimation/evaporation is based on sub-cloud vertical gradients of radar moments. First statistical results of precipitation thermodynamical phase, virga depth, and full sublimation/evaporation altitude above ground will be shown.
We will show investigations on wind direction dependence on virga statistics. Air masses advected from the Arctic Ocean are more humid and lead to more precipitation reaching the ground and thus less virga. Air masses advected over Ny-Ålesund from Easterly directions are often characterized by low-humidity subcloud layers leading to more evaporation/ sublimation and hence a higher fraction of virga. Furthermore, the occurrence frequency of virga and surface precipitation observed during different weather regimes such as cyclones, fronts, and atmospheric rivers is contrasted.
This work was supported by the DFG funded Transregio-project TRR 172 “Arctic Amplification (AC)3“.
Refernces:
Kalesse-Los, H., Kötsche, A., Foth, A., Röttenbacher, J., Vogl, T., and Witthuhn, J.: The Virga-Sniffer – a new tool to identify precipitation evaporation using ground-based remote-sensing observations, Atmos. Meas. Tech., 16, 1683–1704, https://doi.org/10.5194/amt-16-1683-2023, 2023.
How to cite: Foth, A., Monrad-Krohn, L., Aydin, B., Schnitt, S., Mech, M., Ebell, K., Maturilli, M., Maahn, M., and Kalesse-Los, H.: Investigation of subcloud precipitation sublimation and evaporation with active remote sensing in Ny-Ålesund, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9135, https://doi.org/10.5194/egusphere-egu26-9135, 2026.
Marine carbohydrates are produced by a wide range of micro- and macroorganisms in seawater and are transferred to the atmosphere via sea spray aerosol (SSA). Recent laboratory and modelling studies suggest that these compounds can influence fog and cloud microphysics as ice nucleating particles. However, observational evidence from the atmosphere remains limited, as most field studies have relied on ship- or land-based filter samples, leaving their relevance for cloud processes at cloud-relevant altitudes largely unconstrained.
Here, we present new measurements of marine carbohydrates and other SSA components at altitudes between 300 and 1200 m, obtained using a tethered helium balloon in Ny-Ålesund (Svalbard) during 2021-2022. These observations are compared with fresh SSA directly collected at the Kongsfjorden coast and with surface seawater samples to assess contributions beyond local ocean emissions. Our results highlight the key role of meteorological conditions in lifting and redistributing SSA constituents, including marine carbohydrates, to higher atmospheric layers. The study further examines potential additional sources and formation pathways, providing new insights into the atmospheric behaviour of marine carbohydrates and their implications for cloud microphysics.
We gratefully acknowledge the funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—Project Number 268020496—TRR 172, within the framework of the Transregional Collaborative Research Center “ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms (AC)3”
How to cite: Zeppenfeld, S., Schaefer, J., Pilz, C., Ebell, K., Zeising, M., Stratmann, F., Siebert, H., Wehner, B., Wietz, M., Bracher, A., and van Pinxteren, M.: Marine Carbohydrates and Other Sea Spray Aerosol Constituents Across Altitudes in the Lower Troposphere of Ny-Ålesund, Svalbard, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13301, https://doi.org/10.5194/egusphere-egu26-13301, 2026.
Coastal shallow water areas are important carbon dioxide sinks, but their sink strength is significantly reduced by the simultaneous emission of other greenhouse gases such as methane (CH4). These areas are often characterized by strong anthropogenic pressure from adjacent agricultural land use, which leads to increased nutrient input, high biological production, oxygen consumption through remineralization of the organic material produced, and ultimately to increased greenhouse gas production. Despite their outstanding importance for marine greenhouse gas emissions, these areas have been little studied to date and the drivers of the spatial and temporal variability of greenhouse gas distribution are poorly understood. To address this problem, we study a lagoon on the German Baltic Sea coast (Darß-Zingst Bodden chain) using a multidisciplinary approach that combines gas chemical and observational oceanographic methods with modeling. Our investigations in the summer of 2024 and 2025 show that the spatial and temporal variability of CH4 concentration in the water and emissions into the atmosphere are primarily caused by wind-driven oceanographic processes, such as water mass transport and mixing. Notably high CH4 concentrations were recorded primarily in protected reed belts and adjacent drainage ditches, indicating the particular importance of these areas as CH4 sources. The high-frequency measurements of CH4 concentrations (Equilibrator-CRDS) provided evidence that changes in water level and the associated pressure change on the sediment have an impact on the CH4 concentration in the water column. Measurements at the water surface with a floating chamber and an eddy covariance flux tower have shown that gas bubble fluxes play a significant role in atmospheric CH4 fluxes and that the intensity of gas bubble release is influenced by water level fluctuations. Our study thus provides a rare CH4 data set from shallow water areas of the German coast and, through its high-frequency data acquisition, reveals the highly dynamic variability of CH4 concentration development and underscores the importance of oceanographic processes in this context.
How to cite: Schmale, O., Holtermann, P., Brüchert, V., Schumann, R., and Jurasinski, G.: A study on the drivers of methane emissions in a eutrophic lagoon in the Baltic Sea (Darß-Zingst-Bodden chain), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2588, https://doi.org/10.5194/egusphere-egu26-2588, 2026.
Short-term variability plays a key role in controlling air–sea CH₄ exchange in coastal upwelling systems, yet it is largely unresolved by conventional low-frequency sampling. Here, we quantify the influence of synoptic-scale variability on CH₄ content and its air–sea exchange using a buoy-based sensor system in a coastal upwelling bay off central Chile (Coliumo Bay, 36.5°S) during the upwelling season (September 2024–February 2025).
Spectral and wavelet analyses revealed a multiscale structure in surface CH₄ levels and alongshore winds, with variance dominated by periods >10 d and 3–10 d in about ~52-21% and ~40-31%, respectively. The latter variability, comprising synoptic oscillations, was mainly associated with alternating periods of active upwelling and relaxation/downwelling events.
At the synoptic scale, during active upwelling events, CH₄ effluxes averaged 25.38 ± 17.74 μmol m⁻² d⁻¹ whereas during relaxation periods effluxes were reduced by almost half (mean ± SD: 9.16 ± 9.58 μmol m⁻² d-1). These results indicate that during active upwelling events, the advection of subsurface waters rich in CH4 and wind-driven gas transfer are key factors triggering the highest CH₄ effluxes.
When the high-frequency time series is compared with a long-term (2007–2025) monthly time series from the same upwelling system, clear differences in capturing real variability emerge. Based on monthly sampling over 18 years, air–sea CH₄ fluxes were on average 9.43 ± 6.95 μmol m⁻² d-1, with a weak seasonal contrast between upwelling-favorable and non-upwelling seasons (10.5 vs. 7.5 μmol m⁻² d⁻¹). These results demonstrate that synoptic variability in CH₄ concentration and air–sea exchange exceeds seasonal variability.
An uncertainty analysis accounting for aliasing under coastal upwelling conditions indicates that high-frequency observations capture CH₄ dynamics that are otherwise missed, thereby reducing bias in coastal CH4 emission estimates. Our results underscore the need to incorporate high-frequency observations, as episodic events such as wind pulses, extreme rainfall, or atmospheric rivers, together with non-linear surface biogeochemical CH₄ production, are required to achieve a more realistic quantification of CH4 emissions from coastal upwelling systems. Main funding FONDECYT (Chile) N° 1250210
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How to cite: Farías, L., Tenorio, S., and Narvaez, D.: The importance of short-term variability for constraining methane air–sea exchange in a coastal upwelling region , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2867, https://doi.org/10.5194/egusphere-egu26-2867, 2026.
Coastal areas within the Eastern South Atlantic Ocean are known hotspots for production and emissions of climate-relevant trace gases. Local circulation, the occurrence of upward tracer transport events through e.g. coastal upwelling and coastally-trapped waves, and a pronounced oxygen minimum zone are crucial in setting the overall emissions of nitrous oxide (N2O) towards the atmosphere. While previous studies quantified the magnitude of cross- and along-shelf gradients of N2O in the region, its main formation pathways, and its seasonal variability, to date it is unclear at what extent extreme events might affect N2O dynamics. Given the projected increase in frequency and severity of events such as storms and oceanic heat waves, which might temporarily, yet significantly modify environmental conditions under which N2O is produced and transported across the sediment-water-air interfaces, it is therefore critical to assess the role of such events on its distribution and emissions. In this study we combine physical, chemical and microbial observations gathered during two major expeditions in 2018 and 2023 to present evidence of a hitherto unseen enhancement in air-sea fluxes of N2O in association with storm events and mesoscale activity. We show that during periods of sustained winds off Walvis Bay at 23°S, water column mixing down to 100 m depth can lead to a two-fold increase in air-sea N2O fluxes driven by the transport of enriched, near-bottom waters towards the surface, which surpasses by far values observed during typical upwelling events. Observations across a mesoscale cyclonic eddy off Angola centered at 16⎼17°S (a rare feature which is thought to occur in average 2 times per year in the region), show that both extreme warming-driven outgassing at the sea surface and enhanced upward transport of N2O-enriched waters at the eddy core play a role in enhancing the overall emissions from waters otherwise thought to be mostly representative of open ocean conditions (i.e. in near equilibrium with the atmosphere). In this contribution, we discuss the main mechanisms by which these extreme events resulted in enhanced N2O air-sea fluxes and how they might impact current marine N2O emission estimates, which due to the lack of targeted observations, do not capture this source of variability.
How to cite: Arévalo-Martínez, D. L., Bange, H. W., Brandt, P., Dengler, M., Eisnecker, P., Löscher, C. R., Rehder, G., Sanders, T., Slomp, C. P., Steinhoff, T., and Xu, P.: Extreme events in the Eastern South Atlantic Ocean enhance regional coastal N2O emissions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6641, https://doi.org/10.5194/egusphere-egu26-6641, 2026.
In recent decades the polar oceans have experienced changes in surface temperature and regional circulation associated with large-scale patterns of ocean warming. These ocean regions are important contributors to global budgets of greenhouse gases such as carbon-dioxide (CO2) and nitrous-oxide (N2O), and the regional environmental changes have significant influences on the magnitude, trends and variability of air-sea fluxes of these gases (Yasunaka et al. 2024; Zhan et al. 2020).
The Arctic Ocean has been a net sink of atmospheric CO2 in recent decades, but displays significant heterogeneity in carbon uptake among its regional seas, with changing trends due to regional climate change and sea-ice loss. The global ocean is a net source of N2O to the atmosphere overall; however the distribution of N2O fluxes from the Arctic remains poorly characterized, and regional observations indicate several regions of N2O undersaturation in the surface Arctic Ocean (Kitidis et al. 2010; Zhan et al. 2020). The Southern Ocean is a major sink for atmospheric anthropogenic CO2 (e.g., ~40% of global uptake according to recent estimates, Dong et al. 2024). Air-sea CO2 fluxes in the Southern Ocean are strongly influenced by circulation patterns associated with oceanographic fronts, and CO2 fluxes display significant seasonal and decadal variability. Flux estimates are subject to uncertainty due to the regional environmental variability and to the sparse network of CO2 measurements available. Estimates of N2O fluxes from the Southern Ocean are also poorly quantified for similar reasons; i.e., limited measurements and significant spatial and temporal variability. Recent syntheses have suggested the region could contribute ~30% of global ocean N2O emissions (Tian et al. 2020), a disproportionately large component in comparison to the areal extent of the Southern Ocean.
In this work we present recent estimates of air-sea fluxes of CO2 and N2O from these polar regions derived from (i) atmospheric inverse model analyses (using the GEOSChem-LETKF framework of Chen et al. 2021), and (ii) an ocean biogeochemical model (NEMO-PlankTOM; Buitenhuis et al. 2018). We focus on the period 2000-2018, and present estimates for regional fluxes, decadal trends and inter-annual variations. We also compare our results to previous estimates derived from surface ocean pCO2 and pN2O data products and ocean biogeochemistry models.
How to cite: Suntharalingam, P., Ghosh, J., Buitenhuis, E., and Chen, Z.: Variability of Air-Sea Fluxes of CO2 and N2O in Polar Ocean Regions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15183, https://doi.org/10.5194/egusphere-egu26-15183, 2026.
Long-term nutrient loading and warmer, longer summer temperatures have promoted summer cyanobacteria-dominated phytoplankton blooms in the Baltic Sea, shifting the annual chlorophyll maximum toward peak summer. In turn, organic matter production is increasing, altering the carbon cycle by shifting the bioavailable carbon pool to later in the season and towards microbial heterotrophy. These ecosystem changes may have consequential impacts on the production of trace gases, such as volatile organic compounds (VOC). Enhanced stratification and reduced vertical mixing may further regulate VOC water-air exchange. In the coastal zone, significant changes to macroalgae communities have been observed in association with persistent eutrophication. Shifting coastal dynamics, along with increased warming and, consequently, increased decomposition of organic material, will likely impact VOC production. Therefore, the aim of this study is to evaluate the influence of a summertime phytoplankton bloom on the composition and concentrations of VOCs in seawater, and to examine differences between distinct coastal habitats.
Summer sampling was conducted on Utö Island (59º 46'50N, 21º 22'23E; Archipelago Sea), and samples were processed at the Utö Atmospheric and Marine Research Station. Seawater VOCs were collected using the purge and trap method four times across three habitat types along the open coast—open water (250 m off shore; 4.5 m depth), a cove (15 m off shore; 0.5 m depth), and a vegetated beach (on shore; surface). Samples were stored in stainless steel absorbent cartridges and analyzed with Thermal Desorption Gas Chromatography Mass Spectrometry. Phytoplankton community composition and abundance were captured using an Imaging FlowCytobot, complemented by bacterial abundance from flow cytometry and microscopy.
Preliminary results indicate clear temporal variability in open water VOC concentrations. Some compounds such as isoprene were persistently detected throughout the summer whereas other compounds, e.g. toluene and dimethyl disulfide, varied across the season in association with changes in phytoplankton and bacterial abundance. Taxa-specific links between VOCs and phytoplankton composition, as well as the potential influence of abiotic drivers, including dissolved organic matter and vertical mixing, is still under investigation. Further analysis indicates that VOC concentrations are highly dependent on coastal habitat type, with composition and concentration of VOCs from the vegetated beach showing approximately 10-fold higher values as well as a more unique VOC blend, suggesting contributions from macroalgae and sediment processes. In contrast, the cove was highly dominated by bromoform, comprising >50% of the measured proportional VOC signal throughout the summer.
How to cite: Galen, E., Kraft, K., Liu, Y., Vanharanta, M., Ylöstalo, P., Riemann, L., Hellén, H., Seppälä, J., and Rinnan, R.: Linking Baltic Sea water VOC concentrations with a summertime phytoplankton bloom , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9885, https://doi.org/10.5194/egusphere-egu26-9885, 2026.
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 .
How to cite: Sellegri, K., Chamba, G., Gros, V., Rose, C., Berdalet, E., Wohl, C., Dall'Osto, M., and Simo, R.: DMS, MeSH and nanoparticles in semi-controlled deck-borne experiments using Antarctical seawaters: on the effect of UV light, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5384, https://doi.org/10.5194/egusphere-egu26-5384, 2026.
Air–sea gas exchange exerts a critical control on marine biogeochemistry, yet quantifying biologically driven oxygen fluxes in dynamic sea conditions remains challenging. Here, we use membrane inlet mass spectrometry (MIMS) measurements of dissolved gases to estimate net community production (NCP) from biologically driven oxygen anomalies across the Irish Exclusive Economic Zone (EEZ). High-precision dissolved O₂ and Ar measurements were obtained using a Hiden Analytical MIMS system, enabling calculation of O₂/Ar ratios that isolate the biological oxygen signal by normalisation to inert argon and reference to air–sea equilibrium.
Seawater samples collected during multiple research cruises were analysed under controlled temperature conditions. Raw ion currents were corrected using solubility based relative sensitivity factors, and O₂/Ar ratios were converted to biological supersaturation (ΔO₂/Ar) from the temperature and salinity of the sea water sample, providing a robust tracer of biologically driven O₂ fluxes independent of temperature and solubility effects. Data quality was assessed through comparison of flow through cell and dip-probe measurements and analysis of poisoned samples to constrain non-biological influences.
The collected ΔO₂/Ar dataset covers a diverse oceanic condition from coastal to open ocean, from the Irish Exclusive Economic Zone (EEZ) to the North and South Atlantic. Samples were collected in various seasons in 2024, and in 2025, they were collected along the latitudinal transect. The purpose of these observations is to examine the variations in surface-ocean oxygen levels across different regions, seasons, and latitudes, and to analyse the impacts of biological production, stratification, and air-sea gas exchange on different oceanographic conditions. This method will demonstrate how MIMS-based O₂/Ar measurements may assist in identifying short-term air-sea oxygen fluxes and provide more precise constraints on the productivity and carbon cycling of the ocean.
How to cite: Swaraj, A. and Croot, P.: Investigating surface-ocean oxygen dynamics using MIMS-based O₂/Ar measurements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22179, https://doi.org/10.5194/egusphere-egu26-22179, 2026.
Atmospheric nitrogen deposition has broad implications for global ecosystems and human health. It is largely influenced by local weather conditions and atmospheric transport, which are in turn controlled by large-scale atmospheric circulation patterns. Due to the absence of long-term atmospheric nitrogen deposition data series, the mechanisms of interannual variation of nitrogen deposition are still poorly understood. Here, we investigate relationships between atmospheric nitrogen deposition and atmospheric circulation variability and explore the underlying mechanisms. We find that there is a growing imbalance between regional nitrogen emissions and deposition in global hotspots. Atmospheric nitrogen deposition variations exhibit significant relationships with atmospheric circulation modes, with predominant influences from the El Niño–Southern Oscillation (ENSO). Additionally, we captured significant nitrogen deposition anomalies during different phases of ENSO years by altering global temperature, precipitation, and atmospheric circulation. Significant effects of ENSO on atmospheric nitrogen deposition were observed in the Eastern United States, Eastern Europe, and East Asia.
How to cite: He, Q.: Atmospheric circulation impacts on terrestrial atmospheric nitrogen deposition under growing imbalance of regional nitrogen emissions and deposition , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7272, https://doi.org/10.5194/egusphere-egu26-7272, 2026.
Influence of Atmospheric Aerosol Deposition and its Elemental Composition on Marine Productivity in the Central Arabian/Persian Gulf The Arabian Gulf is a shallow, warm oligotrophic, and hypersaline marginal sea of the Indian Ocean. Due to intense evaporation, limited freshwater input, recurrent dust event and harsh environmental conditions, nutrient concentrations and productivity are significantly impacted by the harsh and changing environmental conditions. Atmospheric aerosols can impact surface ocean biology and biogeochemical processes in the Arabian Gulf as a result of the dust events and limited inputs. However, the rates of macro- and micronutrient inputs from the atmosphere to the Arabian Gulf are not well constrained. Both inorganic and organic forms of nitrogen and phosphorus may contribute to productivity in the Arabian/Persian Gulf. Productivity and by proxy precious resources such as fisheries can be closely linked to aerosols nutrient deposition. In this study, we use the Arabian Gulf as a natural laboratory for investigating the temporal variability of atmospheric macro- and micronutrients, the partitioning between organic and inorganic forms of nitrogen and phosphorus, and the role of trace metals in marine productivity. Based on annual time-series aerosol measurements, we provide new insights into atmospheric concentrations of macro- and micronutrients in the central Arabian/Persian Gulf. Additionally, using 1-dimensional biogeochemical model simulations, we investigate the influence of atmospheric aerosol deposition on primary productivity in the Gulf. The results obtained suggest that atmospheric deposition is an important process regulating marine productivity in the Arabian Gulf.
How to cite: Tutsak, E., Al-Thani, J., Yumruktepe, Ç., Yigiterhan, O., M.A.S. Al-Ansari, E., Soliman, Y., and Safi, M.: Influence of Atmospheric Aerosol Deposition and its Elemental Composition on Marine Productivity in the Central Arabian/Persian Gulf , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14409, https://doi.org/10.5194/egusphere-egu26-14409, 2026.
Wet deposition is a major mechanism of phosphorus (P) deposition to the ultra-oligotrophic Eastern Mediterranean, yet long-term constraints on the relative roles of dissolved inorganic phosphorus (DIP) and dissolved organic phosphorus (DOP) remain limited. In this study, 15-year observations of DIP and DOP variability were conducted at an Eastern Mediterranean regional background site, focusing on the temporal variability, drivers, and deposition. Wet deposition samples were collected on an event basis and analyzed for DIP using a colorimetric molybdate-reactive method. Total dissolved phosphorus (TDP) was determined following oxidative digestion, and DOP was defined by subtracting DIP from TDP. Deposition fluxes were calculated by coupling concentration measurements with precipitation depth, enabling assessment of both concentration-driven and rainfall-driven variability.
Across the 15-year period, both DIP and DOP exhibited pronounced event-to-event variability typical of atmospheric deposition in the region. Preliminary results show that DIP was frequently enhanced during dust outbreak episodes consistent with mineral dust influence, indicating efficient wet scavenging of particulate and soluble inorganic P associated with crustal minerals. In contrast, DOP was more frequently associated with air masses bearing marine and continental/anthropogenic impacts. At the interannual scale, variability in both concentrations and fluxes tracked changes in rainfall intensity and event frequency, as well as the occurrence of dust-transport episodes. To better constrain sources and processes, deposition chemistry was evaluated in tandem with air-mass back trajectories, and, where available, supporting aerosol and meteorological data. The results indicate that dust-driven wet deposition delivers episodic pulses of bioavailable DIP. DOP supplies a more sustained, compositionally diverse pool. This pool may become bioavailable following photochemical and microbial transformation after deposition. Overall, the 15-year record show that the organic fraction is significant and that the annual DIP:DOP partitioning can change depending on the transport pathways and rainfall distribution. This has direct implications for regional external nutrient inputs and their future projections in response to changes in dust emissions and hydroclimate.
Acknowledgments
This work has been supported by the HFRI grant # 4050 BIOCAN.
How to cite: Papoutsidaki, K., Tsagkaraki, M., Violaki, K., Kouvarakis, G., Mihalopoulos, N., and Kanakidou, M.: A 15-Year Record of Organic–Inorganic Phosphorus Variability in Eastern Mediterranean Wet Deposition , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19703, https://doi.org/10.5194/egusphere-egu26-19703, 2026.
Harmful Algal Blooms (HABs) represent a growing threat to marine ecosystems, aquaculture, and public health in the Central Eastern Arabian Sea (CEAS). This study utilized 18S rRNA metabarcoding to characterize the absolute abundance and community composition of potentially toxigenic diatoms and dinoflagellates in the coastal waters of Goa. The analysis reveals a distinct and alarming prevalence of multiple genera associated with diverse toxin syndromes.
The dataset was dominated by a massive proliferation of the dinoflagellate Karenia (linked to Neurotoxic Shellfish Poisoning and ichthyotoxicity), which reached extreme abundances exceeding 51,000 reads per sample at the most impacted sites. Co-occurring with this bloom, spatially distinct hotspots of Paralytic Shellfish Toxin (PST) producers were identified, specifically Alexandrium and Gymnodinium spp., with Alexandrium counts peaking at over 5,200 reads. Notably, the potent PST producer Alexandrium tamiyavanichii was positively identified, alongside detections of Gymnodinium catenatum.
The diatom community also exhibited significant toxicity potential; the Amnesic Shellfish Poisoning (ASP) genus Pseudo-nitzschia displayed high relative abundance (up to ~3,700 reads), including the presence of P. pungens. Furthermore, vectors for Diarrhetic Shellfish Poisoning (DSP), including Dinophysis spp. and Phalacroma rotundatum, and Yessotoxin producers (Lingulodinium polyedra, Gonyaulax spinifera) were ubiquitously present at lower background levels.
These findings highlight a complex, multi-risk scenario where ASP, PSP, NSP, and DSP vectors coexist within the same coastal system. The distinct spatial separation observed between peak Karenia, Alexandrium, and Pseudo-nitzschia events suggests that heterogeneous environmental drivers are influencing specific HAB assemblages. This data underscores the critical need for broad-spectrum toxin monitoring beyond single-species surveillance in the region.
How to cite: Zedi, S. and Khandeparker, R.: Hidden Hazards in the Central Eastern Arabian Sea: Metabarcoding Reveals Co-occurrence of ASP, PSP, and NSP Vectors in the Coastal Waters of Goa, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-414, https://doi.org/10.5194/egusphere-egu26-414, 2026.
Atmospheric chemistry in polar areas is a key determinant for climate evolution, and many sets of data and experimental observations from both hemispheres exist to date. However, data on continuous and long-term studies and monitoring in continental polar areas, such as the Antarctic Plateau, are still very scarce. While presenting significant implementation difficulties, such observations are necessary to understand the current climate system of the Southern Ocean and the environmental variables involved in its evolution on a multi-annual scale. Furthermore, the study of atmospheric chemical composition in continental Antarctica can provide important information for the interpretation of chemical stratigraphies from ice cores, which is made complicated in these areas by post-depositional processes due to atmosphere-snow exchanges. To date, there is no permanent observatory on the Antarctic Plateau dedicated to the study of the chemical properties of atmospheric aerosols, excluding the South Pole Observatory, which is nevertheless focused on the study of climate-altering gases and the physical properties of aerosols, except for a few short-term campaigns.
For these reasons, a New Observatory dedicated to the study of the chemical composition of atmospheric aerosol and ozone at the Concordia station (Dome C), on the Antarctic Plateau (CATCH-O Project) is currently in its first phase of implementation. This facility takes advantage of solid infrastructure set up during previous Italian National Antarctic Programs. It will be able to merge Near-Real Time data (ozone concentration and selected ion markers of atmospheric sources and processes) with off-line chemical composition data obtained from sampling and subsequent chemical analysis of several atmospheric source and process markers.
Due to its central location within the Antarctic continent, its elevation (about 3230 m), its distance from the coast (about 1100 km) and from ocean sources and related biogeochemical processes, Dome C can be considered representative of a background atmosphere. In this way, the Atmospheric Chemistry Observatory of Dome C will represent a relevant research opportunity for obtaining a long-term baseline of atmospheric chemical composition in relation to the entire continent.
Here, the already available data obtained by both off-line and on-line measurements within CATCH-O Observatory will be presented for the first time.
How to cite: Traversi, R., Becagli, S., Severi, M., Nava, S., Lucarelli, F., Cristofanelli, P., Putero, D., Malandrino, M., Grotti, M., Barbaro, E., and Roman, M.: Concordia ATmospheric CHemistry – Observatory (CATCH-O): a tighter focus on the atmosphere of the Antarctic Plateau, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5715, https://doi.org/10.5194/egusphere-egu26-5715, 2026.
In this study we tested under field conditions the hypothesis that electrical phenomena may influence chemical composition of snow. The field experiment was conducted at the Akademik Vernadsky Station within the framework of the State Program of Scientific Research of Ukraine in Antarctica during two winter seasons in 2022 and 2023, using a newly designed trap for charged snow. This instrument was constructed to selectively attract charged snow particles from the blowing-snow flux and was deployed during blowing snow events The experiments were performed in winter to ensure that chemical modifications were not affected by photochemical reactions. A similar field experiment was conducted in the Arctic at Ny-Ålesund, Svalbard. Here, we focus on the chemical composition of the snow samples collected by the trap, which were analyzed using ion chromatography and compared with the composition of the background blowing snow.
We found that samples of charged snow were significantly more concentrated than background snow, which is attributed to the sublimation during conditions of blowing snow events. When the measured ion concentrations were compared with the expected concentration ranges and ratios characteristic of sea salt, the charged snow samples were, however, depleted in chloride, with this difference far exceeding the measurement uncertainty. The dependence of chloride “losses” on the fraction of sublimated water indicated a strong change and revealed the presence of a threshold at approximately 80 % sublimated water, beyond which these losses—interpreted as emissions to the atmosphere—increased sharply. Products of chlorine free-radical reactions in the atmosphere have been reported by numerous authors; however, the mechanism responsible for initiating these reactions remains uncertain. The present experiment provides evidence that the charging of snow may serve as such a triggering process. The presence of a similar threshold at 70–80 % sublimated water, after which ion losses increase sharply, was also observed for Br⁻, SO₄²⁻, and Mg²⁺. However, the presence of local sources renders these relationships less significant. The change in the composition at such high sublimation fractions may indicate emission of these ions due to overcoming of the Rayleigh limit indicating that electrical charging affects chemical processes in snow.
In contrast, the experiments conducted in the coastal marine environment at Ny-Alesund indicate that ion ratios characteristic of sea salt were preserved in the charged snow samples, demonstrating that no or only limited chemical transformations took place. The presence of sea ice appears to be critical for the manifestation of chemical effects. When sea ice is present, snow particle charging during blizzards occurs primarily due to frictional and sublimation-driven processes. In the absence of an ice surface, charging is most likely driven by the sorption of marine aerosols maintaining the expected sea salt ratios in the charged snow.
How to cite: Tkachenko, K., Pishniak, D., Razumnyi, S., El-mansi, H., Ginot, P., and Jacobi, H.-W.: Experimental evidence of chemical differences between charged and uncharged snow during blowing snow events, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13392, https://doi.org/10.5194/egusphere-egu26-13392, 2026.
The Arctic is warming at a rate several times faster than the global mean, a phenomenon commonly referred to as Arctic amplification. Short-lived climate forcers, particularly aerosols acting as ice-nucleating particles (INPs), may influence this amplification through aerosol-cloud indirect effects. During the polar night, INPs modulate the ratio of liquid-to-ice in mixed-phase clouds, altering their capacity to trap outgoing longwave radiation and warm the surface. Despite their importance, the sources and transport pathways of INPs in high-latitude regions remain poorly constrained. While truly pristine Arctic environments are rare, cold, polluted sub-Arctic regions such as interior Alaska provide natural laboratories for investigating INP populations under conditions that combine low temperatures with enhanced anthropogenic and regional aerosol influences. Such environments may be particularly relevant to Arctic locations experiencing episodic pollution, long-range aerosol transport, or increasing local emissions. While chemical fingerprinting provides critical insights into particle composition and local abundance, it cannot inherently resolve the geographic origins or transport history of air masses bringing INPs to a given region.
To address this limitation, we apply backward trajectory-based modelling in an attempt to link observed INPs to their potential source regions. We build on recent work investigating the sources of wintertime INPs in the sub-Arctic urban environment of Fairbanks, Alaska, using observations from the Alaskan Layered Pollution and Chemical Analysis (ALPACA) field campaign conducted in January and February 2022. During the campaign, Fairbanks experienced persistent surface-based temperature inversions and extreme cold events that favored the accumulation of locally emitted anthropogenic aerosols. Analysis of ALPACA-2022 data has reported INP concentrations significantly higher at relatively cold freezing temperatures than those typically observed at other high-latitude sites, consistent with three dominant INP classes: heat-labile biological particles, potentially associated with local vegetation such as lichens; organic particles linked to residential wood combustion, supported by correlations with levoglucosan; and a source attributed to road dust, possibly generated by the application of traction gravel on icy roads.
Using a backward trajectory modeling framework, we investigate the spatial origins and atmospheric transport of INP sourced from the Fairbanks region. Backward transport simulations are conducted using the FLEXible PARTicle dispersion model (FLEXPART), driven by 1.33 km resolution wind fields from the Weather Research and Forecasting (WRF) model, including assimilation of meteorological data from the ALPACA campaign. The surface influence and residence time of air masses arriving at the ALPACA measurement site in downtown Fairbanks are quantified. Potential Emission Sensitivity (PES) footprints are calculated by combining with high resolution emissions fields of potential INP sources, based on downscaling emissions using vegetation, road and building datasets. Interpreting PES fields, in conjunction with the observed INP analysis, allows characterization of both the INP sources and their transport pathways in Fairbanks. The results have broad implications for INP sources and aerosol-cloud indirect effects over the wider sub-Arctic and potentially Arctic region.
How to cite: Alkatheeri, A. Y., Law, K., Francis, D., Arnold, S., Lill, E., Greeney, S., Creamean, J., Da Silva, A., Raut, J.-C., Onishi, T., Brett, N., Simpson, W., and Pratt, K.: Characterizing the Sources and Transport of Wintertime Ice-Nucleating Particles in Fairbanks, Alaska, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17322, https://doi.org/10.5194/egusphere-egu26-17322, 2026.
We present a post-processed comprehensive balloon-borne measurement dataset, which was collected from a dedicated Arctic observation campaign conducted from 19 March to 18 April 2024 in the transition from polar night to polar day at the Villum Research Station (VRS, Station Nord, Greenland), as a contribution to the DFG-funded Transregio-project TRR 172 “Arctic Amplification (AC)3. The objective of the balloon-borne observations was to characterize the temporal evolution of the Arctic atmospheric boundary layer (ABL), focusing on key transition periods, including cloud development, low-level jet evolution, and day to night shifts.
The measurements were taken by the Balloon-bornE moduLar Utility for profilinG the lower Atmosphere (BELUGA) tethered-balloon system performing in-situ observations of temperature, humidity, wind speed, turbulence, and thermal infrared irradiance from the surface to several hundred meters altitude, with frequent profiling in high vertical resolution. Twenty-eight research flights delivered more than 300 profiles, with up to 8 profiles per hour, complemented by daily radiosonde launches. For the BELUGA instrumentation at VRS, we specify the data processing procedures. The post-processed Level-2 data (BELUGA and radiosonde) are provided in instrument-separated data subsets listed in a data collection (https://doi.pangaea.de/10.1594/PANGAEA.986431).
One major application of these balloon-borne data is to evaluate different model types—such as numerical weather prediction, single-column models, large-eddy simulations—in representing processes that control the Arctic ABL. As a preparation, we give an overview of the observations, environmental conditions during the campaign, and highlight specific events that are particularly valuable for model comparison. These events include variable cloud scenarios, where transitions between cloudy and cloud-free conditions induce changes in temperature rates and radiative heating rates, thereby influencing the ABL inversion and lapse-rate. Additionally, we examine an observed Arctic low-level jet which we compare with reanalysis.
How to cite: Dorff, H., Siebert, H., Navale, K., Ehrlich, A., Müller, J., Schäfer, M., and Wendisch, M.: Tethered balloon-borne measurements for the characterization of the evolution of the Arctic atmospheric boundary layer at the Villum Research Station (Station Nord, Greenland), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20624, https://doi.org/10.5194/egusphere-egu26-20624, 2026.
The turbulence in the Arctic is often observed to be intermittent as a result of the interaction with non-turbulent motions. Several studies have examined the triggering mechanisms behind the intermittency, yet the understanding of their influence is still insufficient. In this study, turbulence intermittency in the Arctic stable boundary layer is investigated using observations from the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, spanning October 2019 to September 2020. Turbulent and sub-mesoscale motions separated using Multi-Resolution Decomposition (MRD) cospectral analysis are used to quantify the strength of turbulent and sub-meso motions. Previous study showed the evolution of intermittency under strong stratification, when sub-mesoscale energy exceeds 10% of the total mean kinetic energy. While such clear indications are not evident in this available data, we further examine the role of additional factors such as radiative forcing or cloud cover, in the triggering of intermittency in turbulence in this region. The triggering mechanisms are analyzed separately for polar night and polar day regimes, using different radiative forcing thresholds. The study is further extended to analyze the stability correction function (φ) and assess the validity of the classic Monin-Obhukov Similarity Theory (MOST) under such motions. These results are compared with the generalized stochastic model to assess its ability to represent these non-stationary motions associated with intermittency. Following the outcome, the stochastic model may be refined to better capture intermittent turbulence processes in the Arctic.
How to cite: Kuttikulangara, A., Vercauteren, N., Riebold, J., Handorf, D., and Krumshied, S.: Investigating the potential triggering mechanisms of turbulence intermittency in the Arctic Boundary Layer, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20888, https://doi.org/10.5194/egusphere-egu26-20888, 2026.
