Dimethyl sulfide (DMS) is an important trace gas emitted from the ocean. The oxidation of DMS is important for global climate through the role DMS plays in setting the sulfate aerosol background in the troposphere. However, the mechanisms of DMS oxidation are very complex and have proved elusive to accurately determine in spite of decades of research. As a result the representation of DMS oxidation in global chemistry-climate models is often greatly simplified. Recent field observations and laboratory studies have prompted renewed efforts in constraining the uncertainty in the oxidation mechanism of DMS as incorporated in global chemistry-climate models. Here we build on recent laboratory and observational evidence and develop a new DMS mechanism for inclusion in the UKCA chemistry-climate model. We compare our new mechanism to the existing UKCA mechanism and to a range of recently developed mechanisms reported in the literature through a series of global and box model experiments. Our box model experiments highlight that there is significant variance in simulated secondary oxidation products of DMS across mechanisms used in the literature, with divergence in the sensitivity of these products to temperature exhibited. Our global model studies show that our updated and improved DMS scheme performs better than the current scheme when compared against observations. However, sensitivity studies underscore the need for further laboratory and observational constraints.

How to cite: Archibald, A., Cala, B., Archer-Nicholls, S., Abraham, N. L., Griffiths, P., Jacob, L., Shin, M., Revell, L., and Woodhouse, M.: Development, intercomparison and evaluation of an improved mechanism for the oxidation of dimethyl sulfide, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7047, https://doi.org/10.5194/egusphere-egu23-7047, 2023.

Biomass burning is a major contributor to the emission of particle matter in the atmosphere (up to 90 % of primary organic aerosol) and thus has an impact on climate, human health, and ecosystems. Once emitted, biomass burning-derived organic aerosol can be transported to the oceans. However, the impact and fate of this particulate matter and its major components in the marine biological carbon pump and the trophic chain are largely unknown. Understanding these processes is of paramount importance to better asses the carbon cycle. This work presents the first attempt to investigate the bioavailability of two biomass-burning tracers (i.e., levoglucosan and galactosan) in seawater inoculated with marine microorganisms. To do so, a novel method was developed to extract the anhydrosugar from their salty matrix and monitor their evolution for 44 days under controlled conditions. Along with the anhydrosugar concentration, multiple parameters (dissolved organic carbon, inorganic nutrient concentrations, prokaryotic production, heterotrophic prokaryotes abundance, and prokaryotic diversity) were monitored to achieve a complete picture of their fate in seawater. Furthermore, two control experiments (glucose- and non-amended) were run in parallel for comparison purposes. The results show that both levoglucosan and galactosan can be biodegraded at slow rates as their concentrations dropped from 2.5 ± 0.6 and 2.4 ± 0.3 μM to 0.1 ± 0.1 and 1.5 ± 0.7 μM, respectively, over a period of 44 days. The decrease in the levoglucosan and galactosan concentrations was accompanied by an increase in both prokaryotic production (up to 40 and 5 times greater, respectively, when compared to the non-amended experiment) and heterotrophic prokaryotes abundance (for levoglucosan, up to one order of magnitude greater than the non-amended experiment). While glucose was assimilated by heterotrophic prokaryotes within 1.7 days, levoglucosan and galactosan biodegradation did not start until at least 8.7 days after the experiments were set. These delays suggest that the chemical structure of these anhydrosugars can only be tackled by specific enzymatic abilities regulated by slow-growing heterotrophic prokaryotes. Prokaryotic diversity analyses revealed the predominance of a few bacterial genera from the Roseobacter clade that were specifically selected by the addition of the anhydrosugars. These results raise questions about the enzymatic capabilities of this widespread marine bacterial clade and the processing of semi-labile compounds accumulating in surface ocean waters. This work shows that biomass-burning organic compounds have the potential to be biodegraded by prokaryotic bacteria and thus contribute to the trophic chain and the production of CO₂. 

How to cite: González-Sánchez, J. M., Panagiotopoulos, C., Antich, C., Van Wambeke, F., and Misson, B.: What happens to biomass burning-emitted particles in the Ocean? A laboratory experimental approach based on their tracers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6011, https://doi.org/10.5194/egusphere-egu23-6011, 2023.

Atmospheric transport and deposition of dust aerosol is very efficient in supplying iron to large part of global oceans. In this study, an Earth system model with ocean biogeochemistry component is used to explore how dust deposition can impact vertical distribution of dissolved iron (DFe) and phosphate in the upper 1000 m of the global oceans by impacting phytoplankton growth.  Although large areas of the global oceans show positive chlorophyll response following dust deposition, some regions (those having high levels of background DFe from continental shelf sediments and high atmospheric DFe input) experience net scavenging losses of DFe following dust depositions. Such regions experience a reduction in chlorophyll concentrations along with reduction in particulate organic carbon (POC) production and fluxes following dust deposition. While positive chlorophyll response is associated with low levels of background DFe and low atmospheric DFe input compared to regions experiencing negative chlorophyll response, the magnitude of chlorophyll increase depends on the background nitrate-to-iron ratio. With increase in the magnitude of positive chlorophyll response to atmospheric DFe deposition, an increase in POC production and resulting fluxes are encountered. Such an increase in POC flux can play the dual role of increase in scavenging removal of DFe as well as increase in PFe remineralization. The net result is that variation in NREG (Net REGeneration, taken as difference between PFe remineralization and DFe scavenging) in the upper 1000 m of the ocean has significant positive correlation with variation in POC fluxes, indicating that sinking organic matter following positive chlorophyll response to atmospheric iron deposition is the main driver of net DFe regeneration. Furthermore, a depth-wise difference between the impact of sinking POC and PFe fluxes on NREG is also evident. In the upper 150 m, high POC fluxes drive NREG while at deeper depths, PFe fluxes become important in driving NREG due to slow desorption release of iron from sinking PFe mass. As a result, with increase in POC fluxes, the depth of maximum NREG becomes shallower due to the shorter remineralization length scale of POC compared to lithogenic particles. On the contrary, with increases in the magnitude of atmospheric DFe , the depth of maximum NREG increases due to high dust deposition driving increased scavenging. Furthermore, increase in POC fluxes also leads to regeneration of phosphate at shallower depths. In this manner, the magnitude of chlorophyll response to atmospheric iron can significantly control the patterns of nutrient limitations.

How to cite: Banerjee, P.: Variable role of dust deposition on upper ocean nutrient distribution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8622, https://doi.org/10.5194/egusphere-egu23-8622, 2023.

Transparent exopolymer particles (TEP) exhibit the properties of gels and are ubiquitously found in the world oceans. Here we demonstrate that TEP may enter the atmosphere as part of sea spray aerosol and likely influence cloud properties. We show number concentrations of TEP with a diameter > 4.5 µm, hence covering a part of the supermicron particle range measured in ambient aerosol and cloud water samples from the tropical Atlantic Ocean. Furthermore, TEP were analysed in generated aerosol particles using a plunging waterfall tank that was filled with the ambient seawater.

Based on Na⁺ concentrations in seawater and the atmosphere, the enrichment of TEP in the tank generated aerosol particles was well in-line with another study. The TEP enrichments in the ambient atmosphere were, however, up to two orders of magnitude higher compared to the tank study and such high values are thus far not reported for supermicron aerosol particles. We propose that the high enrichment of TEP in the particles and in cloud water result from a combination of enrichment during bubble-bursting transfer from the ocean and secondary in-situ atmospheric formation. We suggest that similar (biotic and abiotic) formation mechanism reported for TEP formation in the (sea)water might take place in the atmosphere as well, as the required conditions (e.g. high concentrations of dissolved TEP precursors such as polysaccharides, presence of bacteria in the cloud water) were given.

TEP concentrations in the atmosphere were two orders of magnitude higher than INP concentrations in the aerosol particles and cloud water, respectively. However, only a part of the TEP population, assumingly the one colonized by bacteria, might contribute to INP population, and are worth further studies.

The study contributes to the international SOLAS program.

Ref. : van Pinxteren, M., Robinson, T.-B., Zeppenfeld, S., Gong, X., Bahlmann, E., Fomba, K. W., Triesch, N., Stratmann, F., Wurl, O., Engel, A., Wex, H., and Herrmann, H.: High number concentrations of transparent exopolymer particles in ambient aerosol particles and cloud water – a case study at the tropical Atlantic Ocean, Atmos. Chem. Phys., 22, 5725–5742, https://doi.org/10.5194/acp-22-5725-2022, 2022.

How to cite: van Pinxteren, M., Robinson, T.-B., Zeppenfeld, S., Wurl, O., Wex, H., Engel, A., and Herrmann, H.: Transparent exopolymer particles (TEP) in the tropical oligotrophic Atlantic Ocean: Sea-to-air transfer and atmospheric in situ formation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1134, https://doi.org/10.5194/egusphere-egu23-1134, 2023.

Understanding ocean-cloud interactions and their effect on climate requires that atmospheric new particle formation is characterized. Yet, the process of particle formation from marine biogenic gaz-phase emissions has not been evidenced in the open ocean lower atmosphere, partly due to the naturally low concentrations of these particles in remote oceanic places. Here we show, using new ship-borne air-sea interface enclosures, that new particles are formed in relation to marine micro-biology present in the seawater. The chemical analysis of newly formed clusters with API-ToF-MS shows unexpected results, implicating nucleating coumpounds and pathways that are usually not taken into account in nucleation processes.

How to cite: Chamba, G., Peltola, M., Barthelmeß, T., Rissanen, M., Rose, C., Iyer, S., Saint-Macary, A., Saiz-Lopez, A., Rocco, M., Safi, K., Deppeler, S., Barr, N., Harvey, M., Engel, A., Dunne, E., Law, C., and Sellegri, K.: Nighttime atmospheric nucleation driven by marine microorganisms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8058, https://doi.org/10.5194/egusphere-egu23-8058, 2023.

Sea spray aerosols (SSA) represent one of the largest sources of atmospheric particles since over two-thirds of the Earth’s surface is covered by oceans. They play an important role in climate and atmospheric chemistry, however, despite this a series of knowledge gaps hinder us from constraining their relevance. One critical question is why the physicochemical properties of nascent particles generated in the laboratory are so different from those measured in the ambient marine atmosphere. For example, a series of studies have highlighted that SSA generated in the laboratory exhibit essentially the same ability to act as cloud condensation nuclei as inorganic sea salt, regardless of the amounts of organic substances present in the seawater from which they were generated (e.g., Collins et al., 2016). This is in stark contrast to observations of ambient marine aerosols - their ability to act as cloud condensation nuclei is often significantly reduced in comparison (Swietlicki et al., 2000).

To address this discrepancy, we prepared a novel experimental setup in which we deployed a chemical ionisation mass spectrometer (CIMS) with an Aim inlet in a setup together with a sea spray simulation chamber, an oxidative flow reactor (OFR), and a differential mobility particle sizer (DMPS) at Graciosa Island, Azores, in the eastern north Atlantic Ocean during summer 2022 as a part of the AGENA campaign.

We used freshly-sampled ocean water to generate SSA that were aged in an OFR for an equivalent period of 3 to 3.5 days in the atmosphere. We recorded the gas-phase chemical composition of nascent and aged aerosols using the AIM-CIMS with multiple reagent ions, collected filter samples for offline analysis of the particle-phase chemical composition, and used a DMPS to compare the particle size distribution and concentration.

The first results of our study show that the volatile organic compounds released from the sampled ocean water considerably nucleate when they are oxidized in the OFR. Furthermore, the chemical analysis of these gases reveals an increase in the concentration of DMS oxidation products, such as methane sulfonic acid, when the nascent SSAs along with the gases in the tank headspace are exposed to oxidants in the OFR. However, we did not observe any substantial differences in the concentration and size distribution of the accumulation and larger-mode particles for primary and aged SSA. This could be attributed to extensive nucleation taking place in the OFR. It is possible that in the real world, these VOCs would rather condense on the primary SSA than form new particles.

In this presentation we will compare the properties of ambient SSA particles in the Eastern North Atlantic and those generated and aged with our experimental setup using real seawater in an attempt to address the discrepancy.

Collins, D. B., et al., Geophys. Res. Lett. 2016, 43 (18), 9975-9983.

Swietlicki, E., et al., Tellus B: Chemical and Physical Meteorology 2000, 52 (2), 201-227

How to cite: Aggarwal, S., Garmash, O., Kilgour, D., Jernigan, C., Zinke, J., Gong, X., Zhou, S., Zhang, J., Freitas, G., Cunha, B., Silva, T., Wang, J., Bertram, T., Thornton, J., Salter, M., Zieger, P., and Mohr, C.: Physicochemical Properties of Nascent vs. Aged Sea Spray Aerosols in the Eastern North Atlantic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15506, https://doi.org/10.5194/egusphere-egu23-15506, 2023.

Reactive volatile organic compounds (VOCs) in the remote marine atmosphere have impacts on climate through affecting atmospheric oxidation capacity (with subsequent effects on methane lifetime), and through affecting remote aerosol abundances, where they may modify cloud condensation nuclei (CCN) concentrations in regions of low CCN abundance. An improved understanding of aerosol and trace gas budgets in the remote marine atmosphere may aid in reducing uncertainties in the extent of anthropogenic warming and cooling contributions to radiative forcing of climate, since they are key components of the background natural atmospheric composition upon which anthropogenic influences are added. Glyoxal (CHOCHO) is a highly reactive oxygenated VOC, which observations have shown is ubiquitous throughout the global troposphere. In the remote marine atmosphere, glyoxal has the potential to act as a source of secondary organic aerosol and to modify the atmospheric oxidising capacity through impacts on radical photochemistry. In our recent work, we demonstrated the potential for acetaldehyde as a source of glyoxal in the remote atmosphere, via a minor oxidation pathway which dominates in-situ glyoxal production in clean marine air masses.

Here we present the first evaluation of global model-simulated glyoxal abundances in the remote marine atmosphere using high temporal (hourly) in situ measurements, and a collection of glyoxal observations synthesised from the literature. Measurements made using a sensitive laser-induced phosphorescence instrument at the Cape Verde Atmospheric Observatory in the tropical Atlantic  over two 4-week campaigns are compared with CAM-chem, a component of the Community Earth System Model (CESM) v2.2 including the MOZART-TS1 tropospheric chemistry mechanism. We show that the global model is capable of reproducing the magnitude of the in situ glyoxal observations from the tropical Atlantic marine boundary layer only when accounting for both the production of glyoxal from acetaldehyde oxidation, and the two-way sea-air exchange of acetaldehyde over the oceans. These model processes also improve the model-simulated glyoxal compared with remote sensing measurements in the tropical Pacific, but with a larger remaining bias. The model is not capable of reproducing observed nighttime glyoxal abundances at Cape Verde, with a large model underestimate. We show that the inclusion of a sea-air emission source of glyoxal, as a proxy for a potential source from the sea surface microlayer, allows the model to reproduce the observed magnitude of nighttime glyoxal. Our results demonstrate that an unconstrained global model is capable of reproducing observed daytime glyoxal abundances in the remote tropical Atlantic atmosphere, and further imply a coupling between acetaldehyde and glyoxal in the remote troposphere. The model results support the potential for a net sea surface to atmosphere source in sustaining nighttime glyoxal concentrations in this region.  

How to cite: Arnold, S., Brett, N., Wang, S., Emmons, L., Feng, W., Walker, H., Heard, D., Stone, D., and Kelly, E.: Evaluation of model-simulated glyoxal in the remote marine atmosphere and dependencies sea-air exchange processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15599, https://doi.org/10.5194/egusphere-egu23-15599, 2023.

The influence of dimethyl sulfide (DMS) on climate is potentially large but highly uncertain. Some of this uncertainty results from the over-simplification of biological drivers of marine DMS production within predictive models. The available models rely on chlorophyll (chl) as the sole biological parameter and often fail to replicate observations, particularly during highly productive events with elevated seawater DMS concentrations. The major precursor for DMS is dimethylsulfoniopropionate (DMSP), an abundant compatible solute produced by many marine eukaryotes and prokaryotes. Despite its importance, knowledge of how, why and by what DMSP is produced is limited. For example, haptophytes and dinoflagellates typically produce 50-100 times more DMSP per unit chl than diatoms and prochlorophytes - yet the relevant enzymes have until recently been poorly characterised, limiting our understanding. Furthermore, although the DMSP synthesis genes and their transcripts are widespread in surface ocean bacterial communities, the contribution by this group of organisms to total DMSP production is so far unquantified.

Here, we explore the diversity and expression of functional DMSP synthesis and lyase genes alongside DMS/P biogeochemical states and rates over a spring-summer time series (March – July 2021) at an established time series station in temperate shelf sea waters, to characterise the biological drivers of DMSP and DMS production.

DMSP concentrations ranged from <5 nmol L^-1 to 160 nmol L^-1, with peaks in mid April and late June. The April peak coincided with significant increases in the transcription of eukaryotic DMSP biosynthesis genes. As the season progressed, the eukaryotic transcripts fell dramatically, whilst an increase in transcription of prokaryotic (cyanobacterial) DMSP biosynthesis genes was observed. DMS concentrations in the spring/summer productive period were characterised by three sharp peaks in early May (27 nmol L^‑1), early June (13 nmol L^-1) and late June (20 nmol L^-1)_,interspersed with lower concentrations of ~2 - 6nmol L^-1. Each peak was associated with distinct prokaryotic community composition. Some relationships were observed between the DMS peaks and the transcription of eukaryotic DMS production genes and prokaryotic DMS degradation genes, demonstrating the fine balance of processes which determine net DMS production in the surface ocean.  Overall, we observed that both eukaryotic and prokaryotic autotrophs significantly contributed to seasonal variation in DMSP production in these temperate waters.

How to cite: Hopkins, F., Airs, R., Williams, B., Ma, Q., Zhu, X., and Todd, J.: Seasonal DMSP production dynamics in temperate waters driven by significant contributions from both eukaryotic and prokaryotic autotrophs, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15168, https://doi.org/10.5194/egusphere-egu23-15168, 2023.

Carbon disulfide (CS2) is one of the most important precursors for atmospheric carbonyl sulphide (OCS), a climate relevant trace gas that can serve as a proxy to quantify terrestrial gross primary production. Currently, limited understanding of the production and consumption processes of CS2 in seawater preclude quantifying its marine emissions, which pose major uncertainties in the atmospheric budget of both OCS and CS2. Here we present controlled incubation experiments with natural dissolved organic matter (DOM) from three different oceanic locations, with and without UV light treatment. We show for the first time that in addition to its photochemical production, CS2 is also naturally degraded by UV light. CS2 is also produced in the dark: while the mechanism of this light independent production process is currently unknown, we show that dark production rates scale with the amount of organic sulphur present in DOM. Our results help to disentangle production and consumption processes of CS2 in seawater, in order to facilitate the interpretation of field measurements and ultimately enable modelling approaches.

How to cite: Lennartz, S., Simon, H., Booge, D., Zhou, L., Dittmar, T., and Marandino, C.: Carbon disulphide in the spotlight: UV-dependent production and consumption processes in seawater and their impact on oceanic emissions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9269, https://doi.org/10.5194/egusphere-egu23-9269, 2023.