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Natural aerosols are an important, yet understudied, part of the Arctic climate system. Natural marine biogenic aerosol components (e.g., methanesulfonic acid, MSA) are becoming increasingly important due to changing environmental conditions. In this study, we combine in situ aerosol observations with atmospheric transport modeling and meteorological reanalysis data in a data-driven framework with the aim to (1) identify the seasonal cycles and source regions of MSA, (2) elucidate the relationships between MSA and atmospheric variables, and (3) project the response of MSA based on trends extrapolated from reanalysis variables and determine which variables are contributing to these projected changes. We have identified the main source areas of MSA to be the Atlantic and Pacific sectors of the Arctic. Using gradient-boosted trees, we were able to explain 84% of the variance and find that the most important variables for MSA are indirectly related to either the gas- or aqueous-phase oxidation of dimethyl sulfide (DMS): shortwave and longwave downwelling radiation, temperature, and low cloud cover. We project MSA to undergo a seasonal shift, with non-monotonic decreases in April/May and increases in June-September, over the next 50 years. Different variables in different months are driving these changes, highlighting the complexity of influences on this natural aerosol component. Although the response of MSA due to changing oceanic variables (sea surface temperature, DMS emissions, and sea ice) and precipitation remains to be seen, here we are able to show that MSA will likely undergo a seasonal shift solely due to changes in atmospheric variables. [ABSTRACT FROM AUTHOR]

As part of the "East Antarctic International Ice Sheet Traverse" (EAIIST) project, surface snow and snow pit samples were collected along a traverse from Dome C toward the geographic South Pole during the 2019–2020 Antarctic campaign. Results on spatial distribution of major ions are here reported to understand deposition and post deposition processes in sites with very low snow accumulation rate in the East Antarctic Plateau where megadune and wind crust areas are present. The volcanic signature of Pinatubo eruption (occurred in 1991) was clearly visible in the non-sea salt SO42− stratigraphy from two snow pits (AGO-5 and PALEO) allowing the determination of annual accumulation rates that revealed to be 25.7 and 22.6 mm of water equivalent/year, respectively at the two sites. Moreover, a decreasing trend in accumulation rate as the distance from the Indian Ocean increases was detected. Mineral dust concentration and size show presence of a criptotephra layer in AGO5 and PALEO stratigraphies which is stratigraphically compatible with the deposition of volcanic ash related to the Puyehue-Cordón Caulle explosive eruption occurred in June 2011. The ssNa+ fraction, accounting for the 92.5 % of the total Na+, is preserved stably in the snow layers and was chosen as marker of sea spray deposition. Despite the very low accumulation rate in this area, the main deposition process of sea spray aerosol is the wet deposition. Conversely, both biogenic and crustal nssSO42− are dry deposited, the total flux of nssSO42− resulted to be constant in the Antarctic plateau, but the biogenic to crustal ratio increases as distance from Dome C increases. The presence and quantification (by nssCa2+) of a dry deposited crustal source, as the biogenic one, sheds light on the interpretation of nssSO42− biogenic stratigraphy during glacial and interglacial time in Antarctic ice cores. NssCl− represent the fraction of Cl− deposited as HCl and arises from the exchange reactions between chloride in the sea salt aerosol and acidic species such as H2SO4 and HNO3 that occurs both into the atmosphere (in this case HCl is deposited by wet deposition) and into the snow (at the expenses of NaCl or MgCl2 deposited as sea salt aerosol). The latter process could be particularly efficient in sites affected by wind crust formation, probably because of a longer exposure time of the snow layers to the atmosphere favouring the HCl volatilization. Another important marker in ice core is HNO3, that in the considered sites is found at very high concentration in the most superficial 3 cm of snow due to the uptake by superficial snow and possibly concentration effects from the layers beneath, but it is reversibly deposited. The depth of the active layer for HNO3 reemission was calculated and it spans from 22 cm to 12 cm; in addition, the concentration preserved in the snow decreases as the accumulation rate decreases, but wind scouring increases the efficiency of re-emission processes in the active layer. The knowledge and quantification of all the above reported processes will allow the interpretation of the ice core stratigraphies in low accumulation site likely hopefully recording, at selected sites, the climate history of more than one million years ago. [ABSTRACT FROM AUTHOR]

Ice nucleating particles (INPs) initiate primary ice formation in Arctic mixed-phase clouds (MPCs), altering cloud radiative properties and modulating precipitation. For atmospheric INPs, the complexity of their spatiotemporal variations, heterogeneous sources and evolution via intricate atmospheric interactions challenge the understanding of their impact on microphysical processes in Arctic MPCs and induce an uncertain representation in climate models. In this work, we performed a comprehensive analysis of atmospheric aerosols at the Arctic coastal site in Ny-Ålesund (Svalbard, Norway) from October to November 2019, including their ice nucleation ability, physicochemical properties and potential sources. Overall, INP concentrations NINP) during the observation season were approximately up to three orders of magnitude lower compared to the global average, with several samples showing degradation of NINP after heat treatment, implying the presence of proteinaceous INPs. Particle fluorescence was substantially associated with INP concentrations at warmer ice nucleation temperatures, indicating that in the far-reaching Arctic, aerosols of biogenic origin throughout the snow- and ice-free season may serve as important INP sources. In addition, case studies revealed the links between elevated NINP to heat-lability, fluorescence, high wind speeds originating from the ocean, augmented concentration of coarse-mode particles and abundant organics. Backward trajectory analysis demonstrated a potential connection between high-latitude dust sources and high INP concentrations, while prolonged air mass history over the ice pack was identified for most scant INP cases. The combination of the above analyses demonstrates the abundance, physicochemical properties and potential sources of INPs in the Arctic are highly variable despite its remote location. [ABSTRACT FROM AUTHOR]

The main purpose of this work is to propose a mechanism of post-depositional processes affecting chlorine and its chlorine-36 cosmogenic nuclide in the upper snowpack of the High Antarctic Plateau. We suggest that the observed decrease of total chlorine content in the upper meters of the snowpack is due to a progressive release of the HCl content from ice. We also propose a consistent framework, combining diffusion in bulk ice and snow microstructure. The observation of the low chlorine content in ice at depth leads to the robust hypothesis that the chemical equilibrium of chlorine between the ice and the snowpack interstitial air (SIA) is close to zero. HCl is thought to diffuse in ice, and to be progressively released in the SIA, and exported to the Antarctic atmosphere by the wind-ventilation. The time required to expel all the mobile species of chlorine (i.e., HCl) from snow depends on the diffusion coefficient of chlorine in ice combined with the snow grain size and its evolution with depth. This work is synthesised in a model combining the microstructure evolution of the upper meters of a snowpack (changes in mean snow grain size) and the diffusion of chlorine in ice applied to single spherical grains. The variability observed in chloride concentration profiles with depth, at a same site but different sampling time or different snow pits, or among different sites of the High Antarctic Plateau, is mostly due to the variations in initial concentrations in HCl and sodium chloride (NaCl) species and the snow grain size evolution. This model offers a common framework for understanding the fate of chlorine in Antarctica, from coastal to inland locations, including low accumulation sites on the plateau, far from the ocean. Applications of this post-depositional model to chlorine and to 36Cl allows to picture a recycling mechanism of chlorine at the scale of Antarctica. In particular, the 36Cl concentration in the surface snow of the Vostok site illustrates this recycling mechanism and the persistent contamination of inland Antarctica by anthropogenic 36Cl originating from the marine nuclear tests of the 1950s to the 1970s. [ABSTRACT FROM AUTHOR]

Large volcanic eruptions occurring in the last glacial period can be detected by their accompanying sulfuric acid deposition in continuous ice cores. Here we employ continuous sulfate and sulfur records from three Greenland and three Antarctic ice cores to estimate the emission strength, the frequency and the climatic forcing of large volcanic eruptions that occurred during the second half of the last glacial period and the early Holocene, 60–9 kyr before 2000 CE (b2k). Over most of the investigated interval the ice cores are synchronized, making it possible to distinguish large eruptions with a global sulfate distribution from eruptions detectable in one hemisphere only. Due to limited data resolution and large variability in the sulfate background signal, particularly in the Greenland glacial climate, we only list Greenland sulfate depositions larger than 20 kgkm-2 and Antarctic sulfate depositions larger than 10 kgkm-2. With those restrictions, we identify 1113 volcanic eruptions in Greenland and 737 eruptions in Antarctica within the 51 kyr period – for which the sulfate deposition of 85 eruptions is found at both poles (bipolar eruptions). Based on the ratio of Greenland and Antarctic sulfate deposition, we estimate the latitudinal band of the bipolar eruptions and assess their approximate climatic forcing based on established methods. A total of 25 of the identified bipolar eruptions are larger than any volcanic eruption occurring in the last 2500 years, and 69 eruptions are estimated to have larger sulfur emission strengths than the Tambora, Indonesia, eruption (1815 CE). Throughout the investigated period, the frequency of volcanic eruptions is rather constant and comparable to that of recent times. During the deglacial period (16–9 kab2k), however, there is a notable increase in the frequency of volcanic events recorded in Greenland and an obvious increase in the fraction of very large eruptions. For Antarctica, the deglacial period cannot be distinguished from other periods. This confirms the suggestion that the isostatic unloading of the Northern Hemisphere (NH) ice sheets may be related to the enhanced NH volcanic activity. Our ice-core-based volcanic sulfate records provide the atmospheric sulfate burden and estimates of climate forcing for further research on climate impact and understanding the mechanism of the Earth system. [ABSTRACT FROM AUTHOR]

We examined the relationships linking atmospheric in-situ data of gas phase methane sulfonic acid (CH3SO3H, MSA), sulfuric acid (H2SO4, SA), iodic acid (HIO3), highly oxidized organic molecules (HOM) and aerosol particle concentrations in the size ranges of 10?50 nm and 100?450 nm with satellite-derived chlorophyll a (Chl-a) and oceanic primary production (PP) during two time spans – the phytoplankton early bloom period, April-May 2017 (30 March?1 June, springtime) and phytoplankton late bloom; June?July 2017 (2 June?4 August, summertime) – in two ocean domains; Greenland Sea and Barents Sea. Atmospheric data were collected at Ny-Ålesund site in Svalbard, Norway. In general, Chl-a and PP in the Barents Sea were higher than in the Greenland Sea during the April?May period, whereas the Greenland Sea had higher Chl-a and PP during June?July. Phytoplankton bloom started by the loss of sea ice coverage in the Barents Sea at the marginal ice zone (MIZ) during April?May, and in the Greenland Sea close to Svalbard Island during June?July. From the April?May period to the June?July period, the correlation between the ocean color data (Chl-a and PP) and MSA decreased in the Barents Sea and increased in the Greenland Sea, which establishes a direct relationship between the sea ice melting, phytoplankton bloom and atmospheric vapour composition. Both MSA and SA concentrations increased strongly during the bloom period, suggesting marine phytoplankton metabolism and resulting dimethyl sulphide (DMS) as the primary source of both MSA and SA in the Arctic atmosphere during spring–summer time. The highest correlation among all the atmospheric components and ocean color properties was observed between HIO3 and Chl-a in both ocean domains during the springtime, but this feature may be connected to processes associated with the melting of sea ice. HOMs showed a low correlation with Chl-a and PP in comparison to other atmospheric vapours. The plausible explanation for such low correlation is that the primary source of volatile organic compounds (VOC) – precursors of HOM – is the soil or terrestrial vegetation of Svalbard archipelago rather than the ocean. In springtime, small-particles (10-50 nm) correlated strongly with Chl-a in the Barents Sea and with PP in both oceanic domains, suggesting that biogenic productivity has a strong impact on new particle formation (NPF) in the springtime. In the summertime, small-particle concentrations showed almost no correlation with biogenic parameters, indicating that compounds not connected with phytoplankton metabolism, such as HOMs, have a critical role in summertime NPF. Larger particles (100?450 nm) showed an anti-correlation with Chl-a and PP in springtime, probably due to dilution of anthropogenic air pollution (arctic haze) during spring. In the end of the Arctic haze period in April, particle-phase SA (non-sea-salt sulphate, ?????? - ????42-) and particle phase MSA (MS-) showed almost no correlation, whereas a connection between the gas phase MSA and SA concentrations was found. The likely reason for this is the same origin for gas phase MSA and SA (DMS oxidation), whereas SA in particle phase mostly originated from a long-distance continental source. [ABSTRACT FROM AUTHOR]