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  • 1. Anhaus, P.
    et al.
    Katlein, C.
    Nicolaus, M.
    Hoppmann, M.
    Haas, C.
    From Bright Windows to Dark Spots: Snow Cover Controls Melt Pond Optical Properties During Refreezing2021In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 48, no 23Article in journal (Refereed)
    Abstract [en]

    Melt ponds have a strong impact on the Arctic surface energy balance and the ice-associated ecosystem because they transmit more solar radiation compared to bare ice. In the existing literature, melt ponds are considered as bright windows to the ocean, even during freeze-up in autumn. In the central Arctic during the summer-autumn transition in 2018, we encountered a situation where more snow accumulated on refrozen melt ponds compared to the adjacent bare ice, leading to a reduction in light transmittance of the ponds even below that of bare ice. Results from a radiative transfer model support this finding. This situation has not been described in the literature before, but has potentially strong implications for example on autumn ecosystem activity, oceanic heat budget, and thermodynamic ice growth.

  • 2.
    Anhaus, Philipp
    University of Bremen.
    Impacts of snow and surface conditions on radiation fluxes through Arctic sea ice during different seasons2022Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Sea ice and its snow cover play a key role within the climate and ecosystem. Due to global environmental changes which are amplifed in the Arctic Ocean, its sea-ice cover will primarily consist of thin and young sea ice with a reduction in extent. In particular, the area where snow accumulates reduces and the fraction of melt-pond covered sea ice and of openings in the sea-ice cover such as leads increase. Those changes of the surface conditions strongly influence the partitioning of solar radiation. The main objective of this dissertation was to establish relationships between the surface conditions that are observed and expected to dominate in the future Arctic and under-ice radiation. A deeper and broad knowledge of such relationships is especially necessary in spring and autumn during which the under-ice radiation can have significant impacts on the annual energy budget. To achieve that, field measurements collected using a variety of instruments during three campaigns for three different sea-ice types, locations, and seasons were analysed and interpreted. A main result was to derive a new parametrization for snow depth retrieval from spectral under-ice radiation measurements. This was successfully achieved with an accuracy of approximately 5 cm for two ice types, in two locations, during two seasons. In contrast to the established theory that melt ponds act as bright windows to the underlying ocean, it was possible to document and analyse cases where a thicker snow cover accumulated on melt ponds compared to on adjacent bare ice. This resulted, surprisingly, in lower levels of under-ice radiation underneath the melt ponds than underneath bare ice. New analyses of relationships between thermodynamics and optics of a refreezing lead and thin ice suggest that radiative transfer in thin ice is often not accurately accounted for using bulk formulations, as they are applicable for thicker ice. The initial states of the lead’s opening and refreezing need to be treated separately and cannot generally be considered windows into the ocean. This dissertation extended our knowledge of the relationships between snow and surface conditions and under-ice radiation. The results point towards impacts on sea-ice energy balance, ocean heat content, thermodynamic ice growth, and ice-and ocean-associated ecosystem activity

  • 3. Anhaus, Philipp
    et al.
    Katlein, Christian
    Nicolaus, Marcel
    Arndt, Stefanie
    Jutila, Arttu
    Haas, Christian
    Snow Depth Retrieval on Arctic Sea Ice Using Under-Ice Hyperspectral Radiation Measurements2021In: Frontiers in Earth Science, E-ISSN 2296-6463, Vol. 9Article in journal (Refereed)
    Abstract [en]

    Radiation transmitted through sea ice and snow has an important impact on the energy partitioning at the atmosphere-ice-ocean interface. Snow depth and ice thickness are crucial in determining its temporal and spatial variations. Under-ice surveys using autonomous robotic vehicles to measure transmitted radiation often lack coincident snow depth and ice thickness measurements so that direct relationships cannot be investigated. Snow and ice imprint distinct features on the spectral shape of transmitted radiation. Here, we use those features to retrieve snow depth. Transmitted radiance was measured underneath landfast level first-year ice using a remotely operated vehicle in the Lincoln Sea in spring 2018. Colocated measurements of snow depth and ice thickness were acquired. Constant ice thickness, clear water conditions, and low in-ice biomass allowed us to separate the spectral features of snow. We successfully retrieved snow depth using two inverse methods based on under-ice optical spectra with 1) normalized difference indices and 2) an idealized two-layer radiative transfer model including spectral snow and sea ice extinction coefficients. The retrieved extinction coefficients were in agreement with previous studies. We then applied the methods to continuous time series of transmittance and snow depth from the landfast first-year ice and from drifting, melt-pond covered multiyear ice in the Central Arctic in autumn 2018. Both methods allow snow depth retrieval accuracies of approximately 5 cm. Our results show that atmospheric variations and absolute light levels have an influence on the snow depth retrieval.

  • 4. Baccarini, Andrea
    et al.
    Karlsson, Linn
    Dommen, Josef
    Duplessis, Patrick
    Vüllers, Jutta
    Brooks, Ian M.
    Saiz-Lopez, Alfonso
    Salter, Matthew
    Tjernström, Michael
    Baltensperger, Urs
    Zieger, Paul
    Schmale, Julia
    Frequent new particle formation over the high Arctic pack ice by enhanced iodine emissions2020In: Nature Communications, E-ISSN 2041-1723, Vol. 11, no 1Article in journal (Refereed)
    Abstract [en]

    In the central Arctic Ocean the formation of clouds and their properties are sensitive to the availability of cloud condensation nuclei (CCN). The vapors responsible for new particle formation (NPF), potentially leading to CCN, have remained unidentified since the first aerosol measurements in 1991. Here, we report that all the observed NPF events from the Arctic Ocean 2018 expedition are driven by iodic acid with little contribution from sulfuric acid. Iodic acid largely explains the growth of ultrafine particles (UFP) in most events. The iodic acid concentration increases significantly from summer towards autumn, possibly linked to the ocean freeze-up and a seasonal rise in ozone. This leads to a one order of magnitude higher UFP concentration in autumn. Measurements of cloud residuals suggest that particles smaller than 30 nm in diameter can activate as CCN. Therefore, iodine NPF has the potential to influence cloud properties over the Arctic Ocean.

  • 5. GM, Showalter
    et al.
    JW, Deming
    Extracellular enzyme activity of model cold-adapted bacteria and Arctic sea-ice microbial communities under subzero hypersaline conditions2021In: Aquatic Microbial Ecology, Vol. 87, p. 99-111Article in journal (Refereed)
    Abstract [en]

    Bacterially produced extracellular enzymes (EEs) play an important role in the cycling of organic matter in the marine environment, breaking down large compounds to those small enough to be transported across the cell membrane. EEs may play an especially important role within the brines of sea ice, as freezing concentrates both bacteria and organic materials into brine pockets, leading to higher encounter rates between EEs and their substrates. However, whether EEs are able to perform under the extreme conditions of sea-ice brines, particularly during winter, is unknown. Here, we characterized EE activity (EEA) of leucine aminopeptidase produced by the psychrophilic bacterium Colwellia psychrerythraea strain 34H and the cold-tolerant Psychrobacter strain 7E, under analogue sea-ice conditions using a standard fluorescence-based activity assay. EEs produced by the psychrophile were active at the most extreme conditions tested, i.e. temperature of -8°C and salt concentration of 120 ppt, with activity enhanced if the EEs concerned were produced under subzero hypersaline conditions. EEs produced by the Psychrobacter strain were less cold- and salt-active. When high-latitude Arctic samples of sea-ice brine, under-ice water, and the sea-surface microlayer were analyzed using the same assay after a freeze-thaw cycle, EEA was highest in the sea-ice samples, with activity at -10°C and salinity of 142 ppt. Overall, these results indicate that EEA can contribute to the degradation of organic material in sea ice through winter, likely sustaining microbial communities in brine pores in the process and altering the nature of organic material released at spring melt.

  • 6. Karlsson, Linn
    et al.
    Baccarini, Andrea
    Duplessis, Patrick
    Baumgardner, Darrel
    Brooks, Ian M.
    Chang, Rachel Y.-W.
    Dada, Lubna
    Dällenbach, Kaspar R.
    Heikkinen, Liine
    Krejci, Radovan
    Leaitch, W. Richard
    Leck, Caroline
    Partridge, Daniel G.
    Salter, Matthew E.
    Wernli, Heini
    Wheeler, Michael J.
    Schmale, Julia
    Zieger, Paul
    Physical and Chemical Properties of Cloud Droplet Residuals and Aerosol Particles During the Arctic Ocean 2018 Expedition2022In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 127, no 11Article in journal (Refereed)
    Abstract [en]

    Detailed knowledge of the physical and chemical properties and sources of particles that form clouds is especially important in pristine areas like the Arctic, where particle concentrations are often low and observations are sparse. Here, we present in situ cloud and aerosol measurements from the central Arctic Ocean in August-September 2018 combined with air parcel source analysis. We provide direct experimental evidence that Aitken mode particles (particles with diameters ≤70 nm) significantly contribute to cloud condensation nuclei (CCN) or cloud droplet residuals, especially after the freeze-up of the sea ice in the transition toward fall. These Aitken mode particles were associated with air that spent more time over the pack ice, while size distributions dominated by accumulation mode particles (particles with diameters ≥70 nm) showed a stronger contribution of oceanic air and slightly different source regions. This was accompanied by changes in the average chemical composition of the accumulation mode aerosol with an increased relative contribution of organic material toward fall. Addition of aerosol mass due to aqueous-phase chemistry during in-cloud processing was probably small over the pack ice given the fact that we observed very similar particle size distributions in both the whole-air and cloud droplet residual data. These aerosol-cloud interaction observations provide valuable insight into the origin and physical and chemical properties of CCN over the pristine central Arctic Ocean.

  • 7. Katlein, C.
    et al.
    Valcic, L.
    Lambert-Girard, S.
    Hoppmann, M.
    New insights into radiative transfer within sea ice derived from autonomous optical propagation measurements2021In: The Cryosphere, Vol. 15, no 1, p. 183-198Article in journal (Refereed)
    Abstract [en]

    The radiative transfer of shortwave solar radiation through the sea ice cover of the polar oceans is a crucial aspect of energy partitioning at the atmosphere–ice–ocean interface. A detailed understanding of how sunlight is reflected and transmitted by the sea ice cover is needed for an accurate representation of critical processes in climate and ecosystem models, such as the ice–albedo feedback. Due to the challenges associated with ice internal measurements, most information about radiative transfer in sea ice has been gained by optical measurements above and below the sea ice. To improve our understanding of radiative transfer processes within the ice itself, we developed a new kind of instrument equipped with a number of multispectral light sensors that can be frozen into the ice. A first prototype consisting of a 2.3 m long chain of 48 sideward planar irradiance sensors with a vertical spacing of 0.05 m was deployed at the geographic North Pole in late August 2018, providing autonomous, vertically resolved light measurements within the ice cover during the autumn season. Here we present the first results of this instrument, discuss the advantages and application of the prototype, and provide first new insights into the spatiotemporal aspect of radiative transfer within the sea ice itself. In particular, we investigate how measured attenuation coefficients relate to the optical properties of the ice pack and show that sideward planar irradiance measurements are equivalent to measurements of total scalar irradiance.

  • 8. Katlein, Christian
    An open-source albedo-wand for the measurement of sea ice albedo2019In: Advances in polar science, ISSN 1674-9928, Vol. 30, no 2, p. 106-117Article in journal (Refereed)
    Abstract [en]

    Surface albedo is defined as the ratio of incident and reflected solar irradiance and describes the ability of a surface to reflect, rather than absorb incident solar shortwave radiation. It is thus a crucial parameter in the climate system, particularly in the polar oceans. Sea ice albedo is a main driver for light transmission into the polar oceans and thus has a high impact on ocean warming, ice melting and marine primary production. During spring and summer, sea ice albedo can exhibit a significant spatial variability caused by meltwater accumulations on the ice. While complex and expensive solutions for albedo measurements are already available, we want to present a simple open-source design that allows for affordable mapping of spatially varying surface albedo on sea ice and beyond. Our solution is based on off-the-shelf components, such as an Arduino microcontroller integrating affordable light sensors, a GPS unit, data recording on memory card and data display into a simple field strengthened unit. We provide example data from two Arctic field deployments showing the capabilities and limitations of this system.

  • 9. Katlein, Christian
    et al.
    Labaste, Matthieu
    Hoppmann, Mario
    Manual Recovery of a Sea Ice Based Ocean Profiler2019In: Frontiers in Marine Science, E-ISSN 2296-7745, Vol. 6Article in journal (Refereed)
    Abstract [en]

    Ice-tethered ocean profiling systems are an essential tool for the year-round observation of physical and biogeochemical properties of the Arctic Ocean. Despite being considered expendable equipment due to the challenging logistics, their recovery is attractive mainly due to two factors: If the sensors can be retrieved, this allows for their post calibration, which helps to assess sensor drift and biofouling. In addition, the recovery of such expensive equipment can ease off financial pressure on autonomous ocean observation programs by enabling the reuse of central elements after refurbishment. Here we present a method how such profiling systems can be recovered from sea ice by 3 people in about 4 h, without the on-site availability of a fully-equipped vessel. The presented technique combines rope techniques from mountain rescue applications with lightweight equipment and procedures similar to those used for the deployment of such instruments. We provide a detailed description of the whole process, provide suggestions for potential improvements as well as suggestions toward improved instrument design favoring recoverability of future deployments. We conclude that good preparation and practice of the relevant rope procedures is critical to mission success and that a well-selected range of necessary equipment makes the process much more efficient.

  • 10. Lawler, M. J.
    et al.
    Saltzman, E. S.
    Karlsson, L.
    Stockholm Univ, Dept Environm Sci, Stockholm, Sweden.
    Zieger, Paul
    Stockholms universitet, Institutionen för miljövetenskap.
    Salter, Matthew E.
    Stockholms universitet, Institutionen för miljövetenskap.
    Baccarini, A.
    Schmale, J.
    Leck, Caroline
    Stockholms universitet, Meteorologiska institutionen (MISU).
    New Insights Into the Composition and Origins of Ultrafine Aerosol in the Summertime High Arctic2021In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 48, no 21, article id e2021GL094395Article in journal (Refereed)
    Abstract [en]

    The summertime high Arctic atmosphere is characterized by extremely low aerosol abundance, such that small natural aerosol inputs have a strong influence on cloud formation and surface temperature. The physical sources and the mechanisms responsible for aerosol formation and development in this climate-critical and changing region are still uncertain. We report time-resolved measurements of high Arctic Aitken mode (∼20–60 nm diameter) aerosol composition during August–September 2018. During a significant Aitken mode formation event, the particles were composed of a combination of primary and secondary materials. These results highlight the importance of primary aerosol sources for high Arctic cloud formation, and they imply the action of a poorly understood atmospheric mechanism separating larger particles into multiple sub-particles.

  • 11. Leck, Caroline
    et al.
    Matrai, Patricia
    Perttu, Anna-Maria
    Gårdfeldt, Katarina
    Expedition report: SWEDARTIC Arctic Ocean 20182019Report (Other academic)
    Abstract [en]

    The expedition Arctic Ocean 2018 with the icebreaker I/B Oden was conducted by the Swedish Polar Research Secretariat in collaboration with National Science Foundation. The main theme for the research was the “Life cycle of clouds in the high Arctic summer with linkages to the microbial life in ocean and ice”.To obtain the best circumstances, I/BO den sailed into the High Arctic where the ship, logistics and scientific staff scouted for asuitable ice floe to sample from. I/B Oden was moored to this floe for approx. 5 weeks in mid-August 2018 such that the scientific work could cover the minimum ice extent period and, most importantly, the refreezing processes. Arctic Ocean 2018 used 5 work packages (WP) to achieve the stated aims of understanding the controlling factors of the proposed negative feedback involving micro-organism and clouds over the Arctic pack ice area. This 5 WP grouping reflects the outcome of the 2 science workshops held prior to the expedition and agreed upon by the participating scientists at the time. WP1: Meteorology and vertical profiling WP2: In-situ characterization of ambient gases, aerosols and clouds WP3: Air-sea interaction WP4: Sea surface microlayer composition WP5: Physics, microbiology and biogeochemistry of ocean water and ice.

    Download full text (pdf)
    Expedition report Arctic Ocean 2018
  • 12. Naakka, T.
    et al.
    Nygård, T.
    Tjernström, Michael
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Vihma, T.
    Pirazzini, R.
    Brooks, I. M.
    The Impact of Radiosounding Observations on Numerical Weather Prediction Analyses in the Arctic2019In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 14, p. 8527-8535Article in journal (Refereed)
    Abstract [en]

    The radiosounding network in the Arctic, despite being sparse, is a crucial part of the atmospheric observing system for weather prediction and reanalysis. The spatial coverage of the network was evaluated using a numerical weather prediction model, comparing radiosonde observations from Arctic land stations and expeditions in the central Arctic Ocean with operational analyses and background fields (12-hr forecasts) from European Centre for Medium-Range Weather Forecasts for January 2016 to September 2018. The results show that the impact of radiosonde observations on analyses has large geographical variation. In data-sparse areas, such as the central Arctic Ocean, high-quality radiosonde observations substantially improve the analyses, while satellite observations are not able to compensate for the large spatial gap in the radiosounding network. In areas where the network is reasonably dense, the quality of background field is more related to how radiosonde observations are utilized in the assimilation and to the quality of those observations.

  • 13. Nghiem, S. V.
    et al.
    Kirpes, R. M.
    Liu, J.
    Pratt, K. A.
    Matrai, P.
    Grannas, A.
    Wernli, H.
    Observations of Arctic Sea Ice Leads and Open Water During the Microbiological-Ocean-Cloud Coupling in the High Arctic Campaign2020In: IGARSS 2020 - 2020 IEEE International Geoscience and Remote Sensing Symposium, 2020, p. 3023-3026Conference paper (Refereed)
    Abstract [en]

    The Microbiological-Ocean-Cloud Coupling in the High Arctic (MOCCHA) campaign was conducted during August-September 2018 to examine the coupling between the changing High Arctic surface and atmospheric composition, including the production of sea spray aerosols (SSA) from sea ice leads. Sentinel-1 satellite SAR data are used for observations of sea ice leads and open water where SSA may originate due to wind forcing. Results from selected Sentinel-1 SAR scenes show that sea ice leads and open water areas can be identified with co-polarized backscatter at larger incidence angles while water misclassification occurs at smaller incidence due to stronger surface scattering. In contrast, the cross-polarized backscatter remains low at low and high incidence angles. Melt on sea ice during the MOCCHA summertime can confound backscatter signatures that misidentify open sea water. Future analyses can be improved using SARs in synergy with other satellite sensors.

  • 14. Nicolaus, Marcel
    et al.
    Hoppmann, Mario
    Arndt, Stefanie
    Hendricks, Stefan
    Katlein, Christian
    Nicolaus, Anja
    Rossmann, Leonard
    Schiller, Martin
    Schwegmann, Sandra
    Snow Depth and Air Temperature Seasonality on Sea Ice Derived From Snow Buoy Measurements2021In: Frontiers in Marine Science, E-ISSN 2296-7745, Vol. 8Article in journal (Refereed)
    Abstract [en]

    Snow depth on sea ice is an essential state variable of the polar climate system and yet one of the least known and most difficult to characterize parameters of the Arctic and Antarctic sea ice systems. Here, we present a new type of autonomous platform to measure snow depth, air temperature, and barometric pressure on drifting Arctic and Antarctic sea ice. "Snow Buoys" are designed to withstand the harshest environmental conditions and to deliver high and consistent data quality with minimal impact on the surface. Our current dataset consists of 79 time series (47 Arctic, 32 Antarctic) since 2013, many of which cover entire seasonal cycles and with individual observation periods of up to 3 years. In addition to a detailed introduction of the platform itself, we describe the processing of the publicly available (near real time) data and discuss limitations. First scientific results reveal characteristic regional differences in the annual cycle of snow depth: in the Weddell Sea, annual net snow accumulation ranged from 0.2 to 0.9 m (mean 0.34 m) with some regions accumulating snow in all months. On Arctic sea ice, the seasonal cycle was more pronounced, showing accumulation from synoptic events mostly between August and April and maxima in autumn. Strongest ablation was observed in June and July, and consistently the entire snow cover melted during summer. Arctic air temperature measurements revealed several above-freezing temperature events in winter that likely impacted snow stratigraphy and thus preconditioned the subsequent spring snow cover. The ongoing Snow Buoy program will be the basis of many future studies and is expected to significantly advance our understanding of snow on sea ice, also providing invaluable in situ validation data for numerical simulations and remote sensing techniques.

  • 15. Porter, G. C. E.
    et al.
    Sikora, S. N. F.
    Adams, M. P.
    Proske, U.
    Harrison, A. D.
    Tarn, M. D.
    Brooks, I. M.
    Murray, B. J.
    Resolving the size of ice-nucleating particles with a balloon deployable aerosol sampler: the SHARK2020In: Atmospheric Measurement Techniques, Vol. 13, no 6, p. 2905-2921Article in journal (Refereed)
    Abstract [en]

    Ice-nucleating particles (INPs) affect cloud development, lifetime, and radiative properties, hence it is important to know the abundance of INPs throughout the atmosphere. A critical factor in determining the lifetime and transport of INPs is their size; however very little size-resolved atmospheric INP concentration information exists. Here we present the development and application of a radio-controlled payload capable of collecting size-resolved aerosol from a tethered balloon for the primary purpose of offline INP analysis. This payload, known as the SHARK (Selective Height Aerosol Research Kit), consists of two complementary cascade impactors for aerosol size-segregation from 0.25 to 10 µm, with an after-filter and top stage to collect particles below and above this range at flow rates of up to 100 L min−1. The SHARK also contains an optical particle counter to quantify aerosol size distribution between 0.38 and 10 µm, and a radiosonde for the measurement of temperature, pressure, GPS altitude, and relative humidity. This is all housed within a weatherproof box, can be run from batteries for up to 11 h, and has a total weight of 9 kg. The radio control and live data link with the radiosonde allow the user to start and stop sampling depending on meteorological conditions and height, which can, for example, allow the user to avoid sampling in very humid or cloudy air, even when the SHARK is out of sight. While the collected aerosol could, in principle, be studied with an array of analytical techniques, this study demonstrates that the collected aerosol can be analysed with an offline droplet freezing instrument to determine size-resolved INP concentrations, activated fractions, and active site densities, producing similar results to those obtained using a standard PM10 aerosol sampler when summed over the appropriate size range. Test data, where the SHARK was sampling near ground level or suspended from a tethered balloon at 20 m altitude, are presented from four contrasting locations having very different size-resolved INP spectra: Hyytiälä (southern Finland), Leeds (northern England), Longyearbyen (Svalbard), and Cardington (southern England).

  • 16. Porter, Grace C. E.
    Ice-nucleating particles in the central Arctic2021Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A small subset of aerosol particles can induce ice-nucleation in supercooled liquid droplets. These ice-nucleating particles (INP) are responsible for the primary, heterogeneous nucleation of ice in clouds, and knowledge of their concentrations, sources and characteristics is necessary to accurately represent these mixed-phased clouds in models. This is particularly important in regions such as the central Arctic Ocean, where there are persistent mixed-phased clouds that help shape the radiative budget of the Arctic but very few measurements of INP, none of which are at cloud altitude. This thesis aimed to tackle the dearth of central Arctic INP data through the design and use of novel instrumentation, and a field campaign aboard an icebreaker which saw measurements of INP measurements made at both ship and cloud level close to the North Pole (88-90°N). Firstly, a high-volume, size-selective aerosol sampler capable of being deployed for hours at a time at altitudes and temperatures relevant for mixed phased clouds was designed and tested. This sampler was used on a 2-month campaign to the central Arctic ocean from August-September 2018, alongside ship-based INP measurements. The central Arctic INP concentrations at sea-level were highly variable, with concentrations as low as could be expected in the Southern Oceans, and as high as those measured in rural farmland. The INP were found to be heat-sensitive, and the most active samples originated from the Arctic coasts of Russia. The samples with the least INP activity were from the pack ice and Canadian Arctic. The concentrations measured at cloud-level were often decoupled from those at the surface, demonstrating the necessity for more airborne measurements of INP. Additionally, the INP at cloud-level were often smaller than expected, at <0.25 μm in aerodynamic diameter. Finally, in order to better probe the characteristics of sampled INP in the future, a microfluidic device capable of sorting ice crystals containing INP active at a specific temperature from the bulk sample was developed.

  • 17. Porter, Grace C. E.
    et al.
    Adams, Michael P.
    Brooks, Ian M.
    Ickes, Luisa
    Karlsson, Linn
    Stockholms universitet, Institutionen för miljövetenskap.
    Leck, Caroline
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Salter, Matthew E.
    Stockholms universitet, Institutionen för miljövetenskap.
    Schmale, Julia
    Siegel, Karolina
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Sikora, Sebastien N. F.
    Tarn, Mark D.
    Vüllers, Jutta
    Wernli, Heini
    Zieger, Paul
    Stockholms universitet, Institutionen för miljövetenskap.
    Zinke, Julika
    Stockholms universitet, Institutionen för miljövetenskap.
    Murray, Benjamin J.
    Highly Active Ice-Nucleating Particles at the Summer North Pole2022In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 127, no 6, article id e2021JD036059Article in journal (Refereed)
    Abstract [en]

    The amount of ice versus supercooled water in clouds is important for their radiative properties and role in climate feedbacks. Hence, knowledge of the concentration of ice-nucleating particles (INPs) is needed. Generally, the concentrations of INPs are found to be very low in remote marine locations allowing cloud water to persist in a supercooled state. We had expected the concentrations of INPs at the North Pole to be very low given the distance from open ocean and terrestrial sources coupled with effective wet scavenging processes. Here we show that during summer 2018 (August and September) high concentrations of biological INPs (active at >−20°C) were sporadically present at the North Pole. In fact, INP concentrations were sometimes as high as those recorded at mid-latitude locations strongly impacted by highly active biological INPs, in strong contrast to the Southern Ocean. Furthermore, using a balloon borne sampler we demonstrated that INP concentrations were often different at the surface versus higher in the boundary layer where clouds form. Back trajectory analysis suggests strong sources of INPs near the Russian coast, possibly associated with wind-driven sea spray production, whereas the pack ice, open leads, and the marginal ice zone were not sources of highly active INPs. These findings suggest that primary ice production, and therefore Arctic climate, is sensitive to transport from locations such as the Russian coast that are already experiencing marked climate change.

  • 18.
    Prytherch, John
    et al.
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Yelland, M. J.
    Wind, Convection and Fetch Dependence of Gas Transfer Velocity in an Arctic Sea‐Ice Lead Determined From Eddy Covariance CO2 Flux Measurements2021In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 35, no 2, article id e2020GB006633Article in journal (Refereed)
    Abstract [en]

    The air‐water exchange of trace gases such as CO2 is usually parameterized in terms of a gas transfer velocity, which can be derived from direct measurements of the air‐sea gas flux. The transfer velocity of poorly soluble gases is driven by near‐surface ocean turbulence, which may be enhanced or suppressed by the presence of sea ice. A lack of measurements means that air‐sea fluxes in polar regions, where the oceanic sink of CO2 is poorly known, are generally estimated using open‐ocean transfer velocities scaled by ice fraction. Here, we describe direct determinations of CO2 gas transfer velocity from eddy covariance flux measurements from a mast fixed to ice adjacent to a sea‐ice lead during the summer‐autumn transition in the central Arctic Ocean. Lead water CO2 uptake is determined using flux footprint analysis of water‐atmosphere and ice‐atmosphere flux measurements made under conditions (low humidity and high CO2 signal) that minimize errors due to humidity cross‐talk. The mean gas transfer velocity is found to have a quadratic dependence on wind speed: k660 = 0.179 U102, which is 30% lower than commonly used open‐ocean parameterizations. As such, current estimates of polar ocean carbon uptake likely overestimate gas exchange rates in typical summertime conditions of weak convective turbulence. Depending on the footprint model chosen, the gas transfer velocities also exhibit a dependence on the dimension of the lead, via its impact on fetch length and hence sea state. Scaling transfer velocity parameterizations for regional gas exchange estimates may therefore require incorporating lead width data.

  • 19. Schanke, Nicole L.
    et al.
    Bolinesi, Francesco
    Mangoni, Olga
    Katlein, Christian
    Anhaus, Philipp
    Hoppmann, Mario
    Lee, Peter A.
    DiTullio, Giacomo R.
    Biogeochemical and ecological variability during the late summer-early autumn transition at an ice-floe drift station in the Central Arctic Ocean2020In: Limnology and Oceanography, Vol. n/a, no n/aArticle in journal (Refereed)
    Abstract [en]

    As the annual expanse of Arctic summer ice-cover steadily decreases, concomitant biogeochemical and ecological changes in this region are likely to occur. Because the Central Arctic Ocean is often nutrient and light limited, it is essential to understand how environmental changes will affect productivity, phytoplankton species composition, and ensuing changes in biogeochemistry in the region. During the transition from late summer to early autumn, water column sampling of various biogeochemical parameters was conducted along an ice-floe drift station near the North Pole. Our results show that as the upper water column stratification weakened during the late summer-early autumn transition, nutrient concentrations, particulate dimethylsulfoniopropionate (DMSPp) levels, photosynthetic efficiency, and biological productivity, as estimated by ΔO2/Ar ratios, all decreased. Chemotaxonomic (CHEMTAX) analysis of phytoplankton pigments revealed a taxonomically diverse picoautotrophic community, with chlorophyll (Chl) c3-containing flagellates and the prasinophyte, Pyramimonas spp., as the most abundant groups, comprising ∼30% and 20% of the total Chl a (TChl a) biomass, respectively. In contrast to previous studies, the picoprasinophyte, Micromonas spp., represented only 5% to 10% of the TChl a biomass. Of the nine taxonomic groups identified, DMSPp was most closely associated with Pyramimonas spp., a Chl b-containing species not usually considered a high DMSP producer. As the extent and duration of open, ice-free waters in the Central Arctic Ocean progressively increases, we suggest that enhanced light transmission could potentially expand the ecological niche of Pyramimonas spp. in the region.

  • 20.
    Showalter, Gordon Maxwell
    University of Washington.
    Acquisition, degradation, and cycling of organic matter within sea-ice brines by bacteria and their viruses2020Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Marine dissolved organic carbon (DOC) is a major component of the global carbon pool, and thus can have significant effects on global carbon cycling. Within the oceans, DOC is largely regulated by microbial communities, which can serve as both a source and sink of organic carbon. Microbial controls on DOC cycling within sea ice are especially relevant to global processes, as sea ice can act as an inhibitor of exchange between the ocean and the atmosphere while also affecting carbon export to the deep sea. However, how sea-ice communities influence DOCcycling, especially in very cold conditions of winter sea ice, is poorly understood. This dissertation explores how bacterial communities, which dominate winter sea ice, may influence DOC cycling. Chapter 1 presents an introduction of sea-ice microbial communities in the low-temperature, high salinity conditions which characterize sea-ice brines. How bacteria within brines swim in response to temperature, salinity, and chemical gradients in sea ice is presented in Chapter 2, which demonstrates a low-temperature record for directed bacterial swimming and suggests explanations for how bacteria position themselves within brines to accessDOC. However, most DOC within the marine environment is too large for bacterial uptake, necessitating degradation by enzymes. Chapter 3 demonstrates bacterial extracellular enzyme activity both in a laboratory setting and in situ, showing growth-dependent enzyme activity down to –8˚C and up to 142 ppt salts and across a freeze-thaw cycle within sea ice and sea-surface microlayer samples. Finally, Chapter 4 presents a model of bacterially and virally mediated DOCcycling. This model uses simple differential equations, explained further in Appendix 1, to probe the potential existence of a viral shunt within sea-ice brines by demonstrating the role of bacteriophage in population dynamics of a theoretical brine, suggesting low viral production, high host-specificity, and virally-driven DOC cycling may be common within this environment. The results of this dissertation have implications for the understanding of DOC within polar seas and demonstrate the potential for active DOC cycling mediated by bacteria and their viruses within winter sea ice, which serves as an analog for very cold ice elsewhere.

  • 21.
    Siegel, Karolina
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Chemical composition of summertime High Arctic aerosols2020Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents new insights into the chemical composition of semi-volatile compounds in aerosol samples collected in the central Arctic Ocean close to the North Pole in September 2018. The central Arctic Ocean is an inaccessible location due to the lack of land areas along with heavy pack ice conditions. Therefore, large knowledge gaps remain to understand the Arctic climate system, and in particular the role of aerosol particles in its pristine atmosphere.

    The chemical composition of the aerosol samples was analysed on a molecular level using High Resolution Time-of-Flight Chemical Ionization Mass Spectrometry coupled to a Filter Inlet for Gases and AEROsols (FIGAERO-HRToF-CIMS). The analysis revealed a significant signal from compounds that are likely from marine sources. One important precursor for marine aerosols is dimethyl sulfide (DMS), a gas released by phytoplankton and ice algae in the Arctic Ocean. DMS oxidises in the atmosphere to produce oxidation products that can contribute to aerosol growth. Analysis of air mass origin with backward trajectories showed that the highest ambient DMS concentrations originated from marine areas around the pack ice. However, no correlation could be shown within the pack ice between ambient DMS and its oxidation product methanesulfonic acid (MSA) in the particle phase.

    As FIGAERO-HRToF-CIMS is commonly used in areas with higher particle concentrations and has never been used in the central Arctic before, this thesis further demonstrates its suitability for measurements of aerosol chemical composition in this remote region.

  • 22. Siegel, Karolina
    et al.
    Karlsson, Linn
    Zieger, Paul
    Baccarini, Andrea
    Schmale, Julia
    Lawler, Michael
    Salter, Matthew
    Leck, Caroline
    Ekman, Annica M. L.
    Riipinen, Ilona
    Mohr, Claudia
    Insights into the molecular composition of semi-volatile aerosols in the summertime central Arctic Ocean using FIGAERO-CIMS2021In: Environ. Sci.: Atmos.Article in journal (Refereed)
    Abstract [en]

    The remote central Arctic during summertime has a pristine atmosphere with very low aerosol particle concentrations. As the region becomes increasingly ice-free during summer, enhanced ocean-atmosphere fluxes of aerosol particles and precursor gases may therefore have impacts on the climate. However, large knowledge gaps remain regarding the sources and physicochemical properties of aerosols in this region. Here, we present insights into the molecular composition of semi-volatile aerosol components collected in September 2018 during the MOCCHA (Microbiology-Ocean-Cloud-Coupling in the High Arctic) campaign as part of the Arctic Ocean 2018 expedition with the Swedish Icebreaker Oden. Analysis was performed offline in the laboratory using an iodide High Resolution Time-of-Flight Chemical Ionization Mass Spectrometer with a Filter Inlet for Gases and AEROsols (FIGAERO-HRToF-CIMS). Our analysis revealed significant signal from organic and sulfur-containing compounds, indicative of marine aerosol sources, with a wide range of carbon numbers and O:C ratios. Several of the sulfur-containing compounds are oxidation products of dimethyl sulfide (DMS), a gas released by phytoplankton and ice algae. Comparison of the time series of particulate and gas-phase DMS oxidation products did not reveal a significant correlation, indicative of the different lifetimes of precursor and oxidation products in the different phases. This is the first time the FIGAERO-HRToF-CIMS was used to investigate the composition of aerosols in the central Arctic. The detailed information on the molecular composition of Arctic aerosols presented here can be used for the assessment of aerosol solubility and volatility, which is relevant for understanding aerosol-cloud interactions.

  • 23.
    Siegel, Karolina
    et al.
    Stockholms universitet, Institutionen för miljövetenskap.
    Neuberger, Almuth
    Stockholms universitet, Institutionen för miljövetenskap.
    Karlsson, Linn
    Stockholms universitet, Institutionen för miljövetenskap.
    Zieger, Paul
    Stockholms universitet, Institutionen för miljövetenskap.
    Mattsson, Fredrik
    Stockholms universitet, Institutionen för miljövetenskap.
    Duplessis, Patrick
    Dada, Lubna
    Daellenbach, Kaspar
    Schmale, Julia
    Baccarini, Andrea
    Krejci, Radovan
    Stockholms universitet, Institutionen för miljövetenskap.
    Svenningsson, Birgitta
    Chang, Rachel
    Ekman, Annica M. L.
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Riipinen, Ilona
    Stockholms universitet, Institutionen för miljövetenskap.
    Mohr, Claudia
    Stockholms universitet, Institutionen för miljövetenskap.
    Using Novel Molecular-Level Chemical Composition Observations of High Arctic Organic Aerosol for Predictions of Cloud Condensation Nuclei2022In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 56, no 19, p. 13888-13899Article in journal (Refereed)
    Abstract [en]

    Predictions of cloud droplet activation in the late summertime (September) central Arctic Ocean are made using κ-Köhler theory with novel observations of the aerosol chemical composition from a high-resolution time-of-flight chemical ionization mass spectrometer with a filter inlet for gases and aerosols (FIGAERO-CIMS) and an aerosol mass spectrometer (AMS), deployed during the Arctic Ocean 2018 expedition onboard the Swedish icebreaker Oden. We find that the hygroscopicity parameter κ of the total aerosol is 0.39 ± 0.19 (mean ± std). The predicted activation diameter of ∼25 to 130 nm particles is overestimated by 5%, leading to an underestimation of the cloud condensation nuclei (CCN) number concentration by 4-8%. From this, we conclude that the aerosol in the High Arctic late summer is acidic and therefore highly cloud active, with a substantial CCN contribution from Aitken mode particles. Variability in the predicted activation diameter is addressed mainly as a result of uncertainties in the aerosol size distribution measurements. The organic κ was on average 0.13, close to the commonly assumed κ of 0.1, and therefore did not significantly influence the predictions. These conclusions are supported by laboratory experiments of the activation potential of seven organic compounds selected as representative of the measured aerosol.

  • 24. Tjernström, Michael
    et al.
    Svensson, Gunilla
    Magnusson, Linus
    Brooks, Ian M.
    Prytherch, John
    Vüllers, Jutta
    Young, Gillian
    Central Arctic Weather Forecasting: Confronting the ECMWF IFS with observations from the Arctic Ocean 2018 expedition2020In: Quarterly Journal of the Royal Meteorological Society, ISSN 1477-870X, Vol. 147, no 735, p. 1278-1299Article in journal (Refereed)
    Abstract [en]

    Forecasts with the European Centre for Medium-Range Weather Forecasts' numerical weather prediction model are evaluated using an extensive set of observations from the Arctic Ocean 2018 expedition on the Swedish icebreaker Oden. The atmospheric model (Cy45r1) is similar to that used for the ERA5 reanalysis (Cy41r2). The evaluation covers one month, with the icebreaker moored to drifting sea ice near the north pole; a total of 125 forecasts issued four times per day were used. Standard surface observations and 6-hourly soundings were assimilated to ensure that the initial model error is small. Model errors can be divided into two groups. First, variables related to dynamics feature errors that grow with forecast length; error spread also grows with time. Initial errors are small, facilitating a robust evaluation of the second group; thermodynamic variables. These feature fast error growth for 6-12 h, after which errors saturates; error spread is roughly constant. Both surface and near-surface air temperatures are too warm in the model. During the summer both are typically above zero in spite of the ongoing melt; however, the warm bias increases as the surface freezes. The warm bias is due to a too warm atmosphere; errors in surface sensible heat flux transfers additional heat from the atmosphere to the surface. The lower troposphere temperature error has a distinct vertical structure; a substantial warm bias in the lowest few 100 meters and a large cold bias around 1 km; this structure features a significant diurnal cycle and is tightly coupled to errors in the modeled clouds. Clouds appear too often and in a too deep layer of the lower atmosphere; the lowest clouds essentially never break up. The largest error in cloud presence is aligned with the largest cold bias at around 1 km.

  • 25. Torstensson, Anders
    et al.
    Margolin, Andrew R.
    Showalter, Gordon M.
    Smith Jr, Walker O.
    Shadwick, Elizabeth H.
    Carpenter, Shelly D.
    Bolinesi, Francesco
    Deming, Jody W.
    Sea-ice microbial communities in the Central Arctic Ocean: Limited responses to short-term pCO2 perturbations2021In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 66, no S1, p. S383-S400Article in journal (Refereed)
    Abstract [en]

    The Arctic Ocean is more susceptible to ocean acidification than other marine environments due to its weaker buffering capacity, while its cold surface water with relatively low salinity promotes atmospheric CO2 uptake. We studied how sea-ice microbial communities in the central Arctic Ocean may be affected by changes in the carbonate system expected as a consequence of ocean acidification. In a series of four experiments during late summer 2018 aboard the icebreaker Oden, we addressed microbial growth, production of dissolved organic carbon (DOC) and extracellular polymeric substances (EPS), photosynthetic activity, and bacterial assemblage structure as sea-ice microbial communities were exposed to elevated partial pressures of CO2 (pCO2). We incubated intact, bottom ice-core sections and dislodged, under-ice algal aggregates (dominated by Melosira arctica) in separate experiments under approximately 400, 650, 1000, and 2000μatm pCO2 for 10 d under different nutrient regimes. The results indicate that the growth of sea-ice algae and bacteria was unaffected by these higher pCO2 levels, and concentrations of DOC and EPS were unaffected by a shifted inorganic C/N balance, resulting from the CO2 enrichment. These central Arctic sea-ice microbial communities thus appear to be largely insensitive to short-term pCO2 perturbations. Given the natural, seasonally driven fluctuations in the carbonate system of sea ice, its resident microorganisms may be sufficiently tolerant of large variations in pCO2 and thus less vulnerable than pelagic communities to the impacts of ocean acidification, increasing the ecological importance of sea-ice microorganisms even as the loss of Arctic sea ice continues.

  • 26. Vüllers, J.
    et al.
    Achtert, P.
    Brooks, I. M.
    Tjernström, M.
    Prytherch, J.
    Burzik, A.
    Neely III, R.
    Meteorological and cloud conditions during the Arctic Ocean 2018 expedition2021In: Atmospheric Chemistry and Physics, Vol. 21, no 1, p. 289-314Article in journal (Refereed)
    Abstract [en]

    The Arctic Ocean 2018 (AO2018) took place in the central Arctic Ocean in August and September 2018 on the Swedish icebreaker Oden. An extensive suite of instrumentation provided detailed measurements of surface water chemistry and biology, sea ice and ocean physical and biogeochemical properties, surface exchange processes, aerosols, clouds, and the state of the atmosphere. The measurements provide important information on the coupling of the ocean and ice surface to the atmosphere and in particular to clouds. This paper provides (i) an overview of the synoptic-scale atmospheric conditions and their climatological anomaly to help interpret the process studies and put the detailed observations from AO2018 into a larger context, both spatially and temporally; (ii) a statistical analysis of the thermodynamic and near-surface meteorological conditions, boundary layer, cloud, and fog characteristics; and (iii) a comparison of the results to observations from earlier Arctic Ocean expeditions – in particular AOE1996 (Arctic Ocean Expedition 1996), SHEBA (Surface Heat Budget of the Arctic Ocean), AOE2001 (Arctic Ocean Experiment 2001), ASCOS (Arctic Summer Cloud Ocean Study), ACSE (Arctic Clouds in Summer Experiment), and AO2016 (Arctic Ocean 2016) – to provide an assessment of the representativeness of the measurements. The results show that near-surface conditions were broadly comparable to earlier experiments; however the thermodynamic vertical structure was quite different. An unusually high frequency of well-mixed boundary layers up to about 1 km depth occurred, and only a few cases of the “prototypical” Arctic summer single-layer stratocumulus deck were observed. Instead, an unexpectedly high amount of multiple cloud layers and mid-level clouds were present throughout the campaign. These differences from previous studies are related to the high frequency of cyclonic activity in the central Arctic in 2018.

  • 27.
    West, Johannes
    et al.
    Stockholms universitet, Institutionen för miljövetenskap.
    Gindorf, Sonja
    Stockholms universitet, Institutionen för miljövetenskap.
    Jonsson, Sofi
    Stockholms universitet, Institutionen för miljövetenskap.
    Photochemical Degradation of Dimethylmercury in Natural Waters2022In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 56, no 9, p. 5920-5928Article in journal (Refereed)
    Abstract [en]

    Photochemical demethylation of dimethylmercury (DMHg) could potentially be an important source of monomethylmercury (MMHg) in sunlit water. Whether or not DMHg is photochemically degraded when dissolved in water is, however, debated. While an early study suggested DMHg dissolved in natural waters to readily degrade, later work claimed DMHg to be stable in seawater under natural sunlight and that early observations may be due to experimental artifacts. Here, we present experimental data showing that DMHg is readily degraded by photochemical processes in different natural waters (including water from a DOC-rich stream, the Baltic Sea, and the Arctic Ocean) as well as in artificial seawater and purified water. For most of the waters, the degradation rate constant (kd) for DMHg measured in indoor experiments exceeded, or was close to, the kd observed for MMHg. Outdoor incubations of DMHg in purified water and Arctic Ocean surface water further confirmed that DMHg is photochemically degraded under natural sunlight. Our study shows that DMHg is photochemically degraded in a range of natural waters and that this process may be a source of MMHg in sunlit waters where the supply or formation of DMHg is sufficient. 

  • 28.
    Zinke, Julika
    et al.
    Stockholms universitet, Institutionen för miljövetenskap.
    Salter, Matthew E.
    Stockholms universitet, Institutionen för miljövetenskap.
    Leck, Caroline
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Lawler, Michael J.
    Porter, Grace C. E.
    Adams, Michael P.
    Brooks, Ian M.
    Murray, Benjamin J.
    Zieger, Paul
    Stockholms universitet, Institutionen för miljövetenskap.
    The development of a miniaturised balloon-borne cloud water sampler and its first deployment in the high Arctic2021In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 73, no 1, p. 1-12, article id 1915614Article in journal (Refereed)
    Abstract [en]

    The chemical composition of cloud water can be used to infer the sources of particles upon which cloud droplets and ice crystals have formed. In order to obtain cloud water for analysis of chemical composition for elevated clouds in the pristine high Arctic, balloon-borne active cloud water sampling systems are the optimal approach. However, such systems have not been feasible to deploy previously due to their weight and the challenging environmental conditions. We have taken advantage of recent developments in battery technology to develop a miniaturised cloud water sampler for balloon-borne collection of cloud water. Our sampler is a bulk sampler with a cloud drop cutoff diameter of approximately 8 µm and an estimated collection efficiency of 70%. The sampler was heated to prevent excessive ice accumulation and was able to operate for several hours under the extreme conditions encountered in the high Arctic. We have tested and deployed the new sampler on a tethered balloon during the Microbiology-Ocean-Cloud-Coupling in the High Arctic (MOCCHA) campaign in August and September 2018 close to the North pole. The sampler was able to successfully retrieve cloud water samples that were analysed to determine their chemical composition as well as their ice-nucleating activity. Given the pristine conditions found in the high Arctic we have placed significant emphasis on the development of a suitable cleaning procedure to minimise background contamination by the sampler itself.

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