Browsing by Subject "ICE"

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  • Golub, Malgorzata; Thiery, Wim; Marce, Rafael; Pierson, Don; Vanderkelen, Inne; Mercado-Bettin, Daniel; Woolway, R. Iestyn; Grant, Luke; Jennings, Eleanor; Kraemer, Benjamin M.; Schewe, Jacob; Zhao, Fang; Frieler, Katja; Mengel, Matthias; Bogomolov, Vasiliy Y.; Bouffard, Damien; Cote, Marianne; Couture, Raoul-Marie; Debolskiy, Andrey; Droppers, Bram; Gal, Gideon; Guo, Mingyang; Janssen, Annette B. G.; Kirillin, Georgiy; Ladwig, Robert; Magee, Madeline; Moore, Tadhg; Perroud, Marjorie; Piccolroaz, Sebastiano; Vinnaa, Love Raaman; Schmid, Martin; Shatwell, Tom; Stepanenko, Victor M.; Tan, Zeli; Woodward, Bronwyn; Yao, Huaxia; Adrian, Rita; Allan, Mathew; Anneville, Orlane; Arvola, Lauri; Atkins, Karen; Boegman, Leon; Carey, Cayelan; Christianson, Kyle; de Eyto, Elvira; DeGasperi, Curtis; Grechushnikova, Maria; Hejzlar, Josef; Joehnk, Klaus; Jones, Ian D.; Laas, Alo; Mackay, Eleanor B.; Mammarella, Ivan; Markensten, Hampus; McBride, Chris; Ozkundakci, Deniz; Potes, Miguel; Rinke, Karsten; Robertson, Dale; Rusak, James A.; Salgado, Rui; van der Linden, Leon; Verburg, Piet; Wain, Danielle; Ward, Nicole K.; Wollrab, Sabine; Zdorovennova, Galina (2022)
    Empirical evidence demonstrates that lakes and reservoirs are warming across the globe. Consequently, there is an increased need to project future changes in lake thermal structure and resulting changes in lake biogeochemistry in order to plan for the likely impacts. Previous studies of the impacts of climate change on lakes have often relied on a single model forced with limited scenario-driven projections of future climate for a relatively small number of lakes. As a result, our understanding of the effects of climate change on lakes is fragmentary, based on scattered studies using different data sources and modelling protocols, and mainly focused on individual lakes or lake regions. This has precluded identification of the main impacts of climate change on lakes at global and regional scales and has likely contributed to the lack of lake water quality considerations in policy-relevant documents, such as the Assessment Reports of the Intergovernmental Panel on Climate Change (IPCC). Here, we describe a simulation protocol developed by the Lake Sector of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) for simulating climate change impacts on lakes using an ensemble of lake models and climate change scenarios for ISIMIP phases 2 and 3. The protocol prescribes lake simulations driven by climate forcing from gridded observations and different Earth system models under various representative greenhouse gas concentration pathways (RCPs), all consistently bias-corrected on a 0.5 degrees x 0.5 degrees global grid. In ISIMIP phase 2, 11 lake models were forced with these data to project the thermal structure of 62 well-studied lakes where data were available for calibration under historical conditions, and using uncalibrated models for 17 500 lakes defined for all global grid cells containing lakes. In ISIMIP phase 3, this approach was expanded to consider more lakes, more models, and more processes. The ISIMIP Lake Sector is the largest international effort to project future water temperature, thermal structure, and ice phenology of lakes at local and global scales and paves the way for future simulations of the impacts of climate change on water quality and biogeochemistry in lakes.
  • Bowles, N. E.; Snodgrass, C.; Gibbings, A.; Sanchez, J. P.; Arnold, J. A.; Eccleston, P.; Andert, T.; Probst, A.; Naletto, G.; Vandaele, A. C.; de Leon, J.; Nathues, A.; Thomas, I. R.; Thomas, N.; Jorda, L.; Da Deppo, V.; Haack, H.; Green, S. F.; Carry, B.; Hanna, K. L. Donaldson; Jorgensen, J. Leif; Kereszturi, A.; DeMeo, F. E.; Patel, M. R.; Davies, J. K.; Clarke, F.; Kinch, K.; Guilbert-Lepoutre, A.; Agarwal, J.; Rivkin, A. S.; Pravec, P.; Fornasier, S.; Granvik, M.; Jones, R. H.; Murdoch, N.; Joy, K. H.; Pascale, E.; Tecza, M.; Barnes, J. M.; Licandro, J.; Greenhagen, B. T.; Calcutt, S. B.; Marriner, C. M.; Warren, T.; Tosh, I. (2018)
    CASTAway is a mission concept to explore our Solar System's main asteroid belt. Asteroids and comets provide a window into the formation and evolution of our Solar System and the composition of these objects can be inferred from space-based remote sensing using spectroscopic techniques. Variations in composition across the asteroid populations provide a tracer for the dynamical evolution of the Solar System. The mission combines a long-range (point source) telescopic survey of over 10,000 objects, targeted close encounters with 10-20 asteroids and serendipitous searches to constrain the distribution of smaller (e.g. 10 m) size objects into a single concept. With a carefully targeted trajectory that loops through the asteroid belt, CASTAway would provide a comprehensive survey of the main belt at multiple scales. The scientific payload comprises a 50 cm diameter telescope that includes an integrated low-resolution (R = 30-100) spectrometer and visible context imager, a thermal (e.g. 6-16 mu m) imager for use during the flybys, and modified star tracker cameras to detect small (similar to 10 m) asteroids. The CASTAway spacecraft and payload have high levels of technology readiness and are designed to fit within the programmatic and cost caps for a European Space Agency medium class mission, while delivering a significant increase in knowledge of our Solar System. (C) 2017 COSPAR. Published by Elsevier Ltd. All rights reserved.
  • Mac Lennan, Eric Michael; Toliou, Athanasia; Granvik, Mikael (2021)
    The near-Earth objects (NEOs) (3200) Phaethon and (155140) 2005 UD are thought to share a common origin, with the former exhibiting dust activity at perihelion that is thought to directly supply the Geminid meteor stream. Both of these objects currently have very small perihelion distances (0.140 au and 0.163 au for Phaethon and 2005 UD, respectively), which results in them having perihelion temperatures around 1000 K. A comparison between NEO population models to discovery statistics suggests that low-perihelion objects are destroyed over time by a, possibly temperature-dependent, mechanism that is efficient at heliocentric distances less than 0.3 au. By implication, the current activity from Phaethon is linked to the destruction mechanism of NEOs close to the Sun. We model the past thermal characteristics of Phaethon and 2005 UD using a combination of a thermophysical model (TPM) and orbital integrations of each object. Temperature characteristics such as maximum daily temperature, maximum thermal gradient, and temperature at different depths are extracted from the model, which is run for a predefined set of semi-major axis and eccentricity values. Next, dynamical integrations of orbital clones of Phaethon and 2005 UD are used to estimate the past orbital elements of each object. These dynamical results are then combined with the temperature characteristics to model the past evolution of thermal characteristics such as maximum (and minimum) surface temperature and thermal gradient. The orbital histories of Phaethon and 2005 UD are characterized by cyclic changes in.., resulting in perihelia values periodically shifting between present-day values and 0.3 au. Currently, Phaethon is experiencing relatively large degrees of heating when compared to the recent 20, 000 yr. We find that the subsurface temperatures are too large over this timescale for water ice to be stable, unless actively supplied somehow. The near-surface thermal gradients strongly suggest that thermal fracturing may be very effective at breaking down and ejecting dust particles. Observations by the DESTINY+ flyby mission will provide important constraints on the mechanics of dust-loss from Phaethon and, potentially, reveal signs of activity from 2005 UD. In addition to simulating the recent dynamical evolution of these objects, we use orbital integrations that start from the Main Belt to assess their early dynamical evolution (origin and delivery mechanism). We find that dwarf planet (2) Pallas is unlikely to be the parent body for Phaethon and 2005 UD, and it is more likely that the source is in the inner part of the asteroid belt in the families of, e.g., (329) Svea or (142) Polana.
  • Navarro-Almaida, D.; Le Gal, R.; Fuente, A.; Riviere-Marichalar, P.; Wakelam; Cazaux, S.; Caselli, P.; Laas, J. C.; Alonso-Albi, T.; Loison, J. C.; Gerin, M.; Kramer, C.; Roueff, E.; Bachillerl, R.; Commercon, B.; Friesen, R.; Garcia-Burillo, S.; Goicoechea, J. R.; Giuliano, B. M.; Jimenez-Serram; Kirk, J. M.; Lattanzi, M.; Malinen, J.; Marcelino, N.; Martin-Domenech, R.; Caro, G. M. Munoz; Pineda, J.; Tercero, B.; Trevino-Morales, S. P.; Roncero, O.; Hacar, A.; Tafalla, M.; Ward-Thompson, D. (2020)
    Context. Sulphur is one of the most abundant elements in the Universe. Surprisingly, sulphuretted molecules are not as abundant as expected in the interstellar medium and the identity of the main sulphur reservoir is still an open question.Aims. Our goal is to investigate the H2S chemistry in dark clouds, as this stable molecule is a potential sulphur reservoir.Methods. Using millimeter observations of CS, SO, H2S, and their isotopologues, we determine the physical conditions and H2S abundances along the cores TMC 1-C, TMC 1-CP, and Barnard 1b. The gas-grain model NAUTILUS is used to model the sulphur chemistry and explore the impact of photo-desorption and chemical desorption on the H2S abundance.Results. Our modeling shows that chemical desorption is the main source of gas-phase H2S in dark cores. The measured H2S abundance can only be fitted if we assume that the chemical desorption rate decreases by more than a factor of 10 when n(H) > 2 x 10(4). This change in the desorption rate is consistent with the formation of thick H2O and CO ice mantles on grain surfaces. The observed SO and H2S abundances are in good agreement with our predictions adopting an undepleted value of the sulphur abundance. However, the CS abundance is overestimated by a factor of 5-10. Along the three cores, atomic S is predicted to be the main sulphur reservoir.Conclusions. The gaseous H2S abundance is well reproduced, assuming undepleted sulphur abundance and chemical desorption as the main source of H2S. The behavior of the observed H2S abundance suggests a changing desorption efficiency, which would probe the snowline in these cold cores. Our model, however, highly overestimates the observed gas-phase CS abundance. Given the uncertainty in the sulphur chemistry, we can only conclude that our data are consistent with a cosmic elemental S abundance with an uncertainty of a factor of 10.
  • Roth, Florian; Sun, Xiaole; Geibel, Marc C.; Prytherch, John; Bruchert, Volker; Bonaglia, Stefano; Broman, Elias; Nascimento, Francisco; Norkko, Alf; Humborg, Christoph (2022)
    Coastal methane (CH4) emissions dominate the global ocean CH4 budget and can offset the "blue carbon" storage capacity of vegetated coastal ecosystems. However, current estimates lack systematic, high-resolution, and long-term data from these intrinsically heterogeneous environments, making coastal budgets sensitive to statistical assumptions and uncertainties. Using continuous CH4 concentrations, delta C-13-CH4 values, and CH4 sea-air fluxes across four seasons in three globally pervasive coastal habitats, we show that the CH4 distribution is spatially patchy over meter-scales and highly variable in time. Areas with mixed vegetation, macroalgae, and their surrounding sediments exhibited a spatiotemporal variability of surface water CH4 concentrations ranging two orders of magnitude (i.e., 6-460 nM CH4) with habitat-specific seasonal and diurnal patterns. We observed (1) delta C-13-CH signatures that revealed habitat-specific CH4 production and consumption pathways, (2) daily peak concentration events that could change >100% within hours across all habitats, and (3) a high thermal sensitivity of the CH4 distribution signified by apparent activation energies of similar to 1 eV that drove seasonal changes. Bootstrapping simulations show that scaling the CH4 distribution from few samples involves large errors, and that similar to 50 concentration samples per day are needed to resolve the scale and drivers of the natural variability and improve the certainty of flux calculations by up to 70%. Finally, we identify northern temperate coastal habitats with mixed vegetation and macroalgae as understudied but seasonally relevant atmospheric CH4 sources (i.e., releasing >= 100 mu mol CH4 m(-2) day(-1) in summer). Due to the large spatial and temporal heterogeneity of coastal environments, high-resolution measurements will improve the reliability of CH4 estimates and confine the habitat-specific contribution to regional and global CH4 budgets.
  • Savijärvi, Hannu; Martinez, G.M.; Fischer, E.; Renno, N.O.; Tamppari, L.K.; Zent, A.; Harri, Ari-Matti (2020)
    Two recalibrated sets of Phoenix (PHX) near-surface TECP air humidity measurements were compared with results from adsorptive single column model simulations during a warm clear-sky polar midsummer period, PHX sols 50-60. The model's 2 m temperatures were close to the observed values. Relative humidity (RH) is very low during the day but at night RH at 2 m reaches nearly 100% by the Zent et al. (2016) recalibration (Z), and 60-70% by the Fischer et al. (2019) recalibration (F). Model values of RH2m are close to Z and F at night and to F during the day. All three imply low water vapor pressures near the surface at night, 0.03-0.05 Pa, with a rapid increase each morning to 0.3-1 Pa and a decrease in the evening by both F and the model simulation. The model's daily adsorbed and desorbed water is in balance for regolith porosity of 16% (instead of 35% for lower latitudes). The depleted layer of nighttime air moisture extends to only about 200 m above the surface; hence the model's precipitable water content stays around the observed similar to 30 mu m throughout the sol. The model's moisture cycle is not sensitive to tortuosity of the regolith but the in-pore molecular diffusivity should be at least 5 cm(2)/s for fair agreement with the observations. In the adsorption experiments there is no fog and just a hint of ground frost, as observed during this period. Strong night frosts appear if adsorption is made weak or absent in the model.
  • Helle, Inari; Mäkinen, Jussi Antti-Eerikki; Nevalainen, Maisa Katariina; Afenyo, Mawuli; Vanhatalo, Jarno (2020)
    Oil spills resulting from maritime accidents pose a poorly understood risk to the Arctic environment. We propose a novel probabilistic method to quantitatively assess these risks. Our method accounts for spatiotemporally varying population distributions, the spreading of oil, and seasonally varying species-specific exposure potential and sensitivity to oil. It quantifies risk with explicit uncertainty estimates, enables one to compare risks over large geographic areas, and produces information on a meaningful scale for decision-making. We demonstrate the method by assessing the short-term risks oil spills pose to polar bears, ringed seals, and walrus in the Kara Sea, the western part of the Northern Sea Route. The risks differ considerably between species, spatial locations, and seasons. Our results support current aspirations to ban heavy fuel oil in the Arctic but show that we should not underestimate the risks of lighter oils either, as these oils can pollute larger areas than heavier ones. Our results also highlight the importance of spatially explicit season-specific oil spill risk assessment in the Arctic and that environmental variability and the lack of data are a major source of uncertainty related to the oil spill impacts.
  • Lehmkuehler, Felix; Forov, Yury; Buening, Thomas; Sahle, Christoph J.; Steinke, Ingo; Julius, Karin; Buslaps, Thomas; Tolan, Metin; Hakala, Mikko; Sternemann, Christian (2016)
    We studied the structure and energetics of supercooled water by means of X-ray Raman and Compton scattering. Under supercooled conditions down to 255 K, the oxygen K-edge measured by X-ray Raman scattering suggests an increase of tetrahedral order similar to the conventional temperature effect observed in non-supercooled water. Compton profile differences indicate contributions beyond the theoretically predicted temperature effect and provide a deeper insight into local structural changes. These contributions suggest a decrease of the electron mean kinetic energy by 3.3 +/- 0.7 kJ (mol K)(-1) that cannot be modeled within established water models. Our surprising results emphasize the need for water models that capture in detail the intramolecular structural changes and quantum effects to explain this complex liquid.
  • Majaneva, Markus; Enberg, Sara; Autio, Riitta; Blomster, Jaanika; Rintala, Janne-Markus (2019)
    The green algae Mamiellophyceae are a group of marine picoeukaryotes. We studied the succession of Mamiellophyceae in the Baltic Sea water column and ice from autumn to summer, using the hypervariable V4 region of the 18S ribosomal RNA (18S rRNA) gene. We show that species of Mamiellophyceae shift in seasonal predominance and that different species characterize sea ice, under-ice water, and the water column in the Baltic Sea.
  • Svensson, J.; Strom, J.; Hansson, M.; Lihavainen, H.; Kerminen, V-M (2013)
  • Dias, Fabio Boeira; Fiedler, R.; Marsland, S. J.; Domingues, C. M.; Clement, L.; Rintoul, S. R.; Mcdonagh, E. L.; Mata, M. M.; Savita, A. (2020)
    Ocean heat storage due to local addition of heat ("added'') and due to changes in heat transport ("redistributed'') were quantified in ocean-only 2xCO2 simulations. While added heat storage dominates globally, redistributionmakes important regional contributions, especially in the tropics. Heat redistribution is dominated by circulation changes, summarized by the super-residual transport, with only minor effects from changes in vertical mixing. While previous studies emphasized the contribution of redistribution feedback at high latitudes, this study shows that redistribution of heat also accounts for 65% of heat storage at low latitudes and 25% in the midlatitude (35 degrees-50 degrees S) Southern Ocean. Tropical warming results from the interplay between increased stratification and equatorward heat transport by the subtropical gyres, which redistributes heat from the subtropics to lower latitudes. The Atlantic pattern is remarkably distinct from other basins, resulting in larger basin-average heat storage. Added heat storage is evenly distributed throughout midlatitude Southern Ocean and dominates the total storage. However, redistribution stores heat north of the Antarctic Circumpolar Current in the Atlantic and Indian sectors, having an important contribution to the peak of heat storage at 45 degrees S. Southern Ocean redistribution results from intensified heat convergence in the subtropical front and reduced stratification in response to surface heat, freshwater, and momentum flux perturbations. These results highlight that the distribution of ocean heat storage reflects both passive uptake of heat and active redistribution of heat by changes in ocean circulation processes. The redistributed heat transportmust therefore be better understood for accurate projection of changes in ocean heat uptake efficiency, ocean heat storage, and thermosteric sea level.
  • Zhang, Yuemei; Ertbjerg, Per (2019)
    The role of protein denaturation in formation of thaw loss is currently not well understood. This study investigated denaturation of myofibrillar and sarcoplasmic proteins of pork loins caused by freezing-thawing in relation to freezing rate. Compared to fast freezing, slow freezing caused 28% larger thaw loss, decreased water-holding capacity of myofibrils and increased surface hydrophobicity, indicating more pronounced denaturation of myofibrillar proteins. We here propose a model: In slow freezing protons are concentrated in the unfrozen water resulting in reduced pH in proximity of structural proteins causing protein denaturation. In parallel, large ice crystals are formed outside of muscle fibers resulting in transversal shrinkage. In fast freezing small ice crystals trap protons and cause less severe protein denaturation and reduced thaw loss. Differential scanning calorimetry and tryptophan fluorescence spectra indicated sarcoplasmic protein denaturation in drip due to freezing-thawing. However, sarcoplasmic protein denaturation was independent of freezing rate.
  • Asmi, Eija; Neitola, Kimmo; Teinila, Kimmo; Rodriguez, Edith; Virkkula, Aki; Backman, John; Bloss, Matthew; Jokela, Jesse; Lihavainen, Heikki; De Leeuw, Gerrit; Paatero, Jussi; Aaltonen, Veijo; Mei, Miguel; Gambarte, Gonzalo; Copes, Gustavo; Albertini, Marco; Perez Fogwill, German; Ferrara, Jonathan; Elena Barlasina, Maria; Sanchez, Ricardo (2018)
    Aerosol particle optical properties were measured continuously between years 2013-2015 at the Marambio station in the Antarctic Peninsula. Annual cycles of particle scattering and absorption were studied and explained using measured particle chemical composition and the analysis of air mass transport patterns. The particle scattering was found elevated during the winter but the absorption did not show any clear annual cycle. The aerosol single scattering albedo at lambda = 637 nm was on average 0.96 +/- 0.10, with a median of 0.99. Aerosol scattering Angstrom exponent increased during summer, indicating an increasing fraction of fine mode particles. The aerosol was mainly composed of sea salt, sulphate and crustal soil minerals, and most of the particle mass were in the coarse mode. Both the particle absorption and scattering were increased during high wind speeds. This was explained by the dominance of the primary marine sea-spray and wind-blown soil dust sources. In contrast, the back-trajectory analysis suggested that long-range transport has only a minor role as a source of absorbing aerosol at the peninsula.
  • Moisseev, Dmitri; von Lerber, Annakaisa; Tiira, Jussi (2017)
    Ground-based observations of ice particle size distribution and ensemble mean density are used to quantify the effect of riming on snowfall. The rime mass fraction is derived from these measurements by following the approach that is used in a single ice-phase category microphysical scheme proposed for the use in numerical weather prediction models. One of the characteristics of the proposed scheme is that the prefactor of a power law relation that links mass and size of ice particles is determined by the rime mass fraction, while the exponent does not change. To derive the rime mass fraction, a mass-dimensional relation representative of unrimed snow is also determined. To check the validity of the proposed retrieval method, the derived rime mass fraction is converted to the effective liquid water path that is compared to microwave radiometer observations. Since dual-polarization radar observations are often used to detect riming, the impact of riming on dual-polarization radar variables is studied for differential reflectivity measurements. It is shown that the relation between rime mass fraction and differential reflectivity is ambiguous, other factors such as change in median volume diameter need also be considered. Given the current interest on sensitivity of precipitation to aerosol pollution, which could inhibit riming, the importance of riming for surface snow accumulation is investigated. It is found that riming is responsible for 5% to 40% of snowfall mass. The study is based on data collected at the University of Helsinki field station in Hyytiala during U.S. Department of Energy Biogenic Aerosols Effects on Clouds and Climate (BAECC) field campaign and the winter 2014/2015. In total 22 winter storms were analyzed, and detailed analysis of two events is presented to illustrate the study.
  • Ruosteenoja, Kimmo; Jylhä, Kirsti; Räisänen, Jouni; Mäkelä, Antti (2018)
    The commentators regard a categorical truncation of supersaturations with respect to ice in climate model output as an inappropriate solution to the supersaturation issue. This view is supported by observational evidence from the East Antarctic Plateau. We accept this criticism to a certain degree. Even so, it is necessary to make a clear distinction between the true supersaturations measured in the atmosphere and the spurious supersaturations existing in archived model output data sets: the latter result, for example, from inconsistencies in the interpolation of temperature and specific humidity to the near-surface level. In the CMIP5 model output data sets, the largest relative humidities in near-surface air are far above those observed. Moreover, supersaturations given at the 2-m height are generally much larger than those at the lowermost tropospheric isobaric levels. Projections of relative humidity for the future may be considerably distorted if founded on unmodified output data sets.
  • Orme, Lisa Claire; Crosta, Xavier; Miettinen, Arto; Divine, Dmitry; Husum, Katrine; Isaksson, Elisabeth; Wacker, Lukas; Mohan, Rahul; Ther, Olivier; Ikehara, Minoru (2020)
    Centennial- and millennial-scale variability of Southern Ocean temperature over the Holocene is poorly known, due to both short instrumental records and sparsely distributed high-resolution temperature reconstructions, with evidence for past temperature variations in the region coming mainly from ice core records. Here we present a high-resolution (similar to 60 year), diatom-based sea surface temperature (SST) reconstruction from the western Indian sector of the Southern Ocean that spans the interval 14.2 to 1.0 ka (calibrated kiloyears before present). During the late deglaciation, the new SST record shows cool temperatures at 14.2-12.9 ka and gradual warming between 12.9 and 11.6 ka in phase with atmospheric temperature evolution. This supports the evolution of the Southern Ocean SST during the deglaciation being linked with a complex combination of processes and drivers associated with reorganisations of atmospheric and oceanic circulation patterns. Specifically, we suggest that Southern Ocean surface warming coincided, within the dating uncertainties, with the reconstructed slowdown of the Atlantic Meridional Overturning Circulation (AMOC), rising atmospheric CO2 levels, changes in the southern westerly winds and enhanced upwelling. During the Holocene the record shows warm and stable temperatures from 11.6 to 8.7 ka followed by a slight cooling and greater variability from 8.7 to 1 ka, with a quasi-periodic variability of 200-260 years identified by spectral analysis. We suggest that the increased variability during the mid- to late Holocene reflects the establishment of centennial variability in SST connected with changes in the high-latitude atmospheric circulation and Southern Ocean convection.
  • Svensson, Jonas; Virkkula, Aki; Meinander, Outi; Kivekäs, Niku; Hannula, Henna-Reetta; Järvinen, Onni; Peltoniemi, Jouni I.; Gritsevich, Maria; Heikkila, Anu; Kontu, Anna; Neitola, Kimmo; Brus, David; Dagsson-Waldhauserova, Pavla; Anttila, Kati; Vehkamäki, Marko; Hienola, Anca; De Leeuw, Gerrit; Lihavainen, Heikki (2016)
    Soot has a pronounced effect on the cryosphere and experiments are still needed to reduce the associated uncertainties. This work presents a series of experiments to address this issue, with soot being deposited onto a natural snow surface after which the albedo changes were monitored. The albedo reduction was the most pronounced for the snow with higher soot content, and it was observed immediately following soot deposition. Compared with a previous laboratory study the effects of soot on the snow were not as prominent in outdoor conditions. During snowmelt, about 50% of the originally deposited soot particles were observed to remain at the snow surface. More detailed experiments are however needed to better explain soot's effect on snow and to better quantify this effect. Our albedo versus soot parameterization agreed relatively well with previously published relationships.
  • Virta, Leena; Soininen, Janne; Norkko, Alf (2020)
    The global biodiversity loss has raised interest in the different facets of diversity, and the importance of diversity for ecosystem functions has been recognized. However, our knowledge on seasonal and inter-annual variation in the composition and diversity of communities is still poor. Here, we investigated the seasonal and inter-annual changes in taxonomic and functional community composition and diversity of benthic diatoms in a coastal habitat of the northern Baltic Sea, where seasonal and inter-annual variation of climate is pronounced. We found that the taxonomic and functional alpha diversity remained stable at seasonal and inter-annual level despite strong changes in community composition. However, alpha diversity decreased during an exceptionally warm winter possibly due to disturbances induced by the lack of ice. This may suggest that climate warming and consequently limited ice cover will affect the diversity of benthic communities.