Arctic warming is expected to trigger large-scale environmental change including remobilization of terrestrial organic carbon (terrOC). Permafrost and peatland systems contain more than twice as much carbon as the atmosphere, and may upon destabilization expose large amounts of their carbon to microbial decomposition and release climate-forcing greenhouse gases (GHG). Remobilization of terrOC also causes lateral leakage of organic matter via Arctic rivers with further translocated organic matter degradation and GHG release, while a remainder is exported to the Arctic Ocean and re-deposited in sediments. Arctic Ocean sediments are thus receptors of terrOC remobilization for a large part of the circum-Arctic drainage basin, and offer an archive to study past terrOC remobilization, e.g. during warming periods of the last deglaciation.
This thesis investigates terrOC in Arctic Ocean sediments to study OC remobilization from permafrost and other terrestrial systems across temporal and spatial scales. As a first – historical – approach, permafrost OC remobilization and degradation during past warming episodes are studied using OC, dual-isotope source apportionment (13C-OC; 14C-OC) and terrestrial biomarkers (lignin phenols, long-chained n-alkanes and n-alkanoic acids) in glacial-cycle sediment cores from the Siberian continental margin. The results reveal that permafrost systems were highly vulnerable to OC release throughout past warming events, foremost during the Bølling–Allerød (14.7-12.9 kyr before present - BP) warming period and the early Holocene climate optimum (11.7-7.5 kyr BP). The sediment record shows that climate warming of about 1°C and 1.5°C (Northern Hemisphere) then triggered large-scale thawing of mostly coastal permafrost and permafrost soils in the Siberian hinterland. These results are consistent with the hypothesis that large-scale permafrost OC remobilization may have contributed to the observed rise in atmospheric CO2 during the last deglaciation, and thereby stresses the importance of permafrost thawing in the light of anthropogenic climate change.
The second – spatial – study angle in this thesis investigates the contemporary Earth system and studies terrOC remobilization from permafrost and other terrestrial sources using terrOC accumulation in surface sediments of the circum-Arctic shelf seas. This includes establishment and application of the Circum-Arctic Sediment Carbon Database (CASCADE), which is a data collection of thousands of observations of OC, 13C-OC, 14C-OC and terrestrial biomarkers from the published literature and yet-unpublished records. This offers the opportunity to study large-scale remobilization of terrOC in the circum-Arctic by integrating input from terrOC sources over large areas. Mass accumulation rates of the different terrOC sources (by 210Pb dating and dual-isotope source apportionment of OC) reveal that surface (incl. permafrost) soils remobilize more than twice as much terrOC as coastal erosion of old Pleistocene permafrost. Furthermore, vulnerabilities of terrOC stocks to large-scale remobilization are discussed, which suggests permafrost soils to be the most vulnerable terrOC pool to remobilization by climate warming.
This thesis highlights the vulnerability of terrOC stores to Arctic warming over time and space, and thus contributes to a better understanding of climate-carbon couplings in the Earth system.
Scientific paper
Atmospheric ageing of inorganic sea spray aerosol: implications for hygroscopicity and cloud activation potential
Bernadette Rosati; Sigurd Christiansen; Anders Dinesen; Pontus Roldin; Andreas Massling; E. Douglas Nilsson; Merete Bilde
Sea spray aerosol (SSA) contributes significantly to natural aerosol particle concentrations globally, in marine areas even dominantly. The potential changes of the omnipresent inorganic fraction of SSA due to atmospheric ageing is largely unexplored. We demonstrate that ageing of liquid NaCl and artificial sea salt aerosol by exposure to ozone and UV light leads to a substantial decrease in hygroscopicity and cloud activation potential. The results point towards surface reactions that are more crucial for small particles and the formation of salt structures with water bound within the aerosols, termed hydrates. Our findings suggest an increased formation of hydrate forming salts during ageing and the presence of hydrates in dried SSA. Field observations indicate a reduced hygroscopic growth of sub-micrometre SSA in the marine atmosphere compared to pure NaCl gfgddwhich is typically attributed to organic matter or sulphates. Aged inorganic sea salt offers an additional explanation for reduced hygroscopicity and cloud activation potential.
Technical report
Provningsjämförelse / Proficiency Test 2021-1, Metaller och spårämnen / Metals and trace elements
Epidemiological studies have consistently linked exposure to PM2.5 with adverse health effects. The oxidative potential (OP) of aerosol particles has been widely suggested as a measure of their potential toxicity. Several acellular chemical assays are now readily employed to measure OP; however, uncertainty remains regarding the atmospheric conditions and specific chemical components of PM2.5 that drive OP. A limited number of studies have simultaneously utilised multiple OP assays with a wide range of concurrent measurements and investigated the seasonality of PM2.5 OP. In this work, filter samples were collected in winter 2016 and summer 2017 during the atmospheric pollution and human health in a Chinese megacity campaign (APHH-Beijing), and PM2.5 OP was analysed using four acellular methods: ascorbic acid (AA), dithiothreitol (DTT), 2,7-dichlorofluorescin/hydrogen peroxidase (DCFH) and electron paramagnetic resonance spectroscopy (EPR). Each assay reflects different oxidising properties of PM2.5, including particle-bound reactive oxygen species (DCFH), superoxide radical production (EPR) and catalytic redox chemistry (DTT/AA), and a combination of these four assays provided a detailed overall picture of the oxidising properties of PM2.5 at a central site in Beijing. Positive correlations of OP (normalised per volume of air) of all four assays with overall PM2.5 mass were observed, with stronger correlations in winter compared to summer. In contrast, when OP assay values were normalised for particle mass, days with higher PM2.5 mass concentrations (µg m−3) were found to have lower mass-normalised OP values as measured by AA and DTT. This finding supports that total PM2.5 mass concentrations alone may not always be the best indicator for particle toxicity. Univariate analysis of OP values and an extensive range of additional measurements, 107 in total, including PM2.5 composition, gas-phase composition and meteorological data, provided detailed insight into the chemical components and atmospheric processes that determine PM2.5 OP variability. Multivariate statistical analyses highlighted associations of OP assay responses with varying chemical components in PM2.5 for both mass- and volume-normalised data. AA and DTT assays were well predicted by a small set of measurements in multiple linear regression (MLR) models and indicated fossil fuel combustion, vehicle emissions and biogenic secondary organic aerosol (SOA) as influential particle sources in the assay response. Mass MLR models of OP associated with compositional source profiles predicted OP almost as well as volume MLR models, illustrating the influence of mass composition on both particle-level OP and total volume OP. Univariate and multivariate analysis showed that different assays cover different chemical spaces, and through comparison of mass- and volume-normalised data we demonstrate that mass-normalised OP provides a more nuanced picture of compositional drivers and sources of OP compared to volume-normalised analysis. This study constitutes one of the most extensive and comprehensive composition datasets currently available and provides a unique opportunity to explore chemical variations in PM2.5 and how they affect both PM2.5 OP and the concentrations of particle-bound reactive oxygen species.
Scientific paper
Persistent Organic Pollutants (POPs) in fish species from different lakes of the Lesser Himalayan Region (LHR), Pakistan: The influence of proximal sources in distribution of POPs.
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.
Scientific paper
Evolution of Turbulent Swirling Flow in a Small‑Scale Cyclone with Increasing Flow Rate: A LES Study
The flow field, vortex behaviour and pressure losses in a small-scale cyclone have been studied at a wide range of flow rate 0.23–39.7 NLPM (measured at 1 atm and 20 ◦C ) using the LES simulations that have been validated based on experimental measurements of the cyclone pressure drop. The following flow characteristics such as (1) the radial distribution of the tangential velocity; (2) the maximum tangential velocity and axial downward flow rate; (3) natural vortex length and rotation frequency of the vortex end; and (4) pressure losses in the cyclone have been analysed as a function of Reynolds number. The radial distribution of the tangential velocity inside the cyclone has been described by a proposed equation for adapted Burger’s vortex. The position of the lower end of the vortex (natural vortex length) as well as its rotational frequency have been investigated with the pressure sensing method. A unique vortex behaviour such as “vortex end jump” was revealed at some Reynolds numbers. Additionally, a deep analysis of the pressure losses in the cyclone has been performed which showed that the main pressure losses (up to 48%) occur in the vortex finder. Four flow regimes were revealed and a one-term power series model has been proposed to describe the effects of the Reynolds number on the Euler number (dimensionless pressure losses).
Scientific paper
Estimating environmental hazard and risks from exposure to per-and polyfluoroalkyl substances (PFAS): Outcome of a SETAC focused topic meeting
Johnson, M.S..; Buck, R.C.; Cousins, I.T.; Fenton, S.; Weis, C.
2021
| Environ. Toxicol. Chem.
| 40
(3)
(543-549)
Scientific paper
Evaluation of anhydrosugars as a molecular proxy for paleofire activity: A case study on a Holocene sediment core from Agios Floros, Peloponnese, Greece
Elin Norström, Johannes West, Katerina Kouli, Christos Katrantsiotis, Martina Hättestrand, Rienk H. Smittenberg
The anhydrosugars, levoglucosan, mannosan and galactosan, are regarded as suitable molecular indicators of natural biomass combustion. Here, we evaluate summed anhydrosugars (SAS) as a paleofire indicator in a 6000 year-long fossil core from Agios Floros fen, Peloponnese, Greece, by analyzing charcoal fragments in parallel, throughout the sediment sequence. Modern surface soil samples from the same region were analysed for the presence of SAS, confirming the biomarker as an indicator of recent fire activity. The highest SAS concentrations in the fossil core were found in sections representing periods of wet conditions, both on local and regional scales and regionally widespread arboreal vegetation. Low amounts, or the absence, of SAS in the fossil core were associated with periods of dryness, regional dominance of non-arboreal vegetation and the presence of a fen rather than a lake ecosystem at the site. Micro-charcoal fragments were generally more abundant under these conditions. This suggests that SAS yield and deposition may vary with fuel availability and fire behavior, which in turn is affected by climate, local moisture and vegetation type. Forest fires result in more SAS compared to grass fires. SAS yield is also favored by low-temperature fires sustained under wet climate conditions. Preservation of SAS is likely to be compromised in the only seasonally wet fen ecosystem under the dry and warm Mediterranean climate conditions. The moist and shallow conditions in the wetland during hot summer months probably promote oxidation and biodegradation of the labile SAS molecules, compared to the more robust charcoal fragments. Thus, a multiproxy approach - using several proxies, both for fire, hydroclimate and vegetation change - is preferred when aiming to reconstruct past biomass burning from wetland ecosystems in a Mediterranean environment. The micro-charcoal record from Agios Floros reveals significant fire activity between 4400 and 2800 cal yr BP. This partly overlaps the Bronze Age period, associated with intense human environmental interaction and climate change in this area of Peloponnese, Greece.
Scientific paper
Baltic Sea Spray Emissions: In Situ Eddy Covariance Fluxes vs. Simulated Tank Sea Spray
We present the first ever evaluation of sea spray aerosol eddy covariance (EC) fluxes at near coastal conditions and with limited fetch, and the first over water with brackish water (on aver-age 7 ppt). The measurements were made on the island of Garpen in the Baltic Sea (56°23’ N, 16°06’ E) in September 2005. We found that wind speed is a major factor that is driving an expo-nential increase in sea spray sea salt emissions, comparable to previous studies over waters with higher salinity. We were able to show that the inclusion of a thermodenuder in the EC system al-lowed for the parallel measurements of the dry unheated aerosol flux (representing both organic and sea salt sea spray emissions) and the heated (300 ˚C) non-volatile sea salt emissions. This study’s experimental approach also included measurements of the artificial sea spray formed in a tank in locally sampled water at the same location as the EC fluxes. We attempted to use the EC aerosol flux measurements to scale the tank measurements to aerosol emissions in order to derive a complete size distribution for the sea spray emission fluxes below the size range (0.3–2 µm dry diameter) of the optical particle counters (OPCs) in the EC system, covering in total 0.01 µm to 2 µm diameter. In the wind directions with long fetches (corresponding to conditions similar to open sea), we were able to distinguish between the aerosol emission fluxes of dry aerosol and heated non-volatile (sea salt only) in the smallest size bins of the OPC, and could therefore indi-rectly estimate the organic sea spray fraction. In agreement with several previous ambient and tank experiments deriving the size resolved chemical mass concentration of sea salt and wa-ter-insoluble organic sea spray, our EC fluxes showed that sea sprays were dominated by sea salt at sizes ≥1 µm diameter, and by organics at the smallest OPC sizes. Since we used direct measures of the sea spray emission fluxes, we confirmed previous suggestions that this size distribution of sea salt and organics is a signature of sea spray aerosols. We were able to show that two sea salt source parameterizations (Mårtensson et al. (2003) and Salter et al. (2015)) agreed fairly well with our observed heated EC aerosol emission fluxes, as long as their predicted emissions were modi-fied for the actual salinity by shifting the particle diameters proportionally to the cubic rote of the salinity. If, in addition, we added organics to the parameterized sea spray following the mono-layer model by Ellison et al. (1999), the combined sea spray parameterizations for sea salt and organics fell reasonably close to the observed fluxes for diameters > 0.15 µm, while one of them overpredicted the sea spray emissions below this size. The organic mono-layer model by El-lison et al. appeared to be able to explain most of the differences we observed between the aerosol emission fluxes with and without the thermodenuder.
Mechanisms of Arctic amplification and Arctic climate change are difficult to pinpoint, and current climate models do not represent the complex local processes and feedbacks at play, in particular for aerosol–climate interactions. This Perspective highlights the role of aerosols in contemporary Arctic climate change and stresses that the Arctic natural aerosol baseline is changing fast and its regional characteristics are very diverse. We argue that to improve understanding of present day and future Arctic, more detailed knowledge is needed on natural Arctic aerosol emissions, their evolution and transport, and the effects on cloud microphysics. In particular, observation and modelling work should focus on the sensitivity of aerosol–climate interactions to the rapidly evolving base state of the Arctic.
Scientific paper
Regulating and Cultural Ecosystem Services of Urban Green Infrastructure in the Nordic Countries: A Systematic Review
Amorim, J.; Engardt, M.; Johansson, C.; Ribeiro, I.; Sannebro, M.
2021
| Int J Environ Res Public Health
| 18
(1219)
(1-19)
In the Nordic countries (Denmark, Finland, Iceland, Norway and Sweden), the Urban Green Infrastructure (UGI) has been traditionally targeted at reducing flood risk. However, other Ecosystem Services (ES) became increasingly relevant in response to the challenges of urbanization and climate change. In total, 90 scientific articles addressing ES considered crucial contributions to the quality of life in cities are reviewed. These are classified as (1) regulating ES that minimize hazards such as heat, floods, air pollution and noise, and (2) cultural ES that promote well-being and health. We conclude that the planning and design of UGI should balance both the provision of ES and their side effects and disservices, aspects that seem to have been only marginally investigated. Climatesensitive planning practices are critical to guarantee that seasonal climate variability is accounted for at high-latitude regions. Nevertheless, diverging and seemingly inconsistent findings, together with gaps in the understanding of long-term effects, create obstacles for practitioners. Additionally, the limited involvement of end users points to a need of better engagement and communication, which in overall call for more collaborative research. Close relationships and interactions among different ES provided by urban greenery were found, yet few studies attempted an integrated evaluation. We argue that promoting interdisciplinary studies is fundamental to attain a holistic understanding of how plant traits affect the resulting ES; of the synergies between biophysical, physiological and psychological processes; and of the potential disservices of UGI, specifically in Nordic cities.
