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  • 1.
    Barrientos, Natalia
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Arctic Ocean benthic foraminifera preservation and Mg/Ca ratios: Implications for bottom water palaeothermometry2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Reconstructions of Arctic Ocean palaeotemperatures are needed to disentangle natural variability from anthropogenic changes and understand the role of ocean heat transport in forcing or providing feedbacks on Arctic climate change. Despite known complications with calcareous microfossil preservation in Arctic Ocean sediments, calcareous benthic foraminifera can be common in interglacial sequences. However, thus far they have been underutilized in palaeoceanographic studies. This thesis explores the application of the Mg/Ca palaeothermometry proxy for reconstructing bottom water temperatures (BWT) in the Arctic Ocean during the late Quaternary. This method, which is supported by previous empirical studies demonstrating a strong temperature control on trace Mg inclusion into foraminiferal shell calcite, has been applied in many ocean regions and time intervals. Until now its application in the Arctic Ocean has been sparingly explored.

    The results of this doctoral thesis are based on benthic foraminifera retrieved from marine sediment cores covering a wide geographical Arctic Ocean area including both the shallow and vast continental shelves and slopes to the intermediate-to-deep waters of the Lomonosov Ridge and Morris Jesup Rise. These provide the first benthic foraminifera Mg/Ca ratios from the central Arctic Ocean region. In the first study, mechanisms that could affect Mg incorporation in Arctic benthic foraminifera are investigated using oceanographic field data and six 'live' modern Arctic species (Elphidium clavatum, Nonionella labradorica, Cassidulina neoteretis, Oridorsalis tener, Cibicidoides wuellerstorfi and Quinqueloculina arctica). The result is new species-specific Mg/Ca–BWT field calibrations that provide important constraints at the cold end of the BWT spectrum (-2 to 1°C) (Paper I). Using the new Mg/Ca–BWT equation for E. clavatum, a palaeotemperature record was generated for the late Holocene (past ca. 4100 yr) from the western Chukchi Sea. The data showed BWT fluctuations from -2 to 1°C that are interpreted as showing pulses of warmer Pacific water inflow at 500–1000 yr periods, thus revealing multi-centennial variability in heat transport into the Arctic Ocean driven by low latitude forcings (Paper II). Complications with foraminiferal calcite preservation that limit Mg/Ca palaeothermometry in the Arctic were discovered and these are tackled in two additional papers. Anomalously high Mg content in benthic foraminifera from the central Arctic Ocean is linked to diagenetic contamination as a result of the unique oceanographic, sedimentary and geochemical environment (Paper III). Lastly, the dramatic post-recovery dissolution of foraminifera from a Chukchi Shelf sediment core during core storage is investigated and attributed to acidification driven by sulphide oxidation in this organic rich and calcite poor shelf setting (Paper IV).

    The findings of this thesis demonstrate that benthic foraminiferal Mg/Ca-palaeothermometry can be applied in the Arctic Ocean and capture small BWT change (on the order of -2 to 2°C) even at low temperatures. In practice, preservational complexities can be limiting and require special sample handling or analysis due to the high potential for diagenetic contamination in the central Arctic Ocean and rapid post coring calcite dissolution in the seasonally productive shelf seas. This Ph.D. project is a component of the multidisciplinary SWERUS-C3 (Swedish-Russian-US Arctic Ocean Climate-Cryosphere- Carbon Interactions) project that included an expedition with Swedish icebreaker Oden to the East Siberian Arctic Ocean.

  • 2.
    Barrientos, Natalia
    et al.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Lear, Caroline H.
    Jakobsson, Martin
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Stranne, Christian
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    O'Regan, Matt
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Cronin, Thomas M.
    Gukov, Aleksandr Y.
    Coxall, Helen K.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Arctic Ocean benthic foraminifera Mg/Ca ratios and global Mg/Ca-temperature calibrations: New constraints at low temperatures2018Ingår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 236, s. 240-259Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We explore the use of Mg/Ca ratios in six Arctic Ocean benthic foraminifera species as bottom water palaeothermometers and expand published Mg/Ca-temperature calibrations to the coldest bottom temperatures (<1 °C). Foraminifera were analyzed in surface sediments at 27 sites in the Chukchi Sea, East Siberian Sea, Laptev Sea, Lomonosov Ridge and Petermann Fjord. The sites span water depths of 52–1157 m and bottom water temperatures (BWT) of −1.8 to +0.9 °C. Benthic foraminifera were alive at time of collection, determined from Rose Bengal (RB) staining. Three infaunal and three epifaunal species were abundant enough for Mg/Ca analysis. As predicted by theory and empirical evidence, cold water Arctic Ocean benthic species produce low Mg/Ca ratios, the exception being the porcelaneous species Quinqueloculina arctica. Our new data provide important constraints at the cold end (<1 °C) when added to existing global datasets. The refined calibrations based on the new and published global data appear best supported for the infaunal species Nonionella labradorica (Mg/Ca = 1.325 ± 0.01 × e^(0.065 ± 0.01 × BWT), r2 = 0.9), Cassidulina neoteretis (Mg/Ca = 1.009 ± 0.02 × e^(0.042 ± 0.01 × BWT), r2 = 0.6) and Elphidium clavatum (Mg/Ca = 0.816 ± 0.06 + 0.125 ± 0.05 × BWT, r2 = 0.4). The latter is based on the new Arctic data only. This suggests that Arctic Ocean infaunal taxa are suitable for capturing at least relative and probably semi-quantitative past changes in BWT. Arctic Oridorsalis tener Mg/Ca data are combined with existing O. umbonatus Mg/Ca data from well saturated core-tops from other regions to produce a temperature calibration with minimal influence of bottom water carbonate saturation state (Mg/Ca = 1.317 ± 0.03 × e^(0.102 ± 0.01 BWT), r2 = 0.7). The same approach for Cibicidoides wuellerstorfi yields Mg/Ca = 1.043 ± 0.03 × e^(0.118 ± 0.1 BWT), r2 = 0.4. Mg/Ca ratios of the porcelaneous epifaunal species Q. arctica show a clear positive relationship between Mg/Ca and Δ[CO32−] indicating that this species is not suitable for Mg/Ca-palaeothermometry at low temperatures, but may be useful in reconstructing carbonate system parameters through time.

  • 3. Berggren, Martin
    et al.
    Gudasz, Cristian
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Guillemette, Francois
    Hensgens, Geert
    Ye, Linlin
    Karlsson, Jan
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Systematic microbial production of optically active dissolved organic matter in subarctic lake water2020Ingår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 65, nr 5, s. 951-961Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The ecology and biogeochemistry of lakes in the subarctic region are particularly sensitive to changes in the abundance and optical properties of dissolved organic matter (DOM). External input of colored DOM to these lakes is an extensively researched topic, but little is known about potential reciprocal feedbacks between the optical properties of DOM and internal microbial processes in the water. We performed 28-day dark laboratory incubation trials on water from 101 subarctic tundra lakes in northern Sweden, measuring the microbial decay of DOM and the resulting dynamics in colored (CDOM) and fluorescent (FDOM) DOM components. While losses in dissolved oxygen during the incubations corresponded to a 20% decrease in mean DOM, conversely the mean CDOM and total FDOM increased by 22% and 30%, respectively. However, the patterns in microbial transformation of the DOM were not the same in all lakes. Notably, along the gradient of increasing ambient CDOM (water brownness), the lakes showed decreased microbial production of protein-like fluorescence, lowered DOM turnover rates and decreasing bacterial growth per unit of DOM. These trends indicate that browning of subarctic lakes systematically change the way that bacteria interact with the ambient DOM pool. Our study underscores that there is no unidirectional causal link between microbial processes and DOM optical properties, but rather reciprocal dependence between the two.

  • 4.
    Bergström, Ann-Kristin
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Lau, Danny C. P.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Isles, Peter D. F.
    Watershed Management Division, Vermont Department of Environmental Conservation, VT, Montpelier, United States.
    Jonsson, Anders
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Creed, Irena F.
    Department of Physical and Environmental Sciences, University of Toronto – Scarborough Campus, ON, Toronto, Canada.
    Biomass, community composition and N:P recycling ratios of zooplankton in northern high-latitude lakes with contrasting levels of N deposition and dissolved organic carbon2022Ingår i: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 67, nr 9, s. 1508-1520Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Global changes are causing decreases in inorganic nitrogen (N) concentrations, increases in coloured dissolved organic carbon (DOC) concentrations, and decreases in dissolved inorganic N to total phosphorus ratios (DIN:TP) in northern lakes. The effects of these changes on phytoplankton and zooplankton biomass and the N:P recycling ratio of zooplankton remain unresolved.

    In 33 Swedish headwater lakes across subarctic-to-boreal gradients with different levels of N deposition (low N in the north [Västerbotten, boreal; Abisko, subarctic] vs. high N in the south [Värmland, boreal; Jämtland, subarctic]), we measured water chemistry, phytoplankton biomass (chlorophyll-a [Chl-a], Chl-a:TP), seston mineral quality (C:P, N:P), as well as zooplankton biomass, community composition, and C:N:P stoichiometry. We estimated nutrient imbalances and the N:P recycling ratios of zooplankton using ecological stoichiometry models.

    There was a large-scale gradient from low lake DIN and DIN:TP in the north to high DIN and DIN:TP in the south, with lower DIN:TP in lakes coinciding with higher DOC within each region. Lower lake DIN was associated with lower phytoplankton biomass (lower Chl-a:TP). Lower lake DIN:TP was associated with richer seston mineral quality (lower seston C:P and N:P) and higher zooplankton biomass.

    Zooplankton community composition differed in the north vs. south, with a dominance of N-requiring calanoid copepods with high N:P in the north and P-requiring cladocerans with low N:P in the south. Also, greater differences in zooplankton community composition were found between subarctic regions (with lower DOC) than between boreal regions (with higher DOC), suggesting that increases in lake DOC and associated declines in lake DIN:TP reduce differences in zooplankton community composition.

    The combination of lower lake DIN, higher lake DOC, and lower lake DIN:TP led to reduced zooplankton N:P recycling ratios, possibly by reducing seston N:P and/or by enhancing calanoid copepod dominance in the zooplankton community.

    Our findings suggest that the combination of declining N deposition and increasing lake browning in northern high-latitude lakes will reduce phytoplankton biomass, but will concurrently enhance seston mineral quality and probably also zooplankton biomass and their recycling efficiency of P relative to N.

  • 5. Dinasquet, Julie
    et al.
    Richert, Inga
    Logares, Ramiro
    Yager, Patricia
    Bertilsson, Stefan
    Riemann, Lasse
    Mixing of water masses caused by a drifting iceberg affects bacterial activity, community composition and substrate utilization capability in the Southern Ocean2017Ingår i: Environmental Microbiology, ISSN 1462-2912, E-ISSN 1462-2920, Vol. 19, nr 6, SI, s. 2453-2467Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The number of icebergs produced from ice-shelf disintegration has increased over the past decade in Antarctica. These drifting icebergs mix the water column, influence stratification and nutrient condition, and can affect local productivity and food web composition. Data on whether icebergs affect bacterioplankton function and composition are scarce, however. We assessed the influence of iceberg drift on bacterial community composition and on their ability to exploit carbon substrates during summer in the coastal Southern Ocean. An elevated bacterial production and a different community composition were observed in iceberg-influenced waters relative to the undisturbed water column nearby. These major differences were confirmed in short-term incubations with bromodeoxyuridine followed by CARD-FISH. Furthermore, one-week bottle incubations amended with inorganic nutrients and carbon substrates (a mix of substrates, glutamine, Nacetylglucosamine, or pyruvate) revealed contrasting capacity of bacterioplankton to utilize specific carbon substrates in the iceberg-influenced waters compared with the undisturbed site. Our study demonstrates that the hydrographical perturbations introduced by a drifting iceberg can affect activity, composition, and substrate utilization capability of marine bacterioplankton. Consequently, in a context of global warming, increased frequency of drifting icebergs in polar regions holds the potential to affect carbon and nutrient biogeochemistry at local and possibly regional scales.

  • 6.
    Fuentes Guerrero, César
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Grain size analysis of a short sediment core from the Lomonosov Ridge, central Arctic Ocean2015Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    ”Trigger core 07” är en 53 cm lång sedimentkärna som togs upp på ett djup av 2522 m från Lomonosovryggen i Arktisk under en dansk-svensk expedition kallad ”Lomonosov Ridge off Greenland 2012”. Den här delen av världen har genomgått kraftiga klimatförändringar under kvartär. Istäcken har vuxit fram och dragit sig tillbaka och avsatt sediment över hela Arktis. Sediment avsatta under istider, kännetecknas av att vara gråa med mycket grovt material, medan sediment avsatta under mellanistider är bruna, vilket är på grund av de höga halterna av mangan och består av finkornigt material. Målet med denna uppsats är att göra en kornstorleksanalys på sedimentkärnan, med syfte i åtanke på att göra en tolkning av informationen i förhållande till istidshistorik och paleo-oceanografi. För att kunna gå tillväga med det, har en korrelation gjorts mellan kärnan och ”piston core 07”, samt en korrelation mellan ”piston core 07” och ”Arctic Coring Expedition, ACEX”. Resultaten visar en brun enhet rik på finkornigt material ned till 32 cm, vilket är typiskt för mellanistider. Den följs av en grå-beige enhet som sträcker sig ned till 49 cm och består av grovkornigt material vilket tyder på istid. Den här enheten kan kopplas till ”Marine Isotope Stage 2, MIS ”, som varade mellan 14000 och 29000 år sedan. 

  • 7.
    Gómez-Gener, Lluís
    et al.
    Stream Biofilm and Ecosystem Research Laboratory, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
    Rocher-Ros, Gerard
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Battin, Tom
    Stream Biofilm and Ecosystem Research Laboratory, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
    Cohen, Matthew J.
    School of Forest Resources and Conservation, University of Florida, FL, Gainesville, United States.
    Dalmagro, Higo J.
    University of Cuiabá, Cuiabá, Brazil.
    Dinsmore, Kerry J.
    Centre for Ecology and Hydrology, Bush Estate, Penicuik, United Kingdom.
    Drake, Travis W.
    Department of Environmental Systems Science, ETH Zürich, Zürich, Switzerland.
    Duvert, Clément
    Research Institute for the Environment and Livelihoods, Charles Darwin University, NT, Darwin, Australia.
    Enrich-Prast, Alex
    Biogas Research Center and Department of Thematic Studies–Environmental Change, Linköping University, Linköping, Sweden; Post-Graduate Program in Geosciences (Environmental Geochemistry), Chemistry Institute, Fluminense Federal University, Niterói, Brazil.
    Horgby, Åsa
    Stream Biofilm and Ecosystem Research Laboratory, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
    Johnson, Mark S.
    Institute for Resources, Environment and Sustainability, University of British Columbia, BC, Vancouver, Canada; Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, BC, Vancouver, Canada.
    Kirk, Lily
    School of Natural Resources and Environment, University of Florida, FL, Gainesville, United States.
    Machado-Silva, Fausto
    Post-Graduate Program in Geosciences (Environmental Geochemistry), Chemistry Institute, Fluminense Federal University, Niterói, Brazil.
    Marzolf, Nicholas S.
    Department of Forestry and Environmental Resources, North Carolina State University, NC, Raleigh, United States.
    McDowell, Mollie J.
    Institute for Resources, Environment and Sustainability, University of British Columbia, BC, Vancouver, Canada; Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, BC, Vancouver, Canada.
    McDowell, William H.
    Department of Natural Resources and the Environment, University of New Hampshire, NH, Durham, United States.
    Miettinen, Heli
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Ojala, Anne K.
    Faculty of Biological and Environmental Sciences, Ecosystems and Environment Research Programme, University of Helsinki, Helsinki, Finland.
    Peter, Hannes
    Stream Biofilm and Ecosystem Research Laboratory, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
    Pumpanen, Jukka
    Department of Environmental and Biological Sciences, University of Eastern Finland, Kuopio, Finland.
    Ran, Lishan
    Department of Geography, The University of Hong Kong, Pokfulam, Hong Kong.
    Riveros-Iregui, Diego A.
    Department of Geography, University of North Carolina at Chapel Hill, NC, Chapel Hill, United States.
    Santos, Isaac R.
    Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden.
    Six, Johan
    Department of Environmental Systems Science, ETH Zürich, Zürich, Switzerland.
    Stanley, Emily H.
    Center for Limnology, University of Wisconsin-Madison, WI, Madison, United States.
    Wallin, Marcus B.
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    White, Shane A.
    National Marine Science Centre, Southern Cross University, NSW, Coffs Harbour, Australia.
    Sponseller, Ryan A.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Global carbon dioxide efflux from rivers enhanced by high nocturnal emissions2021Ingår i: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 14, nr 5, s. 289-294Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Carbon dioxide (CO2) emissions to the atmosphere from running waters are estimated to be four times greater than the total carbon (C) flux to the oceans. However, these fluxes remain poorly constrained because of substantial spatial and temporal variability in dissolved CO2 concentrations. Using a global compilation of high-frequency CO2 measurements, we demonstrate that nocturnal CO2 emissions are on average 27% (0.9 gC m−2 d−1) greater than those estimated from diurnal concentrations alone. Constraints on light availability due to canopy shading or water colour are the principal controls on observed diel (24 hour) variation, suggesting this nocturnal increase arises from daytime fixation of CO2 by photosynthesis. Because current global estimates of CO2 emissions to the atmosphere from running waters (0.65–1.8 PgC yr−1) rely primarily on discrete measurements of dissolved CO2 obtained during the day, they substantially underestimate the magnitude of this flux. Accounting for night-time CO2 emissions may elevate global estimates from running waters to the atmosphere by 0.20–0.55 PgC yr−1.

  • 8. Hauptmann, Demian
    et al.
    Myrstener, Maria
    Spatial and temporal patterns of stream nutrient limitation in an Arctic catchment2023Ingår i: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 850, nr 7, s. 1699-1713Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Arctic stream biofilm responses to ongoing climate-related changes in physical and chemical conditions have major implications for stream food webs and biogeochemical cycles. Yet, such effects have rarely been studied outside summer months or at sub-catchment scales in the Arctic. We used deployments of nutrient diffusing substrates (NDS) to assess the spatial (20 deployments) and seasonal patterns (10 deployments) and physical and chemical drivers of nutrient limitation within an Arctic stream catchment. Results show that nutrient limitation of autotrophic processes was common during summer, but that light inhibited biomass accrual under the ice in winter. Alongside single N, P and C responses, co-limitation dominated the overall pattern of limitation over time and across the catchment. However, the primary limiting nutrient to autotrophs changed from N to P in parts of the catchment with higher N concentrations. As Arctic studies are often conducted at individual sites during summer, these may miss shifts in the drivers of stream productivity that arise from variable nutrient, temperature, and light regimes. Our results caution against focusing on one single most important limiting nutrient, as we found that this can shift seasonally and over small spatial scales in this Arctic catchment.

  • 9.
    Jantunen, Liisa
    et al.
    Environment Canada, Canada.
    Wong, Fiona
    Stockholm University.
    Gawor, Anya
    Environment Canada.
    Kylin, Henrik
    Linköpings universitet, Tema Miljöförändring.
    Helm, Paul
    Ontario Ministry of the Environment, Canada.
    Stern, Gary
    University of Manitoba, Canada.
    Strachan, William
    Environment Canada, Canada.
    Burniston, Deborah
    Environment Canada, Canada.
    Bidleman, Terry
    Umeå University.
    20 Years of Air-Water Gas Exchange Observations for Pesticides in the Western Arctic Ocean2015Ingår i: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 49, nr 23, s. 13844-13852Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Arctic has been contaminated by legacy organochlorine pesticides (OCPs) and currently used pesticides (CUPs) through atmospheric transport and oceanic currents. Here we report the time trends and air−water exchange of OCPs and CUPs from research expeditions conducted between 1993 and 2013. Compounds determined in both air and water were trans- and cis-chlordanes (TC, CC), trans- and cis-nonachlors (TN, CN), heptachlor exo-epoxide (HEPX), dieldrin (DIEL), chlorobornanes (ΣCHBs and toxaphene), dacthal (DAC), endosulfans and metabolite endosulfan sulfate (ENDO-I, ENDO-II, and ENDO SUL), chlorothalonil (CHT), chlorpyrifos (CPF), and trifluralin (TFN). Pentachloronitrobenzene (PCNB and quintozene) and its soil metabolite pentachlorothianisole (PCTA) were also found in air. Concentrations of most OCPs declined in surface water, whereas some CUPs increased (ENDO-I, CHT, and TFN) or showed no significant change (CPF and DAC), and most compounds declined in air. Chlordane compound fractions TC/(TC + CC) and TC/(TC + CC + TN) decreased in water and air, while CC/(TC + CC + TN) increased. TN/(TC + CC + TN) also increased in air and slightly, but not significantly, in water. These changes suggest selective removal of more labile TC and/or a shift in chlordane sources. Water−air fugacity ratios indicated net volatilization (FR > 1.0) or near equilibrium (FR not significantly different from 1.0) for most OCPs but net deposition (FR < 1.0) for ΣCHBs. Net deposition was shown for ENDO-I on all expeditions, while the net exchange direction of other CUPs varied. Understanding the processes and current state of air−surface exchange helps to interpret environmental exposure and evaluate the effectiveness of international protocols and provides insights for the environmental fate of new and emerging chemicals.

  • 10.
    Jantze, Elin J.
    et al.
    Stockholms universitet, Institutionen för naturgeografi och kvartärgeologi (INK).
    Lyon, Steve W.
    Stockholms universitet, Institutionen för naturgeografi och kvartärgeologi (INK).
    Destouni, Georgia
    Stockholms universitet, Institutionen för naturgeografi och kvartärgeologi (INK).
    Subsurface release and transport of dissolved carbon in a discontinuous permafrost region2013Ingår i: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 17, nr 10, s. 3827-3839Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Subsurface hydrological flow pathways and advection rates through the landscape affect the quantity and timing of hydrological transport of dissolved carbon. This study investigates hydrological carbon transport through the subsurface to streams and how it is affected by the distribution of subsurface hydrological pathways and travel times through the landscape. We develop a consistent mechanistic, pathway- and travel time-based modeling approach for release and transport of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC). The model implications are tested against observations in the subarctic Abiskojokken catchment in northernmost Sweden (68 degrees 21'N, 18 degrees 49'E) as a field case example of a discontinuous permafrost region. The results show: (a) For DOC, both concentration and load are essentially flow-independent because their dynamics are instead dominated by the annual renewal and depletion. Specifically, the flow independence is the result of the small characteristic DOC respiration-dissolution time scale, in the range of 1 yr, relative to the average travel time of water through the subsurface to the stream. (b) For DIC, the load is highly flow-dependent due to the large characteristic weathering-dissolution time, much larger than 1 yr, relative to the average subsurface water travel time to the stream. This rate relation keeps the DIC concentration essentially flow-independent, and thereby less fluctuating in time than the DIC load.

  • 11. Kinney, Jaclyn Clement
    et al.
    Assmann, Karen M.
    Maslowski, Wieslaw
    Björk, Göran
    Jakobsson, Martin
    Jutterstrom, Sara
    Lee, Younjoo J.
    Osinski, Robert
    Semiletov, Igor
    Ulfsbo, Adam
    Wåhlstrom, Irene
    SMHI, Oceanografi.
    Anderson, Leif G.
    On the circulation, water mass distribution, and nutrient concentrations of the western Chukchi Sea2022Ingår i: Ocean Science, ISSN 1812-0784, E-ISSN 1812-0792, Vol. 18, nr 1, s. 29-49Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Substantial amounts of nutrients and carbon enter the Arctic Ocean from the Pacific Ocean through the Bering Strait, distributed over three main pathways. Water with low salinities and nutrient concentrations takes an eastern route along the Alaskan coast, as Alaskan Coastal Water. A central pathway exhibits intermediate salinity and nutrient concentrations, while the most nutrient-rich water enters the Bering Strait on its western side. Towards the Arctic Ocean, the flow of these water masses is subject to strong topographic steering within the Chukchi Sea with volume transport modulated by the wind field. In this contribution, we use data from several sections crossing Herald Canyon collected in 2008 and 2014 together with numerical modelling to investigate the circulation and transport in the western part of the Chukchi Sea. We find that a substantial fraction of water from the Chukchi Sea enters the East Siberian Sea south of Wrangel Island and circulates in an anticyclonic direction around the island. This water then contributes to the high-nutrient waters of Herald Canyon. The bottom of the canyon has the highest nutrient concentrations, likely as a result of addition from the degradation of organic matter at the sediment surface in the East Siberian Sea. The flux of nutrients (nitrate, phosphate, and silicate) and dissolved inorganic carbon in Bering Summer Water and Winter Water is computed by combining hydrographic and nutrient observations with geostrophic transport referenced to lowered acoustic Doppler current profiler (LADCP) and surface drift data. Even if there are some general similarities between the years, there are differences in both the temperature–salinity and nutrient characteristics. To assess these differences, and also to get a wider temporal and spatial view, numerical modelling results are applied. According to model results, high-frequency variability dominates the flow in Herald Canyon. This leads us to conclude that this region needs to be monitored over a longer time frame to deduce the temporal variability and potential trends.

  • 12.
    Kylin, Henrik
    Linköpings universitet, Tema Miljöförändring.
    Marine debris on two Arctic beaches in the Russian Far East2020Ingår i: Polar Research, ISSN 0800-0395, E-ISSN 1751-8369, Vol. 39, artikel-id 3381Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In August 2005, marine debris was counted on two Arctic beaches in the RussianFar East. On the north coast of the Chukchi Peninsula east of Kolyuchin Bay, a beach stretch of ca. 2.4 km held a total of 736 items, 0.024 items m‑2, while no more than 0.0011 items m‑2, 12 items in total, were found on a beach stretch of ca. 1.2 km on southern Wrangel Island. The likely explanation for this difference is that the area around the mainland beach is ice-free for a longer period each year, but a contributing factor may be that late spring ice movement removed plastic from the beach on Wrangel Island. The language on the few items with identifiable labels was for the most part Russian or English, making the Chukchi Sea a possible source region. Beaches at the same latitude in the Atlantic may hold more debris on account of the higher human population density, more shipping and transport of floating debris unhindered by a narrow strait that is ice-covered much of the year. Fishing gear blown across the tundra is suggested as a potential threat to reindeer and other terrestrial wildlife.

  • 13.
    Myrstener, Maria
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Gómez-Gener, Lluís
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Rocher-Ros, Gerard
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Giesler, Reiner
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Sponseller, Ryan A.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Nutrients influence seasonal metabolic patterns and total productivity of Arctic streams2021Ingår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 66, nr S1, s. S182-S196Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The seasonality of gross primary production (GPP) in streams is driven by multiple physical and chemical factors, yet incident light is often thought to be most important. In Arctic tundra streams, however, light is available in saturating amounts throughout the summer, but sharp declines in nutrient supply during the terrestrial growing season may constrain aquatic productivity. Given the opposing seasonality of these drivers, we hypothesized that "shoulder seasons"-spring and autumn-represent critical time windows when light and nutrients align to optimize rates of stream productivity in the Arctic. To test this, we measured annual patterns of GPP and biofilm accumulation in eight streams in Arctic Sweden. We found that the aquatic growing season length differed by 4 months across streams and was determined largely by the timing of ice-off in spring. During the growing season, temporal variability in GPP for nitrogen (N) poor streams was correlated with inorganic N concentration, while in more N-rich streams GPP was instead linked to changes in phosphorus and light. Annual GPP varied ninefold among streams and was enhanced by N availability, the length of ice-free period, and low flood frequency. Finally, network scale estimates of GPP highlight the overall significance of the shoulder seasons, which accounted for 48% of annual productivity. We suggest that the timing of ice off and nutrient supply from land interact to regulate the annual metabolic regimes of nutrient poor, Arctic streams, leading to unexpected peaks in productivity that are offset from the terrestrial growing season.

  • 14. Nilsson, Hampus
    et al.
    Pilesjö, Petter
    Hasan, Abdulghani
    Persson, Andreas
    Dynamic spatio-temporal flow modeling with raster DEMs2021Ingår i: Transactions on GIS, ISSN 1361-1682, E-ISSN 1467-9671, Vol. n/a, nr n/aArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    A user-friendly high-resolution intermediate complexity dynamic and spatially distributed flow model is crucial in urban flood modeling. Planners and consultants need to improve the accuracy of floods and estimation of risks. A new flow model will serve as a rapid tool to improve identification of these. This article provides a detailed explanation of a model based on a multiple flow algorithm. Model testing was performed on selected urban and rural areas. Additionally, a sensitivity analysis is conducted to analyze functionality. The model includes basic hydrological processes and is therefore less complex than fully physical models. The data needed to set up and run the new model include spatially and temporally distributed basic geometric and hydrologic variables (i.e., digital elevation model, precipitation, infiltration, and surface roughness). The model is implemented using open-source coding and can easily be applied to any selected area. Outputs are water volumes, depths, and velocities at different modeling times. Using GIS, results can be visualized and utilized for further analyses. The test, applied in urban as well as rural areas, demonstrates its user-friendliness, and that the estimated distributed water depths and water velocity at any time step can be saved and visualized.

  • 15. Nygren, Michelle
    et al.
    Barthel, Roland
    Allen, Diana M.
    Giese, Markus
    Exploring groundwater drought responsiveness in lowland post-glacial environments2022Ingår i: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 30, nr 7, s. 1937-1961Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Groundwater drought response to meteorological forcing depends on initial hydrological conditions. This makes it difficult to characterise groundwater droughts and identify the drought vulnerability of aquifers. The objective is to increase the understanding of groundwater memory and response to meteorological forcing in lowland post-glacial environments. Eighty-one groundwater hydrographs are analysed, using the standardised groundwater level index (SGI) and the precipitation index. Memory and response times are assessed using auto- and cross-correlation functions. Response time is estimated by comparing two approaches: (1) the traditional use of the maximum cross-correlation, and (2) the alternative use of the cross-correlation slope. Results are interpreted for different hydrogeological settings. The analysis showed that sand aquifers have the longest memory and response times, particularly in confined settings where the memory could be over 4 years. Silts and tills have relatively short memories and response times, at less than 1 year, though median values for silt are higher than for unconfined sand aquifers. In this study, estimating response time using the correlation slope is superior at capturing the initial response time of groundwater to precipitation. However, the results showed that groundwater anomalies in lowland post-glacial environments are sometimes more influenced by climate teleconnections than concurrent forcing. This emphasises the need for a holistic approach for the characterisation and projection of groundwater drought, as it develops in simultaneous response to meteorological forcing at different timescales.

  • 16. Olid, C.
    et al.
    Zannella, A.
    Lau, D. C. P.
    The Role of Methane Transport From the Active Layer in Sustaining Methane Emissions and Food Chains in Subarctic Ponds2021Ingår i: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 126, nr 3, artikel-id e2020JG005810Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Groundwater discharge from the seasonally thawed active layer is increasingly recognized as an important pathway for delivering methane (CH4) into Arctic lakes and streams, but its contribution to CH4 emissions from thaw ponds and its influence on the trophic support and nutritional quality of pond food chains remains unexplored. We quantified the transport of CH4 from the active layer through groundwater discharge into thaw ponds in a subarctic catchment in northern Sweden, using radon (222Rn) as groundwater tracer. We analyzed stable isotopes and fatty acids of pond macroinvertebrates to evaluate the potential effects of groundwater-mediated CH4 inputs on the aquatic food chains. Our results indicate that active layer groundwater discharge flows are nontrivial (range 6%–46% of pond volume per day) and the associated CH4 fluxes (median 339 mg C m−2day−1, interquartile range [IQR]: 179–419 mg C m−2 day−1) can sustain the diffusive CH4 emissions from most of the ponds (155 mg C m−2 day−1, IQR: 55–234 mg C m−2 day−1). Consumers in ponds receiving greater CH4 inputs from the active layer had lower stable carbon (C) isotope signatures that indicates a greater trophic reliance on methane oxidizing bacteria (MOB), and they had lower nutritional quality as indicated by their lower tissue concentrations of polyunsaturated fatty acids. Overall, this work links physical (CH4 transport from the active layer), biogeochemical (CH4 emission), and ecological (MOB-consumer interaction) processes to provide direct evidence for the role of active layer groundwater discharge in CH4 cycling of subarctic thaw ponds.

  • 17. Qi, Di
    et al.
    Chen, Liqi
    Chen, Baoshan
    Gao, Zhongyong
    Zhong, Wenli
    Feely, Richard A.
    Anderson, Leif G.
    Sun, Heng
    Chen, Jianfang
    Chen, Min
    Zhan, Liyang
    Zhang, Yuanhui
    Cai, Wei-Jun
    Increase in acidifying water in the western Arctic Ocean2017Ingår i: Nature Climate Change, ISSN 1758-678X, E-ISSN 1758-6798, Vol. 7, nr 3, s. 195-199Artikel i tidskrift (Refereegranskat)
  • 18. Rydén, Jesper
    Statistical analysis of possible trends for extreme floods in northern Sweden2022Ingår i: River Research and Applications, ISSN 1535-1467, Vol. 38, nr 6, s. 1041-1050Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    With ongoing climate change, analysis of trends in maximum annual daily river flow is of interest. Flow magnitude and timing during the year were investigated in this study. Observations from 11 unregulated rivers in northern Sweden were analysed, using extreme-value distributions with time-dependent parameters. The Mann–Kendall test was used to investigate possible trends. The extreme-value statistics revealed no significant trends for the stations considered, but the Mann–Kendall test showed a significant upward trend for some stations. For timing of maximum flow (day of the year), the Mann–Kendall test revealed significant downward trends for two stations (with the longest records). This implies that the day of the maximum flow is occurring earlier in the year in northern Sweden.

  • 19. Ul Hassan, Mahmood
    et al.
    Hayat, Omar
    Noreen, Zahra
    Selecting the best probability distribution for at-site flood frequency analysis; a study of Torne River2019Ingår i: SN Applied Sciences, ISSN 2523-3963, E-ISSN 2523-3971, Vol. 1, nr 12Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    At-site flood frequency analysis is a direct method of estimation of flood frequency at a particular site. The appropriate selection of probability distribution and a parameter estimation method are important for at-site flood frequency analysis. Generalized extreme value, three-parameter log-normal, generalized logistic, Pearson type-III and Gumbel distributions have been considered to describe the annual maximum steam flow at five gauging sites of Torne River in Sweden. To estimate the parameters of distributions, maximum likelihood estimation and L-moments methods are used. The performance of these distributions is assessed based on goodness-of-fit tests and accuracy measures. At most sites, the best-fitted distributions are with LM estimation method. Finally, the most suitable distribution at each site is used to predict the maximum flood magnitude for different return periods.

  • 20. Zhang, Hui
    et al.
    Väliranta, Minna
    Swindles, Graeme T.
    Aquino-López, Marco A.
    Mullan, Donal
    Tan, Ning
    Amesbury, Matthew
    Babeshko, Kirill V.
    Bao, Kunshan
    Bobrov, Anatoly
    Chernyshov, Viktor
    Davies, Marissa A.
    Diaconu, Andrei-Cosmin
    Feurdean, Angelica
    Finkelstein, Sarah A.
    Garneau, Michelle
    Guo, Zhengtang
    Jones, Miriam C.
    Kay, Martin
    Klein, Eric S.
    Lamentowicz, Mariusz
    Magnan, Gabriel
    Marcisz, Katarzyna
    Mazei, Natalia
    Mazei, Yuri
    Payne, Richard
    Pelletier, Nicolas
    Piilo, Sanna R.
    Pratte, Steve
    Roland, Thomas
    Saldaev, Damir
    Shotyk, William
    Sim, Thomas G.
    Sloan, Thomas J.
    Słowiński, Michał
    Talbot, Julie
    Taylor, Liam
    Tsyganov, Andrey N.
    Wetterich, Sebastian
    Xing, Wei
    Zhao, Yan
    Recent climate change has driven divergent hydrological shifts in high-latitude peatlands2022Ingår i: Nature Communications, E-ISSN 2041-1723, Vol. 13, nr 1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-latitude peatlands are changing rapidly in response to climate change, including permafrost thaw. Here, we reconstruct hydrological conditions since the seventeenth century using testate amoeba data from 103 high-latitude peat archives. We show that 54% of the peatlands have been drying and 32% have been wetting over this period, illustrating the complex ecohydrological dynamics of high latitude peatlands and their highly uncertain responses to a warming climate.

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