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| 2. |
- Drake, Henrik, 1979-, et al.
(författare)
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Ancient microbial activity in deep hydraulically conductive fracture zones within the Forsmark target area for deep geological nuclear waste disposal, Sweden
- 2018
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Ingår i: Geosciences. - : MDPI AG. - 2076-3263. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies reveal that organisms from all three domains of life—Archaea, Bacteria, and even Eukarya—can thrive under energy-poor, dark, and anoxic conditions at large depths in the fractured crystalline continental crust. There is a need for an increased understanding of the processes and lifeforms in this vast realm, for example, regarding the spatiotemporal extent and variability of the different processes in the crust. Here, we present a study that set out to detect signs of ancient microbial life in the Forsmark area—the target area for deep geological nuclear waste disposal in Sweden. Stable isotope compositions were determined with high spatial resolution analyses within mineral coatings, and mineralized remains of putative microorganisms were studied in several deep water-conducting fracture zones (down to 663 m depth), from which hydrochemical and gas data exist. Large isotopic variabilities of 13Ccalcite (?36.2 to +20.2‰V-PDB) and 34Spyrite (?11.7 to +37.8‰V-CDT) disclose discrete periods of methanogenesis, and potentially, anaerobic oxidation of methane and related microbial sulfate reduction at several depth intervals. Dominant calcite–water disequilibrium of 18O and 87Sr/86Sr precludes abundant recent precipitation. Instead, the mineral coatings largely reflect an ancient archive of episodic microbial processes in the fracture system, which, according to our microscale Rb–Sr dating of co-genetic adularia and calcite, date back to the mid-Paleozoic. Potential Quaternary precipitation exists mainly at ~400 m depth in one of the boreholes, where mineral–water compositions corresponded.
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| 3. |
- Roth, Florian, et al.
(författare)
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High spatiotemporal variability of methane concentrations challenges estimates of emissions across vegetated coastal ecosystems.
- 2022
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Ingår i: Global change biology. - : Wiley. - 1365-2486 .- 1354-1013. ; 28:14, s. 4308-4322
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Tidskriftsartikel (refereegranskat)abstract
- 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, δ13 C-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., 6-460nM CH4 ) with habitat-specific seasonal and diurnal patterns. We observed (1) δ13 C-CH4 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 ~1eV that drove seasonal changes. Bootstrapping simulations show that scaling the CH4 distribution from few samples involves large errors, and that ~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≥100μmol 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.
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| 4. |
- Cheung, Henry Lok Shan, et al.
(författare)
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Denitrification, anammox, and DNRA in oligotrophic continental shelf sediments
- 2024
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Ingår i: Limnology and Oceanography. - 1939-5590 .- 0024-3590.
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Tidskriftsartikel (refereegranskat)abstract
- Continental shelf sediments are considered hotspots for nitrogen (N) removal. While most investigations have quantified denitrification in shelves receiving large amounts of anthropogenic nutrient supply, we lack insight into the key drivers of N removal on oligotrophic shelves. Here, we measured rates of N removal through denitrification and anammox by the revised-isotope pairing technique (r-IPT) along the Northeastern New Zealand shelf. Denitrification dominated total N2 production at depths between 30 and 128 m with average rates (± SE) ranging from 65 ± 28 to 284 ± 72 μmol N m−2 d−1. N2 production by anammox ranged from 3 ± 1 to 28 ± 11 μmol N m−2 d−1 and accounted for 2–19% of total N2 production. DNRA was negligible in these oligotrophic settings. Parallel microbial community analysis showed that both Proteobacteria and Planctomycetota were key taxa driving denitrification. Denitrification displayed a negative correlation with oxygen penetration depth, and a positive correlation with macrofauna abundance. Our denitrification rates were comparable to oligotrophic shelves from the Arctic, but were lower than those from nutrient-rich Pacific and Atlantic shelves. Based on our results and existing IPT measurements, the global shelf denitrification rate was reassessed to be 53.5 ± 8.1 Tg N yr−1, equivalent to 20 ± 2% of marine N removal. We suggest that previous estimates of global shelf N loss might have been overestimated due to sampling bias toward areas with high N loads in the Northern Hemisphere.
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| 5. |
- Omstedt, Anders, 1949
(författare)
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The Development of Climate Science of the Baltic Sea Region
- 2017
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Ingår i: Oxford Research Encyclopedia of Climate Science. - : Oxford University Press.
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Dramatic climate changes have occurred in the Baltic Sea region caused by changes in orbital movement in the earth–sun system and the melting of the Fennoscandian Ice Sheet. Added to these longer-term changes, changes have occurred at all timescales, caused mainly by variations in large-scale atmospheric pressure systems due to competition between the meandering midlatitude low-pressure systems and highpressure systems. Here we follow the development of climate science of the Baltic Sea from when observations began in the 18th century to the early 21st century. The question of why the water level is sinking around the Baltic Sea coasts could not be answered until the ideas of postglacial uplift and the thermal history of the earth were better understood in the 19th century and periodic behavior in climate related time series attracted scientific interest. Herring and sardine fishing successes and failures have led to investigations of fishery and climate change and to the realization that fisheries themselves have strongly negative effects on the marine environment, calling for international assessment efforts. Scientists later introduced the concept of regime shifts when interpreting their data, attributing these to various causes. The increasing amount of anoxic deep water in the Baltic Sea and eutrophication have prompted debate about what is natural and what is anthropogenic, and the scientific outcome of these debates now forms the basis of international management efforts to reduce nutrient leakage from land. The observed increase in atmospheric CO and its effects on global warming have focused the climate debate on trends and generated a series of international and regional assessments and research programs that have greatly improved our understanding of climate and environmental changes, bolstering the efforts of earth system science, in which both climate and environmental factors are analyzed together.
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| 6. |
- Baresel, Christian, et al.
(författare)
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Uncertainty-Accounting Environmental Policy and Management of Water Systems
- 2007
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Ingår i: Environmental Science & Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 41:10, s. 3653–3659-
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Tidskriftsartikel (refereegranskat)abstract
- Environmental policies for water quality and ecosystemmanagement do not commonly require explicit stochasticaccounts of uncertainty and risk associated with thequantification and prediction of waterborne pollutant loadsand abatement effects. In this study, we formulate andinvestigate a possible environmental policy that does requirean explicit stochastic uncertainty account. We compareboth the environmental and economic resource allocationperformance of such an uncertainty-accounting environmentalpolicy with that of deterministic, risk-prone and riskaverseenvironmental policies under a range of differenthypothetical, yet still possible, scenarios. The comparisonindicates that a stochastic uncertainty-accountingpolicy may perform better than deterministic policies overa range of different scenarios. Even in the absence ofreliable site-specific data, reported literature values appearto be useful for such a stochastic account of uncertainty.
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| 7. |
- Björk, Mats, 1960-, et al.
(författare)
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Methane emissions from macrophyte beach wrack on Baltic seashores
- 2023
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Ingår i: Ambio. - : Springer Nature. - 0044-7447 .- 1654-7209. ; 52:1, s. 171-181
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Tidskriftsartikel (refereegranskat)abstract
- Beach wrack of marine macrophytes is a natural component of many beaches. To test if such wrack emits the potent greenhouse gas methane, field measurements were made at different seasons on beach wrack depositions of different ages, exposure, and distance from the water. Methane emissions varied greatly, from 0 to 176 mg CH4-C m−2 day−1, with a clear positive correlation between emission and temperature. Dry wrack had lower emissions than wet. Using temperature data from 2016 to 2020, seasonal changes in fluxes were calculated for a natural wrack accumulation area. Such calculated average emissions were close to zero during winter, but peaked in summer, with very high emissions when daily temperatures exceeded 20 °C. We conclude that waterlogged beach wrack significantly contributes to greenhouse gas emissions and that emissions might drastically increase with increasing global temperatures. When beach wrack is collected into heaps away from the water, the emissions are however close to zero.
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| 8. |
- Katrantsiotis, Christos, et al.
(författare)
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Seasonal variability in temperature trends and atmospheric circulation systems during the Eemian (Last Interglacial) based on n-alkanes hydrogen isotopes from Northern Finland
- 2021
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Ingår i: Quaternary Science Reviews. - Amsterdam : Elsevier. - 0277-3791 .- 1873-457X. ; 273, s. 107250-107250
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Tidskriftsartikel (refereegranskat)abstract
- The Last Interglacial warm period, the Eemian (ca. 130-116 thousand years ago), serves as a reference for projected future climate in a warmer world. However, there is a limited understanding of the seasonal characteristics of interglacial climate dynamics, especially in high latitude regions. In this study, we aimto provide new insights into seasonal trends in temperature and moisture source location, linked to shifts in atmospheric circulation patterns, for northern Fennoscandia during the Eemian. Our study is based on the distribution and stable hydrogen isotope composition (dD) of n-alkanes in a lake sediment sequence from the Sokli paleolake in NE Finland, placed in a multi-proxy framework. The dD values of predominantly macrophyte-derived mid-chain n-alkanes are interpreted to reflect lake water dD variability influenced by winter precipitation dD (dDprec), ice cover duration and deuterium (D)-depleted meltwater. The dD values of terrestrial plant-derived long-chain n-alkanes primarily reflect soil water dD variability modulated by summer dDprec and by the evaporative enrichment of soil and leaf water. The dDprec variability in our study area is mostly attributed to the temperature effect and the moisture source location linked to the relative dominance between D-depleted continental and polar air masses and Denriched North Atlantic air masses. The biomarker signal further corroborates earlier diatom-based studies and pollen-inferred January and July temperature reconstructions from the same sediment sequence. Three phases of climatic changes can be identified that generally follow the secular variationsin seasonal insolation: (i) an early warming trend succeeded by a period of strong seasonality (ii) a midoptimum phase with gradually decreased seasonality and cooler summers, and (iii) a late climatic instability with a cooling trend. Superimposed on this trend, two abrupt cooling events occur in the early and late Eemian. The Sokli dD variability is generally in good agreement with other North Atlantic and Siberian records, reflecting major changes in the atmospheric circulation patterns during the Eemian as a response to orbital and oceanic forcings.
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| 9. |
- Sobek, Anna, et al.
(författare)
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Organic matter degradation causes enrichment of organic pollutants in hadal sediments
- 2023
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Ingår i: Nature Communications. - 2041-1723. ; 14
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Tidskriftsartikel (refereegranskat)abstract
- Burial of persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs) in deep-sea sediments contributes to 60% of their historical emissions. Yet, empirical data on their occurrence in the deep-ocean is scarce. Estimates of the deep-ocean POP sink are therefore uncertain. Hadal trenches, representing the deepest part of the ocean, are hotspots for organic carbon burial and decomposition. POPs favorably partition to organic carbon, making trenches likely significant sinks for contaminants. Here we show that PCBs occur in both hadal (7720–8085 m) and non-hadal (2560–4050 m) sediment in the Atacama Trench. PCB concentrations normalized to sediment dry weight were similar across sites while those normalized to sediment organic carbon increased exponentially as the inert organic carbon fraction of the sediment increased in degraded hadal sediments. We suggest that the unique deposition dynamics and elevated turnover of organic carbon in hadal trenches increase POP concentrations in the deepest places on Earth.
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| 10. |
- Oni, Stephen, et al.
(författare)
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Local- and landscape-scale impacts of clear-cuts and climate change on surface water dissolved organic carbon in boreal forests
- 2015
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Ingår i: Journal of Geophysical Research - Biogeosciences. - 2169-8953 .- 2169-8961. ; 120:11, s. 2402-2426
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Tidskriftsartikel (refereegranskat)abstract
- Forest harvesting and climate change may significantly increase concentrations and fluxes of dissolved organic carbon (DOC) in boreal surface waters. However, the likely magnitude of any effect will vary depending on the landscape-element type and spatial scale. We used a chain of hydrological, empirical, and process-based biogeochemical models coupled to an ensemble of downscaled Regional Climate Model experiments to develop scenario storylines for local- and landscape-scale effects of forest harvesting and climate change on surface water DOC concentrations and fluxes. Local-scale runoff, soil temperature, and DOC dynamics were simulated for a range of forest and wetland landscape-element types and at the larger landscape scale. The results indicated that climate change will likely lead to greater winter flows and earlier, smaller spring peaks. Both forest harvesting and climate change scenarios resulted in large increases in summer and autumn runoff and higher DOC fluxes. Forest harvesting effects were clearly apparent at local scales. While at the landscape scale, approximately 1 mg L−1 (or 10%) of the DOC in surface waters can be attributed to clear-cuts, both climate change and intensified forestry can each increase DOC concentrations by another 1 mg L−1 in the future, which is less than that seen in many waterbodies recovering from acidification. These effects of forestry and climate change on surface water DOC concentrations are additive at a landscape scale but not at the local scale, where a range of landscape-element specific responses were observed.
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