| 1. |
- Alvarez, Belinda, et al.
(författare)
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Assessing the potential of sponges (Porifera) as indicators of ocean dissolved Si concentrations
- 2017
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Ingår i: Frontiers in Marine Science. - : Frontiers Media SA. - 2296-7745. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- We explore the distribution of sponges along dissolved silica (dSi) concentration gradients to test whether sponge assemblages are related to dSi and to assess the validity of fossil sponges as a palaeoecological tool for inferring dSi concentrations of the past oceans. We extracted sponge records from the publically available Global Biodiversity Information Facility (GBIF) database and linked these records with ocean physiochemical data to evaluate if there is any correspondence between dSi concentrations of the waters sponges inhabit and their distribution. Over 320,000 records of Porifera were available, of which 62,360 met strict quality control criteria. Our analyses was limited to the taxonomic levels of family, order and class. Because dSi concentration is correlated with depth in the modern ocean, we also explored sponge taxa distributions as a function of depth. We observe that while some sponge taxa appear to have dSi preferences (e.g., class Hexactinellida occurs mostly at high dSi), the overall distribution of sponge orders and families along dSi gradients is not sufficiently differentiated to unambiguously relate dSi concentrations to sponge taxa assemblages. We also observe that sponge taxa tend to be similarly distributed along a depth gradient. In other words, both dSi and/or another variable that depth is a surrogate for, may play a role in controlling sponge spatial distribution and the challenge is to distinguish between the two. We conclude that inferences about palaeo-dSi concentrations drawn from the abundance of sponges in the stratigraphic records must be treated cautiously as these animals are adapted to a great range of dSi conditions and likely other underlying variables that are related to depth. Our analysis provides a quantification of the dSi ranges of common sponge taxa, expands on previous knowledge related to their bathymetry preferences and suggest that sponge taxa assemblages are not related to particular dSi conditions.
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| 2. |
- Andrén, Elinor, et al.
(författare)
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Holocene climate and environmental change in north-eastern Kamchatka (Russian Far East), inferred from a multi-proxy study of lake sediments
- 2015
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181 .- 1872-6364. ; 134, s. 41-54
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Tidskriftsartikel (refereegranskat)abstract
- A sediment record from a small lake in the north-eastern part of the Kamchatka Peninsula has been investigated in a multi-proxy study to gain knowledge of Holocene climatic and environmental change. Pollen, diatoms, chironomids and selected geochemical parameters were analysed and the sediment record was dated with radiocarbon. The study shows Holocene changes in the terrestrial vegetation as well as responses of the lake ecosystem to catchment maturity and multiple stressors, such as climate change and volcanic eruptions. Climate change is the major driving force resulting in the recorded environmental changes in the lake, although recurrent tephra deposition events also contributed. The sediment record has an age at the base of about 10,000 cal yrs BP, and during the first 400 years the climate was cold and the lake exhibited extensive ice-cover during winter and relatively low primary production. Soils in the catchment were poor with shrub alder and birches dominatingthe vegetation surrounding the lake. At about 9600–8900 cal yrs BP the climate was cold and moist, and strong seasonal wind stress resulted in reduced ice-cover and increased primary production. After ca. 8900 cal yrs BP the forest density increased around the lake, runoff decreased in a generally drier climate resulting in decreasedprimary production in the lake until ca. 7000 cal yrs BP. This generally dry climate was interrupted by a brief climatic perturbation, possibly attributed to the 8.2 ka event, indicating increasingly windy conditions with thick snow cover, reduced ice-cover and slightly elevated primary production in the lake. The diatom record shows maximum thermal stratification at ca. 6300–5800 cal yrs BP and indicates together with the geochemical proxies a dry and slightly warmer climate resulting in a high productive lake. The most remarkably change in the catchment vegetation occurred at ca. 4200 cal yrs BP in the form of a conspicuous increase in Siberian dwarf pine (Pinus pumila), indicating a shift to a cooler climate with a thicker and more long-lasting snow cover. Thisvegetational change was accompanied by marked shifts in the diatom and chironomid stratigraphies, which are also indicative of colder climate and more extensive ice-cover.
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| 3. |
- Sun, Xiaole, 1983-, et al.
(författare)
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Climate Dependent Diatom Production is Preserved in Biogenic Si Isotope Signatures
- 2011
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 8:11, s. 3491-3499
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to reconstruct diatom production in the subarctic northern tip of the Baltic Sea, Bothnian Bay, based on down-core analysis of Si isotopes in biogenic silica (BSi). Dating of the sediment showed that the samples covered the period 1820 to 2000. The sediment core record can be divided into two periods, an unperturbed period from 1820 to 1950 and a second period affected by human activities (from 1950 to 2000). This has been observed elsewhere in the Baltic Sea. The shift in the sediment core record after 1950 is likely caused by large scale damming of rivers. Diatom production was inferred from the Si isotope composition which ranged between δ30Si −0.18‰ and +0.58‰ in BSi, and assuming fractionation patterns due to the Raleigh distillation, the production was shown to be correlated with air and water temperature, which in turn were correlated with the mixed layer (ML) depth. The sedimentary record showed that the deeper ML depth observed in colder years resulted in less production of diatoms. Pelagic investigations in the 1990's have clearly shown that diatom production in the Baltic Sea is controlled by the ML depth. Especially after cold winters and deep water mixing, diatom production was limited and dissolved silicate (DSi) concentrations were not depleted in the water column after the spring bloom. Our method corroborates these findings and offers a new method to estimate diatom production over much longer periods of time in diatom dominated aquatic systems, i.e. a large part of the world's ocean and coastal seas.
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| 4. |
- Conley, Daniel J., et al.
(författare)
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Biosilicification drives a decline of dissolved si in the oceans through geologic time
- 2017
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Ingår i: Frontiers in Marine Science. - : Frontiers Media SA. - 2296-7745. ; 4:DEC
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Forskningsöversikt (refereegranskat)abstract
- Biosilicification has driven variation in the global Si cycle over geologic time. The evolution of different eukaryotic lineages that convert dissolved Si (DSi) into mineralized structures (higher plants, siliceous sponges, radiolarians, and diatoms) has driven a secular decrease in DSi in the global ocean leading to the low DSi concentrations seen today. Recent studies, however, have questioned the timing previously proposed for the DSi decreases and the concentration changes through deep time, which would have major implications for the cycling of carbon and other key nutrients in the ocean. Here, we combine relevant genomic data with geological data and present new hypotheses regarding the impact of the evolution of biosilicifying organisms on the DSi inventory of the oceans throughout deep time. Although there is no fossil evidence for true silica biomineralization until the late Precambrian, the timing of the evolution of silica transporter genes suggests that bacterial silicon-related metabolism has been present in the oceans since the Archean with eukaryotic silicon metabolism already occurring in the Neoproterozoic. We hypothesize that biological processes have influenced oceanic DSi concentrations since the beginning of oxygenic photosynthesis.
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| 5. |
- Fontorbe, Guillaume, et al.
(författare)
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Enrichment of dissolved silica in the deep equatorial Pacific during the Eocene-Oligocene
- 2017
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Ingår i: Paleoceanography. - 0883-8305 .- 1944-9186. ; 32, s. 848-863
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Tidskriftsartikel (refereegranskat)abstract
- Silicon isotope ratios (expressed as δ30Si) in marine microfossils can provide insights into silica cycling over geologic time. Here we used δ30Si of sponge spicules and radiolarian tests from the Paleogene Equatorial Transect (Ocean Drilling Program Leg 199) spanning the Eocene and Oligocene (~50–23 Ma) to reconstruct dissolved silica (DSi) concentrations in deep waters and to examine upper ocean δ30Si. The δ30Si values range from 3.16 to +0.18‰ and from 0.07 to +1.42‰ for the sponge and radiolarian records, respectively. Both records show a transition toward lower δ30Si values around 37 Ma. The shift in radiolarian δ30Si is interpreted as a consequence of changes in the δ30Si of source DSi to the region. The decrease in sponge δ30Si is interpreted as a transition from low DSi concentrations to higher DSi concentrations, most likely related to the shift toward a solely Southern Ocean source of deep water in the Pacific during the Paleogene that has been suggested by results from paleoceanographic tracers such as neodymium and carbon isotopes. Sponge δ30Si provides relatively direct information about the nutrient content of deep water and is a useful complement to other tracers of deep water circulation in the oceans of the past.
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| 6. |
- Humborg, Christoph, et al.
(författare)
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Silicon and the Baltic Sea Long-term Si decrease in the Baltic Sea - A conceivable ecological risk?
- 2008
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Ingår i: Journal of Marine Systems. - : Elsevier. - 0924-7963 .- 1879-1573. ; 73:3-4, s. 221-222
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Since the pioneering work of Schelske and Stoermer (1971) and Schelske et al., 1983 C.L. Schelske, E.F. Stoermer, D.J. Conley, J.A. Robbins and R.M. Glover, Early eutrophication in the Lower Great-Lakes — new evidence from biogenic silica in sediments, Science 222 (1983), pp. 320–322. View Record in Scopus | Cited By in Scopus (56)Schelske et al. (1983) it has been known that eutrophication of aquatic systems leads to depletion in dissolved silicate (DSi). Early studies on the Nile River have shown that the construction of dams leads to DSi decrease downstream due to the formation of additional deposition sites of biogenic silica (BSi) that was thought to consist mainly of diatoms. In the Baltic Sea there was a perception in the scientific community that DSi concentrations were high and therefore, that DSi concentrations were not limiting for diatom growth. Long-term trend analyses on DSi concentrations in the Baltic have shown decreasing trends in the 1970s and 1980s, whereas similar analysis for the 1990s concluded that DSi concentrations were no longer decreasing, but rather levelling off. Consequently, observations of reduced abundance of diatoms in the early 1990s were attributed to mild winters rather than low DSi concentrations, i.e., a low turbulence regime in the water column favouring non-siliceous algae. However, decadal nutrient trends in the Baltic Sea are significantly influenced by the large and varying internal Si pools in the sediments and deep water masses similar to that described for P dynamics in the Baltic Sea. No one seriously addressed the longer trends in DSi concentrations over the last century, whereas many studies estimated these changes for N and P.The EU funded research project SIBER (Silicate and Baltic Sea Ecosystem Response; EVK3-CT-2002-00069) began in 2002 with the objectives of understanding the major changes in Si dynamics in the Baltic Sea during the last century. The SIBER project addressed various aspects of the biogeochemical Si cycle in the Baltic Sea including constraining Si budgets for the Baltic Sea and its catchment, experiments describing the growth characteristics of Baltic diatoms related to the long-term trends in monitoring data of Baltic Sea diatoms.Si budgets are addressed by several papers in this special issue. Humborg et al. and Sferratore et al. describe riverine Si fluxes. Pastuszak et al. address estuarine Si fluxes. Redfield ratios including DSi and their development in the Baltic Sea are described by Danielsson et al.Possible ecosystem effects of changes in Redfield nutrient ratios are analysed in the paper by Olli et al. who examine phytoplankton responses in the Gulf of Riga and by Wasmund et al. who investigate long-term trends in phytoplankton species in the Kiel Bight. Spilling and Markager describe growth characteristics of Baltic Sea diatoms. Finally, in their paper Conley et al. present a long-term Si budget for the entire Baltic Sea for the first time.The Baltic Sea biogeochemical Si cycle has been fundamentally changed within the last century not only as a consequence of river regulation and lake eutrophication, but also through increases in the sediment accumulation of BSi (Conley et al.). Sediment accumulation of BSi has increased by a factor on 1.9 due to increased diatom growth from marine eutrophication. Results from the SIBER project indicate that DSi concentration were ca. 36 µM a century ago in the Baltic proper compared to ca. 13 µM observed today (Conley et al.). In fact, DSi concentrations have changed much more dramatically compared to N and P regarding the total changes in the available nutrient stocks. Similar changes have occurred in other large water bodies with respect to size and volume, i.e. the North American Great Lakes with long residence times where DSi decreased from 80–100 µM to ca. 25 µM. Surprisingly, such a major change in nutrient inventories has not been reported earlier in this well investigated coastal system. We are only starting to understand the possible ecological consequences, such as the occurrence of different diatom species that are less silicified and its implication for the sedimentation fluxes and carbon flux to benthic communities. The SIBER project has shown that a dramatic change in DSi concentrations is possible within a very short time period, although the situation appears stable today, perhaps since the drivers for this change, i.e. eutrophication and river regulation, have not changed within the last 30 years. However, even a slight increase in N and P loads and/or further damming of rivers may drive the Baltic Sea into Si-limitation.
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| 7. |
- Alfredsson, Hanna, et al.
(författare)
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Amorphous silica pools in permafrost soils of the Central Canadian Arctic and the potential impact of climate change
- 2015
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 124:1-3, s. 441-459
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the distribution, storage and landscape partitioning of soil amorphous silica (ASi) in a central Canadian region dominated by tundra and peatlands to provide a first estimate of the amount of ASi stored in Arctic permafrost ecosystems. We hypothesize that, similar to soil organic matter, Arctic soils store large amounts of ASi which may be affected by projected climate changes and associated changes in permafrost regimes. Average soil ASi storage (top 1 m) ranged between 9600 and 83,500 kg SiO2 ha(-1) among different land-cover types. Lichen tundra contained the lowest amounts of ASi while no significant differences were found in ASi storage among other land-cover types. Clear differences were observed between ASi storage allocated into the top organic versus the mineral horizon of soils. Bog peatlands, fen peatlands and wet shrub tundra stored between 7090 and 45,400 kg SiO2 ha(-1) in the top organic horizon, while the corresponding storage in lichen tundra, moist shrub- and dry shrub tundra only amounted to 1500-1760 kg SiO2 ha(-1). Diatoms and phytoliths are important components of ASi storage in the top organic horizon of peatlands and shrub tundra systems, while it appears to be a negligible component of ASi storage in the mineral horizon of shrub tundra classes. ASi concentrations decrease with depth in the soil profile for fen peatlands and all shrub tundra classes, suggesting recycling of ASi, whereas bog peatlands appeared to act as sinks retaining stored ASi on millennial time scales. Our results provide a conceptual framework to assess the potential effects of climate change impacts on terrestrial Si cycling in the Arctic. We believe that ASi stored in peatlands are particularly sensitive to climate change, because a larger fraction of the ASi pool is stored in perennially frozen ground compared to shrub tundra systems. A likely outcome of climate warming and permafrost thaw could be mobilization of previously frozen ASi, altered soil storage of biogenically derived ASi and an increased Si flux to the Arctic Ocean.
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| 8. |
- Funkey, Carolina, et al.
(författare)
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Hypoxia Sustains Cyanobacteria Blooms in the Baltic Sea
- 2014
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 48:5, s. 2598-2602
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Tidskriftsartikel (refereegranskat)abstract
- Nutrient over-enrichment is one of the classic triggering mechanisms for the occurrence of cyanobacteria blooms in aquatic ecosystems. In the Baltic Sea, cyanobacteria regularly occur in the late summer months and form nuisance accumulations in surface waters and their abundance has intensified significantly in the past 50 years attributed to human-induced eutrophication. However, the natural occurrence of cyanobacteria during the Holocene is debated. In this study, we present records of cyanobacteria pigments, water column redox proxies, and nitrogen isotopic signatures for the past ca. 8000 years from Baltic Sea sediment cores. Our results demonstrate that cyanobacteria abundance and nitrogen fixation are correlated with hypoxia occurring during three main intervals: (1) ca. 7000-4000 B.P. during the Littorina transgression, (2) ca. 1400-700 B.P. during the Medieval Climate Anomaly, and (3) from ca. 1950 A.D. to the present. Issues of preservation were investigated, and we show that organic matter and pigment profiles are not simply an artifact of preservation. These results suggest that cyanobacteria abundance is sustained during periods of hypoxia, most likely because of enhanced recycling of phosphorus in low oxygen conditions.
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| 9. |
- Jilbert, Tom, et al.
(författare)
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Glacio-isostatic control on hypoxia in a high-latitude shelf basin
- 2015
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Ingår i: Geology. - 0091-7613 .- 1943-2682. ; 43:5, s. 427-430
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Tidskriftsartikel (refereegranskat)abstract
- In high-latitude continental shelf environments, late Pleistocene glacial overdeepening and early Holocene eustatic sea-level rise combined to create restricted marine basins with a high vulnerability to oxygen depletion. Here we show that ongoing glacio-isostatic rebound during the Holocene may have played an important role in determining the distribution of past hypoxia in these environments by controlling the physical exchange of water masses and the distribution of large-scale phosphorus (P) sinks. We focus on the Baltic Sea, where sediment records from a large, presently oxic sub-basin show evidence for intense hypoxia and cyanobacteria blooms during the Holocene Thermal Maximum. Using paleobathymetric modeling, we show that this period was characterized by enhanced deep-water exchange, allowing widespread phosphorus regeneration. Intra-basin sills then shoaled over a period of several thousand years, enhancing P burial in one of the sub-basins. Together with climate forcing, this may have caused the termination of hypoxia throughout the Baltic Sea. Similar rearrangements of physical and chemical processes likely occurred in response to glacio-isostatic rebound in other high-latitude shelf basins during the Holocene.
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| 10. |
- Leavitt, Peter R., et al.
(författare)
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Paleolimnological evidence of the effects on lakes of energy and mass transfer from climate and humans
- 2009
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Ingår i: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 54:6, s. 2330-2348
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Forskningsöversikt (refereegranskat)abstract
- The premise of this article is that climate effects on lakes can be quantified most effectively by the integration of process-oriented limnological studies with paleolimnological research, particularly when both disciplines operate within a common conceptual framework. To this end, the energy (E)-mass (m) flux framework (Em flux) is developed and applied to selected retrospective studies to demonstrate that climate variability regulates lake structure and function over diverse temporal and spatial scales through four main pathways: rapid direct transfer of E to the lake surface by irradiance, heat, and wind; slow indirect effects of E via changes in terrestrial development and subsequent m subsidies to lakes; direct influx of m as precipitation, particles, and solutes from the atmosphere; and indirect influx of water, suspended particles, and dissolved substances from the catchment. Sedimentary analyses are used to illustrate the unique effects of each pathway on lakes but suggest that interactions among mechanisms are complex and depend on the landscape position of lakes, catchment characteristics, the range of temporal variation of individual pathways, ontogenetic changes in lake basins, and the selective effects of humans on m transfers. In particular, preliminary synthesis suggests that m influx can overwhelm the direct effects of E transfer to lakes, especially when anthropogenic activities alter m subsidies from catchments.
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