| 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. |
- 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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| 3. |
- 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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| 4. |
- De La Rocha, Christina, et al.
(författare)
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Silica stories
- 2017
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Bok (refereegranskat)abstract
- Do you know silica, the tetrahedra of silicon and oxygen constituting the crystals of New Agers and the desiccant in a box of new shoes? It’s no mere mundane mineral. As chemically reacting silicate rocks, silica set off the chain of events known as the origin of life. As biomineralized opal, it is the cell wall, skeleton, spicules, and scales of organisms ornamenting numerous lobes of the tree of life. Cryptocrystalline silica made into stone tools helped drive the evolution of our hands and our capability for complex grammar, music, and mathematics. As quartz crystals, silica is impressively electric and ubiquitous in modern technology (think sonar, radios, telephones, ultrasound, and cheap but precise watches). Silica is inescapable when we take a drink or mow the lawn and it has already started to save the Earth from the carbon dioxide we’re spewing into the atmosphere. This book tells these scientific tales and more, to give dear, modest silica its due.
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| 5. |
- Nantke, Carla K.M., et al.
(författare)
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Si cycling in transition zones : a study of Si isotopes and biogenic silica accumulation in the Chesapeake Bay through the Holocene
- 2019
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 146:2, s. 145-170
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Tidskriftsartikel (refereegranskat)abstract
- Si fluxes from the continents to the ocean are a key element of the global Si cycle. Due to the ability of coastal ecosystems to process and retain Si, the ‘coastal filter’ has the potential to alter Si fluxes at a global scale. Coastal zones are diverse systems, sensitive to local environmental changes, where Si cycling is currently poorly understood. Here, we present the first palaeoenvironmental study of estuarine biogenic silica (BSi) fluxes and silicon isotope ratios in diatoms (δ30Sidiatom) using hand-picked diatom frustules in two sediment cores (CBdist and CBprox) from the Chesapeake Bay covering the last 12000 and 8000 years, respectively. Constrained by the well-understood Holocene evolution of the Chesapeake Bay, we interpret variations in Si cycling in the context of local climate, vegetation and land use changes. δ30Sidiatom varies between + 0.8 and + 1.7‰ in both sediment cores. A Si mass balance for the Chesapeake Bay suggests much higher rates of Si retention (~ 90%) within the system than seen in other coastal systems. BSi fluxes for both sediment cores co-vary with periods of sea level rise (between 9500 and 7500 a BP) and enhanced erosion due to deforestation (between 250 and 50 a BP). However, differences in δ30Sidiatom and BSi flux between the sites emphasize the importance of the seawater/freshwater mixing ratios and locally variable Si inputs from the catchment. Further, we interpret variations in δ30Sidiatom and the increase in BSi fluxes observed since European settlement (~ 250 a BP) to reflect a growing human influence on the Si cycle in the Chesapeake Bay. Thereby, land use change, especially deforestation, in the catchment is likely the major mechanism.
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| 6. |
- van Helmond, Niels A.G.M., et al.
(författare)
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Recovery from multi-millennial natural coastal hypoxia in the Stockholm Archipelago, Baltic Sea, terminated by modern human activity
- 2020
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Ingår i: Limnology and Oceanography. - : WILEY. - 0024-3590 .- 1939-5590. ; 65:12, s. 3085-3097
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Tidskriftsartikel (refereegranskat)abstract
- Enhanced nutrient input and warming have led to the development of low oxygen (hypoxia) in coastal waters globally. For many coastal areas, insight into redox conditions prior to human impact is lacking. Here, we reconstructed bottom water redox conditions and sea surface temperatures (SSTs) for the coastal Stockholm Archipelago over the past 3000 yr. Elevated sedimentary concentrations of molybdenum indicate (seasonal) hypoxia between 1000b.c.e.and 1500c.e. Biomarker-based (TEX86) SST reconstructions indicate that the recovery from hypoxia after 1500c.e.coincided with a period of significant cooling (similar to 2 degrees C), while human activity in the study area, deduced from trends in sedimentary lead and existing paleobotanical and archeological records, had significantly increased. A strong increase in sedimentary lead and zinc, related to more intense human activity in the 18(th)and 19(th)century, and the onset of modern warming precede the return of hypoxia in the Stockholm Archipelago. We conclude that climatic cooling played an important role in the recovery from natural hypoxia after 1500c.e., but that eutrophication and warming, related to modern human activity, led to the return of hypoxia in the 20(th)century. Our findings imply that ongoing global warming may exacerbate hypoxia in the coastal zone of the Baltic Sea.
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| 7. |
- Voss, Maren, et al.
(författare)
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Origin and fate of dissolved organic matter in four shallow Baltic Sea estuaries
- 2021
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 154:2, s. 385-403
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Tidskriftsartikel (refereegranskat)abstract
- Coastal waters have strong gradients in dissolved organic matter (DOM) quantity and characteristics, originating from terrestrial inputs and autochthonous production. Enclosed seas with high freshwater input therefore experience high DOM concentrations and gradients from freshwater sources to more saline waters. The brackish Baltic Sea experiences such salinity gradients from east to west and from river mouths to the open sea. Furthermore, the catchment areas of the Baltic Sea are very diverse and vary from sparsely populated northern areas to densely populated southern zones. Coastal systems vary from enclosed or open bays, estuaries, fjords, archipelagos and lagoons where the residence time of DOM at these sites varies and may control the extent to which organic matter is biologically, chemically or physically modified or simply diluted with transport off-shore. Data of DOM with simultaneous measurements of dissolved organic (DO) nitrogen (N), carbon (C) and phosphorus (P) across a range of contrasting coastal systems are scarce. Here we present data from the Roskilde Fjord, Vistula and Öre estuaries and Curonian Lagoon; four coastal systems with large differences in salinity, nutrient concentrations, freshwater inflow and catchment characteristics. The C:N:P ratios of DOM of our data, despite high variability, show site specific significant differences resulting largely from differences residence time. Microbial processes seemed to have minor effects, and only in spring did uptake of DON in the Vistula and Öre estuaries take place and not at the other sites or seasons. Resuspension from sediments impacts bottom waters and the entire shallow water column in the Curonian Lagoon. Finally, our data combined with published data show that land use in the catchments seems to impact the DOC:DON and DOC:DOP ratios of the tributaries most.
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| 8. |
- Brylka, Karolina, et al.
(författare)
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Looking for the oldest diatoms
- 2024
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Ingår i: Marine Micropaleontology. - 0377-8398. ; :190
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Tidskriftsartikel (refereegranskat)abstract
- Paleontological observations of ancient flora and fauna provide powerful insights into past diversity and relationshipdynamics between organisms and their environments. Diatoms are globally distributed protists thatinfluence major biogeochemical cycles and sustain oceanic food webs. The fossil diatom record extends 120million years back to the Early Cretaceous where rare deposits were discovered worldwide and are occasionallyrepresented by diverse communities. However scarce, the taxonomic richness and geographical spread of thesediatom communities suggest prior evolutionary events and therefore earlier deposits. To complement the existingfossil information and to discover diatom deposits predating 120 Ma, we examined 33 study sites from cores andoutcrops across oceans and continents. These efforts did not generate new fossil discoveries, however. Ourassessment suggests biogenic silica that comprises the cell wall of diatoms was likely dissolved from Mesozoicsediments through diagenetic processes. Altogether, the search for the oldest diatoms must continue but shouldtarget sediments that experienced shallow burial and concretions.
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| 9. |
- Churakova, Yelena, et al.
(författare)
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Biogenic silica accumulation in picoeukaryotes : Novel players in the marine silica cycle
- 2023
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Ingår i: Environmental Microbiology Reports. - : John Wiley & Sons. - 1758-2229. ; 15:4, s. 282-290
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that the biological control of oceanic silica cycling is dominated by diatoms, with sponges and radiolarians playing additional roles. Recent studies have revealed that some smaller marine organisms (e.g. the picocyanobacterium Synechococcus) also take up silicic acid (dissolved silica, dSi) and accumulate silica, despite not exhibiting silicon dependent cellular structures. Here, we show biogenic silica (bSi) accumulation in five strains of picoeukaryotes (<2-3 mu m), including three novel isolates from the Baltic Sea, and two marine species (Ostreococcus tauri and Micromonas commoda), in cultures grown with added dSi (100 mu M). Average bSi accumulation in these novel biosilicifiers was between 30 and 92 amol Si cell(-1). Growth rate and cell size of the picoeukaryotes were not affected by dSi addition. Still, the purpose of bSi accumulation in these smaller eukaryotic organisms lacking silicon dependent structures remains unclear. In line with the increasing recognition of picoeukaryotes in biogeochemical cycling, our findings suggest that they can also play a significant role in silica cycling.
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| 10. |
- Funkey, Carolina P., et al.
(författare)
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Sediment alkaline-extracted organic matter (AEOM)fluorescence : An archive of Holocene marine organic matter origins
- 2019
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697. ; 676, s. 298-304
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Tidskriftsartikel (refereegranskat)abstract
- Organic matter (OM)is comprised of a complex mixture of substrates, which are difficult to fully characterize. Therefore a range of analytical approaches is applied to provide a better understanding of the dynamics and biogeochemical cycling of aquatic system. One approach is UV–Visible spectroscopy, which includes measurements of spectral absorption and fluorescence of colored and fluorescent fractions of dissolved OM (DOM, CDOM and FDOM). In this study OM fluorescence is characterized by excitation-emission matrix spectroscopy on alkaline extracted DOM from a Baltic Sea sediment core that spanned 8500 years and fluctuating levels of hypoxia. Our results showed that three underlying fluorescence components had strong correlations with carbon, nitrogen content and δ 15 N. Our results demonstrate that optical properties of extracted OM from sediments reveal information about OM quality and quantity similar to those of biomarkers, which can be a useful additional tool for investigating OM deposition.
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