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| 3. |
- Birch, Heather, et al.
(författare)
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Planktonic foraminifera stable isotopes and water column structure : Disentangling ecological signals
- 2013
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Ingår i: Marine Micropaleontology. - : Elsevier BV. - 0377-8398 .- 1872-6186. ; 101, s. 127-145
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Tidskriftsartikel (refereegranskat)abstract
- Differential carbon and oxygen stable isotope (delta C-13 and delta O-18) fractionation between planktonic foraminifera test calcite and sea water related to ecology and life stage confound the potential for reconstructing palaeo-water column temperature and carbon gradients. Multi-species analysis and strict selection of test sizes are useful methods for identifying these fractionation processes, also known as 'vital effects', in fossil taxa. However, there are a limited number of species with adequate size-controlled data sets, needed for ground truthing the approach in the modern. Here we report delta C-13 and delta O-18 measurements made on twelve species of modern planktonic foraminifera across a range of fourteen tightly constrained size windows from a tropical Indian Ocean core top sample. This data set includes more test size windows per species, especially from the smallest (identifiable) test size-classes, and a wider range of species than previously attempted. We use the size controlled delta O-18 calcite trajectories to infer depth habitats and calculate species-specific calcification temperatures. The temperatures are then used to constrain species-specific calcification depths along the modern vertical temperature profile in the western tropical Indian Ocean. By overlaying the per species delta C-13 calcite trajectories on local water column delta C-13(DIC) profiles, we estimate if and when (i.e. at which test sizes) the planktonic foraminifera species investigated approach ambient delta C-13(DIC) values. The profiling shows significant size-controlled delta C-13 deviation from seawater values in all species at some life/growth stage, which we attribute to (i) metabolic fractionation in tests <150-300 mu m (juveniles of all species and small adults), and; (ii) photosymbiont fractionation, affecting large tests (>similar to 300 mu m) of mixed layer photosymbiotic taxa. For most species there is a size-window where these effects appear to be at a minimum, and/or in balance. Exceptions are Globigerinita glutinata, a small (<200 mu m) surface living species, Globigerina bulloides, which is highly opportunistic, and deep living Globorotalia tumida and Globorotaloides hexagonus, the latter two species being affected by various unexplained delta C-13 vital effects. Use of our refined guidelines for test-size selection should improve the potential for making realistic reconstructions of water column delta C-13(DIC) in a modern tropical stratified setting and potentially in the distant geological past when there are no living analogues present.
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- Bird, Clare, et al.
(författare)
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The genetic diversity, morphology, biogeography, and taxonomic designations of Ammonia (Foraminifera) in the Northeast Atlantic
- 2020
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Ingår i: Marine Micropaleontology. - : Elsevier BV. - 0377-8398.
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Tidskriftsartikel (refereegranskat)abstract
- The genetic diversity, morphology and biogeography of Ammonia specimens was investigated across the Northeast (NE) Atlantic margins, to enhance the regional (palaeo)ecological studies based on this genus. Living specimens were collected from 22 sampling locations ranging from Shetland to Portugal to determine the distribution of Ammonia genetic types across the NE Atlantic shelf biomes. We successfully imaged (via scanning electron microscopy, SEM) and genotyped 378 Ammonia specimens, based on the small subunit (SSU) rRNA gene, linking morphology to genetic type. Phylogenetic analyses enabled identification of seven genetic types and subtypes inhabiting the NE Atlantic margins. Where possible, we linked SSU genetic types to the established large subunit (LSU) T-type nomenclature of Hayward et al. (2004). SSU genetic types with no matching T-type LSU gene sequences in GenBank were allocated new T-numbers to bring them in line with the widely adopted T-type nomenclature. The genetic types identified in the NE Atlantic margins are T1, T2, T3, T6, and T15, with both T2 and T3 being split further into the subtypes T2A and T2B, and T3S and T3V respectively. The seven genetic types and subtypes exhibit different biogeographical distributions and/or ecological preferences, but co-occurrence of two or more genetic types is common. A shore-line transect at Dartmouth (South England) demonstrates that sampling position on shore (high, middle or low shore) influences the genetic type collected, the numbers of genetic types that co-occur, and the numbers of individuals collected. We performed morphometric analysis on the SEM images of 158 genotyped Ammonia specimens. T15 and the subtypes T3S and T3V can be morphologically distinguished. We can unequivocally assign the taxonomic names A. batava and A. falsobeccarii to T3S and T15, respectively. However, the end members of T1, T2A, T2B and T6 cannot be unambiguously distinguished, and therefore these genetic types are partially cryptic. However, we confirm that T2A can be assigned to A. aberdoveyensis, but caution must be taken in warm provinces where the presence of T2B will complicate the morphological identification of T2A. We suggest that T6 should not currently be allocated to the Pliocene species A. aomoriensis due to morphological discrepancies with the taxonomic description and to the lack of genetic information. Of significance is that these partially cryptic genetic types frequently co-occur, which has considerable implications for precise species identification and accurate data interpretation.
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- 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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- Cappelli, Carlotta, et al.
(författare)
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Middle Eocene large coccolithaceans : Biostratigraphic implications and paleoclimatic clues
- 2020
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Ingår i: Marine Micropaleontology. - : Elsevier BV. - 0377-8398 .- 1872-6186. ; 154
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Tidskriftsartikel (refereegranskat)abstract
- A combined light microscope-scanning electron microscope study of exceptionally well-preserved calcareous nannofossil assemblages from clay-rich middle Eocene sediments recovered at IODP Site U1410 (NW Atlantic Ocean) has enabled us to document a new evolutionary lineage within Coccolithus-like placoliths that have well-developed near-axial or diagonal cross-bars in their central-area. Based on our observations, we describe a new genus Pletolithus, a new species Pletolithus giganteus and four new combinations (Pletolithus opdykei, Pletolithus staurion, Pletolithus mutatus and Pletolithus gigas). The distinctive ultra-structures of the different morphotypes and the presence of transitional morphologies suggest that Pletolithus evolved from a morphological variant of Coccolithus. The evolution of this group of coccolithaceans is initially characterized by increasing size and the appearance of delicate axial cross-bars in the central-area. Size continues to increase in these coccoliths and the orientation of the cross-bars shifts to asymmetric and diagonal in later representatives. Morphometric measurements on P. gigas and the morphologically similar P. giganteus, provide evidence for the presence of two distinct populations allowing for an objective differentiation of these two species, which in turn provides unambiguous taxonomic definition for the important biostratigraphic marker species P. gigas. These data improve the reliability of middle Eocene biostratigraphy and show that this lineage appeared when a new equilibrium in the environmental conditions was reached and intriguingly it coincides with a remarkable change in the deep circulation of the North Atlantic Ocean.
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- Charrieau, Laurie M., et al.
(författare)
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The effects of multiple stressors on the distribution of coastal benthic foraminifera: A case study from the Skagerrak-Baltic Sea region
- 2018
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Ingår i: Marine Micropaleontology. - : Elsevier BV. - 0377-8398. ; 139, s. 42-56
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Tidskriftsartikel (refereegranskat)abstract
- Coastal ecosystems are subjected to both large natural variability and increasing anthropogenic impact on environmental parameters such as changes in salinity, temperature, and pH. This study documents the distribution of living benthic foraminifera under the influence of multiple environmental stressors in the Skagerrak-Baltic Sea region. Sediment core tops were studied at five sites along a transect from the Skagerrak to the Baltic Sea, with strong environmental gradients, especially in terms of salinity, pH, calcium carbonate saturation and dissolved oxygen concentration in the bottom water and pore water. We found that living foraminiferal densities and species richness were higher at the Skagerrak station, where the general living conditions were relatively beneficial for Foraminifera, with higher salinity and Ωcalc in the water column and higher pH and oxygen concentration in the bottom and pore water. The most common species reported at each station reflect the differences in the environmental conditions between the stations. The dominant species were Cassidulina laevigata and Hyalinea balthica in the Skagerrak, Stainforthia fusiformis, Nonionella aff. stella and Nonionoides turgida in the Kattegat and N. aff. stella and Nonionellina labradorica in the Öresund. The most adverse conditions, such as low salinity, low Ωcalc, low dissolved oxygen concentrations and low pH, were noted at the Baltic Sea stations, where the calcareous tests of the dominant living taxa Ammonia spp. and Elphidium spp. were partially to completely dissolved, probably due to a combination of different stressors affecting the required energy for biomineralization. Even though Foraminifera are able to live in extremely varying environmental conditions, the present results suggest that the benthic coastal ecosystems in the studied region, which are apparently affected by an increase in the range of environmental variability, will probably be even more influenced by a future increase in anthropogenic impacts, including coastal ocean acidification and deoxygenation.
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| 9. |
- Cronin, T. M., et al.
(författare)
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Holocene paleoceanography and glacial history of Lincoln Sea, Ryder Glacier, Northern Greenland, based on foraminifera and ostracodes
- 2022
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Ingår i: Marine Micropaleontology. - : Elsevier BV. - 0377-8398 .- 1872-6186. ; 175
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Tidskriftsartikel (refereegranskat)abstract
- We reconstructed Holocene paleoceanography of the Sherard Osborn Fjord (SOF), N Greenland, and Lincoln Sea in the eastern Arctic Ocean using sediment properties and micropaleontology from cores obtained during the Ryder 2019 Expedition. Our aims were to better understand faunal indicators of water mass influence on Ryder Glacier and the Lincoln Sea at water depths >500 m. Benthic microfaunal reflect glacio-marine interval during late deglaciation ~10.5 to 8.5 ka (kiloannum) during the Holocene Thermal Maximum (HTM) with dominant benthic foraminiferal species Cassidulina neoteretis, Cassidulina reniforme, and the ostracode Rabilimis mirabilis. Casssidulina neoteretis is considered an indicator of Atlantic Water (AW) throughout the Arctic Ocean and Nordic Seas; C. reniforme reflects glacio-marine conditions from the retreating Ryder Glacier. Deglaciation was followed by a period of elevated productivity and diverse ostracode faunal assemblages that suggest AW influence from 8.5 to 6 ka in the Lincoln Sea and inside SOF. The Holocene occurrence of the ostracode species Acetabulastoma arcticum, that appears in low numbers in the Lincoln Sea and briefly (~ 4–3 ka) in SOF, reflects the presence of variable sea ice in this region. Based on the similarities of the Lincoln Sea and fjord ostracodes to modern and glacial-deglacial faunas from the central Arctic Ocean, the AW influence likely originates from recirculation of AW water from the central Arctic Basin. In general, our results suggest a strong but temporally varying influence of AW during the entire 10.5 kyr record of the Lincoln Sea and SOF.
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| 10. |
- Cubillos, Joana C., et al.
(författare)
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Reconstructing calcification in ancient coccolithophores : Individual coccolith weight and morphology of Coccolithus pelagicus (sensu lato)
- 2012
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Ingår i: Marine Micropaleontology. - : Elsevier BV. - 0377-8398 .- 1872-6186. ; 92-93, s. 29-39
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Tidskriftsartikel (refereegranskat)abstract
- We have adapted an existing method to estimate coccolith calcite weight using birefringence (Beaufort, 2005) to suit the large coccoliths of Coccolithus pelagicus, which are only partially birefringent under cross-polarised light microscopy. Fossil and sediment trap material from the South Tasman Rise region of the Southern Ocean was used for calibration and validation. Our approach was tested with only the coccolith central area (CA) considered for measurement, to avoid relying on the less robust proximal shields. Thus our results are relative and intend to quantify intra-specific variations in volumetric calcite weight, expressed as a Weight Index (WI). Our results were overall consistent with mass estimation based on distal shield lengths. However, the WI approach clearly has the advantage in exploring allometric scaling between coccolith size and weight, as well as in measuring the degree of calcification in similarly sized morphotypes. Combining WI and morphometry data (distal shield length, DSL), we demonstrate subtle, but statistically significant changes in shape and thus calcification degree both within and between the tested Coccolithus populations. Most strikingly, it appears that modern Coccolithus populations in the Southern Ocean are, on average, more heavily calcified than their fossil counterparts.
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