| 1. |
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| 2. |
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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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| 4. |
- 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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| 5. |
- 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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| 6. |
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| 7. |
- 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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| 8. |
- 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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| 11. |
- Darling, Kate F., et al.
(författare)
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The genetic diversity, phylogeography and morphology of Elphidiidae (Foraminifera) in the Northeast Atlantic
- 2016
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Ingår i: Marine Micropaleontology. - : Elsevier BV. - 0377-8398. ; 129, s. 1-23
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Tidskriftsartikel (refereegranskat)abstract
- Genetic characterisation (SSU rRNA genotyping) and Scanning Electron Microscope (SEM) imaging of individual tests were used in tandem to determine the modern species richness of the foraminiferal family Elphidiidae (Elphidium, Haynesina and related genera) across the Northeast Atlantic shelf biomes. Specimens were collected at 25 locations from the High Arctic to Iberia, and a total of 1013 individual specimens were successfully SEM imaged and genotyped. Phylogenetic analyses were carried out in combination with 28 other elphidiid sequences from GenBank and seventeen distinct elphidiid genetic types were identified within the sample set, seven being sequenced for the first time. Genetic types cluster into seven main clades which largely represent their general morphological character. Differences between genetic types at the genetic, morphological and biogeographic levels are indicative of species level distinction. Their biogeographic distributions, in combination with elphidiid SSU sequences from GenBank and high resolution images from the literature show that each of them exhibits species-specific rather than clade-specific biogeographies. Due to taxonomic uncertainty and divergent taxonomic concepts between schools, we believe that morphospecies names should not be placed onto molecular phylogenies unless both the morphology and genetic type have been linked to the formally named holotype, or equivalent. Based on strict morphological criteria, we advocate using only a three-stage approach to taxonomy for practical application in micropalaeontological studies. It comprises genotyping, the production of a formal morphological description of the SEM images associated with the genetic type and then the allocation of the most appropriate taxonomic name by comparison with the formal type description. Using this approach, we were able to apply taxonomic names to fifteen genetic types. One of the remaining two may be potentially cryptic, and one is undescribed in the literature. In general, the phylogeographic distribution is in agreement with our knowledge of the ecology and biogeographical distribution of the corresponding morphospecies, highlighting the generally robust taxonomic framework of the Elphidiidae in time and space.
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| 12. |
- Filipsson, Helena L., 1973, et al.
(författare)
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Seasonal study of delta O-18 and delta C-13 in living (stained) benthic foraminifera from two Swedish fjords
- 2004
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Ingår i: Marine Micropaleontology. - : Elsevier BV. - 0377-8398. ; 53:1-2, s. 159-172
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Tidskriftsartikel (refereegranskat)abstract
- In a previous 16-month seasonal study on living (stained) benthic foraminifera from two fjords on the Swedish west coast, it was reported that foraminifera proliferated in response to phytodetritus input; the strongest response came from the opportunistic species Stainforthia fusiformis. In this study, our objective was to find out if that phytodetritus input resulted in a change in the carbon isotopic composition of the foraminiferal tests. We also wanted to examine if variations in salinity and temperature (due to seasonality or deep-water exchanges) were reflected in the delta(18)O values. From S. fusiformis that were obtained from the Havstens Fjord (20 m) and the Gullmar Fjord (119 m) during the 16-month study, we developed a time series of delta(18)O and delta(13)C. After the spring blooms in the Havstens and the Gullmar Fjord, decreases of about 0.2parts per thousand to 0.3parts per thousand in the foraminiferal delta(13)C values were noted; in the Gullmar Fjord after the autumn blooms, decreases of the same order were also noted. Comparing the Havstens and the Gullmar Fjord, we found a 1parts per thousand difference in both delta(13)C and delta(18)O; we attribute this to hydrographic differences between the two fjords. Using calculated values of delta(18)O, together with the measured ones, we noticed that S. fusiformis in the Gullmar Fjord seems to calcify close to equilibrium with respect to the oxygen isotopes. During autumn, water temperatures were relatively high in the Havstens Fjord, and foraminiferal abundance in the fjord was also high after a phytodetritus input; but, the measured delta(18)O values do not reflect these higher temperatures. This apparently contradictory combination of results might be explained by a varying delta(18)O composition of the water during the year, which counterbalances the temperature effect. (C) 2004 Published by Elsevier B.V.
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| 13. |
- Flores, Jose-Abel, et al.
(författare)
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Distribution of large Emiliania huxleyi in the Central and Northeast Atlantic as a tracer of surface ocean dynamics during the last 25,000 years
- 2010
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Ingår i: Marine Micropaleontology. - : Elsevier BV. - 0377-8398 .- 1872-6186. ; 76:3-4, s. 53-66
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Tidskriftsartikel (refereegranskat)abstract
- The coccolithophore species Emiliania huxleyi is characterized by a wide range of sizes. which can be easily distinguished in the light microscope. In this study we have quantified the abundance of large (coccoliths >4 mu m in maximum length) E. huxleyi specimens during the last 25 kyr in sedimentary records from eleven cores and drill sites in the NE Atlantic and W Mediterranean Sea, to prove its usefulness in the reconstruction of water mass dynamics and biostratigraphic potential. During the Last Glacial Maximum this large form, a cold-water indicator, was common in the NE Atlantic and Mediterranean, and its regional variation in abundance indicates a displacement of the climatic zones southwards in agreement with the development of ice sheets and sea ice in the Northern Hemisphere during this period. On the other hand, the gradient between northern and southern surface water masses in the Subtropical Gyre appears to have been more pronounced than at present, while the Portugal and Canary Currents were more intense. In the western Mediterranean basin temperatures were cooler than in the adjacent Atlantic, provoking a quasi-endemism of these specimens until the end of Heinrich Event 1. This may have been due to a restriction in the communication between the Atlantic and Mediterranean through the Strait of Gibraltar, the arrival of cold surface water and the amplification of cooling after the development of ice sheets in the Northern Hemisphere. During the deglaciation, large E. huxleyi specimens decreased in abundance at medium and low latitudes, but were still numerous close to the Subarctic region during the Holocene. In transitional waters this decrease to present day abundances occurred after Termination lb. The abrupt change in abundance of this large E. huxleyi form is proposed as a new biostratigraphic event to characterize the Holocene in mid- to low-latitude water masses in the North Atlantic, although this horizon seems to be diachronous by 5 kyr from tropical to subarctic regions, in agreement with the gradual onset of warm conditions.
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| 14. |
- Godad, Shital P., et al.
(författare)
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Sea surface temperature changes during May and August in the western Arabian Sea over the last 22 kyr : Implications as to shifting of the upwelling season
- 2011
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Ingår i: Marine Micropaleontology. - : Elsevier BV. - 0377-8398 .- 1872-6186. ; 78:1-2, s. 25-29
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Tidskriftsartikel (refereegranskat)abstract
- In the western Arabian Sea (WAS), the highest seasonal sea surface temperature (SST) difference presently occurs between May and August In order to gain an understanding on how monsoonal upwelling modulates the SST difference between these two months, we have computed SST for the months of May and August based on census counts of planktonic foraminifers by using the artificial neural network (ANN) technique. The SST difference between May and August exhibits three distinct phases: i) a moderate SST difference in the late Holocene (0-3.5 ka) is attributable to intense upwelling during August, ii) a minimum SST difference from 4 to 12 ka is due to weak upwelling during the month of August, and iii) the highest SST difference during the last glacial interval (19 to 22 ka) with high Globigerina bulloides % could have been caused by the occurrence of a prolonged upwelling season (from May through July) and maximum difference in the incoming solar radiation between May and August. Overall, variations in the SST difference between May and August show that the timing of intense upwelling in the Western Arabian Sea over the last 22 kyr has been variable over the months of June, July and August.
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| 15. |
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| 16. |
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| 17. |
- Herrmann, Sandra, et al.
(författare)
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Global coccolith size variability in Holocene deep-sea sediments
- 2012
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Ingår i: Marine Micropaleontology. - : Elsevier. - 0377-8398 .- 1872-6186. ; 82-83, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- We report on the size variability of coccoliths - calcite platelets produced by planktic marine haptophyte algae - in globally distributed Holocene surface sediments. The sizes of 400-600 coccoliths in 51 Holocene deep-sea carbonate ooze samples were measured using automated scanning electron microscopy and image analysis processes. The resulting coccolith size histograms are highly variable, but the largest 10% in each sample showed a size increase from the tropics to subpolar regions. This is the opposite trend from the one observed in planktic foraminifera, which have their largest tests in tropical regions. In a subset of 13 samples, which cover the major environmental gradients of today's surface waters, coccolith sizes of the nine most common genera were analyzed. These show that the observed macroecological size variability, which is related to a complex mixture of environmental parameters, is mostly the result of changing species occurrence and abundance (biogeography), rather than size changes within genera and species. This Holocene calibration will help to test evolutionary hypotheses of environmental selection in marine phytoplankton and can serve as a useful benchmark for analyses of coccolith size variability in older deep-sea sediments.
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| 18. |
- LeKieffre, Charlotte, et al.
(författare)
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An overview of cellular ultrastructure in benthic foraminifera : New observations of rotalid species in the context of existing literature
- 2018
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Ingår i: Marine Micropaleontology. - : Elsevier BV. - 0377-8398. ; 138, s. 12-32
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Tidskriftsartikel (refereegranskat)abstract
- We report systematic transmission electron microscope (TEM) observations of the cellular ultrastructure of selected, small rotalid benthic foraminifera. Nine species from different environments (intertidal mudflat, fjord, and basin) were investigated: Ammonia sp., Elphidium oceanense, Haynesina germanica, Bulimina marginata, Globobulimina sp., Nonionellina labradorica, Nonionella sp., Stainforthia fusiformis and Buliminella tenuata. All the observed specimens were fixed just after collection from their natural habitats allowing description of intact and healthy cells. Foraminiferal organelles can be divided into two broad categories: (1) organelles that are present in all eukaryotes, such as the nuclei, mitochondria, endoplasmic reticulum, Golgi apparatus, and peroxisomes; and (2) organelles observed in all foraminifera but not common in all eukaryotic cells, generally with unknown function, such as fibrillar vesicles or electron-opaque bodies. Although the organelles of the first category were observed in all the observed species, their appearance varies. For example, subcellular compartments linked to feeding and metabolism exhibited different sizes and shapes between species, likely due to differences in their diet and/or trophic mechanisms. The organelles of the second category are common in all foraminiferal species investigated and, according to the literature, are frequently present in the cytoplasm of many different species, both benthic and planktonic. This study, thus, provides a detailed overview of the major ultrastructural components in benthic foraminiferal cells from a variety of marine environments, and also highlights the need for further research to better understand the function and role of the various organelles in these fascinating organisms.
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| 19. |
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| 20. |
- Lupi, Claudia, et al.
(författare)
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Do sample preparation techniques affect the relative abundance of Florisphaera profunda?
- 2016
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Ingår i: Marine Micropaleontology. - : Elsevier BV. - 0377-8398 .- 1872-6186. ; 127, s. 42-49
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Tidskriftsartikel (refereegranskat)abstract
- We investigated which method among smearing, settling, filtration, and random settling is the most accurate for determining the relative abundance of Florisphaera profunda. This species is included in paleoproductivity indices because it is one of the most important deep-water dwellers. Therefore, an accurate assessment of its relative abundance is key to monitoring variations in thermocline and nutricline depths. The low birefringence and flat polygonal shape of F. profunda may lead to inaccurate estimates of its relative abundance as it is poorly visible under light microscopy (LM), and different sample preparation may affect the number of specimens on each slide. We studied eight samples from the Ocean Drilling Program (ODP) Site 1209B (Shatslcy Rise, NW Pacific) from the last 450 kyr. Each sample was prepared five times using each technique for a total of 160 slides. Through a rigorous analytical and statistical approach, we demonstrated the high reproducibility of each method and showed good agreement among techniques at low percentages of F. profunda. When the percentage of this species increases, the random settling technique differs from the others. Filtration and random settling preparation techniques were calibrated by spiking samples with microbeads. The ratio of microbeads observed in slides prepared using these two methods reflects bias due to loss of particles in the filtration technique. In addition, a hydrodynamic model for a fluttering and tumbling plate - such as F. profunda nannoliths - is proposed here along with calculated sinking velocities. These findings confirmed the efficiency of the long decantation time proposed for the random settling technique. The analysis of replicates, the validation with microbeads and the estimation of settling velocity of nannofossils in the tube convinced us that the higher relative abundance recorded by the random technique is not due to an imprecision of this method but, on the contrary, reflects the fact that it is more effective.
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| 21. |
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| 22. |
- Nordberg, Kjell, et al.
(författare)
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Stable carbon isotope evidence of the establishment of a new, opportunistic foraminiferal fauna in a Swedish Skagerrak fjord basin, in 1979/1980
- 2009
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Ingår i: Marine Micropaleontology. - : Elsevier BV. - 1872-6186 .- 0377-8398. ; 73:1-2, s. 117-128
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Tidskriftsartikel (refereegranskat)abstract
- Significant faunal changes reported fromrecent, coastal environments,which are not directly influenced by urban and industrial impact, are rarely seen. In Gullmar Fjord on the Swedish west coast, a significant foraminiferal fauna change occurred in connectionwith severe low-oxygen conditions that evolved in thewinter of 1979/1980. A foraminiferal fauna marked by common Skagerrak–Kattegat species, which had previously characterised the deep fjord basin, was replaced by the opportunistic, low-oxygen tolerant species Stainforthia fusiformis (Williamsson). To study this phenomenon further we performed stable oxygen and carbon isotope analyses on the indicator species itself, S. fusiformis, both on specimens from sediment cores representing approximately the last 85 years and on living (stained) individuals taken from a transect across the deep fjord basin. Our purpose was to detail how and why S. fusiformis, came to dominate the fauna. The oxygen isotope results suggest that salinities and temperatures in the deep basin have been relatively constant over the last c. 85 years, while the carbon isotopes show a significant change towards more negative values in association with the faunal shift of 1979/1980. The combined results from both the cores and the surface sediments suggest that S. fusiformis did not inhabit the deep basin until 1980. Before then, almost all specimens of S. fusiformis were small sized and their carbon isotope values suggest they were re-deposited shallow-water specimens that had been transported down to the central, deep basin as part of a suspension load. After a major faunal extinction in 1979–1980, S.fusiformis of all sizes suddenly appeared in large numbers and their carbon isotopic values were similar to the signal from registered in the recent, living fauna within the deep basin. This suggests that the opportunistic S. fusiformis established itself in the deep basin as a consequence of the severe low-oxygen event and the faunal crash of the previously dominating Skagerrak–Kattegat fauna.
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| 23. |
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| 24. |
- Plancq, Julien, et al.
(författare)
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Global shifts in Noelaerhabdaceae assemblages during the late Oligocene-early Miocene
- 2013
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Ingår i: Marine Micropaleontology. - : Elsevier BV. - 0377-8398 .- 1872-6186. ; 103, s. 40-50
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates abundance variations in Noelaerhabdaceae assemblages during the late Oligocene-early Miocene at three subtropical sites in the Atlantic and Pacific oceans (DSDP Sites 516,608 and 588). At these three sites, nannofossil assemblages were characterized by the successive high proportion of Cyclicargolithus, Dictyococcites and Reticulofenestra. Local paleoceanographic changes, such as the input of nutrient-poor water masses, might explain shifts in ecological prominence within the Noelaerhabdaceae at DSDP Site 516 (South Atlantic). But the similar timing of a decline in Cyclicargolithus at the three studied sites more likely corresponds to a global process. Here, we explore possible causes for this long-term taxonomic turnover. A global change in climate, associated with early Miocene glaciations, could have triggered a decline in fitness of the taxon Cyclicargolithus. The ecological niche made vacant because of the decrease in Cyclicargolithus could then have been exploited by Dictyococcites and Reticulofenestra that became prominent in the assemblages after 20.5 Ma. Alternatively, this global turnover might reflect a gradual evolutionary succession and be the result of other selection pressures, such as increased competition between Cyclicargolithus and Dictyococcites/Reticulofenestra. A diversification within Dictyococcites/Reticulofenestra, indicated by an expansion in the size variation within this group since similar to 20.5 Ma, may have contributed to the decreased fitness of Cyclicargolithus.
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| 25. |
- Polovodova Asteman, Irina, 1980, et al.
(författare)
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Too old to be new? A recent discovery of a pteropod Limacina lesueurii (d'Orbigny 1836) at the Swedish west coast (Skagerrak, North Sea)
- 2022
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Ingår i: Marine Micropaleontology. - : Elsevier BV. - 0377-8398 .- 1872-6186. ; 171
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Tidskriftsartikel (refereegranskat)abstract
- The pteropod Limacina lesueurii (d'Orbigny 1836) is a subtropical species, which in the Atlantic Ocean shows maximum abundance between 30°N and 25°S. In the North Sea, this species has so far only been occasionally reported from the coastal waters off the northern Scotland and in the English Channel. In this short note, we for the first time report presence of L. lesueurii in two sediment cores taken in the Kosterfjord (Skagerrak, North Sea). The pteropod, generally absent or occurring in low numbers throughout both cores, showed distinctly higher abundances between 100 and 130 cm core depth, which based on dating by 137Cs, 210Pb and lead pollution records corresponds to ~1920–1950s. During this period positive sea surface temperature anomalies were reported in the North Atlantic and number of oceanic water inflows have been documented for the North Sea. Some of these inflows were accompanied by ”enormous shoals” of L. lesueurii observed in the English Channel and NE of Scotland. We hypothesize that L. lesueurii was transported into the Skagerrak in connection with these and propose this pteropod species as a new valuable stratigraphic marker for oceanic water inflows in the study area.
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| 26. |
- Polovodova, Irina, 1980, et al.
(författare)
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The benthic foraminiferal record of the Medieval Warm Period and the recent warming in the Gullmar Fjord, Swedish west coast : Medieval Warm Period and the recent warming in the Gullmar Fjord
- 2011
-
Ingår i: Marine Micropaleontology. - : Elsevier BV. - 0377-8398. ; 81, s. 96-106
-
Tidskriftsartikel (refereegranskat)abstract
- A high-resolution study of benthic foraminiferal assemblages was performed on a ca. eight metre long sediment core from Gullmar Fjord on the west coast of Sweden. The results of 210Pb- and AMS 14C-datings show that the record includes the two warmest climatic episodes of the last 1500 years: the Medieval Warm Period (MWP) and the recent warming of the 20th century. Both periods are known to be anomalously warm and associated with positive NAO winter indices. Benthic foraminiferal successions of both periods are compared in order to find faunal similarities and common denominators corresponding to past climate changes. During the MWP, Adercotryma glomerata, Cassidulina laevigata and Nonionella iridea dominated the assemblages. Judging from dominance of species sensitive to hypoxia and the highest faunal diversity for the last ca. 2400 years, the foraminiferal record of the MWP suggests an absence of severe low oxygen events. At the same time, faunas and δ13C values both point to high primary productivity and/or increased input of terrestrial organic carbon into the fjord system during the Medieval Warm Period. Comparison of the MWP and recent warming revealed different trends in the faunal record. The thin-shelled foraminifer N. iridea was characteristic of the MWP, but became absent during the second half of the 20th century. The recent Skagerrak–Kattegat fauna was rare or absent during the MWP but established in Gullmar Fjord at the end of the Little Ice Age or in the early 1900s. Also, there are striking differences in the faunal diversity and absolute abundances of foraminifera between both periods. Changes in primary productivity, higher precipitation resulting in intensified land runoff, different oxygen regimes or even changes in the fjord's trophic status are discussed as possible causes of these faunal differences.
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| 27. |
- Polovodova, I., et al.
(författare)
-
The benthic foraminiferal record of the Medieval Warm Period and the recent warming in the Gullmar Fjord, Swedish west coast
- 2011
-
Ingår i: Marine Micropaleontology. - : Elsevier BV. - 1872-6186 .- 0377-8398. ; 81:3-4, s. 95-106
-
Tidskriftsartikel (refereegranskat)abstract
- A high-resolution study of benthic foraminiferal assemblages was performed on a ca. eight metre long sediment core from Gullmar Fjord on the west coast of Sweden. The results of Pb-210- and AMS C-14-datings show that the record includes the two warmest climatic episodes of the last 1500 years: the Medieval Warm Period (MWP) and the recent warming of the 20th century. Both periods are known to be anomalously warm and associated with positive NAO winter indices. Benthic foraminiferal successions of both periods are compared in order to find faunal similarities and common denominators corresponding to past climate changes. During the MWP, Adercotryma glomerata, Cassidulina laevigata and Nonionella iridea dominated the assemblages. Judging from dominance of species sensitive to hypoxia and the highest faunal diversity for the last ca. 2400 years, the foraminiferal record of the MWP suggests an absence of severe low oxygen events. At the same time, faunas and delta C-13 values both point to high primary productivity and/or increased input of terrestrial organic carbon into the fjord system during the Medieval Warm Period. Comparison of the MWP and recent warming revealed different trends in the faunal record. The thin-shelled foraminifer N. iridea was characteristic of the MWP, but became absent during the second half of the 20th century. The recent Skagerrak-Kattegat fauna was rare or absent during the MWP but established in Gullmar Fjord at the end of the Little Ice Age or in the early 1900s. Also, there are striking differences in the faunal diversity and absolute abundances of foraminifera between both periods. Changes in primary productivity, higher precipitation resulting in intensified land runoff, different oxygen regimes or even changes in the fjord's trophic status are discussed as possible causes of these faunal differences. (C) 2011 Elsevier B.V. All rights reserved.
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| 28. |
- Raffi, Isabella, et al.
(författare)
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The response of calcareous nannofossil assemblages to the Paleocene/Eocene Thermal Maximum at the Walvis Ridge in the South Atlantic
- 2009
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Ingår i: Marine Micropaleontology. - : Elsevier. - 0377-8398 .- 1872-6186. ; 70:3-4, s. 201-212
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Tidskriftsartikel (refereegranskat)abstract
- Compositions and abundances of calcareous nannofossil taxa have been determined in a ca 170 kyrs long time interval across the Paleocene/Eocene boundary at 1-cm to 10-cm resolution from two ODP Sites (1262, 1263) drilled along the flank of the Walvis Ridge in the South Atlantic. The results are compared to published data from ODP Site 690 in the Weddell Sea. The assemblages underwent rapid evolution over a 74 kyrs period, indicating stressed, unstable and/or extreme photic zone environments during the PETM hyperthermal. This rapid evolution, which created 5 distinct stratigraphic horizons, is consistent with the restricted brief occurrences of malformed and/or weakly calcified morphotypes. The production of these aberrant morphotypes is possibly caused by major global scale changes in carbon cycling in the ocean–atmosphere system, affecting also photic zone environments. No marked paleoecologically induced changes are observed in abundances of the genera Discoaster, Fasciculithus and Sphenolithus at the Walvis Ridge sites. Surprisingly, there is no significant correlation in abundance between these three genera, presumed to have had a similar paleoecological preference for warm and oligotrophic conditions.
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| 29. |
- Sijinkumar, A. V., et al.
(författare)
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Pulleniatina Minimum Events in the Andaman Sea (NE Indian Ocean) : Implications for winter monsoon and thermocline changes
- 2011
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Ingår i: Marine Micropaleontology. - : Elsevier BV. - 0377-8398 .- 1872-6186. ; 81:3-4, s. 88-94
-
Tidskriftsartikel (refereegranskat)abstract
- The late Quaternary record of Pulleniatina obliquiloculata was investigated from two well dated sediment cores from the Andaman Sea (NE Indian Ocean) to examine its paleoceanographic significance and the presence of the Pulleniatina Minimum Events (PME) in the western North Pacific. As in the Pacific, our study shows that PMEs exist in the Indian Ocean albeit with a lower intensity. The Holocene PME occurs between 4.5 and 3.0 cal ka BP with a considerable reduction in P. obliquiloculata abundance, and which matches well with the Pacific records influenced by the Kuroshio Current. Additionally, two significant minimum events of P. obliquiloculata are also seen during the Younger Dryas (YD) and late Last Glacial Maximum (LGM, 20-18 cal ka BP). Overall, the PMEs of the Andaman Sea are not current driven events like in the western Pacific margin either by the weakening of the Kuroshio Current or reduced winter SSTs. The PMEs of the Andaman Sea are characterised by lower abundances of thermocline species indicating the increased depth of the thermocline (DOT) and reduced winter SSTs mainly during the minimum events of the YD and late LGM. The high SSTs during the Holocene PME make this event a mystery. However, the presence of PMEs in the Andaman Sea suggests that these events are not confined to areas influenced by the Kuroshio Current but may be responding to a broad scale oceanographic-climatic process or mechanism which needs to be explored with a detailed study.
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| 30. |
- Sucheras-Marx, Baptiste, et al.
(författare)
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Middle Jurassic coccolith fluxes : A novel approach by automated quantification
- 2014
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Ingår i: Marine Micropaleontology. - : Elsevier BV. - 0377-8398 .- 1872-6186. ; 111, s. 15-25
-
Tidskriftsartikel (refereegranskat)abstract
- Coccolithophores, major pelagic carbonate producers, underwent important changes during the latest Aalenian-Early Bajocian (ca. - 170 Ma, Middle Jurassic). Specifically, a new genus called Watznaueria diversified and started dominating the coccolith assemblages. While this change in the coccolith assemblages is already known, the impact on coccolith absolute abundances and fluxes is still misunderstood. Here we tested for the first time on Mesozoic deposits an automated counting method using the SYRACO system, and then compared these results with a classic counting method. Two neural networks were created based on the shape, birefringence and size of coccoliths, the first of which contained only one class and the second of which was composed of six classes. Based on the morphological criteria used for the neural networks, coccoliths were not identified at the species level. We quantified coccolith absolute abundances and estimated fluxes for the latest Aalenian-Early Bajocian in two well-dated and correlated sections, Cabo Mondego in Portugal and Chaudon-Norante in France. There is a strong linear correlation between classic and automatic counting (r > 0.8) supporting the latter as a reliable method for coccolith absolute abundance and flux quantification. In spite of under- or over-estimation by automatic counting with respect to classic counting, the absolute abundance stratigraphic trends are remarkably similar. Under- or over-estimation may be reduced by further technical improvements such as automatic focus. At Cabo Mondego, coccolith fluxes increased from 0.2 x 10(9) coccoliths/m(2)/yr in the latest Aalenian to 700 x 10(9) coccoliths/m(2)/yr in the middle of the Laeviuscula ammonite Zone (Early Bajocian), remaining high for the rest of the Early Bajocian. At Chaudon-Norante, a similar trend was observed. This coccolith flux increase is therefore considered to be a supra-regional event matching an important delta C-13(Bulk) (carbonate) Positive excursion. The carbon isotopic positive excursion, along with the onset of radiolarian sedimentation and coccolith fluxes is related to a gradual increase in the fertility of the oceans during the Early Bajocian and is likely associated with warmer and more humid climates and associated enhanced continental weathering.
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| 31. |
- Supraha, Luka, 1987-, et al.
(författare)
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Combination coccospheres from the Eastern Adriatic coast : New, verified and possible life-cycle associations
- 2018
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Ingår i: Marine Micropaleontology. - : ELSEVIER SCIENCE BV. - 0377-8398 .- 1872-6186. ; 141, s. 23-30
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Tidskriftsartikel (refereegranskat)abstract
- Coccolithophore life cycles involve the alternation between morphologically distinct life-cycle phases. This often leads to taxonomic issues where the life-cycle phases of the same species are described as distinct taxa. This issue can be resolved by the observation of combination coccospheres, i.e. cells bearing the coccoliths of both life-cycle phases. This study presents new observations on combination coccospheres from the highly diverse and ecologically important coccolithophore order Syracosphaerales and the genus Alisphaera. New life-cycle associations are revealed between Syracosphaera hirsuta and Corisphaera strigilis, and between Alisphaera unicornis and a nannolith-producing Polycrater galapagensis. The life-cycle association of Syracosphaera marginiporata Anthosphaera sp. type B is verified. A possible association between Rhabdosphaera xiphos and an unidentified holococcolith-bearing morphotype is proposed and needs to be verified in future investigations. The appropriate taxonomic revisions are conducted following the taxonomic principle of priority and recommended practices for naming the coccolithophore life-cycle phases.
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| 32. |
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