| 1. |
|
|
| 2. |
- Birch, Heather, et al.
(author)
-
Planktonic foraminifera stable isotopes and water column structure : Disentangling ecological signals
- 2013
-
In: Marine Micropaleontology. - : Elsevier BV. - 0377-8398 .- 1872-6186. ; 101, s. 127-145
-
Journal article (peer-reviewed)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.
|
|
| 3. |
- Cappelli, Carlotta, et al.
(author)
-
Middle Eocene large coccolithaceans : Biostratigraphic implications and paleoclimatic clues
- 2020
-
In: Marine Micropaleontology. - : Elsevier BV. - 0377-8398 .- 1872-6186. ; 154
-
Journal article (peer-reviewed)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.
|
|
| 4. |
- Cronin, T. M., et al.
(author)
-
Holocene paleoceanography and glacial history of Lincoln Sea, Ryder Glacier, Northern Greenland, based on foraminifera and ostracodes
- 2022
-
In: Marine Micropaleontology. - : Elsevier BV. - 0377-8398 .- 1872-6186. ; 175
-
Journal article (peer-reviewed)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.
|
|
| 5. |
- Cubillos, Joana C., et al.
(author)
-
Reconstructing calcification in ancient coccolithophores : Individual coccolith weight and morphology of Coccolithus pelagicus (sensu lato)
- 2012
-
In: Marine Micropaleontology. - : Elsevier BV. - 0377-8398 .- 1872-6186. ; 92-93, s. 29-39
-
Journal article (peer-reviewed)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.
|
|
| 6. |
- Flores, Jose-Abel, et al.
(author)
-
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
-
In: Marine Micropaleontology. - : Elsevier BV. - 0377-8398 .- 1872-6186. ; 76:3-4, s. 53-66
-
Journal article (peer-reviewed)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.
|
|
| 7. |
- Godad, Shital P., et al.
(author)
-
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
-
In: Marine Micropaleontology. - : Elsevier BV. - 0377-8398 .- 1872-6186. ; 78:1-2, s. 25-29
-
Journal article (peer-reviewed)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.
|
|
| 8. |
|
|
| 9. |
- Herrmann, Sandra, et al.
(author)
-
Global coccolith size variability in Holocene deep-sea sediments
- 2012
-
In: Marine Micropaleontology. - : Elsevier. - 0377-8398 .- 1872-6186. ; 82-83, s. 1-12
-
Journal article (peer-reviewed)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.
|
|
| 10. |
- Lupi, Claudia, et al.
(author)
-
Do sample preparation techniques affect the relative abundance of Florisphaera profunda?
- 2016
-
In: Marine Micropaleontology. - : Elsevier BV. - 0377-8398 .- 1872-6186. ; 127, s. 42-49
-
Journal article (peer-reviewed)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.
|
|
