| 1. |
- 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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| 2. |
- Karatsolis, Boris-Theofanis, 1992-
(författare)
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Latest Miocene – Early Pliocene Paleoclimate and Phytoplankton Productivity
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Paper IPre-Quaternary paleoclimate studies in Australia mainly focus on terrestrial records from the southeastern part of the continent. IODP Expedition 356 drilled on the northwestern Australian shelf, yielding Miocene-Pleistocene paleoclimate records in an area where climate archives are scarce. Post-expedition research revealed a dry-to–humid transition across the latest Miocene and early Pliocene (start of the “Humid Interval”). However, the complex tectonic history of the area makes these interpretations challenging. In this study, we investigate late Miocene to early Pliocene sediment cores from two sites that are only 100 km apart, but situated in two adjacent basins (Northern Carnarvon and Roebuck Basins). Combining lithofacies study, time-series analysis of potassium content (K wt%) and calcareous nannofossil abundance counts (N/g), this work disentangles the complex interplay between basin evolution and climate change between 6.1-4 million years ago (Ma). Overall, the investigated proxies show high correlation between both sites, except during 6.1-5.7 Ma. During this latest Miocene interval, Site U1463 records a gradual increase in K wt%, correlated with basin deepening, whereas Site U1464 records an abrupt rise in K wt% at ~6 Ma. We explain this diachronicity by differential basin subsidence. The tectonic interplay with our paleorecords makes it difficult to pinpoint the exact onset of the “Humid Interval”, but we conclude that high K wt% and coccolith abundances at Site U1464 indicate that humidity was already enhanced since at least 6 Ma. This age is consistent with data supporting a southward movement of the Intertropical Convergence Zone rain belt at ~7 Ma.Paper IIThe early Pliocene was a warm period with increased ocean primary productivity, as part of a global paleoceanographic event called the late Miocene-early Pliocene biogenic bloom (~9-3.5 Ma). Many tectonic and paleoclimatic mechanisms, mainly linked to an increase and redistribution of nutrient supply in the ocean, have been proposed as driving forces for this event. However, the main phase of increased productivity and the termination of this event appear to be diachronous in different ocean basins. Here, we compiled proxy data for early Pliocene paleoproductivity from all major ocean basins, including both calcareous and siliceous plankton groups. After re-evaluating the age model resolution of the available paleo-records, we demonstrate that a main stage of decrease in primary productivity occurred during ~4.6-4.4 Ma. We then show that this productivity collapse coincided with an orbital configuration of long-term reduction in eccentricity amplitude and low amplitude obliquity. This combination of orbital parameters could have significantly affected seasonality and nutrient availability in the global ocean and suggests a previously undescribed paleoclimatic forcing that may have been a crucial step in contributing to the end of the biogenic bloom
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| 3. |
- 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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| 4. |
- 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
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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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| 5. |
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| 6. |
- Winter, Amos, et al.
(författare)
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Poleward expansion of the coccolithophore Emiliania huxleyi
- 2014
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 36:2, s. 316-325
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Tidskriftsartikel (refereegranskat)abstract
- Coccolithophores are one of the most abundant eukaryotic phytoplankton in the oceans and are distinguished by their ability to build calcitic platelets (coccoliths). Of the numerous species, Emiliania huxleyi is considered one of the major calcifiers in the pelagic ocean. There is growing concern that increasing levels of CO2 in the atmosphere and the subsequent acidification of the ocean may disrupt the production of coccoliths. Furthermore, any change in the global distribution and abundance of E. huxleyi relative to non-calcifying groups of phytoplankton (e.g. diatoms) will have important effects on the biogeochemical cycling of carbon and climatic feedbacks. We review different lines of evidence that suggest E. huxleyi is increasingly expanding its range into the polar oceans. These observations contribute to the debate on the climatic effects on natural coccolithophore populations. We postulate that E. huxleyi may be more sensitive to recent environmental changes such as increasing sea surface temperature and salinity than to changing ocean carbonate chemistry, partly because increased availability of CO2(aq) likely alleviates a carbon limitation for the inefficient Rubisco enzyme in these algae. Any potentially important climatic feedbacks of coccolithophores need a better knowledge of the mechanisms and rates of adaptation by natural populations. As more data and modelling work become available, the real significance of this poleward expansion will become clear.
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