| 1. |
- Blaj, Teodora, 1979-
(författare)
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Late Eocene through Oligocene calcareous nannofossils from the paleo-equatorial Pacific Ocean – taxonomy, preservation history, biochronology and evolution
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This study aims to unravel the ecological and evolutionary dynamics within the calcareous nannofossil communities at the Eocene/Oligocene (E/O) transition and during the Oligocene time when Cenozoic 'icehouse' conditions were established. The main question this study aims to answer is whether the changes in the nannofossil assemblages were controlled by intrinsic evolutionary trends or if the changes were controlled by environmental factors such as changes in temperature and nutrient availability in the surface water. These questions are addressed with detailed analyses of the taxonomy, biostratigraphy and fluctuations in abundance and diversity of calcareous nannofossil assemblages from a continuous latest Eocene through Oligocene sediment section from the ODP Site 1218 (8°53.38´N, 135°22.00´W), paleo-equatorial Pacific Ocean. An improved nannofossil taxonomy and biostratigraphy has been established. At the E/O transition, changes in the nannofossil preservation mimics changes in calcium carbonate content. A detailed investigation of late Eocene and Oligocene sediments yields age estimates for ten nannofossil bioevents. Morphometric studies of the Reticulofenestra umbilicus-R. hillae show that these cannot be subdivided into two different morphospecies. Based on different morphometry and stratigraphic ranges, the Oligocene Sphenolithus lineage appears to be the result of a combined anagenetic and cladogenetic evolution. A new nannolith species is described: Triquetrorhabdulus longus. High-resolution nannofossil data indicate changes in the composition, abundance and diversity of the mid-Oligocene assemblages. Intervals of high diversity index coincide with Oi-glaciation events. However, visual examination of the variations in abundance of nannofossil taxa do not appear to correlate with changes in either oxygen or carbon isotopes. This presumably indicates that a dynamic equilibrium did not exist between these Oligocene nannoplankton assemblages and changes in surface water temperature or productivity conditions.
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| 2. |
- Karatsolis, Boris-Theofanis
(författare)
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Late Miocene to Pliocene orbital and climatic forcing on marine productivity
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The late Miocene to Pliocene was a geological time interval of global cooling, albeit in a warmer-than-present world, which is commonly used as a past analogue for future anthropogenic climate change. The investigation of marine sediments recovered by the International Ocean Discovery Program (IODP) sheds light on different paleoclimatic, paleoceanographic and paleobiological characteristics of this period. The NW Australian shelf represents an interesting area for such investigation, because it is strategically positioned near the only remaining equatorial warm-water valve on Earth. In Chapter I and Chapter II, focus is given on calcareous nannofossil time-series data and records of the element potassium (K), which is mainly delivered by rivers to the shelf, at IODP Sites U1463 and U1464. Results demonstrate that humid conditions were probably prevailing earlier than previously thought (at least since ~6 Ma), but that regional tectonics (basin subsidence) has complicated the identification of the exact onset. In addition, nannofossil assemblages data and paleotemperature gradients between the shelfal area and the eastern Indian Ocean reveal a shift in oceanographic and climatic regime that occurred between 5.4-5.2 Ma, as a likely result of an overall long-term increase in seasonality. Finally, an interval of decreasing nannofossil accumulation rates (fluxes) and a distinct change in the dominant nannoplankton species occurred between 4.6-4.4 Ma and is hypothesized to be part of broader changes in ocean nutrient availability. This hypothesis is further explored in Chapter III and Chapter IV through the investigation of a well-established period of globally elevated biogenic sedimentation (and related marine export productivity) known as the late Miocene to early Pliocene biogenic bloom. In Chapter III, age model accuracy and sample resolution of previously published biogenic sediment accumulation rate records are evaluated. The compilation of multiple records shows that an abrupt reduction in ocean paleoproductivity occurred between 4.6-4.4 Ma at (sub)tropical latitudes. This event coincided with a rather unique configuration of the Earth’s orbit, which could have led to a weakened Asian monsoon activity and therefore reduced river runoff and nutrient supply to the ocean. Chapter IV focuses on the comparison between the calcareous nannofossil assemblages at the NW Australian shelf sites and ODP Site 1264 in the South Atlantic Ocean, across the termination of the biogenic bloom. Although the overall decrease in paleoproductivity occurred around the same time, the shift in species dominance across the end of the biogenic bloom, as shown in the tropical Indian Ocean, is not observed at ODP Site 1264.
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| 3. |
- 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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| 4. |
- Jackson, Illiam, 1986-
(författare)
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Morphometric analysis of Cambrian fossils and its evolutionary significance
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Extended Evolutionary Synthesis (EES) is currently emerging as a theoretical alternative to the Modern Synthesis (MS) in which to frame evolutionary observations and interpretations. These alternative frameworks differ fundamentally in their understanding of the relative roles of the genotype, phenotype, development and environment in evolutionary processes and patterns. While the MS represents a gene-centred view of evolution, the EES instead emphasizes the interactions between organism, development and environment. This novel theoretical framework has generated a number of evolutionary predictions that are mutually incompatible with the equivalent of the MS. While research and empirical testing has begun on a number of these in a neontological context, the field of palaeontology has yet to contribute meaningfully to this endeavour. One of the reasons for this is a lack of methodological approaches capable of investigating relevant evolutionary patterns in the fossil record. In this thesis morphometric methods capable of providing relevant data are developed and employed in the analysis of Cambrian fossils. Results of these analyses provide empirical support for the process of evolution through phenotypic plasticity and genetic assimilation hypothesized by the EES. Furthermore, theoretical revision to the species concept in a palaeontological context is suggested. Finally, predictions of the EES specific to the fossil record are made explicit and promising directions of future research are outlined.
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| 5. |
- Šupraha, Luka, 1987-
(författare)
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Phenotypic evolution and adaptive strategies in marine phytoplankton (Coccolithophores)
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Coccolithophores are biogeochemically important marine algae that interact with the carbon cycle through photosynthesis (CO2 sink), calcification (CO2 source) and burial of carbon into oceanic sediments. The group is considered susceptible to the ongoing climate perturbations, in particular to ocean acidification, temperature increase and nutrient limitation. The aim of this thesis was to investigate the adaptation of coccolithophores to environmental change, with the focus on temperature stress and nutrient limitation. The research was conducted in frame of three approaches: experiments testing the physiological response of coccolithophore species Helicosphaera carteri and Coccolithus pelagicus to phosphorus limitation, field studies on coccolithophore life-cycles with a method comparison and an investigation of the phenotypic evolution of the coccolithophore genus Helicosphaera over the past 15 Ma. Experimental results show that the physiology and morphology of large coccolithophores are sensitive to phosphorus limitation, and that the adaptation to low-nutrient conditions can lead to a decrease in calcification rates. Field studies have contributed to our understanding of coccolithophore life cycles, revealing complex ecological patterns within the Mediterranean community which are seemingly regulated by seasonal, temperature-driven environment changes. In addition, the high-throughput sequencing (HTS) molecular method was shown to provide overall good representation of coccolithophore community composition. Finally, the study on Helicosphaera evolution showed that adaptation to decreasing CO2 in higher latitudes involved cell and coccolith size decrease, whereas the adaptation in tropical ecosystems also included a physiological decrease in calcification rates in response to nutrient limitation. This thesis advanced our understanding of coccolithophore adaptive strategies and will improve our predictions on the fate of the group under ongoing climate change.
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