Dissertations / Theses on the topic 'Palaeoceanography'
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1
Beveridge, Neil Alexander Stewart. "Palaeoceanography of the Eastern Atlantic." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337952.
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Grigorov, Ivo. "Southern Ocean palaeoceanography from Thalassiothrix antarctica deposits." Thesis, University of Southampton, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413434.
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King, Stephen Charles. "Late Quaternary palaeoceanography of the Peru Margin." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239459.
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Chepstow-Lusty, Alexander John. "Nannoplankton as indicators of climatic variability in the Upper Pliocene." Thesis, University of Cambridge, 1991. https://www.repository.cam.ac.uk/handle/1810/239128.
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Discoasters are the remains of an enigmatic group of nannoplankton, whose last representatives disappeared globally at 1.89 Ma. The one million years prior to their extinction has been analysed in high time resolution and a global database has been developed from ten sites in the Atlantic, Indian and Pacific Oceans. It has been shown that the variability in Discoaster abundance at low latitudes cannot be attributed solely to changes in sea-surface temperature; discoasters were demonstrated to be suppressed at upwelling sites. In combination with global satellite images of phytoplankton blooms (Lewis, 1989) and maps of modern sea-surface temperatures (CLIMAP, 1981), Discoaster abundance variations were interpreted in terms of the interplay between productivity pressure and sea-surface temperature. Discoasters thrived in the Indian Ocean at Site 709 (4°S) in warm waters with little productivity pressure, whereas Discoaster abundance was suppressed at Sites 677 (l°N) and 662 (l°S) in the Pacific and Atlantic, which although located in warm waters, were affected by upwelling. In addition to the reduced Discoaster abundances associated with upwelling, sea-surface temperature gradients are a significant factor when comparing high and low latitude sites. A marked drop in Discoaster abundance is apparent between 41°N and 56°N (i.e., between Sites 607 and 552). Relative abundances of species in the Discoaster assemblage revealed clearly their contrasting environmental preferences; D. brouweri was produced under a wide range of conditions, favouring warm, low productivity waters; D. asymmetricus and D. tamalis were produced in higher abundances relative to D. brouweri during cooler, low productivity episodes; D. pentaradiatus showed highest absolute abundance in warm, low productivity waters, although increasing in relative abundance at higher latitudes; D. surculus increased in relative abundance in high productivity regions and in cooler waters. At all sites, though most markedly at higher latitudes, Discoaster abundances declined after 2.4 Ma, when glaciation began in the North Atlantic.
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Whiteley, N. J. P. "Investigating of palaeo-circulation in the Southern Atlantic, Southern and Northern Indian Oceans over the last 14Ma using hydrogenetic ferromanganese crusts." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365325.
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Hart, Stephen Francis. "Palaeoceanography and sedimentology of a mid-Cretaceous Greensand." Thesis, University of Oxford, 1991. http://ora.ox.ac.uk/objects/uuid:ac7da904-aad1-4525-8d11-9c520fc131d3.
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The Upper Albian (mid-Cretaceous) sediments of the Anglo-Paris Basin display a range of condensation phenomena, including glauconitic and phosphoritic sands, glauconitic intraformational pebble beds, and mineralised nodular hardgrounds. These are interpreted as the result of sedimentation rate fluctuations controlled by small-scale relative sea-level changes of at least regional nature. The regional signal was modified by local tectonics, including occasional synsedimentary faulting and the development of thinned successions and complex condensation horizons over broad submarine highs. Candidate sequence boundaries, marine flooding surfaces and systems tracts are proposed. Episodic, high-energy storm events record a spectrum of storm intensities and periodicities in the Upper Greensand Formation. Storm processes interacted with early submarine lithification to produce a suite of pebble-shell beds, simple and amalgamated coquinas, and storm-scoured hardgrounds. Analysis of shell bed fabrics and taphonomy indicates the important role of high-energy storms in generating a distinct event stratigraphy. Stable isotope analysis has detected a positive secular change in carbon-isotopic ratios within carbonates of dispar zone age, resolved as two smaller positive shifts across nodular hardgrounds. This correlates with the development of organic-rich sediments in a range of settings world-wide. Analytical problems, including silica diagenesis, have been addressed by a series of parallel control studies. Geochemical and petrographic analysis has confirmed the widespread development of glauconitic minerals throughout the Upper Greensand, and has been used to investigate grain evolution in a range of lithologies. A review of the global development of the Cretaceous glauconitic facies has been used to compile depositional models for a range of settings. Volumetric calculations of Cretaceous glauconite production rates have shown secular changes, with peak Aptian to Santonian values linked to transgressions across the broad shelf seas which developed globally during this time of rising sea-levels and sea-level highstand.
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Chapman, Mark Robert. "Late Pliocene planktonic foraminifera : palaeoceanography and faunal evolution." Thesis, University of East Anglia, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332388.
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Sexton, Philip. "Foraminiferal taphonomy, palaeoecology and palaeoceanography of the Eocene." Thesis, University of Southampton, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416473.
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Little, Mark G. "Late Quaternary palaeoceanography of the Benguela upwelling system." Thesis, University of Edinburgh, 1997. http://hdl.handle.net/1842/12437.
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Planktonic foraminifera recovered from nine cores in the Benguela Current system are used to ascertain the variability of upwelling intensity for the Late Quaternary and its impact on atmosphere-ocean-cryosphere linkages. The analyses from high-resolution planktonic foraminiferal records for cores GeoB 1706, GeoB 1711 and PG/PC 12, reveal striking variations in upwelling intensity during the last 160,000 years. Four species make up over 95% of the variation within the cores, and enable the record to be divided into episodes characterised by particular planktonic foraminiferal assemblages which have meaningful ecological significance when compared to those of the present-day and the relationship to their environment. The cold-water planktonic foraminifer, Neogloboquadrina pachyderma sinistral [N. pachyderma (s))], dominates the modern-day, coastal upwelling centres, and Neogloboquadrina pachyderma dextral and Globigerina bulloides characterise the fringes of the upwelling cells. Globorotalia inflata is representative of the offshore boundary between newly upwelled waters and the transitional, reduced nutrient levels of the sub-tropical waters. In the fossil record, episodes of high N. pachyderma (s) abundances are interpreted as evidence of increased upwelling intensity and the associated increase in nutrients. The N. pachyderma (s) record suggests rapid shifts in the intensity of upwelling, and corresponding trophic domains, that do not follow the typical glacial - interglacial pattern, but instead reflect the shifts of the Angola-Benguela front situated to the north of the Walvis Ridge. Absence of high abundances of N. pachyderma (s) from the continental slope of the southern Cape Basin indicate that Southern Ocean surface water advection has not exerted a major influence on the Benguela Current system. The periods of high abundance in N. pachyderma (s) are referred to as 'PS events' and indicate increased intensity and zonality of the South Atlantic trade winds controlling the Benguela upwelling system. During these intense upwelling phases, total organic carbon, abundance of N. pachyderma (s) and the benthic/planktonic foraminiferal ratio, provide the best indicators for palaeoproductivity away from coastal re-suspension. The offshore record of GeoB 1711 is used as the indicator for maximum offshore divergence and shelf-edge upwelling and is regarded as the best indicator for palaeoceanographic and palaeoproductivity variability.
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Park, Laura Anne. "Late Quaternary palaeoceanography in Disko Bugt, West Greenland." Thesis, Durham University, 2003. http://etheses.dur.ac.uk/1284/.
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This thesis uses foraminiferal, sedimentological and isotope analysis from three piston cores from different depositional environments in Disko Bugt, West Greenland to understand the nature of the relationship between deglacial activity and palaeo-water mass circulation. It has increased the spatial and temporal resolution of marine multiproxy data in the region through the development of a tight radiocarbon chronology. High resolution sampling has furthered the understanding of modes of Holocene palaeoceanographic irculation in Disko Bugt and West Greenland,a nd linked them to likely operating mechanisms of change. Information about past variations in the strength of the dominant water current in West Greenland (the West Greenland Current - WGC), has been successful through the application of foraminiferal water mass indicator species and isotope techniques. New dating relating to the timing of the final retreat of Jakobshavns Isbrae, the most important ice stream draining the West Greenland Ice Sheet, has been determined through evidence of meltwater and sediment fluxes from the calving margin. The high resolution records produced in this thesis clearly document the rapid instability and subsequent retreat of the ice stream to be related to rapid atmospheric warming following the well-documented "8.2 event". Mid-Holocene climatic changes are recorded in the fjord mouth setting of Kangersuneq. Despite considerable dissolution processes operating in the fjord (which are in fact a product of climatic change themselves), a high resolution record of variable and declining warmth of the WGC is recorded from c. 6.3 ka cal BP, prior to the onset of full Neoglacial conditions around 4.1 ka cal BP. The maximum cooling during the Neoglacial period is clearly seen from c. 3.2 to 2.2 ka cal BP in two cores. A distinct warming of the WGC takes place around 2.2 ka cal BP, which can be linked to an increased component of Irminger Current Water. This is also seen in the records from East Greenland and the Nordic Seas. The foraminiferal assemblagesfr om one of the cores show evidence of a distinct climatic amelioration which is associated with the Medieval Warm Period. There is some evidence for a deterioration of oceanographic conditions which is linked to the onset of the Little Ice Age.
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Haslett, Simon K. "Pliocene-Pleistocene radiolarian investigations of the Equatorial oceans." Thesis, University of South Wales, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265674.
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Carden, Giles A. F. "Stable isotopic changes across the Ordovician-Silurian boundary." Thesis, University of Liverpool, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260327.
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Matthewson, Alastair P. "The palaeoclimatology and palaeoceanography of the northwest African margin." Thesis, University of Edinburgh, 1995. http://hdl.handle.net/1842/15288.
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Marine sediments in four piston cores collected from the northwest African continental margin during Biogeochemical Ocean Flux Study cruise 53 (RRS Charles Darwin) were comprehensively studied using a wide range of physical sediment parameters and geochemical techniques. The objective of the study was to examine the Late Quaternary palaeoceanography of the Northwest African continental margin and determine changes in the climate of the north and central African continent over the past 600 kyr. In addition, the core sites formed a transect running SE-NW, enabling the spatial analysis of upwelling intensity and wind vigour proxies. Chronostratigraphy was determined by correlating planktic (G.inflata) and benthic (C.wuellerstorfi) oxygen isotope (δ18O) records with the SPECMAP records of Imbrie et al. (1984) and Martinson et al. (1987). Sediment accumulation rates are greater during glacial stages and generally decrease with distance from the continent. North and central African continental aridity variations are indicated by the Al flux records. The calcium carbonate records also approximate aridity fluctuations due to dilution by lithogenic dust supplied by the Harmattan and northeast Trade wind systems. These changes operate dominantly at the 41 kyr (obliquity) Milankovitch frequency cycle and display highest Saharan dust input and aridity during glacial stages. Zr/Rb, Ti/Al and Lithogenic Component Grain Size profiles indicate an increase in grain size, and hence wind vigour, during glacial stages and the stage 5 interstadials, and hence display a strong 23 kyr (precessional) component of forcing as well as at the 100 kyr (eccentricity) frequency band. The most distal core site in the transect is strongly influenced by the kaolinite-rich Harmattan wind supply, while the three more proximal cores are affected by dust input from the northeast Trade winds. A high-resolution calcium carbonate profile of another core in the transect confirms the presence of high-amplitude, high-frequency climatic perturbations (aridity changes) with mid-termination setbacks similar to the Younger Dryas event which is seen in many north Atlantic climate records. This high latitude climatic deterioration also influenced north African climate, resulting in increased aridity and wind vigour at approximately 11,000 years BP. Similar climatic conditions are noted over the last 7,000 years. A sawtooth pattern in the high-resolution calcium carbonate and Bulk Sediment Grain Size records implies that rapid increases in continental aridity were followed by gradual increases in humidity, and that the insolation-induced African climate system is decoupled from global (ice-volume) climate change operating at a glacial/interglacial timescale.
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Jackson, P. C. "Sedimentology, stratigraphy and palaeoceanography of some Lower Carboniferous hemipelagic sequences." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.353095.
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Hooper, P. W. P. "Late Neogene planktonic forminifera and palaeoceanography of the North Atlantic." Thesis, University of East Anglia, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327884.
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Casford, James S. L. "Centennial-resolution palaeoceanography of the Aegean Sea : 15,000 BP - present." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396193.
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Thornalley, David John Robert. "Palaeoceanography of the South Iceland Rise over the past 21,000 years." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612325.
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de, Abreu Lucia. "High resolution palaeoceanography off Portugal during the last two glacial cycles." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621772.
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Henderson, Gideon Mark. "The uranium and strontium isotope evolution of seawater over the past four hundred thousand years." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338310.
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Hale, Ruth Elisabeth. "Quaternary history of the Polar Front in the Scotia Sea, Antarctica : foraminiferal and stable isotope evidence." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342837.
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Williams, Thomas. "Investigating the circulation of Southern Ocean deep water masses over the last 1.5 million years by geochemical fingerprinting of marine sediments." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/274006.
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The Southern Ocean (SO) is a critical component in the global ocean conveyor. As the only conduit linking the Atlantic, Indian and Pacific Oceans, as well as an important region of upwelling and water mass formation, it is thought to have played a key role in modulating Earth’s past climate. Changes in the circulation of SO deep and bottom waters over the last 1.5 million years are investigated using stable carbon isotope $δ^{13}C$ measurements made on the tests of the benthic foraminfer Cibicidoides ($δ^{13}C_{b}$), and the rare earth element concentrations and Neodymium isotope ($ɛ_{Nd}$) values of marine sediments and their authigenic ferromanganese coatings. Being a proxy for past seawater nutrient contents, $δ^{13}C_{b}$ provides important insights into both past ocean circulation and the potential storage of remineralised organic carbon within the deep ocean, while simultaneously providing information on the past ventilation state of the deep ocean interior. As seawater $ɛ_{Nd}$ remains unaffected by biological fractionation or air-sea exchange processes, reconstructions of past deep and bottom water $ɛ_{Nd}$ provides a tool with which to study past changes in the circulation and mixing of these water masses. A suite of previously published late Holocene (0-6 ka) and Last Glacial Maximum (LGM; 18-24 ka) $δ^{13}C_{b}$ data are used alongside newly acquired $δ^{13}C_{b}$ data from the Amundsen Sea in the eastern Pacific sector of the SO to investigate past changes in the pattern of circum-Antarctic seawater carbon isotope composition. The $δ^{13}C$ signature of deep and bottom waters was much more heterogenous during the LGM than the late Holocene, with negative $δ^{13}C$ excursions occurring within the Atlantic and Indian sectors of the SO below c. 2-3 km water depth. Some of this negative $δ^{13}C$ signal was advected through the SO to the Pacific sector, but this appears to have been restricted by bathymetric barriers within the SO. New $δ^{13}C_{b}$ data spanning the last 800 ka from the Amundsen Sea are presented and suggest differing modes of bottom water formation in the Atlantic vs Pacific sectors of the SO during glacial periods of the last 800 ka. An authigenic $ɛ_{Nd}$ record measured on sediments from a core located in the deep Indian Ocean is used to investigate the palaeocirculation history of modified Circumpolar Deep Water (mCDW) within the Indian Ocean during the last 1.5 million years. Shifts towards more radiogenic $ɛ_{Nd}$ values during glacial periods are interpreted as reflecting a decreased entrainment of deep waters sourced in the North Atlantic (Northern Component Water, NCW) within CDW, which led to a reduced advection of an unradiogenic $ɛ_{Nd}$ NCW signal to the core site. $ɛ_{Nd}$ and REE measurements made on sediments from two cores located on the Pacific-Antarctic Ridge in the western Pacific sector of the SO (to the north of the Ross Sea Embayment) are used to reconstruct the bottom water palaeocirculation in this region across the last 540 ka. The proportion and $ɛ_{Nd}$ signature of Ross Sea Bottom Water (RSBW) bathing these core sites has fluctuated throughout the last 540 ka. These fluctuations suggest the rate and location of bottom water formation within the Ross Sea, and the supply of terrigenous material with radiogenic $ɛ_{Nd}$ values with which to isotopically `labelled' RSBW, may have changed in the past.
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Rutledge, David Charles. "Calcareous nannofossils of the Boreal Lower Cretaceous : applications in biostratigraphy and palaeoceanography." Thesis, University College London (University of London), 1994. http://discovery.ucl.ac.uk/1360347/.
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The marine Lower Cretaceous sediments of northern, Boreal latitudes yield diverse and well-preserved calcareous nannofossil assemblages. The calcareous nannofloras of nine core and outcrop sections (of Ryazanian-Albian age) in England, Germany, the North Sea, and Barents Sea, are examined in detail (utilising 773 samples). Dense sampling of key outcrop sections (in particular, Speeton) enables calibration of the observed nannofossil events against ammonite zones. The Barents Sea sections, which are shown to be highly condensed, yield the northernmost Lower Cretaceous nannofossils to be described. The previously chaotic taxonomy of Lower Cretaceous nannofossils is revised, and a major rationalisation of genera proposed - this involves several generic emendations, and twenty five new combinations. Two new genera, Apertasphaera and Neoparhabdolithus, and nine new species are described - Apertasphaera jakubowskii, Calculites bumettiae, Clepsilithus maculosus, Cyclagelosphaera papilla, Nannoconus inomatus, Nannoconus pseudoseptentrionalis, Rucinolithus windleyae, Tegumentum bergeni and Tubodiscus parvus. In addition, one new subspecies - Rhagodiscus angustus parvus - is described, and a number of species are split into informal varieties, to avoid biostratigraphical ambiguity. Following these revisions, the suprageneric classification is reappraised, and a new family - Family Tubodiscaceae - is proposed. An updated nannofossil zonation scheme for the Ryazanian to Aptian of the Boreal area is presented; this comprises twenty two zones (labelled BC1 to BC22, in ascending order), and a number of additional subzones. Biostratigraphical resolution in the HauterivianBarremian is comparable with current ammonite zonations, and enables detailed sequence stratigraphical interpretation. Following the publication of new data from Tethyan sections (Bergen, 1994), the potential for direct inter-regional correlation is investigated; the nannofossil datums utilised generally support traditional, ammonite-based correlations but suggest that, in Boreal areas, the Hauterivian-Barremian boundary should be placed at the top of the variabilis ammonite Zone, slightly higher than its current position. Finally, the palaeoceanographical applications of Lower Cretaceous nannofossils are considered, in the light of new data on modem nannoplankton. Surface water temperature is believed to have been the principal factor controlling species distribution, throughout the history of nannoplankton; the importance of surface water fertility has probably been exaggerated in previous palaeoceanographical studies, which have been hampered by broad taxonomic concepts. There remains much to be done, in deducing the environmental preferences of Cretaceous nannofossils, but the potential for their application to palaeoenvironmental studies is good.
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Rogerson, Michael. "Palaeoceanography and sedimentology of the Gulf of Cadiz (0-30 ka, BP)." Thesis, University of Southampton, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402542.
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Boyd, Jamie Lorna. "Global and regional assessment of Neogene climate and palaeoceanography using dinoflagellate cysts." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/16324/.
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The Neogene Period (23.03–2.59 Ma) has been referred to as ‘the making of the Modern world’, which eventually, via a relatively consistent cooling trend, culminated in the present day climate conditions on Earth. Researching the Neogene provides important information for understanding how modern patterns of atmospheric and oceanic circulation developed, and how sensitive they are to environmental change. Climate and environmental parameter proxies are used to investigate past changes, and dinoflagellate cysts have great potential as their distribution can be limited by temperature, salinity, nutrient availability and sea ice cover. This project aims to use dinoflagellate cysts to study the evolution of the oceans over the Neogene and to further develop the potential of the climate proxy. This is achieved by collating all of the previously published literature on Neogene dinoflagellate cysts into a database and analysing the data on global and regional scales. This study allows for the first global synthesis, using dinoflagellate cysts, of changes that took place during the Neogene. It was found that, on a global scale, the distribution of Neogene dinoflagellate cysts was strongly controlled by temperature and can be correlated to the previously established cooling trend of the Neogene. However, short term climate changes superimposed on the overall cooling trend of the Neogene, cannot be observed. Changes to marine gateways have been shown to affect the composition of dinoflagellate cyst assemblages regionally, and caused allopatric speciation. New primary data from Cyprus demonstrates an increase in diversity in the Pliocene, which differs to the regional diversity. This reveals the importance of the difference between local and regional signals, and why it is important to understand, and to thoroughly explore, the datasets used in a global compilation.
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Fenton, Mia. "Late Quaternary history of Red Sea outflow." Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264851.
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Paramor, Tracey Jane. "The application of radiolaria to the late Quaternary palaeoceanography of the Scotia Sea." Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311965.
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Maslin, Mark Andrew. "A study of the palaeoceanography of the N.E. Atlantic in the Late Pleistocene." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282952.
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Ellison, Christopher Robert William. "North Atlantic Holocene palaeoceanography : surface and deep ocean variability in the subpolar North Atlantic." Thesis, University of East Anglia, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435126.
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Knutz, Paul C. "Late Pleistocene glacial fluctuations and palaeoceanography on the continental margin of north-west Britain." Thesis, Cardiff University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247749.
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Dean, Jean Margaret. "High resolution palaeoceanography and palaeoclimatology from late Holocene laminated sediments, Saanich Inlet, British Columbia." Thesis, University of Southampton, 2000. https://eprints.soton.ac.uk/42085/.
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Late Holocene (c. 2100 yr BP) varved sediments recovered from Saanich Inlet, Ocean Drilling Program Leg 169S, have been analyzed using high resolution scanning electron microscope techniques. The individual centimetre-scale varves comprise two segments: a biogenic varvesegment which consists of up to 19 alternating diatom ooze and diatomaceous mud laminae, which were deposited during spring through autumn; and a terrigenous varve-segment containing up to 6 laminae dominated by silty clay, which were deposited during winter. The laminae within the varves record individual flux events of a few weeks to months duration. Diatom flux typically reached the fjord floor as a mixture of whole/fragmented aggregates and Zooplankton faecal pellets. The diatom succession within the biogenic varve-segment typically comprises: an early spring Thalassiosira spp. bloom, followed by a late spring Chaetoceros spp. -dominated bloom, a late spring/early summer Skeletonema costatum bloom and a series of one to several summer/autumn Chaetoceros spp. -dominated blooms. Interannual variability in diatom sediment flux is typically recorded by the presence/absence of Thalassiosira spp., S. costatum and the number of summer/autumn Chaetoceros spp. - dominated blooms. The varved sediment documents a major increase in the sedimentation rate at approximately 2100 varve yr BP. This represents a transition from a colder/drier climate during the Tiedmann glacial advance when sediment flux was lower, to a relatively warmer/wetter late Holocene climate when sediment flux increased. As glaciers receded, fluvial input increased throughout the year as a result of increased rainfall during winter months and glacial meltwater during spring through autumn months. This increased fluvial input introduced additional terrigenous sediment throughout the year and additional nutrients enhancing diatom production during spring through autumn. The varved sequence is punctuated by centimetre-scale massive intervals originating from low density turbidity currents initiated above the anoxic zone. A tephra laminae containing volcanic glass has also been observed and might originate from Mount St Helens. Spectral analyses of inter-varve variability in sediment fluxes have shown strong periodicities within El Nino Southern Oscillation (ENSO), Quasi-Biennial Oscillation (QBO) and North Pacific Oscillation (NPO) bands. Thalassiosira spp. flourished in the more stable conditions associated with strong La Nina-type phases of the ENSO cycle. S. costatum blooms were associated with El Nino events when winter storms increased levels of ground water storage, which subsequently increased fluvial input of nutrients during the late spring/early summer. The summer/autumn Chaetoceros spp. blooms were dominated by the NPO, as successive years of increased rainfall/snowfall associated with the colder/wetter NPO regime increased long term mean levels of ground water storage and accumulation of snow, which subsequently increased fluvial input of nutrients during summer and autumn months. Winter terrigenous flux was dominated by NPO at Site 1033 and ENSO at Site 1034. Site 1033 which is the most distal to the terrigenous source, records increased/decreased fluvial input associated with the wetter/dryer regimes of NPO. Site 1034, records the effects of El Nino storms which rework nearshore sediments and deposit them in the deeper offshore regions. QBO frequencies are recorded in the overall sediment flux and biogenic sediment flux at Site 1033 and may represent the alternation of a relatively weaker/s"tronger Aleutian Low Pressure System causing consecutive years to be relatively wetter and drier, affecting sediment fluxes. ENSO operated at approximately 3.5 years, with stronger events occurring at approximately 9 year intervals; QBO operated at approximately 2.4 years; and NPO operated at approximately 15 years. Multi-decadal periodicities of 31 and 42 years are also recorded and might represent stronger NPO regimes.
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Davies, Andrew. "High resolution palaeoceanography and palaeoclimatology from mid and high latitude Late Cretaceous laminated sediments." Thesis, University of Southampton, 2006. https://eprints.soton.ac.uk/41359/.
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Late Cretaceous laminated diatomaceous sediments from the Marca Shale (California) and CESAR 6 core (Arctic Ocean) have been analysed using scanning electron microscopy techniques and found to contain marine varves. The varve interpretation is based on the pervasive occurrence of laminae types that can be related to different seasons and placed into robust annual flux cycles. In the Marca Shale this consists of intermittent near-monospecific laminae of Azpeitiopsis morenoensis deposited in the late summer, succeeded by a ‘fall dump’ mixed assemblage laminae, dominated by fragmented Hemiaulus polymorphus, Stephanopyxis spp. and Stellarima spp. Intermittent near-monospecific Chaetoceros-type resting spore laminae, deposited in spring follow and are in turn overlain by terrigenous laminae, reflecting enhanced fluvial runoff during the summer. A mixed floral diatomaceous and terrigenous laminae couplet constitute the annual flux cycle in the majority of varves. Summer terrigenous flux may indicate that the ~43°N palaeolatitude estimate is incorrect, and deposition actually occurred at lower latitudes or alternatively, that the Marca basin was influenced by intense monsoonal summer storms. The CESAR 6 annual flux cycle consists of alternating diatom resting spore and vegetative cell laminae (often dominated by Hemiaulus), interpreted to represent spring bloom flux and ‘fall dump’/intermittent summer blooms flux, respectively. Near-monospecific Rhizosolenia laminae frequently occur above vegetative laminae, relating to subsequent ‘fall dump’ flux. Common silicoflagellate/setae-rich laminae, often containing diatom hash, occur beneath resting spore laminae, interpreted as the early spring flux of silicoflagellate blooms and grazed diatoms. Seasonally occurring detrital ‘blebs’ and rare detrital laminae are also observed, which may represent ice rafted debris, consistent with Campanian model simulations. Diatom taxa adapted to exploit stratified conditions, sedimented over the summer or in a ‘fall dump’, are important components of both sequences. Spring bloom flux was important in the CESAR 6, but was only a subsidiary component in the Marca Shale. The abundance of Hemiaulus spp. at both localities may be evidence for diatom blooms powered by N2-fixing cyanobacteria. Diatom biostratigraphy indicates a late Late Campanian age for the CESAR 6, although an earliest Maastrichtian age cannot be discounted. Time-series analysis of laminae thickness data from both sequences and bioturbation index data from the Marca Shale, reveal both sites contain strong quasi-biennial signals (mean periodicities of 27.4 and 30.4 months, respectively), inferred to relate to the Quasi-Biennial Oscillation (QBO). The CESAR 6 contains strong sub-decadal/quasi-decadal peaks interpreted to relate to Northern Hemisphere Annular Mode (NAM) variability. Together with the QBO signals, this suggests NAM variability was robust during the Late Cretaceous. Similar frequency peaks occur in the Marca Shale which, supported by several sedimentological lines of evidence, indicates the presence of an El Niño Southern Oscillation (ENSO)-like oscillation. Theory dictates that a weakening of the ‘Bjerknes’ feedback loop in the equatorial Pacific will lead to a reduction or shutdown of ENSO variability, resulting in a permanent El Niño climate. The Late Cretaceous was witness to a severe weakening of the ‘Bjerknes’ feedback, yet the results of this study demonstrate that there was robust ENSO variability during this greenhouse period, adding to the evidence against permanent ‘El Niño’ climate states. A 10.66 year harmonic peak in the CESAR 6 is taken as evidence for modulation of the NAM by solar variability. Peaks at 10.0, 10.3 and 10.8 years in the Marca Shale are interpreted to relate to the solar modulation of strong ENSO events. Both sites also contain multi-decadal peaks, the frequency of which may also have been modulated by solar variability. Quasi-bidecadal peaks are inferred to relate to the NAM or an oscillation analogous to the Pacific Decadal Oscillation (PDO), possibly influenced by the Hale cycle. A 44 year peak in the Marca Shale is also inferred to relate to the PDO. The CESAR 6 contains a harmonic peak at 78.74 years, interpreted to relate to modulation of the NAM over the Gleissberg solar cycle or alternatively, to modulation of the PDO.
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Speed, Craig Duncan. "High-resolution palaeoceanography of extreme early Pliocene carbonate-opal cycles in the eastern equatorial Pacific." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274423.
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Pike, Jennifer. "High resolution palaeoceanography and palaeoclimatology from Late Pleistocene and Holocene laminated sediments, Gulf of California." Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243123.
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Harris, Anthony John. "Cenomanian and Turonian palynology and palaeoceanography of the Western Interior Basin, United States of America." Thesis, Aberystwyth University, 1997. http://hdl.handle.net/2160/d82e4999-0135-407f-9c9a-83b1913ff467.
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Acheson, Ruth. "Palaeoceanography at the juncture between the Indian and South Atlantic oceans during the late quaternary." Thesis, University of Edinburgh, 2001. http://hdl.handle.net/1842/10732.
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This study uses planktonic foraminiferal assemblages and SST proxy (transfer functions and alkenones) data from the Southern Benguela System, offshore the Cape of Good Hope to examine palaeoceanographic change at this important juncture of the thermohaline circulation. The records of watermass characteristics and variation thus derived are used to understand further climatic mechanisms and feedback within the Southern Hemisphere and globally. Various modes of surface circulation are associated with particular climatic intervals through statistical and ecological analysis of faunal census data. Transitions and early interglacials are associated with watermasses including a significant Indian Ocean component. The main feature of glacials is an eutrophic ocean environment interval (OEI) linked to increased upwelling and filament projection into the Cape Basin. Cooler stadials of interglacials are marked by increased abundance of transitional and oligotrophic species associated with the South Atlantic gyre. These environments are seen in a characteristic order through a typical glacial-interglacial cycle as watermasses respond to insolation changes and thermohaline and atmospheric reorganizations. These are driven by northern hemisphere summer insolation cycles through trade wind strength, ITCZ position, and the position of the Agulhas Retroflection. The South Atlantic gyre signal is determined by austral summer insolation, however. SSTs reconstructions provide a direct record of the changing temperature characteristic of regional watermasses and thus are a second constraint on the interpretations derived from planktonic foraminiferal assemblages. Two techniques are used in this study: faunal-based transfer functions (TFT); and alkenones (Uk’37). Past interglacials were at least as warm as today, and during MIS 5.5 and 11.3 exceeded present values. Uk37 SST records are generally similar to the TFT warm season temperatures, but during peak interglacials (MIS 9.3, 7.3 and 5.5) are an additional ~1.5°C warmer. This difference is ascribed to the sensitivity of the foraminiferal TFT to seasonal changes in upwelling and frontal movements.
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Griffin, Helen. "High resolution palaeoceanography and palaeoclimatology from Late Quaternary laminated sediments, Guaymas Basin, Gulf of California." Thesis, University of Southampton, 2012. https://eprints.soton.ac.uk/359060/.
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Kennington, K. "Diatom palaeoceanography of the eastern equatorial Pacific during the Olduvai magnetic sub-chrom (2.0-1.75 Ma)." Thesis, University of East Anglia, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389362.
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Van, Nieuwenhove Nicolas [Verfasser]. "Last interglacial (MIS 5e) palaeoceanography of the nordic seas based on dinoflagellate cyst assemblages / Nicolas van Nieuwenhove." Kiel : Universitätsbibliothek Kiel, 2010. http://d-nb.info/1019951516/34.
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Bull, David. "High resolution palaeoceanography and palaeoclimatology from late Quaternary laminated sediments from the Santa Barbara Basin, California Margin." Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266609.
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Lloyd, Jeremy. "The palaeoceanography and glacial history of the Greenland Sea and Spitsbergen Ice Cap over the last 200ka." Thesis, University of Edinburgh, 1994. http://hdl.handle.net/1842/12450.
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Piston cores from the continental slope of Spitsbergen were analysed using micropalaeontological, stable isotope and sedimentological techniques. The attempted to determine the palaeoceanographic history of the Norwegian-Greenland Sea, and the glacial history of the Spitsbergen ice cap over the last 200ka. The chronostratigraphy of the cores was determined using stable oxygen isotope analysis of planktic foraminifera. These records were correlated to a composite benthic foraminiferal δ18 O stratigraphy from the Norwegian Sea (Duplessy et al., 1988), as well as to other radiometrically dated records from the Norwegian-Greenland Sea to produce an age model. X-ray photographs were used to assess the ice rafted detrital (IRD) content of the cores, dropstones were counted from these x-rays. IRD content was used as a measure of calving rate from the outlet glaciers of the Spitsbergen ice cap. From these counts and the δ18O record a model of relative advance and retreat of the Spitsbergen ice cap was produced. It was found that moisture supply was the over riding factor controlling dropstone input to the Spitsbergen margin. Periods of high moisture supply led to rapid ice advance and hence high calving rate producing peaks in IRD. Peak IRD events were found during interstadial periods, such as substage 5c, as well as during glacial periods when ice was at the shelf edge, and during deglacial periods. Absolute abundance counts of foraminifera suggest glacial periods had a much higher productivity than interglacial periods. This strongly suggests the Spitsbergen margin was at least seasonally ice free during glacial periods. Melting events were recognised from the δ18O record of planktic and benthic foraminifera. The influx of North Atlantic surface waters during deglaciation has been identified from the δ18O record and the faunal assemblages. The initial influx of North Atlantic water during the last deglaciation took place at about 12.3ka, disappeared at 12ka, was present again from 10.5 to 10.3ka, and then from 10ka onwards.
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Foan, Amanda Gillian. "History of the New Caledonia Barrier Reef over the last 1.2Myrs : links with regional palaeoceanography and palaeoclimate." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/22852.
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The timing of glacial-interglacial cycles shows a clear dependence on the periodic variations in the Earth’s orbital parameters. However, the Earth’s climate is an extremely complex, non-linear system, with many internal feedback mechanisms and there are still features of the climate record for which a definitive explanation remains elusive. Understanding reef history is important due to significant predicted feedbacks between changes in global climate and carbonate production via the carbon cycle; phases of rapid reef growth in shallow water areas being associated with increased release of carbon dioxide to the atmosphere. Previous work on Pleistocene reef history, investigated via reef boreholes, shows a large global expansion of reefs between 800-400ka; approximately concurrent with one of the major unexplained alterations in the climate system, the Mid-Pleistocene Transition (MPT). Quaternary reef history is usually investigated via reef boreholes, which provide limited spatial information and are subject to dating uncertainties of the order of ±100kyrs. This means that any inferences made about the relationship between reef expansion and specific changes in the climate system are not well constrained. This thesis instead, presents a novel approach to reconstructing reef growth history, using a trial site near the island of New Caledonia, in the south west Pacific. The initiation of carbonate production on shallow shelves is known to produce a signal in the surrounding deeper basins, via sediment shedding. Therefore, this research set out to independently verify the proposed expansion of the New Caledonia Barrier Reef at ~ 400ka (Marine Isotope Stage [MIS] 11) by examining the composition of turbidites deposited in the New Caledonia Trough. Deep sea sediment core MD06-3019, was collected south west of the New Caledonia Barrier Reef (22oS, 165oE; 3,500m water depth). It is predominantly composed of pelagic carbonate ooze, into which 79 sandy turbidite layers have been deposited. These layers interrupt, but do not disturb, the background sedimentation and source material from the shallow shelf, which is carried to the deep sea via submarine canyons. A core age model based principally on orbital tuning, yields a core bottom age of 1,260ka, ~MIS38. This chronology has allowed the timing of deposition of the turbidite layers within the core to be assigned to within ±10kyr. Turbidite layers vary in width (1-35cm), grain size (φ=4 to -2) and composition, containing among other shelf derived material, well preserved coral fragments from 1.26Ma through to the present day. Patterns in turbidite timing and frequency, grain size and composition (investigated via point counting, carbonate coulometry and aragonite content) have been analysed, to assess whether there are any temporal changes which may reflect variation in shallow shelf reef extent. This included the development of XRF scanning measurements for [Sr], as a new proxy for the aragonite content of samples. A calibration line with the equation: Aragonite %=0.0011* Sr count +2.64 (R2 =0.6105, p-value < 0.001) was obtained for turbidite samples from sediment core MD06-3019. The method shows significant promise as a new proxy for quickly establishing the aragonite content of sediment samples. Corroborating the work of previous investigators, turbidites deposited since MIS11 show an increase in average bulk carbonate and aragonite content, a greater dominance of shallow water bioclasts and a higher occurrence of coral fragments. Additionally, both coarse and fine grained turbidites are present, whereas directly before this period only fine grained turbidites occur. However, there is another significant shift in depositional style further back in the record. Prior to MIS23 both coarse and fine grained turbidites are present, the average carbonate content of turbidite layers is higher and there is a greater dominance of shallow water biota. Coral abundance for turbidites at the base of the core can equal values for turbidites at the top of the core. These results challenge the assumption that the only significant evolution on the western New Caledonia margin over the last 1.2Myrs was the expansion of the barrier reef at MIS11. This suggests that the history of the western New Caledonia margin may be more complicated than initially anticipated. These temporal variations in turbidite deposition are interpreted as reflecting changes in the level of carbonate production on the shallow shelf over the course of the 1.26Myr record. Shallow water carbonate production having decreased substantially during the period MIS23-MIS11. There are many possible controls on the shallow water carbonate production; such as: sea surface temperature and salinity, sea-level and nutrient availability. However, it is hypothesised that the principal control is glacial-interglacial sea-level change. It is proposed that prior to MIS23 sea-level was high enough during certain interglacial periods for significant carbonate production to occur on the shelf. However, from MIS23 onwards the climate proceeded into a period of ‘lukewarm’ interglacials which were both cooler and had lower sea-levels. It is hypothesised that during this period sea-level did not rise enough during highstands to flood the shelf sufficiently to allow for significant shallow water carbonate production. The high sea-levels of the long, warm MIS11then allowed for the expansion of the barrier reef (perhaps on substrates provided by former siliciclastic coast lines, deposited between MIS23-11) and its continuation during subsequent interglacial periods until the current day. This pattern of shallow shelf carbonate production is similar to those proposed for the Belize margin and the Gulf of Papua over the last 1.2Myrs. This thesis provides one of the first detailed investigations of gravity deposits in the New Caledonia Trough, providing information on their composition and timing over an unprecedented 1.26Myr time period. This study demonstrates that deep sea turbidites, sourced from shallow shelf areas, can be used to help reconstruct tropical reef growth histories. The results corroborate the work of previous researchers in the area and provide new insights into the history of reefs along the western New Caledonian margin. The main advantage of this method, compared to traditional borehole techniques, is the 10-fold reduction in the age uncertainty of events, to ±10 kyr. In addition, because turbidite material is sourced from a wide area along the coast, the method is able to provide information on reef history over a larger spatial area than single reef boreholes. This method can now be extended globally to help improve knowledge of the timing and history of tropical reef growth during the Quaternary. This will enable a better understanding of how reefs have impacted on, and been affected by, changes in climate, linked by feedbacks mechanisms via the global carbon cycle.
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Varhelyi, Aron. "Quaternary Arctic foraminiferal isotopes: species reliability and palaeoceanographic application." Thesis, Stockholms universitet, Institutionen för geologiska vetenskaper, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-158047.
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To investigate whether foraminiferal stable isotope (δ18O/δ13C) variations have potential as a chronostratigraphic tool in the Arctic Ocean, this thesis presents new δ18O/δ13C data from five marine sediment cores. Three of those are downcore analyses (PS92/54-1; TC/PC-03; PC-07) and the remaining two are core top analyses (PC-04; PC-08). Seven species of benthic foraminifera (Cassidulina neoteretis, Cibicides lobatulus, Cibicidoides wuellerstorfi, Oridorsalis tener, Quinqueloculina arctica, Stainforthia concava and Triloculina sp.) and one planktic (Neogloboquadrina pachyderma sinistral) were compared against physical properties data, foraminifera counts and existing age models. The stable isotopic data reveal species-specific niches, resulting from vital effects and habitat preferences. As changes in δ13C mainly are related to palaeoproductivity and ocean/atmosphere gas exchange, and has limited use as a dating tool, the focus has been to create high-resolution downcore δ18O records that can be compared to a global benthic stack. Cibicidoides wuellerstorfi is found to be the most common benthic foraminiferal species in the central Lomonosov Ridge cores (TC/PC-03 and PC-07) whereas C. neoteretis and N. pachyderma are most common at the Yermak Plateau (PS92/54-1). Usefulness of C. wuellerstorfi in the central Lomonosov Ridge cores is limited due to low amplitude changes in δ18O over periods interpreted to cover several Marine Isotope Stages. A similar issue was observed in C. neoteretis δ18O on the Yermak Plateau (PS92/54-1). There, C. neoteretis abundances were low during interglacials. Instead, planktic N. pachyderma δ18O at the Yermak Plateau site (PS92/54-1), more closely than any analysed benthic species, resembled the global benthic δ18O stack. This implies potential of N. pachyderma δ18O as a chronostratigraphic tool in this region of the Arctic. Using N. pachyderma δ18O to correlate distal cores in the Arctic Ocean would demand addressing the issues of regional differences in pelagic δ18O, varying calcification depths and poor preservation. Addressing why the range of variability differs between sites in the same MISs is crucial, before attempting to stack downcore δ18O from the relatively abundant Arctic benthic species C. neoteretis.Med siktet på att undersöka huruvida variationer i stabila isotopvärden (δ18O/δ13C) hos foraminiferer har potential som dateringsredskap i Arktiska Oceanen, presenteras härmed ny δ18O/δ13C data från fem marina sedimentkärnor. Tre kärnor analyseras på längden (PS92/54-1; LOMROG III TC/PC-03 och PC-07) medan två analyser begränsas till kärnornas toppskikt (LOMROG I PC-04 och PC-08). Resultat från sju olika arter av bentoniska foraminiferer (Cassidulina neoteretis, Cibicides lobatulus, Cibicidoides wuellerstorfi, Oridorsalis tener, Quinqueloculina arctica, Stainforthia concava and Triloculina sp.) och en planktonisk (Neogloboquadrina pachyderma sinistral) har jämförts mot data som baserats på kärnornas fysiska egenskaper, mängden foraminiferer och befintliga åldersberäkningar. De nya isotopresultaten avslöjar nischer som är specifika för varje art och som, förutom isotopvärdena i det omkringliggande havsvattnet, är beroende av varierande fraktioneringseffekter samt habitatpreferenser. Förändringar i δ13C är mestadels avhängigt paleoproduktivitet och gasutbyte mellan atmosfär och hav. Det har därför begränsad användning som dateringsredskap. Fokus har istället legat på att skapa högupplöst δ18O data som kan jämföras med en global δ18O ’stack’. Cibicidoides wuellerstorfi är den vanligast förekommande arten i TC/PC-03 och PC-07 medan C. neoteretis och N. pachyderma har flest förekomster i PS92/54-1. I den senare kärnan saknas C. neoteretis under perioder där förändringar i δ18O antas vara stora (interglacialer). Istället är det δ18O hos planktoniska N. pachyderma som i högst grad efterliknar en global bentonisk ’stack’. Dessa resultat antyder att N. pachyderma potentiellt kan användas som lokalt dateringsverktyg. För att kunna korrelera mot mer avlägsna sedimentkärnor i Arktiska Oceanen med hjälp av δ18O från N. pachyderma, så behöver hänsyn tas till regionala skillnader i pelagial δ18O, varierande kalcifieringsdjup och dålig bevaring av foraminifererna. Det är viktigt att adressera varför det finns en amplitudskillnad mellan olika sedimentkärnor för samma tidsperioder, innan försök görs att sammanfoga δ18O resultat från den vanligt förekommande Arktiska bentoniska arten C. neoteretis.
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Bendle, James Alexander Paul. "Palaeoceanography of the Holocene and late-glacial N.E. Atlantic : development and application of biomarker proxies of environmental change." Thesis, Durham University, 2003. http://etheses.dur.ac.uk/4019/.
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The aim of this thesis is to develop and apply novel climate proxies to understand the palaeoceanographic evolution of the N.E. Atlantic during the late-Glacial and Holocene. The proxies investigated are based on organic molecular compounds called lipid biomarkers and bulk organic matter properties. The primary focus is on long-chain alkenones, molecules which have been extensively used in mid and low latitude open oceans to reconstruct sea surface temperatures (SSTs) during the Quaternary. Thus, the relative abundance of some alkenones is related to the growth temperature of the algae at the time of the biosynthesis of these molecules (expressed in the U(^K)(_37) and U(^K)(_37)’ indices). In high latitudes and coastal environments, the temperature dependence of alkenones is controversial, and the potential environmental information from alkenones is not yet well understood. In such locations there is increasing abundance of the C(_37:4) alkenone (quantified as %C(_37:4)). The presence of this component has been related to changes in the relative budget of freshwater in the surface ocean. A central aim of this thesis is to carry out an empirical investigation to find out the key environmental factors that control %C(_37:4) to assess its potential as a palaeoceanographic proxy. Research was conducted in the Nordic Seas and N.W. Scotland using samples from the water column, surficial sediment and sediment cores. The research undertaken can be broken down in three main sections: Alkenone distributions in the Nordic Seas. The aim was to clarify and extend the application of alkenones as palaeoceanographic proxies in subpolar to polar environments. Samples of filtered sea surface POM were analysed and extremely high %C(_37:4) values (up to 77%) were measured in polar waters (up to 80% sea-ice cover). Values of %C(_37:4) across the Nordic Seas showed a strong association with water mass type. A combined data-set revealed a stronger correlation of %C(_37:4) to sea surface salinity' (SSS, R(^2) = 0.72) than to SST (R(^2) = 0.5). However, scatter was observed in the relationship of %C(_37:4) to SSS, preventing confirmation of %C(_37:4) as a palaeo-SSS proxy. Values of %C(_37:4) in sea surface POM were high compared to surficial sediments. We discount preferential degradation of the %C(_37:4) alkenone and invoke dilution of the %C(_37:4) signal in sea surface sediments by advected allochthonous matter to explain this. The POM filter data suggest that, overall, U(^K)(_37) is a more appropriate SST index for the Nordic Seas than U(^K)(_37) '. Examination of the scatter in the U(^K)(_37) ' versus SST relationship, shows that regions in the south of the Nordic Seas (including the Icelandic shelf) may yield reliable, alkenone based, palaeoceanographic reconstructions. Comparison of %C(_37:4) distributions with dinocyst proxies in a late Holocene core from the Barents Sea suggests %C(_37:4) may be a general marker for the influence of arctic/polar water in palaeoceanographic reconstructions. The palaeoceanography of the Icelandic shelf iox. the post-Glacial period (0-15 kyr BP) was reconstructed from alkenone indices measured in three cores collected N and W of Iceland. One of the cores, JR51-GC35, contained a continuous record of Holocene sedimentation spanning 0 - 10.1 kyr BP. Superimposed on a general Holocene cooling trend in core JR5I-GC35 were millennial scale oscillations of ~2 C. The timing of the oscillations was in close agreement with the variability in IRD records from the East Greenland shelf and the timing of glacier advances in northern Iceland. A comparison of the U(^K)(_37) -SST records from JR51-GC35 and a published core from the eastern Nordic Seas (MD952011) showed significant differences (superimposed on the general trend) in the timing of millennial scale climate events. This illustrates that Holocene climate evolution in the Nordic Seas was more complex than previously suggested, with significant climatic differences between the eastern and western Nordic Seas caused by the differential variability of the Irminger and Norwegian Currents with time. The potential application for reconstructing past sea-level changes in NW. Scotland of lipid biomarkers (alkenones, n-alkanes and chlorophyll derivatives), and bulk organic parameters (%TOC, C(_nrg)/N) was assessed by a survey of modern basins (at different stages of isolation from the sea) and fossil basins (with known sea-level histories). A logit regression analysis of all the sediment samples was employed to find which of the biomarkers or bulk organic measurements could reliably characterize the sediment samples in terms of a marine/brackish or isolated/lacustrine origin. The results suggested an excellent efficiency for the alkenone index %C(_37:4) at predicting the depositional origin of the sediments. This study suggests alkenones could be used as an indicator of sea-level change in fossil isolation basins.
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Kennedy, Jonathan David. "Palaeoecology, palaeoceanography, mineralogy, and stable isotopes of forminifera and ostracods from the Middle and Upper Jurassic of Great Britain." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358717.
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Snelling, Andrea Marie. "Characterisation of stratigraphy and palaeoceanography using graptolites : exploring new concepts in the Aeronian (Silurian) of Wales, Scotland and Northern Ireland." Thesis, University of Leicester, 2009. http://hdl.handle.net/2381/7532.
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Graptolites, extinct macrozooplankton of the phylum Hemichordata were a major element of the Early Palaeozoic seas. They are here investigated from Wales, Scotland and Northern Ireland and their use beyond biostratigraphy is considered. The leptotheca and convolutus biozones (Aeronian; Silurian) are characterized and correlated across Wales, Scotland and Northern Ireland, and in Scotland subdivision of the convolutus Biozone was possible through identification of Cephalograptus cometa extrema. In the Irish successions, previously unrecognized morphological intermediates within the established Petalolithus-Cephalograptus lineage were recognised and in Wales and Scotland, ‘pre-maxiculus’ morphotypes of Coronograptus are suggested. At all three localities Campograptus lobiferus is the dominant species with intraspecific variation recorded; the type material of this species from Scotland is shown to be unusually large. Use of X-ray images has enhanced biostratigraphy by enabling more specimens and taxa to be recorded, shown how graptolite number varies microstratigraphically and demonstrated that rhabdosomes are systematically aligned. The number and thickness of Aeronian ‘anoxic’ units varies within Wales, and between the Welsh and Scottish successions, indicating diachroneity of anoxia. A schema of microfacies types is constructed for the leptotheca Biozone anoxic unit in Wales and is applied to the Welsh convolutus Biozone anoxic units and to the gregarius to convolutus Biozone strata in Scotland. Facies with less clastic input and no burrows are associated with the best preserved graptolites, with pyrite formation being influenced by variations in palaeoproductivity and clastic input. Levels with well-preserved graptolites are not geochemically distinct, but differences in the major elements indicate provenance differences between the leptotheca and convolutus biozones. A reproducible &delta ^{13}C signal is obtainable from small amounts of carbon from graptolite periderm and periderm &delta^{13}C is different but not consistently so to whole-rock &delta^{13}C. Initial results suggest that periderm &delta^{13}C is not affected by physiology, life habit or metamorphic grade and that for chemostratigraphic study little regard is needed for species composition.
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Drury, Anna Joy. "Late Miocene and early Pliocene palaeoceanography at the eastern Equatorial Pacific IODP Site U1338 : implications for climate evolution and stability." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/29946.
Full textAbstract:
The short-term background climate variability during the climatically stable latest Miocene to early Pliocene (LM-EP) is not well understood, owing to the lack of continuous, high-resolution climate records. Assessing variability during an interval of long-term climatic stability will constrain how sensitivity of major Earth's system components (Earth system response - ESR) to external radiative forcing has changed through time. This study investigated LM-EP climate, focussing on changes in ESR, El-Nino-Southern-Oscillation state, glacio-eustacy and the Messinian Salinity Crisis (MSC), and the origin of the Late Miocene Carbon Isotope Shift (LMCIS). This project produced the first high-resolution benthic foraminiferal δ18O and δ13C record in the eastern equatorial Pacific (IODP Site U1338) from 8.0-3.5 Ma that resolves all Milankovitch cyclicities. A high-resolution, orbitally-based age model, planktic foraminiferal δ18O, δ13C and Mg/Ca, coccolith-rich 'clumped isotopes' Δ47, spectral analyses and multi-site benthic foraminiferal isotope compilations were also produced. Planktic foraminiferal Mg/Ca sea surface temperatures (SSTs) were ~25 °C. Coccolith-rich Δ47 temperatures were unrealistically cold at ~10-15 °C, reflecting moderate coccolith preservation and vital effects that cause higher Δ47. Site U1338 and 982 combined benthic foraminiferal (δ18O; δ13C) wavelet analyses show moderate ESR from 6.3-4.7 Ma and after 3.7 Ma, but lower ERS from 7.0-6.3 Ma. The δ18O-minimum stage ~5.33 Ma, during long-term minimum δ18O, suggests that glacio-eustacy played a role in the MSC termination. The benthic foraminiferal δ13C compilation confirms that the LMCIS was globally synchronous and caused by a negative shift in oceanic reservoir δ13C, driven by changes in the continental carbon flux (increased sea-floor-spreading / C4-grass expansion). Data syntheses show that global warmth, dominant El-Nino state, high cryosphere sensitivity, lower ice volume and short-term ice sheet variations characterised the LM-EP pre-7.0 and post-5.7 Ma. Stable conditions occurred ~7.0-5.7 Ma, with dominant La-Nina, higher ice volume, low cryosphere sensitivity and lower SSTs.
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Dai, Yuhao. "Reconstructing seawater carbonate chemistry using foraminiferal B/Ca." Phd thesis, Canberra, ACT : The Australian National University, 2018. http://hdl.handle.net/1885/144599.
Full textAbstract:
Planktonic B/Ca holds promise of reconstructing the surface
seawater carbonate chemistry, which is linked to the past levels
of atmospheric partial pressure of CO2. However, it is still not
clear to what extent the carbonate chemistry control on
planktonic B/Ca is complicated by physiological activities of
foraminifera. In this thesis, the environmental controls on B/Ca
in two planktonic foraminiferal species, Globigerinoides ruber
(white) and Globigerinoides sacculifer (without final sac-like
chamber), are examined using core-top samples from the Atlantic
Ocean. For an accurate estimation of the ambient calcification
environments, the calcification depths and seasonality of the
studied species at these core-top locations are determined by
planktonic Mg/Ca. The dissolution effect on B/Ca, which is
evident from planktonic B/Ca data from three depth transects,
proves to have little impact on the interpretation of planktonic
B/Ca data from the Atlantic core-tops. While the carbonate
chemistry control on planktonic B/Ca can be detected from these
core-top data, a strong calcification rate control on planktonic
B/Ca is demonstrated by the correlation between B/Ca and Sr/Ca,
where Sr/Ca is employed as an indicator of the calcification
rate. This calcification rate control on planktonic B/Ca
complicates the direct link between planktonic B/Ca and seawater
carbonate chemistry. Nevertheless, based on the different
responses of B/Ca in the two studied species to the calcification
rate, it is possible that B/Ca in some species are less
susceptible to this influence, and thus can be employed for
carbonate chemistry reconstructions.
Benthic B/Ca is a recently developed quantitative proxy for
deepwater carbonate ion concentration ([CO32-]). In this thesis,
deepwater [CO32-] variations during the last 150 thousand years
are reconstructed using two cores from the deep Southwestern
Pacific, a critical but not fully investigated region to regulate
the carbon inventory in the deep ocean. Since Marine Isotope
Stage (MIS) 5a, the deep the SW Pacific [CO32-] varied in concert
with benthic carbon isotopes (δ13Cb). These covariations, on the
timescale of ~10 kyr, are similar to those observed in the deep
Atlantic. This suggests that the deep SW Pacific [CO32-] could be
affected by changes in the Atlantic Overturning Circulation and
the biological pump. However, the deep SW Pacific [CO32-] showed
little change during Termination II (T II), despite that
variations of δ13Cb, neodymium isotopes (εNd), and
foraminifer-bound nitrogen isotopes (δ15N) were similar to those
during Termination I (T I). This difference is interpreted as the
result of coral reef regrowth on continental shelves, which
decreased the whole ocean [CO32-] and counteracted the [CO32-]
increase due to the influences from Atlantic Overturning
Circulation and the biological pump changes during T II.
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Chenot, Elise. "Changements climatiques et océanographiques au cours du Campanien – approche couplée minéralogie et géochimie." Thesis, Bourgogne Franche-Comté, 2018. http://www.theses.fr/2018UBFCK018.
Full textAbstract:
Les causes du refroidissement climatique global qui caractérisent le Crétacé supérieur (~100 – 65 Ma) ne sont pas encore bien établies. L’évolution de la courbe des températures des eaux de fond et de surface des océans montre une accélération de ce refroidissement au cours du Campanien (~84 Ma), aussi l’objectif de ce travail était-il d’explorer les causes possibles de ce refroidissement en se focalisant sur l’étude des sédiments d’âge Campanien de divers bassins sédimentaires téthysiens, boréaux et atlantiques.Le premier objectif fut de déterminer l’extension spatiale des changements de cortèges argileux dans la Téthys et le domaine boréal. La minéralogie des argiles de plusieurs sites (hémi)pélagiques, sélectionnés selon un transect N-S de 5 à 45° N, a révélé une intensification de l’altération continentale au Campanien, marquée notamment par des apports accrus de kaolinite. Au cours du temps, ces apports liés au soulèvement de nouveaux domaines continentaux semblent se propager du Sud au Nord. Cette propagation est très certainement gouvernée par le mouvement antihoraire de la plaque africaine et de son rapprochement progressif de la plaque européenne. L’intensification de l’altération continentale semble aussi s’accompagner de la mise en place d’une ceinture climatique plus humide à l’origine du développement des bauxites.Le Campanien est également marqué par d’importantes modifications paléogéographiques, telles que l’élargissement de l’Atlantique Sud et Nord ainsi que la restriction du domaine téthysien. Le déplacement des masses continentales est probablement à l’origine d’une réorganisation majeure des courants océaniques. Dans le domaine téthysien, au Crétacé supérieur la courantologie est dominée par le « Tethyan Circumglobal Current » (TCC), courant latitudinal traversant l’océan téthysien et le passage des Caraïbes, d’est en ouest, qui semblerait s’intensifier au Campanien. Nous avons donc tenté de reconstituer l’évolution de la circulation profonde du TCC au cours du Crétacé supérieur, grâce une approche fondée sur les isotopes du néodyme (Nd). L’évolution de l’ɛNd des eaux de fond locales de trois sites (hémi)pélagiques situés sur le trajet potentiel de ce courant a été analysé à partir de la fraction carbonatée des sédiments : la coupe de Shahneshin à l’entrée du corridor téthysien (bassin du Zagros, Iran), la coupe de Gubbio – la Bottaccione dans la Téthys centrale (bassin des Marches – Ombrie, Italie) et le forage DSDP Site 146 dans le passage des Caraïbes (bassin du Venezuela, mer des Caraïbes). L’ɛNd de la fraction résiduelle des sédiments a également été déterminée, afin de discuter l’impact potentiel des échanges locaux eau-sédiments. L’évolution de l’ɛNd des eaux de fond locales, couplée à la minéralogie des argiles et à celle de l’ɛNd des résidus a révélé que les signatures minéralogiques et géochimiques des sites de Shahneshin et 146 semblent être affectées de façon significative par des processus locaux (tectonique, volcanisme). Une augmentation de l’écart entre l’ɛNd de l’eau de fond locale et des résidus est cependant compatible avec des apports accrus d’eaux du Pacifique dans l’est de la Téthys au cours du Campanien. Le site de Gubbio semble quant à lui recevoir des apports d’eaux atlantiques en profondeur, suggérant que si le TCC est présent dans cette région, il n’atteint pas la base de la colonne d’eau au niveau de ce siteThe origin of the Late Cretaceous (~100 – 65 Ma) global cooling is not yet well understood. The evolution of sea surface and bottom temperatures shows an acceleration of the cooling during the Campanian stage (~84 Ma). The main goal of this study was to explore the processes driving this cooling, focusing on Campanian sediments from the Tethyan, Boreal and Atlantic realms.The clay mineralogical assemblages of several (hemi)pelagic sites, selected along a S-N transect, from 5° to 45°N, reveal an increase in continental weathering during the Campanian, expressed by enhanced kaolinite inputs. The detrital input related to the uplift of new continental areas seems to evolve from south to north. This propagation is likely linked to the anticlockwise rotation of the African plate and the progressive closure to the Tethys Ocean. Enhanced continental weathering seems also linked to more hydrolysing conditions in the studied regions, resulting in bauxite development.The Campanian stage was characterised by major palaeogeographic changes, such as the widening of south and north Atlantic oceans and the closure of the Tethyan realm. The motion of continental plates is likely responsible for a major reorganization of the oceanic currents. During the Late Cretaceous, the so called “Tethyan Circumglobal Current” (TCC) current flows latitudinally through the Tethyan Ocean to the Caribbean gateway, from east to west, and seems to intensify during the Campanian stage. Thus, we tried to reconstruct the evolution of the deep oceanic circulation within the TCC pathway during the Late Cretaceous, based on a geochemical approach using the neodymium (Nd) isotopes. The evolution of ɛNd of local bottom water of three (hemi)pelagic sites located on the possible pathway of this current has been analysed on the carbonate fraction of the sediments : the Shahneshin section located at the main entrance of the Tethyan passage (Zagros basin, Iran), the Gubbio – la Bottaccione section located at the centre of the Tethys (Umbria – Marche basin, Italy) ocean and the DSDP site 146 located in the Caribbean gateway (Venezuela basin, Caribbean sea). The ɛNd of the insoluble fraction of the sediments was analysed, in order to discuss of the role of local exchanges between water and sediments. The evolution of the deep water ɛNd along with that of residue ɛNd and clay mineralogical assemblages shows that geochemical and mineralogical signatures of Shahneshin and 146 sites are largely controlled by local processes (tectonic and volcanism), although an increased input of radiogenic Pacific waters may be detected at Shahneshin during the Campanian. The Gubbio site seems to be influenced by atlantic waters entering western Tethys, suggesting that the TCC did not reach the base of the water column at this site
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Kanungo, Sudeep. "Biostratigraphy and palaeoceanography of mid-Cretaceous calcareous nannofossils : studies from the Cauvery Basin, SE India; the Anglo-Paris Basin, SE England; the North Atlantic and Pacific Oceans." Thesis, University College London (University of London), 2005. http://discovery.ucl.ac.uk/1445720/.
Full textAbstract:
The applications of mid-Cretaceous (Aptian-Cenomanian) nannofossils in biostratigraphy and palaeoceanography have been advanced based on four specific studies from India, UK, the Atlantic and Pacific Oceans. A biostratigraphic study on outcrop samples from two new sections in the Cauvery Basin (SE India) has significantly improved stratigraphic resolution in the basin using the recent zonation schemes of Bown et al. (1998) and Burnett (1998). In addition to highlighting problems associated with a few marker species for the Cenomanian, the Albian/Cenomanian and Cenomanian/Turonian boundaries have been examined with respect to their nannofossil proxies. Qualitative comparisons of coeval assemblages from India with those from three other palaeogeographical settings (England, France and the Pacific) have confirmed the overall cosmopolitan nature of Albian nannofloras, in which provinces such as the Tethyan, Boreal and Austral cannot be clearly differentiated. A palaeoclimatic study of a short section in the Gault Clay (S. England) suggests a major warming event starting at the mid-/Late Albian boundary in the Weald of the Anglo-Paris Basin. The cold-water species, Repagulum parvidentatum, gives strong evidence for this warming event by showing a rapid decline in its percentage abundance, which precisely coincides with a light oxygen isotope peak and the influx of Tethyan ammonites. A sharp productivity rise based on the well-known fertility index, Zeugrhabdotus noeliae, is found to be concomitant with the warming event. A palaeoceanographic study of the Early Albian OAElb event in the western North Atlantic (Leg 171B), based on its nannofossil productivity record and geochemical data, supports the increased productivity model as a plausible mechanism for this anoxic event. A similar study on the Pacific Ocean (Leg 198, Shatsky Rise) shows a marked temporal variation in the abundance distribution of productivity- related taxa (e.g., Biscutum constans, Zeugrhabdotus noeliae) in relation to the OAEla (Early Aptian) and OAElb (Early Albian) events. Possible explanations for this variation have been proposed, in light of the heightened submarine volcanism in the Pacific during the mid-Cretaceous. Watznaueria is found to be the most abundant taxon in all mid-Cretaceous assemblages and its dominance is considered to be independent of preservation, indicating its broad palaeoecological tolerance rather than resistance to dissolution. On the basis of taxonomic observations, four new species have been erected: Calculites karaiensis, Loxolithus bicyclus, Manivitella fibrosa and Tranolithus simplex.
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Linnert, Christian [Verfasser], Jörg [Gutachter] Mutterlose, Adrian [Gutachter] Immenhauser, and Wolfgang [Gutachter] Friederich. "Case studies of Late Cretaceous calcareous nannofossils : implications for the Cenomanian-Maastrichtian palaeoceanography of the proto-North Atlantic / Christian Linnert ; Gutachter: Jörg Mutterlose, Adrian Immenhauser, Wolfgang Friederich ; Fakultät für Geowissenschaften." Bochum : Ruhr-Universität Bochum, 2011. http://d-nb.info/1240475888/34.
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