Trace Element Ratios and Stable Isotopic Compositions of Planktonic Foraminiferal Shell Collected from the South China Sea:Geochemical Calibration and Paleoceanographic Implication PDF Download

Author: 黃國芳
Publisher:
ISBN:
Category :
Languages : en
Pages : 247

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Author: Lael Vetter
Publisher:
ISBN: 9781303540998
Category :
Languages : en
Pages :

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Planktic foraminifers are abundant in the surface ocean, and the calcite shells of fossil foraminifers form a major component of deep sea sediments. These shells comprise a primary archive of sea surface conditions through the Cenozoic, and measurements of stable isotope and trace element ratios are frequently used in paleoclimate reconstructions. Each individual foraminifer calcifies over the course of days or weeks, and the environmental conditions during its life are locked into the geochemistry of the shell. Typically, measurements pool numerous individual shells in a single, bulk analysis to obtain an estimate of mean environmental conditions. However, observations of living foraminifers indicate that contemporaneous individuals may occupy different depth habitats, and individual foraminifers may migrate vertically during their life cycle. The potential thus exists for a population of foraminifers to capture a range of environmental conditions, and for daily-scale environmental variations to be recorded in the intrashell geochemical heterogeneity of a single individual. This research explores novel analytical methods of measuring geochemical heterogeneity in trace element ratios and stable oxygen and carbon isotope values in the shell calcite of the extant planktic foraminifer Orbulina universa through live culture experiments (Chapters 1 and 2) and measurements on fossil shells (Chapters 3 and 4). Chapter 1 describes the results of a live culture experiment in which oxygen isotope ([delta]18O) and trace element (Ba) labels in synthetic seawater were incorporated into shell calcite during calcification in the laboratory. Chapter 2 describes the results of a similar live culture experiment where O. universa calcified in seawater with modified trace element (Ba, 18Sr) and carbon isotope ([delta]13C) values. Intrashell geochemical measurements were performed using Secondary Ion Mass Spectrometry (SIMS) for [delta]18O and [delta]13C, and laser ablation inductively coupled mass spectrometry (LA-ICP-MS) for trace element analyses. Intrashell trace element analyses were accurately measured with sub-μm resolution using LA-ICP-MS depth profiling. We demonstrate that the full amplitude of isotopic values (labeled and ambient) are resolvable within the spatial resolution of SIMS measurements (3 [mu]m for [delta]18O; 6 [mu]m for [delta]13C). Together, these experimental results provide a quantitative framework for interpreting intrashell [delta]18O, [delta]13C) , and trace element ratio measurements in field samples, and open the possibility for reconstructing daily-scale environmental changes from fossil foraminifer shells.The combination of multiple different geochemical measurements on fragments of the same shell permits researchers to extract novel information from each individual foraminifer. Additionally, a suite of contemporaneous fossil foraminifer shells preserves a record of a range of environmental conditions from different depths in the water column. These types of measurements provide a new dimension of information about the hydrography or stratification of the surface ocean during transient events, such as glacial meltwater entering the ocean. Chapter 3 describes the results of an experiment conducted on fossil specimens of O. universa where each shell was split into fragments and each fragment was subjected to different reagent cleaning protocols. Intrashell LA-ICP-MS depth profiles on shell fragments illustrate the differences between cleaning techniques, and illustrate a method for computing whole-shell Mg/Ca and Ba/Ca ratios from collected depth profiles. In Chapter 4, [delta]18O, Mg/Ca, and Ba/Ca measurements were combined on multiple O. universa shells from selected 1 cm intervals from a core in the Orca Basin, Gulf of Mexico, deposited during the last deglacation (~18 to 11 ka). These combined measurements enable the calculation of [delta]18O(seawater) and salinity for each individual and the reconstruction of water column hydrography during meltwater pulses from the Laurentide Ice Sheet. Results yield computed [delta]18O(water) values of Laurentide Ice Sheet meltwater, and provide key insight into the dynamics of the ice sheet during its collapse.

Author: Bryan E. Bemis
Publisher:
ISBN:
Category :
Languages : en
Pages : 450

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Author: Katherine Davina Holland
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Foraminifera make excellent archives of past oceans and climate because they grow calcium carbonate shells which incorporate trace element and stable isotopes that reflect the seawater conditions in which they grow. This study aims to: (i) improve understanding of the factors that influence trace element and stable isotope incorporation into foraminifera shells, and (ii) improve proxy calibrations for reconstructing past ocean carbonate system parameters and temperature. To do this, I have cultured living foraminifers in seawaters that have a wide range of cation and carbonate chemistry compositions. The shells produced by these foraminifers have been analysed by a laser ablation ICP-MS microanalysis techniques. The study has focused on three specific objectives: (i) formalising the sensitivity of shell trace element to calcium (TE/Ca) ratios to changes in seawater composition, (ii) establishing the response of bulk shell TE/Ca compositions to carbonate system chemistry and shell growth rates linked to the calcite saturation state of seawater, and (iii) characterising the responses of intra-shell TE/Ca and boron isotope composition to changes in the carbonate system chemistry of the foraminiferal microenvironment over diurnal cycles due to variation in respiration, calcification, and symbiont photosynthesis. To quantify the effect that changes in the Mg/Ca ratio of seawater has on the foraminifer shell Mg/Ca thermometer, both seawater [Mg] and [Ca] concentrations were varied independently in culture experiments. Results from these experiments has permitted the shell Mg/Ca thermometer to be recalibrated to account for the effects of past changes in seawater Mg/Ca ratio and [Ca] concentration. Culture experiments on Orbulina universa were also used to investigate the effects of different carbonate system parameters; pH, DIC, carbonate ion, seawater [Ca] and calcite saturation state on shell B/Ca, Mg/Ca, Mn/Ca, Sr/Ca and U/Ca compositions. Seawater DIC concentration was found to form significant correlations with B/Ca, Sr/Ca and Mg/Ca shell compositions, and seawater carbonate ion concentration had the dominant effect on U/Ca. Orbulina universa exhibits a narrow range in shell growth rates over a wide range in calcite saturation state of experimental seawaters, indicating shell growth is highly regulated. Intra-shell B/Ca and U/Ca ratios record significant changes in carbonate system chemistry of the foraminiferal microenvironment over diurnal time scales due to the net effects of photosynthesis-respiration and calcification of the foraminifer and its algal symbionts. Orbulina universa shell composition was also explored for internal variation in boron isotope composition. The resolution of the laser ablation MC-ICP-MS technique used is near the precision limits of modelled changes in microenvironment carbonate system chemistry. The measured bulk shell boron isotope compositions are significantly offset from the predicted boron isotope composition of the seawater borate ion. In summary, this thesis provides new insights into the factors controlling trace element and isotope incorporation into foraminiferal calcite, including the extent to which biological factor influence the composition of precipitated shell calcite relative to external seawater chemistry.

Author: Juanjuan Xia
Publisher:
ISBN:
Category :
Languages : en
Pages : 326

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Author: 鄭郁豫
Publisher:
ISBN:
Category :
Languages : en
Pages : 148

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Author: Annette Bolton
Publisher:
ISBN:
Category : Climatic changes
Languages : en
Pages : 267

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Author: Peter D. Clift
Publisher: Geological Society of London
ISBN: 9781862391116
Category : Science
Languages : en
Pages : 544

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The Arabian Sea region has several features that make it the best area for studies of climate and palaeoceanographic responses to tectonic activity, most notably in the context of the South Asian monsoon and its relationship to the growth of high topography in the adjacent Himalayas and Tibet. The papers range from high resolution, holocene palaeoceanographic studies of the Pakistan margin to regional tectonic reconstructions of the ocean basin and surrounding margins throughout the Cenozoic.

Author: Elizabeth Truswell
Publisher: ANU Press
ISBN: 1760462942
Category : Biography & Autobiography
Languages : en
Pages : 247

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In the southern summer of 1972/73, the Glomar Challenger was the first vessel of the international Deep Sea Drilling Project to venture into the seas surrounding Antarctica, confronting severe weather and ever-present icebergs. A Memory of Ice presents the science and the excitement of that voyage in a manner readable for non-scientists. Woven into the modern story is the history of early explorers, scientists and navigators who had gone before into the Southern Ocean. The departure of the Glomar Challenger from Fremantle took place 100 years after the HMS Challenger weighed anchor from Portsmouth, England, at the start of its four-year voyage, sampling and dredging the world’s oceans. Sailing south, the Glomar Challenger crossed the path of James Cook’s HMS Resolution, then on its circumnavigation of Antarctica in search of the Great South Land. Encounters with Lieutenant Charles Wilkes of the US Exploring Expedition and Douglas Mawson of the Australasian Antarctic Expedition followed. In the Ross Sea, the voyages of the HMS Erebus and HMS Terror under James Clark Ross, with the young Joseph Hooker as botanist, were ever present. The story of the Glomar Challenger’s iconic voyage is largely told through the diaries of the author, then a young scientist experiencing science at sea for the first time. It weaves together the physical history of Antarctica with how we have come to our current knowledge of the polar continent. This is an attractive, lavishly illustrated and curiosity-satisfying read for the general public as well as for scholars of science.

Author: Donald R. Prothero
Publisher: Cambridge University Press
ISBN: 0521433878
Category : Science
Languages : en
Pages : 708

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Provides the latest information in dating and correlation of the strata of late middle Eocene through early Oligocene age in North America.