Author: 鄭郁豫Publisher:
ISBN:
Category :
Languages : en
Pages : 148
Book Description
Reconstruction of Paleotemperature and Paleosalinity of the South China Sea for the Past 170kyrs Using Planktonic Foraminiferal Mg/Ca Ratio and Oxygen Isotopes
Author: 鄭郁豫Paleotemperature Proxies
Author: Jennifer Eve HertzbergPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Paleotemperature proxies enable scientists to reconstruct past ocean temperatures from sediment recovered in deep-sea cores. This dissertation takes an in-depth look at two proxies, Mg/Ca ratios of planktonic foraminifera and the TEX86 index, and applies the Mg/Ca paleothermometer in a novel way to assess past changes in tropical Pacific climate. Chapter II is a reinvestigation of a proposed large salinity effect on Mg/Ca ratios in the foraminifera Globigerinoides ruber based on a recent Atlantic core-top meridional transect study. Shell weight analyses and scanning electron microscopy are used to assess the preservation of similar G. ruber shells used in the core-top study. Shells from the equatorial Atlantic are highly dissolved compared to those from the subtropical gyres, impacting their Mg/Ca-temperatures. When Mg/Ca-temperature calibrations that account for dissolution differences are used, there is no longer an apparent large salinity effect, suggesting that regional differences in preservation, rather than salinity, significantly affect Mg/Ca-temperatures. Chapter III investigates the TEX86 temperature proxy in the eastern Pacific by utilizing Mg/Ca paleothermometry on multiple species of planktonic foraminifera across the Holocene and Last Glacial Maximum (LGM) to determine the recording depth of the TEX86 proxy. Holocene TEX86 temperatures match sea surface temperatures, but during the LGM, there is a cold bias in TEX86 temperatures that are more representative of the upper thermocline. The best explanation for the offset is a decrease in LGM nutrient availability. Therefore, caution should be applied when interpreting TEX86 records based solely on the relationship between core-top/Holocene TEX86 temperatures and modern observational temperatures. Chapter IV reconstructs past changes in the tropical Pacific mean state across Marine Isotope Stage 3 by utilizing Mg/Ca paleothermometry on the thermocline dwelling foraminifera Neogloboquadrina dutertrei from an eastern equatorial Pacific sediment core. The thermocline temperature record reveals interstadials are characterized by a more El Niño-like mean state, with increases in thermocline temperatures up to 6°C. Thermocline warming events are more pronounced from 64-44 kyr when global climate was in a warmer state. From 44-32 kyr, the record shows cooler thermocline temperatures, suggesting a shift to a more La Niña-like mean state, as climate began transitioning into the LGM. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/155637
The South China Sea
Author: Pinxian WangPublisher: Springer Science & Business Media
ISBN: 140209745X
Category : Science
Languages : en
Pages : 506
Book Description
Pinxian Wang and Qianyu Li The South China Sea (SCS) (Fig. 1. 1) offers a special attraction for Earth scientists world-wide because of its location and its well-preserved hemipelagic sediments. As the largest one of the marginal seas separating Asia from the Paci?c, the largest continent from the largest ocean, the SCS functions as a focal point in land-sea int- actions of the Earth system. Climatically, the SCS is located between the Western Paci?c Warm Pool, the centre of global heating at the sea level, and the Tibetan Plateau, the centre of heating at an altitude of 5,000m. Geomorphologically, the SCS lies to the east of the highest peak on earth, Zhumulangma or Everest in the Himalayas (8,848m elevation) and to the west of the deepest trench in the ocean, Philippine Trench (10,497m water depth) (Wang P. 2004). Biogeographically, the SCS belongs to the so-called “East Indies Triangle” where modern marine and terrestrial biodiversity reaches a global maximum (Briggs 1999). Among the major marginal sea basins from the west Paci?c, the SCS presents some of the best conditions for accumulating complete paleoclimatic records in its hemipelagic deposits. These records are favorable for high-resolution pa- oceanographic studies because of high sedimentation rates and good carbonate preservation. It may not be merely a coincidence that two cores from the southern 14 SCS were among the ?rst several cores in the world ocean used by AMS C dating for high-resolution stratigraphy (Andree et al. 1986; Broecker et al. 1988).
A Multiproxy Paleoenvironmental Reconstruction of Late Quaternary Marine Sediments
Author: Bailey G. DonovanPublisher:
ISBN:
Category : Foraminifera
Languages : en
Pages : 112
Book Description
Two gravity cores were collected from 43 km and 90 km offshore of Kuala Terengganu (western Sunda Shelf, southern South China Sea) at ~60 m water depth to characterize late Quaternary paleoenvironments by using bulk sediment magnetic susceptibility (BMS), elemental analysis via X-ray fluorescence spectrometry (XRF), and foraminiferal analyses. Radiocarbon age estimates (using benthic foraminiferal carbonate material) indicated the nearshore core was Holocene (ca. 10,000-6,000 cal years BP) in age while the offshore core was deposited prior to the last glacial maximum (ca. 45,000 cal years BP and possibly older) during marine isotope stage (MIS) 3 (ca. 60,000 - 30,000 yrs BP) within the late Pleistocene. Elemental and BMS data agree well within both cores, except Pleistocene sediments exhibit higher BMS (ca. 1x10-4 si) and higher calcium content (ca. 2%) than Holocene sediments. These data can be interpreted as representing stronger terrestrial influence during the deposition of Pleistocene sediments or a higher dissolution of calcium carbonate. BMS data, elemental data, and micropaleontological evidence, relative abundances of 64 benthic foraminiferal species, indicate that both cores were deposited in an inner shelf environment similar to the modern shelf environment at ca. 50-60 m water depth. However, a higher ratio of planktonic foraminifera (Holocene: 0-1.3%, Pleistocene: 0-8.5%) suggests a greater influence of open marine waters in the Pleistocene sediments. The position of sea level during deposition of the late Pleistocene cored sediments is higher (ca. 60-0 m depending on the data set) than eustatic published sea-level data for MIS 3. This incongruity could be caused by age inaccuracies from limitations of the radiocarbon dating technique, although this seems unlikely as the lower range of age estimates fall within the technique and the uppermost range falls on the border of the limitations of the technique. Other options for the incongruity include large margins of error for late Pleistocene sea-level reconstruction and vertical crustal movement post-deposition from isostatic adjustment or tectonic activity.
Gametogenic Calcification in the Planktonic Foraminifera Orbulina Universa and Glacial to Interglacial Sea Surface Temperatures Across the Subtropical Convergence in the Southwest Pacific Ocean
Author: Christopher Paul HamiltonPublisher:
ISBN:
Category :
Languages : en
Pages : 398
Book Description
Marine Geology and Geophysics of the South China Sea
Author: Xianglong JinPublisher:
ISBN:
Category : Geology
Languages : en
Pages : 276
Book Description
Reconstruction of Sea-surface Temperatures from Asseblages of Planktonic Foraminifera, Supplementary Data To: Kucera, Michal; Weinelt, Mara; Kiefer, Thorsten; Pflaumann, Uwe; Hayes, Angela; Weinelt, Martin; Chen, Min-Te; Mix, Alan C; Barrows, Timothy T; Cortijo, Elsa; Duprat, Josette; Juggins, Steve; Waelbroeck, Claire (2005): Reconstruction of Sea-surface Temperatures from Assemblages of Planktonic Foraminifera: Multi-technique Approach Based on Geographically Constrained Calibration Datasets and Its Application to Glacial Atlantic and Pacific Oceans. Quaternary Science Reviews, 24(7-9), 951-998
Author: Michal KuceraPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
We present a conceptual framework for a new approach to environmental calibration of planktonic foraminifer census counts. This approach is based on simultaneous application of a variety of transfer function techniques, which are trained on geographically constrained calibration data sets. It serves to minimise bias associated with the presence of cryptic species of planktonic foraminifera and provides an objective tool for assessing reliability of environmental estimates in fossil samples, allowing identification of adverse effects of no-analog faunas and technique-specific bias. We have compiled new calibration data sets for the North (N=862) and South (N=321) Atlantic and the Pacific Ocean (N=1111). We show evidence that these data sets offer adequate coverage of the Sea-Surface Temperature (SST) and faunal variation range and that they are not affected by the presence of pre-Holocene samples and/or calcite dissolution. We have applied four transfer function techniques, including Artificial Neural Networks, Revised Analog Method and SIMMAX (with and without distance weighting) on faunal counts in a Last Glacial Maximum (LGM) data set for the Atlantic Ocean (748 samples in 167 cores; based on the GLAMAP-2000 compilation) and a new data set for the Pacific Ocean (265 samples in 82 cores) and show that three of these techniques provide adequate degree of independence for the advantage of a multi-technique approach to be realised. The application of our new approach to the glacial Pacific lends support to the contraction and perhaps even a cooling of the Western Pacific Warm Pool and a substantial (>3?C) cooling of the eastern equatorial Pacific and the eastern boundary currents. Our results do not provide conclusive evidence for LGM warming anywhere in the Pacific. The Atlantic reconstruction shows a number of robust patterns, including substantial cooling of eastern boundary currents with considerable advection of subpolar waters into the Benguela Current, a cooling of the equatorial Atlantic by ~5?C, and steep SST gradients in the mid-latitude North Atlantic. The transfer function techniques generally agree that subtropical gyre areas in both hemispheres did not change significantly since the LGM, although the ANN technique produced glacial SST in the southern gyre 1-2?C warmer than today. We have revisited the issue of sea-ice occurrence in the Nordic Seas and using the distribution of subpolar species of planktonic foraminifera in glacial samples, we conclude that the Norwegian Sea must have been ice-free during the summer.
Calibration of the Planktonic Foraminiferal Mg/Ca Paleothermometer
Author: Martha Clarke McConnellPublisher:
ISBN:
Category :
Languages : en
Pages : 168
Book Description
Paleotemperature and Productivity Reconstruction of Sediment Core D11957P on the Iberian Margin, Supplementary Data To: Lebreiro, Susana Martin; Moreno, JC; Abrantes, Fatima F; Pflaumann, Uwe (1997): Productivity and Paleoceanographic Implications on the Tore Seamount (Iberian Margin) During the Last 225 Kyr: Foraminiferal Evidence. Paleoceanography, 12(5), 718-727
Author: Susana Martin LebreiroPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Foraminifera counts and climatic assemblages from the Tore Seamount are used to approach the glacial and interglacial changes in temperature and productivity on the Iberian Margin over the last 225 kyr. Chronostratigraphy is based on Globigerinoides ruber and Globigerina bulloides oxygen isotopes and supported by foraminifera and carbonate stadial fluctuations. Foraminifera indicate cooling from late interglacial stage 5 to the beginning of Termination I (TI). Neogloboquadnna pachyderma-s reflects cold conditions during glacial stages 4-2. In contrast, glacial stage 6 is dominated by warmer N. pachyderma-d and dutertrei and a restricted arctic assemblage. Past sea surface temperatures confirm the general cooling, reaching 4.3?C (SIMMAX.28) during stage 2. Multiple productivity proxies such as organic carbon, productivity-related foraminifera, and delta13C constrain the changes observed. A productivity increase occurs after interglacial stage 5, enhanced from late glacial stage 3 to TI Present-day satellite-detected phytoplankton plumes off Portugal would have accounted in the past glacial stages for the general productivity increase over the Tore. On top of this, welldefined peaks of organic carbon and productivity-related foraminifera correspond with Heinrich events 1-4.
Cenozoic Plate Reconstruction of the South China Sea Region
Author: Tung-Yi LeePublisher:
ISBN:
Category : Geology, Stratigraphic
Languages : en
Pages : 76
Book Description