| The deep-sea sediments have superior advantages in paleoclimate research for its continuous deposition profile, less post-interference, richness in bearing climate information and strong contrasts. So they play a great role in revealing the climate changes and are more widely used. The North Atlantic region is extremely sensitive to the global changes, so it is considered to be the source and driving force of the global climate change. The records of the Dansgaard-Oeschger Cycles which is found in the ice core of Greenland and the Heinrich events which are found in Atlantic deep-sea sediment reflect the important and special position of the region in paleoceanography and paleoclimate studies. Based on the important improvements achieved by Leg.162and Leg.172during the Ocean Drilling Program (ODP), the Integrated Ocean Drilling (IODP) arranged two Expeditions (303and306) for drilling in North Atlantic, the main goal is to rebuild the standard strata since the Pliocene and to explore the mechanism of climate changes.This dissertation, financially supported by the National Nature Science Funds Project" The Northern Atlantic Deep-Sea Sediment Records of Millennial-Scale Climate Change Research (Grant No.:40601105)", based on the second splicing profiles which are composed by the core of hole A and hole D, Site U1313, Expedition306, and the site located at the upper western flank of the Mid-Atlantic Ridge, and using the data of color reflectance, magnetic susceptibility and density which are measured during the expedition, and analyzing of oxygen and carbon isotopic composition, Mg/Ca ratios, Sr/Ca ratios in planktonic foraminifer (Globigerinoides rubber, White shell), grain size and mineral composition etc., reconstructed the ancient sea surface salinity (SSS), oxygen isotope background values of seawater, ancient sea surface temperature (SST) and the contents of CaCO3, found the environmentally sensitive particle group and its environmental significance, found that a series of sub-orbital scale ancient climate change cycles by using the empirical mode decomposition (EMD) method and wavelet analysis method, and reconstructed the paleoclimate in the early Pleistocene (2420.88-1460.89kaB.P.) in North Atlantic, and identified26glacial-interglacial cycles.The main conclusions are as follows: 1. There are many ice-rafted debris deposition events in Pleistocene (2420.88～1460.89kaB.P.) in North Atlantic, especially during104～124cm10H5Core A (98.97～99.17mcd,2082.63～2086.79kaB.P.), and the significant layers of ice-rafted debris deposition are found with some gravels of3～20mm in diameter.2. The profile mainly is composed by clay and silt, with an average clay content of76.13%, silt of23.84%content and sand of0.03%. The frequency curves of grains show a clear bimodal distribution, which indicates two different sources. Environmentally sensitive grain-size analysis shows that there are two environmentally sensitive grain-size group of components Ⅰ (<1.729um) and component Ⅱ (>1.729um), both of which are sensitive to environmental change, and probably that coarse one was transported by the westerly jet and the fine one input by the warm current of North Atlantic, and their content reflect changes in the level of warm and cold climate. Mineral analysis showed that the sample mainly consists of quartz, feldspar and illite, calcium and other minerals.3. Doing multi-time scale analysis with EMD method and wavelet analysis with multiple parameters such as color reflectance, CaCO3content, mean size, median size, fine clay (%), fine silt (%), fine clay/fine silt ratios, fine clay/>8μm ratios, component Ⅱ and component Ⅰ/component Ⅱ ratios, the results show that not only orbital scale cycle caused by Earth orbital parameters such as the eccentricity (400ka and100ka), precession (23ka and19ka) and tilt angle (41ka), but also a series of sub-orbital-scale cycles such as8ka (7.4-8.12ka),6ka (5.79-6.4ka),4ka (4.24-4.54ka),3ka (3.16-3.65ka),2ka (1.99-2.88ka) and lka (1.38-1.48ka) exist in the Atlantic region in the early Pleistocene.4. Based on the changes of CaCO3content and lightness (L*), the section of115.48-69.43mcd (2420.88-1460.89kaB.P.) can be divided into26sedimentary cycles. According to the distinctive features of Atlantic-type deep-sea CaCO3deposition cycles in Quaternary which is low CaCO3content in glacial time and high CaCO3content in interglacial, it can be inferred that the peak brightness L*corresponds to interglacial, and in2420.88-1460.89kaB.P., the North Atlantic climate fluctuated frequently, and included at least26ice ages, which is in good agreement with the fluctuations of δ18O, SST, CaCO3content and L*.5. Combining the16indexes of CaCO3content, brightness L*, magnetic susceptibility, mean size, median size, fine clay (%), fine silt (%), fine clay/fine silt ratios, fine clay/>8um ratios, components Ⅱ, components Ⅱ b, component Ⅰ/component Ⅱ ratios,δ18O,δ13C, SST and Mg/Ca ratios, the palaeoclimate change process of115.48～69.43mcd (2420.88-1460.89kaB.P.) in Site U1313can be divided into nine stages:Stage A (2420.88-2376.49kaB.P.), time span of44.39ka, including two ice ages. When the coarse particle content increases, it indicates the climate cooling, with the global ice volume increase associated with IRD events, corresponding to the ice age.Stage B (2376.49-2261.53kaB.P.), time span of114.96ka and including three ice ages. Fine particles significantly increased which indicate the global warming; compare to interglacial, the global ice volume reduces, and there is no evidence that IRD events occurred.Stage C (2261.53～2219.64kaB.P.), time span of41.89ka and including only one ice age.Coarse particles increased which indicates the climate cooling, and the global ice volume increase associated with IRD events, corresponding to the ice age.Stage D (2219.64～2092.21kaB.P.), time span of127.43ka and including four glacial stages. The content of coarse particle did not significantly increase or decrease, which indicates the small climate fluctuations; corresponding to the longer interglacial, the global ice volume reduces, and there is no evidence that IRD event occurred.Stage E (2092.21～2019.66kaB.P.), time span of72.55ka and including three ice ages. There are significant deposits of ice floating debris in Section80～138cm of A10H5(98.73～99.29mcd,2077.63～2089.29kaB.P.), which confirmed that the IRD events occurred for many times. The increased content of coarse particles at this stage indicates the climate cooling, which corresponding to the ice age, and the scale of ice age is greater than the adjacent stage, with significant increase in global ice volume.Stage F (2019.66～1914.7kaB.P.), time span of104.96ka and including two glacial stages. The content of coarse particles did not significantly increase or decrease, which indicates the small climate fluctuations, with the global ice volume reduction, corresponding to the longer interglacial, and there is no evidence that IRD events occurred.Stage G (1914.7～1865.57kaB.P.), time span of49.13ka and including only one ice stage. The increased content of coarse particles at this stage indicates the climate cooling, which corresponding to the glacial stage, the global ice volume increased, but the components of Ⅱ b were all zero in this stage, and there is no evidence showing that IRD events occurred for many times.Stage H (1865.57～1683.87kaB.P.), time span of181.7ka and including five glacial stages. The fine particles at this stage were significantly increased, which indicates the global warming, with the global ice volume reduction, corresponding to the interglacial, and there is no evidence that IRD events occurred.Stage Ⅰ (1683.87～1460.89kaB.P.), time span of222.98ka and including five glacial stages. The content of fine particles changed frequently and violently, which indicates the weather’s extreme instabilitythe glaciers’ many retreats, and the rapid conversion of glacial stage and interglacial stage. The global ice volume increased and also reduced rapidly, and the IRD events occurred for many time. |
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