Research On Millennial Scale Climate Change Period Recorded In North Atlantic Deep-sea Sediments In Early Pleistocene

To realize the evolution of climate and environment in the future more clearly, it is important to explore and analyze the processes and mechanism of the environment changes in the past. It is of advantage to reveal climate changes with deep-sea sediment for its continuous deposition profile, less post-interference,richness in bearing climate information and strong contrasts. It is more widely used in paleoclimate research and is the ideal platform for short-term climate study. North Atlantic region is the driver of the global climate change. In this particular region, the interaction of the ice, gas, water brings about a worldwide large scale climate change. The original research of millennial-scale climate change is carried out in North Atlantic firstly, which is an irreplaceable and ideal research area.The samples in this paper were selected from siteU1313 on Expedition 306 in North Atlantic. The grain size and mineral composition of the sample (1.5Ma-1.7Ma) were measured, and then wavelet analysis was carried out on the base of the curve of grain size parameters. It is demonstrated the existence of the millennial scale climate change cycle. There are six parts in the paper:PartⅠThis part mainly introduces the purpose and significance of the study. Both domestic and overseas research progress on the millennial scale climate change and paleooceanography are depicted briefly.PartⅡThis part generally introduces the natural condition of the research area.PartⅢThis part introduces the experimental analysis methods and the data processing methods.PartⅣThis part on the base of the grain size of the parameters change curve,reveals the significance of the environment.PartⅤWith the help the minerals in the samples, the source of the sediment is inferred.PartⅥAccording to the environmental significance of the change of the sample's grain parameters, the millennial scale climate change cycle is discovered.Main conclusions are as follows: 1 The whole profile's mean grain diameter is 2.05μm, median grain diameter is 0.84μm. The sample's composition shows it's a type of clay, indicating that hydrodynamic conditions is stable (or weak). The average skewness is -0.42, which is extremely negative, indicating that the sediment is mainly concentrated in fine grains. The average standard deviation is 1.48, showing it is poorly selected, which also proves the hydrodynamic conditions is stable (or weak). Peaks have correlation with mineral's source and deposition environment. The whole profile'mean peak value is 0.72 in a flat form showing that the sediment came into the new environment without obvious transformation. So it may be a mixture of several mineral sources.2 The clay content of the sample is 82.39% of and that of silt is 17.61%. Fine silt in the sand takes an average level of 14.19%, while coarse silt only takes 0.1%. Clay in the core of the sediment(<4 um) takes up 59% to 88% of the whole content, with its average as 82.39%. Fine silt takes10% -22%, with an average of 14.2%. Fine sand takes 2-15%, with an average of 3.3%. An average of silt content is 0.1%. There's no trace of silt in depth of 77.84-78.28 m, 82.52-82.68 m, 83.05-83.41 m, showing that the sediment environment is comparatively stable. A relatively low level of clay content in depth of 72.45-73.13m and high level of fine silt, powder sand and silt content proves the depositional environment is instable, with critical hydrodynamic conditions. The high content of clay is found in the depth of 82.80-83.33 m, with an average content ratio more than 80%, while powder sand, silt content are comparatively low in the content of the profile, and no traces of silt , which shows that the depositional environment is stable, and hydrodynamics is weak.3 Mineral composition is correlated with the type, source and hydrodynamics of sediment. Quartz and feldspar , terrigenous material, take more in the content of the profile, indicating that they are the main mineral. While mica is less in the sediment. Both quartz and feldspar are of terrigenous material .Grain size distribution curve shows that they have two peaks, which indicate two sources of sediment. Smear slides indicate that the main source of sediment is from both terrigenous and marine materials.4 Wavelet analysis identifies that, in band 1.522-1.540 Ma, 2.11 ka, 3.04 ka, 6.79 ka climate cycles are found during this cycle, 6.79 ka is most notable; for 1.540-1.551 Ma, the cycles is at 2.09 ka, 3.98 ka, 10.05ka, 13.20ka, with 10.05ka the most significant, which represents the main cycle. For 1.599-1.620 Ma, at 1.04ka, 5.00 ka, 7.93ka, 5.00 ka, and it is significant at 7.93 ka, which is the main cycle. For 1.683-1.706 Ma, they are 2.76 ka, 5.17ka, 8.28ka, 21.04ka, 21.73 ka, with 21.04ka as the most significant main cycle. For 1.707-1.742 Ma, they are 2.33 ka, 3.88 ka, 12.94 ka, with 12.94ka as the main cycle. By enlarging on their respective time domain, the author finds out the for 1.526-1.530 Ma there's a cycle at 2.11 ka; for1.530-1.536 Ma at 3.04 ka; for1.683-1.686Ma ,1.691-1.697 Ma , and 1.702-1.705 Ma, the cycles are at 2.76 ka; for 1.713-1.715Ma ,1.717-1.719 Ma ,1.730-1.732 Ma,1.735-1.739 Ma, the cycle exists at 2.33 ka.