Paleoclimatic Variations Record From Chumbur-Kosa Loess Section In The Sea Of Azov Region Since MIS11

The Quaternary period is considered the most important period in global climate change research.The extensive deposits of loess provide a high-resolution record of the Quaternary period,so they can be an important source of information in climate change research of the Quaternary period.Investigating Quaternary loess can help improve our understanding of current global climate change,and will assist in predicting global changes in climate in the future.The loess of the Sea of Azov is located in the loess area of Eastern Europe.It is the transitional zone between the European and Chinese loess sections.Its unique regional environmental characteristics make the loess sections in the area different in structure and composition from other areas.A thorough study of loess sediment in the Azov Sea region helps to understand the paleoclimate change in the Azov Sea region,and understand the different responses to global changes and feedback processes in the climate system.In this thesis,the object of study is the Chumbur-Kosa?CK?loess section of the south Azov Sea.The timescale of the CK loess section can be determined by the OSL method.The correct time scale makes a comparison between regional and global climate possible.We analyzed multi-proxies,such as the magnetic susceptibility,grain size,soil color index,total organic carbon?TOC%?,carbonate abundance?CaCO₃ %?,and a reconstruction of the evolutionary history of paleoclimate since the Middle Pleistocene.The climatic and environmental conditions in the Azov Sea area during the MIS7 period were emphasized.Based on these proxies,the loess section in the study area was compared with the loess section in other areas and climate change media were compared with global scale records.The process of climate evolution and the possible mechanism of its influence are analyzed.The main conclusions of this study include the following.1.There have been nine stages in Azov Sea since 425 ka B.P.:?1?The S4 phase-from 425 to 364 ka B.P.-was a period of relatively warm and wet climate,rising temperatures,abundant precipitation,thick forests with good natural vegetation,strong weathering,and chemical dissolution.?2?The L4 phase-from 364 to 332 ka B.P.-was,compared to the previous stage,a period of colder and drier climate with weak chemical weathering.?3?The S3 phase-from 332 to 292 ka B.P.-had abundant precipitation,a thick forest with good natural vegetation,strong weathering,and chemical dissolution,in conformity with the warm period pattern of this environment.?4?The L3 phase-from 292 to 249 ka B.P.-had obvious glacial features compared with the previous phase.The change in climate proxies clearly reflects the gradual strengthening of the west wind and the weak pedogenesis in the Azov Sea.?5?The L2 stage-from 186 to 128 ka B.P.-had a cold and dry climate,sparse vegetation,and more precipitation in the early stage,but with precipitation gradually reduced,due to the gradual strengthening of the westerly wind.?6?The S1 stage had a warm and wet climate with abundant precipitation but included a decrease in winter temperatures and annual precipitation,relative to the MIS7 phase.?7?The L1 stage included MIS and MIS 2,two relatively cold climate periods,and MIS 3,a relatively warm climate period.In this stage,the soil development process was relatively "complex".?8?The S0 phase had a strong weathering pedogenesis and summer temperatures that were 1-2? higher than modern temperatures,along with precipitation that was higher than the modern level of precipitation in the Azov Sea.2.The S2 phase?from 249 to 186 ka BP?.Compared to other paleosol strata in the CK section,the low magnetic susceptibility values,brightness L* value,the ratio of parameter?Na/K Ca/Mg,Bc,Ki and Rb/Sr ratio? in S2 showed the opposite variations.The increasing precipitation,resulting in the leaching of Ca,Mg and Na in the L2 stage,may be the main reason for the enrichment that occurred in S2.The CK section,at still an early stage in the depletion of Na and Ca,and demonstrates weak chemical weathering.Further analysis shows that climate conditions?in particular,precipitation?may have had a vital influence on chemical weathering formation in the Sea of Azov.In a word,the variation of some climatic proxy indexes in stage S2 of CK is a unique change,which may be the result of the combination of the change of humidity and the change of carbonate leaching intensity.Compared with other interglacial periods,this stage is relatively cold and wet,and is relatively cold interglacial period,but the relative humidity is relatively increased,and the vegetation coverage is better.3.The loess section of the study area was compared with loess sections in other areas and the climate change media was recorded at a global scale.It is found that the CK loess section recorded the climatic information of global change,which can be used to apply the Paleo-analog method to the analysis of global change in the area.On the other hand,the climate in the Sea of Azov is mainly affected by westerlies,and the change of solar radiation intensity is an important factor leading to climate change.