Indian Monsoon Records Since The Early Mid-Pleistocene In The Northwest Gulf Of Bengal

The Indian monsoon is an important part of the Asian monsoon system.It affects many areas in South Asia,Southeast Asia,and the Indian Ocean where is a hot research area in global climate change.The Bay of Bengal is the core area of the Indian monsoon and its precipitation.The inflow of rivers makes sediments an important carrier for the preservation of Indian monsoon information.The species,morphology and preservation status of benthic foraminifera are affected by the marine environment in which they are located.Therefore,the analysis of the characteristics of the species and parameter changes of benthic foraminifera in sediments is of great significance for the reconstruction of ancient marine environment.In this paper,the sedimentary core at station U1446 of voyage IODP353 is selected,and the chronostratigraphic framework is established by deep sea oxygen isotope dating,and the sedimentary age of the sample is calculated based on the sample depth.The sample age is between 373.64ka-685.44 ka,which is in the MIS11-16 period.Through identification and statistics of benthic foraminifers in sediment samples,and factor analysis of benthic foraminifers,combined with the ecological significance of benthic foraminifera indicators,the mid-Pleistocene bottom water environment in the Bay of Bengal was analyzed.The main factor-load,U + B content,etc.were analyzed by frequency spectrum,and the history and driving mechanism of Indian monsoon reflected by the above indicators were discussed.Through systematic paleontological studies of benthic foraminifera in 89 samples from U1446 holes in the Bay of Bengal,a total of 47 genera,87 species,subspecies and undetermined species were identified.Habitat foraminifera species have been systematically described in paleontology and made a chart.Combining with previous studies on the Bay of Bengal area and synthesizing the appearance of benthic foraminifera,the main environmental indicator species(genus)are Uvigerina spp.,Bulimina spp.,Cassidulina carinata,Gavelinopsis praegeri,etc.The periods of benthic foraminifera abundance and sediment flux are low in the interglacial period.The benthic foraminifers preserved during the interglacial period are mostly endophytes.The analysis of the content of Uvigerina + Bulimina,such as the oxygen-deficient species,found that the U + B content showed high values during the interglacial period,indicating that in the samples with benthic foraminifera,Uvigerina and Bulimina have an absolute advantage.High indicates that the bottom water had high organic carbon and low dissolved oxygen.The result of factor analysis of benthic foraminifera showed that the main factor 1 explained 73.48% of the environmental information of the whole group,and the load of the maximum variance factor of the main factor 1 showed obvious cycle change characteristics.It was analyzed by frequency spectrum and found that in the study area,the slope period occupies a higher spectrum intensity,and the slope of the earth axis is the main driving mechanism affecting the Indian summer monsoon.