Benthic Foraminifera Assemblages In The Deep-sea Surface Sediments Of Hangzhou Bay And Their Environmental Implications

Hangzhou Bay is a typical estuarine sedimentary area in China.In modern society,rapid population growth and rapid economic development have brought tremendous pressure on resources and the environment.The contradiction between people and resources and environment has been highlighted.Geological environmental issues,ocean engineering issues,and land-sea interaction problems in the Hangzhou Bay area are increasingly important.The foraminifera has a short life cycle and fast generational replacement.It is an effective recorder of marine sedimentary environment and can well indicate water masses,ocean currents,and depositional environments.It is a sensitive indicator of the paleoenvironmental substitutive.Therefore,understanding the relationship between the foraminifera assemblage in the surface sediments of the Hangzhou Bay area and the modern marine environment and establishing alternative foraminifera indicators for the area are very important for a correct understanding of the ancient marine environment changes in the area.Through the identification and statistics of foraminifera in 199 Deep-sea surface Sediments samples in the study area of Hangzhou Bay,analysis the results of particle size and organic carbon,the percentage content of foraminifera species in the sample and comparative analysis of the typical indicator species and the marine environment of Hangzhou Bay,the following results are obtained:(1)In the study area,the particle size has a good correlation with the TOC results.The TOC value is high,productivity is high,and the particle size is small.The TOC content is higher in the northern part of the study area(A district)than in the southern part(B district).It shows that TOC mainly comes from the Yangtze River flushing fresh water.(2)In the study area,the contents of hypoxic and hypertrophic indicator species such as Epistominella naraensis and Ammonia convexidorsa were high,but the correlation with grain size was not good in A zone.The trend of absolute abundance of benthic foraminifera and particle size is also inconsistent,that is,the correlation with productivity distribution in the study area is not obvious.So,it is speculated that the species of hypoxia originated from the continental shelf of the Yangtze River and entered the Hangzhou Bay area following the trend.That is,the area is greatly affected by the current,which is consistent with previous research results.There is no obvious relationship between shallow water environment species and depth in the area.(3)The absolute abundance of benthic foraminifera in B area and the percentage of hypoxia and high nutrient indicator species were negatively correlated with grain size.The indicator of high oxygen and low nutrient in area B was positively correlated with grain size,and indicate production well in this area.The percentage of shallow water species has a negative correlation with the sampling water depth.The species distribution of this area is greatly influenced by the Qiantang River water.