CONVERSION AND MECHANISM OF ORIGINAL REGION OF POLLEN ON THE 90° E SEA RIDGE OF THE NORTHEAST INDIAN OCEAN SINCE THE LAST DEGLACIAL PERIOD
Pollen in marine sediments is an important indicator to reflect the changes of atmospheric circulation and ocean current transport.Based on the results of AMS 14C dating of planktonic foraminifera,the sporopollen analysis of the columnar sediment(core 18I105A)in the Ninetyeast Ridge of the Northeast Indian Ocean was conducted.18I105A is located at 5.1230° N,90.8407° E,with a water depth of 3094 m and a columnar length of 180 cm.A total of 10 samples of mixed planktonic foraminifera were selected for dating.The dating model showed that the top age of the core was 1.5 cal.ka B.P.and the bottom age was 47 cal.ka B.P.The whole core was sampled at 1 cm intervals,eventually obtaining 180 samples.The palynological analysis of 40 samples was carried out at an average interval of 4 cm,and the depth of the oldest identified samples is 168 cm,and its age is estimated to be 45.1 cal.ka B.P.Through the analysis of the pollen community of those 40 samples in core 18I105 A of the 90° E Sea Ridge in the Indian Ocean,it was found that there was an obvious change in the pollen assemblage at 12.6 cal.ka B.P.The pollen assemblage changed from monolete-spore,Pinus,Cyclobalanopsis and Castanopsis pollen to trilete-spore,Myrtaceae and Ulmaceae pollen.By comparing with the main source area of modern pollen in the Northeast Indian Ocean and with the YDY05 core collected in the north part of 90° E Sea Ridge,it is suggested that the source area of pollen in core 18I105A has changed from Sumatra Island to Sri Lanka and the Indian Peninsula.Before 12.6 cal.ka B.P.,the source area of pollen mainly came from the near source area such as Sumatra Island,and the main transport factor was the Andaman surface current,which was controlled by the rise and fall of sea level.However,in the Holocene,the strengthening of Indian summer monsoon formed strong southwest monsoon flow and sea level rise increased the distance from the source area,hindered the process of pollen transport in the eastern Sumatra Island,which was close to the source area.This process results in the change of the source area to the Indian Peninsula and Sri Lanka,and transporting distance increased and pollen concentration plummeted.At this stage,sea level and summer monsoon played a major controlling role.Before 12.6 cal.ka B.P.,the total concentration of pollen and spores in YDY05 core was much lower than that in 18I105A core,indicating that the source area of spores in YDY05 core was further away.They have similar pollen assemblage types and concentration variation trends,indicating that pollen sediments in 90° E Sea Ridge have similar source areas and influencing factors.The regional climate/precipitation changes recorded by palynology are as follows:The palynology of the 18I105A core recorded the paleoclimatic evolution history of the terrigenous land since 45.1 cal.ka B.P.The climate of Sumatra Island was mainly dry and cold in the marine isotope stages(MIS)3 period,and wet and cold in the MIS 2 period,and the Holocene period recorded a warm and humid climate change in India and Sri Lanka.
90° E Sea Ridgemarine sporopollenterrigenous regionIndian monsoon
万方数据
维普
