Program
 
Special Session 2: Changing ocean environment: from the sedimentary perspective -- processes and records
 

 
 
1435
Deep-sea records of abrupt past monsoon changes: why it matters to understand the mechanisms?
Wednesday 11th @ 1435-1450
Room 4
Harunur Rashid* , Hadal Center for Science and Technology Research Shanghai Ocean University Shanghai, 201306 China and 2Earth and Environmental Sciences Memorial University of Newfoundland Corner Brook, NL A2H 6A6 Canada
Presenter Email: rashid@shou.edu.cn
One of the most remarkable and precise evidence of large magnitude abrupt climate change have been documented in ice-cores, caves, lakes and marine sediments between ~80,000 and 10,000 years before present. These abrupt climate changes are known as the Dansgaard-Oeschger warming and cooling cycles of approximately 1,500 years duration which were periodically terminated by Heinrich massive iceberg rafting events from the late Pleistocene North American Laurentide ice-sheet. Such high-resolution records of past climate changes from the northern Indian Ocean, especially the Bay of Bengal and Andaman Sea, the sink of the Indian summer monsoon, are rare. Here we present the sea-surface temperature (SST) and salinity data from paired ¦Ä18O and Mg/Ca measurements in planktonic foraminifera Globigerinoides ruber from the Bay of Bengal and Andaman Sea sediment cores. Our data suggest that the SST and seawater ¦Ä18O (¦Ä18Osw) were ~3oC colder and ~0.6¡ë depleted, respectively, during the Last Glacial Maximum (LGM) compared to the early Holocene. The most positive ¦Ä18Osw were found between 18.2 and 15.6 ka interval. Depleted LGM ¦Ä18Osw values suggest a wet climate which freshened the sea surface of Andaman Sea and Bay of Bengal. Our data further indicate that the monsoon was stronger in the warm Bølling/Allerød and weaker in the cool Younger Dryas periods. The most depleted early Holocene ¦Ä18Osw values suggest that the monsoon was strongest and wettest resulting in a humid climate. After ~5,000 years, the Indian monsoon weakened significantly, indicating less dilution of the sea surface by the Ganga-Brahmaputra-Meghna outflow and/or less direct rainfall. Our findings are consistent with the broader regional changes in the Indo-Asian monsoon as evident from the published paleoclimatic proxy-records of Hulu and Dongge caves of northeast China and marine sediments of South China Sea and northeast Pacific Ocean. The general pattern and timing of monsoon variability in the northern Indian Ocean parallel the Arabian Sea, Africa, and Asian ice cores and cave records suggesting that a common tropical forcing may have modulated these abrupt climate changes. We further hypothesize that the prevailing late Holocene dry climate may have caused the diminishment and subsequent abandonment of the settlements of the great Indus Valley civilizations of the Indian subcontinent.