Influence of the North Atlantic Climate Events on the Indian Summer Monsoon Driven Climate in South-western Sri Lanka during the Late Pleistocene.

The influence of long term climatic oscillations of the Northern Hemisphere and the Southern Hemisphere on the Indian Summer Monsoon (ISM) driven climates in the southern part of the Indian Peninsular is not well known. Therefore, this study was carried out to understand ISM variability during the late Pleistocene in South-western Sri Lanka and its relationship with the North Atlantic and the Antarctic climates.

A 25m undisturbed terrestrial sediment core was recovered from an alluvial gem field at Ratnapura of South-western Sri Lanka. High resolution Color Reflectance (360-740 nm) was measured along the core axis and the first derivatives of data were subjected to Principal Component Analysis (PCA). Three PCAs explaining 84.3% of the total variability were extracted. Matching of rotated factor loading with standard curves recognized that DSR-PC2 represents Goethite and DSR-PC3 represent Illite respectively. Loss-on-Ignition (LOI) was used to estimate soil organic matter content. Since AMS ¹⁴C radiocarbon results revealed that, the top of the core was >45,000 cal yrs BP, down core plots DSR-a* & b* were tied to δ¹⁸O curve of the NGRIP ice core of Greenland to develop an age model. This age model reveals that, the undisturbed section of the core has a continuous record from 42,500 to 78,000 cal yrs BP.

Color reflectance and LOI data show that, ISM dominating climate in the region was influenced by the Dansgaard Oeschger (DO) events of the North Atlantic. DO events 11 to 20, marked by higher Goethite levels & DSR-a* and lower Illite levels & LOI during warm periods while, lower Goethite contents & DSR-a* and higher Illite contents & LOI during cold periods. Increased rainfall and warm humid climate during warm periods could have increased the weathering of iron minerals, productivity, decomposition of organic matter and transport of fine grained clay and organics, whereas the opposite happened during the dry and cold periods.

Close relationship between ISM driven climate in the equatorial region and the North Atlantic climate events indicates that teleconnection to the Northern Hemisphere, through atmosphere or thermohaline circulation, is more influential for regional climate than that with the Antarctica.