A 100 ka Summer Monsoon Driven Indian Ocean Paleoproductivity Record with Signatures of Northern Hemisphere Climate Events

Southern ocean of Sri Lanka is characterized as a major upwelling center in the Indian Ocean, driven by the Indian summer monsoon. Upwelling induced productivity of the region has a great influence on regional marine biology and economy of the country. Hence this study was carried out to accurately identify the long-term variability of upwelling productivity and the forcing factors in order to better understand the influence of anthropogenic climate change on upwelling.

A 192 cm long sediment core was obtained from the foot of the southern continental slope. An age model, developed using AMS ¹⁴C dates and tying a* values of colour reflectance to the δ¹⁸O record of Greenland NGRIP ice core, shows that the age span of the core is about 110 000 Yrs. Upwelling indicator species (G. bulloides and G. glutinata), non-upwelling productivity indicator species (G. ruber and G. saculifer), other planktonic species and benthic foraminifera were counted in samples taken at 2 cm intervals. Proxies were developed for upwelling intensity, total productivity, mixed-layer thickness, and freshening based on principal component and cluster analysis, relative abundance and density (individuals/g) of foraminifera, chemical composition, and color reflectance.

Total productivity and upwelling records show a synchronized pattern, indicating a strong influence of upwelling on the regional productivity. The striking similarity between NGRIP ice core δO¹⁸ data and upwelling record reveals the influence of Northern Hemisphere climate changes on monsoon-induced upwelling in southern Sri Lanka. A series of cold Heinrich events and warm Dansgaard - Oeschger (DO) events recorded in Greenland ice core data can be identified on both upwelling and total productivity records. Thermocline productivity correlates with the upwelling record, while mix layer productivity shows a counter correlation with upwelling record. TOBA volcanic eruption can be identified around 74 000 yrs ago, as a significantly dense layer of foraminifera, which could be resulted from a mass die out occurred due to extreme conditions .