Asian Monsoon induced erosion during the Miocene recorded at IODP Site U1443 (Exp. 353)

IODP Site U1443 recovered a complete sequence of Oligocene to recent hemi-pelagic/pelagic sediments sitting above the Bengal fan on the northern tip of the Ninety East ridge. We are using this unique sedimentary archive to develop orbital resolution records across key climatic intervals of the Miocene (23-5.6 Ma) to better understand the roles of tectonics, global climate and regional monsoon climate on the weathering and erosion of the watersheds feeding into the Bay of Bengal. Benthic foraminiferal stable isotopes provide an orbital resolution stratigraphic framework and global climatic context while paired planktonic foraminiferal δ¹⁸O and Mg/Ca proxies reflect regional climate and the radiogenic Sr, Nd, Hf and Pb isotope compositions of clays are provenance tracers of continental erosion reflecting rock type and age. The isotopic signatures of clay minerals transported to the central Bay of Bengal suggest that the mixture of erosion sources has remained remarkably consistent during the Miocene and persisted into modern sediments. High resolution data from the peak warmth interval from 15.8 to 15.3 Ma within the Middle Miocene Climatic Optimum (MMCO), and across the major Miocene global cooling step from 14 to 13.5 Ma, exhibit marked fluctuations of all four isotope systems on short timescales. These transient events reflecting slight changes in the balance of different sediment sources were most likely climatically driven given that the rapidity and reversible nature cannot have resulted from tectonic events. Interestingly, while exhibiting little variability during the warm MMCO, the Pb isotope data closely follow benthic δ¹⁸O values during the major mid-Miocene global cooling step. This observation suggests a direct link between deep ocean temperatures and global ice volume and changes in weathering inputs. This global cooling was accompanied by a trend to less radiogenic clay Nd isotope values suggesting a higher contribution of Himalayan sources, possibly supplied as a consequence of increased penetration of monsoon precipitation into the mountains.