The uplift of the Himalayan range and associated surface processes have long been hypothesized to have played a role in the long-term global cooling that characterizes the Cenozoic era. Specifically, high erosion rates triggered by a combination of rapid uplift and/or climate forcing such as heavy monsoon precipitations may have enhanced silicate weathering and/or organic carbon burial – two key long-term CO2 sequestration mechanisms. Mechanistic and quantitative reconstructions of silicate weathering rates and organic carbon burial in the sedimentary fans receiving the products of Himalayan erosion are therefore of paramount importance in order to characterize and quantify the impact of Himalayan uplift and erosion on the global carbon cycle and attendant consequences for the Cenozoic cooling.
I will present a multi-proxy study of sediment cores recovered by IODP expeditions 354, 355 and 362, providing an unprecedented record of silicate weathering and organic carbon burial in the Bengal, Indus and Nicobar Fans spanning the later part of the Cenozoic Era. Silicate weathering rates remain relatively invariant and comparable (or lower) to modern rates. Meanwhile, abundant accumulations of macroscopic (up to several centimeters in length and diameter) debris of well-preserved wood were discovered within coarse sediment units of the Bengal, Indus and Nicobar Fans. The burial of woody debris in coarse sediments at the base of turbidites rapidly overlaid by thick mud-caps appears to reduce their exposure to oxygen, thereby inhibiting their degradation even in the absence of mineral protection. Furthermore, in the Bengal Fan, organic carbon loading and composition (e.g. degradation state) shows systematic temporal variations. While the burial of wood debris appears to decrease slightly in the later part of the record, the organic carbon loading of turbidite mud caps increases sharply at the Plio/Pleistocene transition. These trends and their implications for the global C cycle will be discussed in the context of variations in the strength of the summer monsoon and related surface processes.
Dr. Galy is a tenured Associate Scientist in the Marine Chemistry and Geochemistry department at Woods Hole Oceanographic Institution (MA, USA). He received a master of geological engineering and PhD in geosciences from the Institut National Polytechnique de Lorraine (Nancy, France). His research focuses on multiple aspects of biogeochemistry including carbon cycling in terrestrial and oceanic environments, the long-term evolution of the earth surface and paleo-climate. Valier has worked on deep sea drilling cores since his master thesis, which focused on cores from DSDP Leg 22. In 2015 he sailed as an organic geochemist on IODP expedition 354 to the Bengal Fan.