Abstract
AbstractThe development of the South Asian monsoon (SAM) and Himalaya‐Tibetan Plateau uplift were closely intertwined with some studies suggesting that uplift initiated the monsoon whereas others link tectonics with monsoon‐controlled exhumation. Silicate weathering controls atmospheric CO2 on geological timescales resulting in a large potential for monsoon strength and the Himalayan orogeny to influence global climate but detailed records of SAM‐induced weathering on million year (Myr) timescales are lacking. Here, we present radiogenic Sr, Nd, and Pb isotope compositions of clay minerals produced by silicate weathering and transported to the central Bay of Bengal. The radiogenic isotope data exhibit a relatively small range and demonstrate a remarkably consistent mixture of sources dominated by Himalayan rocks and the Indo‐Burman ranges, which consist of sediments derived from the Himalayas. This suggests that the spatial pattern of regional weathering, which today is highest in the regions of strongest monsoon rains, has persisted in a similar form for the last 27 Myrs. A pronounced increase in primary clay mineral abundance (from 9% to 22%) coincident with global cooling 13.9 Myrs ago points to a shift in the weathering regime given that the clay provenance did not change dramatically. Relatively weaker chemical weathering intensity during the mid and late Miocene cooling suggests increased aridity and changes in the large scale atmospheric circulation in the SAM domain. The establishment of the dry winter monsoon season during the mid and late Miocene may have caused this shift in the weathering regime and can reconcile much of the contrasting evidence for SAM initiation.
Highlights
The collision of India with the Eurasian plate and the subsequent uplift of the Himalayas and Tibetan Plateau (HTP) have been implicated in the development of the Asian monsoon system (Molnar et al, 1993) and the consequent increased drawdown of atmospheric CO2 through enhanced silicate weathering or organic carbon burial (France-Lanord & Derry, 1997; Raymo & Ruddiman, 1992)
The development of the South Asian monsoon (SAM) and Himalaya-Tibetan Plateau uplift were closely intertwined with some studies suggesting that uplift initiated the monsoon whereas others link tectonics with monsoon-controlled exhumation
A reduction of atmospheric CO2 associated with HTP uplift has been invoked as a cause of major global cooling and establishment of permanent Antarctic ice sheets that characterized the transition from the Cenozoic greenhouse to the present icehouse climate (Raymo & Ruddiman, 1992)
Summary
The collision of India with the Eurasian plate and the subsequent uplift of the Himalayas and Tibetan Plateau (HTP) have been implicated in the development of the Asian monsoon system (Molnar et al, 1993) and the consequent increased drawdown of atmospheric CO2 through enhanced silicate weathering or organic carbon burial (France-Lanord & Derry, 1997; Raymo & Ruddiman, 1992). The development of the monsoon has even been suggested to have itself influenced HTP tectonics by increased erosion and exhumation (e.g., Clift et al, 2008; Harris, 2007; Iaffaldano et al, 2011). The orographic insulation caused by the Himalayas is thought to have been an important driver of monsoon evolution (Boos & Kuang, 2010) but our understanding of the interaction of tectonics, monsoon-driven erosion, silicate weathering and global
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