Collaborative Research: NSFGEO-NERC: Solving the conundrum of the Miocene South Asian Monsoon.

The South Asian Monsoon is one of the most important atmospheric circulation systems. It determines the water resources of the planet's most densely inhabited places and directly influences more than one billion people. The South Asian Monsoon regions are undergoing active mountain building and display strong topographic relief.

The region experiences dramatic gradients in rainfall and ocean temperatures and productivity. The varying rainfall patterns may have global economic repercussions. Indeed, extreme climate events in recent years have had large social and economic impacts in the Himalayan regions and beyond.

Modeling predictions based only on instrumental date are unlikely to portray the entire spectrum of the South Asian Monsoon. To better understand modern variability and future changes in the system, long time series of past monsoonal activity are necessary. This project will reconstruct a high-resolution record of the South Asian Monsoon for the past 20 million years.

Modeling studies will help interpret those records. The project will support three graduate students (two at Louisiana State University and one at the University of Oklahoma) and a postdoc at Purdue University. The project will also support the PI’s participation in two outreach programs, the Baton Rouge Rainwater Program and a multi-school Outreach Activities program.

This is a project that is jointly funded by the National Science Foundation’s Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget.

Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with its own country.

The evolution of the South Asian Monsoon represents multi-sphere interactions involving the lithosphere (the uplift of Tibetan Plateau), atmosphere (monsoonal circulations), hydrosphere (hydrological cycle), and biosphere (e.g., C4-grassland expansion, and primary productivity). Understanding how the South Asian monsoon behaved, evolved, and, in turn, was modified by these different processes is key to understanding and quantifying how the monsoon will change in the future.

Decades of efforts have focused on characterizing its multifaceted character and revolutionized our knowledge by offering different perspectives to link the above phenomena. However, due to its complex nature, a vital issue arose. Proxy studies from the ocean and terrestrial records give opposing signals on whether the South Asian Monsoon strengthened or weakened during the Miocene.

In this project, a US-UK team will collaborate to resolve the conundrum. The project will combine state-of-the-art geochemical proxies and numerical modeling to unpack the processes and mechanisms behind the Miocene Asian monsoon perturbations. The project will establish an integrated record of the heterogeneous regional paleohydrology and the long-term histories of upwelling and primary productivity; it will then test the linkage between the above processes and potential driving forces using the high-resolution General Climate Model (GCM) and the updated HadCM3L simulations.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.