Collaborative Research: A new pathway of Indonesian Throughflow in the Indian Ocean: Mechanisms and role in transporting the excess heat and freshwater of the recent hiatus decade

The Indonesian Throughflow (ITF) is a key component of the global thermohaline circulation that affects the large-scale ocean circulation and global climate. During the recent hiatus decade (2003-2012) about two-thirds of the excess heat that entered Earth’s climate system was stored in the Indian Ocean. This project will address the ITF pathway patterns in the South Indian Ocean. The PIs propose a new pathway for heat flow in the Southeast Indian Ocean and will investigate its role in distributing the excess heat and freshwater that entered the South Indian Ocean from the ITF during the hiatus decade. An integral approach will be used that combines analyses of observational and reanalysis datasets with high-resolution ocean model experiments. These methods will be used to characterize the spatial and temporal structure of the flow pathway, investigate the forcing and processes that govern the pathways of ITF waters, and explore the roles of the different pathways in distributing heat and freshwater in the South Indian Ocean. The PIs hypothesize the existence of a flow pathway for waters from the ITF between the Southeast Indian Ocean and the subtropical South Indian Ocean, along which ITF waters spread to the western subtropical South Indian Ocean with a portion leaking to the Southern Ocean. They posit that this pathway was the major conduit for the enhanced ITF heat and freshwater transport of the recent global surface warming hiatus period. To test this observational data will be analyzed in combination with numerical model experiments. Observational data will include data from moorings, drifters, satellites, reanalysis products. Model data will include existing 1/10 degree simulations from Ocean General Circulation Models For the Earth Simulator and new 1/12 degree runs using HYCOM. The overall goals of the research are to explore the potential new pathway of ITF waters in the South Indian Ocean, investigate the governing mechanisms of this new pathway, and quantify its role in transporting the excess heat and fresher ITF waters during the recent hiatus period into the Greater Agulhas Current System of the subtropical Southwest Indian Ocean. The project focuses on the hiatus period 2003-2012 when a dramatic heat increase in the Indian Ocean due to enhanced ITF was observed. 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.