Collaborative Research: Measurements and Modelling of the Indonesian Throughflow International Experiment (MINTIE)

The Indonesian Seas play a fundamental role in controlling the Earth's climate. They are located near the largest centers of atmospheric deep convection and represent the connection of the tropics to the global overturning circulation. In this area, Pacific Warm Pool waters are cooled and freshened forming a unique water mass that it can be traced across the Indian Ocean basin and beyond. Amongst other processes, tidally-driven mixing plays a critical role in this water mass transformation and impacts regional upwelling, sea surface temperature (SST) patterns and thus global climate. This project will be the US component of an international collaborative study, called MINTIE (Measuring and Modeling the INdonesian Throughflow International Experiment), developed for the understanding of the oceanic processes in the region. The international MINTIE observational effort is a novel combination of a 3-year deployment of a transport and water mass resolving mooring array within the major Indonesian Through Flow (ITF) passages. In addition, it includes simultaneous measurements of hydrography using profiling floats, turbulence dissipation and fine-scale shear in the interior seas, and ship-based detailed surveys in the straits. The moored array will be a joint effort between USA, China, and Indonesia, while the float array is a coordinated joint effort between USA, Australian, and Indonesia. The project, in addition to the in-situ measurements utilizes state-of-the-science numerical simulations and diagnostic tools to probe the drivers and dynamics of the Indonesian Through Flow. US graduate and undergraduate students will be supported by the project and trained in sea-going oceanography and cutting-edge numerical modelling. At the same time the students will be exposed to international scientific collaborations. Results and data will be broadly disseminated within and beyond the scientific community through targeted workshops, presentations at oceanographic meetings, and a web site. Insights and quantification of transport controls and mixing processes in this key region will have application in global modelling systems used for ocean and climate forecasts. The participation of US scientists in a collaborative international project maintains US scientific competitiveness. Indonesia, a principal partner, will provide ship time and logistical support; local students and early career scientists who will participate in the field program and analysis advancing an active ocean observing capability in that country. The float deployments will lay the groundwork for an ongoing regional Argo array, which to date has not been possible.

The highly successful INSTANT program, a multinational effort that involved the US and 5 more countries increased significantly our understanding of the Indonesian Through Flow (ITF) over 12 years ago. Since then, sparse ongoing observations and regional modelling studies have exposed our remaining knowledge gaps. We have little knowledge on how the interplay between the ITF, incoming remotely-forced wind-driven planetary wave energy and locally generated internal tidal waves and the mixing they produce impacts export heat and freshwater fluxes and SST. These issues will be addressed using more detailed observations of internal hydrography, mixing rates and Inflowing/outflowing heat and freshwater fluxes. In addition, since the end of INSTANT in 2006, a significant shift has occurred in the Indo-Pacific system, and likely also the ITF. The drivers of this shift remain unexplained. While INSTANT shed light on the mean transport and its variability, shear and dissipation observations were largely absent, water mass observations both in the straits and internal seas were sparse and large uncertainties in transport estimates limited inferences about mixing and transformation processes. The simultaneous observations of water mass and transport variability in inflow and outflow straits, provided by this project, along with hydrography, velocity fine-scale, and dissipation in the internal seas, will shed new light on how and where transformation occurs. These unprecedented observations will be combined with a tailored set of high resolution, tidally resolving and dynamically nested simulations and diagnostic tools that allow quantification of water mass transformation, isolation of drivers of flow and pathway variability and controls on SST.

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.