Collaborative Research: P2C2--Reconstructing Holocene Dynamics of the Indo-Pacific Tropical Rain Belt using Australian Stalagmites and Coupled Climate Models

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This collaborative project generally aims to develop a high resolution aragonite stalagmite record of Holocene Indo-Australian Summer Monsoon (IASM) variability from cave KNI-51, located at the southern margin of the Indo-Pacific tropical rain belt (TRB), a region bounded by the austral and boreal summer intertropical convergence zones. Regional monsoons represent the dominant component of low latitude hydroclimate and are sensitive to a wide array of sub-orbital forcings including solar irradiance, ENSO, and volcanic and anthropogenic aerosols. Tropical societies and ecosystems rely heavily on monsoon rainfall, and thus understanding the origin and nature of decadal-scale hydroclimate variability is critical to understanding the dynamics at play in such systems.Recent field studies of Indo-Pacific hydroclimate suggests that over the last millennium, the TRB may have contracted during the Little Ice Age (LIA) thereby producing reduced monsoon rainfall along both the northern and southern margins of the TRB. In contrast, paleohydrologic and modeling studies show that the global TRB shifted southward meridionally at this time, creating anti-phasing (dry/wet) of rainfall between the TRB northern and southern margins. The researchers have developed a sub-decadal resolved (~4 year) late Holocene (the last 3,000 years) IASM reconstruction from cave KNI-51 that, when integrated with paleomonsoon records from Southeast Asia and the Maritime Continent, reveal not only TRB contraction during the LIA, but expansion and contraction at multi-decadal to centennial time scales over the entirety of the late Holocene. The specific research goals of the project are to extend the KNI-51 stalagmite record through the middle and early Holocene (9,000-3,000 years ago) to examine the nature of TRB dynamics during conditions distinct from those of the late Holocene, including elevated contrasts between summer insolation in the Northern and Southern Hemispheres, lower eustatic sea level (and increased exposure of Indo-Pacific continental shelf), intervals of reduced Atlantic meridional overturning circulation, and the El Nino-Southern Oscillation (ENSO) regime. To better understand atmospheric circulation associated with TRB dynamics, these proxy data will be integrated with climate dynamical analyses of the 6,000 year time slice simulations conducted within the Coupled Model Intercomparison Project phase 5/Paleoclimate Modeling Intercomparison Project phase 3 (CMIP5/PMIP3) framework and with the newly available Last Millennium Ensemble (LME) simulations conducted by the National Center for Atmospheric Research (NCAR).The project involves the potential for a unique view of TRB variability over the last 9,000 years and provides an important test of the skill of CMIP5-class models to accurately reproduce associated Indo-Pacific atmospheric dynamics. As the TRB is closely tied to tropical methane production, this research will help refine estimates of regional tropical methane fluxes during the Holocene. The research will be conducted with extensive involvement of undergraduate students thereby providing experience in advanced paleoclimate research and data analysis techniques.