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

这一合作项目的总体目的是从KNI-51洞穴开发全新世印度-澳大利亚夏季风变化的高分辨率文石石笋记录，KNI-51洞穴位于印度-太平洋热带雨带(TRB)南缘，该地区以南半球和北半球夏季热带辐合带为边界。区域季风是低纬水文气候的主要组成部分，对包括太阳辐照度、ENSO以及火山和人为气溶胶在内的各种亚轨道强迫很敏感。热带社会和生态系统严重依赖季风降水，因此了解十年尺度水气候变率的起源和性质对于了解在这类系统中起作用的动力学至关重要。最近对印度-太平洋水气候的实地研究表明，在过去的1000年里，热带气候可能在小冰期(LIA)期间收缩，从而导致热带气候圈南北边缘的季风降水减少。相比之下，古水文和模拟研究表明，此时全球TRB向南移动，在TRB北部和南部边缘之间造成了降雨的反相位(干/湿)。研究人员从KNI-51洞穴中发展了一种亚十年分辨(~4年)的全新世晚期(最后3000年)的IASM重建，当与东南亚和海洋大陆的古季风记录相结合时，不仅揭示了LIA期间TRB的收缩，而且揭示了整个晚全新世数十年至百年时间尺度的扩张和收缩。该项目的具体研究目标是将KNI-51石笋记录延伸到全新世中期和早期(9000-3000年前)，以考察与全新世晚期不同的条件下TRB动力学的性质，包括南北半球夏季日照反差增大、海平面降低(以及印度-太平洋大陆架暴露增加)、大西洋经向翻转环流减少的间隔以及厄尔尼诺-南方涛动(ENSO)制度。为了更好地了解与TRB动力学有关的大气环流，这些替代数据将与耦合模式对比项目第五阶段/古气候模拟对比项目第三阶段(CMIP5/PMIP3)框架内进行的6000年时间切片模拟的气候动力学分析以及国家大气研究中心(NCAR)新提供的最后千年集合(LME)模拟相结合。该项目涉及对过去9000年TRB变率的独特看法的可能性，并对CMIP5级模式准确再现相关印度-太平洋大气动力学的能力进行了重要的测试。由于TRB与热带甲烷生产密切相关，这项研究将有助于改进对全新世期间区域热带甲烷通量的估计。这项研究将由本科生广泛参与，从而提供先进的古气候研究和数据分析技术方面的经验。

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.