Pacific Rainfall over Millennial Scales (PROMS)

热带南太平洋(TSP)是一片广阔的海洋区域，由5000多个小岛组成，养活着约1000万脆弱的人口，其中57%居住在距离海岸1公里的范围内。这些岛屿上的所有生命都依赖可靠的降水来提供淡水和粮食安全，这意味着降雨位置和强度的变化可通过干旱和洪水造成破坏性和代价高昂的社会影响，历史上有岛屿被遗弃和人口迁移的证据。在TSP中，5700个孤立的太平洋岛屿上的1000多万人和敏感的生态系统依赖于南太平洋辐合区(SPCZ)产生的对流过程产生的降雨，南太平洋辐合区是南半球最大的辐合区，它影响区域、半球和全球气候，进而受到ENSO和其他气候变异性远程模式的影响。SPCZ汇聚的移动和强度导致降水的季节性、年际和更长期的变化，这与严重的干旱、气旋路径导致影响太平洋岛国实现可持续发展目标的能力有关，并在过去推动了大规模的人类迁徙。在过去的1000年里，持续的低降雨期被认为是导致一些环礁岛屿被放弃并决定向东迁移到太平洋的原因之一。在其他岛屿，降雨的变化导致了不同风格的农业系统的发展。然而，与地球其他地区相比，TSP中有关过去降水变化的信息相对有限，部分原因是历史上缺乏合适的替代物和档案来产生高分辨率、连续的记录。从沉积物或石笋重建的降水代用仅限于SPCZ的边缘区域，而且也很短(&lt；600年)或在时间上存在差距。目前的证据表明，SPCZ/TSP降水的十年-百年变化与全球远程气候变率模式有关，特别是在大西洋、太平洋其他地区和南大洋，但我们用来检验理论或验证GCM的数据相对较短(&lt；100年)。为了解决缺乏数据的问题，并在我们对气候多变的外部模式在SPCZ产生变化的过程的理解方面产生阶段性变化，我们将生成来自整个SPCZ区域的高分辨率(10-50年)定量降水记录的新网络，它将捕捉到我们知道发生了巨大变化的3500年期间SPCZ的移动和强度变化。我们将利用新的古气候记录的多代理合成，以及重建候选变率模式，如年代际太平洋涛动(IPO)、大西洋十年变率(AMV)和南方急流指数(SAM)，以测试它们与SPCZ降雨量的关系。使用全球气候/环流模型，我们将使用气候变化模式的合理情景进行一系列实验，要么单独进行，要么相互结合，并由现有和新的代理数据提供信息。这些实验将使我们能够理解不同气候变率模式驱动SPCZ降雨的过程，从而从根本上重新理解在不同的过去和未来气候变率模式下可能发生的十年尺度的SPCZ变化。我们现在能够完成这项研究，是因为目前领导SPCZ和热带南太平洋定量水文气候重建的团队(Sear，Sachs，Langdon，Lade，Croudace)和目前在一系列时间尺度(季节性-数十年)上领导SPCZ的机械理解和建模的团队(Joshi，Matthews，Roberts，Brown，Osborne)之间的及时合作。

The Tropical South Pacific (TSP) is a vast area of ocean containing over 5000 small islands supporting a vulnerable human population of c.10 million of which 57% live within 1 km of the coast. All life on these islands depends on reliable precipitation for the provision of freshwater and food security, meaning that changes in the location and intensity of rainfall can result in damaging and costly societal impacts via droughts and flooding, with historical evidence of island abandonment and population migration.Within the TSP, over 10 million people and sensitive ecosystems on the 5700 isolated Pacific islands depend on rainfall from the convective processes generated in the South Pacific Convergence Zone (SPCZ), which is the largest convergence zone in the Southern Hemisphere, and influences regional, hemispheric and global climate, and in turn is influenced by ENSO and other remote modes of climate variability. Movement and strength of SPCZ convergence results in seasonal, interannual and longer term change in precipitation which are linked to severe droughts, cyclone paths resulting in impacts on Pacific island nations ability to meet Sustainable Development Goals, and in the past drove periods of mass human migration.In the last 1000 years, sustained periods of lower rainfall are thought to have contributed to the abandonment of some Atoll islands and the decision to migrate east into the Pacific. In other islands, changes in rainfall led to the development of different styles of agricultural system. However, compared to other parts of the earth, there is comparatively limited information about past precipitation changes in the TSP, in part because of a historical lack of suitable proxies and archives for producing high resolution, continuous records. Proxies for precipitation reconstructed from sediments or stalagmites are limited to marginal areas to the SPCZ and are also short (<600yrs) or have gaps in the timeseries.Current evidence indicates that decadal-centennial changes in SPCZ/TSP precipitation are linked to global modes of remote climate variability, particularly in the Atlantic, the rest of the Pacific, and the Southern Ocean, but our data to test theories or to validate GCMs is relatively short (<100 years). To address the lack of data and to create a step change in our understanding of the processes by which change is generated in the SPCZ by external modes of climate variability we will generate new network of high resolution (10-50yr) quantitative precipitation records from the whole SPCZ region that will capture its movement and change in strength over a 3500 period when we know large changes have occurred. We will utilise new multiproxy syntheses of palaeoclimate records alongside reconstructions of candidate modes of variability such as the Interdecadal Pacific Oscillation (IPO) and Atlantic Multidecadal Variability (AMV) and Southern jet stream index (SAM) to test for their relationship to SPCZ rainfall. Using a global climate/circulation model we will run a suite of experiments using plausible scenarios of modes of climate variability, either in isolation, or combined with each other, and informed by existing and new proxy data. These experiments will allow us to understand the processes by which different modes of climate variability drive SPCZ rainfall, and thus create fundamental new understanding of the decadal-scale SPCZ changes likely under different past and future modes of climate variability. We can achieve this research now due to the timely collaboration between the team currently leading quantitative hydroclimate reconstruction in the SPCZ and Tropical South Pacific (Sear, Sachs, Langdon, Ladd, Croudace), and the team currently leading the mechanistic understanding and modelling of the SPCZ over a range of time scales (seasonal - multidecadal) (Joshi, Matthews, Roberts, Brown, Osborn).