Pacific Rainfall over Millennial Scales (PROMS)

热带南太平洋（TSP）是一个广阔的海洋区域，包含5000多个小岛，支撑着约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能会通过干旱和洪水造成破坏性和代价高昂的社会影响，历史证据表明岛屿废弃和人口迁移。在TSP中，在5700个孤立的太平洋岛屿上，超过1000万人和敏感的生态系统依赖于南太平洋辐合带（SPCZ）产生的对流过程的降雨，它是南半球最大的辐合带，影响区域、半球和全球气候，反过来又受到ENSO和其他远程气候变率模式的影响。SPCZ的运动和强度收敛导致降水量的季节性、年际和长期变化，这些变化与严重干旱、飓风路径有关，从而影响太平洋岛国实现可持续发展目标的能力，并在过去推动了大规模人类迁移。人们认为，持续的降雨量减少是一些环礁岛被遗弃和决定向东迁移到太平洋的原因。在其他岛屿，降雨量的变化导致了不同类型农业系统的发展。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代理人和档案，以产生高分辨率，连续记录。根据沉积物或石笋重建的降水量代用指标仅限于SPCZ的边缘地区，并且时间序列也很短（<600年）或有间隙。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、太平洋其余地区和南大洋。但我们用来检验理论或验证GCM的数据相对较短（<100年）。为了解决数据的缺乏，并创造一个步骤的变化，在我们的理解的过程中，通过外部模式的气候变率，我们将产生新的网络的高分辨率（10- 50年）的定量降水记录从整个SPCZ区域，将捕捉其运动和强度变化超过3500年期间，当我们知道发生了大的变化。我们将利用新的多代理合成的古气候记录的候选模式的变化，如年代际太平洋涛动（IPO）和大西洋年代际变率（AMV）和南方急流指数（SAM）重建，以测试它们的关系SPCZ降雨。使用全球气候/环流模型，我们将运行一套实验，使用气候变率模式的合理情景，无论是孤立的，还是相互结合，并通过现有的和新的代理数据。这些实验将使我们能够了解不同模式的气候变率驱动SPCZ降雨的过程，从而对不同过去和未来气候变率模式下可能发生的十年尺度SPCZ变化产生根本性的新认识。我们现在能够实现这项研究，是因为目前在SPCZ和热带南太平洋（Sear，Sachs，Langdon，拉德，Croudace）领导定量水文气候重建的团队与目前在一系列时间尺度（季节-数十年）上领导SPCZ的机械理解和建模的团队（Joshi，马修斯，Roberts，Brown，奥斯本）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).