A high-resolution, 35,000-year record of the Australian monsoon and ENSO-variability as reconstructed from Papua New Guinea speleothems

巴布亚新几内亚偏远高地的自给农民不需要说服他们气候变化正在发生。他们的生存取决于他们能从花园里生产什么，最近他们已经能够在越来越高的海拔地区种植作物。巴布亚新几内亚高地是警告我们未来气候变化的行星金丝雀之一。这种对气候变化的敏感性是为什么巴布亚新几内亚是了解我们未来温室世界的关键地点。这也是为什么我去年在巴布亚新几内亚探索洞穴，寻找洞穴沉积物（洞穴沉积物，如石笋），以记录这一关键地区过去的气候变化。巴布亚新几内亚位于西太平洋暖池的中心。这个区域有着地球上最温暖的海洋表面沃茨和最强烈的大气对流。西太平洋暖池通常被称为地球的热力发动机，是推动全球大气环流的巨大能量交换的场所。暖池的变化，例如其温度或位置，可以对地球仪周围的气候产生深远的影响。我们每隔2到7年就能在厄尔尼诺事件中看到这种影响，当时西太平洋暖池向东移动，大气对流中心也随之移动。1997-98年的厄尔尼诺事件是近代历史上最极端的。它在秘鲁和厄瓜多尔造成了灾难性的洪水，在玻利维亚、巴西、印度尼西亚、新几内亚和澳大利亚造成了干旱。在巴布亚新几内亚，由于干旱、霜冻和森林火灾，40%以上的农村人口遭受严重的粮食短缺。在热带地区的珊瑚礁中，高于正常海面的温度导致了大规模的白化，杀死了世界上16%的珊瑚。预测未来气候变率的一个关键未知数是厄尔尼诺南方涛动（ENSO）现象和西太平洋暖池的背景状态将如何反应。ENSO也与亚洲-澳大利亚季风环流相互作用，但这种关系既不一致，也知之甚少。从印度、东南亚到澳大利亚的8亿多人直接依赖于这些季风降雨的稳定性和开始，预测它在一个更温暖的世界中的表现也至关重要。当季风系统在北方和南半球之间季节性地摆动时，信风遇到了一个障碍--1600公里长的山峰链，高达5000米，形成了新几内亚的中央脊柱。这就造成了强烈的季节性，因为信风从西北向东南摆动-面对信风的斜坡经历了雨季，而对面的斜坡则处于雨影中。我从一个沿海山脉（萨拉瓦吉特山脉;南纬6度，东经147度）收集了洞穴沉积物样本，当季风系统在南半球时，该山脉在西北信风季节降雨。这些样品是在海拔850米至3650米的洞穴中收集的（可能是有史以来收集到的海拔最高的洞穴沉积物）。洞穴沉积物是由滴水中缓慢的方解石沉淀形成的，记录了降雨和洞穴上方环境的变化。正是这种降雨量变化和植被反应的信号，我想用地球化学工具和树木年轮研究技术进行调查。在我的博士论文中，我用大堡礁的珊瑚来展示澳大利亚季风强度在过去370年中的变化，以及它与ENSO的变化关系。有了NERC奖学金，我将能够记录ENSO和澳大利亚季风在过去35,000年的变化，这将提高我们对它们将如何影响我们未来气候的理解。

Subsistence farmers in the remote highlands of Papua New Guinea need no convincing that climate change is occurring. Their survival depends on what they can produce from their gardens and recently they have been able to grow crops at higher and higher elevations. The Papua New Guinea highlands are one of the planetary canaries warning us of future climate change. This sensitivity to climate change is why Papua New Guinea is a key site for understanding our future greenhouse world. It is also why I explored caves in Papua New Guinea last year to look for speleothems (cave deposits such as stalagmites) that would capture a record of how climate in this critical region varied in the past. Papua New Guinea sits at the heart of the Western Pacific Warm Pool. This region has the warmest ocean surface waters and the most intense atmospheric convection on Earth. Often referred to as the Earth's heat engine, the Western Pacific Warm Pool is the site of massive energy exchange that drives global atmospheric circulation. A change in the warm pool, for example its temperature or position, can have profound effects on climate around the globe. We see this influence every 2 to 7 years in El Niño events, when the Western Pacific Warm Pool shifts eastward, taking the centre of atmospheric convection with it. The 1997-98 El Niño event was the most extreme in recent history. It caused catastrophic flooding in Peru and Ecuador, and drought in Bolivia, Brazil, Indonesia, New Guinea and Australia. In Papua New Guinea over 40% of the predominantly rural population suffered severe food shortage because of drought, frost and forest fires. At reefs across the tropics, warmer than normal sea surface temperatures caused mass bleaching, killing 16% of the world's coral. One of the key unknowns in predicting future climate variability is how the El Niño Southern Oscillation (ENSO) phenomenon and the background state of the Western Pacific Warm Pool will respond. ENSO also interacts with the Asian-Australian monsoon circulation, but the relationship is both inconsistent and poorly understood. With over 800 million people from across India, South-east Asia to Australia directly dependent on the stability and onset of these monsoonal rains, predicting how it will behave in a warmer world is also critical. As the monsoon system swings seasonally between the Northern and Southern Hemispheres, the trade winds run into a barrier - the 1600 km long mountain chain of peaks up to 5000m high that forms the central spine of New Guinea. This creates strong seasonality as the trade winds swing from NW to SE - the slopes facing the trade winds experience a wet season, while the opposite slopes are in a rain shadow. I have collected speleothem samples from a coastal mountain range (the Sarawaget Range; 6 deg.S, 147 deg.E), which receives rain during the NW trade wind season when the monsoon system is in the Southern Hemisphere. The samples were collected in caves at altitudes ranging from 850m to 3650m (possibly the highest elevation speleothems ever collected). Speleothems form by slow calcite precipitation from drip-water, recording changes in rainfall and the environment above the cave. It is this signal of rainfall variations and the vegetation response that I want to investigate with geochemical tools and tree-ring research techniques. For my PhD I used coral from the Great Barrier Reef to show how the Australian monsoon strength changed over the last 370 years, and its shifting relationship with ENSO. With a NERC fellowship I will be able to document changes in ENSO and the Australian monsoon over the last 35,000 years, which will improve our understanding of how they will impact our future climate.