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上自给自足的农民不需要说服他们气候变化正在发生。它们的生存依赖于它们能从菜园中收获什么，最近它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就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。这也是我去年探索巴布亚新几内亚洞穴寻找洞穴(洞穴沉积物，如石笋)的原因，这些洞穴沉积物将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。这一地区拥有地球上最温暖的海洋表面水域和最强烈的大气对流。西太平洋暖池通常被称为地球的热机，它是推动全球大气循环的大规模能量交换的场所。暖池的变化，例如它的温度或位置，可能会对全球气候产生深远的影响。我们每隔2到7年就会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，带走了大气对流的中心。1997-98年的厄尔尼诺事件是近代史上最极端的一次。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，超过40%的主要是农村人口遭受严重的粮食短缺。在热带的珊瑚礁上，比正常温度更高的海面温度导致了大规模的白化，导致世界上16%的珊瑚死亡。预测未来气候变异性的关键未知数之一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还与亚洲-澳大利亚季风环流相互作用，但这种关系既不一致，又鲜为人知。从印度、东南亚到澳大利亚，超过8亿人直接依赖于这些季风雨的稳定性和开始，预测它在变暖的世界中的表现也是至关重要的。随着季风系统在南北半球之间季节性地摆动，信风遇到了一个屏障--1600公里长的山峰链，高达5000米，构成了新几内亚的中心脊梁。当信风从西北转向东南部时，这就产生了很强的季节性--面对信风的斜坡经历了一个潮湿的季节，而相反的斜坡则处于雨影中。我从沿海山脉(Sarawaget山脉；6°S，147°E)收集了洞穴动物样本，那里在季风系统在南半球的西北信风季节接受降雨。这些样本是在海拔850米到3650米(可能是有史以来收集到的海拔最高的洞穴)的洞穴中采集的。洞穴由滴水中缓慢的方解石沉淀形成，记录了降雨量和洞穴上方环境的变化。正是这种降雨变化和植被响应的信号，我想用地球化学工具和树木年轮研究技术来研究。在我的博士学位中，我使用了来自大堡礁的珊瑚，展示了澳大利亚季风强度在过去370年里是如何变化的，以及它与ENSO关系的变化。有了NERC研究员，我将能够记录过去35,000年来ENSO和澳大利亚季风的变化，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.