Cave guano - a new, unexploited terrestrial environmental proxy in the tropics.

许多热带洞穴居住着蝙蝠和鸟类，它们以洞穴周围的昆虫为食，产生大量的鸟粪（排泄物），堆积在洞穴的地板上。随着时间的推移，这些沉积物可以积累到几米厚，因为它们这样做，沉积物记录了洞穴外环境（植被和气候）变化的时间序列。对这些沉积物的三年研究表明，通过分析鸟粪的化学成分（有机、无机和稳定同位素）和鉴定鸟粪中含有的花粉，可以获得洞穴周围过去数万年来环境变化的记录。例如，在婆罗洲的尼亚洞穴，在过去10万年里积累了7米厚的鸟粪，对沉积物的分析表明，在最后一个冰河时代，气候比今天更干燥，洞穴周围的植被适应了更干燥的条件，与今天洞穴周围潮湿的热带雨林形成鲜明对比。该项目将汇集地球化学、孢粉学和考古学的专业知识，进一步发展这些技术，以便最终将其应用于整个热带地区的类似矿床。该项目还将开始建立一个马来西亚半岛、印度尼西亚和菲律宾鸟粪记录网络。在最后一个冰河时代（20，000年前），全球海平面比今天低约120米，印度尼西亚的大岛与马来西亚半岛相连，形成了一个与欧洲大小相当的大陆，称为孙达兰。没有其他热带地区的陆地和海洋的分布从冰河时代到现在发生了如此显著的变化，或者这些差异可能通过改变部分驱动大气环流的炎热浅海的表面积对全球气候产生如此大的影响。孙达兰也是陆地生物多样性的主要中心，因为海平面的变化一再淹没和暴露岛屿之间的陆桥，推动了生活在那里的生物的物种形成。智人也使用这些陆桥在50- 60 ka到达澳大拉西亚，至少在40，000年前到达尼亚洞穴（婆罗洲）。关于最后一个冰河时期孙达兰的植被和气候的信息非常少，马来西亚和菲律宾的信息完全没有，印度尼西亚的数据非常稀少，这就是为什么这个项目将重点放在提高我们对孙达兰环境历史的理解上。一些模型预测，热带雨林，比亚马逊雨林大，从东到西完全覆盖了赤道的孙达兰。与此形成鲜明对比的是，其他模型预测，雨林收缩到婆罗洲和苏门答腊岛的孤立地区，而稀树草原和林地则扩展到非洲大陆的大部分地区。因此，从鸟粪记录中获取更多关于最后一个冰河时期孙达兰陆地环境的观测数据，将提高我们对过去全球气候变化的理解和建模，并提供有关冰河时期环境的重要信息，早期人类和其他动物为了在这一重要的地理区域生存和迁移而不得不适应冰河时期环境。

Many tropical caves are inhabited by bats and birds that feed on insects in the area surrounding the cave, producing large quantities of guano (excrement) that accumulates on the floor of the cave. Over time these deposits can build up to many metres in thickness and as they do so the deposits record a time series of changes in the environment (vegetation and climate) outside the cave. Three years of studying these deposits has demonstrated that it is possible to obtain records of environmental change around the caves over the last several tens of thousands of year by analysing the chemistry (organic, inorganic and stable-isotopes) of the guano and by identifying the pollen that is also contained in the guano. At Niah Cave in Borneo, for example, seven metres of guano has built up over the last 100,000 years and analysis of the deposits has shown that during the last ice age the climate was drier than it is today, with vegetation adapted to drier conditioners occupying the region around the caves, in contrast to the wet tropical rainforest that occurs around the cave today. This project will bring together expertise from geochemistry, palynology and archaeology to further develop the techniques so that ultimately they can be applied to similar deposits throughout the tropics. The project will also begin to develop a network of guano records from Peninsular Malaysia, Indonesia and the Philippines. During the last ice age (20,000 years ago) global sea-level was ~120m lower than today and the large islands of Indonesia were joined to peninsular Malaysia to form a large landmass, about the size of Europe, known as Sundaland. There is no other tropical area where the distribution of land and sea changed so markedly from the ice-age to the present, or where these differences could potentially have had such large impacts on global climate, through changing the surface area of the hot shallow seas that in part drive atmospheric circulation. Sundaland is also a major centre for terrestial biodiversity as changes in sea-level have repeatedly drowned and exposed land bridges between the islands, driving speciation in the organisms that live there. Homo sapiens also used these land bridges arriving in Australasia by 50-60ka and at Niah Cave (Borneo) at least 40,000 years ago. There is very little information about the vegetation and climate of Sundaland during the last ice age, with no information available at all for Malaysia or the Philippines and very sparse data available for Indonesia, and this is why this project will focusing on improving our understanding of the environmental history of Sundaland. Some models predict that tropical rainforests, larger than those of the Amazon, completely covered equatorial Sundaland from east to west. In stark contrast, other models predict that rainforests contracted to isolated pockets in Borneo and Sumatra, while savannas and woodlands expanded over most of the rest of the continent. Acquiring more observational data from guano records about the terrestrial environments of Sundaland during the last ice-age will therefore improve our understanding and modelling of global climate changes in the past and provide vital information on the ice-age environments that early humans and other animals encountered and had to adapt to in order to survive in and migrate through this biogrographically important region.