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(粪便)，堆积在洞穴的地面上。随着时间的推移，这些沉积物的厚度可以增加到许多米，同时，这些沉积物记录了洞穴外环境(植被和气候)的一系列变化。对这些沉积物进行了三年的研究表明，通过分析鸟粪的化学成分(有机、无机和稳定同位素)并鉴定鸟粪中也含有的花粉，有可能获得过去数万年来洞穴周围环境变化的记录。例如，在婆罗洲的尼亚洞，在过去的10万年里积累了7米的鸟粪，对沉积物的分析表明，在上一个冰河时代，气候比现在更干燥，适应更干燥空调的植被占据了洞穴周围的区域，与今天洞穴周围的潮湿热带雨林形成了鲜明对比。该项目将汇集地球化学、孢粉学和考古学的专业知识，以进一步开发技术，最终将其应用于热带地区的类似矿床。该项目还将开始开发马来西亚半岛、印度尼西亚和菲律宾的海鸟粪记录网络。在上一个冰河时代(20000年前)，全球海平面比今天低约120米，印度尼西亚的几个大岛与马来西亚半岛相连，形成了一个相当于欧洲大小的大陆，被称为孙达兰。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炎热的浅海的表面积来潜在地对全球气候产生如此大的影响，而炎热的浅海在一定程度上推动了大气循环。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了两岛之间的大陆桥，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，在至少40,000年前到达澳大拉西亚和婆罗洲的尼亚洞。关于上一个冰期孙达兰的植被和气候的信息非常少，马来西亚或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专注于提高我们对孙达兰环境历史的了解。一些模型预测，热带雨林比亚马逊的热带雨林更大，从东到西完全覆盖了赤道的孙达兰。与之形成鲜明对比的是，其他模型预测，在婆罗洲和苏门答腊岛，热带雨林会缩小到孤立的区域，而热带草原和林地则会扩张到非洲大陆的大部分其他地区。因此，从上一次冰期期间Sundaland陆地环境的海鸟粪记录中获得更多观测数据，将提高我们对过去全球气候变化的理解和建模，并提供有关早期人类和其他动物为了在这一生物地理学重要区域生存和迁徙而遇到并不得不适应的冰期环境的重要信息。

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.