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

Lead Research Organisation: University of Bristol
Department Name: Chemistry


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 stabble-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 Sundalan. 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.


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Wurster CM (2010) Forest contraction in north equatorial Southeast Asia during the Last Glacial Period. in Proceedings of the National Academy of Sciences of the United States of America

Description The main aims and objectives of the project were to investigate whether sea loch sediments could be successfully age-dated using optically stimulated luminesence techniques. If successful, this methodology could provide long sedimentary archives of sea lochs and their climate signals. Our preliminary data arising from the project, based on a comprison with radiocarbon dated core, is that older sedimentary horizons can be successfully dated.
Exploitation Route The application of OSL dating to these kinds of environments and the methods used to detect bleaching are of interest to the wider luminesnce community, and to geochrnologists in general. The ability to date sea loch sediments is also of interest to any marine geoscientists who work with climate records of sea lochs.
Sectors Environment

Description Luminescence dating work on Loch Sunart has been included in GeoBus outreach activities, which are developed and delivered to secondary schools around Scotland.
First Year Of Impact 2015
Sector Education
Impact Types Societal