Paleoenvironmental change and hominid migration in Australasia: a novel mulitproxy stalagmite biomarker approach

One of the major problems in understanding how early humans interacted with and were affected by their environments is finding accurately dated records that let us look both at how climates changed and how plants and ecosystems responded. This work will use new chemical records preserved in stalagmites to help understand how the environment of the Indonesian region has changed over the past 50 thousand years, and how these changes impacted on early humans in the area. We are particularly interested in whether climatic changes were involved in the extinction of Homo floresiensis (the Flores 'hobbit'). Stalagmites are mound-shaped deposits which grow where calcite-laden drip waters fall onto a cave floor. When a drop of water lands on a stalagmite, it deposits not only a thin film of calcite, but also other chemical signals carried down from the soil above. These include isotopes of oxygen recording climate and rainfall, trace minerals telling of the patterns of past seasons, and organic matter reflecting everything from major changes in the overlying vegetation to how soil microbes are causing wood and plant matter to decay. Stalagmites grow upwards, layer by layer, so when cut vertically, an axis through time becomes visible. The calcite is readily dated using radioactive isotopes, so by sampling along this axis, we can recover the entombed chemical signatures, and build up a record of how the world above has changed through time. The most important thing about stalagmites is that because we can recover independent records of both climate and vegetation change from a single sample, they offer a very useful way to investigate how environments respond to climatic changes, without needing to match separately dated records from lots of different contexts. The Indonesian region is very important to Earth's climate, as three major parts of the global climatic system including El Nino and the Australian Monsoon converge there and the region is a major driver for two improtant circulation systems. The area also has a long and diverse human history, with Homo erectus arriving in Java between 1.9 and 1.2 million years ago, and reaching Flores by 800,000 years ago. Early modern humans (Homo sapiens) arrived approximately 60,000 - 40,000 years ago, and the area recently came to prominence again with the discovery of Homo floresiensis. Current evidence shows that these dwarfed hominids were present on Flores from before 95,000 years ago until at least 12,000 years ago, when they went extinct. The cause of their extinction is not yet known, but may have been due to climatic change, a major volcanic eruption, the arrival of modern humans in the area, or a combination of all three. The focus of our work will be answering three major questions: 1) how climate variation affected vegetation regimes, particularly with reference to switches between forest and savannah vegetation - this is an important issue because substantial vegetation changes would impact heavily on how hominid groups foraged and moved around the area; 2) how we can tell the difference between human management of the environment and climatically driven events; and 3) whether the extinction of Homo floresiensis coincided with substantial environmental change. In particular by creating longer term records, we will identify other climatic and environmental events that the floresiensis population successfully lived through, which will help anthropologists understand what additional tipping points may have been needed to trigger extinction.