Exploring Environmental and Climatic Complexity between Sunda and Sahul: Insights from Wallacea using Multiproxy Speleothem and Lacustrine Records

The climatic and environmental history of Wallacea and the surrounding region is understudied. It is a region at the intersection of multiple global climate systems, with unique biodiversity, and a long and complex history of Hominin occupation. Yet many islands have no published palaeoenvironmental/palaeoclimatic archives, leaving their natural histories to be inferred from broad, regional climate interpretations. This thesis evaluates the records that do exist, their geographic and temporal extents and resolutions. A meta analysis of all existing records in AM shows a paucity of archives from Wallaceae—especially terrestrial records—compared with surrounding areas; temporal sample resolution decreases steeply with time; annually resolved records extend to only ~11,000 years ago; and the purported variability of the Holocene may be an artefact of sampling bias. To address this, the thesis sets out to analyse archives on the large islands of Timor and Seram. A 3 m pollen record from lake Nefona in Timor Barat was radiocarbon dated to ~2000 yr BP. It suggests a past, fluctuating between closed Syzygium rainforest and open Eucalypt savanna, interacting with fire and possibly influenced by human activity. Seven speleothems from Seram and one from Timor were analysed, adding two localities in the region to just eight published previously. Floating chronologies based on annual lamina were anchored using a series of 20 conventional U/Th dates, U/Th using laser ablation, 22 radiocarbon dates, and the 14C bomb pulse. Speleothems were dated to brief windows from MIS 4 through to the modern. Stable isotope and lamina growth rate analyses of these speleothems were conducted at annual resolution, providing insights into the hydrology of the region at times when no other annual resolution records were previously available. CS-μXRF was conducted on specimens, yielding trace elemental analyses as subannual resolution, allowing interpretation of the IASM during the last glacial, deglacial, and Holocene. The one specimen from Timor suggested conditions approximately 2600 years ago were similar to today, but with regular peaks in rainfall every 10–15 years, possibly due to a confluence between ENSO and IOD. Specimens from Seram reveal a complex relationship with the regional climate systems, including a change from year round rainfall (as it is today) to significantly seasonal rainfall, likely driven by the IASM, during somewhat drier times. Further, the apparent driest times in these records, around 10 and 64 ka, appear to have no seasonal pattern. That is, the Seram seems to have a monsoonal climate pattern when it is not very wet (as it is today) nor very dry. This monsoonal “sweet spot” seems to have existed during the last glacial in Seram except in the driest extremes when the IASM may have been entirely inactive.