INTENSE WARMING ON HIGHLAND SUMATRA DURING THE MID HOLOCENE SEA-LEVEL HIGHSTAND

Summary The Indo-Pacific Warm Pool (IPWP) climate and related monsoon systems directly affect approximately half the global population, and knowing their past behaviour is crucial for the understanding of our climate system and potential future change. However, few terrestrial proxy records exist in the tropics to resolve the details of IPWP climate variability. Here we present a 12,200-year record from a peatland situated in the western IPWP region situated at 1500m altitude in highland Sumatra, a region with high influence from the Indian Ocean. We use branched glycerol dialkyl glycerol tetraethers (brGDGTs), bulk and compound-specific stable isotopes, Fourier-Transform Infrared (FTIR) analysis, carbon accumulation rate and long-chain alkane distributions, augmented by pollen and geochemical (XRF) analysis, to reconstruct past temperature, precipitation and environmental changes. We find that not only the Younger Dryas, but also the early Holocene was still cold and affected by a greater ENSO variability. Around 8 ka BP the climate started to warm considerably, ENSO was reduced and temperatures were as much as 3˚C warmer than today around 5 ka BP. This was followed by a temperature decrease with an abrupt shift to colder temperatures and greater influence of El Nino after 3ka BP.