DOI: 10.25921/nqzs-ke30
title: NOAA/WDS Paleoclimatology - Indonesian Vegetation and d13C Fatty Acids Data over the Past 25,000 Years

description: The hydrologic response to climate forcing in the Indo-Pacific warm pool region has varied spatially over the past 25,000 years. For example, drier conditions are inferred,on Java and Borneo for the period following the end of,the Last Glacial Maximum, whereas wetter conditions are reconstructed for northwest Australia. The response of vegetation to these past rainfall variations is poorly constrained. Using a suite of 30 surface marine sediment samples from throughout the Indo-Pacific warm pool, we demonstrate that today the stable isotopic composition of vascular plant fatty acids (d13CFA) reflects the regional vegetation composition. This in turn is controlled by the seasonality of rainfall consistent with dry season water stress. Applying this proxy in a sediment core from offshore northeast Borneo, we show broadly similar vegetation cover during the Last Glacial Maximum and the Holocene, suggesting that, despite generally drier glacial conditions, there was no pronounced dry season. In contrast, d13CFA and pollen data from a core off the coast of Sumba indicate an expansion of C4 herbs during the most recent glaciation, implying enhanced aridity and water stress during the dry season. Holocene  vegetation trends are also consistent with a response to dry season water stress. We therefore conclude that vegetation in tropical monsoon regions is susceptible to increases in water stress arising from an enhanced seasonality of rainfall, as has occurred in past decades.
description: The data set contains fatty acids d13C data and pollen data from 3 cores from the Indo-Pacific Warm Pool covering the last 30 kyr.

Methods: 5_-10 g of sediments were freeze-dried and homogenized before lipid extraction using a microwave-assisted reaction system (MARS). Fatty acids were isolated from the total lipid extract by aminopropyl-silica-gel column chromatography, methylated with methanol of known isotopic composition, and then further purified by aminopropyl-silica-gel chromatography and silver nitrate-silica-gel chromatography. Fatty acid methyl esters were analysed in triplicate for their carbon isotopic composition by means of gas chromatography-isotope ratio monitoring-mass spectrometry (GC-IR-MS) at the Woods Hole Oceanographic Institution. All _13C values were normalized to the Vienna Pee Dee Belemnite (VPDB) scale using multiple pulses of CO2 reference gas. The average standard deviation of replicate measurements was 0.19‰.
Measurements were corrected for the added methyl group on the basis of isotopic mass balance.

For palynological processing 5.3_-7.5ml of sediment were suspended in approximately 40 ml of tetra-sodium-pyrophosphate (_±10%), sieved over 200 and
7 micrometer screens. Following hydrochloric acid (10%) treatment, heavy liquid separation (sodium-polytungstate, SG 2.0, 20 min at 2,000 rpm, twice), acetolyis
and sodium carbonate (20%) treatment, the resulting organic residues were mounted in glycerol and slides sealed with para_n wax. Palynological slides were
counted along evenly spaced transects until a minimum count of 100 dryland rainforest pollen grains was reached. All percentage values presented here are based on the total dryland pollen sum made up of all terrestrial pollen grains counted (that is, excluding mangrove pollen and pteridophyta spores). This
pollen sum varied between 322 and 964, with an average of 527 pollen grains. Pollen taxa were placed into ecological groups according to where they most
commonly occur.