Hydroclimate of the western Indo-Pacific Warm Pool during the past 24,000 years

North Atlantic cooling triggered a zonal mode over the Indian Ocean during Heinrich Stadial 1

Abrupt changes in the Atlantic meridional overturning circulation (AMOC) are thought to affect tropical hydroclimate through adjustment of the latitudinal position of the intertropical convergence zone (ITCZ). Heinrich Stadial 1 (HS1) involves the largest AMOC reduction in recent geological time; however, over the tropical Indian Ocean (IO), proxy records suggest zonal anomalies featuring intense, widespread drought in tropical East Africa versus generally wet but heterogeneous conditions in the Maritime Continent. Here, we synthesize proxy data and an isotope-enabled transient deglacial simulation and show that the southward ITCZ shift over the eastern IO during HS1 strengthens IO Walker circulation, triggering an east-west precipitation dipole across the basin. This dipole reverses the zonal precipitation anomalies caused by the exposed Sunda and Sahul shelves due to glacial lower sea level. Our study illustrates how zonal modes of atmosphere-ocean circulation can amplify or reverse global climate anomalies, highlighting their importance for future climate change.

Seasonality of the altitude effect on leaf wax n-alkane distributions, hydrogen and carbon isotopes along an arid transect in the Qinling Mountains

Reconstructing paleoelevation allows the temporal evolution of biogeochemical processes and hydroclimate regimes to be understood and quantified. A dual-isotope biomarker of clumped hydrogen and carbon isotopes of leaf wax n-alkanes was recently proposed in humid tropical forests, and it was proven to be superior to a single-isotope proxy that was previously reported. However, it remains unknown whether the dual-isotope biomarker is suitable in arid conditions. The present study investigated leaf wax n-alkane distribution, hydrogen (δ²H_wax) and carbon (δ¹³C_wax) isotopes in terrestrial plants along an arid mountainous transect. We found that the effects of seasonality on n-alkane distribution, δ²H_wax and δ¹³C_wax were minimal for all species (p > 0.05), and that species-specific δ²H_wax values remained almost unchanged for most species, in contrast to δ¹³C_wax values. Significant correlations between altitude and δ²H_wax values (R² = 0.54, 0.58, and 0.75 for spring, summer, and autumn, respectively), instead of δ¹³C_wax values (R² = 0.08, 0.43, and 0.12 with p = 0.24, 0.01, and 0.19 for spring, summer, and autumn, respectively), were observed, suggesting that δ²H_wax values, but not δ¹³C_wax values, can be reliably used as a proxy for reconstructing paleoelevation in arid conditions. Therefore, it will be necessary to identify other proxies to supplement δ²H_wax values under a dual-isotope approach in future research.

Hydrogen isotope fractionation variations of n-alkanes and fatty acids in algae and submerged plants from Tibetan Plateau lakes: Implications for palaeoclimatic reconstruction

The hydrogen isotope compositions (δD) of n-alkanes and fatty acids (FAs) are widely applied in palaeoclimatic reconstructions, and the determinations of their hydrogen isotope fractionation factor values (ε) are vital for quantitatively reconstructing past precipitation variations. Currently, studies on n-alkane and FA ε values focus on terrestrial plants, which, however, show large uncertainties because of the influence of evapotranspiration. Therefore, in this study, we analysed the ε values of algae and submerged plants immersed in lakes, which are not affected by evapotranspiration, to understand the hydrogen isotope fractionation of plant lipid synthesis. By investigating the δD values of lipids (n-alkanes and FAs) in algae and submerged plants and the δD values of co-existing water (including lake bottom water, surface sediment water, and leaf water of algae and submerged plants) from five Tibetan Plateau lakes, we find that the n-alkane ε values of algae and submerged plants show narrow changes, ranging from -176 to -159‰ and -167 to -142‰, respectively. The FA ε values of algae and submerged plants also show small variations, ranging from -160 to -121‰ (except Chara) and -161 to -138‰, respectively. Therefore, the average biosynthetic hydrogen isotope fractionation of these plants is -162‰ for n-alkanes and -145‰ for FAs, and the small ε differences between FAs and n-alkanes can be related to the different magnitudes of FA utilization in n-alkane synthesis. Finally, we find that the biosynthetic hydrogen isotope fractionation factors of aquatic plants are close to those of terrestrial grasses but slightly more negative than those of terrestrial woody plants. Thus, our results are helpful for understanding the hydrogen isotope fractionation variations in terrestrial plant lipids, which is beneficial for palaeohydrological reconstructions.

Glacial changes in tropical climate amplified by the Indian Ocean

The mechanisms driving glacial-interglacial changes in the climate of the Indo-Pacific warm pool are poorly understood. Here, we address this question by combining paleoclimate proxies with model simulations of the Last Glacial Maximum climate. We find evidence of two mechanisms explaining key patterns of ocean cooling and rainfall change interpreted from proxy data. Exposure of the Sahul shelf excites a positive ocean-atmosphere feedback involving a stronger surface temperature gradient along the equatorial Indian Ocean and a weaker Walker circulation-a response explaining the drier/wetter dipole across the basin. Northern Hemisphere cooling by ice sheet albedo drives a monsoonal retreat across Africa and the Arabian Peninsula-a response that triggers a weakening of the Indian monsoon via cooling of the Arabian Sea and associated reductions in moisture supply. These results demonstrate the importance of air-sea interactions in the Indian Ocean, amplifying externally forced climate changes over a large part of the tropics.

Late Holocene slowdown of the Indian Ocean Walker circulation

Changes in tropical zonal atmospheric (Walker) circulation induce shifts in rainfall patterns along with devastating floods and severe droughts that dramatically impact the lives of millions of people. Historical records and observations of the Walker circulation over the 20th century disagree on the sign of change and therefore, longer climate records are necessary to better project tropical circulation changes in response to global warming. Here we examine proxies for thermocline depth and rainfall in the eastern tropical Indian Ocean during the globally colder Last Glacial Maximum (19-23 thousand years ago) and for the past 3000 years. We show that increased thermocline depth and rainfall indicate a stronger-than-today Walker circulation during the Last Glacial Maximum, which is supported by an ensemble of climate simulations. Our findings underscore the sensitivity of tropical circulation to temperature change and provide evidence for a further weakening of the Walker circulation in response to greenhouse warming.

The Centipede Genus Scolopendra in Mainland Southeast Asia: Molecular Phylogenetics, Geometric Morphometrics and External Morphology as Tools for Species Delimitation

Seven Scolopendra species from the Southeast Asian mainland delimited based on standard external morphological characters represent monophyletic groups in phylogenetic trees inferred from concatenated sequences of three gene fragments (cytochrome c oxidase subunit 1, 16S rRNA and 28S rRNA) using Maximum likelihood and Bayesian inference. Geometric morphometric description of shape variation in the cephalic plate, forcipular coxosternite, and tergite of the ultimate leg-bearing segment provides additional criteria for distinguishing species. Colouration patterns in some Scolopendra species show a high degree of fit to phylogenetic trees at the population level. The most densely sampled species, Scolopendra dehaani Brandt, 1840, has three subclades with allopatric distributions in mainland SE Asia. The molecular phylogeny of S. pinguis Pocock, 1891, indicated ontogenetic colour variation among its populations. The taxonomic validation of S. dawydoffi Kronmüller, 2012, S. japonica Koch, 1878, and S. dehaani Brandt, 1840, each a former subspecies of S. subspinipes Leach, 1814 sensu Lewis, 2010, as full species was supported by molecular information and additional morphological data. Species delimitation in these taxonomically challenging animals is facilitated by an integrative approach that draws on both morphology and molecular phylogeny.