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Stalagmites being prepared for paleoclimate analysis should typically be slabbed along the central growth axis. This is an important first step because it allows for the highest resolution of sampling with minimal over- or under-sampling of the growth layers. Further, stable isotope ratios and trace element concentrations along the central growth axis most closely record climate variability. Choosing how to slab to best expose the central growth axis for geochemical sampling is challenging based on external morphology alone. High-resolution X-ray computed tomography (XRCT) can provide the ability to discern the internal growth morphology of stalagmites non-destructively, inexpensively, and rapidly. These data can inform selection of optimal slabbing plane(s) and can help identify locations for preliminary U-series dating. We develop a conceptual screening model to assess rapidly the internal morphologies of uncut stalagmites. The specifics of screening the internal morphologies through XRCT scans include investigating the internal porosity of the sample, the number and size of voids and hiatuses, and the presence and absence of growth layers and growth axes. We demonstrate that XRCT scans capture the migration of center of growth in uncut stalagmites of both simple and complex internal morphologies. XRCT scanning facilitates the investigation of stalagmites with complex internal growth banding, opening up avenues to work on such samples when stalagmites with simpler internal morphologies are not available. Further, screening stalagmites for paleoclimate reconstructions using XRCT improves the sustainability of speleothem science by helping researchers select which stalagmites should be returned to caves without destructive slabbing, thereby minimizing impact on caves. 

Between 5 and 4 thousand years ago, crippling megadroughts led to the disruption of ancient civilizations across parts of Africa and Asia, yet the extent of these climate extremes in mainland Southeast Asia (MSEA) has never been defined. This is despite archeological evidence showing a shift in human settlement patterns across the region during this period. We report evidence from stalagmite climate records indicating a major decrease of monsoon rainfall in MSEA during the mid- to late Holocene, coincident with African monsoon failure during the end of the Green Sahara. Through a set of modeling experiments, we show that reduced vegetation and increased dust loads during the Green Sahara termination shifted the Walker circulation eastward and cooled the Indian Ocean, causing a reduction in monsoon rainfall in MSEA. Our results indicate that vegetation-dust climate feedbacks from Sahara drying may have been the catalyst for societal shifts in MSEA via ocean-atmospheric teleconnections.

 

Paleosols preserved in the Red Clay depositional sequence of the Chinese Loess Plateau record information about vegetation and regional hydrology responses to global temperature variation throughout the late Miocene and Pliocene. Reconstructing spatial and temporal patterns of environmental change across the Loess Plateau from carbon isotopes of pedogenic carbonate (δ¹³C_carb) is complicated because multiple factors affect δ¹³C_carbvalues and higher resolution records do not exist along the northern margin of the Loess Plateau. To address these needs, we present paired carbon isotope records of pedogenic carbonate and occluded organic matter (δ¹³C_org) from 697 discrete nodules sampled from 119 different depths at the Jiaxian section, North Central China. Between 7.6 and 2.4 Ma, δ¹³C_carbvalues increase by nearly 5‰, while δ¹³C_orgvalues increase by 2.5‰. These increases are explained by a progressive decline in moisture availability through time, and there is no definitive evidence from these δ¹³C data for C₄vegetation at the Jiaxian site until after 3.6 Ma. Comparison of the Jiaxian record to other Loess Plateau sections reveals a consistent spatial gradient with δ¹³C_carbvalues becoming higher and more variable to the N‐NW. Additionally, an independent index of monsoonal precipitation from a southern site corresponds to fluctuations in δ¹³C_carbvalues at Jiaxian, while southern δ¹³C_carbrecords remain more stable. These spatial patterns are explained by a progressive decline in moisture availability across the Loess Plateau through the Late Miocene and Pliocene, with δ¹³C_carbvalues being more sensitive to moisture availability under consistently more arid conditions to the NW.