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.

Speleothem oxygen isotope records from the Caribbean, Central, and North America reveal climatic controls that include orbital variation, deglacial forcing related to ocean circulation and ice sheet retreat, and the influence of local and remote sea surface temperature variations. Here, we review these records and the global climate teleconnections they suggest following the recent publication of the Speleothem Isotopes Synthesis and Analysis (SISAL) database. We find that low-latitude records generally reflect changes in precipitation, whereas higher latitude records are sensitive to temperature and moisture source variability. Tropical records suggest precipitation variability is forced by orbital precession and North Atlantic Ocean circulation driven changes in atmospheric convection on long timescales, and tropical sea surface temperature variations on short timescales. On millennial timescales, precipitation seasonality in southwestern North America is related to North Atlantic climate variability. Great Basin speleothem records are closely linked with changes in Northern Hemisphere summer insolation. Although speleothems have revealed these critical global climate teleconnections, the paucity of continuous records precludes our ability to investigate climate drivers from the whole of Central and North America for the Pleistocene through modern. This underscores the need to improve spatial and temporal coverage of speleothem records across this climatically variable region.Quaternary 2019, 2, 5 2 of 33 original authors. The challenges found while compiling such data are discussed in [1]. The database archives speleothem oxygen and carbon isotope data, detailed chronologic and analytical information, and important metadata for each cave site and speleothem such as bedrock geology, overburden thickness, and whether cave monitoring was conducted, among other pieces of information that are essential for working with and interpreting speleothem isotope records.Of the 376 records included in SISAL_v1, 42 are from cave sites in Central and North America and the Caribbean [2]. These records cover a vast region, spanning the tropics to mid-latitudes and bordering two oceans, with climate controls that are highly variable both in the modern and through time. Speleothem records from this region have revealed critical climate teleconnections between the polar regions, the tropics, and the mid-latitudes at decadal to orbital timescales [3][4][5][6]. These records have provided evidence for the effects of climate variability on ancient civilizations [7-9], and contributed toward open questions and key debates regarding Earth's climate system [3,10]. Here, we discuss the spatial and temporal coverage of North and Central American and Caribbean speleothem records included in SISAL_v1 and the predominant controls on δ 18 O spel variability in each region. We review the most salient discoveries arising from regional records included in SISAL_v1 and conduct a statistical analysis to underscore observed spatial relationships. O...

Speleothem oxygen isotope records from the Caribbean, Central, and North America reveal climatic controls that include orbital variation, deglacial forcing related to ocean circulation and ice sheet retreat, and the influence of local and remote sea surface temperature variations. Here, we review these records and the global climate teleconnections they suggest following the recent publication of the Speleothem Isotopes Synthesis and Analysis (SISAL) database. We find that low-latitude records generally reflect changes in precipitation, whereas higher latitude records are sensitive to temperature and moisture source variability. Tropical records suggest precipitation variability is forced by orbital precession and North Atlantic Ocean circulation driven changes in atmospheric convection on long timescales, and tropical sea surface temperature variations on short timescales. On millennial timescales, precipitation seasonality in southwestern North America is related to North Atlantic climate variability. Great Basin speleothem records are closely linked with changes in Northern Hemisphere summer insolation. Although speleothems have revealed these critical global climate teleconnections, the paucity of continuous records precludes our ability to investigate climate drivers from the whole of Central and North America for the Pleistocene through modern. This underscores the need to improve spatial and temporal coverage of speleothem records across this climatically variable region.

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 (δ13Ccarb) is complicated because multiple factors affect δ13Ccarb values 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 (δ13Corg) from 697 discrete nodules sampled from 119 different depths at the Jiaxian section, North Central China. Between 7.6 and 2.4 Ma, δ13Ccarb values increase by nearly 5‰, while δ13Corg values 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 C4 vegetation 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 δ13Ccarb values becoming higher and more variable to the N‐NW. Additionally, an independent index of monsoonal precipitation from a southern site corresponds to fluctuations in δ13Ccarb values at Jiaxian, while southern δ13Ccarb records 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 δ13Ccarb values being more sensitive to moisture availability under consistently more arid conditions to the NW.

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Earth's Critical Zone (CZ), the near‐surface layer where rock is weathered and landscapes co‐evolve with life, is profoundly influenced by the type of underlying bedrock. Previous studies employing the CZ framework have focused primarily on landscapes dominated by silicate rocks. However, carbonate rocks crop out on approximately 15% of Earth's ice‐free continental surface and provide important water resources and ecosystem services to ∼1.2 billion people. Unlike silicates, carbonate minerals weather congruently and have high solubilities and rapid dissolution kinetics, enabling the development of large, interconnected pore spaces and preferential flow paths that restructure the CZ. Here we review the state of knowledge of the carbonate CZ, exploring parameters that produce contrasts in the CZ in different carbonate settings and identifying important open questions about carbonate CZ processes. We introduce the concept of a carbonate‐silicate CZ spectrum and examine whether current conceptual models of the CZ, such as the conveyor model, can be applied to carbonate landscapes. We argue that, to advance beyond site‐specific understanding and develop a more general conceptual framework for the role of carbonates in the CZ, we need integrative studies spanning both the carbonate‐silicate spectrum and a range of carbonate settings.

<p>Ice core records from Greenland provide evidence for multiple abrupt warming events recurring at millennial time scales during the last glacial interval. Although climate transitions strongly resembling these Dansgaard-Oeschger (DO) transitions have been identified in several speleothem records, our understanding of the climate and ecosystem impacts of the Greenland warming events in lower latitudes remains incomplete.</p><p>Here, we investigate the influence of DO transitions on the global atmospheric circulation pattern. We comprehensively analyse d18O changes during DO transitions in a globally distributed dataset of speleothems (SISALv2; Comas-Bru et al., 2020). Speleothem d18O signals mostly reflect changes in precipitation amount and moisture source. Thereby this proxy allows us to infer spatially resolved changes in global atmospheric dynamics that are characteristically linked to DO transitions. We confirm the previously proposed shift of the Intertropical Convergence Zone towards more northerly positions. In addition, we find evidence for a similar northward shift of the westerly winds of the Northern Hemisphere. Furthermore, we identify a decreasing trend in the transition amplitudes with increasing distances from the North Atlantic region. This confirms previous suggestions of this region being the core and origin of these past abrupt climate changes.</p><p> </p><p>References:</p><p>Comas-Bru et al., 2020, Earth System Science Data 12, 2579–2606</p><p> </p>

The interannual variability of rainfall caused by the El Niño Southern Oscillation (ENSO) results in significant changes in hydrologic conditions that affect entire countries’ water supply. Forecasting ENSO and its impacts are mainly based on Central Pacific Sea surface temperature (SST) anomalies which satisfactorily correlates with timing and, to a lesser extent, the intensity of drought conditions in the Philippines and the rest of the Western Pacific during the El Niño phase. Changes in sea surface height (SSH) are also brought upon by ENSO through density changes with temperature and oceanographic processes. Here, we report that the associative nature of SSH and drought as measured by surface runoff, has a stronger correlation (r > 0.693, p < 0.05) in terms of the expected timing, with 1 to 3 months lag time, and intensity compared to using traditional ENSO SST indices from the Central Pacific. Furthermore, since SSH is co-located with its corresponding forecasted decrease in runoff, a localized prediction can be made which further increases the accuracy of this predictive tool. In the wake of a changing climate, this work demonstrates the possibility of statistically forecasting the timing of precipitation, and thus the volume of surface water availability, using local SSH as an indicator. A tool which is necessary for time-sensitive management decision making in drought-prone tropical regions.