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The timing and mechanisms of past hydroclimate change in northeast Mexico are poorly constrained, limiting our ability to evaluate climate model performance. To address this, we present a multiproxy speleothem record of past hydroclimate variability spanning 62.5 to 5.1 ka from Tamaulipas, Mexico. Here we show a strong influence of Atlantic and Pacific sea surface temperatures on orbital and millennial scale precipitation changes in the region. Multiple proxies show no clear response to insolation forcing, but strong evidence for dry conditions during Heinrich Stadials. While these trends are consistent with other records from across Mesoamerica and the Caribbean, the relative importance of thermodynamic and dynamic controls in driving this response is debated. An isotope-enabled climate model shows that cool Atlantic SSTs and stronger easterlies drive a strong inter-basin sea surface temperature gradient and a southward shift in moisture convergence, causing drying in this region.

A major research question concerning global pelagic biodiversity remains unanswered: when did the apparent tropical biodiversity depression (i.e., bimodality of latitudinal diversity gradient [LDG]) begin? The bimodal LDG may be a consequence of recent ocean warming or of deep-time evolutionary speciation and extinction processes. Using rich fossil datasets of planktonic foraminifers, we show here that a unimodal (or only weakly bimodal) diversity gradient, with a plateau in the tropics, occurred during the last ice age and has since then developed into a bimodal gradient through species distribution shifts driven by postglacial ocean warming. The bimodal LDG likely emerged before the Anthropocene and industrialization, and perhaps ~15,000 y ago, indicating a strong environmental control of tropical diversity even before the start of anthropogenic warming. However, our model projections suggest that future anthropogenic warming further diminishes tropical pelagic diversity to a level not seen in millions of years. [ABSTRACT FROM AUTHOR]

Abstract: Speleothem records from the South Asian summer monsoon (SASM) region display variability in the ratio of 18O and 16O (δ18O) in calcium carbonate at orbital frequencies. The dominant mode of variability in many of these records reflects cycles of precession. There are several potential explanations for why SASM speleothem records show a strong precession signal, including changes in temperature, precipitation, and circulation. Here we use an Earth system model with water isotope tracers and water‐tagging capability to deconstruct the precession signal found in SASM speleothem records. Our results show that cycles of precession‐eccentricity produce changes in SASM intensity that correlate with local temperature, precipitation, and δ18O. However, neither the amount effect nor temperature differences are responsible for the majority of the SASM δ18O variability. Instead, changes in the relative moisture contributions from different source regions drive much of the SASM δ18O signal, with more nearby moisture sources during Northern Hemisphere summer at aphelion and more distant moisture sources during Northern Hemisphere summer at perihelion. Further, we find that evaporation amplifies the δ18O signal of soil water relative to that of precipitation, providing a better match with the SASM speleothem records. This work helps explain a significant portion of the long‐term variability found in SASM speleothem records. [ABSTRACT FROM AUTHOR]