A stalagmite record of abrupt climate change and possible Westerlies-derived atmospheric precipitation during the Penultimate Glacial Maximum in northern China

The geochemistry and petrography of a stalagmite from Wanxiang Cave in central China provide a paleoclimate record of the Penultimate Glacial Maximum (PGM) suggesting unexpectedly abundant non-monsoonal atmospheric precipitation at the nadir of the PGM. Eleven U-Th (²³⁰Th) ages from 149 to 140ka BP place the stalagmite in Marine Isotope Stage 6b, coincident with the greatest benthic marine δ¹⁸O_calcite values of MIS 6. Carbon and oxygen stable isotope data, measurements of layer-specific width, positions of surfaces of non-deposition or dissolution, changes in the character and thickness of seemingly annual layers, changes in concentration of organic acids within the stalagmite's calcite, and patterns in the Mg concentration of that calcite all combine to give a coherent paleoclimate record. These data suggest that the stalagmite represents a wetter period than before or after its growth, with the wettest and coldest phase at 145 to 144ka BP. This extreme in climate yields a striking correlation with the LR04 stack of oxygen isotope records from marine benthic forams, if the latter is subjected to a 4500-year chronological adjustment previously suggested by U-Th data from corals. The timing of the Wudu stalagmite's deposition combines with findings elsewhere to suggest that the PGM was the most extreme of later Pleistocene glacial maxima. Petrography and U-Th age determinations suggest dramatic changes in climate during the PGM. At the beginning (149-146. ka BP) and end (143-140. ka BP) of the stalagmite's growth, abrupt (century-scale) drying caused lengthy hiatuses as dripwater to the stalagmite diminished. On the other hand, delivery of water to the stalagmite during the wettest phase (145-144. ka BP) caused dissolution of previous layers of the stalagmite.Enhanced atmospheric precipitation during the cold of a glacial maximum is unexpected because, within the spectrum of Holocene climate, cooler conditions lessen the impact of the East Asian monsoon. Changes in the character of stalagmite layers indeed suggest weakened to negligible influence of the East Asian monsoon during the nadir of the PGM. However, data from the stalagmite are compatible with atmospheric precipitation from westerly winds that today reach only northwestern China but that may have been deflected southward in the PGM by southward migration of the Siberian High. This unexpected significance of the Westerlies during the PGM may be a result of the hypothesized extreme nature of the PGM relative to other glacial maxima of the later Pleistocene.