Fig. 1.

The Delingha tree-ring δ¹⁸O record (red line) and normalized speleothem δ¹⁸O records collected from different parts of continental Asia spanning 5 ka to 3 ka. To place the 4.2-ka event in high-resolution and high-precision context, we constrained our analyses to speleothem records with coverage of 5 ka to 3 ka. A regional composite for southern China is shown, which is derived by averaging the six speleothem δ¹⁸O series from Dongge Cave, Xianglong Cave, Wuya Cave, Sanbao Cave 43, Heshang Cave, and Shennong Cave using the Z-score method. Each of the six speleothem records has a temporal resolution better than 20 y, at least five U-Th ages, and dating precision higher than the 60-y average age error (2σ) in the 5- to 3-ka interval. Prior to averaging, each of the six records is first linearly interpolated annually, and then their long-term linear trends in the common period 5 ka to 3 ka are removed to highlight climate fluctuations on multidecadal to centennial timescales before normalization. See ref. 6 for details about each stalagmite record employed in the calculation. The Liu-li Cave in northern China and Kesang Cave (KS06-A-H) in western China speleothem δ¹⁸O records are intentionally included for comparison in that both records have a dating point around 4.2 ka (6). The 100-point low-pass filters are shown for Kesang Cave (KS06-A-H), Liu-li Cave, and southern China records. The Shennong Cave and Mawmluh Cave (ML.1) speleothem δ¹⁸O records have biannual and subannual resolution, and, therefore, we plot their unsmoothed series for comparison. All horizontal lines represent the long-term average calculated over the common period 5 ka to 3 ka. The vertical dashed blue line indicates the Middle to Late Holocene transition as defined by the Delingha δ¹⁸O record via trend-point analysis (2). The gray bar covers the period 3.97 ka to 4.26 ka that is demonstrated as the 4.2-ka event in the midlatitudes of the Northern Hemisphere by the Iranian Gol-E-Zard speleothem record (4).