Synchronous glacier recession on the southeastern Tibetan Plateau and in Southern Hemisphere mid-latitudes during the last deglaciation: a 10Be moraine chronology from the Hengduan Shan

Establishing precise and accurate chronologies of mountain glacier fluctuations between the polar hemispheres can help test proposed hypotheses for millennial-scale climate changes during the last glaciation and the last glacial termination. Here, we address the relative phasing of millennial-scale glacier fluctuations by comparing glacier chronologies along an interhemispheric Australasian transect. We present a 10 Be surface-exposure chronology comprised of 78 new exposure ages and a model-based equilibrium line altitude (ELA) reconstruction targeting glacial landforms deposited during and since the last glacial period in the Hengduan Shan of the humid southeastern Tibetan Plateau (SETP), Sichuan Province, China (30°N, 100°E). Our moraine chronology shows that glaciers achieved maximal extents perhaps as early as Marine Isotope Stage (MIS) 6 and MIS 4. Moraines were constructed during the classic Last Glacial Maximum (LGM) during MIS 2 at 22,800 ± 230 (660) yrs ago (arithmetic mean ± standard error, with external uncertainty given in parentheses), 21,300 ± 310 (660) yrs ago, 21,340 ± 630 (850) yrs ago, and 19,480 ± 350 (630) yrs ago. A sequence of moraines and glacially transported boulders record net ice recession from LGM-to-Holocene extents and afford ages of 16,860 ± 90 (460) yrs ago, 16,160 ± 110 (450) yrs ago, 14,510 ± 110 (410) yrs ago, 14,010 ± 160 (410) yrs ago, 11,430 ± 120 (330) yrs ago, and 10,880 ± 50 (300) yrs ago. An ELA difference (ΔELA) of 500 ± 25 m below the modern value was required to maintain modeled glacier margins at LGM moraines. The subsequent recession to late-Holocene limits corresponded to an overall ELA increase of 400 ± 25 m, equating to a temperature rise of ∼2.2 ± 0.15 °C. Comparison to mountain glacier chronologies in the Southern Alps of New Zealand, on the opposite end of the Australasian transect, indicates that the signature of the last glacial termination as documented here from the SETP resembles that of Southern Hemisphere mid-latitude glaciers. Glacier chronologies in both the SETP and in the Southern Alps record net ice recession during Heinrich Stadial 1, glacier stabilization and moraine construction during the Antarctic Cold Reversal, followed by subsequent recession to Holocene limits. The initial phase of SETP glacier retreat occurred during Heinrich Stadial 1 and corresponds to approximately two-thirds (67%) of the full-glacial to early-Holocene equilibrium line altitude (ELA) rise, or about 50% of the full-glacial to pre-industrial ELA rise. Correspondence among SETP and Southern Hemisphere mid-latitudes glacier chronologies indicates the operation of a mechanism capable of producing coeval climate changes on an interhemispheric basis. We suggest that changes in heat export from the Indo-Pacific Warm Pool afforded a proximal mechanism for driving glacier recession during the last termination in monsoonal High Mountain Asia and discuss implications for how this signal may have been transmitted more broadly in both polar hemispheres.