THE TERMINATION PERIOD OF HEINRICH 2 EVENT RECORDED BY STALAGMITE IN INDIAN MONSOON DOMAIN

The Heinrich 2 (H2) Event is among one of the abrupt cold events, which is first recognized from the North Atlantic Ocean as an ice-rafted debris event during the Last Glacial Period. The detailed structure (e.g., timing, duration) under constraint chronology of this millennial scale climatic event can provide a better understanding of the underlying forcing mechanisms. However, up to now, there are only a few high-resolution and precisely-dated paleoclimate records across the H2 Event, which largely impedes our ability to understand its timing, structure and the potential forcing mechanisms. Here, we present a cave speleothem oxygen isotope (δ¹⁸O) record (stalagmite CHE-2, total length is 940 mm) from the Cherrapunji Cave (25°11'59“N, 92°27'11“E; 1100 m a.s.l.), Northeast India. This record has high resolution (259 oxygen isotope data, an average resolution of 8 years between 24.38 ka B. P. (before present, present=1950 A.D.) to 23.08 ka B. P. and 14 years for other period), and reconstruction of the Indian monsoon during H2 Event is constrained not only by 21 high-precision U-Th ages (average age uncertainty is ±60 years), additionally via annual fluorescent lamination counting (2701 annual bands, further supported by the U-Th ages) using the Laser Scanning Confocal Microscope. The unprecedented δ¹⁸O resolution and chronology of our record allow us to characterize in detail the Indian monsoon history from 25.50 ka B. P. to 24.76 ka B. P. and 24.38 ka B. P. to 22.42 ka B. P. (sample section between 99.5 mm and 437.0 mm). Our new δ¹⁸O record suggests that the total duration of H2 termination spans for 844±3 years (error is determined by the annual fluorescent lamination counting). The termination of the event occurred from 24.280±0.028 ka B. P. to 23.436±0.028 ka B. P. inferred by a δ¹⁸O gradual shift of ca. 1.9%. This process incorporates two negative excursions, from 24.28 ka B. P. to 24.17 ka B. P. and 23.90 ka B. P. to 23.44 ka B. P. and a relatively stable period from 24.17 ka B. P. to 23.90 ka B. P., superimposed on the termination trend are a number of centennial-decadal scale oscillations. The H2 Event in our record coincides within uncertainties with stalagmite records in the East Asian monsoon domain and ice core records from Greenland. Our δ¹⁸O record during the H2 Event, compared with existing records from high and low latitudes, suggests:(1) A large amount of fresh water released into the North Atlantic Ocean weakened the Atlantic Meridional Overturning Circulation, thus reduced temperature in north high latitude and shifted the Intertropical Convergence Zone southward; the signal was propagated to the Asian monsoon domain through the Westerlies; (2) The long and gradual termination of the H2 Event may be causally linked to the gradual warming in Antarctica; (3) Changes in low-latitude and the Tibetan Plateau may have a critical response/feedback on the event, thus further model simulations and more high-resolution H2 records are critical to test these hypothesis. In addition, our precise δ¹⁸O time series may provide new important constraints on the climate model simulation and the causal link of the H2 Event between high-low latitude climate changes.