Meltwater Pulse1A Triggered an Extreme Cooling Event: Evidence From Southern China

Meltwater Pulse 1A injection into the North Atlantic coincided with the Bølling warming event, despite climate model simulations indicating that the Meltwater Pulse 1A should have inevitably lead to an extreme cooling in the northern hemisphere. However, so far no cooling event has been found in paleoclimate records responding to Meltwater Pulse 1A. Here we reconstruct winter temperature based on sedimentary diatoms from Huguangyan Maar Lake in tropical China. The results show that winter temperature dropped by at least 6°C within ∼100 years at 14.8 ± 0.02 ka BP, coeval with the onset of Meltwater Pulse 1A, within dating uncertainty. We argue that Meltwater Pulse 1A weakened the Atlantic Meridional Overturning Circulation (AMOC), resulting in abrupt severe cooling in the Northern Hemisphere that caused a severe winter temperature drop in East Asia by strengthening the winter monsoon. We propose that extreme cooling in winter temperature triggered the Bølling warming by stopping the freshwater release from the ice‐sheet, triggering the AMOC to recover quickly and causing the Bølling event as an overshoot under gradual forcing. Plain Language Summary It is generally accepted that large quantities of meltwater injected into the ocean is reducing Atlantic Meridional Overturning Circulation and will causes a significant cooling event in the Northern Hemisphere. However, it was not a cooling event that coincided with Meltwater pulse1A, the largest freshwater injection of the Late Quaternary, but the abrupt Bølling warming event. This paradox is still debated because so far no cooling event coinciding with Meltwater Pulse 1A has been found in paleoclimatic records. This is mainly due to the lack of suitable proxy and high‐resolution records in high northern latitude regions. Here, we establish the relationship between the diatoms contained in the sediment record and temperature to reconstruct the changes in temperature during the last deglacial from the high‐resolution record of a volcanic lake. We find that an extreme cooling event occurred at the onset of Meltwater Pulse 1A. We think that this extreme cooling triggered the abrupt warming event known as the Bølling warming event. Key Points We provide evidence that winter temperature dropped by at least 6°C just before the Bølling warming event in southern China We argue that this extreme cooling event was caused by the Meltwater Pulse1A event We propose that this extreme cooling event triggered the Bølling warm