Magnetic proxy in the Heqing drill core revealed Indian Summer Monsoon variations linked with AMOC at the orbital -scale during the late Pleistocene

Abstract

Enhanced comprehension of the drivers behind the Indian Summer Monsoon (ISM) is imperative for advancing climate forecasting models. Current observations, climate models, and paleoclimatic data converge on the notion that ISM fluctuations are primarily modulated by shifts in the Intertropical Convergence Zone (ITCZ), which are themselves precipitated by the Atlantic Meridional Overturning Circulation (AMOC). In the epoch of the late Pleistocene, paleoclimate reconstructions have underscored a pronounced linkage between the circulation patterns of Indian Ocean and the vigor of the AMOC, observable across both millennial and orbital timescales. However, little attention has been paid to the linkage between the ISM and the AMOC at the orbital scale.

The extensive and continuous lacustrine sedimentary sequences from Southwest China serve as an unparalleled archive for charting evolutionary trajectory of the ISM. Guided by a refined chronological model forged through geomagnetic paleointensity analysis, the magnetic proxy measurements (ARM/SIRM) from the late Pleistocene evince the dominant precessional cycles. These are mirrored in ISM indicators gleaned from speleothems, lacustrine, and marine sediments across the ISM ambit. Intriguingly, at the precessional frequency, the ISM indicators march in lockstep with AMOC indicators, including the Agulhas Leakage Fauna (ALF) in core CD154-17 K, the δ¹³C in core MD02–2588, and the sea surface temperature (SST) gradient between the tropical and extratropical western Indian Ocean. This consistence lends credence to the hypothesis that ISM variability, propelled by ITCZ migrations, is coupled with the AMOC intensity at the orbital scale. The increased phase lags between Northern Hemisphere Summer Insolation (NHSI) and indicators of AMOC activity, ITCZ migration, ISM intensity suggested a non-negligible latitude differences in climate response to the internal forcing. The phase lag between ISM precipitation and NHSI might be indicative of accumulation of lags between ISM intensity and ITCZ migration, ITCZ migration and AMOC activity, AMOC activity and solar insolation.