Cross-Equatorial Climate Linkages: Insights into Monsoon–Glaciation–Insolation Dynamics from Bakhira Lake Sediments, Ganga Plain, India

Understanding the intricate relationship between northern hemisphere glaciation, solar insolation and Indian monsoon variability is crucial for reconstructing past climate dynamics. This study unravels these connections over the last 24 ka using multiproxy data from the Bakhira Lake sediments, Ganga plain. By integrating geochemical and sedimentological indicators including AMS-dating, we reconstruct shifts in monsoon intensity. The geochemical data indicate that the sediments predominantly originated from the felsic rocks of the Higher Himalayan Crystalline (HHC), with a minor input from the Lesser Himalaya. High smectite contents, higher smectite/(illite + chlorite), Chemical Index of Alteration (CIA), α ^Al Na and Rb/Sr ratios indicate intensified chemical weathering. These geochemical signatures, along with increased sedimentation rates in the Ganga Plain, suggest enhanced monsoonal precipitation during the Bølling–Allerød (B/A) and Early to Mid-Holocene intervals. These intensified phases correspond closely with periods of heightened Northern Hemisphere solar insolation, northward migration of the Intertropical Convergence Zone (ITCZ) and the concurrent glacial retreat in Himalayan and Tibetan regions. Conversely, reduced chemical weathering intensity as shown by low smectite contents, lower smectite/(illite + chlorite) ratios, CIA, α ^Al Na and decreased sedimentation in the basin during LGM, Heinrich event 1 and Younger Dryas reflect weaker monsoon precipitation associated with colder and drier climatic conditions. These cold phases align with enhanced Northern Hemisphere glaciation, a southward displacement of the ITCZ and expanded Himalayan and Tibetan glacial extents. Overall, the sedimentary and geochemical records from Bakhira Lake illustrate strong teleconnections between Indian Summer Monsoon dynamics, Northern Hemisphere glaciation and global climate variability.