A ∼50 ka record of monsoonal variability in the Darjeeling foothill region, eastern Himalayas

• The study estimates palaeomonsoon in the Darjeeling foothill over the past ∼50 ka.
• We suggest three phases of intense monsoon at 46.4–41.2, 31–22.3 and 5.4–4.3 ka.
• Coexistence approach shows an overall weaker monsoon during ∼50–15 ka than present.
• Oscillations in C3/C4 frequency followed monsoon variability through ages.
• Rainfall found to be the most influencing climate driver for floral dynamics.

Pollen, phytoliths and δ 13C signatures of soil organic matter from two fluvial sedimentary sequences of the Darjeeling foothill region, eastern Himalayas are used to portray palaeoclimatic oscillations and their impact on regional plant communities over the last ∼50 ka. Quantitative palaeoclimate estimation using coexistence approach on pollen data and other proxies indicate significant oscillations in precipitation during the late part of MIS 3 (46.4–25.9 ka), early and middle part of MIS 2 (25.9–15.6 ka), and 5.4 to 3.5 ka. Middle to late MIS 3 (ca 46.4–31 ka.) was characterized by a comparatively low monsoonal activity and slightly higher temperature than that during ca 31 ka onwards. Simultaneous expansion of deciduous trees and chloridoid grasses also imply a drier and warmer phase. Between 31 and 22.3 ka (late MIS 3 to mid-MIS 2), higher precipitation and a slightly cooler temperature led to an increase in evergreen elements over deciduous taxa and wet-loving panicoid grasses over dry-loving chloridoid grasses than earlier. After ca 22.3 ka, shrinking of forest cover, expansion of C4 chloridoid grasses, Asteraceae and Cheno-ams in the vegetation with lowering of temperature and precipitation characterized the onset of the LGM which continued till 18.3 ka. End of the LGM is manifested by a restoration in the forest cover and in the temperature and precipitation regime. Later, during 5.4 to 4.3 ka, a strong monsoonal activity supported a dense moist evergreen forest cover that subsequently declined during 4.3 to 3.5 ka. A further increase in deciduous elements and non-arboreals might be a consequence of reduced precipitation and higher temperature during this phase. A comparison between monsoonal rainfall, MAT and palaeoatmospheric CO2 with floral dynamics since last ∼50 ka indicates that these fluctuations in plant succession were mainly driven by monsoonal variations.