Non-summer precipitation drove eco-hydroclimate in the Asian Summer Monsoon transition zone
ID：765
Oral Presentation
2027-01-15 11:20 （China Standard Time）
Session：Session 43 - Biogeochemistry of the South China Sea: The Ten-year expedition of RV Tan Kan Kee
Abstract
The evolution of non-summer precipitation and its role in shaping hydroclimate and vegetation dynamics across the Asian summer monsoon (ASM) region remains poorly understood compared with the well-recognized influence of summer monsoon rainfall. Here we present sub-centennial paired black carbon (BC) abundance and carbon isotopic composition (δ¹³CBC) records from the Red River Basin, a key transition zone of the ASM transition zone, to reconstruct regional fire, humidity and C3/C4 vegetation dynamics over the past 36 kyr. The BC abundance reveals two humid, low-fire intervals (MIS 3 and Holocene) separated by a distinct dry, high-fire phase (MIS 2), indicating a hydroclimatic regime that is decoupled from summer monsoon rainfall variations and highlighting a substantial contribution of non-summer precipitation. Widespread C4 expansion inferred from paired δ¹³CBC across the region before ~18 kyr was largely decoupled from hydroclimate variability, reflecting the overriding influence of persistently low atmospheric CO₂. As CO2 rose, vegetation became increasingly sensitive to hydrological changes. Increased non-summer precipitation outweighed summer rainfall reductions, raising overall humidity and weakening precipitation seasonality, conditions drove a uniquely continuous C3 vegetation expansion throughout the Holocene. Our results demonstrate that non-summer precipitation exerts a previously underappreciated control on eco-hydroclimate variability of the ASM Transition Zone.
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