Feedbacks From Young Permafrost Carbon Remobilization to the Deglacial Methane Rise

The abrupt warming events punctuating the Termination 1 (about 11.7–18 ka Before Present, BP)were marked by sharp rises in the concentration of atmospheric methane (CH4). The role of permafrost organiccarbon (OC) in these rises is still debated, with studies based on top‐down measurements of radiocarbon (14C)content of CH4 trapped in ice cores suggesting minimum contributions from old and strongly 14C‐depletedpermafrost OC. However, organic matter from permafrost can exhibit a continuum of 14C ages(contemporaneous to >50 ky). Here, we investigate the large‐scale permafrost remobilization at the YoungerDryas‐Preboreal transition (ca. 11.6 ka BP) using the sedimentary record deposited at the Lena River paleo‐outlet (Arctic Ocean) to reflect permafrost destabilization in this vast drainage basin. Terrestrial OC was isolatedfrom sediments and characterized geochemically measuring δ13C, Δ14C, and lignin phenol molecular fossils.Results indicate massive remobilization of relatively young (about 2,600 years) permafrost OC from inlandSiberia after abrupt warming triggered severe active layer deepening. Methane emissions from this youngfraction of permafrost OC contributed to the deglacial CH4 rise. This study stresses that underestimatingpermafrost complexities may affect our comprehension of the deglacial permafrost OC‐climate feedback andhelps understand how modern permafrost systems may react to rapid warming events, including enhanced CH4emissions that would amplify anthropogenic climate change.