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 organic carbon (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‐depleted permafrost 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 Younger Dryas‐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 isolated from 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 inland Siberia after abrupt warming triggered severe active layer deepening. Methane emissions from this young fraction of permafrost OC contributed to the deglacial CH4 rise. This study stresses that underestimating permafrost complexities may affect our comprehension of the deglacial permafrost OC‐climate feedback and helps understand how modern permafrost systems may react to rapid warming events, including enhanced CH4 emissions that would amplify anthropogenic climate change. Plain Language Summary Feedback on climate change through methane emissions from organic carbon (OC) released from thawing permafrost soils is still debated. Studies investigating rapid warming events from the last 15,000 years and measuring the radiocarbon content in methane from ancient air trapped in ice cores suggested small contributions from the oldest (10,000 years or more) and most refractory OC fraction to the deglacial methane rise. However, the younger and more reactive OC likely contributed more to methane emissions from permafrost systems. Using terrestrial material from sediments deposited at the paleo‐delta of the Lena River (Arctic Ocean), we investigated large‐scale permafrost OC remobilization across the climate transition to the Preboreal (about 11,600 years ago). Results show that relatively young (about 2,600 years) terrestrial organic matter was largely remobilized from the layer of East Siberian permafrost soils thawing seasonally th