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During the last deglaciation (18–8 kyr BP), shelf flooding andwarming presumably led to a large-scale decomposition of permafrost soils in themid-to-high latitudes of theNorthernHemisphere. Microbial degradation of old organicmatter released from the decomposing permafrost potentially contributed to the deglacial rise in atmospheric CO2 and also to the declining atmospheric radiocarbon contents (ΔC). The significance of permafrost for the atmospheric carbon pool is not well understood as the timing of the carbon activation is poorly constrained by proxy data.Here, we trace themobilization of organicmatter frompermafrost in the Pacific sector of Beringia over the last 22 kyr usingmass-accumulation rates and radiocarbon signatures of terrigenous biomarkers in four sediment cores from the Bering Sea and theNorthwest Pacific.Wefind that pronounced reworking and thus the vulnerability of old organic carbon to remineralization commenced during the early deglaciation (∼16.8 kyr BP)whenmeltwater runoff in the YukonRiver intensified riverbank erosion of permafrost soils andfluvial discharge. Regional deglaciation inAlaska additionallymobilized significant fractions of fossil, petrogenic organicmatter at this time. Permafrost decomposition across Beringia’s Pacific sector occurred in twomajor pulses thatmatch the Bølling-Allerød and Preboreal warm spells and rapidly initiatedwithin centuries. The carbonmobilization likely resulted from massive shelfflooding duringmeltwater pulses 1A (∼14.6 kyr BP) and 1B (∼11.5 kyr BP) followed by permafrost thaw in the hinterland. Ourfindings emphasize that coastal erosionwas amajor control to rapidlymobilize permafrost carbon along Beringia’s Pacific coast at∼14.6 and∼11.5 kyr BP implying that shelfflooding in Beringiamay partly explain the centennial-scale rises in atmospheric CO2 at these times. Around 16.5 kyr BP, themobilization of old terrigenous organicmatter caused by meltwater-floodsmay have additionally contributed to increasingCO2 levels.

Permafrost-carbon mobilization in Beringia caused by deglacial meltwater runoff, sea-level rise and warming