Permafrost Thaw Dynamics Drive the Regime Shifts of Iron-Bound Organic Carbon Sequestration in the East Siberian Arctic Shelf

Abstract

In the changing Arctic, permafrost thaw is shifting from gradual to abrupt. Although iron-bound organic carbon (OC-FeR) critically modulates permafrost carbon-climate feedbacks, its decadal-scale variability and response to this regime shift remain poorly constrained. Focusing on the East Siberian Arctic, a hotspot of land-to-ocean permafrost carbon transfer, we established critical linkages between marine sedimentary OC-FeR burial records and terrestrial permafrost-climate dynamics. Results revealed that coastal OC-FeR reservoirs exhibited temporally-distinct responses to permafrost thawing dynamics. During the pre-2000s, the progressive decline in OC-FeR coincided with watershed-scale soil moisture redistribution driven by gradual active-layer deepening, which preferentially retained OC-FeR in permafrost, attenuating its land-to-ocean fluxes. Since 2000s, although abrupt thaw has rapidly mobilized OC, ∼19% of sedimentary OC remained stabilized as OC-FeR, thus partially decoupling abrupt thaw from immediate permafrost carbon-climate feedbacks. Therefore, this mineralogical buffering mechanism can attenuate the net climate impact of accelerating abrupt thaw across the Northern Hemisphere cryosphere.