Nature Geoscience: [2026] "Limited remineralization of Arctic permafrost-derived organic carbon in nearshore marine sediments," by Manuel Ruben et. al.
"Arctic temperatures are rising at an unparalleled rate (4 times the global average) compared with the previous seven millennia, leading to widespread permafrost thaw + collapse." In coastal regions, Pleistocene-age deposits, rich in organic matter (OM), are particularly vulnerable to thaw + erosion due to their high ice content.
"Despite the high bioavailability of permafrost organic matter [OM], most of it is freeze-locked and has not been actively cycled since at least the Last Glacial Maximum," which peaked 22,000 to 24,000 yrs ago. Once released, this previously freeze-locked OM becomes vulnerable to microbial degradation, potentially intensifying the permafrost carbon feedback + accelerating climate warming.
"While some studies investigated permafrost carbon feedback by seawater incubations, degradation processes that occur after deposition in marine sediments are less explored." OM breakdown in those sediments differs substantially from the water column due to different microbial communities + environmental conditions.
They examined "the fate of permafrost-derived organic carbon in the nearshore sediments of Qikiqtaruk, Canada." Analysis of dual carbon isotopes revealed that nearshore sedimentary organic carbon originated predominantly from eroded ancient permafrost deposits, but the remineralization end-product, dissolved inorganic carbon, diffusing back out of the sediment was younger + predominantly of marine origin.
They estimated "that <10% of land-derived Pleistocene permafrost organic carbon is respired [released] after redeposition in marine sediments." Their findings indicate that despite substantial Pleistocene permafrost organic carbon accumulation in marine sediments due to permafrost thaw + coastal erosion, much of it remains buried, potentially limiting its immediate contribution to atmospheric carbon.
"However, given the high reactivity of permafrost organic carbon entering the ocean, a reactive subfraction may remain in the water column or [had been] degraded prior to redeposition in the analysed sediments, highlighting the need for more comprehensive assessments of permafrost organic carbon degradation and its inclusion into Earth system models."
Short version: more research needed, as always.