Remobilization of Old Permafrost Carbon to Chukchi Sea Sediments During the End of the Last Deglaciation

Abstract

Climate warming is expected to destabilize permafrost carbon (PF‐C) by thaw‐erosion and deepening of the seasonally thawed active layer and thereby promote PF‐C mineralization to CO 2 and CH 4 . A similar PF‐C remobilization might have contributed to the increase in atmospheric CO 2 during deglacial warming after the last glacial maximum. Using carbon isotopes and terrestrial biomarkers (Δ 14 C, δ 13 C, and lignin phenols), this study quantifies deposition of terrestrial carbon originating from permafrost in sediments from the Chukchi Sea (core SWERUS‐L2‐4‐PC1). The sediment core reconstructs remobilization of permafrost carbon during the late Allerød warm period starting at 13,000 cal years before present (BP), the Younger Dryas, and the early Holocene warming until 11,000 cal years BP and compares this period with the late Holocene, from 3,650 years BP until present. Dual‐carbon‐isotope‐based source apportionment demonstrates that Ice Complex Deposit—ice‐ and carbon‐rich permafrost from the late Pleistocene (also referred to as Yedoma)—was the dominant source of organic carbon (66 ± 8%; mean ± standard deviation) to sediments during the end of the deglaciation, with fluxes more than twice as high (8.0 ± 4.6 g·m −2 ·year −1 ) as in the late Holocene (3.1 ± 1.0 g·m −2 ·year −1 ). These results are consistent with late deglacial PF‐C remobilization observed in a Laptev Sea record, yet in contrast with PF‐C sources, which at that location were dominated by active layer material from the Lena River watershed. Release of dormant PF‐C from erosion of coastal permafrost during the end of the last deglaciation indicates vulnerability of Ice Complex Deposit in response to future warming and sea level changes.

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

“…The consistency implies that at least in the North-Pacific realm sea-level rise was a major control for abrupt remobilization of permafrost carbon at 14.6 and 11.5 kyr BP. As for the Arctic sector of Beringia, deglacial reworking of old permafrost carbon caused by inundation of the Chukchi Shelf (at ∼13 kyr BP, figure 2(f)) has been recently reported (Martens et al 2019). Yet, it remains unresolved whether Beringia's Arctic shelves (East Siberian Arctic and Chukchi Shelves, figure 1) released carbon at 14.6 and 11.5 kyr BP along with the Pacific shelves (Martens et al 2019).…”

“…Most studies investigating the contributions of terrestrial carbon to the atmospheric changes are indirect, as they rely on interpreting atmospheric records with carbon-cycle models (Köhler et al 2014, Bauska et al 2016, Crichton et al 2016. However, the assumed timing of carbon release from degrading permafrost is very poorly constrained by proxy data as deglacial records of carbon mobilization are very sparse , Winterfeld et al 2018, Martens et al 2019.…”

“…Biomarker records from the Laptev, Chukchi and Okhotsk Seas provide evidence for rapid thawinduced mobilization of permafrost carbon and subsequent river discharge as well as for coastal erosion of permafrost associated with rapid sea-level rise (Winterfeld et al 2018, Martens et al 2019.…”

“…As such, Beringia may have been relevant for both, the sea-level associated component of the deglacial permafrost feedback (Köhler et al 2014, Winterfeld et al 2018 and greenhouse-gas emissions related to inland permafrost thaw induced by warming. So far, evidence has been obtained for massive remobilization of permafrost carbon from the Lena River catchment (at 11.5 kyr BP) as well as from the East Siberian Arctic and Chukchi Shelves (after ∼9.5 and around ∼13 kyr BP) (Keskitalo et al 2017, Martens et al 2019.…”

“…Yet, the timing of carbon mobilization from degrading permafrost in this region still remains elusive since existing records do not reach beyond ∼13 kyr BP , Keskitalo et al 2017, Martens et al 2019 and some are not continuous (Keskitalo et al 2017, Martens et al 2019.…”