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

Abstract

During the last deglaciation (18-8 kyr BP), shelf flooding and warming presumably led to a large-scale decomposition of permafrost soils in the mid-to-high latitudes of the Northern Hemisphere. Microbial degradation of old organic matter released from the decomposing permafrost potentially contributed to the deglacial rise in atmospheric CO 2 and also to the declining atmospheric radiocarbon contents (Δ 14 C). 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 the mobilization of organic matter from permafrost in the Pacific sector of Beringia over the last 22 kyr using mass-accumulation rates and radiocarbon signatures of terrigenous biomarkers in four sediment cores from the Bering Sea and the Northwest Pacific. We find that pronounced reworking and thus the vulnerability of old organic carbon to remineralization commenced during the early deglaciation (∼16.8 kyr BP) when meltwater runoff in the Yukon River intensified riverbank erosion of permafrost soils and fluvial discharge. Regional deglaciation in Alaska additionally mobilized significant fractions of fossil, petrogenic organic matter at this time. Permafrost decomposition across Beringia's Pacific sector occurred in two major pulses that match the Bølling-Allerød and Preboreal warm spells and rapidly initiated within centuries. The carbon mobilization likely resulted from massive shelf flooding during meltwater pulses 1A (∼14.6 kyr BP) and 1B (∼11.5 kyr BP) followed by permafrost thaw in the hinterland. Our findings emphasize that coastal erosion was a major control to rapidly mobilize permafrost carbon along Beringia's Pacific coast at ∼14.6 and ∼11.5 kyr BP implying that shelf flooding in Beringia may partly explain the centennial-scale rises in atmospheric CO 2 at these times. Around 16.5 kyr BP, the mobilization of old terrigenous organic matter caused by meltwater-floods may have additionally contributed to increasing CO 2 levels.

Deglacial to Holocene variability in surface water characteristics and major floods in the Beaufort Sea

“…The GDGT fraction was separated from other fractions via open column chromatography and eluted with 5 ml DCM:MeOH (1:1 v/v), dried and re-dissolved in hexane:isopropanol (99:1 v/v), and then filtered via a polytetrafluoroethylene filter with a pore size of 0.45 μm. Compound identification and quantification were carried out by a high-performance liquid chromatography/ atmospheric pressure chemical ionization-MS according to the method described by Meyer et al 83 . The MS-detector was set for SIM of the following (M + H) + ions: m/z 1300.3 (OH-GDGT-0), 1298.3 (OH-GDGT-1), 1296.3 (OH-GDGT-2), 1050 (GDGT-IIIa/IIIa′), 1036 (GDGT-IIa/IIa′), 1022 (GDGT-Ia), and 744 (C 46 standard), with a dwell time of 57 ms per ion.…”

“…In this context, one should keep in mind that the second event also coincided with global meltwater pulse 1B (MWP 1B). Recent studies in the Okhotsk Sea and Pacific Beringia provided direct evidence of coastal erosion induced by the rapid sea-level rise 82,83 . In these records, two distinct maxima of terrigenous material were observed within the rapid sea-level rise at ca.…”

Remobilization of dormant carbon from Siberian-Arctic permafrost during three past warming events

“…Two studies from the northeast Pacific suggest that this also happened outside the Arctic Ocean during shelf inundation in the Bering Sea and the Sea of Okhotsk (Fig. 1) (14,18). There is, however, no single continuous archive that explores the remobilization of OC from Arctic permafrost during the last deglaciation, leaving both the magnitude and the onset and end of this hypothetically massive permafrost OC remobilization largely unconstrained.…”

Siberian Permafrost Thawing Accelerated at the Bølling/Allerød and Preboreal Warm Periods During the Last Deglaciation

“…Similarly, the atmospheric carbon dioxide (CO 2 ) record from Antarctic ice cores shows the rapid rises in CO 2 at the onset of the BA and PB that are superimposed on a long-term gradual increase through the last deglaciation (Marcott et al, 2014). On the other hand, growing evidence suggests that the continental shelves flooded, and the subsequent thawed permafrost was an additional and important source of the rapid rise in CO 2 in these warm periods (Meyer et al, 2019;Tesi et al, 2016;Winterfeld et al, 2018). On the other hand, growing evidence suggests that the continental shelves flooded, and the subsequent thawed permafrost was an additional and important source of the rapid rise in CO 2 in these warm periods (Meyer et al, 2019;Tesi et al, 2016;Winterfeld et al, 2018).…”

“…It is commonly understood that the rapid CO 2 rises at the BA and PB were largely controlled by the Atlantic Meridional Overturning Circulation strength and the associated climate teleconnections (Marcott et al, 2014). On the other hand, growing evidence suggests that the continental shelves flooded, and the subsequent thawed permafrost was an additional and important source of the rapid rise in CO 2 in these warm periods (Meyer et al, 2019;Tesi et al, 2016;Winterfeld et al, 2018). Recent modeling and data-based analyses have inferred that permafrost carbon release might make a great contribution to atmospheric CO 2 change during the deglaciation (Crichton et al, 2016;Köhler et al, 2014).…”