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Holocene pore‐ice δ 18 O and δ 2 H records from drained thermokarst lake basins in the Old Crow Flats, Yukon, Canada

2020; Wiley; Volume: 31; Issue: 4 Linguagem: Inglês

10.1002/ppp.2073

1099-1530

Sasiri Bandara, Duane Froese, Trevor J. Porter, Fabrice Calmels,

Methane Hydrates and Related Phenomena

Abstract Thermokarst lakes form following the thaw of ice‐rich permafrost and drain after a few decades to millennia. Drained thermokarst lake basins (DTLBs) become epicenters for peat accumulation and re‐aggradation of ice‐rich permafrost. This re‐aggradation of permafrost may be interrupted by subsequent thermokarst lake formation with sufficient disturbance. Thermokarst lakes and DTLBs are abundant near Old Crow, Yukon, Canada, but little is known about their evolution through the Holocene. In this study, we investigate the hydrology and drainage histories of seven DTLBs from the Old Crow Flats on the basis of cryostratigraphy, radiocarbon dating, and pore‐ice δ 18 O and δ 2 H records. Cryostratigraphic evidence implies only one of the seven studied DTLBs underwent multiple thermokarst cycles. Radiocarbon age–depth models demonstrate a slowdown in the rate of post‐drainage peat accumulation with time. Pore‐ice isotope analyses reveal a spectrum of possible post‐drainage isotopic histories resulting from spatial variability in permafrost, vegetation, and hydrology. Unlike lacustrine silt, post‐drainage peat contains relatively constant pore‐ice isotope trends. In light of our findings, we propose that syngenetic peat permafrost in DTLBs preserve a warm‐season sampling of local meteoric waters. These pore‐ice δ 18 O and δ 2 H records may aid millennial‐scale paleoclimate investigations, as we demonstrate through our reconstruction of Holocene climate change in northern Yukon.