Arctic Permafrost Stability over the Past 1.5 Million Years Inferred from Cave Deposits

Nuclear & Plasma Society

Professor Jeremy Shakun – Earth and Environmental Sciences Department, Boston College

“Arctic permafrost sequesters a substantial stock of perennially frozen organic carbon that could be released to the atmosphere as methane and carbon dioxide upon thawing. This thaw vulnerability of permafrost carbon represents a potentially powerful amplifier of climate change, but little is known about permafrost sensitivity and associated carbon cycling during past intervals of persistent climate warming. I will present a reconstruction of Canadian permafrost history during Pleistocene interglacials from 131 uranium-thorium ages on 74 speleothems, cave deposits that only accumulate during intervals of deep ground thaw. We infer that interglacial permafrost thaw was widespread ~0.5-1.5 million years ago, but deep permafrost persisted in much of Arctic and sub-Arctic North America through warm interglacials of the last ~500,000 years, with deep thaw likely limited to sub-Arctic discontinuous permafrost during the Marine Isotope Stage 11 “super-interglacial”. On Pleistocene timescales, interglacial CO2 concentrations remained within a narrow ~280 ± 20 ppm range and were insensitive to differences in the magnitude of interglacial permafrost thaw inferred here. This implies the existence of processes that attenuated the permafrost-carbon feedback during Pleistocene interglacials, including those when the magnitude of inferred permafrost thaw exceeded numerical model projections for extensive ground thaw over the next several centuries”.

About the Speaker:

Dr. Jeremy Shakun is an Assistant Professor in the Earth and Environmental Sciences Department at Boston College. He is a paleoclimatologist who uses the geologic record to decipher the patterns and mechanisms of past changes in climate and ice sheets on decade to million year time scales. He is particularly motivated by paleoclimate problems that have clear relevance to today.

Meeting Location: Boston College, 202 Kenny Cottle, 140 Commonwealth Avenue, Chestnut Hill, MA 02467