Yedoma Cryostratigraphy of Recently Excavated Sections of the CRREL Permafrost Tunnel Near Fairbanks, Alaska

Mikhail Kanevskiy,Kevin L Bjella,Benjamin M Jones,Nancy H Bigelow,Thomas A Douglas,Yuri Shur,Daniel Fortier,M Torre Jorgenson

doi:10.3389/feart.2021.758800

Abstract

Recent excavation in the new CRREL Permafrost Tunnel in Fox, Alaska provides a unique opportunity to study properties of Yedoma — late Pleistocene ice- and organic-rich syngenetic permafrost. Yedoma has been described at numerous sites across Interior Alaska, mainly within the Yukon-Tanana upland. The most comprehensive data on the structure and properties of Yedoma in this area have been obtained in the CRREL Permafrost Tunnel near Fairbanks — one of the most accessible large-scale exposures of Yedoma permafrost on Earth, which became available to researchers in the mid-1960s. Expansion of the new ∼4-m-high and ∼4-m-wide linear excavations, started in 2011 and ongoing, exposes an additional 300 m of well-preserved Yedoma and provides access to sediments deposited over the past 40,000 years, which will allow us to quantify rates and patterns of formation of syngenetic permafrost, depositional history and biogeochemical characteristics of Yedoma, and its response to a warmer climate. In this paper, we present results of detailed cryostratigraphic studies in the Tunnel and adjacent area. Data from our study include ground-ice content, the stable water isotope composition of the variety of ground-ice bodies, and radiocarbon age dates. Based on cryostratigraphic mapping of the Tunnel and results of drilling above and inside the Tunnel, six main cryostratigraphic units have been distinguished: 1) active layer; 2) modern intermediate layer (ice-rich silt); 3) relatively ice-poor Yedoma silt reworked by thermal erosion and thermokarst during the Holocene; 4) ice-rich late Pleistocene Yedoma silt with large ice wedges; 5) relatively ice-poor fluvial gravel; and 6) ice-poor bedrock. Our studies reveal significant differences in cryostratigraphy of the new and old CRREL Permafrost Tunnel facilities. Original syngenetic permafrost in the new Tunnel has been better preserved and less affected by erosional events during the period of Yedoma formation, although numerous features (e.g., bodies of thermokarst-cave ice, thaw unconformities, buried gullies) indicate the original Yedoma silt in the recently excavated sections was also reworked to some extent by thermokarst and thermal erosion during the late Pleistocene and Holocene.

Highlights

Yedoma is the ice- and organic-rich syngenetic permafrost, which accumulated in unglaciated regions during the late Pleistocene in various regions of Eurasia and North America (Schirrmeister et al, 2013)
We describe cryostratigraphy of the recently excavated sections of the Cold Regions Research and Engineering Laboratory (CRREL) Permafrost Tunnel based on mapping of the walls and ceiling of a 110-m-long section of the main Tunnel and a 50-m-long crosscut connecting the new and old Tunnels
According to radiocarbon dates obtained from Borehole F12, this layer formed during the Holocene (Figure 4); it comprised mainly Yedoma deposits reworked by thermal erosion and slope processes

Summary

Introduction

Yedoma is the ice- and organic-rich syngenetic permafrost, which accumulated in unglaciated regions during the late Pleistocene in various regions of Eurasia and North America (Schirrmeister et al, 2013). Yedoma remnants are abundant in various parts of Siberia, Canada, and Alaska (Kanevskiy et al, 2011; Schirrmeister et al, 2013; Strauss et al, 2017; Strauss et al, 2021; and citations therein). Yedoma in Siberia and North America occurs in an area of ∼450,000 km, including ∼90,000 km in Alaska (Strauss et al, 2021), and contains up to 130 gigatons of organic carbon (Strauss et al, 2017). Yedoma is vulnerable to climate change and disturbance because of its high ice content and silty composition. Growing interest in Yedoma studies during recent decades has been related to the high content of frozen organic matter whose release upon thaw leads to changes in biogeochemical processes and greenhouse gas emission (Grosse et al, 2011; Schuur et al, 2015; Strauss et al, 2017)

Objectives

Methods

Results

Conclusion