G04_P02

Radiocarbon age of plant remains in massive ground ice of the Barrow Permafrost Tunnel, Alaska

Iwahana G¹, Uchida M², Mantoku K², Kobayashi T²

¹University Of Alaska Fairbanks, Fairbanks, United States, ²National Institute for Environmental Studies, Tsukuba, Japan

Permafrost provides paleoenvironmental information from organic matter, gas, water, and sediment contents captured in the perennially frozen ground.  Syngenetic ice wedges that grow laterally in frost cracks of the permafrost sediments are expected to be an alternative paleoenvironmental proxy where information from nearby glacier/ice sheet core or lake sediments is unavailable. Massive ground ice found in the Barrow Permafrost Tunnel at the depth range between 3 and 7 m from the surface has been interpreted as ice-wedge and used to reconstruct environmental changes in the early Holocene. To better understand the development of the massive ground ice, we conducted Radiocarbon dating of plant remains and stable isotope analysis of the ice along with two profiles. Combining with previous results, we mapped the radiocarbon age distribution within the massive ground ice. The age distribution from our dense sampling showed two ice regions with similar ages centering 11,200 and 10,200 yBP divided by a relatively narrow region of intermediate age along with the 5-m profile parallel to the tunnel long-axis. From the other sampling profile that is perpendicular to the tunnel, the youngest age (8,451 yBP) was found from the NW end of the profile. The water stable isotopes from the profile perpendicular to the tunnel showed the lowest anomaly at the SE end, which contradicts the ice-wedge origin assumption. Our results indicate the existence of unknown processes in the massive ice growth or large randomness of cracking locations during ice-wedge development.