Intra-ice and intra-sediment cryopeg brine occurrence in permafrost near Utqiagvik (Barrow)

摘要

Cryopeg is a layer within permafrost containing a significant amount of cryotic unfrozen water due to dissolved salts. To explore the origin and development of cryopeg and associated brines found near Utqiavik, we sampled extensively within the Barrow Permafrost Tunnel. We found two types of cryopeg brines based on their distinctive locations: (a) intra-ice brine (IiB), entirely bounded by massive ground ice, and not previously observed in the Northern Hemisphere; and (b) intra-sediment brine (IsB), found as expected in unfrozen sediments within permafrost. The encountered IiBs were situated in small ellipsoidal or more complex shaped pockets within the massive ice at roughly atmospheric pressure. Radiocarbon dating suggests that the IiB segregated from IsB-bearing cryopeg beneath the massive ice at about 11 ka BP, at the earliest. From geochemical analyses, IsB lenses were interpreted as having developed through repeated evaporation and cryoconcentration of seawater in a lagoonal environment, then isolated when the surrounding sediment froze and became covered by an upper sediment unit around 40 ka BP or earlier. The discovery of IiB and development of origin scenarios for both brine types validate the importance of high-resolution sampling as enabled by the unique facility of a permafrost tunnel.