Intra‐ice and intra‐sediment cryopeg brine occurrence in permafrost near Utqiaġvik (Barrow)

Abstract

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 Utqiaġvik, 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.

Divergent Genomic Adaptations in the Microbiomes of Arctic Subzero Sea-Ice and Cryopeg Brines

“…We used a hand pump and 1.5-m length of sterile Masterflex and Teflon tubing (Cole-Parmer, Vernon Hills, IL, United States) to collect samples in acid-washed 2-L vacuum flasks (initially autoclaved, then acidwashed and ethanol-rinsed between samples). Detailed borehole histories and sampling are provided in Cooper et al (2019) and Iwahana et al (2021). Sample names here are based on borehole name and filtration pore size (see below).…”

“…cryopeg brines found deep within approximately 40,000-yearold permafrost (Meyer et al, 2010;Iwahana et al, 2021) near Utqiaġvik, Alaska. Both of these seawater-sourced habitats share the traits of subzero temperature and hypersalinity (-4 to -3 • C and 75-78 ppt for the sea-ice brines at time of sampling, and -6 • C and 112-140 ppt for the cryopeg brines; Table 1), yet they differ greatly in their environmental age and stability.…”

“…While microbes in sea ice may be presented with sufficient organic matter from sea-ice algae during the spring and summer months, they must also survive the aphotic winter season. In cryopeg brines, where phototrophic primary production is absent, heterotrophic microbes may survive via the products of their extracellular enzymes (Showalter and Deming, 2021), hydrolyzing remnant plant and detrital material from the surrounding permafrost and ice-wedge environments (Iwahana et al, 2021), and via dead microbial matter, as proposed for oceanic subsurface marine sediments (Bradley et al, 2018), yet any metagenomic insights into survival mechanisms employed in situ are currently lacking.…”

Evolutionary Divergence of Marinobacter Strains in Cryopeg Brines as Revealed by Pangenomics

“…Cryopegs are liquid-saturated sediment layers within permafrost that remain unfrozen at subzero temperatures due to their salt content ( Gilichinsky et al, 2003 , 2005 ). The cryopeg system we sampled is approximately 2 km from the modern Arctic coastline and most likely derived from marine sediment that was exposed to subzero temperatures and incorporated into permafrost at least 40 ka BP based on radiocarbon dating ( Meyer et al, 2010a , b ; Iwahana et al, 2021 ). For the last 40 ka, the cryopeg brines have been isolated from external influences, with observations indicating relatively stable subzero temperatures (−8 to −6°C) and hypersalinities (109–140 ppt; Cooper et al, 2019 ; Iwahana et al, 2021 ).…”

“…The cryopeg system we sampled is approximately 2 km from the modern Arctic coastline and most likely derived from marine sediment that was exposed to subzero temperatures and incorporated into permafrost at least 40 ka BP based on radiocarbon dating ( Meyer et al, 2010a , b ; Iwahana et al, 2021 ). For the last 40 ka, the cryopeg brines have been isolated from external influences, with observations indicating relatively stable subzero temperatures (−8 to −6°C) and hypersalinities (109–140 ppt; Cooper et al, 2019 ; Iwahana et al, 2021 ). The microbial communities inhabiting these subzero brines are dense (approximately 10 8 cells ml −1 ), with Marinobacter accounting for, on average, 49% of the prokaryotic community, based on its relative abundance generated by 16S rRNA gene amplicon sequencing ( Cooper et al, 2019 ).…”