DSpace Collection:

Aerogeophysical characterization of an active subglacial lake system in the David Glacier catchment, Antarctica

2020-07-15T00:00:00Z

Title: Aerogeophysical characterization of an active subglacial lake system in the David Glacier catchment, Antarctica Authors: Lindzey, Laura E.; Beem, Lucas H.; Young, Duncan A.; Quartini, Enrica; Blankenship, Donald D.; Lee, Choon-Ki; Lee, Won Sang; Lee, Jong Ik; Lee, Joohan Abstract: In the 2016-2017 austral summer, the University of Texas Institute for Geophysics (UTIG) and the Korea Polar Research Institute (KOPRI) collaborated to perform a helicopter-based radar and laser altimeter survey of lower David Glacier with the goals of characterizing the subglacial water distribution that supports a system of active subglacial lakes and informing the site selection for a potential subglacial access drilling project. This survey overlaps with and expands upon an earlier survey of the Drygalski Ice Tongue and the David Glacier grounding zone from 2011 and 2012 to create a 5 km resolution survey extending 200 km upstream from the grounding zone. The surveyed region covers two active subglacial lakes and includes reflights of ICESat ground tracks that extend the surface elevation record in the region. This is one of the most extensive aerogeophysical surveys of an active lake system and provides higher-resolution boundary conditions and basal characterizations that will enable process studies of these features. This paper introduces a new helicopter-mounted ice-penetrating radar and laser altimetry system, notes a discrepancy between the original surface-elevation-derived lake outlines and locations of possible water collection based on basal geometry and hydraulic potential, and presents radar-based observations of basal conditions that are inconsistent with large collections of ponded water despite laser altimetry showing that the hypothesized active lakes are at a highstand.

Pseudomonas neustonica sp. nov., isolated from the sea surface microlayer of the Ross Sea (Antarctica)

2020-06-01T00:00:00Z

Title: Pseudomonas neustonica sp. nov., isolated from the sea surface microlayer of the Ross Sea (Antarctica) Authors: Jang, Gwang Il; Lee, Inae; Ha, Tran Thu; Yoon, Soo Jung; Hwang, Yeon Ju; Yun, Sukyoung; Lee, Won Sang; Hwang, Chung Yeon Abstract: Gram- stain-negative, aerobic and rod-shaped bacterial strains, designated SSM26T and SSM44, were isolated from a sea surface microlayer sample from the Ross Sea, Antarctica. Analysis of the 16S rRNA gene sequences of strains SSM26T and SSM44 revealed a clear affiliation with the genus Pseudomonas. Based on the results of phylogenetic analysis, strains SSM26(T) and SSM44 showed the closest phylogenetic relationship with the species Pseudomonas sabulinigri KCTC 22137(T) with the 16S rRNA gene sequence similarity level of 98.5 %. Strains SSM26(T) and SSM44 grew optimally at 30 degrees C, pH 7.0-7.5 and 0.5- 10.0 % NaCl (w/v). The major cellular fatty acids were C-18: 1 omega 7c (31.3-34.9 %), C-16:0(15.5-20.2 %), summed feature 3 (C-16:1 omega 7c/ C-16:1 omega 6c; 19.5-25.4 %) and C-12:0 (6.0-9.3 %). The genomic DNA G+C content of each strain was 56.2 mol%. Genomic related-ness analyses based on the average nucleotide identity and the genome- to-genome distance showed that strains SSM26(T) and SSM44 constituted a single species that was clearly distinguishable from its phylogenetically close relatives. The combined phenotypic, chemotaxonomic, genomic and phylogenetic data also showed that strains SSM26(T) and SSM44 could be distin-guished from validly published members of the genus Pseudomonas. Thus, these strains should be classified as representing a novel species in the genus Pseudomonas, for which the name Pseudomonas neustonica sp. nov. is proposed with the type strain SSM26(T) (=KCCM 43193(T)=JCM 31284(T)=PAMC 28426(T)) and a sister strain SSM44 (=KCCM 43194=JCM 31285=PAMC 28427).

Getz Ice Shelf melt enhanced by freshwater discharge from beneath the West Antarctic Ice Sheet

2020-04-27T00:00:00Z

Title: Getz Ice Shelf melt enhanced by freshwater discharge from beneath the West Antarctic Ice Sheet Authors: Wei, Wei; Blankenship, Donald D.; Greenbaum, Jamin S.; Gourmelen, Noel; Dow, Christine F.; Richter, Thomas G.; Greene, Chad A.; Young, Duncan A.; Lee, SangHoon; Kim, Tae-Wan; Lee, Won Sang; Assmann, Karen M. Abstract: Antarctica’s Getz Ice Shelf has been rapidly thin- ning in recent years, producing more meltwater than any other ice shelf in the world. The influx of fresh water is known to substantially influence ocean circulation and bi- ological productivity, but relatively little is known about the factors controlling basal melt rate or how basal melt is spatially distributed beneath the ice shelf. Also unknown is the relative importance of subglacial discharge from the grounded ice sheet in contributing to the export of fresh water from the ice shelf cavity. Here we compare the ob- served spatial distribution of basal melt rate to a new sub-ice- shelf bathymetry map inferred from airborne gravity surveys and to locations of subglacial discharge from the grounded ice sheet. We find that melt rates are high where bathymet- ric troughs provide a pathway for warm Circumpolar Deep Water to enter the ice shelf cavity and that melting is en- hanced where subglacial discharge fresh water flows across the grounding line. This is the first study to address the rela- tive importance of meltwater production of the Getz Ice Shelf from both ocean and subglacial sources.

Variability in high-salinity shelf water production in the Terra Nova Bay polynya, Antarctica

2020-03-01T00:00:00Z

Title: Variability in high-salinity shelf water production in the Terra Nova Bay polynya, Antarctica Authors: Yoon, Seung-Tae; Lee, Won Sang; Stevens, Craig; Jendersie, Stefan; Nam, SungHyun; Yun, Sukyoung; Hwang, Chung Yeon; Jang, Gwang Il; Lee, Jiyeon Abstract: Terra Nova Bay in Antarctica is a formation region for high-salinity shelf water (HSSW), which is a major source of Antarctic Bottom Water. Here, we analyze spatiotemporal salinity variability in Terra Nova Bay with implications for the local HSSW production. The salinity variations in the Drygalski Basin and eastern Terra Nova Bay near Crary Bank in the Ross Sea were investigated by analyzing hydrographic data from instrumented moorings, vessel-based profiles, and available wind and sea-ice products. Near-bed salinity in the eastern Terra Nova Bay (~ 660m) and Drygalski Basin (~ 1200 m) increases each year beginning in September. Significant salinity increases (> 0.04) were observed in 2016 and 2017, which is likely related to active HSSW formation. According to velocity data at identical depths, the salinity increase from September was primarily due to advection of the HSSW originating from the coastal region of the Nansen Ice Shelf. In addition, we show that HSSW can also be formed locally in the upper water column (< 300 m) of the eastern Terra Nova Bay through convection supplied by brine from the surface, which is related to polynya development via winds and ice freezing. While the general consensus is that the salinity of the HSSW was decreasing from 1995 to the late 2000s in the region, the salinity has been increasing since 2016. In 2018, it returned to values comparable to those in the early 2000s.