PSnews No.35

　　Polar Science　　

The followings are published in Vol. 10 Issue 2 (June, 2016)

Net mass balance calculations for the Shirase Drainage Basin, east Antarctica, using the mass budget method
Kazuki Nakamura, Tsutomu Yamanokuchi, Koichiro Doi, Kazuo Shibuya
We quantify the mass budget of the Shirase drainage basin (SHI), Antarctica, by separately estimating snow accumulation (surface mass balance; SMB) and glacier ice mass discharge (IMD). We estimated the SMB in the SHI, using a regional atmospheric climate model (RACMO2.1). The SMB of the mainstream A flow region was 12.1 ± 1.5 Gt a-1 for an area of 1.985 × 105 km2. Obvious overestimation of the model round the coast, ∼0.5 Gt a-1, was corrected for. For calculating the IMD, we employed a 15-m resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) with a digital elevation model (DEM) to determine the heights at the grounding line (GL), after comparison with the interpolated Bamber DEM grid heights; the results of this are referred to as the measured heights. Ice thickness data at the GL were inferred by using a free-board relationship between the measured height and the ice thickness, and considering the measured firn depth correction (4.2 m with the reference ice density of 910 kg m-3) for the nearby blue-ice area. The total IMD was estimated to be 14.0 ± 1.8 Gt a-1. Semi-empirical firn densification model gives the estimate within 0.1-0.2 Gt a-1 difference. The estimated net mass balance, -1.9 Gt a-1, has a two-σ uncertainty of ±3.3 Gt a-1, and probable melt water discharge strongly suggests negative NMB, although the associated uncertainty is large.

Antibiotic resistance in Escherichia coli strains isolated from Antarctic bird feces, water from inside a wastewater treatment plant, and seawater samples collected in the Antarctic Treaty area
Virginia Rabbia, Helia Bello-Toledo, Sebastián Jiménez, Mario Quezada, Mariana Domínguez, Luis Vergara, Claudio Gómez-Fuentes, Nancy Calisto-Ulloa, Daniel González-Acuña, Juana López, Gerardo González-Rocha
Antibiotic resistance is a problem of global concern and is frequently associated with human activity. Studying antibiotic resistance in bacteria isolated from pristine environments, such as Antarctica, extends our understanding of these fragile ecosystems. Escherichia coli strains, important fecal indicator bacteria, were isolated on the Fildes Peninsula (which has the strongest human influence in Antarctica), from seawater, bird droppings, and water samples from inside a local wastewater treatment plant. The strains were subjected to molecular typing with pulsed-field gel electrophoresis to determine their genetic relationships, and tested for antibiotic susceptibility with disk diffusion tests for several antibiotic families: β-lactams, quinolones, aminoglycosides, tetracyclines, phenicols, and trimethoprim-sulfonamide. The highest E. coli count in seawater samples was 2400 cfu/100 mL. Only strains isolated from seawater and the wastewater treatment plant showed any genetic relatedness between groups. Strains of both these groups were resistant to β-lactams, aminoglycosides, tetracycline, and trimethoprim–sulfonamide. In contrast, strains from bird feces were susceptible to all the antibiotics tested. We conclude that naturally occurring antibiotic resistance in E. coli strains isolated from Antarctic bird feces is rare and the bacterial antibiotic resistance found in seawater is probably associated with discharged treated wastewater originating from Fildes Peninsula treatment plants. 　

Observations of vertical tidal motions of a floating iceberg in front of Shirase Glacier, East Antarctica, using a geodetic-mode GPS buoy
Yuichi Aoyama, Tae-Hee Kim, Koichiro Doi, Hideaki Hayakawa, Toshihiro Higashi, Shingo Ohsono, Kazuo Shibuya
A dual-frequency GPS receiver was deployed on a floating iceberg downstream of the calving front of Shirase Glacier, East Antarctica, on 28 December 2011 for utilizing as floating buoy. The three-dimensional position of the buoy was obtained by GPS every 30 s with a 4-5-cm precision for ca. 25 days. The height uncertainty of the 1-h averaged vertical position was ∼0.5 cm, even considering the uncertainties of un-modeled ocean loading effects. The daily evolution of north–south (NS), east–west (EW), and up–down (UD) motions shows periodic UD variations sometimes attaining an amplitude of 1 m. Observed amplitudes of tidal harmonics of major constituents were 88%-93% (O1) and 85%-88% (M2) of values observed in the global ocean tide models FES2004 and TPXO-8 Atlas. The basal melting rate of the iceberg is estimated to be ∼0.6 m/day, based on a firn densification model and using a quasi-linear sinking rate of the iceberg surface. The 30-s sampling frequency geodetic-mode GPS buoy helps to reveal ice-ocean dynamics around the calving front of Antarctic glaciers.

Ice berg cracking events as identified from underwater ambient noise measurements in the shallow waters of Ny-Alesund, Arctic
M. Ashokan, G. Latha, A. Thirunavukkarasu, G. Raguraman, R. Venkatesan
This paper presents the work carried out on the analysis of preliminary underwater ambient noise measurements in the shallow waters of Kongsfjorden fjord, Arctic in the summer season, in which the ice berg cracking noise is identified. In the summer period, the melting of ice cover is fast and hence the ice bergs are free to move and float in the ocean. Underwater ambient noise has been acquired in the Kongsfjorden fjord, Arctic sea on 19th July 2015 at 5 m water depth, where the ocean depth is 50 m. Due to the tensile cracks at the surface of the sea ice by thermal expansion, ice berg calving and bobbing occurred near the experiment site. Analysis of power spectra shows that ice berg calving noise falls in the frequency band 100 Hz-500 Hz and the ice berg bobbing noise falls in the frequency band 200 Hz-400 Hz.

Stretching out the Australasian microtektite strewn field in Victoria Land Transantarctic Mountains
Luigi Folco, Massimo D'Orazio, Maurizio Gemelli, Pierre Rochette
Petrographic and geochemical studies of microtektites collected in newly explored summit plateaus of the Transantarctic Mountains (i.e., Schroeder Spur, Killer Nunatak, Miller Butte in the inland catchment of the Rennick Glacier, and Allan Hills, in the inland catchment of the Mackay-David Glaciers) document a regional distribution of Australasian microtektites in Victoria Land. A geochemical comparison with Australasian microtektites from deep sea sediments at lower latitudes identifies a possible projectile geochemical signature for the first time, and confirms that Transantarctic Mountains microtektites experienced higher thermal regimes. Ballistic calculations reveal that the extraordinary distance of the Transantarctic Mountains microtektites from the hypothetical impact location in Indochina (∼11,000 km) could be more efficiently attained at relatively low ejection angles (20°-40°). Finally, the occurrence of Australasian microtektites (∼0.8 Ma old) on specific glacial surfaces of the Antarctic bedrock constrains the glacial history of the East Antarctic Ice Sheet in Victoria Land. In particular, data from Allan Hills supports a glaciological scenario envisaging an extremely stable East Antarctic Ice Sheet over at least the last ∼1 Ma in the inland catchment of the Mackay/David glaciers. This is consistent with the large accumulation of meteorites in the adjacent blue ice fields.

Response of larch root development to annual changes of water conditions in eastern Siberia
Chisato Takenaka, Mie Miyahara, Takeshi Ohta, Trofim C. Maximov
Eastern Siberia is characterized by continuous permafrost, and has recently been exposed to the effects of climate change. Larch, which is the dominant tree species, has been subject to major environmental changes including fluctuations in soil water content. The purpose of this study was to clarify the responses of mature larch tree roots to changes in soil water conditions. We established a treatment plot in a larch forest, and artificially changed the soil water conditions by covering the ground surface with a vinyl sheet, and from 2004 to 2006 monitored root development through root windows. The vinyl sheet maintained high levels of soil water content, even though the ambient conditions varied from dry in 2004 to wet in 2005 and dry in 2006. In the treatment plot the plants adapted to the wet conditions by decreasing vertical root development. In contrast, roots of plants in the control plot developed to the subsurface layer, even in 2005, and did not develop vertically in 2006 despite the drought. We conclude that larch adapted to the annual changes in soil water content by changing the vertical distribution of roots, and that this reflected a memory effect.

Growth of an Inshore Antarctic fish, Trematomus newnesi (Nototheniidae), off Adelie Land
Kélig Mahé, Romain Elleboode, Christophe Loots, Philippe Koubbi
Dusky rockcod, Trematomus newnesi, is a widely distributed neritic circumpolar Antarctic fish species. We conducted a study on age and growth of T. newnesi in coastal waters of Adélie Land in East Antarctica. A total of 289 specimens were collected in 2003, 2005, 2006 and 2009. They consisted of 122 females, 132 males and 35 immature specimens. Total length (TL) and total weight (W) of these fish ranged from 13.5 to 25 cm and 19.7-174 g respectively for females and from 12 to 20.9 cm and from 24.1 to 144.1 g for males. The TL/W relationship was described by the following parameters: a = 7.2.10−3 and b = 3.127, showing no significant difference between sex (ANCOVA, P < 0.05). Fish age was estimated by counting annual growth increments on polished transverse sections of sagittal otoliths. Age estimates varied from 3 to 14 years. There was a significant relationship between otolith morphological features (weight and radius) and age with no difference between males and females (p > 0.05). The estimated values of Von Bertalanffy growth curve L∞ (cm), W∞ (g) and k were 26.6, 200.6 and 0.13 for females and 24.5, 147.0 and 0.15 for males respectively. The indices of growth performance between sexes were not significant. However, potential difference in growth rate between the morphs cannot be neglected.

Gray whale sightings in the Canadian Beaufort Sea, September 2014
Yuka Iwahara, Amane Fujiwara, Keizo Ito, Kazushi Miyashita, Yoko Mitani
Gray whales (Eschrichtius robustus) are distributed within the productive neritic and estuarine waters of the North Pacific Ocean, the Bering Sea, and adjacent waters of the Arctic Ocean. They migrate to high-latitude feeding grounds each spring. Their main feeding grounds in the Arctic include the Chirikov Basin, the northeastern Chukchi Sea from Pt. Hope to Cape Lisburne and Pt. Lay to Pt. Barrow, and the northwestern Chukchi Sea along the Chukotka coast. Although sightings are rare in the Canadian Beaufort Sea, we observed three gray whales in two groups in this area in September 2014. A mud plume was observed near one of the whales, suggesting the animal had been feeding. In the Alaskan Beaufort Sea, large-scale monitoring of the distributions of marine mammals has been continuously conducted since 1979; however, there has been less monitoring in the Canadian Beaufort Sea. Therefore, it is necessary to record opportunistic sightings, such as those described here.