scholarly journals Partitioning Effects during Terminal Carbon and Electron Flow in Sediments of a Low-Salinity Meltwater Pond near Bratina Island, McMurdo Ice Shelf, Antarctica

1999 ◽  
Vol 65 (12) ◽  
pp. 5493-5499 ◽  
Author(s):  
Douglas O. Mountfort ◽  
Heinrich F. Kaspar ◽  
Malcolm Downes ◽  
Rodney A. Asher
Keyword(s):  
Sulfate Reduction ◽  
Methane Production ◽  
Electron Flow ◽  
Fold Increase ◽  
Cyanobacterial Mats ◽  
Ice Shelf ◽  
Physiological Conditions ◽  
Low Salinity ◽  
Methane Production Rate

ABSTRACT A study of anaerobic sediments below cyanobacterial mats of a low-salinity meltwater pond called Orange Pond on the McMurdo Ice Shelf at temperatures simulating those in the summer season (<5°C) revealed that both sulfate reduction and methane production were important terminal anaerobic processes. Addition of [2-14C]acetate to sediment samples resulted in the passage of label mainly to CO2. Acetate addition (0 to 27 mM) had little effect on methanogenesis (a 1.1-fold increase), and while the rate of acetate dissimilation was greater than the rate of methane production (6.4 nmol cm−3 h−1compared to 2.5 to 6 nmol cm−3 h−1), the portion of methane production attributed to acetate cleavage was <2%. Substantial increases in the methane production rate were observed with H2 (2.4-fold), and H2 uptake was totally accounted for by methane production under physiological conditions. Formate also stimulated methane production (twofold), presumably through H2 release mediated through hydrogen lyase. Addition of sulfate up to 50-fold the natural levels in the sediment (interstitial concentration, ∼0.3 mM) did not substantially inhibit methanogenesis, but the process was inhibited by 50-fold chloride (36 mM). No net rate of methane oxidation was observed when sediments were incubated anaerobically, and denitrification rates were substantially lower than rates for sulfate reduction and methanogenesis. The results indicate that carbon flow from acetate is coupled mainly to sulfate reduction and that methane is largely generated from H2 and CO2 where chloride, but not sulfate, has a modulating role. Rates of methanogenesis at in situ temperatures were four- to fivefold less than maximal rates found at 20°C.

Effects of sulfate concentration and sludge retention time on the interaction between methane production and sulfate reduction for butyrate

1994 ◽  
Vol 30 (8) ◽  
pp. 45-54 ◽  
Author(s):  
O. Mizuno ◽  
Y. Y. Li ◽  
T. Noike
Keyword(s):  
Sulfate Reduction ◽  
Retention Time ◽  
Methane Production ◽  
Electron Flow ◽  
Degradation Pathway ◽  
Sulfate Concentration ◽  
High Concentration ◽  
Total Electron ◽  
Sludge Retention Time ◽  
Wide Range

The effects of sulfate concentration and COD/S ratio on the anaerobic degradation of butyrate were investigated by using 2.0 L anaerobic chemostat-type reactor at 35°C. The study was conducted over a wide range of the COD/S ratio (1.5 to 148) by varying COD concentrations (2500–10000 mg/L) and sulfate concentrations (68–1667 mg-S/L) in the substrate. The sludge retention time at each COD/S ratio was changed from 5 to 20 days. The interaction between methane producing bacteria (MPB) and sulfate-reducing bacteria (SRB) was evidently influenced by COD/S ratio in the substrate. When COD/S ratio was 6.0 or more, methane production was the predominate reaction and over 80% of the total electron flow was used by MPB. At the COD/S ratio of 1.5, SRB utilzed over 50% of the total electron flow. A large amount of sulfate reduction resulted in not only the decrease of methane production, but also the rapid increase of the bacterial growth. The degradation pathway of butyrate and the composition of bacterial populations in the reactor were also dominated by COD/S ratio. In sulfate depleted condition, butyrate was degraded to methane via acetate and hydrogen by MPB. On the other hand, butyrate was firstly degraded into sulfide and acetate in sulfate rich conditions by SRB, and the produced acetate was then degraded by acetate consuming MPB and SRB. The methanogenesis from acetate was inhibited by the high concentration of sulfide.

scholarly journals Localized Basal Freezing Within George VI Ice Shelf, Antarctica

1988 ◽  
Vol 34 (116) ◽  
pp. 71-77 ◽  
Author(s):  
M. Pedley ◽  
J.G. Paren ◽  
J.R. Potter
Keyword(s):  
Freezing Point ◽  
Saline Water ◽  
Thick Layer ◽  
Ice Shelf ◽  
Low Salinity ◽  
Ice Surface ◽  
Salinity Water ◽  
Basal Melting ◽  
Surface Ice

AbstractHobbs Pool is an area of thin ice shelf situated within George VI Ice Shelf, Antarctica. Thicker ice shelf surrounding Hobbs Pool isolates the upper 155 m of the water column from water lying at the same depth else-where under the ice shelf. Summer melt-water lakes drain through crevasses at Hobbs Pool forming a 155 m thick layer of low-salinity water close to its freezing point. Colder and more saline water in the lower part of this layer leads toin-situfreezing of fresher water lying above it. Below 155 m depth, the water temperature and salinity are linearly related by basal melting which is observed elsewhere under the ice shelf. The surface ice shows areas of deformation and deposits of subglacial rock debris which may result from upward particle paths in the area. The raising of subglacial rock debris on to the ice surface may provide a mechanism for the transport of erratics across the ice shelf to Alexander Island from the base of Palmer Land glaciers.

scholarly journals Influences of Pond Geochemistry, Temperature, and Freeze-Thaw on Terminal Anaerobic Processes Occurring in Sediments of Six Ponds of the McMurdo Ice Shelf, near Bratina Island, Antarctica

2003 ◽  
Vol 69 (1) ◽  
pp. 583-592 ◽  
Author(s):  
Douglas O. Mountfort ◽  
Heinrich F. Kaspar ◽  
Rodney A. Asher ◽  
Donna Sutherland
Keyword(s):  
Sulfate Reduction ◽  
Electron Flow ◽  
Chloride Concentration ◽  
Total Carbon ◽  
Ice Shelf ◽  
Anaerobic Processes ◽  
Freeze Thaw ◽  
Thaw Cycle ◽  
Freeze Thaw Cycle ◽  
Pond Sediments

ABSTRACT The effects of freeze-thaw, freezing and sediment geochemistry on terminal anaerobic processes occurring in sediments taken from below cyanobacterial mats in meltwater ponds of the McMurdo Ice Shelf in Antarctica were investigated. Depending on the geochemical and physical status of the sediments (i.e., frozen or thawed), as well as passage of sediment through a freeze-thaw cycle, terminal carbon and electron flow shifted in which the proportions of hydrogen and acetate utilized for methanogenesis and sulfate reduction changed. Thus, in low-sulfate (or chloride) sediment which was thawed and incubated at 4°C, total carbon and electron flow were mediated by acetate-driven sulfate reduction and H2-driven methanogenesis. When the same sediments were incubated frozen, both methanogenesis and sulfate reduction decreased. However, under these conditions methanogenesis was favored over sulfate reduction, and carbon flow from acetate to methane increased relative to sulfate reduction; >70% of methane was contributed by acetate, and more than 80% of acetate was oxidized by pathways not coupled to sulfate reduction. In high-sulfate pond sediments, sulfate reduction was a major process mediating terminal carbon and electron flow in both unfrozen and frozen incubations. However, as with low-sulfate sediments, acetate oxidation became uncoupled from sulfate reduction with freezing. Geochemical and temperature effects could be expressed by linear models in which the log (methanogenesis to sulfate reduction) was negative log linear with respect to either temperature or the log of the sulfate (or chloride) concentration. From these relationships it was possible to predict the ratio for a given temperature (low-sulfate sediments) or sulfate (chloride) concentration. Small transitory changes, such as elevated sulfate reduction coupled to increased acetate turnover, resulted from application of a freeze-thaw cycle to low-salinity pond sediments. The results demonstrate how ecophysiological processes may change in anaerobic systems under extreme conditions (e.g., freezing) and provide new insights into microbial events occurring under these conditions.

scholarly journals Diversity, Abundance, and Activity of Archaeal Populations in Oil-Contaminated Groundwater Accumulated at the Bottom of an Underground Crude Oil Storage Cavity

2002 ◽  
Vol 68 (8) ◽  
pp. 3899-3907 ◽  
Author(s):  
Kazuya Watanabe ◽  
Yumiko Kodama ◽  
Natsuko Hamamura ◽  
Nobuo Kaku
Keyword(s):  
Crude Oil ◽  
Methane Production ◽  
Contaminated Groundwater ◽  
Oil Storage ◽  
Nitrate Consumption ◽  
Related Organism ◽  
The Family ◽  
Methane Production Rate ◽  
Sequence Types

ABSTRACT Fluorescence in situ hybridization has shown that cells labeled with an Archaea-specific probe (ARCH915) accounted for approximately 10% of the total cell count in oil-contaminated groundwater accumulated at the bottom of an underground crude oil storage cavity. Although chemical analyses have revealed vigorous consumption of nitrate in cavity groundwater, the present study found that the methane production rate was higher than the nitrate consumption rate. To characterize the likely archaeal populations responsible for methane production in this system, fragments of 16S ribosomal DNA (rDNA) were amplified by PCR using eight different combinations of universal and Archaea-specific primers. Sequence analysis of 324 clones produced 23 different archaeal sequence types, all of which were affiliated with the kingdom Euryarchaeota. Among them, five sequence types (KuA1, KuA6, KuA12, KuA16, and KuA22) were obtained in abundance. KuA1 and KuA6 were closely related to the known methanogens Methanosaeta concilii (99% identical) and Methanomethylovorans hollandica (98%), respectively. Although no closely related organism was found for KuA12, it could be affiliated with the family Methanomicrobiaceae. KuA16 and KuA22 showed substantial homology only to some environmental clones. Both of these branched deeply in the Euryarchaeota, and may represent novel orders. Quantitative competitive PCR showed that KuA12 was the most abundant, accounting for ∼50% of the total archaeal rDNA copies detected. KuA1 and KuA16 also constituted significant proportions of the total archaeal rDNA copies (7 and 17%, respectively). These results suggest that limited species of novel archaea were enriched in the oil storage cavity. An estimate of specific methane production rates suggests that they were active methanogens.

scholarly journals Localized Basal Freezing Within George VI Ice Shelf, Antarctica

1988 ◽  
Vol 34 (116) ◽  
pp. 71-77 ◽  
Author(s):  
M. Pedley ◽  
J.G. Paren ◽  
J.R. Potter
Keyword(s):  
Freezing Point ◽  
Saline Water ◽  
Thick Layer ◽  
Ice Shelf ◽  
Low Salinity ◽  
Ice Surface ◽  
Salinity Water ◽  
Basal Melting ◽  
Surface Ice

AbstractHobbs Pool is an area of thin ice shelf situated within George VI Ice Shelf, Antarctica. Thicker ice shelf surrounding Hobbs Pool isolates the upper 155 m of the water column from water lying at the same depth else-where under the ice shelf. Summer melt-water lakes drain through crevasses at Hobbs Pool forming a 155 m thick layer of low-salinity water close to its freezing point. Colder and more saline water in the lower part of this layer leads to in-situ freezing of fresher water lying above it. Below 155 m depth, the water temperature and salinity are linearly related by basal melting which is observed elsewhere under the ice shelf. The surface ice shows areas of deformation and deposits of subglacial rock debris which may result from upward particle paths in the area. The raising of subglacial rock debris on to the ice surface may provide a mechanism for the transport of erratics across the ice shelf to Alexander Island from the base of Palmer Land glaciers.

New determinations of tides on the north-western Ross Ice Shelf

2020 ◽  
pp. 1-14
Author(s):  
Richard D. Ray ◽  
Kristine M. Larson ◽  
Bruce J. Haines
Keyword(s):  
Time Series ◽  
Tide Gauge ◽  
High Rate ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
The North ◽  
Global Positioning ◽  
North Western

Abstract New determinations of ocean tides are extracted from high-rate Global Positioning System (GPS) solutions at nine stations sitting on the Ross Ice Shelf. Five are multi-year time series. Three older time series are only 2–3 weeks long. These are not ideal, but they are still useful because they provide the only in situ tide observations in that sector of the ice shelf. The long tide-gauge observations from Scott Base and Cape Roberts are also reanalysed. They allow determination of some previously neglected tidal phenomena in this region, such as third-degree tides, and they provide context for analysis of the shorter datasets. The semidiurnal tides are small at all sites, yet M2 undergoes a clear seasonal cycle, which was first noted by Sir George Darwin while studying measurements from the Discovery expedition. Darwin saw a much larger modulation than we observe, and we consider possible explanations - instrumental or climatic - for this difference.

Growth, nisA Gene Expression, and In Situ Activity of Novel Lactococcus lactis subsp. cremoris Costarter Culture in Commercial Hard Cheese Production

2017 ◽  
Vol 80 (12) ◽  
pp. 2137-2146 ◽  
Author(s):  
Dimitrios Noutsopoulos ◽  
Athanasia Kakouri ◽  
Eleftheria Kartezini ◽  
Dimitrios Pappas ◽  
Efstathios Hatziloukas ◽  
...  
Keyword(s):  
Gene Expression ◽  
Lactococcus Lactis ◽  
Starter Culture ◽  
Fold Increase ◽  
Raw Milk ◽  
Good Growth ◽  
Lactococcus Lactis Subsp ◽  
Quantitative Expression ◽  
Hard Cheese

ABSTRACT This study evaluated in situ expression of the nisA gene by an indigenous, nisin A–producing (NisA+) Lactococcus lactis subsp. cremoris raw milk genotype, represented by strain M78, in traditional Greek Graviera cheeses under real factory-scale manufacturing and ripening conditions. Cheeses were produced with added a mixed thermophilic and mesophilic commercial starter culture (CSC) or with the CSC plus strain M78 (CSC+M78). Cheeses were sampled after curd cooking (day 0), fermentation of the unsalted molds for 24 h (day 1), brining (day 7), and ripening of the brined molds (14 to 15 kg each) for 30 days in a fully controlled industrial room (16.5°C; 91% relative humidity; day 37). Total RNA was directly extracted from the cheese samples, and the expression of nisA gene was evaluated by real-time reverse transcription PCR (qRT-PCR). Agar overlay and well diffusion bioassays were correspondingly used for in situ detection of the M78 NisA+ colonies in the cheese agar plates and antilisterial activity in whole-cheese slurry samples, respectively. Agar overlay assays showed good growth (&gt;8 log CFU/g of cheese) of the NisA+ strain M78 in coculture with the CSC and vice versa. The nisA expression was detected in CSC+M78 cheese samples only, with its expression levels being the highest (16-fold increase compared with those of the control gene) on day 1, followed by significant reduction on day 7 and almost negligible expression on day 37. Based on the results, certain intrinsic and mainly implicit hurdle factors appeared to reduce growth prevalence rates and decrease nisA gene expression, as well as the nisin A–mediated antilisterial activities of the NisA+ strain M78 postfermentation. To our knowledge, this is the first report on quantitative expression of the nisA gene in a Greek cooked hard cheese during commercial manufacturing and ripening conditions by using a novel, rarely isolated, indigenous NisA+ L. lactis subsp. cremoris genotype as costarter culture.

scholarly journals Thermohaline structure and circulation beneath the Langhovde Glacier ice shelf in East Antarctica

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Masahiro Minowa ◽  
Shin Sugiyama ◽  
Masato Ito ◽  
Shiori Yamane ◽  
Shigeru Aoki
Keyword(s):  
Freezing Point ◽  
East Antarctica ◽  
Ice Shelf ◽  
Rate Estimate ◽  
Ice Shelves ◽  
Plume Water ◽  
Warm Deep Water ◽  
Glacier Ice ◽  
Basal Melting

AbstractBasal melting of ice shelves is considered to be the principal driver of recent ice mass loss in Antarctica. Nevertheless, in-situ oceanic data covering the extensive areas of a subshelf cavity are sparse. Here we show comprehensive structures of temperature, salinity and current measured in January 2018 through four boreholes drilled at a ~3-km-long ice shelf of Langhovde Glacier in East Antarctica. The measurements were performed in 302–12 m-thick ocean cavity beneath 234–412 m-thick ice shelf. The data indicate that Modified Warm Deep Water is transported into the grounding zone beneath a stratified buoyant plume. Water at the ice-ocean interface was warmer than the in-situ freezing point by 0.65–0.95°C, leading to a mean basal melt rate estimate of 1.42 m a−1. Our measurements indicate the existence of a density-driven water circulation in the cavity beneath the ice shelf of Langhovde Glacier, similar to that proposed for warm-ocean cavities of larger Antarctic ice shelves.

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