Dissolved gases in perennially ice-covered lakes of the McMurdo Dry Valleys, Antarctica

1998 ◽  
Vol 10 (2) ◽  
pp. 124-133 ◽  
Author(s):  
D.T. Andersen ◽  
C.P. Mckay ◽  
R.A. Wharton
Keyword(s):  
Water Column ◽  
Turbulent Mixing ◽  
Bubble Formation ◽  
Gas Content ◽  
Main Process ◽  
Water Interface ◽  
Dry Valleys ◽  
The Mean ◽  
Ice Water ◽  
Made In

Measurements of dissolved N2, O2, Ar, CO2, and CH4 were made in perennially ice-covered Lake Hoare. Results confirm previous reports that O2 concentrations in the upper water column exceed atmospheric equilibrium and that N2 and Ar are supersaturated throughout the water column. The mean supersaturation of N2 was found to be 2.0 (±0.37) and Ar was 3.8 (±1.1). The ratios of N2/Ar (20.3 ±3.8), and O2/Ar (22.5 ±4.0) at the ice-water interface are consistent with those previously measured, suggesting that bubble formation is the main process for removing gas from the lake. However, the saturations of N2 and Ar greatly exceed those previously predicted for degassing by bubble formation only at the ice-water interface. The data support the hypothesis that removal of gas by bubbles occurs in the water column to a depth of 11 m in Lake Hoare. CO2 concentration increases from near zero at the ice-water interface to 80–100 times saturation at and below the chemocline at c. 28 m. There is considerable variability in the gas concentrations throughout the water column; samples separated in depth by one metre may vary by more than 50% in gas content. It is likely that this phenomenon results from the lack of turbulent mixing in the water column. Methane (c. 2 μg 1−1) was detected below the chemocline and immediately above the sediment/water interface at a depth of 30 m. Samples from lakes Vanda, Joyce, and Miers, also show supersaturations of O2, N2, and Ar at levels similar to levels found in Lake Hoare.

scholarly journals Sea-ice habitat minimizes grazing impact and predation risk for larval Antarctic krill

Polar Biology ◽  
2021 ◽  
Author(s):  
Carmen L. David ◽  
Fokje L. Schaafsma ◽  
Jan A. van Franeker ◽  
Evgeny A. Pakhomov ◽  
Brian P. V. Hunt ◽  
...  
Keyword(s):  
Sea Ice ◽  
Predation Risk ◽  
Water Column ◽  
Antarctic Krill ◽  
Standing Stock ◽  
Euphausia Superba ◽  
Grazing Impact ◽  
Water Interface ◽  
Winter Habitat ◽  
Ice Water

AbstractSurvival of larval Antarctic krill (Euphausia superba) during winter is largely dependent upon the presence of sea ice as it provides an important source of food and shelter. We hypothesized that sea ice provides additional benefits because it hosts fewer competitors and provides reduced predation risk for krill larvae than the water column. To test our hypothesis, zooplankton were sampled in the Weddell-Scotia Confluence Zone at the ice-water interface (0–2 m) and in the water column (0–500 m) during August–October 2013. Grazing by mesozooplankton, expressed as a percentage of the phytoplankton standing stock, was higher in the water column (1.97 ± 1.84%) than at the ice-water interface (0.08 ± 0.09%), due to a high abundance of pelagic copepods. Predation risk by carnivorous macrozooplankton, expressed as a percentage of the mesozooplankton standing stock, was significantly lower at the ice-water interface (0.83 ± 0.57%; main predators amphipods, siphonophores and ctenophores) than in the water column (4.72 ± 5.85%; main predators chaetognaths and medusae). These results emphasize the important role of sea ice as a suitable winter habitat for larval krill with fewer competitors and lower predation risk. These benefits should be taken into account when considering the response of Antarctic krill to projected declines in sea ice. Whether reduced sea-ice algal production may be compensated for by increased water column production remains unclear, but the shelter provided by sea ice would be significantly reduced or disappear, thus increasing the predation risk on krill larvae.

scholarly journals Tank study of physico-chemical controls on gas content and composition during growth of young sea ice

2002 ◽  
Vol 48 (161) ◽  
pp. 177-191 ◽  
Author(s):  
Jean-Louis Tison ◽  
Christian Haas ◽  
Marcia M. Gowing ◽  
Suzanne Sleewaegen ◽  
Alain Bernard
Keyword(s):  
Sea Ice ◽  
Sea Water ◽  
Bubble Nucleation ◽  
Water Dynamics ◽  
Gas Content ◽  
First Year ◽  
Water Interface ◽  
Atmospheric Gases ◽  
Physico Chemical ◽  
Ice Water

AbstractDuring an ice-tank experiment, samples were taken to study the processes of acquisition and alteration of the gas properties in young first-year sea ice during a complete growth–warming–cooling cycle. The goal was to obtain reference levels for total gas content and concentrations of atmospheric gases (O2, N2, CO2) in the absence of significant biological activity. The range of total gas-content values obtained (3.5–18 mL STP kg−1) was similar to previous measurements or estimates. However, major differences occurred between current and quiet basins, showing the role of the water dynamics at the ice–water interface in controlling bubble nucleation processes. Extremely high CO2concentrations were observed in all the experiments (up to 57% in volume parts). It is argued that these could have resulted from two unexpected biases in the experimental settings. Concentrations in bubbles nucleated at the interface are controlled by diffusion both from the ice–water interface towards the well-mixed reservoir and between the interface water and the bubble itself. This double kinetic effect results in a transition of the gas composition in the bubbles from values close to solubility in sea water toward values close to atmospheric, as the ice cover builds up.

scholarly journals Ultra-algae (<5 pm) in the ice, at the ice-water interface and in the under-ice water column (southeastern Hudson Bay, Canada)

1994 ◽  
Vol 115 ◽  
pp. 169-180 ◽  
Author(s):  
B Robineau ◽  
L Legendre ◽  
J-C Therriault ◽  
L Fortier ◽  
G Rosenberg ◽  
...  
Keyword(s):  
Water Column ◽  
Hudson Bay ◽  
Water Interface ◽  
Ice Water

scholarly journals Computational Evaluation of Shock Wave Interaction with a Cylindrical Water Column

2021 ◽  
Vol 11 (11) ◽  
pp. 4934
Author(s):  
Viola Rossano ◽  
Giuliano De Stefano
Keyword(s):  
Shock Wave ◽  
Water Column ◽  
Wave Interaction ◽  
Navier Stokes ◽  
Plane Shock ◽  
Governing Equations ◽  
Computational Evaluation ◽  
Air Water Interface ◽  
The Mean ◽  
The Impact

Computational fluid dynamics was employed to predict the early stages of the aerodynamic breakup of a cylindrical water column, due to the impact of a traveling plane shock wave. The unsteady Reynolds-averaged Navier–Stokes approach was used to simulate the mean turbulent flow in a virtual shock tube device. The compressible flow governing equations were solved by means of a finite volume-based numerical method, where the volume of fluid technique was employed to track the air–water interface on the fixed numerical mesh. The present computational modeling approach for industrial gas dynamics applications was verified by making a comparison with reference experimental and numerical results for the same flow configuration. The engineering analysis of the shock–column interaction was performed in the shear-stripping regime, where an acceptably accurate prediction of the interface deformation was achieved. Both column flattening and sheet shearing at the column equator were correctly reproduced, along with the water body drift.

Coronary Care in a General Hospital

1971 ◽  
Vol 16 (3) ◽  
pp. 173-182 ◽  
Author(s):  
Gavin Shaw ◽  
Bernard Groden ◽  
Evelyn Hastings
Keyword(s):  
Myocardial Infarction ◽  
Intensive Care Unit ◽  
Intensive Care ◽  
General Hospital ◽  
First Year ◽  
Duration Of Stay ◽  
Before And After ◽  
The Mean ◽  
Coronary Care ◽  
Made In

The establishment, staffing and structure and observations made in the first year of the existence of coronary care in an intensive care unit in a general hospital are recorded. Two hundred and twenty eight patients were admitted during the year in whom the diagnosis of myocardial infarction was confirmed. There were 29 deaths in the unit and 14 deaths occurred in the wards of the hospital after discharge from the unit. 49.1 per cent of the patients were admitted within 4 hours of the onset of symptoms and the mean duration of stay in the unit was 86.5 hours. The type of arrhythmia detected in the unit, and the treatment given to the patients both before and after admission to the intensive care unit are described.

scholarly journals Evidence for subglacial ponding across Taylor Glacier, Dry Valleys, Antarctica

2004 ◽  
Vol 39 ◽  
pp. 79-84 ◽  
Author(s):  
Alun Hubbard ◽  
Wendy Lawson ◽  
Brian Anderson ◽  
Bryn Hubbard ◽  
Heinz Blatter
Keyword(s):  
Equipotential Surface ◽  
Dry Valleys ◽  
Flow Paths ◽  
Dielectric Contrast ◽  
Pressure Melting ◽  
Reflective Power ◽  
Taylor Glacier ◽  
High Dielectric ◽  
Ice Water ◽  
Modelling Data

AbstractIce-penetrating radar and modelling data are presented suggesting the presence of a zone of temperate ice, water ponding or saturated sediment beneath the tongue of Taylor Glacier, Dry Valleys, Antarctica. The proposed subglacial zone lies 3–6 km up-glacier of the terminus and is 400– 1000m across. The zone coincides with an extensive topographic overdeepening to 80m below sea level. High values of residual bed reflective power across this zone compared to other regions and the margins of the glacier require a high dielectric contrast between the ice and the bed and are strongly indicative of the presence of basal water or saturated sediment. Analysis of the hydraulic equipotential surface also indicates strong convergence into this zone of subglacial water flow paths. However, thermodynamic modelling reveals that basal temperatures in this region could not exceed –7˚C relative to the pressure-melting point. Such a result is at odds with the radar observations unless the subglacial water is a hypersaline brine.

SURGICAL PROCESS RE-ENGINEERING: CARPAL TUNNEL DECOMPRESSION — A MODEL

Hand Surgery ◽  
2004 ◽  
Vol 09 (01) ◽  
pp. 19-27 ◽  
Author(s):  
J. A. Casaletto ◽  
V. Rajaratnam
Keyword(s):  
Carpal Tunnel ◽  
Carpal Tunnel Release ◽  
Procedure Time ◽  
Original Process ◽  
Depth Analysis ◽  
New Process ◽  
Common Operation ◽  
The Mean ◽  
Operative Findings ◽  
Made In

Surgical process re-engineering is a methodology where the entire surgical process is systematically analysed and re-designed. The process starts with mapping of the current process followed by in-depth analysis of the existing process. A new process is drafted with the aim of making the whole procedure more efficient. The new process is then discussed with all the staff involved in the operating room. Following implementation of the process, surgical process re-engineering should ideally be routinely carried out to continuously improve the procedure. We present an example of surgical process re-engineering which we carried out on the procedure of carpal tunnel release. We used carpal tunnel release as a model as it is a very common operation, with predictable intra-operative findings, and the patient is likely to benefit directly from procedure time reduction. A preliminary mapping of three procedures was done followed by a detailed timed mapping of five routine carpal tunnel decompression procedures. The mapped process was analysed in detail and a number of changes were made in the process. After implementing the new process, a further five procedures were mapped and timed again. In comparison to the original process, we achieved a reduction of 20% in the mean procedure time and a reduction of 42% in the number of steps from 66 to 37.

Effects of Fe addition on sediment P dynamics in a eutrophic lake

2021 ◽  
Author(s):  
Melanie Münch ◽  
Rianne van Kaam ◽  
Karel As ◽  
Stefan Peiffer ◽  
Gerard ter Heerdt ◽  
...  
Keyword(s):  
Water Quality ◽  
Organic Matter ◽  
Surface Water ◽  
Water Column ◽  
Sediment Cores ◽  
Surface Water Quality ◽  
Water Interface ◽  
Eutrophic Lakes ◽  
Fe Addition

&lt;p&gt;The decline of surface water quality due to excess phosphorus (P) input is a global problem of increasing urgency. Finding sustainable measures to restore the surface water quality of eutrophic lakes with respect to P, other than by decreasing P inputs, remains a challenge. The addition of iron (Fe) salts has been shown to be effective in removing dissolved phosphate from the water column of eutrophic lakes. However, the resulting changes in biogeochemical processes in sediments as well as the long-term effects of Fe additions on P dynamics in both sediments and the water column are not well understood.&lt;/p&gt;&lt;p&gt;In this study, we assess the impact of past Fe additions on the sediment P biogeochemistry of Lake Terra Nova, a well-mixed shallow peat lake in the Netherlands. The Fe-treatment in 2010 efficiently reduced P release from the sediments to the surface waters for 6 years. Since then, the internal sediment P source in the lake has been increasing again with a growing trend over the years.&lt;/p&gt;&lt;p&gt;In 2020, we sampled sediments at three locations in Terra Nova, of which one received two times more Fe during treatment than the other two. Sediment cores from all sites were sectioned under oxygen-free conditions. Both the porewaters and sediments were analysed for their chemical composition, with sequential extractions providing insight into the sediment forms of P and Fe. Additional sediment cores were incubated under oxic and anoxic conditions and the respective fluxes of P and Fe across the sediment water interface were measured.&lt;/p&gt;&lt;p&gt;The results suggest that Fe and P dynamics in the lake sediments are strongly coupled. We also find that the P dynamics are sensitive to the amount of Fe supplied, even though enhanced burial of P in the sediment was not detected. The results of the sequential extraction procedure for P, which distinguishes P associated with humic acids and Fe oxides, as well as reduced flux of Fe(II) across the sediment water interface in the anoxic incubations, suggest a major role of organic matter in the interaction of Fe and P in these sediments.&lt;/p&gt;&lt;p&gt;Further research will include investigations of the role of organic matter and sulphur in determining the success of Fe-treatment in sequestering P in lake sediments. Based on these data in combination with reactive transport modelling we aim to constrain conditions for successful lake restoration through Fe addition.&lt;/p&gt;

scholarly journals Physical controls on the storage of methane in landfast sea ice

2014 ◽  
Vol 8 (3) ◽  
pp. 1019-1029 ◽  
Author(s):  
J. Zhou ◽  
J.-L. Tison ◽  
G. Carnat ◽  
N.-X. Geilfus ◽  
B. Delille
Keyword(s):  
Sea Ice ◽  
Bubble Formation ◽  
Gas Bubble ◽  
Physical Processes ◽  
Ice Melt ◽  
Physical Controls ◽  
The Difference ◽  
Landfast Sea Ice ◽  
Ice Water ◽  
Brine Concentration

Abstract. We report on methane (CH4) dynamics in landfast sea ice, brine and under-ice seawater at Barrow in 2009. The CH4 concentrations in under-ice water ranged from 25.9 to 116.4 nmol L−1sw, indicating a supersaturation of 700 to 3100% relative to the atmosphere. In comparison, the CH4 concentrations in sea ice ranged from 3.4 to 17.2 nmol L−1ice and the deduced CH4 concentrations in brine from 13.2 to 677.7 nmol L−1brine. We investigated the processes underlying the difference in CH4 concentrations between sea ice, brine and under-ice water and suggest that biological controls on the storage of CH4 in ice were minor in comparison to the physical controls. Two physical processes regulated the storage of CH4 in our landfast ice samples: bubble formation within the ice and sea ice permeability. Gas bubble formation due to brine concentration and solubility decrease favoured the accumulation of CH4 in the ice at the beginning of ice growth. CH4 retention in sea ice was then twice as efficient as that of salt; this also explains the overall higher CH4 concentrations in brine than in the under-ice water. As sea ice thickened, gas bubble formation became less efficient, CH4 was then mainly trapped in the dissolved state. The increase of sea ice permeability during ice melt marked the end of CH4 storage.

Reaction in a scalar mixing layer

1991 ◽  
Vol 233 ◽  
pp. 211-242 ◽  
Author(s):  
R. W. Bilger ◽  
L. R. Saetran ◽  
L. V. Krishnamoorthy
Keyword(s):  
Chemical Reaction ◽  
Mixing Layer ◽  
Reacting Flow ◽  
Scalar Mixing ◽  
Scalar Theory ◽  
Thermal Mixing ◽  
Fast Chemistry ◽  
The Mean ◽  
Reactive Scalars ◽  
Made In

Reaction in a scalar mixing layer in grid-generated turbulence is studied experimentally by doping half of the flow with nitric oxide and the other half with ozone. The flow conditions and concentrations are such that the chemical reaction is passive and the flow and chemical timescales are of the same order. Conserved scalar theory for such flows is outlined and further developed; it is used as a basis for presentation of the experimental results. Continuous measurements of concentration are limited in their spatial and temporal resolution but capture sufficient of their spectra for adequate second-order correlations to be made. Two components of velocity have been measured simultaneously with hot-wire anemometry. Conserved scalar mixing results, deduced from reacting and non-reacting measurements of concentration, show the independence of concentration level and concentration ratio expected for passive reacting flow. The results are subject to several limitations due to the necessary experimental compromises, but they agree generally with measurements made in thermal mixing layers. Reactive scalar statistics are consistent with the realizability constraints obtainable from conserved scalar theory where such constraints apply, and otherwise are generally found to lie between the conserved scalar theory limits for frozen and very fast chemistry. It is suggested that Toor's (1969) closure for the mean chemical reaction rate could be improved by interpolating between the frozen and equilibrium values for the covariance. The turbulent fluxes of the reactive scalars are found to approximately obey the gradient model but the value of the diffusivity is found to depend on the Damköhler number.

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