Freeze-thaw dynamics and the implications for stratification and brine geochemistry in meltwater ponds on the McMurdo Ice Shelf, Antarctica

2009 ◽  
Vol 21 (3) ◽  
pp. 243-254 ◽  
Author(s):  
B.R. Wait ◽  
R. Nokes ◽  
J.G. Webster-Brown
Keyword(s):  
Water Column ◽  
Major Ions ◽  
Maximum Temperature ◽  
Ice Shelf ◽  
Regional Warming ◽  
Compositional Evolution ◽  
Freeze Thaw ◽  
Air Temperatures ◽  
Chemical Stratification ◽  
Maximum Temperature Gradient

AbstractA high resolution record of water column temperatures was measured in a coastal meltwater pond on the McMurdo Ice Shelf, Antarctica. The maximum temperature gradient measured through the water column was 35°C, with an annual temperature range of 52.1°C within the pond. For most of the year the pond shows reverse temperature stratification with the lowest temperatures measured at the surface of the pond, with the exception of brief periods of normal stratification over winter caused by regional warming events. During freezing, the freezing front propagated downwards from the pond surface, excluding major ions and releasing large amounts of latent heat, both of which had a dramatic effect on the thermal and compositional evolution of the pond. Thawing is dominated by changes in surface air temperatures and the differential absorption of solar radiation. A new conceptual model of the physical freeze-thaw process has been developed that explains the presence of an ‘ice plug’ during melting, which reduces wind-induced mixing, forms a physical barrier to chemical processes, and encourages thermal and chemical stratification. It may also explain the persistence of anoxic and hydrogen sulphide bearing basal brines in summer stratified ponds that are otherwise fully oxidized.

Evidence for physical and chemical stratification in Lake Untersee (central Dronning Maud Land, East Antarctica)

1997 ◽  
Vol 9 (1) ◽  
pp. 43-45 ◽  
Author(s):  
U. Wand ◽  
G. Schwarz ◽  
E. Brüggemann ◽  
K. Bräuer
Keyword(s):  
Electrical Conductivity ◽  
Dissolved Oxygen ◽  
Water Column ◽  
Water Body ◽  
East Antarctica ◽  
Bacterial Sulphate Reduction ◽  
Chemical Stratification ◽  
Dronning Maud Land ◽  
Physical And Chemical ◽  
Vertical Gradients

Lake Untersee is the largest freshwater lake in the interior of East Antarctica. It is a perennially ice-covered, max. 169 m deep, ultra-oligotrophic lake. In contrast to earlier studies, we found clear evidence for physical and chemical stratification in the summer of 1991–92. However, the stratification was restricted to a trough, c. 500 m wide and up to 105 m deep, in the south-western part of the lake. There, the water body was distinctly stratified as indicated by sharp vertical gradients of temperature, pH, dissolved oxygen, and electrical conductivity. The water column was anoxic below 80 m. The chemical stratification is also indicated by changes of ionic ratios. Moreover, there was some evidence for methanogenesis and bacterial sulphate reduction in Lake Untersee.

scholarly journals Evidence of elevation-dependent warming from the Chinese Tian Shan

2021 ◽  
Vol 15 (12) ◽  
pp. 5765-5783
Author(s):  
Lu Gao ◽  
Haijun Deng ◽  
Xiangyong Lei ◽  
Jianhui Wei ◽  
Yaning Chen ◽  
...  
Keyword(s):  
Air Temperature ◽  
Minimum Temperature ◽  
Swiss Alps ◽  
Maximum Temperature ◽  
Current Evidence ◽  
High Mountain ◽  
Regional Warming ◽  
Mean Temperature ◽  
Warming Rate ◽  
Tian Shan

Abstract. The phenomenon in which the warming rate of air temperature is amplified with elevation is termed elevation-dependent warming (EDW). It has been clarified that EDW can accelerate the retreat of glaciers and melting of snow, which can have significant impacts on the regional ecological environment. Owing to the lack of high-density ground observations in high mountains, there is widespread controversy regarding the existence of EDW. Current evidence is mainly derived from typical high-mountain regions such as the Swiss Alps, the Colorado Rocky Mountains, the tropical Andes and the Tibetan Plateau–Himalayas. Rare evidence in other mountain ranges has been reported, especially in arid regions. In this study, EDW features (regional warming amplification and altitude warming amplification) in the Chinese Tian Shan (CTM) were detected using a unique high-resolution (1 km, 6-hourly) air temperature dataset (CTMD) from 1979 to 2016. The results showed that there were significant EDW signals at different altitudes on different timescales. The CTM showed significant regional warming amplification in spring, especially in March, and the warming trends were greater than those of continental China with respect to three temperatures (minimum temperature, mean temperature and maximum temperature). The significance values of EDW above different altitude thresholds are distinct for three temperatures in 12 months. The warming rate of the minimum temperature in winter showed a significant elevation dependence (p<0.01), especially above 3000 m. The greatest altitudinal gradient in the warming rate of the maximum temperature was found above 4000 m in April. For the mean temperature, the warming rates in June and August showed prominent altitude warming amplification but with different significance above 4500 m. Within the CTM, the Tolm Mountains, the eastern part of the Borokoonu Mountains, the Bogda Mountains and the Balikun Mountains are representative regions that showed significant altitude warming amplification on different timescales. This new evidence could partly explain the accelerated melting of snow in the CTM, although the mechanisms remain to be explored.

scholarly journals Geological factors affecting the chemical characteristics of the thermal waters of the carbonate karstified aquifers of Northern Vietnam

2000 ◽  
Vol 4 (2) ◽  
pp. 332-340 ◽  
Author(s):  
C. Drogue ◽  
N. N. Cat ◽  
J. Dazy
Keyword(s):  
Carbonate Rock ◽  
Large Scale ◽  
Sea Water ◽  
Major Ions ◽  
Thermal Waters ◽  
Chemical Characteristics ◽  
Factors Affecting ◽  
Northern Vietnam ◽  
Air Temperatures ◽  
Rock Formations

Abstract. In northern Vietnam, exposed carbonate rock formations cover an area of more than 50,000 km2 .Their accumulated thickness from the Cambrian to the Triassic is in some places as much as 3000 m. Numerous thermal waters (springs and wells) occur in these strongly karstified carbonate massifs. This is the result of significant ancient and present orogenic activity, as the region demonstrates by its strong seismic activity. These karstic formations are water-bearing and strongly recharged by rainfall of between 1600 mm and 2000 mm per year in 90% of the area concerned. In view of the average annual air temperatures (17°C-25°C according to the region), 23 sample springs or wells were chosen with water temperatures of between 29°C and 68°C. Hydrochemical characteristics of these thermal waters emerging in different carbonate-rock units were examined by chemical analyses of major ions. In this large region, thermal waters are divided into four hydrochemical types: the Na-Cl type resulting from the intrusion of sea water for distances of up to several kilometres inland and depths of 1000 m, the Ca-SO4 type, probably resulting from the leaching of deposits of metallic sulphides that are widely distributed in these carbonate-rock units, and finally the Ca-HCO3 and Mg-HCO3 types which are chemically similar to fresh karstic waters in limestones and dolostones. The occurrence of these thermal groundwaters as well as their chemical characteristics seem to indicate the existence of large-scale deepseated groundwater flow systems in the karstic aquifers. Keywords: Vietnam; thermal waters; karst; hydrochemistry

scholarly journals Summer surface melt thins Petermann Gletscher Ice Shelf by enhancing channelized basal melt

2019 ◽  
Vol 65 (252) ◽  
pp. 662-674 ◽  
Author(s):  
PETER WASHAM ◽  
KEITH W. NICHOLLS ◽  
ANDREAS MÜNCHOW ◽  
LAURIE PADMAN
Keyword(s):  
Time Series Data ◽  
Series Data ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Air Temperatures ◽  
External Forcings ◽  
Grounding Line ◽  
A Site ◽  
Strong Seasonality ◽  
Specific Contribution

ABSTRACTIncreasing ocean and air temperatures have contributed to the removal of floating ice shelves from several Greenland outlet glaciers; however, the specific contribution of these external forcings remains poorly understood. Here we use atmospheric, oceanographic and glaciological time series data from the ice shelf of Petermann Gletscher, NW Greenland to quantify the forcing of the ocean and atmosphere on the ice shelf at a site ~16 km from the grounding line within a large sub-ice-shelf channel. Basal melt rates here indicate a strong seasonality, rising from a winter mean of 2 m a−1 to a maximum of 80 m a−1 during the summer melt season. This increase in basal melt rates confirms the direct link between summer atmospheric warming around Greenland and enhanced ocean-forced melting of its remaining ice shelves. We attribute this enhanced melting to increased discharge of subglacial runoff into the ocean at the grounding line, which strengthens under-ice currents and drives a greater ocean heat flux toward the ice base.

Summer–winter transitions in Antarctic ponds: III. Chemical changes

2011 ◽  
Vol 24 (2) ◽  
pp. 121-130 ◽  
Author(s):  
Jenny Webster-Brown ◽  
Ian Hawes ◽  
Karl Safi ◽  
Brian Sorrell ◽  
Nathaniel Wilson
Keyword(s):  
Trace Elements ◽  
Water Column ◽  
Ice Shelf ◽  
Toxic Trace Elements ◽  
Mineral Phases ◽  
Show Evidence ◽  
Speciation Modelling ◽  
Geochemical Speciation ◽  
Inorganic Solutes ◽  
High Concentrations

AbstractObservations were made of water column chemistry in four Na-Cl dominated ponds on the McMurdo Ice Shelf from the end of January to early April in 2008. During that time the ponds went from ice-free to predominantly frozen, with only a small volume of residual hypoxic, saline liquid trapped at the base of each pond. Changes in the concentrations of inorganic solutes with time distinguished Na, Cl, Mg, K, SO4, As, U and Mn as ions and trace elements that behave mainly conservatively during freezing, from those which are affected by biological processes (removing HCO3) and the precipitation of mineral phases such as calcite (removing Ca and more HCO3). Dissolved Fe, Mo, Cu and Zn also show evidence of precipitation from the water column during freezing; geochemical speciation modelling predicts the formation of stable insoluble mineral phases such as Fe oxides and oxyhydroxides while conditions are oxic, and Fe-, Cu-, Mo- and Zn-sulphide minerals in the presence of H2S. Consequently, under winter conditions, residual liquid beneath the ice in such ponds is anticipated to be an anoxic Na-Cl brine with the capacity to develop high concentrations of toxic trace elements such as As and U.

scholarly journals Ice-shelf – ocean interactions at Fimbul Ice Shelf, Antarctica from oxygen isotope ratio measurements

Ocean Science ◽  
2008 ◽  
Vol 4 (1) ◽  
pp. 89-98 ◽  
Author(s):  
M. R. Price ◽  
K. J. Heywood ◽  
K. W. Nicholls
Keyword(s):  
Water Column ◽  
Continental Slope ◽  
Significant Contribution ◽  
Weddell Sea ◽  
Oxygen Isotope Ratio ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Greenwich Meridian ◽  
Melt Water ◽  
Ice Shelf Water

Abstract. Melt water from the floating ice shelves at the margins of the southeastern Weddell Sea makes a significant contribution to the fresh water budget of the region. In February 2005 a multi-institution team conducted an oceanographic campaign at Fimbul Ice Shelf on the Greenwich Meridian as part of the Autosub Under Ice programme. This included a mission of the autonomous submarine Autosub 25 km into the cavity beneath Fimbul Ice Shelf, and a number of ship-based hydrographic sections on the continental shelf and adjacent to the ice shelf front. The measurements reveal two significant sources of glacial melt water at Fimbul Ice Shelf: the main cavity under the ice shelf and an ice tongue, Trolltunga, that protrudes from the main ice front and out over the continental slope into deep water. Glacial melt water is concentrated in a 200 m thick Ice Shelf Water (ISW) layer below the base of the ice shelf at 150–200 m, with a maximum glacial melt concentration of up to 1.16%. Some glacial melt is found throughout the water column, and much of this is from sources other than Fimbul Ice Shelf. However, at least 0.2% of the water in the ISW layer cannot be accounted for by other processes and must have been contributed by the ice shelf. Just downstream of Fimbul Ice Shelf we observe locally created ISW mixing out across the continental slope. The ISW formed here is much less dense than that formed in the southwest Weddell Sea, and will ultimately contribute a freshening (and reduction in δ18O) to the upper 100–150 m of the water column in the southeast Weddell Sea.

scholarly journals Minimum maximum temperature gradient coil design

2012 ◽  
Vol 70 (2) ◽  
pp. 584-594 ◽  
Author(s):  
Peter T. While ◽  
Michael S. Poole ◽  
Larry K. Forbes ◽  
Stuart Crozier
Keyword(s):  
Temperature Gradient ◽  
Gradient Coil ◽  
Maximum Temperature ◽  
Coil Design ◽  
Gradient Coil Design ◽  
Maximum Temperature Gradient

scholarly journals Vertical mixing, critical depths, and phytoplankton growth in the Ross Sea

2014 ◽  
Vol 72 (6) ◽  
pp. 1952-1960 ◽  
Author(s):  
Walker O. Smith ◽  
Randolph M. Jones
Keyword(s):  
Water Column ◽  
Mixed Layer ◽  
Phytoplankton Biomass ◽  
Ross Sea ◽  
Vertical Mixing ◽  
Biomass Accumulation ◽  
Phytoplankton Growth ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Mixed Layers

Abstract Phytoplankton growth and biomass accumulation vary spatially and temporally in the Ross Sea, largely as a function of ice concentrations, vertical mixing depths, and iron concentrations. To assess the role of vertical mixing in bloom initiation, we used a high-resolution numerical model to estimate changes in mixed layer depths from October 1 through early December, the period where phytoplankton growth begins and biomass accumulates, and estimate critical depths for this period. Mixed layers in October ranged from the complete water column (&gt;600 m) to ca. 200 m; over a 60-day period, the mixed layers decreased on average by 70%. Estimated critical depths were exceeded in October, but would allow growth to proceed in late October due to shoaling of mixed layer depths, consistent with the known onset of the spring bloom in the Ross Sea. We also analysed a series of stations sampled near the Ross Ice Shelf during January 2012. Mean vertical profiles for the stations indicated deep vertical mixing; mixed layer depths averaged 60 m and ranged up to 96 m. Chlorophyll concentrations within the mixed layer averaged 6.60 µg l−1, and the pigment contributions were dominated by Phaeocystis antarctica. We suggest that this mesoscale region near the ice shelf is elevated in phytoplankton biomass due to frequent mixing events that redistribute biomass to depth and replenish nutrients, which in turn are utilized by an assemblage capable of utilizing low mean irradiance levels. Thus, the deep mixed layers and high biomass concentrations represent growth over long periods under reduced mixing punctuated by short periods of deeper vertical mixing that redistribute biomass. Water column vertical mixing and phytoplankton biomass in the Ross Sea are consistent with the critical depth concept as originally proposed by Sverdrup.

scholarly journals The cavity under the Amery Ice Shelf, East Antarctica

2008 ◽  
Vol 54 (188) ◽  
pp. 881-887 ◽  
Author(s):  
B.K. Galton-Fenzi ◽  
C. Maraldi ◽  
R. Coleman ◽  
J. Hunter
Keyword(s):  
Water Column ◽  
Ocean Circulation ◽  
East Antarctica ◽  
Ocean Tide ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Ocean Tide Model ◽  
Amery Ice Shelf ◽  
Tidal Constituents

AbstractOcean circulation under ice shelves and associated rates of melting and freezing are strongly influenced by the shape of the sub-ice-shelf cavity. We have refined an existing method and used additional in situ measurements to estimate the cavity shape under the Amery Ice Shelf, East Antarctica. A finite-element hydrodynamic ocean-tide model was used to simulate the major tidal constituents for a range of different sub-Amery Ice Shelf cavity water-column thicknesses. The data are adjusted in the largely unsurveyed southern region of the ice-shelf cavity by comparing the complex error between simulated tides and in situ tides, derived from GPS observations. We show a significant improvement in the simulated tides, with a combined complex error of 1.8 cm, in comparison with past studies which show a complex error of ∼5.3 cm. Our bathymetry incorporates ice-draft data at the grounding line and seismic surveys, which have provided a considerable amount of new data. This technique has particular application when the water column beneath ice shelves is inaccessible and in situ GPS data are available.

Seabed topography under the southern and western Ronne Ice Shelf, derived from seismic surveys

1997 ◽  
Vol 9 (2) ◽  
pp. 201-208 ◽  
Author(s):  
M.R. Johnson ◽  
A.M. Smith
Keyword(s):  
Water Column ◽  
Seismic Reflection ◽  
Seismic Velocity ◽  
Ice Shelf ◽  
Complete Coverage ◽  
Seismic Surveys ◽  
Bathymetric Data ◽  
Ice Surface ◽  
Seabed Topography ◽  
Estimated Error

Seismic reflection measurements of ice thickness and water-column thickness have been made over the southern and western Ronne Ice Shelf, from which, the seabed elevation has been determined. A 2300 km traverse, covering an area over which little bathymetric data previously existed and at a station interval of 15 km, resulted in 152 new measurements of the seabed elevation. The seismic velocity in the ice shelf was determined using shallow refraction surveys for the snow and firn in the upper 100 m of the ice shelf, and by applying a model assuming a simple temperature profile for the deeper ice. Surface elevations were calculated assuming the ice to be in hydrostatic equilibrium. The estimated error in the seabed elevations is ±15 m. With the addition of the new data there is now complete coverage of the seabed elevation and water-column thickness for Ronne Ice Shelf at a spatial resolution of between 10–100 km. The seabed in the area to the south of Korff and Henry ice rises and the Doake Ice Rumples is about 100 m shallower than had previously been speculated, which will affect the validity of previous assumptions of water circulation and ice-ocean interaction in this area.

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