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AbruptSLR

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Subglacial Lake and Meltwater Drainage Systems
« on: June 26, 2013, 08:48:46 PM »
The accompanying figures are from, and they show the extensive subglacial lake and meltwater drainage systems in Antarctica (with increasing warming [due to: surface, ocean, basal, basal friction, albedo, surface melting] these systems should be come more extensive and important in the future):

Predicting subglacial lakes and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets
by: S. J. Livingstone, C. D. Clark, and J. Woodward
The Cryosphere Discuss., 7, 1177–1213, 2013, www.the-cryosphere-discuss.net/7/1177/2013/, doi:10.5194/tcd-7-1177-2013

The caption for the first image is: "In (B), the blue colour illustrates regions below the pressure melting point. This is used as a simple mask to remove all subglacial lakes that fall within the cold-bedded zones. Note, the subglacial drainage network is still treated as though the bed was wholly warm based."

The second image is a close-up of an area taken from the first image, but focused on the WAIS area, and which shows subglacial lakes in the Thwaites Drainage basin.

The caption for the third image is:  "(B) the fraction of the grounded ice-sheet bed occupied by subglacial lakes vs ice-sheet area, with both the Antarctic and Greenland subglacial lake data plotted.
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sidd

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #1 on: June 26, 2013, 09:08:38 PM »
http://www.the-cryosphere-discuss.net/7/2979/2013/tcd-7-2979-2013.html

is a paper about a subglacial lake in unusual bed topo

AbruptSLR

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #2 on: June 26, 2013, 11:18:12 PM »
Sidd,

Great find.  The attached figure from that paper shows that the subglacial lake flows into the Weddell Sea, and as I have long wondered why the GIA was so large in the Weddell Sea area, it now seems possible to me that part of the ice mass loss associated with the large GIA may be due to drainage of basal meltwater from the ice sheet in this area.

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #3 on: June 26, 2013, 11:49:49 PM »
The following abstract and the attached two images are from:

Cascading water underneath Wilkes Land, East Antarctic Ice Sheet, observed using altimetry and digital elevation models
By: T. Flament, E. Berthier, and F. Rémy
The Cryosphere Discuss., 7, 841–871, 2013, www.the-cryosphere-discuss.net/7/841/2013/, doi:10.5194/tcd-7-841-2013

"Abstract
We describe a major subglacial lake drainage close to the ice divide in Wilkes Land, East Antarctica, and the subsequent cascading of water underneath the ice sheet toward the coast. To analyze the event, we combined altimetry data from several sources and bedrock data. We estimated the total volume of water that drained from Lake Cook by differencing digital elevation models (DEM) derived from ASTER and SPOT5 stereo-imagery. With 5.2±0.5 km3, this is the largest single subglacial drainage event reported so far in Antarctica. Elevation differences between ICESat laser altimetry and the SPOT5 DEM indicate that the discharge lasted approximately 2 yr. A 13-m uplift of the surface, corresponding to a refilling of about 0.64±0.32 km3, was observed between the end of the discharge in October 2008 and February 2012. Using Envisat radar altimetry, with its high 35-day temporal resolution, we monitored the subsequent filling and drainage of connected subglacial lakes located downstream. In particular, a transient temporal signal can be detected within the theoretical 500-km long flow paths computed with the BEDMAP2 data set. The volume of water traveling in this wave is inagreement with the volume that drained from Lake CookE2. These observations contribute to a better understanding of the water transport beneath the East Antarctic ice sheet."
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #4 on: June 27, 2013, 12:14:48 AM »
Here is a link to, a figure from, and a summary of, a paper entitled:

Subglacial Lake Whillans — Ice-penetrating radar and GPS observations of a shallow active reservoir beneath a West Antarctic ice stream
By: Knut Christianson, Robert W. Jacobel, Huw J. Horgan, Sridhar Anandakrishnan, Richard B. Alley

http://www.sciencedirect.com/science/article/pii/S0012821X12001276

The caption for the attached figure is:  Surface depression associated with SLW. Variable size black circles indicate subglacial water column depth detected via active-source seismics (Horgan et al., 2012-this issue). SLW outline from Fricker and Scambos (2009) is shown in gray. The background image is MODIS MOA (Haran et al., 2005). Contour spacing is 0.5 m and index contours are plotted every 2 m. White dots represent a subglacial topographic ridge and yellow dots identify “channel-like” features at the down-flow end of the lake. Projection is polar stereographic with true scale at − 71°. Surface elevation is relative to the WGS84 ellipsoid
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #5 on: June 28, 2013, 12:21:16 AM »
I thought that I would post the following summary from the WAIS Workshop about Siple Coast ice stream basal hydrology:

"Subglacial hydrology inferred from analyzes of subglacial water and basal ice from the UpC Sticky Spot
by: Vogel, S.W.; Tulaczyk, S.; Anderson, S.


Basal water plays an important role in the dynamic of the West-Antarctic Ice Sheet. Melting of ice at the base of the ice sheet lubricates the ice sheet bed allowing fast ice streaming. Basal melt is mainly produced under the thick insulating ice in the WAIS interior and under the fast moving ice stream. In the ice stream tributaries basal melting might be negligible and refreezing of basal water might be possible, leading to the accretion of multiple meter-thick clear sediment-containing basal ice layers.

Lacking direct observations from the base of the ice stream tributaries it is currently unclear whether basal melting or freezing occurs underneath ice stream tributaries. Model results assuming low basal shear stresses (1 to 10 kPa) indicate that a 12 to 25 m thick basal ice layer found at the UpC Sticky Spot could have formed in the ice stream tributaries (Vogel and others, in press). Higher basal shear stresses (~ 70 kPa) as suggested from force balance calculations (Joughin and others, in press) would lead to significant amount of basal melting (> 150 m).

Little is known about the hydrological system underneath the WAIS capable to either connect areas of basal melting with areas of basal freezing or draining the basal melt water towards the ocean. Borehole observations found water at the base of Byrd Station (Gow and others, 1968) and suggest that underneath the Siple Coast ice streams a mm to cm thick linked cavity system exists (Engelhardt and Kamb, 1997; Kamb, 2001). However it is unclear whether a 1.5 m thick water filled cavity, found at the UpC Sticky Spot ice stream margin, is just a single large cavity or it belongs to an extensive drainage system.

Chemical and isotopical analyzes of basal water from the 1.5 m thick UpC Sticky Spot cavity and from a location 4 km south of the cavity in the southern Ice Stream C branch indicate two distinct basal water bodies. The water in the ice stream location contains dissolved weathering products indicating that the water has interacted with the sediment bed, while the cavity water has lower solute concentrations and is closer to fresh basal melt water. In case the source and source area of both water bodies was originally the same, isotope analyzes suggest that the cavity water would have traveled faster.

As the water samples were a byproduct of sediment sampling using a piston corer and haven't been specifically sampled for the purpose of chemical analyzes we consider these results preliminary and have to be confirmed by future investigations."

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AbruptSLR

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #6 on: June 28, 2013, 08:19:50 PM »
I thought that I would post this extract from Wikipedia about Lake Ellsworth:

"Lake Ellsworth is a subglacial lake located in West Antarctica under approximately 3.4 km (2.1 mi) of ice. It is approximately 10 km long and is estimated to be 150 m (490 ft) in depth. The lake is named after the American explorer Lincoln Ellsworth.

Lake Ellsworth was discovered in 1996 by British scientist Professor Martin Siegert; it is one of 387 known subglacial Antarctic lakes and it is a target site for exploration due to the speculation that new forms of microbial life could have evolved in the unique habitats of Antarctica’s sub-glacial lakes after half a million years of isolation. Life in subglacial lakes must adapt to total darkness, low nutrient levels, high water pressure and isolation from the atmosphere. Subglacial lakes thus represent unique biological habitats. The lake remains liquid deep below the Antarctic surface because the pressure exerted by thousands of meters of ice drives down the freezing point of water.

On 2 March 2009 the UK's Natural Environment Research Council authorized a team of British scientists to drill through the overlaying ice to the surface of the lake in December 2012. The drilling is overseen by The Scientific Committee on Antarctic Research from the International Council for Science. The British team has spent 16 years developing the technology to explore the lake using methods that will not lead to chemical or biological contamination. Scientists will use a hot water jet to drill a borehole 36 centimeters (14 inches) wide down through the ice to the lake, then a probe will retrieve sediment and water to be analyzed for microorganisms. This will be a test to determine if water correlates with life under extreme pressure, cold and nutrient deficiencies. If the group does not identify life, it would provide a limit where there is water and no life.

Radar surveys indicate that the lake floor sediments are suitable for coring, which could contain a record of ice sheet history. Scientists think that the sediment and water samples could also hold key information about climate change. In January 2012 the drilling was scheduled to start between November 2012 and January 2013. Depending on the weather, the team expected to drill continuously for 100 hours to reach the lake.

On 12 December 2012 the British research team of 12 scientists and engineers began to bore the ice-sheet to obtain water samples. Using a high-pressure hose and sterilised water at near-boiling point, they hope to bore a passage through more than two miles of ice. The drilling process was expected to last five days and would be followed by a rapid sampling operation. Professor Siegert said that the search for life in such an extreme environment could open up possibilities for life on other worlds such as Jupiter's moon Europa. On 25 December 2012 it was announced that the project had been called off, after attempts to link two 300m-deep boreholes failed."

The first attached image shows the location of the aborted drilling operation for Lake Ellsworth.

The second image shows a curve showing the decline in the freezing point of water with increasing pressure (which is why the water in Lake Ellsworth is liquid).  It is important to note here that if subglacial cavities ever advect warm CDW down into the deep glacial basins in the WAIS that the temperature difference between the CDW and the melting point of ice in the deeper portions of these basins will be greater than for that between the CDW and the melting point of ice at the shallower basin lips.  This greater thermal difference will result in greater advective melting once the CDW reaches these depths.
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AbruptSLR

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #7 on: June 30, 2013, 06:46:55 PM »
The following paper, abstract and images (about the identification and formation of subglacial lakes) can be found at:

http://www.sciencedirect.com/science/article/pii/S0277379112003113

Theoretical framework and diagnostic criteria for the identification of palaeo-subglacial lakes
By: Stephen J. Livingstone; Chris D. Clark; Jan A. Piotrowski; Martyn Tranter; Michael J. Bentley; Andy Hodson; Darrel A. Swift; John Woodward; Quaternary Science Reviews; Volume 53, 15 October 2012, Pages 88–110

"Abstract
The Antarctic Ice Sheet is underlain by numerous subglacial lakes, which comprise a significant and active component of its hydrological network. These lakes are widespread and occur at a range of scales under a variety of conditions. At present much glaciological research is concerned with the role of modern subglacial lake systems in Antarctica. Another approach to the exploration of subglacial lakes involves identification of the geological record of subglacial lakes that once existed beneath former ice sheets. This is challenging, both conceptually, in identifying whether and where subglacial lakes may have formed, and also distinguishing the signature of former subglacial lakes in the geological record. In this work we provide a synthesis of subglacial lake types that have been identified or may theoretically exist beneath contemporary or palaeo-ice sheets. This includes a discussion of the formative mechanisms that could trigger onset of (or drain) subglacial lakes. These concepts provide a framework for discussing the probability that subglacial lakes exist(ed) beneath other (palaeo-)ice sheets. Indeed we conclude that the former mid-latitude ice sheets are likely to have hosted subglacial lakes, although the spatial distribution, frequency and type of lakes may have differed from today's ice sheets and between palaeo-ice sheets. Given this possibility, we propose diagnostic criteria for identifying palaeo-subglacial lakes in the geological record. These criteria are derived from contemporary observations, hydrological theory and process-analogues and provide an observational template for detailed field investigations."

The caption for the first attached image is: Cartoon (not drawn to scale) illustrating the effect of ice sheet erosion on subglacial lake genesis. A: glacial overdeepening; B: the overdeepened basin eventually becomes deep enough that subglacial meltwater cannot escape and begins to pond. As a subglacial lake develops sediment will start to accumulate; and C: sedimentation will cause a shallowing of the basin and this may eventually result in the subglacial lake being lost and erosion re-occurring. Thus it is possible that subglacial lakes will repeatedly form and drain over long timescales due to cycles of sedimentation and erosion.

The caption for the second attached figure is: Cartoon (not drawn to scale) illustrating how changes to the basal thermal regime influence subglacial lake genesis. A: cold-bedded glacier that switches to a polythermal regime in B (due to any of the factors highlighted in the diagram). B: warm-bedded conditions permit subglacial meltwater production and ponding in depressions; and C: if the thermal regime switches back towards cold-bedded conditions subglacial lakes in this zone may freeze and become fossil lakes.

The third attached image shows a idealized graph of the relationship of surface ice topography and ice velocity across the location of a subglacial lake.

The fourth images shows a schematic of subglacial lake processes for the Vostok subglacial lake in East Antarctica.
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AbruptSLR

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #8 on: July 01, 2013, 06:13:32 PM »
The following is taken from Wikipedia, and while not all of it current applies to the Anatarctic; the majority of it could apply sometime this century, therefore, I have decided to leave all of this description, and I will note that from a hazard assessment point of view, the consequences of Jokulhlaups could be significant in Antarctica before the end of this century if current trends either continue, or possibly accelerate due to positive feedback:

"A jökulhlaup is a glacial outburst flood. It is an Icelandic term that has been adopted by the English language. It originally referred to the well-known subglacial outburst floods from Vatnajökull, Iceland, which are triggered by geothermal heating and occasionally by a volcanic subglacial eruption, but it is now used to describe any large and abrupt release of water from a subglacial or proglacial lake/reservoir.

Since jökulhlaups emerge from hydrostatically-sealed lakes with floating levels far above the threshold, their peak discharge can be much larger than that of a marginal or extra-marginal lake burst. The hydrograph of a jökulhlaup from Vatnajökull typically either climbs over a period of weeks with the largest flow near the end, or it climbs much faster during the course of some hours. These patterns are suggested to reflect channel melting, and sheet flow under the front, respectively. Similar processes on a very large scale occurred during the deglaciation of North America and Europe after the last ice age (e.g., Lake Agassiz and the English Channel), and presumably at earlier times, although the geological record is not well preserved.

Subglacial water generation
Subglacial meltwater generation is one key to the understanding of subglacial meltwater flow. Meltwater may be produced on the glacier surface (supraglacially), below the glacier (basally) or in both locations. Ablation (surface melting) tends to result in surface pooling. Basal melting results from geothermal heat flux out of the earth, which varies with location, as well as from friction heating which results from the ice moving over the surface below it. Analyses by Piotrowski concluded that, based on basal meltwater production rates, the annual production of subglacial water from one typical northwestern Germany catchment of 642x106 m3 during the last Weichselian glaciation.

Supraglacial and subglacial water flow
Meltwater may flow either above the glacier (supraglacially), below the glacier (subglacially/basally) or as groundwater in an aquifer below the glacier as a result of the hydraulic transmissivity of the subsoil under the glacier. If the rate of production exceeds the rate of loss through the aquifer, then water will collect in surface or subglacial ponds or lakes.
The signatures of supraglacial and basal water flow differ with the passage zone. Supraglacial flow is similar to stream flow in all surface environments—water flows from higher areas to lower areas under the influence of gravity. Basal flow under the glacier exhibits significant differences. In basal flow the water, either produced by melting at the base or drawn downward from the surface by gravity, collects at the base of the glacier in ponds and lakes in a pocket overlain by hundreds of metres of ice. If there is no surface drainage path, water from surface melting will flow downward and collect in crevices in the ice, while water from basal melting collects under the glacier; either source can form a subglacial lake. The hydraulic head of the water collected in a basal lake will increase as water drains through the ice until the pressure grows high enough either to force a path through the ice or to float the ice above it.

Episodic releases
If meltwater accumulates, the discharges are episodic under continental ice sheets as well as under Alpine glaciers. The discharge results when water collects, the overlying ice is lifted, and the water moves outward in a pressurized layer or a growing under-ice lake. Areas where the ice is most easily lifted (i.e. areas with thinner overlying ice sheets) are lifted first. Hence the water may move up the terrain underlying the glacier if it moves toward areas of lower overlying ice. As water collects, additional ice is lifted until a release path is created.

If no preexisting channel is present, the water is initially released in a broad-front jökulhlaup which can have a flow front that is tens of kilometres wide, spreading out in a thin front. As the flow continues, it tends to erode the underlying materials and the overlying ice, creating a tunnel valley channel even as the reduced pressure allows most of the glacial ice to settle back to the underlying surface, sealing off the broad front release and channelizing the flow. The direction of the channel is defined primarily by the overlying ice thickness and second by the gradient of the underlying earth, and may be observed to "run uphill" as the pressure of the ice forces the water to areas of lower ice coverage until it emerges at a glacial face. Hence the configuration of the various tunnel valleys formed by a specific glaciation provides a general mapping of the glacier thickness when the tunnel valleys were formed, particularly if the original surface relief under the glacier was limited.

The rapid, high-volume discharge is highly erosive, as evidenced by the debris found in tunnels and at the mouth of tunnels, which tends to be coarse rocks and boulders. This erosive environment is consistent with creation of tunnels over 400 m deep and 2.5 km wide, as have been observed in the Antarctic.

Piotrowski has developed a detailed analytic model of the process, which predicts a cycle as follows:
1.   Meltwater is produced as a result of geothermal heating from below. Surface ablation water is not considered as it would be minimal at the glacial maximum and evidence indicates that surface water does not penetrate more than 100 meters into a glacier.
2.   Meltwater initially drains through subglacial aquifers.
3.   When the hydraulic transmissivity of the substratum is exceeded, subglacial meltwater accumulates in basins.
4.   Water accumulates sufficiently to open the ice blockage in the tunnel valley which accumulated after the last discharge.
5.   The tunnel valley discharges the meltwater excess—turbulent flow melts out or erodes the excess ice as well as eroding the valley floor.
6.   As the water level drops, the pressure decreases until the tunnel valleys again close with ice and water flow ceases."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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JackTaylor

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AbruptSLR

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #10 on: July 02, 2013, 05:28:28 PM »
JackTaylor,

Great find!  And I am particularly interested in the following quotes from these articles:

"About 400 lakes have been discovered at the base of the Antarctic ice sheet. When they drain, they disrupt subglacial habitats and can cause the ice above to slide more quickly into the sea."

and:

"At present, Antarctica is losing mass at a rate of between 50-100 billion tonnes a year, helping to raise global sea level. This study suggests that a not insignificant fraction of this mass loss could be due to flood events like that seen at Cook SLG.

"This one lake on its own represents 5-10% of [Antarctica's] annual mass imbalance," said Leeds co-author Prof Andy Shepherd.
 
"If there are nearly 400 of these sub-glacial lakes then there's a chance a handful of them are draining each year, and that needs to be considered,""

Every time that I check on the number of subglacial lakes (SGLs) in Antarctica, the count keeps increasing from under 200 a couple of years ago to now nearly 400.  If we keep looking, and the ice velocity acceleration continues to acceleration basal ice melting then we may identify many more subglacial lakes and drainage systems in the future; all of which could increase the risk of SLR contribution from Antarctica in the future.

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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sidd

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #11 on: July 02, 2013, 06:40:13 PM »
The paper about Cook subglacial drainage is at
http://onlinelibrary.wiley.com/doi/10.1002/grl.50689/abstract

sidd

AbruptSLR

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #12 on: July 10, 2013, 08:01:32 PM »
Readers may also want to review Replies #40, 41, and 42 in the following thread regarding the Thwaites Glacier:

http://forum.arctic-sea-ice.net/index.php?topic=72.0#lastPost

Also, I have attached the accompanying cartoon to illustrate how ice can freeze to the bottom of a glacier where it passes over a subglacial lake (or swamp); which can then decrease subsequent basal friction; which can serve to increase the local ice flow velocities.
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AbruptSLR

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #13 on: July 26, 2013, 11:48:22 AM »
Here is another example (see attached pdf) of the triggering of a subglacial lake's rapid drainage:

Scambos, TA, E Berthier and CA Shuman (2011), The triggering of subglacial lake drainage during rapid glacier drawdown: Crane Glacier, Antarctic Peninsula. Ann. Glaciol. 52 (59) 74-82, Times Cited: 5, issn: 0260-3055, ids: 878HF, Published 2011

"ABSTRACT. Ice surface altimetry from ICESat-1 and NASA aircraft altimeter overflights spanning 2002– 09 indicate that a region of lower Crane Glacier, Antarctic Peninsula, shows an unusual temporal pattern of elevation loss: a period of very rapid drawdown (_91ma–1 between September 2004 and September 2005) bounded by periods of large but more moderate rates (23ma–1 until September 2004; 12ma–1 after September 2005). The region of increased drawdown is _4.5 km_2.2km based on satellite (ASTER and SPOT-5) stereo-image digital elevation model (DEM) differencing spanning the event. In a later differential DEM the anomalous drawdown feature is not seen. Bathymetry in Crane Glacier fjord reveals a series of flat-lying, formerly subglacial deeps interpreted as lake sediment basins.  We conclude that the elevation-change feature resulted from drainage of a small, deep subglacial lake.  We infer that the drainage event was induced by hydraulic forcing of subglacial water past a downstream obstruction. However, only a fraction of Crane Glacier’s increase in flow speed that occurred near the time of lake drainage (derived from image feature tracking) appears to be directly attributable to the event; instead, retreat of the ice front off a subglacial ridge 6 km downstream of the lake is likely the dominant cause of renewed fast flow and more negative mass balance in the subsequent 4 years."
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sidd

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #14 on: July 27, 2013, 05:34:53 AM »
good place to mention that subglacial water can flow uphill... the slope of the ice water interface is about 10 times the slope of the ice air interface and in the opposite direction

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #15 on: July 27, 2013, 06:02:30 PM »
Sidd,

I could not agree more with you; and I greatly appreciate your help in getting the correct story out in front of most readers, who are not yet familiar with thinking about the Antarctic case, which is often different from what they are use to (for example subglacial melt water flowing uphill).

ASLR
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #16 on: August 17, 2013, 10:44:20 PM »
The following link leads to an interesting interview about the hydrology of Antarctic subglacial lakes:

http://www.sciencepoles.org/articles/article_detail/mark_skidmore_discusses_the_hydrology_of_subglacial_lakes_in_antarctica
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #17 on: August 22, 2013, 12:11:11 AM »
The following is a very interesting reference focusing on one active subglacial lake that has discharged meltwater from beneath the Institute Ice Stream (near FRIS).  The link has a free pdf.

http://www.the-cryosphere-discuss.net/7/2979/2013/tcd-7-2979-2013.html

Siegert, M. J., Ross, N., Corr, H., Smith, B., Jordan, T., Bingham, R., Ferraccioli, F., Rippin, D., and Le Brocq, A.: Boundary conditions of an active West Antarctic subglacial lake: implications for storage of water beneath the ice sheet, The Cryosphere Discuss., 7, 2979-2999, doi:10.5194/tcd-7-2979-2013, 2013.

"Abstract. Repeat-pass IceSat altimetry has revealed 124 discrete surface height changes across the Antarctic Ice Sheet, interpreted to be caused by subglacial lake discharges (surface lowering) and inputs (surface uplift). Few of these active lakes have been confirmed by radio-echo sounding (RES) despite several attempts (notable exceptions are Lake Whillans and three in the Adventure Subglacial Trench). Here we present targeted RES and radar altimeter data from an "active lake" location within the upstream Institute Ice Stream, into which 0.12 km3 of water is calculated to have flowed between October 2003 and February 2008. We use a series of transects to establish an accurate appreciation of the influences of bed topography and ice-surface elevation on water storage potential. The location of surface height change is over the downslope flank of a distinct topographic hollow, where RES reveals no obvious evidence for deep (> 10 m) water. The regional hydropotential reveals a sink coincident with the surface change, however. Governed by the location of the hydrological sink, basal water will likely "drape" over existing topography in a manner dissimilar to subglacial lakes where flat strong specular RES reflections are measured. The inability of RES to detect the active lake means that more of the Antarctic ice sheet bed may contain stored water than is currently appreciated. Variation in ice surface elevation datasets leads to significant alteration in calculations of the local flow of basal water indicating the value of, and need for, high resolution RES datasets in both space and time to establish and characterise subglacial hydrological processes."

Here is a link to the final pdf:

http://www.the-cryosphere.net/8/15/2014/tc-8-15-2014.pdf
« Last Edit: January 21, 2014, 01:21:30 AM by AbruptSLR »
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #18 on: August 22, 2013, 12:22:54 AM »
The following reference addresses the important issue of how to effectively model the influence of basal meltwater on the acceleration of ice velocities for GIS and AIS glaciers.  The link has a free pdf of the paper:

http://www.the-cryosphere-discuss.net/7/3449/2013/tcd-7-3449-2013.pdf

de Fleurian, B., Gagliardini, O., Zwinger, T., Durand, G., Le Meur, E., Mair, D., and Råback, P.: A subglacial hydrological model dedicated to glacier sliding, The Cryosphere Discuss., 7, 3449-3496, doi:10.5194/tcd-7-3449-2013, 2013

"Abstract. The flow of glaciers and ice-streams is strongly influenced by the presence of water at the interface between ice and bedrock. In this paper, a hydrological model evaluating the subglacial water pressure is developed with the final aim of estimating the sliding velocities of glaciers. The global model fully couples the subglacial hydrology and the ice dynamics through a water-dependent friction law. The hydrological part of the model follows a double continuum approach which relies on the use of porous layers to compute water heads in inefficient and efficient drainage systems. This method has the advantage of a relatively low computational cost that would allow its application to large ice bodies such as Greenland or Antarctica ice-streams. The hydrological model has been implemented in the finite element code Elmer/Ice, which simultaneously computes the ice flow. Herein, we present an application to the Haut Glacier d'Arolla for which we have a large number of observations, making it well suited to the purpose of validating both the hydrology and ice flow model components. The selection of hydrological, under-determined parameters from a wide range of values is guided by comparison of the model results with available glacier observations. Once this selection has been performed, the coupling between subglacial hydrology and ice dynamics is undertaken throughout a melt season. Results indicate that this new modelling approach for subglacial hydrology is able to reproduce the broad temporal and spatial patterns of the observed subglacial hydrological system. Furthermore, the coupling with the ice dynamics shows good agreement with the observed spring speed-up."
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #19 on: August 27, 2013, 12:52:28 AM »
The following linked reference by Bell discusses the importance of correctly modeling the influence of subglacial hydrology on ice mass loss from AIS:


http://www.nature.com/ngeo/journal/v1/n5/abs/ngeo186.html

The role of subglacial water in ice-sheet mass balance
by: Robin E. Bell; Nature Geoscience 1, 297 - 304 (2008); doi:10.1038/ngeo186

"Abstract
In the coming decades, significant changes in the polar regions will increase the contribution of ice sheets to global sea-level rise. Under the ice streams and outlet glaciers that deliver ice to the oceans, water and deformable wet sediments lubricate the base, facilitating fast ice flow. The influence of subglacial water on fast ice flow depends on the geometry and capacity of the subglacial hydrologic system: water moving rapidly through a well-connected system of conduits or channels will have little impact on ice-sheet velocities, but water injected into a spatially dispersed subglacial system may reduce the effective pressure at the base of the ice sheet, and thereby trigger increased ice-sheet velocities. In Greenland, the form of the subglacial hydrologic system encountered by increasing surface melt water will determine the influence of changing atmospheric conditions on ice-sheet mass balance. In Antarctica, subglacial lakes have the capacity to both modulate velocities in ice streams and outlet glaciers and provide nucleation points for new fast ice-flow tributaries. Climate models of ice-sheet responses to global change remain incomplete without a parameterization of subglacial hydrodynamics and ice dynamics."
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #20 on: August 27, 2013, 01:43:24 AM »
The following linked reference (with free access pdf) discusses one method for introducing the influence of subglacial meltwater to Antarctic ice sheets:

http://www.the-cryosphere.net/7/1095/2013/tc-7-1095-2013.pdf

A balanced water layer concept for subglacial hydrology in large-scale ice sheet models; by: S. Goeller, M. Thoma, K. Grosfeld, and H. Miller; The Cryosphere, 7, 1095–1106, 2013; www.the-cryosphere.net/7/1095/2013/; doi:10.5194/tc-7-1095-2013

"Abstract. There is currently no doubt about the existence of a widespread hydrological network under the Antarctic Ice Sheet, which lubricates the ice base and thus leads to increased ice velocities. Consequently, ice models should incorporate basal hydrology to obtain meaningful results for future ice dynamics and their contribution to global sea level rise. Here, we introduce the balanced water layer concept, covering two prominent subglacial hydrological features for ice sheet modeling on a continental scale: the evolution of subglacial lakes and balance water fluxes.  We couple it to the thermomechanical ice-flow model RIMBAY and apply it to asynthetic model domain. In our experiments we demonstrate the dynamic generation of subglacial lakes and their impact on the velocity field of the overlaying ice sheet, resulting in a negative ice mass balance. Furthermore, we introduce an elementary parametrization of the water flux–basal sliding coupling and reveal the predominance of the ice loss through the resulting ice streams against the stabilizing influence of less hydrologically active areas.  We point out that established balance flux schemes quantify these effects only partially as their ability to store subglacial water is lacking."
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #21 on: August 27, 2013, 01:53:04 AM »
The following linked 2006 reference (which maybe a little old) discusses both the Captured Ice Shelf (CIS) hypothesis and the challenging idea that Lake Vostok may be on the verge of a jokulhlaup outburst which (if it occurred) could cause a local ice stream and a significant regional ice mass loss:

http://onlinelibrary.wiley.com/doi/10.1111/j.0435-3676.2006.00278.x/abstract;jsessionid=327F8097B544FB199725D29BE9114446.d01t03?deniedAccessCustomisedMessage=&userIsAuthenticated=false

Erlingsson, U. (2006), Lake Vostok Behaves Like A ‘Captured Lake’ and May Be Near To Creating An Antarctic Jökulhlaup. Geografiska Annaler: Series A, Physical Geography, 88: 1–7. doi: 10.1111/j.0435-3676.2006.00278.x


"Abstract
The most well known sub-glacial lake is probably Grímsvötn under Vatnajökul, Iceland, from where jökulhlaups regularly burst forth. It is created by thermal melting under the ice cap. The Antarctic Lake Vostok, on the other hand, is considered to be located over a region with normal geothermal heat transfer, where it can exist because the ice is so thick that its base is at the pressure melting point. This makes it a candidate for testing the captured ice shelf (CIS) hypothesis, which states that the motion of a totally confined ice shelf creates a hydrostatic seal in the form of an ice rim over the threshold. The CIS hypothesis may offer a source of water for the controversial Laurentian jökulhlaups inferred from field data, implicated in dramatic climatic changes. Here I show that Lake Vostok agrees with the hypothesis, and that it may be on the verge of a jökulhlaup, which could create an ice stream and regional downdraw. The result also implies that the lake may well be of pre-glacial origin, and that it may have experienced jökulhlaups during previous interglacials."
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #22 on: August 27, 2013, 02:02:29 AM »
The following linked 2009 reference (with a free access pdf) includes the extract about Antarctica, after the abstract:

http://rspa.royalsocietypublishing.org/content/early/2009/03/13/rspa.2008.0488.full

Dynamics of subglacial floods; A.C Fowler; 18 March 2009 doi: 10.1098/rspa.2008.0488 Proc. R. Soc. A rspa.2008.0488

Abstract:
"The Nye model of jökulhlaups is able to explain both their periodicity and even the detailed shape of the flood hydrograph. In this paper, we show how the model can be used to predict the shape of the hydrographs from the subglacial lake Grímsvötn beneath Vatnajökull in Iceland, and we comment on three particular issues that have proved contentious in the application of the Nye model: the role of water temperature; the shape of the flood channel; and the value of the bed roughness coefficient."


"Sub-Antarctic floods
Recent observations by Wingham et al. (2006), Bell et al. (2007) and Fricker et al. (2007) have shown that subglacial lakes are not only common beneath Antarctica, but that they undergo rapid deflation, with typical surface elevation changes of the order of metres over times of the order of years. Such deflations (and inflations elsewhere) are interpreted as occurring through drainage of the lakes in subglacial floods, and the question arises whether such long duration floods of such small magnitude can be explained with the Nye model. The answer to this is positive. It can be shown that a year-long flood lowering the ice surface (and thus lake level) by metres can be simulated in the Nye model by increasing the ice closure rate by four orders of magnitude. The inference would be that the closure is due to subglacial till, and thus that such floods are excavated through high-pressure subglacial canals (Walder & Fowler 1994), rather than through Röthlisberger channels."
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #23 on: September 06, 2013, 01:06:44 AM »
The linked reference (with a free pdf) presents an interesting case study of an East Antarctic epishelf lake connected to the ocean:

http://staff.acecrc.org.au/~johunter/galton-fenzi_et_al_2012a.pdf

A decade of change in the hydraulic connection between an Antarctic epishelf lake and the ocean; by: Ben K. GALTON-FENZI, John R. HUNTER, Richard COLEMAN, and Neal YOUNG; Journal of Glaciology, Vol. 58, No. 208, 2012 doi: 10.3189/2012JoG10J206 223


"ABSTRACT. Observations of the water level in Beaver Lake, an epishelf lake in East Antarctica, show a regular tidal signal that is lagged and attenuated from the tides beneath the adjacent Amery Ice Shelf.  The phase lag and amplitude attenuation can be created by a narrow inlet connection between Beaver Lake and the cavity beneath the Amery Ice Shelf. A forced linear damped oscillator is used to determine the inlet dimensions that are required to produce the observed phase lag and amplitude attenuation. The model shows that the observations are consistent with a tidal flow that is restricted by the drag created by flow in the narrow inlet. Analysis shows that the phase lag and amplitude attenuation of the tides in Beaver Lake has increased over the years 1991–2002, probably due to a thickening of the overlying ice shelf. The response is sensitive to subtle variations in the dimensions of the inlet."
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #24 on: September 06, 2013, 01:26:25 AM »
The linked reference presents an interesting case study of the influence of subglacial hydrology on the flow of the Kamb Ice Stream:

http://onlinelibrary.wiley.com/doi/10.1029/2012JF002570/abstract

van der Wel, N., P. Christoffersen, and M. Bougamont (2013), The influence of subglacial hydrology on the flow of Kamb Ice Stream, West Antarctica, J. Geophys. Res. Earth Surf., 118, 97–110, doi:10.1029/2012JF002570.

"Abstract
Ice streams on the Siple Coast, West Antarctica, have a complex history of flow because their basal motion is governed by time-varying basal conditions. Although the mechanical interaction between ice and till is well established, very little is known about the potential effect of regionally scaled water transport in a basal water system, which has only recently become apparent. To investigate the combined effect of hydrological and mechanical processes, we developed the Hydrology, Ice and Till model, in which ice flow is coupled to a Coulomb-plastic till layer and a basal water system consisting of discrete conduits. When the model is applied to Kamb Ice Stream (KIS), results confirm that it is capable of oscillating between fast and stagnant modes of flow. We show that when subglacial conduits are disregarded or do not extend to the grounding line, the oscillatory behavior of the ice stream is governed by the basal thermal regime. When conduits extend to the grounding line, the modelled ice stream oscillation period is increased, peak speeds are reduced, and oscillations may ultimately cease if the volume of water supplied is sufficiently high. Three different hydrological states characterize the behavioral patterns of ice flow and these states are distinguished by conditions at the grounding line. Modelled ice stream velocities were found to oscillate with fast and slow periods typically lasting a few hundred years, although varying according to hydrological activity. Our results indicate that KIS could reactivate this century, given its hydrological setting and ~170 years of stagnation."
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #25 on: September 06, 2013, 01:33:21 AM »
The linked reference presents an interesting case study of the subglacial hydrology under Dome A, Antarctica:


http://onlinelibrary.wiley.com/doi/10.1029/2012JF002555/abstract

Wolovick, M. J., R. E. Bell, T. T. Creyts, and N. Frearson (2013), Identification and control of subglacial water networks under Dome A, Antarctica, J. Geophys. Res. Earth Surf., 118, 140–154, doi:10.1029/2012JF002555.

Abstract:
"Subglacial water in continental Antarctica forms by melting of basal ice due to geothermal or frictional heating. Subglacial networks transport the water from melting areas and can facilitate sliding by the ice sheet over its bed.  Subglacial water flow is driven mainly by gradients in overburden pressure and bed elevation. We identify small (median 850 m) water bodies within the Gamburtsev Subglacial Mountains in East Antarctica organized into long (20–103 km) coherent drainage networks using a dense (5 km) grid of airborne radar data. The individual water bodies are smaller on average than the water bodies contained in existing inventories of Antarctic subglacial water and most are smaller than the mean ice thickness of 2.5 km, reflecting a focusing of basal water by rugged topography. The water system in the Gamburtsev Subglacial Mountains reoccupies a system of alpine overdeepenings created by valley glaciers in the early growth phase of the East Antarctic Ice Sheet. The networks follow valley floors either uphill or downhill depending on the gradient of the ice sheet surface. In cases where the networks follow valley floors uphill they terminate in or near plumes of freeze-on ice, indicating source to sink transport within the basal hydrologic system. Because the ice surface determines drainage direction within the bed-constrained network, the system is bed-routed but surface-directed. Along-flow variability in the structure of the freeze-on plumes suggests variability in the networks on long (10s of ka) timescales, possibly indicating changes in the basal thermal state."
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #26 on: September 06, 2013, 01:40:27 AM »
The linked reference provides interesting results from a physical model comparable to the Whillans Ice Stream:

http://www.ingentaconnect.com/content/igsoc/agl/2013/00000054/00000063/art00035


The impact of subglacial hydrology on the force balance of a physically modelled ice stream; by: Wagman, Benjamin M.; Catania, Ginny A.; Annals of Glaciology, Volume 54, Number 63, July 2013 , pp. 333-342(10); DOI: http://dx.doi.org/10.3189/2013AoG63A345


"Abstract:
We use a physical model to investigate how changes in subglacial hydrology affect ice motion of Antarctic ice streams. Ice streams are modelled using silicone polymer placed over a thin water layer to mimic ice flow dominated by basal sliding. The model ice-stream force balance is calculated and compared directly to the observed force balance of Whillans Ice Stream (WIS). Dynamic similarity between the model and WIS is achieved when their force balances are equivalent. The WIS force balance has evolved over time owing to increased basal resistance. We test two hypotheses: (1) the subglacial water distribution influences the ice-flow speed and thus the force balance; (2) shear margins are locations where transitions in water layer thickness occur. We find that the velocity and force balance are sensitive to pulsed water discharge events and changes in lubrication that result in sticky spots, and that model shear margins tend to overlie water lubrication boundaries. We conclude that local changes in basal lubrication near margins (possibly as a result of the presence of sticky spots or subglacial lakes) influence the stability of ice-stream margin position and may be responsible for large and rapid shifts in margin location. "

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #27 on: December 11, 2013, 02:01:26 AM »
The following link leads to an interview, not only about the effort to re-start drilling into subglacial Lake Ellsworth in about 5-years, but also about other related Antarctic topics:

http://www.sciencepoles.org/interview/lake-ellsworth-and-the-future-of-subglacial-research-in-antarctica
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #28 on: December 19, 2013, 02:30:31 AM »
The following link leads to findings presented at the AGU 2013 conference about new evidence characterizing the nature of the subglacial hydrological system in Antarctica:

http://www.livescience.com/41994-antarctica-new-lakes-streams.html

In the attached image, red dots mark surface changes that scientists think are caused by water moving beneath Antarctica's ice. The blue and magenta colors indicate ice velocity, with the magenta showing the fastest-moving ice.
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #29 on: January 31, 2014, 01:23:29 AM »
Antarctica's Blood Falls flow from a saltwater subglacial lake deep under Taylor Glacier in the remote McMurdo Dry Valleys in Eastern Antarctica.  As the iron-rich water seeps out of a crack in the glacier, it rusts and stains the ice red, and spills onto the frozen surface of Lake Bonney.   ScienceNow reported that over a six-year period, geomicrobiologist Jill Mikucki collected and tested water samples and discovered 17 types of microorganisms that seemed to be able to “breathe” on ferric iron. Genetic analysis suggests that the microbes are similar to those found in the open ocean (note that the saltwater was trapped from the ocean millions of years ago).  See a more complete story and pictures at the following link:

http://www.wunderground.com/news/stunning-secret-blood-falls-20130826
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #30 on: January 31, 2014, 05:58:41 AM »
Has anyone mentioned Livingstone(2013) yet ? open access

http://www.the-cryosphere.net/7/1721/2013/

doi:10.5194/tc-7-1721-2013

"Potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets"

I quote:

"The resultant hysteresis, whereby a retreating ice sheet will have many more subglacial lakes than one advancing, has implica tions for ice-stream formation and flow, bed lubrication and meltwater drainage."

sidd




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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #31 on: January 31, 2014, 04:53:19 PM »
sidd,

Thanks for the Livingstone et al 2013 reference:

Livingstone, S. J., Clark, C. D., Woodward, J., and Kingslake, J.: Potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets, The Cryosphere, 7, 1721-1740, doi:10.5194/tc-7-1721-2013, 2013.

In a retreating environment, like we are entering, I wonder how these growing subglacial hydrological systems will interact with ocean advection and retreating grounding lines.  It looks to me that we could be in for many surprises to come in this regard.

Best,
ASLR
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #32 on: January 31, 2014, 06:02:26 PM »
sidd,

Thanks for the Livingstone et al 2013 reference:

Livingstone, S. J., Clark, C. D., Woodward, J., and Kingslake, J.: Potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets, The Cryosphere, 7, 1721-1740, doi:10.5194/tc-7-1721-2013, 2013.

In a retreating environment, like we are entering, I wonder how these growing subglacial hydrological systems will interact with ocean advection and retreating grounding lines.  It looks to me that we could be in for many surprises to come in this regard.

Best,
ASLR

Are these subglacial lakes salty like sea water or are they freshwater due to the ice cap?

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #33 on: January 31, 2014, 06:43:40 PM »
Shared Humanity,

The vast majority of these subglacial hydrological systems are fresh water; however, a few contain saltwater either because: (a) like the Taylor Glacier subglacial lake, they were captured a long time ago when the glacier was advancing over the ocean; and (b) like the Siple Coast ice streams, the subglacial hydrological system could be connected to the ocean today and tidal action can pump some saltwater beneath the ice stream/glacier.

Best,
ASLR
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #34 on: January 31, 2014, 08:02:11 PM »
Shared Humanity,

I should briefly note that for glaciers like PIG and Thwaites, the weight of ice above their thresholds is sufficient seal off their subglacial hydrologic systems from the ocean most of the time.  However, when the subglacial hydrostatic pressure builds up sufficiently such systems vent fresh subglacial meltwater directly into the ocean, and on these occasions I believe that the vented fresh water will accelerate the advective saline pump action beneath the associated ice shelves (see discussion in other threads like the "surge" thread and the following link:  http://forum.arctic-sea-ice.net/index.php/topic,85.50.html).

Also, the drainage channels that vent the fresh subglacial meltwater into the ocean, will likely serve as a path of accelerated grounding line retreat and for accelerated weakening of the associated ice shelves.

Best,
ASLR
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #35 on: February 05, 2014, 01:43:39 AM »
The linked reference (with a free access pdf), indicates that meaningful progress is being made on modeling the influence of subglacial hydrology on glacier dynamics:

de Fleurian, B., O. Gagliardini, T. Zwinger, G. Durand, E. Le Meur, D. Mair, and P. Råback, 2014. A double continuum hydrological model for glacier applications, The Cryosphere, 8, 137-153, doi:10.5194/tc-8-137-2014

http://www.the-cryosphere.net/8/137/2014/tc-8-137-2014.html

"Abstract. The flow of glaciers and ice streams is strongly influenced by the presence of water at the interface between ice and bed. In this paper, a hydrological model evaluating the subglacial water pressure is developed with the final aim of estimating the sliding velocities of glaciers. The global model fully couples the subglacial hydrology and the ice dynamics through a water-dependent friction law. The hydrological part of the model follows a double continuum approach which relies on the use of porous layers to compute water heads in inefficient and efficient drainage systems. This method has the advantage of a relatively low computational cost that would allow its application to large ice bodies such as Greenland or Antarctica ice streams. The hydrological model has been implemented in the finite element code Elmer/Ice, which simultaneously computes the ice flow. Herein, we present an application to the Haut Glacier d'Arolla for which we have a large number of observations, making it well suited to the purpose of validating both the hydrology and ice flow model components. The selection of hydrological, under-determined parameters from a wide range of values is guided by comparison of the model results with available glacier observations. Once this selection has been performed, the coupling between subglacial hydrology and ice dynamics is undertaken throughout a melt season. Results indicate that this new modelling approach for subglacial hydrology is able to reproduce the broad temporal and spatial patterns of the observed subglacial hydrological system. Furthermore, the coupling with the ice dynamics shows good agreement with the observed spring speed-up."
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #36 on: February 21, 2014, 11:07:33 PM »
The linked references (with a free access pdf) talks about pressurized subglacial meltwater and the dynamics of ice streams:


T. M Kyrke-Smith, R. F Katz and A. C Fowler, (2014),
Subglacial hydrology and the formation of ice streams, Proc. R. Soc. A 2014 470, 20130494.

http://rspa.royalsocietypublishing.org/content/470/2161/20130494.full.pdf


Abstract: "Antarctic ice streams are associated with pressurized subglacial meltwater but the role this water plays in the dynamics of the streams is not known. To address this, we present a model of subglacial water flow below ice sheets, and particularly below ice streams. The base-level flow is fed by subglacial melting and is presumed to take the form of a rough-bedded film, in which the ice is supported by larger clasts, but there is a millimetric water film which submerges the smaller particles. A model for the film is given by two coupled partial differential equations, representing mass conservation of water and ice closure. We assume that there is no sediment transport and solve for water film depth and effective pressure. This is coupled to a vertically integrated, higher order model for ice-sheet dynamics. If there is a sufficiently small amount of meltwater produced (e.g. if ice flux is low), the distributed film and ice sheet are stable, whereas for larger amounts of melt the ice–water system can become unstable, and ice streams form spontaneously as a consequence. We show that this can be explained in terms of a multi-valued sliding law, which arises from a simplified, one-dimensional analysis of the coupled model."
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #37 on: June 10, 2014, 08:20:24 PM »
The linked reference (see also the attached images and associated caption below) provides more evidence of high geothermal flux and associated basal melt water beneath the Thwaites Glacier, both of which will threaten its future stability:

Dustin M. Schroeder, Donald D. Blankenship, Duncan A. Young, and Enrica Quartini, (2014), "Evidence for elevated and spatially variable geothermal flux beneath the West Antarctic Ice Sheet", PNAS, doi: 10.1073/pnas.1405184111

http://www.pnas.org/content/early/2014/06/04/1405184111.abstract

http://www.pnas.org/content/suppl/2014/06/04/1405184111.DCSupplemental


Significance: "Thwaites Glacier is one of the West Antarctica's most prominent, rapidly evolving, and potentially unstable contributors to global sea level rise. Uncertainty in the amount and spatial pattern of geothermal flux and melting beneath this glacier is a major limitation in predicting its future behavior and sea level contribution. In this paper, a combination of radar sounding and subglacial water routing is used to show that large areas at the base of Thwaites Glacier are actively melting in response to geothermal flux consistent with rift-associated magma migration and volcanism. This supports the hypothesis that heterogeneous geothermal flux and local magmatic processes could be critical factors in determining the future behavior of the West Antarctic Ice Sheet."

Abstract: "Heterogeneous hydrologic, lithologic, and geologic basal boundary conditions can exert strong control on the evolution, stability, and sea level contribution of marine ice sheets. Geothermal flux is one of the most dynamically critical ice sheet boundary conditions but is extremely difficult to constrain at the scale required to understand and predict the behavior of rapidly changing glaciers. This lack of observational constraint on geothermal flux is particularly problematic for the glacier catchments of the West Antarctic Ice Sheet within the low topography of the West Antarctic Rift System where geothermal fluxes are expected to be high, heterogeneous, and possibly transient. We use airborne radar sounding data with a subglacial water routing model to estimate the distribution of basal melting and geothermal flux beneath Thwaites Glacier, West Antarctica. We show that the Thwaites Glacier catchment has a minimum average geothermal flux of ∼114 ± 10 mW/m2 with areas of high flux exceeding 200 mW/m2 consistent with hypothesized rift-associated magmatic migration and volcanism. These areas of highest geothermal flux include the westernmost tributary of Thwaites Glacier adjacent to the subaerial Mount Takahe volcano and the upper reaches of the central tributary near the West Antarctic Ice Sheet Divide ice core drilling site."

Also see:
http://www.utexas.edu/news/2014/06/10/antarctic-glacier-melting/

Caption: "This map shows the locations of geothermal flow underneath Thwaites Glacier in West Antarctica that were identified with airborne ice-penetrating radar. The dark magenta triangles show where geothermal flow exceeds 150 milliwatts per square meter, and the light magenta triangles show where flow exceeds 200 milliwatts per square meter. Letters C, D and E denote high melt areas: in the western-most tributary, C; adjacent to the Crary mountains, D; and in the upper portion of the central tributaries, E. Credit: University of Texas Institute Geophysics"

Extract from the University of Texas link: "According to his findings, the minimum average geothermal heat flow beneath Thwaites Glacier is about 100 milliwatts per square meter, with hotspots over 200 milliwatts per square meter. For comparison, the average heat flow of the Earth’s continents is less than 65 milliwatts per square meter.
The presence of water and heat present researchers with significant challenges.
“The combination of variable subglacial geothermal heat flow and the interacting subglacial water system could threaten the stability of Thwaites Glacier in ways that we never before imagined,” Schroeder said."
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wili

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #38 on: June 10, 2014, 08:58:39 PM »
Thanks for this link, ASLR. So do we have any data on what percentage of Thwaites melt is from this due to this geothermal heating, versus the directly GW-connected sources?

Is it possible that GW-triggered melt could be unloading enough ice that it is prompting an increase in this kind of magma flow?

Denialists are already jumping all over this stuff and claiming slr is all due to vulcanism.
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #39 on: June 10, 2014, 10:23:15 PM »
wili,

Denialists will always claim plausible deniability for AGW (including SLR).  I do not believe that enough magma could have yet flowed back underneath Thwaites (due to ice mass loss) to cause the basal heating pattern noted by Schroeder et al 2014; so this geothermal heating has almost certainly been the way that it is ever since the beginning of the Holocene over 10,000 years ago.  So if you want to spar with denialists then ask them why Thwaites has been largely stable for the past 10,000 years and only now indicates signs of instability, if geothermal basal heating is the root of the problem.  Furthermore, PIG has less geothermal heating than Thwaites, yet currently PIG is exhibiting more ice mass loss than Thwaites.  All the models indicate that the fundamental reason that the ASE marine glaciers are exhibiting accelerating ice mass loss now is due to advection of the warm CDW due to the increased westerly wind velocities associated with the anthropogenic ozone hole over Antarctica.

Even if most of the meltwater beneath Thwaites were due to geothermal heating (and it may be); this situation was stable until now, and even if the ozone hole heals itself, the projected accumulation of GHGs over Antarctica will keep the westerly wind velocities high for the foreseeable future; which will keep the increasingly warm CDW advecting into the ASE and causing accelerated grounding line retreat.

Best,
ASLR
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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #40 on: June 11, 2014, 12:26:42 AM »
i am on the road so this is from memory:

1) 100mwatt per square meter is 1e5 watt per square Km. Say Thwaites catchment is 1e4 sq Km, that 1e9 watt or one gigawatt

2)now compare the Dutrieux estimate for 1Gwatt/Km CDW heat delivery of coastline and that Thwaites is 50Km wide

3)as usual a reproof that denialists can't count and will not read (can't read ...?)

sidd

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #41 on: June 11, 2014, 05:29:25 AM »
Thanks, aslr and sidd. Good perspectives.
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #42 on: June 15, 2014, 10:15:21 AM »
The following linked research used observations of ice surface velocities, ice surface elevations, and bed elevations to perform inverse calculations of basal shear stress for both the PIG and Thwaites Glaciers.  The findings indicate that subglacial meltwater distributions can change the basal friction of these key glaciers over periods of decades, which can in-turn control the rate of SLR contribution from these two key glaciers.  This research has direct implications on the recent Schroeder et al (2014) [see Reply #37 in this thread] research on subglacial meltwater beneath the Thwaites Glacier:

Olga V. Sergienko and Richard C. A. Hindmarsh, (2013), "Regular Patterns in Frictional Resistance of Ice-Stream Beds Seen by Surface Data Inversion", Science 29 November 2013: Vol. 342, no. 6162, pp. 1086-1089, DOI: 10.1126/science.1243903

http://www.sciencemag.org/content/342/6162/1086

Abstract: "Fast-flowing glaciers and ice streams are pathways for ice discharge from the interior of the Antarctic Ice Sheet to ice shelves, at rates controlled by conditions at the ice-bed interface. Using recently compiled high-resolution data sets and a standard inverse method, we computed basal shear stress distributions beneath Pine Island and Thwaites Glaciers, which are currently losing mass at an accelerating rate. The inversions reveal the presence of riblike patterns of very high basal shear stress embedded within much larger areas with zero basal shear stress. Their colocation with highs in the gradient of hydraulic potential suggests that subglacial water may control the evolution of these high–shear-stress ribs, potentially causing migration of the grounding line by changes in basal resistance in its vicinity."

The following extract & figure come from the following related website:

http://www.gfdl.noaa.gov/index/news-app/story.91/title.regular-patterns-in-frictional-resistance-of-ice-stream-beds-seen-by-surface-data-inversion

Extract: "The inversions reveal that the basal traction underneath these glaciers has organized spatial patterns such that narrow, rib-like structures with very high basal shear stress are embedded in much larger areas with zero basal shear. Such an organized spatial pattern implies that it arises from the complex interactions of glacier flow, subglacial water and deformable sediments.
The collocation of these high-basal shear ribs with highs in the gradient of hydraulic potential suggests that subglacial water controls evolution of these ribs. The authors theorize that the basal traction ribs arise from the long-term evolution of dynamic instabilities, manifesting themselves as bed-friction variation arising from variations in the effective pressure (the difference between ice overburden and subglacial water pressure) in space.
The presence of such rib-like spatial patterns in the basal shear of these fast flowing glaciers has implications for stability of their grounding lines. Both glaciers have inland-sloping over-deepened beds. The grounding lines in such geometric configurations are thought to be inherently unstable. There is a possibility of their temporal and spatial variability through, for instance, flooding of some of these ribs and reduction of their basal shear stress, that would lead to enhanced ice discharge into the ocean.
The present spatial configuration of basal resistance in these ice streams is not immutable and can potentially change over decades to centuries in response to changes to ice-sheet geometry or water input. Changes in basal shear stress distributions in the vicinity of the grounding line inevitably cause variations in ice flow and its flux through the grounding line, triggering its migration, with consequent changes in ice discharge to the ocean, and the glaciers' contribution to sea level."

Caption for figure: "Mathematical modeling and data from satellites and ground-penetrating radar were used to infer the existence of ribs (in red) indicating areas of high friction between the glacier and the underlying bedrock. These high-friction ribs slow the movement of ice toward the sea. The image on the left is the Pine Island Glacier and the image on the right is the Thwaites Glacier, both in West Antarctica."
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LRC1962

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #43 on: June 15, 2014, 08:14:30 PM »
Based according to this Melting Ice Sheets Could Trigger Unexpected Volcanic Activity(Actual open paper), could it be possible that the new subglacial volcanoes have not been active for a long time, but have been triggered by collapse of Larsen. If this is a new phenomena then you have a new attack on the ice. Compounding that, if the Larsen collapse caused that kind of uplift and IF that triggered the volcanic activity then what will happen as the ice starts melting faster and releasing its pressure on the Western Antarctica. Most conclusions I suspect revolving around  glaciers and volcanoes has been based on Iceland, but the situation in the WAIS is quite different and since very little is know about the bedrock under it, the could also be very different and more unstable.
PS A quick Google shows that unfortunately a lot of media headlines are twisting it to make it look like volcanoes are responsible for the melt. The scientist are then left playing damage control. No, Volcanoes Are Not the Primary Cause For the Melting Ice Caps
« Last Edit: June 15, 2014, 08:22:26 PM by LRC1962 »
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AbruptSLR

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #44 on: June 16, 2014, 03:21:08 AM »
LRC1962,

It is unfortunate that scientists need to spend their time playing damage control by pointing out that " ... volcanoes are not the primary cause for the ASE marine glacier from melting".

Furthermore: no, it is not possible that the Larsen collapse triggered any meaningful volcanic activity in the ASE marine glaciers.

Once the ASE have lost enough ice mass (say in a couple of decades) due to anthropogenically triggered CDW advection into the ASE; then yes the geothermally induced basal ice melting in the ASE marine glaciers will increase, and at some point in the future (say in 60 to 100 years) enough ice mass loss may trigger some future volcanic activity.

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #45 on: June 16, 2014, 05:27:28 AM »
LRC1962,

I would like to note first, that the geothermal and volcanic activity in the Byrd Subglacial Basin is atypically high, has been known for a long time (several decades).  So the Schroeder et al (2014) contribution is really primarily to provide much higher resolution mapping of this basal heat energy than was understood before.  While denialists are implying that this heating is new and corresponds to the recent acceleration in ice mass loss from the ASE region, this can only be at most partially true (denalists love partial truths).

It is absolutely true that multiple factors are contributing to the accelerating ice mass loss in the ASE glacial basins (including: geothermal heating, subglacial meltwater drainage systems/lakes/swamps, pre-existing troughs deepened by prior glacial movements, telecommunication of tropical energy to this area by both the ocean and the atmosphere, etc), and it is true that many of these factors work synergistically; however, the single most important factor is the advection of warm CDW into the ASE due to the anthropogenically induced ozone hole over Antarctica.

Best,
ASLR
« Last Edit: June 16, 2014, 12:10:21 PM by AbruptSLR »
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LRC1962

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #46 on: June 16, 2014, 05:34:28 AM »
Thanks for correction. I am greatly lacking in knowledge and read into what was said. I do not mind learning something every day. Keeps the grey matter from atrophying.
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AbruptSLR

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #47 on: June 17, 2014, 04:48:32 PM »
As my articulation of the implications of the Schroder et al 2014 research may not have been too clear, I provide the following extract from the linked website:

http://www.decodedscience.com/antarctic-ice-sheet-melting-geothermal-heat-contributes-to-warming/46565

Extract: “These two components (warm ocean water and geothermal flux) along with configuration of the subglacial water system, the shape of the ice sheet bed, and the distribution of deformable sediments and bedrock beneath the ice sheet will determine the ultimate timing, pacing, and character of the retreat of Thwaites Glacier and its eventual spread to the rest of the West Antarctic Ice Sheet,” explained Dr. Schroder.
“What is clear is that as Thwaites retreats in response to warm ocean water, its bed will be move across a much more thermally and hydrologically significant piece of geology than was previously thought. So it’s not just the ocean that’s the shaping the fate of the ice sheet, it’s also the earth beneath it.”

Melting Ice Sheets: Looking to the Future
Along with the WAIS as a whole, the Thwaites Glacier is the focal point for much study because of the rapid rate of melt. But it represents only a part of the findings and the study’s results will have wider implications for improving the quality of climate modelling.
“We can apply it to other areas where we expect that high (and spatially varying) geothermal heat flow might be playing a significant role. The most likely candidates are other areas in West Antarctica near to the West Antarctic Rift System,” said Dr. Schroder."
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AbruptSLR

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #48 on: June 21, 2014, 01:06:22 AM »
The following reference discusses an overview of current and future knowledge about Antarctic subglacial hydrology, & the implications of such subglacial hydrological water flow on: ice-stream dynamics, ice sheet mass-balance, and fresh water supply into the Southern Ocean:

Ashmore, David W.; Bingham, Robert G., (2014), "Antarctic subglacial hydrology: an overview of current knowledge and forthcoming scientific challenges", Antarctic Science, 2014, in-press

http://journals.cambridge.org/action/displayIssue?jid=ANS&tab=currentissue

Abstract: "Flood-carved landforms across the deglaciated terrain of Victoria Land, East Antarctica, provide convincing geomorphological evidence for the existence of subglacial drainage networks beneath the Antarctic Ice Sheets, and motivate research into the inaccessible environment beneath the current ice sheet. Unlike at temperate glaciers, and more recently Arctic glaciers, where numerous researchers have explicitly studied “subglacial hydrology,” the acquisition of knowledge about subglacial hydrology in Antarctica has often been a side effect of geophysical and remote-sensing programmes targeted at multiple objectives. Through this research, however, we are steadily building an understanding of Antarctic subglacial hydrology, and this article presents an overview of the current state of knowledge. We first contextualise the discussion by introducing how our conceptualisation of subglacial hydrological behaviour has been developed at temperate and Arctic glaciers, but is less mature in the Antarctic, where our knowledge of subglacial-melt generation and variability, in particular, remain poorly constrained. We overview the discovery and progressive understanding of subglacial lake systems, whereby recent geophysical and remote-sensing observations have shown us that many lakes, once thought to be isolated and stable, form part of a highly dynamic network of subglacial drainage beneath the ice sheet. We then discuss some of the latest findings concerning subglacial water flows other than those directly concerned with lakes. Such water flows have potentially significant impacts on ice-stream dynamics, ice-sheet mass-balance, and supplies of water to the ocean potentially affecting circulation and nutrient productivity. We close by identifying some of the grand challenges that lie ahead for improving our understanding of these processes further."
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AbruptSLR

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Re: Subglacial Lake and Meltwater Drainage Systems
« Reply #49 on: March 26, 2015, 06:45:18 PM »
The linked reference (with an open access pdf) concludes that: "If our model is realistic, it implies that most active lakes are shallow and only exist in the presence of saturated sediment, explaining why they are difficult to detect with classical radar methods. It also implies that the lake-drainage process is sensitive to the composition and strength of the underlying till, suggesting that models could be improved with a realistic treatment of sediment – interfacial water exchange."

This is indicates that current models are likely to be "erring on the side of least drama" with regard to the potential contribution of Antarctic contribution to SLR as: (1) they are likely under estimating the number and extent of subglacier shallow active lakes; and (2) they are under estimating the easy with which these subglacial lakes can be drained by the subglacial water eroding drainage channels through the underlying glacial till:

Carter, S. P., Fricker, H. A., and Siegfried, M. R. (2015), "Active lakes in Antarctica survive on a sedimentary substrate – Part 1: Theory", The Cryosphere Discuss., 9, 2053-2099, doi:10.5194/tcd-9-2053-2015.

http://www.the-cryosphere-discuss.net/9/2053/2015/tcd-9-2053-2015.html

Abstract: "Over the past decade satellite observations have revealed that active subglacial lake systems are widespread under the Antarctic ice sheet, including the ice streams, yet we have insufficient understanding of the lake-drainage process to incorporate it into ice sheet models. Process models for drainage of ice-dammed lakes based on conventional "R-channels" incised into the base of the ice through melting are unable to reproduce the timing and magnitude of drainage from Antarctic subglacial lakes estimated from satellite altimetry given the low hydraulic gradients along which such lakes drain. We developed a process model in which channels are mechanically eroded into deformable subglacial sediment (till) instead ("T-channel"). When applied to the known lakes of the Whillans/Mercer system, the model successfully reproduced the key characteristics of estimated lake volume changes for the period 2003–2009. If our model is realistic, it implies that most active lakes are shallow and only exist in the presence of saturated sediment, explaining why they are difficult to detect with classical radar methods. It also implies that the lake-drainage process is sensitive to the composition and strength of the underlying till, suggesting that models could be improved with a realistic treatment of sediment – interfacial water exchange."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson