olelog

A glacial lake is a lake formed by the melting of glacier ice. In a time like now with global warming most glaciers on earth are retreating, resulting in more and swelling glacial lakes - lakes that are often formed behind terminal/end moraines, also known as moraine dammed glacier lakes. A serious problem with such lakes is that when the water reaches a certain level the dam will burst and an extremely large amount of water will suddenly flow into lower valleys with potential catastrophic results.

Studies of the past 30 years show that the temperatures in the Himalayas are rising up to eight times faster than the global average. Nepal has more than 2,300 glacial lakes and experts say at least 20 are in danger of bursting. One of them is the Imja Glacier above Dengboche, which is retreating by about 70 metres a year, and the melting ice has formed a huge lake that could devastate villages downstream if it bursts. The Imja lake, that was nonexistent in 1960, is now the second largest glacial lake in Nepal and is considered the most dangerous. It covers almost one square kilometre, and is estimated to hold 36 million cubic metres of water.

Information about how many people would be affected by a glacial lake bursting remains limited, but experts say the floodwaters could reach as far as Nepal's southern planes and beyond. Environment secretary Uday Raj Sharma said last week the bursting of the Imja lake would be like a "Nepalese tsunami," comparing it with the 2004 Indian Ocean disaster in which around 220,000 people died.

Global Warming - Imja Glacier - on YouTube (of November 10, 2007):

• http://www.redorbit.com/news/science/1744838/swelling_glacial_lakes_threaten_nepalese_communities/index.html?source=r_science
  
• http://www.theuiaa.org/bursting_glacial_lakes_in_nepal.html
  
• http://news.yahoo.com/s/afp/20090830/wl_sthasia_afp/nepalclimatewarminghimalayasglaciers
  
• http://www.terradaily.com/reports/Melting_glaciers_threaten_Nepal_tsunami_999.html
  
• http://www.globalpolicy.org/component/content/article/212/45218.html (2003)
  
• http://www.youtube.com/watch?v=4OOfOY0zfcA (20070
  

At the so-called Last Glacial Maximum (LGM) the ice sheets grew to their maximum positions between 33,000 and 26,500 years ago due to decreases in northern summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO₂. Nearly all ice sheets were at their maximum extent from 26,500 to some 19,000-20,000 years ago.

Some key questions that remain widely debated are what initiated the last deglaciation of the global ice sheets and what was their subsequent role during deglaciation in climate change, questions may be best assessed from the record of individual ice sheets rather than the integrated record.

In a study published on 7 August 2009 in the journal Science Clark et al. compiled and analyzed more than 5000 dated ages in order to develop a record of maximum regional ice extent around the time of the Last Glacial Maximum.

There is considerable regional variability in the timing of when ice sheets (and various sectors of ice sheets) first reached their local last glacial maxima. mountain glaciers were near or at their maximum extent by around 30,000 years ago. The onset of Northern Hemisphere deglaciation 19,000 to 20,000 years ago was induced by an increase in northern summer insolation, providing the source for an abrupt rise in sea level.

The authors have shown that the duration of the LGM sea-level lowstand (26.500 to 19,000 years ago) is in excellent agreement with the duration of maximum extent of most of the global ice sheets, suggesting that most of the global ice sheets were in near-equilibrium with climate during this 7500-year interval.

Another paper published on 8 August 2009 in Palaeocanography on the Last Glacial maximum concerns the “Impact of strong deep ocean stratification on the glacial carbon cycle”. During the Last Glacial Maximum, the climate was substantially colder and the carbon cycle was clearly different from the late Holocene (the Holocene is the geological epoch after the Ice Age, which means that it began approximately 11 700 years ago).

• http://www.sciencemag.org/cgi/content/abstract/325/5941/710
  
• http://www.agu.org/pubs/crossref/2009/2008PA001707.shtml
  
  

I am just back from a cruise to Svalbard/Spitsbergen and back along the coast of Norway. Fortunately the weather was excellent. It will take me a few days to get back to normal. In the meantime this picture of our cruise ship anchored in the Magdalenafjord (aka Magdalenabukt).


About 60% of the Svalbard archipelago is covered by ice. The behavior of the Svalbard ice masses is intimately bound up with variations of the ocean-atmosphere-glaciation system and can serve as an indicator of global scale change. Recession of the majority of Svalbard glaciers seems to be the result of recent climatic warming, but reaction of particular glaciers is different. It is noteworthy that about 90% of the Svalbard glaciers are emptying into the sea. Nearly 20% of the total coast length are ice cliffs providing a source for icebergs.

It is much easier to navigate along the west coast than the east coast because a branch of the Gulf Stream is stretching out to west coast of Svalbard.
And, actually new research, which reconstructs the extent of ice in the sea between Greenland and Svalbard from the 13^th century to the present indicates that there has never been so little sea ice as there is now. This means that we saw no sea ice on our way to around 80° N (Magdalenafjord: Latitude: 79° 34' 60 N, Longitude: 10° 58' 0 E), apart from extremely small lumps that had just calved off the glaciers. We did however have a clear view to glacier after glacier after glacier after ...

• http://resources.metapress.com/pdf-preview.axd?code=922v30um17650817&size=largest
• http://www.livescience.com/environment/090701-shrinking-sea-ice.html
• http://www.terradaily.com/reports/The_Least_Sea_Ice_In_800_Years_999.html

Sometimes it does. During the very coldest periods of the last ice age, glaciers in Patagonia (in South America) were at their biggest and released their meltwater, containing dust particles, on to barren windy plains, from where dust was blown to Antarctica. When the glaciers retreated even slightly, their meltwater ran into lakes at the edge of the ice, which trapped the dust, so that fewer particles were blown across the Southern ocean to Antarctica. Therefore the very coldest periods of the last ice age correspond with the dustiest periods in Antarctica's past. At least over the past 80,000 years according to findings published in Nature Geoscience.


Perito Moreno Glacier, in the Southern Patagonian Ice Field

When glaciers retreated near the end of the ice age about 21,000 years ago the airborne dust supply to Antarctica shut off because it ended up trapped in lakes that formed at the end of the glaciers. Release of dust at the coldest peaks was 20-50 times more than now, when many glaciers in Patagonia are in retreat. The dust from the Patagonian glaciers can now be studied in layers of dust in Antarctic ice and tell us more about the climate in the past.

• http://www.eurekalert.org/pub_releases/2009-03/uoe-dms032709.php
• http://www.alertnet.org/thenews/newsdesk/LR529703.htm
• http://www.reuters.com/article/latestCrisis/idUSLR529703
• http://news.bbc.co.uk/2/hi/uk_news/scotland/edinburgh_and_east/7971017.stm

The heading caught my eye. “New arctic record of cold water temperature in Storfjorden”. How cold can sea water be? I went on to the subheading which read “scientists ... found the coldest surface water ever measured in the Arctic" - both here and here. Let me remark that the freezing point of sea water is a function of salinity (and pressure). Open ocean sea-water has a salinity of about 35. Fresh water freezes at 0°C and 35 water freezes at about -2°C. The decrease is linear so that water with a salinity of 17 freezes at about -1°C. I therefore expected to read something about extreme saline water (in the Arctic), and my curiosity lead me to the relevant paper in the Journal of Glaciology, luckily with free access. I should of course have studied the title at the Bjerkness Centre better. It said ”scientists find super cooled water in the Arctic“, which is in fact what the paper titled ”Supercooled Water in an Arctic Polynya : Observations and Modeling“ is all about. Super-cooled and coldest is not necessarily the same thing.

It may well have been the the coldest surface water ever measured in the Arctic - but the paper does not really tell. It does however say that: ”The supercooling of 0.037±0.005°C observed directly in the Storfjorden polynya with frazil-ice growth is the strongest observed Arctic supercooling in recent years.“ An opportunity for me to explain what I understand by terms like supercooling, polynia, and frazil ice.

Super-cooled water is (liquid) water at temperatures below the normal freezing point of that water - a freezing-point temperature estimated from the measured salinity and pressure. With an assumed freezing point of -1.95°C and a super-cooling of 0.037°C the “real” temperature would have been -1.987°C - so this is the actual “coldest” temperature we are talking about.

Polynia (in the US spelled polynya) is a loan-word from Russian
which means a natural ice hole, and was adopted in the 19th century by polar explorers to describe navigable portions of the sea.
It is a semipermanent area of open water in sea ice. Polynias are generally believed to be of two types. Coastal polynias characteristically lie just beyond landfast ice (aka as fast ice), i.e. ice that is anchored to the coast and stays in place throughout the winter. They are thought to be caused chiefly by persistent local offshore winds, such as the foehn, or katabatic (downward-driving), winds typically found off the coasts of Greenland and Antarctica. The zone of open sea may be 50-100 km wide. Open-ocean polynias, the larger and longer-lasting of the two types, form within the ice cover and are believed to be caused by the upwelling of deep warmer water. This type is best exemplified by the vast Weddell Polynia in the antarctic Weddell Sea. The Weddell polynia was an enormous area of open ocean that reappeared in the Weddell Sea during 3 consecutive winters (1974-1976). At its largest it measured about 350 by 1000 km. The Weddell polynia reappeared in approximately the same position each year above a sea-bed topographic high, known as the Maud Rise.

Coastal polynias have been referred to as ‘sea-ice factories’. They ‘manufacture’ ice on an enormous scale, perhaps producing much of the ice in the adjacent ocean. It has been calculated that the heat flux to the atmosphere from a coastal polynia is more than 300 Wm^-2, enough to supply a ten centimetre thick layer of ice to the adjacent sea each day. The Storfjorden polynia is a coastal polynia, and in fact the heat flux here was indeed estimated to be about 300 Wm^-2 - and the wind during the super-cooling event to be about 8 m/sec.

Frazil ice is a collection of loose, randomly oriented needle-shaped ice crystals in water. It is a soupy suspension that resembles slush and has the appearance of being slightly oily when seen on the surface of water. It sporadically forms in open, turbulent, supercooled water. Under calm conditions the crystals freeze together to form a continuous sheet of new ice called nilas. It is up to 10 cm thick and looks dark gray. The ice crystals can be characterised as fine spicule, plate or discoid crystals about 1–20mm in diameter and 1–100μm in thickness.

Nilas is a thin elastic crust of gray-colored ice formed on a calm sea. It is characterized by a matte surface, and easily bent by waves and thrust into a pattern of interlocking fingers.

Grease ice is a slurry of ~25% pure frazil ice and ~75% sea water.

Katabatic wind. Down-slope winds flowing from high elevations of mountains, plateaus, and hills down their slopes to the valleys, planes or sea below are called katabatic winds. Katabatic is derived from the Greek, namely from katabaino - to go down. An upslope wind is called anabatic. Kata means down and ana means up. I mentioned another katabatic wind in my post on the (Adriatic) Bora.

Finally a cartoon showing the environment where coastal polynias are produced in the Antarctic by katabatic winds.



Did I remember to mention that Storfjorden is a fjord in Svalbard/Spitsbergen.

Reference:
R. Skogseth, F. Nilsen and L. H. Smedsrud,
Supercooled Water in an Arctic Polynya : Observations and Modeling,
Journal of Glaciology, Vol. 55, pages 43-52, No. 189, 2009

• http://www.ssf.npolar.no/pages/news275.htm
• http://www.bjerknes.uib.no/pages.asp?kat=8&id=1704&lang=2#
• http://www.igsoc.org/journal/55/189/

PS: Colder temperatures are found in salty pockets of water trapped in polar sea ice (said to be) down to -20°C (I have no refrence for that).