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Ice and Snow


Even though I don't work as a glaciologist today, I'm still deeply fashinated by ice. Now more aestetically than scientifically. This crystalline phase of water, the most characteristic and vital substance on Earth, is uniquely beautiful. Ice crystals on the window or rime on trees on a clear and frosty day when the sun makes the surface shine like a million diamonds - it is such a magnificent sight!

Arctis

Arctis

This is a place!
Polar Pointers is the most extensive list of polar links. A few are found below.



Ice core drilling

Nighttime

Night scene at GRIP 1990.

A big ice cap like on Greenland or Antarctica is built up of thousands of layers of yearly accumulated snow. The snow compacts to ice, conserving the atmospheric impurities the snowflakes originally scavenged during the fall, as well as informations about the physical conditions under which the snow formed. Furthermore airbubbles containing samples of the atmosphere are trapped in this proces whereby the snow turns into ice, also called firnification.

Ice cap

A schematic view of an ice cap,
the internal layers and the flow lines.

In this figure an idealized ice sheet is resting on a plane, horizontal base. The ice flow is described by the thick curves, which are flow lines. The ice flows slowly towards the edge of the ice cap, where it either melts or breaks off as ice bergs. The horizontal lines symbolize the annual layers. While sinking they are stretched, thus becomming ever-thinner. Only at the highest point of the ice sheet, Summit, the ice movement is vertical. The GRIP ice core drawn in under Summit, was drilled almost plumb.

Ice core

GRIP: An ice core is taken out of
the drill, which has been tilted to
horizontal position.

We can think of the ice cap as a library containing valuable information about the atmosphere and our climate reaching back in time. The further down we get, the older the history.

By drilling an ice core in the ice cap, we then have a continuous record of annual layers. Analysing the ice by various methods thus reveals some of these climate data.

A few pics from my field seasons in Greenland

C130

North GRIP 1996: A C130 "Hercules" aircraft brings people and equipment the 600 km from the coast to the camp site on the ice cap. All equipment, food and people must be transported to the camp by airplanes. This requires good logistic organisation and quite a lot of flights.

Trench

North GRIP 1996: Trenches for drilling and scientific work are dug out.

Dome skeletal

North GRIP 1996: A big wooden dome is raised in the camp. It will house the kitchen, dining room, shower, toilets, generator, workspace, radiocomunications, sleeping places etc...

Large drilling projects like GRIP and North GRIP require more permanent buildings than just tents. As the camp is established life and work runs almost as at any other work place in spite of the chilly laboratories and other exceptional conditions.

Dome

North GRIP 1996: Electric cables are laid out from the generator in the Main Dome. Electric power is installed in the drill- and science trenches as well as in all minor domes and weatherports.

C130

North GRIP 1997: The runway is groomed in order to keep it hard and flat and comfortable for the big C130 "Hercules" and the Twinn Otter airplanes to land on.

Drilling hall

North GRIP 1996: The drill is electromechanical and is controled by an operating system in the drill trench.

The GRIP, the North GRIP and the american GISP 2 drilling projects are the largest and most work intensive project yet performed on the Inland Ice. This is illustrated by the fact, that the GRIP operation required 3 years of planning and 4 seasons in the field. More than 200 people had been on the ice in this period, while about 500 people had been involved in one way or another.

Core store

North GRIP 1996: When the drillers are ahead of the scientists the core segments are stored on these shelves under the surface for later analyses.

core end

While showing the bottommost piece of the ice core Drill Master Sigfus Johnsen declares the GRIP deep drilling project completed. This core segment is full of silt from the bottom. The whole core measures 3028 m.

Sunset

North GRIP 1996: A calm, clear night view of the camp. This is the time for philosophizing and for admiring the greatness of the huge, waste ice desert.

The drilling project at the Hans Tausen Ice Cap in Peary Land was a small, one-season operation. The camp was relatively primitive and scientists and drillers slept in tents. The drill hit bedrock in about 4 weeks. The retrieved core was 346 m long. In this project only minor amounts of cargo and people had to be transported, thus the little Twin Otter airplane was perfectly suited for the operation.

At Hans Tausen Ice Cap

The Hans Tausen project 1995

At Hans Tausen Ice Cap

Drill tent

Fun picture beer and snow

North GRIP: Field work is hard.
Time for a rest and a cold beer!

Working in the field requires team spirit and good cooperation between all the participants. The daily work might be hard and sometimes awkward, but the time in the camp is usually accompanied by many a good laugh and making new friends.

Analysis of the ice

One of the main goals for ice core analysis is to see how the climate has changed back in time. A picture of the climatic conditions and the variability during thousands of years can be obtained through various measurements of many parameters by different methods. However, discovering indication of i.e. abrupt temperature changes in the ice at a certain depth is of no use at all, if one does not know the age of the specific ice. So dating the ice is absolutely essential.

Cleaning ice

North GRIP 1996: Ice for chemical analysis has to be cleaned very carefully. This is done in a laminar flow bench, where it is also cut into 5 cm segments, ready to be melted in the clean room laboratory in Copenhagen and analysed by ion chromatography.

There are several available methods for dating ice cores. They are based on measurements of stable isotope composition, radiactive decay, ice-flow modelling or stratigraphic observation. Identification of elevated electrical conductivities, due to fallout of soluble volcanic debris acts as reference horizons. Seasonal variations are observed in many parameters, such as acidity, chemical components and insoluble micro particles.

C130

North GRIP 1996: The core has just been taken out of the core barrel. It will immediately be logged, which means it will be measured, registered and cut in smaller pieces.

Seasonal varying parameters reveal the annual layering of snow and ice (when measured along a line perpendicular to the layers). If the analyses are performed so as to give a continuous profile downward from the surface in sufficient detail to allow interpretation, counting of annual layers leads to an absolute time scale along the core.

Line of analysis

GRIP 1990: In the laboratory - the science trench - the examination of the ice runs as in a production line. The core segments pass from group to group and are finally packed in boxes, which later are sent to Copenhagen.

One of the seasonal varying parameters is the so called δ value of 18O. δ is defined as the relative difference between the heavy 18O isotope to the light 16O. The main reason for the seasonal δ variation is that, on its journey to the polar regions, a precipitating air mass is generally cooled more in winter than in summer. The δ's of precipitation falling at a given location therefore generally reach lower values in winter than in summer. The δ annual cycles are obliterated by diffusion in the firn, but if the cycles survive the firnification proces (compression of snow to ice) to the point where mass exchange by diffusion in air becomes negligible, they remain in the ice for thousands of years.

ECM

North GRIP 1996: Electrical Conductivity Measurement, ECM, is a method for measuring the acidity of the ice. It is usually perfomed as one of the very first analyses after the core is drilled. This method is very practical because it is fast and gives a continuous acidity record. Furthermore, because it is performed on solid ice problems with CO2 uptake in melted samples is avoided.

Deposition of acidic components, mainly sulphuric and nitric acid, also vary in an annual way, which can be revealed by the ECM method. This method also detects major volcanic eruptions, because these emit large amounts of acid gases (mainly sulfuric acid) into the atmosphere from where it is later removed by precipitation, causing an acidic enriched layer in the ice core.

C130

One kind of chemical analysis is carried out by ion chromatography in the clean room laboratory in Copenhagen. By this method it is possible to measure the very small concentrations (micro-equiv.) of a series of ions.

The atmospherically transported or generated water soluble ions, such as H+, NH4+, SO42-, Cl-, Na+, Mg+, K+, Ca2+ and others are deposited on polar ice sheets in time-unit sequences. These ionic constituents of the total chemical content are derived from a variety of natural sources of terrestrial, marine and atmospheric origin, with an increasing component attributed to man´s activities. These ions can be measured by ion chromatography.

air bubbles

As the snow is compressed to ice, air is trapped in small bubbles. This gas is a sample of the atmosphere from the period when the pores in the ice were closed off. The air can be extracted and its composition analysed.

Beside the dominating N2 and O2 the atmosphere also contains gases as CH4 and CO2 in very small amounts. Both are greenhouse gases.

From the enclosed air bubbles in the ice these gasses can be measured by a technique where the ice is crushed whereafter the different gas components are caught in cold traps.

coulter technique

In the clean room laboratory, the contents of insoluble micro particles, "dust", is measured by the Coulter Counter method. This method gives the total amount of dust and the size distribution.

Insoluble micro particles (dust) can be measured by the standard Coulter Counter technique or by light-scattering. The annual variation in the deposited dust is a strong parameter for "counting years" back in time, because the dust - in contrast to chemical components - is much more stable in the ice matrix and is believed not to migrate in any significant way.

 

 

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