see the National Snow and Ice Date Center (NSIDC), www.nsidc.org/seaice.
3 UNDERSTANDING THE COLD
Leads, areas of open water, can turn overnight into a fragile Arctic flowerbed
All about Ice and Snow
Ice is frozen water. (OK, so you already knew that.) But just as you gradually learn that there is more than one species of bird, you will discover that there are many types of ice. Ice is an extremely interesting subject (especially for the bored polar explorer who has nothing else to do but look for slight changes in the ice).
Ice can appear in the form of hail, frozen rain, snowflakes, icicles, glaciers, sea ice (7 per cent of the world's oceans) and polar ice-caps and approximately 30 million km2 of Earth are ice-covered.
Calculating ice density in the Antarctic
The colour of ice may vary, depending on:
age
density
possible impurities
light intensity
presence or absence of air.
Fresh water starts to freeze at 0°C (Celsius) or 32°F (Fahrenheit). This standard process may be impaired by atmospheric pressure and/or movements of the water. On a fresh-water lake, when temperatures plummet, the density of the water increases, but levels off at 4°C. As the cooling process continues, colder water at the surface becomes more dense. As soon as the temperatures reach 0°C, a physical transformation of the molecular structure of the fresh water produces ice.
This process, however, is different in salt-water bodies and oceans. Cooling of the ocean surface causes the top layers of water to increase in density and therefore sink, a process which continues until the water reaches freezing point – which itself is lowered by the addition of salt (about −1.8°C for typical sea water).
As soon as salt water solidifies, the main types of ice formed are the following:
Frazil First signs of freezing sea water, with an ‘oily’ look.
Nilas Merging frazil, at first transparent, but soon grey and eventually white.
First-year ice Nilas that has grown in one season up to 1.5–2m deep.
Ice flowers decorating newly born nilas
The impact of the wind over the ice and the currents under the ice makes the Arctic ice mass split open and creates ‘leads’ that represent endless hurdles for expeditioners
By the look of the ice, the following categories can be distinguished:
Pack ice Newer ice.
Ice floes Also known as pan ice.
Hummocks Big piles of ice, part of a pressure ridge.
Pressure ridge Line in the pack ice, where pressure within the ice has pushed the surface layer both upward (‘sail’ −2–3m high) and downward (‘keel’ – below the surface).
Fast ice Old and solid ice, attached to land.
Pancake ice Circular ice, randomly floating on agitated sea water.
Consolidated pancake ice Pancake ice ‘glued’ together in calmer water by frazil.
It is important to know that saline ice will take more than one year to lose the salty flavour that can make your soup inedible if used for cooking. New ocean ice has approximately 10 parts per thousand of salt, while multi-year ice only has 1–3 parts. Older ice is at least a metre thick, and you can see that overturned blocks of ice have ‘lived’. If in doubt, just taste it.
In order to understand the dynamics of sea ice it is important to know that pack ice is constantly in motion, driven by the wind, and that this produces many important changes to its appearance and development. The two most obvious features created are leads and pressure ridges. The impact of the wind results in ice sheets moving by frictional drag; extended masses of ice can move over long distances. It has been estimated that in concentrated pack ice a piece of sea ice can move over 400km upwind. Once in motion, the ice will continue to move under its own momentum long after the wind has died.
Multi-year ice
Ice which has survived one or more summer seasons of partial melt is called ‘multi-year ice’ (more than half the ice in the Arctic falls into this category). Growth continues from year to year until the ice thickness reaches a maximum of about 3m, at which point summer melt matches winter growth and the thickness of the ice oscillates through an annual cycle. This old, multi-year ice is much fresher than first-year ice; it has a lower conductivity and a rougher surface. The low salinity of multi-year ice makes it much stronger than first-year ice.
Multi-year ice pushed up to release some of the pressure on the Arctic ice pack
Snow
Snow is generally white because it reflects the full spectrum of light, which we see as white. However, snow can also be red, green, blue or black. This occurs because of the presence of beautifully coloured (if rare) fungi, as well as bacteria, mosses and algae. These can survive in both the Arctic and Antarctic, especially in humid areas: evidence of life in a habitat where it is least expected.
Most people think of snow simply as frozen water, but it's far more complicated than that. Snow is actually a form of precipitation as ice crystals, hexagonal prisms that form when water freezes up. Prisms are formed because of the molecular structure of water. As these ice crystals are formed, they develop into one of the following:
DON'T EAT SNOW!
If you're wondering how to survive in the cold without any means of thawing ice or snow – it's important to know that it takes more energy to eat snow than it is worth. You use more energy eating it than you gain through hydrating your body with it.
snow crystals Individual, single ice crystals, often with six-fold symmetrical shapes. These grow directly from condensing water vapour in the air, usually around a nucleus of dust or some other foreign material. Typical sizes range from microscopic to at most a few millimetres in diameter.Measuring snow thickness on the Arctic Ocean
snowflakes Collections of snow crystals, loosely bound together into a puffball. These can grow to large sizes (up to about 10cm across) when the snow is especially wet and sticky. A snowflake
