1
Introduction

1. 1.1 Background
2. 1.2 Canada and the Arctic: Historical and Community Synopsis
3. 1.3 The Fascinating Nature of Sea Ice
4. 1.4 Sea Ice in Research and Operational Disciplines
   1. 1.4.1 Sea Ice in Physics
   2. 1.4.2 Sea Ice in Climatology
   3. 1.4.3 Sea Ice in Meteorology
   4. 1.4.4 Sea Ice in Oceanography
   5. 1.4.5 Sea Ice in Marine Biology
   6. 1.4.6 Sea Ice in Marine Navigation
   7. 1.4.7 Sea Ice and Offshore Structures
   8. 1.4.8 Sea Ice as A Transportation Platform
   9. 1.4.9 Sea Ice in Relation to Solid Earth Sciences: Rocks and Plate Tectonics
5. 1.5 Sea Ice and Remote Sensing
6. 1.6 Motivation for the Book Writing
7. 1.7 Organization of the Book
8. 1.8 References

1.1. BACKGROUND

Our world is divided into five regions according to the position of the sun throughout the year: a tropical region around the equator, two temperate regions, and two polar regions. On two equinoxes, 21 March and 23 September, the sun is directly over the equator and the sun's rays reach both the North and South poles. On 21 June (the Summer Solstice), the sun is directly over the Tropic of Cancer (about 23.5° N) in the northern temperate region, and on 22 December (the Winter Solstice) it is positioned directly over the Tropic of Capricorn (about 23.5° S) in the southern temperate region. In the two polar regions, mostly relevant to the material in this book, the sun never sets in their summer and never rises in their winter. The Arctic region (or zone) containing the North polar region (with latitudes greater than "about" 66.5° N) and the Antarctic region (or zone) containing the South polar region (having latitudes greater than "about" 66.5° S) are the primary cryospheric regions of the world. The 66.5° angle comes from the tilt of the earth's rotation axis (23.5°), such that 90° - 23.5° = 66.5°. Recall that cryosphere comprises all regions where water exists in solid form.

Although the latitudes of the Arctic and Antarctic circles depend on the earth's axial tilt, which fluctuates slightly with time (about 2° over a 40,000-year period), the variations in the boundaries of the polar region are very small and negligible. The secondary cryospheric regions include the Alps, Andes, Himalayas, Rockies, etc. Among the secondary cryospheric regions, the Himalayan belt covers and affects the largest effective area of human habitation.

Climate change has been affecting all the cryospheric regions of the world, and the effects can be directly observed and quantified using airborne and space-borne remote sensing as well as land-based instruments. Remotely sensed images of the land- and ocean-based snow and ice information are paramount in understanding the state of health of the earth for sustainability of life. Other methods such as ice core analysis of ice caps and ice shelves, composed mainly of snow in different phases, are also used. After all, snow is the messenger of the sky, and ice is the answer to the cold climate.

Sea ice covers most of the oceanic surface of the primary cryospheric area of the global surface. While not noticeable by the majority of the population of our planet, sea ice observations provide a powerful tool for quantifying climate change and the health of our only home. The world of sea ice encompasses the polar region, particularly the Arctic basin and a belt around the continent of Antarctica. Out of the 71% of the earth's surface that is covered by ocean, about 7%-15% is covered by sea ice at certain times (more in the winter and less in the summer). That is equivalent to 5%-10% of the earth's surface. About 37% of the total oceanic surface is covered by sea ice at one time or another. Sea ice area in the Arctic varies between a minimum of about 4 million km2 in September to a maximum of about 15 km2 in March. The corresponding figures for the Antarctic are 3 million and 18 million km2 in February and September, respectively. However, the maximum volume of the sea ice cover in the Arctic (about 0.05 million km3) is nearly twice the maximum volume in the Antarctic. This is because the mean thickness of sea ice is 3 m and 1.5 m in the Arctic and Antarctic, respectively.

Sea ice can develop very smooth or very rough surfaces. It can be soft or hard, a bare-surface or snow-covered, stagnant (fastened to the shoreline) or mobile pack ice, stiff and silent or crushing with loud noise. It exhibits seasonal variations to which life in the polar regions is closely adapted. In the Arctic region, sea ice starts its growth in September/October and reaches its maximum in February/March, when it covers the entire Arctic basin. This trend is reversed during the summer, and the ice extent reaches its minimum in September. In the Antarctic, the annual fluctuations range between a minimum in February to a maximum in August/September, when ice extends to latitudes between 55°-65° South.

For a limited time during the summer months, certain areas of the polar waters in the Arctic zone are used extensively by ships (ice-strengthened or escorted by icebreakers) where the floating bodies of new and old sea ice and icebergs can prove hazardous. The expected reduction of sea ice extent, the reduction of the navigationally hazardous old ice, and the increase in the duration of summer melting season will certainly increase marine activities in these areas. No doubt, the Arctic waters, particularly the legendary Northwest Passage (NWP) that passes through the Canadian Arctic Archipelago (CAA) and the Beaufort Sea, will be used more in the future for shipping goods between Asia, North America, and Europe.

Sea ice extent in both the Arctic and Antarctic averages the same, about 15 million km2, during winter. However, because the mean thickness of sea ice in the Arctic is larger, the maximum volume of sea ice cover in the Arctic (about 0.045 million km3) is nearly twice that of the Antarctic. In summer, ice extent shrinks significantly to about 50% of the winter coverage in the Arctic. Nearly 90% of the sea ice coverage disappears by the end of the summer in the Antarctic. Ice that melts completely during the summer is called "seasonal ice" or "annual ice." If the ice melts only partially, then the part that survives until the next winter and growth season is called "perennial ice." This can be second-year ice (SYI) or multi-year ice (MYI), depending on how many summers the ice has survived.

As a major component of the cryosphere, sea ice influences the global ocean and atmosphere in a profound manner. Its continuous interaction with the underlying oceans and the overlaying atmosphere leaves major impacts on weather, climate, and ocean current systems. Moreover, ice in one form or the other plays a significant role in the daily life of communities inhabiting the cold regions of the earth. Sea ice in particular influences the coastal areas in most of the circumpolar nations of the Northern Hemisphere. It affects, to a lesser extent, a few countries in the Southern Hemisphere. Of all the countries of the world, Canada has the longest coastline as well as the largest reservoir of fresh-water lakes and rivers with floating ice in them annually at least for half of the year. Except for Alaska, practically all the areas north of the 49° N in North America belong to Canada. While sea ice plays a major role in areas above 60° (north or south), it does not affect areas below that latitude except in the Hudson Bay, Labrador Sea, and the Gulf of St. Lawrence in Canada, and relatively speaking, to a lesser extent in the Baltic Sea, Gulfs of Bothnia and Fin in Europe, the Sea of Okhotsk, north of Japan, and Bohai Bay in China. Above about 35° N in Eurasia and North America, most of the streams, rivers, and lakes (e.g., Black Sea, Sea of Azo, Caspian Sea in Eurasia, and the Great Lakes in North America, to name a few among thousands) have some ice cover each winter. In fact, severity of winters in North America is often measured in terms of ice coverage of the five Great Lakes (Lake Superior, Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario).

In spite of the fact that sea ice covers vast areas of sea surface of the earth, most of the people of the primary cryospheric regions of the world have not seen it or are even aware of it. That is because most people, even within the cold regions of the earth, live far from the areas affected by sea ice. Other than a few thousand multinational scientific observers and a few annual visitors, nobody lives in the South Polar Zone (beyond the Antarctic Circle). Only a few small communities of the Falkland Islands and Argentina consider the Antarctic region their home. On the other hand, beyond the Arctic Circle in circumpolar areas of Alaska, Canada, Norway, and Russia, perhaps a few million people live. This is incomparable to the nearly 3200 million people living in Afghanistan, Bangladesh, China, India, Nepal, Pakistan, and Tibet, who are indirectly affected by the Himalayan cryosphere, but sea ice does not exist in those regions.

It is not uncommon for people who live away from the circumpolar boundaries to be confused between sea ice and icebergs. Yet, general awareness about sea ice has been growing as public information about the decline of sea ice in the Arctic with its positive economic impacts and negative...