MET 112 Global Climate Change- Lecture 12 Glaciers, Ice Sheets, and the Cryosphere Dr. Craig Clements San Jose State University

Definitions Glacier- is a body of moving ice that has been formed on land by compaction and recrystallization of snow. Two requirements must be met before a mass of ice can be called a glacier. (1) ice must be moving, either internally or as a sliding block. (2) the mass must be due to the accumulation and metamorphism of snow. In any region a specific elevation exists called the snowline or firn line, above which some snow remains on the ground perennially and permits the formation of a glacier. In polar climates, snowlines are usually near or at sea level and gradually increase in elevation in climatic zones with a higher annual temperatures.

Mass Balance: an accounting or budgeting of the gains and losses of snow that occur on a glacier during a specific time interval. Definitions Accumulation- the water equivalent of ice and snow added to a glacier during a period (annual, called budget year). Ablation- processes that remove snow or ice including melting evaporation, wind erosion, sublimation or breaking off of large blocks into standing water, called calving.

Accumulation Zone (+) Ablation Zone (-) Equilibrium line Glacier Mass Balance ice

Definitions Glaciers can be placed in three broad categories: Cirque glaciers, valley glaciers, and ice sheets. Ice sheet- a dome-shaped mass of glacier ice that covers surrounding terrain and is greater than 50,000 square kilometers (12 million acres) (e.g., the Greenland and Antarctic ice sheets). Valley glacier- a mountain glacier whose flow is confined by valley walls. A cirque glacier is formed in a cirque, bowl-shaped depressions on the side of mountains. Snow and ice accumulation in corries often occurs as the result of avalanches from higher surrounding slopes.

Cirque Glacier: Teton Glacier Photographer unknown

Glacier Ablation zone Horn: a peak that is shaped by multiple cirques Accumulation zone 22-km long, Grosser Aletshglescher, Switzerland

An ice shelf is a thick, floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface. Ice shelves are found in Antarctica, Greenland and Canada only. Definitions Ice shelves of Antarctica

Russel Glacier, Greenland ice sheet, June 2008

Ice Sheet: Greenland

Melt ponds on the surface of Greenland’s ice sheet.

Moulin: a narrow, tubular chute, hole or crevasse through which water enters a glacier from the surface.

Sea ice is formed from ocean water that freezes. Because the oceans consist of saltwater, this occurs at about -1.8 °C (28.8 °F) Land-fast ice, or simply fast ice, is sea ice that has frozen along coasts ("fastened" to them) or to the sea floor over shallow parts of the continental shelf, and extends out from land into sea. Unlike drift ice, it does not move with currents and wind. Sea ice may be contrasted with icebergs, which are chunks of ice shelves or glaciers that calve into the ocean. Icebergs are compacted snow and hence fresh water. Definitions Drift ice is ice that floats on the surface of the water in cold regions, as opposed to fast ice, which is attached ("fastened") to a shore. Usually drift ice is carried along by winds and sea currents, hence its name, "drift ice".

Aerial view of the pack ice at the east coast of Greenland, drifting southward in the East Greenland current. July 1996.

Sea ice climatologies: Arctic and Antarctic sea ice concentration climatology from , at the approximate seasonal maximum and minimum levels based on passive microwave satellite data. Image provided by National Snow and Ice Data Center, University of Colorado, Boulder.

Glacial Landforms Cirque: a small basin or bowl at the head of a glacial valley Arete: a sharp ridge separating two glacial valleys Moraine: a ridge of debris (broken rocks) found at glacier edges

Glacier Flow and erosion (plucking and abrasion) Landform called: Roche Montanée

Lembert Dome, Tuolumne Meadows, Yosemite National Park, Sierra Nevada, California Roche Montanée

Melting of Yosemite’s Glaciers Photographer unknown

Mt. Lyell Glacier, Yosemite National Park Photographer unknown

What will happen when the snow and glaciers melt in California or around the world? Who will it affect?

Water Resources?

What effect will this have on the oceans?  Melting glaciers can affect the ocean currents.  How and what will this affect?

Oceans and Climate  Oceans act on the climate: 1.Behave strongly as a coupled system 2.Evaporation from the oceans provides the main source of atmospheric water vapor—latent heat of condensation in clouds– provides the largest single heat source for the atmosphere. 3.The atmosphere, in turn, acts through wind stress on the ocean surface as the main driver ocean circulation.

Oceans  Oceans transport heat around the globe  Large heat capacity = large quantity of heat is needed to raise the temperature of the oceans only slightly Entire heat capacity of the atmosphere = 3 m deep in ocean (surface layer of ocean) Internal circulations of the oceans redistribute heat throughout climate system Even small changes in the regional heat transport by oceans could have large implications for climate change.

Oceans Heat Capacity  Total heat transported by the north Atlantic Ocean is over 1000 Terawatts 1 Terawatt = 1 million million watts (10 12 W) A typical power station provides 1000 million watts (10 9 W) Total amount of commercial energy produced produced globally = 12 Terawatts.

Thermohaline Circulation  In polar regions, seawater at the surface of the ocean is intensively cooled by the wind. Wind moving over the water also produces a great deal of evaporation, leading to a decrease in temperature, called evaporative cooling. evaporative cooling  Evaporation removes only molecules of pure water, resulting in an increase in the salinity of the seawater left behind, and thus an increase in the density of the water mass.  To sink deep, ocean water needs to be dense, cold and salty (North Atlantic, Antarctica)

The Great Conveyor Belt

Thermohaline Circulation (THC) Melting of ice leads to the ocean surface to become less salty (lower salinity) and therefore, less dense. It will not sink so easily— THC weakens and less heat will flow northward from tropics. GCMs show this occurring. THC shutting off completely after 2 or 3 centuries. Severe Cooling