Reading

Chapter 7 (all pages) from:

Mutiti, S., Mutiti, C., Manoylov, K., VandeVoort, A., & Bennett, D. (2018). Introduction to environmental science (3^rd ed.). Biological Science Open Textbooks. University System of Georgia. See: MUTITI_et_al_7_water.docx

Hydrosphere

You have probably been studying the hydrosphere since fourth grade. Many of us are knowledgeable about the hydrologic (water) cycle, evaporation, transpiration, precipitation, and so on.

Your reading for this section, Mutiti et al. (2018), Chapter 7 goes into some depth on this topic in order for you to get a refresher and a more in-depth look at the science of water over and above your fourth-grade knowledge. Please read that thoroughly.

Cryosphere

What you may not have as much knowledge of is the frozen part of the hydrosphere. That is presented in brief here.

Frozen water, while part of the hydrosphere, is called the cryosphere. This section barely scratches the surface of cryoscience, but it begins with glaciers.

Glaciers

Glacier: large natural accumulation of land ice affected by present or past flowage

Glacial ice sheets affect global climate
Glaciers reflect sunlight (albedo)
Glacial ice affects global heat transport
Volume of glacial ice affects sea levels
Large bodies of ice are "plastic" because of pressure on ice at bottom of mass
Large body of ice flows in response to gravity
Ice on a slope can slide downwards
Glacial ice builds up when snowfall in winter exceeds snow melted in summer
Each annual layer of snow, melts, refreezes, forms ice
Weight of ice compresses the lower layers into hard crystalline ice

There are two main types of glaciers: icesheets and alpine glaciers.

Ice Sheets

Ice sheet: large thick plate of glacial ice moving outward in all directions. Found in high latitudes. The two major ice sheets on Earth are Greenland and Antarctica.

Greenland Icesheet map

Greenland Ice Sheet

Much of Greenland is covered by a massive ice sheet that is retreating around the edges changing regional ecosystems.

About 80 percent of Greenland is blanketed by an ice sheet, also known as a continental glacier, that reaches a thickness of up to 3 kilometers (2 miles). As glaciers flow toward the sea, they are usually replenished by new snowfall on the interior of the ice sheet that gets compacted into ice. Multiple studies have shown that the balance between glacier melting and replenishment is changing, as is the rate of iceberg calving. Due to rising air and ocean temperatures, the ice sheet is losing mass at an accelerating rate and additional meltwater is flowing into the sea. (NASA, 2021, para. 4)

Melting ice creates under-glacier freshwater rivers. These subsurface rivers flow toward the ocean impeding phytoplankton-rich sea water circulation and impacting local ecosystems through disruption of the marine food chain.

Using Google Earth Pro I calculated the loss of glacial ice from 1984 to 2020 by measuring the terminus of the Kangerlussuaq Glacier. Over that 36-year period approximately 40 mi2 (25,753 acres) of glacial ice disappeared. The glacier’s terminus has retreated 11.9 miles.

Map of Greenland indicating retreating glaciers.

(NASA, 2021)

Satellite image showing 1984 glacial terminus and 2020 retreated terminus.

Kangerlussuaq Glacier showing 11.9 miles of retreat from 1984 to 2020. (Google, 2020)

Antarctic Ice Sheet map

Antarctic Ice Sheet

The continent of Antarctica itself is depressed more than half-a-mile to near sea level under the tremendous load of the ice sheet, with some regions well below sea level. The highest mountains in the Antarctic rise to elevations of over 14,000 ft., about the height of the U.S. Rocky Mountains.

The present Antarctic ice sheet accounts for 90 percent of Earth's total ice volume and 70 percent of its fresh water. It houses enough water to raise global sea level by 200 ft. if completely melted. The ice sheet at the South Pole, nearly two miles thick, is constantly shifting, carrying the United States' South Pole facility with it at the rate of about 30 ft. a year. Nearly 90 percent of the ice flowing across West Antarctica converges into ice streams that are the most dynamic, and perhaps unstable, components of the ice sheet. Recent glaciological observations have yielded evidence that some of these West Antarctic ice streams may be responding to climatic and sea level changes of the recent past, changes that could lead to more rapid retreat and global sea-level rise in the future. A few active volcanoes under the ice may also affect the behavior of the ice!

The Antarctic climate offers a formidable challenge to those who venture there in quest of scientific knowledge. It is the coldest, driest, highest (on average) and windiest continent on Earth. Absolute humidity is lower than on the Sahara. Annual snowfall in much of the interior is less than two inches. Winds that flow down the surface of the ice sheet toward the coast (katabatic winds) commonly reach speeds of 80 miles per hour, and maximum measured wind speeds have exceeded 180 miles per hour. Changes in the weather are dramatic: winds shift from calm to full-gale in a brief period of time. A drop of 65°F was once recorded in 12 minutes. Earth's lowest surface temperature (-126.9°F) was recorded at Russia's Vostok Station in the interior of Antarctica. Coastal locations in summer occasionally rise above the freezing point.

(excerpted from NSF, 1997).

Alpine Glaciers

Alpine glacier: long, narrow mountain glacier occupying the floor of a trough-like valley. Alpine glaciers are found at high altitudes and flow downhill in response to gravity.

Upper part of the glacier is brittle
Lower part is plastic (bendable)
Zone of accumulation: upper part where glacier is growing
Zone of ablation: lower part where glacier is evaporating/melting
Alpine glacier can slide downhill on meltwater and mud
Rate of movement: few centimeters/day to several meters/day
Surge: rapid movement of alpine glacier, up to 60m/day for several months

Alpine Glacier Cut Away with headwall at the top, followed by the firn field in the zone of accumulation. Ice falls one-third of the way down, then leading to the glacial terminus with lateral moraines.

Photograph of the Aletsch Glacier in Switzerland is the largest valley glacier in the Alps.

Aletsch Glacier in Switzerland is the largest valley glacier in the Alps (NASA)

One of the problems with global climate change is that the Earth's glaciers are melting. Watch this photo-rephoto video demonstrating just how evident this problem is.

References

Google. (2020). [Google Earth Pro satellite imagery of Kangerlussuaq Glacier, Greenland]. Retrieved January 8, 2021, from Google Earth Pro.

NASA. (2021). Shrinking margins of Greenland: At least 200 coastal glaciers have retreated over the past 20 years. SciTechDaily. https://scitechdaily.com/shrinking-margins-of-greenland-at-least-200-coastal-glaciers-have-retreated-over-the-past-20-years/

National Science Foundation (NSF). (1997). The United States in Antarctica: Report of the U. S. Antarctic Program external panel. Washington, D. C. https://www.nsf.gov/pubs/1997/antpanel/antpanel.pdf