Ice sheets forms

Fig. 19.11 Kellogg et al. (1997) proposed that marine diatoms of Cenozoic age are transported through the air and are deposited on the East Antarctic ice sheet. The subsequent transport of the diatoms depends on the way the ice sheet moves, (a) If the base of the ice sheet melts, the diatoms (D) are deposited in the basal till and may be brought to the surface in molded till pellets as in the Elephant Moraine (Section 17.3.5). (b) In cases where the base of the ice sheet is frozen to its bed, the diatoms (D) are transported to the edge of the ice sheet where they are deposited in end moraines. The authors also considered the cases (not shown) where the base of the ice sheet freezes to its bed and where the ice sheet forms an ice shelf floating in seawater (Adapted from Kellogg et al. 1997)...

Most of the non-gaseous impurities in ice were once atmospheric aerosols. Atmospheric aerosols raining onto an ice sheet are of two types primary aerosols, which are incorporated directly into the atmosphere as aerosols (these include continental dust and sea spray), and secondary aerosols which form in the atmosphere from gases. In addition to aerosol-derived impurities, some soluble gases in the atmosphere (HNO3 HCl, H2O2, and NH3) adsorb directly onto ice, and so are measured in a core... 

The climate has the ability to shift into radically different states according to ice cores extracted from Greenland s massive ice sheet in the early 1990s. These rods of ice are up to three kilometers long and provide a set of climate records for the past 110,000 years. They allow the investigation of annual layers in the ice cores which are dated using a variety of methods. The composition of the ice provides the temperature at which it formed. 

Smith, H. J., M. Wahlen, D. Mastroianni, K. Taylor, and P. Mayewski, The C02 Concentration of Air Trapped in Greenland Ice Sheet Project 2 Ice Formed during Periods of Rapid Climate Change, J. Geophys. Res., 102, 26577-26582 (1997). 

Freezing, the opposite of melting, is the process by which a liquid changes into a solid. It is the phase change responsible for creating frozen forms of precipitation. Glaciers and ice sheets are formed as the result of the freezing process. 

A snowflake is made up of ice crystals that are stuck together. Snowflakes form high in Earths atmosphere. Hail is a frozen mass of water that often forms inside thunderstorms. Sleet is made up of drops of rain that freeze as they fall to Earths surface. Freezing rain is precipitation that falls as liquid but freezes when it hits the cold ground. Together, these different forms of frozen precipitation move drops of liquid water out of the atmosphere and onto Earths surface where they can melt and seep into oceans and groundwater or freeze and build up to create glaciers and ice sheets. 

There are deeper caves that contain stalactites and stalagmites that could only have formed when the cave was air-filled. Using mass spectrometric UATh dating, Richards et al. (1994) measured sea level low stands down to 50 meters below present sea level. The last extensive thrust of the Wisconsinan ice sheet at about 20 ka is clearly shown. Speleothems recovered from a cave on Andros Island, Bahamas at —45 meters was dated at 139 - 160 ka, showing that sea level must have been at least this low at that time... 

Clathrate hydrates. Chemical systems involving dissolved gases can also form clathrate hydrates at modest pressures and temperatures in a simple low-pressure optical cell. Hydrocarbon clathrate hydrates occur in marine and polar regions where hydrocarbons react with cold water. CO2 hydrates have been reported in seafloor environments near cold CO2 vents. Natural air hydrates occur in ice cores taken from polar ice sheets. Air is trapped and sealed in snow during compaction to form low-porosity ice. 

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