Earth Systems: Cryosphere: School of Earth Sciences SRTM University, Nanded - 431 606 Maharashtra, INDIA
Earth Systems: Cryosphere: School of Earth Sciences SRTM University, Nanded - 431 606 Maharashtra, INDIA
Earth Systems: Cryosphere: School of Earth Sciences SRTM University, Nanded - 431 606 Maharashtra, INDIA
Dr. K. Vijaya Kumar School of Earth Sciences SRTM University, Nanded 431 606 Maharashtra, INDIA (E-mail: vijay_kumar92@hotmail.com)
Cryosphere: An Introduction
Cryosphere is composed of frozen water in ice, snow and in frozen ground. The cryosphere makes-up approximately 2% of the water on Earth. Glacial ice sheets found in Greenland (can be 3 km in thickness) of the north and Antarctica (3.6 km or more in maximum thickness) of the south currently make 95% of the total cryosphere. Glacial ice sheets are the main regulators of global sea level. If all the ice sheets would melt, the sea level would rise up 73 meters, presuming that their area is restricted to the present state. Polar snow fall and polar temperature are the two most important regulators of glacial ice sheets. Snow and ice on high mountains are important fresh water resources. Cryosphere fluctuates through geologic time (glaciation vs. deglaciation).
Two ways n which H2O occurs in solid state is either away from the equator towards poles (Antarctica and Greenland) and with increasing elevation from mean sea level (Himalayan Glaciers). For example, Antarctica froze after it split from South America 34M years ago.
Static response of cryosphere to the global warming would be through simple mass balancing. Due to global warming, atmosphere and ocean temperatures would increase, which increases the rate of melting of ice sheets. However, due to global warming there would be higher evaporation consequently higher precipitation. This would result in counteracting melting of the ice sheets.
As increase in temperatures due to global warming not only results in melting but also makes it softer thereby increases the flow rate of ice. Ice is transported to lower elevations, which results in enhanced melting of the ice sheets.
In the recent times, it has been vehemently argued that the earth is experiencing global warming and the rate of melting of glaciers and ice sheets has accelerated. Nevertheless, it is evident from the above figure that there are domains on the globe which are experiencing cooling alongside warming. But on an average scale, global warming seems to be a reality.
When recent glacier/ice-sheet volume data is compared to that of 1950s, it is evident that almost all the regions on the earth have experienced decrease in the volumes of ice sheets and glacier masses. Ice cores of Antarctica and Greenland provide robust evidence for melting of ice and the data also predicts an increase of 0.5 mm/year sea-level rise.
Solar radiation varies smoothly through time with a strong cyclicity of ~23,000 years, as seen in the time-series of July incoming solar radiation at 65N. In contrast, glacialinterglacial cycles last ~100,000 years and consist of stepwise cooling events followed by rapid warmings, as seen in this time-series inferred from hydrogen isotopes in the Dome Fuji ice core from Antarctica. Atmospheric CO2 measured from bubbles in Dome Fuji ice shows the same pattern as the temperature time-series.
Atmospheric temperatures from the ice cores are calculated based on oxygen isotopic data. 18O (0/00) in the ice cores and temperature have a positive relationship (see figure below). Once we measure oxygen isotopes for the ice cores, and then based on this relationship between Temperature and D/18O atmospheric temperatures can be calculated.
Large, continental ice-sheets in the Northern Hemisphere have grown and retreated many times in the past. Times with large ice-sheets are known as glacial periods (or ice ages) and times without large ice-sheets are interglacial periods. The most recent glacial period occurred between about 120,000 and 11,500 years ago. Since then, the Earth has been in an interglacial period called the Holocene. Glacial periods are colder, dustier and generally drier than interglacial periods. These glacial-interglacial cycles are apparent in many marine and terrestrial paleoclimate records from around the world. Interglacial periods tend to occur during periods of peak solar radiation in the Northern Hemisphere summer. However, full interglacials occur only about every fifth peak in the precession cycle.
In Summary...........
2% of the water on Earth is locked in Cryosphere. 90% cryosphere is within Antarctica and Greenland Volume of Cryosphere is decreasing with time Antarctica and Greenland Ice cores indicate the cyclic behaviour of Glaciations (Glacial and Interglacial periods), based on oxygen and carbon isotope compositions and CO2 and CH4 concentrations.