Monday, August 19, 2019

chemistry (ocean) :: essays research papers

What is an iceberg? Why are they blue or green? An iceberg is a large floating block of freshwater ice that has broken off the edge of a glacier and been carried out to sea; about 90% of its mass lies under the water. The bluish streaks of clear, bubble free ice often seen in icebergs results from the refreezing of melt water which fills crevasses formed in the glacier as it creeps over land. The ice is blue because of the natural light scattering characteristics of pure ice. Occasionally airborne dust or dirt eroded from land ends up on the glacier surface eventually forming a noticeably darkened brown or black layer (in any orientation) within the ice of a floating iceberg. What type of information can scientists obtain from polar ice? Polar Regions and some alpine areas are sufficiently cold that snowfall accumulates from year to year, building up as glaciers. As snow at the surface gets buried with time it gets compressed to form solid ice and this ice carries with it information about the climate when the snow originally fell. By drilling down into a glacier and recovering this old ice, the information can be used to help understand past climate. The information obtained from ice cores can be divided into three types. The first of these types of information comes from the solid and dissolved impurities in the snow. Usually snow that falls in those places is almost pure water, but it still contains traces of dust, and pollutants from human activities. This information can be used to detect major environmental changes in the circulation of the atmosphere. The second type of information obtained from ice cores comes from bubbles in the glacier ice. These bubbles are formed as snow becomes compressed and the air between the flakes gets trapped. The third type of information obtained from ice cores comes from the frozen water itself. In the oceans, one in about every 500 oxygen atoms is the heavy isotope, while one in about 70 hydrogen atoms is heavy. However as the water evaporates and is transported to polar regions, the mix of the heavy isotopes changes. These changes are mostly influenced by temperature and it turns out that by measuring water isotopes in ice cores researchers can infer temperatures when the snow originally fell. In the past 30 years, many ice cores have been drilled to study past climate.

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