Melting Ice and the Rise in Sea Levels
Sea levels have varied considerably over the geologic past, ranging from 4-6 meters above the present levels 125,000 years ago during the last interglacial period, to 120 meters lower than current levels about 20,000 years ago at the height of the last ice age, due to the amount of water contained in the enormous ice sheets.
When the ice began to melt and ice sheets started to diminish at the end of the last ice age sea levels began aa rapid rise, with occasional periods of faster melting, known as meltwater pulses. The first such instance of accelerated melting may have begun 19,000 years ago when sea levels rose 10-15 meters in 500 years, although not all past records indicate this. Another, more apparent, spurt happened 14,600 to 13,500 years ago when sea levels rose 16- 24 meters.
The Younger Dryas cold period saw a slowing of rising sea levels, followed by another spurt 11,500 to 11,000years ago when sea levels might have surged by 28 meters. However, further studies have indicated a less drastic increase.
A fourth spurt in sea levels was revealed by a break in Caribbean coral growth around 7600 years ago. Although this meltwater pulse is less substantiated than the others, stratigraphic data from areas in the United States, China, England, and Denmark seem to corroborate it. It resulted in only a one meter rise in sea levels, but still left evidence in the geologic record.
By 6000 to 5000 years ago, the Mid-Holocene period, the melting of the glaciers had virtually ceased while the Earth’s lithosphere responded to the removal of the ice sheets. Over the past few thousand years, increases in sea levels were probably not more than a few tenths of a millimeter per year.
Sea level trends during the twentieth century, beginning in the mid to late nineteenth until the early twentieth century, have been rising more rapidly. Tide gauges in coastal harbors indicate rises of 1.7-1.8 millimeters per year, apparently in response to global warming. Images from NASA’s MODIS Land Rapid Response Team taken of the west edge of the Greenland ice sheet in 2001, 2002, and 2003 show a greatly expanded area of the meltzone, and glaciers are discharging ice into the sea at a faster rate.
The west Antarctic ice sheet is also showing indications of thinning. The complete melting of either ice sheet would raise sea levels 5-7 meters, although such a meltdown would take centuries. Any future accelerated melting of the west Antarctic ice sheet would not be likely to surpass the sea level rises caused by the meltwater pulses of the post-glacial period
This entry was posted on Wednesday, October 10th, 2007 at 5:45 pm and is filed under Public Relations, Space Agency News. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
