CU Boulder/CIRES - Total Antarctic Ice Balance "In Significant Decline"

[hatrack]

Note to Mods: Press release - given in its entirety.

University of Colorado at Boulder researchers have used data from a pair of NASA satellites orbiting Earth in tandem to determine that the Antarctic ice sheet, which harbors 90 percent of Earth's ice, has lost significant mass in recent years.

The team used measurements taken with the Gravity Recovery and Climate Experiment, or GRACE, to conclude the Antarctic ice sheet is losing up to 36 cubic miles of ice, or 152 cubic kilometers, annually. By comparison, the city of Los Angeles uses about 1 cubic mile of fresh water annually.

"This is the first study to indicate the total mass balance of the Antarctic ice sheet is in significant decline," said Isabella Velicogna of CU-Boulder's Cooperative Institute for Research in Environmental Sciences, chief author of the new study that appears in the March 2 online issue of Science Express. The study was co-authored by CU-Boulder physics Professor John Wahr of CIRES, a joint campus institute of CU-Boulder and the National Oceanic and Atmospheric Administration.

The estimated ice mass in Antarctica is equivalent to 0.4 millimeters of global sea rise annually, with a margin of error of 0.2 millimeters, according to the study. There are about 25 millimeters in an inch.

The most recent Intergovernmental Panel on Climate Change assessment, completed in 2001, predicted the Antarctic ice sheet would gain mass in the 21st century due to increased precipitation in a warming climate. But the new study signals a reduction in the continent's total ice mass, with the bulk of loss occurring in the West Antarctic ice sheet, said Velicogna.

Researchers used GRACE data to calculate the total ice mass in Antarctica between April 2002 and August 2005 for the study, said Velicogna, who also is affiliated with the Jet Propulsion Laboratory in Pasadena.

"The overall balance of the Antarctic ice is dependent on regional changes in the interior and those in the coastal areas," said Velicogna. "The changes we are seeing are probably a good indicator of the changing climatic conditions there."

Launched in 2002 by NASA and Germany, the two GRACE satellites whip around Earth 16 times a day at an altitude of 310 miles, sensing subtle variations in Earth's mass and gravitational pull. Separated by 137 miles at all times, the satellites measure changes in Earth's gravity field caused by regional changes in the planet's mass, including such things as ice sheets, oceans and water stored in the soil and in underground aquifers.

A change in gravity due to a pass over a portion of the Antarctic ice sheet, for example, imperceptibly tugs the lead satellite away from the trailing satellite, said Velicogna. A sensitive ranging system allows researchers to measure the distance of the two satellites down to as small as 1 micron -- about 1/50 the width of a human hair -- and to then calculate the ice mass in particular regions of the continent.

"The strength of GRACE is that we were able to assess the entire Antarctic region in one fell swoop to determine whether it was gaining or losing mass," said Wahr. While the CU researchers were able to differentiate between the East Antarctic ice sheet and West Antarctic ice sheet with GRACE, smaller, subtler changes occurring in coastal areas and even on individual glaciers are better measured with instruments like radar and altimeters, he said.

A study spearheaded by CIRES researchers at CU-Boulder and published in September 2004 concluded that glaciers on the Antarctic Peninsula - which juts north from the West Antarctic ice sheet toward South America -- sped up dramatically following the collapse of Larsen B ice shelf in 2002. Ice shelves on the peninsula -- which has warmed by an average of 4.5 degrees Fahrenheit in the past 60 years -- have decreased by more than 5,200 square miles in the past three decades.

As Earth's fifth largest continent, Antarctica is twice as large as Australia and contains 70 percent of Earth's fresh water resources. The ice sheet, which covers about 98 percent of the continent, has an average thickness of about 6,500 feet. Floating ice shelves constitute about 11 percent of the continent.

The melting of the West Antarctic ice sheet alone - which is about eight times smaller in volume than the East Antarctic ice sheet -- would raise global sea levels by more than 20 feet, according to researchers from the British Antarctic Survey.

Animation of the GRACE mission is available on the Web at http://www.csr.utexas.edu/grace/gallery/animations/.

GRACE is managed for NASA by the Jet Propulsion Laboratory.

END

http://cires.colorado.edu/news/press/2006/06-03-02.html

[phantom power]

1. What happens to the Antarctic plate, if all that weight is removed?

Or if just a significant fraction is removed? Will it float higher on earth's mantle?

[donsu]

2. reports say the earth is bulging in the middle

they are not sure why or how much more it will bulge but think it is connected to the melting artic and glaciers

[FormerRepublican]

3. Yeah, we've got lotsa "joy" in our future...

"The end of the Paleocene (55.5/54.8 Ma) was marked by one of the most significant periods of global change during the Cenozoic, a sudden global climate change, the Paleocene-Eocene Thermal Maximum (PETM), which upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera and on land, a major turnover in mammals.

In an event marking the start of the Eocene, the planet heated up in one of the most rapid and extreme global warming events recorded in geologic history, currently being identified as the 'Paleocene-Eocene Thermal Maximum' or the 'Initial Eocene Thermal Maximum' (PETM or IETM). Sea surface temperatures rose between 5 and 8°C over a period of a few thousand years. In 1990, marine scientists James Kennett and Lowell Stott, both then at the University of California, Santa Barbara, reported analysis of marine sediments showing that, not only had the surface of the Antarctic ocean heated up about 10 degrees at the beginning of the Eocene, but that the entire depth of the ocean had warmed, and its chemistry changed disastrously. There was severely reduced oxygen in deep sea waters, and 30 to 40% of deep sea foraminifera suddenly went extinct. Geologist Jim Zachos of the University of California, Santa Cruz has connected the Eocene heat wave to drastic changes in ocean chemistry that caused the massive worldwide die-off. More recently a synchronous drop in carbon isotope ratios has been identified in many terrestrial environments.

What unleashed the PETM is unclear. Most fingers of blame point to volcanic eruptions that disgorged gigatonnes of carbon dioxide, or coastal reservoirs of methane gas, sealed by icy soil, that were breached by warmer temperatures or receding seas.

Tracking the ratio of carbon isotopes in marine calcium carbonate sediments, Kennett and Stott found a sharp decrease in the amount of heavy carbon in 55-million-year-old marine fossils, a decline that caused the relative ratio of 13C to 12C to plunge. A gas with very low amounts of heavy 13C must have literally flooded the atmosphere. In 1995, Gerry Dickens, University of Michigan, argued that only methane gas had enough light carbon to produce the early Eocene plunge. He proposed that a belch of methane escaped from ice in seafloor sediments as the Earth warmed during the latest Paleocene. The methane escaped from submarine clathrates, ice crystals that trap methane hydrate, a form of methane 'ice' that forms in cold bottom water under great pressures and is widely distributed and plentiful in sediments on the outer edges of continental margins. Methane has a global warming potential (GWP) over a 100 year period of 23<1>, meaning per kilogram it is estimated to be 23 times as effective as carbon dioxide as a greenhouse gas. The massive sublimation and release of sedimentary methane hydrates into the ocean-atmosphere reservoir upset the global carbon cycle and led to runaway global warming.

Scientists Flavia Nunes and Richard Norris of the Scripps Institution of Oceanography in California explored how these warmer temperatures might have affected ocean currents. They measured carbon-13 isotopes from 14 cores that had been drilled into the deep floor in four different ocean basins, taking samples from sediment layers deposited before, during and after the PETM. These isotopes are considered to be an indicator of the nutrients deposited by the water at the time. The higher the isotope value, the likelier that the source came from the deep ocean, the prime source for nutrients. With a painstaking reconstruction, Nunes and Norris found that the world's ocean current system did a U-turn during the PETM -- and then, ultimately, reversed itself. Before the PETM, deep water upwelled in the southern hemisphere; over about 40,000 years, the source of this upwelling shifted to the northern hemisphere; it took another 100,000 years before recovering completely."

http://en.wikipedia.org/wiki/Paleocene-Eocene_Thermal_Maximum