Massive Lake of Meltwater Discovered Under Greenland Ice

Researchers discover a meltwater aquifer beneath the southern Greenland ice sheet

The aquifer, representing a previously unknown storage mode for water within the ice sheet, was discovered in 2011, when researchers drilled deep beneath the ice layer and found water flowing back to the surface despite the freezing air temperatures of -15ºC.

The aquifer covers an area of about 70,000 km², an area the size of Ireland, with depth to the top of the water table of 5 to 50m.

The liquid water is held in firn—partially compacted snow—which has the “capacity to store significant amounts of meltwater in liquid or frozen form,” researchers said, “and thus delay its contribution to sea level. Here we present direct observations from ground and airborne radar, as well as ice cores, of liquid water within firn in the southern Greenland ice sheet.”

Meltwater from the Greenland ice sheet significantly contributes to the  rise in sea levels. About half of Greenland’s mass loss has been attributed to meltwater runoff.

“Surface melt has been spreading and intensifying in Greenland, with the highest ever surface area melt and runoff recorded in 2012,” say the researchers.

A Surprise Discovery

“This discovery was a surprise,” said Prof Rick Forster the lead author from the University of Utah.

“Instead of the water being stored in the air space between subsurface rock particles, the water is stored in the air space between the ice particles, like the juice in a snow cone.”

Scientists are puzzled about the speed, direction and final destination of the meltwater.

“It depends on whether it is currently connected to a system that is draining into the ocean or if it is a bit isolated and completely acting as a storage source without a current connection,” said Forster.

“We don’t know the answer to this right now. It’s massive, it’s a new system we haven’t seen before – we need to understand it more completely if we are to predict sea level rise.”

The research is published in the journal, Nature Geoscience, Published online 22 December 2013.

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Greenland’s Surface Ice Melt

An all-time record high temperature for Greenland may have been set in 2013, according to NSIDC.

The graph above shows the daily percent of the Greenland Ice Sheet surface that has shown melt, as of August 19, 2013 (red), along with the daily surface melt extent for 2012 (blue) and the average melt extent for 1981 to 2010 (dashed line). Two peak extent days are noted. Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia – High-resolution image

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Title: Extensive liquid meltwater storage in firn within the Greenland ice sheet
Authors: Richard R. Forster et al.
Abstract:

Mass loss from the Greenland ice sheet contributes significantly to present sea level rise. High meltwater runoff is responsible for half of Greenland’s mass loss. Surface melt has been spreading and intensifying in Greenland, with the highest ever surface area melt and runoff recorded in 2012. However, how surface melt water reaches the ocean, and how fast it does so, is poorly understood. Firn—partially compacted snow from previous years—potentially has the capacity to store significant amounts of melt water in liquid or frozen form, and thus delay its contribution to sea level. Here we present direct observations from ground and airborne radar, as well as ice cores, of liquid water within firn in the southern Greenland ice sheet. We find a substantial amount of water in this firn aquifer that persists throughout the winter, when snow accumulation and melt rates are high. This represents a previously unknown storage mode for water within the ice sheet. We estimate, using a regional climate model, aquifer area at about 70,000 km² and the depth to the top of the water table as 5–50 m. The perennial firn aquifer could be important for estimates of ice sheet mass and energy budget.

Global temps could rise higher than expected

Global temperatures could rise more than expected, new study shows

The kinds of increases in atmospheric carbon dioxide taking place today could have a significantly larger effect on global temperatures than previously thought, according to a new study led by Yale University geologists. Their findings appear December 20 in the advanced online edition of Nature Geoscience.

The team demonstrated that only a relatively small rise in atmospheric carbon dioxide (CO2) was associated with a period of substantial warming in the mid- and early-Pliocene era, between three to five million years ago, when temperatures were approximately 3 to 4 degrees Celsius warmer than they are today.

Climate sensitivity—the mean global temperature response to a doubling of the concentration of atmospheric CO2—is estimated to be 1.5 to 4.5 degrees Celsius, using current models.

“These models take into account only relatively fast feedbacks, such as changes in atmospheric water vapor and the distribution of sea ice, clouds and aerosols,” said Mark Pagani, associate professor of geology and geophysics at Yale and lead author of the paper. “We wanted to look at Earth-system climate sensitivity, which includes the effects of long-term feedbacks such as change in continental ice-sheets, terrestrial ecosystems and greenhouse gases other than CO2.”

To do this, the team focused on the most recent episode of sustained global warmth with geography similar to today’s. Their reconstructed CO2 concentrations for the past five million years was used to estimate Earth-system climate sensitivity for a fully equilibrated state of the planet, and found that a relatively small rise in CO2 levels was associated with substantial global warming 4.5 million years ago. They also found that the global temperature was 2 to 3 degrees Celsius higher than today while CO2 levels were only between about 365 and 415 parts per million (ppm)—similar to today’s concentration of about 386 ppm.

“This work and other ancient climate reconstructions reveal that Earth’s climate is more sensitive to atmospheric carbon dioxide than is discussed in policy circles,” Pagani said. “Since there is no indication that the future will behave differently than the past, we should expect a couple of degrees of continued warming even if we held CO2 concentrations at the current level.”

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Other authors of the paper include Zhonghui Liu (Yale University and The University of Hong Kong), and Jonathan LaRiviere and Ana Christina Ravelo (University of California, Santa Cruz).

This study used samples provided by the Integrated Ocean Drilling Program and was funded by the National Science Foundation and the Yale Climate and Energy Institute.

Contact: Suzanne Taylor Muzzin
suzanne.taylormuzzin@yale.edu
Yale University

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Global warming likely to be amplified by slow changes to Earth systems

Researchers studying a period of high carbon dioxide levels and warm climate several million years ago have concluded that slow changes such as melting ice sheets amplified the initial warming caused by greenhouse gases.

The study, published in the journal Nature Geoscience, found that a relatively small rise in atmospheric carbon dioxide levels was associated with substantial global warming about 4.5 million years ago during the early Pliocene.

Coauthor Christina Ravelo, professor of ocean sciences at the University of California, Santa Cruz, said the study indicates that the sensitivity of Earth’s temperature to increases in carbon dioxide in the atmosphere is greater than has been expected on the basis of climate models that only include rapid responses.

Carbon dioxide and other greenhouse gases trap heat in the atmosphere, leading to increased atmospheric and sea-surface temperatures. Relatively rapid feedbacks include changes in atmospheric water vapor, clouds, and sea ice. These short-term changes probably set in motion long-term changes in other factors–such as the extent of continental ice sheets, vegetation cover on land, and deep ocean circulation–that lead to additional global warming, Ravelo said.

“The implication is that these slow components of the Earth system, once they have time to change and equilibrate, may amplify the effects of small changes in the greenhouse gas composition of the atmosphere,” she said.

The researchers used sediment cores drilled from the seafloor at six different locations around the world to reconstruct carbon dioxide levels over the past five million years. They found that during the early and middle Pliocene (3 to 5 million years ago), when average global temperatures were at least 2 to 3 degrees Celsius warmer than today, the concentration of carbon dioxide in the atmosphere was similar to today’s levels, about 30 percent higher than preindustrial levels.

“Since there is no indication that the future will behave differently than the past, we should expect a couple of degrees of continued warming even if we held carbon dioxide concentrations at the current level,” said lead author Mark Pagani, an associate professor of geology and geophysics at Yale University.

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Contact: Tim Stephens
stephens@ucsc.edu
831-459-2495
University of California – Santa Cruz

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