Now climatologists from Penn State and the University of Massachusetts have modeled the past 5 million years of the West Antarctic ice sheet and found the ice expanse changes rapidly and is most influenced by ocean temperatures near the continent.
"We found that the West Antarctic ice sheet varied a lot, collapsed and regrew multiple times over that period," said David Pollard, senior scientist, Penn State's College of Earth and Mineral Sciences' Earth and Environmental Systems Institute. "The ice sheets in our model changed in ways that agree well with the data collected by the ANDRILL project."
Pollard and Robert M. DeConto, professor of climatology, U. Mass, report their findings in today's (Mar. 19) issue of Nature. The results of the first ANDRILL drill core near McMurdo Station, Antarctica, are reported in a companion paper in the same issue. The ANtarctic geological DRILLing project is a multinational collaboration to drill back in time into sediment to recover a history of paleoenvironmental changes.
"We found, as expected, that the East Antarctic ice sheet is stable and did not change," said Pollard.
The East Antarctic ice sheet does not slide into the sea and melt away because most of the bedrock below East Antarctic ice is above sea level. However, on the other side of the continent, to the Pacific side of the Transantarctic Mountain Range, much of the bedrock below the ice lies from several hundred to several thousand feet below sea level, leaving the West Antarctic ice vulnerable to melting.
"We found that the ocean's warming and melting the bottom of the floating ice shelves has been the dominant control on West Antarctic ice variations," said Pollard.
When the floating ice shelves melt sufficiently, they no longer buttress the grounded ice upstream, which then flows faster and rapidly drains the massive interior ice. The grounding line, the junction between the floating ice shelf and upstream ice resting on bedrock, retreats converting more grounded ice to floating ice shelves. Eventually, nearly all of the ice sheet on the Pacific side of Antarctica can disappear as it has in the past.
The researchers' computer model needs past variations of snowfall, snow melt and ocean melting below the floating ice to be specified. These are not obtained from the General Circulation Models often used in climate reconstruction because running those models to create 5 million years of climate history would take years. Instead, the researchers related past variations of these quantities to records of deep sea oxygen isotope ratios that indicate temperature changes in the oceans.
"We assume this is all driven by global-scale climate variations including Northern Hemispheric glacial cycles, so we used the changes in the oxygen 18 record to deduce the Antarctic changes," says Pollard. "Our next step will be to test whether this record really represents sea temperatures around Antarctica."
The researchers compared their model's output with the sediment core record from ANDRILL. In these cores, coarse pebbly glacial till represent the glacial periods, while intervals filled with the shells of tiny ocean-living diatoms represent the nonglacial periods. One way the ANDRILL researchers date the layers is using existing datable volcanic layers within the core.
Pollard and DeConto not only looked at the modeling of the overall West Antarctic ice sheet, they also looked at the nearest grid point in their model to the ANDRILL drilling location. They found that, for the most part, the data trend at that grid point matched the data obtained from the sediment core.
"Our modeling extends the reach of the drilling data to justify that the data represent the entire West Antarctic area and not just the spot where they drilled," said Pollard.
Along with the rapid appearance and disappearance of the ice, the researchers noted that both in the ANDRILL record and the model results, during the early portion of the 5 million years, the periodicity of the glaciation and melting was about 40,000 years which matches the Northern Hemisphere's pattern of glaciation and glacier retreat. The basic driver is very likely the tilt of the Earth's axis which varies with the same period, according to Pollard. However, nearer to the present, the cycle time increased to about 100,000 years as expected, driven by Northern Hemispheric ice age cycles.
During past warm periods, the major collapses in the model take a few thousand years. This is also the expected time scale of future collapse of the West Antarctic ice sheet if ocean temperatures warm sufficiently – longer than a few centuries but shorter than ten thousand years.
The researchers note that when atmospheric carbon dioxide levels in the past were about 400 parts per million, in the early part of the ANDRILL record, West Antarctic ice sheet collapses were much more frequent..
"We are a little below 400 parts per million now and heading higher," says Pollard. "One of the next steps is to determine if human activity will make it warm enough to start the collapse."
A'ndrea Elyse Messer | EurekAlert!
Further reports about: > ANDRILL > ANDRILL project > Antarctic Predators > Antarctic ice > Antarctic ice sheet > Antarctica > Earth's magnetic field > Hemispheric > Transantarctic Mountain > West Antarctic ice shelves > West Antarctic ice variations > environmental change > floating ice > glacial period > ice sheet > ocean temperature > ocean's warming and melting > sea level
Modeling magma to find copper
13.01.2017 | Université de Genève
What makes erionite carcinogenic?
13.01.2017 | Friedrich-Schiller-Universität Jena
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...
UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration
"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...
Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.
Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
16.01.2017 | Power and Electrical Engineering
16.01.2017 | Information Technology
16.01.2017 | Power and Electrical Engineering