Page 2/3 - December 23, 2011
Window on the weather
Holland, the climate scientist from NYU, has been a victim of West Antarctic weather in the past, spending weeks sipping hot chocolate and not doing much else while stuck at Byrd field camp.
“It would snow so much that we would have a meal and four hours later the door [to the galley] would be snowed in,” he said. “It was a lot of work getting in and out.”
But Holland did finally get out, completing his mission last season to install three weather stations around the Pine Island Bay region that will provide important data about the atmospheric conditions that influence the ocean currents.
“The idea is that we’re trying to correlate atmospheric and oceanographic observations to see what is causing the PIG [to recede],” explained Holland, who returned to McMurdo Station this season on a pilot project to test a different technology for observing the ocean-ice interaction.
The PIG story actually starts in the atmosphere, where clockwise winds, the “westerlies,” around Antarctica have intensified in recent years.
Photo Credit: Cliff Leight
David Holland, on the ground, sets up an automatic weather station near Pine Island Glacier in 2008. Last year, he set up three similar instruments on rock outcrops in the region to observe atmospheric conditions.
Two camps have emerged about why that’s happening. One group blames the ozone hole over Antarctica, which has cooled the stratosphere over the continent while rest of the planet has warmed. That temperature differential has spun up the winds, they believe. An emerging, alternative hypothesis blames atmospheric influences from the tropics for strengthening the west winds.
The “why” of the atmosphere problem is less important to the PIG researchers than the “what” — what is happening in the ocean as the winds intensify? The leading theory, which Holland’s triangle of weather observatories will help confirm, is that winds are pushing surface waters away from the continent, which draws a current of deeper, warmer water up onto the continental shelf and under the ice.
“We hope the triangle at Pine Island Bay is a proxy for the bigger scale winds,” Holland said.
An emerging picture
Now it’s up to Bindschadler and his team of oceanographers, glaciologists, and the other members of the multidisciplinary group to get the ocean measurements from underneath the ice shelf. But they’re not going in totally blind.
Several airborne and ship-based expeditions to the area in the last several years have provided vital details about features both on and below the ice shelf. New high-resolution satellite imagery from the NSF-funded Polar Geospatial Center (PGC) has also sharpened the picture.
One of the key pieces of information to emerge a couple of years ago came from a joint U.S.-British expedition aboard the USAP research vessel Nathaniel B. Palmer . The BAS scientists sent a robotic submarine underneath the ice shelf, the first-ever such deployment beneath this ice shelf. [See previous story: Pine Island cruise — Scientists deploy robotic sub, moorings to study fast-moving glacier.]
Photo Credit: NASA
At Windless Bight near McMurdo Station, the scientists practiced lowering the ocean profiler down a drill hole into the ocean beneath the ice.
The so-called Autosub mapped the bathymetry, or seafloor topography, underneath a large part of the ice shelf cavity in great detail. It also, quite literally, hit upon a new discovery — a ridge that rose about 350 meters from the seafloor to within about 150 meters of the ice shelf. [See previous story: Rapid retreat — Discovery of seafloor ridge by robotic sub offers insight into ice loss in Antarctica.]
That find was a game-changer for the PIG researchers, according to Bindschadler.
“That was a huge surprise to us. We thought we’d be able to drill any place out there,” he said during an interview at McMurdo, anxiously waiting for the first flight to leave, the expedition’s window of time in the field shrinking daily. “The discovery of that ridge caused us to totally revise our thinking about where we were going to put our profilers.”
The profiler carries instruments along a cable that will measure temperature, salinity and the current. The cable will extend all the way from the surface of the shelf, through roughly 500 meters of ice, and down through the water column, which is about 500 meters deep.
Here’s the problem: The weighted cable, if installed “upstream” of the seafloor feature, would have been dangling too far down and would have become fouled on the ridge, as the motion of the ice shelf carried the cable at the glacially breakneck speed of 18 inches per hour.
NASA’s ongoing IceBridge campaign to observe changes in West Antarctica provided an additional detail about what the cavity looks like below the ice shelf. Data from gravity instruments flown aboard a NASA plane that doubles as a research lab suggest that the ridge doesn’t cross the width of the ice shelf. An open channel appears to exist to the west, where the warm water might freely flow around the ridge.Back 1 2 3 Next
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