Workforce makes use of drill platform to put in devices for learning distinctive glacier motion
By Peter Rejcek, Antarctic Solar Editor
Posted August 22, 2014
In January 2013, U.S. researchers in Antarctica made historical past by drilling by lots of of meters of ice right into a subglacial lake the place they discovered proof of microbial life.
The National Science Foundation -funded mission had been scheduled to return to Subglacial Lake Whillans the next yr to gather further samples, however the U.S. authorities shutdown final October delayed the sub-surface portion of the hassle till the 2014-2015 austral summer time.
As a substitute, a crew with the Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) mission deployed final yr to proceed an effort to know the dynamics of the ice above the buried lake.
“The Whillans Ice Stream has actually bizarre habits, it strikes in stick-slip occasions,” defined Grace Barcheck , a graduate scholar on the University of California Santa Cruz who was one of many crew members who spent a couple of month in West Antarctica in the course of the 2013-14 austral summer time in assist of the analysis.
In 2003, glaciologists first reported within the journal Science that Whillans Ice Stream exhibited what they referred to as “stick-slip” habits. As a substitute of regular motion, the ice stream jerks ahead like clockwork twice a day, kicked awake by tidal movement on the grounding line the place the ice leaves the bedrock and floats. The motion produces a burst of seismic waves, every half-meter leap ahead equal to a magnitude-7 earthquake.
A sequence of different papers – primarily utilizing knowledge from constantly working seismometers and GPS devices on the ice floor – concerning the habits of the ice stream have adopted. An ice stream is a area throughout the ice sheet that strikes quicker than the encompassing ice. [See earlier article — Finding the sticky spot: Stagnating glacier offers array of puzzles for glaciologists to solve.]
Now scientists with the WISSARD mission are attempting to get their ear as near the bottom as doable under the ice to know extra concerning the components concerned within the stick-slip movement. The clockwork motion doubtless performs a job within the subglacial hydrology that periodically drains and fills the shallow lake that shares the identical title with the ice stream.
Slawek Tulaczyk , one of many principal investigators of the WISSARD mission, and the remainder of the crew employed a specifically designed “roving drill” to bore about 700 meters into the ice sheet. They drilled 4 boreholes through which they deployed varied devices able to detecting earthquakes, measuring temperature and monitoring the ice’s bodily adjustments because it strikes.
It seems from earlier analysis by different polar scientists – Sridhar Anandakrishnan at Penn State , Paul Winberry at Central Washington University and Doug Wiens from Washington University in St. Louis – that there are two discrete spots beneath the ice stream which might be concerned within the stick-slip movement, in keeping with Tulaczyk. Two boreholes had been drilled close to every spot, dubbed initiation factors.
Seismometers close to the underside of every borehole, in tandem with a floor array of such devices, will permit the scientists to make use of the wave power from earthquakes and even the movement on the backside of the ice sheet to check the initiation factors. The borehole seismometers, specifically, provide better sensitivity to the exercise on the bedrock.
“If we’re actually shut, now we have a greater sign,” Barcheck famous.
The analysis has implications exterior of glaciology.
“It’s additionally of curiosity to seismology as effectively,” famous Tulaczyk, an affiliate professor of Earth and Planetary Sciences at UC Santa Cruz. Susan Schwartz , additionally from UC Santa Cruz, is the PI on the ice stream investigation.
Tulaczyk defined that the majority earthquakes, significantly the bigger, extra violent ones, are transient, rare and unpredictable. The stick-slip occasions final about 20 minutes at a time.
“Making observations at excessive frequency on the proper place and the appropriate time is uncommon in seismology. We now have this dependable earthquake that comes again each 12 hours,” he mentioned. “I feel in the end Whillans Ice Stream will inform us one thing about how faults break.”
Along with the seismic devices, temperature sensors within the boreholes will present perception into how a lot geothermal warmth could also be affecting the ice on the backside. Measurements in the course of the main 2012-13 WISSARD marketing campaign discovered an unusually excessive quantity of geothermal flux, in keeping with Tulaczyk.
“We actually don’t know if it’s melting or freezing [at the bottom],” he mentioned. “We don’t know a lot about subglacial geothermal flux as a result of there are so few measurements.”
Lastly, strings of inclinometers in every borehole will measure the deformation and shearing of the ice because it undergoes stress when it strikes.
Final yr’s mission had a a lot smaller logistical footprint than the 2012-13 expedition, which employed a big hot-water drill system that required all instrumentation to be sterilized to keep away from contaminating the subglacial lake. There was no such restriction for the roving drill since every borehole stopped in need of the bedrock and sediment under the ice.
“There was no drama on this one. It was the best one I’ve performed,” mentioned Dennis Duling, the chief of the drill crew from the University of Nebraska-Lincoln , which developed the WISSARD hotwater drill system.
The roving drill – principally, a number of high-pressure washers with heaters connected to them and a thousand meters of hose – was cobbled collectively from earlier drilling techniques. Elements had been primarily scavenged from the Kamb-Engelhardt Hot Water Drill , also referred to as the Caltech drill. Different parts got here from the drilling system used to create the IceCube Neutrino Observatory within the ice sheet beneath the South Pole Station .
“It truly is a Frankenstein drill,” Duling mentioned.
Whereas Whillans is certainly one of a number of ice streams that drain from West Antarctica to the Ross Ice Shelf , it’s the just one that apparently behaves with a stick-slip movement, in keeping with Tulaczyk. Its uniform movement throughout the toothpaste-like sediment under – the ice principally unchanged because it strikes – will assist researchers perceive how glaciers transfer over bedrock.
“This place is particular and supplies a window on how ice interacts with the mattress with out having the fuzzy filter of viscous ice movement,” Tulaczyk mentioned.
The WISSARD mission will return to full energy for the 2014-15 season, with scientists planning to drill by the ice close to the grounding zone the place the Ross ice Shelf floats away from the grounded West Antarctic Ice Sheet. Researchers are eager about studying extra concerning the biology, glaciology, hydrology and geology of this subglacial system in a little-explored space of Antarctica.
“It’s like planetary exploration. It’s excessive threat, [but high reward],” Tulaczyk mentioned.
NSF-funded analysis on this article: Susan Schwartz, Andrew Fisher and Slawek Tulaczyk, College of California Santa Cruz, Award No. 1043784 .