Field and CPL Updates
HUGE event at WAIS Divide this week. The hole was deepened to its final depth of 3405 m (as measured with the drill cable). It was a stressful week with long shifts, tense moments, little sleep, and the end of a ten-year effort to get the core. Lets hope the measurements don't take that long too.
Krissy's announcement, and Jeff's comments on the deepening decision, are below and are great reading. The weekly reports are attached.
I encourage you to send a congratulatory email to the camp at: email@example.com
Thanks to everyone for the many years of work that have gone into making this happen!
---------------- from Krissy Dahnert ----------------------
It is with unimaginable joy, appreciation and humility that we write this email. This past Saturday, on the final day of 2011, the Deep Ice Sheet Coring (DISC) Drill collected its final ice core from the WAIS Divide, Antarctica main borehole. This moment has been a long time in the making and words cannot describe the pride we feel in having completed this considerable task. At 9:16am on December 31, 2011, the final core was collected from the bottom of the borehole at the driller's depth of 3405.077 meters. We could not have asked for a better reason to celebrate the New Year.
We would like to thank the drill team for their perseverance throughout this last week of long shifts, little sleep and ever-warming ice at the bottom of the borehole. Many thanks also go out to all of the drillers and engineers who have been a part of this drill's operation since its testing in Greenland in 2006 and its arrival at WAIS Divide Camp, Antarctica in 2007. You all were certainly with us in spirit as the final core was delivered on Saturday. The core quality remained exceptional throughout the entire length of the project. This is a testament to the quality engineering behind this system.
On behalf of IDDO, we would also like to thank everyone who has made this project possible and successful throughout the years. Our mission could not be accomplished without the support of the National Science Foundation (NSF), Raytheon Polar Services (RPSC), Chief Scientists Kendrick Taylor and Jeff Severinghaus, the WAIS Divide Executive Committee, the National Ice Core Laboratory (NICL), the Science Coordination Office (SCO), the 109th New York Air National Guard, IDDO's Technical Advisory Board (TAB) and countless others. We sincerely appreciate your efforts and realize how meaningful this occasion is for everyone.
We are excited for the DISC Drill's next task of Replicate Coring, which will be tested starting later this week. With success, we will be able to provide additional core samples from depths of particular interest. We also look forward to future projects where the DISC Drill can continue to provide high quality ice cores for scientific discovery.
We likely do not have everyone's email addresses, so please feel free to distribute this good news far and wide.
Thank you all for your support throughout this project. We wish you a very Happy New Year.
Krissy Dahnert and Jay Johnson
DISC Drill Lead Drillers
WAIS Divide Camp, Antarctica
Ice Drilling Design and Operations
University of Wisconsin-Madison
--------------- from Jeff Severinghaus --------------
I wanted to provide you with a quick update on our status. Things are going very well. We stopped deepening the borehole yesterday, reaching a final depth of 3400 m (3405 m cable depth). This ensures that the 50 m stewardship buffer is safely in place. The core quality has been beyond excellent, the warm ice surprisingly presented no obstacle at all, and the speed with which the drilling was completed was astounding (5 days). All this suggests to me that the engineering for warm-ice drilling that went into DISC has really paid off.
The pressure measurement that I did went smoothly, giving a pressure value at 3330 m depth that is only very slightly less than the calculated ice hydrostatic pressure (21 m equivalent for a 0.92 density). This is a tribute to the care with which the drillers have mixed ISOPAR and 141b over the years, and indicated to me that it wasn't necessary to add fluid before deepening.
Jakob's pinger unfortunately failed to detect the bed, like Leo's borehole seismometer. This mystery may indicate that the sediments under the bed are extremely low density, water-rich clay sediments such that the acoustic impedance contrast is minimal. Jakob's measurement was also hampered by an unexpected "ringing" of the borehole, which we don't fully understand.
In the absence of the expected precise remaining-ice-thickness estimates, I assembled all the existing information I could about total ice thickness. I called Claude Laird, Dorthe, and John Paden at CRESIS. Prasad and CRESIS staff generously helped provide an error bar and a lot of supporting information with little notice. To summarize:
- Radar: 3470 m plus or minus 20 m, implies stopping depth of 3400
- Thermal models: 3460 to 3480 m (range due to melting point), implies stopping depth of 3410
- Seismic (Leo): 3450 plus or minus 30 m, implies stopping depth of 3370
- Seismic central estimate with neglect of error bar: implies stopping depth of 3400
I can provide you with all the details if you want, but the bottom line is that radar has predicted all four Greenland borehole depths (GISP2, GRIP, NGRIP, NEEM) to within 10 m. I found the argument convincing that radar is inherently a more precise method than seismic, because it uses shorter wavelengths and does not use explosions which are broad-band. Radar also successfully predicted the depth of Old Faithful in the WAIS-D core to within a few meters. Taking all this together, I decided that it was safe to neglect the seismic error bar, and instead go with the seismic central estimate as a conservative estimate of bed depth. Don, Sridhar, Ed W., and Gary were all in accord with this judgment call. This gave 3400 m as the stopping depth (3405 cable depth, because of borehole inclination).
We are on schedule for starting the logging of the extended borehole tomorrow morning. Replicate coring looks likely to start on schedule too.
The camp staff has been exceptional. Dean keeps us in stitches of laughter with his singing and acting. Everyone seems to bend over backwards to be helpful, going far beyond the call of duty. Krissy deserves special praise for leading a highly effective team, and working with us scientists to accommodate our complex borehole access needs while producing, hands down, the best quality ice core I have ever seen.