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SEAT: Satellite Era Accumulation Traverse: How to Drill a Firn Core

January 13th, 2012 by Maria-Jose Viñas

By Lora Koenig and Jessica Williams

Most members of the traverse team have made their way safely back to the U.S. Everyone took a few days to enjoy the summer sun in New Zealand and defrost before returning home. Jessica submitted this blog post and photos from the traverse, with all the scientific details on how we drill and use our firn cores to answer the following question: Is accumulation, or snow fall, changing across West Antarctica?  The photos show how we drilled and processed the cores in the field and are the first set of pictures from the traverse.  Next week, we will get up more photos of the camp, radar, and the Christmas storm.

Randy getting ready to drill a firn core

Here’s Jessica:

As a reminder to those following the blog, the end goal for drilling the ice/firn cores is to correlate the cores with the layering we see in the radar. (Firn is year-old snow; it’s more compacted than fresh snow but it’s not ice yet.) The radars illuminate layers that can be counted like tree rings, but those layers can sometimes be misleading, recording an individual storm event which is not a complete record of yearly accumulation. We use the physical and chemical properties of the ice core to precisely date the radar layers. Our team collected nine firn cores over a range of low to high accumulation sites this season.

The drill barrel is almost a meter long, so we sample the firn cores in increments of 75 to 90 centimeters (29 to 35 inches), and we collect about 25 increments at each site – that gives us a total sample depth of about 17 meters, or 55.7 feet, which should be equivalent to about 35 years worth of snow accumulation data, depending on the accumulation rate at the given site.

Randy and Michelle holding the drill while Jessica separates the core barrel from the chips barrel

Drilling isn’t a fast process. It takes us several hours to collect a core because we have to do some processing in the field. For each core section, we have to lower the drill into the ground until it reaches the desired depth, and once it’s done drilling, we have to pull it back up again; the deeper the hole, the longer it takes us to do this.  Randy was the lead driller. He heaved the 40-lb (18-kg) drill up and down the hole for every core. He is now ready for a strongman competition! Additionally, we have to dissemble the drill barrel for each core section, to get the core out, and then we have to clean the barrel before collecting more sections.

Jessica standing in front of a firn core section.

We do some processing of the core sections in the field, and we do it differently depending on how compact the core looks. The upper meters of core are loose and are more prone to break along weaker layers, whereas the deeper the core section, the firmer and less likely to break it is. But every core section needs to have the loose snow shavings brushed off the outside of the core before we measure its bulk weight and length. The length and weight tell us the density of the snow. For the upper meters of core, we do the sampling in the field. We collect electrical conductivity measurements (a measure of the acidity content in the snow) and then we cut the core into 2-centimeter (0.8-inch) thick samples that we then measure for multiple thicknesses and diameters and bag into individual whirl-pak bags (we can measure the weights of these samples in the lab, seeing as they won’t change). Having the thickness, diameter, and weight values for each 2-cm sample is important because we can then calculate density using those parameters (the density of snow increases with depth).

Jessica cleaning the loose snow off the firn core while Randy takes a downhole depth measurement of the core hole.

Michelle and Jessica measuring the electrical conductivity of the firn cores.

Jessica cutting up the upper meter of firn while Randy bags the samples.

Jessica measuring the thickness and diameter of the cut-up firn sections.

We don’t do all this field sampling for the lower 14 meters (46 feet), which is great because your hands get very cold doing the field processing. For the lower portions of the core, we simply brush off the loose snow shavings and record bulk weight and length. After those measurements, we place the full core section in lay-flat tubing and then slid it into an insulated silver tube and put it in a snow pit to keep it cool and out of the sun until the entire core is complete. We can then wait to perform the remainder of the sampling measurements in the lab.

Jessica measuring the diameters of a full firn core section while Randy labels the protective firn core tubes.

The entire procedure of drilling and processing a firn core takes about six hours when there are three people working together (one drilling, one handling cores, and one recording the data). Randy was the driller, Michelle the handler, and I was the recorder. Once we collect all of the core sections in the tubes, we place them in insulated boxes with the individual bagged samples and a temperature logtag (records the temperature from that point until we get the cores back in the lab several months later – that way we can validate that the cores were well below freezing during the transport). We bury these boxes in a snowpit under a pile of snow to protect them from UV radiation until they are collected and stored into the ice core freezer at the WAIS Divide field camp.

Randy storing the filled silver tubes in a snow pit.

You will have to wait for Ludo’s blog to read about the recovery of the cores and transport to WAIS Divide field camp with a Twin Otter aircraft.

From the freezer at WAIS Divide the cores will then be transported by boat to the US and then to Brigham Young University, where we’ll complete all the lab measurements. In addition to the electrical conductivity and density measurements for every 2-cm sample, we’ll analyze oxygen and hydrogen isotopes that vary seasonally and are used to date the layers in the core. Using the density, layer depth and age, we can determine the accumulation rate for each core and then compare it with the radar. We are just getting in the preliminary results from last year’s cores now so with some luck, we’ll have the first preliminary results from these cores by next fall.

Pine Island Glacier 2011: Probably Not My Last

January 5th, 2012 by Maria-Jose Viñas

By Bob Bindschadler

McMurdo (Antarctica), 30 December — Got up early again this morning, but to no avail. Nowadays, as I leave my dorm, my head spins right to look onto the ice shelf for any sign of fog. It’s become a habit now. This morning it is crystal clear. I can see the Pegasus skiway out there. When I reach the mess hall, I pause at the handwashing station to read the scroll on the TV with information regarding flights. And there it is—Mission E005 to PIG is on a “weather hold”. What that means is that we aren’t expected to appear for a shuttle ride to the skiway. We are simply supposed to wait until the message is updated.

I call the Movement Control Center (MCC) and ask if they have any updated time for our transport to the skiway. They have to check with Air Services (this seems unduly complicated) for the current status. I’m told it is likely that the second mission to PIG today (carrying the helicopter), which was to be in the afternoon, will be cancelled and that our mission will slide to the later slot. The transport time for the later mission is 12:45 PM, so that’s their best guess of what will happen. About 15 minutes into a slow and sad breakfast wherein more of our group show up, that’s exactly what happens. We have another six hours to wait.

I gather what information I can about PIG, but it is pretty limited. It is only just after 6 AM and the regular day workers are not in their offices yet. I go back to my room and catch a short nap.

Later I reemerge and try to put together the story. The weather observations from PIG are indicating visibility limited to 800 meters, 18 knots of wind and blowing snow. The wind is not the problem, but the limited visibility is. It was the reason the flight was put on hold. The webcams indicate some reduced visibility, but a number of us are surprised it is being reported as only 800 meters (0.5 miles). We have little say in this—the eyes on the ground are gospel.

It’s now just past 11:30 AM. Lunch has started and I need to plan for the transportation. I’m going to eat, then see what, if anything, has changed. We may still get our ride to the skiway—a none-too-pleasant 45-minute jostling—and it may come to naught, but it is all we can do at our end.

Pine Island Glacier 2011: False Start

January 5th, 2012 by Maria-Jose Viñas

By Bob Bindschadler

McMurdo (Antarctica), 31 December — That close. We were that close to leaving McMurdo yesterday; literally, a few feet from the airplane. The day started early, but with great promise. Everything was going so smoothly. Everyone showed up for breakfast dressed for the cold weather, our flight lunches were ready for pick-up, transportation was on time and we packed into the monstrous Delta vehicle (a small compartment atop huge tires, designed to span bumps and holes in the road) for the 50-minute drive to Pegasus, the skiway on the McMurdo ice shelf. The only ones ahead of us were the flight crew, the cargo handlers and a few ice runway work crew. This was the last day before the 2-day New Year weekend. We counted ourselves fortunate to be escaping McMurdo and getting to PIG so we could begin sorting our gear and be ready for Monday’s first move onto the ice shelf.

As we transferred from the bumpy Delta to the softer seats of the passenger transporter (used to take passengers from the rougher road traveled by the Delta onto the snow apron where the airplanes are), the pilot came over to say that there was a maintenance issue with the plane. It seems there are ten radios onboard and while all but one have backups, the one without the backup was the one that didn’t work. Maintenance was investigating. Just to cover themselves, the crew had also begun pre-flight checks on the only other airplane available. Usually a second airplane is not available, but PIG seemed to be the only spot on the continent scheduled to receive a flight that had good weather. It was a luxury and gave me more confidence that we were sure to get away. The race was not against the weather today, rather against time; the length of the mission would be over 11 hours and crews are not allowed to have their “duty day” (which starts when they first check weather reports) extend beyond 14 hours. So although it was still only 7:30 in the morning and the mission was set to launch at 0900, we could only delay two hours. If the mission couldn’t get off by 1100, we weren’t going. We waited in the very Spartan and deserted galley for further word.

Pre-flighting the second aircraft turned out to be a judicious move. The radio technician identified the problem, but the replacement part was in Christchurch. The scramble began to get our five pallets of cargo off the first airplane and on to the second. We were called from the galley back to the transporter and were driven to the second airplane, so we could get on quickly once the plane was ready. We waited, and waited, and waited, mentally assisting each forklift that grabbed a pallet from the first plane and lined up in order to deposit it on the tail ramp of the second aircraft. Done. Now what? We stared out the windows, trying to interpret the comings and goings of the ground crew. I’ve taken countless Herc flights in my many years here and I have yet to understand all that goes on inside these Hercs as the crew prepares them. Too much time gone already as 10 AM came and went. Doubt started to seep into our once-excited conversations. Finally, the pilot (a large piece of Air National Guard beefcake) came out and tossed the heavy survival bags (the big red ones in the picture) through the crew entrance door. I joked that he was going to load us the same way. Our mood returned to a spirited banter and we rapidly made sure that our bags were zipped up and everything was set. We expected to be called to board any moment.

That moment didn’t come, didn’t come and still didn’t come. 10:20 AM stretched to 10:30 and even 10:45. Opinions varied on the likelihood of success. At 10:55 AM, the pilot stepped off the airplane, strode across the few feet of packed snow to our vehicle and knocked on the door. When he addressed us, he didn’t mince words; we weren’t going, the mission was a “maintenance cancel”. He explained that the aircraft has two altimeters and that they are checked to be sure they agree to within 75 feet. These did not. Maintenance personnel had tried to determine why, but time had run out for the crew.

Everyone knew what this meant; we would have to wait until Monday for the next try and bad weather was forecast to move into the PIG area on Sunday. This was a crushing blow to our hopes. As far as our project timelines go, the scrubbed mission only translates into a single day delay if we can work through our cargo at PIG faster. Mentally, it just dials up the pressure yet further. It won’t be a relaxed weekend. We can’t accomplish anything here.

Pine Island Glacier 2011: What A Drag

January 5th, 2012 by Maria-Jose Viñas

By Bob Bindschadler

McMurdo (Antarctica), 30 December — This post may read a little rushed because, well, I’m rushing today. The stakeholders meeting Wednesday afternoon resulted in an accelerated timeline and we have been “hot-footing” it ever since.

The “drag” in the title is for bag drag. It is a good thing. It means you are being checked-in, weighed and being given a boarding pass (yup, they use them here, too). It means you are about to go someplace other than the mess hall (for yet another meal). It means you have had to clean out your room (can you believe they have inspections to make sure you are not leaving your bad habits behind?) For us, it means we are going to PIG tomorrow.

This morning I called a meeting of our team to discuss what will happen once we get to PIG Main Camp and what will the sequence of cargo and people be once we start moving over to the Drill Camp. It was our last chance to meet in a comfortable format, all seated around the same table. Things will change radically tomorrow. The camp already has 19 people in it; 23 after the four new arrivals on today’s flight (#4). These are split roughly equally between camp staff and carpenters. We ten will drive the total to a bulging 33. There are two tents up. We will likely have to eat in two or three shifts.

Our work there will focus on finding our traversed cargo, combining it with what will be flown out with us tomorrow, and organizing the total into time-sequenced loads destined for the ice shelf. Monday (or more likely the next good-weather day), we are supposed to receive a Twin Otter from Byrd camp that will begin to move people and cargo to the Drill Camp. We will start with a few people, survival gear and shelter. The Otter will help us again the next day (we hope it will stay overnight, but its orders are not to get stuck at PIG) to continue to move to the Drill Camp. Ultimately we have over 30,000 pounds of stuff to move, so we will not be able to complete the move these two days.

Also on Monday, there will be two Herc flights to PIG (that’s right, TWO), each carrying a partially disassembled helicopter. Once they are reassembled (a two-day task), they will continue to move our stuff (we’re saving some of the most heavy and awkward pieces for them). I hope we can finish this off in one more day, but I’m fearful it will take two more, so it is very likely this moving will be interrupted by bad weather. Thus, we are trying to be careful to ensure that the right people are at the right place with the right pieces to be able to be productive even if the weather is not conducive to helo flying. Yet another puzzle. There have been many and it is the nature of field work.

This next phase will be a bit of a scramble. If we do it right, everyone will be pretty busy and we will be making progress all the time. That scrambling may make future blog entries more difficult. I am in the advance party going to the Drill Camp. Until the dust settles there with most of us arriving and the critical first tasks out of the way, there won’t be any posts, not even short ones, from me coming out from PIG. Again, it is just the nature of the work.

Pine Island Glacier 2011: Acceleration!

January 4th, 2012 by Maria-Jose Viñas

By Bob Bindschadler

McMurdo Station (Antarctica), 28 December — I can’t remember being able to write two good-news messages in a row this entire trip, so I hardly know how to react. On the heels of the successful Twin Otter recce, yesterday’s Herc flight made it to PIG Main Camp. It was scheduled to depart later in the morning to avoid possible fog. As it turned out, there was no fog, but then I had to worry that some other issue would confound the attempt. Taking a pessimistic view seems to be working wonders, because the flight took off early, successfully delivered cargo and camp staff to PIG, and was able to return to McMurdo without even having to refuel. It’s enough to make a scientist superstitious.

The weather continues to hold. That big old high pressure over the middle of West Antarctica is doing a great job and is expected to stay in place through the beginning of the weekend. I spoke with the Guard planner and he said that not only was PIG on their schedule every day this week, but because this weekend is another two-day holiday, they are thinking seriously of scheduling two flights to PIG on Friday. That would be #’s 5 and 6 (assuming success today and tomorrow). And if that wasn’t enough, they are likely going to be raising the ACL (allowed cargo load) so that yet more people and stuff can get out there.

Helos and Otters are in the offing, as well. The first of the helicopters will be “taken down” this evening. This means they will start to disassemble it (blades, rotor, skids and half the transmission come off), so it can squeeze into the Herc cargo bay. It might be ready for a Friday flight to PIG. The second helo would be a day behind. Meanwhile, Otter schedules are being reviewed so NSF can decide what Otter could come to PIG and how long it could stay.

All these developments have led to a whole new series of talks with various players here that have taken on a noticeably different tone. The cargo sequencer is telling us that we should be ready to fly out to PIG as early as Friday. After so many delays and the increasingly dark cloud that had grown over the project, the sudden change is like being hit with a bracing bucket of cold water. Suddenly it is time to start moving again!

The rest of this week will either see us break the back of the delays, or it will likely end the project for this season. Spirits are extremely high.

Notes from the Field