Frosty Friday: Glacial Ice vs. Pure Ice

(890 words, about 4 minute read)

Bubble Gas Free Ice

One of these pieces of ice was made in a lab and the other was made in a glacier. Can you guess which is which?

If you guessed that the ice sample on the right came from a glacier, you’re correct! (Bonus question: can you guess how old those bubbles are?) So, why do these two samples look so different, and what do we use them for?

Glacial ice forms on top of a glacier, starting as fluffy snow and becoming compacted as year upon year of snowfall accumulates over time. When the snow first falls, there is a lot of space for air between the individual snow grains. Over time, additional accumulating snow compresses the layers below. Under all that weight, individual snow grains are pushed closer together. These top layers of a glacier are known as firn, the name glaciologists give to multi-year snow. Within the firn, air from the atmosphere can travel freely between snow grains. Firn officially transitions into ice when the spaces between snow grains are no longer interconnected, closing-off air bubbles in the ice and isolating them from the atmosphere. These bubbles are like time capsules, filled with a sample of the atmosphere as it was when they formed. Thousands of years later (up to 800,000), we can dig up these tiny time capsules by drilling ice cores on the Greenland or Antarctic ice sheets. The chemical composition of gases in the bubbles helps us learn about the earth’s atmosphere and how it has changed over past millennia. This is one way that we are able to reconstruct the earth’s climate history (find more info on our lab website).

So, then what’s up with the clear ice sample? Well, that’s a piece of gas-free ice, which we make ourselves in the lab. You’ll probably notice that it’s completely clear – unlike the glacial ice there are no bubbles and unlike the ice cubes in your freezer it’s not cloudy.

When you make ice cubes in your freezer, the water you use has dissolved gases and minerals in it. Ice can be really picky—as it forms it likes to exclude impurities in the water from becoming part of the ice structure. In an ice cube tray, however, the water starts freezing from the outside and moves inward. This happens on all sides, so the impurities are pushed into the middle of the ice cube and get trapped there—this is why you might have noticed the ice cubes in your freezer look cloudy in the middle.

When making gas free ice, we boil purified water in a vacuum-sealed vessel to drive the dissolved gases out of the water without letting any more ambient gases dissolve into the water. Then, we place our container of degassed water in a cold bath, forcing the water to freeze slowly from the bottom up. You can see this setup in the picture below.

GF Ice Setup

As the ice front advances upward, it pushes any remaining impurities above the ice so that they end up in the remaining water or in the headspace of the vessel. After a few days, we have a sample of ice that’s just like our glacial ice samples but without any gases in it! But why go through all of this trouble just for some super clear ice?

The gases that we try to measure in glacial ice samples are present in trace amounts: parts per million for CO2 (carbon dioxide) and parts per billion for CH4 (methane) and CO (carbon monoxide). This means we have to pay attention to small additions from other sources, such as our lab equipment or modern ambient air. We treat our gas-free ice the same way we would a real sample, and can then compare the results to quantify those extra additions (we call this a “blank”).  For example 14C, a radioactive isotope in the gases that we measure, has many useful applications. 14CO2 in particular is produced in the atmosphere by cosmic rays and gets incorporated into the air bubbles trapped in glacial ice. Cosmic rays also produce 14CO2 directly in the ice itself. To be able to use 14CO2 meaningfully to study the atmosphere, we need to quantify the procedural inclusion of 14CO2 at various stages of the ice core collection and analysis process.  We can do this by comparing gas free ice made in the field, gas free ice made in the lab, and glacial ice samples. As we extract and measure air from our ice samples in the lab, the gas free ice acts as an essential diagnostic tool to quantify how well our gas extraction systems are working and to identify the background amount of 14COfrom the system, which we can subtract from our sample measurement.

So, to summarize! Aside from looking really cool, both ice samples are central to the research we do at the Ice Core Lab. We study the atmospheric trace gases trapped in bubbly glacial ice in order to learn about how Earth’s climate works. To accurately interpret this information we manufacture pure gas-free ice, allowing us to double-check that our equipment and instruments don’t dirty up these valuable, untouched time capsules!

 

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Polar Research Vs. Murphy’s Law

Hello everyone.  Apologies on not providing updates to our research blog sooner, but it has been a very busy time here at the UofR Ice core lab.  I’m glad to announce that we are leaving for our 2014 season in Greenland this coming Monday, May 12th 2014.  But before we get there, let me take you back a bit through the craziness that has occurred here in the past few months in preparation for this season.

I’ve been very busy in the lab testing the performance of our 14C extraction line that we will use to process our field samples that we have started to collect.  That was my main objective this semester after returning from the Antarctic in late January – hard to believe that was only three and a half months ago.  By mid-march I had finished generating a series of test samples that were sent to our colleague Dr. Andrew Smith to be measured on the ANTARES accelerator at ANSTO.  A few weeks later the results were in that our system was exceptionally clean and performing exactly as we had anticipated – I had the green light to go ahead and process the firn air samples we had collected at summit last year.

Photo by Melisa Diaz

Taking good notes is important for sound science!

Time was of the essence too, since the 35L electropolished steel cylinders containing our samples from last year needed to be evacuated and shipped to Greenland to contain the samples we are planning on collecting this upcoming season.  The rush was on, and I began working as hard as I could to process and extract our 14C samples.  Working 10-12 hour days, 6 or 7 days a week became the norm – as deadlines with regards to this season were fast approaching.  Likely as a result of long days spent in the lab, I made a critical mistake one Sunday night – I accidentally fractured part of the glass on our sample line!

Photo by Ben Hmiel

Luckily this occurred while I was setting up the line rather than during sample collection, so I was very thankful that no sample was lost.  As you can see from the photo the damage to the line was minor, and since I was following proper procedure it was isolated to only a single section of the line.  Taking a deep breath – I sent an email off to our glassblower who could hopefully patch up the line and after a day or two of flushing clean air through I could be back in business.  The first essence of panic came to me when I found out that our glassblower (West Scientific Glass) was on vacation, and would not be returning for about a week.  This was troublesome, but manageable, giving me time to catch up on processing cargo and doing other logistics preparation.  Time was running short to process all of the samples, but at least I had a few days to catch up on sleep before the final push came through.

The flowing week Joe came in and repaired the line in his usual perfect fashion, however; the following day as I attempted to flush the line with clean air and get it in operational condition again, I came to find out that the high-pitched whine coming from our Turbomolecular pump was signaling its own death – as it failed to spin up to the high vacuum needed in the procedure.

I wonder what Agilent would do if we returned it looking like this

I wonder what Agilent would do if we returned it looking like this

Aaaah, only when I had recovered from one problem another presented itself to me!  Spending the better part of a day on the phone with the manufacturer – I found there was another pump on the shelf available in their Delaware location that I was able to rush ship to us.  In case that wasn’t going to arrive in time, I also had our colleagues in Boulder, Colorado at INSTAAR ship out a pump that we could use.  In the meantime, Phil was driving a Penske truck with the majority of our cargo (Save the sample tanks and a few things we needed to ship last-minute to the Scotia Air National Guard base).

The day that I finally get the line flushed and in operational condition, we received a rather important email from the NSF regarding the C-130 aircraft that we fly to Greenland:

Dear Greenland Researchers:

The LC-130’s NSF uses to support operations in Greenland are experiencing a fleet-wide mechanical issue. The flight period planned for April 22-May 2 is postponed until further notice. NSF is exploring options for continuing science operations in Greenland while the aircraft are repaired. The 109th Airlift Wing is exploring options to make some aircraft available for missions to Greenland starting in May.

The bleed air lines, which are responsible for moving air away from the engine to heat the aircraft and for other purposes, may have corrosion that could cause significant issues in flight. Each aircraft needs to be inspected. Replacement parts are in limited supply given the number of C-130 aircraft nationwide that potentially need replacement bleed air lines and replacement seals and other parts for re-sealing the engine following inspection or repair.

We are looking at options for supporting the planned science. Science has already been delayed but no projects have been cancelled so far.

Wow.  This came to us at a time when I’m already working at full capacity to get our prior samples processed.  Kind of familiar to last season at Taylor Glacier, where the government shutdown nearly cancelled our season.  I guess the nature of our work is a constant battle against Murphy’s Law – “If something can go wrong, it will”

Many discussions were had at that point about what would happen to our season.  This came ~3 weeks before our scheduled departure, so our options were as varied from a week delay to cancelling the whole season until next year.  It was a very uncomfortable 6 days until we finally got news that the repairs had been made to the planes and the test flights were successful!  We got the green light to go as scheduled.  Good news for our season – bad news for me in that I had to work like a dog to get the rest of the samples processed before we leave.

Photo by Melisa Diaz

This is the most challenging part of extracting samples – one mistake when flamesealing and all that time and effort is wasted!

Well, that was about a week ago and after a series of long days & nights in the lab, I’m proud to say that as of yesterday, I have officially extracted a full suite of 14CH4 & 14CO samples from the firn matrix collected at summit last year.  In fact, as I write this, I am processing the final standard extraction on the system to complete our set of 14C samples that will be shipped to ANSTO to be measured in the coming month.  This will constitute the first major dataset of my PhD!

Bubble wrapped and ready for shipping acoss the world

Bubble wrapped and ready for shipping across the world

As for the season preparation, some science projects, including the IDDO Intermediate Drill Test were delayed about a week and a half.  Hopefully they will still be able to complete their work in their time at summit.  Let’s just hope the weather behaves.  On our end, the sample tanks were cleaned out and shipped off the ANG base on Tuesday with the last of our cargo.  Many thanks to officer Durant at the Rochester airport CBP office for processing the customs registration for us.  Now all that is left is for us to pack up our clothes and make the journey over to Scotia for our flight.  Next you hear from us we should be up above the Arctic Circle!

-Ben