Jenna Epifanio, Graduate Student, Oregon State University
What would you see if you looked into a time capsule from 1.5 million years ago? If the time capsule contained air before it was sealed up, you would find out a lot about the Earth’s climate. Between October and January of last year, I had the opportunity to join a team of researchers to go find some of that air, trapped in a natural time capsule: An Antarctic ice sheet.
using ice to understand earth’s past
Ice on our planet’s polar ice sheets has been preserving records of climate for hundreds of thousands of years, and in the case of Antarctica, a lot longer than that. Antarctica is thought to have first become covered in ice about 30 million years ago, which means if we sample ice at the correct locations on the continent, we might be able to discover some of that extremely old ice.
What makes polar ice a great archive for climate science is the direct nature of what it preserves. Not only do the water chemistry and particles trapped in the ice tell us about the past climate, but ice also collects tiny air bubbles that preserve an undisturbed record of the Earth’s atmosphere. Because ice is formed by layers and layers of snow that become packed down over thousands of years, all of the bubbles that are trapped in the ice sheet are preserved in chronological order – the deeper down in the ice sheet, the older the ice and the air trapped in it. Climate scientists can drill a long ice core and analyze it to determine the chemistry of the ice as well as the composition of atmospheric air in the ice bubbles.
Even though Antarctica glaciated over 30 million years ago, we probably won’t ever find ice that old on the continent. Because ice moves quickly (geologically speaking) and is subject to stress, melting and flow, most of the extremely old ice in Antarctica has already been destroyed. Currently, the oldest record of past climate contained in an ice core goes back 800,000 years. Recently, however, there has been a push to identify ice older than this because of an interesting question about the climate system that we want to answer.
Between 1.2 million and about 900,000 years ago, the Earth went through a dramatic shift in ice age cycles. During what’s known as the Mid Pleistocene Transition (MPT), the Earth changed from having ice ages every 40,000 years to having much colder and longer ice ages every 100,000 years. We know this from ocean sediment records of climate that contain indirect clues – proxies – describing climate conditions. However, an ice core record that covers that period would be invaluable: Instead of using proxy records of climate recorded in the ocean sediments, we would have a sample of the atmosphere itself to measure and answer questions about the climate from that period.
Recently, scientists collected ice that was dated to be 1.5 million to about 2.7 million years old at a location in Antarctica called the Allan Hills. Situated about 140 miles from the U.S Antarctic base, McMurdo station, the Allan Hills is known as a “blue ice area,” and when you see it for the first time, there is no question as to why it bears the name. Blue ice areas (BIAs) are created when winds scour the ice sheet, removing the top layer of uncompressed snow and exposing the blue ice. At the Allan Hills, this process is combined with other physical factors that allow very old ice to be found near the surface. That extremely old ice near the surface is what I, and a few wonderful people from around the country, were there to sample.
The primary goal of the field season was to re-drill an ice core at a location that had been identified to have ice that is 2.7 million years old. The original ice core, collected a few years ago, was fairly small, and has mostly been consumed as samples were chipped off of it in the process of understanding its age. One secondary goal of the expedition was to drill some reconnaissance samples in locations that were good candidates for old ice. Over the seven weeks, we successfully drilled three 150-m ice cores, one of which will very likely contain ice that is 2.7 million years old.
Field work at the bottom of the world
Just arriving in Antarctica is an ordeal. A commercial flight to Christchurch, New Zealand takes about 18 hours. I was the only representative from Oregon State University on the team, so meeting some new and also some familiar faces was the first order of business when I arrived. Along with the other researchers, I met our camp manager, Anna, an impressive and ferocious mountaineering woman on her tenth season in Antarctica. I also met Elizabeth (‘E’) and Tanner, both professional ice core drillers (yep, that’s a real job!), who have a ridiculous amount of experience between the two of them. These tough-as-nails people would teach me how to drill ice cores in one of the most extreme places on the planet. To get from New Zealand to the icy continent, the team and dozens of other researchers and personnel boarded a US Air Force C-17, a gigantic military plane. The trip took five loud, and quite cramped hours, until we landed on the airfield located on the ice near McMurdo station.
We spent ten days at McMurdo Station collecting camp gear, planning meals and food needs, and training in snow survival skills, and then we flew to our remote field site. Multiple Twin Otter flights from McMurdo Station to the Allan Hills were needed to deliver nine people, two ice core drilling rigs, and all of our camping gear. Two other researchers and I were on the last flight, which was delayed due to high winds and poor visibility at the Allan Hills.
The first order of business was to finish setting up camp, and begin setting up our drilling equipment. The next few days were grueling work, lugging gear to different drill sites, drilling anchors in the ice to secure our tents and equipment, and testing the electrical generators that would power the blue ice drill, a 9.5-inch diameter ice core drill that we would use to extract literal TONS of ice over the next seven weeks. The exhaustion that set in at the end of each very long day made sleeping in a tent during 24 hours of daylight some of the easiest sleeping I’d ever done.
It is amazing how quickly you can adapt to harsh conditions. Our team was in the field for seven weeks. That’s seven weeks of waking up in a tent every morning to freezing temperatures, getting dressed, grabbing some warm tea and a quick breakfast, then heading out to our drill sites to continue the drilling from the day before. Drinking water was made by melting ice that we chipped out of the ice sheet at a special “sterile” location. There were no showers, and all my baby-wipes were frozen into a solid block of ice before I got to my tent that first night in the field. The sun never set, and if the wind would stop howling in the middle of the night, I would wake up, disturbed by the sudden change. Those nights were special, though, because you could hear the ice sheet cracking. Loud pops echoed across the ice sheet and reminded you of how incredible it was that you were there.
Science during a pandemic
I should be in Antarctica right now, sleeping in a Scott tent, enjoying the company of some amazing scientists and ice core drillers. The Allan Hills ice core drilling project was funded for two field seasons. Because of the COVID-19 pandemic, the field work has been delayed, and I’m sitting in Corvallis, Oregon, remembering that dramatic place. I don’t feel sorry for myself for missing out on a second season; being there once was the experience of a lifetime, and I’m grateful to have had it. Living through this pandemic does highlight how dramatically nature can change our lives, giving a little bit of perspective as to why understanding climate change is important. Understanding what is natural, normal, and possible for the Earth’s climate system is key to understanding how it will change in the future. Understanding the nature of that change can prepare us for what comes next.
Follow Jenna on Twitter @sciencejenna