Early in the morning on 27 June 2011, I got out of bed, pulled on some clothes, picked up a big duffel bag and a backpack, and left for Arlanda airport. I was on my way to Kangerlussuaq, a town about a third of the way up Greenland's west coast. This trip was a little different for me. I'm an ice sheet modeler, a scientist who works with computer programs that describe how ice sheets grow and shrink. I spend most of my working time sitting in front of a computer, and when I travel, it's usually to tell other scientists about my work. This time, I would camp out, carry heavy field equipment, and dig holes. I used to be a geologist, so these activities wouldn't be completely new. Still, it had been a while. Getting to Greenland from Stockholm is easy enough. You can fly to Copenhagen, then take an Air Greenland flight from there to Kangerlussuaq. My flights were problem-free, except that the Air Greenland flight had to land in Keflavik, Iceland to take on more fuel. Luckily, I had time to spare.

I went to Greenland to learn about the recent history of the Greenland ice sheet. The ice sheet used to be a lot bigger. About 20,000 (twenty thousand) years ago, the ice covered almost all the land on Greenland and connected in the northwest with an even bigger ice sheet coming from Canada. About 15,000 years ago, the ice sheet's margin started to move inward from the coast. It was smaller than the present-day ice sheet sometime between 3,000 and 8,000 years ago, then grew again to about its present size. We think the ice sheet is now shrinking again, based on satellite measurements. So, we have a good picture of the ice sheet's overall history, but a lot of the details are missing. Our present knowledge is a bit like a United States history book that only talks about the presidents (I come from the US), or a Swedish history book that only mentions the kings. There were lots of other people who lived at the same time as the presidents and kings – what did they think, feel, and do? In the same way, we want to know the details of the Greenland Ice Sheet's past. We care about history because it can help us guess at the ice sheet's future behavior. There is a lot of ice on Greenland – the ice sheet is about 3 km thick near its middle. Many scientists wonder about the future of the ice sheet because we believe the earth's atmosphere is getting warmer, and the ice sheet should melt faster in a warmer world. If enough ice melts, it will cause problems in places like Bangladesh, where many people live close to present sea level. If the ice sheet has always changed slowly before, then perhaps it will change slowly this time, and in that case we will probably be able to see changes coming and adapt comfortably to them. But, if the ice sheet has sometimes changed suddenly and in a big way, then we should be concerned. Lots of other people have thought about these problems before me, of course. The history of scientific glaciology in Greenland is a long one. If you're curious about climate history and ice sheets, you might want to read The Two-Mile Time Machine or Earth: The Operator's Manual, by Richard Alley. (Full disclosure: Dr. Alley supervised my Ph. D. program, so I'm biased.)

One of the best things about being a scientist is meeting other scientists. There are interesting, fun people everywhere, of course. But, being curious and a little bit adventurous are part of the job description for scientists, especially those that spend time in the field. So, I was looking forward to meeting my colleagues for this trip. These folks all came from the IGERT program at Dartmouth College, an interdisciplinary program for training Arctic researchers. They were Laura Levy, Julia Bradley-Cook, Courtney Hammond, and Lauren Culler. You can find their blog posts online here: http://dartmouthigert.wordpress.com Laura is a geologist like me; we would be helping each other with field work for the next two weeks. Julia and Lauren are ecologists, and Courtney is a recent psychology grad from Dartmouth who was there to help Julia and to capture the field work experience on film. I had met Laura briefly, but Julia, Lauren, and Courtney were new acquaintances for me. They all knew one another well, of course. When I arrived in Kangerlussuaq, Lauren had already been there over a month, but Laura, Julia, and Courtney were just arriving. They had come over on a big military cargo plane, a Hercules C-130, which the New York National Guard flies between the northeastern US and Greenland as a transport for polar researchers and equipment. Lots of people I know have been on these flights, but I never have, so I was a little jealous! We ate dinner at the Kangerlussuaq International Science Support center, where we would stay periodically during our time in Greenland. Soon, we were discovering people that we had in common. They say that everyone in the world is just six degrees of separation apart from one another. That number has to be smaller for polar scientists!

To learn about ice sheet history, we need to measure time. Geologists learn to look at rocks, dirt, and landscapes and reconstruct what happened from them. For example, glaciers and ice sheets leave behind a carpet of clayey material with rocks called till. Where we see till, we know that glacier ice has covered that spot at some time in the past. If there is windblown sediment, or loess, on top of the till, we know that the loess is younger than the till. But, we need some clever methods to say how long ago these events occurred. Geologists and physicists have many methods for measuring time over Earth's history, but we were using just a few of them. Most people know about radiocarbon dating. If we find twigs or shells, anything that used to be alive, we can use those remains to learn when the plant or animal died. With luck, the time of organism death will be close to the time of a geological event whose age we want to know. Laura has worked extensively with cosmogenic exposure dating. This is a method for learning how long rocks have stood exposed at the earth's surface. Luckily, till surfaces usually have lots of rocks on them, so exposure dating is really useful for learning about glacial history. I was carrying some equipment for a third time-telling method, optically stimulated luminescence (OSL). OSL tells us how long sediment has been buried. It's like the opposite of exposure dating, which tells us how long rocks have been exposed. Sampling for OSL is a bit difficult, because the samples have to be protected from light as far as possible. First, you dig a hole. Then, you smooth one side of the hole so that you can see what kinds of dirt you have exposed. Next, you pound a short length of pipe into the side of the hole with a hammer. Finally, you remove the pipe, seal it, and fill in the hole. With those three methods, one would think that any problem of geological time-telling could be solved. In fact, it's really hard to find good samples. Most field time is spent deciding where to go and what to sample, rather than actually taking the samples.

Pleasures of doing field work near Kangerlussuaq, eating leftover pizza in view of the ice sheet.

I think Napoleon said that “an army marches on its stomach,” and without food no field work can be done. Good field food is lightweight, easy to prepare, and calorie-rich. Taste is also important, but secondary. We ate a lot of peanut butter, beans and rice, chocolate, granola bars, macaroni and cheese, and trail mix. Working near Kangerlussuaq was luxurious by field standards, because we could drive back to town every few days to shower, charge batteries, and visit the grocery store. We mostly used the grocery store for fresh foods, like cheese, cucumbers and peppers. The rest of the food came out of a giant box that Laura had sent over from the US. We had several memorable snacks and meals. There is a pizzeria in Kangerlussuaq, in fact. We saved our leftovers from one pizza dinner and ate them with cucumber while doing field work the next day. Another time, we watched pieces of ice fall off the edge of the ice sheet while we ate cold pasta with stuffed grape leaves and a jelly roll cake (rulltårta). Julia made banana pancakes for one dinner. We ate them with hazelnut spread. Very tasty. Sometimes we added leftover fresh food to whatever we were making for dinner. Packaged macaroni and cheese tastes better if you add leftover fresh cheese and a block of soft tofu. We ate the beans and rice with quesadillas and a side of salsa. The salsa was made from canned tomatoes, cut-up yellow pepper, and hot sauce.

Because scientists get a lot of support from governments, we have a responsibility to tell people who pay taxes what we are doing with the money. One way that scientists provide public benefit in return for research funds is by talking to students about science (and writing blog posts like this one). As it happened, we visited Kangerlussuaq while a group of high school students from the US, Greenland, and Denmark were there, as part of the PolarTREC program. This program was a really amazing opportunity; the students got to go to Greenland and learn about research in the field. Some of them even got to visit the top of the ice sheet to see where the long ice cores were drilled. Laura set up an activity for the students. I followed along. Laura started by talking about why she became a scientist and what her research is about. The students told us about their research projects and what they had done since arriving in Greenland. Then, we went down to the delta surface below the airstrip to look for fish fossils. Kangerlussuaq town is on a delta, a surface of river sediment built up in contact with the ocean. It's flat, perfect for landing planes on. The delta contains hard little knots of calcium carbonate, which can sometimes be cracked open to show the bones of small fish. We were going to look for these on the delta. The students started to find fish fossils almost immediately. Many of the fossils were really great examples. Some of the fossils had all the bones in the same places that they were while the fish were alive, but others were just masses of little, broken bones. We talked about what this meant for the delta environment – the whole fish must have fallen to the bottom in quiet water, but the broken bones indicated that the environment could sometimes be violent, maybe stormy.

There are two big, parallel valleys that run from Kangerlussuaq eastward toward the edge of the ice sheet. The valleys could hardly look more different. Langsöerne (Long Lakes) valley contains two big lakes. Sandflugtdalen (Sand River Valley) has a real river, but is mostly full of sand dunes. A long time before we visited Kangerlussuaq, another geologist noticed that there was a flat bench many meters above the water level in Langsöerne. The bench means that the lake waters used to be a lot higher. If you trace the bench toward the east end of the valley, you see that the water must have been held in by the ice sheet when it was just a little bigger than it is today. We wanted to know how long ago the lake drained, and we had three tools that might tell us the answer (radiocarbon dating, cosmogenic exposure dating, and optically stimulated luminescence).

But, which would we use? – If we could find shells or plant material buried in the beach sands, we could use radiocarbon dating. – If we could find the exact spot where the ice margin was just before the lake drained, we could sample for exposure dating. – OSL could tell us how long the beach sands had been buried. We decided to dig a pit in the bench. The dirt near the top was really fine and blew away easily when we dropped some of it through the air. This type of dirt is loess, and it was probably brought there by the wind. We kept digging. After a surprisingly long time, we hit rocks and sand. These materials looked like an old beach. Laura noticed that the rocks were partly covered by a thin, dark coating. We cleaned off the walls of the pit. We found some organic material in the sands and the loess, but we also saw roots from modern plants that went all the way to the bottom of the pit. We decided not to sample for radiocarbon dating, because the modern roots wouldn't tell us how long ago the beach sands were deposited. Instead, we took a sample for OSL from the beach sands. If we're lucky, this sample will tell us when the sands stopped being washed by the waves, and therefore when the lake drained. The coating on the rocks was still a mystery. Much later, though, we walked down to the present-day lake, where Laura noticed that the rocks there have the same black coating. The black coating must be coming out of the lake water, or maybe there are bacteria living on the rocks. The present is the key to the past.

The worst (or best) part of field work is that it eventually comes to an end. When all the samples are collected and all the sites have been visited, it's time to go home. In actual fact, the field work is never complete, but usually one has airplane tickets with a specific date or something to do at home. We drove back to Kangerlussuaq and spent the morning arranging samples and leftover supplies into boxes. Some supplies would be left behind for future field seasons, but the samples were all going back with us. I drove my boxed-up samples to the airport and handed them over to a staffperson at the Air Greenland counter, where they checked my permits to take the samples and carry them back to Sweden. Everything was in order, it seemed. We had a last pizza dinner, then I got on the airplane. Another successful field season was over.

Our camp, with the edge of the ice sheet in the background.