Taking the temperature of permafrost and archaeology

Today the Saturday Schoolyard talk was about warming permafrost.  The speaker was Dr. Vladimir Romanovsky, head of the Permafrost Laboratory at the Geophysical Institute at UAF.  He gave a really good talk, explaining what permafrost is (permanently frozen ground, basically), why it matters if it melts, and how permafrost researchers go about taking its temperature (with thermistor (temperature sensor) strings down boreholes, mostly).  He then went on to show how permafrost temperatures had changed through time as the atmospheric temperature had changed.

After that, he moved to predictive modeling based on climatic models.  Using even a fairly middle-of-the-road climate model, it doesn’t look too good for permafrost in Alaska by the end of the century.  He also showed active layer (the soil layer at the top that freezes and thaws every year) modeling done on a similar basis some years ago, and pointed out that over the 10 years since the model was run it had been spot on in its predictions.  The active layer is clearly going to be a lot deeper if the predictions hold.

This is not good news for Arctic archaeology.  Compared to most of the rest of the world, where archaeologists are left to puzzle out what people were doing from a few stone tools, waste flakes and potsherds, we get really good organic preservation here, which makes it possible to look at questions that can’t be addressed elsewhere for lack of relevant data.  The reason the preservation is so good is in large part permafrost, and permanently frozen sites.  Last week, when Claire was here, we were getting a lot of well-preserved 1600-1700 year old marine invertebrates from the samples.  They exist because the layer was frozen for most, if not all, of that time.

I’m been thinking a lot about site destruction, and how to determine which areas are at highest risk, in order to prioritize field efforts.  Perhaps because coastal erosion is the big and immediate threat at Nuvuk (and all the other coastal sites I’ve worked at except for Ipuitak, where the immediate threat was the seawall being built to prevent coastal erosion), I’ve tended to focus on that, as well as eroding river banks for sites along rivers.  The melting of exposed ice wedges, which then leads to collapse of the overlying ground is also something I’ve been concerned about.  And these are major threats, which can tumble entire houses upside down on the beach for the waves to destroy.

Undercutting by waves caused the gravel to slump from underneath this grave at Nuvuk.
Storm-driven surf tears into the mound at Ukkuqsi in Barrow.
Tunnel remnants after the storm. The house was to the left, where only thin air can be seen.
Ice wedge in bluffs near Barrow. They can be much larger.
Slump block on beach at Barrow after a storm.
Slumps from thawing ground along a Colville River cut bank.
A Colville River cut bank from the air. Notice the earlier slump that has stabilized and even grown over, and the fresh cut at the bottom from the river's current.

I hadn’t thought much at all about the risks to Arctic archaeology from a significant deepening of the active layer, which will mean that artifacts and ecofacts (animal bones, insects, etc.) will freeze and thaw every year (which is hard on things to begin with, often causing rocks and bones to split) and while they are thawed, they will be decaying.  Even now, really old sites don’t have much organic preservation.  Even sites that are in no danger of eroding are threatened with the gradual invisible loss of a great deal of the information they now contain.

Obviously, if we are going to develop a “threat matrix” for Arctic archaeological sites, this has to be part of it.  I talked to Vlad a bit after the talk, and he thought he had students who could be put to work on this problem, perhaps by combining what we know about site locations in Alaska (by no means a complete listing) and the existing models for permafrost change.  He also said that one could do active layer modeling for a specific site with a year’s worth of soil and air temperatures, so that’s something we definitely need to get started on.

Piles of Wood

One of the great things about doing archaeology in the Arctic is that the preservation can be spectacular.  Artifacts often froze the winter after they were abandoned, and only thawed when they were excavated.  This means we get to find a lot of the bone, wood ivory and leather items that were undoubtedly part of most precontact people’s tool kits.  We don’t have to guess at what people were using or extrapolate from a few stone tools that did manage to be preserved; we can see it firsthand.

This is not always an unmixed blessing.  Arctic archaeology  sometimes suffers from an embarrassment of riches.

Boxes with wood from the Driftwood Feature (DWF).

In the past, archaeologists generally only saved the artifacts from a site.  Animal bones and soil were pretty much ignored, or at best documented in the field (there are a lot of excavated houses in the Arctic where the animal bones are still piled at the edge of the excavation where they were left decades ago).  As archaeological science advanced (radiocarbon dating began about 60 years ago) and people began to do more things with faunal (animal) remains and soil samples, people began to collect a lot more, and to bring it back to museums to save, on the assumption that one day someone would be able to do something informative with it.  The idea is still a good one in theory, but it is bumping up against various realities.  For one thing, in most areas these sorts of things require storage in climate controlled conditions or they will deteriorate and become useless.  They are often quite bulky compared to just the artifacts.  Most museums simply don’t have any place to put all this stuff!  Some of the better-funded places, like the Smithsonian Institution, have built large off-site storage facilities in areas where real estate is a bit less expensive, just to keep all this stuff.  But such places require operational funds and new staff, and that costs money too.  Most places can’t really afford that.  Some institutions have started charging for putting collections there, but there are problems with that as well.

So part of the new reality for archaeology is that we can’t keep everything.  The question is how to decide what to keep and what not to keep.  In general, the artifacts are kept.  No problem there.  The issue is how to deal with the other things.

It’s even more complicated for the Nuvuk project.  We have had several areas where massive amounts of organic material, with some artifacts and faunal remains mixed in, were encountered.  While one might normally choose to excavate this all in the field, in a couple of cases the areas were right at the erosion face, and could literally have vanished overnight.  Combine that with a very cold field situation, where mild hypothermia can dull excavators’ thought processes, it didn’t seem like that was the best plan, since it risked data in a variety of ways.  I decided to take tightly-provenienced (with very accurate information on where they were from) bulk samples, which can then be processed in the lab, where it is warm and we have good lighting, magnifying lenses and water to wash the dirt and gravel off so we can get a good look at everything.  If excavators recognize an artifact in the field, it gets recorded there, but the idea is that we’ll find the less obvious ones in the lab.

Contents of one bucket shot laid out on a tray.
A closer look

One of the areas with a massive amount of organic material was what we called the Driftwood Feature.  This level is about 1 meter (39 inches) below the Thule graves.  It was actually permanently frozen, and therefore everything organic was in great shape.   It looks like there was an Ipuitak dwelling (maybe there were more that had already eroded–we don’t know) on a ridge near the ocean.  Sometime between 300-400 AD there was a huge storm, which washed all sorts of things (driftwood, bark, marine invertebrates, shellfish, peat, etc.) up onto the beach, all the way up to where the people were living.  It left what is called a strand-line.  It looks like they either left in a hurry and didn’t come back, or didn’t survive, since a number of artifacts were still there. The strand-line continued along what had been the beach ridge, and we wanted to see if there was any evidence of more human activity besides the one dwelling.  Because there was so much wood, and a number of the artifacts at the dwelling had been wood, we had a needle in a haystack problem, with the haystack about to fall into the ocean (which it did the next winter).  So we bulk sampled.

Close-up of the Ipiutak layer at DWF. We excavated many square meters of this!

Now we are going through some of the bulk samples.  I’ve been very lucky to have Dr. Claire Alix, a French scholar who specializes in Arctic driftwood and its use by humans, involved with the project since the very early days.  She was based in Fairbanks, Alaska, for many years, but has recently gotten a teaching and research position at the Sorbonne in Paris.  This is wonderful, since Claire is a great person & really deserves it, but it certainly complicates the logistics of her research on this wood!

Dr. Claire Alix in the Nuvuk Lab

Claire arrived on this morning’s plane, and is already hard at work going through samples from 2009 which were excavated after she left the field.  She is looking for all worked (altered by people) items, picking out things that we can’t yet identify for further examination, and recording amounts & types of wood, bark, and other identifiable organics.  The non-worked identified material is then being lab discarded.  I’ve got the computer map up and color-coded so Claire can look at it when she needs to, Laura is unwrapping the samples, and I’ll probably end up doing the data entry in the catalog.  She leaves again on Wednesday night, and won’t be back in the US until sometime after January, so we’ve got a lot to do, and not much time to do it.

Claire and Laura hard at work.
Lab discards--on closer examination they turned out not to be cultural.

Later this fall we are going to start going through soil samples and so forth.  We hope to be able to reduce the volume they take up.  Some of that will be done by separating the actual sample material of interest from the gravel matrix.  Where that isn’t possible (for example with large logs or whalebone) we will have to sub-sample, retaining only a portion of the total sample volume.  Otherwise, we’re going to run out of room.

Meanwhile…

While the dental extern was busy in the lab, Laura was there to help her find things, answer questions, and so forth. I was busy with other things.

A couple of Navy archaeologists (yes, the US Navy has archaeologists) were in Barrow last week to look at a tract that the Navy may be transferring to UIC, the Barrow village corporation, to get an idea of what needs to be done to comply with cultural resource protection laws prior to transferring Federal land. Neither of them has any Arctic experience, and they stopped by my office to pick my brain a bit. The next day they were doing a few STPs on an old beach ridge on the tract, and asked if I’d like to join them. It was a warm sunny day, with not much wind, and therefore many mosquitos. I hiked our from my office building to meet them, we checked out the area a bit & I hiked back. Other than all the bugs, it was great.

Navy archaeologists David Grant and Bruce Larson surveying.

We didn’t find anything cultural that was older than NARL, but we did find a couple very old gravel beaches. We did find some stakes that had probably marked research plots, and a big aluminum object that looked like an aircraft part. It had some cable attached to the front, as if someone had been trying to tow it. Apparently they gave up.  If you happen to recognize this, please let me know and I’ll pass the information on.

Large aluminum mystery object on Navy tract.

The next day I got a call from the City of Barrow. They run the cemeteries, and had been getting reports that a coffin was partially open. They had checked, and indeed a coffin had been frost-heaved and was damaged. They asked if I could come over when they moved the person into a new coffin. We decided to do it the next afternoon, after they got the new coffin built.

Fortunately, the old coffin wasn’t damaged except for a bit of the lid, so we were able to get the dirt off to make it lighter without disturbing the remains. The City crew was able to lift the entire box out and place it in the new larger coffin. It was a tight fit, because the old coffin had been covered with canvas that was nailed on, but that wasn’t clear when they had measured for the new box! Luckily they had left a bit of space, so they were able to pry a bit and get it in. I got the canvas that had frozen in out so it could go along.  I’d mostly been there in case the coffin was fragile and we had to transfer the individual, to make sure that nothing got left, but that wasn’t needed.

Once the coffin was out of the grave, the idea was to dig it a bit deeper, and then rebury the person. The soil profile was pretty interesting. There was clay (which generally is deposited on the bottom of bodies of still water) very close to the surface, despite the fact that the grave was on a mound. Apparently the permafrost has pushed it up a good bit, although it may have been deposited when sea level was higher than today.

Permanently frozen clay exposed in grave in Barrow cemetery.

The crew did what they could with shovels, but thaw was not that deep, as you can see from the picture above, so they were going to get a compressor and jack hammer, to really get the grave deeper, when I left.  If not, frost heaving would just bring the box up again in a few years.