Ice wedges - the science of frozen cracks in the ground

There aren’t that many memorable papers.

I mean, there are thousands of decent or even good papers published every week.  But they all sort of blend together after a while.  I have a hard time keeping them straight sometimes.  Just today, I told my advisor the wrong thing about a paper I included in a literature review I’m writing.  It was not a good paper, and I had confused the methods from the not-so-great paper with those of a much better paper.  My point is that most papers are forgettable to an extent. 

Occasionally, however, you’ll read something that’s like a bolt through the sky.  You’ll sit up and say, “I want to do THAT.”  This week, that paper presented data from ice wedges in Siberia, then reconstructed winter temperatures.  Esoteric, yes.  But also really cool. 

 Ice wedge formation

Ice wedge formation

First, what are ice wedges?  As much as a quarter of land in the northern hemisphere is underlain by permafrost, ground that is below freezing temperatures for two or more years in a row.  During winter, the extreme cold temperatures cause the ground itself to contract, forming fissures and cracks.  Once temperatures rise in spring, snowmelt fills those cracks.  The water re-freezes – after all, the soils around it are well below freezing!  Freezing actually causes water to expand, and the new ice wedge widens the gap slightly, and pushing surrounding frozen soils upwards.  Think a tube of toothpaste – you squeeze the sides together, and the toothpaste comes out the top.  The following winter, the permafrost contracts again, opening a crack in the ice and starting the process over again. See the little diagram I made to get a better idea.

These can get massive, and very, very old.  Meyer et al. (2015) just published a paper taking advantage of the age and sequential way ice wedges are formed.  They went to the Lena River delta (right), one of the largest deltas in the world.  Permafrost abounds, and previous work established the age of different parts of the delta fairly well.  Ice wedges are also common.

 Figure S2 from Meyer et al. (2015).

Figure S2 from Meyer et al. (2015).

So, Meyer et al. went out a few times, to quote the study, “ice wedges have been sampled by chain saw.”

Yeah, science!  And chain saws.  When we sampled ice wedges on the Kolyma River, we used an axe.

Anyway, they cut out sections of the wedges, melted them and preserved the water.  Later, they ran isotopic analyses which told them a) the approximate age of the water using radiocarbon and b) the relative temperature using oxygen isotopes.  I’ll spare you the details of how the isotopes work – don’t worry, I’ll go into excruciating detail on that some other time.  For now, just know that higher oxygen isotopes mean warmer temperatures.  Using this, Meyer and his colleagues re-constructed 8,000 years of winter-spring temperatures. 

The winter-spring temperature reconstructions are almost unique in high-latitudes.  Most of our long-term temperature proxies – tree rings, for instance – are based on annual growing seasons.  Great, we need to know this.  But much of the recent anthropogenic climate warming in the Arctic has been during winter and spring.  We need to know – is this different than in previous natural climate changes?  What impact will winter warming have on carbon sequestration in permafrost?  How will winter warming impact hydrology, weather, the length of the growing season?  These reconstructions are a first stab at answering those types of questions.

The reconstructed climate from ice wedges reveals winter warming, opposite of other summer-biased climate records.  Again, I won’t delve too deeply into these mechanisms right now, but this was likely driven by changes in orbital forcing.  The shape of Earth’s orbit changes through time, on cycles of ~20,000 – 100,000 years.  These changes impact how much energy we receive from the sun, and its distribution.  Meyer and colleagues used models of past climate to show that winter warming was likely driven by these changes in our orbit around the sun.  At the same time, there was a significant increase in carbon dioxide concentrations during the 8,000 year record.  Reconciling this increase in greenhouse gases with a cooling in summer temperatures is accomplished by including these warming winter temperatures.

 Figure 1F from Meyer et al. 2015.  The take-away: winter temperatures have a long-term warming trend, that has jumped up dramatically in the past 50 - 100 years.

Figure 1F from Meyer et al. 2015.  The take-away: winter temperatures have a long-term warming trend, that has jumped up dramatically in the past 50 - 100 years.

Alaskan ice wedges received similar analyses a couple years ago, but we have much less data of any sort from Russia compared to the North American Arctic.  I originally got involved in Arctic research as an undergraduate on a project aiming to correct this.  We went to the Kolyma River in northeast Siberia, and conducted all sorts of research on carbon cycling (see  I returned in 2013, and would love to go back again.  I work mostly on modern carbon cycling, these days.  But I’ve always found paleoclimate fascinating – reading about ancient climate and cultures launched me towards my present career when I was a sophomore in high school.  I want to do paleoclimate, and I want to get back to northeast Siberia.

The Kolyma River is home to a great science station, lots of good researchers spend their summers there.  And guess what else it has?

Ice wedges.





Meyer et al., 2015.  Long-term winter warming trend in the Siberian Arctic during the mid –to-late Holocene.  Nature Geoscience, 8, 122-125.  doi:10.1038/ngeo2349