Core blimey!

I must confess something. I have shamelessly stolen the title of this blog post from Matt’s excellent article about fieldwork in eastern Canada. You can read that article here, but I’m sure he won’t mind as it suits this post rather well!

We’ve described elsewhere how some of the peat records we work with can stretch back well over 10,000 years, but what we haven’t talked about it how we retrieve such records. Peat bogs, by their very nature, constantly accumulate over time and so records of this length can often start many meters below the bog surface. It is not unheard of for some of raised bogs to be over 10m deep!

So, how do we go about obtaining complete cores from such depths? Well, the answer is actually relatively simple: a few bits of basic equipment, a couple of pulled muscles and a lot of muscle power! However, to modify the old adage: ‘there is more than one way to core a peat bog’. In fact, numerous techniques have been employed over the year – many of which have more than a passing resemblance the weird and wonderful inventions of Heath Robinson! Instead we’re going to focus on the most common few.

1. Monolith tins. These are essentially metal boxes of varying sizes (commonly 50x10x10cm) hammered into a peat face. This is a common technique to use when such faces are readily available, revealed by peat-cutting, either by hand or machine, for fuel or fertiliser. When used on the surface of an uncut, intact bog, small trenches may be carefully cut into the surface and later refilled. Once the monolith tin is firmly in place, a bread knife (!) is used to cut around the edges, and the core is carefully removed. These cores are great because they collect so much material for analysis. They’re particularly useful when taken at the bog surface, as the material here is often unconsolidated or ‘fluffy’ and this technique keeps everything together rather more effectively than some other techniques.

2. Wardenaar corer. Wardenaar cores are only taken at the surface of bogs and, like monolith tins, are handy because they collect a good amount of material and don’t disturb the fragile upper sections of the core too much. In many ways they’re preferable to monolith tins because they don’t require us to dig trenches, which, owing to their location in rather wet peatbogs, quickly fill with water!

The corer itself is a rather clever bit of kit. It is made up of two independently moving halves, which can be pushed into the peat alternately. They can be fun to use (as the photo suggests!), but the real work comes when we have to pull the corer up. At over a meter long, pulling a Wardenaar fully-laden with peat out of a squelching, sucking bog is no mean feat! The only downside is that the sheer size of these corers can prevent us from taking them to some of the more remote sites we travel to.

3. D-section corer (AKA the ‘Russian’). Ah, the good old D-section corer. All bogologists have their favourite ‘Russian’ – as they’re known in the trade! A trusty, torpedo-shaped machine that comes in many different shapes and sizes, my personal favourite is the affectionately named 50cm ‘Fat Russian’. These corers can range from 25 to 100cm in length and 4 to over 10cm in diameter.

The Russian is made up of a semi-circular chamber and a blade, which turns on a central axis. The corer is pushed down into the bog using metal rods that are screwed on one by one. When the desired depth is reached, the corer is turned 180 degrees using a handle attached to the rods, sliding the empty chamber around the blade, which is held still by the peat in which it is embedded, encasing an intact sample of peat. Each core section is then brought back to the bog surface, and extruded into plastic guttering.

This process is repeated until all core sections have been taken and the entire sequence has been sampled. Once the cores are taken, we quickly wrap them in all manner of protective materials (cling film, foil, plastic sheeting etc.) to stop them drying out, moving too much or becoming contaminated.

Some bogologists like to take two parallel cores, very close to one another, with core sections that overlap. This guards against any potential disturbance taking place at the top and bottom of each section as the Russian is inserted and retrieved. It can, however, double the number of core sections taken, which, at a couple of kilos each, makes a big difference at the end of a hard day’s coring!

Another thing to remember is that bogs are essentially living systems. As a result, their surfaces are extremely delicate (and often very wet!), so the only way to transport ourselves, our equipment and all our samples out to and back from our coring site is … you guessed it … by foot!

Coring peat bogs is hard work, not to mention hard work – it’s even been known to rain once in a while! But it is great fun, especially when you have a good team around you – there is nothing as satisfying as a turning the blade of the Fat Russian to reveal perfectly sampled peat ready for analysis!

Further reading:

De Vleeschouwer et al. (2010) Coring and sub-sampling of peatlands for palaeoenvironmental research. Mires and Peat, Volume 7, Article 01, 1–10. PDF

ACCROTELM Project – Coring protocol

YouTube – Peat coring in the Black Forest

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