By Rhys Timms (2nd Year PhD Student)
In February 2014 myself, and two intrepid PhD supervisors flew to Orkney, armed with little more than 12 metres of steel rod and 2 ‘russian’ coring devices. Our aim was to extract and document former lake sediments relating to the end of the last ice age in Scotland.
The reason and justification for this, like many other blog entries on these pages, is that palaeoenvironmental science i.e. the study of past environments works on the principles of uniformitarianism i.e. the present is the key to the past, likewise it can be said that the past is the key to the future.
In essence, by understanding the environmental changes of the past, we hope to be able to better understand the future climatic challenges that the human race may face in the coming centuries and most likely within the coming decades.
But how does “hunting tiny bits of Iceland” fit into all of this, and what do I mean by tiny bits of Iceland? When a volcano erupts, huge plumes of volcanic debris can be thrown high into the atmosphere; the solid fraction of this material is called ‘tephra’.
Tephra encompasses all sizes, shapes and compositions and when it falls back to earth it covers the landscape like a blanket. We know from records like those in Scotland that an eruption from Iceland around 12,100 years ago was so large that the edge of this ‘blanket’ stretched as far away as Russia and Italy!
So what is the significance of these tiny bits of volcanic material in old lake basins in Scotland? Well understanding environmental change in the past requires researches to look at many different parts or ‘proxies’ of the past environment, some specialise in looking at pollen which can show us what the vegetation was like, some researchers look at beetles, midges or snails (see Jenni Sherriff’s post “Snail Secrets”) to work out temperature, and all of these things can be found within former lake basins alongside many other useful proxies. I always imagine the work we do is similar to that of a detective, searching for clues and building a bigger picture of events.
What tephra can do is provide a means of linking all these records together. When the tephra falls from the atmosphere is does so almost universally across a whole region, and makes what we call an isochron. This is basically a moment in time preserved and highlighted across a wide area. This means we can see how the landscape was changing over vast spaces at exactly the same point in time! It also allows us to compare information all across Europe, not only on the land but also from the bottom of the sea and even from the huge ice sheet that covers Greenland.
This all sounds quite simple, identify a tephra layer in some old lake sediment, at the bottom of the sea or in some ice and then compare all the environmental information alongside it.
It would be that simple, except the tephra is so small and the layers are so thin, they are invisible to the naked eye!
So in order to work out if we have found any tephra we must concentrate our tephra ‘shards’ i.e. the fragments of volcanic material from the surrounding sediment, and get rid of all the other muck and detritus we don’t want, and how do we do this – we sieve, sieve, sieve…
It can take many weeks and months to process the lake sediment cores, we often work at a 1cm resolution meaning we can have many hundreds of samples to sieve and examine, each sample must be sieved twice using two different size sieve meshes. After all that we use a chemical called sodium polytungstate which enables us to ‘float’ off material we don’t want and concentrate the tephra. It’s a long and drawn out process but in the end we are left with a series of microscope slides which may have millions, thousands, hundreds or no shards at all, we don’t really know until we look but it’s a very important method to our understanding of past climates, and personally I think tephra shards are quite pretty!