ANTARCTIC MOSS PEAT: MY WORK AS A BAS BOTANIST IN THE 1970s by James Fenton I graduated with a degree in botany from the University of Durham in 1973 and my first job was working for the British Antarctic Survey (BAS) as a botanist from 1973-78 under the tutelage of Ron Lewis Smith. I was taken on to study the moss peat banks that occur in the South Orkney Islands and intermittently down the peninsula as far south as Lazerev Bay on Alexander Island. This work built on previous work by Nigel Collins and Royce Longton. The moss banks are formed by two species of moss, Chorisodontium aciphyllum and Polytrichum strictum, the latter also being a species that occurs in Britain. These moss banks can cover extensive areas (see Figs.1&2) and one of my jobs was to map their distribution. They can be over a metre deep, the deepest recorded being 3.4 metres thick discovered above Walker Point on Elephant Island by the 1976 Joint Services Expedition. During the summer months only the top 20 cm or so of the moss banks are unfrozen, the deeper layers being underlain by permafrost. Fig.1. The largest moss peat bank on Signy Island. There is a metre rule visible in the middle distance (1975). All pictures by James Fenton Fig.2. A moss peat bank on the Argentine Islands, dominated by the moss Polytrichum strictum and encrusted by lichens (1973). A metre rule is visible at the bottom. 1
My main job was to find out how fast the moss peat banks were growing and how old they were. The reason they occur in the first place that the rate of growth of the moss is greater than the rate of decomposition of the dead shoots. In other words as the moss shoots grow upwards the depth of the moss layer increases because undecomposed dead shoots are still there underneath. Over a year I measured how much the shoots had grown. I also cropped samples of annual growth at the end of the year, dried the samples and then worked out how much production there had been i.e. how many grams per square metre of dry matter had been produced through photosynthesis. My research showed that the shoots grew about 2 mm a year. However the moss banks as a whole do not increase yearly in depth by this amount as there is some decomposition of the dead shoots and the weight of the moss above squashes down the lower layers (see Fig.3). To measure decomposition of the moss shoot at different depths, I first extracted some shoots, dried them and weighed them. I then put them in nylon mesh bags and returned them to the peat, placing them at the same depth from which I had originally taken them. I left them in the ground for a year and then took them out and reweighed them. By doing this I could calculate how much weight they had lost, i.e. by how much they had decomposed. Fig.3. A close up of moss shoots of Chorisodontium showing how the lower shoots become squashed and face downhill as the top layers slide over the permafrost (Signy Is, 1975). From these measurements I now knew the rate of annual production of the moss and the rate of decomposition, and hence the rate of peat growth. My calculations showed that before the dead moss becomes permanently stored in the permafrost (where it will not decay further) about 50% by weight had decomposed. In other words, the peat accumulates at half the rate the moss shoots at the surface grow. On average the rate of peat growth was about 1 mm a year, equivalent to the accumulation of 89-158 grams dry matter per sq metre per year which is not too dissimilar to peat accumulation rates in the UK. This work was published in the Journal of Ecology. Peat is seen important nowadays in relation to global warming as it permanently removes carbon from the atmosphere at least until erosion sets in. I also drilled through the moss banks to gain samples from the bottom of the frozen peat. Carbon dating of these showed that the oldest moss bank was 5,000 years old. One characteristic of the moss banks is that they often have a vertical edge (see Figs.1&4). This probably results from a complex process of snow drifts on one side of the moss preventing moss growth combined with downslope movement of the whole unfrozen surface over the permafrost. Indeed, this downslope movement appears to be a characteristic of all moss banks on slopes (see Fig.5). 2
Fig.4. An example of a vertical edge, with a metre rule (Signy Island, 1975). Fig.5. A moss bank on Signy Island showing crevasse-type features, illustrating that the top layers are moving downhill (1975). Interestingly, when visiting Cuverville Island in later years (1998/9) I noticed extensive moss banks on the hill slopes with an accumulation of peat at the bottom where it had slid down, broken off and landed on the ground below producing a peat drift instead of a snow drift (see Figs.6&7). I found this interesting, although the groups I was with were more excited about seeing the penguins! Although I have used the term peat, the Antarctic moss banks differ from most peat types in the world because the peat has not accumulated under waterlogged, anaerobic conditions. It forms under dry conditions, but in a climate cold enough to prevent decomposition of all the moss. Hence there has been discussion in international peat circles about whether it should be called peat at all. 3
Fig.6. Moss peat above the penguin colony on Cuverville Island, sliding down hill and landing on the shore below (1998-9). Fig.7. Black peat accumulating below the moss banks of Cuverville Island as shown in Fig.6 (1998-9). My work also involved studying some moss peat that was seen emerging from under retreating glaciers (see Fig.8). This implied that after the peat started forming the climate had cooled and the moss had become covered by ice; the climate was now warming again and the peat reappearing. Hence I wrote a short paper on what this was telling us about climate change in the Antarctic Peninsula: now, of course, climate change is all the rage. Fig.8. Black peat emerging from under the ice after glacial retreat on Signy Island. A metre rule is visible just above the ice (1975). 4
Similar moss peat is found on South Georgia, but there it normally has vascular plants growing amongst the moss. I have recently been working in the Falklands Islands and while there found some Antarctic type peat at Johnson s Harbour as far as I know the first that has been found in the Falklands (see Fig.9). I showed it to Pete Convey, BAS s last remaining terrestrial ecologist, and he was equally excited (I think!) and took some samples as part of a wider research project. Fig.9. Antarctic-type moss peat dominated by Polytrichum being sampled by BAS terrestrial ecologist Pete Convey at Johnsons Harbour, Falkland Islands (2013). One thing that has changed in my time is the number of fur seals: they were a rare site on Signy but now are common even as far south as Rothera. They tend to destroy any moss-dominated vegetation with serious loss of moss communities on Signy Island, so I am told. Happily the older, deeper moss banks are high up and so not under threat. BAS seems to be closing down its terrestrial ecology side of things with Pete Convey, as far as I know, being its last remaining terrestrial ecologist. I think this is a great shame which will make it difficult for BAS to lead on research on Antarctic terrestrial ecosystem in relation to global warming. However the moss banks did reach the international press recently with the BAS press release Moss brought back to life after 1,500 years frozen in ice. And in 2013 there was the press release Moss growth in Antarctica linked to climate change. So I hope my work has contributed in some way to the debate. Altogether I wrote five papers as a result of my research and also gained a PhD under the then Public Research Institutes Scheme: 1978: The growth of Antarctic moss peat banks. PhD thesis, University of London. 1980: The rate of peat accumulation in Antarctic moss banks. Journal of Ecology Vol.68. 1982: Distribution, composition and general characteristics of the moss banks of the maritime Antarctic. British Antarctic Survey Bulletin Vol. 51. Written jointly with R I Lewis Smith. 1982: Vegetation re-exposed after burial by ice and its relationship to changing climate in the South Orkney Islands. British Antarctic Survey Bulletin Vol. 51. 1982: The formation of vertical edges on Antarctic moss peat banks. Arctic & Alpine Research Vol. 14. 1983: Concentric fungal rings in Antarctic moss communities. Transactions of the British Mycological Society, Vol. 80. James Fenton jamesfenton362@btinternet.com 20 July 2014 5