James H C Fenton ECOLOGIST www.fenton.scot
1. The Moss peat banks of Signy & Moe Islands, South Orkney Islands The peat is formed by two species of moss: Polytrichum strictum and Chorisodontium aciphyllum. It is underlain by permafrost at a depth of c.15-20 cm, and is up to two metres thick and 5,000 years old.
Signy Island: Deep moss peat banks on level or gently sloping ground at the northwest end of the island. Note that a metre rule is visible as a scale marker in some photos.
Signy Island: A turf on a steep slope dominated by Polytrichum strictum below Observation Bluff.
Moe Island
All pictures were taken while James was working for the British Antarctic Suvey in the 1970s. Click here for more info. on Antarctic peat.
2. Vertical edges of Antarctic moss peat banks A characteristic of many Antarctic moss peat banks is that one side has a vertical edge. These are visible in many of the photographs above taken on the South Orkney Islands. However the tallest such edge, at 3m height, is at Walker Point, Elephant Island (see picture below). The vertical edges are not erosion features – note the absence of eroded peat at their base. The pictures here demonstrate their formation. All the pictures were taken on Signy Island in 1975. Picture 4 is a key one, showing how moss shoots at the edge of the moss bank break off and hang down. This can happen at periodic intervals, as illustrated in picture 5. The whole structure is supported by the permanently frozen undecomposed moss peat (permafrost). For a description of how they form see: Fenton, J. 1982. The formation of vertical edges on Antarctic moss peat banks. Arctic & Alpine Research Vol. 14. .
1. Moss shoots above a slope
2. Live green shoots sliding downhill over frozen peat
3. Live shoots now hanging over edge
5. Shoots break-apart & hang down
6. Cross section where surface shoots broken off
7. Close-up of break
8. Close-up showing dead shoots facing downhill
9. Three episodes of break-off visible on vertical face
10. Dead shoots build up, all supported by permafrost
11. Overhang at base of the peat
4. Live shoots hanging down over vertical edge
3. Erosion of moss peat banks Although the vertical edges are not erosion features, erosion can sometimes be observed on Antarctic moss peat. This illustrates the point that peat erosion can ba a natural phenomenon, occurring in the absence of grazing, burning or human impact. These pictures all taken in 1975.
4. Ice retreat These pictures show peat (black) which has been exposed as permanent ice has retreated. This indicates that the climate has varied over the years. All photos taken 1975. See the paper: Fenton, J. 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.
5. Other moss peat banks in Antarctica & South Georgia 1 & 2: Moss turf dominated by Chorisodontium aciphyllum at Shingle Cove, Coronation Island (South Orkneys). Pictures taken 1999. 3-8: Moss turf dominated by Polytrichum strictum on steep ground above the penguin colony on Cuverville Island (Antarctic Peninsula). Note that the moss is slowly sliding downhill over the permafrost, with picture 8 showing moss peat which has slid down and accumulated at the bottom of slope. Pictures taken 1988/9. 9: Moss turf dominated by Polytrichum strictum at Galindez Island, Argentine Islands (Antarctic Peninsula). See also the two pictures of Galindez Island under ‘Ice Retreat’ above. Pictures taken 1975. 10: The deepest moss peat bank found: c.3m deep, at Walker Point on Elephant Island (picture from 1976-7 Joint Services Expedition). 11: Turf of Polytrichum strictum at Maiviken, on South Georgia, with the grass Festuca contracta. Picture taken 1975.
1 A collapsed vertical edge: perhaps the underlying permafrost which holds the whole bank together, has thawed. Signy Island. 2 The active layer (unfrozen moss & peat) has slid down over the permafrost (permanently frozen peat). Moe Island.
1. Collapsed vertical edge 2. Slide of unfrozen surface over permafrost 3. Surface erosion 4. Surface erosion 5. Surface erosion 6. Surface erosion 7. Surface erosion 8. Turf of Polytrichum broken off by the wind
3-7 Erosion of the surface of the peat bank, possibly caused by exposure to wind as the peat has become deeper. Pictures 3-5 Signy Is, 6-7 Moe Island.
8 Wind has here blown away a section of Polytrichum turf.
1 2 4 5 8 7 6 1. Peat exposed by retreat of glacial ice 2. Peat exposed by retreat of glacial ice 3. Peat exposed by retreat of a permanent snowpatch 4. Peat exposed by retreat of permanent snowpatch 1. Coronation Island, S. Orkneys 2. Coronation Island, S. Orkneys 6. Cuverville Island. Surface peat is sliding downhill 5. Cuverville Island: surface peat is sliding downhill 7. Cuverville Island. Peat accumulating at bottom of slope 8. Cuverville Island. Peat accumulating at bottom of slope 4. Cuverville Island 3. Cuverville Island 11. Polytrichum turf on S.Georgia with grass 10. Walker Point, Elephant Island 9. Polytrichum turf at Galindez Island (Argentine Islands) 1 2 4 5 8 7 6 3 3 9
Antarctic-type peat formed by Polytrichum strictum has recently been found by the author outside Antarctica in both the Falkland Islands and Scotland. See pictures below.
Polytrichum rhizoids
The surface 5cm of an Antarctic moss turf of Polytrichum strictum showing the tightly-bound moss shoots. In this species the shoots are held together by rhizoids, small root-like outgrowth similar to roots in higher plants. In this picture two-year’s growth of rhizoids are visible growing out of the cut surface of the turf.
See also my paper: The rate of peat accumulation in Antarctic moss banks Journal of Ecology, 1980, Vol.68, No, 1, pp. 211-228
For a full description of this habitat see: James Fenton & Ron Lewis Smith, 1982. Distribution, composition and general characteristics of the moss banks of the maritime Antarctic. British Antarctic Survey Bulletin Vol. 51.
A dome of Polytrichum strictum peat recently found by the author in the Falkland Islands.
A turf of Polytrichum strictum peat recently found by the author on the island of Islay in Scotland.