Subantarctic peatlands and their potential as palaeoenvironmental and palaeoclimatic archives

Subantarctic islands are located within the Antarctic Circumpolar Current and the southern westerly wind belt, the latter called Southern Westerlies, making them unique terrestrial archives to investigate past changes in oceanic and atmospheric circulation patterns in the southern mid-latitudes. The islands are characterised by a treeless, phanerogam-poor flora in which bryophytes are of major importance. Several peat-based Holocene palaeoenvironmental and palaeoclimatic studies have recently been published for South Georgia and Ile de la Possession (Iles Crozet). A range of techniques have been used in these studies, mainly plant macrofossil analysis, but also analyses of diatoms, pollen and non-pollen microfossils, geochemical and geomagnetic measurements. The records are chronologically constrained by radiocarbon dating. This paper brings together these data in order to give an overview of the Subantarctic peat-based palaeoclimatic records. A new plant macrofossil record for the island of South Georgia is added. Evidence for millennial scale Holocene climate variability was found for both islands of which the most striking one occurred in the late Holocene. However, within the uncertainty of the age/depth models, the timing for this climate shift to wetter and/or colder conditions on South Georgia and windier/wetter conditions on Ile de la Possession is different for both islands. Ile de la Possession (Iles Crozet) seems to follow the Northern Hemisphere climate evolution as the event was dated to ∼2800 cal BP, a well-known climate event present in many peat-based records in north-western Europe. In contrast, the South Georgian late Holocene climate records reveal a shift around ∼2200–2000 cal BP.