Changes in penguin populations on the Antarctic Peninsula have been linked to several environmental factors, but the potentially devastating impact of volcanic activity has not been considered. Here we use detailed biogeochemical analyses to track past penguin colony change over the last 8,500 years on Ardley Island, home to one of the Antarctic Peninsula’s largest breeding populations of gentoo penguins. The first sustained penguin colony was established on Ardley Island c. 6,700 years ago, pre-dating sub-fossil evidence of Peninsula-wide occupation by c. 1,000 years. The colony experienced five population maxima during the Holocene. Overall, we find no consistent relationships with local-regional atmospheric and ocean temperatures or sea-ice conditions, although the colony population maximum, c. 4,000–3,000 years ago, corresponds with regionally elevated temperatures. Instead, at least three of the five phases of penguin colony expansion were abruptly ended by large eruptions from the Deception Island volcano, resulting in near-complete local extinction of the colony, with, on average, 400–800 years required for sustainable recovery.

The traditionally conceived genera Orthotrichum Hedw. and Ulota F.Weber are here reclassified into six genera, Orthotrichum, Dorcadion Lindb., Nyholmiella Holmen & E.Warncke, Pulvigera Plášek, Sawicki & Ochyra, Plenogemma Plášek, Sawicki & Ochyra, and Ulota, based on morphological differences and partially on molecular evidence. The genus Pulvigera includes P. lyellii (Hook. & Taylor) Plášek, Sawicki & Ochyra (Orthotrichum lyellii Hook. & Taylor) which was selected as its generitype. The genus Plenogemma includes P. phyllantha (Brid.) Plášek, Sawicki & Ochyra (Ulota phyllantha Brid.) which was selected as its generitype.

The results are presented of a detailed plant macrofossil analysis of a(¹⁴C dated Holocene organic sequence from a sub-Antarctic island, South Georgia. In the peat infilling of a rock basin 31 bryophyte species and many of the principal species of the present-day angiosperm flora, associated with bog communities, have been identified. The zonation of the bryophytes and the seeds and fruits shows a striking correspondence with the sediment stratigraphy, and indicates five ecological phases. The first four reflect a succession from a minerotrophic shallow pool to an ombrotrophic W arnstorfia-Polytrichum bog. After the deposition of a greyish-brown layer, c. 2200 ¹⁴C years BP, a wet Deschampsia-Warnstorfia-Sanionia-Rostkovia bog came into existence, which is still present today. The ecological phases are radiocarbon dated. They can be interpreted in terms of climate development during the Holocene. Climate ameliorated rapidly at about 10 000 ¹⁴C years BP followed by a drier period. Around 7000 14C years BP the climate became wetter and the following c. 2500years probably represent the climatic optimum. Between 4500 and 2600 ¹⁴C years BP, drier conditions prevailed at the study site. The most striking change occurred at 2600 ¹⁴C years BP when a marked change in vegetation and ecology indicates much wetter conditions.