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.

International audienc

Aim The aim here was to assess whether the present-day assemblage of subantarctic flowering plants is the result of a rapid post-Last Glacial Maximum (LGM) colonization or whether subantarctic flowering plants survived on the islands in glacial refugia throughout the LGM. Location The circumpolar subantarctic region, comprising six remote islands and island groups between latitudes 46° and 55° S, including South Georgia in the South Atlantic Ocean, the Prince Edward Islands, Îles Crozet, Îles Kerguelen, the Heard Island group in the South Indian Ocean and Macquarie Island in the South Pacific Ocean. Methods Floristic affinities between the subantarctic islands were assessed by cluster analysis applied to an up-to-date dataset of the phanerogamic flora in order to test for the existence of provincialism within the subantarctic. A review of the primary literature on the palaeobotany, geology and glacial history of the subantarctic islands was carried out and supplemented with additional palaeobotanical data and new field observations from South Georgia, Île de la Possession (Îles Crozet) and Îles Kerguelen. Results First, a strong regionalism was observed, with different floras characterizing the islands in each of the ocean basins, and endemic species being present in the South Indian Ocean and South Pacific Ocean provinces. Second, the majority of the plant species were present at the onset of accumulation of post-glacial organic sediment and there is no evidence for the natural arrival of new immigrants during the subsequent period. Third, a review of geomorphological data suggested that the ice cover was incomplete during the LGM on the majority of the islands, and ice-free biological refugia were probably present even on the most glaciated islands. Main conclusions Several independent lines of evidence favour the survival of a native subantarctic phanerogamic flora in local refugia during the LGM rather than a post-LGM colonization from more distant temperate landmasses in the Southern Hemisphere

International audienc

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 Warnstorfia-Polytrichum bog. After the deposition of a greyish-brown layer, c. 2200 "4C years BP, a wet Deschampsia-Warnstorfia-SanioniaRostkovia 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 '4C years BP the climate became wetter and the following c. 2500years probably represent the climatic optimum. Between 4500 and 2600 '4C 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.

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