ARCHAEOLOGY OF RELICT ADELIE PENGUIN ROOKERIES AS AN AID IN RECONSTRUCTING HOLOCENE DEGLACIATION OF ANTARCTIC COASTS

Deglaciation, in particular the timing of the initial phase of ice recession, is poorly known but it is critical for understanding the cause of glacier retreat, the relationships among climate variations, sea-level rise, and ice-sheets dynamics. Uninhabited by humans before ca. 1900 AD, Antarctica can be regarded as the continent of penguin settling. Unlike Emperor penguins that are able to bread directly on the ice surface, the Adélie Penguins (Pygoscelis adeliae) nest on ice-free areas around Antarctica. Nests are patches of selected pebbles that penguin parents arrange year after year. In a long-term occupied rookery, penguin guano seeps through the permeable pebbly nests and accumulates at their base to form ornithogenic soils. The older is the rookery, the thicker is the accumulation of pebble and guano. A single enduring occupation of a rookery drops a thick layer of superimposed nests, penguin remains, bones and guano. Abandoned penguin nesting sites in areas where the Adélies do not nest at present were recognized as relict rookeries and are common landscape features along the Antarctic coasts. The heritage of penguin communities is preserved in the fossil rookery’s distribution and in ornithogenic soils. Applying the techniques commonly used in archaeological research, through the accurate stratigraphic excavation of penguin settlements, it is possible to identify multi-occupational phases of the rookeries, and to reconstruct the history of penguin populations. Furthermore, penguin guano and remains can be radiocarbon dated. More than 100 conventional and AMS dates (0-12 Kyr) have been so far obtained in the Ross Sea area. Adélie penguins occupied several localities between Ross Island and Terra Nova Bay since 8 kyr BP; coastal deglaciation was completely accomplished about 7 kyr BP. Penguins played a key role in affording a very useful set of dates also: 1) to reconstruct the Holocene curves of the coastal emersion; 2) to investigate the isostatic rebound of the lithosphere unloaded after the retreat of the Antarctic ice sheets; 3) on the Holocene paleoenvironmental conditions that favored or inhibited the presence and distribution of the penguin population; and 4) for studies on Adélie penguin’s DNA evolution.