LA RICOLONIZZAZIONE DELL’ANTARTIDE: STORIE DI PINGUINI E FOCHE, SENTINELLE DEI CAMBIAMENTI CLIMATICI NEGLI ULTIMI 10 MILA ANNI

The re-colonization of Antarctica: stories of penguins and seals, sentinels of climate change in the last ten thousand years. During the Late Pleistocene the Antarctic glacial system expanded and advanced on the coastal margin of the continent forcing penguins, seals and other animals nesting in the deglaciated areas to migrate toward refuge areas located at northern latitudes. The deglaciation that followed the last glacial maximum, in the Ross Sea area, was accomplished around 8000 years ago, freeing the Antarctic coasts that were re-colonized by Adélie penguins and elephant seals. These two species have coexisted, even alternating, in the deglaciated areas of the coastal strip for several millennia. In the ornithogenic soils of the abandoned penguin colonies and in the breeding sites of the elephant seals, recently discovered on the Holocene raised beaches, a precious heritage of organic remains is preserved, allowing us to study different aspects of recent environmental history. The phases of colonization and coexistence between penguins and elephant seals are very complex and reflect the climatic-environmental variations that have characterized the Antarctic scenario for several thousand of years. Penguins and elephant seals, sensitive sentinels of the Antarctic ecosystem, are now playing an important role in the Southern Ocean scenario, interpreting the dramatic role of bellwether of climate change.

Sulfur content in the soils of Skua and Galindez Islands (Maritime Antarctic)

Sulfur is an important nutrient, as well as a part of some aminoacids, enzymes and vitamins. The lack of sulfur in the plant organism is accompanied by a decrease of photosynthetic pigments content and, by external signs, resembles chlorosis caused by nitrogen deficiency. In Maritime Antarctica the main source of sulfur for terrestrial ecosystems are numerous ornithogenic products – guano, feathers, pellets, etc. However, many soils of this region do not contain visual signs of ornithogenous impact. The purpose of this study was to establish whether the sulfur content in these soils is the limiting factor for plant growth and development. It has been found that the total S content in both ornithogenic and non-ornithogenic soils is high, much higher than in the zonal soils of the temperate climate zone. Most of the sulfur is contained in the organic compounds and is not available for plants – more than 80% in ornithogenic and more than 90% in non-ornithogenic soils. It was found that the availability of sulfur is not a limiting factor for the growth and development of plants on the studied soils of Coastal Antarctica. We suggest that sulfur-containing organic substances play an important role as precursors of soil organic matter under Antarctic conditions.

Holocene occupation history of pygoscelid penguins at Stranger Point, King George (25 de Mayo) Island, northern Antarctic Peninsula

We report additional fossil evidence for pygoscelid penguins breeding on King George (25 de Mayo) Island, South Shetland Islands, in the Holocene beginning at ~7000 cal. yr BP. This evidence comes from a raised marine beach deposit formerly studied and described as Pingfo I at Stranger Point, Potter Peninsula. We relocated and exposed deposits at this site and recovered additional samples of penguin bones from five stratigraphic beds that are redescribed here. Most of these bones are from juvenile penguins and exhibit little or no wear indicating minimal transport to the beach deposits. Some of the bones are developed enough to be identifiable to Adélie ( Pygoscelis adeliae), Gentoo ( Pygoscelis papua), and Chinstrap ( Pygoscelis antarctica) penguins, indicating that all three species were breeding at Stranger Point from ~7320 to 4865 cal. yr BP. This breeding occupation corresponds with the first warming and deglaciation that occurred in the northern Antarctic Peninsula by this time and ends with the onset of reglaciation of the Peninsula. At least 31 abandoned penguin mounds and ornithogenic soils also were located and sampled at Stranger Point and indicate that the current occupation of this area by all three pygoscelid penguins dates no older than ~535 cal. yr BP. The absence of ornithogenic soils from earlier Holocene breeding was probably due to glacial activity and soil solifluction during periods of warming in the mid to late Holocene.

Biogeochemistry of ornithogenic soils in Coastal Antarctica

Ornithogenic soils are usually considered to be formed as a result of breeding activities by sea birds. These soils are widespread in polar regions and in Coastal Antarctica in particular. It is believed that the most important impact of birds on soil formation in such environments is accumulation of guano – an important source of chemical elements and energy. In this paper we discuss an alternative point of view. We hypothesized that not only and not so much accumulation of guano, but also other bird-formed products significantly affect soil formation in Coastal Antarctica. An intensive biogenic flux of calcium from marine to terrestrial ecosystems in the food-chain: plankton + microbenthos → Nacella concinna → Larus dominicanus → guano + pellets (Nacella concinna shells) → soil strongly influences soil formation in Argentina islands by significant increase of soil pH values. The role of coral algae as an important source of calcium for terrestrial ecosystems of the Coastal Antarctic was shown. Further promising research priorities in the field of calcium biogeochemistry in polar environments were described.

Soil–landform–plant-community relationships of a periglacial landscape on Potter Peninsula, maritime Antarctica

Integrated studies on the interplay between soils, periglacial geomorphology and plant communities are crucial for the understanding of climate change effects on terrestrial ecosystems of maritime Antarctica, one of the most sensitive areas to global warming. Knowledge on physical environmental factors that influence plant communities can greatly benefit studies on the monitoring of climate change in maritime Antarctica, where new ice-free areas are being constantly exposed, allowing plant growth and organic carbon inputs. The relationship between topography, plant communities and soils was investigated on Potter Peninsula, King George Island, maritime Antarctica. We mapped the occurrence and distribution of plant communities and identified soil–landform–vegetation relationships. The vegetation map was obtained by classification of a QuickBird image, coupled with detailed landform and characterization of 18 soil profiles. The sub-formations were identified and classified, and we also determined the total elemental composition of lichens, mosses and grasses. Plant communities on Potter Peninsula occupy 23% of the ice-free area, at different landscape positions, showing decreasing diversity and biomass from the coastal zone to inland areas where sub-desert conditions prevail. There is a clear dependency between landform and vegetated soils. Soils that have greater moisture or are poorly drained, and with acid to neutral pH, are favourable for moss sub-formations. Saline, organic-matter-rich ornithogenic soils of former penguin rookeries have greater biomass and diversity, with mixed associations of mosses and grasses, while stable felsenmeers and flat rocky cryoplanation surfaces are the preferred sites for Usnea and Himantormia lugubris lichens at the highest surface. Lichens sub-formations cover the largest vegetated area, showing varying associations with mosses.