The Windmill Islands (centred 66°15’S, 110°33’E) are situated in the midst of Wilkes Land in East Continental Antarctica, the only extensive stretch of land to become snow free for 400km in either direction. They lie in the northeast of Vincennes Bay, and to the western side of the Law Dome (a small ice cap 1,300m high and 200km in diameter) on a north-south orientated length of coastline.
The area consists of 5 major peninsulas, the Clark, Bailey, Mitchell and Browning Peninsulas and Robinson Ridge, and a number of islands. The Vanderford Glacier, the major ice outlet for Law Dome, lies at the southern end of the region.
The first ANARE visit to the region was made in 1956. The United States of America established Wilkes Base at the western end of Clark Peninsula in 1957. In 1959, after the International Geophysical Year Program, Wilkes station was handed over to Australia, who maintained it until 1969 when Casey station was built on nearby Bailey Peninsula. In 1988 a replacement Casey Station was opened, following the decommissioning of the old Casey Station.
Murray and Luders (1990) classified the islands into 3 groups based on their topography.
- Those situated off Clark, Bailey and Mitchell Peninsulas are mostly low lying and gradually increase in altitude towards the south.
- The offshore Donovan and Frazier islands to the north have extensive cliffs jutting from the sea.
- The islands between Mitchell Peninsula and the Vanderford Glacier are steep and rough, and have tall cliffs rising up from the deep waters of the southern part of the bay. Some of these islands reach 100m in altitude.
The peninsulas are typically comprised of low, rounded hills (maximum altitude of approximately 100m) and intervening valleys filled with snow or moraines and detritus (Goodwin 1993, Melick, et al 1994, Melick and Seppelt 1997).
The geology of the Windmill Islands has been described by Post et al (1995) as consisting of a multiply-deformed supracrustal sequence, which is intruded by minor porphyritic granites and extensive charnockites. A north-south metamorphic grade is present in the region (Paul and Stüwe 1995) and four major phases of deformation have been recognised. Paul et al (1995) have noted that the Windmill Islands have been subject to repeated tectonothermal activity. Blight and Oliver (1977, 1982) listed 3 main types of bedrock from the area. These are:
- The Windmill Metamorphics,
- The Ardery Charnockite,
- The Ford Granite.
The most extensive of these is the Windmill Metamorphics, which consists of gneisses, schists and migmatites. These are intruded by the Ardery Charnockite which forms an arc sweeping from Robinson Ridge, through Odbert, Ardery, Holl and Peterson Islands to Browning Peninsula. The Ford Granite occupies a small area of Ford and Cloyd Islands. Additionally, two small swarms of dolerite dykes cut through the area. Goodwin (1993) has estimated the uplift rates of the region to be in the vicinity of 0.5–0.6mm per year.
During the Pleistocene period (the last one million years), the Windmill Islands were heavily glaciated (Goodwin 1993, Melick and Seppelt 1997), and covered by an ice sheet approximately 400m thick. The last glacial maximum was approximately 18,000 years ago. At this time the eustatic sea level would have been lower by about 125m. The Vanderford Glacier would have occupied the deep trough in Vincennes Bay to the south of the islands (Cameron 1964), and would also have been responsible for the shaping of a number of U shaped valleys on Holl and Peterson Islands and Browning Peninsula (Goodwin 1993).
Deglaciation of the islands occurred in two separate stages. The southern islands and Browning Peninsula were the first to be free of ice, about 8000 years ago. The northern islands and the remaining peninsulas became ice free around 5500 years ago (Goodwin 1993). Since deglaciation, the Antarctic continent has undergone a period of cooling and drying (Melick and Seppelt 1997).
The climate of the Windmill Islands has been described as frigid-Antarctic (Melick, et al 1994). The mean temperatures for the warmest and the coldest months are 0.3°C and −14.9°C respectively. The extremes of temperature range from 9.2°C and −41°C. Annual precipitation is 175mm a year (rainfall equivalent), which falls primarily as snow, but rain may occasionally fall during the summer. There are approximately 96 days of gale force winds (greater than 54km an hour) a year (Melick, et al 1994). Winds blow principally from the east and east-north-east off Law Dome, or from the south. Wind gusts up to 100km an hour are common (sometimes reaching 160km an hour), but regular katabatic winds (except off the Vanderford Glacier) are rare (Murray and Luders 1990).
During the winter, the sea ice is quite sound, but due to the strong winds is generally safe only for foot travel or light all terrain vehicles. In the Casey station area, the sea ice typically lasts until early January before it breaks out (Woehler et al 1991). Murray and Luders (1990) have also noted that fewer snow drifts accumulate on north facing slopes in the region. In the summer (December and January) there is a high incidence of daily sunshine (Smith 1988) and meltstreams and pools of freshwater are common (Melick et al 1994).
Within the Windmill Islands there exists a diverse and rich mammalian and avian fauna. Studies and surveys of the mammalian fauna have been conducted by Murray and Luders (1990), while records of the avian fauna have been collected by Orton (1968), Franeker et al (1990), Murray and Luders (1990), Woehler et al (1991, 1994) and Melick and Bremmers (1995). The soil fauna has been catalogued by Petz and Foissner (1997). Mammals recorded in the area thus far are:
Weddell seals can be found in the area year round, and until 1970, 50-90 seals were killed each year to provide meat for the stations dogs. Crabeater seals and leopard seals can typically be found in the region after spring when the sea ice has begun to break up. Leopard seals particularly become more common in the area once the Adélie penguins return to the islands. Southern elephant seals may be sighted throughout the year, coming ashore on Browning Peninsula and Peterson Island to moult and breed.
The birds recorded from the Islands are:
- Emperor Penguins
- Adélie Penguins
- Southern Giant-petrels
- Cape petrels
- Southern fulmars
- Antarctic petrels
- Snow petrels
- Wilsons storm-petrel
- South polar skuas
- Kelp gulls
Emperor penguins are regular visitors to the Islands (Murray and Luders 1990) and they have established a small breeding colony on sea ice amongst grounded icebergs in the Peterson Bank area (Melick and Bremmers 1995). They are winter breeders and remain in the area for the entire year.
Adélie penguins are by far the most numerous of the bird species present in the Windmill Islands. In the past they have occupied colony sites on the peninsulas, but are now primarily confined to the offshore islands, possibly due to isostatic rebound and uplift of the peninsulas since deglaciation. Woehler et al (1991) have estimated the Windmill Islands population of Adélie penguins to be 93,092 (plus or minus 9300) pairs, from 14 breeding localities. This represents an increase in numbers of around 209% since the early 1960’s.
Surveys by Woehler et al (1991, 1994) have shown that populations of Adélie penguins have been increasing at all locations throughout the Windmill Islands, except for the population at Shirley Island near Casey Station. The colony here increased at approximately the same rate as other colonies, but then stabilised when Casey Station was opened in 1969. This is probably due to the fact that Shirley Island is a popular place for Casey Station personnel to visit. This period of human visitation directly coincides with the courtship, egg laying, incubation and early brooding phases of the breeding cycle. It has been speculated by Woehler et al (1994) that the level of disturbance at these times each season has been sufficient to prevent an increase in the breeding population of the penguins on Shirley Island.
The tern species found in the region are Arctic Terns only, which come to the islands only to feed as part of their annual migration. Other than the emperor penguins, none of the bird species remain in the area over winter, although some species are occasionally sighted at unusual times.