Palaecol Research Ltd
The past is key to the future!
Norfolk Island Research
Conservation and restoration
Nutrient sources and pathways
Norfolk Island is a semi-autonomous Australian territory in the northern Tasman Sea. The cluster of three main islands and offshore stacks lies astride the Tasman Front, just south of the Tropic of Capricorn. Cooler subantarctic water meets warmer subtropical Pacific water around the islands, and the islands’ seabird fauna includes species characteristic of both water masses. The red-tailed tropicbird (right) is one of the subtropical species breeding on the Norfolk Island group.
The Norfolk group is a mid-ocean volcano, whose submerged sides are 2000 m high. The oldest basalt rocks exposed at the surface were erupted about 3 million years ago, and the massif has been remarkably stable since then. The islands are the highest points of a much larger plateau that is exposed during glacial events, when sea level is 120-150 m lower than at present. The land area has usually been much greater, nearly 90X greater, than it is now. The present arrangement developed about 10,000 years ago, as sea level rose with the melting of the great ice sheets of the Northern Hemisphere. The rising sea isolated many plants and animals on Norfolk, Phillip, and Nepean Islands, but most of the vegetation was drowned. Those changes are likely to have resulted in the extirpation of local populations of plants and probably in the extinction of others. Extirpations are indicated by the presence of “endemic” plants now found only on either Norfolk or Phillip Islands, but whose ranges were continuous a few thousand years before.
The plants and animals were already living on a fraction of their normal range when humans arrived. Peoples’ activities have now restricted the vegetation and animals even more. The new process of restriction and extinction began with the arrival of early Polynesian voyagers at least 1000 years ago. Several plants and birds, for example, now survive in just a few hectares.
Throughout their pre-human history, the islands were home to millions of burrow-nesting seabirds whose droppings and bodies fertilized the soil. The vegetation and invertebrate fauna developed and evolved in the presence of massive quantities of nutrients brought ashore from the surrounding ocean. The elimination of most of the breeding colonies on the Norfolk Island itself is a significant factor in the continuing degradation of the vegetation. Without the seabird guano, the weathered, phosphorus-poor soils cannot support the same diversity of plants and invertebrates as before.
The seabirds were exterminated and extirpated by humans and the mammals that travelled with them to Norfolk Island. The earliest Polynesian settlers brought the Pacific rat Rattus exulans). This small rodent, which migrating humans spread over more than half the Earth’s surface over the past 4000 years, is implicated in the extinction of small birds, lizards, frogs, mammals, and invertebrates throughout the Pacific.
The plants and invertebrates are also under pressure from introduced rodents.
Importance of Norfolk Island to monitoring global warming
Changes in the Tasman Front’s position across the narrow Tasman will reflect the progress of global warming.
The Tasman Sea is rather like the gauge on the side of a boiler… a narrowing which means that the latitude of the Front should move in response to the overall changes which may be obscured by larger circulation patterns in the open ocean.
We have begun tracking some of the pelagic seabirds that nest on Norfolk Island, to see where they go on their migrations and where the obtain food during the breeding season. This information will help the conservation of these remarkable birds, and contribute to understanding of the oceanic food web.
Nutrient sources and pathways
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