During the ice ages, so much of Australia dried out that scientists have wondered how species that require permanent water survived. The discovery North Stradbroke Island's wetlands have been a refuge for water-loving plants and animals for some 200,000 years provides an answer. The discovery could fill one of the biggest missing pieces in the global climate record, revealing how eastern Australia changed over that period. Previously this had to be extrapolated from elsewhere and a handful of sites, many of them discontinuous, from the extremities of the continent.
When ice sheets covered much of North America and Eurasia, the oceans retreated with missing water. Parts of the world that are now close to the coast were often part of an arid interior. The colder conditions also meant less evaporation and therefore rain. Australia, so much of which is dry even today, was particularly affected.
Besides the question of how species reliant on permanent water survived, the absence of long-standing wetlands has been a challenge for paleoclimatologists. Ice cores provide a record of changing conditions in Antarctica and Greenland, and sediments at the bottom of lakes offer something similar for other continents, but what does one do where neither is available?
Look harder, it seems, and North Stradbroke Island, near Brisbane, rewarded the search. “There are more wetlands on North Stradbroke Island dating to the last ice age than anywhere else in Australia," said the University of Adelaide's Dr John Tibby in a statement. Tibby is first author of a paper in the Journal of Quaternary Science revealing the age of the site.
"We cored and dated 16 wetlands on the island and found six dating to the Ice Age or earlier, with one being more than 200,000 years old," said co-author Dr Jonathan Marshall of the Queensland Department of Science, Information Technology, and Innovation. These cores produced resolution well above those at Australia's other sites.
The fact the wetlands predate human habitation of Australia means the oldest cores may reveal the influence Indigenous Australians had on the local landscape – something also seen in cores taken on islands off Tasmania announced the same day.
More immediately, the discovery is proving a treasure trove for exploring how the local climate has changed. “We’re using the chemicals in leaves to determine past rainfall, and fossil algae to tell us how the water in the wetlands has changed," Tibby said. "Using this information, we can glean insights into whether climate changed at the same time Australian megafauna went extinct. Previously, efforts to determine the climate at particular points in Australia's past relied on measurements taken as far away as Antarctica.
The wetlands' extraordinary longevity has been attributed to connections to local groundwater, sustaining them through periods of drought.