S. Anna Florin, University of Wollongong; Andrew Fairbairn, The University of Queensland; Chris Clarkson, The University of Queensland; James Shulmeister, University of Canterbury; Nicholas R Patton, University of Canterbury, and Patrick Roberts, Max Planck Institute for the Science of Human History
Archaeological research provides a long-term perspective on how humans survived various environmental conditions over tens of thousands of years.
In a paper published today in Nature Ecology and Evolution, we’ve tracked rainfall in northern Australia’s Kakadu region over the past 65,000 years. We wanted to know how major changes in rainfall may have affected the region’s Aboriginal communities through time.
Our findings suggest the Kakadu region wasn’t as prone to dry spells as surrounding areas — and it likely functioned as a place of refuge for early Australians as they struggled through harsh and arid conditions.
To generate a rainfall record spanning 65,000 years, we used ancient food waste left behind by the First Australians living at Madjedbebe, a rock shelter on Mirarr country in the Kakadu region.
This site boasts the earliest known evidence of humans living in Australia. It also boasts plenty of Pandanus spiralis, a native plant commonly called “pandanus” or “screw pine”.
This plant, known as “anyakngarra” to the Mirarr people — the Traditional Owners of Madjedbebe — is very important to them.
Its leaves are used for weaving, its trunk to create dye, its fruit flesh is used in a drink and its nuts (the seed kernels within the fruit) are consumed as a rich source of fat and protein.
Anyakngarra’s nuts were also eaten by the First Australians 65,000 years ago. Discarded nut shells have been preserved as burned fragments, disposed of in fireplaces over time.
These small remnants have proven hugely useful for our research team, which includes archaeologists, environmental scientists and Traditional Owners.
By analysing the isotopic composition in ancient anyakngarra nutshells, we could track rainfall at Madjedbebe. Specifically, we detected how much water (and therefore rainfall) was available to anyakngarra plants in the past.
This analysis is possible due to photosynthesis – the process by which plants convert carbon dioxide in the air into sugars. Anyakngarra plants absorb two isotopes of carbon from the atmosphere: ¹²C and ¹³C. Isotopes are different types of atoms within a chemical element that have the same number of protons but a different number of neutrons. Chemically, the isotopes of carbon are the same, but each has a different atomic “weight”.
Explainer: what is an isotope?
When environmental conditions are favourable, an anyakngarra plant will preferentially absorb more ¹²C than ¹³C. But if a plant is stressed by its environment, such as when it’s waterlogged due to seasonal flooding, it begins to absorb more ¹³C.
The isotopic composition (the ratio of ¹²C to ¹³C) is recorded in the sugars used by the plant for new tissue growth, including for the seasonal growth of nuts.
A higher proportion of ¹³C in a nutshell indicates that the plant it came from was waterlogged during its growth season. From this, we can conclude it likely experienced higher levels of rainfall.
Over the past 72,000 years, humans have lived through an ice age in which there were two particularly cold periods called “stadials”. During stadials, glaciers extended to cover parts of North America, northern Europe, northern Asia and Patagonia (in South America).
The height of the second stadial in this ice age was called the Last Glacial Maximum. While this occurred 22,000 to 18,000 years ago, intense cold and dry conditions in Australia started as early as 30,000 years ago.
During this time, water availability was the main challenge in arid northern Australia (rather than low temperatures). The country’s arid zone expanded dramatically and parts of central Australia may have been temporarily abandoned by Aboriginal people.
Yet the “palaeoclimatic” record we generated for Madjedbebe indicates that, although glacial stages did lead to less rainfall, the Kakadu region remained relatively well-watered during these periods.
Our records show that for as long as people have been around, rainfall at Madjedbebe is unlikely to have dropped below current levels. Thus, this area would have helped early Australians survive during long dry spells and may have also attracted others from surrounding areas.
Our findings are supported by other archaeological evidence from Madjedbebe. For instance, our research has revealed more stone tools were left at this site during the glacial periods. This implies more people gathered there at these times.
Also, because the Kakadu region was still drier during glacial periods as compared to inter-glacial periods, people had to travel further for food and other important resources.
This is supported by evidence of an increased number of tools being brought to the site from further away. This points to increased mobility and new social arrangements being made as people adjusted to life in a harsher environment.
Notably, over the past 65,000 years the driest time in the Kakadu region was not during the Last Glacial Maximum. It is today.
Rather than being the result of less rainfall occurring, this is likely due to higher evaporation caused by warmer inter-glacial temperatures. Aboriginal communities currently living in the Kakadu region are experiencing unprecedented aridity.
These difficult conditions are exacerbated by the threat of invasive plants and animals and disruption to cultural practices of landscape management, such as vegetation burning.
While the people of Kakadu have spent thousands of years adapting to environmental change, the scale and intensity of today’s anthropogenic impacts on regional climates and local landscapes poses an altogether different challenge.
S. Anna Florin, Research fellow, University of Wollongong; Andrew Fairbairn, Professor of Archaeology, The University of Queensland; Chris Clarkson, Professor in Archaeology, The University of Queensland; James Shulmeister, Professor, School of Earth and Environmental Sciences, University of Canterbury; Nicholas R Patton, Ph.D. Candidate, University of Canterbury, and Patrick Roberts, Research Group Leader, Max Planck Institute for the Science of Human History
In recent months, three humpback whales were spotted in the East Alligator River in the Northern Territory’s Kakadu National Park. Contrary to its name, the river is full of not alligators but crocodiles. And its shallow waters are no place for a whale the size of a bus.
It was the first time humpback whales had been recorded in the river, and the story made international headlines. In recent days, one whale was spotted near the mouth of the river and scientists are watching it closely.
The whales’ strange detour threw up many questions. How did they end up in the river? What would they eat? Would they get stuck on the muddy river bank?
And of course, there was one big question I was repeatedly asked: in an encounter between a crocodile and a humpback whale, which animal would win?
The humpback whales were first spotted in September this year by marine ecologist Jason Fowler and fellow scientists, during a fishing trip. Fowler told the ABC:
I noticed a big spout, a big blow on the horizon and I thought that’s a big dolphin … We were madly arguing with each other about what we were actually seeing. After four hours of raging debate we agreed we were looking at humpback whales in a river.
The whales had swum about 20 kilometres upstream. Fowler photographed the humpback whales’ dorsal fins as evidence, and reported the unusual sighting to authorities and scientists.
Thankfully, two whales returned to sea on their own, leaving just one in need of help. There was concern it might become stranded in the shallow, murky tidal waters. If this happened, it might be attacked by crocodiles – more on this in a minute.
Experts considered a variety of tactics to encourage the whale back out to sea. These included physical barriers such as nets or boats, and playing the sounds of killer whales – known predators of humpback whales.
But none of these these options was needed. After 17 days, the last whale swam back to sea on its own.
The whale that spent two weeks in the river has recently returned and been spotted swimming around the mouth of the river. It appears to have lost weight – most likely the result of migration. It is now being monitored nearby in Van Diemen Gulf.
Questions are now being raised about the health of the animal, and why it has not headed south for Antarctic feedings waters.
There are various theories as to why they swam into the East Alligator River. Humpback whales are extremely curious, and may have entered the river to explore the area.
Alternatively, they may have made a navigation error – also the possible reason behind September’s mass stranding of pilot whales in Tasmania.
Long-term, a humpback whale’s chances of surviving in the East Alligator River are slim. The lower salinity level may cause them skin problems, and they may become stranded in the shallow waters – unable to move off the muddy bank. Here the animal might die from overheating, or its organs may be crushed by the weight of its body. Or, of course, the whale may be attacked by crocodiles.
In this case, my bet would be on the whale – if it was in relatively good condition and could swim well. Humpback whales are incredible powerful creatures. One flick of their large tail would often be enough to send a crocodile away.
If a croc bit a whale, their teeth would likely penetrate the whale’s skin and thick blubber. But it would take a lot more to do serious harm. Whale skin has been shown to heal after traumatic events, including the case of a humpback whale cut by a boat propeller in Sydney 20 years ago. Dubbed Bladerunner, it survived but still bears deep scars.
The whale sighting continues to fascinate experts. Scientists are hoping to take poo samples from the whale in Van Diemen Gulf, and could also collect whale snot to learn more about its health. However, the best case scenario would be to see the whale swim willingly to offshore waters.
This unusual tale will no doubt go down in Australian whale history. If nothing else, it reminds us of the vulnerability – and resilience – of these marine giants.
The author would like to thank Northern Territory Government whale expert Dr Carol Palmer for her assistance with this article.
Can a uranium mine be rehabilitated to the environmental standards of a national park and World Heritage site?
That’s the challenge faced by the controversial Ranger uranium mine inside Kakadu National Park.
Kakadu has been a national park since the 1970s, but the Ranger mine, while surrounded by Kakadu, has never formally been part of the park. This classification is in the interests of resource extraction, and has failed to recognise or protect the area’s cultural and environmental values.
Kakadu National Park encompasses a precious natural heritage. It protects valuable ecosystems of outstanding value, diversity and beauty, and contains the world’s richest breeding grounds for migratory tropical water birds.
Recent diggings and studies have documented at least 65,000 years of continuous human habitation at a site on the land of the Mirarr people – this is currently the oldest occupation site in Australia.
The boundaries of Kakadu National Park were conveniently drawn around the Ranger mine site through a series of political and administrative negotiations following the Fox Inquiry, which gave a cautious green light for the Ranger operation.
Now, as the mining stops and the repair begins, mining companies and government regulators are being tested on their environmental commitment, and capacity to make meaningful change.
But rehabilitating what is essentially a toxic waste dump is no easy task.
And the inadequacy of the Energy Resources of Australia’s Mine Closure Plan – the key document guiding the rehabilitation – shows they are failing this test so far.
Our new research report – jointly conducted by Sydney Environment Institute and the Australian Conservation Foundation – examines the Mine Closure Plan and finds it is seriously wanting in key areas.
These include significant data deficiencies regarding management of mine tailings (mine residue), land stability, and modelling of toxic contaminants likely to flow off site into Kakadu National Park.
The Mine Closure Plan is almost completely silent on crucial governance questions, such as the Ranger mine’s opaque regulatory processes and rehabilitation, and current and future financing – especially in relation to future site monitoring and mitigation works.
After the price collapse following the Fukushima nuclear crisis, times in the uranium trade have been tough. Coupled with a mandated end to commercial operations by early 2021, Rio Tinto has accepted the era of mining has now been replaced by the need for rehabilitation.
But the challenge for Energy Resources of Australia and Rio Tinto, who own and operate the mine, is not simply to scrape rocks into holes and plant trees. It is to ensure radioactive and contaminated mine tailings are:
physically isolated from the environment for at least 10,000 years [and that] any contaminants arising from the tailings will not result in any detrimental environmental impacts for at least 10,000 years.
These are time-scales of epic proportions, yet the Mine Closure Plan says little to assure the public this can be achieved.
In fact, Energy Resources of Australia concedes it won’t actually be possible to monitor and measure this over the next 10,000 years, so a model will be required instead. But this model has not been publicly released.
And this speaks to a broader problem with the whole process: the success of the rehabilitation will be judged by criteria created by the mining company.
It is naive to assume a mining company is best placed to propose their own rehabilitation criteria, given their corporate imperative to reduce rehabilitation costs and future liabilities.
And the stakes here are very high. The rehabilitation of Ranger will be a closely-watched and long-judged test of the credibility, competence and commitment of the regulators and the mining companies.
The Supervising Scientist Branch – a federal agency charged with tracking and advising, but not regulating, the Ranger operation – also made an assessment that should be ringing alarm bells:
[The company’s current plan] does not yet provide sufficient evidence to demonstrate that the current plan for rehabilitation of the Ranger mine site will achieve the required ERs [Environmental Requirements].
The Supervising Scientist Branch’s disturbing initial analysis is a red flag demanding an effective response.
The Conversation reached out to Energy Resources of Australia for a response to this story. A spokesperson told The Conversation the company is committed to the “full rehabilitation” of the Ranger Project Area:
Energy Resources of Australia (ERA) has committed to update the Closure Plan and submit for approval on an annual basis. Updates to the Closure Plan will be made publicly available.
As noted by ERA at the time of release of the Ranger Mine Closure Plan, there are some aspects of closure planning that will be further developed and refined as a result of ongoing studies and consultation. These will be reflected in future updates to the Closure Plan.
ERA is committed to rehabilitate the Ranger Project Area in accordance with the Environmental Requirements as set out in relevant regulations. The final close out of rehabilitation can only occur when the Commonwealth Minister, on advice of the Supervising Scientist and Traditional Owner representatives, is satisfied that the Environmental Requirements have been met.
Australia has a long history of substandard mine closure and rehabilitation in both the uranium and wider mining sector.
There is a real need to see a better approach at Ranger, and the first step in that journey is by increasing the scrutiny, accountability and transparency surrounding this essential clean up work.
This article was updated at 12.25pm, May 7, to include a response from Energy Resources of Australia.