As summer rolls around each year, cold, nutrient-rich water from the deep sea is driven up to the surface of a section of ocean off the coast near south-west Victoria, giving marine life a crucial “kick along” and ultimately feeding species such as little penguins.
- The Bonney Upwelling takes place annually along the coast from south-west Victoria to South Australia
- The oceanic phenomenon that provides food for marine life ran late this year because of a Sudden Stratospheric Warming in Antarctica
- It is possible animal populations such a little penguins skipped breeding due to the change
But last summer, this process, known as the Bonney upwelling, ran more than a month late, and scientists believe its tardy arrival can be traced back to a warm snap in Antarctica last year known as a sudden stratospheric warming.
Specialists, working with marine species that live along the coast, are still trying to understand how the delay has affected animals that rely on the annual upwelling, which stretches from the Portland coast in Victoria to Robe in South Australia.
The Bureau of Meteorology has already attributed a reduction in the size of the hole in the ozone layer and the hot, dry summer, particularly in eastern Australia, to the sudden warming in Antarctica’s stratosphere.
But biological oceanographer Paul van Ruth, who works in the South Australian Research and Development Institute’s aquatic science research division, believed there was also a clear link between the warming’s effect on wind and the late arrival of the Bonney upwelling.
“Generally, what we would expect would be that westerlies would stop persisting in southern Australia through November and December as we turn towards getting more south-easterly winds through the change of seasons from spring to summer,” he said.
“But this year what happened was the sudden stratospheric warming caused those westerly winds to linger for a lot longer through the season.”
Dr van Ruth said rather than seeing the inundation of cold water indicating the start of the upwelling in early November, it did not arrive until late December.
The upwellings that exist around the world underpin some of the most concentrated, productive areas for marine life, and the Bonney upwelling is no exception.
“That water that comes from the deep ocean is rich in nutrients, so when those nutrients are brought up the phytoplankton at the start of the food web, the plants, can use that for photosynthesis and we get a whole lot of productivity.”
Dr van Ruth said the delay in the upwelling would have had flow-on effects across the ecosystem.
“That’s what the food web banks on to really get it going,” he said.
Little penguin colony had poor breeding season
Warrnambool’s colony of little penguins has been made famous by a unique project which uses trained Maremma dogs to protect the birds from the fox attacks that have ravaged the population over the years.
Middle Island Penguin Project coordinator, Trish Corbett, said this year the penguins arrived in late December, rather than a month or so earlier, and there was almost no breeding during their time on the island.
“So they’ve got good enough food so that they’re heavy enough to put the energy into reproduction.”
Dr Corbett said the later than usual start to upwelling was likely to have had an impact on the penguins’ food availability, and it was “very possible” that is why they did not arrive until late December.
The birds also went into an early moult.
A group of hundreds of thousands of mutton birds, or short-tailed shearwaters, made headlines late last year when they failed to arrive at Port Fairy’s Griffiths Island in late September as usual.
The birds migrate annually from the northern hemisphere and arrive like clockwork, but they arrived in very small numbers and were starving and in poor health.
BirdLife Warrnambool president, Peter Barrand, said although the mutton birds’ problems originated in the northern hemisphere, the upwelling running late which has led to a lack of food was likely to have “exacerbated the already dire straits they were in”.
Pygmy blue whales feed during the upwelling
Blue whale study senior research scientist, Peter Gill, said numbers of the pygmy blue whales, that feed off krill during the Bonney upwelling, have been diminishing since 2012.
He said that has made it difficult to tell what impact one late season would have.
“There’s been a very clear relationship over the years between the pygmy blue whales arriving and the upwelling,” Dr Gill said.
Dr Gill said his March aerial survey showed disappointing results, as there were no signs of the species of krill the whales feed on, and just a few blue whales in transit outside their usual feeding area.