White blooms of plankton appearing east of New Zealand suggest the ocean is responding to climate change, according to research by Victoria University scientists.
Doctorate student Bella Duncan investigated coccolithophores, a white algae with remains known as coccoliths, as part of her master's degree.
Under favourable, warm conditions, these algae grow rapidly and turn the ocean's surface milky white, a natural phenomenon known as a "bloom".
Ms Duncan says satellite and ship-based observations show coccolith blooms are moving south as the ocean warms and becomes less turbulent.
She says the movement is similar to 130,000 years ago, when the last major warm period occurred.
"Our results show that during that last warm period, when the ocean was about one to two degrees warmer than present, sediments on the seabed were mainly made up of coccoliths," she said.
Professor Lionel Carter, who co-supervised the research, said coccoliths were deposited on the ocean floor and formed white mud similar to the White Cliffs of Dover.
The iconic British landmark was also formed during a warm period 70 million years ago.
"The same process appears to be happening now, suggesting the New Zealand ocean is currently responding the present phase of global warming," Prof Carter said.
"This is also a trend that has been increasingly observed in other parts of the world."
Prof Carter said the ramifications on fish stocks, uptake of carbon dioxide and general ocean health had yet to be evaluated, but "it is clear that change is under way".
The study has been published in the international journal Global and Planetary Change.