University of Otago marine science researcher Dr Pete Russell and University of Auckland physics researcher Dr Christopher Horvat said Oma passed near Vanuatu in 2019, and while it was "a relatively benign cyclone", it produced a massive and "exceedingly rare" phytoplankton bloom that occurred only once every 1500 years.
Dr Russell said it was the single most abnormal event in the history of South Pacific chlorophyll measurements.
"Such an extreme event can produce a large amount of biomass in a part of the ocean that is typically a biological desert.
"We don’t yet know about the fate of this biomass, but one possibility is that it could end up on the bottom of the ocean, sequestering carbon."
He said cyclones were one of the mechanisms that dissipated heat from the tropics.
Warming oceans meant more heat to dissipate, and this meant more intense storms and perhaps longer storm seasons, resulting in more storms.
"By examining sediment cores from the last inter-glacial period, we may get a heads up on what cyclone activity to expect with ocean temperatures 1-plus degrees higher than today," he said.
The pair discovered that if a storm hovered above a patch of ocean long enough, physical interactions between the cyclone winds and ocean would cause water to rise near its eye, bringing nutrient rich water to the surface which seeds a phytoplankton bloom.
Dr Horvat said these events may be biological hotspots, causing large amounts of biological material to be produced in areas typically devoid of upper-ocean life.
"These cyclones can do amazing things. Other than have strong winds, they can also dramatically affect the plants and animals living in the upper ocean and change the cycling of carbon by leading to blooms.
"Along with these bloom events in the open ocean, cyclone activity results in both coastal upwelling and runoff from the land that also deliver nutrients into the photic zone, generating blooms.
"These blooms could be an integral part of the local marine ecosystems of our Pacific neighbours, supporting higher food chains."
The duo said they knew too little about the blooms to declare them as being good or bad, but believed there was potential for them to support open ocean ecosystems that were nutrient limited. They hoped to investigate this further — in particular, the influence on fisheries for Pacific islands.
