Source: Earth Sciences New Zealand
A new study shows a significant change in Antarctic phytoplankton over time that could cascade through the marine food web and affect the ocean’s capacity as a carbon sink.
The study reveals that diatoms, a major group of microscopic phytoplankton, are declining across large areas of the Southern Ocean due to being outcompeted by smaller, less nutritious phytoplankton species.
Earth Sciences New Zealand (formerly NIWA) principal scientist Dr Matt Pinkerton says that as microscopic single-celled algae are the first link in the ocean food web and support krill, any changes to these phytoplankton communities may have a negative flow-on effect.
“Phytoplankton are often described as the ‘grass of the ocean’. These tiny marine algae sustain the Antarctic food web, supporting a diverse array of Antarctic life, from zooplankton to fish, seabed corals, and apex predators, including seals, whales, and penguins. Changes at the base of the marine food web will ripple through from the grazers of these algae to the whole system.”
The study in Nature Climate Change, was led by Dr Alexander Hayward, a former NIWA and University of Otago PhD student, who is now a climate scientist at the Danish Meteorological Institute in Copenhagen.
“We may be witnessing a fundamental reorganisation of life around Antarctica,” Dr Hayward said.
Satellite data, along with samples collected from the Ross Sea as part of New Zealand’s Antarctic Science Platform (ASP), were analysed together with data from other regions of the Southern Ocean. The researchers from Denmark, New Zealand, Australia, Spain and the USA, developed methods to track changes in different Southern Ocean phytoplankton communities over time.
The researchers found that the gradual increase in Antarctic sea-ice between 1997 and 2016 was accompanied by a change in the phytoplankton community. However, as the sea-ice subsequently decreased between 2016 and 2023, the phytoplankton community changed again.
Earth Sciences NZ principal scientist Cliff Law says the flow-on effects could also disrupt the ocean’s ability to lock away carbon.
“These billions of green cells in the surface ocean that nobody really thinks about are absolutely vital. The diatoms are particularly important in sequestering carbon, absorbing it at the ocean surface and carrying down to the deep as they sink, thereby locking it away from the atmosphere.”
Dr Pinkerton says projecting the future effects of climate change on Antarctic ecosystems is complex but critical.
“Understanding how Southern Ocean phytoplankton communities respond to climate change will help us to prepare for flow-on effects on the rest of the ecosystem. Our research has developed advanced food web models for the Ross Sea region. These new models include more information and have a better consideration of uncertainties in order to make them more useful for informing decision-making about marine management.”
Research into the impact of climate change on plankton and marine food webs in the Ross Sea will continue as part of the Antarctic Science Platform Tranche 2, with further research voyages of Earth Sciences New Zealand’s RV Tangaroa to this region. The scientists say increased use of sensors on unmanned buoys (ARGO) and satellite data will improve understanding of how changes in sea ice may result in ecosystem change.