Shrinking ice is arguably one of the most visible indicators of climate change – particularly in the Arctic. However, a European Space Agency-funded study used information from satellites to show that Antarctica is now experiencing similar dramatic changes, with profound consequences for key plankton species that underpin the region’s marine food web.
About 10 years ago, the amount of sea ice around Antarctica suddenly declined.
After many years of relatively stable sea-ice coverage, an expanse of ocean nearly the size of Greenland lost its seasonal ice within just a few years. At first, researchers thought the decline might be temporary. Today, however, this abrupt, step-like drop is understood to have been the onset of a new ‘low-ice era’.
The ecological consequences are profound. The speed of ice loss in 2016–2017 caught both climate models and field researchers off guard. Most computer simulations struggle to capture sudden tipping-point events, and the rapid environmental change left scientists little time to collect direct observations of how Antarctic organisms were responding.
The team analysed data from ESA's Climate Change Initiative’s Ocean Colour Project, a climate data record of ocean colour measurements collected from a variety of satellite missions, to see how sunlight reflects off the ocean surface at specific wavelengths, allowing them to infer biological conditions from space.
Using these optical signals, scientists categorised the Southern Ocean into different seascapes, similar to the way landscapes on land are classified.
Each seascape reflects distinct biological conditions, revealing information about phytoplankton – microscopic algae that form the foundation of Antarctic food webs. Variations in reflected light indicate not only how much phytoplankton is present but also which types dominate.
The results, published in Inter-Research Marine Ecology Progress Series, were unexpected. Large and remote regions of the Southern Ocean shifted from extremely low phytoplankton levels to more moderate productivity.
On average, nearly 70% of the region now supports higher summer phytoplankton concentrations than before the sea-ice decline began about ten years ago.
Antarctic krill are shrimp-like crustaceans of the Southern Ocean, numbering about 800 trillion individuals (excluding eggs and larvae). Found throughout the region and at all depths, they are a key food source for a wide range of species from brittlestars to great whales. By grazing on phytoplankton, they shape food webs and drive cycles of carbon, nitrogen and other essential elements. In effect, krill are a cornerstone species, feeding penguins, whales, seals and fish.
Salps, jelly-like filter feeders, alternate between solitary life and long chain formations that can bloom densely. They are also vital to the ecosystem, often thriving when krill decline and potentially increasing with climate change. Studying salps can reveal broader shifts affecting krill and the wider marine system.
This apparent boost in food seems to be benefiting salps much more than krill. But Salps contain little carbon and contribute less to transporting carbon to the deep ocean than krill – a process crucial for regulating Earth’s climate.
Because salps are not commercially harvested, contribute differently to carbon storage, or support alternative food webs compared with krill, a long-term shift in dominance between these species could alter nutrient cycles and ecological relationships across the Southern Ocean.
The transformation underway suggests that Antarctica’s changing ice cover is not only a physical signal of climate change but also a driver of deep biological reorganisation in one of Earth’s most important marine environments.
In this ESA-funded study, satellite data provide continuous, large-scale, and long-term monitoring of the Southern Ocean, making them an essential and uniquely powerful tool.
They enable a better understanding of how rapid Antarctic sea-ice loss is reshaping the feeding habitats of two key plankton species, with far-reaching implications for the entire polar food web.
As the Antarctic probably enters a lasting low-ice era, satellite data from ESA will be highly valuable to guide future research and support conservation strategies and global climate policy.
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