Antarctic sea ice loss changes marine life

About 10 years ago, the amount of sea ice around Antarctica suddenly decreased.

After years of relatively stable sea ice cover, a vast ocean nearly the size of Greenland lost seasonal ice in just a few years. Initially, researchers thought the decline might be temporary. Today, however, this sudden, step-like decline is considered the beginning of a new “low ice age.”

The ecological consequences are profound. The pace of ice loss from 2016 to 2017 caught climate models and field researchers off guard. Most computer simulations struggle to capture sudden tipping point events, and rapid environmental changes leave scientists with little time to collect direct observations of how Antarctic organisms respond.

See changes from space
Funded by the ESA Earth Observation Science Society Biodiversity in the Open Ocean ProjectA team of researchers led by the UK’s Plymouth Marine Laboratory used satellite technology rather than traditional field surveys to tackle the problem.

The team analyzed data from the European Space Agency’s Climate Change Initiative ocean color schemeis a climate data record of ocean color measurements collected from various satellite missions designed to understand how sunlight reflects from the ocean surface at specific wavelengths, allowing them to infer biological conditions from space.

Using these optical signals, scientists divided the Southern Ocean into different seascapes, similar to how land landscapes are classified.

Each seascape reflects different biological conditions, revealing information about phytoplankton, the microscopic algae that form the basis of the Antarctic food web. Changes in reflected light indicate not only how much phytoplankton is present, but also which types are dominant.

this resultpublished in Marine Ecology Cross-Research Progress Seriesunexpected. Phytoplankton levels in large, remote areas of the Southern Ocean shifted from very low to moderately productive levels.

On average, nearly 70 percent of the region now has higher summer phytoplankton concentrations than before sea ice began to decline about a decade ago.

Krill and salps
Researchers also combined sea views acquired by satellite with krill basea large historical salp and krill database designed to examine how the new low-ice age has altered the feeding habitats of these key species.

Antarctic krill are shrimp-like crustaceans in the Southern Ocean, numbering approximately 800 trillion individuals (excluding eggs and larvae). They are found throughout the region and at all depths, and are a major food source for species ranging from brittle stars to large whales. By eating phytoplankton, they shape the food web and drive cycles of carbon, nitrogen and other essential elements. In fact, krill are a keystone species that provide food for penguins, whales, seals and fish.

Salps are jelly-like filter feeders that alternate between solitary lives and long-chain forms that can produce dense blooms. They’re also vital to ecosystems, tending to thrive when krill populations decline and may increase with climate change. Studying salps could reveal broader changes affecting krill and the wider ocean system.

winners and losers
At first glance, the increase in phytoplankton following reduced sea ice appears to be beneficial. However, sea ice provides shelter and nursery habitat and supports dense blooms of diatoms, a type of macroalgae that efficiently transfer energy into the Antarctic food web.

The apparent increase in food seemed to benefit the salps far more than the krill. But salps contain very little carbon, and they contribute less to transporting carbon into the deep ocean than krill, a key process in regulating Earth’s climate.

The new Antarctic reality
Scientists are only beginning to understand how this emerging low-ice age will reshape Antarctic ecosystems.

Because salps are not commercially fished, contribute differently to carbon storage, or support alternative food webs compared to krill, long-term shifts in dominance between these species could alter nutrient cycling and ecological relationships throughout the Southern Ocean.

The ongoing transformation shows that Antarctic ice sheet changes are not only a physical signal of climate change but also a driver of deep biological reorganization in one of Earth’s most important marine environments.

In this ESA-funded study, satellite data provided continuous, large-scale and long-term monitoring of the Southern Ocean, making it an important and uniquely powerful tool.

They provide a better understanding of how the loss of Antarctic sea ice is rapidly reshaping the feeding habitats of two major plankton species, with profound consequences for the entire polar food web.

As Antarctica may enter a persistent low-ice age, ESA satellite data will be valuable in guiding future research and supporting conservation strategies and global climate policy.