Changing Life: Ocean

Almost all Antarctic life begins and ends in the Southern Ocean.

As the global climate changes, the Southern Ocean is becoming warmer and more acidic, with impacts on many Antarctic species.

On the west coast of the Antarctic Peninsula, this is happening faster than almost any other place on earth.

On the Peninsula, scientists report that the ice-loving phytoplankton communities that underpin Antarctic ecosystems are changing.

Some colonies of ‘true’ Antarctic species, such as Adélie penguins, have relocated, while species adapted to warmer conditions flourish.

Antarctic surface temperature trends for 1957-2006 — Temperature increase in Antarctica between 1957 and 2006, measured in degrees Celsius. Image credit: NASA

The Antarctic Peninsula is one of the most rapidly warming places in the Southern Hemisphere, and the waters off its western shores are warming faster than almost any other place on earth. Rising sea temperatures, changing ocean chemistry and declining winter sea ice are causing a cascade of changes in marine ecosystems around the Antarctic Peninsula. Antarctic researchers are reporting massive disruptions to ecological processes with changes to entire communities, especially those living on the Antarctic Peninsula. The rapid rate of change is putting immense pressure on local species to adapt, relocate or face local extinction.

One of the most visible impacts of the climate crisis on the Antarctic Peninsula has been the dramatic decline in Adélie and chinstrap penguin colonies.

The number of Adélie and chinstrap penguins in breeding colonies across the northern Antarctic Peninsula and South Shetland Islands has plummeted since the 1980s. Population counts at some colonies in 2019 recorded a decline of well over 50 percent in 40 years, with some estimates as high as 80 percent.

The speed and severity of the changes observed in some Antarctic penguin populations have astonished researchers, who raised the alarm about the impacts of a changing climate on Antarctic ecosystems. Further investigation revealed the whole Southern Ocean food web around the Antarctic Peninsula was undergoing rapid change.

Antarctic krill are in decline

Since the 1970s, the number of krill around the Antarctic Peninsula has decreased dramatically.

While Antarctic krill thrive across the Southern Ocean, the largest populations are found in the southwest Atlantic Ocean. This region is also where the majority of commercial krill fishing takes place. In parts of this area, some estimates suggest numbers have declined by 70 to 80 percent since the 1970s. The collapse of Adélie and chinstrap penguin colonies in this region has also been linked to shrinking krill populations.

Research has shown that as the Southern Ocean becomes more acidic, it may become more difficult for krill larvae to develop and hatch successfully.

Early research also suggests that climate change could reduce the size of krill by almost half, reducing the amount of food available for larger predators like penguins, seals and whales.

As krill decline, salps have moved in to fill the void. Salps are gelatinous zooplankton made mostly of water, and offer little nutritional value to penguins, seals and whales. Unlike Antarctic krill, salps thrive in ice-free waters, and are found all around the world.

Phytoplankton bloom off chatham islands_ Jeff Schmaltz MODIS Land Rapid Response Team

Phytoplankton communities are changing

The dominant types of phytoplankton (microscopic plants) are changing, and the overall biomass of phytoplankton is decreasing.

Across the Antarctic Peninsula there has been a shift from large phytoplankton (such as diatoms, which are a preferred food source for krill) to smaller varieties, which are favored by salps. Read the research.

Image credit: NASA

The ocean around parts of Antarctica is warming rapidly, mostly due to an influx of warm deep-water currents. This warm water is being driven towards the Antarctic coast by westerly winds, which are strengthening due to changing air temperatures caused by the climate crisis.

Warmer ocean temperatures are causing sea ice to form later and melt earlier, and floating glaciers (ice shelves) to melt more quickly, introducing more freshwater into the surface layers of the ocean. These changes have a profound impact on delicately balanced Antarctic ecosystems.

Researchers have identified several other interconnected causes for the changes we are seeing in Antarctic Peninsula ecosystems including ocean acidification, overfishing, a shorter sea ice season, and the recovery of predator populations, such as seals and baleen whales, after decades of exploitation.

gentoo penguin with chicks — Gentoo penguin with chicks. Image credit: Canva.com

gentoo underwater — Gentoo underwater Image credit: Canva.com

Antarctic researchers are working to piece together a complex web of interconnected elements to explain how the climate crisis is affecting life on the Antarctic Peninsula, and predict how this may change into the future.

This uncertainty is part of why it is so important that we protect these fragile ecosystems from the unpredictable changes caused by the climate crisis – to help support a resilient, flourishing future for life in Antarctica.

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