The rhythmic expansion and contraction of Antarctic sea ice is like a heartbeat.
But lately there has been a jump in rhythm. During each of the last two summers, the ice around Antarctica has retreated further than ever before.
And just as a change in our heart rate affects our whole body, a change in the sea ice around Antarctica affects the whole world.
Today, researchers from the Australian Antarctic Program Partnership (AAPP) and the Australian Center for Excellence in Antarctic Science (ACEAS) have joined forces to release a science briefing for policy makers, On thin ice.
Together we call for rapid reductions in greenhouse gas emissions to slow global warming. We also need to do more research in the field, to get to grips with sea ice science before it’s too late.
The Seasonal Expansion and Contraction of Antarctic Sea Ice (Animation by NASA/GSFC Science Visualization Studio)
The shrinking white cap on our blue planet
One of the largest seasonal cycles on Earth occurs in the ocean around Antarctica. During the fall and winter, the ocean’s surface freezes as sea ice moves north, and in the spring the ice melts as the sunlight returns.
We have been able to measure sea ice from satellites since the late 1970s. In that time we have seen a regular cycle of freezing and melting. In winter, sea ice covers an area more than twice the size of Australia (about 20 million square miles), and in summer it retreats to cover less than a fifth of that area (about 3 million square miles). kilometres).
In 2022, the summer minimum was less than 2 million square kilometers for the first time since satellite recording began. This summer, the minimum was even lower: just 1.7 million square kilometers.
The annual freeze pumps cold salt water down into the ocean’s deep abyss. The water then flows to the north. About 40% of the global ocean can be reduced to the Antarctic coastline.
By exchanging water between the surface ocean and the abyss, sea ice buildup helps to trap heat and carbon dioxide in the deep ocean. It also helps bring long-lost nutrients back to the surface, supporting ocean life around the world.
Read more: Deluges of Antarctic meltwater are slowing the currents that cause our vital ocean to ‘topple over’ – and threaten to collapse
Sea ice not only plays a vital role in pumping seawater across the planet, it also insulates the ocean below. During the long days of the Antarctic summer, the sunlight usually falls on the bright white surface of the sea ice and it is reflected in space.
This year there is less sea ice than usual and so the ocean, which is dark in comparison, is absorbing much more solar energy than usual. This will accelerate ocean warming and is likely to hinder sea ice growth in winter.
Towards stormy seas
The Southern Ocean is a stormy place; the nicknames “Roaring Forties” and “Furious Fifties” are well deserved. When there is less ice, the coastline is more exposed to storms. Waves crash on coastlines and ice shelves that are normally sheltered behind a vast sea ice sheet. This mistreatment can lead to the collapse of ice shelves and an increase in the rate of sea level rise as ice sheets slide off land faster into the ocean.
Sea ice supports many levels of the food web. When sea ice melts, it releases iron, which promotes the growth of phytoplankton. In the spring, we see phytoplankton blooms following the retreating edge of the sea ice. If less ice forms, less iron is released in the spring and less phytoplankton grows.
Read more: Smoke from the Black Summer fires caused an algal bloom bigger than Australia in the Southern Ocean
Krill, the tiny crustaceans that provide food for whales, seals and penguins, need sea ice. Many larger species, such as penguins and seals, rely on sea ice to reproduce. The impact of sea ice changes on these larger animals varies greatly between species, but all are closely linked to the rhythm of ice formation and melting. Changes in sea ice heartbeats will disrupt the finely balanced ecosystems of the Southern Ocean.
Wendy Piper AAD, Author provided
A diagnosis for policymakers
Long-term measurements show the subsurface Southern Ocean getting warmer. This warming is caused by our greenhouse gas emissions. We don’t yet know if this ocean warming is directly responsible for the record lows of recent summers, but it is a likely culprit.
As scientists in Australia and around the world try to understand these recent events, new evidence will come to light for a better understanding of what is causing the sea ice around Antarctica to melt.
Dr. Phil Reid, BoM, Author provided
If you notice a change in your heart rate, you would probably see a doctor. Just as doctors conduct tests and collect information, climate scientists conduct fieldwork, collect observations and run simulations to better understand the health of our planet.
This crucial work requires specialized icebreakers with advanced observation equipment, powerful computers and high-tech satellites. International cooperation, data sharing and government support are the only ways to provide the necessary resources.
After noticing the first signs of heart problems, a doctor may recommend exercising more or switching to a low-fat diet. Maintaining the health of our planet requires the same kind of intervention: we must rapidly reduce our consumption of fossil fuels and improve our scientific capabilities.
