How waves, ponds and green algae are accelerating sea ice melt in Antarctica

Luke Bennetts, The University of Melbourne; Bonnie Light, University of Washington; Petteri Uotila, University of Helsinki; Philip Reid, Australian Bureau of Meteorology, and Rob Massom, Australian Antarctic Division

Picture sea ice in your mind. You probably imagine brilliant white, snow-covered floes floating on the surface of the ocean, home to penguins in the south of the globe or polar bears in the north.

But our new research shows Antarctic sea ice can turn into rafts of rotting floes (the free-floating pieces of ice) or an icy green slush when it interacts with waves in the stormiest ocean on the planet.

We now know the wave-driven processes that cause the surface of the sea ice to melt are a “missing link” in understanding what’s driving the increasing Antarctic sea ice melt each summer.

These processes can dramatically increase the rate the ice melts, with major implications for the global climate and Antarctic marine ecosystems.

Our planetary heartbeat

Each year, the sea ice that hugs the coast of Antarctica expands from 3 million square kilometres in summer to 19 million square kilometres in winter, stretching far north into the Southern Ocean. As the sun rises and the temperatures increase, it retreats again.

This remarkable seasonal change is like a heartbeat within our planet’s climate system, moderating global temperatures, driving ocean circulation and forming a unique habitat for a plethora of living organisms, all adapted to its seasonal rhythms.

The annual summer sea ice melt is particularly remarkable because it occurs over only three months. But even the most sophisticated climate models underestimate the rapid rate of sea ice retreat each summer.

 

A NASA image from space shows sea ice at its maximum in Antarctica. NASA, CC BY

How do waves melt sea ice?

Until now, the waves travelling from the ice-free ocean into the area covered in sea ice had only been studied for their role in breaking up ice floes. We knew these smaller floes were prone to melting around their sides and bottoms as the ocean was heated by the sun as summer progressed.

But this is not the full story.

We now know waves also flood over ice floes, washing away the bright snow cover that shields the underlying ice from sunlight and creating ponds of seawater on the floe surfaces.

Due to their reduced brightness, the snow-free ice and these “wave ponds” absorb substantially more solar heat than snow-covered ice, and this melts the ice from the top down. Moreover, the snow-free ice and wave ponds are oases in which algae thrive, turning the ice and ponds green and absorbing even more heat from the sun.

The waves also pulverise the floes into small fragments and slush. Under the right conditions, the combination of wave flooding, algal greening and pulverisation turns the sea ice cover into a slushy mixture, resembling a green soup.

We estimate that flooding, ponding and pulverisation can increase summer-time ice thinning by over 4 centimetres per day. Algal greening can add an additional 1 centimetre of thinning per day. These are extraordinary accelerators of ice melt, considering that most Antarctic sea ice is less than 1 metre thick at the end of winter.

Waves are also generated deep within the Antarctic sea-ice region by winds blowing over large openings in the ice cover. In this way, wave melt processes eat away at the ice cover from within, as well as from the edge throughout summer.

 

In this picture of sea ice you can see the effects of wave pulverisation and algae, which darkens the ice. Robert Massom, CC BY-ND

Feedbacks could trigger further melt

Our ice melt estimates are significant, yet they are likely underestimates. They do not account for amplifications to melting caused by so-called “positive feedbacks”.

For example, the ice darkening caused by waves removing the snow, ponding and pulverisation substantially increases the amount of sunlight absorbed by the ice. This causes additional surface and interior melting, which further reduces the ice brightness. And this causes more vertical melting, and so on, in an amplifying cycle.

We propose that this positive feedback is strengthened by algal greening that further darkens the ice, leading to further absorption of sunlight and melting.

Exactly how much these feedbacks would cause further ice melt is tricky to quantify, so we have left this as an exciting future research challenge.

Ponds at both poles

The Antarctic “wave ponds” we have observed are the seawater equivalent of “melt ponds”. These form extensively across Arctic sea ice in summer from pooling snow meltwater.

These freshwater melt ponds have been intensively studied and integrated into climate models, because of their important role in the rapid decline in the coverage and thickness of Arctic sea ice over recent decades.

Unlike melt ponds, seawater wave ponds occur year-round. Although they only occur in regions where sea ice interacts with ocean waves, this encompasses a large proportion of Antarctic sea ice over the course of a year.

The future of Antarctic sea ice

The effects of wave melt, greening and associated feedbacks are likely to intensify on sea ice around Antarctica over coming decades. Climate change is predicted to increase wind speeds and wave heights across the polar Southern Ocean.

This disruption of the annual sea ice cycle and further sea ice loss has serious consequences for global climate and marine ecosystems.

We need further observations using autonomous camera systems on icebreakers and modelling research to better understand these wave processes and their overall influence on Antarctica’s sea ice cycle.

These advances are vital to understanding the causes of recent dramatic sea-ice losses around Antarctica, and promise vital insights about the future of the icy south and our Earth system.

Luke Bennetts, Professor of Applied Mathematics, The University of Melbourne; Bonnie Light, Physicist, University of Washington; Petteri Uotila, Professor, University of Helsinki; Philip Reid, Scientist, Australian Bureau of Meteorology, and Rob Massom, Leader, Sea Ice Section, Antarctic Climate Program, Australian Antarctic Division

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Read More........→June 12, 2026

Microbes in Antarctica survive the freezing and dark winter by living on air

Ry Holland, Monash University

Winter in Antarctica is long and dark. Temperatures remain well below freezing. In many places, the Sun sets in April and does not rise above the horizon again until August. Without sunlight, photosynthetic life such as plants, mosses and algae cannot make energy.

But that’s not to say all life stops.

In a new study published in The ISME Journal, my colleagues and I show that Antarctic microbes make energy from the air at temperatures as low as –20°C. This finding improves our understanding of how life survives at temperature extremes in Antarctica – and how climate change will affect this important process.

How to make energy from air

In 2017, scientists showed that a large number of Antarctic microbes can generate energy from atmospheric gases present at very low concentrations.

This process is called “aerotrophy”. By using enzymes that are very finely tuned to “sniff out” the hydrogen and carbon monoxide in the atmosphere, these microbes have found a way to make energy from the air itself – a huge advantage in Antarctica’s nutrient-poor desert soils.

What remained unknown until now was the temperature limits of this process. Could aerotrophy be a way to power the continent’s soil communities through the winter?

Taking the lab down south

Measuring how quickly these microbes consume such a small amount of fuel can be difficult.

From 2022–24, we collected surface soil samples from different areas across East Antarctica and analysed them in our lab.

We measured how quickly they can use the atmospheric gases. We also extracted all the DNA from the soil microbes and sequenced it. This tells us what microbes are present, what genes they have, and what they are capable of using as energy sources.

We showed aerotrophy happening in the lab at representative summer (4°C) and winter (–20°C) temperatures. This means hydrogen and carbon monoxide are a viable food source not just over the summer months, but year-round. What was even more surprising though, was the upper temperature limit.

Soil temperatures in Antarctica rarely rise above 20°C. Yet we found microbes in these soils that continued to generate energy from hydrogen up to a staggering 75°C. It seems as though microbes in Antarctic soils are well adapted to the continent’s cold temperatures, but not restricted to them. It’s a bit like seeing a penguin thrive in a tropical jungle.

We also wanted to see this process occurring in Antarctica itself, so two years ago we brought the lab down south. We collected fresh soil samples, sealed them in the glass vials, and took gas samples.

For the first time, it was clear that under real-world conditions these soil microbes were still munching their way through hydrogen.

The primary producers of Antarctica

DNA sequencing has showed us that the vast majority of microbes in Antarctic soils encode the genes to gain energy from hydrogen. Many of these bacteria also have genes to take carbon from the atmosphere.

These aerotrophs are “primary producers”, generating new biomass from the air itself.

In most land-based ecosystems, photosynthesis is thought to be the bottom of the food chain. Photosynthesis takes energy from sunlight and carbon from the atmosphere and turns it into yummy organic compounds.

It’s what makes plants grow. Plants are primary producers that are eaten by herbivores, which are then eaten by carnivores.

In Antarctica’s desert soils, photosynthesis is relatively rare. Instead, we hypothesise that aerotrophy fulfils the primary producer role in many places.

This makes sense because, unlike sunlight-dependent photosythesis, we now know that aerotrophy can happen year-round. Another benefit is that it doesn’t require liquid water, whereas photosynthesis does.

Hydrogen in a heating world

Aerotrophy clearly has an important role in Antarctic ecosystems. So next, we wanted to determine how global warming might affect this process.

Under low-emissions scenarios, we predict a 4% increase in how quickly aerotrophs use atmospheric hydrogen. Under very high-emissions scenarios, this increase rises to 35%. The numbers are similar for carbon monoxide.

Although hydrogen isn’t a greenhouse gas itself, it is important because it affects how long some greenhouse gases, including methane, hang around in the atmosphere.

Soils (including the microbes that live in them) are responsible for 82% of all hydrogen consumed on Earth globally. In other words, they are a hydrogen sink. This is a crucial component in the global hydrogen cycle.

There are a lot of factors that determine how microorganisms will respond to climate change. Temperature is just one of them. This study is an important piece of the puzzle as scientists figure out how resilient Antarctica’s unique microbal ecosystems are.

Ry Holland, Research Fellow in Microbial Ecology, Monash University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Read More........→March 12, 2026