This knowledge gap was reflected in the latest report from the Intergovernmental Panel on Climate Change (IPCC). It contains projections from models in which important processes affecting the ice sheets, known as feedbacks and tipping points, are absent because scientific understanding is lacking.
Projected sea level rise will have widespread effects in Australia and around the world. But current projections of ice sheet melt are so wide that developing ways for societies to adapt will be incredibly expensive and difficult.
If the world is to effectively adapt to sea level rise with minimal cost, we must quickly address the uncertainty surrounding Antarctica’s melting ice sheet. This requires significant investment in scientific capacity.
The great unknown
Ice loss from the Antarctic and Greenland ice sheets was the largest contributor to sea level rise in recent decades. Even if all greenhouse gas emissions ceased today, the heat already in the ocean and atmosphere would cause substantial ice loss and a corresponding rise in sea levels. But exactly how much, and how fast, remains unclear.
Scientific understanding of ice sheet processes, and of the variability of the forces that affect ice sheets, is incredibly limited. This is largely because much of the ice sheets are in very remote and harsh environments, and so difficult to access.
This lack of information is one of the main sources of uncertainty in the models used to estimate ice mass loss.
At the moment, quantifying how much the Greenland and Antarctic ice sheets will contribute to sea level rise primarily involves an international scientific collaboration known as the “Ice Sheet Model Intercomparison Project for CMIP6”, or ISMIP6, of which we are part.
The project includes experts in ice sheet and climate modelling and observations. It produces computer simulations of what might happen if the polar regions melt under different climate scenarios, to improve projections of sea level rise.
The project also investigates ice sheet–climate feedbacks. In other words, it looks at how processes in the oceans and atmosphere will affect the Antarctic and Greenland ice sheets, including whether the changes might cause them to collapse – leading to large and sudden increases in sea level.
Research has identified so-called “basal melt” as the most significant driver of Antarctic ice loss. Basal melt refers to the melting of ice shelves from underneath, and in the case of Antarctica, interactions with the ocean are thought to be the main cause. But gathering scientific observations beneath ice shelves is a major logistical challenge, leading to a dearth of data about this phenomenon.
This and other constraints mean the rate of progress in ice sheet modelling has been insufficient to date, and so active ice sheet models are not included in climate models.
Scientists must instead make projections using the ice sheet models in isolation. This hinders scientific attempts to accurately simulate the feedback between ice and climate.
For example, it creates much uncertainty in how the interaction between the ocean and the ice shelf will affect ice mass loss, and how the very cold, fresh meltwater will make its way back to global oceans and cause sea level rise, and potentially disrupt currents.
Despite the uncertainties ISMIP6 is dealing with, it has published a series of recent research including a key paper published in Nature in May. This found if the world met the Paris Agreement target of limiting global warming to 1.5℃ this century, land ice melt would cause global sea level rise of about 13cm by 2100, in the most optimistic scenario. This is compared to a rise of 25cm under the world’s current emissions-reduction pledges.
The study also outlines a pessimistic, but still plausible, basal melt scenario for Antarctica in which sea levels could be five times higher than in the main scenarios.
The below graph shows the IPCC’s latest sea level projections. The shaded area reflects the large uncertainties in models using the same basic data sets and approaches. The dotted line reflects deep uncertainty about tipping points and thresholds in ice sheet stability.
IPCC reports are intended to guide global policy-makers in coming years and decades. But the uncertainties about ice melt from Antarctica limit the usefulness of projections by the IPCC and others.
It’s crucial that ice sheet models are improved, tested robustly against real-world observations, then integrated into the next generation of international climate models – including those being developed in Australia.
International collaborations such as NECKLACE and RISE are seeking to coordinate international effort between models and observations. Significant investment across these projects is needed.
Sea levels will continue rising in the coming decades and centuries. Ice sheet projections must be narrowed down to ensure current and future generations can adapt safely and efficiently.
The authors would like to acknowledge the contributions of Dr Ben Galton-Fenzi, Dr Rupert Gladstone, Dr Thomas Zwinger and David Reilly to the research from which this article draws.
It is also the foundation of a rules-based international order for a continent without a permanent population.
The treaty is remarkably short and contains only 14 articles. Principal provisions include promoting the freedom of scientific research, the use of the continent only for peaceful purposes, and the prohibition of military activities, nuclear tests and the disposal of radioactive waste.
However, since the treaty was negotiated in a very different era and there have been a number of environmental, resource and geopolitical disputes related to Antarctica in recent decades, it begs the question: is it still fit for purpose?
What the treaty says about territorial claims
The most important provision of the treaty is Article IV, which effectively seeks to neutralise territorial sovereignty in Antarctica.
For the Antarctic territorial claimants, this meant a limit was placed on making any new claim or enlargement of an existing claim.
Likewise, no formal recognition was given to any of the seven territorial claims on the continent, by Argentina, Australia, Chile, France, New Zealand, Norway and the United Kingdom.
Russia, the United States and China — signatories with significant Antarctic interests who have not formally made territorial claims — are also bound by the limitations of Article IV.
The treaty also put a freeze on any disputes between claimants over their territories on the continent. Claimants agreed to abide by the rules and obligations of the treaty, which meant countries that don’t recognise claims (such as China and Russia) are free to go about scientific research and peaceful activities.
Though the compact has held for 60 years, there have been tensions from time to time. Argentina and the UK, for instance, have overlapping claims to territory on the continent. When combined with their ongoing dispute over the nearby Falkland (Malvinas) Islands, their Antarctic relationship remains frosty.
As disputes have arisen over the years, many have been addressed through the expansion of the treaty framework with these agreements. This framework is now referred to as the “Antarctic Treaty System”.
These measures have been a great success, but tensions have arisen in recent years over the promotion of Southern Ocean marine reserves. Agreement was reached in 2016 on a Ross Sea Marine Protected Area, and momentum is building for a broader network of Southern Ocean marine protected areas. China and Russia have resisted these initiatives.
Membership of the treaty has grown in the intervening years, with 54 signatories today.
Scientific engagement in Antarctica is considered critical to exercising influence under the treaty. New treaty parties have to meet certain criteria relating to active scientific programs before they are able to participate in meetings as “consultative parties”. A total of 29 treaty parties, including Australia, meet these scientific engagement thresholds.
Building, operating and conducting scientific research programs are key to the success not only of the treaty, but also to the claimants’ credibility in Antarctica. Australia, for instance, has permitted Belarus, China, France, India, Italy, Russia, and the US to conduct scientific programs at their own research bases within its Antarctic territory, which covers 42% of the continent.
While the Antarctic Treaty has been able to successfully respond to a range of challenges, circumstances are radically different in the 2020s compared to the 1950s. Antarctica is much more accessible, partly due to technology but also climate change. More countries now have substantive interests in the continent than the original 12. Some global resources are becoming scarce, especially oil.
This will inevitably result in increased attention being given to the potential for Antarctic mining to take place sometime in the future. Calls to revisit the prohibition on Antarctic mining would seem inevitable.
There is also uncertainty as to China’s intentions in Antarctica. China joined the treaty in 1983, became a consultative party in 1985, and in 2017 hosted a consultative party meeting in Beijing.
China has a developing scientific program on the continent, with four research stations (three of which are in Australia’s Antarctic Territory), and a fifth planned. While Australia and China cooperate on a number of Antarctic scientific and logistics programs, the direction of China’s Antarctic engagement and long-term support for treaty is not clear.
There is considerable speculation as to China’s interests in Antarctic resources, especially fisheries and minerals, and whether China may seek to exploit weaknesses in the treaty system to secure access to those resources.
All of the treaty signatories, but especially those with significant stakes in the continent, need to give the future of the treaty more attention.
The Australian parliament, for instance, last conducted an inquiry into the Australian Antarctic Territory in 2018. None of the 22 recommendations, however, had a precise focus on the Antarctic Treaty.
The mining ban under the Madrid Protocol to the treaty could be subject to review in 2048. If the treaty’s signatories wish to ensure it remains fit for purpose in 2048 and beyond, more strategic thinking needs to be given to Antarctica’s future.
I’ve heard the gravity changes when Antarctica melts will lower the seas around New Zealand. Will that save us from sea level rise?
The gravitational changes when Antarctica melts do indeed affect sea levels all over the world — but not enough to save New Zealand from rising seas.
The ice ages and their effects on sea level, geology, flora and fauna were topics of intense scientific and public interest all through the 19th century. Here’s how James Croll explained the “gravity effect” of melting ice in his 1875 book Climate and Time in their Geologic Relations:
Let us now consider the effect that this condition of things would have upon the level of the sea. It would evidently tend to produce an elevation of the sea-level on the northern hemisphere in two ways. First, the addition to the sea occasioned by the melting of the ice from off the Antarctic land would tend to raise the general level of the sea. Secondly, the removal of the ice would also tend to shift the earth’s centre of gravity to the north of its present position – and as the sea must shift along with the centre, a rise of the sea on the northern hemisphere would necessarily take place.
His back-of-the-envelope calculation suggested the effect on sea level from ice melting in Antarctica would be about a third bigger than average in the northern hemisphere and a third smaller in the south.
A more detailed mathematical study by Robert Woodward in 1888 has falling sea level as far as 2000km from Antarctica, but still rising by a third more than average in the north.
Woodward’s method is the basis of determining what is now called the “sea-level fingerprint” of melting ice. Two other factors also come into play.
The elasticity of the earth’s surface means the land will bounce up when it has less ice weighing it down. This pushes water away.
If the ice is not at the pole, its melting shifts the south pole (the axis of rotation), redistributing water.
Combining these effects gives the sea-level fingerprints of one metre of sea-level rise from either the West Antarctic Ice Sheet (WAIS) and Greenland (GIS), as shown here:
Woodward’s method from 1888 holds up pretty well – some locations in the northern hemisphere can get a third more than the average sea level rise. New Zealand gets a little bit below the average effect from Antarctica, and a little more than average from Greenland. Overall, New Zealand can expect slightly higher than average sea level rise.
Combining the sea-level fingerprints of all known sources of melting ice, together with other known changes of local land level such as subsidence and uplift, gives a good fit to the observed pattern of sea level rise around the world. For example, sea level has been falling near West Antarctica, due to the gravity effect.
Sea-level rise is accelerating, but the future rate is uncertain
The global average rise in sea level is 110mm for 1900-1993 and 100mm for 1993–2020. The recent acceleration is mostly due to increased thermal expansion of the top two kilometres of the oceans (warm water is less dense and expands) and increased melting of Greenland.
But the Gravity Recovery and Climate Experiment satellite has revealed the melting of Antarctica has accelerated by a factor of five in recent decades. Future changes in Antarctica represent a major source of uncertainty when trying to forecast sea levels.
Much of West Antarctica lies below sea level and is potentially subject to an instability in which warming ocean water melts the ice front from below. This would cause the ice sheet to peel off the ocean floor, accelerating the flow of the glacier towards the sea.
In fact, this has been directly observed, both in the location of glacial “grounding lines”, some of which have retreated by tens of kilometres in recent decades, and most recently by the Icefin submersible robot which visited the grounding line of the Thwaites Glacier, 2000km east of Scott Base, and found the water temperature to be 2℃ above the local freezing point.
The big question is whether this instability has been irreversibly set into motion. Some glaciologists say it has, but the balance of opinion, summarised by the IPCC’s report on the cryosphere, is that:
Observed grounding line retreat … is not definitive proof that Marine Ice Sheet Instability is underway. Whether unstable West Antarctic Ice Sheet retreat has begun or is imminent remains a critical uncertainty.
The IPCC special report on 1.5℃ concluded that “these instabilities could be triggered at around 1.5℃ to 2℃ of global warming”.
What’s in store for New Zealand
Predictions for New Zealand range from a further 0.46 metres of sea-level rise by 2100 (under a low-emission scenario, with warming kept under 2℃) to 1.05 metres (under a high-emission scenario).
A continued rise in sea levels over future centuries may be inevitable — there are 66m of sea level rise locked up in ice at present — but the rate will depend on how fast we can reduce emissions.
A five-year, NZ$7m research project, NZ SeaRise, is now underway, seeking to improve predictions of sea-level rise out to 2100 and beyond and their implications for local planning.
Eric Jorden Raes, Dalhousie UniversityAboard an Australian research vessel, the RV Investigator, we sailed for 63 days from Antarctica’s ice edge to the warm equator in the South Pacific and collected 387 water samples.
Our goal? To determine how the genetic code of thousands of different micro-organisms can provide insights into the ocean’s functional diversity — the range of tasks performed by bacteria in the ocean.
Our research was published yesterday in Nature Communications. It showed how bacteria can help us measure shifts in energy production at the base of the food web. These results are important, as they highlight an emerging opportunity to use genetic data for large-scale ecosystem assessments in different marine environments.
In light of our rapidly changing climate, this kind of information is critical, as it will allow us to unpack the complexity of nature step by step. Ultimately, it will help us mitigate human pressures to protect and restore our precious marine ecosystems.
Why should we care about marine bacteria?
The oceans cover 71% of our planet and sustain life on Earth. In the upper 100 meters, the sunlit part of the oceans, microscopic life is abundant. In fact, it’s responsible for producing up to 50% of all the oxygen in the world.
But the role of bacteria go beyond oxygen production. Bacteria sustain, inject and control the fluxes of energy, nutrients and organic matter in our oceans. They provide the energy and food for the entire marine food web, from tiny crustaceans to fish larvae, whales and the fish we eat.
These micro-organisms also execute key roles in numerous biogeochemical cycles (the carbon, nitrogen, phosphorus, sulphur and iron cycles, to name a few).
So, it’s important to quantify their various tasks and understand how the different bacterial species and their functions respond to environmental changes.
Global ocean research initiatives — such as GO-SHIP and GEOTRACES — have been measuring the state of oceans in expeditions like ours for decades. They survey temperature, salinity, nutrients, trace metals (iron, cobalt and more) and other essential ocean variables.
Only recently, however, have these programs begun measuring biological variables, such as bacterial gene data, in their global sampling expeditions.
Including bacterial gene data to measure the state of the ocean means we can try to fill critical knowledge gaps about how the diversity of bacteria impacts their various tasks. One hypothesis is whether a greater diversity of bacteria leads to a better resilience in an ecosystem, allowing it to withstand the effects of climate change.
In our paper, we addressed a fundamental question in this global field of marine microbial ecology: what is the relationship between bacterial identity and function? In other words, who is doing what?
What we found
We showed it’s possible to link the genetic code of marine bacteria to the various functions and tasks they execute, and to quantify how these functions changed from Antarctica to the equator.
The functions that changed include taking in carbon dioxide from the atmosphere, bacterial growth, strategies to cope with limited nutrients, and breaking down organic matter.
Another key finding is that “oceanographic fronts” can act as boundaries within a seemingly uniform ocean, resulting in unique assemblages of bacteria with specific tasks. Oceanographic fronts are distinct water masses defined by, for instance, sharp changes in temperature and salinity. Where the waters meet and mix, there’s high turbulence.
The change we recorded in energy production across the subtropical front, which separates the colder waters from the Southern Ocean from the warmer waters in the tropics, was a clear example of how oceanographic fronts influenced bacterial functions in the ocean.
Tracking changes in our ecosystems
As a result of our research, scientists may start using the functional diversity of bacteria as an indicator to track changes in our ecosystems, like canaries in a coal mine.
So the functional diversity of bacteria can be used to measure how human growth and urbanisation impact coastal areas and estuaries.
For example, we can more accurately and holistically measure the environmental footprint of aquaculture pens, which are known to affect water quality by increasing concentrations of nutrients such as carbon, nitrogen and phosphorus – all favourite elements utilised by bacteria.
Likewise, we can track changes in the environmental services rendered by estuaries, such as their important role in removing excessive nitrogen that enters the waterways due to agriculture run-off and urban waste.
With 44% of the world’s population living along coastlines, the input of nitrogen to marine ecosystems, including estuaries, is predicted to increase, putting a strain on the marine life there.
Ultimately, interrogating the bacterial diversity using gene data, along with the opportunity to predict what this microscopic life is or will be doing in future, will help us better understand nature’s complex interactions that sustain life in our oceans.
In December, Antarctica lost its status as the last continent free of COVID-19 when 36 people at the Chilean Bernardo O’Higgins research station tested positive. The station’s isolation from other bases and fewer researchers in the continent means the outbreak is now likely contained.
However, we know all too well how unpredictable — and pervasive — the virus can be. And while there’s currently less risk for humans in Antarctica, the potential for the COVID-19 virus to jump to Antarctica’s unique and already vulnerable wildlife has scientists extremely concerned.
We’re among a global team of 15 scientists who assessed the risks of the COVID-19 virus to Antarctic wildlife, and the pathways the virus could take into the fragile ecosystem. Antarctic wildlife haven’t yet been tested for the COVID-19 virus, and if it does make its way into these charismatic animals, we don’t know how it could affect them or the continent’s ecosystem stability.
Jumping from animals to humans, and back to animals
The COVID-19 virus is one of seven coronaviruses found in people — all have animal origins (dubbed “zoonoses”), and vary in their ability to infect different hosts. The COVID-19 virus is thought to have originated in an animal and spread to people through an unknown intermediate host, while the SARS outbreak of 2002-2004 likely came from raccoon dogs or civets.
Given the general ubiquity of coronaviruses and the rapid saturation of the global environment with the COVID-19 virus, it’s paramount we explore the risk for it to spread from people to other animals, known as “reverse zoonoses”.
The World Organisation for Animal Health is monitoring cases of the COVID-19 virus in animals. To date, only a few species around the globe have been found to be susceptible, including mink, felines (such as lions, tigers and cats), dogs and a ferret.
Whether the animal gets sick and recovers depends on the species. For example, researchers found infected adolescent cats got sick but could fight off the virus, while dogs were much more resistant.
While mink, dogs or cats are not in Antarctica, more than 100 million flying seabirds, 45% of the world’s penguin species, 50% of the world’s seal populations and 17% of the world’s whale and dolphin species inhabit the continent.
In a 2020 study, researchers ran computer simulations and found cetaceans — whales, dolphins or porpoises — have a high susceptibility of infection from the virus, based on the makeup of their genetic receptors to the virus. Seals and birds had a lower risk of infection.
We concluded that direct contact with people poses the greatest risk for spreading the virus to wildlife, with researchers more likely vectors than tourists. Researchers have closer contact with wildlife: many Antarctic species are found near research stations, and wildlife studies often require direct handling and close proximity to animals.
Tourists, however, are still a concerning vector, as they visit penguin roosts and seal haul-out sites (where seals rest or breed) in large numbers. For instance, a staggering 73,991 tourists travelled to the continent between October 2019 and April 2020, when COVID-19 was just emerging.
Each visitor to Antarctica carries millions of microbial passengers, such as bacteria, and many of these microbes are left behind when the visitors leave. Most are likely benign and probably die off. But if the pandemic has taught us anything, it takes only one powerful organism to jump hosts to cause a pandemic.
How to protect Antarctic wildlife
There are guidelines for visitors to reduce the risk of introducing infectious microbes. This includes cleaning clothes and equipment before heading to Antarctica and between animal colonies, and keeping at least five metres away from animals.
These rules are no longer enough in COVID times, and more measures must be taken.
The first and most crucial step to protect Antarctic wildlife is controlling human-to-human spread, particularly at research stations. Everyone heading to Antarctica should be tested and quarantined prior to travelling, with regular ongoing tests throughout the season. The fewer people with COVID-19 in Antarctica, the less opportunity the virus has to jump to animal hosts.
Second, close contact with wildlife should be restricted to essential scientific purposes only. All handling procedures should be re-evaluated, given how much we just don’t know about the virus.
We recommend all scientific personnel wear appropriate protective equipment (including masks) at all times when handling, or in close proximity to, Antarctic wildlife. Similar recommendations are in place for those working with wildlife in Australia.
Migrating animals that may have picked up COVID-19 from other parts of the world could also spread it to other wildlife in Antarctica. Skuas, for example, migrate to Antarctica from the South American coast, where there are enormous cases of COVID-19.
And then there’s the issue of sewage. Around 37% of bases release untreated sewage directly into the Antarctic ecosystem. Meanwhile, an estimated 57,000 to 114,000 litres of sewage per day is dumped from ships into the Southern Ocean.
Fragments of the COVID virus can be found in wastewater, but these fragments aren’t infectious, so sewage isn’t considered a transmission risk. However, there are other potentially dangerous microbes found in sewage that could be spread to animals, such as antibiotic-resistant bacteria.
We can curb the general risk of microbes from sewage if the Antarctic Treaty formally recognises microbes as invasive species and a threat to the Antarctic ecosystem. This would support better biosecurity practices and environmental control of waste.
In these early stages of the pandemic, scientists are scrambling to understand complexity of COVID-19 and the virus’s characteristics. Meanwhile, the virus continues to evolve.
Until the true risk of cross-species transmission is known, precautions must be taken to reduce the risk of spread to all wildlife. We don’t want to see the human footprint becoming an epidemic among Antarctic wildlife, a scenario that can be mitigated by better processes and behaviours.
Two-thirds of the world’s oceans fall outside national jurisdictions – they belong to no one and everyone.
These international waters, known as the high seas, harbour a plethora of natural resources and millions of unique marine species.
But they are being damaged irretrievably. Research shows unsustainable fisheries are one of the greatest threats to marine biodiversity in the high seas.
According to a 2019 global assessment report on biodiversity and ecosystem services, 66% of the world’s oceans are experiencing detrimental and increasing cumulative impacts from human activities.
In the high seas, human activities are regulated by a patchwork of international legal agreements under the 1982 UN Convention on the Law of the Sea (UNCLOS). But this piecemeal approach is failing to safeguard the ecosystems we depend on.
A decade ago, world leaders updated an earlier pledge to establish a network of marine protected areas (MPAs) with a mandate to protect 10% of the world’s oceans by 2020.
But MPAs cover only 7.66% of the ocean across the globe. Most protected sites are in national waters where it’s easy to implement and manage protection under the provision of a single country.
In the more remote areas of the high seas, only 1.18% of marine ecosystems have been gifted sanctuary.
The Southern Ocean accounts for a large portion of this meagre percentage, hosting two MPAs. The South Orkney Islands southern shelf MPA covers 94,000 square kilometres, while the Ross Sea region MPA stretches across more than 2 million square kilometres, making it the largest in the world.
The Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) is responsible for this achievement. Unlike other international fisheries management bodies, the commission’s legal convention allows for the closing of marine areas for conservation purposes.
A comparable mandate for MPAs in other areas of the high seas has been nowhere in sight — until now.
In 2017, the UN started negotiations towards a new comprehensive international treaty for the high seas. The treaty aims to improve the conservation and sustainable use of marine organisms in areas beyond national jurisdiction. It would also implement a global legal mechanism to establish MPAs in international waters.
This innovative international agreement provides an opportunity to work across institutional boundaries towards comprehensive high seas governance and protection. It is crucial to use lessons drawn from existing high seas marine protection initiatives, such as those in the Southern Ocean, to inform the treaty’s development.
The final round of treaty negotiations is pending, delayed by the COVID-19 pandemic, and significant detail within the treaty’s draft text remains undeveloped and open for further debate.
Lessons from Southern Ocean management
CCAMLR comprises 26 member states (including the European Union) and meets annually to make conservation-based decisions by unanimous consensus. In 2002, the commission committed to establishing a representative network of MPAs in Antarctica in alignment with globally agreed targets for the world’s oceans.
The two established MPAs in the high seas are far from an ecologically representative network of protection. In October 2020, the commission continued negotiations for three additional MPAs, which would meet the 10% target for the Southern Ocean, if agreed.
But not a single proposal was agreed. For one of the proposals, the East Antarctic MPA, this marks the eighth year of failed negotiations.
CCAMLR’s progress towards its commitment for a representative MPA network may have ground to a halt, but the commission has gained invaluable knowledge about the challenges in establishing MPAs in international waters. CCAMLR has demonstrated that with an effective convention and legal framework, MPAs in the high seas are possible.
The commission understands the extent to which robust scientific information must inform MPA proposals and how to navigate inevitable trade-offs between conservation and economic interests. Such knowledge is important for the UN treaty process.
As the high seas treaty moves closer to adoption, it stands to outpace the commission regarding progress towards improved marine conservation. Already, researchers have identified high-priority areas for protection in the high seas, including in Antarctica.
Many species cross the Southern Ocean boundary into other regions. This makes it even more important for CCAMLR to integrate its management across regional fisheries organisations – and the new treaty could facilitate this engagement.
But the window of time is closing with only one round of negotiation left for the UN treaty. Research tells us Antarctic decision-makers need to use the opportunity to ensure the treaty supports marine protection commitments.
Stronger Antarctic leadership is urgently needed to safeguard the Southern Ocean — and beyond.
In 2018, a map named after an oceanographer went viral.
The so-called Spilhaus projection, in which Earth is viewed from above the South Pole, was designed to show the connected nature of the ocean basins.
It is a perspective that comes naturally to those who live in the ocean-dominated southern hemisphere.
The Southern Ocean, also called the Antarctic Ocean (or even the Austral ocean), is like no other and best described in superlatives.
Storing heat and carbon
Let’s first look at the Southern Ocean’s capacity to store excess heat and carbon. The world’s oceans take up more than 90% of the excess heat generated by the burning of fossil fuels and a third of the additional carbon dioxide.
The Southern Ocean, south of 30°S, is estimated to store about 75% of this global oceanic uptake of excess heat and about 35% of the global uptake of excess carbon from the atmosphere. It is the primary storage of heat and carbon for the planet.
The Southern Ocean connects all major ocean basins, except the Arctic. The link is the Antarctic Circumpolar Current (ACC) – the largest ocean current on the planet. It carries more than 100 times the flow of all the rivers on Earth and transports enough water to fill Lake Ontario in just a few hours.
A combination of strong winds and a nearly uninterrupted passage around Antarctica give the ACC its strong flows and speed.
The Roaring Forties, Furious Fifties and Screaming Sixties are all popular names for the strong westerly winds that blow, nearly uninterrupted, across the Southern Ocean, creating equally impressive waves. This results in a massively energetic – and hard to measure – ocean surface.
But the heat and carbon exchanges across this complicated interface are globally important, and oceanographers have designed tools specifically for this challenging environment.
To really comprehend the Southern Ocean, one must think in three dimensions. Waters with different properties mix both horizontally and vertically in eddies.
Relatively warm subtropical water is mixed south, deep cool water from the North Atlantic rises back up toward the surface and colder polar water masses mix northward and sink back down.
This complex interplay is guided by the wind and by the shape of the seafloor.
To the north, there are only three major constrictions: the 850km-wide Drake Passage, and the submarine Kerguelan and Campbell Plateaus. To the south, the ACC butts up against Antarctica.
Here the ocean plays another crucial role in the global climate system by bringing relatively warm — and warming — Circumpolar Deep Water into contact with the ice fringing Antarctica.
Annual thaw and freeze of sea ice
The annual cycle of sea ice growing and melting around Antarctica is one of the defining rhythms of our planet and an important facet of the Southern Ocean. The two polar regions couldn’t be more different in this regard.
The Arctic is a small, deep ocean surrounded by land with only narrow exits. The Antarctic is a large landmass with a continental shelf surrounded by ocean. Each year, 15 million square kilometres of sea ice advance and retreat in these waters.
In contrast to the clear and dramatic changes in the north, the rhythm of Antarctic sea ice has followed less obvious patterns. In the face of a warming ocean, it was actually slowly expanding northward until around 2016, when it suddenly started to contract.
Looking at the annual cycle of Antarctic sea ice, one might think it simply grows and melts in place as things get cold and warmer through the year. But in truth, much of the sea ice production happens in polynya – sea ice factories near the coast where cold and fast Antarctic winds both create and blow away new sea ice as fast as it appears.
This process brings us back to global ocean circulation. When the new ice grows, the salt from the freezing sea water gets squeezed out and mixes with the seawater below, creating colder and saltier seawater that sinks to the seafloor and drains northward.
Polynya are in effect a metro stop on a global transport system that sees water sinking at the poles, flowing north to be mixed upwards in a cycle lasting close to 1,000 years.
Not all ice shelves respond the same
Computer simulations have shown how the ice shelves at Antarctica’s fringe have waxed and waned over past millennia.
Because these floating extensions of the ice sheet interact directly with the ocean, they make the ice sheet sensitive to climate. Ocean warming and changes in the source of the water coming into contact with an ice shelf can cause it – and in turn the whole ice sheet – to change.
But not all ice shelves will respond to warming in the same way. Some ocean cavities are cold and slowly evolving. Others are actually described as hot – in polar terms – because of their interaction with Circumpolar Deep Water. The latter are changing rapidly right now.
We can observe many cryosphere processes from space, but to truly understand how far the ocean reaches beneath the ice we have to go hundreds of metres beneath the ice surface.
Making climate predictions requires an understanding of detailed processes that happen on short timescales, such as tidal cycles, in parts of the planet we are only beginning to explore.
How do we sample something so big and so stormy? With robots.
Satellites have been observing the ocean surface since the 1980s. This technology can measure properties such as temperature and ocean surface height, and even be used to estimate biological productivity. But satellites can’t see beneath the surface.
When the game-changing Argo programme started in the 1990s, it revolutionised earth science by building a network of drifting ocean sentinels measuring temperature and salinity down to a depth of two kilometres.
The research vessel Kaharoa holds the record for the most deployments of Argo probes in the Southern Ocean, including its most recent storm-tossed, COVID-19-impacted voyage south of Australia and into the Indian Ocean.
The Argo program is only the start of a new era of ocean observation. Deep Argo probes dive to depths of 6km to detect how far down ocean warming is penetrating.
The past and future Southern Ocean
Earth hasn’t always looked as it does today. At times in the planet’s past, the Southern Ocean didn’t even exist. Continents and ocean basins were in different positions and the climate system operated very differently.
From the narrow view of human evolution, the Southern Ocean has been a stable component of a climate system and subject to relatively benign glacial oscillations. But glacial cycles play out over tens of thousands of years.
We are imposing a very rapid climate transient. The nearly three centuries since the start of the industrial revolution is shorter than the blink of an eye in geological context.
Future changes in the short (say by 2050) and long (by 2300) term are difficult to project. While the physics are relatively clear about what will happen, predicting when it will happen is more challenging.
Simulation tools that get the ocean, atmosphere and ice processes right are only starting to include ice shelf cavities and ocean eddies. The most recent synthesis of climate models shows progress in the simulated workings of the Southern Ocean. But sea ice remains a challenge to simulate well.
This is the frontier: a global research community working to connect data with rapidly improving computer models to better understand how this unique ocean operates.
Life in a sub-zero ocean
At first glance, Antarctica seems an inhospitable and almost barren environment of ice and snow, speckled with occasional seabirds and seals.
But diving beneath the surface reveals an ocean bursting with life and complex ecosystems, from single-celled algae and tiny spineless creatures to the well-known top predators: penguins, seals and whales.
It’s not easy to study life in the Southern Ocean. Waves can be more than 20 metres high, and icebergs and sea ice lurk among them.
The water temperature is often sub-zero – freshwater freezes at 0℃, but saltwater freezes at closer to -2℃. Although scuba diving is possible, a lot of research on life in the Southern Ocean is done through remote sampling.
Marine scientists use robotic tools such as remotely operated underwater vehicles to look at and collect samples, and grabs and dredges to bring up bottom-dwelling organisms. We take genetic samples from marine mammals by shooting tiny biopsy tubes (like needles), attached to a cord for retrieval, into the animal’s flesh from a distance.
We can glean wider information on diversity from environmental DNA (eDNA). Traces of organisms are filtered from samples of water and analysed using genetic tools that can usually identify what sorts of species are or were present.
Every expedition reveals new species – some of which are potentially commercially valuable, and all of which are important parts of the Southern Ocean ecosystem. Our knowledge of the diversity of the region is growing rapidly.
Nonetheless, the Southern Ocean is vast, and much of it remains either unsampled or undersampled.
Down at the bottom of the food chain
In the Southern Ocean, primary producers (organisms at the start of the food chain) range from single-celled algae – such as diatoms with intricately detailed shells made of silica – through to large macroalgae like kelp.
Kelp and other large seaweeds generally only survive where icebergs don’t often scrape the seafloor. Diatoms are diverse, and some species thrive on the underside of sea ice.
Ice algae form an important food source for krill, small crustaceans that are a critical part of Southern Ocean food webs.
Astonishingly, the cold Southern Ocean is also home to hot hydrothermal vent systems. These communities, which include huge densities of crustaceans and echinoderms, get their energy from chemicals that seep out of Earth’s crust, rather than from the Sun.
Antarctic invertebrates make up more than 90% of the species in the Southern Ocean. More than 50% are unique to this ocean.
These invertebrates are often much larger than their relatives in more northern, warmer waters. This phenomenon is know as “polar gigantism” and is found across many groups, with giant sea spiders, huge sponges and scale worms the size of a forearm.
Nobody is quite sure why Antarctic invertebrates grow so large, but it may be related to high oxygen levels, slow growth rates or the absence of key predatory groups such as sharks and brachyuran crabs.
Higher up in the food chain
In the marine food chain, Antarctic krill swim between the algal primary producers and the iconic top predators we always associate with Antarctica.
Baleen whales get much of their energy from great gulps of swarming krill (10,000–30,000 individual animals per cubic metre), and the pink streaks in penguin and seal poo show they are also keen on these tasty crustaceans.
Fish and cephalopods (squid and octopus) thrive in the Southern Ocean, providing food for deep-diving marine mammals such as elephant seals. Some fish species are so well adapted to the oxygen-rich cold waters they no longer produce red blood cells but instead produce antifreeze proteins in their blood to help them survive in the subzero waters.
Protecting marine environments
Arguably the most voracious predators in the Southern Ocean are humans.
Antarctica might be remote, but in the 200 or so years since its discovery, the seas around Antarctica have been heavily exploited by people.
First came the sealers, then the whalers, driving species to the brink of extinction. Even penguins were harvested for their oil.
More recently, fish and krill (which is fished for food or dietary supplements) have been the main targets, and populations of some species have declined sharply as a consequence.
When more indirect impacts like ocean warming and acidification combine with fishing, this can lead to declining populations of krill, which in turn leads to reduced numbers of top predators such as whales.
Fishing in the Southern Ocean can be hard to regulate because these waters do not belong to any one nation. To help manage the impact of fisheries, quotas that limit catches are now managed by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR).
This international body is also working to establish more marine protected areas.
Without these efforts to manage catches, critical parts of the food web (such as krill) could be exploited to such an extent that ecosystems could collapse.
Changing environments mean changing ecosystems
More than 21,000 tourists and scientists visit Antarctica each year, potentially bringing pollution, diseases and invasive species. To manage human impacts on Antarctic ecosystems, and to help with political negotiations, the Antarctic Treaty came into force on June 23, 1961.
The impacts of global climate change and ocean acidification are nonetheless evident in the Southern Ocean, with warming ocean temperatures, reduction in sea ice and collapsing ice shelves.
Increasingly, research is showing that even the distant Southern Ocean is not truly cut off from the rest of the world, with warming, plastic pollution and non-native species making their way to Antarctic waters from beyond the mighty polar front.
Rafts of floating seaweeds from outside the Antarctic, some carrying animal passengers, are able to cross the Southern Ocean and reach Antarctic shores. At the moment, they don’t seem able to survive the extreme climate of Antarctica, but that could change with warming.
New species moving in and setting up shop will put a lot of pressure on Antarctica’s unique plants and animals.
It’s not all doom and gloom, though. Over the several decades since the Antarctic Treaty came into force, we’ve seen that nations can work together to help resolve challenges facing the Antarctic. One example is the establishment of Antarctic Marine Protected Areas (MPAs).
This level of international cooperation should give us hope not just for the future of the Southern Ocean, but also for other key challenges the world faces.
Five profiles open our series on the global ocean, delving into ancient Indian Ocean trade networks, Pacific plastic pollution, Arctic light and life, Atlantic fisheries and the Southern Ocean’s impact on global climate. All brought to you from The Conversation’s international network.
Antarctica Day celebrates the icy continent and its unique governance system. It’s the anniversary of the Antarctic Treaty’s adoption on December 1 1959. Framed in a spirit of global co-operation, the treaty acknowledges Antarctica does not belong to any one country. Article IV states:
No acts or activities taking place while the present Treaty is in force shall constitute a basis for asserting, supporting or denying a claim to territorial sovereignty in Antarctica or create any rights of sovereignty in Antarctica.
These five cities on the Southern Ocean rim — Cape Town, Christchurch, Hobart, Punta Arenas and Ushuaia — share a unique interest in Antarctica and an opportunity to shape its future.
How do their residents feel about Antarctica?
Our survey of 1,659 residents of these cities in July this year found they care deeply about the icy continent. Overall, and for many particular groups, environmental care greatly outweighs economic interests. Many residents express hope that this care might translate into more protective policies and action.
However, emotions were mixed, with pessimism and sadness also common responses. When we asked people how they feel about “the future of Antarctica in the next 20 years”, “hope” took first place, followed closely by “pessimism” and “sadness”.
The survey is part of the Antarctic Cities Project, which finishes this month. For the past four years an international team of researchers, city officials, national Antarctic programs and youth groups have worked together to develop a framework to strengthen Antarctic connections and a sense of guardianship for the continent. The framework encompasses the cities’ own urban sustainability strategies within a wider concern for the planet.
Our work focuses on shifting from the limited idea of “gateway” to this broader sense of becoming Antarctic “custodial cities”.
Our online survey of the cities’ residents over the age of 18 asked:
how informed they felt about the relationship between their city and Antarctica
their opinion on how important Antarctica is to their city’s identity
how responsible they, their families and friends think they are for the future of Antarctica.
We posed the question: “Why is it important for your city to develop an identity in relation to Antarctica?” The response “it drives us to take care of the environment” was most common (57%) across all five cities. Other responses included:
“it creates a unique brand for our cities” (36%)
“it creates more jobs” (32%)
“it attracts more tourists” (31%)
“it reinforces residents’ attachment to place” (29%).
Caring for the environment was the most selected option for all ages. Women felt this particularly strongly. Men favoured the more economically oriented options, “it generates more jobs” and “it attracts more tourists”.
Women and people between the ages of 31 and 40 reported higher levels of “hope” and lower levels of “indifference”. Indifference was higher among people between 18 and 30, reaching 16.42%. In this age group, and with men overall, “pessimism” significantly outweighed “hope”. Punta Arenas and Ushuaia residents expressed more “hope” than in other cities.
Young people’s expressions of pessimism and indifference bear witness to the urgent work of reforming our relationship to the Antarctic region. They will be the beneficiaries, and increasingly the drivers, of this reform.
A decade of co-operative custodianship
The cities first came together with the 2009 signing in Christchurch of a statement of intent to promote peaceful co-operation. Though it expired 18 months later, various city and national government policies have reinforced the five cities’ “Antarctic gateway” status. They have put forward visions for enhancing and capitalising on their Antarctic identities, a key part of their relationship to the world.
In an example of action at a local level, the City of Christchurch is moving towards a custodianship model by basing its 2018 Antarctic strategy on two key principles:
embracing the Maori principle of Kaitiakitanga –
meaning guardianship, protection, preservation or sheltering –
and a customary way of caring for the environment based on traditional Māori world view to guide the city’s involvement in the region
taking a leadership role in sustainable actions for the benefit of the Antarctic region and the city.
In coming together, the five cities are showing they can play an important role in defining how Antarctica is imagined, how discourse is framed and how the continent is vicariously experienced.
The Antarctic Cities Project has created an interlinked network of organisations that can learn from and benefit each other. This network of local government, national Antarctic programs, youth groups and polar organisations has produced Antarctic Futures, an educational online serious game.
During 2020 we began work on a Charter of Principles for Antarctic Cities in collaboration with the Hobart and Christchurch city councils. It draws from Christchurch’s 2018 Antarctic Gateway Strategy and the 2017 Tasmanian Antarctic Gateway Strategy. This charter will guide sustainable urban practice and embrace Antarctica’s significance to the economies of these cities while charting ways forward for sustainable development.
The charter aims to celebrate the unique polar heritage of these cities and emphasises the crucial role of youth organisations for engaging with the future of Antarctica. And it acknowledges that human connections with Antarctica extend well beyond the last two centuries, embracing Indigenous conceptions of caring for Country, both land and water.
In the Anthropocene, global public consciousness of, and responsibility for, the icy continent in a time of climate change is increasing. These cities’ relationship with the region to their south and to each other is a valuable part of their urban identity and Antarctica’s future – something worth celebrating on Antarctica Day.
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