Plastic debris is gradually broken down into smaller and smaller fragments in the ocean, until it forms particles smaller than 5mm, known as microplastics. Our new research shows that powerful currents sweep these microplastics along the seafloor into large “drifts”, which concentrate them in astounding quantities. We found up to 1.9 million pieces of microplastic in a 5cm-thick layer covering just one square metre – the highest levels of microplastics yet recorded on the ocean floor.
While microplastics have been found on the seafloor worldwide, scientists weren’t sure how they got there and how they spread. We thought that microplastics would separate out according to how big or dense they were, in a similar manner to natural sediment. But plastics are different – some float, but more than half of them sink.
We’ve now discovered how a global network of deep-sea currents transports microplastics, creating plastic hotspots within vast sediment drifts. By catching a ride on these currents, microplastics may be accumulating where deep-sea life is abundant.
From bedroom floors to the seafloor
We surveyed an area of the Mediterranean off the western coast of Italy, known as the Tyrrhenian Sea, and studied the bottom currents that flow near the seafloor. These currents are driven by differences in water salinity and temperature as part of a system of ocean circulation that spans the globe. Seafloor drifts of sediment can be many kilometres across and hundreds of metres high, forming where these currents lose their strength.
We analysed sediment samples from the seafloor taken at depths of several hundred metres. To avoid disturbing the surface layer of sediment, we used samples taken with box-cores, which are like big cookie cutters. In the laboratory, we separated microplastics from the sediment and counted them under microscopes, analysing them using infra-red spectroscopy to find out what kinds of plastic polymer types were there.
Most microplastics found on the seafloor are fibres from clothes and textiles. These are particularly insidious, as they can be eaten and absorbed by organisms. Although microplastics on their own are often non-toxic, studies show the build-up of toxins on their surfaces can harm organisms if ingested.
These deep ocean currents also carry oxygenated water and nutrients, meaning that the seafloor hotspots where microplastics accumulate may also be home to important ecosystems such as deep-sea coral reefs that have evolved to depend on these flows, but are now receiving huge quantities of microplastics instead.
What was once a hidden problem has now been uncovered – natural currents and the flow of plastic waste into the ocean are turning parts of the seafloor into repositories for microplastics. The cheap plastic goods we take for granted eventually end up somewhere. The clothes that may only last weeks in your wardrobe linger for decades to centuries on the seafloor, potentially harming the unique and poorly understood creatures that live there.
Climate change has been steadily warming the ocean, which absorbs most of the heat trapped by greenhouse gases in the atmosphere, for 100 years. This warming is altering marine ecosystems and having a direct impact on fish populations. About half of the world’s population relies on fish as a vital source of protein, and the fishing industry employs more the 56 million people worldwide.
Overall, ocean warming reduced catch potential – the greatest amount of fish that can be caught year after year – by a net 4% over the past 80 years. In some regions, the effects of warming have been much larger. The North Sea, which has large commercial fisheries, and the seas of East Asia, which support some of the fastest-growing human populations, experienced losses of 15% to 35%.
Although ocean warming has already challenged the ability of ocean fisheries to provide food and income, swift reductions in greenhouse gas emissions and reforms to fisheries management could lessen many of the negative impacts of continued warming.
How and why does ocean warming affect fish?
My collaborators and I like to say that fish are like Goldilocks: They don’t want their water too hot or too cold, but just right.
Put another way, most fish species have evolved narrow temperature tolerances. Supporting the cellular machinery necessary to tolerate wider temperatures demands a lot of energy. This evolutionary strategy saves energy when temperatures are “just right,” but it becomes a problem when fish find themselves in warming water. As their bodies begin to fail, they must divert energy from searching for food or avoiding predators to maintaining basic bodily functions and searching for cooler waters.
Thus, as the oceans warm, fish move to track their preferred temperatures. Most fish are moving poleward or into deeper waters. For some species, warming expands their ranges. In other cases it contracts their ranges by reducing the amount of ocean they can thermally tolerate. These shifts change where fish go, their abundance and their catch potential.
Warming can also modify the availability of key prey species. For example, if warming causes zooplankton – small invertebrates at the bottom of the ocean food web – to bloom early, they may not be available when juvenile fish need them most. Alternatively, warming can sometimes enhance the strength of zooplankton blooms, thereby increasing the productivity of juvenile fish.
Understanding how the complex impacts of warming on fish populations balance out is crucial for projecting how climate change could affect the ocean’s potential to provide food and income for people.
Impacts of historical warming on marine fisheries
Sustainable fisheries are like healthy bank accounts. If people live off the interest and don’t overly deplete the principal, both people and the bank thrive. If a fish population is overfished, the population’s “principal” shrinks too much to generate high long-term yields.
Similarly, stresses on fish populations from environmental change can reduce population growth rates, much as an interest rate reduction reduces the growth rate of savings in a bank account.
In our study we combined maps of historical ocean temperatures with estimates of historical fish abundance and exploitation. This allowed us to assess how warming has affected those interest rates and returns from the global fisheries bank account.
Losers outweigh winners
We found that warming has damaged some fisheries and benefited others. The losers outweighed the winners, resulting in a net 4% decline in sustainable catch potential over the last 80 years. This represents a cumulative loss of 1.4 million metric tons previously available for food and income.
Some regions have been hit especially hard. The North Sea, with large commercial fisheries for species like Atlantic cod, haddock and herring, has experienced a 35% loss in sustainable catch potential since 1930. The waters of East Asia, neighbored by some of the fastest-growing human populations in the world, saw losses of 8% to 35% across three seas.
Other species and regions benefited from warming. Black sea bass, a popular species among recreational anglers on the U.S. East Coast, expanded its range and catch potential as waters previously too cool for it warmed. In the Baltic Sea, juvenile herring and sprat – another small herring-like fish – have more food available to them in warm years than in cool years, and have also benefited from warming. However, these climate winners can tolerate only so much warming, and may see declines as temperatures continue to rise.
Management boosts fishes’ resilience
Our work suggests three encouraging pieces of news for fish populations.
First, well-managed fisheries, such as Atlantic scallops on the U.S. East Coast, were among the most resilient to warming. Others with a history of overfishing, such as Atlantic cod in the Irish and North seas, were among the most vulnerable. These findings suggest that preventing overfishing and rebuilding overfished populations will enhance resilience and maximize long-term food and income potential.
Second, new research suggests that swift climate-adaptive management reforms can make it possible for fish to feed humans and generate income into the future. This will require scientific agencies to work with the fishing industry on new methods for assessing fish populations’ health, set catch limits that account for the effects of climate change and establish new international institutions to ensure that management remains strong as fish migrate poleward from one nation’s waters into another’s. These agencies would be similar to multinational organizations that manage tuna, swordfish and marlin today.
Finally, nations will have to aggressively curb greenhouse gas emissions. Even the best fishery management reforms will be unable to compensate for the 4 degree Celsius ocean temperature increase that scientists project will occur by the end of this century if greenhouse gas emissions are not reduced.
A landmark scientific report has confirmed that climate change is altering the world’s seas and ice at an unprecedented rate. Australia depends on the ocean that surrounds us for our health and prosperity. So what does this mean for us, and life on Earth?
The Intergovernmental Panel on Climate Change (IPCC) findings were launched in Monaco on Wednesday night. They provide the most definitive scientific evidence yet of warmer, more acidic and less productive seas. Glaciers and ice sheets are melting, causing sea level to rise at an accelerating rate.
The implications for Australia are serious. Extreme sea level events that used to hit once a century will occur once a year in many of the world’s coastal places by 2050. This situation is inevitable, even if greenhouse gas emissions are dramatically curbed.
The findings, titled the Special Report on the Ocean and Cryosphere in a Changing Climate, strengthen the already compelling case for countries to meet their emission reduction goals under the 2015 Paris agreement.
A rapid and dramatic cut in greenhouse gas emissions would prevent the most catastrophic damage to the ocean and cryosphere (frozen polar and mountain regions). This would help protect the ecosystems and people that rely on them.
The report entailed two years of work by 104 authors and review editors from 36 countries, who assessed nearly 7,000 scientific papers and responded to more than 30,000 review comments.
The picture is worse than we thought
Mountain glaciers and polar ice sheets are shrinking and, together with expansion of the warming ocean, are contributing to an increasing rate of sea level rise.
During the last century, global sea levels rose about 15cm. Seas are now rising more than twice as fast – 3.6mm per year – and accelerating, the report shows.
The IPCC’s projections are more dire than in its 2014 oceans report. It has revised upwards by 10% the effect of the melting Antarctic ice sheet on sea level rise by 2100. Antarctica appears to be changing more rapidly than was thought possible even five years ago, and further work is needed to understand just how quickly ice will be lost from Antarctica in future.
If you live near the Australian coast, change is coming
By 2050, more than one billion of the world’s people will live on coastal land less than 10 metres above sea level. They will be exposed to combinations of sea level rise, extreme winds, waves, storm surges and flooding from intensified storms and tropical cyclones.
Many of Australia’s coastal cities and communities can expect to experience what was previously a once-in-a-century extreme coastal flooding event at least once every year by the middle of this century.
Our island neighbours in Indonesia and the Pacific will also be hit hard. The report warns that some island nations are likely to become uninhabitable – although the extent of this is hard to assess accurately.
Some change is inevitable and we will have to adapt. But the report also delivered a strong message about the choices that still remain. In the case of extreme sea level events around Australia, we believe a marked global reduction in greenhouse as emissions would buy us more than 10 years of extra time, in some places, to protect our coastal communities and infrastructure from the rising ocean.
More frequent extreme events are often occurring at the same time or in quick succession. Tasmania’s summer of 2015-16 is a good example. The state experienced record-breaking drought which worsened the fire threat in the highlands. An unprecedented marine heatwave along the east coast damaged kelp forests and caused disease and death of shellfish, and the state’s northeast suffered severe flooding.
This string of events stretched emergency services, energy supplies and the aquaculture and manufacturing industries. The total economic cost to the state government was an estimated A$445 million. The impacts on the food, energy and manufacturing sectors cut Tasmania’s anticipated economic growth by about half.
Reefs and fish stocks are suffering
The ocean has taken a huge hit from climate change – taking up heat, absorbing carbon dioxide that makes the water more acidic, and losing oxygen. It will bring ocean conditions unlike anything we have seen before.
Heat build-up in the surface ocean has already triggered a marked rise in the intensity, frequency and duration of marine heatwaves. Ocean heatwaves are expected to become between four and ten times more common this century, depending on how rapidly global warming continues.
The report said coral reefs, including the Great Barrier Reef, are already at very high risk from climate change and are expected to suffer significant losses and local extinctions. This would occur even if global warming is limited to 1.5℃ – a threshold the world is set to overshoot by a wide margin.
This report reinforces the findings of earlier reports on the importance of limiting global warming warming to 1.5℃ if we are to avoid major impacts on the land, the ocean and frozen areas.
Even if we act now to drastically reduce greenhouse gas emissions, some damage is already locked in and our ocean and frozen regions will continue to change for decades to centuries to come.
In Australia, we will need to adapt our coastal cities and communities to unavoidable sea level rise. There are a range of possible options, from building barriers to planned relocation, to protecting the coral reefs and mangroves that provide natural coastal defences.
But if we want to give adaptation the best chance of working, the clear message of this new report is that we need to reduce greenhouse gas emissions as quickly as possible.
Climate change is rapidly changing the oceans, driving coral reefs around the world to breaking point. Widely publicised marine heatwaves aren’t the only threat corals are facing: the seas are increasingly acidic, have less oxygen in them, and are gradually warming as a whole.
Each of these problems reduces coral growth and fitness, making it harder for reefs to recover from sudden events such as massive heatwaves.
Our research, published today in Marine Ecology Progress Series, investigates corals on the Great Barrier Reef that are surprisingly good at surviving in increasingly hostile waters. Finding out how these “super corals” can live in extreme environments may help us unlock the secret of coral resilience helping to save our iconic reefs.
Coral conservation under climate change
The central cause of these problems is climate change, so the central solution is reducing carbon emissions. Unfortunately, this is not happening rapidly enough to help coral reefs, so scientists also need to explore more immediate conservation options.
To that end, many researchers have been looking at coral that manages to grow in typically hostile conditions, such as around tide pools and intertidal reef zones, trying to unlock how they become so resilient.
These extreme coral habitats are not only natural laboratories, they house a stockpile of extremely tolerant “super corals”.
What exactly is a super coral?
“Super coral” generally refers to species that can survive both extreme conditions and rapid changes in their environment. But “super” is not a very precise term!
Our previous research quantified these traits so other ecologists can more easily use super coral in conservation. There are a few things that need to be established to determine whether a coral is “super”:
What hazard can the coral survive? For example, can it deal with high temperature, or acidic water?
How long did the hazard last? Was it a short heatwave, or a long-term stressor such as ocean warming?
Did the coral survive because of a quality such as genetic adaption, or was it tucked away in a particularly safe spot?
How much area does the coral cover? Is it a small pocket of resilience, or a whole reef?
Is the coral trading off other important qualities to survive in hazardous conditions?
Is the coral super enough to survive the changes coming down the line? Is it likely to cope with future climate change?
We discovered mangrove lagoons near coral reefs can often house corals living in very extreme conditions – specifically, warm, more acidic and low oxygen seawater.
Previously we have reported corals living in extreme mangroves of the Seychelles, Indonesia, New Caledonia – and in our current study living on the Great Barrier Reef. We report diverse coral populations surviving in conditions more hostile than is predicted over the next 100 years of climate change.
Importantly, while some of these sites only have isolated populations, other areas have actively building reef frameworks.
Particularly significant were the two mangrove lagoons on the Great Barrier Reef. They housed 34 coral species, living in more acidic water with very little oxygen. Temperatures varied widely, over 7℃ in the period we studied – and included periods of very high temperatures that are known to cause stress in other corals.
While coral cover was often low and the rate at which they build their skeleton was reduced, there were established coral colonies capable of surviving in these conditions.
The success of these corals reflect their ability to adapt to daily or weekly conditions, and also their flexible relationship with various symbiotic micro-algae that provide the coral with essential resources.
While we are still in the early phases of understanding exactly how these corals can aid conservation, extreme mangrove coral populations hold a reservoir of stress-hardened corals. Notably the geographic size of these mangrove locations are small, but they have a disproportionately high conservation value for reef systems.
Unlike the many species which stalk the shallow, coastal waters that fisheries exploit all year round, pelagic sharks roam the vast open oceans. These are the long-distance travellers of the submarine world and include the world’s largest fish, the whale shark, and also one of the fastest fish in the sea, the shortfin mako shark, capable of swimming at 40mph.
Because these species range far from shore, you might expect them to escape most of the lines and nets that fishing vessels cast. But over the last 50 years, industrial scale fisheries have extended their reach across the world’s oceans and tens of millions of pelagic sharks are now caught every year for their valuable fins and meat.
On average, large pelagic sharks account for over half of all shark species identified in catches worldwide. The toll this has taken on species such as the shortfin mako has prompted calls to introduce catch limits in the high seas – areas of the ocean beyond national jurisdiction where there is little or no management for the majority of shark species.
We wanted to know where the ocean’s shark hotspots are – the places where lots of different species gather – and how much these places are worked by fishing boats. We took up the challenge of finding out where pelagic sharks hang out by satellite tracking their movements with electronic tags. This approach by our international team of over 150 scientists from 26 countries has an important advantage over fishery catch records. Rather than showing where a fishing boat found them, it can precisely map all of the places sharks visit.
Nowhere to hide
For a new study published in Nature we tracked nearly 2,000 sharks from 23 different species, including great whites, blue sharks, shortfin mako and tiger sharks. We were able to map their positions in unprecedented detail and discern the most visited hotspots where sharks feed, breed and rest.
Hotspots were often located in frontal zones – boundaries in the sea between different water masses that can have the best conditions of temperature and nutrients for phytoplankton to bloom, which attracts masses of zooplankton, as well as the fish and squid that sharks eat.
Then we calculated how much these hotspots overlapped with global fleets of large, longline fishing vessels, which we also tracked by satellite. This type of fishing gear is used very widely on the high seas and catches more pelagic sharks than trawls and other gear. Each longline vessel is capable of deploying a 100km long line bearing over 1,000 baited hooks.
We found that even the most remote parts of the ocean that are many miles from land offer pelagic sharks little refuge from industrial-scale fishing fleets. One in four of the places sharks visited each month overlapped with the areas longline fishing vessels operated in.
Sharks such as the North Atlantic blue and the shortfin mako – which fishers also target for their fins and meat – were much more likely to encounter these vessels, with as much as 76% of the places these species visited most in each month overlapping with where longline vessels were fishing. Even internationally protected species such as great whites and porbeagle sharks encountered longline vessels in half of their tracked range.
It’s now clear that much of the world’s fishing activity on the high seas is centred on shark hotspots, which longlines rake for much of the year. Many large sharks, which are already endangered, face a future without refuge from industrial fishing in the places they gather.
High seas marine protected areas
The maps of shark hotspots and longline fishing activity that we created can at least provide a blueprint for where large-scale marine protected areas aimed at conserving sharks could be set. Outside of these, strict quotas could reduce catches.
The United Nations is creating a high seas treaty for protecting ocean biodiversity – negotiations are due to continue in August 2019 in New York. They’ll consider large-scale marine protected areas for the high seas and we’ll suggest where these could be located to best protect pelagic sharks.
Satellite monitoring could give real-time signals of where sharks and other threatened creatures such as turtles and whales are gathering. Tracking where these species roam and where fishers interact with them will help patrol vessels monitor these high-risk zones more efficiently.
Such management action is overdue for many shark populations in the high seas. Take North Atlantic shortfin makos – not only are they overfished
and endangered, but now we know they have no respite from longline fishing during many months of the year in the places they gather most often. Some of these shark hotspots may not exist in the near future if action isn’t taken now to conserve these species and the habitats they depend on.
In the midst of a raging heatwave, most people think of the ocean as a nice place to cool down. But heatwaves can strike in the ocean as well as on land. And when they do, marine organisms of all kinds – plankton, seaweed, corals, snails, fish, birds and mammals – also feel the wrath of soaring temperatures.
Our new research, published today in Nature Climate Change, makes abundantly clear the destructive force of marine heatwaves. We compared the effects on ecosystems of eight marine heatwaves from around the world, including four El Niño events (1982-83, 1986-87, 1991-92, 1997-98), three extreme heat events in the Mediterranean Sea (1999, 2003, 2006) and one in Western Australia in 2011. We found that these events can significantly damage the health of corals, kelps and seagrasses.
This is concerning, because these species form the foundation of many ecosystems, from the tropics to polar waters. Thousands of other species – not to mention a wealth of human activities – depend on them.
We identified southeastern Australia, southeast Asia, northwestern Africa, Europe and eastern Canada as the places where marine species are most at risk of extreme heat in the future.
Marine heatwaves are defined as periods of five days or more during which ocean temperatures are unusually high, compared with the long-term average for any given place. Just like their counterparts on land, marine heatwaves have been getting more frequent, hotter and longer in recent decades. Globally, there were 54% more heatwave days per year between 1987 and 2016 than in 1925–54.
Although the heatwaves we studied varied widely in their maximum intensity and duration, we found that all of them had negative impacts on a broad range of different types of marine species.
Humans also depend on these species, either directly or indirectly, because they underpin a wealth of ecological goods and services. For example, many marine ecosystems support commercial and recreational fisheries, contribute to carbon storage and nutrient cycling, offer venues for tourism and recreation, or are culturally or scientifically significant.
Marine heatwaves have had negative impacts on virtually all these “ecosystem services”. For example, seagrass meadows in the Mediterranean Sea, which store significant amounts of carbon, are harmed by extreme temperatures recorded during marine heatwaves. In the summers of both 2003 and 2006, marine heatwaves led to widespread seagrass deaths.
The marine heatwaves off the west coast of Australia in 2011 and northeast America in 2012 led to dramatic changes in the regionally important abalone and lobster fisheries, respectively. Several marine heatwaves associated with El Niño events caused widespread coral bleaching with consequences for biodiversity, fisheries, coastal erosion and tourism.
All evidence suggests that marine heatwaves are linked to human mediated climate change and will continue to intensify with ongoing global warming. The impacts can only be minimised by combining rapid, meaningful reductions in greenhouse emissions with a more adaptable and pragmatic approach to the management of marine ecosystems.
Many people in Australia will head to the beach this summer and that’ll most likely include a dip or a plunge into the sea. But have you ever wondered where those ocean waters come from, and what influence they may have?
Australia is surrounded by ocean currents that have a strong controlling influence on things such as climate, ecosystems, fish migrations, the transport of ocean debris and on water quality.
Our 15 year simulation indicates that water from the Pacific Ocean enters the Indonesian Archipelago through the Mindanao current (north) and Halmahera Sea (south).
It then enters the Indian ocean as the Indonesian Throughflow between many Indonesian Islands, with flow through the Timor Passage being the most dominant.
Most of this water flows west as the South Equatorial Current. Re-circulation of the SEC creates the Eastern Gyre that contributes to the Holloway Current. This in turn feeds the Leeuwin Current – the longest boundary current in the world (Ocean currents that flow adjacent to a coastline are called boundary currents)
The Leeuwin Current is the major boundary current along the west coast and as it moves southward. Indian Ocean water is supplied by the South Indian Counter Current increasing the Leeuwin Current transport by 60%.
The Leeuwin Current turns east at Cape Leeuwin, in Western Australia’s south-west, and continues to Tasmania as the South Australian and Zeehan Currents.
There is a strong seasonal variation in the strength of the boundary currents in the Indian Ocean with a progression southwards of the peak transport along the coast.
The Holloway Current peaks in April/May (coinciding with changes in the monsoon winds), the Leeuwin Current reaches a maximum along the west and south coasts in June and August.
In the Pacific Ocean, the northern branches of the South Equatorial Current are the main inputs initiating the Hiri Current and East Australian Current.
At around latitude 15 degrees south the currents split in two: southward to form the East Australian Current, and northward to form the Hiri Current which contributes to a clockwise gyre in the Gulf of Papua.
The East Australian Current is the dominant current in the region transporting 33 million cubic metres of water per second southward.
At around 32S, the East Australian Current separates from the coast and 60% of the water flows eastward to New Zealand as the Tasman Front. The remaining 40% flows southward as the East Australian Current extension and contributes to the Tasman Outflow.
The Tasman outflow is the major conduit of water from the Pacific to Indian Ocean and contributes to the Flinders Current, flowing westward from Tasmania and past Cape Leeuwin into the Indian Ocean.
Along the southern continental slope, the Flinders Current appears as an undercurrent beneath the Leeuwin Current and a surface current further offshore. The Flinders Current contributes to the Leeuwin Undercurrent directly as a northward flow, flowing to the north-west of Australia in water depths 300 metres to 800 metres.
Impact of the currents
Understanding ocean circulation is a fundamental tenet of physical oceanography and scientists have been charting the pathways of ocean currents since the American hydrographer Matthew Maury, one of the founders of oceanography, who first charted the Gulf Stream in 1855.
One of the first maps of circulation around Australia was by Halliday (1921) who showed the movement of “warm” and “cold” waters around Australia. Although some of the major features (such as the East Australian Current) were correctly identified, a more fine scale description is now available.
The unique feature of ocean currents around Australia is that along both east and west coasts they transport warmer water southwards and influence the local climate, particularly air temperature and rainfall, as well as species distribution.
For example, the south west of Australia is up to 5C warmer in winter and receives more than double the rainfall compared to regions located on similar latitudes along western coastlines of other continents.
Similarly many tropical species of fish are found in the southwest of Australia that hitch a ride on the ocean currents.
The Pacific Ocean is the origin of waters around Australia with a direct link to the east and an indirect link to west.
Ocean water from the Pacific Ocean flows through the Indonesian Archipelago, a region subject to high solar heating and rainfall runoff, creating lower density water. This water, augmented by water from the Indian Ocean, flows around the western and southern coasts, converging along the southern coast of Tasmania.
So next time you head for a dip in the coastal waters around Australian, spare a thought for where that water has come from and where it may be going next.
What sort of life do you associate with Antarctica? Penguins? Seals? Whales?
Actually, life in Antarctic waters is much broader than this, and surprisingly diverse. Hidden under the cover of sea-ice for most of the year, and living in cold water near the seafloor, are thousands of unique and colourful species.
Our research has generated new techniques to map where these species live, and predict how this might change in the future.
Biodiversity is nature’s most valuable resource, and mapping how it is distributed is a crucial step in conserving life and ecosystems in Antarctica.
The ocean surrounding the Antarctic continent is an unusual place. Here, water temperatures reach below freezing-point, and the ocean is covered in ice for most of the year.
While commonly known for its massive icebergs and iconic penguins, Antarctica’s best-kept secret lies on the seafloor far below the ocean surface. In this remote and isolated environment, a unique and diverse community of animals has evolved, half of which aren’t found anywhere else on the planet.
Colourful corals and sponges cover the seafloor, where rocks provide hard substrate for attachment. These creatures filter the water for microscopic algae that sink from the ocean surface during the highly productive summer season between December and March.
In turn, these habitat-forming animals provide the structure for all sorts of mobile animals, such as featherstars, seastars, crustaceans, sea spiders and giant isopods (marine equivalents of “slaters” or “woodlice”).
Biodiversity is a term that describes the variety of all life forms on Earth. The unprecedented rate of biodiversity loss is one of the biggest challenges of our time. And despite its remoteness, Antarctica’s biodiversity is not protected from human impact through climate change, pollution and fisheries.
Although scientists have broadly known about Antarctica’s unique marine biodiversity for some time, we still lack knowledge of where each species lives and where important hotspots of biodiversity are located. This is an issue because it hinders us from understanding how the ecosystem functions – and makes it hard to assess potential threats.
Why don’t we know more about the distribution of Antarctic marine species? Primarily, because sampling at the seafloor a few thousand metres below the surface is difficult and expensive, and the Antarctic continental shelf is vast and remote. It usually takes the Australian Icebreaker Aurora Australis ten days to reach the icy continent.
To make the most of the sparse and patchy biological data that we do have, in our research we take advantage of the fact that species usually have a set of preferred environmental conditions. We use the species’ relationship with their environment to build statistical models that predict where species are most likely to occur.
This allows us to map their distribution in places where we have no biological samples and only environmental data. Critically, until now important environmental factors that influence the distribution of seafloor species have been missing.
In a recent study, we were able to predictively map how much food from the ocean-surface was available for consumption by corals, sponges and other suspension feeders at the seafloor.
Although biological samples are still scarce, this allowed us to map the distribution of seafloor biodiversity in a region in East Antarctica with high accuracy.
Further, estimates of how and where the supply of food increased after the tip of a massive glacier broke off and changed ocean conditions in the region allowed us to predict where abundances of habitat forming fauna such as corals and sponges will increase in the future.
Antarctica is one of the few regions where the total biomass of seafloor animals is likely to increase in the future. Retreating ice-shelves increase the amount of suitable habitat available and allow more food to reach the seafloor.
For the first time in history, we now have the information, computational power and research capacity to map the distribution of life on the entire continental shelf around Antarctica, identify previously unknown hotspots of biodiversity, and assess how the unique biodiversity of the Antarctic will change into the future.
Large waves after the loss of sea ice can trigger Antarctic ice shelf disintegration over a period of just days, according to our new research.
With other research also published today in Nature showing that the rate of annual ice loss from the vulnerable Antarctic Peninsula has quadrupled since 1992, our study of catastrophic ice shelf collapses during that time shows how the lack of a protective buffer of sea ice can leave ice shelves, already weakened by climate warming, wide open to attack by waves.
Antarctica is covered by an ice sheet that is several kilometres thick in places. It covers an area of 14 million square kilometres – roughly twice the size of Australia. This ice sheet holds more than 90% of the world’s ice, which is enough to raise global mean sea level by 57 metres.
As snow falls and compacts on the ice sheet, the sheet thickens and flows out towards the coast, and then onto the ocean surface. The resulting “ice shelves” (and glacier tongues) buttress three-quarters of the Antarctic coastline. Ice shelves act as a crucial braking system for fast-flowing glaciers on the land, and thus moderate the ice sheet’s contribution to sea-level rise.
In the southern summer of 2002, scientists monitoring the Antarctic Peninsula (the northernmost part of mainland Antarctica) by satellite witnessed a dramatic ice shelf disintegration that was stunning in its abruptness and scale. In just 35 days, 3,250 square km of the Larsen B Ice Shelf (twice the size of Queensland’s Fraser Island) shattered, releasing an estimated 720 billion tonnes of icebergs into the Weddell Sea.
This wasn’t the first such recorded event. In January 1995, roughly 1,500 square km of the nearby Larsen A Ice Shelf suddenly disintegrated after several decades of warming and years of gradual retreat. To the southwest, the Wilkins Ice Shelf suffered a series of strikingly similar disintegration events in 1998, 2008 and 2009 — not only in summer but also in two of the Southern Hemisphere’s coldest months, May and July.
These sudden, large-scale fracturing events removed features that had been stable for centuries – up to 11,500 years in the case of Larsen B. While ice shelf disintegrations don’t directly raise sea level (because the ice shelves are already floating), the removal of shelf ice allows the glaciers behind them to accelerate their discharge of land-based ice into the ocean – and this does raise sea levels. Previousresearch has shown that the removal of Larsen B caused its tributary glaciers to flow eight times faster in the year following its disintegration.
The ocean around ice shelves is typically covered by a very different (but equally important) type of ice, called sea ice. This is formed from frozen seawater and is generally no more than a few metres thick. But it stretches far out into the ocean, doubling the area of the Antarctic ice cap when at its maximum extent in winter, and varying in extent throughout the year.
The response of Antarctic sea ice to climate change and variability is complex, and differs between regions. Around the Antarctic Peninsula, in the Bellingshausen and northwestern Weddell seas, it has clearly declined in extent and annual duration since satellite monitoring began in 1979, at a similar rate to the Arctic’s rapidly receding sea ice.
The Southern Ocean is also host to the largest waves on the planet, and these waves are becoming more extreme. Our new study focuses on “long-period” swell waves (with swells that last up to about 20 seconds). These are generated by distant storms and carry huge amounts of energy across the oceans, and can potentially flex the vulnerable outer margins of ice shelves.
The earliest whalers and polar pioneers knew that sea ice can damp these waves — Sir Ernest Shackleton reported it in his iconic book South!. Sea ice thus acts as a “buffer” that protects the Antarctic coastline, and its ice shelves, from destructive ocean swells.
Strikingly, all five of the sudden major ice shelf disintegrations listed above happened during periods when sea ice was abnormally low or even absent in these regions. This means that intense swell waves crashed directly onto the vulnerable ice shelf fronts.
The straw that broke the camel’s back
The Antarctic Peninsula has experienced particularly strong climate warming (roughly 0.5℃ per decade since the late 1940s), which has caused intense surface melting on its ice shelves and exacerbated their structural weaknesses such as fractures. These destabilising processes are the underlying drivers of ice shelf collapse. But they do not explain why the observed disintegrations were so abrupt.
Our new study suggests that the trigger mechanism was swell waves flexing and working weaknesses at the shelf fronts in the absence of sea ice, to the point where they calved away the shelf fronts in the form of long, thin “sliver-bergs”. The removal of these “keystone blocks” in turn led to the catastrophic breakup of the ice shelf interior, which was weakened by years of melt.
Our research thus underlines the complex and interdependent nature of the various types of Antarctic ice – particularly the important role of sea ice in forming a protective “buffer” for shelf ice. While much of the focus so far has been on the possibility of ice shelves melting from below as the sea beneath them warms, our research suggests an important role for sea ice and ocean swells too.
In July 2017 an immense iceberg broke away from the Larsen C Ice Shelf, just south of Larsen B, prompting fears that it could disintegrate like its neighbours.
Our research suggests that four key factors will determine whether it does: extensive flooding and fracturing across the ice shelf; reduced sea ice coverage offshore; extensive fracturing of the ice shelf front; and calving of sliver-bergs.
If temperatures continue to rise around the Antarctic, ice shelves will become weaker and sea ice less extensive, which would imply an increased likelihood of future disintegrations.
However, the picture is not that clear-cut, as not all remaining ice shelves are likely to respond in the same way to sea ice loss and swell wave impacts. Their response will also depend on their glaciological characteristics, physical setting, and the degree and nature of surface flooding. Some ice shelves may well be capable of surviving prolonged absences of sea ice.
Irrespective of these differences, we need to include sea ice and ocean waves in our models of ice sheet behaviour. This will be a key step towards better forecasting the fate of Antarctica’s remaining ice shelves, and how much our seas will rise in response to projected climate change over coming decades. In parallel, our new findings underline the need to better understand and model the mechanisms responsible for recent sea ice trends around Antarctica, to enable prediction of likely future change in the exposure of ice shelves to ocean swells.
Luke Bennetts, Lecturer in applied mathematics, University of Adelaide; Rob Massom, Leader, Sea Ice Group, Antarctica & the Global System program, Australian Antarctic Division and Antarctic Climate and Ecosystems CRC, and Vernon Squire, Deputy Vice-Chancellor Academic, Professor of Applied Mathematics
There is something special and awe-inspiring about watching new land form. This is what is now happening in Hawai’i as its Kīlauea volcano erupts. Lava is reaching the ocean and building land while producing spectacular plumes of steam. These eruptions are hugely important for the creation of new land. But they are also dangerous. Where the lava meets the ocean, corrosive acid mist is produced and glass particles are shattered and flung into the air. Volcanic explosions can also hurl lava blocks hundreds of metres and produce waves of scalding hot water.
At Kīlauea, lava is erupting from a line of vents on the volcano’s flanks, and is moving downslope to the edge of the island, where it enters the ocean. This is a process that has been witnessed many times at Hawai’i and other volcanic islands. And it is through many thousands of such eruptions that volcanic islands like Hawai’i form.
The new lava being added to Hawai’i by this latest Kīlauea eruption replaces older land that is being lost by erosion, and so prolongs the island’s lifespan. In contrast, older islands to the north-west have no active volcanoes, so they are being eroded by the ocean and will eventually disappear beneath the waves. The opposite is happening to the south-east of Hawai’i, where an underwater volcano (Lōʻihi Seamount) is building the foundations of what will eventually become the next volcanic island in this area.
How lava gets to the ocean at Hawai’i
The lava erupting from the current Kīlauea vents has a temperature of roughly 1150 degrees °C, and has a journey of between 4.5km and 5.5km to reach the ocean. As this lava moves swiftly in channels, it loses little heat and so it can enter the ocean at a temperature of over 1000 degrees°C.
What happens when lava meets the ocean?
We are witnessing one of the most spectacular sights in nature – billowing white plumes of steam (technically water droplets) as hot lava boils seawater. Although these billowing steam clouds appear harmless, they are dangerous because they contain small glass shards (fragmented lava) and acid mist (from seawater). This acid mist known as “laze” (lava haze) can be hot and corrosive. If anyone goes to near it, they can experience breathing difficulties and irritation of their eyes and skin.
Apart from the laze, the entry of lava into the ocean is usually a gentle process, and when steam is free to expand and move away, there are no violent steam-driven explosions.
But a hidden danger lurks beneath the ocean. The lava entering the sea breaks up into blobs (known as pillows), angular blocks, and smaller fragments of glass that form a steep slope beneath the water. This is called a lava delta.
A newly formed lava delta is an unstable beast, and it can collapse without warning. This can trap water within the hot rock, leading to violent steam-driven explosions that can hurl metre-sized blocks up to 250 metres. Explosions occur because when the water turns to steam it suddenly expands to around 1,700 times its original volume. Waves of scalding water can also injure people who are too close. People have died and been seriously injured during lava delta collapses
So, the ocean entry points where lava and seawater meet are doubly dangerous, and anyone in the area should pay careful attention to official advice on staying away from them.
What more can we learn from these eruptions?
Once lava deltas have cooled and become stable they represent new land. Studies have revealed that lava deltas have distinctive features, and this has enabled volcanologists to recognise lava deltas in older rocks.
Remarkable examples of lava deltas have been discovered near the top of extinct volcanoes (called tuyas) in Iceland and Antarctica. These deltas can only form in water and the only plausible source of this water in this case is melted ice. This means that these volcanoes had melted water-filled holes up to 1.5km deep in ice sheets, which is an astonishing feat. In fact, these lava deltas are the only remaining evidence of long-vanished ice sheets.
It is a privilege to see these incredible scenes of lava meeting the ocean. The ongoing eruptions form part of the natural process that enables beautiful volcano islands like Hawai’i to exist. But the creation of new land here can also bring danger to those who get too close, whether it be collapsing lava deltas or acid mist.