Explainer: how the Antarctic Circumpolar Current helps keep Antarctica frozen



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The Antarctic Circumpolar Current keeps Antarctica cold.
Shutterstock

Helen Phillips, University of Tasmania; Benoit Legresy, CSIRO, and Nathan Bindoff, University of Tasmania

The Antarctic Circumpolar Current, or ACC, is the strongest ocean current on our planet. It extends from the sea surface to the bottom of the ocean, and encircles Antarctica.

Scientists deploying a vertical microstructure profiler (VMP-2000), which measures temperature, salinity, pressure and turbulence, from RV Investigator in the Antarctic Circumpolar Current, November 2018.
Nathan Bindoff

It is vital for Earth’s health because it keeps Antarctica cool and frozen. It is also changing as the world’s climate warms. Scientists like us are studying the current to find out how it might affect the future of Antarctica’s ice sheets, and the world’s sea levels.

The ACC carries an estimated 165 million to 182 million cubic metres of water every second (a unit also called a “Sverdrup”) from west to east, more than 100 times the flow of all the rivers on Earth. It provides the main connection between the Indian, Pacific and Atlantic Oceans.

The tightest geographical constriction through which the current flows is Drake Passage, where only 800 km separates South America from Antarctica. While elsewhere the ACC appears to have a broad domain, it must also navigate steep undersea mountains that constrain its path and steer it north and south across the Southern Ocean.




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What is the Antarctic Circumpolar Current?

A satellite view over Antarctica reveals a frozen continent surrounded by icy waters. Moving northward, away from Antarctica, the water temperatures rise slowly at first and then rapidly across a sharp gradient. It is the ACC that maintains this boundary.

Map of the ocean surface temperature as measured by satellites and analysed by the European Copernicus Marine Services. The sea ice extent around the antarctic continent for this day appears in light blue. The two black lines indicate the long term position of the southern and northern front of the Antarctic Circumpolar Current.

The ACC is created by the combined effects of strong westerly winds across the Southern Ocean, and the big change in surface temperatures between the Equator and the poles.

Ocean density increases as water gets colder and as it gets more salty. The warm, salty surface waters of the subtropics are much lighter than the cold, fresher waters close to Antarctica. We can imagine that the depth of constant density levels slopes up towards Antarctica.

The westerly winds make this slope steeper, and the ACC rides eastward along it, faster where the slope is steeper, and weaker where it’s flatter.

Fronts and bottom water

In the ACC there are sharp changes in water density known as fronts. The Subantarctic Front to the north and Polar Front further south are the two main fronts of the ACC (the black lines in the images). Both are known to split into two or three branches in some parts of the Southern Ocean, and merge together in other parts.

Scientists can figure out the density and speed of the current by measuring the ocean’s height, using altimeters. For instance, denser waters sit lower and lighter waters stand taller, and differences between the height of the sea surface give the speed of the current.

Map of how fast the waters around Antarctica are moving in an easterly direction. It is produced using 23 years of satellite altimetry (ocean height) observations as provided by the European Copernicus Marine Services.
Author provided

The path of the ACC is a meandering one, because of the steering effect of the sea floor, and also because of instabilities in the current.

The ACC also plays a part in the meridional (or global) overturning circulation, which brings deep waters formed in the North Atlantic southward into the Southern Ocean. Once there it becomes known as Circumpolar Deep Water, and is carried around Antarctica by the ACC. It slowly rises toward the surface south of the Polar Front.

Once it surfaces, some of the water flows northward again and sinks north of the Subarctic Front. The remaining part flows toward Antarctica where it is transformed into the densest water in the ocean, sinking to the sea floor and flowing northward in the abyss as Antarctic Bottom Water. These pathways are the main way that the oceans absorb heat and carbon dioxide and sequester it in the deep ocean.

Changing current

The ACC is not immune to climate change. The Southern Ocean has warmed and freshened in the upper 2,000 m. Rapid warming and freshening has also been found in the Antarctic Bottom Water, the deepest layer of the ocean.

Waters south of the Polar Front are becoming fresher due to increased rainfall there, and waters to the north of the Polar Front are becoming saltier due to increased evaporation. These changes are caused by human activity, primarily through adding greenhouse gases to the atmosphere, and depletion of the ozone layer. The ozone hole is now recovering but greenhouse gases continue to rise globally.

Winds have strengthened by about 40% over the Southern Ocean over the past 40 years. Surprisingly, this has not translated into an increase in the strength of the ACC. Instead there has been an increase in eddies that move heat towards the pole, particularly in hotspots such as Drake Passage, Kerguelen Plateau, and between Tasmania and New Zealand.

We have observed much change already. The question now is how this increased transfer of heat across the ACC will impact the stability of the Antarctic ice sheet, and consequently the rate of global sea-level rise.The Conversation

Helen Phillips, Senior Research Fellow, Institute for Marine and Antarctic Studies, University of Tasmania; Benoit Legresy, , CSIRO, and Nathan Bindoff, Professor of Physical Oceanography, Institute for Marine and Antarctic Studies, University of Tasmania

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

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Explainer: what any country can and can’t do in Antarctica, in the name of science



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In Antarctica, many countries want a piece of the action.
Flickr/Christopher Michel, CC BY

Julia Jabour, University of Tasmania

Antarctica is owned by no one, but there are plenty of countries interested in this frozen island continent at the bottom of the Earth.

While there are some regulations on who can do what there, scientific research has no definition in Antarctic law. So any research by a country conducted in or about Antarctica can be interpreted as legitimate Antarctic science.




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There are 30 countries – including Australia – operating bases and ships, and flying aircraft to and from runways across the continent.

Russia and China have increased their presence in Antarctica over the past decade, with China now reportedly interested in building its first permanent airfield.

It is not surprising there is significant interest in who is doing what, where – especially if countries ramp up their investment in Antarctic infrastructure with new stations, ships or runways.

Their actions might raise eyebrows and fuel speculation. But the freedom of countries to behave autonomously is guided by the laws that apply to this sovereign-neutral continent.

Treaties and signatories

There are 12 original signatories to the 1959 Antarctic Treaty, including Australia, and they do not have to prove their commitment to the treaty since they wrote the rules.

Another 41 countries have signed on since 1959, and they do need to prove commitment.

Non-signatory countries, such as Iran or Indonesia, are freed from many of these legal obligations.

Until such time as the Antarctic Treaty has been designated customary international law applicable to all states by a high authority (such as the International Court of Justice), non-signatories can essentially do what they like in Antarctica.

The appliance of science

Autonomous freedom of activity by signatory countries is legitimised through the fact that science is the currency of credibility in Antarctica. This is important for two reasons:

  1. scientific research has legal priority
  2. new signatories can become decision-makers when they do science.

The “freedom of scientific investigation” is preserved in Article II of the Antarctic Treaty. It directs that signatories to the treaty can conduct scientific research of any kind anywhere in the Antarctic, without anybody else’s permission.

The Scientific Committee on Antarctic Research (SCAR) coordinates Antarctic research, but being a member is not a prerequisite for doing Antarctic science.

Further, the treaty outlines the process for new signatories (that is, other than the original 12) to achieve Consultative Party (decision-making) status.

Decisions are made by consensus (that is, everyone agrees or there is no formal objection). So every country’s “vote” counts and new countries aspire to gain a seat at the table to further their national agendas.

They become Consultative Parties by conducting “substantial scientific research activity” (Article IX.2) and when this has been accomplished to the satisfaction of the other decision-makers, they will be accepted.

Piggy backing

Demonstrating interest in Antarctic science was initially interpreted as building a base or dispatching an expedition (Article IX.2). But after the adoption of the environmental protocol to the treaty in 1991, this was re-interpreted.

Parties were encouraged (but not legally bound) to consider piggy-backing on existing national scientific expeditions of other countries, and to share stations and other resources such as ships and aircraft where possible.

Currently there is only one jointly operated scientific base – Concordia, occupied by both France and Italy. The Novolazarevskaya airfield is a joint operation coordinated by Russia.

This encouragement was designed to reduce the potential for expansion of the footprint of human activities.

In 2017 the Consultative Parties adopted revised guidelines for how to become a decision maker. These outline new rules on a concept that has never been articulated publicly in an Antarctic forum before – evaluating the quality of scientific research.

This could put the brakes on the rapid addition of new signatories to the table.

There are limits

Although there is freedom to conduct science anywhere in Antarctica, what any country cannot do is lay claim to territory on the basis of its research efforts.

The treaty expressly excludes new claims or the extension of existing claims. Signatories that conduct research, and support those endeavours by building a base and infrastructure such as an airstrip, cannot use those actions as a basis of a claim while the treaty is in force.

Seven countries claim Antarctic territory: Argentina, Australia, Chile, France, New Zealand, Norway and the United Kingdom. Two others – the United States and the Russian Federation – have reserved their rights to claim any or all of Antarctica in the future.

These paper claims are acknowledged by Article IV of the treaty. But its artful craftsmanship prevents conflict over the claims and reservations during the life of the Treaty – which incidentally has neither an expiry nor a future review date.

Because the Article II freedoms permit research to be undertaken anywhere on the continent, the borders delineating claims become irrelevant to all but the claimant.

A party has an option of recognising a claim, or not, and does not need anyone’s permission to build a station or send an expedition. This means that the claimants have very limited capacity to exercise sovereignty in their territory. This effectively reduces their power to that of jurisdiction only over their own nationals.




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The sting in the tail is that conducting substantial scientific research activity in Antarctica – including the building of support infrastructure – is the pathway new states must take to achieve decision-making status.

This is only constrained by the legal requirement to undertake an environmental impact assessment of any activity prior to its commencement.

Irrespective of whether the activity’s proponent complies with best practice environmental evaluation, under the rules, no other party can veto that activity.

Essentially, any country – whether a party to the treaty or not – can do whatever they like in Antarctica.The Conversation

Julia Jabour, Leader, Ocean and Antarctic Governance Research Program, University of Tasmania

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

Why remote Antarctica is so important in a warming world


Chris Fogwill, Keele University; Chris Turney, UNSW, and Zoe Robinson, Keele University

Ever since the ancient Greeks speculated a continent must exist in the south polar regions to balance those in the north, Antarctica has been popularly described as remote and extreme. Over the past two centuries, these factors have combined to create, in the human psyche, an almost mythical land – an idea reinforced by tales of heroism and adventure from the Edwardian golden age of “heroic exploration” and pioneers such as Robert Falcon Scott, Roald Amundsen and Ernest Shackleton.

Recent research, however, is casting new light on the importance of the southernmost continent, overturning centuries of misunderstanding and highlighting the role of Antarctica in how our planet works and the role it may play in a future, warmer world.

Heroic exploration, 1913.
wiki

What was once thought to be a largely unchanging mass of snow and ice is anything but. Antarctica holds a staggering amount of water. The three ice sheets that cover the continent contain around 70% of our planet’s fresh water, all of which we now know to be vulnerable to warming air and oceans. If all the ice sheets were to melt, Antarctica would raise global sea levels by at least 56m.

Where, when, and how quickly they might melt is a major focus of research. No one is suggesting all the ice sheets will melt over the next century but, given their size, even small losses could have global repercussions. Possible scenarios are deeply concerning: in addition to rising sea levels, meltwater would slow down the world’s ocean circulation, while shifting wind belts may affect the climate in the southern hemisphere.

In 2014, NASA reported that several major Antarctic ice streams, which hold enough water to trigger the equivalent of a one-and-a-half metre sea level rise, are now irreversibly in retreat. With more than 150m people exposed to the threat of sea level rise and sea levels now rising at a faster rate globally than any time in the past 3,000 years, these are sobering statistics for island nations and coastal cities worldwide.

An immediate and acute threat

Recent storm surges following hurricanes have demonstrated that rising sea levels are a future threat for densely populated regions such as Florida and New York. Meanwhile the threat for low-lying islands in areas such as the Pacific is immediate and acute.

Much of the continent’s ice is slowly sliding towards the sea.
R Bindschadler / wiki

Multiple factors mean that the vulnerability to global sea level rise is geographically variable and unequal, while there are also regional differences in the extremity of sea level rise itself. At present, the consensus of the IPPC 2013 report suggests a rise of between 40 and 80cm over the next century, with Antarctica only contributing around 5cm of this. Recent projections, however, suggest that Antarctic contributions may be up to ten times higher.

Studies also suggest that in a world 1.5-2°C warmer than today we will be locked into millennia of irreversible sea level rise, due to the slow response time of the Antarctic ice sheets to atmospheric and ocean warming.

We may already be living in such a world. Recent evidence shows global temperatures are close to 1.5°C warmer than pre-industrial times and, after the COP23 meeting in Bonn in November, it is apparent that keeping temperature rise within 2°C is unlikely.

So we now need to reconsider future sea level projections given the potential global impact from Antarctica. Given that 93% of the heat from anthropogenic global warming has gone into the ocean, and these warming ocean waters are now meeting the floating margins of the Antarctic ice sheet, the potential for rapid ice sheet melt in a 2°C world is high.

In polar regions, surface temperatures are projected to rise twice as fast as the global average, due to a phenomenon known as polar amplification. However, there is still hope to avoid this sword of Damocles, as studies suggest that a major reduction in greenhouse gases over the next decade would mean that irreversible sea level rise could be avoided. It is therefore crucial to reduce CO₂ levels now for the benefit of future generations, or adapt to a world in which more of our shorelines are significantly redrawn.

This is both a scientific and societal issue. We have choices: technological innovations are providing new ways to reduce CO₂ emissions, and offer the reality of a low-carbon future. This may help minimise sea level rise from Antarctica and make mitigation a viable possibility.

Given what rising sea levels could mean for human societies across the world, we must maintain our longstanding view of Antarctica as the most remote and isolated continent.The Conversation

Chris Fogwill, Professor of Glaciology and Palaeoclimatology, Keele University; Chris Turney, Professor of Earth Sciences and Climate Change, UNSW, and Zoe Robinson, Reader in Physical Geography and Sustainability/Director of Education for Sustainability, Keele University

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

Antarctica’s ‘moss forests’ are drying and dying



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Lush moss beds in East Antarctica’s Windmill Islands.
Sharon Robinson, Author provided

Melinda Waterman, University of Wollongong; Johanna Turnbull, University of Wollongong, and Sharon Robinson, University of Wollongong

The lush moss beds that grow near East Antarctica’s coast are among the only plants that can withstand life on the frozen continent. But our new research shows that these slow-growing plants are changing at a far faster rate than anticipated.

We began monitoring plant ecosystems 18 years ago, near Australia’s Casey Station in the Windmill Islands, East Antarctica.

Casey Station is on East Antarctica’s coast. Click map to zoom.
Australian Antarctic Data Centre

As we report in Nature Climate Change today, within just 13 years we observed significant changes in the composition and health of these moss beds, due to the drying effects of weather changes prompted by damage to the ozone layer.

Living on the edge

Visitors to Antarctica expect to see a stark landscape of white and blue: ice, water, and sky. But in some places summer brings a surprisingly verdant green, as lush mosses emerge from under their winter snow blanket.

Because it contains the best moss beds on continental Antarctica, Casey Station is dubbed the Daintree of the Antarctic. Individual plants have been growing here for at least 100 years; fertilised by ancient penguin poo.




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Antarctic mosses are extremophiles, the only plants that can survive the continent’s frigid winters. They live in a frozen desert where life-sustaining water is mostly locked up as ice, and they grow at a glacial pace – typically just 1 mm a year.

These mosses are home to tardigrades and other organisms, all of which survive harsh conditions by drying out and becoming dormant. When meltwater is available, mosses soak it up like a sponge and spring back to life.

The short summer growing season runs from December to March. Day temperatures finally rise above freezing, providing water from melting snow. Overnight temperatures drop below zero and mosses refreeze. Harsh, drying winds reach speeds of 200 km per hour. This is life on the edge.

Tough turf

When we first began monitoring the moss beds, they were dominated by Schistidium antarctici, a species found only in Antarctica. These areas were typically submerged through most of the summer, favouring the water-loving Schistidium. But as the area dries, two hardy, global species have encroached on Schistidium’s turf.

Like tree rings, mosses preserve a record of past climate in their shoots. From this we found nearly half of the mosses showed evidence of drying.

Healthy green moss has turned red or grey, indicating that plants are under stress and dying. This is due to the area drying because of colder summers and stronger winds. This increased desertification of East Antarctica is caused by both climate change and ozone depletion.

Moss beds, with moss in the foreground showing signs of stress.
Sharon Robinson, Author provided

Since the 1970s, man-made substances have thinned Earth’s protective sunscreen, the ozone layer, creating a hole that appears directly over Antarctica during the southern spring (September–November). This has dramatically affected the southern hemisphere’s climate. Westerly winds have moved closer to Antarctica and strengthened, shielding much of continental East Antarctica from global warming.

Our study shows that these effects are contributing to drying of East Antarctica, which is in turn altering plant communities and affecting the health of some native plant species. East Antarctica’s mosses can be viewed as sentinels for a rapidly drying coastal climate.

But there is good news. The ozone layer is slowly recovering as pollutants are phased out thanks to the 1987 Montreal Protocol. What is likely to happen to Antarctic coastal climates when ozone levels recover fully by the middle of this century?




Read more:
The ozone hole leaves a lasting impression on southern climate


Unlike other polar regions, East Antarctica has so far experienced little or no warming.

Antarctic ice-free areas are currently less than 1% of the continent but are predicted to expand over the coming century. Our research suggests that this may isolate moss beds from snow banks, which are their water reservoirs. Ironically, increased ice melt may be bad news for some Antarctic mosses.

East Antarctica is drying – first at the hands of ozone depletion, and then by climate change. How its native mosses fare in the future depends on how we control greenhouse gas emissions. But with decisive action and continued monitoring, we can hopefully preserve these fascinating ecosystems for the future.The Conversation

Melinda Waterman, Associate lecturer, University of Wollongong; Johanna Turnbull, Associate Lecturer in Biology, University of Wollongong, and Sharon Robinson, Professor, University of Wollongong

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

Sledging songs, penguins and melting ice: how Antarctica has inspired Australian composers



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Most people will never visit Antarctica but music can evoke the continent in myriad ways.
Photo: Meredith Nash

Carolyn Philpott, University of Tasmania

When Douglas Mawson led Australasia’s first expedition to Antarctica in 1911–14, his crew took along a folding organ, a concertina, a flute, a piccolo and a mouth organ, as well as a gramophone, records and a hymn book.

Program for The Washerwoman’s Secret: the first ‘opera’ on the continent.
Courtesy of The Mawson Centre, South Australian Museum. Used with permission.

His men’s diaries detail numerous musical activities that took place on board the Aurora and in the huts they built on the ice. Their band – the “Adélie Land Band” – was such a hit that, as Mawson wrote, “Men crawled out of their beds all eager to be in it”.

They even staged the first “opera” on the continent: an original production titled The Washerwoman’s Secret, billed as a “Grand Opera in Five Acts” and performed at Cape Denison, Commonwealth Bay, on 12 October 1912. As biological collector Charles Laseron recalled, it had a “complicated and highly dramatic plot”. The expedition doctor, Archibald McLean, reportedly stole the show by dressing like a woman, singing in a contralto register and acting out several awkward “love” scenes. The “arias” sung were original creations, accompanied by geologist Frank Stillwell on the organ.

Mawson’s men also wrote new lyrics for existing tunes to sing for both leisure and while at work (such as “sledging songs”). These both entertained and boosted morale.

Frank Hurley: ‘A winter evening at the hut’ (1911).
National Library of Australia, http://nla.gov.au/nla.obj-136188901.

In the past 30 years, a spate of professional Australian composers and musicians have also engaged with Antarctica creatively. Interest has no doubt been spurred by the celebration of centenaries relating to the Heroic Age, support for arts residencies as part of Australia’s Antarctic science program, and increased media focus on the continent due to climate change.




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The most widely known Australian composition about Antarctica is perhaps Nigel Westlake’s Antarctica suite for guitar and orchestra (1992). Derived from his film score for John Weiley’s 1991 IMAX documentary Antarctica: An Adventure of a Different Nature, the four-movement suite explores some of the film’s primary themes.

The opening movement (“The Last Place on Earth”) employs sparse, static textures and dramatic gestures to represent the desolation and grandeur of the ice sheet.

The second (“Wooden Ships”) is a nostalgic tribute to the pioneering Antarctic explorers. The penultimate movement (“Penguin Ballet”) vividly evokes the fluid, playful movements of penguins underwater.

The final one opens with a slow, static section titled “The Ice Core” and ends with an uplifting “Finale”, inspired by the optimism surrounding the signing of the Protocol on Environmental Protection to the Antarctic Treaty (“Madrid Protocol”) in 1991. Through performances, recordings and broadcasts, Westlake’s suite has encouraged audiences to reflect on Antarctica’s unique environment, the history of human presence there, Antarctic science and the importance of protecting the continent.

Love, death and serious science

More recently, Hobart-based composers Scott McIntyre and Joe Bugden produced a chamber opera each to commemorate the centenary of the Terra Nova and Aurora expeditions, respectively.




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McIntyre’s Fire on the Snow is based on Douglas Stewart’s 1941 radio play of the same name about Robert Falcon Scott’s final, ill-fated expedition. The chamber opera features, in the composer’s words, “Music devoid of warmth, music that [is] brittle, like ice, the howl of the wind, the slow onset of death”.

Similarly, Bugden’s The Call of Aurora is serious in tone. Based on his own libretto, it explores themes of love, death, madness and isolation by focusing on Mawson’s longing for his fiancee, Paquita, his experience of the deaths of Belgrave Ninnis and Xavier Mertz, and his management of the mad wireless operator, Sidney Jeffryes.

McIntyre has also produced a series of shorter compositions, including a song cycle, Songs of the South (2014), based on those originally written during the Terra Nova and Aurora expeditions. Two of McIntyre’s songs were inspired by “sledging songs”, while others were derived from songs written by Mawson’s men about Christmas Day and one of the team’s dogs, Basilisk.

The Australian Antarctic Arts Fellowship scheme has supported classical harpist Alice Giles and sound artist Philip Samartzis on residencies in Antarctica. Giles performed harp music there in 2011 to commemorate the Australasian Antarctic Expedition (her grandfather, Cecil Thomas Madigan, was the expedition’s meteorologist).

Philip Samartzis in Iceberg Alley (Antarctic Sound), Antarctica, in March 2010.
Photograph by Ian
Aitkinson, used with permission
.

The sound of ice cracking

Samartzis’s two fellowships (2009 and 2015) enabled him to document in sound the impact of extreme climate and weather events on Australian research stations in Antarctica and on Macquarie Island, as well as on the icebreaker Aurora Australis.

His suite of compositions “Antarctica: An Absent Presence” (2016) captures a rich variety of sounds including those made by seals, wind, blizzards, ice when it cracks and calves, helicopters, trucks and generators.

Scientific research has proven fertile ground for composers.
Stuart Greenbaum’s choral work Antarctica (2002) uses a text by Melbourne poet Ross Baglin about sea level rise due to the melting Antarctic ice sheet. The music, written for treble choir, two violins and organ, is a poignant elegy to a place (and world) under threat.




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Matthew Dewey’s symphony ex Oceano (2013) was written in response to research on the Southern Ocean undertaken by scientists at the Institute for Marine and Antarctic Studies and the CSIRO. The music takes the listener on a journey, exploring not only the strength of the ocean’s currents and enormity of its scale and influence, but also the microscopic life that lives within it.

The second movement, for instance, is dedicated to phytoplankton – microscopic organisms that produce over half the world’s oxygen. Invisible to the naked eye, they are visible in vast blooms from space.

Antarctica: The Musical, which premiered in Hobart in 2016, features music and lyrics by songwriter Dugald McLaren and a book by ecologist Dana Bergstrom (both of whom have spent time there). Focusing on the experiences of a group of scientists living on the continent for a year and the challenges they face, it conveys a strong message of concern for the region’s changing environment.

Most people will never visit Antarctica. It is an inhospitable place at the margins of our world. But music enables audiences to come to know the continent as a place of both the imaginary and of urgent, practical scientific work.The Conversation

Carolyn Philpott, Senior Lecturer in Musicology, Conservatorium of Music; Associate Head – Research, School of Creative Arts; Adjunct Researcher, Institute for Marine and Antarctic Studies, University of Tasmania

This article was originally published on The Conversation. Read the original article.

Antarctic seas host a surprising mix of lifeforms – and now we can map them



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In contrast to common perceptions, Antarctic seafloor communities are highly diverse. This image shows a deep East Antarctic reef with plenty of corals, sponges and brittlestars. Can you spot the octopus?
Australian Antarctic Division

Jan Jansen, University of Tasmania; Craig Johnson, University of Tasmania, and Nicole Hill, University of Tasmania

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.

A diverse seafloor community living under the ice near Casey station in East Antarctica.

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.




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Surprises on the seafloor

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.

These solitary sea squirts stand up to half a metre tall at 220m depth in the dark, cold waters of East-Antarctica. Images such as this one were taken with cameras towed behind the Australian Icebreaker Aurora Australis.
Australian Antarctic Division

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”).

The Antarctic seafloor is also home to a unique group of fish that have evolved proteins to stop their blood from freezing.

Most Antarctic fish have evolved ‘anti-freeze blood’ allowing them to survive in water temperature below zero degrees C.
Australian Antarctic Division

Mapping biodiversity is hard

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.




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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.

A selection of the diverse and colourful species found on the Antarctic seafloor.
Huw Griffiths/British Antarctic Survey

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.




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Using predictions to make a map

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.

The science behind linking food-particles from the ocean surface to the biodiversity of Antarctic seafloor fauna. Satellites (1) can detect the amount of algae at the ocean-surface. Algae-production is particularly high in ice-free areas (2) compared to under the sea-ice (3). Algae sink from the surface (4) and reach the seafloor. Where ocean-currents are high (5), many corals feed from the suspended particles. In areas with slow currents (6), particles settle onto the seafloor and feed deposit-feeding animals such as seacucumbers.
Jansen et al. (2018), Nature Ecology & Evolution 2, 71-80.

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.

Colourful and diverse communities are also found living in shallow waters.
Australian Antarctic Division

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.


The Conversation


Read more:
How a trip to Antarctica became a real-life experiment in decision-making


Jan Jansen, Quantitative Marine Ecologist, University of Tasmania; Craig Johnson, Professor, University of Tasmania, and Nicole Hill, Research fellow, University of Tasmania

This article was originally published on The Conversation. Read the original article.

How an alien seaweed invasion spawned an Antarctic mystery



File 20180716 44070 1h9dsso.jpg?ixlib=rb 1.1
Southern bull kelp can drift huge distances before washing ashore.
Ceridwen Fraser, Author provided

Adele Morrison, Australian National University; Andy Hogg, Australian National University; Ceridwen Fraser, Australian National University, and Erik van Sebille, Utrecht University

Two small pieces of seaweed found by a Chilean scientist on an Antarctic beach set in train research that may transform our understanding of ocean drift and reveal what the future holds for Antarctic ecosystems affected by climate change.

It all started in January 2017, when sharp-eyed marine biologist Erasmo Macaya spotted two clumps of southern bull kelp washed up on the tide line of an Antarctic beach.

Most of us would have walked right on by, but it stopped Macaya in his tracks. To him it was as if an alien had just landed – and in many ways that was exactly what had happened.

The kelp that washed up on Antarctica’s Prince George Island.
Erasmo Macaya, Author provided

Every piece of science he knew said that this species of kelp should never have ended up in Antarctica. Its home was the regions around New Zealand, Chile and the sub-Antarctic islands. Indeed, a genetic test later confirmed that the pieces he found had travelled tens of thousands of kilometres from the Kerguelen and South Georgia islands.

So how did the kelp get to Antarctica?

The ocean barrier

Many scientists considered such a journey impossible, because of the fierce barrier of winds and currents that encircle Antarctica. These winds – known to sailors as the Roaring Forties – combine with the world’s strongest ocean current, the Antarctic Circumpolar Current, and the Coriolis force generated by Earth’s rotation.

Together, these forces push floating objects east and north, away from Antarctica. Before Macaya’s discovery, this barrier was thought to be impenetrable to floating debris.

Ocean currents in the Southern Ocean push floating objects east and north away from Antarctica.
Author provided

But if kelp and other organisms could make it to Antarctica, this would have profound consequences for Antarctic ecosystems. So was there a way for the kelp to drift through that barrier?




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Why I’m spending three months sailing right around Antarctica for science


Surfing kelp

We took up the challenge, using our ocean models. The mystery deepened when our first modelling attempts suggested that the Southern Ocean was indeed uncrossable by floating kelp. Even ocean eddies – the “weather” of the ocean – were not able to push floating objects southward away from the main ocean currents.

Yet the kelp had undeniably made the crossing. This led us to think about other influences on ocean drift that could play a role. We decided to add a very small effect known as Stokes drift to our models.

You can think of Stokes drift as deep ocean surfing. Waves can push floating objects in unusual directions. In the kelp’s case, each time a wave passes, the kelp will move a short distance with the wave. This drift is slow when waves are small, but in regions with large waves (such as the Southern Ocean) it can be much faster.

During storms around Antarctica, waves are typically 10-15m high. The largest wave ever recorded in the Southern Hemisphere, more than 23m, was in the Southern Ocean off New Zealand. Stokes drift must be large here.

When we added this factor to our ocean models, the change was instant. The massive waves generated by Antarctic storms pushed a small proportion of floating objects southwards. As we report in Nature Climate Change today, this conceivably explains the kelp’s voyage to Antarctica.

Modelling virtual kelp pathways with surface ocean currents and wave motion.

We calculated that the kelp specimens must have drifted at least 20,000km to reach Antarctica – the longest biological rafting events ever recorded.

Our results will also change the way that drift pathways for floating objects – such as plastics, aeroplane crash debris, pumice from volcanoes, driftwood, seaweeds, and messages in bottles – will be calculated, particularly in stormy oceans.

What this means for Antarctica

The implications don’t stop there. Until now, Antarctica was thought to be an isolated ecosystem, largely insulated from environmental change. This is not in fact true.

Southern bull kelp can carry many other species of plants and animals when it detaches and floats out to sea. The discovery that this kelp can raft to Antarctica means we could see major ecological changes in Antarctic marine ecosystems as the climate warms.

So far there is almost no evidence of natural colonisations of Antarctica from northern regions in the past few tens of thousands of years. Many Antarctic plants and animals are distinct from those found on other continents and sub-Antarctic islands.

In fact, the kelp strands Macaya found are the first recorded foreign organisms to have drifted across the Southern Ocean. But our models suggest these are unlikely to be the only ones to have made the trip.

This means that Antarctica’s ecological differences are not really due to physical isolation. It is more likely that the harsh Antarctic climate prevents new plants and animals from establishing themselves.

But Antarctica is changing. Parts of the frozen continent are among the fastest-warming regions on Earth. As Antarctica and the ocean around it warms, the kelp rafts – and other floating organisms, including invertebrates hanging onto the kelp, seeds, driftwood that could harbour insects, and larvae – may one day be able to colonise.

By the end of this century, when parts of Antarctica are expected to be similar to current sub-Antarctic environments, we might see many new species colonising Antarctica, bringing dramatic ecosystem change.

Other human-caused influences may also be felt. If kelp can break through the barrier, then floating plastic debris from the large garbage patches in the South Atlantic and South Pacific, just north of the Southern Ocean, could conceivably make a similar journey.




Read more:
The winners and losers of Antarctica’s great thaw


Plastic litter is still very rare in the waters around Antarctica. But with ever-growing amounts of plastic entering our oceans and the new drift pathways we have discovered, more plastic will likely find its way south to pollute one of our last near-pristine environments.

The ConversationAnd all of this has been revealed through the discovery of two small pieces of kelp on a distant beach, and the application of a relatively insignificant piece of ocean physics. From these small beginnings we now know that one of the world’s last great wildernesses might not escape our influence.

Adele Morrison, Research Fellow, Australian National University; Andy Hogg, Associate Professor, Australian National University; Ceridwen Fraser, Senior lecturer, Australian National University, and Erik van Sebille, Associate Professor in Oceanography and Climate Change, Utrecht University

This article was originally published on The Conversation. Read the original article.