Case studies

The 2016 state of the environment report found emerging indications of improvement in Antarctic stratospheric ozone concentrations. Measures of the size and depth of the Antarctic ozone hole generally indicate that ozone depletion started to become significant in the late 1970s, reached a peak between the late 1990s and early 2000s, and is currently improving towards recovery to 1980 levels in the mid-to-late 21st century (WMO 2018).

The latest comprehensive assessment of ozone depletion by the World Meteorological Organization and the United Nations Environment Programme found evidence of Antarctic ozone recovery, with international controls on ozone-depleting substances due to the Montreal Protocol having ‘made a substantial contribution to the observed trends’ (WMO 2018).

However, ozone depletion shows significant year-to-year variability, and in any particular year is more strongly influenced by meteorological factors than changes in the atmospheric concentrations of ozone-depleting substances (Solomon et al. 2015). In particular, the amount of ozone destruction is strongly related to the temperature of the Antarctic stratosphere during the winter and spring, with colder temperatures causing a larger ozone hole.

The severity of ozone depletion varies on seasonal and interannual timescales (Figure 2a). The largest observed measures of depletion generally occurred in 2006, and subsequent years have all shown less ozone loss. Tully et al. (2019) showed that ozone depletion decreased from 2001 to 2017, in line with the decline in the estimated atmospheric concentration of ozone-depleting substances (Figure 2b).

The year 2019 was notable in having the smallest Antarctic ozone hole since 1988 (Kramarova et al. 2020). This was mainly because of the strong and rapid warming of the Antarctic stratosphere that occurred during spring of that year (Klekociuk et al. 2021). The stratospheric warming was related to climate patterns that produced hot and dry conditions across Australia in the 2019–20 summer (Lim et al. 2020); see case study: Antarctic temperature extremes. In contrast, a large amount of Antarctic ozone destruction occurred in 2020, rivalling the total loss observed in 2006 (Figure 2b). In this case, low temperatures and relatively stable circulation in the Antarctic stratosphere were the main determining factors.

Figure 2 Ozone mass deficit metric

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Figure 2 Ozone mass deficit metric

EESC = equivalent effective stratospheric chlorine; Mt = megatonne; OMI = Ozone Monitoring Instrument; OMPS = Ozone Mapping and Profiler Suite; ppb = parts per billion; TOMS = Total Ozone Mapping Spectrometer

(a) Estimated daily mass of ozone destroyed within the ozone hole, shown for individual years from 2015 to 2020 as a function of day of year from July to December. (b) Estimated total annual ozone mass loss associated with the ozone hole from 1979 to 2020 (green dots) and EESC (blue line), a measure of the stratospheric concentration of ozone-depleting substances. These figures are obtained from CSIRO analysis of daily total column ozone measurements provided from the OMPS on the Suomi National Polar-orbiting Partnership satellite. In (a), the light-blue background shows the range of daily values for 1979–2019 obtained with the TOMS instrument (1979–2003), the OMI (2004–11) and OMPS (2012–19). Gaps in the timeseries are when no TOMS measurements were made.

Source: CSIRO; after Klekociuk et al. (2021)

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During the 2019–20 summer, unprecedented maximum daily temperatures were observed in parts of coastal Antarctica (Robinson et al. 2020). The consequences of this event for the ice-free areas of Antarctica are of concern, as these regions are key oases of biodiversity where plants and animals have adapted over millennia to a specific narrow range of physical conditions, particularly in terms of air and surface temperature, and low and highly seasonal availability of water. By increasing the availability of water, warmer conditions may benefit certain Antarctic organisms that are drought stressed (particularly in terms of growth and reproduction). However, excessive or prolonged exposure to temperatures well above zero can lead to detrimental effects such as heat stress, increased likelihood of community dislocation from flooding, and potential for future drought stress when local water reserves are disrupted.

A persistent pattern of above-average temperatures that began in East Antarctica during the spring and generally moved eastwards, arriving in the Antarctic Peninsula region by late summer, caused the extreme temperatures (Figure 3). An important trigger for these unusual conditions was the strongly negative phase of the Southern Annular Mode (SAM) during most of spring and summer, with southward movement of warm air masses across the Southern Ocean. The state of the SAM was supported by El Niño conditions in the Pacific Ocean, and by the positive phase of the Indian Ocean Dipole (Lim et al. 2020). Tropical surface conditions also aided the strong warming of the Antarctic stratosphere during spring, and may have influenced Antarctic surface temperatures during the summer.

Figure 3 Patterns of average maximum temperatures across the Southern Hemisphere in November–December 2019

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Figure 3 Patterns of average maximum temperatures across the Southern Hemisphere in November–December 2019

Note: Shown are differences in the maximum daily temperature averaged over November and December 2019 with respect to the climatological average for 1980–2010. The scale is degrees Celsius.

Source: After Robinson et al. (2020). Royal Netherlands Meteorological Institute Climate Explorer using data from the European Centre for Medium-range Weather Forecasts, fifth Reanalysis.

Ice-core CO₂ records

The oldest ice-core record obtained from Antarctica, the EPICA Dome C record, reaches back 800,000 years (Lüthi et al. 2008, Bereiter et al. 2015). Temperature reconstructions, which are based on the correlation of stable isotope concentration ratios (primarily ¹⁸O/¹⁶O and ²H/¹H; O = oxygen and H = hydrogen) with temperature, and concentration measurements of CO₂ and other stable gases in this and other deep ice cores, provide unique insight into the climate system. The data demonstrate the close coupling that has existed over millennia between the carbon cycle and Earth’s climate. This provides the clearest known evidence that changes in atmospheric CO₂ accompanied and contributed to the ice age cycles that dominated climate, sea level and ice-sheet variability over this interval.

The Law Dome ice-core record, drilled to bedrock around 100 km inland from Australia’s Casey Station, provides the world’s most detailed CO₂ record of the past 2,000 years (Figure 4a). The Law Dome data show that atmospheric CO₂ concentrations have increased by close to 50% (from 280 to 417 parts per million) since the start of the Industrial Revolution; they are now higher and accelerating faster than at any time during the past 800,000 years (Figure 4b). Furthermore, studies of the changing isotopic composition of CO₂ in the Law Dome and other Antarctic ice cores reveal unequivocally that the primary origin of this CO₂ increase is the burning of fossil fuels (Rubino et al. 2013).

Ice cores and past climate variability in Australia

Analysis of ice cores can also show the changes in the chemical composition and accumulation rates of snow on the Antarctic ice sheet over time. At ice-core sites such as Law Dome near Casey Station, the chemistry and accumulation rates have been reconstructed at subannual resolution over the past few thousand years (Roberts et al. 2015). Trends and natural variability in these parameters shed light on past environmental conditions in Antarctica, and on conditions in the surrounding oceans and continents. Two examples of connection established between the ice-core data and the Australian climate follow.

Since the late 1960s, south-west Western Australia has been subject to an extended drought, with a decline in winter rainfall of around 20% that has had a major impact on regional agriculture. Comparison of Australian rainfall data with snowfall at Law Dome, as measured from ice cores, reveals that high snowfall accumulation at Law Dome is associated with atmospheric circulation patterns that bring dry conditions in south-west Western Australia. Based on this correlation, the long-term ice-core record can be used to evaluate whether the present drought is unusual. It shows that the recent amount of snowfall accumulation at Law Dome is the largest it has been in the past 1,200 years; comparable but smaller events occurred around 400 AD and 750 AD (van Ommen & Morgan 2010).

Eastern Australia is also subject to large rainfall variability on annual to multi-decadal timescales, including the millennium drought between 1995 and 2009. The El Niño–Southern Oscillation, which strongly affects rainfall in eastern Australia, also affects winds around Antarctica, which in turn influence the chemical (sodium ion) composition of the snow at the Law Dome ice-core site. This link has been used to reconstruct past rainfall in key eastern Australian catchments. Results show that the short period of modern rainfall observations is not representative of the full range of past climate variability, and that droughts worse than the millennium drought are not only possible but likely (Vance et al. 2015).

Figure 4 History of climate and atmospheric composition from Antarctic ice-core records

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Figure 4 History of climate and atmospheric composition from Antarctic ice-core records

CO₂ = carbon dioxide; ppm = parts per million

(a) Law Dome ice-core CO₂ record, the world’s most accurate and detailed CO₂ record for the past 2,000 years. Note the clear increase in CO₂ from the start of the Industrial Revolution and the agreement of the ice-core measurements with more recent atmospheric data from Kennaook/Cape Grim, Tasmania. (b) Data from a composite of Antarctic deep ice cores reveals past changes in Antarctic (b) CO₂ and (c) temperature over the past 800,000 years. The modern rise is outside the bounds of natural variability over this period. Note the close coupling of temperature and CO₂ throughout the ice age cycles, which have approximately a 100,000-year periodicity.

Sources: Kennaook/Cape Grim CO₂ – Kennaook/Cape Grim Baseline Air Pollution Station (Australian Bureau of Meteorology, and CSIRO Oceans and Atmosphere); Law Dome CO₂ – MacFarling Meure et al. (2006); Antarctic ice-core composite CO₂ – Bereiter et al. (2015); Antarctic temperature change – Jouzel et al. (2007).

In some regions, ice-shelf thinning and loss carry additional significance for future mass loss because of potential instability of the ice sheet (Figure 6a). In areas where ice is grounded below sea level on a bed that deepens inland, initial ice retreat, once triggered, can lead to accelerated discharge and further retreat, which is irreversible (Schoof 2007). Some studies indicate that this process is already underway in regions of West Antarctica (Rignot et al. 2014).

Regions of East Antarctica known to be changing are associated with regions thought to be vulnerable to this type of retreat process. Recent work mapping the bed beneath the East Antarctic Ice Sheet reveals extensive areas grounded below sea level that may be similarly vulnerable to loss (Roberts et al. 2011, Young et al. 2011, Fretwell et al. 2013). In East Antarctica, there are 2 regions where future large-scale retreat could occur (Figure 6b). The Wilkes and Aurora subglacial basins each cover extensive areas of ice grounded more than 1 km below sea level. Ice thinning and loss in the margins of these regions may lead to large-scale retreat on centennial timescales (Golledge et al. 2015, Pollard et al. 2015).

Figure 6 East Antarctic vulnerability to ice retreat

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Figure 6 East Antarctic vulnerability to ice retreat

Notes:

1. Marine ice-sheet instability (MISI) causes regions of the ice sheet on retrograde slopes to be vulnerable to irreversible retreat, as any retreat of the grounding line increases flux and thinning.
2. Regions of East Antarctica vulnerable to MISI include the Wilkes and Aurora subglacial basins.

Source: Produced using the Norwegian Polar Institute’s Quantarctica package.

In mid-2016, the overall Antarctic sea ice extent declined suddenly and rapidly (Parkinson 2019). This followed decades of a gradual increasing trend and occurred immediately after a persistent period of well-above-average coverage in 2012–15 (Reid & Massom 2015). By the 2016–17 summer, the sea ice area had reached its lowest recorded anomaly (since 1979) by some margin. This event was remarkable not just for its magnitude but also for its timing, starting a month or so before the usual start of the spring melt and ice-edge retreat (Reid et al. 2017). The sea ice loss was widely distributed; the Australian Antarctic Territory sector was the only region without a significantly reduced sea ice cover (Figure 8) during this event.

This unprecedented and unanticipated event has challenged our understanding of Antarctic sea ice and the processes driving change and variability.

Most of the research to date on this event has focused on the role of the atmosphere. The event followed a significant El Niño in 2015–16, which may have preconditioned the ocean–sea ice system for a sudden sea ice loss (Nicolas et al. 2017, Stuecker et al. 2017, Schlosser et al. 2018). However, previous stronger El Niño events have not resulted in such losses. Several studies have focused on the impact of a very unusual atmospheric circulation in late 2016, with weak westerly winds but anomalously strong alternating meridional (i.e. northerly and southerly) winds (Stuecker et al. 2017, Turner et al. 2017, Wang et al. 2019). This atmospheric anomaly certainly contributed to the spring decline, but only really developed in October, after the retreat had begun in August (Reid et al. 2017). There is evidence that the ocean played a significant role (Meehl et al. 2019), and this is a subject of ongoing research.

Overall sea ice coverage partially recovered in the 2017 winter (Reid et al. 2018), although summer sea ice extent remained below average until 2020–21, suggesting that this was a relatively short-lived event, rather than a dramatic start of the projected decline in Antarctic sea ice. However, it is unknown at this stage whether there was an anthropogenic influence on this abrupt and dramatic event, or whether the likelihood of such events will increase in future.

Figure 8 December 2016 sea ice concentration anomaly

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Figure 8 December 2016 sea ice concentration anomaly

Note: The anomaly is shown with respect to the 1979–2008 December mean. The black line shows climatological ice edge; the magenta line shows December 2016 ice edge.

Source: Goddard merged sea ice concentration (Peng et al. 2013)

Credit: Dr Will Hobbs, Australian Antarctic Program Partnership

Seabirds make a living in the world’s vast oceans. As a result of their highly developed sense of smell, albatrosses and petrels can detect potential food sources over large distances by navigating through an ‘olfactory landscape’. A change in an olfactory feature may provide the cue to a seabird that it has reached its foraging destination (Nevitt 2000, Nevitt 2008). Crushed prey, such as krill, squid and fish, release certain scents (e.g. aromatic organic compounds such as pyrazines) that seabirds are able to detect. For this reason, seabirds may be attracted to fishing vessels, where they prey on discards, bait or fish lost in the fishing operation. Thus, foraging areas of seabirds and fishing grounds of commercial operators may overlap, exposing the birds to the risk of incidental mortality through interactions with fishing gear. Since the way seabirds interact with fisheries varies among species, the question arises: for which seabird species do commercial fisheries pose a risk?

To answer this question, a method called DNA metabarcoding has been employed. This technique enables the identification of multiple taxa (groups of animals) in one sample (Figure 9). Researchers collect samples of seabird scats at their colonies, and extract remaining genetic material (DNA) of the ingested prey. By comparing the samples with the DNA of known marine species, researchers can determine the diet composition of individuals or groups.

Figure 9 DNA metabarcoding

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Figure 9 DNA metabarcoding

Note: DNA was extracted from scats of many different predators. 1. Through DNA metabarcoding, the prey species ingested by predators were identified and compared to species caught by commercial fishing vessels. 2. DNA metabarcoding can also be used to identify seabird species to detect whether they have returned to a previously occupied breeding island.

Source: Julie McInnes

A DNA metabarcoding study on Tasmania’s shy albatross (Thalassarche cauta; Figure 10) showed that most birds captured their prey naturally, rather than eating fish captured by commercial fishers. However, at times a quarter of the population was consuming fisheries discards. Albatross foraging areas overlapped with commercial fishing operations in 6 Commonwealth fisheries in south-eastern Australia. The level of probable engagement of these albatrosses with fishing vessels varied with season, and was consistently high during the brood period (McInnes et al. 2021).

These examples show the versatility of DNA metabarcoding in the study of seabirds. This noninvasive technique provides valuable insights into seabird ecology, and offers an effective tool for wildlife and fisheries managers (McInnes et al. 2017).

Figure 10 Colony of shy albatrosses at Albatross Island, Tasmania

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Figure 10 Colony of shy albatrosses at Albatross Island, Tasmania

Photo: Julie McInnes

A different use of DNA metabarcoding is the identification of burrowing petrels. At Macquarie Island, at least 9 species of burrowing petrels were abundant before non-native predators were introduced. Cats preyed on chicks, and rats consumed eggs and perhaps small chicks. Thousands of rabbits overgrazed large areas of the island; this led to erosion and eventually loss of habitat of burrowing petrels.

After the eradication of the introduced species, feathers and scats were collected across the island to determine which species were present in the recovering ecosystem. Directly accessing burrows to identify petrel species causes disturbance, and the burrows are sometimes deep enough for their occupants to be out of reach. Using DNA metabarcoding on shed feathers and scats collected at burrow entrances confirmed the return of 8 different petrel species to the island, including the difficult-to-detect soft-plumaged petrel (Pterodroma mollis) and fairy prions (Pachyptila turtur) (McInnes et al. 2021).

Figure 11 Sooty shearwater (Ardenna grisea), one of the species identified by DNA metabarcoding

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Figure 11 Sooty shearwater (Ardenna grisea), one of the species identified by DNA metabarcoding

Photo: Julie McInnes

Emperor penguins are an iconic Antarctic species, and the only vertebrate that breeds throughout the winter. The first emperor penguin colony was discovered in the southern Ross Sea in 1901. By 2010, 32 others had been located, although the continued existence of some was uncertain (Wienecke 2009, Wienecke 2010).

The first synoptic survey of this species used satellite imagery to examine the entire coast of Antarctica, and confirmed and discovered new colonies, bringing the total to 46 (Fretwell et al. 2012). By 2019, this number had increased to 54, of which 50 still existed; in 2020, a further 8 small colonies were found (Fretwell & Trathan 2019). There are now 22 confirmed emperor penguin colonies in the Australian Antarctic Territory.

Researchers visiting the West Antarctic Ice Shelf (68.63°S, 77.97°E) in December 2009 recorded for the first time an emperor penguin colony on top of an ice shelf (Wienecke 2012) (Figure 12). Subsequently, satellite imagery enabled observations of changing locations of some emperor penguin colonies. Four had also relocated onto ice shelves in years when the sea ice conditions were poor (Fretwell et al. 2014).

Satellite imagery enables observations relating to changes in sea ice conditions and emperor penguin breeding success. For example, 10 years of remote observation documented significant variation in the second largest colony at Halley Bay, West Antarctica. From 2016 to 2018, this colony experienced near-complete breeding failure in 3 consecutive years due to low sea ice extent and early sea ice breakout at a time when the penguin chicks were far from fledging. Since 2015, the population size at the Dawson–Lambton colony, 55 km from Halley Bay, has increased massively (1000%); this may indicate that the penguins from Halley Bay relocated to the Dawson–Lambert colony (Fretwell & Trathan 2019).

Early ice breakup also led to the demise of large numbers of emperor penguin chicks at Cape Crozier (77.5°S, 169.3°E) in the Ross Sea, one of the two most southerly emperor penguin colonies (Figure 13). Increasing wind speeds and increasing temperatures appear to have contributed to this event (Schmidt & Ballard 2020).

Figure 12 Emperor penguins on top of the West Antarctic Ice Shelf, December 2009

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Figure 12 Emperor penguins on top of the West Antarctic Ice Shelf, December 2009

Photos: Barbara Wienecke

Because of their critical dependence on sea ice, emperor penguins are particularly vulnerable to the effects of climate change (Trathan et al. 2020). Although use of satellite imagery is vital for continent-wide observations of the impact of variations in sea ice conditions on this species, ground visits are still necessary to obtain reliable estimates of population sizes.

Figure 13 Emperor penguin colony at Cape Crozier, southern Ross Sea

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Figure 13 Emperor penguin colony at Cape Crozier, southern Ross Sea

(a) 24 November 2018; the edge of the fast ice is about 2 km from the colony (yellow marker). (b) 5 December 2018; a severe storm on 4 December blew out the fast ice. Many chicks were caught out on 2 large ice floes that subsequently disappeared.

Images: Sentinel2, European Space Agency. Contains modified Copernicus Sentinel data (2021), processed by Sentinel Hub.

tunapri Palawa milangkani milaythina paywuta. tunapri muylatina muka-ti, nipakawa nuritinga kani pakana milaythina & muka liyanana Antarctica.

muka tina, pinungana & muta tapilti Antarctica-tu paywuta.

Nuyina, lukrapina lakarana, tapilti makuminya maytawinya-ta & yula; nara kipli muka-ti mapiya Antarctica.

liyanana panitha; muka ningina latu. warr!  waranta pumili manina ngayapi, narakupa milaythina-nara-mapali & tina muka kitina, maytawinya lakarana.

manta manta.

(Tasmanian Aboriginal knowledge comes from Country, and is connected to country since the beginning of time.

This knowledge embraces sea Country, and the waters which carry our stories that connect us with the icy land and seas of Antarctica.

Marine animals, fish and birds migrate from northern lands to Antarctica and back, every year as they have done since creation.

The big ice-breaker Nuyina follows the path of the muttonbird and whale that feed in the waters around Antarctica.

But the ice is melting; ocean temperatures are rising!  We must bring our planet back to life, care for our Country and the ocean’s lifeworlds – from the smallest krill to the largest whale, for all the times to come.)

 In palawa kani, the language of Tasmanian Aboriginal peoples, with thanks to the Tasmanian Aboriginal Centre.

Australia’s new Antarctic icebreaker, RSV Nuyina (Figure 14), which arrived in Hobart in October 2021, will be the main lifeline to Australia’s Antarctic and subantarctic research stations. It will be the central platform of the nation’s Antarctic and Southern Ocean scientific research, and provide expanded and improved capabilities to manage Australia’s environmental footprint in the region.

‘nuyina’ – pronounced noy‑yee‑nah – means ‘southern lights’ in palawa kani, the language of Tasmanian Indigenous people.

The southern lights, also known as the aurora australis, are a phenomenon in the high altitudes of the atmosphere over Antarctica that reaches northwards to light up Australian – and particularly Tasmanian – skies. The first Australian Antarctic ship, Sir Douglas Mawson’s SY Aurora, was named after the same phenomenon, as was Australia’s first icebreaker, the RSV Aurora Australis, retired from service in 2020. The name RSV Nuyina continues this theme and forms another chapter in the story of connection between Australia and Antarctica, in both human and physical terms.

The naming of the RSV Nuyina recognises the long connection that Tasmanian Aboriginal people have with the evocative southern lights and the waters to the south of the island. Tasmanian Indigenous people were the most southerly on the planet during the last ice age. The adaptability and resilience of the Tasmanian Indigenous people, who travelled in canoes to small islets in the Southern Ocean, are qualities emulated by our modern-day Antarctic expeditioners as they travel south.

Australian schoolchildren suggested the ship’s name through the ‘Name our Icebreaker’ competition in 2017 that aimed to engage Australian students and expand their understanding of Antarctica; its environment, climate and history; and Australia’s role there.

Aboriginal language was the inspiration for one-fifth of all the valid ship names submitted by Australian children. In many of the competition entries, students spoke of their desire for reconciliation with, and recognition of, Australia’s Indigenous peoples. Using an Indigenous name for the new ship acknowledges all the children who wanted to recognise the interwoven history of Indigenous people and the great southern land – Antarctica.

Tasmanian Indigenous peoples speak palawa kani today. Development of the language draws on extensive historical and linguistic research of written records and spoken recordings, and Aboriginal cultural knowledge. Since not enough remains of any of the 6–12 original Tasmanian languages to form a full language today, palawa kani combines authentic elements from many of these languages. Language workers used a standard process of linguistic analysis to transcribe early English spellings into phonetics, to compare the sounds. In this way, they could retrieve a language, as close to the original sounds as possible, and reproduce these sounds in the standardised spelling system developed for palawa kani. This language flourishes in Aboriginal community life, and 3 generations of children have grown up learning it. palawa kani features increasingly in public life, including in gazetted Tasmanian placenames.

Figure 14 Australia’s new icebreaker RSV Nuyina during sea trials

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Figure 14 Australia’s new icebreaker RSV Nuyina during sea trials

Photo: © Commonwealth of Australia 2020