Chilled Calypso

Humanity wants to discover the reasons behind thinning ice, acidic water and rising temperatures in the Southern Ocean. Susan Pepperell finds that NIWA scientists are racing against time in taking on this challenge.

In late summer, the sea ice near the Mertz region of Antarctica should mostly be gone. Or at least it should have broken into small enough pieces to allow a ship to pass through into open water without too much cause for concern.

But last summer the sea ice didn't break up and disperse as usual. Instead, it refroze, thickened and stayed put.

From his Wellington base, Dr Mike Williams had been closely monitoring satellite images showing what was happening to the sea ice some 3500 kilometres south. The NIWA Marine Physicist was about to lead a 42-day voyage to the eastern coast of Antarctica aboard NIWA's deepwater research vessel Tangaroa, and part of the plan was to pass through the sea- ice zone to retrieve crucial data recorded by instruments moored to the seafloor.

If the sea ice didn't budge, Tangaroa – ice-strengthened, but not an icebreaker – wouldn't make it, and Williams and his team would need to change focus.

Tangaroa slipped out to sea on a sunny Wellington day in early February. Onboard were 16 crew and 22 scientists – oceanographers, geologists, biologists and technicians – from three research institutes: NIWA, the Australian Antarctic Climate and Ecosystem Cooperative Research Centre, and the French equivalent, L'ocean (Laboratoire d'Océanographie et du Climat).

The team was well prepared. Survival training had taught them how to get into a cumbersome immersion suit, the  signs of exposure they might observe in their colleagues and what frostbite looked like and how to avoid it.

They were also given survival bags and a box of equipment and food in case they had to abandon ship on to the ice and wait to be rescued.

Each scientist worked in 12-hour shifts, battling seasickness, fatigue and an environment that became increasingly unfriendly the further south they went.

Also onboard was a range of complex scientific equipment for measuring water, atmosphere, ice and sediment and taking samples that, in the coming months and years, will help scientists understand what is causing the Southern Ocean to change, and what those changes might mean to sea levels, rainfall, wind patterns and temperatures around the world.

The information gathered on this voyage contributes to the pool of information gathered by other scientists from previous voyages, with the aim of enhancing the sum of knowledge of the role the Southern Ocean plays in global climate change.

"In some ways the true value of this trip was in how it fitted together with the larger question of what's going on in the Southern Ocean," says Williams.

"There is a bigger, better story to tell from multiple voyages and the information they all provide."

Tangaroa's destination was the Mertz Polynya, an open area of water surrounded by ice off the eastern coast of Antarctica.

Polynyas are typically small, but common around Antarctica, and are exceptionally efficient at making sea ice – the water on the surface freezes and forms sea ice, then strong winds come across from the coast blowing the ice away, allowing the surface water to refreeze and start the whole process again.

The Mertz Polynya is of special interest to scientists because it is one of the few places in the Southern Ocean where 'Antarctic bottom water' is formed. This oxygen-rich water is exceptionally dense because it contains the salt crystals left behind to sink when sea ice forms. Because of its density, this bottom water is one of the main drivers of ocean currents.

Polynyas are also delicate and easily disturbed. Three and a half years ago, in February 2010, a large iceberg – a remnant of one that had broken free from the Ross Ice Shelf in the late 1980s – collided with the tongue of the Mertz Glacier, causing a huge piece of roughly 25,000 square kilometres to break off.

Ice conditions in the region then changed. The glacier tongue had been helping to hold back the sea ice, and its calving resulted in the polynya being less effective at forming Antarctic bottom waters. Less bottom water affects deep water circulation, the crucial carbon cycle and, ultimately, the Earth's climate.

But this environmental 'accident' is far from being the only culprit to cause changes in the Southern Ocean.

Due south

Head south from New Zealand for 700 kilometres and you will come across Campbell Island, a nature reserve known for its albatross population and rugged terrain. South from there, the vast Southern Ocean encircles Antarctica.

Officially named in just 2000 by the International Hydrographic Organization, the Southern Ocean comprises the southern parts of the Atlantic, Indian and Pacific oceans, and includes the Amundsen Sea, Drake Passage, Ross Sea, Bellingshausen Sea, Weddell Sea and part of the Scotia Sea.

The Southern Ocean is home to the world's strongest ocean current, the Antarctic Circumpolar Current. Driven by strong westerly winds, this exceptionally powerful current flows clockwise around Antarctica and makes the Southern Ocean one of the most turbulent, vigorous areas on the planet.

But probably the best known feature of the Southern Ocean is its rich and abundant wildlife. More than 10,000 species, including penguins, whales, fish and seabirds, thrive here in mostly sub-zero temperatures. A close watch is kept on these species to ensure any changes to their populations are quickly identified.

Governance of the waters of the Southern Ocean is complex and managed via a number of international protocols, conventions and organisations. The Antarctic Treaty, of which 50 countries are members, is the principal governing document and reserves the continent as a place of scientific endeavour. It also bans all military activity, prevents development and includes protocols on environmental protection.

In 1982, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) was set up with the objective of conserving Antarctic marine life and ensuring unique ecosystems in the region were not adversely affected by activities such as fishing.

Conservation of Antarctic Marine Living Resources website 

It has 25 member countries and was established mainly because of concern that increasing krill catches could seriously affect the Antarctic food chain. Similar concern has been expressed about the Patagonian toothfish, also known as Chilean sea bass.

Membership of CCAMLR is voluntary and decisions are reached by consensus. The organisation came to international attention in July when a New Zealand-led plan to create a 2.27 million square kilometre marine reserve in the Ross Sea was blocked by Russia.

Deep trouble

Scientific research in the Southern Ocean has become more critical in recent decades in determining the impacts of climate change, both in New Zealand and globally. However, understanding the consequences and the extent of that change remains a significant challenge.

What is known is that the Southern Ocean is getting warmer and more acidic, despite having an incredible capacity to absorb heat and carbon dioxide. Wind patterns have also changed, which is linked to the ozone hole and increased greenhouse gases.

Climate modelling suggests more change, including higher sea levels, less sea ice and different rainfall patterns – all of which will influence climates in New Zealand and around the globe. Given this level of significance, it was perhaps not surprising that in May this year the Deep South (the Southern Ocean and Antarctica) was named as one of 10 National Science Challenges identified by the New Zealand Government.

The challenges, according to Science and Innovation Minister Steven Joyce, were designed to take a more strategic approach to science investment and tackle "some of the biggest science-based issues and opportunities facing New Zealand".

More government funding has been allocated and Joyce is calling for greater collaboration across institutions and disciplines.

Specific details about the challenge – understanding the role of the Antarctic and the Southern Ocean in determining our climate and future environment – should be known in the next few months, but NIWA is expected to take a lead role.

If there is something for the Minister to be heartened by, it is the high level of collaboration that already exists in the  science community when it comes to Antarctica and the Southern Ocean.

As Mike Williams says: "There's nothing like six weeks on a boat to get to know someone and forge relationships."

Gathering more information to help understand some of the "biggest science-based issues facing New Zealand" was precisely what the scientists on Tangaroa were doing in February.

As they headed south, the team collected samples from the surface waters and the atmosphere. They towed a CPR to collect and preserve plankton, and deployed a CTD (Conductivity, Temperature and Depth profiler) that measures salinity, temperature, pressure and oxygen on its way to the seafloor. Water samples were collected at different depths on the way back for analysis onboard or back on shore, and other instruments measured the speed of currents.

Once they came close to the Antarctic coast, and with the Mertz Polynya cut off, the team's focus went onto the Antarctic Continental Slope and the heavy, dense water that flows over it to the bottom of the ocean.

Scientists know this mass of bottom water is changing. It is not as dense or as salty as it was 10 years ago, and it is much fresher and warmer than it was 40 years ago, due to increasing levels of carbon dioxide in the atmosphere – a key part of global warming.

Increased carbon dioxide in the atmosphere in turn leads to warmer oceans that are increasingly acidic. Increased acidification affects marine life, in particular animals whose shells and skeletons are made from calcium carbonate.

Warmer sea temperatures also affect the growth of phytoplankton that are not only vital to the ocean food chain, but are also an important link in moderating climate change.

As Williams says: "How much can the ocean take? When we look at climate variability over the last decade, the atmosphere has not changed as much as in previous decades. But for carbon, the story is not as clear."

The Southern Ocean is changing, but the full impact of the changes is not yet fully understood. However, scientists know that further research and analysis is needed now for a better understanding of how these processes are linked to climate change.

Technological advances are helping fill in the gaps, and scenario modelling is becoming increasingly important in forecasting future changes. However, there is a collective sense of urgency expressed by the science community that the changes need to be understood at least at the pace with which they are occurring.

Six months after Tangaroa returned to Wellington, work is progressing on analysing the huge amount of information collected on the six-week voyage.

NIWA is taking a leadership role in ensuring this takes place as soon as possible and the wealth of data will be available for scientists around the world to examine and work on. Decisions are still being made on just who is looking at what, but Williams says it will be nothing if not collaborative.

"Now, six months later, I'm starting to look at the data and the papers we might write, the stories we might tell. The hard, demanding part is over and I'm now doing what I most enjoy – trying to unlock the mystery."

End


Read the Mertz Polynya blog post series written during the voyage

Continuous Plankton Recorder

Metal boxes shaped like fish are playing a key role in monitoring changes in the Southern Ocean.

Officially called Continuous Plankton Recorders (CPR), these instruments were invented in 1926 and are towed by ships all over the Southern Ocean as part of an international programme to keep an eye on plankton levels and quality.

In February, NIWA Biologist Mark Fenwick was on Tangaroa for this 42-day journey to the east coast of Antarctica.

He was part of the team deploying the CPR behind the vessel as it headed south. "We ran it from just south of Stewart Island to about 60 degrees south at about a depth of 10 metres, collecting plankton samples and preserving them for analysis."

Water is fed through an aperture of about one square centimetre and filters the plankton between two moving bands of silk.

With the aid of an ingenious water-powered propeller, the silk spools into a storage tank of formaldehyde where the plankton are preserved until they can be analysed. The silk from this journey will be analysed in Hobart by the Australian Antarctic Division. While the technology is old, the CPR nevertheless provides vital consistency over time.

Fenwick's work is part of the Southern Ocean Continuous Plankton Recorder Survey, an international programme which has been running for more than 20 years.

Data from previous surveys have revealed significant changes to the number and distribution of plankton in the Southern Ocean. Given that they are a crucial source of concentrated food for krill, the staple diet of fish and whales, any changes act as an early warning sign that all is not well in the ocean food chain.

This programme has covered more than half the ocean, taken tens of thousands of samples, with a CPR being towed for more than 300,000 kilometres.

Fenwick says the February CPR sampling would add vital information as scientists sought to discover what is driving changes in the Southern Ocean.

Meanwhile, NIWA scientists are also near the end of a five- year study funded by the Ministry for Primary Industries to map changes in the distribution of plankton species in surface waters between New Zealand and the Ross Sea. It is due to be completed in October.

Campbell Island rockhopper penguins

Right now the rockhopper penguins of Campbell Island should be happily splashing about somewhere in the Southern Ocean feeding.

Exactly where they spend the winter is not known, but NIWA scientists hope to be closer to finding out by the end of the year.

In April, Marine Ecologist David Thompson and his team placed electronic tags that record light levels on about 50 rockhoppers as part of ongoing research to find out what these birds can tell us about changes in the Southern Ocean.

The tags will be retrieved after the penguins return to the island to breed in October and the data are analysed to determine their movements.

There are so many unknowns about the rockhopper that Thompson calls it "a bit of a black box".

What is known is that the species on Campbell Island declined from about 800,000 breeding pairs to just 152,000 pairs between 1942 and 1985.

"We know that there are far fewer than there were in the 1940s, and that the population is a bit lower than it was in the 1980s.

"However, we don't know if the 1940s population was the largest it had ever been or whether the decline between the 1940s and '80s was something that happened naturally over time. And we don't know if the population has bottomed out and will recover, or whether there are other things at play."

Adding to the sum of unknowns is that the birds don't breed in one place on the island, but in many sub-colonies, some of which have disappeared in recent years and some of which have increased in size.

For the past three summers, doctorate student Kyle Morrison has spent several months counting the rockhoppers on Campbell Island.

He is currently writing up his research and says it appears the rockhopper penguin population has stabilised in recent years, possibly due to greater availability of food.

Campbell Island is rugged, inhospitable and a long way south of New Zealand. It's costly to get there, and rockhoppers don't make it easy for scientists to get to know them.

"They are bold and aggressive birds for their size," Morrison says, "but also extremely charismatic."

The best way to find out about how the population is faring is to count them.

"It sounds easy, but it's actually very difficult," says Thompson. You need to do it over several years – they live for about 20 to 30 years, so they tend to survive quite well. Tracking changes in size, therefore, involves a lot of work over many years."

Also complicating matters is that the birds tend to live at the bottom of cliffs or on very steep slopes, where they are often obscured.

"Counting birds on the island is fraught with problems, and the resources required to do it properly over a number of years are quite mind-boggling."

However, the threatened rockhoppers are not the only species breeding on Campbell Island whose population has declined. They keep ever-diminishing company with the southern elephant seal and the grey-headed albatross.

"There is no convincing explanation of why all three are declining, but it's certainly telling us something about the Southern Ocean."

Core sampling

At the bottom of the sea, a scientist can go back in time. That's where there is layer upon layer of sand, mud and microfossils that have built up over tens of thousands of years.

Each layer has a story to tell of environmental change, each skeletal remain can be identified and its chemical composition revealed, and each core compared with the next to build up a more complete history of the ocean.

For NIWA Marine Geologist Dr Helen Bostock, the sediment at the bottom of the sea will tell her something about what has happened to the water masses in the Southern Ocean over the last 30,000 years or more.

She was on Tangaroa for its February journey to the Mertz region of Antarctica. Her interest lies in learning what happens to the sea over long periods of time, and to do that she and her team took core samples – some up to six metres long – from the ocean floor.

The corers were driven into the sediment by a two tonne weight.

Once back onboard, the cores were cut into 1 metre sections and split lengthwise, and the team set to work recording what they could see before the whole lot was wrapped up and stored for further analysis back on land.

"We look for distinct colour or composition changes in the sediment, we analyse the chemistry of organisms and changes in the microfossils, which provide clues about changes in temperature and nutrients. And from all that, we piece together all the different data to come up with a theory to explain what might have happened over time."

The ages of the core layers won't be known until the sediment has been dated, which will be done by identifying when particular fossils became extinct or by radiocarbon dating.

"The Southern Ocean is thought to have played an important role in causing large natural climate transitions, but we still know very little about this region," says Bostock.

"We hope this will provide a small piece of information to the giant puzzle of understanding Earth's changing oceans and climate."

Sea ice

Dr Craig Stevens calls his work the "easiest oceanography there is – you don't get seasick".

But 'easy' is a relative term when the alternative to being on a ship is spending several weeks at a time living and working in insulated containers in Antarctica where it is minus 30 degrees outside.

The NIWA scientist's interest is in how sea ice grows. He is part of a collaborative project working with other scientists from NIWA, Callaghan Innovation, and Otago and Victoria universities examining changes to the Antarctic sea ice.

"Sea ice is the biggest annual geophysical change on earth; the bottom of the planet effectively turns white, and the coverage controls the way the ocean works."

It also provides the perfect environment for algae that are eaten by krill, and so forms a home for the bottom of the food chain.

While the Southern Ocean from which this sea ice is formed is getting fresher and warmer, and sea levels are rising, unlike in the Arctic region, the area of sea ice around Antarctica on the whole doesn't seem to be changing much. Certainly, there are regions where it is changing, but large regions stubbornly maintain the same coverage – or are even expanding. A theory being explored is that the giant ice shelves, features not found in the Arctic, play a controlling role in the growth of sea ice, and so a warming world might see more Antarctic sea ice up to a point.

"Understanding the role of sea ice in the Earth's system has never been more important. But understanding how this role will change over the next century is vital for our society as a whole."

A large part of Stevens' work involves connecting sea ice and ice shelf processes through their interactions with the ocean beneath.

About half of the Antarctic coastline is surrounded by enormous ice shelves, huge frozen expanses up to more than a kilometre thick, which are responsible for maintaining sea levels by holding back giant polar ice sheets.

Stevens and his colleagues are studying how water mixing at the face of the ice shelves is affecting their resilience and stability. Stability, they believe, plays a huge role in rising sea levels.

"A warmer ocean will melt the underside of an ice shelf more quickly, a thinner shelf is more prone to collapse and this in turn unlocks the Antarctic ice sheet, enabling the ice to flow more rapidly into the ocean – thus increasing sea levels dramatically.

"We are trying to understand the building blocks of how this rapidly changing climate system works. We can't assume it is operating in the way it has in the past."

Research subject: Antarctica