01.04.2012

Secrets of the Ice

Leading scientist explains importance of Antarctic ice sheets and ocean currents in climate change
Antarctica. The word conjures images of snow and ice, severe cold, howling winds, gigantic seas and magnificent mountains and volcanoes -Mt. Erebus, 3800 metres high, has been in an almost continuous eruptive state since 1987. Antarctica is also the land of past heroes: Amundsen, Scott and Shackleton. Amundsen was the first man to stand at the South Pole on December 14 1911, just over 100 years ago, beating his rival Scott, to whom he left a letter wishing him well, by a mere five weeks.

I have always wanted to go to the Antarctic, ever since I was asked as a schoolboy to read The Fire on the Snow, a chilling radio play in verse by Douglas Stewart, first broadcast on ABC radio in 1936, and soon to have its world premiere as an opera by Australian composer Scott McIntyre at the Tasmania Conservatorium of Music in July 2012.

Just over a year ago, during a typical cold winter in Britain, where I work as a Professor of Earth Sciences at Cambridge University, I was asked if I wanted to join an oceanographic expedition Down South in January and February. I jumped at the chance. We were to be on the research vessel RRS James Clark Ross, named after an intrepid Antarctic explorer and run by the British Antarctic Survey, making measurements and taking samples in the northern Weddell Sea, south east of the Drake Passage between South America and Antarctica, and directly east of the Antarctic Peninsula.

After months of preparation, such as developing and discussing a plan for the science to be conducted on the cruise, building and checking new instruments, monitoring sea ice conditions and getting warm clothing and boots together, we were finally ready to go. We flew from RAF Brize Norton on a commercial twin-engined Airbus A330 fitted out entirely with (closely spaced) 'economy' seats, except, chillingly, at the central portion at the back, which had space for two horizontal stretchers for returning wounded soldiers or airmen. After a long flight via Wideawake Airfield on Ascension Island, a joint facility of the United States Air Force and the Royal Air Force, where we were corralled like animals, we reached Mount Pleasant Airport in the Falkland Islands. From there, we were taken by bus through numerous marked and fenced-off mine fields - remnants of the Falklands war - to the RRS James Clark Ross in Port Stanley.

Each of the 20 scientists had a cabin of his or her own. I was one of the lucky ones to have a large four berth cabin to myself. The cabin was approximately 3 x 5m, in addition to a compact, but perfectly satisfactory, bathroom of shower and accessories. The second most important feature to me - after my comfortable lower bunk - was a long desk under three giant portholes to the outside world. My eyes lit up when I saw the Ethernet cord for my laptop; but my patience was frequently truly tested by the unbelievable slowness of the internet, often slower I'm sure than the dial-up days of the '90s. How did Newton do science without a reliable, rapid network?

I knew my routine would be to rise from my bed at 11:45 pm (local time) each night, dress rapidly and appear in the main laboratory minutes, or maybe even seconds, before midnight to commence my four hour scientific watch. Those on watch would take data, prepare for future work, discuss how the expedition was progressing and of course drink lots of coffee to keep awake. At four o'clock, I would hand over to my scientific replacement and go to bed. Breakfast was at 7:30 - not 7:29 or 7:31 but, as the stewards would occasionally remind us, 7:30. Lunch 12:00. Dinner 6:30 at sea and 6:00 while in port - or was it the other way around? Why the difference in time anyway? Whatever, I have never seen food eaten so quickly. The stewards had other jobs on board and subtly rushed us through our meals, which were often all over in under 20 minutes. I once saw a graduate student sitting opposite me heartily eat five courses in just 15 minutes.

After breakfast I tended to work on the data on hand and generally talk science, as well as having to carry out some of the usual tasks while in my office of writing letters of recommendation, reading and refereeing scientific papers and writing reviews of scientific fields for publication in international scientific journals. I often had to skip lunch, or have it earlier in the separate, self serve crew's mess because my second scientific watch was from 12:00 to 16:00. I sometimes slept after that, in order to be fresh for dinner. After dinner I would relax, sleep for a few hours and the whole process would repeat itself. For 15 days. After about three days, my memory became somewhat blurred: had I sent off that email; remembered to charge up my laptop; noted the day's events in my diary, already?

But back to the beginning. After many safety demonstrations and practices, spread over the first two days on board, we slipped our moorings and headed south to enjoy our expedition on board a ship which costs about £UK20,000 per day to run. Two days and approximately 750 km later, we were 'on station' ready to carry out our first experiment.

The aim of the expedition was to investigate the changes and variability in time and space of the important currents along the Antarctic margins and to take biological samples of the krill and fish who live and breed there. The main instruments used to take the physical measurements were sea gliders, first introduced in 1989 by three independent groups. One was called Slocum, after Joshua Slocum, the first solo navigator of the world by sailboat. These gliders are steel cylinders approximately two meters high and 40cm diameter with short, stubby wings about 30cm long, and a very small rudder. They are all painted a bright yellow to make them easier to see on recovery.

Sea gliders have no motors for propulsion, but use minimal amounts of power from small lithium batteries to operate pumps and valves to transfer oil back and forth between an internal and external bladder. This configuration does not change the mass of the glider, but it does change the volume, and hence density. Increase the density and the glider slowly sinks; decrease the density and the glider will rise - all the way to the surface if commanded to do so. They can also move sideways by re-arranging their internal distribution of mass. Much of the time is spent in slow, free gliding, needing no energy input, at around 1km/hr. They are controlled by signals transmitted by satellite on instructions sent from far away. Gliders have gone to depths as great as 1000m and been recovered and can function without any maintenance for up to six months. All of which makes them very useful instruments, like drones of the sea - and of great interest to the military.

We employed three of these gliders, after having first christened each one and wishing them luck by throwing a glass of gin over them. In friendly fashion, one of them, slightly fatter than the other two, was nicknamed the "flying pig". The gliders were controlled from onboard via 'home' computers in Caltech, Southern California, the University of East Anglia, England and from a commercial company in North Carolina.

During operation, often tracing a sawtooth pattern through the water, the gliders take continuous measurements of temperature and salinity (the traditional physical properties of sea water) as well as current speed, bottom depth, chlorophyll fluorescence and other such variables. They transmit their data back to 'home base' every time they surface, at which time they take a GPS fix to aid the navigation.

Why do oceanographers want these variables - laboriously obtained in the past by time-intensive, boring measurement - taken from a research vessel costing many tens of thousands of dollars to run each day? Because they tell us about the state of the oceans, which cover 70% of the Earth's surface. The oceans, the only form of transport between many countries in the past, play a large role in determining the Earth's climate and are the breeding grounds for fish. Unfortunately, they have also become a huge rubbish dump for much of mankind's waste.

The Southern Ocean, which surrounds the Antarctic continent, plays a role in all these functions and is the source of the best swells to hit Australian beaches - they are generated by storms in Antarctica. It also has a crucial influence on climate. This is because the Southern Ocean is the only water mass which goes around the world without being blocked by land (in contrast to the atmosphere) and induces a strong flow - the Antarctic Circumpolar Current, from west to east around Antarctica - which connects the Atlantic, Indian and Pacific Oceans, redistributing heat and other quantities that influence temperature and rainfall throughout the world. The current is so strong that it transports 150 times more water around the Antarctic than the total volume flow of all rivers in the world.

As well as the mainly horizontal, wind-driven currents, influenced strongly by the rotation of the Earth, there are strong downward flows driven by the formation of sea ice each year - the Antarctic ice cover in winter is approximately twice that in summer. When ice freezes from sea water, of salinity approximately 3.5% by mass, the ice contains very little salt. The 'released' salt mixes with the surrounding water, making it more dense. The dense water sinks to the bottom of the ocean (due to the influence of gravity) and then flows northward in a current which has been detected as far north as 45º N, acting as a giant conveyor belt transporting heat and salt in the oceans. Any newly formed ice also has an important direct effect on the climate because its whiteness reflects back to outer space almost all of the incident heat of the sun. This is in contrast to the relatively dark sea from which it came and which, in contrast, tends to absorb all the incident heat. This is called the albedo effect, with the albedo for any surface being the ratio of reflected to incident energy.

The sea surface (worldwide) is a tremendous place for the exchange of gases, such as carbon dioxide and oxygen, between atmosphere and ocean. The ocean is the largest active reservoir of carbon dioxide of the three major sites: biosphere (forests, grasslands and marine plankton); the atmosphere; and the ocean. Mankind currently releases 32 billion tonnes of carbon dioxide annually into the atmosphere, mainly by burning fossil fuels. Just under half of this remains in the atmosphere, while approximately one third is taken into the ocean, with the residue absorbed by the Earth's biosphere. Despite this apportioning, the ocean contains approximately 50 times more carbon dioxide than the atmosphere. The ocean is thus a large, and important, sink of the greenhouse gas that may make it impossible for us to live comfortably on our planet.

The ice cover of the world has two direct dramatic effects. First, it alters the effective albedo of the Earth. Second, and considerably more important, the rising atmospheric temperature is causing the melting of the giant ice sheets, averaging some two kilometres thickness, which have built up from the snow falling over the continent for the last 35 million years. These ice sheets, containing 30 million cubic kilometres of frozen water, flow over the continent and out to sea at a rate of 500 m/yr, to slowly melt, putting more water into the ocean and thus inexorably raising sea levels.

If all the ice on the continent were to melt it would raise the sea level by approximately 70 metres. Thus even the melting of a fraction of the ice held in Antarctica could cause considerable destruction, and possibly be easily sufficient to cause extensive flood damage to at least much of Bangladesh, London, Melbourne, New York, Rotterdam, Shanghai and Tokyo.

Because of my training as a physical oceanographer, I have said little about the important biological aspects of the Antarctic and our expedition. Conditions are relatively harsh in the cold environment of Antarctic waters, and the ecosystem is constantly changing and adapting to destructive and stochastic influences such as iceberg scouring and seasonal effects associated with freezing in the winter. Krill - more than half a billion tonnes of which are present in the Southern Ocean - are shrimp-like marine crustaceans. They are near the bottom of the food chain, feeding mainly on phytoplankton, but contributing a large part of the diet of whales, seals, penguins, squid and fish. They form swarms of many millions. Our instruments showed that these swarms can be hundreds of metres in horizontal extent and rise to near the ocean surface during the times of darkness, while descending to depths of hundreds of metres at midday.

Looking back over the expedition, I have many fabulous memories. The 20 scientists on board (mainly) bonded together and new friendships and scientific collaborations were struck up. We saw pods of whales on many occasions. During one of the first, a barnacle encrusted humpback whale came to within a few metres of the side of the ship and slowly and gracefully rose through the surface, stuck his or her head a metre or so out of the water and looked at us with beady eyes. I hope we passed muster. We also saw many, many penguins, some 'flying' through the air out of the water. There were seals basking on top of large icebergs, enjoying the warm sunshine. We were frequently followed by a few of the famous flying albatrosses, with their prominent curved yellow beaks, and by many petrels.

From a scientific point of view, ordered life only begins at the end of a cruise. After an exhausting but exhilarating time, working around the clock, starting scientific watches at midnight, having little sleep and being somewhat disoriented, the scientists connected with the cruise get their hands on the data, which needs careful and extensive exploration, using the most powerful computers to which we have easy access. This processing and then interpreting of the data can take many, many months - indeed, an extreme example is one of the most famous collections of data in the Southern Ocean in 1928 that was not written about fully until the early 1960s. These days, however, there is a greater pressure on scientists to distribute the results of their work quickly.

Having examined the data and its implications as completely as possible, there follows the task of preparing the results for publication in the scientific literature and presenting them before one's scientific colleagues at big international meetings and the interested public at other forums. An additional, important exercise is to explain the results and interpretations to politicians and policy makers who have to make decisions regarding how effects in the Southern Ocean influence the way we live.

Let the fun begin.

Australian-born Herbert Huppert was educated in Sydney and graduated from the University of Sydney with a first class honours degree in Applied Mathematics before completing a PhD in California. His association with the University of Cambridge began in 1968 and he has been Professor of Theoretical Geophysics since 1989 and Fellow of King's College, Cambridge since 1970. He is regarded as a leading authority in Earth sciences, in the fields of meteorology, oceanography and geology. He was elected to the Royal Society in 1987. In 2005 he was the only non-American recipient of a prize from the United States National Academy of Sciences, being awarded the Arthur L. Day Prize Lectureship for contributions to the Earth sciences. Professor Huppert's fields of research include CO2 sequestration, exchange flows and the fluid mechanics of solidification.


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