The Frozen Ocean

  By Mel Fitzpatrick, 18 May 2012

Mawson Deputy Station Leader, Australian Antarctic Division

Have you ever wanted to walk on water? Down here in Antarctica, we often do! We’re lucky that for much of the year the ocean surface is frozen over. 

In autumn, the ocean loses heat to the atmosphere and small crystals begin to form on the surface. As these aggregate, they form large sheets of ice or small circular pancakes, depending on whether conditions are calm or windy. The ice continues to accumulate into larger areas called floes, and before you know it there is a thin blanket over the ocean thick enough to walk, or even drive on. 

Reaching an average thickness of a metre in a single growing season, the maximum coverage of sea ice around Antarctica occurs in late September each year. At its peak, the sea ice covers about 20 million square kilometres! That’s more than the area of the Antarctic continent and more than twice the area of Australia.

On a calm day, I measure the sea ice thickness about 2km from Mawson. After six weeks of growth, the ice is almost 80cm thick here. (Photo credit: Malcolm Arnold)

Part of our role at Mawson station is to collect measurements of the sea ice thickness and growth during the winter season for researchers at the University of Tasmania. The data form part of the Antarctic “State of the Environment Report”.

Once a week, we head out to four different sites at Mawson and use a small hand auger to drill through the ice. We measure how thick the snow is on top of the sea ice. Snow is a very good insulator, so once it covers the sea ice it slows down the rate of heat loss from the ocean to the atmosphere, which slows the growth of ice underneath. 

We also use a tape measure to find the ice thickness and to check the depth of the ocean below the surface. For the last month, the ice in Mawson Harbour has been growing about 10cm a week and is now over 90cm thick.

To visit all the sites is about a 6 kilometre walk and can be quite a delightful half-day out. Last week we had perfectly calm conditions, with a pale pink sky and mountain views in the distance.  This week, however, the wind was blowing 35 knots and the temperature was about -15 deg C. Put something warm on and watch my video to see how much fun it is to work in these conditions!

 

 

 

The amazing thing about sea ice is how it changes the appearance of the ocean from very dark to very bright. The ocean surface reflects about 7% of the sun’s light. But freeze the ocean and cover that sea ice with just a few millimetres of snow and it will reflect about 90% of the sunlight that hits it! This is the largest seasonal change in the Earth’s albedo (reflectivity) anywhere on the planet. It affects how much energy the Earth absorbs from the sun, and thus affects the balance of heat that drives the atmospheric circulation. In addition, when the ocean surface freezes, salt is rejected into the water below, forming dense, highly saline water that sinks then heads north, maintaining the circulation of the planet’s oceans.

The seasonal freezing of the ocean around Antarctica is very important for both atmospheric and oceanic processes. Sea ice reaches about a metre thick during a single winter growing season and covers roughly an area twice the size of Australia.

What the new sea ice growth means for life at Mawson is that soon we can start to venture out along the coast in both directions. Until now we have been confined to foot travel, but in the next few weeks we will be able to drive vehicles on the ice as well.

Mawson Harbour sea ice

There are Emperor Penguin colonies near Mawson that we will visit throughout the winter. Look out for my next post on our first visit to Auster Rookery, about 50 km east of Mawson.

With spectacular sunsets and sunrises, the days are becoming noticeably shorter as we head into winter.

 

 

Meet Dr Melanie Fitzpatrick - Special Guest Blogger

 

Four years ago, Catalyst met glaciologist Dr Melanie Fitzpatrick

 

 

This year, Melanie is spending her first full winter “on the ice”. She’s living and working with 14 other hardy souls at one of the most remote locations on the planet – Mawson station in East Antarctica.

 

Catalyst is presenting a regular blog from Mel, direct from Mawson, to share with you her experiences of daily life and scientific work in this incredible icescape.

 

Want to know more about Mel’s work in Antarctica? Ask her a question via the comments tab!

Arriving at Mawson

  By Mel Fitzpatrick

(Photo: Selwyn Saunders)

The journey to this end of the earth is a long and arduous one.  Leaving from the tip of Western Australia in mid-February it took us more than two weeks by ship to reach the most distant of the three Australian stations, Mawson.  

 

Crossing the windiest, roughest, longest-fetch ocean on the globe (in the wrong direction – heading west!) in a 100-metre long orange ship gives me a sense of isolation, separateness, and disconnection from the rest of the world.  

 

 Mel’s travels – the voyage of Aurora Australis to Mawson, Feb 2012. The ship has returned – Mel is staying with 14 others over the winter (Australian Antarctic Division)

 

We are remote.  We are in a wild place, humbled by its dimensions - so huge a space, a horizon, an ocean, a continent.  The continent of Antarctica itself covers roughly half again the area of either Australia or the lower 48 US states.  It is simply quite enormous. The sea around Antarctica freezes every winter, doubling the area locked under a white, snowy blanket.  This fascinating ocean platform is home to the tiniest of plankton and algae, and the largest of whales.  It inspires in me a sense of wonder and awe at this amazing world we live in – in its fragility and delicate balance, as well as in its power and enormity.  But I also struggle with our place here, with our presence, with our impact…  We come to the end of the earth to discover what we have done to it, how we have affected the planet, and how we can redress the impacts.  What have we learned about living, about treading lightly, about preserving what we have?  I wonder…

 

A frequent companion around the ship, the Light-mantled Sooty Albatross is captured in silhouette. (Photo: Mel Fitzpatrick)

 

As I arrive here – my tenth trip to the vast South land – the poignancy of the visit does not surpass me. It is one hundred years since Douglas Mawson set sail on a great adventure that would epitomise the best and worst of the heroic age. A century later, the Antarctica environment is just as inhospitable and challenging for human habitation. We can only ever be temporary visitors to this place.

 

View the live webcam at Mawson station: http://www.antarctica.gov.au/webcams/mawson 

 

Mawson station is the longest continuously-operating station on the Antarctic continent. Located just inside the Antarctic Circle at 67.60°S, 62.88°E, it’s very long way west of Commonwealth Bay, the original home of Douglas Mawson’s “blizzard”.  Mawson station was established in 1954 and is currently home to a small group of over-wintering personnel, with scientists visiting each summer.

Aurora Australis at Mawson - the station is re-supplied during a five-day visit to Mawson each year. (Photo: Mel Fitzpatrick)

 

At Mawson, two wind turbines provide enough electricity for over half our energy needs, the rest coming from diesel generation. (Photo: Mel Fitzpatrick)

 

As the autumnal equinox passes, our nights here begin to lengthen.  Sea ice forms on the harbour next to Mawson station, and the nightly aurora continue to deprive me of sleep.  Daily minimum temperatures in autumn so far have hovered between minus 10°C and minus 20°C.  Over this time, the wind has varied from a single lack-lustre windless afternoon to a roaring 80 knots, keeping us on our toes.  Arriving as the autumn descends makes for a cold transition from the end of summer in Australia!

 

The southern lights, aka Aurora Australis. In a year of high solar activity, stunning aurora grace the view from my bedroom window. (Photo: Mel Fitzpatrick)

 

But today, I have woken to a clear, calm and windless day. Perfect time to head off for some sea ice measurements! As part of our science data collection, each week we drill through the newly forming ice and measure the thickness and quality of the sea ice. Later this morning, I'll pack up some instruments, put on my ice spikes, and head off for a 6km walk on the frozen ocean surface to measure three different sites near the station. Should be a great day out! Look out for my next post for an update.