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The ridiculously cold Southern Ocean

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By Mark Robinson
Sunday, April 13, 2014, 9:29 AM

The cold hit me like a punch to the gut.  

This was a full on, breath-removing contraction of every muscle in my body. For what seemed like a brief eternity, I could not get a breath in. This was not entirely a bad thing, considering I was underwater, submerged in some of the coldest waters in the world. Welcome to the Southern Ocean.

The Southern Ocean surrounds the continent of Antarctica and because of that, the water regularly gets below the temperature of the ice in your summer drink. What I mean by this is that the unique properties of seawater allow it drop below freezing and still stay liquid. 

Unearthed: Tune into The Weather Network for more of Mark's adventures tonight at 7 p.m. and 10 p.m. EDT for the premiere of the latest episode of "Unearthed."

So, yes, you can actually end up fully frozen in the water of the Southern Ocean if you stay in too long. I’ve got to figure out a way to get The Weather Network to send me to the Caribbean instead of the planetary equivalent of deep freezer. And yet, I wasn’t going to pass up the opportunity of seeing (and experiencing) the Southern Ocean. 

The seas surrounding Antarctica are a unique place because of the way the continent is shaped. Think of the Antarctic as a continent surrounded by an ocean, while the better-known Arctic, is an ocean surrounded by continents. This difference in geography between the two poles has drastic implications on the climate and ocean circulation.  

A massive current sweeps around the continent like a snake chasing its tail. This mass of moving water is known as the Antarctic Circumpolar Current and at 21 000 km in length, it is the longest ocean current in the world. It’s a massive current as well, carrying with it the equivalent of 100 times the amount of water of every river on earth. That’s 130 million cubic metres of water per second moving around Antarctica. 

The unique manner in which this current moves around the continent helps to create a zone of mixing and upwelling known as the Antarctic Convergence. The zone is created as cold, northward flowing Antarctic waters meet the warmer waters of the Atlantic and Pacific oceans.  The colder water sinks below the warmer and a kind of natural border is created; sort of like the treeline in the Arctic. Passing over the zone, you can actually see the change in the colour of the water. It goes from the deep blue of the southern Atlantic to the light azure of the Southern Ocean itself. 

That change meant that we were also travelling across an ecological barrier. Deep under us, the southward moving masses of water from the Atlantic were giving way to the eastward moving water of the Circumpolar Current.  This zone is stupendously productive thanks to the upwelling and mixing of the two oceans and forms the basis for a huge part of the ocean’s food web. Phytoplankton grows in huge abundance and that in turn allows a massive proliferation of the organisms that form the basis of the oceanic food web; krill. These small crustaceans are food for fish and other larger ocean creatures. In turn, the fish are eaten by seals, seabirds (such as albatrosses), and even penguins.

The “barrier” of Antarctic Convergence means that for the most part, the Antarctic is isolated biologically from the rest of the planet. This barrier has been in place ever since the Drake Passage opened up a few million years ago. 

However, because scientific research is so difficult in Antarctic waters, only a small segment of the species in the Southern Ocean have been identified or studied. We really don’t know that much about the ecosystems deep beneath the icy waters of the Southern Ocean. This lack of knowledge leads to controversies like whether or not the invading king crab (which happens to be delicious with butter and lemon) is really a native Antarctic species.  

Crabs weren’t on the menu as we passed through the zone, but the thermometers that measure the water temperature around the ship measured a fast drop of around 2 C. This meant that the water we were passing through was very close to 0 C, the freezing point of water. 

Seawater has some unique properties when it comes to temperature.  Freshwater freezes at 0 C as long as it’s not totally pure (supercooling is something I’ll get into in another column). Saltwater (brine) can get as low as -20 C before it freezes solid depending on how much salt is in it.  Natural seawater is only about 3.5 per cent dissolved salts which means that it typically freezes at about -2.0 C. The coldest seawater ever recorded was about -2.6 C and that was under an iceshelf in Antarctica.

Icy brine is created from the process of freezing saltwater. As seawater freezes, the dissolved salts are excluded in a process known as 'brine rejection'. This brine is colder and more dense than the forming ice and so tends to sink downwards.  As the seawater freezes completely, this very cold brine sinks down through the ocean and begins a process that drives the ocean currents and affects every aspect of the global climate system. 

As the Antarctic winter begins, areas of seawater around the continent freeze into huge ice shelves. From these ice shelves, equally huge amounts of cold, dense brine sink down along the underwater slopes around the continent and from there along the bottom of the Southern Ocean.  Eventually, these masses of water move northwards beneath the Pacific Ocean. 

This Antarctic Bottom Water is also formed as polynas (areas of open water amongst the ice) allow highly oxygenated seawater to cool to the point where it gets dense enough to sink before it freezes. Together, these processes create currents so massive that they drive the ocean circulation across the planet.

Of course, all this dramatic, wonderful, scientific knowledge was crushed out of my brain when I hit the water by the single resounding thought:

“Gahhhhhhh! Cold! So very, very cold! Why did I do this?!”  

I think I heard a distinct 'pop'. Of course, that might have been my brain directing every neuron to get my muscles moving me out of the searing cold and back out onto the pebbled beach that I leaped from. I hit the land so fast that George barely had time to turn the camera my way before (between hysterical laughter) and ask me how it was.

The cold was so intense that I quite literally could not breathe and he was forced to wait until I wrapped a sweatshirt around myself and could draw breath once more. Amazingly, I wasn’t all that deep down chilled. The cold was searing, but only felt skin deep. Once I’d toweled off and got a shirt on, the cold air was endurable and the sun almost felt warm.  

Chalk one up for modern sweatshirt materials, but the Southern Ocean is a vast and unforgiving place. Being in it for just a moment is one thing, but living it is something else. The animals and plants of Antarctica have long evolved to withstand and even thrive in the icy water, but I’d much prefer the warm, circulating waters of the shipboard hot tub.  

I’m leaving the Southern Ocean to the penguins!

Unearthed: Tune into The Weather Network for more of Mark's adventures tonight at 7 p.m. and 10 p.m. EDT for the premiere of the latest episode of "Unearthed."

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