Wondrously wonderful water

Before I dive in to talk about the physics that make certain regions in the Southern Ocean more awesome than others, I’m going to take this opportunity to elucidate why water is such a big deal. The biggest, really. I don’t know if you’ve been following stories about ‘other earths’, but scientists who are into that sort of thing are perpetually searching for planets orbiting at the right distance from their suns – within the ‘goldilocks zone’. More importantly, however, they’ve been searching for a planet that looks like it could hold water in liquid form.

Why water, of all things? Surely there are other variables equally – if not more – important? Well, actually no. For there to be life, there needs to be water. And it all starts because of the very nature of the molecule H2O: One Oxygen (O) and two hydrogens (H2)

Oxygen is a bit of a player. Not content with one hydrogen in his life, he keeps things unofficial and strings another hydrogen along. These two hydrogens don’t seem to mind so much because they stick around through thick or thin. In other words: through solid, liquid or gas. But you should know a little more about Oxygen – aside from being the charismatic charmer, he enjoys power. As a result, he hoards the electrons from the bonds he shares with his hydrogens, keeping them closer to him. This allows Oxygen to be slightly more negatively charged than the (slightly positive) hydrogens he strings along.

I’m making Oxygen sound like a bad guy. He’s not, really… maybe just keep him away from your sister…

Hilarious image by Elli Gorgievska – thank you my friend, you’re the BEST!

When Oxygen and his two hydrogens hang out with more H2O molecules, the slightly negative charge on the O allows for a weakly interacting force with other (slightly positive) hydrogens. Not enough to upset a fellow Oxygen, you understand… just enough for a bit of a ‘vibe’.

Strangely enough, it’s thanks to this weird set-up that life exists. Because of the unequal sharing of electrons between Oxygen and hydrogen, and the ‘vibes’ between H2O molecules, water is endowed with several properties that make it unlike any other substance on earth. To name but a few: water is a universal solvent, it has an extremely high heat capacity and it has surface tension. These are all very important things and I’m happy to go into detail as to why (you need only ask), but the trait I like best is that H2O exists in all three states in nature. Liquid, solid, gas. Can you think of one other substance on earth that can claim the same? That’s a trick question. There aren’t any.

At atmospheric pressure, as water gets to around 0 degrees (or even lower for salt water), it’s able to change state into a solid. The molecules become sluggish at cold temperatures (I can empathise now that I live in Scotland) and they start to organise themselves into hexagonal crystals as freezing point is reached. That ‘vibe’ between H2O molecules dominates the intermolecular forces now, and molecules are able to pack in a less compact way versus liquid water.

Ice is 8.3% less dense than liquid water, making it lighter. Hey presto! Ice floats!

To help visualise ice floating… mmm (http://bigflavors.blogspot.co.uk/2010/05/st-germain-gin-tonic.html)

This phenomenon is ESSENTIAL for life on earth, otherwise natural bodies of water would freeze from the bottom up. Think about this for a second… the entire water column would solidify (possibly permanently) and anything unable to survive being frozen (for example… um…) would die. Luckily, what we get instead is ice forming above the water column.

Ice sheets are brilliant because they’re generally thin enough to allow for diffuse light penetration, but thick enough to protect the underlying water from weather extremes. Sheltered environments below the ice act as nurseries for bacteria and algae, which in turn provide food for zooplankton like krill. Sound like something I’ve mentioned before? Like… maybe a food chain? The marginal ice zone may not seem like the kind of place that could support vast amounts of life, but I know a few elephant seals that would disagree with that sentiment.

Bloom at the marginal ice edge captured by MODIS (February 27, 2012) (Image courtesy Jeff Schmaltz, LANCE/EOSDIS MODIS Rapid Response Team at NASA)

This week, my new friends Donald and Luke dragged me to an amazing talk by Dr. Robert Mulvaney from the British Antarctic Survey (BAS). His team collects ice-cores from the Antarctic Peninsula, allowing him to go way back into the climatological record. Super deep ice-cores (up to 3650m at Vostok!) contain air bubbles that became trapped when snow fell on the continent hundreds of thousands of years ago. By extracting these bubbles, scientists can measure levels of carbon dioxide and methane in the atmosphere as far back as 800,000 years ago (when earth’s magnetic poles were opposite to the ones we have today and homo sapiens were only just starting to settle in Britain!)

Dr Robert Mulvaney removing an ice core from the drill (Image courtesy of BAS)

After the talk, I got to hold 120,000 year old ice from a core collected off Fletcher Promontory. Antarctic ice! From thousands of years ago! In my hands!! Also: as it melts, the escaping bubbles of gas make snap crackle pop sounds, in case you were wondering.


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