Autumn Equinox photo challenge:
On the journey around the Sun we are approaching another key moment in our celestial dance with our star. Next Friday September 23rd is the Autumn Equinox. Equinox means equal night, and that day Earth is in balance. There are approximately 12 hours of day and 12 hours of night. In a sense the planet is in neutral, but from that moment onward the northern hemisphere marches towards Autumn while the southern hemisphere approaches Spring. In the north days will be getting shorter and the Sun won't rise as high in the sky and it will gradually get colder.
To mark this moment we plan on featuring the best photos on our blog next week friday that reflect the Equinox. What we're looking for are shots that show the Sun and it's relationship to our planet and the journey into Autumn, or Spring if you live down-under. Let your imagination run wild. The more creative the better! Get those shutters snapping and see what you can capture.
To ensure they are considered for this special feature email them to firstname.lastname@example.org, or add them to our photography pool or hashtag your photos with #bbc23degrees on twitter.
Ice is an important contributor to our weather, but finding out about the Earth's ice was very hard work. It's still less than a hundred years since Amundsen first reached the South Pole (he arrived on the 14th of December 1911, beating Scott by 35 days). My favourite polar expedition is one that is rarely mentioned because it wasn't an expedition in the normal sense. It was made by a ship called the Fram, and there were no sleds or dogs, and there wasn't even any navigation. The Fram was designed to become a piece of pack ice, and it spent three whole years doing just that (from 1893-‐1896). Its voyage was not only a fantastic oceanographic experiment but also an amazing illustration of the dynamic nature of the Arctic.
We tend to think of polar ice as being a bit like giant dollops of whipped cream on top of a dessert, as smooth white splodges that from space almost look as though they're about the run down the sides of the Earth.
Ice at the South Pole is fairly static, but things are very different at the North Pole because the Arctic is an ocean, not a continent. In the Arctic ocean the ice is dense pack ice, always moving, breaking apart and reforming. Pushed by ocean currents below and by wind above, Arctic ice never gets to sit still. The ocean at the North Pole is about 4.2 km deep, and there's no flag there and no base because no piece of ice is ever over the North Pole for any length of time.
Fridtjof Nansen designed the Fram to test the theory that there was an ocean current that crossed the entire Arctic basin. He reasoned that if the jostling ice chunks were pushed along from one side to the other, a ship could be pushed along too. It would be a bit like a conveyer belt to the North Pole, and all he would need was patience and the right ship. The danger was that the ship would be crushed by the huge slow-‐moving pieces of ice, so the Fram was designed with a very round keel so that it would be lifted out of the water and carried rather than crushed. This plan worked beautifully, except that the Fram never quite got to the pole. The ship and her crew were pushed about all over the place [link to map], eventually drifting to the edge of the Arctic ocean and freedom after three years. The furthest north she reached was nearly 86 degrees, 280 miles from the pole.
Even though she didn't get to the North Pole, the Fram clearly demonstrated the dynamic nature of ice in the Arctic, and we now know that individual pieces of ice can indeed travel from Siberia to Greenland in 3-‐4 years, or can go round a sort of giant ice-‐roundabout (called the Beaufort Gyre) in 7-‐10 years. Most polar expedition stories are about humans struggling against natural forces to achieve their goal, but I like the Fram's exploits because they're about humans working with the enormous forces of this planet instead of against them. What are your favourite examples of that?
In Antarctica, it's getting colder. The sun last shone on the south pole in March, and the tilt of our planet means that each day complete darkness swallows up a bit more of the continent. Since there's no incoming energy from the sun, the land and the ocean can only cool down. And it's at this time of year in the south that an innocuous little fact, one that most of us take entirely for granted, quietly makes the huge Southern Ocean a much more hospitable place for almost all marine life.
Ice floats. Icebergs, ice cubes, ice on a freezing river... they all float. And this is weird, because when most substances freeze they get more dense and so the bits that are frozen solid will sink to the bottom of the unfrozen liquid. Water has the quirk that when it freezes, the molecules form a rigid crystal structure with gaps between the atoms that weren't there before. The consequence is that ice is less dense than the water it froze from, and so it floats.
If frozen water sank, just imagine what would happen. Ponds, lakes and the oceans would freeze from the bottom up. There would be nowhere warm and protected under the ice for living things to hide, and the water would just keep freezing upwards until there was no liquid left. All water-based life would have much more of a struggle to survive.
As it is, ice actually acts as an insulating lid, keeping the water below it warm. Heat is lost from the liquid water surface about a hundred times faster than from the ice surface, so less heat is lost overall from an ice-covered ocean. At this time of year, sea ice is growing rapidly in the Antarctic, and it's as if the ocean is responding to the cold by growing itself a blanket. Every year in the Antarctic, 19 million square kilometers of sea ice is formed, and each summer almost all of it melts.
This ice is also a bit like a floating pantry. Lots of algae and krill live on the bottom of it, and these are an important source of food for fish and other Antarctic life.
Sea ice is amazing stuff. It's different to icebergs - those are huge lumps of ice that have fallen off glaciers into the ocean. Sea ice is the ocean freezing at its surface, thickening into large mobile slabs as the winter season goes on. My favourite thing about this ice is that even though the ocean is salty, sea ice isn't. As the water freezes, the salt molecules are squeezed out, first into little brine pockets and later (especially if the ice lasts more than one year) into the ocean. You could hack off a bit of multi-year sea ice, stick it in your drink and never notice its salty origins.
So when you look at ice cubes jostling around in your glass this summer, think about the ice on the other side of the world, jostling around Antarctica in the dark. It's keeping a huge amount of extra heat in the Southern Ocean until the sun comes back, and all just because it floats.
Orbit: Earth's Extraordinary Journey explores the relationship between the Earth's orbit and the weather. Previously '23 Degrees' (working title); on this blog the weather community were invited to discuss their experiences of severe weather as and when events developed and share their iwitness footage throughout 2011. The audience were provided with an insight to the making of the series and exclusive behind the scenes footage. Follow us on Twitter.
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