Muddy history books borrowed from the ocean floor library

Geologists chop up a mud core into manageable chunks. This is the first time the mud has seen the light of day for thousands of years. Photograph: Helen Czerski

Position

53° 46.74 S
38° 06.67 W

This has been the week of mud. It's amazing what geologists can dig up from the ocean floor, given a winch and a glorified drainpipe. Throughout this trip, the ship's sonar systems have been painting a picture of the ocean floor kilometres below us, showing us the mountains and valleys of the deep. But hidden in hollows and trenches in that subsurface landscape are pockets of geological treasure, and this week the ship has been treasure-hunting.

One of the oddest concepts in oceanography is something called marine snow. There are tiny organisms living close to the ocean surface that build themselves from carbonate and silica in the water. When they die, they leave behind delicate but solid shell fragments and these have nowhere to go but down. Throughout the vast oceans of the world, unimaginable numbers of these shards of life are slowly sinking until they can't sink any further. They settle on the ocean floor, on top of the billions from last year and the billions from the year before that. The ocean floor is a cemetery.

But this cemetery has a story to tell. When the organisms are alive and building themselves, they are using what's around them, and in doing so they're building the chemistry of the ocean into their own shells. If there's more carbon-14 than carbon-12 in the ocean, there is in the shell too. These chemical signatures tell us about temperature, ice ages, ecology and much more. Down beneath me on this ship, there's a history book. If you could only dig down through those layers on the ocean floor, you could look back in time and see what the planet was like tens or hundreds of thousands of years ago.

That's where the drainpipe comes in.

When the geologists have found a pocket of sediment, the crew stick a weight shaped like the back end of a dart on to a metal pipe up to 18 metres long. This is lowered over the side of the ship, nose downwards, and off it goes. It sinks until it hits the soft sediment at speed and stabs down into it. It works just like an apple corer, and when you lift it out, a core of stabbed mud comes with it. Et voilà. One geological mud record. The cores collected today were between six and 18 metres long and the geologists think that this is enough to get mud tens and possibly hundreds of thousands of years old. Interestingly, that doesn't necessarily stop the mud being quite smelly.

I can see why this view would spawn sea monsters in your mind if you'd been staring at it for long enough. Photograph: Helen Czerski

We've spent this week sailing around South Georgia, looking for good sites to collect these muddy history books from the ocean floor library. There has been very little to look at on the surface except flat ocean and mist and grey cloud. I can easily see how superstitious early seafarers could transform the shifting mists into monsters.

The routine of the ship is starting to take its toll on us. There can be very little to distinguish one day from the next. Our latitude and longitude change, and the timing of our work changes slightly, but there are only a limited number of different things that happen. The ship's time stays the same as we travel east and west, so sunset and sunrise times change, but otherwise you wouldn't really know we were moving. A few days ago while I was in the gym, doing the same thing I do almost every day, my iPod shuffled to the Eagles song "Hotel California" and I felt a frisson of deeply felt empathy. You can check out any time you like, but you can never leave …

A grumpy-looking gentoo penguin in mid-moult. He looks a bit like someone put him in on the wrong wash cycle. Photograph: Robin Pascal

Penguins to the rescue! Yesterday we saw land for the first time in three weeks. We made a port call at Bird Island, one of the British Antarctic Survey's permanent bases down here, to drop off supplies and to collect waste. After all these weeks of thinking about the shape of the ocean floor beneath us, it was weird to see it poke through the water surface. Three weeks ago, this place would have looked bleak, but now it looks amazingly alive, like the wildlife haven it is. Plenty of birds and seals make their home here, where they can shelter from the otherwise unrelenting ocean.

The curvy bumps of the land looked odd: green seemed like a completely alien colour. Land is strange stuff when you've only had ocean to look at.

We carried the cargo along the jetty, past lounging fur seals and unruffled penguins. Penguins don't get any less entertaining. Everyone can watch them and their antics for hours. But we didn't have hours. Very soon it was time to get back on the ship and the land vanished into the mist again.

There's just one more week of Southern Ocean science to go.