Viene la tormenta?

24 September 2012 by Anonymous (not verified)

Guest post - Adrian Martin (National Oceanography Centre)
La tormenta
Ever since I was a boy I've loved making models. From glue smeared aeroplanes to the computer models of ecosystems I use in my work. So it's natural to wonder how I found myself on a real boat in the middle of the Atlantic, at 4 in the morning, playing submarine yo-yo with what is essentially a gramophone needle on a pole. It is fair to say that not all marine modellers and theoreticians have been to sea. 'I don't do field work and even if I did... the Atlantic? I'm allergic to seafood!' But a little dose of salt can add something: an understanding
of what is possible and how difficult it may be to obtain it. So say hello to my little friend, the MSS turbulence profiler. It may look like a bazooka with ginger dreadlocks but there is a reason for that. The tubular shape allows it to sink straight down, with nary a wobble, while the dreadlocks minimise disturbance of the water as it sinks, which might affect the very sensitive measurements. But, OK, the ginger colour is gratuitous. At the end of the profiler is the shear probe. The movement of the water tweaks the end of the needle. This is converted into an electrical signal, fed through a computer and, baddabing, we have a precise measurement of mixing in the ocean. There has been some debate on board of just how sensitive this delicate spike
of metal is at recording movements of the water, in precise scientific quantities of hand-held food mixer per Olympic swimming pool. Though a final number of pools was never decided upon it was generally felt that
one mixer would easily suffice for quite a few pools [Ed's note: the first calculation had "quite a few" equal to about 100,000, subsequently revised downwards], putting to one side the practical issues of how one could reach all parts of the pool with the mixer and whether the pool attendants would ask you to leave before you did. Mixing is vital in the ocean: to help maintain the global circulation of water, to maintain the exchange of carbon dioxide between the atmosphere and the ocean and to bring nutrients up from the compost heap of deeper waters to help the surface algae population to grow.

The latter is my usual interest. It's alive! But understanding the physics of its environment is crucial to understand why it is. Mixing varies throughout the day, with the tides, changing air temperature and
winds. As a result we're studying it round the clock and I'm on the 4am to 8am shift. Being out on the deck for long periods does give ample time to see wildlife, with whales and dolphins being high on the
bragging list. Fish and squid can be seen too, often directly below us as we yo-yo the probe through the water. They come at night mostly. To the untrained eye, fish seem to come in two types: fish, and fish
chased by dolphins. The difference? They seemed...faster. But for now we have a break from mixing detail. We are towing a device called SeaSoar to map the properties of the upper ocean over a region 100km
across and to a depth of nearly half a kilometre. This allows us to build maps, like weather charts, that reveal how the ocean moves. But we're up against time. Worse weather is moving in. We're only just
northwest of the Bay of Biscay which has an unenviable reputation for storms. These go to eleven. And beyond. Thankfully the forecast is currently predicting something less boisterous for us. With intelligent
cooperation, we may all sit out the blow as comfortably as possible. Then we'll be back out on deck with the mix-o-meter waiting for the sun to rise.
The signal for the end of the 4 to 8 am watch