Jeremy, Wednesday 15 October 2008
I am writing this from Monkey Island – the open space on top of the bridge where we can watch the world go by. And right now I am surrounded on all sides by absolutely nothing. There are no islands, no ships, no dolphins, no birds, just gently rolling dark blue water in all directions, except up. The complete absence of everything is because we have now got near to the centre of the North Atlantic gyre, which is one of the biggest marine deserts on earth.
Of course, unlike the Sahara desert, which is 2000 miles due east of us, there is no shortage of water here. But that water contains very very little of certain key elements that life needs to grow, especially nitrogen and phosphorus (the same nutrient elements as I should be adding to my lawn back home to get the grass to grow a bit better next summer). Any trace of these elements in the water gets hoovered up by plant plankton.
Now, you would expect that the nice marine ecosystem would sensibly recycle these elements. However, the ecosystem is in fact hopelessly inefficient and when they die the plankton sink out of the water column taking the nutrients with them. So, the sunny wind-mixed top 60m or so of the ocean is almost lifeless.
Almost but not quite - some specialist plant-plankton have adapted to this harsh environment including particularly many of our friends the coccolithophores, the cacti of the oceanic deserts.
So, Martine’s filtering is yielding a wonderful array of exotic specimens for the microscope. From the surface layers we need to pump several litres of sea-water to get enough to find on our filters. Deeper down, where the water is more nutrient-rich, different specialist forms adapted to low light levels occur at slightly higher abundances, although down there they have a range of things to compete with including cheerily-named cyanobacteria which several other people are studying on the cruise (more on them, the people not the cyanobacteria, another time).
As we sail south each station has a slightly different water column structure and ecology. Observing the changing coccolithophore communities in the field is both a great way to ensure we get the possible results and extremely rewarding – coccolith heaven, I am back to the microscope.