For this member of the AMT team, activity concentrates around two contrasting times of the day: in the dark hours before dawn, when the zooplankton nets are deployed; and at or around local solar noon, when optical profiles of the water column are made.
Recovering the optical profiler on a sunny Sunday
The optical profiler is a cylindrical stainless steel frame within which are mounted various optical instruments. The profiler descends and ascends through the top 200 metres of the ocean, and the instruments measure the way that light behaves in the water column – being scattered, absorbed and attenuated with depth. Life in the ocean depends upon the primary producers (plant cells) at the bottom of the food chain, which in turn rely upon the penetration of light sufficient for photosynthesis and growth – generally at depths of less than 200 metres.
Another important component of life in the ocean is the zooplankton: small floating animals, predominantly crustaceans between a tenth of a millimetre and a few millimetres in length. On AMT our principal means of sampling these animals is the ‘Bongo Net’. This is a pair of steel rings side by side carrying nets, which are hauled from 200m depth to the surface, capturing as it goes any organisms greater in size than the mesh aperture (0.2 mm). Half past four in the morning is not always a great time to be a marine scientist.
Deploying a single zooplankton net at 04:30
I don’t suppose it’s any better for a few thousand zooplankton, in the volume swept by the net, who have decided that at night it is safe to venture into the surface waters to feed.
Sunday lunchtime: another optical profile. Warm sunshine, clear blue skies: not a cloud more than 10 degrees above the horizon. Just enough breeze to prevent you overheating. The water is crystal blue and clear enough to see the optics rig still descending at 40 metres depth. The rig reaches the bottom of the profile and begins its ascent on the stroke of solar noon. Just another day in paradise…