D341: Porcupine Abyssal Plain cruise 2009


Cruise blog

Thursday 16 July 2009

The ARIES (Auto Recorded Instrumented Sampler) was deployed last night to sample zooplankton and was recovered at O4:00 am this morning. A drifting mooring equipped with more Deep-IODA systems (Marseille group) will be deployed today followed by the recovery of the main PAP surface-seafloor mooring. Sensors from the mooring will be maintained and re-calibrated ready for a full year deployment at sea. A number of other station activities will also take place (e.g. SAPS, coring, nets, snowcatcher).

How do the sensors work?
The ZPS zooplankton sampler works by filtering water at a rate of 25 Litres per minute. Zooplankton are caught on a mesh and the samples are kept in a sealed container (with preservative e.g. formalin) to analyse back in the laboratory. Sampling has been set to occur every 12 hrs at midday and midnight. These times have been chosen specifically because of the biology of the zooplankton and their diurnal routine. In daylight hours zooplankton avoid predators by staying in the dark depths of the ocean (~ 200 m) to avoid being eaten. However, the food is more abundant in shallower waters so under the cover of night they move upwards to feed on phytoplankton (microscopic marine plants). They then retreat down to deeper waters as the sun rises and the surface waters become sunlit again. Comparing samples collected in the light and dark will provide information on the level of migration occurring at this time of the year and the abundance and diversity of zooplankton populations at 50m. A microcat (temperature and conductivity/salinity sensor) has also been deployed just above the zooplankton sampler to gain information on the physical properties of the ocean which is intimately linked with the biology.

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