PAP Cruise : Monday 11th August 2009

R HollandMy name is Ross Holland and I’m the Marine Flow Cytometry technician at the National Oceanography Centre, Southampton. This is my eleventh cruise on the RRS Discovery, and it’s been fun as always! Time is running out for me to write an entry for the blog, as I just finished analysing my last sample of the cruise just before dinner today! I thought it was about time I got involved by telling you a little bit about what I have been doing for the last five weeks.

Flow cytometers, the machines I am responsible for, are instruments used by Marine Microbiologists to study the very smallest forms of life in the oceans, the bacteria, protozoans and the pico-phytoplankton, many of which are less than one thousandth of a millimetre in size. These groups of organisms may be very small, but they are the most abundant life forms in the oceans, and so it is very important to know what they are up to! There may be as many as 3 million of them per millilitre of seawater, don’t let this put you off swimming in the sea though, marine bacteria are perfectly harmless.

During this cruise the focus of our efforts has been on these organisms and their abundance and function at previously little-studied depths.

Our standard flow cytometer works by passing a sample of seawater through a laser beam. Each cell that passes through the laser beam, scatters light and fluoresces in a specific way, and by detecting the exact way in which the particle reacts, we can assign it to a different group of organisms. In addition, the cytometer can actually physically ‘pick out’ groups of cells we are interested in. By incubating them with different labelled substances, we can sort a few tens of thousands of cells out and then measure the rate of uptake of these substances, and get an idea about how active each group of cells is.

Also on this cruise I have been involved in using the sophisticated new size fractionating plankton net developed by Mike Zubkov and Kev Saw. This has been used to catch large numbers of much bigger phytoplankton and zooplankton for us to count on our newest flow cytometer at NOCS, the Flow Cam. This cunning device actually takes a photograph of every cell it counts and can recognise the group of organisms it belongs to just from the photograph. From this we can tell a great deal about the ecology of the waters we are studying around the PAP site!

Ross Holland

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