Bremerhaven, 27th January 2009. Shortly after receiving permission from the German Federal Ministry for Research RV Polarstern commenced the iron fertilization experiment LOHAFEX. The first step was to deploy a drifting buoy equipped with GPS Telemetry in the centre of an oceanic eddy found to be suitable for the experiment. The water column in the vicinity of the buoy was then intensely sampled to obtain baseline values prior to fertilisation. In the mean time two tanks of 6 m3 volume were each filled with 775 kg of iron sulphate dissolved in sea water. At midday today the iron sulphate solution was released through a hose trailing in the ship’s propeller wash at 15 m depth while she spiralled around the drifting buoy in widening concentric circles one km apart. An area of 150 km2 will be fertilised with a total of 10 tonnes of iron sulphate which will take about 30 hours to complete depending on the weather. Wind speeds at the moment are Beaufort 7 and the air temperature is 9°C. The scientists were delighted to be able to start the experiment as the remaining time to monitor its effects have shrunk to 40 days.

Since the iron is rapidly taken up by the biota, the inert gas sulphur hexafluoride (SF6) is continuously added in trace amounts to the iron solution in order to mark the fertilised patch as SF6 can be measured at very low concentrations. A total of 480 g of this biologically inert gas is sufficient to mark the entire 150 km2. A tank is emptied in about 2.5 hours and is filled while the contents of the other is being released. This procedure will last until 10 tonnes of iron sulphate have been administered to the experimental patch of 20 km diameter.

After fertilisation is completed, the ship will return to the centre of the patch and again sample the water column to determine iron concentrations and the first response of the organisms to it. The iron-limited algae will increase their photosynthetic efficiency hours after iron input. However, it will take about 2 weeks before their biomass increases significantly.

Depending on the response of the algae, another 10 tonnes of iron sulphate will be added to the fertilised patch to compensate for losses due to precipitation and sinking of the iron which is quickly converted to rust particles if not taken up. This re-fertilisation was necessary in most previous experiments because of the slow algal growth rates in cold water.

Key data from Lohafex will be published regularly here...