Lohafex provides new insights on plankt...( The Indo-German team of scientists f...)

The Indo-German team of scientists from the National Institute of Oceanography and the Alfred Wegener Institute has returned from its expedition on research vessel Polarstern. The cooperative project Lohafex has yielded new insights on how ocean ecosystems function. But it has dampened hopes on the potential of the Southern Ocean to sequester significant amounts of carbon dioxide (CO₂) and thus mitigate global warming. On 17 March the scientists reached Punta Arenas, Chile, together with colleagues from five other countries. They carried out an ocean iron fertilization experiment in the south-western Atlantic for arduous two and a half months in the notorious Roaring Forties. The scientists fertilized a 300 square kilometre patch of ocean inside the core of an eddy (a clockwise rotating water column with an area of about 10,000 square kilometres) with six tonnes of dissolved iron. They followed the effects of the fertilization on the plankton continuously for 39 days. Additionally they investigated ocean chemistry, particularly concentrations of CO₂ and other greenhouse gases.

As expected, iron addition stimulated growth of the planktonic algae (phytoplankton), which doubled their biomass within the first two weeks by taking up CO₂ from the water. "However, the increasing grazing pressure of small crustacean zooplankton (copepods) prevented further growth of the phytoplankton bloom," explains Dr Wajih Naqvi, co-chief scientist from the National Institute of Oceanography of the Council of Scientific and Industrial Research. Those algal species, which regularly make blooms in coastal regions including the Antarctic, were most heavily grazed. As a result, only a modest amount of carbon sank out of the surface layer by the end of the experiment. Hence, the transfer of CO₂ from the atmosphere to the ocean to compensate the deficit caused by the LOHAFEX bloom was minor com
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