Eat my dust, says the sea

Leibniz-Institut fur Meerwissenschaften an der Universitat Kiel: Scientists from the Leibniz Institute of Marine Sciences (IFM-GEOMAR) in Kiel, Germany, have returned after six weeks on the Cape Verde Islands, 800 kilometres off the West African coast. They collected air and water samples in the search for a link between Saharan dust storms and the biological productivity of the ocean. The results were intriguing: the waters off Cape Verde contain huge amounts of the recently discovered cyanobacteria “UCYN-A”, an enigmatic fertilizer alga whose characteristics are puzzling to scientists. By feeding Saharan dust to the algae, they are now testing if the abundance of UCYN-A is promoted by the Saharan dust which is so common there.

The tropical Atlantic waters around Cape Verde are very low in plant nutrients. Nitrogen is in especially short supply and limits the growth of the phytoplankton, the tiny plants that are at the basis of the food chain in the ocean. In this area, the nutrients fall out from the sky: Trade winds carry Saharan dust rich in iron and phosphorus which can fertilize the surface of the ocean. This was one of the reasons for the IFM-GEOMAR and other German and UK institutions to establish an observatory on the Cape Verde island Sao Vicente. The Tenatso Observatory now supports long-term measurements of dust and greenhouse gases as well as an oceanographic mooring and regular sampling expeditions by the small Cape Verdean research vessel Islandia.

“We’re testing whether Saharan dust can promote the growth of a particular type of microbe, a cyanobacteria. These cyanobacteria can fertilize the surface of the ocean by fixing the abundant nitrogen gas that is dissolved in seawater”, says Prof. Julie LaRoche from IFM-GEOMAR, co-leader of the expedition. There is plenty of nitrogen gas in the atmosphere but it needs to be "fixed" so that it turns into a fertilizer which is available to phytoplankton. The enigmatic cyanobacteria UCYN-A seems to be a very special nitrogen fixer. In contrast to other cyanobacteria, it is probably incapable of producing oxygen. This in turns enables it to fix nitrogen during the day while others cannot….

NASA satellite image of a sand storm above the Cape Verde Islands