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13th Biennial Challenger Conference for Marine Science8th -11th September 2008 |
Nutrient limitation influences phytoplankton community structure and constrains oceanic primary production. Consequently, nutrient limitation plays an important role in the global carbon cycle and hence the world’s climate. It has become evident during the last two decades that the atmosphere forms a significant transport pathway for nutrients and iron to the ocean.
Recent bottle bioassay experiments in the Atlantic Ocean have shown that the nutrients (N, P, Fe) released from dust stimulate primary productivity. The effects of dust-released nutrients have also been observed in the field. The (sub)tropical North Atlantic surface waters underlying the track of Saharan dust feature high levels of nitrogen fixation. These waters also show high iron concentrations, a key element for diazotrophs due to the high Fe requirement of nitrogenase. The dust stimulated nitrogen fixation thereby provides an important source of new nitrogen.
The current paradigm for the North Atlantic is that the system would not suffer from iron limitation as there is a sufficient supply through Saharan dust inputs. Nevertheless, recent work has shown seasonal iron limitation in the high latitude North Atlantic as a result of unfavourable deep water Fe to N supply ratios and low dust inputs.
There are still uncertainties about the amounts of dust delivered to the North Atlantic, the percentage dissolution of elements from dust in seawater, and the effects on micororganisms. Work is currently conducted, as part of the SOLAS (Surface Ocean Lower Atmosphere Studies) programme, at the Cape Verde Observatory and research cruises to address these questions.