4 research outputs found
Iron Fertilization and the Trichodesmiumresponse on the West Florida Shelf
Prior laboratory studies of Trichodesmium have shown a high iron requirement that is consistent with the biochemical demand for iron in the enzyme nitrogenase. Summer delivery of iron, in the form of Saharan dust, may provide an explanation for Trichodesmium blooms observed in offshore waters of the West Florida shelf over the last 50 yr. During ecology and oceanography of harmful algal blooms (ECOHAB) field studies, background iron levels (0.1â0.5 nmol kgâ1) were found at the surface during periods of minimal dust delivery (May 2000 and October 1999). In contrast, total dissolved iron concentrations on the order of âŒ16 nmol kgâ1 were measured at the West Florida shelfßbreak after a July 1999 Saharan dust event that was identified by advanced very high resolution radiometer (AVHRR) imagery, groundßbased radiometers, air mass analysis, and aerosol samples (dust and nonßseaßsalt nitrate) collected throughout South Florida. The Trichodesmium response following this July dust event was a 100âfold increase over background biomass, reaching a surface stock of âŒ20 colonies Lâ1. Surface dissolved concentrations of both inorganic and organic phosphorus decreased below detectable limits during this bloom. Dissolved organic nitrogen concentrations associated with the bloom (15â20 ”M) were 3â4âfold greater than background and much larger than ambient NO3â concentrations (\u3c0.5 ”mol kgâ1). If all dissolved organic nitrogen (DON) is converted to urea and ammonium, this organic nitrogen could have supported the red tide of \u3e20 ”g chl Lâ1 of the toxic dinoflagellate, Gymnodinium breve, found along the West Florida coast during October 1999