AME 64:135-147 (2011)  -  DOI: https://doi.org/10.3354/ame01511

ABSTRACT: The abundance and nitrogen fixation rates of Trichodesmium sp. integrated down to the deep chlorophyll maximum as well as nitrogen fixation rates in size-fractionated discrete surface water samples were measured across the Mediterranean Sea. The abundance of Trichodesmium sp. was generally low (<50 trichomes m^–3), except at one station in the Tyrrhenian Sea where the water temperature was >20°C and Trichodesmium sp. was present at a higher density (ca. 700 trichomes m^–3). Across the basin, size-fractionated nitrogen fixation rates were low (<250 nmol N₂ m^–3 h^–1). The highest rate was measured at a station characterized by relatively high concentrations of total ­dissolved P and dissolved Fe. High δ¹⁵N values (8.04 ± 2.03‰) of the particulate organic nitrogen were in accordance with the observed low water column nitrogen fixation rates across the Mediterranean Sea.

KEY WORDS: Nitrogen fixation · Trichodesmium sp. · Mediterranean Sea