Latitudinal distribution of Trichodesmium spp. and N2 fixation in the Atlantic Ocean

[摘要] We have determined the latitudinal distribution ofTrichodesmium spp. abundance andcommunity N₂ fixation in the Atlantic Ocean along a meridional transectfrom ca. 30° N to 30° S in November–December 2007 and April–May 2008.The observations from both cruises were highly consistent in terms ofabsolute magnitude and latitudinal distribution, showing a strongassociation between Trichodesmium abundance and community N₂ fixation. The highestTrichodesmium abundances (mean = 220 trichomes L^−1,) and community N₂ fixationrates (mean = 60 μmol m⁻² d⁻¹) occurred in the Equatorialregion between 5° S–15° N. In the South Atlantic gyre, Trichodesmium abundance wasvery low (ca. 1 trichome L⁻¹) but N₂ fixation was alwaysmeasurable, averaging 3 and 10 μmol m² d⁻¹ in 2007 and 2008,respectively. We suggest that N₂ fixation in the South Atlantic wassustained by other, presumably unicellular, diazotrophs. Comparing thesedistributions with the geographical pattern in atmospheric dust depositionpoints to iron supply as the main factor determining the large scalelatitudinal variability of Trichodesmium spp. abundance and N₂ fixation in theAtlantic Ocean. We observed a marked South to North decrease in surfacephosphate concentration, which argues against a role for phosphorusavailability in controlling the large scale distribution of N₂fixation. Scaling up from all our measurements (42 stations) results inconservative estimates for total N₂ fixation of ∼6 TgN yr⁻¹in the North Atlantic (0–40° N) and ~1.2 TgN yr⁻¹ in the SouthAtlantic (0–40° S).

[学科分类] 地球化学与岩石