Environmental controls on the biogeography of diazotrophy and Trichodesmiumin the Atlantic Ocean

• Main Authors: Snow, J.T (Author), Schlosser, C. (Author), Woodward, E.M.S (Author), Mills, M.M (Author), Achterberg, E.P (Author), Mahaffey, C.A (Author), Bibby, T.S (Author), Moore, C.M (Author)
• Format: Article
• Language: English
• Published: 2015-06.
• Subjects: Article
• Online Access: Get fulltext; Get fulltext

 The cyanobacterium Trichodesmium is responsible for a significant proportion of the annual 'new' nitrogen introduced into the global ocean. Despite being arguably the best studied marine diazotroph, the factors controlling the distribution and growth of Trichodesmium remain a subject of debate, with sea surface temperature, the partial pressure of CO2 and nutrients including iron (Fe) and phosphorus (P), all suggested to be important. Synthesising data from 7 cruises collectively spanning large temporal and spatial scales across the Atlantic Ocean, including 2 previously unreported studies crossing the largely under-sampled South Atlantic gyre, we assessed the relationship between proposed environmental drivers and both community N2 fixation rates and the distribution of Trichodesmium. Simple linear regression analysis would suggest no relationship between any of the sampled environmental variables and N2 fixation rates. However, considering the concentrations of iron and phosphorus together within a simplified resource-ratio framework, illustrated using an idealised numerical model, indicates the combined effects these nutrients have on Trichodesmium and broader diazotroph biogeography, alongside the reciprocal maintenance of different biogeographic provinces of the (sub)-tropical Atlantic in states of Fe or P oligotrophy by diazotrophy. The qualitative principles of the resource-ratio framework are argued to be consistent with both the previously described North-south Atlantic contrast in Trichodesmium abundance and the presence and consequence of a substantial non-Trichodesmium diazotrophic community in the western South Atlantic subtropical gyre. A comprehensive, observation-based explanation of the interactions between Trichodesmium and the wider diazotrophic community with iron and phosphorus in the Atlantic Ocean is thus revealed.