Fine scales shaping nitrogen fIxation in the GUlf stREam  

Project funding

While most of the North Atlantic subtropical gyre does not have enough phosphate to sustain diazotroph activity (Ward et al. 2013), the Gulf Stream transports water from the Slope Sea into the subtropical gyre through a series of mesoscale eddies and other structures, providing more phosphate than needed for non-diazotrophic plankton growth and allowing a niche for diazotrophs to thrive (Palter et al. 2011). Moreover, the Gulf Stream transports waters >20oC all year, which is higher than the temperature of subtropical waters and closer to the optimal temperature for growth of diazotrophs.

Therefore, the environment near the Gulf Stream has many of the elements required for diazotrophs to thrive. Moreover, the rich spectrum of mesoscale eddies associated with the Gulf Stream is certain to drive a down-gradient flux of excess phosphate into the subtropical gyre. This dynamic environment is thus perfect to study the effect of fine scale structures on diazotroph activity and diversity.

Specific aims

Aim 1) To survey fine scale structures in the Gulf Stream: Fine scale structures will be characterized with in situ measurements of current speed, temperature and salinity, vertical nutrient fluxes and satellite altimetry data.

Aim 2) To implement high-resolution measurements of diazotrophy: Near real-time on-cruise measurements of diazotroph abundance and activity will be implemented with innovative underway equipment. Measurements will be provided every ~15-60 min, which at a navigation speed of ~12 Km h-1 will provide data every 3-12 Km. This spatiotemporal resolution is >10-50 times higher than the conventional measurements of diazotroph abundance and activity measurements compiled in the ‘global diazotroph database’(Luo et al. 2012). Moreover, an autonomous sampler will be deployed to recover plankton biomass as the equipment drifts along the Gulf Stream.

Aim 3) To identify the effect of fine scale structures on diazotrophs: Physical and biological data collected within fine scale structures will be merged and correlated to reveal spatiotemporal patterns of the effects of physics on biology.

Bridges members involved

Cora Hörstmann

Project collaborators

Stéphanie Barrillon, Andrea Doglioli, Anne Petrenko, Gérald Grégori, Olivier Grosso (MIO, France)

Sam Wilson (Newcastle University, UK)

Sophie Cravatte (LEGOS, France)

M. Dolores Pérez-Hernández (ULPGC, Spain)

Borja Aguiar-González (ULPGC, Spain)