On the relationships of DINxs, nitrogen fixation and differential remineralization in the North Atlantic ocean

We use a combination of simple scalings and analytical expressions as well as an 10 idealized numerical model of basin-scale circulation, biogeochemical cycles and ecology, to elucidate and illustrate factors which regulate the distribution of tracer DINxs = NO − 3 − 16PO 4 , its temporal variability, and the distribution of diazotrophs in the North Atlantic. We infer that the observed subsurface maximum of DINxs in the subtropical thermocline and increase in temporal variability of DINxs with depth are both consistent with 15 an enhanced remineralization rate for organic phosphorus, relative to organic nitrogen. The observed confinement of diazotrophs largely to warm, tropical waters can be (partly) explained in terms of resource control, competitive in more oligotrophic, nitrogen limited waters, but themselves inviable due to phosphorus limitation in the most oligotrophic waters of the models subtropics. 20