Diazotroph connectomics in Gulf Stream eddies supports N2 fixation in the North Atlantic

Abstract

Abstract Mesoscale oceanic eddies contribute to the redistribution of resources for plankton to thrive, but due to their fluid trapping capacity, eddies can also isolate plankton communities, subjecting them to rapidly changing environmental conditions. Diazotrophs, with their ability to fix dinitrogen (N2), are key members of the plankton community, providing reactive nitrogen for other organisms, particularly in large nutrient-depleted regions such as subtropical gyres. However, there is still limited knowledge about how mesoscale structures characterized by specific local environmental conditions can affect the distribution and metabolic response of diazotrophs compared to the large-scale dynamics of an oceanic region. Here, we investigated diazotroph diversity and activity within the Gulf Stream and two associated eddies, a region with intense mesoscale activity known for its significant role in nutrient transport into the North Atlantic Subtropical Gyre. We show that eddy edges are hotspots for diazotroph activity with potential community connectivity between eddies. Using a long-term mesoscale eddy database, we quantified eddies that, having shed off the Gulf Stream, occur over the summer season and estimated that they provide ~ 21 µmol N m− 2 yr− 1 to the region. Our analysis warrants to include mesoscale eddies as hotspots for reactive nitrogen input in the oceanic nitrogen cycle.