New N inputs via biological N 2 -fixation play a critical role in supporting oceanic primary production and influencing global biogeochemical cycles. Numerous studies have documented significant N 2 -fixation rates in the North Atlantic, but relatively little is known of the pathways and fluxes of new N through planktonic food webs. Here, we report the natural abundance of 15 N in, and contribution of diazotroph N (N D ) inputs to, suspended particles and mesozooplankton collected along two transects in the subtropical North Atlantic Ocean (STNA). Samples were collected in April–May 2000 along the two main transects to evaluate spatial trends of 15 N within the Western Atlantic and across the basin. We found that N 2 -fixation is a key component in supporting both primary and secondary productions throughout the STNA. N D contribution was generally higher for suspended particles than for mesozooplankton, and we observed a high N D contribution to suspended particles over large spatial scales in the western and central STNA. Mesozooplankton N D incorporation suggests that diazotroph production supports oceanic food webs over longer timescales (e.g., weeks to months) than that of particle turnover (e.g., days). Larger mesozooplankton (1000–4000μm) generally incorporated more N D than smaller mesozooplankton (250–1000μm), and thus may exert a stronger influence on an N D movement within the water column. Spatial and vertical patterns of variation in mesozooplankton δ 15 N also suggest either broad geographical differences in an N D contribution to secondary production, or temporal variations in N D incorporation via mesozooplankton communities.