In two contrasting regions of the ocean, the equatorial Pacific and the southern ocean, the &dgr;15N of core top sediments were strongly related to [NO-3] in surface waters. With distance from the equator in the equatorial Pacific, &dgr;15N increased from 7%0 to 16%0 as [NO -3] decreased from 8&mgr;M to <0.1 &mgr;M. Going from 60¿ to 30¿ S in the SE Indian Ocean, core top &dgr;15N increased from 5%0 to 11%0 as surface [NO-3] decreased from 25&mgr;M to ≤0.1 &mgr;M. These results are strong evidence that sedimentary &dgr;15N in these regions is recording the increasing isotopic enrichment of near-surface NO3 with its depletion by phytoplankton. In the case of the equatorial Pacific, &dgr;15N values for sinking particles collected at 150 m matched well the core top sediment values, demonstrating little diagenetic alteration of the near-surface generated isotopic signal. These equatorial Pacific data sets have variations with near-surface [NO-3] consistent with Rayleigh fractionation kinetics for a fractionation factor (&egr;&mgr;) of 2.5%0. This value is substantially lower than previously found for temperate or polar regions, perhaps as a result of differences in phytoplankton species assemblage or growth condition. In the southern ocean south of the polar front, comparison of &dgr;15N values for opal-rich sediments south and sinking particles indicates an apparent +5%0 diagenetic enrichment relative to the surface-generated signal that requires further investigation. This exception aside, our observations show that the surface-water relationship of increasing &dgr;15N with increasing NO-3 depletion is generally transmitted to and preserved in the sediments, an important requirement for further development and application of this important paleooceanographic tool.