* Corresponding author. Fax: 001 508 999 8197; e-mail: maltabet@umassd.edu.  Current address: Marine Science Institute, University of California, Santa Barbara, CA 93106, U.S.A. Deep-Sea Research I 46 (1999) 655— 679 The nitrogen isotope biogeochemistry of sinking particles from the margin of the Eastern North Pacific Mark A. Altabet *, Cynthia Pilskaln, Robert Thunell, Carol Pride, Daniel Sigman, Francisco Chavez, Roger Francois Department of Chemistry and Biochemistry and Center for Marine Science and Technology, University of Massachusetts, Dartmouth, N. Dartmouth, MA 02747, USA Department of Oceanography, University of Maine, 5741 Libby Hall, Orono, ME 04469, USA Department of Geological Sciences, University of South Carolina, Columbia, SC 29208, USA Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA Monterey Bay Aquarium Research Institute, P.O. Box 628, Moss Landing, CA 95039-0628, USA Received 3 October 1997; received in revised form 13 July 1998; accepted 11 August 1998 Abstract The nitrogen isotopic composition of time-series sediment trap samples, dissolved NO  , and surficial sediments was determined in three regions along the margin of the eastern North Pacific: Monterey Bay, San Pedro Basin, and the Gulf of California (Carmen and Guaymas Basins). Complex physical regimes are present in all three areas, and each is influenced seasonally by coastal upwelling. Nevertheless, sediment trap material evidently records the isotopic composition of new nitrogen sources, since average N is generally indistinguishable from N values for subsurface NO  . Surficial sediments are also very similar to the average N value of the sediment traps, being within 1. This difference in N between trap material and sediment is much less than the previously observed 4 difference for the deep sea. Better organic matter preservation at our margin sites is a likely explanation, which may be due to either low bottom O  concentrations or higher organic matter input to the sediments. All sites have N for sub-euphotic zone NO  (8—10) substantially elevated from the oceanic average (4.5—5). This isotopic enrichment is a result of denitrification in suboxic subsurface waters (Gulf of California) or northward transport of denitrification influenced water (Mon- terey Bay and San Pedro Basin). Our results therefore suggest that downcore N data, depending on site location, would record the intensity of denitrification and the transport of its isotopic signature along the California margin. Temporal variations in N for the sediment traps do appear to respond to upwelling or convective injections of NO  to surface waters as 0967-0637/99/$ — see front matter  1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 7 - 0 6 3 7 ( 9 8 ) 0 0 0 8 4 - 3