delta_N_C

 PI:              Mark Altabet and Roger Francois
 of:              University of Massachusetts, Dartmouth (Altabet)
                         Woods Hole Oceanographic Institution (Francois)
 dataset:         Natural nitrogen and carbon stable isotopic composition
 project/cruise:  AESOPS/NBP-97-1 - Ross Sea Process Cruise 2
 ship:            Nathaniel B. Palmer

 Methods for nitrate isotopic reported in:
     Sigman, D. M., M. A. Altabet, R. Michener, D. C. McCorkle, B. Fry and R. M.
     Holmes. (1997). Natural Abundance-level measurement of the nitrogen isotopic
     composition of oceanic nitrate: an adaptation of the ammonia diffusion
     method. Mar. Chem. 57, 227-242.

 Methods for POM isotopic composition in:
     Altabet, M. A., and R. Francois, 1994.  Sedimentary N isotopic ratio as a
     recorder for surface ocean nitrate utilization.  Global Biogeochemical
     Cycles., 8, 103-116.

 Parameter    Description                                        Units

 event        event number, from event log
 sta          station number, from event log
 cast         cast number, from event log
 cast_type    CTD = Ctd rosette
              TM = Trace Metal rosette
 bot          rosette bottle number
 depth_n      nominal or target sample depth                     meters
 dN15_NO3     delta 15N of dissolved nitrate relative            per mil (ppt)
                  to atmospheric N2.
 dN15_POM     delta 15N of particulate organic matter relative   per mil (ppt)
                  to atmospheric N2
 dC13_POM     delta 13C of particulate organic matter relative   per mil (ppt)
                  to the PDB standard