Δ15N
In geochemistry, hydrology, palaeoecology, palaeoclimatology, and palaeoceanography, δ15N (pronounced "delta fifteen n") or delta-N-15 is a measure of the ratio of the two stable isotopes of nitrogen, 15N:14N. == Formulas == Two very similar expressions for δ15N are in wide use in hydrology. Both have the form 1000 ⋅ s − a a {\displaystyle 1000\cdot {\frac {s-a}{a}}} ‰ (‰ = permil or parts per thousand) where s and a are the relative abundances of 15N in respectively the sample and the atmosphere.