Frozen samples were dried at 60 °C in the land-based laboratory. The
isotope, particulate organic carbon (POC) and particulate organic nitrogen
(PON) samples were ground to fine powder and weighed in tin capsules.
Measurements were made by means of Flash combustion in a CE
Instruments Flash EA 1112 at 1020 °C in a Finnigan Delta S isotope ratio
mass-spectrometer via a Conflow III open split interface. Calibration for
the total POC and PON determinationswas done dailywith anacetanilide
standard. The stable nitrogen and carbon isotope ratios measured for
each sample were corrected with the values obtained from standards
with defined nitrogen and carbon element and isotopic compositions (International
Atomic Energy Agency IAEA: IAEA-N1, IAEA-N2, IAEA-N3,
NBS 22, IAEA-C3 and IAEA-CH-6) by mass balance. Values are reported