Skip to Main Content
Table 1.

Measurements, estimates, and assumptions and caveats from the Northeast Pacific EXPORTS cruise

MeasurementEstimatesAssumptions and Caveats
Chlorophyll a (chl aPhytoplankton biomass Changes in C: chl a due to cell physiology and photoacclimation 
13C-DIC uptake rate (13C-ρDIC), 6 hra Gross primary production (GPP) Could be some 13C respiration; conversion to daily rates by normalizing to PAR 
13C-DIC uptake rate (13C-ρDIC), 24 hra Net primary production (NPP) Assumes heterotrophic respiration of 13C is negligible 
15N-NO3- uptake rate (15N-ρNO3-), 24 hra New production Assumes steady state system; assumes negligible nitrification; conversion using Redfield ratio 
15N-NH4+ uptake rate (15N-ρNH4+), 24 hra Regenerated production Low NH4+ concentrations in euphotic zone (violates tracer method requirement); conversion using Redfield ratio; potential for isotope dilution of NH4+ pool due to remineralization 
13C-ρDIC – 15N-ρNO3-based new production Regenerated production Assumes coupled C and N uptake and Redfield stoichiometry 
(15NρNO3*6.6)13CρDIC, 6 hra f-ratio Assumes coupled C and N uptake and Redfield stoichiometry 
13C-ρDIC/chlorophyll a, 15N-ρNO3/chlorophyll a Carbon and nitrate assimilation rate or biomass-specific uptake rates Assumes chl a is an accurate proxy for phytoplankton biomass 
MeasurementEstimatesAssumptions and Caveats
Chlorophyll a (chl aPhytoplankton biomass Changes in C: chl a due to cell physiology and photoacclimation 
13C-DIC uptake rate (13C-ρDIC), 6 hra Gross primary production (GPP) Could be some 13C respiration; conversion to daily rates by normalizing to PAR 
13C-DIC uptake rate (13C-ρDIC), 24 hra Net primary production (NPP) Assumes heterotrophic respiration of 13C is negligible 
15N-NO3- uptake rate (15N-ρNO3-), 24 hra New production Assumes steady state system; assumes negligible nitrification; conversion using Redfield ratio 
15N-NH4+ uptake rate (15N-ρNH4+), 24 hra Regenerated production Low NH4+ concentrations in euphotic zone (violates tracer method requirement); conversion using Redfield ratio; potential for isotope dilution of NH4+ pool due to remineralization 
13C-ρDIC – 15N-ρNO3-based new production Regenerated production Assumes coupled C and N uptake and Redfield stoichiometry 
(15NρNO3*6.6)13CρDIC, 6 hra f-ratio Assumes coupled C and N uptake and Redfield stoichiometry 
13C-ρDIC/chlorophyll a, 15N-ρNO3/chlorophyll a Carbon and nitrate assimilation rate or biomass-specific uptake rates Assumes chl a is an accurate proxy for phytoplankton biomass 

aIncubation time used.

Close Modal

or Create an Account

Close Modal
Close Modal