Estimates from Gas Tracers: Net Production and Gross Primary Production
"Explore the processes of net community production (NCP) and gross primary production (GPP) through gas tracers like O2 and Ar in oceanic environments. Learn about measuring techniques, sampling methods, and data analysis for understanding biological productivity in marine ecosystems."
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Net Community Production and Gross Primary Production Estimates from Gas Tracers Rachel H. R. Stanley rachel.stanley@wellesley.edu or rstanley@whoi.edu O2
NCP from O2/Ar Solubility in Seawater NEM = Photosyn. Resp. NCP= k [O2]sat (O2/Ar) Net community production (NCP) = photosynthesis minus community respiration Photosynthesis produces O2 and respiration consumes O2 Argon: an inert gas, similar solubility to O2, acts as abiotic analogue Ratio O2/Ar NCP
GPP from Triple Oxygen Isotopes 17 = measure of ratio of 16O, 17O, and 18O = ln( 17O/1000+1)-0.5179ln( 18O/1000+1)x106 GPP = gross primary production = total photosynthetic flux Atmosphere UV Radiation Mass Independent Fractionation more 17O then 18O GPP 17 of O2 = 0 per meg Photosynthetic O2 Mass Dependent Fractionation derived from H2O more 18O than 17O Calculate GPP 17 of O2 = 249 per meg Ocean
Discrete Sampling for Gross Primary Production Mixed layer GPP can be calculated from triple oxygen isotopes. If time-series, then can calculate below mixed layer GPP as well. Sample from CTD niskens: ~0.75L of water needed per sample PLAN: 300 total samples, surface at all stations, and short profiles on of stations. Zoe Sandwith (WHOI) will collect samples bonus NCP measured on same samples NCP/GPP, akin to the f-ratio Complications: steady-state assumption, physical transport, gas exchange
Continuous Sampling for NCP At-sea quadrupole mass spectrometer used to sample O2/Ar for continuous, real-time estimates of mixed layer NCP PLAN: set-up quadrupole mass spec in wetlab with feed from underway water, run for entire cruise. Zoe Sandwith (WHOI) will run mass spec. Temporal resolution : ~7 minutes several km spatial resolution, depending on ship speed Need some vertical profiles of O2/Ar from CTD to correct for entrainment/physical transport Complications: bubbles in underway line, room temperature and humidity, steady-state assumption, physical transport, gas exchange
Sample Data: Continuous NCP Compared to Export Fluxes From Estapa et al., 2017
Sample Data: Peaks in NCP may be linked to subsurface hotspots pressure (dbar) 0 50 100 0 pressure (dbar) 50 From Stanley et al., in press, DSR I 100 0 100 200 300 Distance (km)
Sample Data: Rates in Arctic Ocean Net CO2 drawdown Total photosynthesis NCP
