Using different flavours of oxygen to measure biological production from ship-based and autonomous platforms

Transcription

1 Using different flavours of oxygen to measure biological production from ship-based and autonomous platforms Jan Kaiser University of East Anglia Centre for Ocean and Atmospheric Sciences School of Environmental Sciences Norwich United Kingdom

2 Flavours of oxygen molecular dioxygen: O 2 oxygen triple isotopologues: 16 O 2, 16 O 18 O, 16 O 17 O abiotic gas exchange analogue: O 2 and Ar "abiotic" deep-water mixing analogue: O 2 and N 2 O

3 Sampling and analysis continuous O 2 concentration measurements by optode continuous O 2 /Ar ratio measurements by MIMS or EIMS O 2 isotopologues by isotope-ratio mass spectrometry (IRMS) N 2 O concentrations by laser cavity absorption spectroscopy

4 Platforms

5 Production (P), respiration (R) [N = P R], gas exchange, mixing Ar pressure change temperature change salinity change bubble injection mixing (O 2 )/% +1.0ºC p > 0 T > 0 S > 0 O 2 atmosphere CO ºC S = 35 (Ar)/% Ar p < 0 T < 0 S < 0-1.0ºC O 2 autotrophs CO 2 surface ocean heterotrophs thermocline

6 In vitro vs. in situ net production Williams et al. Ann. Rev. Mar. Sci In vitro observations In situ observations 50 Net community production (mmol O 2 m 2 day 1 ) a Minimum value. b Maximum value.

7 Advantages & disadvantages + in principle, unambiguous measurement of N and P + no sampling biases (bottle effects, temperature, light) + ease of sampling (non-research vessels, no incubations) + integrates over O 2 residence time in the mixed layer (days to weeks) + scalable / high spatial coverage possible uncertainty of gas exchange coefficient (±20 %) currency is O 2, not C photosynthetic coefficient? P includes other non-carbon fixing, H 2 O-splitting reactions integrates vertically over mixed layer depth, but may include contributions from below piston velocity k/(m d 1 ) Liss & Merlivat (1986) Wanninkhof (1992) Nightingale et al. (2000) Sweeney et al. (2007) Huebert et al. (2004), O wind speed u(10 m)/(m s 1 )

8 Using Ar to correct for the physical O 2 component

9 Net community production N = P R O 2 mass balance: Biological O 2 flux: z mix c(o 2 ) t F bio (O 2 /Ar) = kc sat (O 2 ) (O 2 /Ar) N F bio (O 2 /Ar) = N k(o 2 )c sat (O 2 ) (O 2 ) +F inj χ(o 2 ) + F exch α(o 2 )χ(o 2 ) Sc(O 2 ) +K z c(o 2 ) z z mix = N + K z c sat (O 2 ) (O 2 /Ar) z z mix Kaiser et al. Geophys. Res. Lett. 2005

10 Production in the Bellingshausen Sea Latitude / (º S) F g (k w, (O 2 )) Mixture of open ocean and coastal sampling locations Effect of Ar correction: outgassing mmol m -2 d -1 mmol m -2 d -1 ingassing F bio (k w, (O 2 /Ar)) Longitude / (º W) Longitude / (º W) Latitude / (º S) Castro-Morales et al. Biogeosciences 2013

11 Castro-Morales et al. Biogeosciences 2013 Entrainment correction "removes" apparent net heterotrophic areas

12 Using N 2 O to correct for vertical fluxes

13 Using N 2 O as "abiotic" analogue to correct for vertical O 2 fluxes Upwelling brings up high N 2 O high CO 2 low O2 high nutrient Re-equilibration by gasexchange and net production. N 2 O has negligible surface sources and sinks: Steinhoff et al. Biogeosci. 2012; Kaiser Biogeosci. 2012

14 Correction of F bio (O 2 /Ar) for vertical mixing using N 2 O to give N(O 2 /Ar) Cassar et al. Gephys. Res. Lett. 2014

15 Gross production using oxygen triple isotopologues ( 16 O 2, 16 O 17 O, 16 O 18 O)

16 Oxygen isotope transfer from O 2 to CO 2 via O 3 O 2 + hν O + O O 2 + O( 3 P) + M O 3 + M tropopause O 3 + hν O 2 + O( 1 D) O( 1 D) + CO 2 CO 2 + O( 3 P) CO 2 O 2

17 17 O excess, ( 17 O), of photosynthetic O 2 ( 17 O) = δ( 17 O) λδ( 18 O) Choose λ = γ R = = 17 ε R / 18 ε R, where ε R is the respiratory kinetic isotope fractionation Reference: tropospheric Air-O 2 photosynthetic O 2 : max ( 17 O) = 249 ppm (???) (180 to 264 ppm)

18 Effect of photosynthesis, respiration and gas exchange on O 2 analogues Hendricks et al. Deep-Sea Res. I 2004

19 Calculating the ratio of gross O 2 gross production P to gross O 2 influx: g = P / (kc sat ) Luz & Barkan (2000): g = P (17 O) sat ( 17 O) kc sat max ( 17 O) ( 17 O) Prokopenko et al. (2011): Kaiser (2011):

20 Castro-Morales et al. Biogeosciences 2013; Hendricks et al. DSR I 2004 Gross O 2 production in the Bellingshausen Sea

21 Unrecognised systematic uncertainties due to phytoplankton composition Relative deviation from base case, max ( 17 O) = 185 ppm a" b" rel.% dev.% rel.% dev.% f" g" Kaiser & Abe Biogeosciences 2012

22 Nicholson et al. Global Biogeochem. Cycles 2014 Global measurements and modelling of oxygen triple isotopologues

23 Net community production from underwater ocean gliders

24 RRS James Clark Ross cruise JR255A "GENTOO", Jan Ship track coloured by sea surface temperature 0 Iceberg Antarctic Peninsula Glider tracks Sea ice edge 2-2

25 Biddle al. Geophys. Res. Lett Glider O 2 measurements

26 Depth-integrated net community production t = 16 d N(O 2 ) = (27±4) mmol m 2 d 1 Biddle al. Geophys. Res. Lett. 2015

27 Juranek et al. Geophys. Res. Lett In-situ measurements can help avoid ship sampling biases

28 Intake design on research ships Moon pool

29 Conclusions To understand variability on small to large scales, collaboration of all scientific disciplines is required. Novel sensors and autonomous observation platforms will be key elements of future ocean biogeochemistry. Biogeochemical data can supplement and sometimes substitute physical measurements. Acknowledgements: present and former members of the Kaiser Lab; collaborators and colleagues at UEA, NOC, BAS, PML, CSIC, AWI, Princeton, Duke, etc. Funding: NERC, Royal Society, EU FP 7, DFG