1. 1 Oxygen Cycle: Triple Isotopes An anomalous isotopic composition of atmospheric O 2 yields a very useful means to estimate photosynthesis rates. Potentially, this method could make a significant impact on our understanding of the ocean’s biological pump

2. 2 Anomalous  17 O and  18 O Composition of Stratospheric O 2 and CO 2 2O 2 + energy  O 3 + O( 1 D) O( 1 D) + CO 2  CO 2 + O

3. 3 Isotopic Notation Express the 17 O/ 16 O anomaly using 17 Δ notation 17 Δ = (  17 O – 0.516*  18 O)*1000 Units are per meg, 1 per meg = 1 ‰ / 1000 AIR is the standard and has a 17 Δ = 0 per meg Since air is depleted in 17 O/ 16 O, most other species will have positive 17 Δ values on this scale The coefficient of 0.516 was chosen to equal the slope of  17 O vs  18 O observed during respiration. (Luz and Barkan, 2000)

4. 4 Slope of  17 O vs  18 O during Respiration

5. 5 17 Δ of water equilibrated with Air (Luz and Barkan, 2003) (Sarma et al, 2006)

6. 6 17 Δ of Biologically Produced O 2 (Luz and Barkan, 2000)

7. 7 17 Δ of Photosynthetic O 2 Lab Experiments 17 Δ (per meg vs AIR) Marine Plankton 244±20; 252±5 Sea of Galilee Plankton159±10

8. 8 Ocean Range of 17 Δ Values Purely Photosynthetic O 2 249 per meg Purely Gas Exchange O 2 16 per meg Half Photo + Half Gas Exchange O 2 130 per meg Measuring 17 Δ yields a direct estimate of the proportion of O 2 from air and photosynthesis.

9. 9 Measured 17 Δ in the Surface Ocean Oligotrophic N. Pacific (Juranek)20-30 Oligotrophic N. Atlantic (Luz) 30-50 Southern Ocean (Bender)20-50 Equatorial Pacific (Bender, Juranek)50-90 Sagami Bay (Sarma)80-100 California Current System (Munro)25-100 Sea of Galilee (Luz and Barken)100-140 17 Δ (per meg)

10. 10 Near HawaiiNear Bermuda L. Juranek (U.Washington)B. Luz (Hebrew U.)

11. 11 Mixed Layer O 2 and 17 Δ*O 2 Budget dO 2 /dt = kam*Sol*pO 2atm – kam*Sol*pO 2ml + Photo – Resp d( 17 Δ*O 2 /dt) = kam*Sol*pO 2atm * 17 Δ air – kam*Sol*pO 2ml * 17 Δ diss + Photo* 17 Δ photo – Resp* 17 Δ diss - -assume respiration doesn’t change the 17 Δ of the dissolved O 2 Substituting for Resp yields an expression for gross Photo: Photo = kam*pO 2atm *Sol*( 17 Δ air – 17 Δ diss )/( 17 Δ photo – 17 Δ diss )

12. 12 If one estimates air-sea O 2 gas transfer rates (Kam) from wind speed measurements, then one can calculate the gross Primary Production rate from a single measurement ( 17 Δ of dissolved O 2 ) PPg = Kam*Sol*pO 2atm * ( 17  air – 17  diss ) ( 17  diss – 17  photo ) Estimating gross Photosynthesis rates from 17 Δ

13. 13 Advantages over the 14 C-PP Method a.In situ PP rates not in vitro PP rates -there are no bottle effects. b.Much simpler field method -no time consuming bottle incubations c.Integrates over the lifetime of O 2 in the mixed layer -typically 10-20 days (i.e., 50-100m / 5m/d) d.Measures gross PP rates -not an ambiguous rate between gross and net PP -recycling of 14 C-labeled OC in the bottle and use of non- 14 C labeled CO 2 during photosynthesis yield biases in PP rates that are difficult to quantify

14. 14 Disadvantages of the 17 Δ-PP Method a.Measures gross PP rate integrated over the mixed layer depth, not the photic layer depth. b.Uncertainty of method depends primarily on uncertainty of gas exchange rate (  30%) and 17 Δ measurement. c.Need to convert from O 2 production to organic carbon production -a 10-20% reduction for Mehler reaction and photorespiration -divide O 2 production by the Photosynthetic Quotient (PQ) of ~1.1 (NH 4 based PP) to ~1.4 (NO 3 based PP) d.In some situations, upwelling or mixing can bias the 17 Δ in the mixed layer usually causing an overestimation of gross PP.

15. 15 17 Δ gross PP rates in the Surface Ocean Oligotrophic N. Pacific (Juranek)800 - 1500 Oligotrophic N. Atlantic (Luz) 300 - 1000 Southern Ocean (Hendricks)600 - 3000 Equatorial Pacific (Juranek)1000 - 2000 Sagami Bay (Sarma)1500 - 3000 California Current System (Munro)100 - 3000 Sea of Galilee (Luz&Barkan)1600 – 16000 Global Ocean (at 1gmC/m 2 /d)130 PgC/yr Gross PP (mg C m -2 d -1 )

16. 16 Comparison of 17 O-PP versus 14 C-PP BATS and HOTS = 1.6±0.4; CalCOFI = 2.7±1.6

17. 17 Estimating the ratio of net to gross PP Photo = kam*pO 2atm *Sol*( 17 Δ air – 17 Δ diss )/( 17 Δ photo – 17 Δ diss ) dO 2 /dt = kam*pO 2atm *Sol*(1 – pO 2 /pO 2atm ) + Photo – Resp -assuming net community productivity (NCP) = gross Photosynthesis – total Respiration and substituting for kam*pO 2atm *Sol yields: NCP/ Photo = (O 2 /O 2atm – 1)* ( 17 Δ photo – 17 Δ diss ) / ( 17 Δ air – 17 Δ diss )

18. 18 Estimates of NCP/PPg from 17 Δ and O 2 /Ar Measurements

19. 19 Ratio of NCP/PPg in Surface Ocean -at HOT and BATS:0.13±0.03 -Southern Ocean: 0.17±.13 -Equatorial Pacific: 0.12±0.11 -California Current0.16±0.12 Coastal Ocean has NCP/PPg ratio that is similar to open oligotrophic ocean. (Unexpected). Could be our best estimate of export ratio and efficiency of biological pump.

20. 20 Estimates of Carbon Export (NCP) Rates -at HOT and BATS: 10±5 mmols C m -2 d -1 -in the Southern Ocean: 13±4 -in the Equatorial Pacific: 6.9±6.2 -California Current (CalCOFI): 14±10 -Globally, at 10 mmols m -2 d -1, yields 16 Pg C/yr (higher than previous estimates of 6-10 Pg C/yr)

21. 21 Future of 17 Δ + O 2 /Ar Ocean Research Improved ability to catch PP events. Obtain large scale synoptic surveys of ocean PP rates. Improve resolution of short spatial and temporal scale variability in marine PP. Validation of satellite PP rates.

22. 22 Repeated Survey of 17 Δ-PPg (using Container Ship) vs Satellite PP