1 Changes in O 2 over Earth’s History

2 Annual Cycle in Atmospheric O 2 Barrow 71ºN Samoa 14ºS C. Grim 43ºS (1 ppm O 2 = 5 per meg)

3 Oxygen Isotopes 16 O = 99.74%, 17 O = 0.05%, 18 O = 0.21%  18 O (‰) = [( 18 O/ 16 O) sample /( 18 O/ 16 O) std –1]*1000  17 O (‰) = [( 17 O/ 16 O) sample /( 17 O/ 16 O) std –1]* Δ (per meg) = [  17 O – 0.518*  18 O]*1000 Standards: SMOW or AIR  18 O of O 2 in air = ‰ vs SMOW)

4 Molecular O 2 Cycle Important Processes - photosynthesis, respiration - air-water gas exchange, mixing, circulation Photosynthesis (O 2 is from the water molecule) CO 2 + 2H 2 O* +light  CH 2 O + *O 2 (2NADP + 2H 2 O + light  2NADPH 2 + O 2 ) Respiration H 2 O + *O 2 + CH 2 O  CO 2 + 2H 2 O* (2NADPH 2 + O 2  2NADP + 2H 2 O )

5 Isotope KIE during Photosynthesis (Guy et al., 1993) Fractionation effect during photosynthesis by S ynechocystis (Helman et al., 2005) Little or no fractionation during photosynthetic production of O 2 (<1‰)

6  18 O of Precipitation Globally Mean  18 O of precipitation ~ -4 ‰ (assuming mean temp = 15ºC)

7  18 O (‰) of Surface Ocean

8 Respiration KIEs for  18 O of O 2

9 Atmospheric Dole Effect  18 O of O2 in air is ‰ (vs SMOW) At steady-state, the  18 O of O 2 produced by photosynthesis has to equal the  18 O of O 2 consumed by respiration. ( 18 O/ 16 O) water *  photo = ( 18 O/ 16 O) O2air *  resp Since  photo = 1.000, then  resp = ( 18 O/ 16 O) water / ( 18 O/ 16 O) O2air For marine photosynthesis:  resp = / = For terrestrial photosynthesis:  resp = / = For 50/50 split:  resp = / =

10 Variations in  18 O-O 2 over glacial cycles (Petite et al., 1999)

11 Processes Affecting Concentration and  18 O of dissolved O 2 in Surface Layer g Advection, Inflow Air-Water O 2 Gas Exchange Turbulent Mixing, Entrainment, Upwelling, Eddies, etc. Organic Carbon Export (= P – R) Photosynthesis Respiration

12 Effects of Respiration, Photosynthesis and Gas Exchange on  18 O and O 2 O 2 Concentration  - Photosynthesis decreases  18 O - Respiration increases  18 O - Gas Exchange drives  18 O toward equilibrium (24.2 ‰)

13  18 O-O 2 in Amazon Lakes and Rivers Lakes= squares; Amazon R. = circles; Tributaries = triangles

14 R/P of Amazon Lakes and Rivers Lakes= squares; Amazon R. = circles; Tributaries = triangles

15 Diurnal Cycles in O 2 and  18 O in Lakes Tonle Sap provides 75% of fish harvested in Cambodia (D. Lockwood, unpub data) Tonle Sap Lake, Cambodia (vs AIR) Flooded Forest Pond, Canada To detect a diurnal O 2 and  18 O cycle typically high rates of photosynthesis, low gas exchange rates and shallow water body.

16 Seasonal Cycle in O 2 and  18 O in Mekong R.

17  18 O-O 2 in Oligotrophic Surface Ocean The overall range (variability) in  18 O (0.3 ‰) and O 2 saturation (1%) is much smaller than in freshwater systems because of lower photosynthesis rates and higher air-sea gas exchange rates.

18 Diurnal  18 O-O 2 Cycle in Coastal Ocean Sagami Bay, Japan (Sarma, 2005) (vs AIR)

19 Depth Trends in  18 O and O 2sat at ALOHA

20  18 O vs O 2sat Trend in Thermocline of the Pacific Ocean Red = Rayleigh predicted KIE of for respiration

21 Calculated KIE  for Respiration Assumes open system at steady-state.

22 Oxygen Cycle: Use of Triple Isotopes A mass independent reaction during ozone production in the stratosphere causes an anomalous isotopic composition of atmospheric O 2 (and CO 2 ). This O 2 isotopic anomaly is a very useful tracer to estimate photosynthesis (productivity) rates on land and in aquatic systems (ocean, lakes, rivers, etc.). Potentially, this method could make a significant impact on our understanding of the ocean’s biological pump

23 Anomalous  17 O and  18 O Composition of Atmospheric O 2 and CO 2 2O 2 + energy  O 3 + O( 1 D) O( 1 D) + CO 2  CO 2 + O Result: Small amount of O 2 (CO 2 ) in stratospheric has an anomalously low (high) 17 O/ 18 O. This O 2 mixes into troposphere. Lab ExperimentsField Measurements

24 Isotopic Notation for 17 O Anomaly Express the 17 O/ 16 O anomaly using 17 Δ notation 17 Δ = (  17 O – 0.518*  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 was chosen to equal the slope of  17 O vs  18 O observed during respiration. (Luz and Barkan, 2000)

25 Slope of  17 O vs  18 O during Respiration

26 17 Δ of O 2 in water equilibrated with Air (Luz and Barkan, 2003) (Sarma et al, 2006)

27 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 Puget Sound Plankton~ 200

28 Ocean Range of 17 Δ Values Purely Photosynthetic O per meg Purely Atmospheric O 2 16 per meg Half Photo + Half Atmos O per meg Measuring 17 Δ yields a direct estimate of the proportion of O 2 from air and photosynthesis.

29 Measured 17 Δ in the Surface Ocean Oligotrophic N. Pacific (Quay)20-40 Oligotrophic N. Atlantic (Luz) Southern Ocean (Hendricks)20-50 Equatorial Pacific (Hendricks, Juranek)50-90 Sagami Bay (Sarma) California Current System (Munro) Sea of Galilee (Luz and Barken) Δ (per meg)

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

31 Mixed Layer O 2 and 17 Δ*O 2 Budget dO 2 /dt = k am *Sol*pO 2atm – k am *Sol*pO 2ml + Photo – Resp - where k am = air-sea gas transfer rate and Sol=O 2 solubility d( 17 Δ*O 2 /dt) = k am *Sol*pO 2atm * 17 Δ air – k am *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 -ignore mixing and advection fluxes for now Substituting for k am *Sol*pO 2ml yields an expression for gross Photo: Photo = k am *pO 2atm *Sol*( 17 Δ air – 17 Δ diss )/( 17 Δ photo – 17 Δ diss )

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

33 Advantages of 17 Δ-PP over 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 days (i.e., m / 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

34 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 is significant and 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, mixing or entrainment can bias the 17 Δ in the mixed layer causing an overestimation of gross PP.

35 17 Δ Gross PP rates in the Surface Ocean Oligotrophic N. Pacific (Juranek) Oligotrophic N. Atlantic (Luz) Southern Ocean (Hendricks) Equatorial Pacific (Juranek) Sagami Bay (Sarma) California Current System (Munro) Sea of Galilee (Luz&Barkan)1600 – Global Ocean (at 1 gmC/m 2 /d)130 PgC/yr Gross PP (mg C m -2 d -1 )

36 Comparison of 17 O-PPg versus bottle 14 C-PP BATS and HOTS = 1.6±0.4; CalCOFI = 2.7±1.6

37 Estimating the ratio of net to gross PP Photo = k am *pO 2atm *Sol*( 17 Δ air – 17 Δ diss )/( 17 Δ photo – 17 Δ diss ) dO 2 /dt = k am *pO 2atm *Sol*(1 – pO 2 /pO 2atm ) + Photo – Resp -assuming net community productivity (NCP) = gross Photosynthesis – total Respiration and substituting for k am *pO 2atm *Sol yields: NCP/ Photo = (O 2 /O 2atm – 1)* ( 17 Δ photo – 17 Δ diss ) / ( 17 Δ air – 17 Δ diss ) the NCP/PPg ratio yields an estimate of the efficiency of organic carbon recycling in the ocean -if all photosynthetically produced organic carbon was respired to CO2 in the mixed layer then NCP/PPg = 0

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

39 Ratio of NCP/PPg in Surface Ocean -at HOT and BATS:0.13±0.03 -Southern Ocean: 0.17±0.13 -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 most accurate estimate of the efficiency of ocean’s biological pump.

40 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)

41 Future of 17 Δ and O 2 /Ar Ocean Research Improved ability to detect PP events. Applicable to obtain large scale synoptic surveys of ocean PP rates. Improve resolution of short spatial and temporal scale variability in marine PP in certain regions (e.g., coastal). Useful for validation of satellite PP rates.

42 Basin Scale Trends in 17 Δ-PPg in Pacific Ocean (using a container ship as sample collection platform)