1

Changes in O2 over Earth’s History

2

Annual Cycle in Atmospheric O2

Barrow 71ºN

Samoa 14ºS

C. Grim 43ºS

(1 ppm O2 = 5 per meg)

3

Oxygen Isotopes

16O = 99.74%, 17O = 0.05%, 18O = 0.21%

18O (‰) = [(18O/16O)sample/(18O/16O)std –1]*1000

17O (‰) = [(17O/16O)sample/(17O/16O)std –1]*1000

17Δ (per meg) = [17O – 0.518*18O]*1000

Standards: SMOW or AIR

18O of O2 in air = +23.5 ‰ vs SMOW)

4

Molecular O2 Cycle

Important Processes

- photosynthesis, respiration

- air-water gas exchange, mixing, circulation

Photosynthesis (O2 is from the water molecule)

CO2 + 2H2O* +light CH2O + *O2

(2NADP + 2H2O + light 2NADPH2 + O2)

Respiration

H2O + *O2 + CH2O CO2 + 2H2O*

(2NADPH2 + O2 2NADP + 2H2O )

5

Isotope KIE during Photosynthesis

(Guy et al., 1993)

Fractionation effect during photosynthesis by Synechocystis

(Helman et al., 2005)

Little or no fractionation during photosynthetic production of O2 (<1‰)

6

18O of Precipitation Globally

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

7

18O (‰) of Surface Ocean

8

Respiration KIEs for 18O of O2

9

Atmospheric Dole Effect

• 18O of O2 in air is +23.5 ‰ (vs SMOW)

• At steady-state, the 18O of O2 produced by photosynthesis has to equal the 18O of O2 consumed by respiration.

(18O/16O)water* photo = (18O/16O)O2air* resp

• Since photo = 1.000, then

resp = (18O/16O)water / (18O/16O)O2air

For marine photosynthesis: resp = 1.000 / 1.0235 = 0.9770

For terrestrial photosynthesis: resp = 1.008 / 1.0235 = 0.9849

For 50/50 split: resp = 1.004 / 1.0235 = 0.9809

10

Variations in 18O-O2 over glacial cycles

(Petite et al., 1999)

11

Processes Affecting Concentration and 18O of dissolved O2 in Surface Layer

g

Advection, Inflow

Air-Water O2 Gas Exchange

Turbulent Mixing, Entrainment, Upwelling, Eddies, etc.

Organic Carbon Export (= P – R)

Photosynthesis

Respiration

12

Effects of Respiration, Photosynthesis and Gas Exchange on 18O and O2

O2 Concentration

- Photosynthesis decreases 18O- Respiration increases 18O- Gas Exchange drives 18O toward equilibrium (24.2 ‰)

13

18O-O2 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 O2 and 18O in Lakes

-14

-12

-10

-8

-6

-4

-2

0

6:00 AM 12:00 PM 6:00 PM 12:00 AM 6:00 AM 12:00 PM

18

O (‰

)

8

10

12

14

16

18

20

22

O/A

rd18O O/Ar

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 O2 and 18O cycle typically high rates of photosynthesis, low gas exchange rates and shallow water body.

16

Seasonal Cycle in O2 and 18O in Mekong R.

0

2

4

6

8

10

12

14

16

J-05

A-05

S-05

O-05

N-05

D-05

J-06

F-06

M-06

A-06

M-06

J-06

J-06

A-06

S-06

O-06

N-06

R:P

0

5000

10000

15000

20000

25000

30000

35000

40000

Dis

char

ge

(m3/s

)

R:P = 10

2

4

6

8

10

12

14

16

J-05

A-05

S-05

O-05

N-05

D-05

J-06

F-06

M-06

A-06

M-06

J-06

J-06

A-06

S-06

O-06

N-06

R:P

0

5000

10000

15000

20000

25000

30000

35000

40000

Dis

char

ge

(m3/s

)

R:P = 10

2

4

6

8

10

12

14

16

J-05

A-05

S-05

O-05

N-05

D-05

J-06

F-06

M-06

A-06

M-06

J-06

J-06

A-06

S-06

O-06

N-06

R:P

0

5000

10000

15000

20000

25000

30000

35000

40000

Dis

char

ge

(m3/s

)

R:P = 1

-2.00

-1.00

0.00

1.00

2.00

3.00

4.00

J J A S O N D J F M A M J J A S O N D

18O

vs.

AIR

(‰

)

180

190

200

210

220

230

240

Dis

solv

ed O

2 (

uM

)o

r %

sat

ura

tio

n

d18O

O2

O2sat

O2sat

[O2] (µM)

18O (‰)

18O

vs.

air

(‰)

RainyRainy

[O2] (µM)

Dry-2.00

-1.00

0.00

1.00

2.00

3.00

4.00

J J A S O N D J F M A M J J A S O N D

18O

vs.

AIR

(‰

)

180

190

200

210

220

230

240

Dis

solv

ed O

2 (

uM

)o

r %

sat

ura

tio

n

d18O

O2

O2sat

O2sat

[O2] (µM)

18O (‰)

18O

vs.

air

(‰)

RainyRainy

[O2] (µM)

-2.00

-1.00

0.00

1.00

2.00

3.00

4.00

J J A S O N D J F M A M J J A S O N D

18O

vs.

AIR

(‰

)

180

190

200

210

220

230

240

Dis

solv

ed O

2 (

uM

)o

r %

sat

ura

tio

n

d18O

O2

O2sat

O2sat

[O2] (µM)

18O (‰)

18O

vs.

air

(‰)

RainyRainy

[O2] (µM)

Dry-2.00

-1.00

0.00

1.00

2.00

3.00

4.00

J J A S O N D J F M A M J J A S O N D

18O

vs.

AIR

(‰

)

180

190

200

210

220

230

240

Dis

solv

ed O

2 (

uM

)o

r %

sat

ura

tio

n

d18O

O2

O2sat

O2sat

[O2] (µM)

18O (‰)

18O

vs.

air

(‰)

RainyRainy

[O2] (µM)

Dry-2.00

-1.00

0.00

1.00

2.00

3.00

4.00

J J A S O N D J F M A M J J A S O N D

18O

vs.

AIR

(‰

)

180

190

200

210

220

230

240

Dis

solv

ed O

2 (

uM

)o

r %

sat

ura

tio

n

d18O

O2

O2sat

O2sat

[O2] (µM)

18O (‰)

18O

vs.

air

(‰)

RainyRainy

[O2] (µM)

-2.00

-1.00

0.00

1.00

2.00

3.00

4.00

J J A S O N D J F M A M J J A S O N D

18O

vs.

AIR

(‰

)

180

190

200

210

220

230

240

Dis

solv

ed O

2 (

uM

)o

r %

sat

ura

tio

n

d18O

O2

O2sat

O2sat

[O2] (µM)

18O (‰)

18O

vs.

air

(‰)

RainyRainy

[O2] (µM)

Dry

17

18O-O2 in Oligotrophic Surface Ocean

ALOHA Surface Layer

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

Biological O2 Sat'n (%)

del

18O

(‰)

Mar 06 May 06 Jun 06 Jul 06 Aug 06 Oct 06 Nov 06 'Feb 07

'Mar 07 'May 07 'Jun 07 'Dec 06 Equil

The overall range (variability) in 18O (0.3 ‰) and O2 saturation (1%) is much smaller than in freshwater systems because of lower photosynthesis rates and higher air-sea gas exchange rates.

18

Diurnal 18O-O2 Cycle in Coastal Ocean

Sagami Bay, Japan (Sarma, 2005)

(vs AIR)

19

Depth Trends in 18O and O2sat at ALOHA

0

50

100

150

200

250

300

350

-1.0 0.0 1.0 2.0 3.0 4.0 5.0

18O vs AIR (per mil)

Dep

th (m

)

Feb 02

Oct 02

Feb 03

0

50

100

150

200

250

300

350

0.760 0.840 0.920 1.000

Fraction O2sat

Dep

th (m

)Feb 02

Oct 02

Feb 03

20

18O vs O2sat Trend in Thermocline of the Pacific Ocean

Pacific Ocean (1972-78)

02468

101214161820

0.00 0.20 0.40 0.60 0.80 1.00 1.20

O2/O2sat

del1

8O (o

/oo

vs A

IR)

Red = Rayleigh predicted KIE of 0.9945 for respiration

21

Calculated KIEfor Respiration

Pacific Ocean

-23

-20

-17

-14

-11

-8

-5

0 1000 2000 3000 4000 5000 6000Depth (m)

KIE

res

pira

tion

(‰)

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 O2 (and CO2).

• This O2 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 17O and 18O Composition of Atmospheric O2 and CO2

2O2 + energy O3 + O(1D) O(1D) + CO2 CO2 + O

Result: Small amount of O2 (CO2) in stratospheric has an anomalously low (high) 17O/18O. This O2 mixes into troposphere.

Lab Experiments Field Measurements

24

Isotopic Notation for 17O Anomaly

• Express the 17O/16O anomaly using 17Δ notation

17Δ = (17O – 0.518*18O)*1000

• Units are per meg, 1 per meg = 1 ‰ / 1000

• AIR is the standard and has a 17Δ = 0 per meg

• Since air is depleted in 17O/16O, most other species will have positive 17Δ values on this scale

• The coefficient of 0.518 was chosen to equal the slope of 17O vs 18O observed during respiration.

(Luz and Barkan, 2000)

25

Slope of 17O vs 18O during Respiration

26

17Δ of O2 in water equilibrated with Air

(Luz and Barkan, 2003) (Sarma et al, 2006)

27

17Δ of Photosynthetic O2

Lab Experiments 17Δ (per meg vs AIR)

Marine Plankton 244±20; 252±5

Sea of Galilee Plankton 159±10

Puget Sound Plankton ~ 200

28

Ocean Range of 17Δ Values

Purely Photosynthetic O2 249 per meg

Purely Atmospheric O216 per meg

Half Photo + Half Atmos O2 130 per meg

Measuring 17Δ yields a direct estimate of the proportion of O2 from air and photosynthesis.

29

Measured 17Δ in the Surface Ocean

• Oligotrophic N. Pacific (Quay) 20-40• Oligotrophic N. Atlantic (Luz) 30-50• Southern Ocean (Hendricks) 20-50• Equatorial Pacific (Hendricks, Juranek) 50-90 • Sagami Bay (Sarma) 80-100 • California Current System (Munro) 25-100• Sea of Galilee (Luz and Barken) 100-140

17Δ (per meg)

30

0

50

100

150

200

250

300

350

17 (per meg)

dept

h (m

)

21-Feb-0225-Feb-0313-Jun-016-Oct-02

0

50

100

150

200

250

300

350

17 (per meg)

dept

h (m

)13-Mar-00

10-Jul-00

16-Oct-00

25-Jan-01

Near Hawaii Near Bermuda

L. Juranek (U.Washington) B. Luz (Hebrew U.)

31

Mixed Layer O2 and 17Δ*O2 Budget

• dO2/dt = kam*Sol*pO2atm – kam*Sol*pO2ml + Photo – Resp

  -where kam = air-sea gas transfer rate and Sol=O2 solubility

• d(17Δ*O2/dt) = kam*Sol*pO2atm*17Δair – kam*Sol*pO2ml*17Δdiss +

Photo*17Δphoto – Resp*17Δdiss

         -assume respiration doesn’t change the 17Δ of the dissolved O2

-ignore mixing and advection fluxes for now

• Substituting for kam*Sol*pO2ml yields an expression for gross Photo:

Photo = kam*pO2atm*Sol*(17Δair – 17Δdiss)/(17Δphoto – 17Δdiss)

32

• If one estimates air-sea O2 gas transfer rates (kam) from wind speed measurements, then one can calculate the gross Primary Production (PPg) rate from a single measurement (17Δ of dissolved O2)

PPg = kam* O2sat * (17air – 17diss)

(17diss – 17photo)

Estimating gross Photosynthesis rates from 17Δ

33

Advantages of 17Δ-PP over 14C-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 O2 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 14C-labeled OC in the bottle and use of non-14C labeled CO2 during photosynthesis yield

biases in PP rates that are difficult to quantify

 

34

Disadvantages of the 17Δ-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 17Δ measurement.

c. Need to convert from O2 production to organic carbon

production

         -a 10-20% reduction for Mehler reaction and photorespiration

   -divide O2 production by the Photosynthetic Quotient (PQ) of

~1.1 (NH4 based PP) to ~1.4 (NO3 based PP)

d. In some situations, upwelling, mixing or entrainment can bias the 17Δ in the mixed layer causing an overestimation of gross PP.

35

17Δ 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 1 gmC/m2/d) 130 PgC/yr

Gross PP (mg C m-2 d-1)

36

Comparison of 17O-PPg versus bottle 14C-PP

BATS and HOTS = 1.6±0.4; CalCOFI = 2.7±1.6

37

Estimating the ratio of net to gross PP

• Photo = kam*pO2atm*Sol*(17Δair – 17Δdiss)/(17Δphoto – 17Δdiss)

 

• dO2/dt = kam*pO2atm*Sol*(1 – pO2/pO2atm) + Photo – Resp

-assuming net community productivity (NCP) = gross Photosynthesis – total Respiration and substituting for kam*pO2atm*Sol yields:

NCP/ Photo = (O2/O2atm – 1)* (17Δphoto – 17Δdiss) / (17Δair – 17Δdiss)

• 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 17Δ and O2/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 Current 0.16±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 17Δ and O2/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 17Δ-PPg in Pacific Ocean (using a container ship as

sample collection platform)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

-45 -35 -25 -15 -5 5 15 25 35Latitude along transect

17

GPP

and

sat. P

P (m

g C

m-2

d-1

) C-based sat PPVGPM sat PP

in situ GPPChl*10^4

August 2005

0

10

20

30

40

50

60

70

80

90

100

-40 -30 -20 -10 0 10 20 30

Latitude

17

O (p

er m

eg)

Aug 2004

Feb 2005

Aug 2005