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Changes in O 2 over Earth’s History. Annual Cycle in Atmospheric O 2. Barrow 71ºN Samoa 14ºS C. Grim 43ºS (1 ppm O 2 = 5 per meg). Oxygen Isotopes. 16 O = 99.74%, 17 O = 0.05%, 18 O = 0.21% d 18 O (‰) = [( 18 O/ 16 O) sample /( 18 O/ 16 O) std –1]*1000 - PowerPoint PPT Presentation
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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