O2 Cycle by yurtgc548

VIEWS: 3 PAGES: 42

									Changes in O2 over Earth’s History




                                     1
Annual Cycle in
Atmospheric O2

 Barrow 71ºN
 Samoa 14ºS
 C. Grim 43ºS


 (1 ppm O2 = 5 per meg)




                          2
                Oxygen Isotopes
16O   = 99.74%, 17O = 0.05%, 18O = 0.21%

d18O (‰) = [(18O/16O)sample/(18O/16O)std –1]*1000

d17O (‰) = [(17O/16O)sample/(17O/16O)std –1]*1000

17Δ (per   meg) = [d17O – 0.518*d18O]*1000

Standards: SMOW or AIR

(d18O of O2 in air = +23.5 ‰ vs SMOW)
                                                    3
            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 )                   4
         Isotope KIE during Photosynthesis
                                 Fractionation effect during
                                 photosynthesis by Synechocystis




(Guy et al., 1993)                   (Helman et al., 2005)

    Little or no fractionation during photosynthetic
    production of O2 (<1‰)                                   5
           d18O of Precipitation Globally




Mean d18O of precipitation ~ -4 ‰ (assuming mean temp = 15ºC)
                                                           6
d18O (‰) of Surface Ocean




                            7
Respiration KIEs
 for d18O of O2




                   8
               Atmospheric Dole Effect
• d18O of O2 in air is +23.5 ‰ (vs SMOW)
• At steady-state, the d18O of O2 produced by photosynthesis has
to equal the d18O 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                  9
Variations in d18O-O2 over glacial cycles




                           (Petite et al., 1999)   10
     Processes Affecting Concentration and d18O of
             dissolved O2 in Surface Layer
                    Air-Water O2 Gas Exchange

                                g


Advection,                          Photosynthesis
Inflow                              Respiration




             Organic Carbon         Turbulent Mixing,
             Export (= P – R)       Entrainment, Upwelling,   11
                                    Eddies, etc.
 Effects of Respiration, Photosynthesis and
       Gas Exchange on d18O and O2




                         O2 Concentration 
- Photosynthesis decreases d18O
- Respiration increases d18O
- Gas Exchange drives d18O toward equilibrium (24.2 ‰)   12
   d18O-O2 in Amazon Lakes and Rivers




Lakes= squares; Amazon R. = circles; Tributaries = triangles
                                                         13
      R/P of Amazon Lakes and Rivers




                                                          14
Lakes= squares; Amazon R. = circles; Tributaries = triangles
                                Diurnal Cycles in O2 and d18O in Lakes
                           Tonle Sap Lake, Cambodia                                          Flooded Forest Pond, Canada
                      0                                                         22
d 18O (‰) (vs AIR)




                      -2                                                        20
                      -4                                                        18
                      -6                                                        16




                                                                                      O/Ar
                      -8                                                        14
                     -10                                                        12
                     -12                                                        10
                     -14                                                         8
                      6:00 AM   12:00 PM   6:00 PM    12:00 AM   6:00 AM   12:00 PM

                                               d18O      O/Ar



                                                          Tonle Sap provides                  To detect a diurnal O2 and
                                                          75% of fish harvested
                                                          in Cambodia (D.                     d18O cycle typically high
                                                          Lockwood, unpub                     rates of photosynthesis,
                                                          data)                               low gas exchange rates and
                                                                                                                       15
                                                                                              shallow water body.
                     Seasonal Cycle in O2 and d18O in Mekong R.

                    4.00                                            240                             16                                             40000
                             O2sat
                                                                                                    14                                             35000
                    3.00                                            230




                                                                              Dissolved O 2 (uM)
                                                                               or % saturation
                              d18O (‰)                                                              12                                             30000




                                                                                                                                                           Discharge (m3/s)
                    2.00                                            220
d1818Ovs. air (‰)
  d O vs. AIR (‰)




                                                                                                    10                                             25000




                                                                                              R:P
                    1.00                                            210   [O2] (µM)                 8                                              20000

                                 [O2] (µM)                                                          6                                              15000
                    0.00                                            200
                                                                                                    4                                              10000
                                                                                        d18O
                    -1.00                                           190                             2                                              5000
                                                                                 =
                                                                             R:P O21
                              Rainy          Dry        Rainy                                       0                                              0
                    -2.00                                           180                       J- A- S- O- N- D- J- F- M- A- M- J- J- A- S- O- N-
                            J J A S O N D J F M A M J J A S O N D                       O2sat 05 05 05 05 05 05 06 06 06 06 06 06 06 06 06 06 06




                                                                                                                                               16
d18O-O2 in Oligotrophic Surface Ocean

                                                       ALOHA Surface Layer
                0.70

                0.60

                0.50
    del18O(‰)




                0.40

                0.30

                0.20

                0.10
                       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 (%)

                             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 d18O (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.                                                                                                  17
Diurnal d18O-O2 Cycle in Coastal Ocean


 (vs AIR)




      Sagami Bay, Japan (Sarma, 2005)    18
                  Depth Trends in d18O and O2sat at ALOHA

                      d 18O vs AIR (per mil)                                 Fraction O2sat
               -1.0   0.0     1.0    2.0   3.0   4.0   5.0                 0.760   0.840     0.920        1.000
              0                                                            0


             50                                                           50


            100                                                          100
Depth (m)




                                                             Depth (m)
            150                                                          150


            200                                                          200


            250                                                          250

                            Feb 02                                                 Feb 02
            300             Oct 02                                       300       Oct 02
                            Feb 03                                                 Feb 03
            350                                                          350

                                                                                                             19
d18O vs O2sat Trend in Thermocline of the
               Pacific Ocean
                                          Pacific Ocean (1972-78)
                          20
                          18
   del18O (o/oo vs AIR)




                          16
                          14
                          12
                          10
                           8
                           6
                           4
                           2
                           0
                            0.00   0.20      0.40     0.60     0.80   1.00   1.20
                                                    O2/O2sat


Red = Rayleigh predicted KIE of 0.9945 for respiration                          20
                       Calculated KIEfor Respiration

                       -5
                                                             Pacific Ocean
                       -8
KIE respiration (‰)




                      -11

                      -14

                      -17

                      -20

                      -23
                            0   1000   2000     3000      4000    5000       6000
                                              Depth (m)

                      Assumes open system at steady-state.                          21
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
                                                   22
    Anomalous d17O and d18O Composition of
          Atmospheric O2 and CO2
     Lab Experiments                     Field Measurements




2O2 + energy  O3 + O(1D)               O(1D) + CO2  CO2 + O
Result: Small amount of O2 (CO2) in stratospheric has an
                                                              23
anomalously low (high) 17O/18O. This O2 mixes into troposphere.
     Isotopic Notation for 17O Anomaly
• Express the 17O/16O anomaly using 17Δ notation
      17Δ =   (d17O – 0.518*d18O)*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 d17O vs d18O observed during respiration.
                          (Luz and Barkan, 2000)
                                                     24
Slope of d17O vs d18O during Respiration




                                           25
       17Δ   of O2 in water equilibrated with Air




(Luz and Barkan, 2003)           (Sarma et al, 2006)
                                                       26
     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




                                                27
            Ocean Range of 17Δ Values


         Purely Photosynthetic O2           249 per meg




Half Photo + Half Atmos O2                 130 per meg




                                           16 per meg
        Purely Atmospheric O2

     Measuring 17Δ yields a direct estimate of the
                                                          28
     proportion of O2 from air and photosynthesis.
      Measured 17Δ in the Surface Ocean
                                          17Δ (per   meg)
•   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



                                                        29
                           Near Hawaii                                                                  Near Bermuda
                                 17 (per meg)                                                                17 (per meg)




                                             0
                                                    0
                                                           0
                                                                  0
                                                                         0




                                                                                                                         0
                                                                                                                         0
                                                                                                                         0
                                                                                                                         0
                                                                                                                         0
                                                                                                   20
                                                                                                        40
                                                                                                             60
                                                                                                                  80
                                                                                                                       10
                                                                                                                       12
                                                                                                                       14
                                                                                                                       16
                                                                                                                       18
                      20
                           40
                                60
                                     80
                                          10
                                                 12
                                                        14
                                                               16
                                                                      18




                                                                                               0
                  0




              0                                                                            0

             50                                                                           50

            100                                                                          100




                                                                             depth (m)
depth (m)




            150                                                                          150

            200                                                                          200
                                                 21-Feb-02                                                               13-Mar-00
            250                                                                          250                             10-Jul-00
                                                 25-Feb-03
                                                 13-Jun-01                                                               16-Oct-00
            300                                                                          300
                                                 6-Oct-02                                                                 25-Jan-01
            350                                                                          350

                  L. Juranek (U.Washington)                                                         B. Luz (Hebrew U.)          30
        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)

                                                                      31
Estimating gross Photosynthesis rates from 17Δ

  • 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 * (17air – 17diss)
                     (17diss – 17photo)




                                                     32
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     33
       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.
                                                               34
    17Δ   Gross PP rates in the Surface Ocean
                                   Gross PP (mg C m-2 d-1)

•   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

                                                       35
Comparison of 17O-PPg versus bottle 14C-PP




    BATS and HOTS = 1.6±0.4; CalCOFI = 2.7±1.6   36
       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      37
respired to CO2 in the mixed layer then NCP/PPg = 0
Estimates of NCP/PPg from 17Δ and O2/Ar
              Measurements




                                      38
   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.
                                                    39
  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)


                                                    40
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.

                                                     41
  Basin Scale Trends in
17Δ-PPg in Pacific Ocean

 (using a container ship as
sample collection platform)



                                                                                                                 5000                                                    August 2005
                   100
                                                                                                                                                                           C-based sat PP




                                                                                 GPP and sat. PP (mg C m d )
                                                                                                                 4500




                                                                                                         -2 -1
                    90         Aug 2004                                                                                                                                    VGPM sat PP
                    80         Feb 2005                                                                          4000                                                      in situ GPP
                               Aug 2005                                                                                                                                    Chl*10^4
                    70                                                                                           3500
  17O (per meg)




                    60                                                                                           3000
                    50                                                                                           2500
                    40                                                                                           2000
                    30                                                                                           1500
                    20
                                                                                                                 1000
                    10
                                                                                                                  500
                                                                                17




                     0
                         -40        -30   -20   -10          0   10   20   30
                                                                                                                    0
                                                                                                                        -45   -35   -25   -15        -5       5     15     25          35
                                                  Latitude
                                                                                                                                          Latitude along transect               42

								
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