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E ffect of surfactants on N 2 O emissions from biologically productive regions. Annette Kock, Jens Schafstall, Tim Fischer, Marcus Dengler, Peter Brandt and Hermann W. Bange. Effects of N 2 O in the atmosphere.  N 2 O as greenhouse gas  Ozone depletion in the stratosphere.

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slide1

Effect of surfactants on N2O emissions from biologically productive regions

Annette Kock, Jens Schafstall, Tim Fischer, Marcus Dengler, Peter Brandt and Hermann W. Bange

slide2

Effects of N2O in the atmosphere

 N2O as greenhouse gas  Ozone depletion in the stratosphere

Ravishankara et al., 2009:

„Nitrous Oxide (N2O): The dominant ozone-depleting substance in the 21st century.“

(Intergovernmental Panel on Climate Change (IPCC), 2007)

320

310

N2O Mole Fraction [ppb]

300

http://agage.eas.gatech.edu/data.htm

1980

1990

2000

2010

Year

slide4

N2O in the marine N cycle

Oxidation state

+V

NO3-

oxic

suboxic/

anoxic

NO2-

Denitrification

Nitrification

N2O

±0

N2

NH2OH

-III

NH4+

Org. N

slide5

Global distribution of ΔpN2O

-20

0

10

20

30

40

50

60

150

(Suntharalingam & Sarmiento 2000)

slide6

N2O distribution off Mauritania

N2O [nmol L-1]

P347

Jan 07

0

40

50

35

100

30

P348

Feb 07

150

25

200

200

20

400

ATA3

Feb 08

15

600

Depth [m]

10

800

5

1000

21°W

20°W

19°W

18°W

17°W

slide7

N2O mixed layer budget in the Mauritanian upwelling

Atmosphere

Gas exchange

Mixed layer

N2O production

Pycnocline

Continent

Vertical advection

Diapycnal flux

Subsurface ocean

slide8

N2O fluxes off Mauritania

  • Diapycnal flux calculated by microstructure measurements of small scale turbulence in combination with N2O-profiles from the water column.
  • Quantification of sea-to-air flux from surface N2O concentrations and in-situ wind speeds.

0

ΔN2O [nmol L-1]

12

50

21°N

10

20°N

100

8

Depth [m]

19°N

150

6

18°N

4

200

17°N

2

18°W

17°W

16.8°W

16.6°W

16.5°W

16.4°W

16.3°W

16°N

0

24°W

22°W

16°W

1e-006

1e-005

0.0001

0.001

0.01

20°W

18°W

Kρ [m2 s-1]

slide9

Comparison of sea-to-air and diapycnal flux

Projection of all Stations to 18°N

Diapycnal flux

Sea-to-air flux

0

Water depth [m]

2000

4000

24°W

22°W

20°W

18°W

16°W

slide10

N2O mixed layer budget in the Mauritanian uwpelling

Atmosphere

Sea-to-air flux

-0.069 nmol m-2 s-1

Potential N2O production rate

in the mixed layer

Flux difference

Mixed Layer

N2O production

25m

+0.048 nmol m-2 s-1

~60 nmol L-1 yr-1

Pycnocline

Continent

Vertical advection

Diapycnal flux

+0.019 nmol m-2 s-1

+0.002 nmol m-2 s-1

Subsurface ocean

slide11

N2O Production in the mixed layer?

Potential N2O production rate:

~60 nmol L-1 yr-1

PRO

CONTRA

  • Evidence for nitrification in the euphotic zone -> N2O production in the mixed layer (e.g. Yool et al. 2007, Clark et al. 2008).
  • Previous mixed layer budget calculations for N2O indicate strong near-surface production (e.g. Dore & Karl, 1996; Morell et al., 2001)
  • N2O production rate below the mixed layer: <3.3 nmol L-1 yr -1(Freing et al., 2012).
  • N2O yield increases with decreasing oxygen concentrations (Goreau et al., 1980; Löscher et al., 2012).
  • Measurements of nitrification rates in the Mauritanian upwelling: higher nitrification rates at greater depths than in the surface (Rees et al., 2011).
  • Surface N2O distribution linked to upwelling
slide12

Effect of surfactants on N2O gas exchange in laboratory studies

K. Richter, p.c., see poster „The Schmidt Number Dependency of Air-Sea

Gas Exchange with Varying Surfactant Coverage”

20

20

x3

x3

x3

20

slide13

Effect of surfactants on N2O gas exchange in the field?

  • Good conditions for occurrence of surfactants in upwelling areas (Wurl et al., 2011; Gasparovic et al., 1998 ).

Recalculation of sea-to-air flux using gas exchange parameterization of Tsai & Liu (2003).

Nightingale et al. 2000

Tsai & Liu 2003,

surfactant-influenced

Similar findings:

Calculations of net community production based on CO2/N2O O2/N2O (Steinhoff et al., 2012; see poster „Biological productivity in the Mauritanian upwelling estimated with a triple gas approach”)

slide14

N2O mixed layer budget with reduced gas exchange

Atmosphere

Sea-to-air flux

(Parameterization Tsai & Liu 2003)

-0.020 nmol m-2 s-1

Flux difference

Mixed layer

N2O production

-0.001 nmol m-2 s-1

Pycnocline

Continent

Vertical advection

Diapycnal flux

+0.019 nmol m-2 s-1

+0.002 nmol m-2 s-1

Subsurface ocean

slide15

temperature diurnal cycle 0°N 10°W

Diurnal stratification in the equatorial Atlantic

0

Intense solar irradiation:

→ Evolution of a diurnal stratification within the mixed layer

→ Supersaturated N2O concentrations in the deeper mixed layer cut off from the sea-surface while near-surface waters may quickly equilibrate.

5

Depth [m]

10

20:00

5:00

10:00

15:00

0:00

Time

Glider measurements of temperature during

MSM 18-2 & MSM 18-3, equatorial Atlantic, May-July 2011

slide16

Consequences?

Favorable conditions for surfactants:

Areas with high primary productivity, high solar irradiation, low to moderate wind speeds.

→ Most eastern boundary upwelling systems, equatorial upwelling, coastal areas.

data from Denman et al., 2007

slide17

Summary & Conclusions

  • Mixed layer budget off Mauritania reveals large discrepancy between sea-to-air flux and supply from subsurface layer.
  • Mixed layer source of N2O would require extremely high production rates to compensate discrepancy.
  • Reduced gas exchange in line with findings by Steinhoff et al., 2012 and K. Richter.
  • Potential for reduced N2O emissions from other upwelling areas, too.
  • Effect of surfactants on N2O emissions from other productive regions needs to be investigated.
  • Other possible causes for budget imbalance need to be considered!
  • Poster: „Physical processes controlling greenhouse gas emission in upwelling regions of the ocean: a N2O case study”
slide23

Future activities

  • R/V Meteor Cruise 91 (Peruvian upwelling), December 2012:
  • Evaluate potential processes that influence the mixed layer budget of N2O:
  • High resolution N2O profiles of mixed layer
  • Microstructure measurements
  • High resolution underway pCO2/pN2O
  • Determination of the role of the organic matter
  • and gel particles in the surface microlayer for
  • the air-sea gas exchange of trace gases.
  • Air-sea gas echange processes and atmos. fluxes
  • Determination of the upwelling velocity
slide24

Advances in measurement techniques

Better precision of underway measurements using OA-ICOS N2O analyzer allows flux calculation even at low ΔN2O

MSM 18-2,

equatorial Atlantic

May/June 2011

Arevalo, 2012

slide27

N2O in the marine N cycle

Oxidation state

+V

NO3-

  • Nitrification
  • Bacterial and archaeal ammonium oxidation
  • N2O production during archaeal nitrification (Santoro et al. 2011, Löscher et al. 2012)
  • N2O production increases with decreasing oxygen (Goreau et al. 1980, Löscher et al., 2012)
  • Light inhibition of nitrification (e.g. Guerrero & Jones, 1996) challenged by in-situ measurements of nitrification rates (e.g. Clark et al. 2008)

oxic

suboxic/

anoxic

NO2-

Denitrification

Nitrification

N2O

±0

N2

NH2OH

-III

NH4+

Org. N