Effect of surfactants on N2O emissions
from biologically productive regions
Annette Kock, Jens Schafstall, Tim Fischer, Marcus Dengler,
Peter Brandt and Hermann W. Bange
Effects of N2O in the atmosphere
100 yr global warming
potential
298 x
CO2
Atmospheric lifetime
114 yr
(Intergovernmental Panel on Climate
Change (IPCC), 2007)
http://agage.eas.gatech.edu/data.htm
 Ozone depletion in the
stratosphere
Ravishankara et al., 2009:
„Nitrous Oxide (N2O): The dominant
ozone-depleting substance in the 21st
century.“
N2O Mole Fraction [ppb]
 N2O as greenhouse gas
320
310
300
1980
1990
2000
2010
Year
2
Sources of N2O to the atmosphere
Denman et al., 2007
N2O in the marine N cycle
Oxidation state
+V
NO3NO2-
oxic
suboxic/
anoxic
N 2O
±0
N2
NH2OH
-III
NH4+
Org. N
4
Global distribution of ΔpN2O
-20
0
10
20
30
40
50
60 150
(Suntharalingam & Sarmiento 2000)
N2O distribution off Mauritania
P347
Jan 07
N2O [nmol L-1]
0
40
50
35
100
30
P348
Feb 07
150
25
200
200
20
ATA3
Feb 08
Depth [m]
400
15
600
10
800
1000
21°W
5
20°W
19°W
18°W
17°W
N2O mixed layer budget in the Mauritanian upwelling
Atmosphere
Gas exchange
FN 2O  k w  ([ N 2O]surface  [ N 2O]eq )
Mixed layer
N2O production
Vertical advection
Diapycnal flux
FN 2O  K  
Subsurface
ocean
d [N 2 O]
dz
Continent
Pycnocline
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 insitu wind speeds.
0
ΔN2O [nmol L-1]
12
21°N
10
50
Depth [m]
20°N
8
100
19°N
6
18°N
150
4
17°N
200
2
16°N
18°W
17°W
16.8°W
16.6°W
16.5°W
16.4°W
24°W
1e-006
1e-005
0.0001
Kρ [m2 s-1]
0.001
16.3°W
22°W
0.01
20°W
18°W
16°W
0
Comparison of sea-to-air and diapycnal flux
Projection of all Stations to 18°N
Diapycnal flux
Sea-to-air flux
Water depth [m]
0
2000
4000
24°W
22°W
20°W
18°W
16°W
N2O mixed layer budget in the Mauritanian uwpelling
Atmosphere
Sea-to-air flux
-0.069 nmol m-2 s-1
Mixed Layer
25m
N2O production
Potential N2O
production rate
inFlux
thedifference
mixed layer
-1 -2
+0.048
~60 nmol
nmolLm
yrs-1-1
Vertical advection
+0.002 nmol m-2 s-1
Subsurface
ocean
Diapycnal flux
+0.019 nmol m-2 s-1
Continent
Pycnocline
N2O Production in the mixed layer?
Potential N2O production rate: ~60 nmol L-1 yr-1
PRO
• 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)
CONTRA
• 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
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”
x3
20
20
x3
x3
20
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 ).
Nightingale et al. 2000
Tsai & Liu 2003,
surfactant-influenced
Recalculation of sea-to-air flux using
gas exchange parameterization of
Tsai & Liu (2003).
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”)
N2O mixed layer budget with reduced gas exchange
Atmosphere
Mixed layer
Sea-to-air flux
(Parameterization Tsai & Liu 2003)
-0.020 nmol m-2 s-1
N2O production
Flux difference
-0.001 nmol m-2 s-1
Vertical advection
+0.002 nmol m-2 s-1
Subsurface
ocean
Diapycnal flux
+0.019 nmol m-2 s-1
Continent
Pycnocline
Diurnal stratification in the equatorial Atlantic
Intense solar irradiation:
→ Supersaturated N2O
concentrations in the
deeper mixed layer cut
off from the seasurface while nearsurface waters may
quickly equilibrate.
Depth [m]
→ Evolution of a diurnal
stratification within
the mixed layer
0
temperature diurnal cycle 0°N 10°W
5
10
0:00
5:00
10:00
15:00
Time
20:00
Glider measurements of temperature during
MSM 18-2 & MSM 18-3, equatorial Atlantic, MayJuly 2011
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
Summary & Conclusions
• Mixed layer budget off Mauritania reveals large discrepancy between seato-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”
diurnal stratification in the equatorial Atlantic
Ekman vertical velocities from QuikScat wind fields
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
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
Diurnal stratification in the equatorial Atlantic Ocean
Effect of surfactants on N2O gas exchange – laboratory results
Kerstin Richter, p.c.
N2O in the marine N cycle
Oxidation state
+V
NO3NO2-
oxic
suboxic/
anoxic
N2
NH2OH
-III
• Bacterial and archaeal
ammonium oxidation
• N2O production during
archaeal nitrification
(Santoro et al. 2011, Löscher
et al. 2012)
N 2O
±0
Nitrification
NH4+
Org. N
• 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)
27