Effect 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 100 yr global warming potential 298 x CO 2 Atmospheric lifetime114 yr (Intergovernmental Panel on Climate Change (IPCC), 2007) 2 Ravishankara et al., 2009: „Nitrous Oxide (N 2 O): The dominant ozone-depleting substance in the 21 st century.“ N 2 O Mole Fraction [ppb] Year

Sources of N 2 O to the atmosphere Denman et al., 2007

N 2 O in the marine N cycle 4 suboxic/ anoxic NH 4 + NO 2 - NO 3 - NH 2 OH N2N2 -III +V ±0 Denitrification Org. N Oxidation state oxic N2ON2O Nitrification

Global distribution of ΔpN 2 O (Suntharalingam & Sarmiento 2000)

N 2 O distribution off Mauritania Depth [m] 21°W20°W19°W18°W17°W N 2 O [nmol L -1 ] P347 Jan 07 P348 Feb 07 ATA3 Feb 08

N 2 O mixed layer budget in the Mauritanian upwelling Atmosphere Subsurface ocean Pycnocline Gas exchange Diapycnal fluxVertical advection N 2 O productionMixed layer Continent

Depth [m] K ρ [m 2 s -1 ] 1e-0061e °W17°W16.8°W16.6°W16.5°W16.4°W16.3°W N 2 O fluxes off Mauritania Diapycnal flux calculated by microstructure measurements of small scale turbulence in combination with N 2 O-profiles from the water column. Quantification of sea-to-air flux from surface N 2 O concentrations and in- situ wind speeds. 21°N 20°N 19°N 16°N 24°W 22°W16°W 20°W18°W ΔN 2 O [nmol L -1 ] °N 17°N

Projection of all Stations to 18°N Diapycnal flux Sea-to-air flux Water depth [m] °W22°W20°W18°W16°W Comparison of sea-to-air and diapycnal flux

N 2 O mixed layer budget in the Mauritanian uwpelling Atmosphere Pycnocline Sea-to-air flux Diapycnal fluxVertical advection N 2 O productionMixed Layer Continent 25m nmol m -2 s -1 Flux difference ~60 nmol L -1 yr -1 Potential N 2 O production rate in the mixed layer nmol m -2 s nmol m -2 s nmol m -2 s -1 Subsurface ocean

N 2 O Production in the mixed layer? Potential N 2 O production rate: Evidence for nitrification in the euphotic zone -> N 2 O production in the mixed layer (e.g. Yool et al. 2007, Clark et al. 2008). Previous mixed layer budget calculations for N 2 O indicate strong near-surface production (e.g. Dore & Karl, 1996; Morell et al., 2001) PRO N 2 O production rate below the mixed layer: <3.3 nmol L -1 yr -1 (Freing et al., 2012). N 2 O 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 N 2 O distribution linked to upwelling CONTRA ~60 nmol L -1 yr -1

Effect of surfactants on N 2 O gas exchange in laboratory studies 20 K. Richter, p.c., see poster „The Schmidt Number Dependency of Air-Sea Gas Exchange with Varying Surfactant Coverage” x3

Nightingale et al Tsai & Liu 2003, surfactant-influenced Good conditions for occurrence of surfactants in upwelling areas (Wurl et al., 2011; Gasparovic et al., 1998 ). Similar findings: Calculations of net community production based on CO 2 /N 2 O O 2 /N 2 O (Steinhoff et al., 2012; see poster „Biological productivity in the Mauritanian upwelling estimated with a triple gas approach”) Recalculation of sea-to-air flux using gas exchange parameterization of Tsai & Liu (2003). Effect of surfactants on N 2 O gas exchange in the field?

N 2 O mixed layer budget with reduced gas exchange Atmosphere Pycnocline Diapycnal fluxVertical advection N 2 O productionMixed layer Continent nmol m -2 s -1 Flux difference nmol m -2 s nmol m -2 s nmol m -2 s -1 Sea-to-air flux (Parameterization Tsai & Liu 2003) Subsurface ocean

Diurnal stratification in the equatorial Atlantic 5:0010:0015:00 20:00 Time temperature diurnal cycle 0°N 10°W :00 Depth [m] 0 → Evolution of a diurnal stratification within the mixed layer → Supersaturated N 2 O concentrations in the deeper mixed layer cut off from the sea- surface while near- surface waters may quickly equilibrate. Glider measurements of temperature during MSM 18-2 & MSM 18-3, equatorial Atlantic, May- July 2011 Intense solar irradiation:

Consequences? data from Denman et al., 2007 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.

Summary & Conclusions Mixed layer budget off Mauritania reveals large discrepancy between sea- to-air flux and supply from subsurface layer. Mixed layer source of N 2 O 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 N 2 O emissions from other upwelling areas, too. Effect of surfactants on N 2 O 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 N 2 O 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 N 2 O: High resolution N 2 O profiles of mixed layer Microstructure measurements High resolution underway pCO 2 /pN 2 O 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 N 2 O analyzer allows flux calculation even at low ΔN 2 O Arevalo, 2012 MSM 18-2, equatorial Atlantic May/June 2011

Diurnal stratification in the equatorial Atlantic Ocean

Kerstin Richter, p.c. Effect of surfactants on N 2 O gas exchange – laboratory results

N 2 O in the marine N cycle 27 suboxic/ anoxic Nitrification Bacterial and archaeal ammonium oxidation N 2 O production during archaeal nitrification (Santoro et al. 2011, Löscher et al. 2012) N 2 O 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) NH 4 + NO 2 - NO 3 - NH 2 OH N2N2 -III +V ±0 Denitrification Org. N Oxidation state oxic N2ON2O Nitrification