Arevalo-Martinez, Damian L.

Bange, Hermann W.

Brandt, Peter

Dengler, Marcus

Fischer, Tim

Kock, Annette

Thomsen, Sören

OceanRep

Multidiurnal warm layer and inhibited gas exchange  in the Peruvian upwelling regimeTim Fischer  ,  Annette Kock ,  Damian L. Arévalo-Martínez  ,  Marcus Dengler  ,  Peter Brandt  ,  Sören Thomsen  ,  and Hermann W. Bange*,1 21 1 1      (1) GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany - Research Division 1 - Physical Oceanography*contact: tscher@geomar.deAbstract ID:    EGU2015-11426BMBF-Verbundvorhaben SOPRAN2 2         (2) GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany - Research Division 2 - Chemical Oceanography                                                                                                                        This study was supported by the German Federal Ministry of Education and Research through                                                                                                                        the joint project SOPRAN  (Surface Processes in the Anthropocene)  under grant no. SOPRAN IIFKZ 03F0611A and SOPRAN III FKZ 03F0662A. The friendly support of all crew members of research vessel METEOR during cruise M91 is highly appreciated.Particular thanks to Rudi Link for helping to construct the sampling equipment, and to the bravehearted who sampled N2O during long hours in the dinghy,drifting in the waves while sacricing their health. Thanks to Gerd Krahmann who processed the glider hydrographic data. The daily ASCAT global wind elddata were provided by A. Bentamy and D. Croize-Fillon of Ifremer, France.Acknowledgements                                                                    Calleja, M. Ll., Duarte, C. M., Vaquer-Sunyer, R., Agusti, S., and Herndl, G. J. (2013):   Prevalence of strong vertical CO2 and O2 variability in the top meters of the ocean, Global Biogeochemical Cycles,  27,  941-949,                                                                    doi: 10.1002/bgc.20081  -----   Kock, A., Schafstall, J., Dengler, M., Brandt, P., and Bange. H.W. (2012):    Sea-to-air and diapycnal nitrous oxide uxes in the eastern tropical North Atlantic Ocean,  Biogeosciences, 9,957-964 -----  Naqvi, S.W.A., Bange, H.W., Farías, L., Monteiro, P.M.S., Scranton, M.I., and Zhang, J. (2010): Marine hypoxia/anoxia as a source of CH4 and N2O, Biogeosciences, 7, 2159-2190, doi:10.5194/bg-7-2159-2010   ----  Nevison, C.D., Lueker, T.J., and Weiss, R.F. (2004):   Quantifying the nitrous oxide source from coastal upweling, Global Biogeochemical Cycles,  18,  GB1018, doi:10.1029/2003GB002110   -----   Soloviev, A., Edson, J., McGillis, W., Schluessel, P., and Wanninkhof, R. (2002):  Fine thermohaline structure and gas-exchange in the near-surface layer of the ocean during GasEx-98,   in:   Donelan, M.A., Drennan, W.M., Saltzman, E.S., and Wanninkhof, R. (eds.):   Gas transfer at water surfaces,  AGU Geophysical Monograph Series 127, Washington D.C., 181-185  -----ReferencesMultidiurnal shallow stratificationexists in the upwelling regime,observed by glider fleet.Nitrous oxide (N2O) observations in top 10 m show vertical concentration gradients.A 1-D model constrained by theglider timeseries reproduces N2O gradients of the observed kind.Conclusions  Multidiurnal shallow stratification (MDSS) with persistent mixing inhibition is a plausible cause for substantial surface N2O depletion observed.  Just diurnal shallow stratification would not be sufficient.  Bias of N2O emission estimates is highest where strongest MDSS and highest concentra-tions occur, i.e. where impact of bias is highest.Motivation to look for gas gradients in top 10 metersProfiles far from ship's influence allow detection of shallow gradientsNight time stratifica-tion, high concentra-tions and strong gradi-ents are associated4 regions of dense hydrographic observationsFound different grades of persistent stratificationHLD is mainly deter-mined by windspeedModel schematicThe stratified layer is extremely low in mixingExample runModelled gradients vs. region and supplyResulting emission overestimation when sampling ata specified depth          model      observationHypothetic mechanism:  Mixing is inhibited in a thin stratified layer that is not eroded for one or more nights. The surface layer (the ’multidiurnal warm layer‘) is thus isolated from gas supply from below, while the continuing outgassing causes surface depletion.In the Maurita-nian upwelling regime, N2O supply from below is much lower than the calculated N2O emissions.[Kock et al., 2012]Do we estimate gas emissions from adequate concentrations ?0.1 - 1 mpump1 - 10 mNiskinN2Oconcentrationstraticationday   /   nightwaterdepth5000 m 3000 m 150 m 100 mN2 = 10-6 N2 = 10-4N2 = 7 10-4N2 = 10-3Vertical concentration gradients in top layer exist and vary regionally.Shape of concentration proles resembles density proles at night.< 15 15 − 60 > 60−0.6−0.4−0.200.20.40.6nmol/kglog 10 conc ( 5 m ) / conc ( 10 m )Ratio ofN2O at 5mandN2O at 10m  from 45 CTD casts0 6 12 18 2410−610−510−410−3local hourN2Stratication of top 10m vs. time of dayfor regions of high and low N2O concentra-tions.proles withN2O > 15 nmol/kg at 5mproles withN2O < 15 nmol/kg at 5m  78 oW   77 oW   76 oW   14 oS   13 oS   12 oS IIIIII IVExtracted compositehydrographic timeseries:IIIIIIIV37 days31 days22 days10 days1 2 3 5 101003001000300010000ASCAT windspeed [m/s]waterdepth [m]HLD [m]  0.512351020local daysdepth in m5 10 15 20 25 30 3505101520log10 N25 10 15 20 25 30 35−10−50510local daysdepth in m       wind in m/slocal days5 10 15 20 25 3005101520log10 N2depth in m5 10 15 20 25 30−10−50510local daysdepth in m       wind in m/slocal days5 10 15 2005101520local days  5 1005101520log10 N2 log10 N2depth in m5 10 15 20−10−50510local days5 10−10−50510local daysdepth in m       wind in m/sRegion III Region IIIRegion IV Region IVRegion II Region IIRegion I Region Istratication timeseries HLD and ASCAT wind timeseries(Homogeneous Layer Depth: N2<10-4)Exchange across the stratied barrier layer is only via entrainment. For the vertical movement of the barrier the observed HLD timeseries are used. outgassingcontinuous       supplystratied barriermovingverticallylocal daysdepth in mmodel N 2O concentrations in nmol/kg  5 10 15 20 25 30 35246810 10203040506070800 20 40 60 80 100050100150200nmol/kgconcentrations at0.5 m0 20 40 60 80 100050100150200nmol/kgconc. at10 m51median78median−20 0 20 40 60 800246810percentdepth in mIIIIII−20 0 20 40 60 800246810percentdepth in mABCDIV−6−5−4−3stratication and dissipation rate,from glider with microstructure probeN2 of O(10-3) and dissipation rate of O(10-8) result in a vertical exchange coecient K of O(10-6).7 gliders, 250 gliderdays in total,in Jan. and Feb. 2013  80 oW   79 oW   78 oW   77 oW   76 oW   15 oS   14 oS   13 oS   12 oS   11 oS   10 oS    9 oS AB CDB D A CRegion I, supply ux 0.4 nmol/m2/sWebb                             x1x2conc. at 0.5 mconc. at 10 mbest matchto concentrationsobservedin the regionconstant supply flux in nmol/m2/sRegionIIIIIIIV0.4 0.8 1.50.20.10.050.02510121316182529435178951491712728.99.51112151723271281608.28.59.51012131820861059.39.410.611131419202932515689973948728828334959

Multidiurnal warm layer and inhibited gas exchange in the Peruvian upwelling regime

T. Fischer, A. Kock, D.L. Arévalo-Martínez, M. Dengler, P. Brandt, H.W. BangeMultidiurnal warm layer  and inhibited gas exchange  in the Peruvian upwelling regime BMBF-Verbundvorhaben SOPRANRD 1   Ocean Circulation and Climate DynamicsDüsternbrooker Weg 20D-24105 Kielcontact: tfischer@geomar.de      www.geomar.deMeasuring nitrous oxide (N2O) in the top 10 meters of the Peruvian upwellingVertical N2O gradients exist and are associated with a shallow stratified layerExistence of multidiurnal shallow stratification is verified by glider surveysReferences                                                                    Calleja, M. Ll., Duarte, C. M., Vaquer-Sunyer, R., Agusti, S., and Herndl, G. J. (2013): Prevalence of strong vertical CO2 and O2 varia-                                                                    bility in the top meters of the ocean, Global Biogeochem. Cycles, 27, 941-949, doi: 10.1002/bgc.20081  -----   Kock, A., Schafstall, J., Dengler, M., Brandt, P., and Bange. H.W. (2012):    Sea-to-air and diapycnal nitrous oxide uxes in the eastern tropical North Atlantic Ocean,   Biogeosciences,    9,957-964 -----  Naqvi, S.W.A., Bange, H.W., Farías, L., Monteiro, P.M.S., Scranton, M.I., and Zhang, J. (2010): Marine hypoxia/anoxia as a source of CH4 and N2O, Biogeo-sciences, 7, 2159-2190, doi:10.5194/bg-7-2159-2010   -----  Nevison, C.D., Lueker, T.J., , and Weiss, R.F. (2004): Quantifying the nitrous oxide source from coastal up-weling, Global Biogeochem. Cycles, 18, GB1018, doi:10.1029/2003GB002110  ----  Soloviev, A., Edson, J., McGillis, W., Schluessel, P., and Wanninkhof, R. (2002): Fine thermohaline structure and gas-exchange in the near-surface layer of the ocean during GasEx-98,  in:  Donelan, M.A., Drennan, W.M., Saltzman, E.S., and Wannink-hof, R. (eds.): Gas transfer at water surfaces, AGU Geophysical Monograph Series 127, Washington D.C., 181-185  -----Acknowledgments                                                                                                                        This study was supported by the German Federal Ministry of Education and Research through                                                                                                                        the joint project SOPRAN  (Surface Processes in the Anthropocene)  under grant no. SOPRAN IIFKZ 03F0611A and SOPRAN III FKZ 03F0662A. The friendly support of all crew members of research vessel METEOR during cruise M91 is highly appreciated.Particular thanks to Rudi Link for helping to construct the sampling equipment, and to the bravehearted who sampled N2O during long hours in the dinghy,drifting in the waves while sacricing their health. Thanks to Gerd Krahmann who processed the glider hydrographic data. The daily ASCAT global wind elddata were provided by A. Bentamy and D. Croize-Fillon of Ifremer, France.A 1-D model constrained by glider timeseries can reproduce the N2O gradientsHypothesis:  Mixing is inhibited in a shallow stratified layer that is not eroded over one or more nights. The subsequent isolation of the surface layer (the ’multidiurnal warm layer‘) from deeper layers, and the continuing out-gassing cause sur-face depletion.CTDstations0 6 12 18 2410−610−510−410−3local hourN2< 15 15 − 60 > 60−0.6−0.4−0.200.20.40.6nmol/kglog 10 conc ( 5 m ) / conc ( 10 m )N2Oconcentrationstraticationday   /   nightwaterdepth5000 m 3000 m 150 m 100 mN2 = 10-6 N2 = 10-4N2 = 7 10-4N2 = 10-3Stratication of top 10m vs. time of dayfor regions of high and low N2O concentra-tions.proles withN2O > 15 nmol/kg at 5mproles withN2O < 15 nmol/kg at 5mStronger N2O gradients are associated with higher N2O concentrations and night time straticationRatio ofN2O at 5mandN2O at 10m  from 45 CTD castsDo we estimate gas emissions from adequate concentrations ?MotivationShallow sampling away from ship‘s inuenceIn the Maurita-nian upwelling regime, N2O supply from below is too low to explain the measured N2O emissions.[Kock et al., 2012]N2O measurements during Meteor cruise M91 in December 20120.1 - 1 mpump1 - 10 mNiskinShip based prolesVertical concentration gradients in top layer exist and vary regionally.Shape of concentration proles resembles density proles at night.Glider eet in Jan/Feb 2013 4 regional stratication timeseries with dierent grades of multidiurnal stratication Depth of homogeneous sur-face layer (HLD) is mainly de-termined by wind speedSimple 1-D two layer model Region 1  -  multidiurnal stratication causes distinct gradient Region 3  -  diurnal stratication not sucient for strong gradientExchange across the stra-tied barrier layer is only via entrainment. For the vertical movement of the barrier the observed HLD timeseries are used. Region 1 - strong multidiurnal stratication Region 2 - episodes of MDS Region 3 - frequent mixing Region 4 - diurnalstraticationtimeseriesHLD and windtimeserieslocal daysdepth in m5 10 15 20 25 30 3505101520local days5 10 15 20 25 3005101520local days5 10 15 2005101520local days  5 1005101520 −6−5−4−35 10 15 20 25 30 35−10−50510local daysdepth in m       wind in m/s5 10 15 20 25 30−10−50510local days5 10 15 20−10−50510local days5 10−10−50510local dayslog10 N2 log10 N2 log10 N2 log10 N21 2 3 5 101003001000300010000ASCAT windspeed [m/s]waterdepth [m]HLD [m]  0.512351020  78 oW   77 oW   76 oW   14 oS   13 oS   12 oS 123 4In total 250 glider days were perfor-med by 8 gliders in 4 main regions, recording hydrography. local daysdepth in mmodel N2O concentrations in nmol/kg  5 10 15 20 25 30 35246810 10203040506070800 20 40 60 80 100050100150200nmol/kg0.5 m0 20 40 60 80 100050100150200nmol/kg10 mResulting concentration distributions5077local daysdepth in mmodel N2O concentrations in nmol/kg  2 4 6 8 10 12 14 16 18 20 22246810 10203040506070800 10 20 30 40020406080100nmol/kg0.5 m0 10 20 30 40020406080100nmol/kg10 mResulting concentration distributions2427medianmedianmedianmedianoutgassingcontinuous       supplystratied barriermovingvertically

Multidiurnal warm layer and inhibited gas exchange in the Peruvian upwelling regime

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