Modelling some Southern Ocean biogeochemical paradox P. Monfray (IPSL, Paris) Acknowledgments: L.Bopp, O.Aumont, C.Le Quéré & J.Orr Prepared for JGOFS-SOSG, Hawaï, February 16th, 2002 or How S.O. response to global change ? or How bad we understand the S.O. ?

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Dufresne et al., 2002Friedlingstein et al., 2001

Aumont et al., 2001 PISCES

A- External Geochemical Impact

Do dust change could affect the SO ?

Diatoms change (%) X 100 Bopp L., 2001

Export Production Change Export Production +6 % But gyres increases … and PP decreases Bopp L., 2001

>>> Be careful with iron geo-engineering… diatoms should reduce surface primary production, food quality and marine resources Aumont et al., 2001

Bopp L., 2001

Do Si change could affect the SO ?

Fe (Mahowald, 1999) + Si (Tréguer et al., 2000) ?  But effect negligible in PISCES-OPA model  Is it correct?

Nutrient co-limitation Diatoms  Do the model too limited by Fe and not enough by Si?  Relative Si co-limitation to Fe co-limitations is a key stone for SO response…  Data ? Aumont et al., 2001

Do [CO 2 ] d change could affect the SO ?  In Eq.Pac, a jump from 0.5 to 2 x CO2 advantages diatoms proportion by a factor 2 (Tortell et al., OSC, 2002)  What about taxonomic response to CO2 in S.O. ???  At LGM, this effect have opposite effect than Fe and Si  What about the future ???

B- Climate Impact

Do stratification change could affect the SO ?

Climate impact on ocean physics at 2xCO2 Bopp et al., 2001  Major Stratification

Robust for different biological or physical models Moyenne Zonale (2xCO 2 -1xCO 2 ) -30 %+30 % Export production change at 2xCO2 Global diminution of -5 to -10 % But opposition between low latitudes (-20%) / high latitudes (+20%) Simulation P3ZD-OPA-LMD 30 gC m -2 an gC m -2 an -1 Bopp L., 2001

Shift from Diatom to Nanoplankton at 2xCO2 Diatoms Nanoplanktons Bopp L., 2001

Do grazing could play a role ?

Nutrient limitation case (HAMOCC3) Grazing control case ( P3ZD) Seasonal Cycle at 1xCO2 at 2xCO2 2xCO 2 < 1xCO 2 2xCO 2 > 1xCO 2 Export gC m -2 y -1 JanDec JanDec Export change under stratification in North-Pacific  What about S.O. ? Bopp L., 2001

Combining climate and external geochemical impacts  The paleo-productivity challenge

Export Production Change at LGM  Increase in whole Austral Ocean Bopp L., 2001

Modelling Dust + Circulation + SST + Sea-ice / PISCES-OPA simulation (Export, LGM-Present, gC m -2 y -1 ) Export Production at LGM Export Production at LGM LGM < Present LGM > Present Ambiguous Data LGM ~ Present From K.E. Kohfeld’s compilation (proxies : C-org, CaCO3, Ba, assemblages…) Bopp et al., 2002b

Do UV change could affect the SO ?  Important in lab experiment, but repair processes  Who knows at local, regional or bassin scale ?

C- Impact of SO on atmospheric chemistry

Do SO change could impact atmospheric CO2 ?

Anthropogenic CO2 fluxes at 700m  The S.O.: a priori the main CO2 regulator  But efficiency could be half by stratification change  Physical change is the main uncertainty Bopp L., 2001

Do SO change could impact DMS ?

2xCO2 - 1xCO2 Potential impact on DMS cycle Bopp et al., 2002 Aumont et al., 2002  Speciation change is the main uncertainty  Phaeocystis ?

D- How to improve our knowledge on present change and response ?

Do Antarctic Circumpolar Waves (ACW) could be used as a climate change experiment ? ACW SST: ± 1°C MLD: ± 50m Biological response: 1-2 wk Geochemical response: 1 yr 2CO2 climate SST: 0.5-2°C MLD: m Biological response: 1-2 wk Geochemical response: 1-10 yr ?

SST SSHChl Austral Ocean (45°S-60°S)  No simple relationship between stratification (SSH) and Chl Le Quéré et al.,, 2001

 East-West Dependence Le Quéré et al.,, 2001

Stratification increases Chl: light nutrient limitation ? Stratification reduces Chl: deep nutrient limitation ? Le Quéré et al.,, 2001

Do O2 could be used as a climate change diagnostic ?

Oxygen outgassing due to climate change Effet Thermique Stratification Années Flux d ’O 2 (mol m -2 an -1 ) Bopp et al.,, 2001b

Années  Diminution of dissolved oxygen due to climate change. Bopp et al.,, 2001b

S.O. Global Change A provocative summary-1 A- External Geochemical Impact Do dust change could affect the SO: Paleo: ++, Futur: +?  Role of Fe from continental margins ? Do Si change could affect the SO: Paleo: +? Futur: - ? Do [CO 2 ] d change could affect the SO:Paleo: +?, Futur: ++?  Response of diverse planktonic assemblages ? B- Climate Impact Do stratification change could affect the SO geochemistry: Paleo: ++?, Futur: +++? Do stratification change could affect the SO biology: Paleo: ++?, Futur: +++?  Responses of taxonomic groups and grazing to stratification (light) and temperature increases? To sea-ice change?

S.O. Global Change A provocative summary-2 C- Feedback on atmospheric chemistry CO2: SO a key stone for uptake BUT need better physics and dynamics DMS: Potential impact on clouds BUT need speciation dynamics D- How to improve our knowledge on present change and response ? Use ACW as a climate change experiment for biology  Need in depth analysis, both spatial and time patterns, of joint satellite surveys (Chl, SST, SSH, etc) Use O2 (or other proxy) as an imprint of convection/climate variability and change  Need data mining  Need to setup new JGOFS or ARGO long time surveys Develop lab experiments to evaluate biological responses to dissolved CO2  Need diverse planktonic assemblages, but how to jump in open condition? Determine role of the relative Fe sources (margins, atmospheric, oceanic)  Need to study some key areas dominated by one main source (South blue Pacific, Kerguelen plume) or various sources (South Atlantic) Others ?

References Aumont, O., Belviso, S. and Monfray, P.. DMSP and DMS sea surface distributions simulated from a global 3-D ocean carbon cycle model, J. Geophys. Res., in press, Aumont O., E. Maier-Reimer, Blain S. and Monfray P., An ecosystem model of the global ocean including Fe, Si, P co-limitations, Global Biogeochemical Cycles, submitted, Bopp, Climate changes and marine biogeochemistry, modelling LGM and industrial era, Thesis, University of Paris VI, 318 pp, Bopp L., P. Monfray, O. Aumont, J-L. Dufresne, H. LeTreut, G. Madec, L. Terray, et J.C. Orr, Potential impact of climate change on marine export production, Global Biogeochemical Cycles, 15, 81-99, 2001 Bopp L., O. Aumont, S. Belviso et P. Monfray, Potential impact of climate change on marine DMS (dimethylsulfide) emissions, Tellus, in revision, Bopp L., C. LeQuéré, A.C. Manning, M. Heimann et P. Monfray,Climate-induced oceanic oxygen fluxes: Implications for the contemporary carbon budget, Global Biogeochemical Cycles, in press, 2001b Bopp L., K.E. Kohfeld, C. Le Quéré, O. Aumont, O. Marti, I. Tegen, S.P. Harrison and I.C. Prentice, Dust impact on marine biota and atmospheric pCO2 during glacial periods, Paleoceanography,submitted, 2002b Dufresne J.L., P. Friedlingstein, M. Berthelot, Bopp L., P. Ciais, L Fairhead, H. Le Treut et P. Monfray, On the magnitude of positive feedback between future climate change and the carbon cycle, Geophysical Research Letters, in press, Friedlingstein P., Bopp L., P. Ciais, J-L. Dufresne, L. Fairhead, H. LeTreut, P. Monfray and J.C. Orr, Positive feedback of the carbon cycle on future climate change, Geophysical Research Letters, 28, , Le Quéré C., Bopp L. et I. Tegen, Antarctic Circumpolar Wave impact on marine biology, Geophysical Research Letters, submitted, 2001.