Acidification of the Arctic Ocean

1. EPOCA Kickoff Meeting, Gijon, 11 June 2008 Acidification of the Arctic Ocean James C. Orr1, Sara Jutterström2, Laurent Bopp3, Leif G. Anderson2, Victoria J. Fabry4, Thomas Frölicher5, Peter Jones6, Fortunat Joos5, Ernst Maier-Reimer7, Joachim Segschneider7, Marco Steinacher5 and Didier Swingedouw8 1MEL/IAEA, Monaco 2Dept. of Chemistry, Götenborg University, Sweden 3LSCE/IPSL, CEA-CNRS-UVSQ, Gif-sur-Yvette, France 4Dept. of Biological Sciences, California State University San Marcos, USA 5Climate & Environmental Physics, University of Bern, Switzerland 6Ocean Sciences Div., Bedford Inst. of Oceanography, Dartmouth, Canada 7Max Planck Institut für Meteorologie, Hamburg, Germany. 8Université Catholique de Louvain, Institut d’Astronomie et de Geophysique Georges Lemaitre, Louvain-La-Neuve, Belgium Funding: EU (GOSAC, NOCES), NASA, DOE, Swiss NSF, CSIRO

2. Decline of surface pH and [CO32-] during the 21st century • pH reduced by 0.3 to 0.4 by 2100 under IS92a (i.e., a 100% to 150% increase in [H+]) • [CO32-] decline results in surface undersaturation (A < 1) in S. Ocean: down to 55+/-5 mol/kg (in 2100, IS92a) 1765 1994 2100s 2100i Aragonite Saturation Calcite Saturation Orr et al. 2005 (Nature)

3. Surface ocean is supersaturated everywhere For at least 400 kyr & probably 25Ma Aragonite saturation horizon (where [CO32-]A = 0) Southern Ocean (down to ~1000 m) North Atlantic (down to ~3000 m) Present state of ocean saturation w.r.t. aragonite: [CO32-]A= [CO32-]- [CO32-]Asat By 2100… Large changes in subsurface saturation state ([CO32-]A) [in mol kg-1] • Surface undersaturation ([CO32-]A < 0) • Southern Ocean • Subarctic Pacific • Shoaling of the aragonite saturation horizon (i.e., [CO32-]A = 0) • Southern Ocean • (by ~1000 m) • North Atlantic • (by ~3000 m) Atlantic Pacific

4. Uncertainty due to Emissions Scenario (IS92a vs. IPCC SRES scenarios) *From Bern “reduced complexity” model (G.-K Plattner & F. Joos)

5. Models: Coupled climate model: IPSL/CM4.1 BGC model: PISCES • Atmosphere: LMD • Ocean: OPA/ORCA-LIM Model PO43- Diatoms NH4+ DSi Nano-phyto • Resolution: 2° nominal (½° tropics) • Isopycnal Diffusion & GM • TKE Model (prognostic Kz) • Sea ice model (LIM) NO3- DFe MicroZoo DOM Meso Zoo POM Big Part. Small Part. Euphotic Layer (100-150m) Aumont & Bopp(2006)

6. Without sulfate aerosols IPCC Scenarios used for 4th Assessment Report (AR4) With sulfate aerosols Ctl now Ctl preind Ctl preind Year Year

7. Atmospheric CO2 from 3 coupled carbon-climate models 2xCO2 Year Atmospheric CO2 • Three fully coupled atmosphere-ocean models (IPCC AR4 WG1 contributors), • including ocean & terrestrial carbon modules (C4MIP, Friedlingstein et al., 2006) • IPSL.CM4 LOOP (OPA/ORCA2, PISCES) • MPIM (MPIOM, HAMOCC5.1) • NCAR CSM1.4 (NCOM, OCMIP2+ prognostic)

8. Changes differ between 2 Polar Oceans: pH & [CO32-] pH Carbonate Arctic Southern Ocean

9. Surface Arctic projected to reach “ΩA < 1” from 10 to 32 years sooner than Southern Ocean (on average), i.e., lower atmospheric pCO2 by 56-122 μatm Model-only projections under SRES A2 scenario

10. Two “trans-Arctic” sections: (1) Combined AOS-94 + ODEN91 & (2) Beringia 2005 Barents Sea Fram Strait Kara Sea Nansen Basin Amundsen Basin Makarov Basin Laptev Sea Canada Basin East Siberian Sea Chukchi Sea

11. Trans-Arctic Model vs. Data Evaluation: Temperature (oC) Salinity

12. Trans-ArcticModel vs. Data: arag • Data  • Model  • Model – Data  • MLD too deep • Surface [CO32-] too high • Overall pattern, but less structure

13. Model minus Data: [CO32-] along AOS94-ODEN91 IPSL1 IPSL2 MPIM NCAR

14. Model minus Data: [CO32-] along Beringia 2005 IPSL1 IPSL2 NCAR MPIM

15. Models vs. Data: mean profile (distance-weighted) Beringia 2005 AOS94-ODEN91

16. Beringia 2005 AOS94-ODEN91

17. Projected [CO32-]A : saturation w.r.t. Aragoniteprojections from model only (under A2 scenario)

18. Projected [CO32-]A : saturation w.r.t. Aragoniteprojections from model only (under A2 scenario)

19. Projected [CO32-]A : Saturation w.r.t. Aragonite*Beringia (2005) baseline + model perturbations (A2)

20. Projected [CO32-]C : Saturation w.r.t. Calcite*Beringia (2005) baseline + model perturbations (A2)

21. Data-model approach improves consistency of projected undersaturation in Arctic surface waters “Data-Model” projections under SRES A2 scenario along Beringia section

22. Without sulfate aerosols IPCC Scenarios in use for 4th Assessment Report (AR4) With sulfate aerosols Ctl now Ctl preind Ctl preind Year Year

23. Undersaturation is strongest in the Arctic:  simulation with +1% increase per year Aragonite undersaturation[CO32-]Arag at 2xCO2 *Model approach (model results only)

24. Why?: Perturbation in [CO32-] due only to climate change is large and negative in the Arctic (2xCO2)

25. Mean Arctic profiles at 2xCO2 with & without terrestrial ice melt S T Control +CO2 + CO2 & Climate & Ice melt DIC Alk + CO2 & Climate CO32-

26. Mean Arctic profiles at 4xCO2 with & without terrestrial ice melt T S Control +CO2 + CO2 & Climate & Ice melt DIC Alk + CO2 & Climate CO32-

27. Simulated changes in surface [CO32-] at 2xCO2 2xCO2

28. Arctic Marine Calcifiers • Pelagic: • Foraminifera [calcite] • Shelled pteropod (Limacina helicina) [aragonite] • Coccolithophores (Coccolithus pelagicus, Emiliana huxleyi) [calcite] not the dominant Arctic primary producer • Benthic: • Molluscs dominate, particularly bivalve molluscs [calcite & aragonite] • Gastropods, scaphopods (tusk shells) [aragonite] • Echinoderms (Brittle stars, sea stars, sea urchins, sea cucumbers) [high Mg-calcite in internal ossicles] • Benthic forams [calcite], • Coralline red algae [high Mg calcite] • Bryzoans • BUT, No Cold-water corals yet discovered (perhaps too cold) How will Arctic ecosystems respond to ocean acidification?

29. Effects on other other Arctic animals?

30. Conclusions • With 2 transArctic data sections & 3 models, we projected changes in [CO32-] and saturation under SRES A2 scenario • Changes w.r.t. Aragonite: • Now - some near-subsurface waters already undersaturated (Canada Basin), due to anthropogenic CO2 increase • in 10 years - some surface waters become undersaturated • in 40 years - average surface waters become undersaturated • Changes w.r.t. Calcite: • in 10 years - near-subsurface waters become undersaturated • in 50 years - some surface waters become undersaturated • in 70 years - average surface waters become undersaturated • Changes occur 10 to 30 years sooner in Arctic, relative to the Southern Ocean • Uncertainties remain (circulation, climate change, terrestrial ice melt/runoff, sea ice, riverine Alk & DIC delivery) • Potential loss of Arctic marine calcifiers by 2100? • Need for low-temp undersaturated perturbation studies (bivalves, echinoderms, coccolithophores, cold-water corals,…) • Need impact studies in currently undersaturated zones (shelves)

32. [CO32-]ARAG Aragonite Saturation along trans-Arctic sections *Data-Model approach • Future [CO32-] computed on section after adding model perturbations to data: DIC, Alk, T, S, SiO2, & PO43- • (Historical + SRES A2) • Deep saturation horizons resist change • Undersaturation invades from surface • Aragonite: surface undersat. by 2050 Aragonite Calcite

33. [CO32-]CALC Calcite Saturation along trans-Arctic sections *Data-Model approach • Future [CO32-] computed on section after adding model perturbations to data: DIC, Alk, T, S, SiO2, & PO43- • (Historical + SRES A2) • Deep saturation horizons resist change • Undersaturation invades from surface • Calcite: surface undersat. by 2100 Aragonite Calcite

34. Simulated changes in surface [CO32-] at 4xCO2 4xCO2