Acidification of the Arctic Ocean
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Acidification of the Arctic Ocean
EPOCA Kickoff Meeting, Gijon, 11 June 2008
Funding: EU (GOSAC, NOCES), NASA, DOE, Swiss NSF, CSIRO
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, USA5Climate & Environmental Physics, University of Bern, Switzerland6Ocean Sciences Div., Bedford Inst. of Oceanography, Dartmouth,
Canada7Max Planck Institut für Meteorologie, Hamburg, Germany.8Université Catholique de Louvain, Institut d’Astronomie et de
Geophysique Georges Lemaitre, Louvain-La-Neuve, Belgium
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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) Aragonite Saturation
Calcite Saturation
176519942100s
2100i
Orr et al. 2005 (Nature)Orr et al. 2005 (Nature)
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Present state of ocean saturation w.r.t. aragonite: [CO3
2-]A= [CO32-] - [CO3
2-]Asat
By 2100… Large changes in subsurface saturation state ([CO3
2-]A) [in mol kg-1]
• Surface ocean is supersaturated everywhere– For at least 400 kyr– & probably 25Ma
• Aragonite saturation horizon (where [CO3
2-]A = 0)
– Southern Ocean
(down to ~1000 m)– North Atlantic
(down to ~3000 m)
• Surface undersaturation ([CO3
2-]A < 0)
– Southern Ocean– Subarctic Pacific
• Shoaling of the aragonite saturation horizon (i.e., [CO3
2-]A = 0)
– Southern Ocean
(by ~1000 m)– North Atlantic
(by ~3000 m)
Paci
fic
Atl
anti
c
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Uncertainty due to Emissions Scenario (IS92a vs. IPCC SRES scenarios)
*From Bern “reduced complexity” model (G.-K Plattner & F. Joos)
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Aumont & Bopp (2006)
Models:
Euphotic Layer (100-150m)
BGC model: PISCESCoupled climate model: IPSL/CM4.1
•Atmosphere: LMD •Ocean: OPA/ORCA-LIM Model
- Resolution: 2° nominal (½° tropics)
- Isopycnal Diffusion & GM
- TKE Model (prognostic Kz)
- Sea ice model (LIM)
PO43-
Diatoms
MicroZoo
POM
DOM
DSi
DFeNano-phyto
Meso Zoo
NO3-
NH4+
Small Part. Big Part.
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IPCC Scenarios used for 4th Assessment Report (AR4)
With sulfate aerosols
Without sulfate aerosols
Year
Year
Ctl now
Ctl preindCtl preind
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Atmospheric CO2
Atmospheric CO2 from 3 coupled carbon-climate models
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)
2xCO2
Year
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Changes differ between 2 Polar Oceans: pH & [CO3
2-]S
ou
thern
Oce
an
Arc
tic
pH Carbonate
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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
Year
Arctic (> 70N) S. Ocean (<60S) Arctic - S. Ocean
IPSL 2061 2071 -10
MPIM 2023 2055 -32
NCAR 2038 2065 -27
Atmospheric pCO2 (uatm)
Arctic (> 70N) S. Ocean (<60S) Arctic - S. Ocean
IPSL 554 610 -56
MPIM 424 546 -122
NCAR 444 560 -116
Model-only projections under SRES A2 scenario
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Two “trans-Arctic” sections: (1) Combined AOS-94 + ODEN91 & (2) Beringia 2005
Chukchi
Sea
East Siberian
Sea
Laptev Sea
KaraSea
BarentsSea
Canada Basin
Amun
dsen
Bas
in
Nanse
n Bas
in
FramStrait
Mak
arov
Bas
in
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Trans-Arctic Model vs. Data Evaluation:
Temperature (oC) Salinity
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Trans-ArcticModel vs. Data: arag
• Data
• Model
• Model – Data• MLD too deep
• Surface [CO32-] too high
• Overall pattern, but less structure
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Model minus Data: [CO32-] along AOS94-
ODEN91
IPSL1 IPSL2
NCAR MPIM
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Model minus Data: [CO32-] along Beringia
2005
IPSL1 IPSL2
NCAR MPIM
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Models vs. Data: mean profile (distance-weighted)
AO
S9
4-O
DE
N9
1B
eri
ng
ia 2
00
5
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AO
S9
4-O
DE
N9
1B
eri
ng
ia 2
00
5
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Projected [CO32-]A : saturation w.r.t.
Aragoniteprojections from model only (under A2 scenario)
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Projected [CO32-]A : saturation w.r.t.
Aragoniteprojections from model only (under A2 scenario)
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Projected [CO32-]A : Saturation w.r.t.
Aragonite *Beringia (2005) baseline + model perturbations (A2)
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Projected [CO32-]C : Saturation w.r.t. Calcite
*Beringia (2005) baseline + model perturbations (A2)
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Data-model approach improves consistency of projected undersaturation in Arctic surface waters
A (δpCO2)
1st signs Average Calcite 1st signs
IPSL 2014 (+22) 2046 (+117) 2059 (+168)
MPIM 2014 (+18) 2048 (+136) 2070 (+244)
NCAR 2014 (+16) 2048 (+126) 2060 (+180)
“Data-Model” projections under SRES A2 scenario along Beringia section
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IPCC Scenarios in use for 4th Assessment Report (AR4)
With sulfate aerosols
Without sulfate aerosols
Year
Year
Ctl now
Ctl preindCtl preind
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Undersaturation is strongest in the Arctic: simulation with +1% increase per year
*Model approach (model results only)
Aragonite undersaturation [CO32-]Arag at 2xCO2
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Why?: Perturbation in [CO32-] due only to
climate change is large and negative in the Arctic (2xCO2)
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Mean Arctic profiles at 2xCO2 with & without terrestrial ice melt
CO32-
ST
AlkDIC
+ CO2& Climate& Ice melt
Control
+CO2
+ CO2
& Climate
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Mean Arctic profiles at 4xCO2 with & without terrestrial ice melt
CO32-
ST
AlkDIC+ CO2& Climate& Ice melt
Control
+CO2
+ CO2
& Climate
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Simulated changes in surface [CO32-] at
2xCO2 Arctic Southern Ocean
Preindustrial 125 114
CO2 only 65 64
CO2 + clim (no land ice) 63 66
CO2 + clim + land ice 57 64
Change (total) -68 -51
Change (CO2) -60 -51
Change (clim + land ice) -8 0
Change (land ice) -5 -2
Fraction (CO2) 0.88 0.998
Fraction (clim + land ice) 0.12 0.002
Fraction (land ice) 0.08
2xC
O2
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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?
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Effects on other other Arctic animals?
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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)
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Aragonite Saturation along trans-Arctic sections
• Future [CO32-]
computed on section after adding model perturbations to data: DIC, Alk, T, S, SiO2, & PO4
3-
(Historical + SRES A2)
• Deep saturation horizons resist change
• Undersaturation invades from surface– Aragonite: surface
undersat. by 2050
Aragonite
Calcite
*Data-Model approach
[CO32-]ARAG
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Calcite Saturation along trans-Arctic sections
Aragonite
Calcite
*Data-Model approach
[CO32-]CALC
• Future [CO32-]
computed on section after adding model perturbations to data: DIC, Alk, T, S, SiO2, & PO4
3-
(Historical + SRES A2)
• Deep saturation horizons resist change
• Undersaturation invades from surface– Calcite: surface
undersat. by 2100
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Simulated changes in surface [CO32-] at
4xCO2 Arctic Southern Ocean
Preindustrial 125 114
CO2 only 36 39
CO2 + clim (no land ice) 35 39
CO2 + clim + land ice 26 38
Change (total) -100 -76
Change (CO2) -89 -76
Change (clim + land ice) -10 0
Change (land ice) -9 -1
Fraction (CO2) 0.89 0.995
Fraction (clim + land ice) 0.11 0.005
Fraction (land ice) 0.10
4xC
O2
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