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

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)

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

Uncertainty due to Emissions Scenario (IS92a vs. IPCC SRES scenarios)

*From Bern “reduced complexity” model (G.-K Plattner & F. Joos)

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.

IPCC Scenarios used for 4th Assessment Report (AR4)

With sulfate aerosols

Without sulfate aerosols

Year

Year

Ctl now

Ctl preindCtl preind

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

Changes differ between 2 Polar Oceans: pH & [CO3

2-]S

ou

thern

Oce

an

Arc

tic

pH Carbonate

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

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

Trans-Arctic Model vs. Data Evaluation:

Temperature (oC) Salinity

Trans-ArcticModel vs. Data: arag

• Data

• Model

• Model – Data• MLD too deep

• Surface [CO32-] too high

• Overall pattern, but less structure

Model minus Data: [CO32-] along AOS94-

ODEN91

IPSL1 IPSL2

NCAR MPIM

Model minus Data: [CO32-] along Beringia

2005

IPSL1 IPSL2

NCAR MPIM

Models vs. Data: mean profile (distance-weighted)

AO

S9

4-O

DE

N9

1B

eri

ng

ia 2

00

5

AO

S9

4-O

DE

N9

1B

eri

ng

ia 2

00

5

Projected [CO32-]A : saturation w.r.t.

Aragoniteprojections from model only (under A2 scenario)

Projected [CO32-]A : saturation w.r.t.

Aragoniteprojections from model only (under A2 scenario)

Projected [CO32-]A : Saturation w.r.t.

Aragonite *Beringia (2005) baseline + model perturbations (A2)

Projected [CO32-]C : Saturation w.r.t. Calcite

*Beringia (2005) baseline + model perturbations (A2)

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

IPCC Scenarios in use for 4th Assessment Report (AR4)

With sulfate aerosols

Without sulfate aerosols

Year

Year

Ctl now

Ctl preindCtl preind

Undersaturation is strongest in the Arctic: simulation with +1% increase per year

*Model approach (model results only)

Aragonite undersaturation [CO32-]Arag at 2xCO2

Why?: Perturbation in [CO32-] due only to

climate change is large and negative in the Arctic (2xCO2)

Mean Arctic profiles at 2xCO2 with & without terrestrial ice melt

CO32-

ST

AlkDIC

+ CO2& Climate& Ice melt

Control

+CO2

+ CO2

& Climate

Mean Arctic profiles at 4xCO2 with & without terrestrial ice melt

CO32-

ST

AlkDIC+ CO2& Climate& Ice melt

Control

+CO2

+ CO2

& Climate

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

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?

Effects on other other Arctic animals?

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)

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

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

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