Download Orr_EPOCA_ArcticAcid_Nice_11jun2008

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
Funding: EU (GOSAC,
Georges
Lemaitre,
Louvain-La-Neuve,
Belgium
NOCES),
NASA,
DOE, Swiss
NSF, CSIRO
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)
By
Present
2100…state
Large
of changes
ocean saturation
in subsurface
w.r.t.
2-] 22-] = [CO
2-] sat
saturation
)
[in

mol
aragonite:state
[CO([CO
]
[CO
3 A
3 A kg-1]
3 3A
Pacific
• Shoaling of the aragonite
horizon (i.e.,
• saturation
Aragonite saturation
horizon
2[CO
]A = 0)32-]A = 0)
(where
3 [CO
–
– Southern
Southern Ocean
Ocean
(by
~1000
m) m)
(down
to ~1000
–
– North
North Atlantic
Atlantic
(by
~3000
m) m)
(down
to ~3000
Atlantic
• Surface undersaturation
ocean is
2supersaturated
([CO
3 ]A < 0) everywhere
– Southern
For at least
Ocean
400 kyr
– Subarctic
& probablyPacific
25Ma
Uncertainty due to Emissions Scenario
(IS92a vs. IPCC SRES scenarios)
*From Bern “reduced complexity” model (G.-K Plattner & F. Joos)
Models:
BGC model: PISCES
Coupled 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-
NH4+
Diatoms
DSi
NO3-
Nano-phyto
DFe
MicroZoo
DOM
Meso Zoo
POM
Small Part.
Euphotic Layer
(100-150m)
Aumont & Bopp (2006)
Big Part.
IPCC Scenarios used for 4th
Assessment Report (AR4)
Without sulfate aerosols
With sulfate aerosols
Ctl now
Ctl preind
Ctl preind
Year
Year
Atmospheric CO2 from 3 coupled carbon-climate models
Atmospheric CO2
2xCO2
Year
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)
Changes differ between 2 Polar Oceans: pH & [CO32-]
Southern Ocean
Arctic
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
Arctic (> 70N)
S. Ocean (<60S)
Arctic - S. Ocean
IPSL
554
610
-56
MPIM
424
546
-122
NCAR
444
560
-116
Atmospheric pCO2 (uatm)
Model-only projections under SRES A2 scenario
Two “trans-Arctic” sections:
(1) Combined AOS-94 + ODEN91 & (2) Beringia 2005
Barents
Sea
Kara
Sea
Fram
Strait
Trans-Arctic Model vs. Data Evaluation:
Temperature (oC)
Salinity
Trans-Arctic
Model 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
MPIM
NCAR
Model minus Data: [CO32-] along Beringia 2005
IPSL1
MPIM
IPSL2
NCAR
AOS94-ODEN91
Beringia 2005
Models vs. Data: mean profile (distance-weighted)
AOS94-ODEN91
Beringia 2005
Projected [CO32-]A : saturation w.r.t. Aragonite
projections from model only (under A2 scenario)
Projected [CO32-]A : saturation w.r.t. Aragonite
projections 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)
Without sulfate aerosols
With sulfate aerosols
Ctl now
Ctl preind
Ctl preind
Year
Year
Undersaturation is strongest in the Arctic:
 simulation with +1% increase per year
Aragonite undersaturation [CO32-]Arag at 2xCO2
*Model approach (model results only)
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
T
S
DIC
Alk
Control
+ CO2
& Climate
& Ice melt
+CO2
+ CO2
& Climate
CO32-
Mean Arctic profiles
at 4xCO2
with & without
terrestrial ice melt
T
S
DIC
Alk
Control
+CO2
+ CO2
& Climate
& Ice melt
+ CO2
& Climate
CO32-
Simulated changes in surface [CO32-] at 2xCO2
Arctic
Southern Ocean
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
2xCO2
Preindustrial
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
*Data-Model approach
•
Future [CO32-] computed
on section after adding
model perturbations to
data: DIC, Alk, T, S, SiO2, &
Aragonite
PO43(Historical + SRES A2)
•
Deep saturation horizons
resist change
•
Undersaturation invades
from surface
– Aragonite: surface
undersat. by 2050
Calcite
[CO32-]ARAG
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, &
Aragonite
PO43(Historical + SRES A2)
•
Deep saturation horizons
resist change
•
Undersaturation invades
from surface
– Calcite: surface
undersat. by 2100
Calcite
[CO32-]CALC
Simulated changes in surface [CO32-] at 4xCO2
Arctic
Southern Ocean
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
-9
-1
Fraction (CO2)
0.89
0.995
Fraction (clim + land ice)
0.11
0.005
Fraction (land ice)
0.10
4xCO2
Preindustrial
Change (land ice)