Southern Ocean Physical Controls on the The Southern Ocean … · the Cdis reservoir, particularly...

eddy stirring

south north

CO2 Feair-seagas transfer

trace metalsupply

depth

biologicalfalloutrespiration/

regeneration

DIC+

N +Fe -

diapycnalmixing

DIC+

N +Fe -

DIC-

N -Fe +

Physical Controls on the Air‐Sea Partitioning of CO2

Ric Williams (Liverpool)

Thanks to Mick Follows (MIT), Jon Lauderdale (MIT), Phil Goodwin (Southampton), Andy Ridgwell (Bristol), Alessandro Tagliabue (Liverpool), and other collaborators.

• how much heat & CO2 is being sequestered?

• what are the controlling mechanisms?

• what are the wider climate implications?

Challenges for the community

MeridionalOverturning in theSouthern Ocean

Andy Hogg

The SouthernOcean

Upper Cell(i) Theory

(ii) Observations

(iii) Models

(iv) Complications

Lower Cell(i) The Basics

(ii) Observations

(iii) Models

(iv) Complications

Conclusions

The Southern Ocean

MODE / INTERMEDIATE WATER

EKMAN TRANSPORT

DEEP WATER

SOUTH AMERICAANTARCTICA

BUOYANCY LOSS

WESTERLIES

BUOYANCY GAIN

EDDIES

ACC

BOTTOM WATER

Image from Morrison et al., 2015: "Upwelling in the Southern Ocean." Phys. Today.

I “Wind-driven” Antarctic Circumpolar Current (ACC)I Upper & lower overturning cellsI Buoyancy fluxes also drive circulation

eddy stirring

south north


trace metalsupply

depth


regeneration

DIC+

N +Fe -

diapycnalmixing

DIC+

N +Fe -

DIC-

N -Fe +

1. Mechanisms

2. Frameworks

3. Effect of residual circulation

4. Global implications

Lecture overview

Physical Controls on the Air‐Sea Partitioning of CO2

Ric Williams (Liverpool)

Thanks to Mick Follows (MIT), Jon Lauderdale (MIT), Phil Goodwin (Southampton), Andy Ridgwell (Bristol), Alessandro Tagliabue (Liverpool), and other collaborators.

MeridionalOverturning in theSouthern Ocean

Andy Hogg

The SouthernOcean

Upper Cell(i) Theory

(ii) Observations

(iii) Models

(iv) Complications

Lower Cell(i) The Basics

(ii) Observations

(iii) Models

(iv) Complications

Conclusions

The Southern Ocean

MODE / INTERMEDIATE WATER

EKMAN TRANSPORT

DEEP WATER

SOUTH AMERICAANTARCTICA

BUOYANCY LOSS

WESTERLIES

BUOYANCY GAIN

EDDIES

ACC

BOTTOM WATER

Image from Morrison et al., 2015: "Upwelling in the Southern Ocean." Phys. Today.

I “Wind-driven” Antarctic Circumpolar Current (ACC)I Upper & lower overturning cellsI Buoyancy fluxes also drive circulation

atmosphere

ocean

reactions in seawater

1. Mechanisms

carbonate chemistry

buffer factor

atmosphere

ocean

air-sea exchange

air-sea exchange timescale

month 1/10 170

1. Mechanisms

Kg air-sea transfer velocity h mixed layer depth

physicsrate limiting processes on annual timescale:

subduction into main thermoclineentrainment into winter mixed layerresulting annual air-sea uptake

fine-scale dynamical processes only important in modifying these processes

atmosphere

mixedlayer

ocean interior

uptakeoutgassing

CO2 CO2 CO2 CO2

warming cooling

atmosphere

mixerlayer

ocean interior

biologicalfallout

biologicaldrawdown

(a) physical transport and solubility (b) physical transport and biology

entrainment ofcarbon-rich waters

respiration and regeneration

physical transfer from surface to interior

physical transfer from interior to surface

1. Mechanisms

biology

biological drawdown can respond to fine-scale delivery of nutrients & trace metals

affects DIC profile

atmosphere

mixedlayer

ocean interior

uptakeoutgassing

CO2 CO2 CO2 CO2

warming cooling

atmosphere

mixerlayer

ocean interior

biologicalfallout

biologicaldrawdown






1. Mechanisms

Prevailing view:biological response is not directly important for the anthropogenic response, but is crucial for glacial-interglacial cycles.

physics biology

see first order opposing signs in the physical & biological responses

atmosphere

mixedlayer

ocean interior

uptakeoutgassing

CO2 CO2 CO2 CO2

warming cooling

atmosphere

mixerlayer

ocean interior

biologicalfallout

biologicaldrawdown






1. Mechanisms

thermocline

N

N pre

N =N pre+ N reg

atmosphere

mixed layer preformed & regenerated

in mixed layer

in ocean interior

2. Frameworks

efficiency of the biology

Ito & Follows (2005)

Tagliabue)et)al.)(2014,)Nature)Geoscience))

preformed +regenerated +benthic - scavenged

Dissolved free iron flux to surface dominated by winter entrainment

Tagliabue)et)al.)(2014,)GRL))

Supply of preformed & benthic Fe to the Southern Ocean

preformed

benthic

2. Frameworks Dissolved free iron

saturated

in mixed layer

disequilibrium

2. Frameworks Dissolved inorganic carbon, DIC

= Csat + Cdis

thermoclineC pre

atmosphere

mixed layerC pre= C sat +!C

C

DIC dis

in ocean interior thermocline

DIC

C pre

DIC=C pre+ C reg

atmosphere

mixed layer

2. Frameworks Dissolved inorganic carbon, DIC

Csat + Cdis + Csoft + Ccarb

saturated soft tissueregenerated

carbonatetissueregenerated

disequilibrium

DIC = Cpre + Creg

Hsurface heat loss/

density gainsurface heat gain/

density loss

eastward winds

diapycnalmixing

eddy stirring

Ekman transport

eddy transport

upper limb of overturning

dept

h

south north

lower limb ofoverturning

eddy stirring

south north


trace metalsupply

depth


regeneration

DIC+

N +Fe -

diapycnalmixing

DIC+

N +Fe -

DIC-

N -Fe +

3. Residual circulation

• air-sea carbon uptake affected by how far surface waters are away from saturation

• air-sea carbon anomalies eroded on annual & longer timescales

• expect opposing preformed & regenerated nutrient responses

Consider effect of changes in residual circulation

Hsurface heat loss/


density loss

eastward winds

diapycnalmixing

eddy stirring

Ekman transport

eddy transport


dept

h

south north


ψres=ψEul+ψeddy,,(ψeddy≈KGMSi),


MIT model 2.8ox2.8o, fixed KGM in eddy closure, integrated 5000 years with online biogeochemistry(Lauderdale et al., 2013, Climate Dynamics)

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example: stronger westerly wind stress

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generally stronger ψres=ψEul+ψeddy,,(ψeddy≈KGMSi),generally thicker subtropical thermocline

preformed carbon anomalyincreases via greater subduction

stronger westerly wind

regenerated carbon anomaly decreases, as more nutrients are subducted �

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�Creg

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increases via greater subduction

stronger westerly wind 3. Residual circulation

�Cpre

from T, S & Alk decreases from warmer thermocline

increases due to shorter residence time

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Wind-driven changes in the Southern Ocean carbon reservoirs 21

Fig. 12 Zonally-averaged Atlantic Ocean anomaly (mmol C m�3) of the Cdis reservoir for (a) increased, (b) decreased,

(c) northward-shifted and (d) southward-shifted westerly winds.

back into the deep ocean in regions of bottom water formation in the Southern Ocean, resulting in a306

relatively large increase in �Cdis in the abyss.307

When these anomalies are integrated (Table 2), the deep ocean changes dominate the net anomaly in308

the Cdis reservoir, particularly for southward shifted winds.309

3.4 Summary of the relationship between carbon components and ocean physics310

The close relationship between changes in atmospheric CO2 and the Southern Ocean residual circulation311

reveals a strong control by ocean physics (Figure 2b). A mechanistic view of the changes in the carbon312

components is obtained by applying the carbon framework to the model experiments. Changes in residual313

circulation explain 83% of the variance in the total saturated pool of DIC, including changes resulting314

from atmospheric CO2 and potential temperature, salinity and alkalinity anomalies. When considered315

separately, the relationship between the residual circulation and �Csat(✓,S,Apre) is fairly close for all316

experiments, controlled by ventilated changes in pycnocline depth. For southward-shifted winds of 10�,317

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27 experiments: variety of winds, GM values, limited buoyancy forcing changes

R2=0.89

stronger residual cell, greater atmospheric CO2

eddy stirring

south north


trace metalsupply

depth


regeneration

DIC+

N +Fe -

diapycnalmixing

DIC+

N +Fe -

DIC-

N -Fe +

Residual circulation (Sv)

Atmospheric CO2 (ppm)

(Lauderdale et al., 2013, Climate Dynamics)


0 30

260

300

Consistent with paleo argument: enhanced upwelling driving last deglacial (Anderson et al., 2009)

Glo

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n an

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tC)

-150.00

-125.00

-100.00

-75.00

-50.00

-25.00

0.00

25.00

50.00

75.00

100.00

125.00

150.00L2

013

Cons

tant

KG

M

F200

5 Va

riabl

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HMM

2011

Var

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V199

7 Va

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L201

3 Co

nsta

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GM

F200

5 Va

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HMM

2011

Var

iabl

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V199

7 Va

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L201

3 Co

nsta

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GM

F200

5 Va

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HMM

2011

Var

iabl

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M

V199

7 Va

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L201

3 Co

nsta

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GM

F200

5 Va

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M

HMM

2011

Var

iabl

e KG

M

V199

7 Va

riabl

e KG

M

Atmospheric CO2 Preformed Carbon Regenerated Carbon

Increased SH Winds

Decreased SH Winds

North-shifted Winds

South-shifted Winds

Glo

bal c

arbo

n an

omal

y (G

tC)

-150.00

-125.00

-100.00

-75.00

-50.00

-25.00

0.00

25.00

50.00

75.00

100.00

125.00

150.00

L201

3 Co

nsta

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GM

F200

5 Va

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HMM

2011

Var

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V199

7 Va

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L201

3 Co

nsta

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GM

F200

5 Va

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HMM

2011

Var

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V199

7 Va

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L201

3 Co

nsta

nt K

GM

F200

5 Va

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e KG

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HMM

2011

Var

iabl

e KG

M

V199

7 Va

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e KG

M

L201

3 Co

nsta

nt K

GM

F200

5 Va

riabl

e KG

M

HMM

2011

Var

iabl

e KG

M

V199

7 Va

riabl

e KG

M


Increased SH Winds

Decreased SH Winds

North-shifted Winds

South-shifted Winds

Glo

bal c

arbo

n an

omal

y (G

tC)

-150.00

-125.00

-100.00

-75.00

-50.00

-25.00

0.00

25.00

50.00

75.00

100.00

125.00

150.00

L201

3 Co

nsta

nt K

GM

F200

5 Va

riabl

e KG

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HMM

2011

Var

iabl

e KG

M

V199

7 Va

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e KG

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L201

3 Co

nsta

nt K

GM

F200

5 Va

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HMM

2011

Var

iabl

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V199

7 Va

riabl

e KG

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L201

3 Co

nsta

nt K

GM

F200

5 Va

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e KG

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HMM

2011

Var

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V199

7 Va

riabl

e KG

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L201

3 Co

nsta

nt K

GM

F200

5 Va

riabl

e KG

M

HMM

2011

Var

iabl

e KG

M

V199

7 Va

riabl

e KG

M


Increased SH Winds

Decreased SH Winds

North-shifted Winds

South-shifted Winds

weaker winds

stronger winds

Carbon anomaly (PgC)

Glo

bal c

arbo

n an

omal

y (G

tC)

-150.00-125.00-100.00

-75.00-50.00-25.00

0.0025.0050.0075.00

100.00125.00150.00

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x


Constant KGMLauderdale et al

(2013)

Variable KGMFerreira et al

(2005)

Variable KGMHoffman &

Morales Maqueda (2011)

Variable KGMVisbeck et al

(1997)

Glo

bal c

arbo

n an

omal

y (G

tC)

-150.00-125.00-100.00

-75.00-50.00-25.00

0.0025.0050.0075.00

100.00125.00150.00

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x



(2013)


(2005)




(1997)

Glo

bal c

arbo

n an

omal

y (G

tC)

-150.00-125.00-100.00

-75.00-50.00-25.00

0.0025.0050.0075.00

100.00125.00150.00

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x



(2013)


(2005)




(1997)

wind changes & different eddy closures

• atmospheric CO2 increase due to contraction of regenerated carbon pool

see Jon Lauderdale poster


• opposing sign of regenerated and preformed carbon anomalies

Eddy KGM closures:constant Hoffman & Morales Maqueda (2011)Ferreira et al. (2005)Visbeck et al. (1997)

Glo

bal c

arbo

n an

omal

y (G

tC)

-150.00

-125.00

-100.00

-75.00

-50.00

-25.00

0.00

25.00

50.00

75.00

100.00

125.00

150.00

L201

3 Co

nsta

nt K

GM

F200

5 Va

riabl

e KG

M

HMM

2011

Var

iabl

e KG

M

V199

7 Va

riabl

e KG

M

L201

3 Co

nsta

nt K

GM

F200

5 Va

riabl

e KG

M

HMM

2011

Var

iabl

e KG

M

V199

7 Va

riabl

e KG

M

L201

3 Co

nsta

nt K

GM

F200

5 Va

riabl

e KG

M

HMM

2011

Var

iabl

e KG

M

V199

7 Va

riabl

e KG

M

L201

3 Co

nsta

nt K

GM

F200

5 Va

riabl

e KG

M

HMM

2011

Var

iabl

e KG

M

V199

7 Va

riabl

e KG

M


Increased SH Winds

Decreased SH Winds

North-shifted Winds

South-shifted Winds

northward shift

Glo

bal c

arbo

n an

omal

y (G

tC)

-150.00

-125.00

-100.00

-75.00

-50.00

-25.00

0.00

25.00

50.00

75.00

100.00

125.00

150.00

L201

3 Co

nsta

nt K

GM

F200

5 Va

riabl

e KG

M

HMM

2011

Var

iabl

e KG

M

V199

7 Va

riabl

e KG

M

L201

3 Co

nsta

nt K

GM

F200

5 Va

riabl

e KG

M

HMM

2011

Var

iabl

e KG

M

V199

7 Va

riabl

e KG

M

L201

3 Co

nsta

nt K

GM

F200

5 Va

riabl

e KG

M

HMM

2011

Var

iabl

e KG

M

V199

7 Va

riabl

e KG

M

L201

3 Co

nsta

nt K

GM

F200

5 Va

riabl

e KG

M

HMM

2011

Var

iabl

e KG

M

V199

7 Va

riabl

e KG

M


Increased SH Winds

Decreased SH Winds

North-shifted Winds

South-shifted Winds

Glo

bal c

arbo

n an

omal

y (G

tC)

-150.00

-125.00

-100.00

-75.00

-50.00

-25.00

0.00

25.00

50.00

75.00

100.00

125.00

150.00

L201

3 Co

nsta

nt K

GM

F200

5 Va

riabl

e KG

M

HMM

2011

Var

iabl

e KG

M

V199

7 Va

riabl

e KG

M

L201

3 Co

nsta

nt K

GM

F200

5 Va

riabl

e KG

M

HMM

2011

Var

iabl

e KG

M

V199

7 Va

riabl

e KG

M

L201

3 Co

nsta

nt K

GM

F200

5 Va

riabl

e KG

M

HMM

2011

Var

iabl

e KG

M

V199

7 Va

riabl

e KG

M

L201

3 Co

nsta

nt K

GM

F200

5 Va

riabl

e KG

M

HMM

2011

Var

iabl

e KG

M

V199

7 Va

riabl

e KG

M


Increased SH Winds

Decreased SH Winds

North-shifted Winds

South-shifted Winds

Carbon anomaly (PgC)

southwardshift

see Jon Lauderdale poster


• opposing sign of regenerated and preformed carbon anomalies

• atmospheric CO2 increase due to contraction of preformed carbon pool

Glo

bal c

arbo

n an

omal

y (G

tC)

-150.00-125.00-100.00

-75.00-50.00-25.00

0.0025.0050.0075.00

100.00125.00150.00

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x



(2013)


(2005)




(1997)

Glo

bal c

arbo

n an

omal

y (G

tC)

-150.00-125.00-100.00

-75.00-50.00-25.00

0.0025.0050.0075.00

100.00125.00150.00

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x



(2013)


(2005)




(1997)

Glo

bal c

arbo

n an

omal

y (G

tC)

-150.00-125.00-100.00

-75.00-50.00-25.00

0.0025.0050.0075.00

100.00125.00150.00

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x

Incr

ease

d Ta

ux

Decr

ease

d Ta

ux

North

-shi

fted

Taux

Sout

h-sh

ifted

Tau

x



(2013)


(2005)




(1997)

Eddy KGM closures:constant Hoffman & Morales Maqueda (2011)Ferreira et al. (2005)Visbeck et al. (1997)

wind changes & different eddy closures

4. Global implications

Southern Ocean probably playing a crucial role:• sequestering heat• sequestering anthropogenic CO2

Ultimately important for global climate change

terrestrial(2000 PgC)

fossilfuels

(accessible4000 PgC)

atmosphere (600 PgC)

ocean heatuptake

radiative forcingfrom CO2

surface warming

carbon emissions

ocean(38000 PgC)

ocean CO uptake

2

How does global warming link to carbon emissions?

2. Warming from CO2

1. IPCC context

3. Long term SST response (~500y)

4. Short term SST response (multi decades)

Work with Phil Goodwin (Southampton) & Andy Ridgwell (Bristol)

Wednesday, 28 January 15

IPCC (2013)

NATURE CLIMATE CHANGE | VOL 3 | DECEMBER 2013 | www.nature.com/natureclimatechange 1013

interview

■ The IPCC Working Group I AR5 has recently been released. What is the most important finding?I think the most important !nding is in the last part of the Summary for Policymakers, regarding the cumulative carbon budget (that is, the total emissions since the late 1800s) and the linear relationship to the temperature response of the climate system (Fig. 1). Cumulative emissions will largely determine the increases in global surface temperature and the e#ects of climate change will persist for many centuries even if emissions are stopped. For the !rst time, we present this evidence — which is !rmly anchored in the science of a complex system — to policymakers. It is a compelling way to make a policy relevant statement: a speci!c temperature target implies a limited carbon budget. $is has direct implications for policy, as limiting climate change will require sustained and substantial reductions in greenhouse gas emissions.

■ In your view, has public interest in climate change decreased? Why?$e decreased public attention on climate started some time ago. People have been confronted with other serious issues — particularly in the last 5 years or so — such as the !nancial crisis, migration and associated problems that are a#ecting people’s living conditions. What is important to realise is that climate change also a#ects conditions of living in a fundamental way, but does not always manifest across regions in the same manner. Take precipitation, for example: there are areas where it is becoming much drier, and others where they say “Oh we don’t su#er from drought, but we have our frequent %oods”. Regional climate challenges are becoming evident to people, but they are not as immediate an impact as these other problems that people have to deal with daily.

■ What is your role as co-chair and how did the experience differ from your previous IPCC positions as a draft author of a summary report and a leading author?$e role of co-chair is very di#erent. I have been a coordinating lead author of chapters in the third and fourth assessment

reports (TAR and AR4). In 2008 I was elected to co-chair. Together with my Chinese colleague Dahe Qin, we took responsibility for the production of the Working Group I (WGI) contribution to AR5, which means the basic assessment report, the technical summaries and the Summary for Policymakers. Obviously this is together with authors and a technical support unit (which is customarily funded by the government of the developed country co-chair), who assist the co-chair and lead authors to organize and steer the process.

■ After AR4 it was discovered that non-peer reviewed publications had been cited. What measures were put in place to ensure that the best science was used in the latest report?Working Group I bases its assessment primarily on peer-reviewed literature, but other scienti!c literature is also admissible, for example, information on speci!c regional issues. We instructed the lead authors right from the beginning to centre our assessment !rmly in the scienti!c community. It is not enough to have 10 or 12 lead authors per chapter; it’s important that you mobilize the scienti!c community through the inclusion of contributing authors. $is is a long tradition in WGI and in my view, one of the elements that ensures we have an additional mechanism for error correction

before we publish. In other words, we realise that the expertise of an elected lead author team is not fully comprehensive, with knowledge of every little detail. A humble author team needs to realize that it has some gaps and bring in other experts from outside. We recommended this at every lead author meeting, and I have personal experience of how to bring in further expertise at this scale. Colleagues are very willing to contribute a !gure, a paragraph, check speci!c parts of the assessment and so on — we have collaborated with more than 600 scientists, who will be listed in the report as contributing authors. Having said that, I cannot guarantee that there won’t be any errors. It is a human endeavour, so there may be mistakes that we have overlooked but we have a clear protocol for addressing necessary corrections.

■ Are there research and knowledge gaps that need to be addressed?It is not our task to identify and point to research gaps or to suggest that governments direct funding to speci!c areas. However, when you make a comprehensive assessment of the current science you can easily identify areas where you would like to have more science and more progress — !elds where the state of knowledge does not provide conclusions with more than medium con!dence, there is an absence of best estimates or there are projected ranges that you would like reduced.

I can name a few areas, which are already evident from the chapter structure that we identi!ed and outlined for this report. $ere is still large uncertainty in the understanding of clouds and aerosols, although it doesn’t impact globally on the stringency of the overall message we deliver in the Summary for Policymakers. But we would prefer much lower uncertainties. Another issue concerns the availability, coverage and quality of precipitation measurements. $is is a big limitation as we don’t have a su&cient number of observations to properly assess model simulations of changes in the water cycle, and the detection and attribution of climate change.

State of the scienceThe Intergovernmental Panel on Climate Change (IPCC) released its fifth assessment report (AR5) on the physical science of climate change on 27th September this year. Nature Climate Change speaks to the co-chair of the working group responsible for the report, Thomas Stocker.

UN

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© 2013 Macmillan Publishers Limited. All rights reserved

most important finding is the linear temperature response to total emissions

Prof. Tom Stocker, co-chair of IPCC AR5 (2013):

1. IPCC context

nearly insensitive to emission scenario

Wednesday, 28 January 15

surface temperature anomaly, (oC) since 1870

cumulative carbon emission, Iem (PgC) since 1870

�T

global surfacetemperature

change

change in cumulative

carbon emissions

�T =✓

@T

@Iem

◆�Iem


change


carbon emissions

warming dependence on radiative forcing, Rfrom CO2

radiative forcing R

dependence on carbon

emissions, Iem

�T =✓

@T

@R

◆ ✓@R

@Iem

◆�Iem


change


carbon emissions

forcing R dependence on carbon emissions

=0.5 to 1.2 K(W m-2)-1

normalised ocean heat uptake (relative to R)

�T =✓

@T

@R

◆ ✓@R

@Iem

◆�Iem

constants:

time-varying variables:

warming dependence on forcing, R

from CO2

climate parameter=5.35 Wm-2

= 3500PgC

normalised ocean carbon undersaturation (relative to Iem)

radiative forcing from CO2

buffered ocean+atmos C inventory

Goodwin et al. (2015) Nature Geoscience

atmosphere

(a) change in surface warming only due to ocean heat uptake

(b) change in radiative forcing only due to ocean carbon uptakelater response after emissionsinital response from emissions

inital response from emissions later response after emissions

(assume unchanged)

less excess CO in atmosphere

more excess CO in ocean

2

ocean heat uptake

surface ocean

interior ocean


increased

surface warming

2

increased surface warming

reduced ocean heat uptake

radiative forcing

excess CO in atmosphere2

ocean undersaturated in excess CO

from COradiative forcingincreased

radiative forcingreduced

ocean CO uptake 2ocean CO

uptake2

2from CO

from CO2

22

surface warming increases in time due to weakening ocean heat uptake

how does surface warming vary in time?

atmosphere

(a) change in surface warming only due to ocean heat uptake

(b) change in radiative forcing only due to ocean carbon uptakelater response after emissionsinital response from emissions

inital response from emissions later response after emissions

(assume unchanged)

less excess CO in atmosphere

more excess CO in ocean

2

ocean heat uptake

surface ocean

interior ocean


increased

surface warming

2

increased surface warming

reduced ocean heat uptake

radiative forcing

excess CO in atmosphere2

ocean undersaturated in excess CO

from COradiative forcingincreased

radiative forcingreduced

ocean CO uptake 2ocean CO

uptake2

2from CO

from CO2

22

radiative forcing decreases in time due to ocean carbon uptake

how does radiative forcing from CO2 vary in time?

test in a coarse-resolution atmosphere-ocean model (GENIE) with coupled circulation & biogeochemistry

cumulative carbon emissions, Iem (PgC)500 1000 1500 2000 2500 3000

0

0.5

T (K

) erro

r

500 1000 1500 2000 2500 30000

1

2

3

4

5

T (

K)

(b) discrepancy of surface warming (model minus theory)

(a) 21st century surface warming from theory

!!

B1 IMAGEA1T MESSAGEB2 MESSAGEA1 AIMA2 ASFA1G MINICAM

tem

pera

ture

chan

ge

RCP 4.5RCP 6.0RCP 8.5

response from year 2000 to 2100 driven by IPCC

scenarios

(Goodwin et al., 2015, Nature Geoscience)

why the similar transient response?

T

heat uptake in deep ocean

thermal response anthropogenic carbon response

radiative forcingatmosphere

ocean

R

N

(a) initial response to carbon emissions on decadal timescales

(b) upper ocean equilibrates with the atmosphere after decades to centuries

(c) deep ocean equilibrates with the atmosphere after many centuries

ocean heat uptake

!

T

deep ocean heat uptake


ocean

R

!

upper ocean heat uptake ceases

T


ocean

R

climate response!


deep ocean heat uptake ceases

atmosphere

ocean

2excess CO increased from emissions

ocean uptake of CO

upper ocean undersaturated

deep ocean undersaturated

atmosphere

ocean

2excess CO relative to the deep ocean

upper ocean saturated

deep ocean under saturated

atmosphere

ocean


deep ocean saturated

CO in equilibrium with ocean2

high DIC

high DIC

higher DIC

low DIC

cold

cold

cool

warm

warmer

warmer

moderate DIC

moderate DIC

2

high latitude uptake of CO2

heat uptake in deep ocean deep ocean undersaturated

equator N. high latitudeS. high latitude

dept

h thermocline

surface warming

high latitude warming

ocean uptake of CO ceases2

Nclimate response

climate responseT

heat uptake in deep ocean

thermal response anthropogenic carbon response


ocean

R

N

(a) initial response to carbon emissions on decadal timescales

(b) upper ocean equilibrates with the atmosphere after decades to centuries

(c) deep ocean equilibrates with the atmosphere after many centuries

ocean heat uptake

!

T

deep ocean heat uptake


ocean

R

!


T


ocean

R

climate response!


deep ocean heat uptake ceases

atmosphere

ocean

2excess CO increased from emissions

ocean uptake of CO

upper ocean undersaturated

deep ocean undersaturated

atmosphere

ocean

2excess CO relative to the deep ocean


deep ocean under saturated

atmosphere

ocean


deep ocean saturated

CO in equilibrium with ocean2

high DIC

high DIC

higher DIC

low DIC

cold

cold

cool

warm

warmer

warmer

moderate DIC

moderate DIC

2

high latitude uptake of CO2

heat uptake in deep ocean deep ocean undersaturated

equator N. high latitudeS. high latitude

dept

h thermocline

surface warming

high latitude warming

ocean uptake of CO ceases2

Nclimate response

climate response

heat & carbon sequestration mainly achieved via ventilation process

heat & carbon sequestration can though differ via air-sea timescales & biology ....

6. Challenges

Hsurface heat loss/


density loss

eastward winds

diapycnalmixing

eddy stirring

Ekman transport

eddy transport


dept

h

south north


eddy stirring

south north


trace metalsupply

depth


regeneration

DIC+

N +Fe -

diapycnalmixing

DIC+

N +Fe -

DIC-

N -Fe +

1. Southern Ocean likely to be crucial in sequestering heat & carbon

rate limiting processes unclear, probably: subduction into main thermocline entrainment into winter mixed layer mismatch drives annual air-sea transfer

2. Residual circulation crucial for communication with the rest of ocean: stronger residual circulation increases atmospheric CO2.

link to carbon transport is unclearalso role of deep cell is unclear

3. Global climate implications from ocean heat & carbon drawdown

Partly compensating due to ventilation Mismatch in heat & carbon uptake likely to be important


0

0.5

T (K

) erro

r

500 1000 1500 2000 2500 30000

1

2

3

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T (

K)



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Southern Ocean Physical Controls on the The Southern Ocean … · the Cdis reservoir, particularly...

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Transcript of Southern Ocean Physical Controls on the The Southern Ocean … · the Cdis reservoir, particularly...