brice loose

GAs transfer through Polar Sea ice (GAPS): What we know and what we guess about air-sea exchange in ice

covered waters

Brice Loose

Gas transport pathways in the ice pack

Air-sea flux

Diffusive flux

How does diffusive flux compare to air-sea flux?

Southern Ocean at 90% ice cover:

Gosink et al., (1976), Loose et al., (in press).D = O(10-5 cm2 s-1)

- FD = 0.014 ∆C (through 50 cm of ice)

Takahashi et. al., (2009). - FG = 1.7 ∆C

f

1-f

pCO2 ~ 420 ppm

Thin film model

Henry’s law in the viscous sub-layer:

Cwi = HCai

leads to:F = K(Ca-HCw)

Conductance through resistors in series:

1/K = 1/kw + 1/ka

Liss and Slater, 1974

In practice kw << ka,

So K = kw

Turbulence in the ice zone

dA

Sea ice in ocean carbon estimates

Scaling between k and open water area

Implies that k is uniquely dependent on wind/fetch

f

1-f

k (

gas

tran

sfer

velo

city

)

f (open water fraction)0.1

Turbulence production beneath ice

Contents1. Laboratory snapshots of k vs. open water scaling

relationship.

2. Field estimates of k (there are only two).

3. Serial resistance to ocean-atmosphere exchange.

Robin boundary condition

4. Sensitivity example: CO2 in the Southern Ocean Seasonal Ice Zone

5. How to parameterize k for the ice pack?

Turbulent energy dissipation

Kinetic energy balance

Effects of stratification

US Army Cold Regions Research and Engineering Lab (CRREL)

€

d

dtCwV( )

€

kw =h

Δtln

C f −Ceq

Ci −Ceq

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟,

Control volume measurements:

• SF6 - evasion from the water

• O2 - evasion and invasion

• Well-mixed tank:

• Windless gas-exchange

condition

Freeze experiments at CRREL

Scaling relationship between k and f

Field estimates of k in ice cover.

Fanning and Torres, 1991

– 222Rn:226Ra activity, Barents Sea, 1986, 1988

– Late winter, f ~ 0.1. k = 1.4 m d-1

– Late summer, f > 0.3. k = 2.8 m d-1

Takahashi et. al., 2009 (hypothesis)

– Open ocean k ~ 3.7 m d-1

– Winter, f =0.1, k = 0.37 m d-1

Field estimates of k in ice cover.

Ice Station Weddell, 1992

Field estimates of k in ice cover.

Ice S

tati

on

Wedd

ell,

19

92

Mass balance between isopycnal and the surface.

M = 3He, CFC-11, S and water

Solved for k (and FCDW, ML )

Isopycnal tracer inventory

€

1

ρ sw

dM

dt= k CATM −C t

( ) +CCDWFCDW +C tΔML

FCDW

Isopycnal surface

Ocean surface

ML

k from tracer inventory

Day 143 -148: f = 0.17, k = 0.31 m d-

1

Day 123-142: f < 0.04, k = 0.16 m d-1

All estimates of k in ice cover

Serial resistance to ocean-atmosphere exchange

Surface renewal model

Equate:€

F = k C − HXatm( )

€

−D∂C

∂z= F

€

C(0, t) −D

k

∂

∂zC(0, t)

z=0

= HXatm

€

D

kL>>1⇒ interface - controlled

D

kL<<1⇒ diffusion - controlled

Xatm

Ocean surfaceC

L

Serial resistance to ocean-atmosphere exchange

Surface renewal model

Equate:€

F = k C − HXatm( )

€

−D∂C

∂z= F

€

C(0, t) −D

k

∂

∂zC(0, t)

z=0

= HXatm

€

D

kL>>1⇒ interface - controlled

D

kL<<1⇒ diffusion - controlled

Xatm

Ocean surfaceC

L

Serial resistance to ocean-atmosphere exchange

€

D

kCFC −11L=

4300

0.1 2.6( )100≈160

Ocean surface

Ice-free (summer) Ice-cover (winter)

100 m

D = 4300 m2d-1

D = 4.3 m2d-1

€

D

kCFC −11L=

4.3

2.6( )100≈ 0.02

100 m

3. Sensitivity example: CO2 in the Southern Ocean seasonal ice

zone (SIZ)

Gas transport scenarios

Seasonal forcing in a transport model

Three scenarios:

S1 - k fS2 - k f0.5

S3 - k = CTE

€

∂C∂t

−∂

∂zD(z ,t)

∂C

∂z

⎛

⎝ ⎜

⎞

⎠ ⎟= F∑

C = Dissolved inorganic carbonZ = depth

D (

10-3

m2s-1

)

€

C(0, t) −D

k

∂

∂zC(0, t)

z=0

= HXatm

Primary Production

Primary prod. curveIntegrates to 57 g C m-2yr-1

(Arrigo et al., 2008)

pCO2 and DIC at the air-sea interface

Annual FCO2 through ice zone

Springtime fluxes

Marginal ice zone

Region of ocean surface exposed in past 30

days

SO - Accounts for ~ 9% of annual primary

production.

Arrigo et. al., 2008

Conclusions

Sea ice cover is not sufficient to determine the value of k.

Despite ice cover, gas flux through leads accounts for 20-45% of net annual FCO2 in the seasonal ice zone.

Large gas fluxes in the spring MIZ compensate for restricted exchange during winter.

We need a scaling law for k in the sea ice zone

4. How to parameterize k for the ice pack?

4. How to parameterize k for the ice pack

4. How to parameterize k for the ice pack

€

k ∝ ευ( )1/4

Sc−n

Zappa et al., (2007)

Turbulence dissipation

Viscosity Molecular diffusivity

4. How to parameterize k for the ice pack?

€

ε =u*2 ∂u

∂z+b'w'

Ice/water current shear

Wind-driven shear

Buoyant convection/strat

ification

4. How to parameterize k for the ice pack?

Winter mixed-layer:

€

ε ∝ κu*2N

€

ε ∝ u*3κ /z

[Tennekes and Driedonks, 1981]

Spring Melt (stratification):

4. How to parameterize k for the ice pack?

Winter mixed-layer:

€

ε ∝ κu*2N

€

ε ∝ u*3κ /z

[Tennekes and Driedonks, 1981]

Spring Melt (stratification):

January 2011-2013

GAPS: (Gas Transfer through Polar Sea ice).

Spring 2011

BRAS D’OR LAKES: In situ measurements of biological production and air-sea gas exchange during ice melt.

Spring 2011BRAS D’OR LAKES: In situ measurements of biological

production and air-sea gas exchange during ice melt. • Quantification of biological production associated with ice

melting in a “natural laboratory” that serves as an analogy of the MIZ.

• Development of a method for simultaneously measuring air-sea gas exchange and biological production in ice melt zones from simple platforms.

Spring 2011

Surface Process Instrument Platform

Acknowledgements

Postdoc Advisor - Bill JenkinsThesis Advisor - Peter Schlosser

Collaborators/Contributors - Wade McGillis, Stan Jacobs, Martin Stute, Juerg Matter, Chris Zappa, Eugene Gorman, Philip Orton, Bob Newton, Anthony Dachille, Tom Protus and Bernard Gallagher.

At CRREL: Don Perovich, Jackie Richter-Menge, Chris Polashenski, Bruce Elder, David Ringelberg, Mike Reynolds.

Support: NSF IGERT Fellowship, NSF AnSlope Program, LDEO Climate Center, US SOLAS Program.

Thank you!

CO2 Flux from SIZ

S1: 2.3 g C m-2 month-1

S2: 2.8 g C m-2 month-1

S3: 3.9 g C m-2 month-1

Primary Production

Primary prod. Curve

Integrates to 57 g C m-2yr-1

(Arrigo et. al., 2008)

Processes folded into bulk diffusion rate

1. Molecular diffusion in liquid phase

2. Molecular diffusion in gas phase

3. Gas advection via liquid transport

4. Solubility partitioning between liquid and gas

5. Sorption onto soil grains

Part 1) k from tracer inventory