gas transfer through polar sea ice (gaps): what we know and what we guess about air-sea exchange in...
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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