Modelling sea ice salinity: 1D , 3D modelling and implications for ecosystems
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Modelling sea ice salinity: 1D, 3D modelling and
implications for ecosystems
Martin Vancoppenollecoll.: T. Fichefet, H. Goosse, C.M. Bitz,
S. Bouillon, G. Madec, M.A. Morales Maqueda, J.-L. Tison, C. Lancelot, B. Delille, F. Jardon, F. Vivier
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Approach and questions
What aspects of sea ice desalination are relevant for large-scale sea ice mass balance and ocean circulation?
How to represent ice salinity in models ?
What are the implications for ecosystem models ?
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Why modelling ice salinity ?
Simulated change in Arctic sea ice thickness (1979-2006)
Variable salinity – S=5 Albedo + 10%Variable salinity – MY profile
Vancoppenolle et al., Ocean Modelling, 2009b
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Thermal properties of sea ice
Thermal properties
Diffusion of heat
Growth / melt rates
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Ice-ocean salt / freshwater exchanges
drainage growth / melt
Growing ice Melting ice
Snow ice
Congelation Brine drainage Melt Brine drainage
Lateral meltwater flow
Flushing
Freshwater flux / Salt flux
Virtual salt flux(upper ocean
salinity tendency)
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Outline
1D modelling
3D modelling
Perspectives for ecosystems
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1D MODELLING
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Is Thermal Effect Important ?
S (ppt)
h (m
)
Vancoppenolle, Fichefet and Bitz (GRL 2005)
• Sea ice model with brine thermodynamic effect (Bitz and Lipscomb, 1999) • Run for 50 years using climatological forcing• Using with various salinity profiles
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How we model ice salinity (1D) ? Thermal equilibrium
All salt is locked within brine inclusions
Salt transport breaks equilibrium
m = freezing point salinity-temperature ratio [0.054 °C/ppt]
e = brine volume frac. [-] S = ice bulk salinity [ppt] T = ice temperature [°C] s = brine salinty [ppt] vz = percolation velocity
(function of meltwater production) [m/s]
Ds = salt diffusivity in brine [m2/s]
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Parameterizing Brine Drainage
Gravity Drainage Convection if Ra is >5
(Notz & Worster, 2008)
Flushing Percolation if
Surface melting min(e) > 5%
30 % of meltwater percolates (Vancoppenolle, Bitz and Fichefet, JGR 2007)
Vancoppenolle, Goosse, et al. (JGR 2010)
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1d Simulations of Brine Drainage
Multiyear desalination of Arctic sea ice
(Vancoppenolle, Fichefet and Bitz, JGR 06)
Desalination of Antarctic sea ice (Vancoppenolle, Goosse et al., JGR 10)
Summer desalination of Arctic sea ice(Vancoppenolle, Bitz and Fichefet, JGR 07)
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Winter desalination is sensitive to diffusivity parameterization
Turbulent diff.Model (solid)Obs (dash)Molecular Diff.
Winter salinity profileData from Tison et al.
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Winter desalination is sensitive to diffusivity parameterization
Antarctic sea ice simulations, June.
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Summer desalination is sensitive to model parameters
Simulated surface salinity at Point Barrow (Alaska), June, for several sensitivity exps.
Penetration of penetrating radiation
Fraction of vertical percolation
Brine volume fractionpermeability threshold
0
0.3
0.5
0.2
0.3
0.5
10%
8%5%
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Sensitivity to parameters and forcing: summary
Gravity drainage Diffusivity parameters Critical rayleigh number Turbulent diffusivity
Flushing Snow depth Superimposed ice
formation Penetration of radiation
(io) in the ice Fraction of meltwater
that is allowed to percolate vertically
Brine volume fraction permeability threshold
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Full-depth convection
Results of a run in Antarctic sea ice with high snowfallSep 17 (1 – thin solid); Sep 24 (2 – dot); Oct 1 (3 – solid thin); Oct 8 (dash)
1 – 2 – 3 – 4
4 – 3 – 2 – 1
1 – 2 – 4 – 3
4 – 3 – 2 - 1
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3D MODELLING
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Approach• Problems:
– Ice thickness categories– Advection of tracers is expensive
• Approach: develop a simple S equation– 1 equation for vertical mean salinity– Shape of profile function of vertical
mean salinity• Include this simple S equation LIM
– Salt content (S.h) for each ice category
– Horizontal transport (Prather, 86)– Remapping in thickness space
(Lipscomb, JGR01)– Ridging / Rafting
Vancoppenolle et al. (OM 2009a, 2009b)
Comparison at Point Barrow (AK)
Red diam: OBSSolid: Simple eq. Dash: Transport eq.
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Simulated Hemispheric Mean Salinitywith a 3D Ice-Ocean Model
Forced by Reanalyses
Hemispheric mean ice salinity simulated by NEMO-LIM3:Arctic (black) and Antarctic (grey).(différences
hémisphériques : percolation, glace blanche, âge de la glace + cycle
saisonnier, variablité
interannuelle)
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Comparison to Obs
Ice salinity vs thickness in the model and from Cox and Weeks (1974) regressions computed
using ice core data
S (‰
)
hi(m)
MarJunSepDec
Comparison to observations in various regions(compilation from > 1000 cores)
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Geographical Distribution Arctic
Winter maximum In winter, salinity reflects
thickness / age of sea ice Summer low / constant values
Antarctic Weakear contrasts Fall maximum Local maxima due to polynyas
and maximum snow fall
Mar Sep
Sep.Mar
Ice salinity (1979-2006) averaged overice thickness categories
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Impact (Arctic)
2 configurations Prescribed salinity Simulated salinity
Ice thicker for varying salinity Differences up to 1m Difference in volume ~ 10%
More ice growth at the ice base (due to reduced energy of melting)
More surface melt(due to reduced specific heat)
More bottom melt(enhanced ice-albedo feedback)
Varying – prescribed salinity
Vancoppenolle et al., 2009b
1979-2008 Annual mean thickness difference
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Impact (Antarctic)
2 configurations Prescribed salinity Simulated salinity
Ice thicker for varying salinity Mean volume difference ~ 20%
Importance of ice-ocean interactions Including variations of S
Induce more ice formation with less salt rejection
Reduces vertical mixing in the upper ocean
Reduces the oceanic heat flux Increases sea ice formation
Varying – prescribed salinity
Mean 1979-2009 Ice thickness difference
Vancoppenolle et al., 2009b
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Impact on Upper Ocean
Mean 1979-2006 difference in sea surface salinity
Varying - prescribed Varying – prescribed S
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ECOSYSTEM MODELLING
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Why modelling salinity ?2) Ecosystems
Biophysical couplings associated with ice salinity Nutrient distribution Diatom transport mode Brine salinity inhibition of growth Brine volume fraction
Vertical structure of ice ecosystems
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Modelling Sea Ice Ecosystems Energy-conserving
thermodynamics and salt transport
1-stream Beer law with attenuation by chlorophyll-a
Tracer transport Ecosystem model
(diatoms and silicates)
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Brine-Ecosystem Coupling Ecosystem variables (n=1, 2)
(diatoms=DAF, silicates=DSi)
C = bulk concentration z = brine concentration e = brine volume fraction
Evolution equation
Physical sources & sinks
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A typical run
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Comparison to Observations
December Chlorophyll-a profile solid black: simulated (dots = STD)
horizontal lines: obs at ISPOLred : double snow
After calibration of µ, l, ws
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Role of diatom transport mode Different scenarios:
(a) diatoms follow brine motion (b) diatoms are locked in ice without
following brine motion (c) diatoms follow brine motion and
stick on brine inclusion walls Observations
Highest biomass is achieved if algae move with brine and stick on brine’s walls.
If algae are not sticky but mobile, they are rejected of the ice as salt, which inhibits the community development.
The nutrient pump increases the availability of nutrients and hence promotes community development.
Total biomass (mg chl-a/m2) as a function of time (months) for the different scenarios of brine-biology interactions. Note the log scale on the y axis.
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Role of convection on biomass
Biomass in silica units Dissolved Silica Total Silica
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Why nutrients are not limiting in winter?
Salt is rejected from ice due to thermodynamic constrains
on brine salinity Common sense: nutrients should
be rejected from the ice Nutrient fluxes are proportional
to: Ocean-brine gradient of nutrient
concentration Diffusivity (high for growing ice)
Hence, nutrients can be fluxed to the ice.time scales of nutrient uptake is much slower than convection
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Conclusions (1) Ice salinity can reasonably well be simulated
1d models: winter convection, full-depth convection, flushing Timing, magnitude and model sensitivity are uncertain
Ice salinity is an important actor of large-scale ice-ocean dynamics
Ice salinity affect thermodynamics in the Arctic and ice-ocean interactions in the Antarctic
Ice salinity is increasing now as the amount of FY ice increases. Hence, the sensitivity of coupled models may depend on how salinity could be represented
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Conclusions (2)
Brine-ecosystem multi-layer models are quite different from single-layer based models
Brine dynamics allow to simulate vertical structure in ecosystem in a reasonable way
There are brine dynamics-nutrient interactions Transport mode of diatoms is important Brine salinity limitation is the second
important factor after light limiation
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Remaining problems (1)
No thermo-haline coupled term in brine transport equations
Physical inconsistencies in the model (ice/brine density, freezing point, …)
Model results rely on uncertain parameterizations
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Remaining problems (2)• Non-destructive method-based time series
Better account of spatial variability (Hajo’s talk) Less errors at high brine volumes (Phillip’s talk)
• How should vertical diffusivity be parameterized ?• Permeability-porosity relation for wide range of T,S• What are the pathways of seawater during surface flooding ?• Full-depth convection: when, how, how often ?• How to represent 3D subfloe-scale circulations ?• What is the impact of ridged ice desalination?• How to represent gas transfer?• How to design a sound model-data comparison
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The truth about Louvain-la-Neuve Ice Model
THANKS TO: Cc Bitz, Ralph Timmermann, Steve Ackley, Thierry Fichefet, Hugues Goosse, Gurvan Madec and NEMO team, Jean-Louis Tison, Tony Worby, Hajo Eicken, Bruno Delille, Miguel Angel Morales Maqueda, Bruno Tremblay, Ioulia Nikolskaia , Oiivier Lecomte,
Olivier Lietaer, Sylvain Bouillon, Anne de Montety, Christiane Lancelot and Ivan Grozny + forgotten!
The principle is very basic:
A terrific vibration with maximal resonance…
nice model huh?I found inspiration from an African instrument, but I improved it…
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Further reading
Vancoppenolle, M., H. Goosse, A. de Montety, T. Fichefet, B. Tremblay and J.-L. Tison (2010). Modelling brine and nutrient dynamics in Antarctic sea ice : the case of dissolved silica. Journal of Geophysical Research, 115(C2), C02005, doi:/10.1029.2009JC005369.
Vancoppenolle, M., T. Fichefet, H. Goosse, S. Bouillon, G. Madec and M.A. Morales Maqueda (2009a). Simulating the mass balance and salinity of Arctic and Antarctic sea ice. 1. Model description and validation, Ocean Modelling, 27, 33-53, doi:10.1016/j.ocemod.2008.10.005.
Vancoppenolle, M., T. Fichefet, and H. Goosse (2009b). Simulating the mass balance and salinity of Arctic and Antarctic sea ice. 2. Importance of sea ice salinity variations, Ocean Modelling, 27, 54-69.
Vancoppenolle, M. (2008b). Modelling the mass balance and salinity of Arctic and Antarctic sea ice, Phd Thesis, Université Catholique de Louvain, ISBN 978-2-87463-113-9.
Vancoppenolle, M., C. M. Bitz, and T. Fichefet (2007), Summer landfast sea ice desalination at Point Barrow, Alaska: Modeling and observations, Journal of Geophysical Research, 112, C04022, doi:10.1029/2006JC003493.
Vancoppenolle, M., T. Fichefet and C.-M. Bitz (2006) : Modeling the salinity profile of undeformed Arctic sea ice, Geophysical Research Letters, L21501, doi://2006GL028342.
Vancoppenolle, M., T. Fichefet, and C.M. Bitz (2005) : On the sensitivity of undeformed Arctic sea ice to its vertical salinity profile, Geophysical Research Letters, L16502, doi://2005GL023427.