Influence of snow depth and surface flooding on light transmittance through Antarctic sea ice

Influence of snow depth and surface flooding on light transmittance through Antarctic sea ice

ocean Antarctic

snow ice

2

Temporal evolution of surface properties

Year-round snow cover Seasonal changes in snow properties dominated by e.g.

§  Diurnal freeze-thaw cycles

§  Internal snowmelt

ice

ocean

snow lead

atmosphere

melt pond

Ice and snow

transport (dri3)

Lateral mel6ng Bo9om

mel6ng/ freezing

Internal mel6ng

Ice thickness

Snow depth Snowfall

Flooding Snow-ice forma2on Internal snowmelt

Superimposed ice forma2on

snow

ice

Internal ice layers

Surface energy budget

lead

Incoming short-

wave radia4on Reflected short- wave radia4on Absorp4on

Transmission Sca<ering

Ocean heat flux Incoming/

Outgoing long- wave radia4on Turbulent

heat flux

melt pond

Conduc4ve heat flux

ice

ocean snow

atmosphere Energy budget

Incoming short- wave radia3on

Reflected short- wave radia3on

Absorp3on

Transmission Sca;ering

Ocean heat flux

ice

ocean snow

atmosphere Energy budget

Importance of transmitted heat fluxes

Mass budget of sea ice


bottom melt

Energy budget of the upper ocean


warming of the upper ocean

Under-ice ecosystem


changing habitat conditions for ice-associated organisms

lead

Incoming/

Outgoing long- wave radia5on Turbulent

heat flux

melt pond

ice

ocean snow

atmosphere Energy budget

Study side and measurements

Measurements:

§  Spectral solar radiation measurements: Remotely Operated Vehicle (ROV)

§  Total sea-ice thickness: Multi-frequency electromagnetic induction (GEM-2)

§  Snow depth: Magna Probe WISKEY

= Winter study on Sea ice and KEY species 14 August to 16 October 2013

Arndt et al., 2017 (under review, JGR)

Physical properties of the pack ice floe

Sea-ice thickness, I:

mean(I) = 0.93 ± 0.45 m

Snow depth, S:

mean(S) = 0.39 ± 0.13 m

Transmittance, T:

mean(T) = 0.0024 (0.24%) mode(T) = 0.0008 (0.08%)

Antarctic pack ice transmits less than 0.1% of the incoming solar radiation during early spring

Physical properties of the pack ice floe

Sea-ice thickness, I:

mean(I) = 0.93 ± 0.45 m

Snow depth, S:

mean(S) = 0.39 ± 0.13 m

Ice freeboard, F:

mean(F) = -0.08 ± 0.10 m

Physical properties of the pack ice floe

Ice freeboard, F:

mean(F) = -0.08 ± 0.10 m

ice water

S

I

snow ^(dry)

ice water

S_dry

I

slush

S_wet

= -F

F ρ_s S

ρ_i

ρ_s

ρ_i ρ_sl=ρ_i

snow ^(dry)

Non-flooded Flooded

ice water

S

I

snow ^(dry)

ice water

S_dry

I

slush

S_wet

= -F

F ρ_s S

ρ_i

ρ_s

ρ_i ρ_sl=ρ_i

snow ^(dry)

Non-flooded Flooded

Spectral optical properties

Spectral optical properties

Normalized difference indices (NDI) of under-ice irradiance spectra:

!"# = !_! !_! − !_!(!_!)

!_! !_! + !_!(!_!)

λ₁, λ₂: wavelength pairs (Mundy et al., 2007)

Correlation surfaces of normalized difference indices (NDI) for snow depth

Non-flooded Flooded

correlation: 0.52 correlation: 0.57

The heterogeneous snow on Antarctic pack ice obscures a direct correlation between the under-ice light field and snow depth

Katlein, Arndt et al., 2015

Summer&

Melt& Freeze&

Winter& Winter&

snow% snow%

ice% ^melt%_pond%

ocean%

Optical properties highly correlated with snow surface properties (e.g.

melt ponds)

Light transmittance significant higher
 (summer FYI: 0.09, summer MYI: 0.05)

Comparison with Arctic studies

Conclusions

Antarctic pack ice transmits less than 0.1% of the incoming solar radiation during early spring

Ice freeboard and related flooding at the snow/ice interface dominates the spatial variability of the under-ice light regime Limitation in the use of snow-NDI prevents estimating light transmission from snow depth and vice versa

In contrast to Arctic sea ice, the dependency of light

transmittance of Antarctic sea ice on its surface properties is more obscure

Ice freeboard

Transmittance

Snow depth correlation

Arndt et al., 2017 (under review, JGR)

Outlook

New field data sets for improved process understanding of the vertical snow layer

Comparison of relations of surface properties and (spectral) light transmittance in the Weddell Sea (WISKEY) with East Antarctic (e.g. SIPEX-2)

Antarctic-wide up-scaling approaches of the under-ice light field require more detailed field data and analysis

Application of existing Chlorophyll-a –NDI for Weddell Sea on WISKY data set to investigate spatial variabilities in Chlorophyll-a (Meiners, Arndt et al., in prep.)