stefanie arndt, klaus m. meiners, robert ricker,...
TRANSCRIPT
Influence of snow depth and surface flooding on light transmittance through Antarctic sea ice
Stefanie Arndt, Klaus M. Meiners, Robert Ricker, Thomas Krumpen, Christian Katlein, Marcel Nicolaus
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
meltpond
Iceandsnowtransport(dri3)
Lateralmel6ng
Bo9ommel6ng/freezing
Internalmel6ng
Icethickness
Snowdepth
Snowfall
Flooding
Snow-iceforma2on
Internalsnowmelt
Superimposediceforma2on
snow
ice
Internalicelayers
3
Surface energy budget
lead
Incomingshort-waveradia4on Reflectedshort-
waveradia4on
Absorp4on
Transmission
Sca<ering
Oceanheatflux
Incoming/Outgoinglong-waveradia4on
Turbulentheatflux
meltpond
Conduc4veheatflux
ice
ocean
snow
atmosphere Energybudget
Incomingshort-waveradia3on
Reflectedshort-waveradia3on
Absorp3on
Transmission
Sca;ering
Oceanheatflux
ice
ocean
snow
atmosphere Energybudget
4
Importance of transmitted heat fluxes
Mass budget of sea icebottom melt
Energy budget of the upper oceanwarming of the upper ocean
Under-ice ecosystemchanging habitat conditions for ice-associated organisms
lead
Incoming/Outgoinglong-waveradia5on
Turbulentheatflux
meltpond
ice
ocean
snow
atmosphere Energybudget
5
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)
6
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
7
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
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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
Sdry
I
slush Swet= -F
S F ρs
ρi
ρs
ρi
ρsl=ρi
snow (dry)
Non-flooded Flooded
ice
water
S
I
snow (dry)
ice
water
Sdry
I
slush Swet= -F
S F ρs
ρi
ρs
ρi
ρsl=ρi
snow (dry)
Non-flooded Flooded
9
Spectral optical properties
10
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
12
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)
13
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.)