Freezing lakes and lake ice

Содержание

1. Freezing lakes and lake ice
2. Subglacial lakes
3. Epiglacial lakesAt Lasarevskaya station, Dronning Maud LandVatnajökull, Iceland
4. Supraglacial lakes on DML
5. Supraglacial lakesLakes (’wetlands’)grow in blue ice spotsSolid
6. Topics and motivationLake structure (vertical/lateral)Surface mass and
7. Supraglacial lakes in DMLlee side, separation zoneBlue
8. 15 January 200573°02.8’S 13°28.7’W200 m above sea level400 m below top of nunatak 15 January 2011
9. FieldworkProfiling the lake structureIce and water samplesPumping
10. DML supraglacial lakes are seasonalForm in November
11. Soft, bog-like boundary zoneThe hydraulic conductivity in
12. SampleProfileProfiling of the lakeCover (0-30 cm)Water body
13. Evolution of the vertical profile2014 – 2015: stophere end of December
14. Qs0
15. Heat and mass budget of Lake SuvivesiRadiation
16. Supraglacial lakes: temperature structureNegative radiation balance at
17. Albedo 0.4 – 0.6
18. Stability accounted for(significant)
19. Слайд 19
20. PAR scalar irradiance at 60 cm depth2500 unitsCorrespondto planarIrradiancepower of50 W/m2
21. Three summers2004-05 and 2010-11Surface ice layer 0
22. Scaling of lake bodyGrowth (H)k – light
23. Ice growthMean temp -15ºC, 10 months: 2
24. Water quality and ecosystems of supraglacial lakesUltraoligotrophic
25. Слайд 25
26. ConclusionsSupraglacial lakes presently seasonal in DMLNet liquid
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Subglacial lakes

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Слайд 1Freezing lakes and lake ice
Introduction
(2) Growth and melting
(3) Proglacial lakes
(4)

Lake ice climatology

Слайд 2Subglacial lakes

Слайд 3Epiglacial lakes
At Lasarevskaya
station,
Dronning Maud Land

Vatnajökull, Iceland

Слайд 4Supraglacial lakes on DML

Слайд 5Supraglacial lakes
Lakes (’wetlands’)grow in blue ice spots
Solid body  melts

to a lake, inversely as in wintertime boreal lakes
Formation and

closure solved with a 2-phase model
Layered structure due to radiation absorption by sediments

Ice cover (0-10 cm)

Water body 120+x cm)

Interim layer 20 - 20+x cm

Slush, sedment particles
20 – 20+x cm

Hard glacier ice

Supraglacial lakesLakes (’wetlands’)grow in blue ice spotsSolid body  melts to a lake, inversely as in wintertime

Слайд 6Topics and motivation
Lake structure (vertical/lateral)
Surface mass and heat balances
Thermodynamics
Conclusions

Absorption of

solar radiation ~ 5 times more than for snow cover
Seasonal

[stable]  perennial [unstable]
Water very clean, ultra-oligotrophic  life in extreme conditions

Study Lakes at nunataks
Basen (Lake Suvivesi, main lake)
Plogen and Fossilryggen
(comparisons), 30 and 50 km
distance from Basen

Topics and motivationLake structure (vertical/lateral)Surface mass and heat balancesThermodynamicsConclusionsAbsorption of solar radiation ~ 5 times more than

Слайд 7Supraglacial lakes in DML
lee side,
separation zone
Blue ice surface
Blue ice

spots (1% of surface area)
 Negative surface

mass balance
Often in the vicinity of nunataks

Supraglacial lakes in DMLlee side, separation zoneBlue ice surfaceBlue ice spots (1% of surface area)

Слайд 815 January 2005
73°02.8’S 13°28.7’W
200 m above sea level
400 m below

top of nunatak

15 January 2011

Слайд 9Fieldwork
Profiling the lake structure
Ice and water samples
Pumping tests (hydraulic conductivity)
Radiation

balance
Weather station at lake and at Aboa on Basen

FieldworkProfiling the lake structureIce and water samplesPumping tests (hydraulic conductivity)Radiation balanceWeather station at lake and at Aboa

Слайд 10DML supraglacial lakes are seasonal
Form in November – December
Lake

Suvivesi max extent 5 km2
Lake Suvivesi max depth 1.5 –

2 m
Close in April – May  Seasonal
Change to perennial ?: Residual subsurface water pocket  Volume increase year by year  Catastrophic breakage

DML supraglacial lakes are seasonalForm in November – December Lake Suvivesi max extent 5 km2Lake Suvivesi max

Слайд 11Soft, bog-like boundary zone
The hydraulic conductivity in the bog varied
from

0.25 to 30 cm s-1 . By a controlled experiment,
the

conductivity of closely packed slush mass was
obtained as 6.3 cm s-1 .

Margin ‘bog’
Core lake

Soft, bog-like boundary zoneThe hydraulic conductivity in the bog variedfrom 0.25 to 30 cm s-1 . By

Слайд 12Sample
Profile
Profiling of the lake
Cover (0-30 cm)
Water body
(max 120+x cm)
Internal

ice layer (20 - 20+x cm)
Slush, particles (20 – 20+x

cm)

Hard glacier

SampleProfileProfiling of the lakeCover (0-30 cm)Water body (max 120+x cm)Internal ice layer (20 - 20+x cm)Slush, particles

Слайд 13Evolution of the vertical profile
2014 – 2015: stop
here end of

December

Слайд 14Qs0

Слайд 15Heat and mass budget of Lake Suvivesi
Radiation balance dominant
Solar altitude

40 deg at midsummer noon
Clear sky typical
Light attenuation depth 

1 m (strong scattering)

Surface normally covered by thin ice
Sublimation 5 – 10 cm in summer

Net radiation at surface close to zero
Radiation into ice >> 0
Sensible heat flux around zero (T_air < T_surface)
Latent heat flux < 0 and significant, dry air
Liquid precipitation very rare

Heat and mass budget of Lake SuvivesiRadiation balance dominantSolar altitude 40 deg at midsummer noonClear sky typicalLight

Слайд 16Supraglacial lakes: temperature structure
Negative radiation balance at surface (cold skin

phenomenon)
Temperature increases down to warm layer  light penetration and

thermal diffusion
Heat loss to deep ice from lake bottom, stable and small, 1 – 5 W/m2

Lake
body

Supraglacial lakes: temperature structureNegative radiation balance at surface (cold skin phenomenon)Temperature increases down to warm layer 

Слайд 17Albedo 0.4 – 0.6

Слайд 18Stability accounted for
(significant)

Слайд 19

Слайд 20PAR scalar irradiance at 60 cm depth
2500 units
Correspond
to planar
Irradiance
power of
50

W/m2

PAR scalar irradiance at 60 cm depth2500 unitsCorrespondto planarIrradiancepower of50 W/m2

Слайд 21Three summers
2004-05 and 2010-11
Surface ice layer 0 – 10 cm

at min ( surface heat balance ~ 0)
Liquid water layer

production ~ 1 m (2 cm/day or 60 W/m2 solar power)

2014-2015 (cold)
Surface ice layer 20 – 30 cm at min ( surface heat balance < 0)
Liquid water layer production ~ 1/2 m (1 cm/day or 30 W/m2 solar power)

Difference: 2014 – 15 higher reflectance and more windy weather

Three summers2004-05 and 2010-11Surface ice layer 0 – 10 cm at min ( surface heat balance ~

Слайд 22Scaling of lake body
Growth (H)
k – light atten. depth
Q* -

sunlight to ice
t – length of summer
n0 –porosity of ice

when strength lost
rL – latent heat of freezing

Closing (h)
S – freezing-degree-days
a  thermal conductivity, latent heat, porosity
b  ice-air heat transfer

Surface ice layer:
h0=kT0/Q0(T0)

Scaling of lake bodyGrowth (H)k – light atten. depthQ* - sunlight to icet – length of summern0

Слайд 23Ice growth
Mean temp
-15ºC, 10 months: 2 m growth
Bottom growth:

flux ~ 3 W/m2  1 mm/day or 30 cm/10

months
In present climate lakes close up.

cold deep ice

cold winter air

Month (Jan – Dec)

Ice growthMean temp -15ºC, 10 months: 2 m growthBottom growth: flux ~ 3 W/m2  1 mm/day

Слайд 24Water quality and ecosystems of supraglacial lakes
Ultraoligotrophic
Conductivity < 10

mS/cm (25°C)
Phytoplankton < 10 mg/m3
Lakes have own ecosystem overwintering in

the ice
Light well available in summer (snow-free surface)
Phosphorus limiting factor
Species ~ 50 (global)

Macro algae

Skua

ciliates

Water quality and ecosystems of supraglacial lakesUltraoligotrophic Conductivity < 10 mS/cm (25°C)Phytoplankton < 10 mg/m3Lakes have own

Слайд 25

Слайд 26Conclusions
Supraglacial lakes presently seasonal in DML
Net liquid water production ½

- 1 m layer, sensitive to turbulent heat fluxes
Possess ice

cover
Potential winter ice growth 2 m
Light attenuation depth ~ 1 m ~ lake depth

Future efforts
All-year data (automatic station)
1-D to 3-D modelling
Lakes from different sectors of Antarctica (collaboration with AARI, SPb)

ConclusionsSupraglacial lakes presently seasonal in DMLNet liquid water production ½ - 1 m layer, sensitive to turbulent

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Freezing lakes and lake ice

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Слайды и текст этой презентации

Слайд 1Freezing lakes and lake iceIntroduction(2) Growth and melting(3) Proglacial lakes(4)

Lake ice climatology

Слайд 2Subglacial lakes

Слайд 3Epiglacial lakesAt Lasarevskaya station, Dronning Maud LandVatnajökull, Iceland

Слайд 4Supraglacial lakes on DML

Слайд 5Supraglacial lakesLakes (’wetlands’)grow in blue ice spotsSolid body  melts

to a lake, inversely as in wintertime boreal lakesFormation and

Слайд 6Topics and motivationLake structure (vertical/lateral)Surface mass and heat balancesThermodynamicsConclusionsAbsorption of

solar radiation ~ 5 times more than for snow coverSeasonal

Слайд 7Supraglacial lakes in DMLlee side, separation zoneBlue ice surfaceBlue ice

spots (1% of surface area)  Negative surface

Слайд 815 January 200573°02.8’S 13°28.7’W200 m above sea level400 m below

top of nunatak 15 January 2011

Слайд 9FieldworkProfiling the lake structureIce and water samplesPumping tests (hydraulic conductivity)Radiation

balanceWeather station at lake and at Aboa on Basen

Слайд 10DML supraglacial lakes are seasonalForm in November – December Lake

Suvivesi max extent 5 km2Lake Suvivesi max depth 1.5 –

Слайд 11Soft, bog-like boundary zoneThe hydraulic conductivity in the bog variedfrom

0.25 to 30 cm s-1 . By a controlled experiment,the

Слайд 12SampleProfileProfiling of the lakeCover (0-30 cm)Water body (max 120+x cm)Internal

ice layer (20 - 20+x cm)Slush, particles (20 – 20+x

Слайд 13Evolution of the vertical profile2014 – 2015: stophere end of

December

Слайд 14Qs0

Слайд 15Heat and mass budget of Lake SuvivesiRadiation balance dominantSolar altitude

40 deg at midsummer noonClear sky typicalLight attenuation depth 

Слайд 16Supraglacial lakes: temperature structureNegative radiation balance at surface (cold skin

phenomenon)Temperature increases down to warm layer  light penetration and