Sea-Ice Mass Balance

(1)

Sea-Ice Mass Balance

Inﬂuenced by Ice Shelves

Mario Hoppmann

^1,2

Stephan Paul

3

Marcel Nicolaus

¹ Mario.Hoppmann@awi.de ^Contact:

Marcel.Nicolaus@awi.de paul@uni-trier.de

Background

Study area

Top: Our study area of Atka Bay is located near the Ekström Ice Shelf in the southeas- tern part of the Weddell Sea, Antarctica. Floating ice shelves are light grey, grounded ice and land are dark grey. Bottom: TerraSAR-X image from November 2012 showing our sampling sites on the fast ice in 2012 (white circles). The colored borders indicate diﬀerent sea-ice regimes; Green: deformed second-year ice;

blue: ﬁrst year ice; red: new ice (September)

Methods

Selected Results

Mass balance

Energy Balance

External forcing

Biomass

Drillings,

ůĞĐƚƌŽŵĂŐŶĞƟĐƐ

Snow

Thermistor strings ͬƵƚŽŵĂƟĐǁĞĂƚŚĞƌƐƚĂƟŽŶ

Sea-ice cores Under-ice

CTD casts

Camera

Spectral radiometer

Upscaling

Sea Ice / Ocean model

&ĂƐƚ/ĐĞEĞƚǁŽƌŬ

^ŶŽǁƉŝƚƐ͕

ƐŶŽǁďƵŽǇƐ

Platelets

Remote sensing

Research Questions

1. Which are the most important formation processes of Atka Bay land fast sea-ice, and to what extent do nearby ice shelves inﬂuence sea-ice

growth?

2. How does the snow cover inﬂuence landfast sea-ice mass balance and energy budget?

3. What is the seasonality of surface energy budget and particularly, light transfer through snow and sea ice?

4. Which are the most important sea-ice and snow processes aﬀecting the backscatter of visible, thermal and microwave parts of the electro

magnetic spectrum with regard to satellite observations?

5. How representative is the fast ice cover of Atka Bay, compared to other fast ice regions around the coastline?

We are most grateful to the overwintering teams at Neumayer III for their commitment and the outstanding ﬁeld work in this harsh environment. We highly acknowledge the professional advice and help of numerous scientists, technicians and other supporters at AWI and University of Trier who are involved in our project. This work was supported by the Deutsche Forschungsgemeinschaft (DFG) in the framework of the priority programme "Antarctic Research with comparative investigations in Arctic ice areas" by grants NI 1092/2, HE 2740/12.

We use a variety of methods to investigate the research questions outlined above. The in- terdisciplinary nature of this project combines methods of Geophysics, Meteorology, Ocea- nography, Biology, Optics and traditional Sea Ice Physics with numerical simulations and remote sensing. Pioneering methods include multifrequency EM, a mobile under-ice camera and a special conﬁguration of spectral radiation measurements.

Top right: Sea-ice thickness, snow depth, free- board and sub-ice platelet layer thickness at dril- ling sites on Atka Bay landfast sea ice in 2012.

The large sea-ice thickness is mostly a result of in- corporation of accumulated platelets. A thick snow cover insulates the sea ice and is responsi- ble for surface ﬂooding.

Top left: Sensible and latent heat ﬂuxes measured by an Eddy Covariance station at ATKA03 in Nov/Dec 2012.

- On average, sensible and latent heat ﬂuxes are directed from surface to atmosphere (3 W/m² and 10 W/m² respectively).

- Sea ice emerged as a CO₂ sink ( -2 µmol/m²).

- Large ﬂuctuations ( -15 to +6 µmol/m²) correspond to storm events and/or high temperatures.

Grounding Line

Sea Floor

Ekström Ice Shelf

Neumayer III

Landfast Sea Ice

20 km 200

0

500

1000 [m]

Marine Ice

ĂƐĂůŵĞůƟŶŐ

platelet layer

1 Warm, saline water masses enter the ice shelf cavity ϮĂƐĂůŵĞůƟŶŐůĞĂĚƐƚŽƚŚĞĨŽƌŵĂƟŽŶŽĨǀĞƌǇĐŽůĚ͕ůĞƐƐ saline Ice Shelf Water (ISW).

3 ISW rises, the plume becomes supercooled (freezing point depends on pressure!). Supercooling is relieved ƚŚƌŽƵŐŚĨŽƌŵĂƟŽŶŽĨĐƌǇƐƚĂůƐ͕ƐŽĐĂůůĞĚŝĐĞƉůĂƚĞůĞƚƐ͘

ϰƌǇƐƚĂůƐŇŽĂƚƵƉǁĂƌĚƐ͕ĂŶĚĂĐĐƵŵƵůĂƚĞďĞůŽǁůĂŶĚĨĂƐƚ sea ice, where they are incorporated into the fabric.

1 2 3

4 ^ĐŚĞŵĞŽĨŝĐĞƉůĂƚĞůĞƚĨŽƌŵĂƟŽŶ;͞/ĐĞWƵŵƉ͞Ϳ

Top: Electromagnetic thickness survey in November 2012. The ﬁlled area (bright blue) represents EM31 total thickness (sea ice + snow) ; the triangles indicate simul- taneously measured snow depths; the green squares are sea-ice thicknesses from regular drillings; the blue circles represent platelet layer depths.

Right: Sea-ice crystal structure from a core retrieved at ATKA11 in December 2012.

Sea ice started to grow in September, when platelets were already present at the surface. Short periods of columnar growth are interrupted by a platelet-dominated fabric. The top 15 cm show a characteristic snow-ice texture as a consequence of ﬂooding under heavy snow load. Mixed columnar/platelet and pure platelet texture account for more than 50 % of the total core length. Crystal alignments are shown in Schmidt diagrams on the right. Similar results were obtained for ATKA24 (181 cm).

? ??

Sorasen Ridge

Quar Ice Shelf

Ekström Ice Shelf

Jelbart Ice Shelf

Halvfarryggen Ridge

Unneruskollen Island

0 12,5 25 50 75 100

Kilometers

Weddell Sea

Atka Bay Weddell Sea

#*

#

*

#

*

#*

#

*

#*

7°30'W 7°40'W

7°50'W 8°0'W

8°10'W 8°20'W

70°30'S 70°28'S

70°32'S

70°34'S

70°36'S

70°38'S

70°40'S

0 1,5 3 6 9 12

km

Ü

Ekström Ice Shelf Seasonal

Landfast Sea Ice

Atka Bay

Atka Ice Rise

TerraSAR-X 2012-11-27

Neumayer III

ATKA03 ATKA07

ATKA11

ATKA16 ATKA21

ATKA24 Iceberg B15G

Sea ice fastened to coasts, icebergs and ice shelves is of crucial importance for climate- and ecosystems. At the same time, it is not represented in climate models and many processes aﬀecting its energy- and mass balance are currently only poorly understood. Near Antarctic ice shelves, which fringe about 44 % of the coastline, this landfast sea ice exhi- bits unique characteristics that distinguish it from most other sea ice:

1. Ice platelets form and grow in supercooled water masses, which originate from cavi- ties below the ice shelves. These crystals rise to the surface, where they accumulate be- neath the solid sea-ice cover. Through freezing of interstitial water they are incorporated into the sea-ice fabric as platelet ice.

2. A thick and highly stratiﬁed snow cover accumulates on the fast ice, altering the re- sponse of the surface to remote sensing and aﬀecting sea-ice energy- and mass balance.

Combining a variety of methods from diﬀerent disciplines, we aim to improve our under- standing of Antarctic sea-ice, its interaction with ice shelves and its role in the climate system. Here we present our major research questions, introduce our methods and present some exemplary results.

1 Alfred Wegener Institute, Bremerhaven, Germany; ²Jacobs University Bremen, Germany; ³University of Trier, Germany

Günther Heinemann

³

Sascha Willmes

³

Ralph Timmermann

¹

NI 1092/2 HE 2740/12

−50

−30

−10 10 30 50

25.11.2012 30.11.2012 5.12.2012 10.12.2012 15.12.2012 20.12.2012 25.12.2012 30.12.2012

−50

−30

−10 10 30 50

Turbulent Sensible Heatflux in W/m²

−50

−30

−10 10 30 50

−50

−30

−10 10 30 50

Turbulent Latent Heatflux in W/m²

25.11.2012 30.11.2012 5.12.2012 10.12.2012 15.12.2012 20.12.2012 25.12.2012 30.12.2012

−15

−10

−5 0 5 10

−15

−10

−5 0 5 10

Turbulent Flux of CO2 in µmol/m²

Jun Jul Aug Sep Oct Nov Dec Jan Feb

−9

−8

−7

−6

−5

−4

−3

−2

−1 0 1

−9

−8

−7

−6

−5

−4

−3

−2

−1 0 1

−9

−8

−7

−6

−5

−4

−3

−2

−1 0 1

−9

−8

−7

−6

−5

−4

−3

−2

−1 0 1

−9

−8

−7

−6

−5

−4

−3

−2

−1 0 1

−9

−8

−7

−6

−5

−4

−3

−2

−1 0 1

ATKA03 ATKA07

ATKA11

ATKA16

ATKA24 ATKA21

Date in 2012/13

Distance to sea-ice surface [m]

max snow depth min snow depth max ice thickness min ice thickness mean freeboard mean platelet depth IMB ice thickness

−8.1 −8 −7.9 −7.8 −7.7 −7.6 −7.5

−8

−6

−4

−2 0

Longitude

Depth [m]

ATKA11 ATKA16 ATKA21

ATKA24

ATKA03 ATKA07

3 cm

15 cm

25 cm

35 cm

53 cm

63 cm

73 cm

snow ice granular columnar

platelet

columnar/platelet

707 axes

521 axes

176 axes

269 axes

187 axes

Questions? Don‘t hesitate to ask

Sea ice + snow (m)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

0 0.2 0.4 0.6 0.8 1 1.2 1.4

total thickness [m]

probability density

Mean: 2.4796 Median: 2.76 StdDev: 0.84963

EM-survey:

see results