Sea-Ice Mass Balance
Influenced by Ice Shelves
Mario Hoppmann
1,2Marcel Nicolaus
1Ralph Timmermann
1Mario.Hoppmann@awi.de Contact:
Marcel.Nicolaus@awi.de heinemann@uni-trier.de
Background Study area
Top: Our study area of Atka Bay is located near the Ekström Ice Shelf in the southeastern part of the Weddell Sea, Antarctica. Floating ice shelves are light grey, grounded ice and land are dark grey. Bottom: TerraSAR-X image from June 2010 showing our drilling sites in 2010 (red), 2011 (black) and the site of autonomous measurements in 2011 (AWS).
Methods
Some 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
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^ŶŽǁƉŝƚƐ͕
ƐŶŽǁďƵŽLJƐ
Platelets
Remote sensing
Research Questions
1. Which are the most important formation processes of Atka Bay landfast 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 backscat- ter of visible, thermal and microwave parts of the electromagnetic 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. We would like to express our gratitude towards the German Research Council (DFG), which partly funded this research in its priority program “Antarctic Research with comparative investigations in Arctic ice areas” (NI 1092/2, HE 2740/12 ).
We use a variety of methods to investigate the research questions outlined above. The interdisciplinary nature of this project combines methods of Geophysics, Meteorology, Oceanography, Biology, Optics and traditional Sea Ice Physics with numerical simulati- ons and remote sensing. Pioneering methods include multifrequency EM, a mobile under-ice camera and a special configuration of spectral radiation measurements.
−8.1 −8 −7.9 −7.8 −7.7 −7.6 −7.5
−4
−2 0 2
Longitude
Depth [m] snow (stake)
sea ice (EM31) snow (drillings) sea ice (drillings)
Jun Jul Aug Sep Oct Nov Dec Jan Feb
−3
−2.5
−2
−1.5
−1
−0.5 0 0.5 1 1.5
Jun Jul Aug Sep Oct Nov Dec Jan Feb
−3
−2.5
−2
−1.5
−1
−0.5 0 0.5 1 1.5
Jun Jul Aug Sep Oct Nov Dec Jan Feb
−3
−2.5
−2
−1.5
−1
−0.5 0 0.5 1 1.5
Jun Jul Aug Sep Oct Nov Dec Jan Feb
−3
−2.5
−2
−1.5
−1
−0.5 0 0.5 1 1.5
Distance from top of sea-ice (m)
Jun Jul Aug Sep Oct Nov Dec Jan Feb
−3
−2.5
−2
−1.5
−1
−0.5 0 0.5 1 1.5
Jun Jul Aug Sep Oct Nov Dec Jan Feb
−3
−2.5
−2
−1.5
−1
−0.5 0 0.5 1 1.5
max snow depth min snow depth mean freeboard min ice thickness max ice thickness
B03
B24 B21
B16
B11 B07
2011
1.5 2 2.5 3 3.5 4 4.5
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14
Total thickness [m]
Frequency
Sea-ice thickness, snow depth and freeboard at drilling sites on Atka Bay landfast sea ice in 2011.
Each measurement comprised five drillings.
Ice platelets were observed in half of the boreholes.
Sea-ice in the West is influenced by pressure ridging, as opposed to the thermodynamically grown East. Snow depth is higher in the West, due to redistribution by easterly winds.
Electromagnetic thickness survey and manual snow
measurements on 18 November 2011. Results agree well with manual drillings.
Left: total thickness distribution (sea-ice+snow) from above EM survey. Modal thickness is 2.6 m.
Right: Temperatures of air, snow, sea ice and ocean in August and September 2011 measured by thermistor string. Evolution of sea-ice interfaces and thermody- namic properties can be derived.
Top: wind forcing between August and December 2011: per- sistent easterly winds are stron- gest, and force sea-ice towards West.
Middle: snow depth measured by ultrasonic pinger; accumulati- on is highest in July, October and November.
Bottom: daily mean surface Albedo varies between 0.53 and 0.98, and stays around 0.85 later in the season.
Grounding Line
Sea Floor
Ekström Ice Shelf
Neumayer IIILandfast Sea Ice
20 km 200
0
500
1000 [m]
Marine Ice
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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
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Sorasen Ridge
Quar Ice Shelf
Ekström Ice Shelf
Jelbart Ice Shelf
Halvfarryggen Ridge
Unneruskollen Island
µ
Weddell Sea 0 12,5 25 50 75 100KilometersAtka Bay
Rüssel
Ice Rumple
Sichel
Ice Rumple
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A24 A17 A21
A12 A14 A11
A07 A08 A03 A04
A00
B21 B24 B11 B16
B03 B07
Neumayer
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AWS
0 2 4 8 12 16
km
Ekström Ice Shelf
Atka Ice Rise
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Atka Bay
TerraSAR-X 2011-06-05 DLR 2011 in collab. with A.Humbert LAN0013
Weddell Sea
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 pro- cesses 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 two 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 partly multi-year 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.
In order to improve our understanding of these processes, we perform a continuous measurement program on the landfast sea ice of Atka Bay, Antarctica, contributing to the international Antarctic Fast Ice Network (AFIN). In addition, we will intensify our measurements during two field campaigns. Here we present our major research que- stions, introduce our methods and present first results.
1 Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany; 2 Jacobs University Bremen, Germany; 3 University of Trier, Germany
