Thickness

  
    
Ice thickness is a key parameter describing the state of the ice cover. During HOTRAX, we measured thickness in three ways: the ice watch, drilling holes, and EM-31surface surveys.

Surface ice surveys followed horizontal transects, which ranged from lengths of hundreds of meters to several kilometers, along which ice thickness and snow depth were measured every five meters. Ice thickness was determined using an EM-31 electromagnetic induction sensor, and snow depth was measured using a calibrated ski pole.

The Geonics EM-31is an electromagnetic induction device that determines the apparent conductivity of the underlying medium based on measurements of the secondary electromagnetic field induced in the underlying ice and the seawater by a transmitter coil . Sea ice tends to have low sea ice conductivities (<50 mS m-1) compared to high seawater conductivities (>2500 mS m-1). The signal received by the instrument is controlled by eddy currents generated at the ice-seawater interface and its strength is related to the ice thickness. The two coplanar transmitter and receiver antenna coils are mounted at a spacing of 3.66 m and operate at 9.8 kHz. The instrument package was carried as shown on the right.


The EM-31 instrument - the ultimate fashion accessory.
   

Summary table of snow depth and ice thickness surveys
 
        Snow depth (cm) Ice thickness (cm)
Site Date Latitude Longitude Count Mean Median Std dev Min. Max. Count % > 6m Mean Median Std dev Min. Max.
1 12-Aug 76 2.119 N 157 55.807 W             208 0.5% 153.6 120.6 68.5 97.1 456.7
2 16-Aug 78 26.319 N 162 40.739 W             209 0.0% 106.2 107.7 12.7 67.5 172.1
3 18-Aug 78 17.493 N 176 40.739 W             134 0.0% 120.2 123.7 24.3 64.3 182.1
4 22-Aug 81 13.565 N 177 11.679 W             227 0.0% 120.0 119.3 8.3 61.4 142.4
5 25-Aug 83 07.844 N 174 40.283 W             449 0.2% 164.8 149.1 52.7 7.9 554.4
6 26-Aug 83 17.947 N 171 53.294             312 0.0% 149.4 133.3 38.9 91.2 317.5
7 26-Aug 83 20.028 N 171 59.351 W             100 24.2% 247.0 212.7 100.6 70.3 690.9
8 27-Aug 84 18.540 N 160 38.867 W             416 9.2% 187.0 158.5 82.4 7.9 725.9
9 28-Aug 84 18.6350 160 25.164 W             244 2.4% 183.9 161.7 55.5 71.9 505.6
10 29-Aug 8418.423 N 149 04.907W             200 21.6% 258.3 248.5 60.7 157.1 534.8
12 30-Aug 83 57.277 N 143 11.516 W 427 1.6 0.0 3.1 0.0 16.0 422 1.2% 187.0 169.5 64.0 55.4 534.8
13 31-Aug 84 10.249 N 150 59.71 W 265 8.0 8.0 3.2 0.0 26.0 257 3.0% 165.1 152.6 47.1 110.2 526.8
14 31-Aug 84 10.249 N 150 59.71 W 109 10.6 10.0 3.7 5.0 26.0 103 5.5% 284.0 252.1 94.8 137.5 611.3
15 2-Sep 85 07.337 N 154 47.979 W 100 5.3 4.0 4.1 1.0 32.0 100 0.0% 171.7 153.1 46.6 110.5 359.0
16 2-Sep 85 58.992 N 162 13.885 W 205 10.0 9.0 3.3 3.0 20.0 203 1.0% 187.8 191.6 40.2 122.5 292.0
17 6-Sep 87 37.205 N 155 52.531 E 255 10.8 10.0 5.7 0.5 45.0 246 3.5% 185.8 157.2 74.3 72.6 535.4
18 6-Sep 87 39.610 N 150 54.091 E 227 8.7 9.0 5.7 0.0 46.0 225 0.9% 141.0 135.8 49.9 61.6 362.8
19 9-Sep 88 27.337 N 146 31.937 E 275 11.6 10.0 5.9 2.0 34.0 266 3.3% 168.8 147.0 65.2 98.0 479.1
20 10-Sep 88 43.065 N 170 97.170 E 235 9.2 8.0 7.0 0.0 41.0 203 13.6% 224.3 202.1 91.6 99.0 547.4
21 10-Sep 88 48 801 N 164 08.136 E 430 7.4 6.0 5.3 0.0 46.0 420 2.3% 173.6 164.1 52.3 88.8 575.3
22 11-Sep 89 28.89 N 169 47.9 E 235 12.4 12.0 6.7 2.0 36.0 201 14.5% 195.2 171.2 77.6 97.5 548.4
23 12-Sep 90 N 0 E 222 12.2 11.0 6.4 2.0 47.0 217 2.3% 164.4 137.6 66.0 101.5 536.4
24 13-Sep 89 22.447 N 89 05.3 W 242 16.0 15.0 8.9 0.0 53.0 187 22.7% 230.9 218.8 96.0 90.2 489.1
25 14-Sep 88 46.932 N 75 6.2 E 241 17.4 17.0 6.0 0.0 40.0 236 2.1% 183.2 173.4 52.2 96.4 426.4
26 15-Sep 88 03.333 N 58 44.9 E 426 16.8 16.0 7.1 1.0 53.0 293 31.2% 230.7 198.6 102.3 104.2 685.9
27 17-Sep 87 28.301 N 57 35.3 E 368 14.8 15.0 4.9 1.0 32.0 362 1.6% 164.4 150.4 58.9 92.7 463.1
28 18-Sep 86 39.394 N 55 37.1 E 409 16.6 15.0 8.8 0.0 53.0 161 60.6% 221.0 201.9 109.5 62.2 610.3
29 20-Sep 85 56.25 N 48 20.1 E 431 12.5 12.0 4.6 0.0 36.0 429 0.5% 159.1 155.9 23.3 99.8 328.1