16:30 〜 16:45
[AOS15-05] Distributions and fluctuations of sea ice thickness off the Lützow-Holm Bay, East Antarctica measured by Shipborne Electro-Magnetic induction device
Sea ice thickness off the Lützow-Holm Bay, East Antarctica has been measured by the Shipborne Electro-Magnetic induction device (SEM) onboard icebreakers Shirase (5002) and Shirase (5003) under the Japanese Antarctic Research Expedition (JARE). Since JARE42 (2000). over two decades, SEM has provided the record of total thickness (snow + sea ice) distributions and their interannual variability along the way to/from Syowa station (68.0°-69.1°S, 37.4°-39.6°E).
In this region, sea ice generally consists of first-year drift ice and multi-year fast ice and covered by thick snow. In contrast to stationary growth of landfast ice, drift ice sometime increases their thickness quickly in order to ice deformation process such as rafted ice and pressure ridge formed by strong wave or wind. Ship-based visual observations by the observer or the video monitoring system can record thickness of snow and ice for the ice floe when they are broken and turned sideway along the ship hull. Although this method is valid on the level parts of ice floes, it is very difficult to apply to the deformed ice, because the thick deformed ice is difficult to turn sideway and sometime separates into broken pieces. On the other hand, SEM can measure total thickness not only level ice but also such highly deformed ice without looking the broken side of ice floe.
Calibration and validation of SEM have been conducted by comparing with ice core samples and drill-hole total thickness at the anchoring point of Shirase each year. This study summarized the long-term results of validation of SEM and the distributions and fluctuations of total thickness derived from JARE42-JARE64 voyages. Figure 1 shows the results of the distributions of SEM total thickness from JARE64 (2022). During this expedition, Shirase was stuck by thick defromed drift ice compressed by strong northeasterlly wind in the area of 68.20°-68.38°S.
In this region, sea ice generally consists of first-year drift ice and multi-year fast ice and covered by thick snow. In contrast to stationary growth of landfast ice, drift ice sometime increases their thickness quickly in order to ice deformation process such as rafted ice and pressure ridge formed by strong wave or wind. Ship-based visual observations by the observer or the video monitoring system can record thickness of snow and ice for the ice floe when they are broken and turned sideway along the ship hull. Although this method is valid on the level parts of ice floes, it is very difficult to apply to the deformed ice, because the thick deformed ice is difficult to turn sideway and sometime separates into broken pieces. On the other hand, SEM can measure total thickness not only level ice but also such highly deformed ice without looking the broken side of ice floe.
Calibration and validation of SEM have been conducted by comparing with ice core samples and drill-hole total thickness at the anchoring point of Shirase each year. This study summarized the long-term results of validation of SEM and the distributions and fluctuations of total thickness derived from JARE42-JARE64 voyages. Figure 1 shows the results of the distributions of SEM total thickness from JARE64 (2022). During this expedition, Shirase was stuck by thick defromed drift ice compressed by strong northeasterlly wind in the area of 68.20°-68.38°S.