Drill hole measurements of fast ice and sub-ice platelet layer thickness, and snow depth in McMurdo Sound - November/December 2011@en

The thicknesses of sea ice and sub-ice platelet layer were measured at regular intervals on fast ice in McMurdo Sound, Antarctica in November and December of 2011. Thirty-metre cross-profiles were established at each site, and snow depths were measured at 0.5 m intervals along the transect lines with a metal ruler. A mean snow depth for each site was derived from these 120 measurements. Freeboard, sea ice thickness and sub-ice platelet layer thickness were recorded at five locations at each site - at the central crossing point and at the end points of each transect. The mean of these was then calculated and taken as representative of the site. Ice thicknesses were measured by using a tape measure with a brass T-anchor attached at the zero mark. This was deployed vertically through the drill-hole and allowed to rotate to a horizontal alignment when exiting the bottom of the drill-hole at the ice-ocean interface. From this position the anchor is slowly pulled upwards until some resistance is met and the first measurement is taken. This resistance is taken to mark the sub-ice platelet layer/ocean interface. The tape measure is then pulled harder, forcing the bar to pass through the sub-ice platelet layer until it sits flush against the sea ice/sub-ice platelet layer interface where a second measurement is taken. Measurement sites were about 5 km apart.2011年11月至12月，研究人员于南极洲麦克默多湾（McMurdo Sound）的固定冰（fast ice）上按固定间隔开展观测，采集海冰厚度与冰下片状冰晶层（sub-ice platelet layer）厚度数据。每个观测站点均布设了30米长的交叉断面测线，沿测线以0.5米为间隔使用金属钢尺测量积雪深度，总计获得120组测量值，据此计算得到各站点的平均积雪深度。在每个站点的5个位置记录干舷（freeboard）、海冰厚度及冰下片状冰晶层厚度，分别为断面交叉中心点与各测线的端点位置，随后对这5组测量值取平均，作为该站点的代表性观测数据。冰厚测量采用零点末端附有黄铜T形锚的卷尺完成：将卷尺垂直穿过钻孔，当锚在冰-洋界面处穿出钻孔底部后，卷尺可旋转至水平姿态。此时缓慢向上提拉卷尺，直至感受到阻力，此时记录第一组测量值，该阻力对应的位置标记为冰下片状冰晶层-海洋界面。随后继续用力提拉卷尺，使T形锚穿过冰下片状冰晶层，直至其紧贴海冰-冰下片状冰晶层界面，此时记录第二组测量值。各测量站点之间的间距约为5千米。