Supercooled water in an Arctic polynya: observations and modeling
Supercooled water in an Arctic polynya: observations and modeling
复制标题
北极冰间湖中的过冷水：观测和建模
DOI：
10.3189/002214309788608840
复制
发表时间：
2009
影响因子：
3.4
通讯作者：
L. Smedsrud
中科院分区：
文献类型：
--
作者：
R. Skogseth;F. Nilsen;L. Smedsrud
摘要 介绍了 2006 年 4 月对斯瓦尔巴群岛 Storfjorden 活动冰间湖进行的原位实地测量。估计为 400 W m−2 的地表热通量产生了碎冰，在由东北冷风驱动的冰间湖事件结束时，碎冰被平流远离固定冰边缘。通过附带的水样校准了冰间湖固定冰边缘的电导率、温度和深度，并揭示了在 5 m 深的水柱中持续 3 天的过冷事件。由于冰生长过程中盐水的释放，表面盐度达到 35.9 psu。测得的最大过冷度为地表附近原位冰点以下0.037±0.005℃，底部为0.016±0.005℃；表面和底部之间的平均过冷梯度为0.020±0.005°C。这些测量结果与一维碎冰模型的结果一致，证实了这种过冷水平是可以预期的。由于表面层的平流作用，水中的冰浓度被模拟为低于 0.02 g L−1。从沿固定冰边缘平流受阻的地方采集的 7 个冰片/油脂冰样本显示，平均盐度为 26.2 psu，表明油脂冰中含有 25% 的冰片和 75% 的海水。在测量期间，由于较少的盐水取代了新形成的富含盐水的陆架水流向 Storfjorden 的更深部分，水柱盐度有所下降。当风向转向东方时，过冷现象就停止了，气温升高，温暖且盐分减少的海水被北向的埃克曼输送带推入斯托峡湾。这是对活跃的北极冰间湖进行的首次现场观测，同时对水文学和碎冰进行采样，并且过冷度是近年来利用现代精确仪器观测到的最大值。
Abstract In situ field measurements of an active polynya in Storfjorden, Svalbard, during April 2006 are presented. A surface heat flux, estimated to be 400 W m−2, produced frazil ice that was advected away from the fast ice edge during the end of a polynya event driven by cold winds from the northeast. Conductivity, temperature and depth casts from the fast ice edge of the polynya were calibrated by accompanying water samples, and reveal a supercooling event that lasted for 3 days in a 5 m deep water column. Surface salinity reached 35.9 psu from brine release during ice growth. The maximum supercooling measured was 0.037 ± 0.005 ° C below the in situ freezing point near the surface and 0.016 ± 0.005 ° C at the bottom; the mean supercooling gradient was 0.020 ± 0.005 ° C between the surface and the bottom. These measurements are consistent with results from a one-dimensional frazil ice model, confirming that such supercooling levels can be expected. Frazil ice concentrations in the water were modeled to be lower than 0.02 g L−1, due to advection in the surface layer. Seven frazil/grease ice samples taken from a place where advection was blocked along the fast ice edge showed a mean salinity of 26.2 psu, indicating 25% frazil ice and 75% sea water in the grease ice. The water-column salinity decreased during the measurement period due to less saline water replacing newly formed brine-enriched shelf water flowing down to deeper parts of Storfjorden. The supercooling ceased when the wind direction turned to the east, with higher air temperatures and warmer and less saline water being pushed into Storfjorden by the northward Ekman transport. These are the first in situ observations from an active Arctic polynya with concurrent sampling of hydrography and frazil ice, and the supercooling is the maximum observed in recent years with modern and accurate instrumentation.