北极阿蒙森湾一年冰物理和光学性质的观测研究

Physical and optical properties of the first-year ice in the Amundsen Gulf of the Arctic

利用加拿大环极冰间水道系统研究项目,作者对2007年11月24日至2008年1月26日北极群岛阿蒙森湾海域秋冬季节一年冰的物理和光学性质进行了观测研究。结果显示,观测期间的海冰厚度整体在27~108 cm范围内变化,积雪厚度仅为0~6 cm。海冰温度、盐度和密度在冰内的分布特征为:海冰表层最低温度为–22.4℃,底层最高温度为–2.2℃,冰内温度随深度单调增大;盐度变化范围为3.30~11.70,冰内盐度剖面呈现"C"形,即表层和底层盐度较大,而中间层盐度较小;海冰的平均密度略大,为(0.91±0.03)g/cm^(3)。通过观测人造光源在海冰中的透射辐射谱分布,发现一年冰的光谱透射辐射在490 nm和589 nm处呈明显的双峰结构,但随着海冰厚度的增加,双峰结构逐渐减弱,体现了海冰对于不同谱段辐射能衰减作用的差异。在可见光范围内,裸冰和雪覆冰的吸收率最小值出现在490 nm,在443~490 nm范围内二者的吸收率随波长增大而降低,在490~683 nm范围内二者的吸收率随波长增大而升高,但雪覆冰的吸收率在可见光范围内基本保持不变,体现了雪覆冰吸收率的光谱独立性。一年冰的谱衰减系数随波长呈"U"字形分布,紫光和红光谱段的衰减系数较大,中间谱段的衰减系数较小,589 nm波长的衰减系数最小,为1.7 m^(-1)。将谱衰减系数在可见光范围内积分,得到一年冰的积分漫射衰减系数约为2.3 m^(-1),略高于多年浮冰的漫射衰减系数1.5 m^(-1)。阿蒙森湾一年冰与加拿大海盆北部多年浮冰辐射光学性质的差异,主要源于陆源物质输入引起的海冰内含物组分的改变,而不同组分对光谱的吸收和散射性质不同,进一步导致了光学性质的整体变化。

In the Canadian Circumpolar Flaw Lead System Study,the physical and optical properties of first-year ice during the freezing season were observed at the Amundsen Gulf from November 24 th,2007 to January 26 th,2008.The results show that the thickness of sea ice during this period ranged from 27 cm to 108 cm,while the snow depth varied between 0 cm and 6 cm.The changes of temperature,salinity and density in the interior of sea ice are respectively:temperature within the sea ice rose monotonically along with the increasing of depth,reaching a maximum of-2.2℃at the surface and a minimum of-22.4℃at the bottom;the salinity ranged from 3.30 to 11.70 with a C-shaped pattern in its vertical section,which means that the salinity of upper surface and bottom layer is larger than that in the middle part;the average density of the sea ice was slightly larger,which is(0.91±0.03)g/cm^(3).With the special designing of artificial light source and in-situ instrumentation,an obvious two-peek structure at 490 nm and 589 nm was found in the spectral distribution of the transmitted radiation through the first-year ice.The twopeak structure weakens as the thickness of sea ice increases,indicating the spectrum dependence of the attenuation.In the visible band,the spectral absorbance of both bare ice and snow-covered ice reaches its minimum at 490 nm,and rises as the wavelength moves towards 443 nm or 683 nm.However,for snow-covered ice,the variation of absorption rate is little enough to present a spectral independence.In addition,the spectral distribution of the attenuation coefficient was U-shaped in the visible band,with a minimum of 1.7 m^(-1) at 589 nm.The integral diffuse attenuation coefficient of the first-year ice in visible band was about 2.3 m^(-1),which was slightly higher than 1.5 m^(-1),the diffuse attenuation coefficient of multi-year floe ice.The difference of the optical properties between first-year ice in the Amundsen Gulf and multi-year ice in the north of Canada Basin is mainly attributed to various components of the sea ice inclusions caused by the input of terrestrial materials with different absorption and scattering properties.