| 摘要: |
| 利用1999年北极科学考察期间在海冰边缘区的三次考察数据, 研究了北冰洋海冰边缘区的温度和盐度结构。将海冰边缘区分为机制不同的两大类, 一类是暖水海冰边缘区, 主要热源是外部暖水进入海冰边缘区携带的热量；另一类是冷水海冰边缘区, 主要热源是太阳辐射加热。文中主要对冷水海冰边缘区进行了研究。虽然两个冷水海冰边缘区(R区与T区)温度结构不尽相同, 但都存在表层以下水体中的温度极大值现象, R区的温度极大值位于20m左右, T区的位于40—50m左右的深度, 可以认为是海冰边缘区的典型温度特征。作者认为, 次表层暖水的热源是太阳辐射的直接加热, 为此, 建立了太阳加热引起海水次表层增暖的物理模型和简单的数学模型, 获得了冰下海水在太阳辐射的作用下增暖的解析解。结果表明, 部分太阳辐射能穿过海冰加热冰下海水, 加热之初温度的极大值出现在近表层, 随着时间的推移, 海温极大值的位置向下移动, 最终可以达到40m左右, 证明了仅仅依靠太阳的短波辐射就可以形成中间暖的水层。文中阐明, 开阔海水更多的是上混合层和跃层结构, 冰下海水主要是次表层暖水结构；冷水海冰边缘区的海水主要带有冰下海水的特征。由于次表层暖水的形成与海冰厚度关系很大, 近十几年北冰洋海冰厚度的显著减少势必加强次表层暖水, 可能是北冰洋增暖的又一个重要现象, 对全球气候变化有意义深远的影响。
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| 关键词: 北冰洋,楚科奇海,海冰边缘区,温度结构,太阳辐射 |
| DOI：10.11693/hyhz200304004004 |
| 分类号: |
| 基金项目:国家自然科学基金资助项目,49876008号和中国科学院重大资助项目,KZ951-A1-205号 |
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| TEMPERATURE AND SALINITY STRUCTURES IN SUMMER MARGINAL ICE ZONE OF ARCTIC OCEAN AND AN ANALYTICAL STUDY ON THEIR THERMODYNAMICS |
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ZHAO Jin-Ping, SHI Jiu-Xin, JIAO Yu-Tian
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First Institute of Oceanography, State Oceanic Administration
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| Abstract: |
| In this study, in situ observations by small boat and CTD in Arctic Ocean marginal ice zone (MIZ) in the 1999 Chinese expedition cruise are described, to delineate the temperature and salinity structures of water under ice sheet. The T-S structure can be divided into two different MIZs: the warm-water MIZ with the temperature above 0℃, with its heat source being possibly from open water which is transported under ice by an additional barotropic pressure exerted by regional forcing, and the so-called cold-water MIZ with the temperature less than -0.50℃. This paper mainly deals with the water temperature and salinity structures of the cold-water MIZ. In the cold-water MIZ, water temperature is vertically non-uniform, with cold surface water and cold deep water (>100 m) being present. Although the vertical structures measured by different casts are much different, a relative warm water is generally observed in subsurface water, which is called subsurface warmer waters (SWWs). The SWWs were observed in both Rand Tregions, with temperature maxima in different depths. In the R region, temperature maxima appeared in 20ml evel and those in the Tregion in 40-
50 m depths. The SWW is a key factor to affect heat exchange through icy sea surface, as the warmer water is possibly the heat source supplying heat export from surface by long-wave radiation and sensible and latent heat. The physical mechanism to generate the SWW is proposed: the solar radiation is considered as the main heating energy source. Most solar energy arriving ice surface is reflected from the surface and absorbed by ice. Little part of solar energy can penetrate ice sheet to heat the water.To verify the mechanism, a simple analytical model is established, in which heating and vertical diffusion are considered. The analytical solution displays that part of solar radiation penetrating sea ice can heat up seawater underneath the ice, and generate a temperature maxima in the water. The maximum temperature occurs in the water immediately underneath the ice at first, then the maximum goes down with the time. The final depth of maximum temperature may reach 40 meters if the ice thickness is around 1.2 m. Therefore, the SWW is formed by three reasons: the solar radiation into water, the greenhouse effect of sea ice, and the cooling by the heat absorption of ice sheet. Under certain non-ice conditions with calm wind and low airtemperature, the thermodynamics is similar to those of ice covered, and the SWW canbe also formed. The result obtained can explain the cause of the SWW in polar regions. Solar radiation absorbed by seawater depends strongly on ice thickness. If ice thickness exceeds 2.5m, no SWWs will exist on the basis of the result in this paper. In the Arctic Ocean, sea ice extent and thickness have an obvious trend to decrease in ten years, 10% for ice extent and 40% for ice thickness. The reduction of Arctic sea ice could increase and enhance the subsurface warm water phenomenon. This enhanced SWW will exert more effect on air-sea interaction on ice-covered ocean and, therefore, change the action of the Arctic Ocean on the global climate.
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| Key words: Arctic Ocean, Chukchi Sea, Marginal ice zone, Temperature structure, Solar radiation |
