长江口海水的密度

DENSITY OF CHANGJIANG RIVER ESTUARY SEAWATER

为了核对1980年国际海水状态方程应用于中国近岸海水的可靠性,高精度的磁力浮沉子密度计在15—25℃,盐度5—35,一个大气压条件下,测量了长江口附近海水及其人工稀释海水的相对密度。结果表明,海水密度直接测量值系统地偏高于状态方程计算值,二者之间的偏差随水样盐度值降低而增大,且与海水[Ca^(2+))/s比值成明显正相关关系。经计算机拟合,导出了长江口附近海水及其稀释海水的状态方程,该方程计算值与实验值的平均标准偏差为±3.9×10^(-3)kg/m^3。

In order to check the validity of the International Equation of State of Seawater, 1980 (UNESCO Equation), in its application to Chinese coastal waters, we have measured the relative density of seawater from the estuary of Changjiang River and seawater solutions diluted with the Changjiang River water at one atmosphere from 5-35 salinity and 15-25℃ with a high precision magnetic float densimeter designed by us. The average standard deviation of measurement values was±2.3×10-3 kg/m3. The statistical results have shown that for all samples from the estuary of Chingjiang River, the measured density with our densimeter was always higher than the density calculated by the UNESCO Equation, the average difference, for seawater samples taken in dryseason and floodseason, being (6.3±2.3)×10-3 kg/m3 and (8.1±2.3)×10-3 kg/m3, respectively. The average difference between the measured and calculated densities increased with decreased salinity and reached 47.2×10-3 kg/m3 (Changjiang River water). We have also found linear correlation relationships between this average difference and [Ca2+]/s value. Our experimental average value of [Ca2+]/s, [SO2-]/s, [Mg2+]/s and [Sr2+]/s was 0.01183±1.0×10-4, 0.07698±1.7×10-4, 0.03743±8.1×10-5 and 2.26×10-4, respectively, at the salinities of samples range from 30 to 35. The experimental value of [Ca2+]/s for the Wuhu section of Changjiang River was 0.2597. The resulting densities of all samples have been fitted to an equation of the form: d - dw = B1s1/2 + B2s + 53s3/2 + + B4s2, where dw is the density of SMOW and B1, B2, B3, B4 are temperature dependent parameters. The average standard deviation between calculated densities of this equation and experimental value was ±3.9×10-3 kg/m3.