Definition of Salinity


Principle of constant proportion states that the absolute amount of salt in sea water varies, but the relative proportions of the ions is constant. Because of this principle, it is necessary to test for only one salt ion, usually chlorine, to determine the total amount of salt present.



Most common substance on the earth’s surface Ocean water makes up 98% of water inventory 96.5% is water, 3.5% is salt and dissolved minerals Accumulated on the surface from mass degassing of earth’s interior… still happening, but much less Only substance that exists naturally in all three states in the normal temperature range of earth Solid, Liquid, and Gas
溶解力强：水分子有很强的极性
密度变化异常
不遵从“热胀冷缩”。最大密度时温度是4摄氏度
密度变化异常是由水分子的缔合造成的．
温度<4，有利于水分子的缔合；冻结为冰时，全部缔合成一个巨大的分子缔合体（分子晶 体）．由于晶体结构排列松散，故密度减小．当温度从04度以前，主要过程是较大的缔合分 子逐渐分解成为较小的分子，所以体积收缩，密度增大．＞4度时，热运动加强，导致体积膨 胀，密度所温度增高而减小
Lehodey,P. et al., 2000. El Nino Southern Oscillation and tuna in the western Pacific. Science
Temperature distribution in California coastal area
长江水的扩展
The effect of Temperature
The effect of Salinity
T↓，D↑ T↓, D↓
•S>24.7, the density will continue to increase with decreasing temperature until the water freezes

Ocean and Sea
Four Principle Ocean Hydrological features of ocean, sea, fjord(bay), strait(channel)

§2 海水的物理性质 Physical Properties of Sea Water
2.1 Water

电导温度Salinity Based on Conductivity(1969)

实用盐标Practical Salinity Scale of 1978
The standard KCl solution contains a mass of 32.435 6 grams of KCl in a mass of 1.000 000 kg of solution.
海水组成恒定性原理

1) 传统的盐度定义(1902)： 1kg海水中将(Br-,I-)以氯置换，碳酸盐分 解为氧化物,有机物全部氧化,所余固体物质 的总克数。(480度加热48小时） 利用"海水组成恒定性"，测定出其中某 一主要成分的含量，便可推算出海水盐度。
2) 氯度: 1kg海水中将(Br-,I-)以氯代替，所含氯的总克数。 转换为盐度的关系式为：S‰=0.030+1.8050Cl‰
分子结构(Molecular structure)：极性，分子缔合力
Hydrogen
Hydrogen
105 deg
Oxygen
Hydrogen Bonds–polar molecules give water a structure that is responsible for a number of unique and important properties
Measuring Salinity
Evaporate

Easy to do, but residue is complex Traditional method prior to mid-’60’s Determine chlorinity and use empirical formula S = 1.80655 Cl
T
No Salt
Ice 0.917
Salt 20
25
30
35
Table 4.4 When S is constant and greater than 24.7, the density decreases as T increases When T is constant, the density increases with increasing S
热性质特殊
沸点(boiling point)和融点(melting point)、比热(specific heat)、蒸发潜热 (latent heat of vaporization)等热性质比氧的同族化合物高
2.2 温度、盐度和密度的概念及关系 Temperature, Salinity and Density
ρ(S,t,p)∝S,t-1,p

st (sigma-t)(条件密度): Shorthand method of expressing the density of a sample of seawater at atmospheric pressure as determined by its in situ temperature and salinity
Salinity is presented as numbers (dimensionless) but may find different terms: psu (practical salinity units) gram/kilogram gram/liter o/oo At exactly one atmosphere and 15oC, S = 35.0
2.2.1 Temperature

Measurement Absolute Temperature T
Unit: Kelvin (K) t [℃] = T [K]-273.15


The practical temperature scale (1887, 1927, 1948, 1968, and 1990)
Titration

Conductivity

Uses a “resistance bridge” Current - CTD’s
2.2.3 Den物体的质量


m V
Unit: kg/m3 specific volume(比容)：单位质量物体的体积 α =1/ρ (m3 · -1) kg
-1 0
1.01606 1.02010 1.02413
0.99984 1.01607 1.02008
1
2 3 4
0.99990 1.01605 1.02005
0.99994 1.01603 1.02001 0.99996 1.01598 1.01995 0.99997 1.01593 1.01988


The density of seawater is greater than the density of freshwater because seawater contains dissolved salts. The density of pure water at 3.98°C, or approximately 4°C, is 1.0 g/cm3. The density of seawater of average salinity is about 1.0278 g/cm3. Because of this, fresh water will float on ocean water.
5
10 15 20 25 30
0.99996 1.01586 1.01980
0.99970 1.01532 1.01980 0.99910 1.01450 1.01832 0.99820 1.01342 1.01720 0.99704 1.01210 1.01585 0.99565 1.01057 1.01428
• S< 24.7, the density will increase with decreasing temperature until it reaches a maximum value and will then decrease until the water freezes - just as pure water behaves.

Salinity Based on Chlorinity
(1902) (1969)
where chlorinity Cl is defined as “the mass of silver required to precipitate completely the halogens in 0.328 523 4 kg of the sea-water sample.”