Lecture 4 (Ch. 5 of text) Properties of Seawater (Part I)
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Transcript of Lecture 4 (Ch. 5 of text) Properties of Seawater (Part I)
Lecture 4 (Ch. 5 of text) Properties of Seawater (Part I)
Biology is wet and dynamic
- Random walks in biology 1983, by H. C. Berg
The most common molecule on the Earth - water
Soup as salty as the seawater
Learning Objectives
1. Understand the nature of the water molecule and its unique properties and how these are altered by the presence of salt in solution.
Review of following terminologies:AtomsTemperatureHeatSpecific HeatThermodynamicsInternal Energy and Entropy
2. Know the types of materials that are dissolved in sea water, their importance and how they vary with time.
3. Explain variations in salinity, temperature, and pressure within the sea and how they alter the chemical and physical properties of the ocean.
• The smallest unit of a substance that retains all of its chemical properties
• Subatomic particles include protons, neutrons, and electrons
• A stable atom of an element is electrically neutral
• An ion is an atom with either positive- (excess protons) or negative- (excess electrons) charged
• Atoms that chemically bonded to another (either same type or different one) comprise a molecule
• An element has isotopes due to its varied no. of neutrons in nucleus
Atomic Structure (Ch.5.1)
Periodic Table
More likely to loose electrons and be positively charged
More likely to gain electrons and be negatively charged
The charge of an ion is the single most important reason for its ability to bond with other elements
稀土元素
錒系元素
Basic physical notions (Ch. 5.2)
States of Matter (e.g. water)Thermodynamics: the kinetic theory of heat
H2O: the only substance that can co-exist naturally as a gas, liquid, and solid states on the Earth’s surface
聚合體
Phase diagram for water
Precisely, what does the temperature reading mean?
Why does the hot-air balloon move upward?
a mercury thermometer
What is temperature?
State variables
using Kinetic temperature definition
it is a measure of the average translational kinetic energy associated with the disordered microscopic motion of atoms and molecules.
It is measured in (Celsius, Kelvin, and Fahrenheit).
Thermal Equilibrium = Maximum Entropy
Concept of Entropy ( 熵 )
dS = dQrev
T= 0; dQrev : heat being reversibly qqqqqqqqqadded or removed
Heat may be defined as energy in transit from a high temperature object to a lower temperature object.
However, the concept of temperature is complicated by internal degrees of freedom
Box is solid (Constant volume)
Q
Heat:1) Represents the transfer of energy from high to low temperature. Therefore, heat has units of Energy
2) An object does not possess "heat"; the appropriate term for the microscopic energy in an object is internal energy.
What is Internal Energy?
Internal energy = Measure of the Kinetic energy and potential energy on atomic and molecular scales.
State variables
There is a difference betweenTemperature and Internal Energy
k = 1.38x10-23 J/◦K
Change of Internal Energy
First Law of Thermodynamics
V S
U UU S V
S V
Temperature Pressure
Specific Heat Capacity?
Amount of energy needed to raisetemperature of unit volume of water by onedegree C. Units: energy/(mass * degree)
http://hyperphysics.phy-astr.gsu.edu/hbase/heacon.html#heacon
Flow chart of thermodynamics
http://hyperphysics.phy-astr.gsu.edu/hbase/heacon.html#heacon
Flow chart of thermodynamics
Facts:
– Water has one of highest heat capacities
ccknown, makes water excellent heat
cctransfer material
– Allows ocean currents to modulate global
ccclimate
The amazing water molecule (Ch. 5.3)
(Covalent bond)
(in electricity) (hydrogen bonding)
Plus
high heat capacity (thermal inertial) and solvent power
Liquid/gas state only
共價鍵結
Sodium ChlorideRock SALT
NaCl
Na Cl Ionic bond
Cation Anion
Water is a powerful solvent – for example
陽離子 陰離子
Cation: in greek, downward, descend; anode 陽極
Anion: in greek, go up, ascend; cathode 陰極
Hydration: Water (as solvent) dissolves salts (as solute) by surrounding the atoms in the salt molecule and neutralizing the ionic bond holding the molecule together.
外層覆蓋物
All solid-state substances sink in their own liquids, except the water !
Mickey’s ears loosen when entering the ice house (109.50 )
Properties of Seawater
• Salinity• Temperature• Density • Pressure
Salinity:
the total weight in grams of dissolved salt in 1 KG of seawater expressed as ‰ (part per thousand PPT)
Another factor contributing to the dissolution of salts is acidity
10log [ ]pH H
Carbonic Acid
2 2 2 3 3H O CO H CO H HCO
Bicarbonate Ion
Sources for acidity in the ocean
( 重碳酸鹽離子 )
3 8 2 2
2 2 5 4 2
2 2
2 2 ( ) 4
KAlSi O H O CO
K Al Si O OH SiO
H
Example:
Kaolinite
Dissolved Silica
Orthoclase ( 正長石 )
Major constituent (conservative ions)of Seawater (c.f. Table 5.1)
Seawater Rivers
35 PPT 0.088 PPT
( 鉀)
Sources of Salt in Seawater
Weathering and erosion of rocks on land
Rate of supply of salts from rivers: 1015 grams/year !
落塵
陽離子交換
The "steady state" results from the removal rate of salts from the ocean being equal to the input rate.
Surprisingly, The Ocean DOES NOT get saltier at least during the past 1.5 billion years
This balance holds because the removal rate of salts is related to their concentration, and increases when their concentration increases
Sinks of Salt in Seawater
Removal of salt from seawater occurs by
(1) inorganic process, such as a. evaporation-precipitation loop through the formation of supersaturated solution, b. wind, c. adsorption, and
(2) organic process such as diatoms having silica shells and forams with carbonate shells that are precipitated from the uptake of Si4+ and Ca2+ from seawater (Ch. 4)
石膏
The equilibrium state of salinity of seawater gives a hint toward the grand sedimentary cycle in geologic time frame
If rivers are the primary supply of salts. Why is CALCIUM and BICARBONATE so little in seawater?
Seawater Rivers
35 PPT 0.088 PPT
HCO3 and Ca are used biologically veryrapidly (non-conservative)
Na and Cl are removed very slowly, byabsorption on clay particles (conservative)
… different processes removing different elements
Elements have different residence times, decided by reactive speed and demanding by ocean biota (see Table 5.8)
Residence timethe average time a component spends in a system (such as monthly stipend in your account).
T
CR
r
C = total amountr = the removal rate (units of [C]/time)
Rapid biological removal
slow absorption removal
The ocean gets thoroughly stirred, bycurrents, every ~1,600 years,.
This is called the mixing time of theocean: the time it takes the ocean to mixthoroughly
Salts stay in seawater much longer than 1,600 years
Salt well mixed Constant proportion of relative constituents salts of seawater
The Hydrological Cycle
Surface Salinity (which season?) Evaporation − Precipitation
Subsidence regions (c.f. Fig.5-12 of text)
Spread out of Mediterranean seawater
Effects of salinity on the properties of water
Chemical/physical structure of the oceans (Ch.5.5)
JanuaryWinter
JulySummer
July-JanuarySummer-Winter
Why is the deep ocean cold?
Transfer of Heat to the Ocean (heat flux)
Absorption of solar radiation decreases rapidly with depth
Vertical Structure of Temperature
Thermocline
Outstanding question: what sets the depth of the thermocline?
Vertical Structure of Temperature
Salinity
Temperature
How do the water masses move? c.f. Fig.5.13b
Vertical profiles
DENSITY: controls the movement and stability of the ocean water masses
Next time we will talk more about
DENSITY and PRESSURE in the OCEAN