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