Lecture 3Physical Properties of Ocean Water

- Salinity and Light -

Part 1 - What’s in seawater

Salinity

Freshwater

101.07 kg/100 l 103.6 kg/100 l

Seawater

How much salt is in seawater?

Salt in the ocean

- 5.5 x 109 tonnes

- cover the earth to a depth of 45 m

Component Ions in Seawater

Comparison of fresh and salt water

Ion Concentration

-measured in ppt (parts per thousand or ‰)

Average in seawater is about 35 ‰(freshwater is about 3.3 ‰)

Salinity – Red Sea

41‰

33‰

- evaporation- isolation from open ocean- little freshwater input

The effects of all these ions

Seawater freezes at a lower temperature

Ice

Liquid

Fresh water

Salt water

Part 2 – How do we measure salinity?

Forchhammer - Law of Constant Proportions

Ratio of ions Na+ : Cl- : SO4-- : Mg++: K+ : Ca++ :CO3

--

Constant - worldwide

Calculation of salinity from chlorinity

chlorinity - wt. of Cl-, Br-, I- ions

Salinity % = 1.80655 x chlorinity

Salinity and conductivity

Salinity and refraction

Refractometer

Part 3 – Where do all these ions come from?

Sources – provide elements to system

Sinks – remove elements from system

Sources of Inputs of Salts in Oceans

• Rivers (largest transport of chemicals to ocean)

– Rain + CO2 H2CO3

– Si, Al, Na, K, Mg

• Volcanoes

– Cl, S, CO2

• Dust / Rain

– Fe, Si

• Anthropogenic

– CO2, P

Example 2 Geochemical Cycle

Cycling of Sea Salt

Bottom sediments

Organisms die

River discharge & runoff

Leaching from rocks

CO3-2

Ca+2

SO4-2

Mg+2

N+

precipitation

Ca+2

K+

Mg+2

adsorbed by clays

Sedimentsuplifted

Volcanic activityCl2

H2SRainfall

Cl-

SO4-2

Hydrothermal Vents: A Source & SINK

Minor source

Consume other elements

Lead, Sulfur, Copper, Iron, Cobalt, Gold

Mostly Gypsum & Zinc

Sinks

• Biological activity

• Interaction with particulate matter: clays and organic matter absorb dissolved metals

Residence time = AMOUNT OF ELEMENT IN OCEAN RATE OF ADDITION OR REMOVAL

Residence time

Residence Time - Concentration

Element Res. Time (yrs)

Na 60 x 106

Cl 80 x 106

Mg 10 x 106

K 6 x 106

SO4 9 x 106

Ca 1 x 106

Mn 7 x 103

Fe 0.1 x 103

Concentration

Crust (%) Ocean (mg/l)

2.4 10 770

0.013 19 500

2.3 1 290

2.1 380

0.026 905

4.1 412

0.5 0.0002

2.4 0.002

Gases in Ocean Water

Gases in Atmosphere & Oceans

Percent Gas Phase by Volume

Gas Atmosphere Surface Ocean Total Ocean

N2 79% 48% 11%

O2 21% 36% 6%

CO2 0.04% 15% 83%

Seawater pH

• Pure water pH = 7

• Seawater pH = 7.5 – 8.1

• Seawater is very well buffered!

The Carbonate System in Seawater

CO2 in seawater is controlled by:

1. Exchange with the atmosphere

2. Photosynthesis/Respiration:

6CO2 + 6H2 O C6 H12 O6 + 6O2

Importance of CO3--

CO3--

Normal pH range of seawater

Average pH of seawater

H2CO3

(carbonic acid)

HCO3-

(bicarbonate ion)

CO3--

(carbonate ion)

Rel

ativ

e ab

un

dan

ce o

f ca

rbon

ic a

cid

, b

icar

bon

alte

ion

an

d c

arb

onat

e io

n in

se

awat

er

100%

50%

0%

pH

4 5 6 7 8 9 10 11 12

Light Transmission

• transparent in visible part of spectrum

• Absorbed as is goes deeper in the water column

• strongly absorbs infrared (heat) and ultraviolet (prevents damage to DNA)

Light Transmission

Light penetration

Absorption of frequencies of light

Light penetration and location

Irradiance (E/m2/s

Pho

tosy

nthe

tic

Rat

e (%

O2 /

mim

)Photosynthesis and Light

Light

0

5

10

15

20

25

30

35

40

45

50

Depth

Percent surface light

.01 .1 1 10 100

Turbid coastal water

Clear open ocean water

Limit for Laminaria (kelp)

Limit for foliose algae

Next time

Tides