Physical Properties of Ocean Water Lecture 3 Physical Properties of Ocean Water - Salinity and Light -

Part 1 - What’s in seawater

Salinity Freshwater Seawater 101.07 kg/100 l 103.6 kg/100 l How much salt is in seawater? Freshwater Seawater 101.07 kg/100 l 103.6 kg/100 l

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

-measured in ppt (parts per thousand or ‰) Ion Concentration -measured in ppt (parts per thousand or ‰) Average in seawater is about 34 - 35 ‰ (freshwater is about 3.3 ‰)

Salinity – Red Sea - evaporation - isolation from open ocean - little freshwater input 41‰ 33‰

The effects of all these ions Seawater freezes at a lower temperature Fresh water Salt water Liquid Ice

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 Volcanic activity Sediments uplifted H2S Rainfall Volcanic activity Cl- SO4-2 Sediments uplifted River discharge & runoff Ca+2 K+ Mg+2 CO3-2 Ca+2 SO4-2 Mg+2 N+ Organisms die adsorbed by clays Leaching from rocks precipitation Bottom sediments

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

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 100% 50% 0% HCO3- (bicarbonate ion) H2CO3 (carbonic acid) CO3-- (carbonate ion) Relative abundance of carbonic acid, bicarbonalte ion and carbonate ion in seawater Average pH of seawater Normal pH range of seawater 4 5 6 7 8 9 10 11 12 pH

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 penetration

Absorption of frequencies of light

Light penetration and location

Photosynthesis and Light Photosynthetic Rate (%O2/mim) Irradiance (mE/m2/s

Light Depth Percent surface light Turbid coastal water 5 10 15 20 25 30 35 40 45 50 Depth Clear open ocean water Limit for foliose algae Limit for Laminaria (kelp) .01 .1 1 10 100 Percent surface light

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