CHAPTER 5 Water and Seawater

S Types of Bonding Water Molecule Formation & Configuration Unusual Properties Hydrogen Bonding Heat Capacity Phases of Water Adding Salts to Water Constituents of Seawater Sampling Devices Effects of Density and Salinity Hydrologic Cycle Composition of River Water Residence Times Dissolved Gases pH of Seawater

P Covalent Bonding

P Ionic Bonding

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WATER’S UNUSUAL PROPERTIES

Hydrogen bonding Polarity means small negative charge at O end Small positive charge at H end Attraction between + and – ends of water molecules to each other or other ions Fig. 5.3

P Hydrogen bonding Hydrogen bonds are weaker than covalent bonds but still strong enough to result in: High surface tension High solubility of chemical compounds in water Solid, liquid, gas at Earth’s surface Unusual thermal properties Unusual density

Surface tension S

CALORIE P the amount of energy required to raise the temperature of 1 gm of liquid water 1 degree Centigrade

HEAT CAPACITY (SPECIFIC HEAT) The amount of energy required to raise the temperature of 1 gm of a substance 1 degree Centigrade

P Soil (average) 0.70 Granite 0.19** Quartz 0.19** ** ** (liquid) 0.5 (ice) 0.5

What does this mean? If we had 3 cookie sheets each 1 cm deep One filled with water, one with soil and one with sand The amount of incoming energy that would heat the water 1oC, would heat the soil 1.4oC and the sand 5oC

Unusual thermal properties of H2O Water - high heat capacity Amount of heat required to raise the temperature of 1 gram of any substance 1o C Water can take in/lose lots of heat without changing temperature very much Rocks - low heat capacity Rocks quickly change temperature as they gain/lose heat

Day/Night Temperature Differences Large on land, small in the ocean

Global thermostatic effects Moderate temperature on Earth’s surface Equatorial oceans (hot) don’t boil Polar oceans (cold) don’t freeze solid Marine effect Oceans moderate temperature changes day/night; different seasons Continental effect Land areas have greater range of temperatures day/night and during different seasons

Unusual thermal properties of H2O H2O has high boiling point H2O has high freezing point Most H2O is in the form of water (liquid) on Earth’s surface (good for life) High latent (hidden) heats of Vaporization/condensation Melting/freezing Evaporation

P Specific Heat = 1.0 calories/ gm Specific Heat = 0.5 calories/gm Fig. 5.6

Water molecules in different states of matter P Water molecules in different states of matter Fig. 5.5

Show water phase animation

Changes of state due to adding or subtracting heat P Changes of state due to adding or subtracting heat Heat is energy of moving molecules Temperature is measurement of average kinetic energy

Elements within columns share similar properties

P

Ionic bonding, loosely held together

P Dipolar water molecules break ionic bonds by surrounding sodium and chloride ions

CONSTITUENTS OF SEAWATER

Salinity P Total amount of solid material dissolved in water Typical salinity is 3.5% or 35o/oo Six elements make up 99% of dissolved solids in seawater Fig. 5.12

% = PERCENT OR PARTS PER HUNDRED (PPH) SALINITY UNITS % = PERCENT OR PARTS PER HUNDRED (PPH) Since open ocean salinity varies from 3.3-3.7%, we move the decimal one place to the right and express it as 0/00 OT PARTS PER THOUSAND (PPT) 3.3-3.7% BECOMES 33-37 o/oo

Measuring salinity Evaporation Chemical analysis Principle of constant proportions Major dissolved constituents in same proportion regardless of total salinity Measure amount of chlorine (chlorinity) Electrical conductivity Salinometer CTD

Salinity variations Open ocean salinity 33 to 37 o/oo Coastal areas salinity varies more widely Influx of freshwater lowers salinity or creates brackish conditions Greater rate of evaporation raises salinity or creates hypersaline conditions Salinity may vary with seasons (dry/rain)

9/23 P > 100 ppm >1, <100 ppm < 1 ppm

Forchammer’s Principle (Rule of Constant Proportions) Although the salinity of seawater may change from place to place, the ratio of ions to each other remains constant Importance: You only need to measure one ion to calculate the concentration of others - this can be the cheapest or easiest one to measure

How to change salinity Add water Remove water Add dissolved substances P How to change salinity Add water Remove water Add dissolved substances Remove dissolved substances

Processes that add/subtract water from oceans Salinity increases through: Salinity decreases through: Precipitation (rain or snow) Runoff (river flow) Melting icebergs Melting sea ice Evaporation Formation of sea ice

S Nansen bottle

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Reversing Thermometer - takes only a single measurement Expendable Bathythermograph (XBT) - Takes a continuous profile as it falls through the water column

S Water-sampling bottles

S Salinity is most commonly measured by electrical conductivity

P Density of water Density of water increases as temperature decreases down to 4oC From 4oC to 0oC density of water decreases as temperature decreases Density of ice is less than density of water

Density of water P Fig. 5.10

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Freshwater lake 10oC 8oC 6oC 5oC 4oC

Freshwater lake 8oC 6oC 5oC 4oC

Freshwater lake 6oC 5oC 4oC

Freshwater lake 5oC 4oC

Freshwater lake ice 0oC 1oC 2oC 3oC 4oC

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