Chapters 6 & 7 Water

Importance of Water Most abundant component of living things –Marine organisms: 70-80% water by mass –Terrestrial organisms: 66% water by mass Provide buoyancy and a medium to marine organisms High heat capacity influences overall climate of Earth

Physical Properties Excellent solvent High boiling point and freezing point More dense in liquid form than in solid Provide buoyancy and a medium to marine organisms

Structure of Water Water is formed as the result of a covalent bond between 2 hydrogen atoms and one oxygen atom Covalent bond: bond formed by sharing of electrons

Water is a Polar Molecule Polar Molecule: a molecule that has a slightly positive charge at one end, and a slightly negative charge at one end Caused by unequal sharing of electrons Oxygen is more electronegative than Hydrogen

Water Molecules Form Hydrogen Bonds Hydrogen Bond: weak attraction between the positive hydrogen end of one water molecule and the negative oxygen end of another water molecule

Properties of Water Influenced by Hydrogen Bonding High heat capacity High boiling point High freezing point AdhesionCohesion Density of ice

High Heat Capacity Heat Capacity: the amount of heat required to change the temperature of a substance. Hydrogen bonding gives water its high heat capacity Allows water to store and carry a tramendous amount of heat energy Provides a stable environment for marine organisms

Freezing and Boiling Point High boiling point reflects the large amount of energy it takes to break the hydrogen bonds High freezing/melting point indicates that a large amount of energy is required to overcome the hydrogen bonds that hold water molecules in position to form a solid.

Cohesion Def: The attraction of water molecules to other water molecules Gives water a high surface tension –Surface molecules have a higher attraction for other water molecules than for air molecules

Adhesion Occurs when water is attracted to surface objects that carry an electrical charge Ability of water to get things wet Ability of water to rise in narrow spaces –Capillary action

Water and Light Water has an ability to selectively absorb certain wavelengths of light. –Low energy wavelengths are quickly absorbed –High energy wavelengths penetrate deeper –Atlantic Ocean 55% of the light is absorbed within 1 meter –Clear water Less than 1% of light entering can penetrate deeper than 100 meters

Light Spectrum Absorption by Water

Chemical Properties Classified as acids or bases –Acids: release H + when added to water –Bases: Bind H + and remove them from solution pH Scale –Indicator of the number of H + in a volume of solution –Ranges from 0-14 >7 Acid <7 Base <7 Base

pH of Water pH of pure water is 7 Ocean water –Determined by the substances that are dissolved in it –Slightly alkaline Average pH of 8 Due to seawater containing large amounts of bicarbonate and carbonate

Salt water Named so because of the high quantity of dissolved salts compared to freshwater Salinity of ocean water is important –Environmental factor that strongly influences marine organisms –Dissolved substances dictate the distribution and kinds of marine organisms in a certain environment

Saltwater Composition Most salts present in their ionic form 99% made up of Na +, Mg 2+, Ca 2+, K +, Cl - and SO 4 2+ Trace elements –Present in concentration of less than one part per million

Principle of Constant Proportions Proportions of several key inorganic elements and compounds dissolved in seawater DO NOT CHANGE, regardless of overall salinity. Useful to marine scientists, because if you know how much of one element there is, you can determine how much there is of all the others. Only the amount of water, and therefore the salinity, changes.

Salinity Seawater –3.5% salt –96.5% water –Average salinity of 35 parts per thousand NaCl is the most common salt present Affected by evaporation and precipitation Can change in certain location –Higher salinity around the poles

Sea Salt Cycling Original sources –Rocks and other parts of the Earth’s crust and interior Processes that contribute –Rocks release ions as they are broken down –Volcanic eruptions –River water/runoff

Gases in Seawater Oxygen, nitrogen and carbon dioxide Dissolve at the surface of the sea from the atmosphere and are introduced by biological processes

Gases from Biological Processes Gases are produced as by-products –Photosynthesis: Oxygen Added only near the surface –Decomposition: Carbon dioxide Add at all depths Oxygen-minimum zone –Just below the sunlight surface waters –Area where oxygen is depleted by the resident animal life but not replaced by photosynthesis

Solubility of Gases Amount of oxygen and carbon dioxide in seawater is greater than it is in the atmosphere. Amount of nitrogen is less. Amount of gas that water can hold depends on –Temperature –Salinity –Pressure

Solubility of Gases Cold water hold more gas than warm Low salinity allows more gas to dissolve

Day Two

Uneven Heating of the Earth 3 primary causes –Earth is spherical –Axis of rotation is tilted –Distance from the sun varies throughout the year Let’s take a closer look.

Angle of Incidence Light from a single source doesn’t strike a sphere evenly Small part receives perpendicular light rays, while other parts receive slanted light rays

Orbital Inclination Axis is tilted at 23.5° Equator doesn’t receive perpendicular light rays all year Perpendicular rays travel between the Tropic of Cancer (23.5°N) and the Tropic of Capricorn (23.5°S) Causes the seasons

Elliptical Orbit Receives more heat when the orbit is closer to the sun Little effect on the temperature –Closer to the sun in the winter (Northern Hemisphere)

Biological Importance Autumn color change of leaves Terrestrial birds and other animals migrate Gray whale migration in the ocean

Convection The vertical movement of currents caused by temperature differences in a fluid Results when the sun warms the air in contact with it, and the air rises The warm rising air is replaced by cooler dense air Causes a global wind pattern between the poles and the equator

Coriolis Effect The tendency for the path of a moving object to deflect to the right in the Northern Hemisphere and the left in the Southern Hemisphere Explains why we have winds in all directions Influences ocean currents Major factor in distributing heat, nutrients and types of life

Coriolis Effect Caused by the Earth’s rotation Greater at higher latitudes Along the equator, the effect is zero

Air and the Coriolis Effect Deflects the air to the right as it travels in the Northern Hemisphere and to the left in the Southern Hemisphere Atmospheric circulation cells –Regions of wind patterns –Make up 6 distinct air masses with individual flow patterns

Hadley Cells Most important atmospheric circulation cells Found between the equator and 30°N or S latitude Responsible for the trade winds

Ferrel Cells Found between 30° and 60° latitude Creates the westerlies –Blow toward the east Important to sailing vessels trying to reach Europe

Polar Cells Lie between 60° and the poles Sends cooler air back down towards the equator Produce the polar easterlies

Ocean Currents Produced when wind blowing across the ocean surface pushed and pulls the water, causing it to move Move water in predictable patterns within ocean basins

Surface Currents Winds transfer energy to water by friction –Produces waves that transfer energy to water –Cause mass of water beneath the moving air flow Forms a surface current Main driving forces are the trade winds

Gyres Water flows in a circular pattern around the edge of an ocean basin 5 major in the world –3 in the Southern Hemisphere –2 in the Northern Hemisphere

Current Classification Distinguished on the basis of –Distinct temperatures –Flow characteristics –Position

Western-boundary Currents Fastest and deepest currents Found along western boundaries of ocean basins Move warm water toward the poles Carry little nutrients-not productive Move large volumes of water Gulf Stream

Eastern-boundary Currents Carry cold water toward the equator Slow moving Move smaller volumes of water More productive Contribute to nutrient mixing of surface waters

Transverse Currents Connect eastern and western boundary currents Each current flows uninterrupted into the next

Currents Beneath the Surface Movement caused by friction Coriolis effect applies Each layer slides horizontally over the layer beneath it –Lower layers move slower Ekman spiral –Spiral flow of water that results from the movement of the layers Ekman transport –Net movement of water to 100 m depth