 Who has been to an ocean?  How do we study them?  Have they always been here?

 The scientific study of earth’s oceans  Ocean currents  Chemical composition  Seafloor sediments & topography  Marine life How?

 Ocean floor topography  Sonar: a boat emits a sound that bounces off the ocean floor. The boat records the time it takes and calculates the distance.  Side-scan sonar: sound waves leave the boat at an angle so underwater hills can be mapped.

 Satellites: monitor ocean properties from space  Ocean surface temps  Ocean currents  Wave conditions Crazy

 Imagine a world without oceans.  Have they always been here? How did they form?

 Earth is about 4.6 billion years old  Geologic clues indicate that oceans have existed most of that time.  Sediments deposited in water  Lava that cooled underwater

 2 hypothesized sources of water 1. meteorite impacts 2. Volcanism  Meteorite impacts  Water was released when meteors hit the ground  Possibly enough to fill ocean basins over time

 Meteorites contain 0.5% water  Early earth may have had the same amount of water  That would be enough to fill the oceans  But it would need a way to be released from the crust

 Volcanism  When volcanoes erupt they release carbon dioxide and water vapor  Eruptions early in earth’s history slowly moved water from inside the earth into the atmosphere  When temps cooled the water vapor condensed into the oceans

 71% of earth’s surface is covered by oceans  Our bodies are about 70% water. Coincidence?  97% of earth’s water is saltwater  Average depth of the oceans is 3800 m (2.4 miles).

 Pacific: largest ocean, larger than all landmasses combined  Atlantic  Indian  Artic  Antarctic

 Seas: saltwater bodies that are smaller than oceans and mostly landlocked.  Examples?

 Oceanography: study of oceans. Uses technology  2 hypothesized sources of the earth’s water  Blue Planet: oceans and water distribution

 Ever swam in an ocean? Accidentally taste the water?  96.5% water and 3.5% dissolved salts  Mostly NaCl

 Salinity: the amount of dissolved salts in seawater  Overall, the average salinity of the oceans is 3.5% (35 ppt)  But salinity can actually vary from place to place

 Salinity is higher where evaporation exceeds precipitation. Why?  Salinity is lower in places where freshwater is added. Examples?  Where is the world’s saltiest water?

 Sources of sea salt:  Volcanic gases contain chlorine and sulfur dioxide. These gases dissolve in water and form ions  Weathering of rocks on earth’s surface (sodium, calcium, potassium, iron). These ions are flushed into the ocean by rivers

 Overall salinity is always at 3.5%. Therefore, salts are always being removed at about the same rate they are being added. It is balanced.

 Removal of salts: salt precipitation, salt spray, marine animals use them to form shells

 Density: ions in seawater increase the density  Freshwater: 1.00 g/cm 3  Seawater: g/cm 3  What effect does this have?

 Light absorption:  Water absorbs light  Light penetrates only the upper 100m of seawater  Below that depth it is dark and there’s not enough light for photosynthesis What does this mean for sea life?

 Surface temperatures: average 15 Celsius. Warmer or colder at the poles?  Water temp decreases significantly with depth.  Deep ocean water is always cold, even in the tropics.

 Temperature Profile: water temp vs. depth

 Surface layer: top, sunlit layer of ocean water. About 100m thick

 Thermocline: transition layer. Temp decreases rapidly with depth.

 Bottom Layer: cold, dark, uniform temps near freezing.

 Surface and thermocline layers are absent at the poles where water is cold everywhere.  What causes ocean layering? How is cold water different than warm water?

 Deep water is colder, saltier and therefore more dense. It sinks and doesn’t mix with other layers.  This water migrates slowly toward the equator as one mass.  Where is the densest water in the world?

 Salinity averages 3.5% but can vary between locations  Sources & removal of salt  Ocean layers based on density & temp  Water masses

 Oceans are always in motion  Waves  Tides  Currents  upwelling

 Wave: rhythmic movement that carries energy through space or matter (ocean water)  We all know what a water wave looks like. How does it work?

 Caused by wind blowing on the ocean surface  Water molecule moves in a circle while the energy moves forward.  Observe an animation of wave motion. Observe an animation of wave motion.

 Crest: highest point of the wave  Trough: lowest point of the wave  Wavelength: length between crests  Wave height: vertical distance from crest to trough

 Wavelength determines depth of water disturbance: depth = 1/2 wavelength  Wave speed increases with wavelength

 3 factors:  Wind speed  Wind duration  Fetch – expanse of water the wind blows across More = larger waves (think hurricanes)

 Waves spilling over, like when they hit a shore. Called breakers.  1. wave approaches the shore, water is more shallow  2. friction with bottom slows the wave  3. waves from behind catch up, decreasing wavelength. This increases wave height.  4. wave is too tall and spills over.

 Tides: periodic rise and fall of sea level  High tide & low tide  Any experience with this?

 Tidal range: difference between water levels of high and low tide  Tidal range can change based on topography and latitude  Bay of Fundy near Novia Scotia has the greatest tidal range, about 15m

 Generally, a daily cycle of high and low tides takes 24hrs and 50min  What causes tides?

 The moon  NOVA | What Causes the Tides? NOVA | What Causes the Tides?

 The sun also plays a role  Spring tides: larger tidal ranges that occur when the sun and moon align.  Neap tides: lower tidal ranges that occur when the sun and moon’s gravitational forces are acting against one another

 Are a result of gravitational interactions between the earth, moon, and sun.

 Remember water masses?  The movement of water masses is an example of an ocean current.  Density current: ocean current that is caused by differences in temp and salinity.  Density currents move slowly in deep ocean waters.

 Surface currents: currents near the surface that are caused by wind.  Can move as fast as 100km/day! Think about getting caught in that current.  Follow global wind patterns.

 Winds and landmasses cause ocean currents to form closed loops called gyres.  Clockwise loops in the N. hemisphere. Counterclockwise in the S. hemisphere. Why?

 Gyres are one way the earth looks to balance heat distribution.  Warm water flows toward the poles, where it cools, and then moves back toward the equator.  Cold water moves slowly.

 How do you think the currents can affect weather?

 Currents flow horizontally  Upwelling is the upward (vertical) motion of water.  Occur on the western coasts of continents where surface currents pull surface waters to the west.  Cold, nutrient rich water replaces the surface water.

 Cold water is nutrient rich which is good for marine life. Some of the world’s best fishing areas are of the coasts of Peru and California.

 Wave characteristics and motion  Tides and their causes.  Currents – surface and density  Upwelling