15.1 The Oceans

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

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

Technology 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.

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

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

Ocean history 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

Where did the water come from? 2 hypothesized sources of water Comet impacts Water was released when meteors hit the ground Possibly enough to fill ocean basins over time Meteorite impacts Contain up to 0.5% water Would have been more than sufficient to fill oceans

Water release 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

Blue Planet 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).

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

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

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

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

Salinity 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 variation 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? With a salinity higher than 40 percent, the Antarctic pond is even saltier than the Middle East's Dead Sea (34 percent) and Utah's Great Salt Lake (whose salinity varies between 5 and 27 percent). Average salinity of Earth’s oceans is 3.5% or 35 ppt.

Salt Cycle 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

Salt Cycle 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.

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

Physical properties of seawater Density: ions in seawater increase the density Freshwater: 1.00 g/cm3 Seawater: 1.02-1.03 g/cm3 What effect does this have?

Physical properties… 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?

Ocean Layering 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.

Ocean layering Temperature Profile: water temp vs. depth

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

Ocean layers Thermocline: transition layer. Temp decreases rapidly with depth.

Ocean Layers Bottom Layer: cold, dark, uniform temps near freezing.

Layers 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?

Water Masses 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? Antarctic bottom water (southern Atlantic, Pacific, and Indian oceans)

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

15.3 Ocean Movements Oceans are always in motion Waves Tides Currents upwelling

Waves 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?

Waves 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.

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

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

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

Breaking waves 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.

Breaking waves

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

Tides 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

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

Cause of Tides The moon NOVA | What Causes the Tides?

Cause of 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

Cause of tides

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

Ocean currents 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.

currents 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.

Gyres 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 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?

Upwelling 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.

Upwelling 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.

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