Salt Water
What’s the significance of Oceans? Oceans and the atmosphere keep temperatures fairly constant. -70C to 55C, a range of only 125C Mercury has a range of 610C Oceans distribute heat around the planet. Oceans moderate climate in a region. At the same latitude, temp. range is smaller in lands near oceans than farther away. (summer not as hot, winter not as cold)
Composition of Ocean Water Remember, Water is a polar molecule so it can dissolve many substances.
Salinity Over millions of years, salts have been taken from rock and soil as water moves through. Average salinity is 3.5% Estuaries have a lower than average salinity. The Dead Sea has a higher than average salinity (30%). Some of the salt in the oceans comes from undersea volcanoes and hydrothermal vents. When water evaporates from the surface of the ocean, the salt is left behind. After millions of years, the oceans have developed a noticeably salty taste. The sea is called "dead" because its high salinity prevents macroscopic aquatic organisms, such as fish and aquatic plants, from living in it, though minuscule quantities of bacteria and microbial fungi are present. Why do you think its called the Dead Sea?
Water Density Density increases as… Salinity increases Temperature decreases Pressure increases Differences in water density are responsible for deep ocean currents.
Parts of the Water Column: Vertical Divisions The entire ocean is divided into 2 vertical zones based on light penetration (like lake zones). Photic Zone- surface to 200 m deep. Photosynthesis can occur here
Aphotic zone- not enough light for photosynthesis. Makes up the majority of the ocean, but smallest amount of life is found there. Subdivided based on depth
Parts of the Water Column: Horizontal Divisions Divided by the sea floor: Intertidal zone- nearest to shore, between the high and low tide marks. Land and organisms can be exposed to air. Neritic zone- low tide mark to the end of the continental shelf. Oceanic zone- the rest of the ocean, past the end of the continental shelf.
Ocean floor averages 3,790 m Mariana Trench is 10,994 m (6.831 miles) James Cameron descends the Mariana Trench
Ocean Movement Results from many factors: Wind Tides Coriolis effect Water density differences Shape of the ocean basins
Waves Waves transfer energy. The size of a wave and the distance it travels depends on the amount of energy that it carries. Ocean Surface Waves: originate from wind blowing steady winds or high storm winds
Ocean Waves Factors that create the largest ocean waves: When the wind is very strong When the wind blows steadily for a long time When the wind blows over a long distance
Wave Formation Wind blowing across the water transfers energy to the water. The energy first creates tiny ripples that create an uneven surface for the wind to catch so that it may create larger waves. These waves travel across the ocean out of the area where the wind is blowing.
Water Molecule Movement Water molecules in waves make circles or ellipses. Energy transfers between molecules The molecules themselves mostly bob up and down in place.
Wave Breaks or“breakers” Develop as waves become too tall to be supported by their base. As waves approach shore, friction with the ground builds. The bottom of the wave slows down but the top of the wave continues at the same speed. The crest falls over and crashes down.
Tides The daily rise and fall of sea level at any given place. Caused by: the pull of the Moon’s gravity on Earth (primary cause) the pull of the Sun’s gravity on Earth. The Moon has a greater effect although it is much smaller than the Sun, it is much closer.
Located on the Gulf of Maine, the Bay of Fundy has the greatest tidal ranges on Earth at 38.4 feet. What is the science of why the tidal range is so extreme in the Bay of Fundy, while most places the difference between high and low tide is just a meter or so. The most important effect is resonance - the tides are high in the Bay of Fundy because the size of the bay is just right to match the natural gravitational pushing cycle of the Moon that causes the tides. Imagine you are pushing someone on a swing. The energy of the person on the swing is much more than you give them in any one push, but if you provide the push at just the right time, you keep building up the resonant response. In our case the swing is the flow of water in and out of the bay, and the push is provided by ocean tides caused in turn by the gravitational influence of the Moon mainly (another post will talk about tides in general).
Daily Tide Patterns Water bulges are created by the moon’s gravitational pull on the Earth. High Tides: the two bulges formed on opposite sides of the Earth, aligned with the moon.
Daily Tide Patterns Low Tides: form between the two high tides, where less water remains.
Daily Tide Patterns Tidal Range: the difference between the ocean level at high tide and low tide. Tidal range depends on slope of the seafloor. Water appears to move a greater distance on a gentle slope than on a steep slope.
Monthly Tide Patterns Spring Tides: extreme high and low tides. Have a greater tidal range Occur whenever the Moon is in full-moon or new-moon phase (Earth-Sun-Moon align).
Monthly Tide Patterns Neap Tides: moderate high and low tides. Have the smallest tidal range. Occur when the Moon is at 1st or Last quarter (Earth-Sun-Moon form right angle).
Ocean bulges and tides
Surface Currents Ocean water that moves in a predictable way along the ocean surface. Can flow thousands of kilometers and reach depth of hundreds of meters. Remain unchanged by storms
Surface Currents Distribute heat around Earth Influence climate around the planet Are created by: Global wind patterns Rotation of the Earth Shape of the ocean basins
Global Wind Patterns Blow in the same directions all the time Are related to the unequal heating of Earth by the Sun (more solar radiation at the equator than the poles). Also due to the rotation of the Earth, Coriolis effect.
Coriolis Effect Describes how Earth’s rotation steers winds and surface ocean currents. Wind or water that travels toward the poles from the equator is deflected to the east. Wind or water that travels toward the equator from the poles gets bent to the west. Coriolis effect video BBC
In the Northern Hemisphere surface currents bend to the right. In the Southern Hemisphere surface currents bend to the left.
Wind Belts trade winds: east to west between the equator and 30oN and 30oS westerlies: west to east in the middle latitudes polar easterlies: east to west between 50o and 60o north and south of the equator and the north and south pole
Shape of Ocean Basins When a surface current collides with land, the current must change direction. Atlantic South Equatorial Current travels westward along the equator until it reaches South America. At Brazil, some of it goes north and some goes south. Because of Coriolis effect, the water goes right in the Northern Hemisphere and left in the Southern Hemisphere.
Gyres The Pacific and Atlantic Oceans have a circular pattern of surface currents. Circle clockwise in the Northern Hemisphere Circle counterclockwise in the Southern. The Indian Ocean only has a counterclockwise gyre.
Local Surface Currents Currents found along shorelines: Rip current- potentially dangerous currents that carry large amounts of water offshore quickly. Longshore current- Longshore currents move water and sediment parallel to the shore in the direction of the prevailing local winds.
Currents and Climate Surface ocean circulation brings warm equatorial waters towards the poles and cooler polar water towards the equator.
Gulf Stream The Gulf Stream is a river of warm water in the Atlantic Ocean, about 160 kilometers wide and about 1 km deep. Water is heated as it travels along the equator. The warm water then flows up the east coast of North America and across the Atlantic Ocean to Europe. London vs. Quebec, Canada (at the same latitude) London’s average January temperature is 3.8oC (38oF) Quebec’s average January temperature is -12oC (10oF). The Gulf Stream picks up a lot of water = London gets a lot of rain. Quebec is much drier and receives its precipitation as snow.
Deep Currents Thermohaline circulation drives deep ocean circulation. Thermo means heat Haline refers to salinity Differences in temperature and salinity affect the density of seawater. Deep currents are the result of density differences in water masses because of their different temperature and salinity.
Density Lower temperature and higher salinity yield the densest water. As water cools the molecules move less = take up less space = denser water. If salt is added, there are more molecules per amt. of space = denser water.
Sinking Water Downwelling: very cold, very saline water sinks. Cold polar air cools the water and lowers its temperature, making it more dense. Fresh water freezes out of seawater to become sea ice, which also increases the salinity of the remaining water.
Thermohaline Circulation This very dense downwelling water pushes deeper water out of its way. That deeper water mixes with less dense water as it flows. Surface water is pulled to replace the sinking water, which in turn eventually becomes cold and salty enough to sink.
This creates deep-ocean currents driving the global conveyer belt. It is estimated that it can take 1,000 years for a "parcel" of water to complete the journey along the global conveyor belt.
Upwellings: rising of cold, nutrient-rich waters biologically rich areas where surface waters are blown away from a shore where equatorial waters are blown outward.
Upwellings & Foodweb Bring nutrients to the surface. Those nutrients support the growth of plankton and form the base of a rich ecosystem. California, South America, South Africa, and the Arabian Sea all benefit from offshore upwelling.