- Slides: 17
What causes tides? Tides- the daily rise and fall of Earth’s waters on its coastlines. As the tide come in, the level of water of the beach rises gradually. When the water reaches its highest point, it is high tide. When the water reaches its lowest point, it is low tide. Tides occur in all bodies of water, most noticeable in the ocean
Gravity and tides Tides are caused by the interaction of Earth, the moon, and the sun. Gravity is the force exerted by an object that pulls other objects toward it. The moon pulls on the water on the side of Earth’s closest to it more strongly than it pulls on the center of the Earth.
The gravitational attraction of the moon causes the oceans to bulge out in the direction of the moon. Another bulge occurs on the opposite side, since the Earth is also being pulled toward the moon (and away from the water on the far side). Earth’s rotation through the tidal bulges causes most coastlines to experience two high tides and two low tides every 25 hours.
When the sun and moon are aligned, there are exceptionally strong gravitational forces, causing very high and very low tides which are called spring tides, though they have nothing to do with the season. When the sun and moon are not aligned, the gravitational forces cancel each other out, and the tides are not as dramatically high and low. These are called neap tides.
Earth turns completely around once everyday. High tide occurs about 12 and 25 minutes apart in any location. High tide and low tide are not always a dramatic change. Certain landforms can interrupt the water’s movements. Basin at mouth of river, speed and depth of water increase in narrow channel; causing dramatic tides.
Monthly tide cycle Changes in the positions of Earth, the moon, and the sun affect the heights of the tides during a month. spring tide- combination gravitational pull (sun/moon) produces the greatest difference between the heights of high and low tide. Neap tide- a tide with the least difference between low and high tide. During the neap tide the sun pulls some of the water away from the moon side.
Tide tables Scientists can predict tides quite accurately for many locations. Knowing the times and heights of tides is important to sailors, marine scientists, fisherman, coastal residents. This table lists the highest and lowest tides for one week at the mouth of the Savannah River, where it meets the Atlantic Ocean in Georgia Tide table Day Highest Lowest High Tide Low Tide (m) 1 1. 9 0. 2 2 2. 1 0. 1 3 2. 3 0. 0 4 2. 4 -0. 2 5 2. 5 -0. 2 6 2. 6 -0. 3 7 1. 9 0. 3
Tide tables Graphing- use the data in the table to make a graph. On the horizontal axis, mark the days. On the vertical axis, mark the heights ranging from 3. 0 to 1. 0 meters Graphing- plot the tide heights for each day on the graph. Connect the high tide points with one line and the low tide points with another line. Interpreting data- how do the high and low tides change during the week? Inferring- what type of tide might be occurring on day 6? explain Tide table Day Highest Lowest High Tide Low Tide (m) 1 1. 9 0. 2 2 2. 1 0. 1 3 2. 3 0. 0 4 2. 4 -0. 2 5 2. 5 -0. 2 6 2. 6 -0. 3 7 1. 9 0. 3
Energy from tides The movement of huge amounts of water between high and low tide is a source of potential energy (energy that is stored and can be used).
Currents and climate Surface currents Current is a large stream of moving water that flows through the oceans. Unlike waves, currents carry water from one place to another. Surface currents, which affect water to a depth of several hundred meters, are driven mainly by winds. Major ocean currents
Why do currents move in these circular patterns? Coriolis effect If Earth were still, winds and currents would move in a straight line. Because Earth rotates the path of winds and currents curve. In northern hemisphere, causes currents to curve to the right. In southern hemisphere, currents curve to the left. Gulf stream Largest/most powerful current in North Atlantic, caused by strong winds from west. 30 km wide, 300 m deep, and carries 100 times more volume than Mississippi river.
Effects on climate Climate is the pattern of temperature and precipitation typical of an area over a long period of time. Currents affect climate by moving cold and warm water around the globe. A surface current warms or cools the air above it, influencing the climate of the land near the coast.
El nino When changes in wind patterns and currents occur. Example el nino, an abnormal climate event that occurs every two to seven years in the Pacific Ocean. El nino begins when an unusual pattern of winds forms over the western Pacific. Causes warm water to move eastward toward South American coast. Can last for one to two year before the usual winds and currents return. Causes shifts in weather patterns around the world.
El nino Major el nino occurred between 1997 -1998 and caused an especially warm winter in the northeastern United States. Also responsible for heavy rains, flooding, and mudslides in California, as well as a string of deadly tornadoes in Florida Scientist do not fully understand the conditions that cause El Nino, they have been able to predict its occurrence using computer models of world climate.
Deep currents These deep currents are caused by differences in the density of ocean water. Deep currents move and mix water around the world. They carry cold water from the poles toward the equater.
upwelling Is the movement of cold water upward from the deep ocean. Brings up tiny ocean organisms, minerals, and other nutrients from the deeper layers of the water. Without this motion, the surface waters of the open ocean would be very scarce in nutrients.