Ocean water moves in two directions: horizontally and vertically. Horizontal movements are referred to as currents, while vertical changes are called upwellings or downwellings. This abiotic system is responsible for the transfer of heat, variations in biodiversity, and Earth's climate system. Tides are the repeated rise and fall of sea level at any given place. The pull of the moon’s gravity on Earth is the primary cause of tides. The pull of the sun’s gravity is a secondary cause. Although the moon has much less mass than the sun, its effect on Earth’s tides is greater because it is so... Show more

Ocean water moves in two directions: horizontally and vertically. Horizontal movements are referred to as currents, while vertical changes are called upwellings or downwellings. This abiotic system is responsible for the transfer of heat, variations in biodiversity, and Earth's climate system.

Tides are the repeated rise and fall of sea level at any given place. The pull of the moon’s gravity on Earth is the primary cause of tides. The pull of the sun’s gravity is a secondary cause. Although the moon has much less mass than the sun, its effect on Earth’s tides is greater because it is so much closer to Earth.    
As the moon revolves around Earth, its gravity pulls Earth toward it. The lithosphere is unable to move much but ocean water can, and it bulges outward toward the moon. This creates a high tide on the side of Earth facing the moon. The moon’s gravity pulling Earth toward it leaves behind water on the opposite side of the planet. This creates another high tide bulge on the opposite side of Earth from the moon. Because so much water is pulled into the two high tide bulges low tides occur at places in between. Earth rotates beneath the moon once each day, so any given place on the coast will experience two high tides and two low tides every day.    

The difference in water levels between high and low tides is called the tidal range. This range is greatest during spring tides and least during neap tides.    
- Spring tides occur when the gravitational pull of both the moon and the sun are in the same direction. This happens when the moon is in its new or full moon phase, so spring tides occur about twice a month. The high tides are higher and the low tides are lower than at other times of the month.    
- Neap tides occur when the gravitational pull of the moon and the sun are at right angles to each other. This happens during the first and third quarter phases of the moon, so spring tides also occur about twice a month.    
The high tides are lower and the low tides are higher than at other times of the month.    

Show less