Tides

Gravity and Ocean Water

· Sun and Moon exert a gravitational pull on Earth

- Level of ocean surface rises and falls because of this gravitational pull= tides!

· Moon’s gravitational pull causes a bulge of ocean water on the side nearest to the Moon

- Sun’s bulge is smaller since the sun is further away

- Water fill in bulges, less water between bulges

§ Bulges of water= high tide

§ Area between bulges= low tide

Daily Tide Patterns

· Every coastal area has 1 high tide and 1 low tide a day

· Many things influence tide patters

- Location on surface, shape of ocean floor and coastline, and Coriolis Effect

Semidiurnal Tides

· 2 high tides, 2 low tides a day

- caused by Earth’s rotation

Diurnal Tides

· 1 high tide and 1 low tides a day

Mixed Tides

· have a mix of diurnal and semidiurnal tides

Time of Tides

· Due to motion of Earth and moon in space, the tide cycle repeats every 24 hours and 50 min.

Monthly Tide Cycles

· Due to changing positions of Sun, Moon and Earth tide heights vary through the month

· Spring Tide occurs twice a month during new and full moon

- Sun, Moon and Earth align

- Highest high tide and lowest low tide

· Neap Tide: occurs during 1^st and 3^rd quarter Moon

- Sun, moon and Earth form a 90º angle (right angle)

- Lowest high tide, highest low tide

Tides and Living Things

· Some organisms live on the shore between levels of highest high tide and lowest low tide

- Adapt to high tide (water life) and low tide (exposed to air and sun)

· Fish come closer to shore during high tide

- Feed on near shore organisms

- Some spawn during spring tide- bury their eggs- eggs then hatch during next spring tide