Tides and CurrentsNotes

How often do tides occur?

• There is about 12 hours and 25 minutes between two high tides or between 2 low tides.

• If it is high tide in the afternoon today, then a week from today it will be low tide in the afternoon.

What causes tides?

• Sun’s gravitational pull • Moon’s gravitational pull

– Because of the nature of gravity and proximity the moon’s pull is over twice that of the much larger sun

• These result in tidal bulges (high tides) on opposite sides of the Earth

Why is there a bulge on the opposite side from the gravitational pull?

• Inertia– Tendency of an object to

stay moving in a straight line

• On the far side, the gravitational pull of the moon is weaker because it is farther away

• On the far side, the force of inertia is greater than the gravitational pull so it bulges

What is a spring tide?

• Extreme differences between high and low tide

• Sun, earth and moon are in a straight line

• Effects of moon and sun are cumulative

What is a neap tide?

• Moderate differences between high and low tide

• Sun, earth and moon are at right angles (90o) and the effect of the sun and moon slightly cancel each other out.

What else can affect tides?

• Shape of the shoreline– Isolated islands tend to have smaller tide differences

• Shape of a estuary– Funnel shape=large tidal differences– Narrow inlet and shallow water=smaller tidal differences

• Local wind patterns– Can move water in or out exacerbating tides

What are the tidal ranges of the Bay?

• Not very large difference between high and low tide– CBBT: 2-4 feet– Huntington Beach: 2-3

feet– Mobjack Bay: 2-2.5 feet

– Bay of Fundy: spring tide is 47.5 feet

What are surface currents?

• Continuous, directed movement of water

• Mostly caused by wind– Move at 45o angle to

wind due to Coriolis effect

– Responsible for about 40% of the global heat transport

What else causes currents?• Thermohaline circulation

– Thermotemperature– Halinesalt

• Differences in the density of water due to heat fluxes and freshwater input results in water circulation

What are the major ocean currents?

Describe the location and direction of the following: Gulf Stream, Labrador, Equatorial Counter, California, Antarctic Circumpolar

Why do currents matter to marine life?

• Move nutrients from deep water to the surface

• Disperse waste• Act as boundaries to animals because of

changes in temperature

Great Pacific Garbage Patch