1. TIDES

2. Tides and Waves •Regular rise & fall of sea that occurs:
–1X day (24.8 hrs) OR 2X day (12.4 hrs)
Crest (high tide), trough (low tide)
Waves with very long:
–Period (24.8 or 12.4 hrs)
–Wavelength (½ of Earth’s circumference)
Shallow-water waves (long wavelength)
Never in H2O deeper than ½ their wavelength

3. Causes of Tides 1. Gravitational attraction between: – Earth & moon
– Earth & sun
– Pulls ocean toward moon & sun
2. Inertia (Centrifugal): Moving objects continue in a straight line
– Earth’s motion around center of mass of Earth-moon system
– Earth's orbiting around sun
– Push outward from center of rotation

4. Forces Produce 2 Tidal Bulges
Excess gravity on moon side of Earth Ocean bulges toward moon.
Deficiency of gravity on side facing away from moon
Centrifugal force pulls ocean away from the moon.

5. 2 high tides and 2 low tides each day (in most places)
Earth rotates between bulges daily
Low Tide
High Tide
High Tide
Low Tide

6. 3 Types of Daily Tides 1. Diurnal: 1 high & 1 low tide a day
– High Latitudes (~90°)
2. Semidiurnal: 2 high & 2 low tides of
~ same height daily
– Most common
3. Mixed: Successive high &/or low tides have different heights
– Common in low latitudes (~0-35°)

7. ~ 90
~ 60
~ 0-35

9. Monthly Tides: Sun & Moon Together
Spring tides: Earth, sun, & moon are aligned (new & full lunar phases)
–Solar tide has additive effect on lunar tide
–Extra-high, high tides & very low, low tides

10. Monthly Tides: Sun & Moon Together
•Neap tides: Sun & moon are at right angles
•Solar tide partially cancels out lunar tide
•Produces moderate tides

13. Movement of Tidal Water Towards and Away from Land
• Generates tidal currents
Ebb Current:
flow of water away from land with approaching low tide
Flood Current:
flow of water
towards land with
approaching high tide

14. Tides and Marine Organisms
• Intertidal species must adapt to stresses:
– Crashing waves, abrasion (High tide)
– Heat, sun, dryness, No O2 (Low tide)

15. Tide and Marine Organism
Mix nutrients & gases (CO2 & O2)
Important to movement & migration
– Plankton (floaters & drifters) carried into tide pools.

16. Animal Reproduction
Larvae require tides to move them toward or away from coast
Recruitment
Crab Larvae
Seastar Larvae

17. California Grunion
• Come out of water to spawn (lay & fertilize eggs) on beach
At night from Feb-Sep
At highest spring tides (full or new moon)
In 10 days babies hatch & wash out to sea at next high spring tide.