TIDES

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 http://www.youtube.com/watch?v=u3LtEF9WPt4

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

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.

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

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°)

~ 90 ~ 60 ~ 0-35

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

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

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

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

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

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

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.