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Oceanography

I. Tides - tides are a long wave (picture Earth with no continents)
- crest of the wave passes a point = high tide
- trough of the wave = low tide

A. Earth-Moon system - two tidal crests - one towards moon, one away from moon

1. Gravitational attraction - cause bulge towards the moon, its gravitational forces pull the water towards it.

2. Barycenter - rotation of the Earth and the moon around one another
   Barycenter of this rotation is not at the Earth's axis, but inside the Earth towards the moon. The result is a wobble in the Earth's rotation around the sun

3. Centrifugal force - causes bulge opposite from moon.
   Centrifugal force pulls the water away from the Earth, as a ball is pulled away from the string you are swinging it on - gravity keeps the water from flying away from the Earth.

4. Lunar day - Globe
   a. Moon takes 28 days to entirely circle the earth.
   b. Lunar day = 24 hr 50 min, so the moon appears to rise 50 min later every day, so the tides are 50 min later every day
   c. Lunar semidiurnal tides = approx. 2 highs and lows every day, shifting in time as lunar day falls behind our Earth's day

B. Earth-Moon-Sun system - Globe

1. Tidal range - height difference between low and high tides, varies from day to day.
   Why, if the lunar cycle is regular? Because of the impact of the Sun's gravitation al attraction

2. Sun/Moon gravitational interaction
   - Fig. 9-6b, Fig. 9-14, Globe
   a. Spring tides - when moon and sun are in alignment, gravitational forces are summed, creating high highs and low lows
   b. Neap tides - when moon is at 90° to suns position
   - gravitational forces are not summed

C. Tide types - determined by tide frequency and range - Fig 1-16 - impacted by coastal topography, ocean/by basin shape & direction

1. Semidiurnal - two equal high and low tides each day, east coast

2. Diurnal - one high and low each day, rare; Gulf of Mexico

3. Mixed - combined characteristics of diurnal and semidiurnal, two high and two low tides each day, but not equal, west coast

II. Ocean circulation - very important, transfers heat around the globe, moves nutrients, moves eggs and larvae of marine organisms, moves predators and prey into contact with one another (animals have evolved in response to these currents.

A. Tidal - incoming and outgoing tides move a lot of water and organics and organisms, particularly in bays and estuaries.

B. Longshore - result of waves striking the beach at an angle, move lots of sand and organisms (larvae, etc.), strictly a coastal phenomenon

C. Wind-driven - majority of the open ocean currents are wind driven

1. Major winds - Tradewinds, Westerlies

2. Oceanic gyres = Winds + Coriolis + Ekman + Position of landmasses can explain oceanic currents - See gyres on current map
   e.g. Atlantic circulation

D. Upwelling

1. Coastal upwelling

2. Equatorial upwelling

F. Thermohaline - deep ocean circulation due to salinity and density

1. Density
   a. Cold is more dense that hot (until freezing)
   b. More saline (salinity = salty) is more dense than less
   c. More dense will sink if not mixed

2. Thermohaline mixing
   a. As water freezes, the salts are excluded.
   b. The frozen water rises, as it is less dense, and the salts remain in the layer below the ice.
   c. This layer is now more dense, because it is more saline, and it sinks, beginning deep sea thermohaline circulation.

G. Regional currents - primarily wind driven currents, no upwelling etc to consider here.

1. Gulf Stream

2. Labrador current

3. Northern Maine Current

III. Bathymetry - depth and topography of the bottom.

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