Oceans in Motion

What causes the tide

gravitational forces between the moon and Earth, also influenced by the sun, tilt of Earth, topography

Monthly tide cycle

2 spring and 2 neap tides per month

Waves (surface water movement)

wind driven, only move water about one half a wavelength

Wavelength

distance between peak of two waves

Wave trough

“lull” between two wave peaks

Wave height

distance from wave trough to wave peak

Depth of water movement

1.3 times wave height

Stoke’s drift

displacement of water in the direction of wave movement, wave movement is circular but not a closed circle

Fetch

the uninterupted distance over open water that the wind blows in a single constant direction

Near shore currents

created by wind (=waves) and shore topography, 3 types: longshore current, undertow, rip current

Undertow current

the seaward return of water along the bottom underneath breaking waves

Longshore current

when waves hit shore at an angle, pushing water and material down the shore

Rip current

surface current forms where waves converge and return to sea through channel

Gyres

mass movement of surface water driven by wind and coriolis force

Eckman spiral

created by the deflection of movement by coriolis force, water moves on averages 90 degrees to the wind

Coastal upwelling

wind driven, brings nutrients to the surface (high NPP)

Equatorial upwelling

due to trade winds and Eckman transport, follows ITCZ, diverging water replaced from below

Downwelling

sinking water, caused by density difference in converging currents

Deep currents (Thermohaline circulation)

driven by temp and salinity gradients, “deepwater formation”

Deepwater formation

sinking water takes oxygen and carbon dioxide down