Chapter 3 Part 2: The World Ocean

stratification

water layers with different densities; densest water sinks to the bottom, least dense remains at the surface

water column

a vertical section of water extending from the surface down

temperature distribution

deep water: cold and dense

surface water: usually warm and less dense

profile

graph depicting temperature, salinity, or other characteristics at various depths

pynocline

zone of quick density increase with depth

thermocline

zone of rapid temperature drop with depth

halocline

zone of rapid salinity increase with depth

stability factors

low stability: more dense water over less dense water leads to easier mixing

high stability: increased density with depth limits mixing

downwelling

occurs when surface water becomes denser than deep water; happens typically in winter when cooling increases density

upwelling

winds blow across the ocean, pushing surface water away, causing deeper nutrient-rich water to rise

resulting water is colder and rich in nutrients

thermohaline circulation

“great ocean conveyor belt”

movement patterns of water masses influenced by temperature (thermo) and salinity (haline)

surface layer

mixed layer from surface down to 200 meters, influenced by wind, waves, and currents

intermediate layer

from 200 to 1,500 meters, characterized by thermocline with rapid temperature drop

deep/bottom layers

below 1,500 meters, uniformly cold

ocean motion

constant motion through waves, currents, and tides

coriolis effect

earth’s rotation causes moving objects to bend rather than travel in a straight line

deflects winds and currents: right (clockwise) in the northern hemisphere, left (counterclockwise) in southern

trade winds

known for being the steadiest winds on earth, moving from east to west in the tropics

winds bent 45 degrees towards the equator due to the Coriolis effect

westerlies

found at middle latitudes, moving from west to east

polar easterlies

at high latitudes, these winds are variable and move from east to west

ekman spiral

surface winds initiate surface current at a 45 degree angle due to the Coriolis effect; this movement propagates to layers below, creating an angled flow

equatorial currents

wind-driven surface currents moving parallel to the equator under trade winds’ influence

gyres

large, circular systems formed by the combination of equatorial currents, influenced by the Coriolis effect

crest

highest part of a wave

trough

lowest part of a wave

wavelength

distance between crests

wave height

vertical distance from trough to crest

period

time taken for two successive crests to pass a fixed point (in seconds)

generative forces

created primarily by wind; stronger and longer winds produce larger waves

fetch

distance over which the wind blows; longer fetch results in bigger waves

seas (wind waves)

formed during storms, sharp crests and flat troughs

swells

after the storm, waves smooth out into rounded crests and troughs, exhibiting ideal circular motion

tides

rhythmic rise and fall of sea levels, heavily impacting nearshore sea life

influenced by the gravitational forces of the moon and sun along with earth’s rotation

centrifugal force

causes water to bulge outward on the side away from the moon

gravitational force

pulls water toward the moon, creating tidal bulges

spring tides

occurs when the earth, moon, and sun align (full and new moons); leads to highest high tides and lowest low tides (twice monthly)

neap tides

result when the sun and moon are at right angles (quarter moons); leads to lower high tides and higher low tides (also twice monthly)

semidiurnal tides

two high and two low tides daily

mixed semidiurnal tides

successive high tides at different heights

diurnal tides

rare, characterized by one high and one low tide daily

what three factors affect wave height?

wind speed, wind duration, and fetch

tide table

a table indicating the times of high and low tides at a particular place