Oceanography Exam 3

Thermohaline circulation

Global ocean circulation driven by density differences caused by temperature and salinity; moves water between surface and deep ocean

What drives thermohaline circulation

Temperature and salinity (density differences)

Where does deep water form primarily

Atlantic Ocean at high (polar) latitudes

Where does deep water get its properties

At the surface in polar regions before sinking

Why does deep water form more in the Atlantic than Pacific

The Atlantic is saltier, making water denser

Why is ice formation important for deep water formation

It leaves salt behind, increasing density so water sinks

Where is the oldest ocean water found

North Pacific deep ocean

Colder vs warmer water density

Colder water is denser

Saltier vs fresher water density

Saltier water is denser

Thermocline

Layer where temperature decreases rapidly with depth

NADW

Cold, salty deep water in the North Atlantic

AAIW

Intermediate depth water formed near Antarctica

AABW

Coldest, densest bottom water from Antarctica

MIW

Warm, salty intermediate water from the Mediterranean

Wave height (H)

Distance from crest to trough

Wave amplitude (A)

Half of wave height

Wavelength (L)

Distance between two crests

Wave crest

Top of a wave

Wave trough

Bottom of a wave

Wave base

Depth where wave motion stops (L/2)

Deep water wave

Wave where depth is greater than half the wavelength (D > L/2)

Wave period (T)

Time between two wave crests passing a point

Wave frequency (f)

Number of waves per second (f = 1/T)

Wave celerity (C)

Wave speed

Wave speed formula

C = L/T

Deep water wave speed formulas

C = 1.56T and C = 1.25√L

Do particles move in deep water waves

No net movement; energy moves, not water

Swell

Long-period waves that travel faster and reach shore before storms

Wind wave size depends on

Wind speed, duration, and fetch

Fetch

Distance wind blows over water

Wave steepness formula

S = H/L

Breaking wave condition

Occurs when steepness > 1/7

Fully developed sea

When waves reach maximum size for given wind conditions

Tides

Rise and fall of sea level due to gravitational pull of Moon and Sun

Tidal range

Difference between high and low tide

Flood tide

Incoming tide

Ebb tide

Outgoing tide

Tides in Northeastern US

Semi-diurnal (2 tides per day)

Semi-diurnal tides

Two high and two low tides per day

Diurnal tides

One high and one low tide per day

Mixed tides

Combination of diurnal and semi-diurnal (unequal tides)

Time between high tides in New England

12 hours and 25 minutes

Lunar day length

24 hours and 50 minutes

Why tides occur twice daily

Two tidal bulges caused by Moon’s gravity and Earth’s rotation

Direction tides rotate in Northern Hemisphere

Counterclockwise

Full moon

Earth is between the Sun and Moon

New moon

Moon is between Earth and Sun

Spring tides

Largest tides during full and new moon

Neap tides

Smallest tides during quarter moons

How often spring and neap tides occur

Twice per month

Why solar tides are smaller

The Sun is farther away than the Moon

Perigee

Point where Moon is closest to Earth

Apogee

Point where Moon is farthest from Earth

Supermoon

Full moon at perigee

Micromoon

Full moon at apogee

Where semi-diurnal tides occur

East Coast of US

Where mixed tides occur

West Coast of US

Where diurnal tides occur

Gulf of Mexico

Shallow water wave condition

Depth ≤ L/20

Motion in shallow water waves

Flattened, not circular

What happens as waves enter shallow water

Height increases, wavelength decreases, steepness increases

Shallow water wave speed equation

C = 3.13√D

What controls shallow water wave speed

Water depth only

Wave period in shallow water

Stays the same

Tsunami

A large wave caused by seafloor displacement

Cause of tsunami

Earthquake shifts ocean floor vertically

Uplift

Rising of seafloor

Subsidence

Sinking of seafloor

How tsunamis are detected

DART buoy system

Why tsunami is shallow-water wave

Wavelength is extremely long relative to depth

Tsunami speed in open ocean

Comparable to a jet (~400–500 mph)

Tsunami speed near shore

Comparable to a car (~30–100 mph)

Deep vs shallow wave difference

Deep depends on wavelength/period; shallow depends on depth

Ebb tide definition

Current associated with outgoing tide

Semi-diurnal tides definition

Occur twice per day

Time between successive high tides

12 hours and 25 minutes

Neap tides frequency

Twice per month

Tides during new moon

Larger than average (spring tides)

Wave period definition

Time between successive wave crests

Wave base definition

Depth where motion stops

Orbital motion depth limit

Little motion below wave base

Breaking wave steepness

H/L = 1/7

Wave celerity definition

Wave speed

Wave velocity formula

C = L/T

Fetch definition

Distance wind blows

Swell definition

Long-period waves that travel far from storms

Shallow water wave criteria

D ≤ L/20