Oceanography Exam 3

Thermohaline Circulation

Density driven circulation of the ocean below the pycnocline

• Temperature and salinity important in production of deep and intermediate water masses

• causes deep water to always be cold

Water mass

an identifiable body of water that can be recognized by physical and chemical characteristics

North Atlantic Deep Water

(NADW) forms in the northern North Atlantic (Greenland-Norwegian Sea)

Antarctic Bottom Water

(AABW) forms in the southern South Atlantic (Weddell Sea of Antarctica)

Circumpolar Water

• Sometimes called “Common Water”

• Deep waters of the Indian & Pacific oceans are a mix of NADW and

  AABW

Antarctic Intermediate Water

AAIW forms at the Antarctic Convergence (Polar Front), then sinks and flows north into the South Atlantic, Caribbean Sea, Gulf of Mexico and North Atlantic

Mediterranean Intermediate Water

MIW, warm, salty water mass produced in the Mediterranean Sea due to high evaporation rates in the subtropics. MIW is among the densest waters formed in the ocean today.

global conveyor

the complete circuit of global ocean circulation involving horizontal flow of surface and deep waters, and the vertical flow of downwelling and upwelling.

Surface

Where does deep water acquire its physical and chemical characteristics?

Deep water forms in

• Polar Regions

• High Latitude

• North Atlantic & Antarctica

Brine

• Sea Ice causes this

• important in the development of Antarctic Bottom Wate

North Pacific

Oldest waters in the world found here

Wave Catalysts

• Sun & Moon

• Storms & Earthquakes

• Wind

• Storms, Sun & Moon

• Wind and ordinary gravity waves

Transverse

• Particles move up and down

• Ex: Rope, S-waves

Longitudinal

• Particles move back and forth

• Ex: P-waves

Orbital

• Moves in loops (circles)

• Ex: Ocean Waves

Crest

Top of a wave

Wavelength

Length of a wave

Wave Height

Height of a wave

Amplitude

• intensity or strength of the wave

• the maximum displacement or distance moved by a point on a wave measured from its equilibrium (rest) position

Trough

Bottom of a wave

Wave Base

Maximum depth at which a water wave causes significant water motion

Wave Base Depth

Equation: L/2

deep-water wave

• an ocean surface wave that occurs in water deep enough that the seabed does not affect the motion of the wave

• wave that travels in water where the depth is greater than half its wavelength,

• Depth > L/2

Wave Period

• The time it takes for successive crests (or troughs) to pass a fixed point

• Typical Units: Seconds

Wave Frequencies

• Number of waves that pass a fixed point per

  unit of time

• Typical Units: 1/seconds or Hertz (Hz)

Celerity

• the speed at which a wave travels

• C=L/T

swell

• Waves with long wavelengths & periods arriving from a distant source

• can be a sign that a storm is coming

Wind Waves

1. Wind blows across the sea and transmits energy to the water surface

by way of friction

2. Light winds form small ripples or capillary waves

3. As water gains energy, H and L increase

• Crests of waves are pulled back down to sea surface by gravity

Fetch

distance wind blows over

Duration

time wind has been blowing

Wave Steepness

S = H/L

Breaking Criterion

If wave steepness (H/L) exceeds 1/7 or 0.14 wave breaks

Fully Developed Sea

Max waves for given wind of sufficient fetch sufficient duration

Shallow Water

When a wave enters this its:

• Wavelength: SHORTENS

• Wave Height: INCREASES

• Wave Speed: SLOWS DOWN

Deep Water Wave

DOES NOT interact with bottom

Shallow Water Wave

DOES interact with bottom

Shallow Water Wave Criterion

Depth is less than 1/20th of the Wavelength, i.e.: D<L/20

Tides

very long-period waves that move through the oceans, in response to the forces exerted by the moon and sun

High Tide

tide crest

Low Tide

tide trough

Tidal Range

Difference between high tide and low tide

Flood Tide

Incoming tide → water rising (low → high)

Ebb Tide

Outgoing tide → water falling (high → low)

Two tides per day

How many tides per day are there in the Northeastern US?

Semidiurnal Tides

Two high tides and two low tides each day

Two Tides Reason

Moon’s gravity pulls harder on the side of Earth closest to it than the far side.

This difference creates two ocean bulges.

one facing the Moon and one on the opposite side.

• These bulges create two

high tides per day.

• The low points in

between result in two

low tides per day too!

Lunar Day

24 hr & 50 min

Time between consecutive tides

12 hrs and 25 minutes

New Moon

happens

Moon is between Earth

and the Sun, so we

can’t see its lit side.

Full Moon

happens when Earth

is between the Sun

and Moon, so we

see the lit side.

Spring tides

larger tides in the month

Neap tides

smaller tides in the month

Perigee

• Moon is closer to the Earth and looks slightly larger

Apogee

Moon is farther from the Earth and looks slightly smaller

Diurnal

One high and

one low tide

each (lunar)

day

Mixed

Characteristics of both diurnal

and semidiurnal with successive

high and/or low tides having

significantly different heights

Tsunami

A series of waves caused by sudden displacement of water (often by an earthquake)

Uplift

Rise in land elevation

Subsidence

Fall in land evaluation

Shallow Tsunami

As water depths decrease

the Tsunami’s:

1. Wave Length Shortens

2. Wave Height Increases

3. Steepness Increases