Transcript Lecture 5: Oceans & Tides

Lecture 5: Oceans &
Tides
Corresponding Reading Material
~ Levinton: chapters 2 and 3
The Oceanic Environment
Notes for Marine Biology:
Function, Biodiversity, Ecology
By Jeffrey S. Levinton
©Jeffrey S. Levinton 2001
The Ocean and Marginal Seas
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The worlds oceans: oceans and marginal
seas
Oceans cover 71% of earth’s surface
Southern hemisphere 80%, Northern
hemisphere 61%
84% deeper than 2000m
Greatest depth ~ 11,000 m in Marianas
Trench
Marginal Seas
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Examples: Gulf of Mexico, Mediterranean
Sea
Affected strongly by regional climate,
precipitation-evaporation balance, river
input of fresh water and dissolved solids,
often with limited exchange with the open
ocean (e.g., sill partially cutting
Mediterranean from Atlantic)
Marginal Seas 2
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Often have recent history of major change
Mediterranean: completely dry a few million
years ago
Baltic Sea: less than 11,000 years old
Topographic Features
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Continental shelf (1° slope)
Continental slope (2.9° slope)
Continental Rise
Abyssal Plain
Submarine Canyons
Oceanic Ridge Systems
Slope
Abyssal plain
Mid-ocean ridge
Abyssal plain
Marginal sea
Volcanic island
Depth (km)
Topographic Features 2
Eurasian
Eurasian
American
Caribbean
Philippine
Arabian
Pacific Cocos
Nazca
American African
Antarctic
Earth’s surface is divided into plates: borders are ridge systems, faults
The Oceanic Crust: Crust is formed at ridges, moved
laterally, and destroyed by subduction, which forms
trenches
Continental
crust
Inactive fault
Continent
Trench
Oceanic
crust
Intermediate, deepfocus earthquakes
Ridge
Fault
Continental
Crust
Mantle
Evidence of Plate Tecontics
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Fossils from different continents of same
species or similar species
Sonar data of sea floor
Magnetic field reversals and age of rocks near
sea floor spreading centers
Seismic waves and how they move through
liquids and solids
Properties of Water
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Water has a high heat capacity (specific
heat)
~ Heat Capacity = measure of the
heat required to raise the
temperature of 1 gram of
substance 1°C
This means water can absorb (or release)
large amounts of heat while changing
relatively little in temperature
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Due to the lattice structure of water when it
changes from a liquid to a gas, the solid ice
floats on the liquid water.
Properties of Water
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The water molecule was a high
dissolving power
~ The water molecule is polar
~ Water molecules can form
hydrogen bonds
Salinity
Definition: g of dissolved salts per 100g of
seawater; units are o/oo or ppt
 Controlled by:
+ evaporation, sea-ice formation
- precipitation, river runoff
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Salinity in open ocean is 32-38 o/oo
Important elements in seawater
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Chlorine (19,000 mg/l)
Sodium (10,500
Magnesium (1,300)
Sulfur (900)
Calcium (400)
Potassium (380)
Bromine (65)
Carbon (28 - variable)
Principle of Constant Element Ratios
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Ratios between many major elements
are constant all over the ocean, even
though salinity varies
Light
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What happens when light passes through water?
1. Scattering = occurs as light is bounced between air of water
molecules, dust particles, water droplets, or other objects before being
absorbed
2. Absorption = water molecules vibrate and the light’s electromagnetic
energy is converted to heat
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Each color in the visible spectrum of light has a different wavelength.
The longer the wavelength the easier the color is scattered.
~ This means the color red is absorbed first and violet last.
Photic Zone = illuminated zone of the ocean’s surface
~ Open Ocean: Water absorbs most light by 200 m
~ Coastal Zone: Due to suspended particles most light is absorbed in
10-50 m
Apothic Zone = lightless zone beneath the surface
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Temperature
Oceanic range (1.9 - 40 °C) less than
terrestrial range (-68.5-58 °C)
 Deep ocean is cold (2 - 4) degrees
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The Ocean
Circulation in the Ocean
©Jeffrey S. Levinton 2001
Coriolis Effect - Earth’s Rotation
Latitude
Equator
Eastward Velocity
(km/h)
1670
30° N. latitude
1440
60° N. latitude
830
Coriolis Effect - Movement of fluids, in relation to earth
beneath, results in deflections
North
Increasing deflection
of moving water
parcel to the right
Equator
No deflection
Increasing deflection
of moving water
parcel to the left
South
Ocean Circulation
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The circulation of deep water is driven by
density differences.
 The deep ocean is layered with the densest
water on the bottom and the lightest on top.
 Water tends to move horizontally in
throughout the deep ocean (along the lines of
equal density)
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Circulation of surface waters are driven
by winds
Coriolis Effect = deflection of moving
air or water caused by the rotation of the
Earth
Wind-driven Circulation 3
Wind systems
Westerlies
NE Tradewinds
Doldrums
SE Tradewinds
Westerlies
Surface currents
Subpolar
gyre
Subtropical
gyre
Subtropical
gyre
West wind drift
Coriolis Effect and Deflection
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Surface winds move over water
Coriolis effect causes movement of water at an
angle to the wind (to right in northern
hemisphere)
Water movement drags water beneath, and to
right of water above
Result: Shifting of water movement - Ekman
Spiral (actually friction binds water together and
all water moves at a right angle to wind (right of
wind in n. hemisphere)
Circulation Recap
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Coriolis effect - rotation of Earth, prop. to
sine of latitude, Right deflection in N.
hemisphere, Left deflection in S.
hemisphere - upwelling, deflection of
currents
Coastal Winds + Coriolis Effect = Upwelling
Surface water movement
Peru
WIND
Nutrient-rich water
Southern hemisphere: water moves to the left of wind
Oceanic Circulation
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Surface currents are controlled by the
interaction of the planetary wind system and
the earth’s rotation.
Winds and Coriolis effect combine to cause
upwelling, which bring s nutrient rich cold
waters from the deep ocean to the coastal
regions
Pages 25 through 29 in your textbook.
The Oceanic Environment:
Ecological terms
Habitats
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Intertidal
Subtidal
Continental shelf or Neritic - waters and bottoms
on the continental shelf
Oceanic or Pelagic - waters and bottoms seaward of
the shelf
Epipelagic zone - upper 150 m of water depth
Mesopelagic zone - 150 m - 2000 m depth
Bathypelagic zone - 2000 m - 4000 m depth
Abyssopelagic zone - 4000 m - 6000 m depth
Hadal - trench environments
Life Habits
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Plankton
Nekton
Benthos
Infaunal versus epifaunal (epibenthic)
Semi-infaunal
Boring
What are the Tides??
What Are the Tides?
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Tides = periodic, short-term changes in the height of the ocean surface at a particular
placed
Are the longest of the waves
Are huge shallow-water waves
Causes of the Tides:
Combination of the gravitational force of the moon and the sun, rotation of
the Earth, and the shape of oceanic basins.
High Tide
Low Tide
What Causes the Tides?
Spring Tides vs. Neap Tides
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During each phase of the new moon and full
moon the earth, sun, and moon come into
alignment creating spring tides. When they are
not in alignment neap tides occur.
Spring Tide- A tide which results in the
greatest range between high and low tide
Neap Tide- A tide which results in the least
tidal range between high and low tide
Tides
Spring
Tide
m
E
m
Sun
m
Neap
Tide
Sun
E
m
E = Earth
m = Moon
Tidal height (cm)
Tidal height (cm)
Tides
Day
Connecticut
Day
Washington State
Types of Tides
Semidiurnal Tides = the coastline
experiences two high tides and two low
tides of nearly equal level each lunar day.
This type is more likely to occur when
the moon is over the equator.
Mixed semidiurnal tides = the
coastline experiences successive high
tides or low tides that are significantly
different heights through the cycle. These
tides also tend to occur as the moon
moves furthest north or south of the
equator.
Diurnal Tides = the coastline
experiences one high tide and one low
tide each lunar day. This tends to occur
in certain areas when the moon is at its
furthest from the equator.
Three largest tides in
the world:
1. Bay of Fundy
2. Estuary of the River
Severn
3. Puerto Punta Peñasco,
Sonora, Mexico
Bay of Fundy
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The Bay of Fundy is located on the
west coast of Novia Scotia
It has the largest tidal range in the
world of 53 ft. (16 m)
100 billion tons of water flow into
and out of the bay on and average
tide.
~ creates strong rip
currents, swirling whirlpools,
and up-wellings.
The energy created by this great
movement of water can be used as
a clean renewable energy source.
Why is the tidal range so large at the
Bay of Fundy?
Bay of Fundy
Bay of Fundy
Estuary of the River Severn
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Has the second largest tidal
range in the world
Average height difference
between low and high tides is
47 ft.
Located in Britain
Pictures of Clevedon Pier on
the River Severn
•From one high tide to to the next high tide takes
12 hours and 25 minutes.
•A tidal day takes 24 hours and 50 minutes,
not 24 hours.
•WHY??