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Transcript
The Oceans
• The marine environment
• Ocean-climate relationships
© 2011 Pearson Education, Inc.
Central Case: Collapse of the cod fisheries
• No fish has had more impact on
civilization than the Atlantic
cod
• Cod have been fished for
centuries
• Large ships and technology
have destroyed the cod fishery
• Even protected stocks are not
recovering
- Young cod are being preyed
on
• But other species are recovering
in protected areas
© 2011 Pearson Education, Inc.
Cod are groundfish
• Fish that live or feed along the
bottom
- Halibut, pollack, flounder
• Cod eat small fish and
invertebrates
• They inhabit cool waters on
both sides of the Atlantic
• The 24 stocks (populations) of
cod crashed
- Overfishing and destroyed
habitat
© 2011 Pearson Education, Inc.
The U.S. and Canada
have paid billions to
retrain fishermen who
lost their jobs
Oceans cover most of the Earth’s surface
• Oceans influence climate, team with biodiversity,
provide resources, and help transportation and
commerce
• Oceans cover 71% of Earth’s surface and contain 97.5%
of its water
• Oceans influence the
atmosphere, lithosphere,
and biosphere
© 2011 Pearson Education, Inc.
Seafloor topography can be rugged
• The seafloor consists of:
- Underwater volcanoes
- Steep canyons
- Mountain ranges
- Mounds of debris
- Trenches
- Some flat areas
• Some island chains are formed by reefs or volcanoes
- Topographically complex areas serve as habitat and
productive fishing grounds
© 2011 Pearson Education, Inc.
Underwater volcanoes
http://news.discovery.com/videos/earthunderwater-volcano-caught-on-video.html
© 2011 Pearson Education, Inc.
Steep canyons
http://news.discovery.com/videos/earthvolcanoes-slide-silently-to-theirdeath.html
© 2011 Pearson Education, Inc.
Mountain ranges
© 2011 Pearson Education, Inc.
Mounds of debris
© 2011 Pearson Education, Inc.
Trenches
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
A stylized bathymetric profile of the ocean
A stylized map reflects the
ocean’s bathymetry
(depths) and topography
(landforms)
© 2011 Pearson Education, Inc.
Ocean water contains salt
• Ocean water is 96.5%
water
- Plus, ions of dissolved
salts
• Evaporation removes pure
water
- Leaving salt behind
• Low levels of nutrients
(nitrogen and phosphorus)
• Oxygen is added by plants,
bacteria, and atmospheric
diffusion
© 2011 Pearson Education, Inc.
Ocean water is vertically structured
• Temperature declines with depth
• Heavier (colder, saltier) water sinks
- Light (warmer, less salty) water stays near the surface
• Temperatures are more stable than land temperatures
- Water has high heat capacity (heat required to
increase temperature by a given amount)
- It takes more energy to warm water than air
• Oceans regulate Earth’s climate
- They absorb and release heat
- The ocean’s surface circulation moves heat around
© 2011 Pearson Education, Inc.
The ocean has several layers
• Surface zone
- Warmed by sunlight and stirred by wind
- Consistent water density
• Pycnocline = below the
surface zone
- Density increases with
depth
• Deep zone = below the
pycnocline
- Dense, sluggish water
- Unaffected by winds,
storms, sunlight, or temperature
© 2011 Pearson Education, Inc.
Ocean water flows horizontally in currents
• Currents = vast riverlike flows in the oceans
- Driven by density differences, heating and cooling,
gravity, and wind
- Influence global climate and El Niño and La Niña
- Transport heat, nutrients, pollution, the larvae of
many marine species, and people
• Some currents such as the Gulf Stream are rapid and
powerful
- The warm water moderates Europe’s climate
© 2011 Pearson Education, Inc.
Currents form patterns across the globe
© 2011 Pearson Education, Inc.
Sargasso Sea
© 2011 Pearson Education, Inc.
Vertical movement affects ecosystems
• Upwelling = the upward flow of cold, deep water
toward the surface
- High primary productivity and lucrative fisheries
- Also occurs where strong winds blow away from, or
parallel to, coastlines
• Downwellings = oxygen-rich water sinks where surface
currents come together
© 2011 Pearson Education, Inc.
Currents affect climate
• Horizontal and vertical movement of oceans affects
global and regional climates
• Thermohaline circulation = a worldwide current system
- Warmer, fresher water moves along the surface
- Cooler, saltier, denser water moves beneath the surface
• North Atlantic Deep Water (NADW) = one part of the
thermohaline conveyor belt
- Water in the Gulf Stream flows to Europe
- Released heat keeps Europe warmer that it would be
- Sinking cooler water creates a region of downwelling
© 2011 Pearson Education, Inc.
The North Atlantic Deep Water
• Interrupting the thermohaline circulation could trigger
rapid climate change
- Melting ice from Greenland will run into the North
Atlantic
- Making surface waters even less dense
- Stopping NADW formation and shutting down the
northward flow of warm water
- Europe would rapidly cool
• This circulation is already slowing
- But Greenland may not have enough runoff to stop it
© 2011 Pearson Education, Inc.
El Niño–Southern Oscillation (ENSO)
• ENSO = a systematic shift in atmospheric pressure, sea
surface temperature, and ocean circulation
- In the tropical Pacific Ocean
• Normal winds blow east to west, from high to low
pressure
- This forms a large convective loop in the atmosphere
• Winds push water west, causing it to “pile up”
- Nutrient-rich, cold water along Peru and Ecuador rises
from the deep
• Decreased pressure in the eastern Pacific triggers El Niño
- Warm water flows eastward, suppressing upwellings
© 2011 Pearson Education, Inc.
El Nino And La Nina
© 2011 Pearson Education, Inc.
El Nino
Effects of El Niño and La Niña
• Coastal industries (e.g., Peru’s anchovy fisheries) are
devastated
- Worldwide, fishermen lost $8 billion in 1982–1983
• Global weather patterns change
- Rainstorms, floods, drought, fires
• La Niña = the opposite of El Niño
- Cold waters rise to the surface and extend westward
• ENSO cycles are periodic but irregular (every 2–8
years)
- Globally warming sea and air may be increasing the
strength and frequency of these cycles
© 2011 Pearson Education, Inc.
ENSO, El Niño, and La Niña
Normal conditions
El Niño conditions
© 2011 Pearson Education, Inc.
Climate change is altering the oceans
• Global climate change will affect ocean chemistry and
biology
• Burning fossil fuels and removing vegetation increase
CO2, which warms the planet
- Oceans absorb carbon dioxide (CO2) from the air
• But oceans may not be able to absorb much more CO2
• Increased CO2 in the ocean makes it more acidic
- Ocean acidification makes chemicals less available for
sea creatures (e.g., corals) to form shells
- Fewer coral reefs decrease biodiversity and ecosystem
services
© 2011 Pearson Education, Inc.
I The Oceans
1.
What benefits do you derive from the oceans? How does your
behavior affect the oceans? Give specific examples.
2.
What proportion of Earth’s surface do oceans cover?
3.
What is the average salinity of ocean water?
4.
How are density, salinity and temperature related in each layer
of ocean water?
5.
What factors drive ocean currents?
6.
Give an example of how a surface current affects climate
regionally.
7.
What is causing ocean acidification? What consequences do
scientists expect ocean acidification to bring about?
© 2011 Pearson Education, Inc.