AP Environmental Science Mr. Grant Lesson 79

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AP Environmental Science

Mr. GrantLesson 79

The Oceans


Objectives:

• Define the terms photic zone, pelagic zone and benthic zone.

• Identify physical, geographical, chemical, and biological aspects of the marine environment.

• Explain how the oceans influence, and are influenced by, climate.


Photic Zone: The surface layer of a body of water. In the photic zone, enough light is present for organisms to photosynthesize. In the ocean, around 90% of the life can be found in the photic zone.

Pelagic Zone: A term that refers to open area of a sea or large lake, away from the bottom or out of sight of shore.

Benthic Zone: The bottom of a sea or lake.

Define the terms photic zone, pelagic zone and benthic zone.


Identify physical, geographical, chemical, and biological aspects of the marine environment.• Oceans cover 71% of Earth’s surface and contain over 97% of

its surface water.

• Seafloor topography can be complex.

• Ocean water contains 96.5% H2O by mass and various dissolved salts.

• Colder, saltier water is denser and sinks. Water temperatures vary with latitude, and temperature variation is greater than surface layers.

• Surface currents move horizontally through the oceans, driven by wind and other factors.

• Vertical water movement includes upwelling and down welling, which affect the distribution of nutrients and life.


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


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

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


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


A stylized bathymetric profile of the oceanA stylized map reflects the ocean’s bathymetry (depths) and topography (landforms)


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


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


Explain how he oceans influence, and are influenced by, climate.

• The thermohaline circulation shapes regional climate, or instance, keeping Europe warm. Global warming could potentially shut down existing circulation patterns.

• El Niño and La Niña events alter climate and affect fisheries.

• The oceans sequester atmospheric carbon and have slowed global climate change, but they could become saturated.

• Absorption of excess carbon dioxide leads to ocean acidification, which hinders corals in forming reefs.


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


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


Currents form patterns across the globe


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


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


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


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


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


ENSO, El Niño, and La Niña

Normal conditions El Niño conditions


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

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AP Environmental Science Mr. Grant Lesson 79