Ocean Properties

Ocean PropertiesOcean Properties

Ocean ConceptsOcean Concepts• Buoyancy• Temperature• Light• Density• Pressure• Depth• Sound

Buoyancy

Buoyancy & Isostasy

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Archimedes Principle of Buoyancy

A floating object displaces a volume of fluid equal in mass to the floating object

empty loaded with fish

Displaced water

• Objects that are more dense than water will sink.• Objects that are less dense than water will float.• Objects that are the same density as water will neither

sink nor float.

float

Neutrally buoyant

sink

• Blubber

• Swim bladder

• Pneumatophore

Organisms adaptation to buoyancy in water

• Air chambers

• Large liver & heterocercal tail

• Buoyancy Compensator Device

(BCD)

Organisms adaptation to buoyancy in water

Temperature

IsothermsIsotherms

Lines of equal temperature

60o

30o

0o

30o

60o

polar

polar

temperate

tropic

temperate

Sea Surface TemperatureSea Surface Temperature

Oct. 2010

Sea Surface TemperatureSea Surface Temperature

Sea Surface TemperatureSea Surface Temperature

10-24-10 to 10-27-2010

Properties of Light in the Ocean

The Electromagnetic Radiation Spectrum

Only green and blue wavelengths pass through water a great distance.

Light Absorption in the Ocean

• Light Intensity–decreases with depth

–0-100 m (photic zone)

–100-1000m (dysphotic zone)

–>1000 (aphotic zone)

Coral Reef Communities

Hermatypic corals:• possess zooxanthellae• are reef builders

Light: Clear water Warm temperature: 18-32oCLow nutrientsLow productivity in water

Ahermatypic corals:• no zooxanthellae• rely on tentacular feeding• can live in aphotic zone

Cauliflower coral(Pocillopora meandrina)

6 m

0 m

25 m

13 m

Lobe coral(Porites lobata)

Finger coral(Porites compressa)

Plate coral(Porites rus)

High light levelsModerate wave energy

Moderate light levelsOccasional storm wave energy

Low light levelsLow wave energy

Very low light, Primarily downwelling No wave energy

Water color and life in the ocean

• Ocean color is influenced by:– The amount of turbidity from runoff– The amount of photosynthetic pigment, which

corresponds to the amount of productivity

• Yellow-green = highly productive water– Found in coastal and upwelling areas (eutrophic)

• Clear indigo blue = low productivity water– Found in the tropics and open ocean (oligotrophic)

Light Penetration in the Ocean

~65% of visible light is absorbed in the 1st m

Photic Zone

Aphotic Zone

No Photosynthesis

100m

0 m

Wavelength (nm)400 700600500

Photosynthesis

Dysphotic Zone

1000m

Light Absorption in the Ocean• Spectral Characteristics

– red wavelengths absorbed more readily by water than blue wavelengths

– blue light penetrates deepest in the oceans

Light effects organisms residing in the photic and aphotic zone.

• Phytoplankton productivity• Algae- green, brown, red• Predator/Prey relationships• Diurnal vertical migration• Bioluminescence- luminescent organs on

underside mimic downwelling light

Refraction- as light enters the water, it bends; this is due to light traveling through different densities

Light entering the ocean is weakened by scattering and absorption.

Density

DensityDensity

Air0.08 lbs

1 ft

1 ftfw

62.4 lbs

1 ft

1 ftsw

64 lbs

1 ft

1 ft

Piston example:

Air is compressible Water is incompressible

64 lbs

64 lbs

Water doesn’t change density under pressure

Ocean Layers• Photic zone: 0-100m

- neustonic layer: 0-1m • Mesopelagic (dysphotic or twilight) zone:

100-1000m • Aphotic zone: bathypelagic zone 1000-

4000m• Abyssal and Hadal (trench) zones:

6000m

Describe biological and physical characteristics of each depth

Temperature Salinity DensityLow High Low High Low High

surface 0 m

100 m

1000 m

Thermocline + Halocline = Pycnocline

thermocline pycnoclinehalocline

Thermocline

• El Nino– Disruption of thermocline

• Upwelling areas– Cool, nutrient-rich deep water is brought to

the sunlit surface– Peru fisheries

Thermocline

Temperature profile

depth

Peru Anchovy Fishery

Peru Anchovy Fishery

• Upwelling zone off Peru

• Fishery began 1950

• Greatest fish catches for any single species

• Fish exported for domestic animal feed

• Fishery collapsed due to El Niño and overfishing

= El Niño19571965197219761982-83

Peru Anchovy Fishery

Peru Anchovy Fishery

Normal Year

El Niño Year

Sound in Water

Speed of sound- faster in ocean (higher density)

1500 m/sec, which is 4x faster than in air

Difficult to determine direction of sound

Can hear many things such as ships miles away, shrimp eating, helicopters overhead, and whales communicating.

Sound in Water

source of noise

Dep

th (

m)

0

1000

2000

3000

4000

Speed of Sound (m/sec)

1,475 1,500

sofar layermin speed

high speed

high speed

Dep

th (

m)

0

500

1000

1500

2000

SOFAR Channel

Distance

SOFAR channel

sound rays

The depth at which the speed of sound is minimum; Thus, loud noises can be heard for thousands of km

Sound generated by Navy test in Indian Ocean at sofar layer was heard as far away as the Oregon coast. May affect behavior and anatomy of marine organisms

Sofar LayerSofar Layer

Diurnal vertical migration

Organisms within the deep scattering layer undertake a daily migration to hide in deep, darker waters during daytime

Deep sea scattering layer:Deep sea scattering layer:Composite echogram of hydroacoustic data showing a distinct krill scattering layer.Black line represents surface tracking of a blue whale feeding

patchiness

Ocean Productivity

Regional productivity

• Photosynthetic productivity varies due to:

– Amount of sunlight – Availability of nutrients

• Thermocline (a layer of rapidly changing temperature) limits nutrient supply

• Examine three open ocean regions:1. Polar oceans (>60° latitude)2. Tropical oceans (<30° latitude)3. Temperate oceans (30-60° latitude)

Productivity in tropical, temperate, and polar oceans

Zooplankton

Productivity polar oceans

Productivity in tropical oceans

Productivity in temperate oceans

O2 Minimum Zone (OMZ)

O2 Content (ml/L)

Wat

er d

epth

(m

)

What causes the O2 minimum layer?

Marine snow

Why are there high levels of O2 at depth?

O2 Dead Zones

Inquiry1. What zone does photosynthesis occur?2. Why does light appear to bend when it enters

water?3. Which wavelength of light penetrates the

ocean the deepest?4. What is SOFAR?5. Describe the relationship between El Nino and

Peru Upwelling.6. What causes the OMZ?7. How do sharks maintain buoyancy?8. What areas in the ocean are the most

productive?9. Why is the open ocean considered a biological

desert?