Chapter 1 The Growth of Oceanography ©2003 Jones and Bartlett Publishers.

Chapter 1

The Growth of Oceanography

©2003 Jones and Bartlett Publishers

There is a basic difference between the terms oceanography and oceanology.

•Oceanography is the recording and description of the physical, chemical and biological characteristics of the ocean.

– This term inadequately describes modern scientific ocean investigations.

•Oceanology is the scientific study of the sea by applying traditional sciences, such as physics, chemistry, mathematics, etc., to all aspects of the ocean.

Oceanography: What is it?1-1

There are three major stages in the history of ocean research

1-2Historical Review of Oceanography

• Ocean exploration was the period when people explored the ocean boundaries.

– Notable explorers include: The Phoenicians, Phytheas, The Polynesians, Herodotus, the Vikings, Bartholomew Diaz, Vasco de Gama, Ferdinand Magellan and Sebastian del Cano.

• Early scientific investigations began when people began to describe the ocean.

– Notable scientists include: James Cook, Matthew, Fountaine Maury, Charles Darwin, C. Wyville Thomson, and Fridjof Nansen.

• Modern oceanography or oceanology.

- Application of modern scientific methods to study of ocean systems.

The Circumglobal Voyage of Magellan1519 - 1522

The Voyage of The Beagle (Darwin)1831 - 1836

The Challenger Expedition1872 - 1876

Drift Route of the Fram1893 - 1896

Fridtjof Nansen

Fridtjof Nansen’s “Farthest North”


As is true in most sciences…

The history of scientific achievements in oceanography is punctuated by advances in sampling technology.


Then…

Deploying Nansen bottle,RV Atlantis, Ca. 1920’s


…andnow

CTD-rosette system to measure temperature,Salinity, oxygen, etc. continuously.


Deploying CTD-rosette aboardRV Townsend Cromwell, Hawaii, 2001

…andnow


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Antarctica CTD ProfileRV Nathaniel B. Palmer Dec, 2000.Position: 140.7 E Long, 65.9 S Lat.

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Then…

Beebe’s bathysphere,Ca. 1930


…and now.

WHOI’s Alvin


Discovery of deep-sea hydrothermal vents and ecosystem separate from surface of Earth


Studying hydrothermal vent communities may helpus understand if life is possible on other planets.


Hawaii

Maui


Surface Drifters

Current and future oceanographic research include:

• More international efforts because of cost and scale of research.

• Greater use of submersibles for deep ocean exploration.

• Increased use of computers for modeling complex ocean processes.

• Use of remote sensing and other in-situ instruments.

1-3Current and Future Oceanographic Research

The Scientific Method

• Scientific Hypothesis: a tentative, explanatory, interpretative generalization about natural phenomena.

•Hypotheses are derived by inductive reasoning.

•Reason from the specific and known to the general and unknown.

•Arise from observation.

•Tentativeness requires they be verified by experimentation.

•Cannot be supported by logic alone.

1-4

The Process of Science

Graphical Representations

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Example: Increase in wind-inducedmixing of water column resultsin decrease in phytoplankton biomass.

INVERSE

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Typical ‘x-y’ graph Oceanographic profile graph


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AnatomyOf agraph

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Chapter 2

The Planet Oceanus

©2003 Jones and Bartlett Publishers

2-1 The Earth’s Structure

Earth consists of a series of concentric layers or spheres which differ in chemistry and physical properties.

Earth’s structure can be described in terms of layers with different compositions or different physical properties.

2-1 The Earth’s Compositional Structure

Crust -surf to ~ 50 km -low-density rock -silicon, aluminum & oxygen -oceanic & continentalMantle -50 to 2900 km -hot, dense rock -iron, magnesium, silicon, oxygenCore -2900 to 6371 km -iron & nickel -outer core is molten -inner core is solidAtmosphere -40 km -gaseous envelope, oxygen and nitrogenHydrosphere -4 km -contains all ‘free’ water Biosphere -all living & non-living organic matter

Physical state is determined by the combined effects of pressure and temperature.

• Increasing temperature provides additional energy to the atoms and molecules of matter allowing them to move farther apart, eventually causing the material to melt.

• Increasing pressure raises the melting point of a material.

• Both pressure and temperature increase toward the center of the Earth, but at variable rates, causing Earth’s interior physical structure to vary accordingly

2-1 The Earth’s Physical Structure

2-1 The Earth’s Physical Structure

Lithosphere -crust & outer mantle -pressure high, temp low -rocks are rigid

Asthenosphere -mantle to ~ 350 km -temp high enough to melt -weak, plastic rock

Mesosphere -below Astheno -pressure high, mp raised -rocks are rigid

Outer core -temp high -rock is melted

Inner core -pressure high, mp raised -solid iron & nickel

•Physiography and bathymetry (submarine landscape) allow the sea floor to be subdivided into three distinct provinces:

– continental margins– deep ocean basins– midoceanic ridges.

2-2The Physiography of the Ocean Floor

Continental margins:

- submerged edges of the continents

- consist of massive wedges of sediment eroded from the land and overlying water and deposited along the continental edge

- Features include:

*Continental shelf

*Continental slope

-submarine canyons.

*Continental rise.


• Deep Ocean Province

-is between the continental margins and the midocean ridge

-Features include:

*Abyssal plains: flat & covered w/ sediment.

*Abyssal hills: buried volcanoes < 1 km tall.

*Seamounts & guyots: buried volcanoes >1km tall, some w/ tops eroded.

*Deep sea trenches: deepest on Earth; earthquake sites along ocean margins.


Midoceanic Ridge Province: -continuous submarine mountain range.

-covers ~1/3 of the ocean floor & extends ~ 60,000 km around Earth.

-Features include:

*Rift valley: opposite sides of ridge pulled apart form valley in center.

*Transform fault: offset ridge segments- active.

*Fracture zone: inactive TF moved out into ocean basins.


How do continents and ocean basins differ?- Crustal composition:

- Continents coarse-grained igneous granite 2.7 – 2.8 g/cm3

- Ocean basins fine-grained volcanic basalt 2.9 g/cm3

- Mantle rock is denser, ~3.3 g/cm3

- Moho discontinuity- boundary of crust & mantle (deeper over continents, 35km, versus 5 km over ocean)


Granite-igneous rock, formed from molten rock.

Basalt-volcanic origin; denser than granite.

How do continents and ocean basins differ?:

- Elevation: - Bimodal distribution: 29% of Earth’s crust is above sea-level, 71% below.


How do continents and ocean basins differ?: - Elevation (height) and composition (density):

- Isostatic Balance (isostasy)

- P = gh - Pressure (P) is equal to force of gravity (g) x density () x height of water (h).- Assume that the force of gravity (g) is the same everywhere (is constant).- Then a balance between and h maintains constant P at bottom of container.

- If is high, then h must be low.

- If is low then h must be high.

- i.e., h of continental crust is > h of ocean crust, because the of continental crust < of ocean crust.


Isostasy refers to the balance of an object “floating” upon a fluid medium. Height of the mass above and below the surface of the medium is controlled by the thickness of the mass and its density (similar to ice floating in water).

2-3Geologic Differences between Continents and Ocean Basins

Isostasy•Greater the density of the mass, the lower

it will sink in the medium.

•Greater the thickness of the mass, the higher a portion of it will rise above the medium.


• Sea floor is thin (4 to 10 km), has greater density and does not rise as high above the mantle.

• Continents are thick (30 to 40 km), have low density and rise high above the supporting mantle rocks.


Oceanic Crust Versus Continental Crust

•Echo sounding and side-scan sonar.

•seismic reflection

•Seismic refraction

•altimetry

2-5 Geophysical Surveying

•Echo sounding and seismic reflection rely on sound pulses that reflect off the ocean floor and off sedimentary layers.



Seismic reflection reveals sub-surface features.

•Seismic refraction examines how sound waves are bent (refracted) as they travel through material. They reveal densities, depths, and thicknesses of rock layers. (penetrates deeper than seismic reflection)


2-5 Geophysical SurveyingEND OF LECTURE 1

Chapter 1 The Growth of Oceanography ©2003 Jones and Bartlett Publishers.

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Transcript of Chapter 1 The Growth of Oceanography ©2003 Jones and Bartlett Publishers.