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Transcript
Theme 1: The Growth of Oceanography
Pinet, P., (2003) Invitation to Oceanography, Jones and Bartlett, USA. Chap 1.
To understand the growth of oceanography we will consider the following topics:
- Historical review of oceanography
- Current and future oceanographic research
The roots of oceanography can be traced to ocean exploration. The earliest explorers had to be able
to chart their courses, a process known as piloting. When out at sea there are no references to go by
once the land is out of sight. The stars and the sun could possibly be used. The earliest seafarers had to
be able to chart their course by a process called piloting. Piloting required the early navigators to plot
their courses according to the stars and landmarks. At sea level it can be hard to see landmarks.
Shipping was forced to stay near the coast.
The earliest records of exploration date back to the:
o Egyptians: 4000BC, shores of eastern Mediterranean Sea
o Phoenicians: 6th C BC, entire Mediterranean Sea and into the Atlantic
o Greeks: 3rd C BC, entire Mediterranean
Herodotus (450BC) was a Greek explorer who compiled a map of the world showing the
Mediterranean Sea as the centre surrounded by three land masses (North Africa, Europe, and Asia).
Pytheas (325BC) also a Greek, was the first to circumnavigate England and gauge the length of
its shoreline. He discovered tides in the Atlantic Ocean vary regularly with the phases of the moon.
Seneca (54BC – 30AD), a Greek, proposed the hydrologic cycle based on observations of river
flow and sea level.
The Romans consolidated Greek exploration as testified by the numerous Roman shipwrecks.
Byzantine, Ottoman and Arab seafarers contributed further to geographical knowledge. Al-Idrisi, in the
employ of Count Roger, plotted a world map in 1154, which is south-oriented. According to al-Idrisi, the
world was flat and measured 22,900 miles around the edge. He believed that it was encircled by water
which held it “stable in space like the yolk of an egg”.
During the 15th and 16th Centuries, explorations by Europeans increased. They crossed the
Atlantic Ocean and eventually reached the Pacific Ocean. In 1492, Columbus discovered the Americas.
The purpose of these voyages was to find faster and safer trade routes. Columbus was looking for a
trade route to India, for spices, which at the time were very expensive because of the long route over
land.
Catalan Map of 1375: This was the sort of map available to the Portuguese monarch Henry the
Navigator and his scholars. Well-known areas are correctly charted but, outside the well-traversed
ways, the picture was very sketchy. Note the wealth of detail given to the Maltese islands.
European explorers included:
o Bartholomew Diaz – rounded the Cape of Good Hope
o Vasco de Gama
o Ferdinand Magellan – circumnavigation of the globe
A Portuguese map of about 1558 by Bastiam Lopez shows that by this time, maps were getting
better. They were very richly decorated.
The next stage in the development of Oceanography was early scientific investigation. The
ocean had initially only been seen as an obstacle in getting from one place to another. The roots of
early scientific study can be traced back to the British:
o Activities were promoted by the Royal Society of London
o The British government provided generous support
The 18th century was marked by improvements in navigation and mapping, and an accumulation
of data for charts (temperature, currents). Calculating longitude was a major problem (the ‘vertical’
lines). John Harrison was awarded GBP20,000 in 1765 for a chronometer.
In the United States, Benjamin Franklin (1769–1770) published the first chart of the Gulf Stream.
In Britain, James Cook (1768-1779) constructed charts of coastlines especially for the South Pacific. He
also discovered the Hawaiian Islands. He circumnavigated the southern hemisphere at about 60oS to
determine the existence of Antarctica.
In the 19th Century, there was a lot of curiosity about the oceans, and voyages for scientific
purposes were initiated.
Charles Darwin, the British Naturalist, in his Voyage of the Beagle (1831-1836), studied geology
and biology of the South American coastline. He developed the theory of organic evolution based on
natural selection. He published On The Origin of the Species in 1859.
Edward Forbes, a British Naturalist (1815-1854) conducted a series of dredging exercises in the
Aegean Sea. He observed that specific marine communities existed at specific depths. He extrapolated
his observations and proposed the hypothesis that no life (azoic) existed in the oceans below 300
fathoms (550m). This is not a valid hypothis.
Matthew Fontaine Maury, a US Naval officer, who retired from active duty and was placed in
charge of the library of the US navy started compiling information on winds and currents. He also
published a book about the physical geography of the sea in 1855. He is considered the ‘father of
physical oceanography’.
C Wyville Thompson, a British explorer, directed the Challenger Expedition (1872-1876). This
was the first major scientific expedition, on a globe-encircling voyage. It studied chemical, physical and
biological phenomena in the oceans, taking measurements and making collections of specimens. It is
disproved Forbes’ ‘azoic theory’ by collecting sea life from waters as deep as 9000m. Measurements
were made in all oceans except for the northern Indian Ocean and the Antarctic Ocean.
Modern oceanography dates back to the development of major interdisciplinary expeditions, ex:
the Meteor Expedition, a German ship from 1925-1927. They started looking at bottom topography, and
vertical profiles of salinity, temperature and oxygen. Subsequent growth was molded by the World
Wars and the urgent need for information on the physical structure of the oceans.
The development of institutions dedicated to the study of the oceans further enhanced the
growth of oceanography.
o Scripps Institution of Oceanography 1903
o Woods Hole Oceanographic Institution 1930
o Lamont Doherty Geological Observatory 1949
Today ocean research is conducted by investigators in specialized marine institutions, as well as
universities, and state and federal agencies. The emphasis is on interdisciplinary, process oriented
research and international co-operation. Oceanography is very expensive, and not many countries can
afford it.
Today there is a greater focus on international efforts and large scale interdisciplinary
expeditions (many scientists/many ships). There is also a greater reliance on remote sensing and
unmanned platforms (Topex). Phenomenal growth of scuba diving allows greater access to the seabed.
Deep sea drilling ships, such as the Joides Resolution and the Glomar Challenger are in use today. They
can extract cores of the sea bed, to determine the layers there.
The growth of scuba (self-contained underwater breathing apparatus) diving has vastly
increased our knowledge of oceanic processes within the first 50m of the sea. Scuba diving has its
restrictions:
o Barotrauma (burst lung)
o Nitrogen Narcosis limits compressed air diving to 50 metres max
o Decompression sickness (the bends) – dive computers
Alternatives to solve the problem of decompression and Nitrogen Narcosis can be mixed gases,
such as Nitrox (N2 and O2), and Trimix (O2, Nitrox and Heliox), or rebreathers.
It is important to study the oceans because they:
o Have a major influence on weather and climate
o Are a source of food, energy, medical drugs
o Are important in transportation
o Have military significance
o Are an important recreational resource
o Have a major influence on the health of the planet
The study of the ocean predates written history. With time, oceanography has become more
specialized and technical. Future oceanographers will rely increasingly on large computers and
mathematical models.
Theme 2 – The Origin of Ocean Basins
Pinet – Chap 2
Earth’s structure is a series of concentric shells, each with a distinct chemical composition,
layered on the basis of density sorted out during the process of cooling.
Earth’s interior is made up of several layers. The physical characteristics of each layer are
determined by:
o The chemical composition of the rocks
o Temperature
o Pressure
The Earth’s interior is structured into 3 layers:
o Crust
o Mantle
o Core
The crust is the outermost layer. It is relatively thin, made of low density material, mostly
aluminium, silicon and oxygen. There is a continental crust, and an oceanic crust. The latter is very thin
(only between 3-10km thick), while continental crust is 35-50km thick. The mantle lies below the crust
and is relatively thicker and is composed of higher density material, mostly magnesium, iron, silicon and
oxygen. It is about 2900km thick. The core is below the mantle, and is the thickest of all layers. It is
very dense, largely composed of iron and nickel. The outer part is molten, but the inner core is solid.
The crust and mantle compose the lithosphere (outermost – up to 200km depth),
asthenosphere (200-350km depth; relatively plastic) and mesosphere (innermost). Most of the
knowledge we have about the earth’s interior has been gained through the study of earthquakes.
The lithosphere consists of the crust and uppermost mantle; it is hard, rigid and brittle. The
upper asthenosphere is below the lithosphere. Here, a portion of the mantle rocks are melted; it is
molten and plastic. The lower asthenosphere lies closer to the mesosphere. The higher pressure causes
mantle rocks to solidify. It is solid and rigid. The mesosphere consists of the lower mantle, and is largely
solid due to the increasing pressure.
The earth’s exterior consists of 3 layers.
The Hydrosphere includes:
o Oceans, lakes, rivers, groundwater, ice, snow
o 97% of this ‘surface’ water is in oceans
o Represents only about 10% of entire reservoir on earth.
chemically bonded to rocks of crust and mantle.
The Atmosphere
The Biosphere consists of all organic matter, living or dead
The remaining 90% is
Physiography/Bathymetry of the Ocean Floor
The ocean basins are subdivided into 3 major bathymetric provinces:
o Continental margins
o Deep-ocean basins
o Mid-ocean ridges
The continental margins are the drowned edges of the continents. They consist of sedimentary
deposits from the erosion of the continents. They include the continental shelf, slope and rise.
Sometimes, continental slopes are characterized by submarine canyons that carry material that is
deposited on the continental rise.
The continental shelves are broad, gently sloping plains. The average width is 60km, and the
seaward edge is generally about 130-200m water depth. The continental slope lies seaward of the shelf
break. The slope here steepens considerably. The continental rise lies at the base of the slope, where
the slope lessens and the bottom flattens out. There are thick sedimentary deposits, in many cases
1000s of metres thick.
The deep sea bed is the abyssal plain, which can have small mounds called abyssal hills. There
are also deep-sea trenches, and submarine volcanoes. Seamounts are dead or inactive volcanoes, but
guyots are like volcanoes with a truncated top; these used to be above the surface, eroded by surface
processes then sank again.