Mapping the Mapping the SeafloorSeafloor

Mapping the SeafloorMapping the Seafloor

Depth SoundingsDepth Soundings The earliest soundings were made with a The earliest soundings were made with a

hand line of rope weighted at one end. hand line of rope weighted at one end. Sticky tallow was often smeared on the Sticky tallow was often smeared on the

weight to pick up sand and other weight to pick up sand and other sediments from the seafloor. The weight sediments from the seafloor. The weight was then dropped overboard and the was then dropped overboard and the rope allowed to run free until the weight rope allowed to run free until the weight reached the bottom.reached the bottom.

The length of the line let out was an The length of the line let out was an approximate measurement of the water approximate measurement of the water depth.depth.

This type of sounding is only reliable only This type of sounding is only reliable only in in calm, shallow areascalm, shallow areas Near continental shelves, in inland seas, and Near continental shelves, in inland seas, and

near med ocean islands.near med ocean islands. The first The first successfulsuccessful deep water soundings deep water soundings

were made with large balls of were made with large balls of twinetwine. . A heavy weight was attached and tossed A heavy weight was attached and tossed

overboard, pulling twine from the ball until it overboard, pulling twine from the ball until it hit bottom. hit bottom.

Then the ball of twine was cut from the weight Then the ball of twine was cut from the weight and the twine that had run out.and the twine that had run out.

Because the weight of a length of twine was Because the weight of a length of twine was known, the depth of the ocean at that point known, the depth of the ocean at that point could be determined.could be determined.

Sonar SoundingsSonar Soundings Modern oceanographers use Modern oceanographers use

sophisticated sophisticated remote-sensingremote-sensing techniques to gather data.techniques to gather data.

The data is then plotted on charts and The data is then plotted on charts and maps and used to create models that maps and used to create models that help us understand what seafloor help us understand what seafloor features are like.features are like.

In 1930 the In 1930 the echo-sounding sonar echo-sounding sonar devicesdevices (fathometers) replaced (fathometers) replaced sounding lines.sounding lines.

The term SONAR is formed from the The term SONAR is formed from the term term sosound und nanavigation vigation rranging.anging.

Sonar works by sending out pulses of sound waves Sonar works by sending out pulses of sound waves from a ship. from a ship. Instruments record the time it takes for the sound Instruments record the time it takes for the sound

waves to travel to the bottom, reflect, and return waves to travel to the bottom, reflect, and return to the ship.to the ship.

Because the velocity of sound in seawater is Because the velocity of sound in seawater is known to be about 1,460 meters per second, the known to be about 1,460 meters per second, the depth can be calculated. depth can be calculated.

The speed does vary with the temperature and The speed does vary with the temperature and salinity in different regions of the ocean.salinity in different regions of the ocean.

Sonar Soundings cont.Sonar Soundings cont.

The advantage of using sonar is that a The advantage of using sonar is that a vessel can keep moving at normal vessel can keep moving at normal speed while soundings are made.speed while soundings are made.

Recording a series of soundings on a Recording a series of soundings on a strip of paper or making a computer strip of paper or making a computer printout produces a two-dimensional printout produces a two-dimensional visual visual profileprofile also called an also called an echogramechogram or or sonographsonograph

Research vessels cross the ocean Research vessels cross the ocean making sonar profiles along navigated making sonar profiles along navigated parallel course called parallel course called transect lines.transect lines. Only one beam is used.Only one beam is used.

Sonar Soundings cont.Sonar Soundings cont.

Swath MappingSwath Mapping Developed in 1970’s Developed in 1970’s Instead of a single line of sounding, this makes Instead of a single line of sounding, this makes

many measures of depth within a two-dimensional many measures of depth within a two-dimensional area of the seafloor.area of the seafloor.

With swath mapping one transect the With swath mapping one transect the

area sounded may be 10-60 km wide.area sounded may be 10-60 km wide. Details are so clear that small scale features Details are so clear that small scale features

can be clearly identified.can be clearly identified. Features 10m across can be detected.Features 10m across can be detected. Scientists use detailed swath mapping and Scientists use detailed swath mapping and

image mapping to learn more about the image mapping to learn more about the

processes that formed the sea floor.processes that formed the sea floor.

There 2 types of swath There 2 types of swath mapping:mapping:1. 1. multibeam sonarmultibeam sonar – – sends out and tracks sends out and tracks up to 16 closely up to 16 closely spaced sonar beams spaced sonar beams at a timeat a time2. 2. side-scanning side-scanning sonarsonar – uses – uses computers to computers to translate the translate the multiple echoes into multiple echoes into detailed three detailed three dimensional images dimensional images of the seafloor of the seafloor featuresfeatures

© 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Bathymetry

Multibeamsystems can provide more accurate measurements than echo sounders. Multibeam systems collect data from as many as 121 beams to measure the contours of the ocean floor.

Claims to the OceanClaims to the Ocean Nations considered the ocean open to everyone Nations considered the ocean open to everyone

((Freedom of the SeaFreedom of the Sea)) Ocean resources were available on a first come, first Ocean resources were available on a first come, first

served basis.served basis. In an effort to find fuel, food and minerals to be used In an effort to find fuel, food and minerals to be used

by 6 billion people, 40% of the oceans have been by 6 billion people, 40% of the oceans have been claimed. claimed.

The claimed regions are called The claimed regions are called Zones.Zones. Coastal nations claimed a territorial zone or sea of 3 Coastal nations claimed a territorial zone or sea of 3

nautical miles from shore.nautical miles from shore. They had full control of the zone but allowed nonmilitary They had full control of the zone but allowed nonmilitary

commercial ships to pass through.commercial ships to pass through. Many nations claim 12 nautical miles. This was Many nations claim 12 nautical miles. This was

complicated by straits.complicated by straits.

1958 – United Nations agreed upon a 1958 – United Nations agreed upon a “Law “Law of the Sea”of the Sea” which provided for passage which provided for passage provisions for ships, subs and airplanesprovisions for ships, subs and airplanes

Today we have “Today we have “EExclusive xclusive EEconomic conomic ZZones”ones” Nations claim sovereign rights to all resources, Nations claim sovereign rights to all resources,

living or nonliving up to 200 nautical miles from living or nonliving up to 200 nautical miles from shore.shore.

The U.S. made their claim in 1958.The U.S. made their claim in 1958. The U.S. EEZ is larger than the land area of the The U.S. EEZ is larger than the land area of the

U.S.U.S.

Claims to the OceanClaims to the Ocean

The world’s EEZ zones, shown as a white extensionof land territory.

By 1990 The two federal agencies, the By 1990 The two federal agencies, the U.S. U.S. Geological SurveyGeological Survey and the and the National Oceanic National Oceanic and Atmospheric Administrationand Atmospheric Administration, planned to , planned to complete swath mapping and assessment of the complete swath mapping and assessment of the living and nonliving resources of the U.S.EEZ.living and nonliving resources of the U.S.EEZ. It is not finished.It is not finished.

In 1982 the new In 1982 the new Law of the Sea ConventionLaw of the Sea Convention (LOSC) was written by the United Nations(LOSC) was written by the United Nations acknowledged the 12 mile territorial sea, making acknowledged the 12 mile territorial sea, making

provisions for international straits and allows for 299 provisions for international straits and allows for 299 mile EEZ.mile EEZ.

All waters beyond the EEZ’s of nations are the All waters beyond the EEZ’s of nations are the High High SeasSeas and the seabed and subsoil beneath are called and the seabed and subsoil beneath are called ““the Areathe Area”.”.

LOSC proposes that the U.N. administer the High Seas LOSC proposes that the U.N. administer the High Seas and the Area and that all nations share their ocean and the Area and that all nations share their ocean technologies and the wealth obtained from those technologies and the wealth obtained from those technologies.technologies.

Today’s Today’s bathymetric mapsbathymetric maps of the of the ocean accurately show ocean accurately show ocean ocean

depthsdepths determined by determined by seismographic techniques.seismographic techniques.

Importance of Accurate Importance of Accurate MapsMaps

Detailed, accurate maps and models Detailed, accurate maps and models of geological features are used by of geological features are used by scientists to scientists to explainexplain how the features how the features of the earth of the earth form form and how they and how they change over time.change over time.

Bathymetric MapsBathymetric Maps•Data typically comes from a sonar mounted beneath or over the side of a boat, "pinging" a beam of sound downward at the seafloor.

•The amount of time it takes for the sound or light to travel through the water, bounce off the seafloor, and return to the sounder tells the equipment what the distance to the seafloor is.

•Data is supplied on the elevations and depressions of the ocean floor.

•By drawing contour lines connecting points of equal depth, oceanographers have found that:

- the floor of the ocean has features like land-form features•undersea mountains, ridges and other masses

Contour MapsContour Maps Use Use colorscolors to represent to represent different different

elevationselevations UseUse shades of blue shades of blue to to show show

changes in depth.changes in depth. Features Features above sea levelabove sea level are are

positivepositive numbers numbers Features Features below sea levelbelow sea level are are

negative numbers.negative numbers.

http://academic.brooklyn.cuny.edu/geology/leveson/core/linksa/elevation.html

Contour MapContour Map

Practice with Contour Practice with Contour MapsMaps

http://images.google.com/imgres?imgurl=http://www.compassdude.com/i/topographic-map.jpg&imgrefurl=http://www.compassdude.com/contour-quiz.shtml&usg=__4CtaFcJqaR3245QEHHtlIXe4uBI=&h=340&w=425&sz=25&hl=en&start=1&um=1&tbnid=OfWlKA2F3GBMOM:&tbnh=101&tbnw=126&prev=/images%3Fq%3Dcontour%2Bmap%26hl%3Den%26rlz%3D1B3DVFA_enUS226US229%26sa%3DN%26um%3D1

Three-Dimensional Three-Dimensional MapsMaps

The most realistic maps are The most realistic maps are contour mapscontour maps and and three-three-dimensional raised relief maps.dimensional raised relief maps.

Both use colors and shades to Both use colors and shades to convey information about features.convey information about features.

Landform models can also be Landform models can also be sculpted to show the effects of sculpted to show the effects of erosion, etc. erosion, etc.

Three-Dimensional Three-Dimensional Raised Relief MapRaised Relief Map

3-D Contour Map3-D Contour Map

Contour MapContour Map2 Dimensional vs. 3 2 Dimensional vs. 3

DimensionalDimensional