Morfologi Dasar Laut Seafloor Morphology

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Morfologi Dasar Laut

Seafloor Morphology

Kuliah # 4

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WHY DO WE CARE ABOUT THE

GEOMORPHOLOGY OF THE OCEAN

FLOOR? (in the context of Oceanography)

•The ocean circulation pattern and tides, both regional and basin wide scales are heavily controlled by the topography of the ocean

•The nature of the earth, its origin and its characteristics have a profound effect on the properties and the composition of the biota that are contained in its basin.

•The structure and distribution of sediments can be understood

based on the geomorphology of the ocean floor. These sediments

are important because they tell us about the geochemistry of the

ocean floor. Also they can be used to reconstruct ocean circulation

of the past and improve our understanding of the climate system.

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Lintasan ARLINDO (Arus Lintas Indonesia)

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Konsekuensi:

Fisik: Distribusi menegak - Suhu

- Cahaya - dll

Biologi:

- Kelimpahan plankton - sebaran jenis ikan

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• Viper fish – have long sharp teeth to catch prey

•

Angler Fish - use a light on top of head to catch their prey

•

Hatchet Fish - has a light that attracts their prey

•

Lantern Fish - swim to the surface to catch prey

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DEEP SEA FISHERIES (TRAWL)

Contoh beberapa species laut dalam (TUMST-IPB, 2003) Trawl Survey: 9-24 December 2003

RTV Umitaka Maru, Tokyo University of Marine Science and Technology Location: Southern coast of Java, Eastern Indian Ocean

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Characteristics Of Fish From

Different Depths Of The Pelagic

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Salah satu contoh:

konsekuensi kimiawi

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• Continental margins (Tepi benua)

• Deep ocean basins (Dasar lautan)

• Mid-oceanic ridges (Punggung laut)

Physiography and bathymetry (submarine

landscape) allow the sea floor to be subdivided

into three distinct provinces:

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Continental margins have several components:

•

Continental shelves (paparan benua):

The shallow, submerged edge of the continent (bagian dari daratan pada masa lalu dan tertutup oleh fluktuasi permukaan laut; lebar: 65 km - 100 km, dasar tertutup endapan tebal dari silt, pasir dan lumpur dari sungai)

•

Shelf breaks (paparan transisi):

the abrupt transition from continental shelf to the continental slope.

•

Continental slopes (Lereng benua)

:

The transition between the continental shelf and the deep-ocean floor (Lerengan curam: kedalaman dari 200 m ke 3000 m; permukaan banyak batuan sedikit endapan karena kecuraman; bisa terdapat submarine canyons – berasosiasi dengan keberadaan system sungai pada masa lalu dan dengan turbidity current.

•

Continental rises (Tanjakan benua)

:

Thick accumulations of sediment found at the base of the continental slope ( akumulasi endapan dari turbidity current, longsoran bawah laut, dan proses bawaan lainnya)

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There are two types of continental margins:

• Passive margins

, also called “Atlantic-type” margins, face the edges of diverging tectonic plates. Very little volcanic or earthquake activity is

associated with passive margins.

• Active margins

, known as “Pacific-type” margins, are located near the edges of converging plates, where one plate dives beneath another at an oceanic trench, in the process of subduction. Active margins are therefore sites of extensive volcanic and earthquake activity.

Continental Margins

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Continental Margins

Note the difference between active versus passive continental margins, illustrated below. The active margin (at left) has subduction at an

oceanic trench occurring next to it. The passive margin (at right) faces the diverging plate boundary of the mid-ocean ridge.

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Subduction at oceanic trenches causes the descending plate to melt, forming Volcanic Arcs or Island Arcs: lines of volcanic islands and seamounts running parallel to the edges of trenches.

Subduction also causes many earthquakes.

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Island Arcs

• Curving chains of volcanic islands called island arcs are usually found paralleling the concave edges of the trenches.

The island arcs are formed by magma rising from the subduction zone. The Aleutian Islands and the Lesser Antilles are examples of island arc chains.

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Submarine canyons are a common feature of continental shelves and slopes.

Underwater landslides or avalanches called turbidity currents ^commonly

flow down submarine canyons. The debris settles out to build up a submarine fan at the base of the canyon.

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Submarine Canyons

• On some continental margins, submarine canyons cut deeply into the shelf at right angles to the coastline,

usually starting a short distance off the coast and going down to several thousand meters in depth.

The Monterey Bay Submarine

Canyon is deeper and larger in

volume than the Grand Canyon.

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Locations of Submarine Canyons

• In general, submarine canyons are generally located

offshore from locations where large rivers empty into the

sea and deposit sediments near the continental slope.

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Formation of Submarine Canyons

The canyons are cut by turbidity currents, submarine

“mudslides” of water and sediments

Most rivers transport to the sea a large load of small rock particles, such as sand silt and clay, called sediments.

Sediment that accumulates out at the edge of the shelf can become unstable.

A small jolt from a tremor or earthquake can dislodge the accumulation of sediment.

These sediments are suspended in the moving water, then fall

to the sea floor when the water velocity drops to zero at the

edge of the sea.

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Turbidity Currents

• Once dislodged, the sediment quickly mixes with seawater to form an emulsion with a density greater than the surrounding water.

As the dense mixture slides downhill, it accelerates and erodes a small groove into the continental slope.

When it reaches the continental rise, where the slope lessens, the turbidity current loses speed.

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Turbidite Fans

• It finally runs out of momentum at the abyssal seafloor and

and deposits the sediment in a fan shaped pattern (known as a turbidite fan) just seaward from the mouth of the canyon..

A succession of turbidity currents over time carves out the deep canyon in the continental shelf and slope.

Submarine canyons often match up with rivers along the coast because the

sediment that accumulates is transported to the sea by rivers.

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• Deep Ocean Province is between the continental margins and the mid-oceanic ridge and includes a variety of features from mountainous to flat plains: Abyssal plains, Abyssal hills,

Seamounts, and Deep sea trenches.

Deep Ocean Basin

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• Abyssal plains:

are broad flat areas of sediment-covered ocean floor found between the continental margins and the mid-ocean ridges.

• Abyssal hills:

are small, extinct volcanoes or rock intrusions that poke up through the sediments coating the abyssal plains.

• Seamounts:

are volcanoes that rise up from the sea floor but which do not stick up above sea level.

• Guyots:

are flat-topped seamounts. Today they occur far below sea level, but at one time they were islands that poked up above the surface.

They were eroded flat by wave action, then gradually sank downward as the sea floor underneath them cooled.

Deep-Ocean Basins (Basin Laut Dalam)

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Oceanic trenches are the deepest parts of the sea floor. They are formed by subduction, where one plate dives beneath another in an area of plate convergence.

Notice that most trenches (and therefore most subduction) occur in the Pacific ocean basin.

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• Mid-Oceanic Ridge Province consists of a continuous submarine mountain range that covers about one third of the ocean floor and extends for about 60,000 km around the Earth.

Mid-Ocean Ridge

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At the centers of ridges, where magma comes up and erupts onto the sea floor, water may circulate through cracks in the rock and become very hot. Hydrothermal vents are sites where this

superheated water containing dissolved minerals and gases

escapes through fissures, or vents. This escaping hot water forms chimneys called smokers.

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• In the interior of most ocean basins, the flat expanse of the abyssal plain is broken sharply by an ocean ridge.

The oceanic ridge system runs for over 40,000 miles.

The ridges are composed of young basaltic rock of volcanic origin and devoid of sediments.

The peaks typically rise 2–3 kilometers above the sea floor.

The ridge crest is split by a rift valley, where the oceanic crust is separating and spreading, that can be up to 6 kilometers deep and 20 kilometers wide.

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An oceanic ridge is a broad, low mountain range of young, basaltic rock at an active spreading center of an ocean. These are areas of sea floor spreading and the formation of new oceanic crust.

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Early bathymetric studies were often performed using a weighted line dropped to measure the depth.

Advances in Bathymetry

•

Echo sounding

•

Multi-beam Systems

•

Satellite Altimetry

How did early scientists study the ocean floor?

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Echo sounding

is a method of measuring depth using powerful sound pulses. The time it takes for the sound pulse to travel to the sea bed and bounce back is a measure of the depth.

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Multi-beam systems

can provide more accurate

measurements than echo

sounders. Multi- beam systems collect data from as many as 121 beams to measure the contours of the ocean floor.

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

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Geophysical Surveying

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

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Geophysical Surveying

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TOPEX/Poseidon satellite launched in 1992.

Satellite altimetry

is an indirect way of measuring depth and detecting sea floor features. Satellites measure the sea surface height from their orbits by bouncing rapid pulses of radar energy off the ocean surface. Sea floor features like submerged mountains -- see figure below -- have more mass than sea water. This extra mass pulls the sea surface into gentle

“hills” above the features. Thus we can “see” features below the surface by measuring the variations in sea surface height that these features cause! Yes -- its amazing!!

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Model of the shape of the Earth

http://www.esri.com/news/arcuser/0703/geoid1of3.html

geoid: The equipotential surface of the Earth's gravity field which best fits, in a least squares sense, global mean sea level (MSL)

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Bathymetry from Altimetry Satellite