Physical oceanography is the study of
physical
Physical may refer to:
* Physical examination, a regular overall check-up with a doctor
* ''Physical'' (Olivia Newton-John album), 1981
** "Physical" (Olivia Newton-John song)
* ''Physical'' (Gabe Gurnsey album)
* "Physical" (Alcazar song) (2004)
* ...
conditions and physical processes within the
ocean
The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wor ...
, especially the motions and physical properties of ocean waters.
Physical oceanography is one of several sub-domains into which
oceanography is divided. Others include
biological,
chemical and
geological oceanography.
Physical oceanography may be subdivided into ''descriptive'' and ''dynamical'' physical oceanography.
Descriptive physical oceanography seeks to research the ocean through observations and complex numerical models, which describe the fluid motions as precisely as possible.
Dynamical physical oceanography focuses primarily upon the processes that govern the motion of fluids with emphasis upon theoretical research and numerical models. These are part of the large field of
Geophysical Fluid Dynamics (GFD) that is shared together with
meteorology
Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did no ...
. GFD is a sub field of
Fluid dynamics describing flows occurring on spatial and temporal scales that are greatly influenced by the
Coriolis force.
Physical setting
Roughly 97% of the planet's water is in its oceans, and the oceans are the source of the vast majority of
water vapor
(99.9839 °C)
, -
, Boiling point
,
, -
, specific gas constant
, 461.5 J/( kg·K)
, -
, Heat of vaporization
, 2.27 MJ/kg
, -
, Heat capacity
, 1.864 kJ/(kg·K)
Water vapor, water vapour or aqueous vapor is the gaseous p ...
that condenses in the atmosphere and falls as
rain or
snow
Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes.
It consists of frozen crystalline water throughou ...
on the continents.
The tremendous
heat capacity
Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to an object to produce a unit change in its temperature. The SI unit of heat capacity is joule per kelvin (J/K).
Heat cap ...
of the oceans moderates the planet's
climate
Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologi ...
, and its absorption of various gases affects the composition of the
atmosphere.
The ocean's influence extends even to the composition of
volcanic
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often found where tectonic plat ...
rocks through seafloor
metamorphism, as well as to that of volcanic gases and
magma
Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natura ...
s created at
subduction zones.
From sea level, the oceans are far deeper than the
continent
A continent is any of several large landmasses. Generally identified by convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continents. Ordered from largest in area to smallest, these seven ...
s are tall; examination of the Earth's
hypsographic curve shows that the average elevation of Earth's landmasses is only , while the ocean's average depth is . Though this apparent discrepancy is great, for both land and sea, the respective extremes such as
mountains and
trenches are rare.
Temperature, salinity and density
Because the vast majority of the world ocean's volume is deep water, the mean temperature of seawater is low; roughly 75% of the ocean's volume has a temperature from 0° – 5 °C (Pinet 1996). The same percentage falls in a salinity range between 34 and 35 ppt (3.4–3.5%) (Pinet 1996). There is still quite a bit of variation, however. Surface temperatures can range from below freezing near the poles to 35 °C in restricted tropical seas, while salinity can vary from 10 to 41 ppt (1.0–4.1%).
The vertical structure of the temperature can be divided into three basic layers, a surface
mixed layer, where gradients are low, a
thermocline where gradients are high, and a poorly stratified abyss.
In terms of temperature, the ocean's layers are highly
latitude
In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north ...
-dependent; the
thermocline is pronounced in the tropics, but nonexistent in polar waters (Marshak 2001). The
halocline
In oceanography, a halocline (from Greek ''hals'', ''halos'' 'salt' and ''klinein'' 'to slope') is a cline, a subtype of chemocline caused by a strong, vertical salinity gradient within a body of water. Because salinity (in concert with te ...
usually lies near the surface, where evaporation raises salinity in the tropics, or meltwater dilutes it in polar regions.
These variations of salinity and temperature with depth change the density of the seawater, creating the
pycnocline.
Circulation
Energy for the ocean circulation (and for the atmospheric circulation) comes from solar radiation and gravitational energy from the sun and moon. The amount of sunlight absorbed at the surface varies strongly with latitude, being greater at the equator than at the poles, and this engenders fluid motion in both the atmosphere and ocean that acts to redistribute heat from the equator towards the poles, thereby reducing the temperature gradients that would exist in the absence of fluid motion. Perhaps three quarters of this heat is carried in the atmosphere; the rest is carried in the ocean.
The atmosphere is heated from below, which leads to convection, the largest expression of which is the
Hadley circulation. By contrast the ocean is heated from above, which tends to suppress convection. Instead ocean deep water is formed in polar regions where cold salty waters sink in fairly restricted areas. This is the beginning of the
thermohaline circulation.
Oceanic currents are largely driven by the surface wind stress; hence the large-scale
atmospheric circulation is important to understanding the ocean circulation. The Hadley circulation leads to Easterly winds in the tropics and Westerlies in mid-latitudes. This leads to slow equatorward flow throughout most of a subtropical ocean basin (the
Sverdrup balance
The Sverdrup balance, or Sverdrup relation, is a theoretical relationship between the wind stress exerted on the surface of the open ocean and the vertically integrated meridional (north-south) transport of ocean water.
History
Aside from the ...
). The return flow occurs in an intense, narrow, poleward
western boundary current
Boundary currents are ocean currents with dynamics determined by the presence of a coastline, and fall into two distinct categories: western boundary currents and eastern boundary currents.
Eastern boundary currents
Eastern boundary currents are ...
. Like the atmosphere, the ocean is far wider than it is deep, and hence horizontal motion is in general much faster than vertical motion. In the southern hemisphere there is a continuous belt of ocean, and hence the mid-latitude westerlies force the strong
Antarctic Circumpolar Current. In the northern hemisphere the land masses prevent this and the ocean circulation is broken into smaller
gyres in the Atlantic and Pacific basins.
Coriolis effect
The
Coriolis effect results in a deflection of fluid flows (to the right in the Northern Hemisphere and left in the Southern Hemisphere). This has profound effects on the flow of the oceans. In particular it means the flow goes ''around'' high and low pressure systems, permitting them to persist for long periods of time. As a result, tiny variations in pressure can produce measurable currents. A slope of one part in one million in sea surface height, for example, will result in a current of 10 cm/s at mid-latitudes. The fact that the Coriolis effect is largest at the poles and weak at the equator results in sharp, relatively steady western boundary currents which are absent on eastern boundaries. Also see
secondary circulation effects.
Ekman transport
Ekman transport results in the net transport of surface water 90 degrees to the right of the wind in the Northern Hemisphere, and 90 degrees to the left of the wind in the Southern Hemisphere. As the wind blows across the surface of the ocean, it "grabs" onto a thin layer of the surface water. In turn, that thin sheet of water transfers motion energy to the thin layer of water under it, and so on. However, because of the Coriolis Effect, the direction of travel of the layers of water slowly move farther and farther to the right as they get deeper in the Northern Hemisphere, and to the left in the Southern Hemisphere. In most cases, the very bottom layer of water affected by the wind is at a depth of 100 m – 150 m and is traveling about 180 degrees, completely opposite of the direction that the wind is blowing. Overall, the net transport of water would be 90 degrees from the original direction of the wind.
Langmuir circulation
Langmuir circulation results in the occurrence of thin, visible stripes, called
windrow
A windrow is a row of cut (mown) hay or small grain crop. It is allowed to dry before being baled, combined, or rolled. For hay, the windrow is often formed by a hay rake, which rakes hay that has been cut by a mowing machine or by scythe into ...
s on the surface of the ocean parallel to the direction that the wind is blowing. If the wind is blowing with more than 3 m s
−1, it can create parallel windrows alternating upwelling and downwelling about 5–300 m apart. These windrows are created by adjacent ovular water cells (extending to about deep) alternating rotating clockwise and counterclockwise. In the
convergence zones debris, foam and seaweed accumulates, while at the
divergence
In vector calculus, divergence is a vector operator that operates on a vector field, producing a scalar field giving the quantity of the vector field's source at each point. More technically, the divergence represents the volume density of ...
zones plankton are caught and carried to the surface. If there are many plankton in the divergence zone fish are often attracted to feed on them.
Ocean–atmosphere interface
At the ocean-atmosphere interface, the ocean and atmosphere exchange fluxes of heat, moisture and momentum.
; Heat
The important
heat
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...
terms at the surface are the sensible heat
flux, the latent heat flux, the incoming
solar radiation and the balance of long-wave (
infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
)
radiation. In general, the tropical oceans will tend to show a net gain of heat, and the polar oceans a net loss, the result of a net transfer of energy polewards in the oceans.
The oceans' large heat capacity moderates the climate of areas adjacent to the oceans, leading to a
maritime climate at such locations. This can be a result of heat storage in summer and release in winter; or of transport of heat from warmer locations: a particularly notable example of this is
Western Europe
Western Europe is the western region of Europe. The region's countries and territories vary depending on context.
The concept of "the West" appeared in Europe in juxtaposition to "the East" and originally applied to the ancient Mediterranean ...
, which is heated at least in part by the
north atlantic drift.
;Momentum
Surface winds tend to be of order meters per second; ocean currents of order centimeters per second. Hence from the point of view of the atmosphere, the ocean can be considered effectively stationary; from the point of view of the ocean, the atmosphere imposes a significant wind
stress on its surface, and this forces large-scale currents in the ocean.
Through the wind stress, the wind generates
ocean surface waves; the longer waves have a
phase velocity tending towards the
wind speed.
Momentum of the surface winds is transferred into the energy
flux by the ocean surface waves. The increased
roughness of the ocean surface, by the presence of the waves, changes the wind near the surface.
;Moisture
The ocean can gain
moisture from
rainfall, or lose it through
evaporation. Evaporative loss leaves the ocean saltier; the
Mediterranean
The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on ...
and
Persian Gulf
The Persian Gulf ( fa, خلیج فارس, translit=xalij-e fârs, lit=Gulf of Fars, ), sometimes called the ( ar, اَلْخَلِيْجُ ٱلْعَرَبِيُّ, Al-Khalīj al-ˁArabī), is a mediterranean sea in Western Asia. The bo ...
for example have strong evaporative loss; the resulting plume of dense salty water may be traced through the
Straits of Gibraltar into the
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...
. At one time, it was believed that
evaporation/
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
was a major driver of ocean currents; it is now known to be only a very minor factor.
Planetary waves
;Kelvin Waves
A
Kelvin wave is any
progressive wave
In physics, mathematics, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. Waves can be periodic, in which case those quantities oscillate repeatedly about an equilibrium (re ...
that is channeled between two boundaries or opposing forces (usually between the
Coriolis force and a
coastline
The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in ...
or the
equator). There are two types, coastal and equatorial. Kelvin waves are
gravity
In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
driven and
non-dispersive. This means that Kelvin waves can retain their shape and direction over long periods of time. They are usually created by a sudden shift in the wind, such as the change of the
trade winds at the beginning of the
El Niño-Southern Oscillation
EL, El or el may refer to:
Religion
* El (deity), a Semitic word for "God"
People
* EL (rapper) (born 1983), stage name of Elorm Adablah, a Ghanaian rapper and sound engineer
* El DeBarge, music artist
* El Franco Lee (1949–2016), American ...
.
Coastal Kelvin waves follow
shorelines and will always propagate in a
counterclockwise
Two-dimensional rotation can occur in two possible directions. Clockwise motion (abbreviated CW) proceeds in the same direction as a clock's hands: from the top to the right, then down and then to the left, and back up to the top. The opposite ...
direction in the
Northern hemisphere (with the
shoreline to the right of the direction of travel) and
clockwise
Two-dimensional rotation can occur in two possible directions. Clockwise motion (abbreviated CW) proceeds in the same direction as a clock's hands: from the top to the right, then down and then to the left, and back up to the top. The opposite ...
in the
Southern hemisphere.
Equatorial Kelvin waves propagate to the east in the
Northern
Northern may refer to the following:
Geography
* North, a point in direction
* Northern Europe, the northern part or region of Europe
* Northern Highland, a region of Wisconsin, United States
* Northern Province, Sri Lanka
* Northern Range, a r ...
and
Southern hemispheres, using the
equator as a
guide.
Kelvin waves are known to have very high speeds, typically around 2–3 meters per second. They have
wavelengths of thousands of kilometers and
amplitudes in the tens of meters.
;Rossby Waves
Rossby waves, or
planetary waves are huge, slow waves generated in the
troposphere by
temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
differences between the
ocean
The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wor ...
and the
continent
A continent is any of several large landmasses. Generally identified by convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continents. Ordered from largest in area to smallest, these seven ...
s. Their major
restoring force is the change in
Coriolis force with
latitude
In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north ...
. Their wave
amplitudes are usually in the tens of meters and very large
wavelengths. They are usually found at low or mid latitudes.
There are two types of Rossby waves,
barotropic
In fluid dynamics, a barotropic fluid is a fluid whose density is a function of pressure only. The barotropic fluid is a useful model of fluid behavior in a wide variety of scientific fields, from meteorology to astrophysics.
The density of most ...
and
baroclinic. Barotropic Rossby waves have the highest speeds and do not vary vertically. Baroclinic Rossby waves are much slower.
The special identifying feature of Rossby waves is that the
phase velocity of each individual wave always has a westward component, but the
group velocity can be in any direction. Usually the shorter Rossby waves have an eastward group velocity and the longer ones have a westward group velocity.
Climate variability
The interaction of ocean circulation, which serves as a type of
heat pump, and biological effects such as the concentration of
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
can result in global
climate changes on a time scale of decades. Known
climate oscillations resulting from these interactions, include the
Pacific decadal oscillation,
North Atlantic oscillation, and
Arctic oscillation. The oceanic process of
thermohaline circulation is a significant component of heat redistribution across the globe, and changes in this circulation can have major impacts upon the climate.
La Niña–El Niño
and
Antarctic circumpolar wave
This is a coupled
ocean
The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wor ...
/
atmosphere wave that circles the
Southern Ocean about every eight years. Since it is a wave-2 phenomenon (there are two peaks and two troughs in a
latitude circle) at each fixed point in space a signal with a
period of four years is seen. The wave moves eastward in the direction of the
Antarctic Circumpolar Current.
Ocean currents
Among the most important
ocean current
An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences. Depth conto ...
s are the:
*
Antarctic Circumpolar Current
*
Deep ocean (density-driven)
* Western boundary currents
**
Gulf Stream
**
Kuroshio Current
**
Labrador Current
**
Oyashio Current
**
Agulhas Current
The Agulhas Current () is the western boundary current of the southwest Indian Ocean. It flows south along the east coast of Africa from 27°S to 40°S. It is narrow, swift and strong. It is suggested that it is the largest western boundary curren ...
**
Brazil Current
The Brazil Current is a warm water current that flows south along the Brazilian south coast to the mouth of the Río de la Plata.
Description
This current is caused by diversion of a portion of the Atlantic South Equatorial Current from wher ...
**
East Australia Current
* Eastern Boundary currents
**
California Current
**
Canary Current
**
Peru Current
The Humboldt Current, also called the Peru Current, is a cold, low-salinity ocean current that flows north along the western coast of South America.Montecino, Vivian, and Carina B. Lange. "The Humboldt Current System: Ecosystem components and pr ...
**
Benguela Current
Antarctic circumpolar
The ocean body surrounding the
Antarctic is currently the only continuous body of water where there is a wide latitude band of open water. It interconnects the
Atlantic
The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...
,
Pacific and
Indian
Indian or Indians may refer to:
Peoples South Asia
* Indian people, people of Indian nationality, or people who have an Indian ancestor
** Non-resident Indian, a citizen of India who has temporarily emigrated to another country
* South Asia ...
oceans, and provide an uninterrupted stretch for the prevailing westerly winds to significantly increase wave amplitudes. It is generally accepted that these prevailing winds are primarily responsible for the circumpolar current transport. This current is now thought to vary with time, possibly in an oscillatory manner.
Deep ocean
In the
Norwegian Sea evaporative cooling is predominant, and the sinking water mass, the
North Atlantic Deep Water (NADW), fills the basin and spills southwards through crevasses in the
submarine sills that connect
Greenland
Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland ...
,
Iceland
Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its ...
and
Britain. It then flows along the western boundary of the Atlantic with some part of the flow moving eastward along the equator and then poleward into the ocean basins. The NADW is entrained into the Circumpolar Current, and can be traced into the Indian and Pacific basins. Flow from the
Arctic Ocean Basin into the Pacific, however, is blocked by the narrow shallows of the
Bering Strait.
Also see
marine geology about that explores the
geology
Geology () is a branch of natural science concerned with Earth and other Astronomical object, astronomical objects, the features or rock (geology), rocks of which it is composed, and the processes by which they change over time. Modern geology ...
of the ocean floor including
plate tectonics
Plate tectonics (from the la, label= Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of larg ...
that create deep ocean trenches.
Western boundary
An idealised subtropical ocean basin forced by winds circling around a high pressure (anticyclonic) systems such as the Azores-Bermuda high develops a
gyre circulation with slow steady flows towards the equator in the interior. As discussed by
Henry Stommel, these flows are balanced in the region of the western boundary, where a thin fast polewards flow called a
western boundary current
Boundary currents are ocean currents with dynamics determined by the presence of a coastline, and fall into two distinct categories: western boundary currents and eastern boundary currents.
Eastern boundary currents
Eastern boundary currents are ...
develops. Flow in the real ocean is more complex, but the
Gulf stream, Agulhas and
Kuroshio
The , also known as the Black or or the is a north-flowing, warm ocean current on the west side of the North Pacific Ocean basin. It was named for the deep blue appearance of its waters. Similar to the Gulf Stream in the North Atlantic, the Ku ...
are examples of such currents. They are narrow (approximately 100 km across) and fast (approximately 1.5 m/s).
Equatorwards western boundary currents occur in tropical and polar locations, e.g. the East Greenland and Labrador currents, in the Atlantic and the
Oyashio. They are forced by winds circulation around low pressure (cyclonic).
;Gulf stream
The Gulf Stream, together with its northern extension,
North Atlantic Current, is a powerful, warm, and swift Atlantic Ocean current that originates in the
Gulf of Mexico, exits through the Strait of Florida, and follows the eastern coastlines of the United States and Newfoundland to the northeast before crossing the Atlantic Ocean.
;Kuroshio
The
Kuroshio Current is an ocean current found in the western Pacific Ocean off the east coast of
Taiwan
Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the no ...
and flowing northeastward past
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
, where it merges with the easterly drift of the
North Pacific Current. It is analogous to the Gulf Stream in the Atlantic Ocean, transporting warm, tropical water northward towards the polar region.
Heat flux
Heat storage
Ocean heat flux is a turbulent and complex system which utilizes atmospheric measurement techniques such as
eddy covariance to measure the rate of heat transfer expressed in the unit of or
petawatts.
Heat flux is the flow of energy per unit of area per unit of time. Most of the Earth's heat storage is within its seas with smaller fractions of the heat transfer in processes such as evaporation, radiation, diffusion, or absorption into the sea floor. The majority of the ocean heat flux is through
advection or the movement of the ocean's currents. For example, the majority of the warm water movement in the south Atlantic is thought to have originated in the Indian Ocean. Another example of advection is the nonequatorial Pacific heating which results from subsurface processes related to atmospheric anticlines. Recent warming observations of
Antarctic bottom water in the
Southern Ocean is of concern to ocean scientists because bottom water changes will effect currents, nutrients, and biota elsewhere. The international awareness of global warming has focused scientific research on this topic since the 1988 creation of the
Intergovernmental Panel on Climate Change. Improved ocean observation, instrumentation, theory, and funding has increased scientific reporting on regional and global issues related to heat.
Sea level change
Tide gauges and satellite altimetry suggest an increase in sea level of 1.5–3 mm/yr over the past 100 years.
The
IPCC predicts that by 2081–2100,
global warming
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
will lead to a sea level rise of 260 to 820 mm.
Rapid variations
Tides
The rise and fall of the oceans due to tidal effects is a key influence upon the coastal areas. Ocean tides on the planet Earth are created by the gravitational effects of the
Sun and
Moon. The tides produced by these two bodies are roughly comparable in magnitude, but the orbital motion of the Moon results in tidal patterns that vary over the course of a month.
The ebb and flow of the tides produce a cyclical current along the coast, and the strength of this current can be quite dramatic along narrow estuaries. Incoming tides can also produce a
tidal bore
Tidal is the adjectival form of tide.
Tidal may also refer to:
* ''Tidal'' (album), a 1996 album by Fiona Apple
* Tidal (king), a king involved in the Battle of the Vale of Siddim
* TidalCycles, a live coding environment for music
* Tidal (se ...
along a river or narrow bay as the water flow against the current results in a wave on the surface.
''Tide and Current'' (Wyban 1992) clearly illustrates the impact of these natural cycles on the lifestyle and livelihood of
Native Hawaiians tending coastal fishponds. ''Aia ke ola ka hana'' meaning . . . ''Life is in labor''.
''
Tidal resonance'' occurs in the
Bay of Fundy since the time it takes for a large
wave to travel from the mouth of the
bay
A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a gulf, sea, sound, or bight. A cove is a small, circular bay with a na ...
to the opposite end, then reflect and travel back to the mouth of the bay coincides with the tidal rhythm producing the world's highest tides.
As the surface tide oscillates over topography, such as submerged seamounts or ridges, it generates
internal waves at the tidal frequency, which are known as
internal tides
Internal tides are generated as the surface tides move stratified water up and down sloping topography, which produces a wave in the ocean interior. So internal tides are internal waves at a tidal frequency. The other major source of internal wa ...
.
Tsunamis
A series of surface waves can be generated due to large-scale displacement of the ocean water. These can be caused by sub-marine
landslides, seafloor deformations due to
earthquake
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, fr ...
s, or the impact of a large
meteorite.
The waves can travel with a velocity of up to several hundred km/hour across the ocean surface, but in mid-ocean they are barely detectable with
wavelengths spanning hundreds of kilometers.
Tsunamis, originally called tidal waves, were renamed because they are not related to the tides. They are regarded as
shallow-water waves, or waves in water with a depth less than 1/20 their wavelength. Tsunamis have very large periods, high speeds, and great wave heights.
The primary impact of these waves is along the coastal shoreline, as large amounts of ocean water are cyclically propelled inland and then drawn out to sea. This can result in significant modifications to the coastline regions where the waves strike with sufficient energy.
The tsunami that occurred in
Lituya Bay, Alaska on July 9, 1958 was high and is the biggest tsunami ever measured, almost taller than the
Sears Tower in Chicago and about taller than the former
World Trade Center in New York.
Surface waves
The wind generates ocean surface waves, which have a large impact on
offshore structures,
ships,
Coastal erosion
Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms. The landwar ...
and
sedimentation, as well as
harbours. After their generation by the wind, ocean surface waves can travel (as
swell) over long distances.
See also
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Climate change (general concept)
Climate variability includes all the variations in the climate that last longer than individual weather events, whereas the term climate change only refers to those variations that persist for a longer period of time, typically decades or more ...
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CORA dataset temperature and salinity oceanographic dataset
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Downwelling
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Geophysical fluid dynamics
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Global Sea Level Observing System
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Global warming
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
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Hydrothermal circulation
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List of ocean circulation models
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List of Oceanic Landforms
*
Marginal sea
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Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on ...
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Ocean
The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wor ...
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Oceanography
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Thermohaline circulation
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Upwelling
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World Ocean Atlas
The World Ocean Atlas (WOA) is a data product of the Ocean Climate Laboratory of the National Oceanographic Data Center (U.S.). The WOA consists of a climatology of fields of ''in situ'' ocean properties for the World Ocean. It was first produc ...
*
World Ocean Circulation Experiment
The World Ocean Circulation Experiment (WOCE) was a component of the international World Climate Research Program, and aimed to establish the role of the World Ocean in the Earth's climate system. WOCE's field phase ran between 1990 and 1998, and ...
References
Further reading
*
*Samelson, R. M. (2011) ''The Theory of Large-Scale Ocean Circulation''. Cambridge: Cambridge University Press.
doi: 10.1017/CBO9780511736605.*
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External links
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NASA OceanographyOcean Motion and Surface Currents(digital book)
University-National Oceanographic Laboratory SystemPacific Disaster CenterPacific Tsunami Museum Hilo, HawaiiScience of Tsunami Hazards''(journal)''
NEMOacademic software for oceanography
History of Salinity Determination
{{Authority control
Physical oceanography,
Physical geography