Coastal Morphology and processes

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Coastal morphology and processes
1.a. Define coast, coastal area, shore, beach, geomorphology
The shore is a zone that lies between the lowest tide level (low tide) and the highest elevation on land that
is affected by storm waves. The width of the shore varies between a few meters and hundreds of meters.
Shoreline: The demarcation line between water and land is called shoreline. . The line delineating the
shoreline on Nautical Charts (Sea Maps) approximates this Mean High Water Line. The shoreline is not
easy to identify in the nature in contrast to the coastline, which is based on a clear morphological shift
between the shore and the coast.
Coast: A strip of land of indefinite length and width (may be tens of Km) that extends from the seashore
inland to the first major change in terrain features. The coast extends inland from the shore as far as ocean-
related coast land that is affected by storm waves. The width of the coast may vary from less than 1
kilometer (0.6 mile) to many tens of kilometers
Coastline: Technically the line that forms the boundary between the COAST and the SHORE. The
coastline marks the boundary between the shore and the coast. It is the landward limit of the effect of the
highest storm waves on the shore
Coastal area: Coastal areas are commonly defined as the interface or transition areas between land and
sea,including large inland lakes. Coastal areas are diverse in function and form, dynamic and do not lend
themselves well to definition by strict spatial boundaries. Unlike watersheds, there are no exact natural
boundaries that unambiguously delineate coastal areas
Coastal zone:Coastal zone means the coastal waters (including the land therein and thereunder) and the
adjacent shorelands (including the waters therein and thereunder), strongly influenced by each and in
proximity to the shorelines of the several coastal states, and includes islands, transitional and intertidal
areas, salt marshes, wetlands and beaches.
The beach is an accumulation of Unconsolidated sediments(sand, shingle, cobbles ,pebbles, cobblestones,
shell etc.) extending from the mean low tide line to some physio-graphic change such as a sea cliff or dune
field or to point where permanent vegetation is established. A shore of unconsolidated material is usually
called a beach.A beachmay continue from the coastline acrossthe Nearshore region to the line of breakers.
Thus, the beach is the entire active area of a coast that experience changes due to breaking waves. The area
of the beach above the shoreline is often called recreational beach.
Geomorphology: geomorphology is the scientific study of the origin and evolution of topographic and
bathymetric features created by physical, biological or chemical processes operating at or near the earth’s
surface. Geomorphologists seek to understand why landscapes look the way they do, to understand
landform history and dynamics and to predict changes through a combination of field observations, physical
experiments and numerical modeling. Geomorphologists work within disciplines such as physical
geography, geology, geodesy, engineering geology, archaeology and geotechnical engineering.
b. classify coastal zone ofBangladesh/types ofcoast/geomorphology and evolution of the coast of
Bangladesh.(according to pramanik /brammer)

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Pramanik (1983) has divided the Bangladesh coastal zone into three regions namely eastern, central and
western coastal region.
1.Eastern coastal zone: the eastern coastal zone starts from Bodormokam, the southern tip of mainland
Teknaf to the Feni river estuary. This zone is very narrow. A series of small hills are run parallel to this
zone. Karnafully, Sangu and Matamuhury River fall into the Bay of Bengal in this area. The Naf river falls
to the Bay of Bengal dividing Bangladesh from Myanmar. Soil characteristics of the eastern coastal zone
are dominated by submerged sands and mudflats (Islam, 2001). Two of the country’s most important sandy
beaches from tourists’ perspective, namely Patenga and Cox’s Bazar are located in this coastal zone.
Fish farming, fishing in the bay, salt production and tourism are main economic activities of the zone.
2.Central coastal zone Central coastal zone extends from Feni river estuary to the eastern corner of the
Sundarbans, covering Noakhali, Barisal, and Bhola and Patuakhali districts. The zone receives a large
volume of discharge from the Ganges-Bhrahmputra-Meghna river system, forming high volume of silty
deposition. More than 70 % of the sediment load of the region is silt; with an additional 10 % sand
(Coleman, 1969; cited in Allison et al., 2003).Because of the sediment discharge and strong current, the
morphology of the zone is very dynamic and thus erosion and accretion rates in the area are very high
(Coleman, 1969; cited in Allison et al., 2003). Numerous islands are located in the area including the
country’s only island district Bhola.Kuakata, an attractive sandy beach is located at the zone under
Khepupara upazilla of Patuakhali district.
3.The western coastal zone is covered by the Sundarbans mangrove forest, covering greater Khulna and
part of Patuakhali district. Because of presence of mangrove forest, the zone is relatively stable in terms of
soil erosion. The area lies at 0.9 to 2.1 metre above mean sea level (Iftekhar and Islam, 2004). Soil
characteristics of the western coastal zone are silty loams or alluvium. Islam (2003).Most of the people are
depended on agricultural land, livestock, fisheries,forestry, waterways,salt production, seaport facilities,
sites of archeological importance and tourism.

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c. beach profile /types ofcoast
Based on river discharge (water and sediment), wave climate and relative strength of tide- induced (tidal
range TR) and wave-induced forces (H = annual mean nearshore wave height H), the following
classification may also be given: riverine-dominated coasts,
1.wave energy-dominated coasts (TR/H= 0.5 to 1),
2.tide energy-dominated coasts (TR/H > 3),
3.mixed energy coasts (TR/H = 1 to 3).
Based on typical coastal features (morphological), another classification
can be made: barrier island coasts, delta coasts, dune coasts, cliff coasts, coral reef coasts,
mangrove coasts, marsh grass coasts,etc.
Based on sediment composition of the beach material, the following classification can be made:
1. mud coasts,
2.sand coasts (quartz, coral sand),
3. gravel/shingle coasts,
4. rock and cliff coasts.
About 5% to 10% of the world's coasts consists of muddy coasts;
about 10% to 15% consists of sandy coasts and

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about 75% to 85% consists of rock, cliff and gravel-type coasts.
2. a. sea level rise
A sea level rise is an increase in the volume of water in the world’s oceans,resulting in an increase in
global mean sea level. Sea level rise is usually attributed to global climate change by thermal expansion
of the water in the oceans and by melting of ice sheets and glaciers on land. Melting of floating ice
shelves or icebergs at sea raises sea levels only slightly.
b. impacts of sea level on coast
Why/causes of sea level rising
There are two ways in which global warming is causing sea levels to rise are: (a) thermal expansion and
(b) the melting of glaciers, ice caps etc. Global warming or increases in temperatures (due to increase in
the concentrations of greenhouse gases) cause the oceans to warm and expand in volume inducing a rise
in the sea levels. Furthermore, warmer climate facilitates melting of glaciers, ice caps and ice sheets
causing further addition of water to the oceans. In fact,the major cause of SLR is the thermal expansion
of the oceans which contributes substantially in recent time. For example, thermal expansion accounts for
about 25% of the observed SLR since 1960 and about 50% from 1993 to 2003. The glaciers and
Greenland and West Antarctica mass loss due to melting of ice sheets contributed to SLR was around
30% and <15% of the global SLR between 1993 and 2009 respectively.
Sea level rising and impacts
Sea-level-rise (SLR) is the average increase in the level of world’s oceans. SLR is one of the most
catastrophic consequences of global warming/climate change. SLR will cause forced migrations, of which
small island and poor developing countries are particularly susceptible. Regions at most risk include heavily
populated deltaic regions in South, Southeast and East Asia (Bangladesh, China, India, Indonesia, and
Myanmar). SLR will cause a number of ecological and socioeconomics impact in particular on coastal
systems including
1: impacts on water resources: Saltwater intrusion into freshwater aquifers, deltas and estuaries (e.g.
chloride contamination of freshwater aquifers)
2: agriculture: Salinization of agricultural land and rice production (e.g. inundation of rice land and rice
production in Vietnam, Myanmar, Bangladesh),
3: Losses of wetlands: Sea-level rise can cause significant impacts on coastal wetlands .Coastal wetlands
(salt marshes, mangroves, and intertidal areas) are sensitive to sea-level rise since they are closely
linked to sea level. They provide flood and storm protection, waste assimilation, nutrient cycling functions,
food production (nursery areas for fisheries), nature conservation (habitat for wildlife) and other
ecosystems services. It has been projected that most losses of coastalwetlands may occur from a rise of 0.2
m sea level.
4: impacts on fisheries: SLR would cause loss of agricultural land due to flooding of lands and intrusion of
seawater, as a result, agriculture in the low-lying coastal area or adjacent to deltas may be
affected.Significant rice land is projected to be inundated in many countries, most notably in Southeast
Asia, South Asia, and East Asia (e.g. Vietnam, Egypt, Myanmar,and Bangladesh)(Dasgupta et al. 2009).
Rice is a major staple crop of half of world’s population and may results in food security crisis in those
regions/countries if SLR increases in the line of projections. A 1.5 meter of sea level rise in Bangladesh
may flood about 16% of the country’s land area (22,000 square kilometres) of which southern subregions

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are more vulnerable where rice production could be unsuitable (Kibria, 2011). A 32 and 88 cm SLR
would significantly reduce paddy production in Bagerhat, Khulna and Satkhira districts of Bangladesh
whereas shrimp production (Penaeus monodon) will significantly increase in theseareas (Hassan and Shah
2006)However, SLR also will also create new areas for brackish water fish/shrimp aquaculture.
5: impacts on biodiversity: Loss of biodiversity (e.g. a 28 cm SLR will cause a decline of 96% tiger habitat
in Sundarbans or Sundarban Bangladesh)
6: impacts on human health: Increase in human health risk (e.g. increase in cholera outbreak and
hypertension)
7: coastal flooding and inundation: Inundation of low-lying coastal regions (e.g. densely populated South,
Southeast and East Asia are highly threatened)
8: impacts on population exposure, displacement and climate refugee:
Displacement of people (e.g. globally 72-187 million people will be displaced & most of them are from
South, Southeast and East Asia and
(9: Impact on coastal infrastructure (e.g. commercial and residential buildings, air ports, ports, hospitals,
schools which are close to the coast are at greater risk). Coast defenses, flood warning system, planned
retreat, elevated storm shelters, growing salt tolerant rice, rearing Euryhaline fish species is some of the
adaptation options that can be taken to reduce impacts from sea-level-rise
c. major causes of sea level rise
Sea levels change for three main reasons:
1) As water warms and cools it expands and contracts;
2) The amount of water contained as ice on land surfaces changes over time;
3) The Earth’s surface is dynamic and can move vertically.
The first two reasons are directly caused by global temperature changes.
3. a. define sand , sediment , weather, erosion
Soil is a complex, unconsolidated mixture of inorganic, organic, and living material that is found on the
immediate surface of the earth that supports plant life.
Sand : loose granular material that results from the disintegration of rocks, consists of particles smaller
than gravel but coarser than silt,
erosion is the action of surface processes (such as water flow or wind) that remove soil, rock, or dissolved
material from one location on the Earth's crust, then transport it away to another location. The particulate
breakdown of rock or soil into clastic sediment is referred to as physical or mechanical erosion; this
contrasts with chemical erosion, where soil or rock material is removed from an area by its dissolving into
a solvent (typically water), followed by the flow away of that solution. Eroded sediment or solutes may be
transported just a few millimeters, or for thousands of kilometers.
Coastal erosion involves the breaking down and removal of material along a coastline by the movement
of wind & water. It leads to the formation of many landforms and, combined with deposition, plays an
important role in shaping the coastline.

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Sediment is a naturally occurring material that is - broken down by processes of weathering and erosion,
and is subsequently transported by the action of wind, water,or ice, and/or by the force of gravity acting
on the particles and deposited in any other places.
Factors govern coastal erosion
1. Exposure: wave and current attack will be concentrated on headlands, capes and other protruding
coastalforms;
2. High tides (spring tide), storm surge levels and storm intensity: flooding, wave overtopping and
breaching may occur;
3. Persistent oblique wave attack: wave-induced currents increase with increasing wave angle; net
littoral drift will be relatively large in case of one dominant wave direction;
4. Unconsolidated sediments: low sandy coasts can be relatively easily eroded; bluffs, cliffs and
rock-type coasts are more erosion resistant;
5. Absence of nearshore bars/banks/shoals: relief is important for offshore dissipation of energy
(wave breaking);
6. Presence of nearby sinks: trapping of sediment by inlets, back-barrier basins (lagoons), ebb
shoals, offshore sand banks, harbour basins, deep navigation channels, offshore canyons, etc.
b. types ofweathering processes
Weathering is the breaking down of rocks soil and minerals as well as wood and artificial materials
through contact with the earth’s atmospheric conditions (heat,temperature, ice, and pressure),water and
biological organisms.
Types: differences in the types and rates of weathering, depend primarily on four factors:
(1) The structure and composition of the rocks, particularly rock strength and resistance to weathering
processes
(2) Climate, particularly temperature and humidity regimes (thus, the term weathering);
(3) the land surface configuration, its slope and relief; and
(4) The type and density of vegetative cover
1: physical weathering or mechanical weathering: disintegrates rocks,breaking them into fragmentswithout
altering their chemical composition. The mechanical disintegration of rocks by physical weathering is
important to gradation processes in two ways. First, smaller rock particles are more easily removed and
transported
2: chemical weathering: decomposes rock through a variety of chemical reactions that cause minerals to
weaken and decay. Chemical weathering, or decomposition, prepares rocks for erosion and transportation
in three ways. First, chemical alteration forms new minerals that are softer and less resistant to erosion.
Second, chemical weathering createsnewmineral substances—through chemical reactions, often involving
water that are greater in volume than the original mineral material. This volume increase causes expansion
that fractures rocks, thereby accelerating both physical and chemical weathering by increasing the surface
area exposed and by weakening the rock mass.Third, chemical weathering may dissolve minerals in a
chemically active water solution (weak acid), making them easy to remove and transport. As more and
more minerals are removed, the number and size of pore spacesandother openings in the rock are increased,
allowing the rate of weathering to increase

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3: biological weathering: Biological weathering takes place when rocks are worn away by living
organisms. Trees and other plants can grow within the cracks in a rock formation. As the roots grow
bigger they push open cracks in the rocks making them wider and deeper. Over time the growing tree
eventually prizes the rock apart.
Tiny organisms like bacteria, algae and moss can grow on rocks and produce chemicals which can break
down the surface layer of the rock. Burrowing animals such as rabbits can accelerate the formation of
cracks.
c. sources ofsediment in land formation: There are four sources of sediment: cosmogenous (from outer
space), volcanogenous (ash from volcanic eruptions), terrigenous (continents erosion and river runoff),
and biogenous (skeletons of marine creatures).
Major sources of sand and sediment for land formation
1: erosion of the land, rocks
2: weathering
3: sediment, silt
4: Wave, currents,tide
5: shell or fragments of mollusks
d. sediment types
Sediments are classified according to their size. In order to define them from the smallest size to the
largest size: clay, silt, sand, pebble, cobble, and boulder.
• Based on the sources, sediments (marine sediments) are of four kinds-
1. lithogenous: Lithogenous are from the land, they form through the weathering process and are
composed of small particles from weathered rock and volcanic activity.And within Lithogenous
sediments there are two sub categories:
Terrigenous and red clay. Terrigenous sediments are produced when the weathering process occurs above
water. Wind and other natural sources then carry these particles to the ocean where they sink.
Red clay, also known as abyssal clay however, is mostly located in the ocean and is formed from a
combination of Terrigenous material and volcanic ash.
2. biogenous: Biogenous sediments are formed from the remnants of organisms that refused to be
dissolved.Good examples of these organisms include shellfish, clams,anything that has a shell.Other things
that could avoid being dissolved include bones and teeth and other appendages.In deeper waters,shells of
plankton and other microscopic organisms form these kinds of sediments.
3. hydrogenous: Hydrogenous sediments are sediments solidified out of ocean water.As such,chemical
reactions create these kinds of sediments. The precipitation of dissolved chemicals from seawater. These
kinds of sediments are found commonly near hydrothermal vents.
4. cosmogenous: Cosmogenous sediments are probably the most interesting of all four kinds of sediment
because they are alien in nature.These kinds of sediments are carried to earth on meteorites or asteroids.

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They are usually a conglomeration of different kinds of metals and due to their nature, are not easy to
find.
Suspended: Grains in suspension move with the water mass in which they are
contained. This is generally fine-grained material, but larger grains can be carried if the velocity of water
motion is very great.
Bed load :Bed-load transport involves particles that are too heavy to be put into suspension and are
moved along the bottom in a rolling or sliding motion.
Saltation: Intermediate between the two is a process called saltation in which the particles move in a
series of jumps. A particle is thrown into suspension either by fluid turbulence or grain impact, and moves
with the water until it falls again to the bottom. This is an important process in the movement of sand in
both nearshore and shelf settings because wave action can periodically throw sediment into the water
column to be moved by weaker,unidirectional currents to a new spot. Repetition of this with each wave
can result in effective grain transport.
4. a. define tide / Wave Propagation/wave Refraction/wave Diffraction/wave Reflection/Longshore
Currents/Rip Currents
LONGSHORE CURRENT or NEARSHORE CURRENT
The Longshore current is the dominating current in the Nearshore zone, it is running parallel to the shore.
The Longshore current is generated by the shore-parallel component of the stresses associated with the
breaking process for obliquely incoming waves,the so-called radiation stresses,and by the surplus water
which is carried across the breaker zone towards the coastline.
RIP CURRENTS
At certain intervals along the shoreline, the Longshore current will form a rip current. It is a local current
directed away from the shore, bringing the surplus water carried over the bars in the breaking process,
back into deep water. The rip opening in the bars will often form the lowest section of the coastal profile;

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a local setback in the shoreline is often seen opposite the rip opening. The rip opening travels slowly
downstream.
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted
by the Moon and the Sun and the rotation of Earth.
Tides are long-period waves that roll around the planet as the ocean is "pulled" back and forth by the
gravitational pull of the moon and the sun as these bodies interact with the Earth in their monthly and
yearly orbits. noaa
The times and amplitude of tides at any given locale are influenced by the alignment of the Sun and
Moon, by the pattern of tides in the deep ocean, by the amphidromic systems of the oceans,and the shape
of the coastline and near-shore bathymetry
b. tide generating forces
1. The Effect of Centrifugal Force. It is this little known aspect of the moon's orbital motion which is responsible for
one of the two force components creating the tides. As the earth and moon whirl around this common center-of-mass,
the centrifugal force produced is always directed away from the center of revolution. All points in or on the surface
of the earth acting as a coherent body acquire this component of centrifugal force. And, since the center-of-mass of
the earth is always on the opposite side of this common center of revolution from the position of the moon, the
centrifugal force produced at any point in or on the earth will always be directed away from the moon. This fact is
indicated by the common direction of the arrows (representing the centrifugal force Fc) at points A, C, and B in Fig.
1, and the thin arrows at these same points in Fig. 1
2. The Effect of Gravitational Force. While the effect of this centrifugal force is constant forall positions on the earth,
the effect of the external gravitational force produced by another astronomical body may be different at different
positions on the earth because the magnitude of the gravitational force exerted varies with the distance of the attracting
body. According to Newton's Universal Law of Gravity, gravitational force varies inversely as the second power of
the distance from the attracting body. Thus, in the theory of the tides, a variable influence is introduced based upon
the different distances of various positions on the earth's surface from the moon's center-of-mass. The relative
gravitational attraction (Fg) exerted by the moon at various positions on the earth is indicated in Fig. 2 by arrows
heavier than those representing the centrifugal force components.

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c. types oftide (basis on day/lunar /location)
Diurnal tide cycle ). An area has a diurnal tidal cycle if it experiences one high and one low tide every
lunar day. Many areas in the Gulf of Mexico experience these types of tides.

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Semidiurnal tide cycle (). An area has a semidiurnal tidal cycle if it experiences two high and two low
tides of approximately equal size every lunar day. Many areas on the eastern coast of North America
experience these tidal cycles.
Mixed Semidiurnal tide cycle (). An area has a mixed semidiurnal tidal cycle if it experiences two high
and two low tides of different size every lunar day. Many areas on the western coast of North America
experience these tidal cycles.
Basis on lunar day
1. The tide which occurs when the moon is new or full; the effects of the Sun and moon being reinforced
so that this tide is of maximum range. Spring tides occur twice each lunar month all year long
without regard to the season
2. A tide in which the difference between high and low tide is the least. Neap tides occur twice a
month when the Sun and Moon are at right angles to the Earth. When this is the case,their total
gravitational pull on the Earth's water is weakened because it comes from two different
directions.

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5. a. current: The term "current" describes the motion of the ocean.
Current: A body of water or air moving in a definite direction, especially through a surrounding body of
water or air in which there is less movement.
Ocean Current: An ocean current is a continuous, directed movement of seawater generated by forces
acting upon this mean flow, such as breaking waves,wind, the Coriolis effect,temperature and salinity
differences.
Currents affect the Earth's climate by driving warm water from the Equator and cold water from the poles
around the Earth. The warm Gulf Stream, for instance, brings milder winter weather to Bergen, Norway,
than to New York, much further south.
b. causes ofcurrent :
Ocean currents are driven by three main factors:
1. The rise and fall of the tides: Tides create a current in the oceans,which are strongest near the shore,
and in bays and estuaries along the coast. These are called "tidal currents." Tidal currents change in a very
regular pattern and can be predicted for future dates. In some locations, strong tidal currents can travel at
speeds of eight knots or more.
2. Wind: Winds drive currents that are at or near the ocean's surface. Near coastalareas winds tend to
drive currents on a localized scale and can result in phenomena like coastal upwelling. On a more global
scale, in the open ocean,winds drive currents that circulate water for thousands of miles throughout the
ocean basins.
3. Thermohaline circulation: This is a process driven by density differences in water due to temperature
(thermo) and salinity (haline) variations in different parts of the ocean. Currents driven by thermohaline
circulation occur at both deep and shallow ocean levels and move much slower than tidal or surface
currents.
c. patter of current / types :Ocean circulation is the large scale movement of waters in the ocean basins.
Winds drive surface circulation, and the cooling and sinking of waters in the polar regions drive deep
circulation. Surface circulation carriesthe warmupper waterspoleward from the tropics. Surface circulation
carries the warm upper waters poleward from the tropics. Heat is disbursed along the way from the waters
to the atmosphere. At the poles, the water is further cooled during winter, and sinks to the deep ocean. This
is especially true in the North Atlantic and along Antarctica. Deep ocean water gradually returns to the
surface nearly everywhere in the ocean. Once at the surface it is carried back to the tropics, and the cycle
begins again. The more efficient the cycle, the more heat is transferred,and the warmer the climate.Due to
the rotation of the earth, currents are deflected to the right in the northern hemisphere and to the left in the
southern hemisphere. This effect is known as the "Coriolis force." The deflection leads to highs and lows
of sea level directly proportional to the speedof the surface currents.The changesin sea level due to currents
are the ocean topography
The three main patterns ofocean circulation are –
i. gyres : a gyre is any large system of circulating ocean currents,particularly those involved with large
wind movements. Gyres are caused by the Coriolis effect; planetary vorticity along with horizontal and
vertical friction, determine the circulation patterns from the wind curl (torque).

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ii. upwelling : : Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense,
cooler, and usually nutrient-rich water towards the ocean surface,replacing the warmer,usually nutrient-
depleted surface water. The nutrient-rich upwelled water stimulates the growth and reproduction of
primary producers such as phytoplankton. Due to the biomass of phytoplankton and presence of cool
water in these regions, upwelling zones can be identified by cool sea surface temperatures (SST) and high
concentrations of chlorophyll-a.
iii. thermohaline circulation. Thermohaline circulation (THC) is a part of the large-scale ocean circulation
that is driven by global density gradients created by surface heat and freshwater fluxes. The adjective
thermohaline derives from thermo- referring to temperature and -haline referring to salt content, factors
which together determine the density of sea water. Wind-driven surface currents (such as the Gulf Stream)
travel polewards from the equatorial Atlantic Ocean, cooling en route, and eventually sinking at high
latitudes (forming North Atlantic Deep Water). This dense water then flows into the ocean basins. While
the bulk of it upwells in the Southern Ocean, the oldest waters (with a transit time of around 1000
years)upwell in the North Pacific.