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Physical & Chemical Oceanography
Transcript of Physical & Chemical Oceanography
On average tthe salinity of the ocean is 35 parts per thousand (35
Chemical composition of sea water
Sea water remains fairly constant for millions of years
Minamata Bay Disaster 1932-1968
Volcanoes Emit Gases
Gases such as Carbon Dioxide,
sulphur dioxide, hydrogen sulphide,
& hydrogen chloride dissolve into
atmospheric water and enter sea water in
precipitation (rain) as part of the
hydrological cycle (the water cycle).
What is it?
Runoff refers to the flow of water from LAND, resulting from rain or melting snow and ice.
Salinity can vary locally when the ocean is diluted by a river or when glaciers melt
(lowering the salinity)
Locally things change....
Atmospheric Dissolution (gases from the atmosphere dissolving into the ocean water)
Underwater volcanoes also emit gases
such as chlorine, introducing a major
source of the chloride ions present in
Runoff is an important part of the hydrological cycle, much of water from runoff may eventually drain into the oceans either directly or indirectly or from rivers.
Urban runoff may pick up and carry with it a variety of pollutants: pesticides, fertilizers, & oil-derived
substances. Concentrations may be low to begin with but become more concentrated as these pollutants are passed up the food web.
It started out quite simply, with the strangeness of cats "dancing" in the street--and sometimes collapsing and dying. Who would have known, in a modest Japanese fishing village in the 1950s, that when friends or family members occasionally shouted uncontrollably, slurred their speech, or dropped their chopsticks at dinner, that one was witnessing the subtle early symptoms of a debilitating nervous condition caused by ingesting mercury? Yet when such scattered, apparently unconnected, and mildly mysterious events began to haunt the town of Minamata, Japan, they were the first signs of one of the most dramatic and emotionally moving cases of industrial pollution in history.
Gases in Sea Water
Gases dissolved in sea water are in equilibrium with the atmosphere.
Concentrations of gases depends on
temperature of water
salinity of water
Which gases are dissolved in sea water?
As Temperature Increases, Density Decreases
Warm water tends to form layer on top of colder, denser water
Results in formation of temperature gradient
Temperature decreases with depth
Decreases from 25oC at surface to 1oC at depths of 2000m
Interface between two layers is thermocline
Gradient of salinity occurs in oceans
As salinity increases, density increases
Lower salinity water forms layer over higher salinity water
Region of significant change in salinity with depth is the halocline
Wind sets up turbulence & currents
Mixing of surface layers results
Mixing occurs to 200m depth
Temperature changes sets up mixing
Surface layer cools
Water will sink
Mixing of Ocean Layers
Concentration of O
Dependent upon many factors
Temperature of water
Higher temperatures result in decreased solubility
Salinity of water
Oxygen slightly less soluble in saline water
Variability of O2 Concentration
In Surface layers of ocean:
Concentration of dissolved oxygen is high
Possibly supersaturated with oxygen
Two main processes in surface water leading to increased O2 concentration:
Mixing by waves helps atmospheric O2 to dissolve into sea water
Photosynthesis of algae
Phytoplankton produce oxygen as a by-product
What increases Concentration of O2?
Removal of O2
Marine organisms remove O2 by respiration
Concentration changes with depth
High at surface layers
Decreases to a minimum as depth increases
At a point increases again as depth continues to increase
Depth at which concentration of dissolved oxygen is lowest is the
oxygen minimum layer.
Usually at 100m to 1000m
What decreases Concentration of O2 ?
What causes the tides?
Earth, Moon, Sun
The regular rise and fall of sea level is referred to as the tide and is due to the gravitational effects of the Sun, Moon, Earth and the rotation of the Earth.
Tides have a cycle of approximately 12.5 hours;
so most coastal areas experience two high tides and two low tides every day.
The tidal amplitude varies. When the Earth, Moon and Sun are aligned, the amplitude is greatest,
resulting in what are known as spring tides (see Figure below). At other phases of the Moon, such as
first quarter, the tidal range is smaller; these are referred to as neap tides.
What influences tidal amplitude?
The shape of the coastline can influence the tidal range. For example, where the tide enters a tapering river mouth, the height of the tide is increased by the opposite sides of the channel. A similar effect occurs in a bay.
Changes in wind and air pressure can have a significant effect on the tidal range. For example, a strong on-shore wind and low atmospheric pressure can produce a
‘tidal surge’ resulting in an exceptionally high tide
Oceanic Tidal Range vs. Near Shore Tidal Range
Oceanic tidal range is about 0.6 m while inland waters range from 0 to 12 m.
Explain how wind, temperature, density, the Coriolis effect and the shape of the sea bed produce
ocean currents and upwelling.
Ocean currents are the continuous, directional movement of ocean water, driven by forces acting on the water,
including waves, wind, the Coriolis effect, temperature, salinity and tides. The contours of the sea
bed influence the strength and direction of the current.
Impact of the CORIOLIS EFFECT
Surface ocean currents are generally driven by the wind and characteristically have a clockwise spiral in the northern hemisphere and a counter-clockwise spiral in the southern hemisphere.
Use of a simple float.....
Plastic bottle weighted so that it is just floating & attached with a measured length of string
Current speed=distance moved by the float / time (or)
Speed = d/t
Direction of current determined using a compass
Measurement of current speed & direction
Deep Ocean Currents are driven by temperature and density gradients
Deep Ocean Currents
Defined: Upwelling is a process in which deep, cold water rises toward the surface
Upwelling areas are regions where vast amounts of vertical movement of water occurs.
Areas where deflection of water is driven up near the surface like at a mid-ocean ridge or continental slope.
Winds blowing across the ocean surface push water away. Water then rises up from beneath the surface to replace the water that was pushed away. This process is known as “upwelling.”
How does Upwelling Occur?
Coriolis Effect: Due to the rotation of the Earth, water moves to the right in northern hemisphere and left in the southern hemisphere.
Surface currents are directed by both wind and Coriolis effect.
El Nino Southern Oscillation
Sequence of events that occurs in the southern Pacific Ocean. This is a change from normal conditions.
After viewing the video, write a description of El Nino.
Water that rises to the surface as a result of upwelling is typically colder and is rich in nutrients. These nutrients “fertilize” surface waters, meaning that these surface waters often have high biological productivity. Therefore, good fishing grounds typically are found where upwelling is common.
What are the benefits of Upwelling?
In normal conditions, cold water, rich in nutrients, flows in a northerly direction along the west cost of South America and influences upwelling making the waters there normally very productive.
NORMAL, Non El Nino Periods in South America
In normal conditions, cold water, rich in nutrients, flows in a northerly direction along the west cost of South America.
Upwelling normally occurs off the coast of South America
This northerly flow is accompanied by an upwelling of nutrients, caused by winds blowing form the south.
Upwelling leads to productive fisheries
This results in the water having a high productivity, with very large numbers of anchovies and sardines feeding in the plankton-rich water.
Upwelling is Good
This high productivity supports a substantial fisheries industry and many species of sea birds and other organisms.
People in South America that depend on fishing, Do NOT like when El Nino Visits
Explain the seasonal differences in temperature between the Asian continent and the Indian
Ocean, and explain how these differences give rise to the patterns of monsoon winds.
Asia is considered to be the largest content and there is wide range of climatic conditions, varying from hot and wet to cold and dry.
A monsoon is a seasonal wind of the Indian Ocean.
Land masses absorb heat faster than the sea and therefore heat up more quickly.
In the winter months,the sea is warmer than the land mass and air over the sea rises as it warms and becomes less dense.
This draws in cooler air from the land, from a north-easterly direction.
In India, this occurs in the post-monsoon season, during the months of October to December.
In the summer months, from May until August, the land heats up quickly and there is relatively large temperature difference between Central Asia and the Indian Ocean.
Air over the land warms, becomes less dense and rises.
This draws in air saturated with water vapour from the Indian Ocean, from a south-westerly direction.
The summer monsoons bring thunderstorms and exceptionally heavy rain.
It has been estimated that these summer monsoons bring over 80% of
India’s annual rainfall.
As the Indian land mass cools during September, this monsoon weakens
and is replaced with the dry, north-east post-monsoon
El Nino Conditions
Approximately every 7 to 10 years, the prevailing winds stop blowing in their normal pattern from
the east or south-east.
Warm equatorial water is blown by abnormal winds from the west. As a result, pressure gradients in the west and east Pacific Ocean are reversed, causing a reversal of wind direction and equatorial currents. This creates a large area of warm water; upwelling stops and so the supply of nutrients to the surface water is reduced.
The increase in temperature results in the death of many cold-water species and, coupled with the lack of nutrients, this causes the primary production to decrease dramatically. This affects higher trophic levels in food chains and food webs with the consequent collapse of commercial fish stocks