Oceanography

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• Physical properties affecting oceanic waters
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• Temperature
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• • influencing global radiation balance, heat budget & making the global hydrological cycle functional.
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• Density
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• • dynamics of ocean water and circulating heat ‐determines whether the water will sink or will float.
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• Salinity
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• • Freezing and boiling points ‐ saline water freezes slowly • Evaporation ‐ more saline water is less evaporated. Interdependence of temperature, density and salinity
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• salinity factor has little control over seawater density at least in the tropical and subtropical oceans whereas seawater temperature emerges as the most potent factor of seawater density.
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• Impact of climate change
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• Hydrological cycle ‐‐ is changing, with the wetter parts of the world getting wetter and the drier parts drier.
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• Amount of heat stored in the ocean increased. Over the past century, increase in ocean water temperature of 0.6 degree.
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• In the tropical and middle latitudes, there has been a rise in salinity. While, in the higher latitudes water is getting less salty because of fresh water inflow by the melting ice cap.
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• Ocean acidification ‐ due to increased levels of atmospheric carbon dioxide, which dissolves in the water.
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• With rising temperature density decreases, shrinking zones of sharp changes in ocean water temperature (thermocline), density (pycnocline) and salinity (halocline).
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• impact on the surface ocean flows but also on water masses and thermohaline circulation. This is due to complex linkages between temperature, density and salinity.
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• Density of Ocean water:
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• • Temperature: (High T – low density) Water at poles is denser than in tropics. Temperature of surface ocean water decreases between 45‐degree N‐S and poles
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• • Salinity: High salinity seawater is denser and sinks below lower salinity water, leading to stratification.
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• • Pressure: Increasing density values demonstrate the compressibility of seawater under the tremendous pressures present in the deep ocean.
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• • Other Factors: Rainwater, surface run‐off brought by rivers flowing into oceans, and melt water from ice and snow are minor factors that lower down density.
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• • While, evaporation, cooling of surface water and process of ice formation tend to increase density of the ocean water. Partially or completely enclosed seas don’t intermix much with surrounding water.
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• • In the tropics they have higher evaporation resulting in higher density while near poles they have lesser evaporation resulting in comparatively low density.
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• • Latitudinal Variation Between 20 degrees and 30 degree N and S, water has high salinity due to high rate of evaporation, thereby leading to higher density.
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• Salinity
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• • Salinity is lower than average 35 % in the equatorial waters due to high daily rainfall
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• • Seasonal Variation As salinity, temperature and density of water are interrelated. For instance, in Red Sea, salinity is as high as 41 ppt, while in the Arctic, it fluctuates from 0‐35 ppt, seasonally.
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• • In hot and dry regions, where evaporation is high, the salinity sometimes reaches to 70 ppt.
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• • Ocean salinity declines due to rains as well as in summers when ice melts.
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• • Relationship with Ocean Currents Waters of low salinity and density flow on the surface of waters of high salinity, while waters of high salinity flow at the deep oceans towards waters of low salinity. Ex‐ less saline waters of the Atlantic flow on the surface into the enclosed Mediterranean Sea
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• • In the northern Atlantic Ocean, creation of gyres due to Gulf Stream, Canary Current and North Equatorial
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• Current, increases the salinity.
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• • In areas where convergence of ocean currents occurs, water of relatively higher density moves downwards, while, in areas of divergences, ascending motion of bottom water of higher density and lower temperature towards the surface.
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• Ocean currents

• • attributed to density differences in different layers of ocean waters. Heavier water sinks and causes the overlying surface water to move in its space. This gives rise to global oceanic circulation.
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• • Other factors ‐ Accumulation of water on east coasts leads to gravity induced movements down the slope.
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• • Expansion due to heat ‐ Even though water is considered practically incompressible, minor expansion due to excess solar heat in equatorial regions causes a slight gradient and water tends to flow down the slope.
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• • Modification ‐ Wind, Coast line and inundation, large river discharge, presence of partially enclosed seas.
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• • Periodic reversals due to heating and accumulation can such as in case of El‐ Nino current caused by a stronger counter equatorial current.
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• • Coriolis force‐ produce large circular currents in all the
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• Ocean basins. Ex ‐Sargasso Sea.
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• Ocean currents ‐ direct and indirect effects on the climate of the regions.
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• • West coasts of the continents in Tropical and subtropical are bordered by cold currents. Their average temperatures are relatively low with narrow diurnal and annual ranges. There is fog, but generally areas are arid due to the desiccating effect leading to formation of deserts in the area. Example. Cold Peruvian current‐ Atacama Desert.
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• • East coasts of continent in middle latitudes are bordered by warm currents ‐ cause a distinct marine climate. cool summer and relatively mild winters. E.g. China type of climate.
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• • Warm currents flow parallel to east coasts of the continents in tropical and subtropical latitudes. This result in warm and rainy climates. E.g. Florida.
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• • Foggy weather and drizzle in the mixing zones of warm and cold current.
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• Sargasso Sea‐ vast patch of sea in the North Atlantic Ocean located between latitudes 20N and 35 N and longitudes 30W and 70W. genus of free‐floating seaweed called Sargassum. Only sea without a land boundary.
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• Reasons behind formation:
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• • It lies within the Northern Atlantic Subtropical Gyre. It is encircled by the Gulf Stream in the west, north Atlantic drift in the north, Canary current in the east and North Equatorial and Antilles current in the south.
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• • North Atlantic that encircle it, bring into it millions of tons of floating sargassum weed. The plants have become adapted to life in the open sea, need no roots or holdfasts for attachment
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• • The surrounding ocean currents form a virtual fence and the region provides ideal conditions for them to grow.
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• High salinity of Sargasso Sea: ‐High salt content of 36 %
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• • Prevention of mixing of fresh water from surrounding oceans and poles due to virtual boundary created by the ocean currents.
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• • Low wind conditions prevent intermixing with fresh water.
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• • High temperature in the region owing to its subtropical location and very less cloud cover. This causes high evaporation.
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• • Gulf Stream brings in high salinity water to the sea.
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• Diagram of sargosa in north atlantic.
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• Tides:
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• • Tides are great bulges of water caused by the gravity of the Moon and Sun. Attracted by gravity, these bulges move around the Earth’s oceans, causing water levels to rise and fall.
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• • Combined effects of the gravitational forces exerted by the Moon and the Sun and the rotation of Earth cause occurrence of tides in oceans. As the Earth spins, different areas of the planet face the moon, and this rotation causes the tides to cycle around the planet.
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• Role played by tides in maintaining coastal ecosystems:
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• • Affect reproductive activities of fish and ocean plants: Floating plants and animals ride the tidal currents between the breeding areas and deeper waters.
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• • The tides help remove pollutants and circulate nutrients required for survival of ocean plants and animals. Ex: seawater in and out of tidal bays and estuaries.
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• • Moderate temperature: The tides and tidal currents mix arctic water that can’t absorb lots of sunlight with warmer tropic water that does. The stirring produces more predictable and habitable climate conditions in coastal areas.
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• • Tides play vital role for the growth and formation of mangroves, its canopy and formation of zonation in the mangrove ecosystem and associated diversity.
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• • Help maintain mudflats that provide flora and fauna with habitation.
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• Conclusion: in addition to benefits to mankind (navigation, energy), tides have very important role in maintaining coastal ecosystem.