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6/5/24, 4:16 PM CSIR (Council of Scientific & Industrial Research) Earth Sciences Physical Oceanography(Ocean Sciences): Study Material P… CSIR (Council of Scientific & Industrial Research) Earth Sciences Ocean Sciences-Physical Oceanography Study Material (Page 1 of 20)...

6/5/24, 4:16 PM CSIR (Council of Scientific & Industrial Research) Earth Sciences Physical Oceanography(Ocean Sciences): Study Material P… CSIR (Council of Scientific & Industrial Research) Earth Sciences Ocean Sciences-Physical Oceanography Study Material (Page 1 of 20) 1 Relationship between Densities Use the above buttons to track progress on page The density of sea water indicates, density of a substance is the stated mass per unit volume in grams per cubic meter. The density of distilled water in 4°𝐶 temperature is 1.00 g/ 𝑐 𝑚 3. Due to presence of salts and other Substances the density of sea water ranges from 1.027 to 1.028 gm/ 𝑐 𝑚 3 which is 2 - 3% higher that distilled water. A substance will loat or sink, it is decided by density. Less dense substance tends to loat up - ward whereas substance with greater dense sinks. Vertical circulation on a large scale changes the sea water density. 1.1 Factors Affecting Sea Water Density The density of sea water is determined by three major factors. That are- Temperature, Salinity and Pressure Factors Effecting Sea Water Density Temperature https://www.doorsteptutor.com/Exams/CSIR/Earth-Sciences/Study-Material/Topic-Ocean-Sciences-19/Subtopic-Physical-Oceanography-0/Compl… 1/9 6/5/24, 4:16 PM CSIR (Council of Scientific & Industrial Research) Earth Sciences Physical Oceanography(Ocean Sciences): Study Material P… Density of sea water changes due to the minute change in temperature. Energy of water molecules increases when it heated up. This led to the thermal expansion of the molecules and occupies more volume. As a result, the density of warm water is less than the cold water. In case of cold water, lesser heat helps the molecule to come close together. Thus, ultimately helps to increase the density. For this reason, warm water loats on cold water. Highest density of distilled. water has4°𝐶been observed at If the temperature increased the water began to expand because of increasing space between the molecules and that lead to the decrease in density. Salinity There is a positive relation between sea water density and salinity. Greater salinity leads to. This is because there is more salt packed into the greater water. density Pressure Pressure is directly related to. sea water density High pressure leads to decrease in volume of water molecules. As a result, water molecules get closer and density will increase. The effect of pressure on sea water is small. 10 metre increase in depth lead to 1 atmosphere increase in density. Factors Affecting Sea Water Density 1.2 Vertical Distribution of Sea Water Density https://www.doorsteptutor.com/Exams/CSIR/Earth-Sciences/Study-Material/Topic-Ocean-Sciences-19/Subtopic-Physical-Oceanography-0/Compl… 2/9 6/5/24, 4:16 PM CSIR (Council of Scientific & Industrial Research) Earth Sciences Physical Oceanography(Ocean Sciences): Study Material P… Vertically three distinctive layer of sea water density has been observed. They are- Surface Layer It covers 2% volume of the sea water. Average depth of this layer varies from 100 to 200 metre. Due to the thermal expansion in this layer. is density lower Deep Layer It covers 80% volume of the sea water. This layer contains 100 metre depth. Lower temperature led to higher density. in this layer Cold water from poles and higher latitude circulates into the deep layer in low latitudes. Pycnocline Layer Depth 300 - 1000 m Boundary separating two liquid layers of different densities. Contains 18% of the ocean water. No mixed layer or Pycnocline exists in the highest latitudes (above 60 degrees) Vertical Distribution of Sea Water Density 1.3 Relation between the Three Layers The Pycnocline encompasses both the halocline ( salinity gradients) and the thermocline (temperature gradients ) and refers to the rapid change in density with depth. Because density is a function of temperature and salinity, the pycnocline is a function of the thermocline and halocline. https://www.doorsteptutor.com/Exams/CSIR/Earth-Sciences/Study-Material/Topic-Ocean-Sciences-19/Subtopic-Physical-Oceanography-0/Compl… 3/9 6/5/24, 4:16 PM CSIR (Council of Scientific & Industrial Research) Earth Sciences Physical Oceanography(Ocean Sciences): Study Material P… Relation between the Three Layers 2 Upwelling and Sinking with Special Reference to the Indian Ocean Use the above buttons to track Upwelling and sinking are theprogress part of ocean on pageimportant role in circulation. These processes play heat and oxygen distribution of the ocean. Upwelling is a process in which cold water from the bottom come to nutrient rich of surface the ocean. Sinking or is the move - layer ment of water from surface to the of downwelling bottom. Therefore, the the reverse of upwelling is sinking. ocean Upwelling and Sinking Upwelling occurs when conditions cause surface waters so to that deep water comes up from below to replace them. diverge Thermohaline circulation causes upwelling and downwelling of the ocean water. Ekman transport is responsible for the upwelling and sinking of the ocean water. Upwelling waters may originate below the Pycnocline (where density of ocean water gradually declines) and are therefore colder than the surface waters they replace. Wind blowing parallel to shore or off shore can cause. Thecoastal friction of upwelling wind blowing along the ocean surface causes the water to begin moving, the Coriolis effect de - lects it to the right (in the Northern Hemisphere) , and the resultant Ekman transport moves it off - shore. https://www.doorsteptutor.com/Exams/CSIR/Earth-Sciences/Study-Material/Topic-Ocean-Sciences-19/Subtopic-Physical-Oceanography-0/Compl… 4/9 6/5/24, 4:16 PM CSIR (Council of Scientific & Industrial Research) Earth Sciences Physical Oceanography(Ocean Sciences): Study Material P… Sinking causes when conditions cause surface waters to converge so it comes to the bottom of the ocean. 2.1 Significance of Upwelling Moderate rates of upwelling for long duration (8 months or longer) provide the ultimate combination for a large ishery. Surface water where upwelling is prevalent is always rich in nutrients. Nutrients rich surface layer helps in the higher growth of phytoplankton. Since phytoplankton form the base of marine food webs, the world՚s most productive isheries are located in areas of coastal upwelling zone. It is estimated that about 80% of the world՚s ish catch is in the upwelling regions of the world oceans. Phosphates and nitrates in higher concentration are common in the regions of upwelling as the nutrient rich sub-surface water is brought to the surface. Upwelling can also in luence weather. Wind blowing from the north along the California coast causes off - shore movement of surface water and subsequent coastal upwelling. As a result, the overlying air becomes chilled, contributing to San Francisco՚s famous fog banks and cool summers. Along the Somali coast during intense upwelling the surface temperature falls below 14°𝐶 while during sinking it is above 28°𝐶. 2.2 Significance of Sinking Sinking helps in the supply of dissolved gasses and nutrients into the deeper ocean. The transport of water through sinking assist in the distribution of living organisms. Sinking reduces biological productivity in the surface layer. Sinking has no direct effect on the climate. 2.3 Ekman Transport Surface water of the ocean moves parallel to the wind direction. Winds drag the surface water along with it. The topmost layer of the ocean water r in the Northern Hemisphere lows at about 45° to the right of the wind direction. Because of the Coriolis force the water de lected in the right direction in the northern hemisphere and in southern hemisphere the de lection occurs in the left direction. The next layer of the topmost layer of water moves at an angle to the right of the overlying water. The same thing happens in the layer below that, and the next layer, and so on. Each layer slides horizontally over the one beneath it like cards in a deck, with each lower card moving at an angle slightly to the right of the one above. Because of frictional losses, each lower layer also moves more slowly than the layer above. This spiral movement of water is known as Ekman Spiral. https://www.doorsteptutor.com/Exams/CSIR/Earth-Sciences/Study-Material/Topic-Ocean-Sciences-19/Subtopic-Physical-Oceanography-0/Compl… 5/9 6/5/24, 4:16 PM CSIR (Council of Scientific & Industrial Research) Earth Sciences Physical Oceanography(Ocean Sciences): Study Material P… Due to friction between the layers of water in the ocean and the Coriolis Effect, the net result of wind blowing across the surface of the water is transportation of a layer of water 90 degrees to the direction of the wind. This is known as Ekman Transport. Upwelling is caused by Ekman Transport. If the coast is to the left of the wind direction upwelling occurs in northern hemisphere. It gives a chance of the deeper layer that rises on the left and replaces them. Rightward position of coast towards wind direction helps in the sinking process. Ekman Transport 2.4 Thermohaline Circulation The slow circulation of water at great depths is driven by density differences rather than by wind energy. Because density is largely a function of water temperature and salinity, the movement of water caused by differences in density is called thermohaline circulation (therme, “heat;” halos, “salt” ). The whole ocean is involved in slow thermohaline circulation, a process responsible for the large-scale vertical movement (upwelling and Sinking) of ocean water and the circulation of the global ocean as a whole. https://www.doorsteptutor.com/Exams/CSIR/Earth-Sciences/Study-Material/Topic-Ocean-Sciences-19/Subtopic-Physical-Oceanography-0/Compl… 6/9 6/5/24, 4:16 PM CSIR (Council of Scientific & Industrial Research) Earth Sciences Physical Oceanography(Ocean Sciences): Study Material P… Thermohaline Circulation 2.5 Upwelling and Sinking in Indian Ocean Major coastal upwelling regions are associated with eastern boundary currents. The current sys - tem itself is referred as the upwelling region. Somali and Arabian coast, East coast of India experi - ences seasonal upwelling. Peru Current System Peru Current system experiences unusual phenomena known as “Elnino.” El Niñ o is a warming of the tropical eastern Paciic. When the trade winds falter during an Elnino event, warm equatorial water that would normally low westward in the equatorial Paciic backs up to low east. The normal northward low of the cold Peru Current is interrupted or overridden by the warm water. When the Peru Current slows and its upwelled water lacks nutrients, ish, and seabirds depen - dent on the abundant life it contains die or migrate elsewhere. https://www.doorsteptutor.com/Exams/CSIR/Earth-Sciences/Study-Material/Topic-Ocean-Sciences-19/Subtopic-Physical-Oceanography-0/Compl… 7/9 6/5/24, 4:16 PM CSIR (Council of Scientific & Industrial Research) Earth Sciences Physical Oceanography(Ocean Sciences): Study Material P… Normal Conditions EI Nino Conditions Benguela Current System Upwelling in this region is closely associated to the wind. Upwelling is highest during summer. The upwelling shifts from summer to winter to the northern region with the shift of the rind. Equatorial Upwelling Winds from the east drive 3 westerly currents on both side of the equator. The north equatorial current of the Indian Ocean and the South Equatorial currents in the Atlantic and the Paci ic Ocean. https://www.doorsteptutor.com/Exams/CSIR/Earth-Sciences/Study-Material/Topic-Ocean-Sciences-19/Subtopic-Physical-Oceanography-0/Compl… 8/9 6/5/24, 4:16 PM CSIR (Council of Scientific & Industrial Research) Earth Sciences Physical Oceanography(Ocean Sciences): Study Material P… Due to Ekman transport it de lected to right direction in the northern hemisphere. In the southern hemisphere it de lected in the left direction. As a result, there is a de icit of surface water observed between the two currents. Water from the bottom comes to the surface to ill this void. This phenomenon is known as Equatorial Upwelling. Indian Ocean Large sinking occurs in the convergence Antarctic region of Indian Ocean. The various stages of sinking between the subtropical convergence and Antarctic water mass lead to the formation of Antarctic water mass. Under the in luence of Strong monsoon water from the Somali coast drifted away and cause large scale upwelling. Under the in luence of prevailing wind upwelling occurs from February to April and sinking occurs from September to November along the east coast of India. West coast of India experiences upwelling and sinking in the different time of the year. https://www.doorsteptutor.com/Exams/CSIR/Earth-Sciences/Study-Material/Topic-Ocean-Sciences-19/Subtopic-Physical-Oceanography-0/Compl… 9/9