Part 4 Chap 15.1 Composition of seawater

Chapter 15.1 : 

Chapter 15.1 The Composition of Seawater

Seawater : 

Seawater Anyone who has been to a beach or played in the ocean knows seawater is not the same as freshwater Seawater contains dissolved substances that give it a salty taste We refer to the total amount of solid material dissolved in water as its salinity

Seawater : 

Seawater Dissolved substances in seawater Sodium chloride Other salts Metals Dissolved gases In some way, every known naturally occurring element is found in seawater

Seawater : 

Seawater The salt content of seawater makes it unsuitable for everyday things we take for granted It can’t be used for drinking It can’t be used for irrigation It is highly corrosive to many materials

Seawater : 

Seawater Why can’t we drink seawater? The salinity of seawater is four times greater than the salinity of body fluids So, when we take in seawater, osmosis takes over The seawater looks “drier” than our body fluids, so water enters the digestive tract to hydrate the seawater Once entering the digestive tract, it leaves our body in the normal fashion (urination) Water leaving our body dehydrates our important organs and us along with it

Seawater : 

Seawater The salinity of seawater Salinity is the total amount of solid material dissolved in water The salinity of seawater is 3.5% or 35 g for every 1000g of water

Seawater : 

Seawater Most of the salt is seawater is sodium chloride NaCl This is what you put on your french fries, just regular table salt

Seawater : 

Seawater Where do these sea salts come from? Chemical weathering of rocks on the continents Approximately 2.3 billion metric tons per year goes into the oceans from runoff from rivers and streams The Earth’s interior Volcanic eruptions provide large quantities of water vapor and other gases into the atmosphere which make their way into the oceans

Seawater : 

Seawater So, is the ocean getting saltier? Evidence suggests that the composition of seawater is stable and has been for millions of years So, what happens to all of the added material? Some components are removed by organisms as they build hard structures Some chemically precipitate out of water as sediment Some are exchanged at the oceanic ridge at hydrothermal vents

Seawater : 

Seawater Melting icebergs, formation of sea ice, river runoff, evaporation Which of these would increase the salinity of water? Which would decrease the salinity of water?

Seawater : 

Seawater Processes that increase salinity Evaporation Formation of sea ice Processes that decrease salinity Precipitation Runoff from land Icebergs melting Sea ice melting

Seawater : 

Seawater Think of the north pole Does the salinity of the water change? When would it be the most saline? When would it be the least?

Seawater : 

Seawater Besides the simple ratio of water to amount of salt in it, other things affect the seawater as well Temperature variations with depth Density differences Ocean layering

Seawater : 

Seawater Temperature variation with depth Water is warmed by the sun The temperature varies with the amount of solar radiation received Less sunlight equals lower temperatures Latitude has a major impact on the amount received Higher latitudes receive less sunlight than lower latitudes

Seawater : 

Seawater The graph to the right shows variations of ocean surface temps with latitude and surface salinity with latitude How much of an impact do you think surface temps have on salinity? Why?

Seawater : 

Seawater The amount of sunlight received to heat the water does not have a major impact on the salinity, but it does have a impact on what can live where Some marine species cannot withstand large temperature changes

Seawater : 

Seawater The deeper in the water an object is, the colder water it is going to be in The place in the seawater where there is a rapid change in temperature with depth is a layer known as the thermocline It occurs between 300 and 1000 meters below the surface It is important because it creates a vertical barrier to many types of marine life

Seawater : 

Seawater As the graphs below show, the thermocline is affected by the latitude High latitudes do not have a thermocline Waters that do not have a thermocline are referred to as isocline

Seawater : 

Seawater Meanings Thermo means heat Cline means slope Iso means same A thermocline is a slope of heat An isocline means the temperature does not have a changing slope for temperature. All is the same Somewhere below 1000 m, even tropical waters are the same temperature as polar waters. At that point, an isocline has been achieved

Seawater : 

Seawater Variations in ocean density Density is another ratio It is the amount of mass compared to the amount of area the mass takes up It is mass divided by volume Density is an important property of water in that it determines the water’s vertical position in the ocean Denser waters are heavier and therefore deeper than less dense waters

Seawater : 

Seawater What affects seawater density? Two main things affect the density Salinity Increasing the amount of salt increases the mass, so water gets more dense Removing salt removes mass, so water gets less dense Temperature Hotter water is less dense than cold water because the molecules are spread out farther from each other So… cold water with lots of salt is the densest water in the ocean

Seawater : 

Seawater Density variation with depth Which is more important in determining density: temperature or salinity? Salinity in the oceans is relatively uniform But, as the temperature goes down, the density goes up This is because the water molecules get closer together, putting more mass in a smaller area

Seawater : 

Seawater The place in the seawater where there is a rapid change in density with depth is a layer known as pycnocline Pycno means density so “density slope” The pycnocline is located 300m to 1000m below the surface just like the thermocline

Seawater : 

Seawater Below is the pycnocline graph Like the thermocline, the pycnocline does not exist in the polar regions or deep in the water

Seawater : 

Seawater Comparing the thermocline and pycnocline graphs

Seawater : 

Seawater Ocean layering The ocean is layered according to density. Low density water is at the top Denser water is found below Oceanographers break this down into three main layers Surface mixed zone Transition zone Deep zone

Seawater : 

Seawater The three main layers

Seawater : 

Seawater Surface mixed zone Water temps are the warmest The mixed zone is the area of the surface created by the mixing of water by waves, currents, and tides It has a nearly uniform temperature (depending on latitude) Extends down to 300m to 450 m Accounts for 2% of the ocean water

Seawater : 

Seawater Transition zone Below the mixed zone and above the deep zone Temperature falls quickly with depth May include the thermocline and pycnocline (depending on latitude) Accounts for 18% of the ocean water

Seawater : 

Seawater Deep zone Below the transition zone Sunlight never reaches this area Water temp is just a few degrees above freezing Very high water density Accounts for 80% of ocean water

Seawater : 

Seawater An exception to remember In the highest latitudes, the three layered structure does not exist because there is no rapid change in temperature or density with depth So, good vertical mixing between surface and deep waters can take place here Cold, high-density waters form at the surface, sink, and initiate deep ocean currents