in this video we will learn some basics about the ocean and why water is so special so obviously if you look at the earth from space we see that most of the service is covered by oceans with just a small fraction of earth covered by continents if we break it down the ocean is 70.8 percent of earth's surface area and the land is 29.2 percent usually we subdivide the ocean into different parts or the different oceans of the world there are four primary oceans the pacific atlantic indian and arctic the pacific is the largest then the atlantic then the indian the arctic is the smallest scientists also consider a fifth ocean which we call the southern ocean which is the ocean that rings around antarctica to the south if we compare the ocean to land surface we see that the depth of the ocean is on average twelve thousand feet this is much deeper than the average height of land at just under three thousand feet if we look at the deepest point in the ocean which is the marianas trench we see that is 36 000 plus feet whereas the tallest mountain on earth mount everest is only 29 000 feet high so the ocean is actually much larger in terms of depth than the land surface is high now let's talk about the water in the ocean what are some of the important properties what is the water molecule why is water special and what is salinity so first of all the water molecule itself what is a molecule and what is an atom so an atom is the smallest unit of a substance that retains its chemical properties a molecule is a group of atoms that's bonded or joined together chemically so here's an example of a molecule the molecule has a nucleus which contains positively charged protons neutrally charged neutrons and electrons orbiting around the nucleus the water molecule is h2o made up of two hydrogen atoms and one oxygen atom that are bonded together hydrogen atoms are smaller than oxygen atoms they contain only one proton and one electron oxygen atoms contain eight protons eight neutrons and eight electrons here are three different ways of showing the water molecule you'll notice that the oxygen molecule or the oxygen atom is in the center with the two hydrogen atoms on either side a lot of times we say that the water molecule looks like mickey mouse with two mouse ears on either side this is because the water molecule is not a linear molecule but a dipole molecule so the way that the oxygen and hydrogen atoms are connected is with covalent bonds these are bonds where electrons are shared between the oxygen and the hydrogen however because of the way that this molecule is structured electrons prefer to be located near the oxygen giving the oxygen a slightly negative charge and giving the hydrogen a slightly positive charge all of this creates the water molecule that we know when you have two water molecules nearby to one another they will attract one another we call this hydrogen bonds and this is simply because positives and negatives attract on the water molecule itself the hydrogens are slightly positively charged and the oxygens are slightly negatively charged so the hydrogen from one molecule will attract the oxygen of the next molecule this makes water a very stable substance it also it specifically it gives it a high melting and boiling point and a high heat capacity meaning it takes a large amount of heat to change its temperature water's heat capacity is defined as the amount of energy it takes to raise one gram of water by one degree celsius water has a very high heat capacity and this table compares the heat capacity of water to several other substances you'll see that water has a heat capacity of one whereas most other substances have a heat capacity that's less including aluminum granite glass brass and lead this means it takes a huge amount of energy to heat in cool water meaning it's hard to change the temperature of water we'll see that that is very important for the effects of our global ocean on climate this table shows many cities around the world or around the country and their high and low temperatures throughout the year as well as the temperature range that they experience for example say chicago has a high temperature of 51 a low temperature of 25 so on average it has a temperature range of 26 degrees fahrenheit miami has a high temperature of 85 a low temperature of 73 and an average temperature range of 12 degrees fahrenheit what i want you to do is to take a moment and observe the different cities and decide if you see any patterns pause the slide when you divide the coastal cities and the interior cities into two groups you notice a pattern the coastal cities have a much lower temperature range between the high and low temperature on average whereas the interior cities have a much greater range of temperatures this is because of the moderating effect of the ocean if a city is on the water it takes a lot more energy for water to heat up and cool down meaning it's not going to have as big of a seasonal temperature contrast this moderating effect then translates to the coastal cities whose temperature is influenced by their proximity to the ocean interior cities don't have that effect and therefore the land can heat up really quickly in the summer and cool down really quickly in the winter making a larger temperature range at those cities another special property of water is that water is most dense at 4 degrees celsius which is approximately 39 degrees fahrenheit also the density of ice is much lower than liquid water so what does this mean that means that as i cool water off it's going to get more and more dense until we reach 4 degrees celsius then the density will drop off and when it turns into ice it will suddenly get a lot less dense this is why ice floats on water we take this property of water for granted but it's important to note that most other substances do not have this type of a pattern for most substances the solid form of a substance has a much higher density than the liquid form of a substance than the liquid form of a substance this means that ice can float on water it also means that water at four degrees celsius is going to be at the bottom of the ocean because it has the highest density and therefore it will sink we're going to come back to this idea later when we talk about how different types of ocean water masses form the last concept to discuss about water and why it's so special is salinity we all know that ocean water is salty whereas rain water or lake water is fresh why is ocean water salty it's salty because the water contains dissolved salts or dissolved solids in the water most salts in ocean water are made of sodium chloride nacl same as table salt how do we measure salinity we measure the mass of dissolved solids in grams per kilogram of seawater the units of salinity are parts per thousand which is abbreviated as ppt it can also be written as grams per kilogram g over kg or it can be written with a symbol that looks like a percent symbol with an extra zero on the bottom it doesn't come across extremely well in the powerpoint so just think of writing a percentage symbol that has an extra circle on the bottom this also means parts per thousand the average ocean salinity is 35 parts per thousand this means that if i had one kilogram or a thousand grams of seawater there are 35 grams of salt dissolved in it how do we change the salinity of the ocean because we know that some places have saltier in some places are not as salty even within the same ocean so it's important for us to know how we can change the salinity if we want to increase the salinity of a water body make it saltier we can either add salt or we can remove fresh water only leaving the salt behind if we want to decrease the salinity we can remove salt or add fresh water to dilute it let's go into these in more depth to increase the salinity we can add salt how do we add salt to the ocean the most common way this happens is through volcanic eruptions how can we remove fresh water from the ocean this is actually a lot more common it turns out that processes that remove water from the ocean usually remove only the water not the salt this is true for evaporation where water evaporates from the ocean into the atmosphere through phase change from liquid to gas this is also true when sea ice forms which is when water moves out of the ocean by freezing to form icebergs that float on top of the water the icebergs are actually made of fresh water leaving the salt behind in the ocean so when that water freezes into ice it leaves the ocean saltier underneath it if we wanted to decrease the salinity we could either remove salt from the ocean or dilute it using fresh water sources of fresh water into the ocean include precipitation such as rain or snow runoff from rivers as well as melting glaciers and sea ice salt can also be removed from the ocean most commonly through salt spray think about if you ever go to the ocean and you come home and your hair feels all grimy that's salt spray on your hair you have removed salt from the ocean there are also chemical reactions that can happen at the sea floor that remove salt from the ocean now it's time to test yourself answer the following question pause the video and then answer the following questions then you can check your work number one draw a clearly labeled diagram of a water molecule number two if a body of water with a mass of five kilograms has 10 grams of salt dissolved in it what is its salinity there's an equation below to help you and don't forget units in your answer number three as sea ice melts does salinity increase or decrease why pause the video and answer the questions the answer to number one can be found on previous slides check back to see if you were able to correctly draw a water molecule number two if this particular body of water has 10 grams of salt dissolved in it then 10 grams goes in the numerator of our equation the total mass of the body of water is 5 kilograms so that goes in the denominator therefore salinity equals 10 grams divided by 5 kilograms 10 divided by 5 is 2 and then we could either display our answer as grams per kilograms parts per thousand displayed as ppt or parts per thousand displayed as our percentage sign with an extra zero on the bottom any of those answers would be considered correct number three as sea ice melts salinity decreases because sea ice is purely fresh water therefore as it melts it dilutes the ocean water finally let's talk about global ocean properties what are the patterns of temperature salinity and density out in the ocean this map shows sea surface temperature in february where warmer colors indicate warmer temperatures and cool colors indicate cool temperatures so we see near the equator there are warm ocean waters near the poles there are purple colder ocean waters the white represents sea ice or ice is floating on the ocean this next map shows the average salinity of ocean water in the year 2005. pink values show values that are high salinity blue values show low salinity and yellow values show intermediate values of salinity remember the average salinity of the ocean is 35 parts per thousand when we look at this graph there's really a lot of information we can take away from it i would recommend even pausing the video here for a minute and really examining this in great detail some of the takeaway points are that near 30 degrees north and south we see values of salinity that are much higher with respect to the rest of the ocean think back to what we talked about with atmospheric circulation what was special about 30 degrees north and south do you remember yes it was the fact that our subtropical high pressure areas were also located at 30 degrees north and south subtropical high pressure we said was related to clear skies and dry conditions this is where the major deserts of the world were located these dry conditions also affect the salinity of the ocean water by evaporation sunny skies with no rain leads to evaporation which drives salinity up the opposite is true near the equator where the inter-tropical convergence zone lies and rain is frequent the equator is less salty than the area immediately to the north and south of it because of this rain there are many other patterns that can be identified on this map take your time and look it over many different factors govern salinity but on a global scale when we look at that salinity map the two biggest factors that affect salinity are evaporation and precipitation which are directly related back to the features of the atmosphere we learned about last week so remember near the equator we have precipitation at 30 degrees north and south we have evaporation and near 60 degrees north and south we have precipitation that means that salinity is going to be relatively high at 30 degrees north and south and low near the equator and 60 degrees north and south another property of the ocean that we're going to spend a lot of time talking about is density the reason we care about density is because denser water will tend to sink beneath less dense water less dense water rises up density is affected by both temperature and salinity where cold water and salty water are both more dense than warm water or less salty water it turns out temperature is the biggest factor affecting density and the colder the water the more dense it will be but the saltiness of the water will also have an effect and saltier water also tends to be more dense in the ocean density always increases with depth and this is because density is the factor that decides where different water masses will layer in the ocean denser water masses always sink beneath less dense water masses in the global ocean we have warmed surface waters near the equator [Music] this layer is relatively shallow compared to the entire depth of the ocean if you think about it the ocean is four kilometers deep and our tropical suns can really only penetrate maybe half a kilometer at max into the ocean therefore most of the ocean is made up of a deep layer of cold dense water this deep water forms near the polar regions and then sinks down to the bottom the piconecline layer is the name of the layer that forms the boundary between the surface layer and the deep layer in the ocean all this refers to is the fact that density increases rapidly at the peak nocline layer above the picocline you'll have low density surface water and below the peak nocline you'll find high density deep water eighty percent of water in the ocean falls into this deep layer beneath the picocline now take another moment to test yourself number one why is sea surface temperature strongly related to latitude number two which regions on the globe have the highest and lowest values of salinity explain why these regions stand out i'm not going to recap the answers to these questions but feel free to go back and use the material to help you answer them