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The Ocean System

The Ocean System. The Ocean covers 70% of the Earth’s surface. There is one ocean with many ocean basins, such as the North and South Pacific, Atlantic and India. New Zealand is surrounded by ocean. M ajor currents that control the world’s climate flow past us. .

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The Ocean System

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  1. The Ocean System

  2. The Ocean covers 70% of the Earth’s surface. There is one ocean with many ocean basins, such as the North and South Pacific, Atlantic and India. New Zealand is surrounded by ocean. Major currents that control the world’s climate flow past us.

  3. (above) Cross section of a typical ocean basin flanked by passive continental margins. The submerged outer edge of a continent is called the continental margin. The deep-sea floor beyond the continental margin is properly called the ocean basin.

  4. Features of the ocean The labelled zones represent light levels http://www.srh.noaa.gov/jetstream/ocean/oceanprofile.htm

  5. Sunlight does not travel well in the ocean. Scattering and absorption weaken light: • Scattering occurs when light is bounced between air and water molecules, dust and other objects. • Absorption occurswhen light’s electromagnetic energy is converted to heat in the molecules of seawater.

  6. The electromagnetic spectrum showing light spectrum Microwaves http://www.srh.noaa.gov/jetstream/ocean/oceanprofile.htm

  7. A spectrum showing the relative wavelengths of the different colours.

  8. Powers of Ten 100 = 1 1 103 = 1000 kilo 106 = 1,000,000 mega 109 = 1,000,000,000giga 1012 = 1,000,000,000,000 tera 100 = 1 10-2 = 0.01 centi 10-3= 0.001 milli 10-6= 0.000 001 micro 10-9 = 0.000 000 001 nano 10-12 = 0.000 000 000 001 pico http://www.srh.noaa.gov/jetstream/ocean/oceanprofile.htm

  9. Light absorption in the open ocean. 65% of light entering the ocean is absorbed within the first metre. Only 1% of light reaches 100m. In the open ocean, blue light penetrates the deepest

  10. Density and the Ocean • Density is how much mass is contained in a given unit volume (density = mass/volume). • Temperature, salinity and pressure work together to determine water density • Cold, salty water is much denser than warm, fresher water and will sink below the less dense layer.

  11. Density and Oceans Cont… Ocean water is divided into 3 layers, based on density. • surface mixed zone formed from less dense waters. Temperature of this layer can change because of weather. Salinity can change because of the evaporation or dilution of water. • pycnoclineor transition zone. The density changes rapidly. This zone is a barrier between surface zone and bottom layer, and not much water moves between the two zones. • deep zoneor bottom layer, where the water remains cold and dense. The polar regions are the only places where deep waters are exposed totheatmosphere.

  12. Density layers in the ocean http://www.onr.navy.mil/focus/ocean/images/water/density.jpg

  13. 2% of ocean water 18% of ocean water Surface zone Pycnocline 80% of ocean water Deep zone Increasing latitude, north or south

  14. Salinity • Most of the salt (NaCl) in the ocean comes from land from water running over rocks containing salt and carrying it into the sea. • Some has come from undersea volcanoes and hydrothermal vents • 1 gram of salt in 1,000 grams of water gives a salinity (the amount of salt) of 1 part per thousand, or 1 ppt. • Average ocean salinity is 35 ppt or 3.5 % and varies between 32 – 37 ppt. Rainfall and river runoff reduce salinity, evaporation and ice formation increase salinity.

  15. Salinity Cont… • Freshwater salinity is less than 0.5 ppt. • Water between 0.5 ppt and 17 ppt is called brackish. E.g. estuaries, where fresh water meets salty water. • Most marine organisms keep the salinity inside their bodies at about the same concentration as the water outside their bodies.

  16. Temperature • The Sun warms up the surface layer of the ocean and the temperature follows the Sun. Average about 17 C. • http://www.srh.noaa.gov/jetstream/ocean/layers_ocean.htm • Wind and waves mix up the surface layer from top to bottom. • The temperature of the surface waters varies mainly with latitude. • The polar seas (high latitude) can be as cold as -2 C, ,tropical seas (low latitude) as warm as 36 C. • Ocean water freezes at -1.94 C. So sea ice can form at high latitudes.

  17. Temperature http://scijinks.nasa.gov/_media/en/site/weather-v-climate/Earth-lighting-winter-solstice-L.png

  18. The red ice cubes are made with fresh water and the blue ones are made with salt water

  19. Instruments oceanographers use: This instrument is called a CTD which measures temperature and density as different depths in the ocean

  20. This is an Argos float which measures temperature and salinity of the top 2000m of the ocean.

  21. These buoys are anchored on the bottom of the ocean and can take measurements up to 4 km deep

  22. Ocean Circulation • There are two main types of ocean currents. • Surface currents which are driven by winds • Deep currents called thermohalinecirculation which is driven by density. • The deep ocean is layered with the densest water on the bottom and the lightest water on top.

  23. Main Drivers of Ocean Circulation Solar Radiation Precipitation (rain) and Evaporation • Density Salinity Temperature Density Gradient Heating and Cooling Ocean Circulation Wind Wind Stress

  24. Main Drivers of Ocean Circulation Solar Radiation Precipitation (rain) and Evaporation • Density Salinity Temperature Density Gradient Heatingand Cooling Ocean Circulation Wind Wind Stress

  25. Density and Ocean Circulation • Water tends to move horizontally throughout the deep ocean, moving along lines of equal density. • Vertical circulation is limited because it is easier for water to move along lines of constant density (isopycnals) than across them.

  26. The thermohaline current: • Circulates around the whole globe. • Is driven by the density of the ocean water. • Salinity and temperature of the ocean affects density – salty, cold water is dense and sinks. • Precipitation and evaporation + heating and cooling affects density • Part flows on the surface of the oceans and part flows at depths of 2 – 5 km. • Transports so much heat around the globe that it plays a critical role in the earth’s climate.

  27. Thethermohaline circulation – the Global Ocean Conveyor belt At the earth's poles, when water forms ice, salt doesn't freeze. The dense cold, salt water formed sinks to the ocean floor. More water moves in to replace it, creating a current that travels right around the globe. The current connects all the oceans of Earth, Arctic, Atlantic, Southern (where it gets recharged with more cold water) Indian and Pacific Ocean. As it nears the equator, it warms up and rises to the surface - calledupwelling.

  28. Thethermohaline circulation – the Global Ocean Conveyor belt This current moves very slowly; a few cm per second. It can take 1,000 years to complete one full circuit of the globe. It moves a vast amount of water and distributes heat around Earth, regulating temperatures. . The water transported around the globe enriches the carbon dioxide-poor, nutrient-depleted surface waters by carrying them down to deeper layers where nutrients are abundant. These nutrients and carbon dioxide, when distributed through the upper layers, enable the growth of algae and seaweed that ultimately support all forms of life.

  29. Thethermohaline circulation – the Global Ocean Conveyor belt cont. Wind-driven surface currents (such as the Gulf Stream) travel polewards from the equatorial Atlantic Ocean, cooling en route, and eventually sinking at high latitudes (forming North Atlantic Deep Water). This dense water then flows into the ocean basins. While the bulk of it upwells in the Southern Ocean, the oldest waters (with a transit time of around 1600 years)upwell in the North Pacific. Extensive mixing therefore takes place between the ocean basins, reducing differences between them and making the Earth's oceans a global system. On their journey, the water masses transport both energy (in the form of heat) and matter (solids, dissolved substances and gases) around the globe. As such, the state of the circulation has a large impact on the climate of the Earth

  30. The thermohaline circulation – distributes heat all around the planet

  31. The thermohaline circulation – distributes heat all around the planet

  32. The thermohaline circulation – distributes heat all around the planet https://www.noc.soton.ac.uk/o4s/gl/c/conveyor2.php

  33. Thermohaline circulation from the south

  34. The thermohaline current in 3D

  35. Ocean basins

  36. Underwater features of Ocean basins

  37. The thermohaline current flows past New Zealand. With thanks to Lionel Carter

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