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Exploring Ocean Geography: Depths and Extents

Discover the vastness and importance of ocean basins, shallow seas, and mid-ocean ridges. Learn about salinity, density, and pressure in seawater. Understand the unique geological features and phenomena in our oceans.

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Exploring Ocean Geography: Depths and Extents

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  1. GEOGRAPHY OF THE OCEANS – from Knauss Chapter 1 Oceans cover ~70% of the surface area of the earth. The horizontal extent of ocean basins is huge in comparison to their depth The small depth-to-width ratio (~1/1000) is important to remember: 1) We often view vertical crossections having exaggerated aspect ratios 2) Small depth-to-width ratio implies a velocity scaling. In the ocean vertical velocities are many orders of magnitude smaller and horizontal velocities

  2. vertical exaggeration = 180:1 vertical exaggeration = 30:1 From: Introduction to Physical Oceanography by R.H.Stewart http://www-ocean.tamu.edu/education/common/notes/PDF_files See Figure 1.12b in Knauss for a similar plot

  3. Land has a mean elevation of ~1 km, very little surface above 3 km Oceans have a mean depth of ~4 km, very little surface below 6 km Although contributing little to total ocean surface area, shallow seas forming over continental shelves (typical depth 0.1 km), are important because of their fisheries and because of their oil/gas resources (i.e., East China Sea, Bering Sea, North Sea, etc.) This is what we call a hypsographic plot or curve. It shows the frequency distribution of height (continents) and depth (oceans) From Stewart, see Figure 1.7 in Knauss for a similar plot

  4. MID-OCEAN RIDGES – from Pilson Chapter 13 Along mid-ocean ridges, molten magma (T~1000 oC) is located relatively close to the sea floor (~2 km below) Via the action of tectonic processes, new plate material is continually being formed along mid-ocean ridges Seawater penetrates into these heated zones and its chemical composition is altered by the addition of some substances (calcium and silica) and by the removal of others (magnesium and potassium) In the case of silica, the mid-ocean ridge source is comparable to silica delivered to the ocean in river water Precipitated silica is the main component of diatom shells See Figure 13.1 in Pilson (p. 322) and Figure 3.14 in Stewart (p.35)

  5. PROPERTIES OF SEA WATER – from Knauss chapter 1 Salinity = mass of salt per kilogram of seawater 0.035 kg of salt per kg of seawater is typical {dimensionless} expressed as part per thousand by mass {g per kg} Density = mass of seawater per cubic meter of seawater {kg m-3} typical value 1027 kg m-3 Specific Volume = volume of seawater per kilogram seawater {m3 kg-1} typical value 0.0098 m3 kg-1 specific volume is the reciprocal of density Pressure = weight of the seawater (a force!) per square meter {N m –2 or Pa} typical value at the ocean surface is 1x105 Pa (roughly one atmosphere) increases by approximately 1x105 Pa (i.e., 10 decibar) every 10 meter of depth

  6. Hydrostatic Equation in differential form - Hydrostatic Equation in integral form - (1.2) Where did the minus sign go?

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