Chapter 13: Exploring the Oceans

Our Ocean About 71% of the Earth’s surface is covered with water. Where is all that water found? In the ocean, of course! Just look at a map…most of it is blue, which represents our oceans. The four major oceans are the Atlantic, Pacific, Arctic, and Indian. Since there are no defined boundaries, we usually just refer to the ocean as the “world ocean” because they are all connected.

How Did the Ocean Form? We need to go back millions of years ago when the Earth first formed. It was very hot and volcanically active. As we have learned, there are lots of gases contained within the lava in volcanoes, so when there are eruptions, these gases are released. Water vapor is one of the most common gases found in lava, and this helped to form a young atmosphere. As more and more water vapor was added to the atmosphere, clouds formed, and precipitation fell for many millions of years. Over time, our oceans filled up!

What is Ocean Water Like? Have you ever been to the beach, gotten smacked in the face by a wave, and ended up with a mouthful of salt water? Yuck! The ocean has lots of elements dissolved in it, but the two in greatest abundance are sodium (Na) and chlorine (Cl). That makes NaCl…table salt! Where do these elements come from? The rivers dissolve the minerals of the continents and dump them into the ocean.

Saltiness The saltiness of the ocean is called its salinity. This is defined by the amount of dissolved solids in a given amount of liquid. The unit of measurement for salinity is parts per thousand (ppt). In other words, grams of solids per kilograms of water. The average salinity of the ocean is 35 ppt.

What Affects Salinity? Many factors can change the saltiness of ocean water. 1.Evaporation: water is being removed, leaving the salts behind (higher salinity). 2.Freshwater input: during precipitation and at deltas, lots of fresh water is added (lower salinity). 3.Freezing: just like evaporation, water freezing is just that…only water! The salts are left behind (higher salinity). 4.Confined space: if a body of water is enclosed by land like the Mediterranean Sea the salinity will increase.

Ocean Temperature As you travel deeper into the ocean, the temperature decreases dramatically. Why? There is no sunlight in the deep ocean to heat the water! Three temperature zones: 1. Surface (sea level down to 300 m): temperature varies depending on sunlight 2. Thermocline (300 m-700 m): has a rapid decrease in temperature with depth 3. Deep (700 m-bottom): is pretty much always cold no matter what

Temperature, cont’d Water is unique because once it absorbs solar radiation from the Sun, it holds on to it for a long time. This helps to regulate the temperatures in the atmosphere. The ocean will warm or cool the air above it, therefore allowing coastal cities to be warmer or cooler than inland cities. Ocean currents distribute the warmer waters to colder regions and colder waters to warmer regions. The heat budget in the ocean and atmosphere is balanced!

The Immense Ocean Floor Part of the continents is underwater along our coastlines. This partially submerged outer extension of the continental crust is called the margin. The two types of margins are active (near plate boundaries) and passive (NOT near plate boundaries) Margins are divided into regions: 1.Shelf 2.Shelf break 3.Slope 4.Rise (only in passive) 5.Abyssal plain 6.Trench (only in active) Passive are found in the Atlantic and active are in the Pacific