Earth Science Practice Test: Oceans

Seawater contains about 35 grams of dissolved salts in every kilogram of water, which is 35 parts per thousand, or 3.5%. The trap is mixing up 3.5% with 3.5 parts per thousand.

Steady winds such as the trade winds and westerlies push the surface water, and the Coriolis effect and the continents shape the currents into large loops called gyres. Density differences drive the deep currents.

Cold, salty water is denser than the water around it, so it sinks and spreads along the bottom. This thermohaline circulation moves water around the globe over centuries.

The Moon's gravity pulls on Earth's oceans, creating bulges of water that coasts pass through as Earth rotates. The Sun also has an effect, but it is less than half as strong as the Moon's.

When the three bodies line up, at new moon and full moon, the Sun's and Moon's pulls add together. At the quarter moons they pull at right angles, producing smaller neap tides. The name has nothing to do with the season.

The Gulf Stream carries warm water north and east toward Europe, helping keep Western Europe milder than other places at the same latitude. The California and Humboldt Currents are cold currents in the Pacific.

Upwelling brings cold, nutrient-rich deep water to the sunlit surface, where it feeds huge numbers of phytoplankton. These support the whole food chain, up to large schools of fish.

Trenches form where one plate bends down and sinks under another. The Mariana Trench in the western Pacific is the deepest known place in the ocean. Continental shelves are the shallowest parts.

The sound travels 1,500 m/s × 4 s = 6,000 m in total, but that is down and back. Half of it, 3,000 m, is the depth. The answer 6,000 m forgets to divide by 2.

In an ocean wave, energy moves forward, but the water particles move in circular paths and return almost to where they started. A floating object follows that circle instead of riding the wave to shore.