1. The oceans cover almost 71% of the globe, while the continents account for the remaining 29% of Earth's surface. Although both the Northern and Southern Hemispheres have more water than land, the ocean truly dominates the Southern Hemisphere. A much greater percentage of Earth's land area is in the Northern Hemisphere
2. (a) The Pacific Ocean is largest in area and the Indian Ocean is smallest.
(b) The Pacific Ocean is the deepest and the Arctic Ocean is the shallowest.
(c) The Indian Ocean is almost entirely within the Southern Hemisphere.
(d) The Arctic Ocean is exclusively in the Northern Hemisphere.
3. The average depth of the ocean basins is 3800 meters below sea level, and the average elevation of the continents is a mere 840 meters.
4. Salinity refers to the proportion of dissolved salts to pure water in the ocean. The average salinity is about 35 parts per thousand (35‰).
5. The six most abundant components dissolved in seawater are sodium, chlorine, sulfate, magnesium, calcium, and potassium. Sodium and chlorine together form sodium chloride or salt.
6. Some of the material is the product of chemical weathering on the continents. These dissolved substances are delivered to the oceans chiefly by streams. Other elements, such as chlorine, bromine, sulfur, and boron come from volcanic outgassing.
7. Variations in surface salinity are primarily the consequence of changes in the water content of the solution caused by the addition of water by rains or rivers, or the loss of water by evaporation. Loss of water by evaporation in the Red Sea increases its salinity to 42‰ or more. Conversely, the addition of fresh water by rivers to the Baltic Sea reduces salinity to a very low level of only 2-7‰.
8. Since the velocity of sound waves in water is 1500 meters per second and the total travel time is 6 seconds, the water depth is 4500 meters.
9. Satellites equipped with radar altimeters are able to determine features on the seafloor by measuring subtle differences in elevation on the ocean surface. The satellites bounce microwaves off of the ocean surface, which is affected by the gravitational pull of seafloor features. Therefore, mountains and ridges produce elevated areas on the ocean surface while canyons and trenches cause slight depressions.
10. The three subdivisions of a passive continental margin are 1) the continental shelf, which is the flooded extension of the continent; 2) the continental slope, which marks the boundary between continental and oceanic crust and has the steepest slope; and 3) the continental rise.
11. Along active continental margins the leading edge of the continent is overrunning oceanic lithosphere. Here sediments from the ocean floor and pieces of oceanic crust are being scraped from the descending plate and plastered against the edge of the overriding continent forming an accretionary wedge. On the other hand, passive continental margins are not associated with plate boundaries. Along passive continental margins weathered materials eroded from the adjacent landmass accumulate to form a thick, broad wedge of relatively undisturbed sediments.
12. Since the canyons reach depths far below the maximum lowering of sea level during the Ice Age, they must have been created by some process other than stream erosion, one that operates below the oceanic surface, perhaps turbidity currents.
13. The floor of the Pacific lacks extensive abyssal plains because the trenches that surround this ocean basin act as sediment traps.
14. Mid-ocean ridges are spreading centers; that is, they are divergent plate boundaries where magma wells up from below, creating new oceanic crust. Ocean trenches form where crustal plates plunge back into the mantle. Thus, these long, narrow depressions are associated with convergent plate boundaries.
15. Terrigenous sediment consists primarily of mineral grains derived from weathering on the continents. Biogenous sediment includes material of marine organic origin; whereas hydrogenous sediment consists of minerals that crystallize from seawater.
16. Most
sea-floor sediments contain the remains of organisms that once lived near the
sea surface. Since the numbers
and types of organisms living near the sea
surface vary as climate (especially temperature) fluctuates, sea-floor
sediments hold important clues to changes in
climate through time.