Читать книгу Life in the Open Ocean - Joseph J. Torres - Страница 13

A few facts about the open ocean are important to help put the vastness of the oceans in perspective. To appreciate the total living space available to pelagic fauna, we need to consider both the ocean’s surface area and the volume beneath the surface: the ocean’s horizontal and vertical extent. The ocean basins cover 71% of the planet and their average depth is 3800 m (Sverdrup et al. 1942). Since the Earth is a sphere with a radius of 6371 km, its total surface area is calculated at 5.1 × 10⁸ km². The surface area of the world’s oceans at 3.6 × 10⁸ km² is ~71% of the total surface area of our planet. Consider volume. The average depth of the ocean basins is ~3800 m so the volume of water contained in the ocean is ~1.335 × 10⁹ km³. The volume of the moon is 2.2 × 10¹⁰ km³; the volume of the world’s oceans could form a body over half (60% in fact) the size of our moon. Thus the oceans contain an immense volume of water that affords habitat to the creatures that live within it.

We can arrive at a similar volume measurement for terrestrial systems by assuming that biologically useful space on land is defined by the height of a tall tree (0.05 km). Using 29% of the total surface area of the Earth for the terrestrial ecosystems and multiplying that by the height of the tree, we arrive at one useful‐volume estimate of 7.4 × 10⁶ km³, which is only 0.5% of the volume in the oceans (cf. Herring 2002).

It is interesting to look at extremes. The highest point on Earth above sea level is Mt Everest at 8.55 km. The lowest point on Earth is in the Pacific Ocean, the Challenger Deep in the Marianas Trench near the Philippines at 10.93 km below sea level.

The total living space in the pelagic realm can also be compared with that in the terrestrial biome by evaluating surface area. The Hypsographic Curve of the world in Figure 1.1 expresses graphically the amounts of the planet’s surface, by elevation, above and below sea level. From the Curve it is easy to see that over 60% of the Earth’s surface is covered by water of depths greater than 1000 m. Since 97% of all the water on Earth is contained in the oceans, the open sea at 1000 m deep and below is therefore the Earth’s “average environment”!

Freshwater in rivers and lakes accounts for about 1% of the Earth’s water; glaciers, polar ice, and groundwater contain about 2% more. The remainder of the Earth’s water is in the vastness of the oceans.