National Geographic : 1942 Jan
San Diego Can't Believe It "One hears there are 'deserts' on sea floors, where no plant life grows. Is that true?" "Yes, only where light reaches down can sea vegetation grow. In the open sea, where water is clear, light penetrates to a depth of 300 feet; near the coast, where waters are more turbid, light reaches a depth of only about 100 feet. Plants are therefore not found attached to the bottom where coastal depths exceed 100 feet; but floating micro scopic plants are found all over the ocean sur face, in what we call the 'surface layers.' " Plant Harvests of the Sea "You speak of the 'harvest of the sea,' and of our increasing dependence on the sea for food; of 'aquiculture' as compared with agri culture. Do you mean that, besides fish, we might also learn to eat plants from the sea?" "Why not! Hawaii eats 26 kinds of sea plants, and Japan gathers 70 different species of edible marine plants." "Dr. Sverdrup, I have heard that Nature plows the sea, just as farmers plow their fields, to keep the surface water fertile. I think you call that process 'upwelling'; just what goes on, when that happens?" "Without upwelling marine life would soon perish. To live, sea plants, on which fish feed, must extract such nutrient salts as phosphates and nitrates directly from sea water. You hear a lot now about growing tomatoes, cucum bers, etc., without soil, simply by planting them in water impregnated with the right chemicals. Sea plants have grown without soil as far back as the geological history of the earth goes. "But, were sea water motionless, its sur face plants would soon exhaust all chemicals needed for their growth. So nature 'plows,' or upwells the water. This occurs as pre vailing winds carry the warmer surface water away from the coast, and colder water rises from depths of 500 to 600 feet, to take its place. This cold water coming up brings with it fresh fertilizing salts, just as deep land plow ing brings up fresh nutrient salts. Good fish ing, then, is found only where this overturn of water masses occurs." "Then the Institution's research must be useful to commercial fisheries?" "Yes, we are working now with the United States Fish and Wildlife Service. In our spe cial boat we make systematic cruises to study ocean currents, the intensity of upwelling, sea water chemistry, distribution of microscopic organisms, etc. All this information is very useful to the Service in its studies of sardine spawning and fish food plants in general." "One hears that the sea is a kind of air conditioner which helps give southern Califor- nia its fine climate. How does that work?" "The sea acts as a thermostatic control. Ocean temperature remains low in summer, high in winter. Down the California coast flows a current of cold water from the re gions south of the Aleutian Islands; hence water temperatures here are low as compared with those along other coasts in similar latitudes." "Do you also study the ocean floor at great depths?" "Yes, but not at the greatest depths. As you know, off Japan the U.S.S. Ramapo found a depth of 34,626 feet; there's a hole off the Philippines that's 35,400 feet deep. "Wherever we've gone, our geologists have studied the topography of the ocean floor, the types of sediment which are being laid down, and they've also brought up interesting fos sils, including the bones of a big extinct sea cow." Kelp Gathered from the Waves Dense beds of kelp cover an area of almost 150 square miles in shallow waters off this coast. With its odd-looking, bladderlike float ers, this big seaweed is of much commercial value (page 76). Many varieties exist, but the rockweed, or "giant kelp," which San Diego cuts and treats is known as Macrocystis pyrifera. It is valu able for its content of algin, solvents, and minerals; also it has food properties useful to men and beasts. Algin, a nutritious element, is widely used not only in the chemical and textile industries, but also in the manufacture of foods as a stabilizing agent. Algin goes into ice cream to make it smooth and of a more pleasing consistency. It also contains a vitamin useful in poultry feeds, and men who raise foxes on fur farms feed algin to their animals to in crease the litter. Several products obtained from kelp are used in munitions. During the first World War, San Diego cut enormous tonnages of kelp, used in making potash, iodine, and acetone. Big seagoing lawn mowers steam out from San Diego to cut off the top stipes, or stems, of the kelp, which is a tremendously long plant growing upright in the sea. These stems are then hauled in like fresh cut alfalfa and processed in a mystery factory which stands behind "keep out" signs in the south of town. Wide attention is focused now on San Diego County's great Palomar Observatory, which stands 5,568 feet high on the mountain of that name 75 miles by road northeast of the city (page 67).