DEEP-SEA EXPLORATION. 60 DEEP-SEA EXPLORATION. Deep-Sea Life. The surface of the sea nearly everywhere bears an abundance of minute animal and'phmt life. In this surface life, or 'plankton,' as it is called collectively, many groups of inver- tebrates are represented. The phosphorescence often seen upon the surface of the sea is due en- tirely to their presence. These almost micro- scopic creatures are constantly dying and falling to the bottom. They constitute the principal food of the smaller animals <hvelling there, and their renuiins form a large part of the deep-sea oozes. The most important forms among them, considered with reference to abysmal deposits, are the Globigerinidie and the radiolarians, which are enormously abundant. The mitrine deposUs on the ocean floor arc gen- erally referred to three groups: Those of the con- tinental slopes are called Terrigenous Deposits, derived from the land through the wearing ac- tion of rivers, tides, and currents. These coast- wise deposits are the blue, green, coral, or vol- canic muds, and are characteristic of the adja- cent land slopes from which they are derived. Farther oil' shore, generally about 200 miles, oc- cur the Pelagic Deposits, made up of dead ma- rine organisms from the surface — the minute sur- face life already referred to: Here we find oozes, such as diatom, radiolarian, or globerina oozes which depend respectively upon the character of the surface life prevailing above them. Beyond these, in the deeper parts of the ocean, are the Red Clay Dei)0sits. which cover about half the ocean lloor. 'ibis region is not aflected by matter from the land, and receives little pelagic matter from the surface. It lies so deep that the shells of surface organisms falling down are removed through the solvent action of the deep water. The red clay is believed to have formed very slowly, not more than a few fet of matter hav- ing accumulated since the Tertiary period. Intermediate Depth.s. The (|uestion as to the existence of life at intermediate de])ths has been given general reconsideration since the perfecting of closing tow-nets for the exploration of such depths. The experience gained with the various intermediate nets used on board the Albatross has shown no mingling of surface and bottom forms. The latter occur, of course, at all depths along the Continental slopes. Sec DiSTRiBU- rioN OF .Akimai.s. From the evidence now at hand with respect to light in the sea, it seems certain that the sun- light does not extend below a couple of hundred fathoms, and even there becomes very dim. Be- low this the vast body of the ocean is absolutely dark, being illuminated only where phosphores- cent creatures may shed a certain amount of steady or intermittent radiance (sec below). CoxorrioNS and I.ii-e at Creat Depths. It is always cold at the bottom of the sea, the inlluence of the warm surf:iee waters not extending below a few hundred feet. In the great depths the temperature is always close to the freezing point. In warm equatorial seas, where the depths ex- ceed 400 fathoms the difference between surface and bottom temperatures nsuallv ranges from 40' to 49° F. It has been found that from 100 fathoms down, or throughoit the waters beyond the influence of the sun, temperatures remain practically constant. At the surface of the sea the lines of equal temperatures are jiarallel with the equator, although siibject to deflections by currents, while at the bottom they follow the general trend of the continents. The cold water of the depths comes from regions far to the north and south of the tropics, the coldness being due to the water in polar or subpolar regions sinking and gradually spreading itself over the ocean floor. If for any reason the cold polar waters should cease to flow downward toward the deep tropical basins, the deep-sea water would rise in temperature, and deep-sea life wimld ])erish from lack of the air which the polar currents absorl> at the surface and carry down with them. So far as is known, the bottom cirrents are extremely slow, and, as the water is not all'ccted by storms, it is likely that the lower part of the deep sea is a place of calm repose. There is a tremendous pressure of water in the depths: so great, in fact, that it will crush all ob- jects that are not constructed to resist it. All deep-sea instruments are made to withstand a pressure increasing about a ton to the square inch with each 1000 fathoms of depth. At the greatest depth known there would, therefore, be a pressure of nearly six tons to each square inch of surface. The tissues of deep-sea animals are so permeated by fluids, however, that a balance is maintained, and at the bottom they may be as firm as animals of the shallow waters. Jlost of these creatures are so soft that when withdrawn from the pressure which keeps them in a firm condition at the bottom and brought to the sni face, they must be treated carefully to prevent their going to pieces. The bones of aliysmal fishes are especially cartilaginous. W'lu'u deep- sea creatures are dragged to the surface from deep water they are always dead, and doubtless die during an early stage of their upward jrvir- ney. PiiospiiouE.scENCE AND CoLOR. J t has been men- tioned that no light reaches the abyssal regions, which are absohitely dark so far as sunlight is concerned; hence plant life is unknown there, and all the animals of the depths are carnivorous. Deep-sea dredging, however, has brought up so many phosphorescent animals that there can be' little doubt of considerable phosphorescent light in the depths.- The amount of such light given ofl' at the surface is no measure of that produced under normal conditions at the bottom. Phos- phorescent organs take many forms in the depths, and occur in both fishes and invertebrates. The colors of deep-sea animals are usually as brilliant as those of animals living luider the influence of light, although not so varied. The reds, yellows, purples, and greens predominate, and the colors, when they occur at all. are apt to be in solid masses, in striking contrast, or the whole animal is of a luiiforin brilliant eohn'ation. There is a conspicuous absence of blue. The fishes, as a rule, are dark-colored, but many of the crustaceans, holothuiians, and starfish are brilliant. EXPLANATION OF PLATE. 1. Metliod and theory of deep-sea dredpinp, as practiced on the U. S. H. AUintross. 2. The deep-sea dredj?© and it8 derrick. 3. (Jatheriiij:: the purfuee life, by liand nets, and by Ji towiiiK net ri^^ed to the port boom. 4. The tanples, Hliowinj; its riKginK. •'>■ The Townsend int#niiediat« net. oi>en and closed, ttaviiigheen ennk to the depth desired, it is towed for a time and then a slidln^j weight in allowed to ran riown t he line; striking the ring which holds npright the iron arm hooked to the tow-rope, it tlisiodges the ring and releases the nrm. which falls, permitting a weight be- neath it to slide down and pinch together the folding rtni of the nettinu: bag. which may then be drawn up without loss of contents.
