DEEP-SEA EXPLORATION. 



742 



DEEP-SEA EXPLORATION. 



Deep-Sea Life. The surface of the sea nearly 

 everywhere bears an abundance of minute animal 

 and plant 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 dwelling there, and 

 their remains form a large part of the deep-sea 

 oozes. The most important forms among them, 

 considered with reference to abysmal deposits, are 

 the Globigerinidse and the radiolarians, which 

 are enormously abundant. 



The marine deposits on the ocean floor are 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 off 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 globigerina 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 Deposits, which cover about half the 

 ocean floor. This region is not affected 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 feet of matter hav- 

 ing accumulated since the Tertiary period. 



Intermediate Depths. The question as to the 

 existence of life at intermediate depths 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. See Distbibu- 

 TioN OF Animals. 



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 (see below). 



Conditions and Life at Gbeat Depths. It is 

 always cold at the bottom of the sea, the influence 

 of the warm surface waters not extending below 

 a few hundred feet. In the great depths the 

 temperature is always close to the freezmg-pomt. 

 In warm equatorial seas, where the depths ex- 

 ceed 400 fathoms the difference between surface 

 and bottom temperatures usually ranges from 40° 

 to 49° F. It has been found that from 100 

 fathoms down, or throughout the waters beyond 

 the influence of the sun, temperatures remain 

 practically constant. At the surface of the sea 

 the lines of equal temperatures are parallel with 

 the equator, although subject 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 would perish from 

 lack of the air which the polar currents absorb 

 at the surface and carry do^vn with them. So far 

 as is known, the bottom currents are extremely 

 slow, and, as the wa'ter is not affected 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. Most 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 sur- 

 face, they must be treated carefully to prevent 

 their going to pieces. The bones of abysmal 

 fishes are especially cartilaginous. When 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 jour- 

 ney. 



Phosphorescence and Coior. It has been men- 

 tioned that no light reaches the abyssal regions, 

 which are absolutely 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 

 off 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 under 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 uniform brilliant coloration. 

 There is a conspicuous absence of blue. The 

 flshes, as a rule, are dark-colored, but many of 

 the crustaceans, holothurians, and starfish are 

 brilliant. 



EXPLANATION OP PLATE. 



1. Method and theory of deep-sea dredglnp;, as prastfced 

 on the U. S. S. Albatross. 2. The deep-sea dredge and its . 

 derrick. 3. Gathering the surface life, by hand nets, and 

 by a towing net rigged to the port boom. i. The tangles, 

 showing its rigging. 6. The Townsend intermediate net, 

 open and closed. Having been sunk to the depth desired, 

 it is towed for a time and then a sliding weight is allowed 

 to run down the line; striking the ring which holds upright 

 the iron arm hooked to the tow-rope, it dislodges the ring 

 and releases the arm, which falls, permitting a weight be- 

 neath it to slide down and pinch together the folding rim 

 of the netting bag, which may then be drawn up without 

 loss of contents. 



