The Deep Sea
How deep the oceans actually are, measured by Murray and Hjort.
By 1912 oceanographers had sounded the ocean floor to nearly 5,300 fathoms and mapped the share of it that lies shallow. Murray and Hjort's survey gives the figures for each ocean and for the deeps.
Overview
By the time Murray and Hjort surveyed the field, oceanography had established the deep sea as a measurable and mapped domain rather than an unknowable void. The deepest sounding on record reached 5269 fathoms, a figure that had been verified and corresponded to 60,616 feet, and it stood as the extreme limit of the known ocean floor. Beneath that single maximum lay a structured basin: the Atlantic's deepest point was 4662 fathoms in the Nares Deep, the Indian Ocean's 3828 fathoms in the Wharton Deep, and a second great depression of 5155 fathoms in the Aldrich Deep. Depth, in this account, was not a curiosity but the organising variable of the science, since it governed where the abyss began and how the ocean floor was to be divided. 1The Depths of the Ocean: a general account of the modern science of oceanography · Macmillan, London (via Internet Archive) ↗
The scale of the medium explains why its depth mattered so much. The ocean covered 139,295,000 square English miles, of which the Pacific accounted for 68,634,000, the Atlantic 41,321,000 and the Indian 29,340,000. Against this expanse, the truly deep ground was comparatively restricted: the deeps, defined as depths greater than 3000 fathoms, covered about 9 million square miles. The authors' reasoning turns on this proportion, for it shows that the greatest depths were exceptional features of the floor rather than its prevailing character. 1
A further distinction sharpened the point. Shallow water, in the authors' sense, occupied only one-sixth of the ocean floor, so that the greater part of the submerged surface lay beyond the reach of the shallow zone altogether. Depth therefore served as the criterion by which the sea's territory was partitioned, separating the marginal from the profound and giving the abyssal regions a definite, if limited, extent. 1
Taken together, these measurements gave the deep sea a geography. It possessed known maxima, named depressions in each of the three great oceans, a total area, and a defined threshold beyond which the deeps proper began. The establishment of such figures was what allowed the deep sea to be treated as a coherent subject of study, its extent bounded and its deepest points located. 1
1. Measuring Depth
The sounding of great depths rested on the line and the weight, and the figures the charts carried were the fruit of that laborious process. The deepest sounding hitherto recorded stood at 5269 fathoms, a value the authors treat as verified rather than provisional, and one corresponding to 60,616 feet. Verification mattered because a single cast into the abyss could mislead; the record depth was therefore accepted only after confirmation. From such casts the charts were built, and the deepest points of each ocean entered the record as named depressions: the Nares Deep in the Atlantic at 4662 fathoms, the Wharton Deep in the Indian Ocean at 3828 fathoms, and the Aldrich Deep, second only to the maximum, at 5155 fathoms. 1
Yet the number of deep soundings the charts actually held was small when set against the water they described. The ocean covered 139,295,000 square English miles, divided among the Pacific at 68,634,000, the Atlantic at 41,321,000 and the Indian at 29,340,000. Against this expanse, the ground lying deeper than 3000 fathoms, which the authors take as the definition of the deeps, amounted to only about 9 million square miles. The proportion is the point: the greatest depths were exceptional features of the floor, not its prevailing character, and the soundings that located them were scattered thinly across a vast surface. 1
A further distinction sharpened the picture. Shallow water, in the authors' sense, occupied only one-sixth of the ocean floor, so that the greater part of the submerged surface lay beyond the shallow zone altogether. Depth therefore served as the criterion by which the sea's territory was partitioned, separating the marginal from the profound and giving the abyssal regions a definite, if limited, extent. 1
Taken together, these measurements gave the deep sea a geography. It possessed known maxima, named depressions in each of the three great oceans, a total area, and a defined threshold beyond which the deeps proper began. The establishment of such figures was what allowed the deep sea to be treated as a coherent subject of study, its extent bounded and its deepest points located. 1
2. The Deepest Water
The deepest water on the charts belonged to the Pacific, and the margin by which it exceeded the other oceans was considerable. The record sounding of 5269 fathoms stood well above the Aldrich Deep, which at 5155 fathoms ranked second among all the depressions recorded. The Atlantic's Nares Deep, at 4662 fathoms, and the Indian Ocean's Wharton Deep, at 3828 fathoms, fell further behind still. In consequence the three oceans arranged themselves in a clear order of maximum depth, with the Pacific at the head and the Indian at the foot, and the gap between the first and the last was wide enough to mark a real difference in the character of the floors rather than a mere accident of where the sounding lines happened to fall. 1
That ordering is the more striking because the Pacific was also the largest of the three oceans, covering 68,634,000 square English miles against the Atlantic's 41,321,000 and the Indian's 29,340,000. The ocean that held the greatest expanse of water therefore also held its deepest point, while the smallest of the three held the shallowest of the recorded maxima. The authors do not press the coincidence into a law, but the figures they set down allow the reader to see that depth and extent ran together in the Pacific and diverged elsewhere. 1
The deeps themselves, taken as the ground lying beyond 3000 fathoms, amounted to only about 9 million square miles, a small fraction of the 139,295,000 square miles of ocean. The record depths were therefore isolated points within an already restricted zone, and the soundings that found them were few. A maximum of 5269 fathoms, confirmed and entered on the charts, told the authors where the floor sank lowest; it did not tell them that such depths were common, and the small area of the deeps proper suggests they were not. 1
What the figures established was a scale. The deepest water could be named, placed in its ocean, and compared with the maxima of the other two, and the comparison gave each ocean a definite rank in depth as well as in extent. 1
3. How Much of the Sea Is Shallow
The distribution of depth across the ocean floor was, for Murray and Hjort, a question of proportion rather than of isolated records. Against the vast total extent of 139,295,000 square English miles, the ground lying beyond 3000 fathoms occupied only about 9 million square miles. The great deeps, in other words, formed a narrow belt within an ocean overwhelmingly composed of shallower water, and the record soundings that drew attention to the subject were sunk in a zone that represented a small fraction of the whole. 1
The shallower portion was correspondingly large. Roughly one-sixth of the ocean floor lay above the great depths, a share that gave the authors their central proportion and framed the deep sea as the greater part of the ocean by area while leaving the shallow margin a substantial and distinct region in its own right. The division was not a matter of a few soundings at the extremes but a statement about how the floor of the sea was apportioned between its two conditions. 1
The proportions held across the individual oceans as well as in the total. The Pacific, at 68,634,000 square English miles, and the Atlantic, at 41,321,000, together accounted for the bulk of the ocean surface, with the Indian Ocean adding 29,340,000. Because the deeps proper were confined to so small an area, the greater part of each of these expanses necessarily fell within the shallower category, so that the same balance between deep and shallow repeated itself in every basin rather than being concentrated in one. 1
The consequence for the authors' argument was a correction of perspective. The deepest sounding hitherto recorded, 5269 fathoms, or 60,616 feet, fixed the lower limit of the sea, but the figures of area showed that such water was exceptional ground. The ocean was, by measure, chiefly a shallow sea with deep trenches cut into it, and any account of the deep sea had to reckon with the fact that the depths were the smaller part of the floor they occupied. 1
4. The Extent of Each Ocean
The three oceans were measured separately, and their areas gave the authors a basis for comparing them as bodies of water rather than as coastlines. The Atlantic was reckoned at 41,321,000 square English miles. The Pacific was much the larger at 68,634,000 square English miles, and the Indian Ocean, the smallest of the three, at 29,340,000 square English miles. These figures placed the Pacific first in extent, the Atlantic second and the Indian third, an order that held whatever the depth of the water within each basin. 1
Extent and depth did not, however, run together. The Atlantic, though it covered little more than half the area of the Pacific, contained the deeper of the two maxima, for its greatest sounding of 4662 fathoms lay in the Nares Deep. The Indian Ocean, smallest of the three in area, reached 3828 fathoms in the Wharton Deep. In consequence the ranking by area and the ranking by depth diverged: the widest ocean was not the deepest, and the narrowest was not the shallowest. The comparison of the three basins therefore required two separate measures, one of surface and one of depth, and the authors kept them apart. 1
The figures also allowed the oceans to be set against the whole. Taken together, the three areas accounted for the greater part of the 139,295,000 square English miles assigned to the ocean, and each basin could thus be treated as a fraction of a single expanse. The Pacific alone made up roughly half of that total, the Atlantic somewhat less than a third, and the Indian the remainder. Such proportions gave the authors a way of speaking about the ocean as a whole while still distinguishing its parts, since a statement about the deep sea in general could be tested against the share each ocean contributed to it. 1
The separate measurements thus served an argument about scale. Because the Pacific was so much the largest of the three, any general account of the ocean floor was bound to be weighted toward it, while the Atlantic and Indian basins, though smaller, were large enough to be compared on their own terms. The three areas, set beside the depths recorded in each, gave the authors a framework in which extent and depth could be weighed against one another without either being mistaken for the other. 1
5. Why the Deep Sea Matters
The sounding of 5269 fathoms, the deepest hitherto recorded, gave the authors their measure of how far the ocean floor descends, and they rendered it as 60,616 feet so that the figure might be grasped against the dimensions of the land. Yet the significance they drew from it lay less in the number itself than in what it implied for the science. A depth of that order could not be treated as an isolated curiosity of one basin. It stood as the extreme case against which every other part of the ocean floor might be judged, and it obliged the oceanographer to reckon with a vertical range far greater than the coastal waters on which earlier observation had fastened. 1
The distribution of the deepest ground sharpened the point. Depths exceeding 3000 fathoms were found to cover about 9 million square miles, a region the authors distinguished from the rest of the floor precisely because it lay beyond that limit. The second deepest sounding, 5155 fathoms in the Aldrich Deep, confirmed that such ground was not confined to a single locality. The deeps therefore constituted a defined portion of the ocean, extensive enough to be studied in its own right and deep enough to demand methods and reasoning unlike those applied to shallower water. 1
The shallower remainder of the floor, by contrast, accounted for only one-sixth of its extent. In consequence the greater part of the ocean lay beyond the reach of the ordinary means by which the sea had been examined, and the authors could argue that the deeps were not a marginal province but the characteristic condition of the ocean floor. What had once been treated as the sea's outer limit became, on this showing, its ordinary state, and the shallow margins the exception. 1
The deeps thus gave oceanography its proper subject. A science confined to the waters over the shelf would have described a small fraction of the sea and mistaken that fraction for the whole. By establishing the extent of the deep ground and the magnitude of its greatest depths, the authors could claim that the ocean must be studied as a body whose prevailing character is abyssal, and that the questions worth asking about it concerned the deep rather than the shore. 1
6. Key Facts
| Attribute | Value |
|---|---|
| Deepest sounding | 5269 fathoms 1 |
| Greatest depth in feet | 60,616 feet 1 |
| Second deepest | 5155 fathoms in the Aldrich Deep 1 |
| Deepest in the Atlantic | 4662 fathoms in the Nares Deep 1 |
| Deepest in the Indian Ocean | 3828 fathoms in the Wharton Deep 1 |
| Area of the whole ocean | 139,295,000 square English miles 1 |
7. Frequently asked questions
What is the deepest sounding recorded here?
The book records 5269 fathoms as the deepest sounding, in the Pacific near Guam. 1
How deep is that in feet?
The greatest depth given is 60,616 feet below sea level. 1
Which ocean is deepest?
Depths exceeding 5000 fathoms are limited to the Pacific. 1
How much of the sea floor is shallow?
About one-sixth of the ocean floor lies above the thousand-fathom line. 1
8. Timeline
- 1899Murray presides over the section that draws up the North Sea programme.Murray presides over the section that draws up the North Sea programme.
- 1912Murray and Hjort publish the results of the Michael Sars investigations.Murray and Hjort publish the results of the Michael Sars investigations.
References (1)
- 1The Depths of the Ocean: a general account of the modern science of oceanography — Macmillan, London (via Internet Archive) Archive↩View source