THE DEEPEST DEPTHS

Rear-Admiral Steve Ritchie CB, DSC, FRICS.


 

This article is taken from No Day Too Long - An Hydrographer's Tale

© Rear-Admiral G.S. Ritchie CB, DSC, FRICS

 

On the way south from Japan to New Zealand Dr Gaskall had said that he wished to carry out one of his seismic experiments in a deep trench in order to find out something of the structure of the sea-floor in such an area. Accordingly, as the ship moved into the Marianas Trench between Guam and Ulithi, John Swallow was active with seismic gear, using it purely as a reflection or sounding machine to record the time of the double passage of sound from the small charge he exploded until it returned as an echo from the sea-bed to his hydrophone, thus giving them the depth. The soundings rapidly increased and soon Swallow was reporting over 5,000 fathoms and finally 5663 fathoms.

 

 

This was an exiting report, for it was known to be nearly as deep as any sounding so far recorded, but unfortunately it was about 1,000 fathoms beyond the scope of the deep echo-sounder at this time. However, using the taut-wire machine, with 140 pounds of scrap iron attached to the end of the wire, as a sounding machine, a depth of 5,899 fathoms was recorded. This was a new depth record for the world.

 

The history of deep sounding in the oceans is not a long one. It was during Lord Mulgrave's expedition to the Arctic in 1773 that some of the earliest attempts of deep sounding were made, the greatest depth being 683 fathoms, whence a sample of sediment was obtained.

 

In 1817-1818 Sir John Ross, during a voyage to Baffin Bay made some deep sea soundings using a "deep sea clam" on the end of his rope which brought up several pounds of greenish mud from his deepest sounding of 1,050 fathoms.

 

Sir James Clark Ross led an expedition to the Antarctic in the ships Erebus and Terror in the years 1839-1843, during which time he really started systematic deep sounding. He had a line of 3,600 fathoms long which he allowed to run out from a large reel fitted in one of theship's boats. The line was marked every 100 fathoms and while it ran out the time as noted as each mark left the reel. When the time interval between the marks appreciably lengthened, the weight at the line's end was assumed to have reached the bottom and the amount run out taken to indicate the depth. The procedure was necessarily one for calm weather and this restricted the number of successful casts made in the open sea; however, the first "abysmal" soundings as the oceanographic textbooks called them, were thus obtained to a depth of 2,425 fathoms.

 

One of the early snags of deep sounding was that a heavy weight was needed to take the line down, but to recover such a weight with the bottom sample adhering to it a very bulky line was required. There was in the United States Navy at this time the now famous officer Lieutenant Maury, who had produced numerous wind and current charts and Sailing Directions for mariners. Working under him as a Midshipman Brooke, who about the year 1859 constructed an apparatus which took a sample of the sea-bed and then detached the bulk of the heavy weight that had taken it down, leaving only a light tube, inside which the sample was retained, to be hauled back to the surface. This invention speeded up the sounding of the oceans and in 1854 Maury was able to make the first bathymetric chart of the North Atlantic. This apparatus, modified by Lieutenant Baillie, Royal Navy, and named after him was still in use in the 1950's.

 

Baillie rod and sinkers, used to collect ocean bed samples from the Mariana Trench

 

 

The earlier Challenger Expedition is said to have carried wire for sounding purposes, but for some reason this was not used, and the method using marked rope and timed intervals was employed for taking the many ocean soundings that this vessel made. Her deepest for the voyage was 4,500 fathoms recorded in the Marianas Trench where we too found our deepest sounding referred to above.

 

The USS Tuscarora was also at sea employed upon oceanographic work at the time of the Challenger Expedition and it was from her decks that piano wire was first used for sounding great depths. With this wire she recorded 4,665 fathoms in the Kuril Trench north-east of Japan.

 

The first ship to sound at a greater depth than 5,000 fathoms was the British surveying vessel Penguin in 1895. Her captain was Andrew Balfour, who had been a sub-lieutenant in Challenger during the Expedition and, ever since, had been fired with enthusiasm to find a great depth. He took two soundings with piano wire on a steam sounding machine which had by then come into use; these soundings were taken in the Kermadec Trench in the South Pacific, north east of New Zealand. On the first occasion the wire parted, as so often happens, while the Baillie rod was being hauled to the surface. As the rod is comparatively light, the parting of the wire is not readily apparent and it is only as the hours pass that the surveyors, constantly feeling the wire, for it takes over 4 hours to haul in the sampler from 5,000 fathoms. It took Andrew Balfour far longer, for when he recorded a sounding of 5,155 fathoms he insisted that, to avoid parting the wire again, watches of two seamen at a time hove in the whole five miles using the manual handle on the machine, so that no undue strain of an unfeeling steam engine would be imparted to the thin wire as the ship rolled in the heavy swell. He never left the winch himself throughout the whole long day, and thankfully and excitedly he ladled the sediment from the sampler onto a plate he kept beside him in readiness for this supreme moment.

 

The German ship Planet shifted the scene of the greatest depth once again to the Northern Hemisphere - in the Philippine Trench close eastward of the islands which gave it the name. And here some years later the Dutch vessel Willebord Snellius subsequently found 5,539 fathoms, using early audio-frequency sounding methods.

 

The USS Ramapo moved the scene once more to the Japan Trench with 5,673 fathoms, using audio-frequency methods, but the German Emden returning from the Philippine Trench, found just a few more fathoms to make it 5,686.

 

This was the state of great depth sounding when World War II came. At the close of the Pacific War the United States was once again to take the lead in the friendly rivalry of deep ocean discovery. Dr. H.H. Hess, a university professor, had studied the shape of the ocean floor for many years and had produced the best bathymetric chart of the North Pacific available before the war. Like so many others of his calling, he joined the Services and his knowledge of the sea took him into the Navy, where he eventually commanded a large fleet oiler, the USS Cape Johnson. Commander Hess's crew was composed of Reserves and he had no difficulty in persuading them that it was normal in the Navy to carry out standard oceanographic observations as the vessel proceeded upon her naval duties across the oceans. Thus the ship was able to add much to the knowledge of oceanography and eventually sounded with her echo-sounding machine in the Philippine Trench, recording there a depth of 5,740 fathoms, now known as "Cape Johnson Depth", from which the Danish research ship Galathea later dredged up forms of life including sea anemones, a number of worms and some living bacteria.

 

The scene of the greatest depth having once again shifted to Marianas Trench, we were determined to make a survey of the deep area and to get a sample of sediment from the depths. During the visit to New Zealand the ship enjoyed great assistance from knowledgeable technicians in the Royal New Zealand Dockyard at Devonport, who managed to boost the echo-sounder to record the greatest depths: here also extra wire for the sounding machine was obtained.

 

 

 

HMS Challenger entering Suva, Fiji, in 1951, during her world voyage.

 

It was an exiting time as Challenger steamed back into the trench on the way northwards from Manus to Japan, for on this occasion she was not restricted to spot soundings here and there; enthusiasm rose as the water became deeper and deeper, and still the officer with the headphones sitting before the sounder could hear the small answering signal returning from the depths first eight, then slowly nine, ten, eleven, twelve, thirteen and finally fourteen seconds after the metallic sound of the outgoing signal had been heard - for such is the time the sound takes to reach the sea-bed and return from 5,9000 fathoms.

 

Sounding lines were run at right angles to the east-west axis of the trench, thus obtaining profiles across this giant crack on the surface of the globe. Such trenches do not have spectacular slopes as one might find in a canyon on land, but descended slowly and steadily to meet in a small flat expanse at the bottom from which the echo returns more clearly than from any other part. On completion of the mapping it appeared that there was a considerable area of a depth greater than 5,9000 fathoms and that a sounding of 5.940 fathoms existed. But the 6,000 fathom barrier remained inviolate.

 

Challenger's soundings in the Marianas Trech (depth in fathoms)

 

A sample from the trench was also obtained with the Baillie rod after three attempts. It is difficult when using the steam sounding machine in such depths to know just when the sampler has reached the bottom, and during the short delay between realising this and the application of the brake to stop more wire running out a certain amount will have coiled itself on the sea-floor beside the sampler. When the winch begins to heave, these coils become kinks, and often, perhaps hours later when the sample seems to be almost on deck, the wire finally parts at the kink and the six hour task has to be done all over again. This difficulty was overcome by laying up the whole of the last 100 fathoms of piano wire within a piece of rope which obviated the kinking as the superfluous wire coiled onto the sea-bed six and three quarters land miles below.

 

Excitements on deck was tense when, at long last, the ceaseless chugging of the winch was slowed and Petty Officer Greenshields grasped the rope and hauled it hand-over-hand. Even before the sampler could be clearly sighted a brown cloud was seen spreading from it, indicating that the rod must contain a sample of what the surveyor has termed "red clay", the deposit of the great depths.

 

Very considerable areas of the ocean floor are composed of ooze formed by countless millions of skeletons of microscopic and macroscopic plankton which have lived a brief life near the sea's surface and, having died there, sunk slowly to form this deposit. At greater depths than 3,000 fathoms or so the calcareous plankton are no more and only the skeletons of silicate forms remain, for the calcareous forms have been eroded away during their long fall and have once again become an integral part of sea water. The silicate forms continue unscathed to the great depths, where are found the skeletons of diatoms (the plants), and radiolarians (the animals), that, with red volcanic dust which has fallen upon the sea surface miles above, form the really deep ocean deposits.

 

Such a sample now lay secure in a pickle jar, and this I took home with me when I left the ship a month later. Back in London, I made my way to that striking building of many turrets which houses the British Museum of Natural History in the Cromwell Road. It was the first of many visits to this treasure house, and I was taking the cherished deep-bottom sample to Dr J.D.H. Wiseman, an expert in such matters. A guide took me from the main hall, where stuffed elephants stood with the oversized statues of Darwin and Huxley, down to the cellars beneath. Here we passed along a maze of corridors lined with racks on which were stacked spare or forgotten stuffed animals, their horns, their hoofs, their heads and their bones, like some nightmare Aladdin's cave. At last the guide reached a locked door on which he rapped with a conspiratorial air, and we were admitted to Dr Wiseman's presence.

 

The small pickle jar looked insignificance as it was placed upon the table among many other jars of more imposing size and content, but Dr Wiseman's enthusiasm made up for this, and soon he and his companions were inspecting the sample through microscopes, searching for the skeletons of the planktonic animals and plants it contained, which had once floated near the blue surface of the far-away Pacific Ocean.

 

When using the echo-sounder in the Trench we had actually recorded a deepest sounding of 5,960 fathoms (10,900 metres) in position 11š19'N, 142š15'E. This sounding was repeatedly made using earphones to hear the return of the signal as the stylus passed across the graduated depth scale, whilst the timing of the speed of the echo-sounding machine, a necessary part of the process, was made with a hand held stopwatch. For these reasons I considered it prudent to subtract one scale division of 20 fathoms when officially reporting a new greatest depth of 5,940 fathoms (10,863 metres). With hindsight this caution on my part appears to have been a mistake.

 

In 1957 I provided Professor C.V. Udintsev of the Soviet Union with our sounding data in the Marianas Trench, which he then visited in his research vessel Vityaz. He subsequently reported that he had found depths of more than 11,000 metres.

 

In January 1960 Jacques Piccard and Lieutenant Don Walsh of the United States Navy descended in the bathyscaph Trieste to the floor of the Challenger Deep, recording a depth of 10,900 metres on their depth gauge.

 

Later Dr Robert I. Fisher of Scripps Institute of Oceanography visited the vicinity of Challenger Deep on a number of occasions. In 1962 with the Proa Expedition in M.V. Spencer F. Baird, using the advanced precision depth recorders with stable electrical frequency sources then available, Fisher recorded a greatest depth of 10,915 metres.

 

In 1984 the Japanese Hydrographer reported a greatest depth of 10,924 metres as having been recorded by the survey vessel Takuyo, using a multi-beam echo-sounder during a sounding run of about 500 miles in the vicinity of the Challenger Deep.

 

All of the soundings referred to above have been corrected for sound velocity in the water column to give true depth, either by the use of various tables available, or by temperature and salinity measurements obtained at depth in the area concerned.

 

When one takes into account the great technical advances since 1951, the Challenger measurements made with our crude methods agrees very creditably with those of Fisher (1962) and the Japanese (1984).

 

Books by Steve Ritchie still in print

No day too long - An hydrographers tale (1992), The Pentland Press.

The Admiralty Chart - British Naval Hydrography in the nineteenth century (new edition) (1995), The Pentland Press.

 

Rear-Admiral Steve Ritchie served in the RN Surveying Service for thirty five years, during which time he commanded four of her Majesty's surveying ships world-wide. He was Hydrographer of the Navy from 1966 to 1971 and President of the International Hydrographic Bureau in Monaco from 1972 to 1982.