The western Mediterranean is cut off by a bank crossing the narrow strait between Sicily and Cape Bon, usually known as the Adventure Bank, on which the depth is nowhere 200 fathoms. The mean depth of the western basin is estimated at 881 fathoms, and the deepest sounding recorded is 2040 fathoms. In the eastern Mediterranean the mean depth is nearly the same as in the western basin.
The Sicilian-Ionian basin has a mean depth of 885 fathoms, and the Levant basin, 793 fathoms. Deep water is found close up to the coast of Sicily, Greece, Crete and the edge of the African plateau.
The steepest slope observed occurs off the island of Sapienza, near Navarino, where 1720 fathoms has been obtained only 10 miles from land.
Another bank i ioo fathoms from the surface runs south from the east end of Crete, separating the Pola Deep from the depths of the Levant basin, in which a depth of 1960 fathoms was recorded near Makri on the coast of Asia Minor.
of Corsica, from which it is separated by the Strait of Bonifacio, which is some 50 fathoms deep. The harbour of Golfo degli Aranci, in the north-eastern portion of the island, is 138 m.
The mean depth over this ridge is about 250 fathoms, and the maximum depth nowhere reaches 500 fathoms. The main basin of the Atlantic is thus cut off from the Arctic basin, with which the area north of the ridge has complete deep-water communication.
This intermediate region, which has Atlantic characteristics down to 300 fathoms, and at greater depths belongs more properly to the Arctic Sea, commonly receives the name of Norwegian Sea.
In these troughs the depth is seldom much less than 3000 fathoms, and this is exceeded in a series of patches to which Murray has given the name of "Deeps."
The western trough extends northwards into Davis Strait, forming a depression in the Telegraph plateau; to the south of Newfoundland and Nova Scotia are Sigsbee Deep, Libbey Deep and Suhm Deep, each of small area; north-east of the Bahamas Nares Deep forms the largest and deepest depression in the Atlantic, in which a sounding of 4561 fathoms was obtained (70 m.
long., in which he recorded a depth exceeding 4000 fathoms. The Scottish Antarctic expedition has shown this sounding to be erroneous; the " Scotia " obtained samples of bottom, in almost the same spot, from a depth of 2660 fathoms. Combining the results of recent soundings, Dr W.
Mean Karstens, 2047 fathoms. If we include the enclosed depth, and seas, the North Atlantic has a mean depth of 1800 bottom fathoms. The South Atlantic has a mean depth of deposits.
The greater part of the bottom of the Atlantic is covered by a deposit of Globigerina ooze, roughly the area between l000 and 3000 fathoms, or about 60% of the whole.
From the surface to 500 fathoms the general form of the isothermals remains the same, except that instead of an equatorial maximum belt there is a focus of maximum temperature off the eastern coast of the United States.
Below 500 fathoms the western centres of maximum disappear, and higher temperatures occur in the eastern Atlantic off the Iberian peninsula and north-western Africa down to at least 1000 fathoms; at still greater depths temperature gradually becomes more and more uniform.
The communication between the Atlantic and Arctic basins being cut off, as already described, at a depth of about 300 fathoms, the temperatures in the Norwegian Sea below that level are essentially Arctic, usually below the freezing-point of fresh water, except where the distribution is modified by the surface circulation.
This distribution is most marked at about 300 fathoms, and disappears at soo fathoms, beyond which depth the lines tend to become parallel and to run east and west, the gradient slowly diminishing.
Teredo navalis, it has been found necessary, for depths not exceeding 300 fathoms, to protect the core with a thin layer of brass tape.
The grappling of the cable and raising it to the surface from a depth of 2000 fathoms seldom occupy less than twenty-four hours, and since any extra strain due to the pitching of the vessel must be avoided, it is clear that the state of the sea and weather is the predominating factor in the time necessary for effecting the long series of operations which, in the most favourable circumstances, are required for a repair.
As to cost, one transatlantic cable repair cost 75,000; the repair of the Aden-Bombay cable, broken in a depth of 1900 fathoms, was effected with the expenditure of 176 miles of new cable, and after a lapse of 251 days, 103 being spent in actual work, which for the remainder of the time was interrupted by the monsoon; a repair of the Lisbon-Porthcurnow cable, broken in the Bay of Biscay in 2700 fathoms, eleven years after the cable was laid, took 215 days, with an expenditure of 300 miles of cable.
A third curve, from the south-easternmost promontory of the Peloponnese through Cerigo, Crete, Carpathos and Rhodes, marks off the outer deeps of the open Mediterranean from the shallow seas of the archipelago, but the Cretan Sea, in which depths occur over 1000 fathoms, intervenes, north of the line, between it and the Aegean proper.
The greater part of this trough is over 600 fathoms deep. The profusion of islands and their usually bold elevation give beauty and picturesqueness to the sea, but its navigation is difficult and dangerous, notwithstanding the large number of safe and commodious gulfs and bays.
of the Andamans are the dangerous Western Banks and Dalrymple Bank, rising to within a few fathoms of the surface of the sea and forming, with the two Sentinel Islands ï¿½, the tops of a line of submarine hills parallel to the Andamans.
The furrows are the great ocean basins, and these would still persist even if the land surface were enlarged to the 1400 fathoms contour.
The only part of the sea-bed the configuration of which is at all well known is the zone bordering the coasts where the depth is less than about loo fathoms or 200 metres, i.e.
above sea-level, and the mean depth of the oceans as 2080 fathoms or 12,480 ft.
or 1700 fathoms below sea-level.
area containing all dry land, the transitional area including the submarine slopes down to 1000 fathoms, and the abysmal area consisting of the floor of the ocean beyond that depth; and Mill proposed to take the line of mean-sphere level, instead of the empirical depth of moo fathoms, as the boundary between the transitional and abysmal areas.
(1250 fathoms) below according sea-level.
An elevation of small extent is distinguished as a " dome " when it is more than 100 fathoms from the surface, a " bank " when it is nearer the surface than 100 fathoms but deeper than 6 fathoms, and a " shoal " when it comes within 6 fathoms of the surface and so becomes a serious danger to shipping.
in width and from 3 to 5 fathoms deep, navigable for steamers of good size.
By an invention probably due to Humfray Cole and published in 1 578 by William Bourne in his Inventions and Devices, it was proposed to register a ship's speed by means of a "little small close boat," with a wheel, or wheels, and an axle-tree to turn clockwork in the little boat, with dials and pointers indicating fathoms, leagues, scores of leagues and hundreds of leagues.
The portion nearest the log-ship is known as the "stray line"; its length varies from ro to 20 fathoms, but should be sufficient to ensure that the log-ship shall be outside the disturbing element of the ship's wake.
Owing to the increased friction produced by a rotator making approximately 900 revolutions per mile, towed at the end of a line varying from 40 fathoms for a 12 -knot FIG.
speed to 60 fathoms for 20 knots, the pull of the line and rotator is borne by coned rollers, having their outlines tapering to a common point in their rotation, thus giving a broad rolling surface.
Many were taken at 10 fathoms and deeper with the line, and all were of exceptionally large size, several measuring 18 in.
long, reaches there a depth of over 600 fathoms, with a maximum depth of 880 fathoms, i.e.
and spreading under its waters, so as to leave only a narrow channel, 230 to 2 4 7 fathoms deep, along the opposite coast.
The depth of the middle portion of the lake has not yet been measured, but must exceed 500 fathoms. It was expected that an underground ridge would be found connecting Olkhon with Svyatoi Nos; but depths exceeding 622 fathoms have been sounded even along that line.
215 surround it, and most of its area has a depth exceeding 400 fathoms, the maximum depths along three lines of soundings taken across it being 491, 485, and 476 fathoms respectively.
is generally found at a depth of 20 fathoms, as also on the surface in the middle of the lake.
At a depth of 500 fathoms there is a nearly uniform temperature of 38°.
Generally, while there is a relative poverty of zoological groups, there is a great wealth of species within the group. Of gammarids, there are as many as 300 species, and those living at great depths (33 o to 380 fathoms) tend to assume abyssal characters similar to those displayed by the deep-sea fauna of the ocean.
They live in the mud, which they eat, in comparatively shallow waters up to 50 fathoms.
The greatest depth is 1030 fathoms (1227 Russian fathoms) near the centre, there being only one basin.
The steepest incline outside loo fathoms is to the southeast of the Crimea and at Amastra; the incline to the greater depths is also steep off the Caucasus and between Trebizond and Batum.
The existence of sulphuretted hydrogen in great quantities below loo fathoms, the extensive chemical precipitation of calcium carbonate, the stagnant nature of its deep waters, and the absence of deep-sea life are conditions which make it impossible to discuss it along with the physical and biological conditions of the Mediterranean proper.
The depths of the Black Sea are lifeless, higher organic life not being known to exist below loo fathoms. Fossiliferous remains of Dreissena, Cardium and other molluscs have, however, been dredged up, which help to show that conditions formerly existed in the Black Sea similar to those that exist at the present day in the Caspian Sea.
During summer the surface salinity of the Black Sea is from 1.70 to 2'00% down to 50 fathoms, whereas in the greater depths it attains a salinity of 2.25%.
The temperature is rather remarkable, there being an intermediate cold layer between 25 and 50 fathoms. This is due to the sinking of the cold surface water (which in winter reaches freezing-point) on to the top of the denser more saline water of the greater depths.
The temperature down to 25 fathoms is from 78.3° to 46.2° F., and in the cold layer, between 25 and 50 fathoms, is from 46.2° to 43.5° F., rising again in greater depths to 48.2° F.
The Sea of Azov is exceedingly shallow, being only about 6 fathoms in its deepest part, and it is largely influenced by the river Don.
A submarine ridge, about 300 fathoms deep at its deepest, unites Greenland with Iceland (across Denmark Strait), the Faeroes and Scotland.
These fjords are very deep; the greatest depth found by Ryder in Scoresby Sound was 300 fathoms, but there are certainly still greater depths; like the Norwegian fjords they have, however, probably all of them, a threshold or sill, with shallow water, near their mouths.
Finally, the plankton (and again the vegetable forms in particular) are practically restricted to the upper hundred fathoms or so of the sea.
Daly estimates that the maximum lowering of ocean level due to this cause would only amount to 36 fathoms, but even that would be the cause of very marked geological effects.
Finally, Glandiceps abyssicola (Spengelidae) was dredged during the "Challenger" expedition in the Atlantic Ocean off the coast of Africa at a depth of 2500 fathoms.
The natural harbour, which, with a depth diminishing from 70 to 30 fathoms, strikes in from the northwest so as to cut the island into two fairly equal portions, with an isthmus not more than 14 m.
long and anchorage in six fathoms. A considerable trade is done.
Below 150 fathoms they are rare, but a few such as Terebratulina wyvillei are found down to 2000 fathoms. Lingula is essentially a very shallow water form.
It is a widelydistributed species, being found throughout the northern and temperate seas of Europe, Asia and America, extending as far south as Gibraltar, but not entering the Mediterranean, and inhabits water from 25 to 50 fathoms deep, where it always feeds close to the bottom.
long), however, prefer deep water, down to 70 fathoms. The flesh is not so highly valued as that of the cod and haddock.
The levels are supposed to be I o fathoms (60 ft.) apart.
The extreme depth of the strait approaches 50 fathoms, and it contains two small islands known as the Diomede Islands.
The southern coast in particular is deeply indented; and there two bold peninsulas, extending for several miles into the sea, form two capacious natural harbours, namely, Deep Water Bay, with the village of Stanley to the east, and Tytam Bay, which has a safe, well-protected entrance showing a depth of 10 to 16 fathoms. An in-shore island on the west coast, called Aberdeen, or Taplishan, affords protection to the Shekpywan or Aberdeen harbour, an inlet provided with a granite graving dock, the caisson gate of which is 60 ft.
There is good anchorage throughout the entire channel separating the island from the mainland, except in the Ly-ee-mun Pass, where the water is deep; the best anchorage is in Hong-Kong roads, in front of Victoria, where, over good holding ground, the depth is 5 to 9 fathoms. The inner anchorage of Victoria Bay, about a m.
off shore and out of the strength of the tide, is 6 to 7 fathoms. Victoria, the seat of government and of trade, is the chief centre of population, but a tract on the mainland is covered with public buildings and villa residences.
long, with an extreme breadth of nearly 3 m., with a large but shallow lagoon approached from the north by a passage two fathoms deep. The atoll is growing outwards on every side, and at one place rises 19 ft.
There the bottom slopes very abruptly, descending precipitously at a point not far from the north-east coast of the main island, where soundings have shown 4655 fathoms. This, the deepest sea-bed in the world, is called the Tuscarora Deep, after the name of the United States man-of-war which made the survey.
On the other hand, the average depth of the Japan Sea is only 1200 fathoms, and its maximum depth is 3200.
above sea-level, has a maximum depth of 93 fathoms, and empties itself at one end over a fall (Kegon) 250 ft.
These last have not been found anywhere except at the entrance of the Bay of Tokyo at a depth of some 200 fathoms.
long by 3 to 6 broad, with 12 to 32 fathoms of water.
Dr Livingstone obtained a depth of 326 fathoms opposite Mount Kabogo, south of Ujiji.
Mr Hore often failed to find bottom with a line of 168 fathoms. The French explorer, Victor Giraud, reported 647 metres (about 350 fathoms) off Mrumbi on the west coast, and Moore depths of 200 fathoms and upwards near the south end.
It has a depth of 6 to io fathoms, with a good bottom, and large ships can anchor at a cable's length from the shore.
to the south, with a depth of 4 to 9 fathoms, Dockyard Bay and Artillery Bay.
During Nansen's expedition on the " Fram " in 1894-1895, Scott Hansen made observations with a Sterneck's half-seconds pendulum on the ice where the sea was more than 1600 fathoms deep and found only an insignificant deviation from the number of swings corresponding to a normal ellipsoid.
The annual range of temperature between summer and winter of a surface layer of water about 25 fathoms thick in the Baltic is as much as 20° F., but this only corresponds to a difference of level of 14 in.
- The hand-lead attached to a line with samples of the deposits, and also observations of temperature divided into fathoms was a well-known aid to navigation even and salinity in different depths, as well as dredgings for the in high antiquity, and its use is mentioned in Herodotus (ii.
" Challenger " round the world says " of measured seas the Sardonian is the deepest with full under the scientific direction of Sir Wyville Thomson and the one thousand fathoms " (i.
This epoch-making great discoverers of the modern period were only familiar with expedition lasted from Christmas 1872 to the end of May 1876, the hand-lead, and the lines in use did not exceed 200 fathoms and gave the first wide and general view of the physical and in length.
He spliced together all the sounding-lines on board, rightly said that since the days of Columbus and Magellan no and with a weight of 1501b attached he found bottom in 683 such revelation regarding the surface of our planet had been fathoms and secured a sample of fine soft blue mud.
Polar explorers making sections across the great expanses of water with everfrequently repeated those experiments in deep-sea soundings, increasing accuracy, and in that work the government surveying both William Scoresby and Sir John Ross obtaining notable ships have also been engaged, vast stretches of the Indian and results, though not reaching depths of more than 1200 fathoms. Pacific Oceans having been opened up to knowledge by H.M.SS.
All attempts to dispense with a lead and line and to measure the depth by determining the pressure at the bottom have hitherto failed when applied to depths greater than 200 fathoms; a new hydraulic manometer has been tried on board the German surveying ship " Planet."
It is improbable, however, that the smooth and slender wire is much influenced by currents, and the best deep-sea soundings may be taken as accurate to within 5 fathoms.
Kriimmel has calculated the mean depth to be 2010 fathoms (12,060 ft.), while the mean elevation of the surface of the continents above sea-level is only 2300 ft.
(5268 fathoms) below sea-level.
The continental shelf is the gentle slope which extends from the edge of the land to a depth usually about loo, though in some cases as much as 300 fathoms, and is there demarcated by an abrupt increase in the steepness of the slope to ocean depths.
Amongst these are the dome, an isolated elevation rising steeply but not coming within too fathoms of the surface; the bank, an elevation coming nearer the surface than too fathoms, but not so near as 6 fathoms; and finally the shoal or reef, which comes within 6 fathoms of the surface, and so may constitute a danger to shipping.
In particular Sir John Murray considers that only deeps exceeding 3000 fathoms in depth should be named, and in his charts he has named these deeps after persons whether the individuals thus honoured had themselves discovered or explored the deeps in question or not.
Such valleys are very clearly indicated in the belts of the western Baltic by furrows a thousand yards wide and twenty to thirty fathoms deeper than the neighbouring sea-bed.
all soundings exceeding 4000 fathoms, occur in trenches, and there are only a few small trenches known (on the west coast of Central America) in which the maximum depth is less than 3000 fathoms. Jlost trenches are narrow, but of considerable length, and their steeper side is believed to be due in every case to a great fracture of the earth's crust..
As the result of all the deep-sea surveys now available we know that the central rise of the Atlantic starts from Iceland as the Reykjanes Ridge with less than loon fathoms of water over it in most parts and runs south-westward until in 51° N.
the depth over it is less than 150o fathoms, thence to 12° N.
the depths are between 1500 and 2000 fathoms, and then it rises again to about 150o fathoms and runs eastward under the name of the Equatorial Ridge.
the rise resumes a southerly direction and from Ascension to Tristan d'Acunha, the depth is in many places less than r50o fathoms. The soundings of Bruce's Antarctic expedition in the " Scotia " showed that the rise cannot be traced beyond 55° S.
where the depths increase rapidly to over 2000 fathoms. The whole length of the rise which divides the Atlantic into an eastern and a western basin may be taken as 7500 nautical miles.
Brownson, U.S.N., obtained a sounding of 4561 fathoms in 19° 36' N., 66° 26' W.
The Brazilian Basin has also a large area lying at a depth greater than 2500 fathoms and culminates in the Romanche Deep close to the Equatorial Ridge in o° rr' S., 18° 15' W.
The North African Basin has several deeps with more than 3300 fathoms to the northwest and the south-west of the Cape Verde Islands, but the South African Basin is less deep. In the South Atlantic there is no connexion between the Central Rise and the Antarctic Shelf, for the Indo-Atlantic Antarctic Basin stretches from near the South Sandwich Islands towards Kerguelen with depths exceeding 2500 fathoms and reaching in places 3100.
It was long believed on the strength of a sounding of " 4000 fathoms, no bottom " reported by Sir James Ross in 68° 22' S., 12° 49' W., that the Indo-Atlantic Basin was of enormous depth, but W.
Bruce, in the " Scotia," showed in 1904 that the real depth at that point is only 2660 fathoms.
In the Indian Ocean the Kerguelen Rise stretches broadly southward, east of the island which gives it a name, to the Antarctic Shelf with the greatest depths upon it usually less than 2000 fathoms, and it stretches northward beyond New Amsterdam to 30° S.
This rise is separated from the Crozet Rise by a depression extending to 2675 fathoms, through which the Kerguelen Trough (which lies north of Kerguelen) is brought into free communication with the Indo-Atlantic Antarctic Basin.
The Australian Shelf rises steeply as a rule from depths, of 2500 to 3000 fathoms. A broad depression with depths of from 3300 to 3500 fathoms lies to the east of the Cocos Islands and extends into the angle between the Malay Archipelago and Australia.
On the north this depression sinks into the long and narrow Sunda Trench south of Java, and here in 10 15' S., 108° 5' E., the German surveying-ship " Planet " obtained a sounding of 3828 fathoms in 1906.
" Sealark " and the German surveying-ship " Planet " to have a somewhat complicated configuration, the island groups and banks of atolls which occur there rising abruptly as a rule from depths of about 2000 fathoms or more.
Between the Seychelles and Sokotra (0° - 9 ° N.) there are great stretches of the ocean floor forming an almost level expanse at a depth of 2800 fathoms. The Arabian Gulf and Gulf of Aden are also very uniform with depths of about 1900 fathoms, while the floor of the Bay of Bengal rises very gradually northwards and is 1000 fathoms deep close up to the Ganges Shelf.
Half of this basin lies deeper than 2750 fathoms, and the greater part of it belongs to the northern hemisphere.
From the floor of this vast and profound depression numerous isolated volcanic cones rise with abrupt slopes, and even between the islands of the Hawaiian group there are depths of more than 2000 fathoms. The Society Islands and Tahiti crown a rise coming within 150o fathoms of the surface, two similar rises form the foundation of the Paumotu group where Agassiz found soundings of.
2187 fathoms between Marokar and Hao.
The Tuscarora Deep of the Japan Trench (4655 fathoms in 44° 55' N., 152° 26' E.) was famed for many years as the deepest depression of the earth's crust.
This great trench is continued along the Luchu.Islands where the cable-steamer " Stephan " sounded in 4080 fathoms, and through the Bonin Trench (with a maximum of 3595 fathoms) to the famous Marianne Trench in which the U.S.S.
" Nero " in 1899 found 5269 fathoms in 12° 43' N., 1 45° 49' E., the greatest depth yet measured.
The northern part of the Marianne Trench leads to a wave-like configuration of the ocean floor, the depth to the east of Saipan being over 4300 fathoms, followed by a rise to 1089 fathoms and then a descent to 3167 fathoms.
The trenches of Yap (4122 fathoms) and Palau (Pelew) (4450 fathoms) are not immediately connected with that of Marianne.
To the east of the Philippines a sounding of 3490 fathoms is found close to the Strait of St Bernardino and north-east of Talaut.
there is a trench with 4648 fathoms. To the north-east the Japan Trench adjoins the Aleutian Trench, where a depth of 4038 fathoms has been found south-west of Attu.
The Tonga and Kermadec trenches, both deeper than 4000 fathoms, stretch from the Samoa Islands southwards toward New Zealand for a distance of 1600 nautical miles.
The deepest sounding obtained in the Tonga Trench is 5022 fathoms in 2 3° 39.4' S ., 1 75° 4' W., and in the Kermadec Trench, 5155 fathoms, 30 27.7' S., 176° 39' W.
There are no depths, however, much exceeding 2500 fathoms amongst these depressions.
The south-eastern part of the Pacific is mainly occupied by the Easter Island Rise with depths rarely so great as 2000 fathoms; but close to the continent of South America the Atacama Trench is a typical example of the deepest form of depression culminating with 4175 fathoms in 25° 42' S., 71° 31.5' W.
right up to the Antarctic Shelf, with depths ranging down to 2500-3000 fathoms, and communicating with the main Pacific Basin to the east of New Zealand.
m.) with depths down to 2200 fathoms. A rise between Spitsbergen and Greenland separates the Norwegian Trough (greatest depth 2005 fathoms in 68° 21' N., 2° 5' W.) which in turn is divided from the Atlantic by the Wyville Thomson Ridge which runs between the Faeroe and Shetland islands and is covered by only 314 fathoms of water at the deepest point.
The ridge across Denmark Strait west of Iceland nowhere exceeds 300 fathoms in depth, so that the deeper water of the North Polar Basin is effectively separated from that of the Atlantic. A third small basin occupies Baffin Bay and contains a maximum depth of 1050 fathoms. Depths of from loo to 300 fathoms are not uncommon amongst the channels of the Arctic Archipelago north of North America, and Bering Strait, through which the surface water of the Arctic Sea meets that of the Pacific, is only 28 fathoms deep.
The Central American Sea communicates with the Atlantic through the channels between the Antilles, none of which is quite 1000 fathoms deep, and it sinks to a depth of 2843 fathoms in the Caribbean Basin, 3428 fathoms in the Cayman Trench and 2080 fathoms in the Gulf of Mexico.
The China Sea on the north has a maximum depth of 2715 fathoms off the Philippines, the Sulu Basin reaches 2550 fathoms, and the Celebes Basin 2795 fathoms. Some of the channels between the islands are of very great depth, Macassar Strait exceeding 1000 fathoms, the Molucca Passage exceeding 2000 fathoms, and the Halmahera Trough sinking as deep as 2575 fathoms. The deepest of all is the Banda Basin, a large area of which lies below 2500 fathoms and reaches 3557 fathomsin the Kei Trench.
A depth of 2789 fathoms also occurs north of Flores.
The Mediterranean Sea, the best-known member of the intercontinental class, is separated from the Atlantic Ocean by a ridge running from Cape Spartel to Cape Trafalgar on which the greatest depth is only 175 fathoms. The depth increases so rapidly towards the east that soundings exceeding 500 fathoms occur off Gibraltar.
The Balearic Basin, between Spain and the rise bearing Corsica and Sardinia, has a maximum depth of 1742 fathoms, and the Tyrrhenian Basin between that rise, Italy and Sicily deepens to 2040 fathoms. The larger Eastern Mediterranean Basin stretches eastward from Sicily with large tracts more than 2000 fathoms below the surface, and the greatest depth ascertained during the detailed researches of the Austrian expedition on board the " Pola " was 2046 fathoms in 35° 44' 8' N., 21° 46.8' E.
The Adriatic Sea though very shallow in the north deepens southward to about 9 00 fathoms, and the Aegean Sea has a maximum depth of 1230 fathoms north of Crete.
lies the extremely shallow Gulf of Azov; but the greater part of the sea consists of a deep basin, the central part of which is an almost flat expanse at a uniform depth of 1220 fathoms.
The Persian Gulf nowhere exceeds 50 fathoms, the southern part of Hudson .Bay does not exceed Too fathoms except at one spot, though in the less-known fjords of the northern part depths up to 200 fathoms have been reported.
The Baltic Sea exceeds 50 fathoms in few places except the broad central portion, though small caldron-like depressions here and there may sink below zoo fathoms. The Red Sea on the other hand, though shut off from the Indian Ocean by shallows of the Strait of Bab-elMandeb with little more than ioo fathoms, sinks to a very considerable depth in its central trough, which reaches 1209 fathoms in 20° N.
In the North Sea the depth of ioo fathoms is only exceeded to any extent in the Norwegian gully, which has a maximum depth of 383 fathoms in the Skagerrack.
In the Bering Sea the trough north of Buldir in the Aleutian Islands sinks to 2237 fathoms, and in the Sea of Okhotsk, north-west of the Kuriles, to 1859 fathoms. Similar conditions prevail in the East China Sea and the Andaman Sea.
The Sea of Japan has a wide shelf only in the north, the central part forms a broad basin with depths of 1650 fathoms. The Laurentian Sea (Gulf of St Lawrence) has a narrow branching gully running between wide shelves, in which a depth of 312 fathoms is found south of Anticosti.
In depths down to ico fathoms the old-fashioned hand-lead, hollow below and " armed " with tallow, suffices to bring up a sample large enough to be recognizable.
Captain Phipps in 1773 secured samples of soft blue clay in this manner from a depth of 683 fathoms, but as a rule when sounding in great depths the sample is washed off the tallow before it can be brought on board.
Shallow W Ate R Deposits (in less than too fathoms) III.
It is particularly in evidence round the whole of the Antarctic Shelf, where it occurs down to depths of 2500 fathoms. It is the chief deposit, according to Nansen, of the North Polar Basin and, according to Schmelck and Bdggild, of the Norwegian Sea also, where it is largely mixed with the shells of the bottom-living foraminifer Biloculina.
The formation of the blue mud is largely aided by the putrefaction of organic matter, and as a result the water deeper than 120 fathoms is extraordinarily deficient in dissolved oxygen and abounds in sulphuretted hydrogen, the formation of which is brought about by a special bacterium, the only form of life found at depths greater than 120 fathoms in the Black Sea.
It is a remarkable geographical fact that on the rises and in the basins of moderate depth of the open ocean the organic oozes preponderate, but in the abysmal depressions below 2500 or 3000 fathoms, whether these lie in the middle or near the edges of the great ocean spaces, there is found only the red clay, with a minimum of calcium carbonate, though sometimes with a considerable admixture of the siliceous remains of radiolarians.
Out of 118 samples of globigerina ooze obtained by the " Challenger " expedition 84 came from depths of 1500 to 2500 fathoms, 13 from depths of loon to 150o and only 16 from Scot.
depths greater than 2500 fathoms. Viewed as a whole this deposit may be taken as a partial precipitation of the plankton living in the upper waters of the open sea.
These shells do not retain their individuality at depths greater than 1400 or 1500 fathoms, and in fact pteropod ooze is only found in small patches on the ridges near the Azores, Antilles, Canaries, Sokotra, Nicobar, Fiji and the Paumotu islands, and on the central rise of the South Atlantic between Ascension and Tristan d'Acunha.
Red clay was discovered and named by Sir Wyville Thomson on the " Challenger " in 1873 when sounding in depths of 2700 fathoms on the way from the Canary Islands to St Thomas.
Red clay is the deposit peculiar to the abysmal area; 70 carefully investigated samples collected by the " Challenger " came from an average depth of 2730 fathoms, 97 specimens collected by the " Tuscarora " came from an average depth of 2860 fathoms, and 26 samples obtained by the " Albatross " in the Central Pacific came from an average depth of 2620 fathoms. Red clay has not yet been found in depths less than 2200 fathoms. The main ingredient of the deposit is a stiff clay which is plastic when fresh, but dries to a stony hardness.
A very interesting feature is the small proportion of calcium carbonate, the amount present being usually less as the depth is greater; red clay from depths exceeding 3000 fathoms does not contain so much as 1% of calcareous matter.
In the North Sea north of the Dogger Bank, for instance, the disk is visible in calm weather to a depth of from io to 16 fathoms, but in rough weather only to 62 fathoms. Knipovitch occasionally observed great transparency in the cold waters of the Murman Sea, where he could see the disk in as much as 25 fathoms, and a similar phenomenon has often been reported from Icelandic waters.
Luksch found the disk visible as a rule to from 22 to 27 fathoms, and off the Syrian coast even to 33 fathoms. In the open Atlantic there are `great differences in transparency; Kriimmel observed a 6 ft.
disk to depths of 31 and 36 fathoms in the Sargasso Sea, but in the cold currents of the north and also in the equatorial current the depth of visibility was only from zi to 162 fathoms. to the tropical parts of the Indian and the Pacific Oceans the depth of visibility increases again to from 20 to 27 fathoms. Some allowance should be made for the elevation of the sun at the time of observation.
Mill has shown that in the North Sea off the Firth of Forth the average depth of visibility of a disk in the winter half-year was 4; fathoms and in the summer half-year 62 fathoms, and, although the greater frequency of rough weather in winter might tend to obscure the effect, individual observations made it plain that the angle of the sun was the main factor in increasing the depth to which the disk remained visible.
Fol and Sarasin detected the last traces of sunlight in the western Mediterranean at a depth of 254 to 260 fathoms, and Luksch in the eastern Mediterranean at 328 fathoms and in the Red Sea at 273 fathoms. The chief cause of the different depths to which light penetrates in sea-water is the varying turbidity due to the presence of mineral particles in suspension or to plankton.
Buchanan found a mean of 20 experiments made by piezometers sunk in great depths on board the " Challenger " give a coefficient of compressibility K=491 X 107; but six of these experiments made at depths of from 2740 to 3125 fathoms gave K=480Xio 7.
The compressibility is in itself very small, but so great in its effect on the density of deep water in situ that the specific gravity (0 0 /4°) at 2000 fathoms increases by o 017 and at 3000 fathoms by o 026.
In other words, water which has a specific gravity of 1 0280 at the surface would at the same temperature have a specific gravity of 1 0450 at 2000 and I 0540 at 3000 fathoms. If the whole mass of water in the ocean were relieved from pressure its volume would expand from 319 million cub.
The radio-activity of sea-water is extraordinarily small; indeed in samples taken from 50 fathoms in the Bay of Danzig it was imperceptible, and R.
When these processes continue for a long time in deep water shut off from free circulation so that it does not become aerated by contact with the atmosphere the water becomes unfit to support the life of fishes, and when the accumulation of putrefying organic matter gives rise to sulphuretted hydrogen as in the Black Sea below 125 fathoms, life, other than bacterial, is impossible.
The water from the greatest depths of the Black Sea, I160 fathoms, contains 6 cc. of sulphuretted hydrogen per litre.
Dittmar's analysis of the " Challenger " samples indicated an excess of oxygen in the surface water of high southern latitudes and a deficiency at depths below 50 fathoms.
The amount of carbonic acid in solution may also be increased by submarine exhalations in regions of volcanic disturbance, but it must be remembered that the critical pressure for this gas is 73 atmospheres, which is reached at a depth of 400 fathoms, so that carbonic acid produced at the bottom of the ocean must be in liquid form.
frequently the case in fjord basins; for instance, in the Gullmar Fjord at a depth of 50 fathoms with water of 34.14 per mille salinity and ' Meddelelser om Gronland (Copenhagen, 1904), p. 331.
The use of a sliding weight is not recommended in depths much exceeding 200 fathoms on account of the time required and the risk of the line sagging at a low angle and so stopping the weight.
In deep water the closing mechanism is usually actuated by a screw propeller which begins to work when the line is being hauled in and can be set so as to close the waterbottle in a very few fathoms. A small but heavy water-bottle has been devised by Martin Knudsen, provided with a pressure gauge or bathometer, by which samples may be collected from any moderate depth down to about roc fathoms, on board a vessel going at full speed.
Buchanan pointed out in 1876, that the great contrasts in surface salinity between the tropical maxima and the equatorial minima give place at the moderate depth of 200 fathoms to a practically uniform salinity in all parts of the ocean.
In the North Atlantic a strong submarine current flowing outward from the Mediterranean leaves the Strait of Gibraltar with a salinity of 38 per mille, and can be traced as far as Madeira and the Bay of Biscay in depths of from 600 to 2800 fathoms, still with a salinity of 35.6 per mille, whereas off the Azores at equal depths the salinity is from 0.5 to 0.7 per mille less.
In the tropical and subtropical belts of the Atlantic and Indian Oceans south of the equator the salinity diminishes rapidly from the surface downwards, and at 500 fathoms reaches a minimum of 34.3 or 34.4 p e r mille; after that it increases again to 800 fathoms, where it is almost 34.7 or 34.8, and this salinity holds good to the bottom, even to the greatest depths, as was first shown by the " Gauss " and afterwards by the " Planet " between Durban and Ceylon.
Our knowledge of the Pacific in this respect is still very imperfect, but it appears to be less salt than the other oceans at depths below 800 fathoms, as on the surface, the salinity at considerable depths being 34.6 to 34.7 in the Western part of the ocean, and about 34.4 to 34.5 in the eastern, so that, although the data are by no means satisfactory, it is impossible to assign a mass-salinity of more than 34.7 per mille for the whole body of Pacific water.
This can be used with certainty to 02° C. for water down to 250 fathoms, after taking account of the slight disturbance produced by the expansion of the greatly compressed deep water.
Aime showed that on a calm bright day in the Mediterranean the temperature rose o 1° C. between the early morning and noon at a depth of about 12 fathoms. Luksch deduced a much greater penetration of solar warmth from the comparison of observations at different hours at neighbouring stations in the eastern Mediterranean, but his methods were not exact enough to give confidence in the result.
How closely two bodies of water at different temperatures may come together is shown by the fact that in the Baltic in August between 10 and 11 fathoms there is sometimes a fall of temperature from 57° to 46.5° F.
The observations of Aime in 1845 and of Semmola in the Gulf of Naples in 1881 show that the surface water in winter cools until the whole mass of water from the surface to the bottom, in 1600 fathoms or more, assumes the same temperature.
Thus at 300 fathoms greater differences than 9° F.
and 50 S., in Boo fathoms the differences are less than 5.5° and in 1500 fathoms less than 2°.
the temperature at loo fathoms is only 52° F.
Curve B shows the typical distribution of temperature in an enclosed sea, in this case the Sulu Basin of the Malay Sea, where from the level of the barrier to the bottom the temperature remains uniform or homothermic. Curve C shows a typical summer condition in the polar seas, where layers of sea-water at different temperatures are superimposed, the arrangement from the surface to 200 fathoms is termed FIG.
dichathermic (SL a, apart), from 1000 to 2000 fathoms it is termed katathermic (Kai-6, down).
The nature of the change of temperature with depth below 2500 fathoms is entirely dependent on the position of the sub-oceanic elevations, for the rises and ridges act as true submarine watersheds.
As the Arctic Basin is shut off from the North Atlantic by ridges rising to within 300 fathoms of the surface and from the Pacific by the shallow shelf of the Bering Sea, and as the ice-laden East Greenland and Labrador currents consist of fresh surface water which cannot appreciably influence the underlying mass, the Arctic region has no practical effect upon the bottom temperature of the three great oceans, which is entirely dominated by the influence of the Antarctic. The existence of deep-lying and extensive rises or ridges in high southern latitudes has been indicated by the deep-sea temperature observations of Antarctic expeditions.
in 61° S., 63° W., at a depth of 2018 fathoms. The conditions of temperature in the South Atlantic are characteristic. South of 55° S.
in approximately 3000 fathoms the bottom temperature is 31.1° F.; in the Cape Trough it is 32.7° in 45° S., and 33.8° to 34.3° in 35° S., while north of the Walfisch Ridge and east of the South Atlantic Rise bottom temperatures of 36° to 36.7° F.
in depths of 2700 fathoms or more, but north of 35° S.
Thus in the Central American Sea below 93 o fathoms, the depth on the bar, no water is found at a temperature lower than that prevailing in the open ocean at that depth, viz.
39.6° F., not even at the bottom of the great Bartlett Deep in 3439 fathoms. Such homothermic masses of water are characteristic of all deep enclosed seas.
Thus in the Malay Sea the various minor seas or basins are homothermic below the depth of the rim, at the temperature prevailing at that depth in the open ocean: in the China Sea below 875 fathoms with 36.5° F.; in the Sulu Sea (depth 2550 fathoms) below 400 fathoms with 50 5° F.; in the Celebes Sea below 820 fathoms with 38.6° F.; in the Banda Sea below 902 fathoms with 37.9° F.
In other enclosed seas which are shut off from the ocean by a very shallow sill the rule holds good that the homothermic water below the level of the sill is at the lowest temperature reached by the surface water in the coldest season of the year, provided always that the stratification of salinity is such as to permit of convection being set up. To this group belongs the Arctic Sea; the Norwegian Sea is homothermic below J50 fathoms at 29.8° F., but this cold water does not penetrate into the Arctic Basin on account of the ridge between Spitsbergen and Greenland, and there the water below 1400 fathoms has a temperature of 30 6° to 30.7° F.
The Mediterranean Sea also belongs to this group; its various deep basins are homothermic (at the winter surface temperature) below the level of their respective sills - the Balearic Basin below 190 fathoms at 55° F.; the Eastern Basin below 270 fathoms at 55.9° F; the Ionian Sea at 56.3° F.; and at 56.7° south of Cyprus.
Similarly in the Red Sea the water below 380 fathoms is homothermic at 70.7° F.
The temperature at 550 fathoms is raised to 49° or 50 F.
has been observed by Matthews: - It is noticeable that there is a marked vertical temperature gradient only at the end of summer when a warm surface layer is formed, though in August 1904 that was only 8 fathoms thick.
per hour, the drift-current depth in latitude 5° would be approximately 104 fathoms, in latitude 15°, 55 fathoms, and in latitude 45° only from 33 to 38 fathoms. A strong wind of 38 m.
an hour would produce a drift-current depth of 82 fathoms in latitude 45°, and a light breeze of 3 m.
an hour only 22 fathoms. It follows that a pure trade-wind drift cannot reach to any great depth, and this seems to be confirmed by observation, as when tow-nets are sunk to depths of 50 fathoms and more in the region of the equatorial current they always show a strong drift away from the side of the ship, the ship itself following the surface current.
Vertical movements are also produced by difference of temperature in the water, but these can only be feeble, as below 'coo fathoms the temperature differences between tropical and polar waters are very small.
The existence of a layer of water of low salinity at a depth of 500 fathoms in the tropical oceans of the southern hemisphere is to be referred to this action of the melting ice of the Antarctic regions.
i bore is commenced at the dip, and reaches a seam of coal A, at 40 fathoms; at this depth it is considered proper to remove nearer to the outcrop so that lower strata may be bored into at a less depth, and a second bore is commenced.
i was 40 fathoms in depth, we multiply the depth by the rate of inclination, 40 X 8 = 320 fathoms, which gives the point at which the coal seam A should reach the surface.
But there is generally a certain depth of alluvial cover which requires to be deducted, and which we call a fathoms, then (40 - 3 =37)X 8 = 296 fathoms; or say 286 fathoms is the distance that the second bore should be placed to the rise of the first, so as to have, for certain, the seam of coal A in clear connexion with the seam of coal B.
The Kerguelen plateau rises in many parts to within 1500 fathoms of the surface of the sea.
The anchorage is fairly protected from the sea, but the depth of water is only 3 to 4 fathoms. The channel between the island on Diu and the mainland is navigable only by fishing boats and small craft.
long, in 20 fathoms of water, protecting the harbour on the south and west.
They bought practically all of what is now Essex county from the Indians for "fifty double hands of powder, one hundred bars of lead, twenty axes, twenty coats, ten guns, twenty pistols, ten kettles, ten swords, four blankets, four barrels of beer, ten pairs of breeches, fifty knives, twenty horses, eighteen hundred and fifty fathoms of wampum, six ankers of liquor (or something equivalent), and three troopers' coats."
and the Asiatic mainland, all rest on a great submerged bank, nowhere more than ioo fathoms below sea-level, which may be considered a continuation of the continent; while to the east the depth of the sea has been found at various places to be from 1000 to 2500 fathoms. As the value of this fact was particularly emphasized by Wallace, the limit of the shallow water, which is found in the narrow but deep channel between Bali and Lombok, and strikes north to the east of Borneo, has received the name of "Wallace's Line."
The town is traversed by canals, and the harbour, which has from 4 to 8 fathoms water, is landlocked by several islands.
The eastern region is characterized by great uniformity of depth; the 2000-fathom line keeps close to the American coast except off the Isthmus of Panama, whence an ill-defined ridge of less than 2000 fathoms runs south-westwards, and again off the coast of South America in about 40° S., where a similar bank runs west and unites with the former.
Practically the whole of the north-east Pacific is therefore more than 2000 fathoms deep, and the south-east has two roughly triangular spaces, including the greater part of the area, between 2000 and 3000 fathoms. Notwithstanding this great average depth, the " deeps " or areas over 3000 fathoms are small in number and extent.
Depths of less than 2000 fathoms occur continuously on a bank extending from south-eastern Asia, on which stands the Malay Archipelago.
The most considerable areas over 3000 fathoms are the Aldrich deep, an irregular triangle nearly as large as Australia, situated to the east of New Zealand, in which a sounding of 5155 fathoms was obtained by H.M.S.
A long strip within the Tuscarora deep forms the largest continuous area with a depth greater than 4000 fathoms. All the rest of the western Pacific is a region of quite irregular contour.
The average depth varies from 1500 to 2500 fathoms, and from this level innumerable volcanic ridges and peaks rise almost or quite to the surface, their summits for the most part occupied by atolls and reefs of coral formation, while interspersed with these are depressions, mostly of small area, among which the deepest soundings recorded have been obtained.
The United States telegraph ship " Nero," while surveying for a cable between Hawaii and the Philippines, sounded in 1900 the greatest depth yet known between Midway Islands and Guam (12° 43' N., 1 45° 49' E.) in 5269 fathoms, or almost exactly 6 m.
In the Sulu Sea, for example, a temperature of 10.3° C. is reached at 400 fathoms, and this remains constant to the bottom in 2500 fathoms.
The Golfo Dulce has an average depth of too fathoms and contains no islands.
The Tempisque enters the Pacific at the head of the Gulf of Nicoya, and tends to silt up that already shallow inlet (5-10 fathoms) with its alluvial deposits.
It was therefore equal to 79,200 in., and divided decimally into 10 furlongs 100 chains, or 1000 fathoms. For the existence of this fathom (half the Belgic pertica) we have the proof of its half, or yard, needing to be suppressed by statute (9) in 1439, as "the yard and full hand," or about 40 in., -- evidently the yard of the most usual old English foot of 13.22, which would be 39.66.
The depth ranges from 18 to 19 fathoms at the entrance to 42 fathoms along the inner shore line.
The depth of water at the main entrance is 41 to 5 fathoms and in the western bay 3 to 4 fathoms. For lack of docks and quayage, large vessels lie off Steamer Point and all cargo is handled by means of lighters, the labour being either Somali or Arab.
There are no good harbours, and the only anchorage for large vessels is Tai-chung, or Yung-su, at the east end, with 9 to 13 fathoms of water.
Some are littoral, living between tide-marks; others are found at very various depths, up to 2800 fathoms. A few species have invaded the fresh waters, while the pulmonate and terrestrial Gastropods are distributed over the whole surface of the land in all latitudes and to a height of 15,000 ft.
The harbour is eleven to thirteen fathoms deep at the entrance (indicated by a lighthouse), decreasing to five fathoms near the shore.
broad, and 20 fathoms deep, on the borders of SchaumburgLippe; the Dummersee, on the borders of Oldenburg, about 12 m.
There is anchorage for steamers in 5 to 6 fathoms. Vessels were loaded and discharged by lighters from the beach.
The north part of the sea is very shallow, and between the southern promontory of Istria and Rimini the depth rarely exceeds 25 fathoms. Between Sebenico and Ortona a well-marked depression occurs, a considerable area of which exceeds Ioo fathoms in depth.
The deepest part of the sea lies east of Monte Gargano, south of Ragusa, and west of Durazzo, where a large basin gives depths of 500 fathoms and upwards, and a small area in the south of this basin falls below 800.
The mean depth of the sea is estimated at 133 fathoms. The bora (north-east wind), and the prevalence of sudden squalls from this quarter or the south-east, are dangers to navigation in winter.
Neomenia and its allies are marine animals living at depths of 15 to Boo fathoms on soft muddy ground; they are found crawling on corals and hydrozoa, on which they feed.
4, by an average radius of 1200 Dutch fathoms (7874 ft.) from the outer glacis of the fortress.
around being then only three fathoms deep. Lying in the fairway of vessels making or leaving the Tay and Forth, besides ports farther north, it was a constant menace to navigation.
This is the shallowest part, barely reaching a depth of 20 fathoms. It is being gradually 1 By the triangulation of 1840 its level was found to be 84 ft.
lat.) reaches 437 fathoms. This, the middle section of the Caspian, which extends as far as the Apsheron peninsula, receives the Terek and several smaller streams (e.g.
It is separated from (3), the southern and deepest section of the Caspian, by a submarine ridge (30 to 150 fathoms of water), which links the main range of the Caucasus on the west with the Kopet-dagh in the Transcaspian region on the east.
The depth in this section ranges from 300 to 500 fathoms, with a maximum of 602 fathoms.
The Knipovich expedition in 1004 found no traces of organic life below the depth of 220 fathoms except micro-organisms and a single Oligochaete; but above that level there exist abundant evidences of rich pelagic life, more particularly from the surface down to a depth of 80 fathoms.
from Baku was 72.9°, but that below io fathoms it sank rapidly, and at 200 fathoms and below it was constant at 21.2°.
Kinsale, with the neighbouring villages of Scilly and Cove, is much frequented by summer visitors, and is the headquarters of the South of Ireland Fishing Company, with a fishery pier and a commodious harbour with 6 to 8 fathoms of water; but the general trade is of little importance owing to the proximity of Queenstown and Cork.
The channel between Cape Bon in Tunis and the south-west of Sicily (a distance of 80 m.) is, on the whole, shallower than the Straits of Messina, being for the most part under 100 fathoms in depth, and exceeding 200 fathoms only for a very short interval, while the Straits of Messina, have almost everywhere a depth exceeding 150 fathoms. The geological structure in the neighbourhood of this strait shows that the island must originally have been formed by a rupture between it and the mainland, but that this rupture must have taken place at a period long antecedent to the advent of man, so that the name Rhegium cannot be based even on the tradition of any such catastrophe.
It is the most numerous genus, and consists for the most part of shallow-water (less than 50 fathoms) tropical and subtropical forms. They often live in tubular burrowings in coral-rock.
At more than one point a depth exceeding 1000 fathoms has been ascertained.
Its port has a depth of 4 to 6 fathoms, and a roadstead 32 m.
wide, and sending three arms inland which are from 40 to 160 fathoms deep, as well as Clayoquot, Esperanza, Kyuquot and Quatsino Sounds, which also penetrate deeply into the island.
It is tidal, spring tides rising about 9 ft.; the water is somewhat salter than the Indian Ocean, and seldom exceeds 10 fathoms in depth; with the exception of the Shatt al `Arab, the Jarrahi and the Hindiyan rivers, which mingle their waters with those of the sea at the W.
Pearling Industry.-The pearling grounds of Bahrein are in over six fathoms of water, mostly beyond the three-mile limit.
in width, with a depth of about seven fathoms at low water, are situated at either end of the detached breakwater.
The coral banks which surround Sokotra and The Brothers are united and are not more than 30 fathoms below sea-level; a valley some loo fathoms deep divides them from the bank around Abd-el-Kuri, while between Abd-el-Kuri and Cape Guardafui are depths of over 500 fathoms.
Outside the delta, in the Bay of Bengal, is a deep depression known as the " swatch of no ground "; all around it the soundings are only of 5 to io fathoms, but they very rapidly deepen to over 300 fathoms. Mr J.
The depth of the sea around the shore rarely exceeds a maximum depth of 1 to 3 fathoms, and the coast as a whole offers few accessible ports.
At a great distance from its mouth it has still a depth of three fathoms, and in all its physical features it is comparable to the Kapuas and Barito.
The depth in the main entrance varies from 10 to 17 fathoms, and vessels drawing 20 ft.
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