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FISHERIES AND MARINE SERVICE
Translation Series No. 3818
I. Morphology of the ocean and distribution
of water masses
by Keiji Nasu
Original title:
From:
I. Kaiyo no keitai to suikai bunpu
Oceanic Environments and Living Resources in the World
p. 3-10, 1975
Translated by the Translation Bureau( HCK/RR )
Multilingual Services Division
Department of the Secretary of State of Canada
Department of the Environment
Fisheries and Marine Service
Pacific Biological Station
Nanaimo, B.C.
1976
15 pages typescript
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F I 1,1 1^TRANSLATED FROM - TRADUCTION DE
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English
AUTHOR - AUTEUR
Kei j i NASU
TITLE IN ENGLISH - TITRE ANGLAIS
Oceanographic Environments and Living Resources in the World:
1.
Morphology of the Ocean and Distribution of Water masses
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Oceanographic Environments and Living Resources in the World
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Sekai no kaiyô kanky3 to siLlen seibutsu (Oceanographic Environments and Living esources in the World),
pp. 3-10.
OCeanographic . Environments and Living Resources in the World:
I. Morphology of the Ocean and Distribution of Water Masses
by Keiji NASU
1.
Area
• The oceans occupy 70.8%, or approximately two-thirds,
of the earth's surface area, but their distribution is nonhomogeneous. To wit, the proportion of the earth's surface
area covered by ocean is smaller in the northern hemishphere
60.7% - and greater in the soutnern hemisphere - 80.9%.
More-
over, there is a large variation by latitude. As is shown in
• UNEDITED TRANSLATION
For informat;cri enly
YIZADUCTION I■ ICN REViSEr:
Inforiradion teulotwerd'
:•05..203-t 0-.31
3
2
Table 1-1, the proportion is smallest, in the northern hemisphere, for latitudes 65
70 0 1
(28.7%), and generally in-
4
creases, with the exception of high-latitude oceanographic
regions north of 70 0 E, as the equator is approached.
On the
other hand, in the Southern hemisphere, while high latitude
regions exhibit the smallest proportion of earth's surface area
covered by ocean (with a minimum value of 10.7% for 8O- 75 N*),
as in the northern hemisphere, the proportion in general decreases
as the equator is approached.
Table 1-1
Distribution of ocean and land in 5 0 steps (Kossinna 1921) .
mrthern hgAishztre
Iedtcude» Ocean, Land Ocean Land
rIU° knirj
0. 979
85 ,-80
Land
Ocean
(15-b
Land
0. 978
100. 0
Ocean
Fry
100. 0
2. 145
0. 384
86. 9
13. 1
3. 742
1. 112
77. 1
22. 9
0. 522
4. 332
10. 7
89. 3
4.414
2.326
65. 5
34. 5
2. 604
4.136
38.6
61.4
2.456
6.116
28.7
71. 3
6.816
1. 756
79. 5
20. 5
65 ,-60
3.123
7.210
30.2
69.8
10. 301
0. 032
M. 7
0.3
60-55
5.399
6.613
45.0
55. 0
12. 006
0. 006
99.9
0. 1
55-50
5. 529
8. 066
40. 7
59. 3
13. 388
0. 207
98. 5
1.5
50 ,45
6.612
8.45S
43.8
56. 2
14. 693
0. 377
97. 5
2.5
8.411
8.016
51.2
48. 8
15. 833
0. 594
96..4
3. 6
40 ,45
10.029
7.627
56.8
43. 2
16. 483
1. 173
MA
6. 6
35,-30
10. 806
7. 943
57. 7
42. 3
15. 782
2. 967
84. 2
15. 8
11. 747
7. 952
59. 6
40.1
15.438
4.261
78. 4
21.6
75 ,-70
.0cean
Southern hemisu.here
2. 929
100. 0
25,-20
13. 354
7. 145
65. 2
34, 8
15. 450
5. 049
MA
24. 6
20,-15
14.981
6.164
70.8
29.2
16. 147
4.998
76..1
23. 6
15 ,-10
16. 553
5. 080
76. 5
23.5
17.211
4.422
79. 6
20. 4
10 ,-, 5
16.628
5. 332
75. 7
24. 3
16.808
5.062
76A
23. 1
5,-• 0
17. 387
4. 737
78. 6
21. 4
16. 792
5.332 1 75.9
24. 1
90 ,-.0' 154.695 M0.281
60.7
39.3 206.364
361.059 X 10 6 km 2 (70.8%)
148.892 X 10.6 km 2 (29.2%)
* translators note: sic
48. 611.
80. 9
19. 1
-
Laad
3
Moreover, while the average depth of water in the world's
oceans has been calculated to be approximately 3800 m, this distribution also exhibits large geographical variations. These
variations, in average and maximum ocean depth, area, and volume,
are clearly shown in Table 1-2 for the Pacific,-Atlantic, and
Indian Oceans, and for other oceanographic regionsa Also, of the
Table 1-2
Depth, area, and volume of the principal oceans of the world
-(Kossinna 1921)
Oceanoraphic region
Area
Average depth
Volume
2
(10" km ) (10n km3)
paGifià,_:0ceanft
'
Atlant.ic 0 cea.n*_-__;
Indian
Arctic Ocean---- _-----American Mediterranean___'
Mediterranean - Black
Australia-Asiatic I4Ied. __
Red sea
Persian Gulf _
Bering Sea
Sea of Okhotsk.
Sea of Japan
East China Sea
( m) - `
179.679
106. 463
74. 917
723.699
354. 679
291. 945
4, 028
14. 090
16. 980
1, 205
4. 319
2. 966
8.143
9. 573
4. 238
9. 873
2,216
0. 438
0. 239
2. 568
1. 528
1. 008
1. 249
0. 215
0. 006
3. 259
1. 279
1. 361
0. 235
1, 370.323
361. 059
I
3, 332
3,897
1,429
Maximum depth.
=- / (m)
11, 033
9,199
7, 480
5, 440
6, 415
1, 212
4,404
7, 315
491
2,211
25
1,437
838
1,350
188
91
3, 575
3, 374
3, 610
2, 631
3, 795
11, 034
all seas*
* including adjacent seas
three great oceans shown above - Atlantic, Pacific, and Indiwn the maximum values of areaf volume, and depth occur in the Pacific,
with the greatest depth in the world observed up to the present
time beint; the 11, 034 cn of the Mariana Trench.
4
Table I-3 shows the per cent of ares.::c by depth for
the Atlantic, Pacific, and Indian Oceans.
The percent of
area. for the continental shelf is greatest in the Atlantic, wi -th
132-3%; it is
5.7t in the Pacific, and 4.2% in the Indian Ocean;
the average for all oceans is 7.6%. Moreover, the area for water
63pths, of less than 100 m
depths currently considered suitable for
_development of deep-sea resouxas»isalsogreatest in the Atlantic, with
7.1%, followed by 3.1% in both the Pacific and Indian Oceans,
and an average value of less than 4.3% for all oceans. However,
the area for depths of 4000 - 5000 m, corresponding to the sea
bed, accounts for 33.0% - the greatest percentage - of total
sea area, and this holds true also for each of the three great
oceans, Atlantic, Pacific, and Indian.
Table I-3
Distribution of depth in the Pacific, Atlantic, and
Indian Oceans
Depth
\ PaCific‘Atlantic,Indian All seas
0- 200m
200,-1, 000
1, 000,-2, 000
2, 000.-3, 000
3, 000-4, 000
4,000.-5, 000
5, 000-6, 000
6, 000-7, 000
> 7,000
5.7
3. 1
3.9
5.2
18. 5
35. 2
26. 6
1.6
0. 2
13. 3
4.2
7. 1
5.3
3. 1
3.4
8. 8
18. 5
25. 8
20. 6
7. 4
24. 0
38. 1
19. 4
0.4
0. 6
7.6
4.3
4. 2
6.8
19.6
33. 0
23.3
1. 1
0.1
5
2.
2'opo6ra2 y of the ocean floor
It is well itnown that water depth and topography are
important conditions in the formation of fishing grounds. Particulars will be dealt:,with later, but the phenomenon or upWell3.n.g
currents which develop in the vicinity of archipelagoes and
capes, and also on the continental borders and around features
which project sharply from the flat sea bed, has been well
clarified, both experimentally and theoretically.
Moreover,
according to recent theoretical research (Kishi, Matsunobara
1973), the development of
currents in submarine can-
yons nas oeen clarified, and Soviet survey reports show also
that, in terms of the fishing industry, development of bottomfish resources lying along submarine canyons is promising.
Productivity is generally high in continental shelf
regions of depth less than 200 m, with the formation of fishing
grounds favorable for surface and bottom fish. Moreover, water
depth is also a limiting factor in bottom fish trawling
grounds,
with operations generally being carried out at
present down to depths of 500 - 600 m. However, trawling operations at depths of greater than 600 m are also being realized,
and since 1975 surveys of the "Shinkai Maru"
(3345 tons), with
the principal ^,im of developing deep-sea trawline grounds, have
also entered the stage of practical implementation. 4ith this
sort of background, submarine topography will become pa.rticularly
important in trie development of future fisning grounds for surface
and oottom,.fish.
Accordin6,ly, as foreign literature comprises
6
the principal source of diverse literature on the subject,
the following is a brief list of English-language terminology
relating to submarine topography.
As is shown in Diagram I-1, submarine topographical
features can be broadly classified into four groups:
(1)
Continental shelf; (2) continental slope; (3) oceanic
plateau; and (4) trenches.
Diagram I-1
Land and sa depth curve
- - -
'>4119
6
•
1
6
4
.
-
2
1, ° \.....
-2
-
(
6
-8
10
Fl-
14,
0
(3) oceanic
(1)
(2) continental slope
continental shelf
(4) deep-sea region
plateau
(1)
Continental shelf: indicates tne shallow region corres-
ponding to the borders of tne continents, up to the area where
the slope leading to tne deep sea increases abruptly.
In general,
water depth above the continental shelf is about 200 m or less,
but as the definition includes the area where the continental
slope increases abruptly, depths of 100 m or less are also
observed.
only
The area of the continental shelf comprises
of the area for all seas, but the distribution density
of life is extremely hi gn and is extremely important for the
6
7
fishing industry.
Diagram I-2 shows the world distribution.
Diagram 1-2
1Vjrid continental shelf distribution
hatched lines
(2)
the region extending from the borders
Continental slo-pe:
of the continental shelf out to the area adjoining the oceanic
plateau having depths in the vicinity of 2500 m. Slope of the
ocean bottom is generally steep, with an average slope of 3°- 40.
(3)
Oceanic plateau: the extremely gently sloping ocean-bottom
plateau extending from water depths of 2500 m out to
approximately 6000 m.
The area occupied is extremely large,
amounting to 78% of the total ocean area.
(4)
lleep-sea rfLion:
in general, the region comprised of depths
of water of 6U00 m or greater. In many cases formed close
to
the continents.
The above is a broad classification of submarine topography into four main 6roups, but in detail, tne presence of
rugged formations provides for even more complexity. Rccordingly,
7
8
as topography relating to the production of marine products
is particularly important, the following is an explanation of
tnose topographic features lying in the vicinity of islands
and projecting - from the ocean floor.
(1)
Island shelf: topography extending out from island and
archipelag-o coast-lines to the point whereLtheSea-bedzslope;.out to
thedeep Searincreasesabruptly.
(ii)
Island slope: slope from the periphery of the island shelf
out to the deep-sea region.
long and broad sea-bed region protruding from the
(iii)Rise:
ocean floor, having smooth and gentle sea-bed slope as sides.
Ridg2:
long and narrow sea-bed feature projecting from
the ocean bottom. Side slopes are steep, corresponding to continental mountain ranges.
Depths of water above the peaks vary
with location, but in general are less than 2000 m.
(v) Plateau: summits are extremely broad and flat projections,
with peripheral areas having relatively steeply:4-oping surfaces.
(vi)Sea mount: isolated projections on the sea bed of 1000 m or
greater.
(vil)Seapeak,:.(or crest): sea mount wnose highest peaks are
pointed.
In general, horizontal sections are circular or ellipt-
ical in shape.
(viii)Shoal:
•
indicates protruding submarine topographic features
lying in a relatively narrow region. In some cases may be navigational hazards;
good
fishing grounds for tuna and bonito.
9
(ix)
Banx: Sea ridges of small stature. Bottom texture is usua?_lxT muddy, with no
dangerous reefs.
(x)
Reef:
Like the shoals, productivity is hi^li, narticularly for trawl fishnzq.
formed of rocks and coral reefs, and occasionally
exposed above the surface of the sea; a navigational hazard.
(xi)
Guyot, tablemount:
the development of echo sounding has
provided a clear understanding of the complex topographical
features comprising the ocean floor. Namely, foll.owin.g the
Second World War, circular or elliptically shaped summits
of heights of the order of 3000 m have been discovered projecting from the ocean floor in the Western Pacific at depths
of 5000 m or greater; these have been named guyots.
The above is a listing of the main submarina topographical
features, and of these, the continental shelves and topographic
features projecting from the ocean floor are in general highly
productive regions.
For example, the inflow of nutrient salts from the land
to the continental shelf is large, and there is vigorous mixing
of sea water due to waves, current, and tide. In addition, since
sun-light reaches nearly to the ocean bottom, there is a phenomenal proliferation of plankton. Also, environmental conditions
are favorable for the proliferation and growth of young fish,
providing good fishing grounds
for surface fish such as
sardines and mackerel, bottom fisn such as flounder, dnd also for
shellfisn.
8
Trawling grounds have already been established, through
the development of recent fishing technology, on the continental
slopes at depths up to 500 - 600 m, but due to the lack of data
on biota
at depths greater that 500 - -600 m, future
developmental research is anticipated.
Prejecting7.submarinefeatures such as reefs, shoals, and
sea mounts are higaly productive regions, due to the formation,
in general, of upflowing currents, which,bringdeep-waterUayers
abundant in nutrient salts upward into the layer of sunlight
penetration. Consequent/y, the discovery and developmental
study of these types of projecting submarine topographical features
have.an important significance in the devel9pment of new fishing
grounds.
Also, while some data. has been obtained on the distribution of guyots, as these are eea-bed regions which become abruptly
shallow, as discussed previously, inference-4 of their existence
from marine charts, particularly in Offshore waters, where there
are few sounding points, is extemely difficult. .Consequently, the most efficacious
technique for the discovery Of guyots was implenented in the Pacific during the
Second World War by Dr. Hess of Princeton University, involving
the continuous utilization of echo sounding.
In way of reference,
the following is a listing of the main oceanographic regions over
which guyots are presently known to be distributed:
Be t ween th e Hawaiian and Mariana island groups;
ographic region south of the Aleutian chain;
the ocean-
the Gulf of Alaska;
the Gulf of California in North. America; the Southwest Pacific;
and the Northwest Indian Ocean.
il
3.
Distribution of water masses
Diagram 1-3 shows the boundaries of the water masses
.
which occur in the world's oceans, and Diagram 1-4 shows the
(1) for trie principal water masses in each of the
.cunres
T-S
oceans. These diagrams are from Sverdrup (1346),
and the
following is a short.sumary.
The central water masses in each of the oceans develop
in the vicinity of the subtropical convergences which are distributed in the 35 ô - 45° 1atitude belts in both the northern and
southern hemispheres.
The T-S
curves
for the central water
masses in the South Atlantic, Indian, and Western South Pacific
oceans, as shown in Diagram 1-4, all present similar patterns:
this is due to the similar conditions of atmospheric circulation and heating and cooling effects, etc., of the offshore seas.
In addition, the fact that -the Eastern South Pacific central
Water mass is
low
in
is due to the phenomenon of mix-
salinity
ing with the Peru Current, the northward-moving, low salinity
-
Subantarctic water mass.
The fact that the high salinity
-
low salinity
-
North Atlantic and
Central Water masses are completely different has
its origin in differences in atmospheric circulation and the
anounts of precipitation and evaporation, and is particularly related to
the distribution of land ancl oceans in high latitudes.
12
Dia6ram I-3
Boundary distributions of upper-surface water masses
in the oceans (Sverdrup et al., 1942)^
WC,'AN CEr4ipAL WATEA
Fi0g, 4. Approximate boundaries of the ui+per water masses of the ocean. Squares indicate the re,ions in which
the central water masses are formed: crosses indicate the lines along which the antarctic and arctic intermediate
waters sink (S^^erdrup. Johnson and Fleming, 1942). Ë^rrCIWS 1nCliclte the direction of slnlcinC7.
-
Diagram I-4
T-S curves of the principal water masses in the Pacificp
Atlantic, and Indian Oceans (Sverdrup et al., 1946)
^
^+• SUBARCTK WATER
Af:AFCT^ INTE•C.\(CDeATE W
N A. OEE?I L BOTTCkA WATFR
---^-- F_CIRCUA1PCLfv1 WAT°_R (cx• I ep
*`l'ranslator's note: The figures in the Japariese text are the szne as those
fotnlcl in the ^,iicyclopedi.a of 0cean raL_Lhhy, which have been used here for
convenience.
13
The Subantarctic Water mass is distributed in the region
which lies between the Antarctic Convergence and the central
water masses in the oceans of the southern hemisphere; it is
thought that it ha s its origins in the Antarctic Ocean.
ition it is believed that this ici-salinit
In add-
Subantarctic Water
mass is formed through mixing and vertical circulation which
occurs in the oaean region lying between the _Subtropical Convergence and the Subantarctic Convergence.
Additionally, the Antarctic Convergence in the southern
hemisphere forms the well-defined southern boundary of the Subantarctic Water mass;
in the northern hemisphere, a convergence
corresponding to this discontinuous curve is found onlY in the
Western Atlantic, and in the majority of ()dean regions no welldefined boundary of the Subarctic Water mass exists.
.
As Table I-1 clearly indicates, these comparative differ-
ences in the northern and southern hemispheres nave their origins
in the differing distributions of land and ocean, it is believed.
The intermediate waters lie in the lower layers of the
central water masses common to each of the oceans, and of these,
the Antarctic Intermediate water is the most widely distributed.
lamimal
salinity is
a
distinguishing characteristic of the
Antarctic Intermediate water, but tnis characteristic vanishes
as one travels nortaward away from the Antarctic Convergence.
In the Atlantic Ocean it extends to the vicinity of 20 N, and
in the Indian and South. _Pacific oceans, it extends to 10 0 3 .
14
The
minima1
salinity of the Hquatorial Water mass found
in the Pacific is interpreted as indicating the n.orthern
boundary of the intermediate water.
The Arctic Intermediate Water in the North Atlantic,
symmetrical with the South. Pacific, forms eastward of the
Grand Banks which lie off the coast of Newfoundland; being
of small size, this is restricted to the Northwest Atlantic:
On the other hand, the Arctic Intermediate Water in
the North Pacifi.c is distributed over the ocean region from
20.`> to 40rj N, with the exception of the Subarctic Intermediate
Water which extends soutin off
the west coast of America.
These intermediate waters develop pri.marily,.in the Subarctic
ocean region (the ocean region which extends north from the
Subarctic boundary).
Conspicuously dense waters are f.ormed in t.ne Subarctic
ocean regions in the Atlantic and Antarctic oceans. High-density
water sinking at high latitudes in the North Atlantic continues
to expand and move southward, while sinking Antarctic Bottom
Water in the vicinity of. Antarctica moves in the opposite direction, northward, up to the vicinity of 350 N. Also, southwardmoving Deep Water in tne North Atlantic crosses the equator and
forces southward Antarctic Bottom 4rater to upwell in the Antarctic
as Warm Deep Water.
15
In this fashion, through the interchange with southward-moving North Atlantic Deep Water, Antarctic Bottom Water
and Antarctic Intermediate Water move northward, and in the
South Atlantic, Antarctic Bottom Water and Intermediate Water
mix with southward-moving Deep Water', cool, and decrease in salinity,
then nove south again
to become one of the factors in the form-
ation of Antarctic Circumpolar Water.
While no southward motion of Deep Water has been observed
in the Indian Ocean into.the southern hemisphere, north of the
equator it mixes with water masses in the Red Sea system and
*becomes a high- salinity
water mass.