The surface waters off the coast of Kerala, south-west India

Deep-Sea Research, 1967, Vol. 14, pp. 295 to 320. Pergamon Press Ltd. Printedin Great Britain.

The surface waters off the coast of Kerala, south-west India MOLLIE DARBYSHIRE (Received 30 December 1966) Abstract--The surface waters between the coast of Kerala and the meridian 72°E are studied. T-S diagrams and temperature-depth profiles are drawn. A sharp thermocline is found to be associated with the Arabian Sea Water. This occurs immediately below the surface in summer, but in winter the upper limits sink to a depth of about 100 m and the top layer is occupied by a water mass o f considerably lower salinity which is termed here Equatorial Surface Water. The movements o f this water mass can be correlated with the current system o f the north equatorial region. During the latter part o f the monsoon season and for a few weeks afterwards, there is a very strong flow of fresh water from the backwaters which extend seawards as tongues o f very low salinity water at the surface. The effect of the freshwater influx on the annual salinity pattern is discussed.

INTRODUCTION

THE SURFACE waters off the coast of Kerala show a very interesting seasonal pattern. While the surface temperature is largely determined by the amount of radiation from the sun, the subsurface temperature gradient and the surface and subsurface salinities are controlled by the movement of two water masses with the changing currents of the Arabian Sea. The coastfine is an emergent type and is formed of a number of long narrow sandbanks running parallel to the original shoreline. There are often several rows of these and between them is a complicated system of channels or backwaters. Narrow gaps exist between the islands as at the entrance to Cochin harbour. The backwaters and the rivers flowing into them extend for many miles and after heavy rainfall there is a very large volume of almost fresh water flowing into the sea. This causes a very marked lowering of the salinity of the surface water near the shore at certain times. The area studied here extends westwards from the coast to the meridian 72°E, between the latitudes 12°N and the most southerly point of the Indian subcontinent at 8°N (see maps, Fig. 1). Temperature and salinity measurements have been made in this area by the Central Marine Fisheries Research Institute using vessels of the Indo-Norwegian Project. These have been published in an OCEANOGRAPHICSTATION LIST (1962). A number of publications based on these data include : SASTRY, RAMA and MYRLAND (1959), JAYARAMANet al. (1960), RAMAMIRTHAMand JAYARAMAN (1960), and PATIL and RAMAMIRTnAM (1963). The authors of all these have concentrated mainly on drawing vertical sections of temperature, salinity and density. In the present study it is proposed rather to examine the seasonal salinity variations and to discuss the movement of two water masses with very different salinity characteristics. Data from unpublished reports of the Indian Naval Physical Laboratory, Cochin, have also been used to gain additional information mainly during the monsoon season. 295

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The stations were worked during cruises of I.N.S. Kistna as part of the programme of the International Indian Ocean Expedition. The year may be conveniently divided into four seasons, each of which will now be discussed in turn. THE

POST-MONSOON

SEASON

Very simple conditions are found in October after the period of the south-west monsoon. Coastal observations south of 9°N are the only ones available for this month. The position of five lines of stations between 8° 45'N and Cape Comorin is shown in Fig. lb. The T - S diagrams for each line separately are shown in Fig. 3, data above 100 m being differentiated from that below this depth. The temperaturedepth profiles for the line in 8° 30'N is shown in Fig. 4. There is a temperature range from 29 ° to 20°C in the top 100 metres. The greatest change of temperature with depth, i.e. the thermoeline, is found immediately below the surface and there is no mixed layer above it. The T - S diagrams show a slight decrease of salinity with depth

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in the t o p 100 metres, the salinity values at all depths decreasing t o w a r d s the south o f the area. A l o n g the line south-west o f C a p e C o m o r i n a l m o s t isohaline c o n d i t i o n s exist f r o m the surface to 500 m. I n latitude 8°N d a t a f r o m the two inner stations are shown b y m e a n s o f crosses. The o u t e r stations have the same p a t t e r n as the other lines b u t near the shore some lower salinity surface water appears. F o u r lines o f stations between 9°N a n d 9 ° 3 0 ' N were w o r k e d in the last h a l f o f September. These lines are also shown in Fig. 1 a n d the T - S d a t a is p l o t t e d in Fig. 5.

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At the offshore stations there is a similar relationship between temperature and salinity as found south of 9°N in October but at the inshore stations there is a decrease in salinity which is caused by the discharge of freshwater from the backwaters during and after the monsoon season. This effect is thus found in late September north of 9°N but is not apparent several weeks later to the south of 9°N (see Fig. 3). This could be due to the lapse of time or to the difference in volume of freshwater flow into the two areas. In late September and early October, with the exception of some inshore water near Cape Comorin, we can say that only one water mass is found above 100 m. This is the normal Arabian Sea Water which decreases in salinity from the surface downwards. Between 100 and 500 m the temperature range is from 20 ° to 10°C while the salinity changes very little, usually having a value between 35.0 and 35"5%o. This water mass is very similar to the Indian Ocean Equatorial Water described by SVERDRUP,JOHNSON and FLEMING (1942) which can be defined by the straight line on the T - S diagram joining the points 4 °, 34"90%o and 17°, 35"25%0. THE

SEASON

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SINKING

After October conditions begin to change and to become more complicated. T - S diagrams for a line of stations in about the latitude of Cochin, 10°N, worked four times during the months November to January are shown in Figs. 6-9 (for position see Fig. lb). In the top 100 metres there is now an increase of salinity with depth, the gradient becoming steeper as the season progresses. A marked salinity maximum develops at about 100 m depth and by January surface salinities as low as 30%0 are observed. This top layer becomes almost isothermal with a temperature of about 28°C. In Fig. 8 a slight temperature inversion indicates that salinity has now become the controlling factor in determining density. Temperature--depth profiles for the months of August to January are plotted in Fig. 10. Values from deep water stations in latitude 10°N have been selected wherever possible but in the early months only shallow water stations were available. From

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August to October the thermocline extends almost to the surface but during November the upper limit of the thermocline sinks to a depth of between 75 and 100 m and an isothermal layer is found above it. Figure 11 illustrates the salinity--depth profiles at each station on the four cruises mentioned. In November there is very little difference between the stations, except at the surface, but in December and January it is clear that as well as a marked vertical salinity gradient at each station, there is also an horizontal gradient at all depths, salinity increasing outwards from the coast. The lowest density water would thus be found at the surface near the shore and the surfaces of equal density would slope down towards the coast, giving a gradient current towards the north. The T - S curves for December at 12°N and January at 11 ° 15'N are shown in Fig. 12. Here again an almost isothermal layer with a steep vertical salinity gradient is found above 100 m. However the horizontal salinity gradient is negligible compared with that in the latitude of Cochin as shown in Fig. 11. °C 10

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An east-west section across the whole Arabian Sea in 8°N, in November 1962 compiled from data of the I.N.P.L. is given in Fig. 13. Low salinity surface water is only found east of 72°E in this latitude and there are steep salinity gradients in both the horizontal and vertical directions in this water mass. The temperature-depth relationship varies very little across the whole section. Three water masses can now be identified and these are illustrated very well in Fig. 6. Here there is a salinity minimum at 17°C, 34"9%o and a maximum at 26°C, 35.5%°. Indian Ocean Equatorial Water is found at temperatures less than 17°C and Arabian Sea Water between 17° and 26°C. Above these two is now a new water mass covering a small range of temperature and a large range of salinity. Since Indian Ocean Equatorial Water and the Arabian Sea Water are now found at greater depths than formerly, sinking must be taking place due to the inflow of lower density water from some other area. The current near the shore is from south to north at this season, as suggested by the density pattern confirmed by local observation, so the new water must have come from the region near the equator. As it is confined to the surface layer it will be termed here Equatorial Surface Water*. However, although relatively low salinity water is found neat the equator in all the oceans (SvERDRtJP, JOHNSON and FLEMING, 1942), the surface values do not normally fall below 34~0o. *Equatorial Surface Water is the term suggested here to describe the rather low salinity water found at the surface in the equatorial region the of Indian Ocean. This would, be comparable to the terms Tropical Water and. Subtropical Water already in use for surface waters in higher latitudes.

It should not be confused with Indian Ocean Equatorial Water which is found at mid-depths.

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To account for salinities in the range 30-34%0 as found here, there must be an addition of very low salinity water from some other area. Very low salinity water is found in the north of the Bay of Bengal during and after the north-east monsoon rains. The currents in this bay follow an anti-clockwise pattern from August to October. After this, with the re-establishment of the westward equatorial current, this pattern breaks down in the south so that during the months of November, December and January three limbs of the anti-clockwise gyral remain within the bay combined with a westward drift across the southern open end. One branch of this system thus flows down the east coast of India, turns westwards south of Cape Comorin and then possibly northwards to follow the west coast. This branch could be the means of transport of very low salinity water from the north of the Bay of Bengal to join the equatorial water flowing northwards off the coast of Kerala. The values of salinity at the maximum and minimum vary considerably with time and position. RAMAMIRTHAMand JAYARAMAN (1960) have described sinking conditions and current towards the north during the months of November to January. Here we have found that Equatorial Surface Water and its associated current was confined to the east of 72°E in the latitude of Cape Comorin and a similar situation probably exists in other latitudes as the current would tend to follow the line of the coast. The Equatorial Surface Water penetrates as far as 12°N but the current has become very weak by then. The salinity maximum at the upper limit of the thermocline is only found beyond the shelf edge so that the Equatorial Surface Water covers the whole of the continental shelf. The thermocline is directly associated with the Arabian Sea Water and does not depend solely on changes in solar radiation.

THE

SEASON

OF

STABLE

CONDITIONS

After the sinking comes atime of relatively stable conditions from February to April. In February 1958 a number of stations were worked in the region of the Laccadive Islands. The position of the stations and contours drawn from the surface salinity and salinity maximum at each station are shown in Fig. 2a. Both values increase from south to north. All stations were worked to a depth of 1500 m and a few to 2000 m. The temperature-depth profile in Fig. 14 shows that temperatures of about 4°C occur at 2000 m. The thermocline remains between 100 and 200 m and there is again an isothermal layer of temperature 28°C above this. The T - S data are plotted in Fig. 15. The straight line is the relationship for Indian Ocean Equatorial Water given by Sverdrup. Salinities seem to be slightly lower here but the agreement is quite good on the whole. The values between 17°C and 27°C correspond to the Arabian Sea Water, while above the thermocline is the Equatorial Surface Water with its steep salinity gradient. The situation remains much the same as in January. The current near the coast is illustrated in Fig. 16 where salinity--depth profiles for a line of stations in March 1960 in latitude 10° 40'N are plotted. Here, in contrast to Fig. 11, there is a decrease of salinity outwards from the coast, suggesting a gradient current towards the south. This is not so strong as the current towards the north in December and January. Another survey of the Laccadive Islands region was made in April 1959 and has been described by JAYARAMEN et al. (1960). The surface salinity and maximum salinity contours are shown in Fig. 2b and the T - S data are plotted in Fig. 17. Three

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33

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.4

-6

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34

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.4

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,4

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-8

36

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'

0

I0-

\4a"L'/i~--'----'J---3"~2-1~'~3~1

20-

3040m

so-

7080-

I~-

Fig. 16. Salinity-depth profiles for a line of stations in latitude 10° 40'N in March 1960. Numbers refer to the stations proceeding from the coast outwards.

oC "8

10

11

12

I

I

13 1

14 I

15

16

I

1

17 I

18 I

19

20

I

21

I

I

22 r

23 I

24

25

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26 I

27 I

28

29

I

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30

31

I I ,~32q8~

32 I

33 !

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OO

Fig. 17. T - S diagram for the Laccadive Islands region in April 1959. • above 100 m, O 100 m and below. (Same area as Fig. 2b).

The surface waters off the coast of Kerala, south-west India

311

°C 11 12 13 14 15 16 I

I

I

I

I

I

17 18 19 20 I

I

I

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21 22 23 24 25 26 27 28 29 30 I

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t

l

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r

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-300

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Fig. 18. Temperature-depth profile for a line o f stations near the coast in latitude 8 ° 06'N in April 1958.

oC 10 11 12

13 14

15 16

17 18 17 2~1 21

22 213 24 2~

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.G Fig. 19. T - S diagram for a line o f stations near the coast in latitude 8 ° 06'N in April 1958.

THE

MONSOON

SEASON

The south-west monsoon from May to September covers the return to conditions found in October which have been described earlier. This is a season of heavy rainfall, strong winds, and severe storms at sea. It is very difficult in these conditions to make measurements from a small ship at sea. For this reason there is a paucity of data in the station lists of the Indo-Norwegian Project. Data is available from the I.N.P.L. but most of the stations lie outside our area. They have been included however in order to obtain some information for this season and to give a picture of conditions over a wider area. A line of stations running westwards from the coast in latitude 10°N in May 1959 was worked by the Indo-Norwegian Project and the temperature-depth profile and T - S data are given in Figs. 21 and 22. Surface temperatures remain high and the thermocline extends almost to the surface. The salinity gradient in the top 100 m has decreased considerably and the salinity maximum is less clearly defined.

312

MOLLIEDARBYSHIRE APRIL

FEBRUARY 11" 4~7

N 12°

4~1 4~5 416

0

4?

10" 432 4~1 430 2i14 [

2~3

212

213

212

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,

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150Fig. 20. Vertical temperature and salinity sections drawn up from the Laccadive Islands survey in February 1958 and April 1959. The direction is roughly north-south in a mean longitude 72 ° 40'. The station numbers are marked at the top.

Three north-south sections drawn from I.N.P.L. data for July and August 1963 are given in Figs. 23-25. In Fig. 23, slightly to the east of Cape Comorin, the surface temperature is only 26°C at 8°N and values increase steadily southwards. The 17 ° isotherm, marking the upper limit of the Indian Ocean Equatorial Water is found at about 150 m over the whole section. Above this there is a layer in which the salinity increases from the surface downwards, from about 34"5 to 35'25~oo. This belongs to the Equatorial Surface Water and there is a complete absence of Arabian Sea Water. In Fig. 24, in 72°E, the surface temperature is 28°C at 9°N and increases to a 13

14

15

16

17,

18 19 ~

~ 0 ;100

*C

211 212 213 214 215 26 ~

28 29 130 d~3132 ° • ,,¢" ..~.~....

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2~I .~.. . ~ ' 2 ' ' ~ Fig. 21. Temperature-depth profile for a line o f stations near the coast in latitude 10°N in May 1959.

313

The surface waters off the coast of Kerala, south-west India

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if

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24

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7"

245

246

6" 248

247

5"

4"

3"

2"

1°

0°

249

250

251

252

253

254

255

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28"8

28"8

29-3

29"4

29.1

29.3

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3+5

50-

m0-

150-

N 200

Fig. 23. Vertical section of salinity and temperature in a north-south direction in 78°E in July 1963. Surface temperatures are marked at the top and the small numbers refer to the stations numbers in the I.N.S. Kistna survey. 9"

8*

7*

6"

292

293

294

295

5*

4*

3"

2*

1"

o*

296

297

298

299

/ ,oo+i

'

.......... J" ....

Fig. 24. Vertical section of salinity and temperature in a north-south direction in 72°E in August 1962. Surface temperatures are marked at the top and the small numbers refer to the station numbers in the I.N.S. Kistna survey.

-

Z

281

20£

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100-

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11" 290

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Fig. 25. Vertical s ~ t i o n of salinity and temperature in a n o r t h - s o u t h direction in 68°E in August 1963. Surface temperatures are marked at the top and the small numbers refer to the station numbers in the I.N.S. Kistna survey.

28.1

19"

282

~o

10" I

291

~2

r~

315

The surface waters off the coast of Kerala, south-west India

maximum of 30°C at 3°N. The upper limit of the Indian Ocean Equatorial Waters is again at about 150 m. North of 7°N Arabian Sea Water is found from this depth up to the surface and between 0 ° and 2°N Equatorial Surface Water occupies this layer. From 2 ° to 7°N appears to be the zone of mixing. In Fig. 25, 68°E, surface temperatures are extremely uniform at about 28°C. The whole of the top 200 m from 20 ° to 10°N shown here is occupied by Arabian Sea Water. Salinities are highest in the north and decrease gradually southwards. During the period from May to September there is retreat of Equatorial Water southwards and an upward movement of Arabian Sea Water to the surface. This is quite different from the wind upwelling occurring on the western coasts of the continents in certain latitudes. Here the surface temperatures at the end of the summer decrease to about 27°C and since the thermal gradient near the surface is so steep, water of

% 29

28

27

...., 10

m o)

26

,..~:~..:~,~.~.~

25

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24

,

~ ......-":-:.7.'-.~~.~ "°'°,., "~ ° "-"-~.~

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21

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19

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.,

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4

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..............................

5

3

...............

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7 ....................

8

9

Fig. 26. Temperature-depth profiles for a line of stations near the coast in latitude 9 ° in September 1957. Numbers refer to stations proceeding from the coast outwards,

less than 22°C is found over much of the shelf below 10 m. It only requires a slight slope upwards of the equal density surfaces towards the coast to bring this relatively cold water to the surface near the shore. Such a situation is illustrated in Fig. 26 where temperature-depth profiles along a line west of Quilon, 9°N, are plotted. Wind upwelling cannot take place as the prevailing winds are onshore from the west or south-west and the cold water although about 6 ° colder than normal, has only moved upwards a matter of 10 or 20 m. A pattern of density surfaces sloping upwards towards the coast is consistent with the locally observed southerly current. Towards the end of the monsoon season, the most striking feature near the shore is the influx of freshwater from the rivers and backwaters. This is particularly noticeable at Cochin where a tongue of low salinity water extended out to sea at the surface as shown in Fig. 27. The temperature and salinity variation during the year in the

316

MOLLIED ~ v s m ~

Cochin backwaters has been described by RAMAMIRTHAMand JAYARAMAN(1963). They found lowest salinities, almost freshwater, from July to October, and tongues of low salinity extending seawards at the surface. At the bottom, high salinities, 33-34~o, were found at the seaward end of the backwater at this time. The temperature of the bottom water was low, particularly in October when water less than 23 ° penetrated far into the backwaters. This cold dense water was identified by the authors as upwelled Arabian Sea Water. Towards the end of October a very marked change in 36 o

30

28

26

24

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i

t

22 t

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16 i

14 i

30

28

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34

32

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Fig. 27. Salinity-depth profiles for two lines of stations in latitude 9 ° 58'N, on 25WAugust, 1958 and 2 September 1958. Numbers refer to stations proceeding from the coast outwards.

conditions occurred within a period of about ten days when the bottom temperature increased by more than 4°C. This may be compared with the sudden sinking of the thermodine illustrated in Fig. 10. ANNUAL

SURFACE

SALINITY

VARIATION

Changes of surface salinity during the year in the latitude of Cochin are illustrated in Fig. 28 which covers a period of 21 months. Unfortunately data beyond the shelf edge are only available for part of the year. The main seasonal pattern due to the movements of the water masses stand out dearly, offshore salinities being highest in summer and lowest in January. During the months of November to January, the season of upweUing, there is a marked horizontal salinity gradient with downward slope towards the coast corresponding to a current towards the north. Isohaline

317

The surface waters off the coast of Kerala, south-west India

75".30'

Sh~f edge

7.6*

Cop.st Jury 1958 Aug Sep

34"5

Oct Nov

3~.~ - - - t ~ ~ 34 ~

I I

•

Dec

~

Jan 1959 Feb

I

i I

-34

-34.5 H

Mar Apr May June

Jury Aug Sep Oct Nov Dec Jan 1960 Feb Mar

Fig. 28. Salinity variation in latitude 10°N over a period of 21 months. conditions are found in February, March and April which suggests that there is no current parallel to the shore. A southerly current was shown in Fig. 15 in March in 10 ° 40' but this was rather weak. From May onwards one might expect to find the highest salinities near the coast, consistent with a current towards the south, but any such pattern is masked by the freshwater from the backwaters. Unlike the low salinity water found in January, this only extends a short distance from the shore. In October and early November one would expect isohaline conditions rather like

318

MOLLIEDARBYSHIRE

February to April. However the two years show very different conditions and no conclusions can be drawn. GENERAL CIRCULATION IN THE EQUATORIAL ZONE In the equatorial regions of the oceans there is a well defined pattern of circulation. The wind driven surface currents set up by the north-east and south-east trade winds are towards the west, both north and south of the equator. The mean water transport is towards the north-west to the north of the equator and towards the south-west to the south of the equator. A divergence thus occurs at the equator with water moving away at the surface and being replaced by vertical upwelling. The gradient currents set up in response to this density distribution will persist to a greater depth than the wind driven currents and will be towards the west on both sides of the equator due to the opposite Coriolis effects. The North and South Equatorial currents are due both to wind and to density gradients and their latitude varies with the season as does that of the trade wind belts. In the Indian Ocean this ideal pattern only obtains during the northern winter. In the northern summer the trade winds north of the equator are replaced by the south-west monsoon winds blowing towards the low pressure areas over the interior of the Asian continent. The surface current now flows towards the east and the mean transport is towards the south-east. The divergence and the density gradients and currents associated with it disappear and the general direction of mass transport is from north to south. The wind driven Equatorial currents flow in the opposite directions and are much weaker than in the northern winter. These wind and current patterns are very well illustrated in the diagrams of SCHOTT (1935) and his charts of surface salinity are of particular interest. These show that in the Indian Ocean, the salinity minimum, which would ideally occur at the equator, is displaced considerably towards the south. To the north of the equator, however, are areas of very low salinity in the Bay of Bengal and the South China Sea, and the addition of these waters to the equatorial stream gives an increase in salinity from east to west in both summer and winter. Marked seasonal variations in salinity exist near the southern tip of India. In the northern summer, salinities here are between 34.5 and 35"5~oo, but in the northern winter a tongue of low salinity water less than 34~oo at its core, extends from the Bay of Bengal west of Ceylon and for some distance up the west coast of India. The movements of the water masses in the south-eastern Arabian Sea, which have been discussed in this study, agree well with the reversing equatorial current pattern and with the salinity distribution shown by SCHOTT(1955). In winter the Equatorial Surface Water moves northwestward, the current being strongest near the coast. The lower density water forms a surface layer on top of the Arabian Sea Water and a zone of convergence exists somewhere between 8 ° and 12°N. In summer, when the current reverses direction, the Equatorial Surface Water is carded away to the south-east and the Arabian Sea Water rises to the surface again. CONCLUSIONS

The Arabian Sea Water normally found in this area decreases in salinity from the surface downwards. This sinks in winter to be replaced at the surface by a water

The surface waters off the coast of Kerala, south-west India

319

mass known here as Equatorial Surface Water. This increases in salinity from the surface downwards and often has a very marked salinity gradient. A subsurface salinity maximum exists at the boundary of the two water masses. The main features of the water masses and currents found in the four seasons may be summarised as follows : - 1. Late September to early November--the post-monsoon season

This is a time of reversal from monsoon to normal equatorial currents and the current systems are generally weak. Arabian Sea Water is found at the surface. The freshwater flow from the backwaters continues for several weeks after the end of the monsoon and the low salinity water near the shore disappears only gradually. 2.

November to January--the season of sinking

A sudden change takes place in early November with the onset of the northern winter. The coastal current flows northwards bringing in low density Equatorial Surface Water and there is a rather rapid sinking of the Arabian Sea Water and the thermocline associated with it. 3.

February to April - - the season o f stable conditions

The current system again becomes weak at the end of the northern winter and conditions remain similar to those in January. There is a gradual heating up on the surface layers to temperatures of over 30°C. 4.

M a y to early September--the south-west monsoon season

The coastal current flows towards the south and there is a retreat of Equatorial Surface Water and an upward movement of Arabian Sea Water. Relatively low temperature water, about 22°C, occurs at the surface near the shore due to the tilting upwards of the thermoeline layer towards the coast. There is no system of wind upwelling. By July and August the backwaters are discharging very low salinity water and this extends seawards in tongues at the surface near the entrance to the backwaters. Salinity is thus the main key to the water movements in this area and study of the salinity variations helps us to understand both the main pattern of movement of water masses and the secondary pattern of the interaction between the sea and the backwaters. Acknowledeements--This research was done during a stay of three months at the Oceanography Department of the University of Kerala, in Ernakulam. Thanks are due to Professor C. V. KURIAN, head of that department for his help, and to Dr. D. SCRINIVASAN,of the Indian Naval Physical Laboratory, Cochin, for the loan of the station lists of the I.N.S. Kistna. The author also extends grateful thanks to Mrs. EtLE~N PmTCHARD of the Marine Science Laboratories, Menai Bridge, for the drawing of the diagrams.

REFERENCES

JAYARAMANR., C. P. RAMAMmTHAM,K. V. SUNDARARAMANand C. P. NAIR ARAVINDAKSHAN (1960) Hydrography of the Laccadives offshore waters. J.mar. biol. Ass. India, 2 (1), 2.4-34. PATILM. R. and C. P. RAMAMIR'rt-IAM(1963) Hydrography of the Laccadives offshore waters --a study of the winter conditions. J. mar. biol. Ass. India, 5 (2), 159-169.

320

MOLLIEDARBYSHI~

~THAM C. P. and R. JAYARAMAN(1960) Hydrographical features of the continental shelf waters off Cochin during the years 1958 and 1959. J. mar. biol. Ass. India, 2 (2), 199-207. ~TnAM C. P. and R. JAYARAMAN(1963) Some aspects of the hydrographic conditions of the backwaters around Willingdon Island (Cochin). J. mar. biol. Ass. India, 5 (2), 170-177. SASSY A. A. ~ and P. MYRLAND (1959) Distribution of temperature, salinity and density in the Arabian Sea along the South Malabar coast (South India) during the post-monsoon season. Ind. J. Fish., 6 (2), 223-255. SCHOTT G. (1935) Geographic des Indischen andStillen Ozeans. Deutsche Seewarte, Hamburg, 413 pp. SWRDRtrP H. U., M. W. JOHNSON and R. H. FLEMING(1942) The Oceans,p. 692, Prentice-Hall, New York.

CENTRAL MARINE Fisrmmr.s Rr.SEARCH INsrtrtYrE, OCEANOGRAPHIC STATIONLIST(1962) Ind. J. Fish., 9 (I), 213-431. INDIANNAVALPHYSICALLABORATORY. I.N.S. Kistna STATION LISTS. (1962 and 1963). Unpublished APPENDIX Data from the following stations were used in the preparation of the figures. Those prefixed I.N.P.L. are to be found in the I.N.S. Kistna station lists of the Indian Naval Physical Laboratory, while all the others are in the oceanographic station list of the Central Marine Fisherties Research Institute (see references). Fig. 2 (a) (b) Fig. 3

Fig. 4 Fig. 5

Fig. 6 Fig. 7 Fig. 8 Fig. 9 Fig. 12

205-219 423-448 33-42 44-52 53-62 63-72 72-76 and 80 ,44--52 17-24 25-32 1-9 10-16 93-102 351-356 358-364 366, 367, 369-372 184-193 381-387

Fig. 13 1.N.P.L. Fig. 14 Fig. 15 Fig. 16 Fig. 17 Fig. 18 Fig. 19 Fig. 20

81-95 205-219 205-219 567-574 432--448 246-256 246-256 A.A.Aa a8 ' 430--432, 210-214 Fig. 21 481-485 Fig. 22 481-488 Fig. 23 I.N.P.L. 245-255 Fig. 24 I.N.P.L. 292-299 Fig. 25 1.N.P.L. 281-291 Fig. 26 1-9 Fig. 27 299, 301,302, 303-306 and 308