TJC ok,-t-t- LMteS T~(F~/O ++-.-4s I 7.. 423horizon.documentation.ird.fr/exl-doc/pleins_textes/pleins_textes_7/b... · Tahiti - California (4) Tahiti - Panama (5) Other minor routes

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_- . EXPERIMENT I N THE EASTERN AND WESTERN PACIFIC 2

4g4 / Pmceekrgr 2.2 AN EXPENDABLE BATHYTIiERMOGRAPH AND SEA-SURFACE TEMPERATURE ..

-.. .. .

'.. J. R, Donguy, C. Benin Cent re ORSTOM de Nouméa,

BoSte P o s t a l e A 5 , Nouméa, New Caledonia

.. IHTBODUCTIOB

t i o n system with t h e h e l p of merchant sh ips . Pac i f ic ; from west t o e a s t , t h e r e a re t h e fo l lowing main r o u t e s (F igu re 1).

Since 1969, t h e Cent re ORSTOM d e Nouméa h a s ope ra t ed a s u r f a c e observa- Seve ra l r o u t e s a r e used i n t h e t r o p i c a l

Noumda - Hong Kong (1) I I

Nouméa - Japan (2)

Australia - C a l i f o r n i a (3) T a h i t i - C a l i f o r n i a ( 4 ) T a h i t i - Panama ( 5 )

Other minor r o u t e s a re a l s o ope ra t ed , such as Noumka and T a h i t i - New Zealand, Nouméa - U a l l i s I s l a n d and T a h i t i - Honolulu.

The o b s e r v a t i o n s c o n s i s t , mainly o f SST measurements, and su r face s a l i n i t y sampling.

S t a r t i n g from 1977, ch lo rophy l l de t e rmina t ions and zooplankton sampling have been ob ta ined a l o n g s e v e r a l rou te s . ment, XBTs have been ga the red a l o n g r o u t e s (1) ( 2 ) (3) and (5), r o u t e ( 4 ) be ing operated by t h e US.

I n 1979, as a r e s u l t o f a US-French agree-

I n t h i s s tudy on ly t h e r o u t e s ( 2 ) and (5) w i l l be t aken i n t o considera- t ion .

TAHITI-PANAMA

Ava i l ab le d a t a of SST s t a r t in 1955. They have been provided by t h e Fregch "Meteorologie Ba$ionale" grid ga the red by merchant s h i p s between T a h i t i (17'33 S, 149 37 W) and Panama (8 57 H, 79 33 W ) . These d a t a end i n 1973 bu t t h e same observa- t i o n s s t a r t aga in a long t h e same r o u t e i n October 1974, o p e r a t e d by t h e Cent re ORSTOM de Nouméa; t h e y a re s t i l l running.

1978 s e r i e s (F igure 2) . (1980). i s warm; e q u a t o r i a l upwelling. Warm water south of 1 S i s due t o t h e sou the rn S u m e r and, c l o s e t o t h e equator , t o t h e absence of e q u a t o r i a l upwell ing.

The SSTs have been p resen ted i n a space-time diagram cove r ing t h e 1955- The main conclus ions have been drawn by Donguy and Benin

The seasona l v a r i a t i o n s a r e obvious: from January t o June , t h e s u r f a c e water from J u l y t o December, i t i s cold.o On t h e equa to r , c o l d water i a due t o t h e

The 1955-1978 SSTs show no t on ly seasona l v a r i a t i o n s but a l s o year- to-year v a r i a t i o n a o f t h e e q u a t o r i a l upwel l ing i n t e n s i t y . we l l ing is s t r o n g , as i n 1955, 1967, 1970, 1973, 1975. I n o t h e r s , t h e e q u a t o r i a l UP- we l l ing i s weak, a s i n 1957, 1963, 1965, 1969, 1972, 1976. These y e a r s were marked by E l Niño events .

I n some y e a r s , t h e e q u a t o r i a l up-

Only two y e a r s o f XBT o b s e r v a t i o n s a r e a t p r e s e n t a v a i l a b l e . As XBTs somet imeS. fa i l , t h e o b s e r v a t i o n s a r e i r r e g u l a r l y l o c a t e d and spaced. hand, between Polynes ia and Panamab two se a r a t e d r o u t e s appear: Panama, t h e o t h e r from Mururoa ( 2 2 S - 141 W) t o Panama. The SST from XETs a l s o shows seasonal v a r i a t i o n s , wi th w a r m water from January t o June, and from J u l y t o December c o l d water due t o t h e e q u a t o r i a l upwel l ing and t h e sou the rn w i n t e r (F igu re 3).

On t h e o t h e r one from Papeete to 8

- ~. ___. .. -. -- , ----- .

.-

Figure 1 - Surface sampling routes operated by ORSTOM.

PANAML

6 h

O

5 5

10 s

15 s TAHITI

I 1957 I 1968 2 3 4 5 1955 6 7 8 9 1011 11 I I 2 3 4 5 195B 6 7 I 9 1 0 1 1 I2 1 1 3 4 5 6 7 8 9 1 0 1 1 I 2 1 1 3 4 5 6 7 I l U l I I I 1 1 1 4 i b

1 1 1 1 1 1 1 1 1 ~ ~ ~ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 , 1 1 1 1 ~ 1 1 1 I I

1 1963 I 1900 I 1901 I 19G2 1959 I 5 6 7 8 9 101112 1 1 1 4 5 6 I fi 9 I O I I I Z I 2 3 4 d 6 I I 9 1011 II 1 1 3 4 5 6 7 8 9 1011 12 I 2 3 4 5 6 1 8 9 1011 12

PANAMA I I 1 1 1 1 1 1 1 ~ ~ 1 , 1 1 1 1 , 1 1 1 1 1 1

TAHITI

Figure 2(a) & (b) - Space-time isopleths of sea-surface temperature, Tahiti-Panama, 1955-63.

. . . . .

I 1964 I 1365 I 1966 I 1967 I 1968 I I I 1 1 1 3 4 5 6 7 8 9 1 0 1 1 12 1 2 3 4 5 6 7 8 9 1011 11 1 2 3 4 5 6 7 8 9 1 0 1 1 12 1 2 3 4 5 6 1 8 9 101112 1 2 3 4 5 8 '

PANAMA I' 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I I , I I I I ,

. .- 5N

O

6S

10 5

15 s

TAHl TI

1972 . I I 1970 I 1971 I 1908 I 19G9 I 6 I I o 1 0 1 1 I I I I 3 4 5 fi 7 a , 9 i o 1 1 1 1 i I 3 4 5 6 I fi 9 m i 1 II I i 3.4 5 E i I 9 1 0 1 1 IZ i i 3 I 5 6 7 I 9 1011 II

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ~ ~ ~ ~ 1 1 1 ~ 1 1 1 1 1 1 1 1 1 1 1 1 , 1 PANAMA

I

ON

O

as

10s

1G s

7AtdlTl

Figure 2(c) & (d) - Space-time isopleths of sea-surface temperature, Tahiti-Panama, 1964-72.

,

c.

PANAMA

5N.

0 -

5s-

TAHITI

I I 1973

11121 i 1 3 4 6 6 1 I 0 U ) l I I Z I , , , ,

PANAMA I 1

10 s

15 S

TAHITI

.-

I

Figure 2(e) 6: (f) - Space-time isopleths of sea-surface temperature, Tahiti-Panama,' 1973-78.

t I

i SST trom XBT PAPEETE-PANAMA

I s e o i s e l 1479 v

1

S S T f r o m XBT %?% - P A N A M A

1 9 7 9 1 9 8 0 I s e l

I 1

I

-5N

-O

-ss

-90s

'1 5s

2 0 s i l

Figure 3 - Sea-surface temperature from XBTs, Polynesia-Panama, 1979-1981.

-i-- O The variations of the depth of the sea-surface temperature minus 1 c, {fidore 4 ) as a space-time diagram, show interesting features. Along both the routes, UtVeen Polynesia and Panama, this depth is at a maximum in the cold season and during rglutorial upwelling( and at a minimum in the warm season and during the absence of ee equatorial upwelling. .1 conclude at, a first approach that along these routes cold water exists with a great dckness, and'warm water exists with a small thickness.

As this depth is representative of the mixed layer thickness,

...- S S T -1'C DEPTH i n m e t e r s PAPEETE - P A N A M A

1 9 7 9 I S 8 0 ' 1 9 8 1 I 1

% . . eo5

S S T - 1'C DEPTH ia -.ta,. -4- - P A N A M A

1 9 1 9 l e s o l e e l . I I

O Figure 4 - Depth (m) of sea-surface temperature minus 1 C, Polynesia-Panama,

1979-81.

.. _.

These f e a t u r e s a r e confirmed by c o n s i d e r a t i o n o f t h e h e a t conten t , from t h e s u r f a c e t o 100 meters ( F i g u r e 5). On t h e equa to r , d u r i n g t h e absence of t h e e q u a t o r i a l upwel l ing January-June 1980), t h e hea t con ten t is no t much g r e a t e r than du r ing $he upwel l ing 18 u n i t s i n g t e a d of 17) when t h e SST i s very d i f f e r e n t (more than 25 C i n s t e a d of l e s s t h a n 23 C ) . con ten t maximum appears du r ing t h e w a r m season but a n o t h e r a p p e a r s a l s o du r ing t h e c o l d season.

I n t h e same way, i n t h e t r c p i c a l a r e a a hea t

H E A T C O N T E N T 0-100m. P A P E E T E - P A N A M A 1 9 S P 1 9 8 1 1979

I

I 1

223 H E A T C O N T E N T 0,400m. 140w-PANAMA

I I l S 7 3 l e s o 1 9 8 1

I

Figure 5 - Heat c o n t e n t , 0-loom, Polynesia-Panama, 1979-81.

The surface observations started in 1969 but were restricted at 10°N

The merchant ships, according to theig

It starts at Nouméa

mtil 1972. gathered regularly from Nouméa to Japan. destination,'.hav% two different sailing routes, one crossing the equator at 150 E,

(22 16 S, 166 27 E) and ends at Hachimohe (40 32 N, 141 32 E).

south of 10's. Between thgse latigudes, there are not seasonal varhations: temgerature varies from 28 C to 30 C, with long periods of cold (28 C)oand warm (30 C ) waters. Except for short periods with temperature less than 28 C on the equator, the equatorial upwelling is not marked by water colder than elsewhere. Surface conditions in the North-West Pacific Ocean have been discussed by Donguy and

From 1972 to the present, sea-surface temperature and salinity are

. theoother at i60 E. Only this last one is cogsidered hgre.

The sea-surface temperature shows seasonal variations north of 10°N and the

-" Benin (1977). I I

Only two years of XBT observations are at present availab&e. tige diagram (Figure 6 ) seasonal variations of SST appear south of 10 S and north of 10 N and, as deduced from the SST sampling, there are not seasonal variations in the equatorial zone.

On a space-

SST from X B T J A P A N - N E W .C A L E D O N I A 1978 1 9 8 6 I S 8 1

I I

I Wk 27 25

Figure 6 - Sea-surface temperature from XBTs, Japan-Nouméa, 1979-81. The nixed layer depth may be represented by the depth of SST minus 1°C

in a space-time diagram (Figure 7). i n small thickness, whereas cold water occurs in great thickness, as in the Eastern Pacific. The equatorial area, on the contrary, is characterized by a trough close t o the equator with a mixed layer depth more than 100 meters. This feature is. COR- aistent with the dynamic heights computed from the XBT observations (Figure 81, assuming durect relations of Ast with the temperature. rith a line of dynamic height maximum. area is characterized by the importance of the Eastward Counter-Currents.

In tropical areas warm water is usually present

The trough is consistent From June 1979 t.0 April 1981, the equatorial

n

- I S , -

SST-1 'C DEPTH inmeters J A P A N - N E W - C A L E D O N I A

1 9 8 1

I . .

I -'ION . \ I I

I l I I I

i

F i g u e 7 - 2epth (ri) o f s ea - su r face t e m p r a t u r e z i ~ - . i s 1 O C, J s ~ a n - Y o u z 4 a , 1379-81.

~~

. . - 133 - ..

The 0-103m heat content (Figure 9) shows weak seasonal variations in the tropical area- On the equator, there is no change during the series: a maximum of teat content occurs. from 5's to the equator and does not seen to have seasonal varia- t i o n s . This maximum is low and characteristic of a post El Niño period. Eefore El Nifio, we expect a stronger heat content in the equatorial area,

1,

.,,.

Figur@ 9 - Heat content, O - l O O m , Japan-Nouméa, 1979-81.

CONCLUSION

The XBT experirqent has been running f o r only two years in the Pacific Ocean, However, interesting results have appeared already but are only characteristic of the present post El Niño period. ,

. . REFERENCES 'Onguy, J. R. and C. Henin, 1977: Navifacial conditions in the North-West Pacific

Ocean. Journal of the Oceanographical Society of Japan, z, 183-189. - and to the intertropical convergence zone o f the winds. Deep-sea Research, 3, 693-714.

. , 1980: Surface conditions in the eastern equatorial Pacific related

Q

I s