Seasonal variations of temperature and salinity in the Gulf
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Deep-Sea Research, Vol. 26/6A, pp. 661 to 672 0011-7471/79/0601-0661 $02.00/0 (~) Pergamon Press Ltd 1979. Printed in Great Britain Seasonal variations of temperature and salinity in the Gulf of Elat (Aqaba) N. PALDOR* a n d D. A. ANATI* (Received 13 January 1978 ; in revisedJorm 19 September 1978 ; accepted 13 January 1979) Abstract--The distributions of temperatures, salinites, and their month-to-month variations in the upper 300m in the Gulf of Elat (Aqaba) from 1974 to 1977 are described. Both temperature and salinity are high in summer (~ 26C, ~ 41!I,,,,,at the surface), and low in winter (~ 21C, ~ 40.57~;,,, at the surface). The summer transition of salinity occurs 2 to 3 months later (August, September) than that of temperature (May, June, July). The water column is stratified throughout the year but much less so in winter and less so in the north (far away from the straits) than in the south (near the straits). The winter stratification is mainly due to salt, while the summer stratification is mainly due to temperature. An attempt to estimate the temperature and salinity distributions at the Straits of Tiran from neighbouring stations was only partially satisfactory. INTRODUCTION THE GULF OF ELAT ( A q a b a ) is a fingerlike extension projecting n o r t h - n o r t h e a s t w a r d from the Red Sea. It is 1 8 0 k m long and 1 4 k m wide on the average a n d small e n o u g h that a t m o s p h e r i c c o n d i t i o n s m a y be assumed, for most purposes, to be uniform over the whole surface (ASSAF a n d KESSLER, 1974), yet it is large e n o u g h to be influenced by the r o t a t i o n of the earth. The climate is arid, with a yearly average net e v a p o r a t i o n of 1 cm d a y - 1 (ASSAF and KESSLER, 1974). W i n d s b l o w along the m a i n axis, p r e d o m i n a n t l y from the north, switching a b r u p t l y to southerlies in short gales of a few d a y s ' d u r a t i o n and at p r e d i c t a b l e seasons, m u c h as in a w i n d - t u n n e l experiment. T h e gulf is confined at its s o u t h e r n end by the short Straits of Tiran, ' s h o r t ' in the d y n a m i c sense (ANATI, ASSAF a n d THOMPSON, 1977), so that friction can be neglected in s t r a i t - d y n a m i c s considerations. The similarity of the gulf to the Red Sea p r o p e r (e.g. AssAr a n d ANATI, 1974; ANATI, 1977) m a k e s its study useful in u n d e r s t a n d i n g the latter, which is c o n s i d e r a b l y m o r e difficult to explore. Unfortunately, there has been no m a j o r expedition in the gulf since the Pola cruise a l m o s t a century ago (1895-1896). Some m i n o r field w o r k carried out in the present century was briefly reviewed by ANATI (1974). Existing studies deal m a i n l y with the steady state, not because time v a r i a t i o n s are negligible, but chiefly for want of data. Since 1974 intense field work, the D C P E t , has been u n d e r t a k e n (KLINKER, REISS, KROPACH, LEVANON, HARPAZ, HALICZ a n d ASSAE, 1977) a n d for the first time m o n t h - t o - m o n t h v a r i a t i o n s can be reported. T h e present study uses the D C P E d a t a a n d concentrates on the seasonal cycle of t e m p e r a t u r e a n d salinity. *The Weizmann Institute of Science, Rehovot, Israel. t The Data Collection Program in the Gulf of Elat is operated by the H. Steinitz Marine Biological Laboratory in Elat and sponsored by the Hebrew University of Jerusalem, the Israel Ocenographic and Limnological Research in Haifa, the Weizman Institute of Science in Rehovot, the Israel National Academy of Sciences and Humanities in Jerusalem, and the Israel-U.S.A. Binational Science Foundation. 661 662 N. PALDOR and D. A. ANATI Time variations include more than the seasonal cycle, for instance secular changes. But a comparison of observation from the Pola expedition of 1896 (LuKSCH, 1901) with those during 1974 to 1977 reveals no significant changes in the last 80 years in the April temperatures and salinities (within the standard deviation of D C P E stations); we shall thus disregard secular changes. Random year-to-year variations should not be ignored, but the available data are too infrequent to distinguish among different years within any reasonable stastical significance. Consequently such variations will be ignored in the present study, and each measurement will be assumed to represent the month it was taken irrespective of the year. When more data become available, other components of the time variation may be observed, but the present work will concentrate on seasonal variations. THE DATA AND DATA PROCESSING Most of the data were collected in 1974 to 1977, within the framework of D C P E and are supplemented by Snapir Stas 2 and 3 occupied in September 1967 near the Straits of Tiran. The data comprise 150 hydrostations, or 768 samples. Apart from the two indispensable Snapir stations we have adhered to D C P E stations for the advantage of using data from a single source, with a standard treatment and the same sampling methods.* D C P E stations are commonly occupied at nine fixed sites labelled A to H and J (Fig. 1). Measurements at sites O and N were taken only in 1976 and 1977 and in the present work are included (for averaging purposes) with those taken at site A. One of the goals of this study is to estimate the distribution of temperature and salinity at the Straits of Tiran and its seasonal variation. Direct measurements in the straits themselves are not available. To procure an approximate estimate, measurements from site H (just outside the gulf) and site G (just inside) were averaged (see detailes below). We have not analyzed the whole depth of the basin (~1800m), although deep observations were made at some stations. However, the aim is to examine seasonal variations that occur mostly above sill depth (252m), and the present study uses measurements from the upper 300m only; this includes roughly one-third of the total volume of the gulf. From the available data, the following parameters were computed: (1) The average temperature T and average salinity S. These represent the storage of heat and salt down to 300m. All available observations at sites A to G and J (A includes O and N) during a specific month t, at the depths of 0, 50, 100, 150, 200, and 300m, were averaged with equal weight given to each site: TIt) = id k (1) E ~j" mr it) J and a similar expression for ,~(t). i runs over m i (t), the number of sites sampled at month t at depth j, j runs over depths, and k runs over nij(t), the number of measurements at site i, * DCPE stations occupied between July 1975 and June 1976 are given in REISS and PAPERNA (1976). Thanks to Z. REISSand O. H. OREN for kindly supplying the additional data used in this study. Seasonal variations of temperature and salinity in the Gulf of Elat (Aqaba) 663 34730' ~OO' 1 29o~O ' i" g o "-.a 2geO0' ~8o3Q ' 28o00' Fig. 1. Location of sites A to H, J, N, and O in the Gulf of Elat. depth j, time t. a~ is the weight assigned to the depth j: 0~ 1 = 0.3, ~2 = ~3 = 0~4 = 1, ~5 = ~6 = 1.5 (2) according to the thickness of the layer represented by the depth j. (2) The surJace temperature Toand the surface salinity S o. These are necessary for the determination of the evaporation, were computed from the relationship Z Z ~,~ (t)/n. it) To = i k (3) m 1 (t) (3) The temperature and salinity of the upper layer T~, $1, and the lower layer T 2, S 2, separately. In a two-layer thermohaline circulation (see e.g. ANATI et al., 1977), the upper and lower layers are conceptually the continuation of each other. Water enters the gulf 664 N. PALDORand D. A. ANATI t h r o u g h the u p p e r p a r t of the straits as type (T s, Sff), flows n o r t h w a r d s , sinks to the lower layer, returns to the south, a n d flows out of the gulf t h r o u g h the lower part of the straits, modified into type (T5s, SIS). It is therefore i m p o r t a n t , for m o d e l l i n g purposes, to asses these parameters. T h e p r o b l e m is the d e t e r m i n a t i o n of the b o u n d a r y between the layers. F r o m the Snapir t e m p e r a t u r e section (ANA~I, 1974, Fig. 2) there is no clearly defined interface, but it a p p e a r s to be located somewhere between 90 and 150m. F r o m MORCOS (1970, Fig. 1 1E) the center of the t h e r m o c l i n e at the straits is a b o u t 2 0 0 m deep. ANATI (1977), from theoretical considerations, d e d u c e d that a d e p t h of a b o u t 7 5 m would be consistent with overmixing. In the present w o r k the u p p e r m o s t three m e a s u r e m e n t s (0, 50, and 100m) are assumed to represent the n o r t h b o u n d inflow, a n d all the others the s o u t h b o u n d outflow. This choice is not b e y o n d d o u b t ; cross-axial~ sections in the gulf (roughly east-west) would enable us to observe the actual d e p t h of the interface and verify this point, but they are not available. (4) The temperature and salinity of the inflow and outflow (T s, S], T2, $2) at the straits. • s s T h e i m p o r t a n c e of these p a r a m e t e r s was e m p h a s i z e d by ANATI (1977), who deduced the rate of e v a p o r a t i o n , the water transports, a n d the heat fluxes from them. F o r want of d a t a from the straits themselves, these variables are estimated by averaging m e a s u r e m e n t s at sites G a n d H, just n o r t h a n d south of the straits. F o r this purpose, the time series of (T 1, St, T 2, S 2) at each of these two sites were first c o m p u t e d , with values for missing m o n t h s i n t e r p o l a t e d by a cubic spline. The m o n t h s of J a n u a r y a n d F e b r u a r y were repeated after D e c e m b e r as m o n t h s 13 a n d 14, better to estimate the values for December. A l t h o u g h this is the best one can d o with the available data, o u r estimates of (Tis, T s2, Si s, Si s) are not entirely satisfactory. RESULTS Results of the c o m p u t a t i o n s are given in T a b l e 1. To asses which m o n t h s best represent winter, summer, o r transition periods we p l o t t e d T s, TO, T s, Ts , T~, a n d T2 versus m o n t h s of the year (Fig. 2). Each of the six variables plotted in Fig. 2 displays its Table 1. Monthly variation of temperature T and salinity S in the Gu!f of Elat (Aqaba). J F M A M J J A S 0 N D 7" 21.57 21.81 21.10 21.43 21.43 22.01 22.44 23.05 22.95 22.88 23.01 22.46 TO 21.79 21.51 20.75 24.39 23.82 25.28 26.68 26.53 24.99 25.21 23.77 22.90 T~ 21.68 21.59 21.06 22.05 22.05 23.39 24.18 25.69 24.68 24.66 23.69 22.99 Tz 21.51 21.46 21.13 21.01 21.05 21.17 21.34 21.66 21.67 21.86 22.28 22.16 Tis 22.16 22.45 21.73 22.70 22.68 23.21 25.41 24.91 24.90 25.77 24.52 22.94 s T~ 21.83 21.84 21.90 21.38 21.10 21.32 21.75 21.60 21.68 22.32 22.24 21.97 40.56 40.63 40.56 40.60 40.60 40.56 40.62 40.62 40.78 40.70 40.70 40.57 So 40.55 40.67 40.57 40.51 40.58 40.58 40.65 40.72 40.75 40.75 40.64 40.56 Sl 40.53 40.62 40.51 40.52 40.60 40.51 40.60 40.60 40.77 40.77 40.68 40.55 $2 40.57 40.64 40.58 40.64 40.60 40.59 40.64 40.63 40.79 40.67 40.71 40.58 S'~ 40.39 40.45 40.30 40.38 40.50 40.46 40.38 40.81 40.67 40.59 40.53 40.43 Ss 40.50 40.55 40.47 40.50 40.60 40.57 40.54 41.03 40.68 40.67 40.65 40.56 AS 0.11 0.10 0A7 0.12 0.10 0.11 0.16 0.22 0.10 0.08 0.12 0.13 Overbars indicate averages in the upper 300m over the whole basin. Subscripts 0, I, 2, indicate surface values, upper 150-m averages, and 150 to 300-m averages. Superscript s indicates values at the Straits of Tiran. S e a s o n a l v a r i a t i o n s o f t e m p e r a t u r e a n d s a l i n i t y in l h e G u l f o f E l a t ( A q a b a ) 665 26 ,A, ?,y _ L~ 24 n,- i--- (z w IE 22 a. ~_ - - ~ ' 5 - - --. Ld I-- 20 i i i i i d g M A M d d A S 0 N O MONTH OF THE YEAR Fig. 2. Annual variation of the average surface temperature To, the average temperature of the s uppermost 300m, T,, and the temperature at the upper layer Tj, T s . and the lower layer T2, T2 in the gulf and in the Straits of Tiran. own seasonal pattern ; there is a delay in the response of the deeper layers as documented by 7"and especially by Tfi and T2. In Ti~, T o, and 7"the minimal values occur in March. It s is prominent in Tis and T0, less so in T. T~ and T2, on the other hand, reach their minimal s value about two months later. The highest summer temperatures occur in July and August at the surface (To) and in July to October in Tis, but between August and November in T, October-November in Tfi s, and November in T2. The above mentioned delay is therefore rather conspicuous. It probably results from a combination of an advective effect and the slow downwards propagation of heat and will not be analyzed within the framework of this presentation. The two peaks in T( (July and October) coincide with the most frequent occurrence of southerly winds (KESSLER, 1977). As with the temperature, low winter and high summer values of salinity are observed (Fig. 3). The transition however, occurs considerably later in the season (August, September instead of May, June, July) so that the spring warming (Fig. 2) occurs in water with low salinities typical of winter. In October we unexpectedly observed $1 to be greater than $2. Sa and $2 were calculated from 36 and 33 October measurements, respectively, and a close examination reveals that this inequality is consistent with the data and not due to a few particularly erratic measurements. Furthermore, the AS anomaly in October (AS < 0) was detected at every site except G (See Table 2). The average October AS, from Table 2, is -0.103";;<,, with a standard deviation of 0.06"~;,, and shows a marked trend for lower values with greater distance from the straits, a trend that was found to be a general feature at all seasons (see Fig. 8). The salinities at the straits (interpolated as mentioned above) are not included in Fig. 3 because of their erratic variations, combined with the fact that they are estimated rather than measured. High values (S~ > 41'!,;,, in August) and low values (Ss = 40.3<'~<,<,in March) would appear in the diagram (see Table 1). The highest rate of change of salinity concides with the highest surface temperatures. t) S.R.(A). 266 I 666 N. PAt, DOR and D. A. ANAT! s 40.7 --g So >_ 40.6 I-- --J <£ s GO 40.5 J F M A M J J A S 0 N D MONTH OF THE YEAR Fig. 3. Annual variation of the surface salinity So, the average salinity of the uppermost 300 m, S, the salinity of the upper layer S~, and the lower layer $2, in the Gulf of Elat. Table 2, The salinity of the upper layer, $1, the salinity of the lower laver $2, and their d(~erences AS = $ 2 - S 1 for six sites in the Gu!f of Elat, in the month of October. Site S1 S2 AS = $ 2 - S l A 40.770 40.623 -0.147 B 40.788 40.604 -0.184 D 40.722 40.604 -0.118 J 40.742 40.647 -0.094 E 40.832 40.744 -0.089 G 40.767 40.780 +0.013 Although this does not take into account wind speed and air moisture, it is consistent with the fact that evaporation is highest when the saturation vapor pressure of the air at sea level is highest. Winter and summer profiles of temperature for north and south sites within the gulf are shown in Fig. 4. The surface water is consistently about 2°C colder in the north than in the south and between 300 and 500m the water is homogeneous. The apparently paradoxical warming in winter of the water below 300m (0.2°C) may be accidental and within sampling error. We cannot tell from the standard deviations what is the confidence level of this temperature difference because it is based on too few data: for site G we have only one station in February and one in September; for site A, the only three February stations give 21.37+0.11 and the three September stations give 20.984-0.10. Standard deviations at 300m may be as high as 0.5°C at other sites and months. On the other hand, there is enough confidence in the higher temperature differences between A and G in the upper layers. Significantly, the water in the upper 100m in s u m m e r undergoes some cooling between G and A, while that in the layer below 150m (the assumed return current), being sealed from the atmospheric influence by the stratification, remains Seasonal variations of temperature and salinity in the Gulf of Elat (Aqaba) 667 TEMPERATURE (°C) ' 2 21 ~ I00- 200- 300- z 400- o 500- Fig. 4. Vertical distribution of temperature in winter (February) and in summer (September) for the north site (A) and the south site (G) within the Gulf of Elat. Although the months of March and August are better representatives of typical winter and summer, the data for February and September are more complete. unchanged along its way from A to G. In winter the stratification is weaker (see also Fig. 7), and the cooling reache s a greater depth. To observe the annual changes in the type of water of the upper mass (T~, $1), observations at all the sites for any given months were plotted on a c o m m o n T-S diagram (Fig. 5). The spring warming occurs at a lower salinity than the a u t u m n cooling, so that the trajectory in the T-S space takes the shape of a crescent. August is definitely the warmest m o n t h and March the coldest. The area of each polygon can be taken as a measure of the horizontal inhomogeneity within the gull'; it appears from Fig. 5 that there is not much seasonal change in this parameter, except tor July and August. This may be an indication that the warm, summer Red Sea water undergoes enhanced evaporation and cooling, so that the north end is all the more saline and colder than the south end of the gulf. The crescent shape of the yearly trajectory in the T-S space is even clearer when we plot single sites separately; Fig. 6 compares the north Red Sea proper (site H) with the north of the gulf (site A), displaying the narrower range of annual variation at A. The overall salinity difference of about AS ~ 0.3",,,, (4) 668 N. PALDOR and D. A. ANAI'I I f Y I ' I ] 28 ~ J ~ 2 7 O J ~ J 1 tM rr 26 [E Ld D_ IM 24 [E lit == ZD CO c 22 I.-/-~ , I , I 40.4 40.6 40.8 SALINITY S, (%0) [ ' I u ' I / ,,~ 2 4 ~ ~ ° ~ - 22 bJn" -- r J 40 4 40 6 40.8 SALINITY S, (%0) Fig. 5. T-S diagram of the upper water mass (T~, S 1), for summer and winter in the Gulf of Elat. h. Letters A-J denote the sites shown in Fig. 1. Thin diagonal lines are lines of constant c Thick lines define a closed polygon for each month around the types of water found at each site. Note the low temperature in the north (site A) in the early summer (May to August) and the high salinity there in winter (January to April). as seen in the figure, impliesa time lag r = O AS/ES (5) between H and A along the surface. With a depth of D = 150m and an evaporation rate o f E = 1 c m d a y - 1 (AssAF a n d KESSLER, 1 9 7 4 ) , e q u a t i o n (4) y i e l d s r ~ 4 months (6) Seasonal variations of temperature and salinity in the Gulf of Elat (Aqaba) 669 I ' I ' I ' I ~ ' / L Oct J 270j 26 (D / o / / 24 / / LIJ / / El/ / / t-- <~ rY iii rl 2 2 March Iii H- March / ~ ?.90f I ~ I i .-t//]/ i I 402 40.4 40.6 40.8 SALINITY (%o) Fig. 6. T-S diagram comparing the annual evolution of the upper water mass (T1, $1) within the Gulf of Elat (site A) with that just outside the gulf (site H). Thin diagonal lines are lines of constant % Note the typical 'crescent' shape and the tendency for lower temperatures and higher salinities at site A. The type of water for site H in August is based on one station only and is probably exceptionally high in salinity. No measurements at site H are available for February or May. The total residence time was estimated at about 2 years (ANATI, 1974); as z is expected to be somewhat less than half the residence time, the z of (6) is short but of the expected order. To provide an independent check of (6), we use the heat-balance equation. z = DAT Cp/H (7) which, with (6) and with H = - l l 4 w m -2 (ASSAF and KESSLER, 1974), gives an overall temperature difference of AT = - 1.88°C, (8) in agreement with Fig. 6. DISCUSSION From the 3 years of data it appears that summer temperatures in the water column prevail over 5 to 6 months, April to October, while a typical winter period is relatively 670 N. PALDORand D. A. ANATI 25 ? 24 2~ "0 / 0 i,i 13::: z) I- 2 5 n-- N Ld G_ W 22 t'-- I I I I V I~ .~Z9"? ''-----5- 4 0 I~ 40"4 m I~ 40.6 407 408 40.9 SALINITY ( % o ) Fig. 7. Water types in the upper (l) and lower (2) layers in the Gulf of Elat. Site A is at the northern end of the gulf, site G at the southern end (near the Strait of Tiran). The upper layer values are computed from the standard depths 0, 50, and 100m, and the lower layer values from the standard depths 150, 200, and 300m. i 012--I O.I-I O.C', 28°00 ' ' 29J00 ' 29°30 Lot N -°11 -02 I I I I I I I I .dO ~ ....i::iiiiiiiiiii ............................... :::::::::::::::::::::: Fig. 8. Variation of AS = S z - $1 along the main axis of the Gulf of Elat (roughly north-southl. Solid circles k average for February, March, April. Crosses average for June, July, August, September. Open circles October. Shaded area is the bottom relief. short ( J a n u a r y , F e b r u a r y , a n d M a r c h ) . T h e peaks in w i n t e r o r s u m m e r t e m p e r a t u r e o c c u r at different times d e p e n d i n g o n the d e p t h , with a delay in the d e e p e r layers. T h e t e m p e r a t u r e s in the n o r t h are c o n s i s t e n t l y lower t h a n in the south, h o w e v e r site B is a n e x c e p t i o n to this rule with its o c c a s i o n a l high surface t e m p e r a t u r e s , p a r t i c u l a r l y in the s p r i n g (27.2°C in April 1975, 29.2cC in M a y 1976). T h e lowest t e m p e r a t u r e was m e a s u r e d at site D in M a r c h 1975 (20.4°C) at the surface. Seasonal variations of temperature and salinity in the Gulf of Elat (Aqaba) 671 The period of high summer salinity is shorter (2 to 3 months) and occurs later in the season than that of the high summer temperature. The narrow overall range of salinities is illustrated in Fig. 5. Considering the small size of the gulf or, equivalently, the short residence time of its water, this narrow range is not surprising. The highest salinities were ,~,,, at site A', from among 17 measurements with salinity above 41 ..... 16 were at site A; the only exception (41.02".,/;o)was at site E. The highest salinity was at site A in August 1975 (41.571'~i,,), and the lowest at site B in November 1974 (40.03"~,,,). One of the questions these data may be able to answer is how the vertical structure changes through the seasonal cycle. Figure 7 displays on a T-S diagram the points (T1, S 1) and (T2, $2) for north and south, winter and summer. Site A (north) is vertically more homogeneous than site G (south), both in winter and summer, as would be expected from circulation models of semiclosed basins in arid zones. Note also the smaller overall ranges of temperature and salinity at site A than at site G and the changing character of the stratification between winter and summer: the winter column is mainly salinity stratified while the summer column is mainly temperature stratified. From the two-layer thermohaline circulation model, the difference in salinity between lower and upper layers, AS = S z - $ 1 , is expected to be (i) positive (evaporation exceeds precipitation), (ii) decreasing towards the north (further away from the straits), (iii) decreasing roughly linearly (uniform evaporation rate), and (iv) nearly vanishing at the northern end (where the deep water is presumably formed). To compare these features with observations, AS was computed for the months of February, March, and April, with missing sites interpolated, and then averaged over the three months. The same procedure was applied to the months of June, July, August, and September (Fig. 8). The salinity difference AS does display the expected properties. The unexplained negative AS values in October (Table 2) are added for comparison. An important parameter for the solution of the balance equations (Knudsen's relation) is the salinity difference between lower and upper layers at the straits, A S s = SzS_ Sl.S As direct measurements of AS s at the straits are not available, indirect estimates will be used. Southwards extrapolation of AS from Fig. 8 gives an estimate that is rather independent of season, A S s ~ 0.15°i;,, (9A) while from Table 1 the seasonal variation is greater, and the average value is A S s ~ 0.1 P'i'i,,. (9B) Both values are close to, but below, the previous estimate by ANATI (1974, Fig. 1), of A S s ~ 0.22'!,;,,. (9C) As a final remark, the need for direct measurements at the Strait of Tiran, the bottleneck of the gulf, is emphasized by the present work. Data from various seasons and locations within the gulf are now available, but one still has to estimate indirectly the current structure and types of water masses flowing in and out of the basin through the straits. East-west sections would also be useful, as practically all the existing studies of the gulf use a two-dimensional model, while motions and variations in the third, cross-axial direction, are not necessarily negligible. Finally, a theoretical time-dependent dynamic model of semi-closed basins would enable us to gain some understanding of the processes 672 N. PALDOR and D. A. ANATI that control this gulf, and semi-closed basins in general. The present work is meant to be used for the calibration of such theoretical models. Acknowledgements~hanks to PROFESSOR Z. REISS for commenting on an early version of this work, for interesting discussions of the material, and for his constant interest in the subject. This work was supported by the U.S. Israel Binational Science Foundation, Jerusalem, Israel. REFERENCES ANATI D. A. (1974) Water transports in the Gulf of Aqaba. Eoceanooraphic physique de la Mer Rouge. CNEXO publ. No. 2, 1974, 165-173. ANATI D. A. (1977) Balances and transports in the Red Sea and the Gulf of Elat (Aqaba). Israel Journal of Earth Science, 25, 104 110. ANATI D. A., G. ASSAF and R. O. R. Y. THOMPSON (1977) Laboratory models of sea straits. Journal Fluid Mechanics, 81,341 351. ASSAF G. and D. A. ANATI (1974) Stress distribution in the Red Sea and in the Gulf of Aqaba. Journal of Physical Oceanography, 4, 663 668, ASSAFG. and J. K ESSCER(1974) Climate and energy in the GulfofAqaba (Elat). Monthly Weather Review, 104, 381 -385. KESSLERJ. (19771 Climatic characteristics of southern Sinai. Meteorological Service Publication. In Hebrew. 183. KLINKER J., Z. REISS,C. KROPACH, I. LEVANON,H. HARPAZ, E. HAI,ICZ and G. ASSAF(1977) Observations on the circulation pattern in the Gulf of Elat (Aqaba), Red Sea. Israel Journal of Earth Science, 25, 85-103. LUKSCH J. (1901) Physical ozeanogr. Unters., Expedition S. M. Pola in das Rothe Meer. Bericht der Kommission fur Ozeanographisehe Forschungen, LXIX, 351 442. MORCOS S. A. (1970) Physical and chemical oceanography of the Red Sea. Oceanography and Marine Biology Annual Review, 8, 73-202. RHss Z. and I. PAPERNA (1976) Fifth report of the H. Streinitz Marine Biology Laboratory, Elat 28 68.