The water circulation of the Egyptian Mediterranean waters was computed during winter and summer seasons using the dynamic method. The reference level was set at the 1000db surface. The results showed that the surface circulation is dominated by the Atlantic water inflow along the North African coast and by two major gyres, the Mersa Matruth anticyclonic gyre and El-Arish cyclonic gyre. The results showed a seasonal reversal of El-Arish gyre, being cyclonic in winter and anticyclonic in summer. El-Arish gyre had not been previously measured. The geostrophic current velocity at the edges of the Mersa Matruth gyre varied between 12.5 and 29.1cm/sec in winter and between 6.5 and 13.1cm/sec in summer. The current velocity reached its maximum values (>40cm/sec) at El-Arish gyre. The current velocity at the two gyres decreased with increasing depth. The North African Current affects the surface waters down to a depth of 100m, and that its mean velocity varies between 6 and 38cm/sec

Eid, F.M.

Said, M.A.

Aquatic Commons

Pakistan Journal of Marine Sciences, Vo1.3(2), 91-100, 1994. 
CIRCULATION PATTERN OF THE EGYPTIAN MEDITERRA-
NEAN WATERS DURING WINTER AND SUMMER SEASONS 
M.A. Said and F.M. Eid 
National Institute of Oceanography and Fisheries, Kayet Bey, Alexandria (MAS); 
Oceanography Department, Faculty of Science, Alexandria University, 
Alexandria, Egypt (FME). 
ABSTRACT: The water circulation of the Egyptian Mediterranean waters was computed during winter and 
summer seasons using the dynamic method. The reference level was set at the 1000 db surface. The results showed 
that the surface circulation is dominated by the Atlantic water inflow along the North African coast and by two 
major gyres, the MersaMatruh anticyclonic gyre and El-Arish cyclonic gyre. The results showed a seasonal reversal 
of El-Arish gyre, being cyclonic in winter and anticyclonic in summer. El-Arish gyre had not been previously 
measured. The geostrophic current velocity at the edges of the Mersa Matruh gyre varied between 12.5 and 29.1 
em/sec in winter and between 6.5 anq 13.1 em/sec in summer. The current velocity reached its maximum values 
(>40crn/sec) at El-Arish gyre. The. current velocity at the two gyres decreased with increasing depth. The North 
African Current affects the surface waters down to a depth of 100 m, and that its mean velocity varies between 6 
and 38 em/sec. 
KEY WORDS: Water circulation- current velocity- Mediterranean Sea- Egypt. 
INTRODUCTION 
Direct current measurements in the southeastern Mediterranean off the Egyptian 
coast were very scarce. A few current measurements using an Ekman current-meter 
were made in 1969 between Port-Said and Abu Qir Bay (Hassan, 1969). Gerges 
(1981) studied the monthly patterns of surface currents obtained by averaging all 
current measurements carried out in each one-degree square along the Egyptian coast 
over a period of 50 years, up to the early Seventies. 
The scarcity of direct current measurements for the Egyptian coast has led to the 
use of indirect methods; by constructing T -S diagrams, and sections of horizontal and 
vertical distributions of some physical and chemical properties of seawater such as 
salinity, temperature and ·oxygen (Halim et al., 1967; Hassan, i969; Marcos and 
Hassan, 1976; Saad, 1984; Abdel-Moati and Said, 1987 and Said and Karam, 1990), 
and by the dynamic method (Sharaf El-Din, 1976; Sharaf El-Din and Karam, 1976). 
From the temperature and salinity data taken in front of the Nile Delta during the 
period 1948-1971, the seasonal dynamic topography for that area was studied by 
Karam (1977). 
Little is known about the circulation pattern of the Egyptian Mediterranean waters. 
The aim of the present work is to reconstruct the water circulation maps using the 
more recent observations, compare them with the previous works and define the more 
accurate details of the current system during the winter and summer seasons on the 
Egyptian Mediterranean shelf. 
92 Pakistan Journal of Marine Sciences, Vol.3(2), 1994. 
MATERIALS AND METHODS 
Selected oceanographic data used in the present work are from several expedlttons 
carried out by Egypt and different countries for the last 2 7 years ( 19 5 9-1986). Water 
temperature and salinity data have been taken from 162 hydrographic stations in 
winter, and from 152 stations in summer. Winter data were collected during the period 
from January to March, while summer data were collected from July to September. 
Vertically unstable station data have been corrected for temperature and/or salinity. 
Only few observations have been rejected because of poor quality, due perhaps to 
personal instrumental-and/or location errors. 
The average values of temperature and salinity of these data were computed, using 
the optimum interpolation of the correlation algorithm, for stations distributed in a 
regular grid half degree latitude by half degree longitude for the winter and summer 
seasons as shown in Fig. 1. The optimum selection of the grid size have been chosen 
according to Said (l984a). 
. .. 
' N 
0 (A) 33 0 33 
3 
'J----- !:,... --~ 1/~~,~~~v ' f I ~-I 
' 
' 
"'\....l__...,jll 
\ 
' 
32 
I 
26° 28° 30° 32° 34 E 
26° 28° 30° 32 0 
, 
, N ; ,._, 
33 (B) {'::1 0 __ , 33 
26° 28° 30° 32° 34° E 
Fig. l(A). Egyptian Mediterranean coast, and the regular net at which the average 
temperature and salinity were calculated for the winter and summer seasons; 
(B) Bathymetry of the Egyptian Mediterranean coast. 
Said and Eid: Circulation pattern of the Egyptian Mediterranean waters 93 
The computed averages of water temperature and salinity were used for computing 
the dynamic height. The reference level was set at the 1000 db surface. In the shallow 
parts of the study area where the depths were less than the depth of the reference level, 
Groen's (1948) method was applied. 
The dynamic heigh anomaly differences between stations were substituted in the 
Sandstrom and Halland-H!insen (1903) formula to compute the geostrophic currents. 
The current components are then averaged to obtain the current speed and direction 
at the centre of each grid. 
r-------~----~--,---------r---------~----------~~N 
0 
2 
26 28 30 
Fig.2. Dynamic relief (dyn. m) for the sea surface during: (A) winter and (B) summe 
RESULTS AND DISCUSSION 
Charts of surface circulation constructed for the winter and summer seasons are 
shown in Figs. 2A and B. ·The surface circulation is dominated by the Atlantic water 
inflow along the North African coast and by the Mersa Matruh anticyclonic gyre in 
the western part of the Egyptian coast. This gyre. has been called the Egyptian 
anticyclonic gyre by Said (1984b and 1990), the Egypt high by Brenner (1989) and 
·Mersa Matruh by Ozsoy et al. (1989): 
94 Pakistan Journal of Marine Sciences, Vol.3(2), 1994. 
In the eastern side of the Egyptian coast off E1-Arish city, the circulation is 
cyclonic in winter. ·This circulation exhibits a strong winter to summer variability, 
reversing from cyclonic to anticyclonic (Figs.2A and B). In the scientific literature 
there is no evidence of the existence of such a gyre. ·Consequently, we will call it 
El-Arish gyre. This gyre is more intense in winter and weaker in summer. This may 
be due to the circulation of the atmospheric cyclones over the Eastern Mediterranean 
that are present mainly in the winter. To the east ofEl-Arish gyre, the southern extents 
of the Shikmona gyre is observed in the botll seasons. This gyre was discussed in 
details in POEM-I-85 and POEM-II-86 by Ozsoy eta!. (1989). 
The geostrophic current velocity at the edges ofMersa Matruh gyre varies between 
. . 
12.5 and 29.1 em/sec in winter, and between 6.5 and 13.1 em/sec in summer (Figs.4A 
and B). The current velocity reaches its maximum values (>40 em/sec) at El-Arish 
gyre in winter. The current velocity at the two gyres decreases with increasing depth. 
0 
33 (A) 
0 
31 
0 
33 
0 
32 
(B) 
0 
26 
I 
-- 0-20 em. sec ·1 
--~ 0-40 cm.sec·1 
0 
---+ 0-10 cm.sec -1 . 
3cf 
3cf 
32" 
3 
0 
34 
0 
32 
N 
0 
33 
Fig 3. Surface geostrophic current along the Egyptian Mediterranean coast during: 
(A) winter and (B) summer. 
The dynamic chart for the surface (Fig.2A) during winter indicates the existence 
of a current carrying water from west to east. This inflow of water is deflected to the 
Said and Eid: Circulation pattern of the Egyptian Mediterranean waters 95 
26° 28° 30° 32' 34° 
N 
0 (A) 30 33 
--sJ )~~__...) 
__ 6 ·s 
0 320 32 
' 
0 f 31° 31 
' \ 
26° 28° 3r:f' 32' 34° E 
0 28° 30° 32° 34° 26 
32° 
Fig. 4. Dynamic relief (dyn. m) at the 50 db surface during: (A) winter and (B) 
summer. 
3J 
0 
32 
0 
33 
- 0-20 cm.sec -1 
__ .., 040 cm.sec -1 
----+ 0-10 cm.sec -1 
26' 
28° 
N 
:i 
\ • .1' ~ ~ .-..-/- - .._ 
I • I ....._..,. ....... / < {" \ \ 
t I I I 
A • I ...-~. I I I 
t 
I 
"' 
3d' 32° 34° E 
0 
30 
:i 
0 
32 
30 32' 34 E 
Fig. 5. Geostrophic current pattern at the 50 db surface along the Egyptian 
Mediterranean coast during: (A) winter and (B) summer. 
96 Pakistan Journal of Marine Sciences, Vol.3(2), 1994. 
26° 28° 30° 32° 34" 
0 
33 
0 
32 
0 
31 
26° 28 30 32° 34 
26° 28° 
0 
30 32° 34° 
H 
0 
' 33 33 
0 
32 
0 
31 
34° E 
Fig. 6. Dynamic relief (dyn. m) at the 100 db surface during: (A) winter and (B) 
summer. 
N 
0 (A) :f 33 t _./"'_, .. \ ,/ , "'-/----- ..... ~ '-.... t I / " \ . . I \ ... \ .I '-..,." ,/ 12 0 l' I 1' 32 I ~ ! r I \ 
' 
' I 
3f 31" 
I ( 
- 0-20 cm.sec"1 '\ 
-- _. 0-40 cm.sec •1 
26° 28 30 3 34° E 
26° za• 0 30 31 34' 
0 
33 
(B) 
0 
32 
__,. 0-10 em. sec "1 
26° 28" 32° 34° E 
Fig.7. Geostrophic current pattern at the 100 db surface along the Egyptian 
Mediterranean coast dunng: (A) winter and (B) summer. 
Said and Bid: Circulation pattern of the Egyptian Mediterranean waters 97 
N 
0 
33 
. 
32 
,. 
Jf f . \ 
N 
32° 34° E 
Fig. 8. Dynamic relief (dyn. m) at the 250 db surface during: (A) winter and (B) 
summer. 
0 
31 
(A) 
(B) 
I 
i 
'\. • f' 
- 0-20 crn.sec •1 
~ 0-10 cm.sec -1 
26° 28° 
\ " 
r 
.. _ __,\.J \,I\ 
" ./ '-.. I \ / __.\ .,-
N 
3( E 
Fig. 9. Geostrophic curr.etit pattern at the 250 db surface along the Egyptian 
Mediterranean coast during: (A) winter and (B) summer. 
98 Pakistan Journal of Marine Sciences, Vo1.3(2), 1994. 
southeastern direction in front of the Nile Delta. In summer, the inflow from the west 
.flows eastward parallel to the coast and bifurcates into two parts. The great part of 
this flow is directed to t'1e east and a minor part is carried to the southeast and bends 
southward to the coast at approximately the 30°E longitude. This surface water flows 
into the Mediterranean from the Atlantic through the strait of Gibraltar with a salinity 
value of 36.25 ppt. Salinity increases to reach 37.25 ppt in the Strait of Sicily and to 
values higher than. 38.50 ppt in the Levantine Sea forming the Modified Atlantic 
Water. The currents west to east path across the Mediterranean can be tracked by a 
subsurface salinity minimum (Lacombe and Tchernia, 1960), the signature of its 
Atlantic origin. 
Another flow of water entering the eastern part of the area from the Levantine Sea, 
originates a current of velocity range 10-25 em/sec moving to the west in winter and 
reverse its direction to the east in summer. (Figs. 2A and B). This flow may be 
incoming from the Cyprus high or from the Levantine cyclonic gyre. 
Dynamic topography for the upper 50 and 100m levels (Figs.4A-7B) reveals the 
same general pattern of those observed at the surface for the winter and summer 
seasons. Except in summer, El-Arish gyre is completely absent while the Mersa 
Matruh gyre at 100m level splits into two centres (Fig.6B). 
At the deeper levels (Figs.8A-9B), small eddies appear within the major gyres as 
well as between them. The Mersa Matruh gyre is intensified and split into multiple 
centres. The eddy centres are shifted horizontally with depth. These features were 
also observed and discussed by Ozsoy et a/. (1989). At the 500 m level, the Mersa 
Martuh gyre could be obs.erved during the both seasons, while El-Arishgyre could 
still be identified only in winter and consists of two. small gyres. 
Winter gcostrophic current charts for the 250 and 500 m levels indicate that, the 
Levantinc Intermediate Water is transported from the Levantine Sea to the eastern. 
coast of Egypt and flows away from the continental shelf to the open sea in the 
northwest direction. The current velocity of the intermediate water reaches 5-12 
em/sec. 
The general features of the circulation of the intermediate layers on the Egytian 
Mediterranean shelf coinr..:ide with the movements of waters described by Said and 
Karam (1990). In their work they concluded that; 11 ln winter, a low-salinity tongue 
extends from the open sea in the north to the eastern coast of Egypt, in which 
low~salinity water (<38.95 ppt) is carried southward and reaches the Egyptian coast 
with its salinity increasing to about 39.10 ppt. This water. is combined with the 
intermediate water formed on the Egyptian shelf from the three regions of tis 
formation. These saline waters flow away from the continental shelf to the open sea 
in the northwest direction11 with values as low as 38.95 ppt. 
Comparing SharafEl-Din and Karam's (1976) and Karam's (1977) maps with the 
results of the present worl} one can find that the two major gyres (Mersa Matmh and 
El-Arish) were absent in the previous works. These gyres arc clearly observed in the 
present work. This is due to the significant increase in the number of the hydrographic 
stations which were c.arried out in study area during recent years, and the method used 
for obtaining the average data in a regular net for the study area. 
Said and Eid: Circulation pattern of the Egyptian Mediterranean waters 99 
CONCLUSION 
The oceanographic data used in the present study were selected from several 
expeditions carried out by Egypt and different countries for the last 27 years 
(1959-1986). The average values of temperature and sal1nity of tl1ese data were 
computed, using the optimum interpolation of the correlation algorithm, for stations 
distributed in a regular grid of half degree latitude by half degree longitude for the 
separate winter and summer seasons. 
The surface circulation of the Egyptian Mediterranean waters is dominated by the 
Atlantic water inflow along the North African Coast, and by Mersa Matruh 
anticyclonic gyre. A new cyclonic gyre called El-Arish gyre was observed in the 
eastern part of the study area. The results showed a seasonal reversal circulation of 
El-Arish gyre, being cyclonic in winter and anticyclonic in summer. At deper levels 
(250 and 500m), small eddies appear within the major gyres as well as between them. 
The Mersa Matruh gyre is intensified and split into multiple centres. The eddy centres 
are shifted horizontally with depth. The geostrophic current velocity at the edges of 
Mersa Matruh gyre varied betweenl2.5 and 29.1 em/sec in winter and betwen6.5 and 
13.1 cni/sec in summer. ·The current velocity reached its maximum values (>40 
em/sec) at Ef-Arish gyre. The current velocity at the two gyres decreased with 
increasing depth. The North African Current affects the surface waters down to a depth 
of 100 m, and that its mean velocity varies between 6 and 38 em/sec. 
More observations are needed to define the year to year variabilities of these gyres, 
and their responses to atmospheric forcing. 
REFERENCES 
Abdel-Moati, A.R. and M.A. Said, 1987. Hydrographic structure of the Mediterranean shelf waters off the Egyptian 
coast during 1983-1986. Journal Thalassographica 10: 23-39. 
Brenner, S. 1988. Structure and evaluation of warm core eddies in the Eastern Mediterranean Levantine Basin. 
Journal ofGeophysics Research 94: 12593-12602. 
Gerges, M.A. 1981. Average monthly patters of surface currents measured in the southeastern Mediterranean off 
the Egyptian coast. Rapports Commission InternationaleMer Mediterranee 27: 77-81. 
Groen, P. 1948. Methods for estimating dynamic slopes and currents in shallow water: Journal ofM arine Research 
7: 313-316. 
Halim, Y., S.K. Guergues and H.H. Saleh, 1967. Hydrographic conditions and plankton in the southeastern 
Mediterranean during the last normal Nile flood (1964). Revue Gesemten Hydrobiolgi 52: 401-425. 
Hassan, H.M. 1969. The hydrography of the Mediterranean waters along the Egyptian coast. M.Sc. Thesis, 
Alexandria University. Pp.214. 
Karam, A.M. 1977. Study of currents infront of the Nile Delta using physical and dynamical methods. M.Sc. 
Thesis, Alexandria University. Pp.107. 
Lacombe, H. and P. Tchernia. 1960. Quelques trait generaux de l'hydrologie Mediterraneenne. Cah. Oceanogr. 
12: 525-547. . 
Marcos, S.A. and H.M. Hassan. 1976. The water masses and circulation in the southeastern Mediterranean. Acta 
Atriatica 18: 195-218. 
Ozsoy, E., A. Hecht and U. Unluata. 1989. Circulation and hydrography of the Levatitine Basin: Results of POEM 
Coordinated Experiment 1985/1986. Progress in Oceanography 22: 125-170. 
Saad, N.N. 1984. Hydrograhpicstructure of the continental shelf area from El-Agamy to El-Arish. M.Sc. Thesis, 
Alexandria University. Pp.l04 . . 
Said, M.A. 1984a. The spatial statistical structure of water temperature and salinity of the Mediterranean Sea . 
. Journal ofMeteorology, Climatoloty and Hydrology 2: 56-61 (In Russian). 
Said, M.A. 1984b. Water circulation in the central and eastern basins of the Mediterranean Sea and the formation 
of the intermediate water masses. Ph.D. Thesis, Odessa (USSR). Pp. 163 (In Russian). 
100 Pakistan Journal of Marine Sciences, Vol.3(2), 1994. 
Said, M.A. 1990. Horizontal circulation of the Eastern Mediterranean waters during winter and summer seasons. 
Acta Adriatica 31: 5-21. 
Said, M.A. and A.M. Karam. 1990. On the formation of the intermediate water masses otT the Egyptian 
Mediterranean coast. Archivji1r Hydrobiolgie 120: 111-122. 
Sandstrom, J.W. and Helland-Hansen. 1903. Uber die Berechnung Von Meeresstromungen. Report of the 
Nonvegian Fisheries Marine Investigation Board 2: Pp.43. 
SharafEl-Din, S.H. 1976. Current regime over the continental shelfinfront of the Nile Delta. Rapports Commission 
InternationaleMer Mediterranee 23: 71-73. 
SharafEl-Din, S.H. and A.M. Karam. 1976. Geostrophic currents in the southeastern sector ofthe Mediterranean 
Sea.ActaAdriatica 18:221-235. 
(Received: 5 April1994) 


Circulation pattern of the Egyptian Mediterranean waters during winter and summer seasons

http://aquaticcommons.org/16130/1/PJMS3.2_091.pdf

Circulation pattern of the Egyptian Mediterranean waters during winter and summer seasons

Abstract

Similar works

Full text

Available Versions

Aquatic Commons