37
Estimation of the salt storage and the salt content in the Gulf of Suez
Mohamed Gad a, , Fahmy Eid b, Sayed Sharaf El-Din b, Ahmed Radwan c , Girgis Soliman a
a National Institute of Oceanography and Fisheries, Suez and Aqaba Gulfs Branch, Suez, Egypt
b Oceanography Department, Faculty of Science, Alexandria University, Alexandria, Egypt
c
National Institute of Oceanography and Fisheries, Mediterranean Sea Branch, Alexandria, Egypt
Abstract. this paper aims at evaluating the salt storage and the salt content in the Gulf of Suez over the 1889 to 2011 period using available hydrographic data. Unfortunately, neither the salt storage nor the salt content has been computed in the Gulf through any former survey; consequently, the current study may be considered as the first endeavor to conduct these research topics in that region. The results revealed that the salt storage decreased over the year-round from the north to the south where its maxima were found at the head of the Gulf; however, its minima were located at the entrance of the Gulf. In spite of its pronounced increase with depth in winter and most spring along the Gulf, the salt storage lowered generally with depth in summer over there. On the one hand, the salt content reached its maximum value of approximately 3.5589 (109 ton) in the middle part of the Gulf in December within the water column of 50 m depth; but on the other, the salt content per unit volume attained its highest one of almost 43.8979 Kg/m3 in the extreme northern part of the Gulf in October within the same water column.
Keywords: Gulf of Suez, Salt storage, Salt content
Corresponding author at: National Institute of Oceanography and Fisheries, Suez and Aqaba Gulfs Branch, Suez, Egypt.
E-mail address: mohamed.gad@niof.sci.eg
1 Introduction
The Gulf of Suez is a strategic national security zone which connects the Red Sea Proper with the Mediterranean Sea through the Suez Canal. It has great economic importance for international navigation, offshore and onshore oil production, tourism, and fisheries.
The Gulf, covering an area of approximately 10,000 km2, is a shallow basin of about 300 km long and almost 65 m depth over its main axis (Figure 1). There is a group of islands and coral reef barriers at the entrance of the Gulf, where the bottom slopes to depths of more than 500 m (Morcos, 1970). The Gulf is obviously narrow; however, its widest area is located to the south from Zafarana, where the width reaches about 54 km. In the northern part of the Gulf, the slopes of the western and eastern sides are very simple so the depths attain only 2 m at 2 km far from the shore (Nawar, 1981).
The Gulf is classified as an inverse (or negative) estuarine system, where freshwater losses from evaporation exceed freshwater additions from precipitation. Indeed, the previous studies mentioned that the water circulation of the Gulf is generally acted in two opposite directions: warm less saline water intrudes into the Gulf from the Red Sea proper at the surface and colder more saline water flows near the bottom of the Gulf into the Red Sea proper (Anwar, 2003; El-Sabh and Beltagy, 1983; Gad, 2016; Gorgy and Shaheen, 1964; Luksch, 1901; Maillard, 1974;
Mohamed, 1940; Morcos, 1970; Murray and Babcock, 1982; Said et al., 2009; Sofianos and Johns, 2017; Soliman, 1995; Vercelli, 1927;
Wyrtki, 1974) . Actually, the bottom dense water of the Gulf is approved as an essential source for the formation of the deep water in the Red Sea (Cember, 1988; Maillard, 1974;
Sofianos and Johns, 2017; Woelk and Quadfasel, 1996; Wyrtki, 1974).
Figure 1 Bathymetric chart of the Gulf of Suez
In addition to the familiar factors which mainly control the salt and water balances in oceanic basins (evaporation, water exchange with adjacent seas, precipitation, and river runoff), there were two another factors in the case of the Gulf of Suez: the extensive salt layers at the bottom of the Gulf (Morcos, 1970) and the salt deposits in the Great Bitter Lake waters that reached the Suez Bay (the head of the Gulf) in September during the southern current regime in the Suez Canal (Morcos and Gerges, 1974; Morcos, 1960;
Morcos and Messieh, 1973; Morcos and Soliman, 2001; Sharaf El-Din, 1974).
However, Soliman and Morcos (1990) found that the salt deposits had insignificant influence on the water salinity in the Great Bitter Lake after the deepening and widening of the Suez Canal and the Bitter Lakes in 1976. Combined with very slight precipitation and absent river runoff in the Gulf region, the evaporation was 0.7 cm/day in winter and 1.2 cm/day in summer at Suez; however, it was 1 cm/day in winter and1.75 cm/day during summer at the entrance of the Gulf (Soliman, 1995).
Knowledge of the salt distribution in the world ocean and its annual and inter-annual variability is of great significance in the investigation of the ocean role in the Earth’s climate such as dynamics of thermohaline circulation of the global ocean, hydrological cycle of the earth and climate modeling efforts. Furthermore, salinity plays an important role in the formation of water masses since it affects the depth of penetrative convection (Levitus, 1986). Using historical data, Reid (1965) concluded that the low surface salinity prevented deep water formation in the North Pacific Ocean. Indeed, the formation of water masses is substantial for studying heat transport and various substances, such as pollutants that presently threaten the marine entities and the ecosystems
particularly in the northwestern coast of the Gulf of Suez (Fahmy et al., 2005; Hamed and Emara, 2006; Mohamed et al., 1997).
Moreover, Soliman (1996) attributed the lower values of the salinity at the extreme northern part of the Suez Bay, than those at its middle region during 1991, to the huge amounts of domestic sewage and fresh water drain released at the northern extremity of the Bay.
Globally, the annual cycle of the salt storage was studied in the world ocean (Levitus, 1986), in the Indian Ocean (Shi et al., 2003), and in the Red Sea (Alraddadi, 2013; Hassan, 2010; Kamel and Eid, 2005); however, the yearly cycle of the salt content was described by a few investigators such as Hassan (2010) in the Red Sea and Morcos and Soliman (2001) in the Suez Canal.
The lack of synoptic oceanographic data, on basin-wide scales, may greatly reduce the studies carried out in the Gulf of Suez.
Actually, this indicator reflects the importance of the present work which may be deemed as the first attempt to calculate the salt storage together with the salt content in the Gulf region. The material and methods are demonstrated in section 2, results and discussions in section 3 and conclusions in section 4.
2 Material and Methods
2.1 Data sources 2.1.1 Hydrographic data
The hydrographic datasets, figure 2, used throughout the current study were retrieved from national and international data centers in the period from 1889 to 2011 at the standard depths (the surface, 10 m, 20 m, 30 m, 50 m, and 75 m) as the following:
1. Monthly profiles of water temperature and salinity between1889 and 2011 were obtained from the world ocean database (WOD09) of the National Oceanographic Data
Center (NODC -NOAA),
(www.nodc.noaa.gov). Those datasets were the main source of all existing hydrographic data for the Gulf region. Alraddadi (2013), Hassan (2010) together with Kamel and Eid (2005) utilized the datasets of the NODC for similar oceanographic studies.
2. The Egyptian National Oceanographic Data Center (ENODC), which is affiliated to the National Institute of Oceanography and
Fisheries (NIOF)
(http://www.niof.sci.eg/index.php/res-
data/oceanography-fisheries), supplied the current investigation with water temperature and salinity stations which were collected by different Expeditions in the Gulf as follows:
i.The Egyptian R/V MABAHISS, during the period 22–26 of December 1934.
ii.The French R/V Cdt. ROBERT GIRAUD during the period 14.1–11.2.1963.
iii.The Japanese R/V SHOYO MARU during the period 23–24 of March 1959.
iv.The American R/V ATLANTIS in February 1965.
v.The Russian R/V ICHTIOLOG in September 1966.
vi. The French R/V MARION DUFRESNE in June and October 1982.
vii. The Egyptian R/V Al-Sadat Ward El- Hadith in August 1996.
viii.The Egyptian NIOF R/V in discrete time intervals such as January and March 1979, March 1990, November 1990 to October 1991, September and January 1993, and August 2004.
2.1.2 Bathymetric data
One hundred thirty-three lateral bathymetric sections, with an equal zonal interval of one minute, were extracted from the data library of the International Research Institute for Climate and Society, Columbia University, (http://iridl.ldeo.columbia.edu/). Indeed, those sections were already utilized to calculate the salt content in the Gulf and to draw the bathymetric map, which is given in figure 1.
2.2 Methodology
2.2.1 Estimation of σt value
A few unsteady water temperature and salinity stations were excluded to guarantee a better quality for the used hydrographic data as much as possible. The σt values were estimated from the filtered values of temperature and salinity at the standard depths (the surface, 10 m, 20 m, 30 m, 50 m, and 75 m) in the Gulf of Suez using the equation of Mamayev (2010):
(1)
Where: T is water temperature (oC) and S is water salinity (psu).
Figure 2 Distribution of hydrographic data from January to December between 1889 and 2011 (♦:
T (oC) and S (psu) observations; ●: T (oC) observations only, and ▲: S (psu) observations only).
2.2.2 Estimation of the monthly averages of water temperature, Salinity, and σt value To overcome the lack of data, the Gulf was divided into five lateral sub-basins, figure 3, as follows: I (29.96°N – 29.5°N), II (29.5°N – 29°N), III (29°N – 28.5°N), IV (28.5°N – 28°N), and V (28°N – 27.5°N). The monthly mean of water temperature (°C), salinity (psu) and σt value at the surface was obtained by averaging all stations of water temperature (°C), water salinity (psu) and σt, respectively, within the two borders of each sub-basin. The same procedure was repeated at each level to get complete datasets (i, j, n) of monthly averages concerning temperature (°C), salinity (psu) and σt ;where: i is the number of the sub- basin (1,…., 5), j is the number specified for the successive levels at the surface, 10 m, 20 m, 30 m, 50 m, and 75 m depths (j= 0,1,……, 5), and n is the month (1,……, 12).
2.2.3 Estimation of the salt storage
The computation of the salt storage (SS) is given by Levitus (1986):
(2) Where: SS is the salt storage within the within a certain layer (kg/m2), C is the conversion factor (= 1 kg/1000 gm), ρ is the mean density of the layer (kg/m3), S is the mean salinity of the layer (psu), and dz: is the thickness of the layer (m).
Simple mathematical model was applied using the finite difference method to estimate the monthly salt storage values with a certain limit of accuracy SS (k, i, n) within a specified layer (k= 1,…,5) for each sub-basin i (1,…,5) at each month n (1,…...,12) as follows:
(3) Where: SS (k, i, n) is the salt storage within the specified layer (k) in the sub-basin (i) in the month (n), and Z (j): is the depth of the level j (j = 0,…, 5).
2.2.4 Estimation of the salt content
The salt content (SC) within a certain layer is given by Morcos and Soliman (2001):
Figure 3 Locations of selected sub-basins (I, II, III, IV, and V) over the Gulf.
(4) (4)
(5) (5)
(6) (6)
Where: SC (k, i, n): is the salt content within the specified layer (k) in the sub-basin (i) in the month (n), and : is the volume of the layer.
Due to the topographic complexity of the Gulf, the following procedure was considered:
i. The Gulf was divided laterally into 133 bathymetric sections with an equal zonal interval of one minute.
ii. The width of each section was defined from the Admiralty chart.
iii. For each section, the depth profile was drawn between the two sides of the Gulf.
iv. The two cross-sectional areas for each layer were estimated for the profile sequences (0 – 10 m, 10 – 20 m, 20 – 30 m, 30 – 50 m, and 50 – 75 m depths).
v. The volume between two successive profiles was estimated for each layer.
vi. The volume of the water column for each sub-basin, as the summation of the successive layers from the surface to the required depth, was estimated as V (k, i) (Table 1).
vii. To calculate the volume of the water columns in the sub-basin V, the lower limit of the sub-basin latitude interval, 27.5°N, was adjusted to become 27.73°N.
sub-
basin Water
column
0→10 0→20 0→30 0→50 0→75
I 10.83 19.45 26.65 34.29
II 16.30 30.53 42.62 62.63
III 21.08 39.74 56.02 82.35
IV 19.16 35.89 50.18 71.42
V 12.60 22.31 30.07 42.18 52.57
3 Results and Discussions
The monthly values of the salt storage (ton/m2) were computed within the successive layers (0 – 10 m, 10 – 20 m, 20 – 30 m, 30 – 50 m, and 50 – 75 m) in the five sub-basins (I, II, III, IV, and V) along the Gulf from 1889 to 2011, table 2. In the sub-basin I, the maximum values of the salt storage were found in October within the first and the second layers and in December within the third and the fourth layers; however, the minimum ones were located in February within the first and the second layers, in April within the third layer, and in July within the fourth layer.
Indeed, the existence of the salt storage
maxima in autumn (October – December) indicates that evaporation was not the main factor for maintaining the salt storage maximums (Levitus, 1986; Morcos and Soliman, 2001); moreover, this feature was also observed in the sub-basins II, III, and IV.
On the other hand, the exchange between the different water masses may contribute to the presence of the salt storage maxima in the sub- basin I, where the high saline water may reach in September from the Great Bitter Lake during the southern current regime in the Suez Canal (Morcos and Gerges, 1974; Morcos, 1960; Morcos and Messieh, 1973; Morcos and Soliman, 2001; Sharaf El-Din, 1974).
Table 1 Volumes (10 9 m3) of the water columns of 10 m, 20 m, 30 m, 50 m, and 75 m depths in the five sub-basins (I, II, III, IV, and V) along the Gulf.
Overall, the salt storage increased from the south to the north, where the minima were found in the sub-basin V; however, the maxima were obtained in the sub-basin I, figure 4. Vertically, the salt storage grew evidently with depth in winter (January – March) and most spring (April – May) over the Gulf; however, it decreased generally with depth in early summer and summer (June – September) there. In the sub-basin V, the water homogeneity may lead to the same approximate value of the salt storage, in
winter, with about 0.414, 0.415, and 0.4143 ton/m2 within the upper three layers (0 – 10 m), (10 – 20 m), and (20 – 30 m), respectively;
however, the salt storage within the deeper layer manifested an evident increase which may be relevant to the outflowing colder saline water from the Gulf to the Red Sea (Anwar, 2003; El-Sabh and Beltagy, 1983; Gad, 2016;
Gorgy and Shaheen, 1964; Luksch, 1901;
Maillard, 1974; Mohamed, 1940; Morcos, 1970; Murray and Babcock, 1982; Said et al., 2009; Sofianos and Johns, 2017; Soliman, Table 2 Monthly values of the salt storage (ton/m2) within the successive water layers (0 – 10 m, 10 – 20 m, 20 – 30 m, 30 – 50 m, and 50 -75 m) in the five sub-basins (I, II, III, IV, and V) over the Gulf from 1889 to 2011.
sub- basin
sub-basin interval
(oN)
layer thickness
(m) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
I 29.96→29.5 0→10 0.4301 0.4270 0.4348 0.4309 0.4343 0.4366 0.4354 0.4352 0.4368 0.4385 0.4372 0.4361 I 29.96→29.5 10→20 0.4303 0.4297 0.4351 0.4328 0.4358 0.4343 0.4344 0.4353 0.4361 0.4374 0.4372 0.4368 I 29.96→29.5 20→30 0.4327 0.4336 0.4350 0.4325 0.4355 0.4344 0.4346 0.4359 0.4361 0.4375 0.4380 0.4382 I 29.96→29.5 30→50 0.8671 0.8683 0.8697 0.8664 0.8671 0.8640 0.8638 0.8668 0.8695 0.8758 0.8771 0.8782 II 29.5→29 0→10 0.4285 0.4299 0.4292 0.4273 0.4302 0.4312 0.4317 0.4338 0.4319 0.4336 0.4340 0.4320 II 29.5→29 10→20 0.4301 0.4300 0.4298 0.4287 0.4326 0.4301 0.4308 0.4338 0.4319 0.4339 0.4343 0.4333 II 29.5→29 20→30 0.4299 0.4302 0.4309 0.4300 0.4332 0.4302 0.4309 0.4344 0.4320 0.4334 0.4348 0.4349 II 29.5→29 30→50 0.8627 0.8624 0.8648 0.8641 0.8614 0.8455 0.8567 0.8622 0.8640 0.8676 0.8716 0.8729 III 29→28.5 0→10 0.4210 0.4203 0.4267 0.4231 0.4258 0.4253 0.4267 0.4311 0.4284 0.4316 0.4294 0.4311 III 29→28.5 10→20 0.4212 0.4211 0.4275 0.4262 0.4270 0.4248 0.4259 0.4312 0.4292 0.4312 0.4297 0.4315 III 29→28.5 20→30 0.4219 0.4222 0.4287 0.4281 0.4265 0.4248 0.4259 0.4305 0.4302 0.4316 0.4300 0.4310 III 29→28.5 30→50 0.8497 0.8502 0.8592 0.8568 0.8516 0.8471 0.8478 0.8528 0.8610 0.8633 0.8628 0.8651 IV 28.5→28 0→10 0.4170 0.4178 0.4195 0.4176 0.4222 0.4190 0.4212 0.4210 0.4233 0.4251 0.4233 0.4203 IV 28.5→28 10→20 0.4172 0.4179 0.4194 0.4188 0.4217 0.4186 0.4206 0.4201 0.4231 0.4255 0.4236 0.4207 IV 28.5→28 20→30 0.4180 0.4184 0.4206 0.4191 0.4197 0.4189 0.4201 0.4196 0.4234 0.4265 0.4239 0.4217 IV 28.5→28 30→50 0.8398 0.8408 0.8454 0.8437 0.8406 0.8376 0.8386 0.8382 0.8362 0.8571 0.8505 0.8471 V 28→27.5 0→10 0.4139 0.4157 0.4143 0.4140 0.4170 0.4115 0.4172 0.4198 0.4198 0.4127 0.4178 0.4165 V 28→27.5 10→20 0.4136 0.4151 0.4143 0.4140 0.4141 0.4118 0.4164 0.4179 0.4198 0.4141 0.4179 0.4157 V 28→27.5 20→30 0.4138 0.4149 0.4143 0.4140 0.4139 0.4130 0.4155 0.4153 0.4193 0.4147 0.4178 0.4151 V 28→27.5 30→50 0.8288 0.8315 0.8284 0.8284 0.8310 0.8279 0.8313 0.8306 0.8368 0.8287 0.8378 0.8322 V 28→27.5 50→75 1.0367 1.0401 1.0406 1.0386 1.0356 1.0364 1.0387 1.0384 1.0384 1.0342 1.0468 1.0473
1995; Vercelli, 1927; Wyrtki, 1974). Up to June, the situation started to change at the same sub-basin V where the salt storage decreased with depth; for instance, the salt storage values within the five layers, with an equal interval of 10 m depth, were 0.4172 ton/m2, 0.4164 ton/m2, 0.4155 ton/m2, 0.4156 ton/m2, and 0.4154 ton/m2 in July, 0.4198 ton/m2, 0.4198 ton/m2, 0.4193 ton/m2, 0.4184 ton/m2, 0.4153 ton/m2 in September, and 0.4127 ton/m2, 0.4141 ton/m2, 0.4147 ton/m2, 0.4144 ton/m2, 0.4136 ton/m2 in October, respectively. These aforementioned values indicate that the salt storage decreased with depth, specifically near the bottom, in the sub- basin V in summer; however, the maximum evaporation existed over there in that season (Soliman, 1995).
Figure 4 Annual cycles of the salt storage (10- 2 ton/m2) within the successive water layers (0 – 10 m, 10 – 20 m, 20 – 30 m, 30 – 50 m, and 50 -75 m) in the five sub-basins (I, II, III, IV, and V) along the Gulf from 1889 to 2011.
Patzert (1972) and (1974) mentioned that the mean sea level in the northern part of the Red Sea is high in winter and low in summer as a result of the monsoon system of the Arabian Sea; accordingly, the water flow is directed northward in winter, against the action of the predominant north-northwesterly winds, and to the south in summer. He also added that the strong southerly flow in the surface layer of the northern Red Sea during summer must make the surface layer divergent and cause the water between 100 m and 200 m depths to upwell; consequently, the current study supposes that the upwelled less saline water may intrude from the Red Sea into the entrance of the Gulf of Suez and extend northward in the Gulf in order to attain the situation of the salt storage decrease with depth during summer along the Gulf. This hypothesis may be produced from the elusiveness of the water circulation in the Gulf together with its exchange with the Red Sea proper over the year-round (Eladawy et al., 2018; Gad, 2016; Sofianos and Johns, 2017;
Soliman, 1995).
The monthly values of salt content (109 ton) within the water columns of 10 m, 20 m, 30 m, 50 m, and 75 m depths were computed at the different sub-basins over the Gulf, table 3. The annual cycles of the salt content presented their maxima in the sub-basin III (the sub- basin V) in October and December (September) within the water columns of 10 m, 20 m, 30 m, and 50 m depth (75 m depth);
however, they demonstrated their minima in the sub-basin I (sub-basin V) in February (January) within the water columns of 10 m, 20 m, 30 m, and 50 m depth (75 m depth).
These resultant variations are mainly attributed to the great variability in the capacity of each sub-basin along the Gulf, as given in table 1, where the sub-basin III had the maximum capacity; but, the sub-basin I had the minimum one. For instance; within the water column of 50 m depth, the maximum value of the salt content was 3.5589 (109 ton) in the sub-basin III in December; however, the minimum one
was 1.4657 (109 ton) in the sub-basin I in February. The consequent range of variation in the salt content was 2.0932 (109 ton) within
that water column over the Gulf and all over the year.
Table 3 Monthly values of the salt content (109 ton) within the water columns of 10 m, 20 m, 30 m, 50 m, and 75 m depths in the five sub-basins (I, II, III, IV, and V) over the Gulf from 1889 to 2011.
column thicknes s (m)
sub- basi n
sub-basin interval
(oN)
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 0→10 I 29.96→29.
5 0.4656 0.4585 0.4704 0.4665 0.4678 0.4715 0.4703 0.4711 0.4718 0.4747 0.4747 0.4721 0→10 II 29.5→29 0.6987 0.7009 0.6998 0.6967 0.7014 0.7030 0.7039 0.7074 0.7042 0.7070 0.7076 0.7043 0→10 III 29→28.5 0.8876 0.8862 0.8997 0.8921 0.8979 0.8967 0.8996 0.9089 0.9033 0.9099 0.9055 0.9089 0→10 IV 28.5→28 0.7991 0.8008 0.8040 0.8004 0.8091 0.8029 0.8073 0.8069 0.8112 0.8147 0.8113 0.8055 0→10 V 28→27.73 0.5234 0.5239 0.5211 0.5214 0.5257 0.5278 0.5275 0.5251 0.5308 0.5209 0.5244 0.5251 0→20 I 29.96→29.
5 0.8364 0.8302 0.8454 0.8375 0.8409 0.8469 0.8459 0.8484 0.8487 0.8532 0.8532 0.8498 0→20 II 29.5→29 1.3063 1.3120 1.3111 1.3061 1.3143 1.3160 1.3188 1.3264 1.3184 1.3232 1.3257 1.3221 0→20 III 29→28.5 1.6734 1.6723 1.6971 1.6857 1.6871 1.6880 1.6966 1.7154 1.7056 1.7156 1.7065 1.7109 0→20 IV 28.5→28 1.4975 1.4999 1.5071 1.4979 1.5025 1.5025 1.5114 1.5113 1.5189 1.5272 1.5194 1.5092 0→20 V 28→27.73 0.9280 0.9286 0.9230 0.9259 0.9319 0.9355 0.9350 0.9301 0.9386 0.9229 0.9285 0.9296 0→30 I 29.96→29.
5 1.1479 1.1387 1.1588 1.1479 1.1527 1.1606 1.1586 1.1615 1.1616 1.1690 1.1690 1.1661 0→30 II 29.5→29 1.8253 1.8329 1.8344 1.8268 1.8361 1.8381 1.8405 1.8516 1.8408 1.8461 1.8520 1.8480 0→30 III 29→28.5 2.3628 2.3611 2.3970 2.3812 2.3829 2.3826 2.3904 2.4106 2.4056 2.4197 2.4076 2.4116 0→30 IV 28.5→28 2.0964 2.0996 2.1113 2.0971 2.1086 2.1041 2.1117 2.1107 2.1256 2.1383 2.1258 2.1141 0→30 V 28→27.73 1.2538 1.2534 1.2430 1.2515 1.2584 1.2610 1.2587 1.2514 1.2659 1.2445 1.2530 1.2552 0→50 I 29.96→29.
5 1.4778 1.4657 1.4895 1.4784 1.4816 1.4909 1.4864 1.4874 1.4914 1.5053 1.5053 1.4888 0→50 II 29.5→29 2.6893 2.6981 2.6993 2.6924 2.6808 2.6535 2.6900 2.7006 2.7050 2.7170 2.7261 2.7223 0→50 III 29→28.5 3.4919 3.4891 3.5246 3.4959 3.4909 3.4878 3.4995 3.5213 3.5371 3.5560 3.5479 3.5589 0→50 IV 28.5→28 2.9934 2.9985 3.0136 3.0000 2.9940 2.9888 3.0014 3.0033 2.9846 3.0533 3.0330 3.0165 0→50 V 28→27.73 1.7643 1.7646 1.7570 1.7464 1.7618 1.7696 1.7714 1.7668 1.7739 1.7587 1.7673 1.7683 0→75 V 28→27.73 2.1745 2.2038 2.2089 2.2117 2.2254 2.2321 2.2326 2.2254 2.2348 2.2075 2.2152 2.2164
Generally, it is difficult to make any comparability between the amounts of the salt content (109 ton), given in table 3, because they are directly proportional to the volumes of the water columns over the Gulf. Table 4 was produced to give the monthly values of salt content per unit volume (Kg/m3) within the aforesaid water columns along the Gulf, where the maxima were found in the sub-basin
I (sub-basin V) in October - November (September) within the water columns of 10 m, 20 m, 30 m, and 50 m depths (75 m depth);
however, the minima were located in the sub- basin V in October (March, April, and January) within the water columns of 10 m and 20 m depths (within the water column of 30 m, 50 m, and 75 m depths, respectively). For example; within the water column of 50 m
depth, the salt content per unit volume reached its highest value of approximately 43.8979 Kg/m3 in the sub-basin I in October; however, it attained its lowest one of almost 41.4062 Kg/m3 in the sub-basin V in April. The resultant range of variation of the salt content per unit volume was 2.4917 Kg/m3 withinthat water column around the year and along the Gulf.
Actually, the comparison of those results of the salt content (109 ton), in table 3, with those of the salt content per unit volume (Kg/m3), in table 4, indicates obvious differences between the locations of the maxima. In other words, the highest values of the salt content were observed in the sub-basin III, of the maximum capacity, in October; however, the maximum values of the salt content per unit volume were mostly found in October - November in the sub-basin I where the outflowing salty water, from the Great Bitter Lake, may arrive the Suez Bay in September (Morcos and Gerges, 1974; Morcos, 1960; Morcos and Messieh, 1973; Morcos and Soliman, 2001; Sharaf El- Din, 1974).
Table 4 Monthly values of the salt content per unit volume (Kg/m3) within the water columns of 10 m, 20 m, 30 m, 50 m, and 75 m depths in the five sub-basins (I, II, III, IV, and V) along the
Gulf from 1889 to 2011.
column thickness (m)
sub- basin
sub-basin interval
(oN)
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
0→10 I 29.96→29.5 43.0079 42.3552 43.4573 43.0930 43.2118 43.5558 43.4477 43.5177 43.5820 43.8495 43.8495 43.6113
0→10 II 29.5→29 42.8510 42.9895 42.9228 42.7323 43.0194 43.1178 43.1732 43.3842 43.1871 43.3624 43.4014 43.1958
0→10 III 29→28.5 42.0985 42.0303 42.6703 42.3113 42.5846 42.5290 42.6679 43.1062 42.8414 43.1569 42.9442 43.1066
0→10 IV 28.5→28 41.6987 41.7849 41.9503 41.7623 42.2174 41.8972 42.1247 42.1046 42.3297 42.5085 42.3336 42.0296
0→10 V 28→27.73 41.5491 41.5914 41.3686 41.3956 41.7317 41.8966 41.8739 41.6831 42.1381 41.3497 41.6267 41.6883
0→20 I 29.96→29.5 42.9966 42.6779 43.4555 43.0490 43.2272 43.5342 43.4832 43.6111 43.6253 43.8571 43.8571 43.6822
0→20 II 29.5→29 42.7908 42.9787 42.9488 42.7857 43.0544 43.1099 43.2018 43.4491 43.1879 43.3446 43.4274 43.3083
0→20 III 29→28.5 42.1108 42.0836 42.7074 42.4197 42.4548 42.4774 42.6949 43.1680 42.9221 43.1741 42.9442 43.0557
0→20 IV 28.5→28 41.7210 41.7863 41.9884 41.7303 41.8592 41.8603 42.1076 42.1050 42.3165 42.5465 42.3296 42.0459
0→20 V 28→27.73 41.5929 41.6222 41.3696 41.5002 41.7693 41.9295 41.9067 41.6883 42.0677 41.3666 41.6140 41.6648
0→30 I 29.96→29.5 43.0709 42.7259 43.4775 43.0706 43.2482 43.5465 43.4697 43.5808 43.5825 43.8605 43.8605 43.7532
0→30 II 29.5→29 42.8270 43.0036 43.0393 42.8608 43.0795 43.1254 43.1828 43.4439 43.1904 43.3152 43.4538 43.3598
0→30 III 29→28.5 42.1776 42.1471 42.7873 42.5059 42.5369 42.5315 42.6705 43.0311 42.9411 43.1926 42.9765 43.0487
0→30 IV 28.5→28 41.7759 41.8402 42.0747 41.7907 42.0208 41.9304 42.0823 42.0615 42.3591 42.6121 42.3625 42.1291
0→30 V 28→27.73 41.6972 41.6852 41.3387 41.6203 41.8515 41.9382 41.8616 41.6174 42.1003 41.3884 41.6722 41.7446
0→50 I 29.96→29.5 43.0966 42.7412 43.4379 43.1142 43.2061 43.4776 43.3473 43.3747 43.4911 43.8979 43.8979 43.4166
0→50 II 29.5→29 42.9391 43.0802 43.0991 42.9886 42.8042 42.3683 42.9515 43.1201 43.1898 43.3826 43.5279 43.4664
0→50 III 29→28.5 42.4020 42.3682 42.7994 42.4497 42.3896 42.3523 42.4936 42.7590 42.9505 43.1799 43.0821 43.2147
0→50 IV 28.5→28 41.9104 41.9825 42.1937 42.0027 41.9198 41.8464 42.0235 42.0496 41.7879 42.7494 42.4648 42.2347
0→50 V 28→27.73 41.8302 41.8366 41.6562 41.4062 41.7698 41.9566 41.9978 41.8889 42.0580 41.6979 41.9001 41.9256
0→75 V 28→27.73 41.3672 41.9241 42.0225 42.0748 42.3353 42.4631 42.4721 42.3366 42.5151 41.9959 42.1412 42.1645
4. Conclusions
Using available hydrographic data between 1889 and 2011, the salt storage and salt content were estimated for the first time in the Gulf of Suez. To cope with the lack of data, the Gulf was divided into five lateral sub- basins which were: I (29.96°N – 29.5°N), II (29.5°N – 29°N), III (29°N – 28.5°N), IV (28.5°N – 28°N), and V (28°N – 27.5°N).
Concerning the latitude interval of the sub- basin V, its lower limit was modified to become 27.73°N in order to compute the salt content. The findings revealed that the salt storage increased from the south to the north around the year, where its minima were found in the sub-basin V; however, its maxima were located in the sub-basin I. Moreover, the salt storage increased prominently with depth in winter and most spring along the Gulf;
however, it exhibited an overall decrease with depth over there. On the one hand, the maximum values of the salt content were almost observed in the sub-basin III; but on the other, the highest ones of the salt content per
unit volume were nearly noticed in the sub- basin I, over the year. Eventually, the present work may shed light on the necessity for further observational and modeling studies to improve our understanding of the elusive water circulation in the Gulf together with its interactions with the Red Sea proper and the Suez Canal all over the year.
Acknowledgments
This work was part of the MSc thesis of the first author who would like to express his deep gratitude and appreciation to the supervision committee, particularly Prof. Girgis Soliman for hydrographic data supply and fruitful discussions. Special thanks to the National Oceanographic Data Center (NODC – NOAA), the International Research Institute for Climate and Society (Columbia University), and the Egyptian National Oceanographic Data Center (chiefly Prof.
Ibrahim Maiyza and Associate Prof. Tarek El- Gizery) for providing hydrographic and bathymetric data.
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ﻟا ﺞ ﻠﺧ ﻲﻓ ﻲ ﻠ ﻟا ﻟا و ﻲ ﻠ ﻟا نو ﻟا ﯾ ﻘﺗ
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