Atmospheric dry deposition of mineral dust to the Gulf of Aqaba, Red Sea: rate and trace elements.

Marine Pollution Bulletin xxx (2014) xxx–xxx

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Atmospheric dry deposition of mineral dust to the Gulf of Aqaba, Red Sea: Rate and trace elements Ahmed A. Al-Taani ⇑, Maen Rashdan, Safaa Khashashneh Dept. of Earth and Environmental Sciences, Faculty of Science, Yarmouk University, Irbid 21163, Jordan

a r t i c l e

i n f o

Article history: Available online xxxx Keywords: Trace elements Dry fluxes Enrichment factor Gulf of Aqaba Red Sea Jordan

a b s t r a c t Atmospheric dry deposition to the Gulf of Aqaba (GoA) is particularly a significant source of trace elements. Amid desert regions, the Gulf receives high fluxes of mineral dust with an average rate of 34.68 g/m2/year measured in 2012. Patterns of dry deposition showed seasonal fluxes with highest rates observed in summer and lowest in winter. The observed variations were attributed to wind direction, timing of deposition and sources of dust. The average dry fluxes of Al, Fe, Mn, Cr, Cd, Cu, Pb and Zn were 551, 440, 10.29, 1.42, 0.04, 0.68, 1.42 and 4.02 mg/m2/year, respectively. While the dry deposition fluxes were enriched in Cd, Cu, Pb and Zn indicating their dominant anthropogenic sources, they appeared to be less influenced compared to the neighboring Mediterranean area and other industrial countries, but were similar to or slightly higher than those in remote areas. The enrichment values for Fe and Mn were low, consistent with their crustal origin. The fluxes of all elements suggested the impacts of both crustal (due to climate change) and anthropogenic sources became stronger in this region. The Sahara dust was probably a minor contributor to dry deposition in the GoA. Ó 2014 Elsevier Ltd. All rights reserved.

The Gulf of Aqaba (GoA) is a partially-enclosed basin which is located in an extremely arid region with negligible rainfall and virtually no surface runoff. It is surrounded by the Sinai and Negev Deserts to the west and by the Arabian Desert to the east. The Gulf’s location amid desert regions makes it subject to intense and frequent dust storms, where a large fraction of the aerosols delivered to the Gulf is principally derived from adjacent arid lands (Chase et al., 2006). The GoA also receives long-range atmospheric dust from distant deserts (e.g.: Sahara dust (Abed et al., 2009)). In addition to the desert mineral dust, the GoA is influenced by air masses containing anthropogenic aerosols originating from Europe during most of the year (Kouvarakis et al., 2001). However, the source of dry deposition to the Gulf depends on the timing of deposition, where the GoA is affected by two different wind directions; the prevailing northerly and the southerly winter winds. The atmospheric dry deposition to the Gulf is expected to increase due to the impacts of climate change. As aridity and potentially dust fluxes are expected to increase in the future (Tegen et al., 2004; Woodward et al., 2005), dust-dominated systems may become more common in this region. These aeolian fluxes to the GoA are likely to play a significant role in modifying the chemical composition of seawater. While dust deposition can ⇑ Corresponding author. Tel.: +962 779610469; fax: +962 7211117. E-mail address: [email protected] (A.A. Al-Taani).

stimulate the surface marine productivity by providing important nutrients (Dulac et al., 1996; Bergametti et al., 1992; Bishop et al., 2002; Jickells et al., 2005) especially in oligotrophic water (Duce et al., 2008) as that of the GoA (Levanon-Spanier et al., 1979; Batayneh et al., 2014), it may also contribute toxic elements and other contaminants which may affect the primary productivity and the marine biodiversity. The GoA has regular seasonal cycles of water mixing (during winter) and stratification (in summer). The impacts of airborne contaminants to the Gulf are likely to be significant during the summer stratification period, where metals, nutrients and phytoplankton are trapped in the euphotic zone (Mackey et al., 2007). In the GoA, atmospheric dry deposition is the major external source of trace elements and is likely to exceed their supply from continental runoff input (Chase et al., 2011). This has led to the widespread realization of the importance of dust deposition, particularly the elements contained in the mineral dust. Although the GoA has been studied with regard to air pollutants and their impacts on the marine ecosystem, little information currently exists on the relative contribution of trace metals from atmospheric dry deposition to the Gulf. This study is designed to quantify the atmospheric dry fluxes to the GoA with emphasis on the northeastern corner (Jordanian side of the GoA), and to investigate their relative contribution of trace metals. Furthermore, it compares the present results with those

http://dx.doi.org/10.1016/j.marpolbul.2014.11.047 0025-326X/Ó 2014 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Al-Taani, A.A., et al. Atmospheric dry deposition of mineral dust to the Gulf of Aqaba, Red Sea: Rate and trace elements. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.11.047

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A.A. Al-Taani et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx

previously reported for the same region (and other coastal regions) to help provide a baseline for evaluating future changes of atmospheric fluxes in this region. The GoA is the eastern segment of the V-shaped northern extension of the Red Sea (Fig. 1). It is about 180 km long with a maximum width of 25 km, decreasing to about 5 km at the northern tip. It extends from the Jordan shoreline in the north to the Strait of Tiran in the south. The surface water of the GoA is oligotrophic with a shallow but stable thermocline for most of the year, except during the winter, when winds drive convective mixing of deep (higher-nutrients) and surface waters. The water temperature in the upper 200 m varies from 20 °C in the winter to 26 °C in the summer. The high evaporation rate of seawater (365 cm/year), sparse rainfall and negligible runoff, result in high salinity (in the upper 200 m) ranging from 40.3‰ to 40.8‰ in the winter and from 40.5‰ to 46.6‰ in the summer (Badran and Foster, 1998; Manasrah et al., 2004, 2007; Al-Taani et al., 2014). Water lost to evaporation is primarily compensated by inflow in the upper 80 m of water from the Red Sea to the GoA (Murray et al., 1984). The GoA hosts one of the most diverse coral communities in the world that are particularly susceptible to pollution including airborne dust. The susceptibility of GoA to pollution is due to its relatively small volume, the lack of significant wave activity and the low rate of water exchange between the GoA and the Red Sea. The average residence time of water in the Gulf ranges between one and three years (Klinker et al., 1976; Paldor and Anati, 1979; Hulings, 1979). The prevailing northerly wind, with an average speed of approximately 18–28 km/h and a maximum activity during the summer months, accounts for most of deposition events. However, the southerly wind patterns dominate during winter, may be initiated by Khamaseen wind blowing in the spring, are responsible for sand and dust storm events in southern Jordan and the adjacent regions (Abed et al., 2009). The Khamaseen winds mobilize dust from the interior of North Africa (Sahara desert) to the east and northeast over the eastern Mediterranean countries, including Jordan (Abed et al., 2009). Dust samples were collected in 2012 for different months to evaluate seasonal differences in dry deposition. The dust samples were obtained from three sites distributed along the Jordan GoA coast (Fig. 1) using three funnel-like stainless steel traps (0.5 m 0.45 m) placed on the roof of a 20 m high building. The variations in particle size of dust depend on, among others, the height of collection, where the average diameter of the dust

particle size decreases with increasing the height of collecting point (Rosen, 1964; Ahmed et al., 1987). The first trap was placed near the Phosphate Loading Berth (PLB), which is the southernmost portion of the main Aqaba port. The second trap was placed next to the Marine Science Station (MSS), which is a protected Marine Reserve area located about 5 km south of PLB. The third site was selected in the vicinity of the Industrial Complex (IC) about 16 km to the south of MSS. Following samples collection, dust trapped samples were washed into a nylon bag using distilled water. Dust samples were filtered using What-man filter paper No. 41/5 cm, oven-dried at 55 °C, ground and homogenized. 0.2 g of dust sample was placed in a 100 ml polyethylene bottle and 4 ml of HCl (25%), 4 ml of HNO3 (25%) and 2 ml of HF (40–48%) were added. The mixture was sonicated in water-bath at 70 °C for 2 h. Following 2 h, 50 ml of H3BO3 (39 g/l) was added to the solution and was re-sonicated until solution became clear. Then 40 ml of distilled water was added to obtain a 100 ml solution. The solution of the digested samples was analyzed for metal contents by Atomic Absorption Spectrophotometry (NOVA A300, Analytik Jena, Leybold, Germany). The average dry deposition rates to the northeastern GoA in different seasonal period during 2012 are presented in Table 1. The seasonal flux variations in atmospheric deposition were apparent, with highest value observed in the summer months (60.05 mg/ m2/day) and lowest occurred in the winter season (3.70 mg/m2/ day). The average deposition rates in fall and spring seasons were 19.32 and 11.95 mg/m2/day, respectively. The airborne dust fluxes in the summer account for about 63.21% of the total deposition rate observed during the study period, whereas the winter dust constitutes about 3.89% (Table 1). The total atmospheric inputs were estimated to be 95.01 mg/m2/day. The high fluxes of atmospheric deposition observed in the GoA are related to dust storms resulting in large contributions of mineral dust to the dry deposition. Dust storms in this desert region, frequently observed in the summer and triggered by the strong northerly winds, can mobilize large quantities of soil and transport particle-rich air masses toward the Gulf. As these dust-laden air masses are pushed up and over the GoA, larger particles are removed via gravitational settling such that the air mass becomes enriched in fine particles, and finally deposits particulates on the water surface. In addition to the southward winds, the prevailing dry conditions, during the summer months, accelerate dust emissions and bring the dust to its maximum activities. While the surrounding deserts are potentially an important source of mineral dust to the Gulf, it is believed that the dry-lands located north of the GoA are particularly the major source, where much of that materials end up in downwind marine ecosystems of the Gulf. The GoA is located downwind in close proximity to the arid dust producing area of Wadi Araba (and other adjacent deserts), where the strong northerly winds blow over an extensive lands with high percent of fine material, that are delivered to the Gulf (Yusuf, 2007). Although the dry deposition fluxes to the GoA showed temporal fluctuations, it is likely that the rate of deposition varies spatially. This is because the deposition events are dependent on the

Table 1 Seasonal deposition rates (mg/m2/day) to the GoA in 2012.

Fig. 1. Location map of the Gulf of Aqaba and the collection sites (PLB, MSS and IC).

Season

Deposition rate

Percent (%)

Spring Summer Fall Winter Total

11.95 60.05 19.32 3.70 95.01

12.57 63.21 20.33 3.89 100


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locations of the sampling sites (to the source area) and the timing of dust events (where the area is subject to two differing wind directions with varying intensity). Yusuf (2007) observed larger dust particle sizes in the northern GoA decreasing southwards with the increasing distance from the arid lands of Wadi Araba. This is consistent with the prevailing northerly winds being the major transporter of airborne dust, in particular, from the adjacent desert region located to the north of the GoA. Yusuf (2007) also concluded that the mineralogical composition of the aeolian dust collected in the GoA was closely related to the geology of Wadi Araba. The relatively lower atmospheric inputs in winter are attributed to the weak dust storms during the typical southerly wind conditions. In addition, higher moisture content of air in the source region (in Wadi Araba) during winter, favors soil and dust cohesion and prohibiting surface deflation and fine particles lifting. While Wadi Araba (and the surrounding deserts) is a primary source of dust to the GoA, other sources may potentially contribute long range transported materials to the area (e.g.: the Saharan deserts (Abed et al., 2009)). The northwards winds are likely to bring dust from local (Sinia, Negev and Arabia) and regional (Sahara) deserts, where winds move vertically and lift large quantities of soil dust (Chen et al., 2008). Previous studies showed that the annual average deposition rate to the GoA varied from 28 g/m2/year in Eilat city at the upper northwestern end of the GoA (Chase et al., 2006) to about 30.78 g/ m2/year in Aqaba city at the northeasternmost edge of the GoA (Yusuf, 2007), making the GoA one of the highest dust deposition rate areas on Earth (Chase et al., 2006). However, the deposition rates measured in present study are higher than those reported for GoA (Table 2), suggesting that dust fluxes to the GoA have increased during the last decay. Among others, this is attributed to climate variability and land use change in dust source regions which may have influenced the flux of aeolian material to downwind ecosystems. However, our measurements resembled those reported for the adjacent Mediterranean Sea (Table 2). Herut and Krom (1996) reported an average deposition rate to the SE Mediterranean

coastal region of about 36 g/m2/year, while Ganor and Mamane (1982) estimated the dry deposition fluxes to E Mediterranean Sea in the range of 20.08–40.15 g/m2/year, though later study by Herut et al. (2001) observed lower rate of 21 g/m2/year. In the Dead Sea area (north of the GoA), Singer et al. (2003) estimated the dry deposition fluxes to be in the range of 25.5–60.5 g/m2/year during the period 1997–1999. Lower annual rates of dust deposition have been reported by Behairy et al. (1985) for Jeddah city, on the western coast of Saudi Arabia (south of the GoA), with approximately 22.27 g/m2/year, which has recently been found to increase up to about 401 g/m2/year (Rifaat et al., 2007). Globally, the rates measured in this study in NE GoA were higher than those reported by Hsu et al. (2009) and Gao et al. (1997) for the south and north of the East China Sea, but relatively comparable to those observed for the Yellow Sea (Zhang et al., 1993; Gao et al., 1992). Mackey et al. (2010) calculated the midrange values of dust deposition rates to various oceans utilizing dust emissions modeled by Mahowald et al. (2005) (Table 2). The majority of these values were lower than that measured in this study, except for the dust fluxes to NW Africa (Atlantic Ocean), which are attributed to its proximity to the Sahara desert, one of the largest dust producing regions in the world (Engelstaedter et al., 2006). The atmospheric dry fluxes in this study are expectably higher than those measured in areas distant from dust sources (e.g.: the Pacific Ocean), but are comparable to (e.g.: E Mediterranean coast) or lower than (e.g.: the NW Africa) those rates measured in areas closer to dust producing regions. However, it is noteworthy that the methods of measuring and analyzing dry deposition were different among the various studies, thus, comparisons with previously published data must be made cautiously. Some studies extrapolated a few months of data to obtain annual flux. This practice is questionable, as dust flux can vary temporally (as well as spatially). Nonetheless, the Middle East region (including the GoA, the eastern and southeastern Mediterranean Sea, the Dead Sea and the Red Sea) appears to receive high fluxes of dry deposition areas,

Table 2 Average annual rates of dry deposition (g/m2/year) to the GoA compared with other marine and coastal regions. Site

Deposition rate

Reference

GoA

Aqaba city (NE GoA) Aqaba city (NE GoA) Eilat city (NW GoA)

34.68 30.78 28

Present study Yusuf (2007)b Chase et al. (2006)

Mediterranean Sea

SE Mediterranean Sea E Mediterranean Sea E Mediterranean Sea

36 20.08–40.15 21

Herut and Krom (1996) Ganor and Mamane (1982) Herut et al. (2001)

25.5–60.5

Singer et al. (2003)c

Dead Sea Red Sea

Jeddah (Saudi Arabia)

22.27

Behairy et al. (1985)

East China Sea

S East China Sea N East China Sea Yellow Sea Beijing (China) and Mallipo (Korea)

5.8 13 36.8 9-76

Hsu et al. (2009) Gao et al. (1997) Zhang et al. (1993) Gao et al. (1992)

Pacific Ocean

Tropical North Pacific Ocean North Pacific Ocean Coastal California W South America

0.02 1.5 5a 10a

Arimoto et al. (1985) GESAMP (1989), Duce et al. (1991) Mahowald et al. (2005) Mahowald et al. (2005)

Atlantic Ocean

NW Africa SW Africa

50a 20a

Mahowald et al. (2005) Mahowald et al. (2005)

Indian Ocean

Arabian Peninsula W India W Australia

20a 20a 5a

Mahowald et al. (2005) Mahowald et al. (2005) Mahowald et al. (2005)

Yellow Sea

a b c

Midrange value of dust deposition rate. Data taken in 1998. Data taken between 1997 and 1999.


4


and are likely to have substantial impacts on both the terrestrial and marine ecosystems. Therefore, the atmospheric dry deposition is an important flux of elements to the GoA (and the whole region) and the primary external source of trace elements. In addition, it is likely that variations in the dust sources and rates to the GoA are associated with fluctuations in the concentrations of elements contained in the dust particles. The annual atmospheric inputs of trace elements to the GoA, compared to other regions, are presented in Table 3. These fluxes of trace elements primarily represent the dry deposition as wet deposition and reverine inputs in such an arid region are almost negligible (Chen et al., 2008). High Al flux of 551 mg/m2/year (Table 3) to the NE GoA was observed, suggesting the relatively strong impact of mineral dust in this region. This is consistent with Sanders (1983) conclusions that Al concentration is relatively high in the atmosphere near arid and semiarid areas. This high average of Al was larger than that previously estimated at the northwestern edge of GoA (Eilat) of about 342 mg/m2/year (Chen et al., 2008). The increase in the atmospheric input of Al to the GoA compared to results of Chen et al. (2008), is probably related to increase in dust storm frequency in this region as a result of climate change. This is supported by the high atmospheric inputs of other crustally derived elements observed in the present study (as discussed later). The Al flux was also higher than fluxes to the NW Mediterranean Sea (120 mg/m2/year) and the NE Atlantic Ocean (5.11 mg/ m2/year), but somewhat similar to those observed in the eastern and southeastern Mediterranean Sea (of about 520 mg/m2/year) and those estimated at the coastal region of western Taiwan (567 mg/m2/year) (Table 3). Similarly, the fluxes of Fe, with an annual average of about 440 mg/m2/year, were twice those previously estimated for the NW GoA (Eilat) of 216 mg/m2/year, five times the NW Mediterranean Sea (88 mg/m2/year) and eleven times those of the North Sea coasts (22 mg/m2/year). In contrast, the deposition rate of Fe in the present study was relatively similar to those estimated for the eastern and southeastern Mediterranean Sea of about 420 and 464 mg/m2/year, respectively (Table 3), but lower than those measured in the western coast of Taiwan (during dry monsoon season) (Yang et al., 2003) (Table 3). The atmospheric deposition rate of Fe to the ocean surface varies over three orders of magnitude, from minimum values in the remote Pacific and Southern Ocean to maximum values near desert source regions (Duce and Tindale, 1991; Fung et al., 2000). While nutrient limitation of primary productivity in the ocean has

traditionally been attributed to nitrogen, Fe availability has recently been found to be important (Chase et al., 2006; Chen et al., 2008). In the GoA, a surface water enrichment of Fe occurs during the stratified summer (Chase et al., 2006), where mixing of water column in winter results in lower Fe concentrations. The annual dry fluxes of Mn to the NE GoA (10.29 mg/m2/year) were significantly larger than those fluxes reported for the NW GoA (of about 5.28 mg/m2/year), the NW Mediterranean Sea, the NE Atlantic Ocean, the North Sea and the western coast of Taiwan (Table 3). However, the measured rates of atmospheric Mn to the GoA in this study was comparable to those estimated for the eastern and southeastern Mediterranean Sea of about 420 and 463 mg/ m2/year, respectively, but lower than that reported in Japan of about 18 mg/m2/year (Table 3). The relatively high dry deposition fluxes of Mn (and Cr, Cu, Ni and Pb) reported in Japan were attributed to emissions from electric steel furnaces (Sakata et al., 2006). The average dry deposition rates of Cr, Cd, Cu, Pb and Zn are 1.42, 0.04, 0.68, 1.42 and 4.02 mg/m2/year, respectively. These fluxes of elements were relatively higher than those previously observed for GoA (Eilat) of about 0.96, 0.012, 0.38, 0.8 and 1.68 mg/m2/year, respectively (Chen et al., 2008) (Table 3), and than those reported for the adjacent SE Mediterranean Sea of 0.1, 0.008, 0.2, 1.31 and 2.39, respectively (Table 3). In contrast, the dry fluxes of Cu, Pb and Zn measured in the eastern and northwestern Mediterranean coast were higher than those measured this study, whereas Cd showed lower values in the eastern Mediterranean Sea but similar fluxes in NW Mediterranean Sea (Table 3). In addition, the dry fluxes of Cr, Cd, Cu, Pb and Zn showed values that were higher in the industrial countries of Japan (Sakata et al, 2006), USA (Sabin et al., 2006; Shahin et al., 2000) and Taiwan (Yang et al., 2003), but lower or slightly similar to those obtained in remote areas of the NE Atlantic Ocean (Spokes et al., 2001) and the North Sea (Injuk et al., 1998) (Table 3). Trace elements in atmospheric dry deposition can be of crustal or anthropogenic origins. The air masses in this region are often influenced by multiple sources, including: mineral dust originating from Sahara and the adjacent deserts (Negev, Wadi Araba, Sinai and Arabian deserts), as well as by anthropogenic aerosols transported from Europe. However, the concentrations of trace elements and their sources are dependent on the wind directions and intensity. The degree to which trace elements in the aerosols are enriched, or depleted, relative to a specific source can be assessed by the enrichment factors (Chester et al., 1996). Enrichment factors of trace element in airborne dust relative to their crustal compositions were estimated (by normalizing the

Table 3 Average dry deposition fluxes of selected trace elements (mg/m2/year) to the Gulf of Aqaba, Jordan, and other marine or coastal regions.

a

Site

Al

Fe

Mn

GoA (Aqaba)

551

440

10.29

GoA (Eilat)

342

216

5.28

E Mediterranean Sea

520

420

9

SE Mediterranean Sea

521

464

10.5

NW Mediterranean Sea

120 –

88 –

2.07 –

Cr

Cd

Cu

Pb

Zn

1.42

0.04

0.68

1.42

4.02

Present study

0.96

0.012

0.38

0.8

1.68

Chen et al. (2008)

–

0.007

2.9

6.36

7.58

Kocak et al. (2005)

0.1

0.008

0.2

1.31

2.39

Herut et al. (2001)

– –

– 0.033

1.19 1.61

1.85 2.56

3.2 41.61

Chester et al., 1996 Migon et al. (1997)

–

NE Atlantic Ocean

5.11

–

0.8

–

North Sea

–

22

0.89

1.1

USA Los Angelesa Chicagoa

– –

– –

– –

1.93 2.08

– –

Reference

–

1.24

3.47

Spokes et al. (2001)

0.42

0.49

1.47

Injuk et al. (1998)

8.76 23

5.84 13.87

47.45 43.8

Sabin et al. (2006) Shahin et al. (2000)

Taiwan, W Coast

567

668

6.94

–

0.077

10, enriched element, is an indicator of anthropogenic source, while EF value of 10) observed for Cd, Pb, Zn and Cu (Fig. 2) in samples collected from the GoA, indicate their dominant anthropogenic origin and strong contribution from non-crustal sources. Cd was the most enriched element in the GoA dry depositions followed by Pb, Zn and Cu. The low EF levels for Fe, Mn and Cr (Fig. 2) are indicator of their crustal origin, probably from Wadi Araba (as concluded by Yusuf (2007)), the surrounding deserts or from North African Sahara. With the exception of Cr, our calculated EF for all elements in the NE GoA were higher than those previously reported for the NW GoA (Eilat) (Chen et al., 2008). This suggests that the impact of both crustal (due to climate change) and anthropogenic sources became stronger. However, our EF values of trace elements were relatively similar to those estimated for the E Mediterranean (Herut et al., 2001) (Fig. 2), except for Cu, Zn and Pb. This is probably attributed to their similar meteorological conditions (due to the geographic proximity of the two regions) and the same source of crustal dust. However, because the E Mediterranean coast are located closer to Europe, it receives air masses rich in Cu, Zn and Pb of anthropogenic sources, and subsequently higher EF values of these elements were observed in this region relative to those estimated in present study for the NE GoA. These results also indicate that non-crustal sources had less influence on air mass over the Gulf compared to the E Mediterranean area (Chen et al., 2008). In contrast, the crustally derived elements (Fe, Mn and Cr) in the W Mediterranean coast showed lower enrichment values compared to that of the GoA, but higher EF levels for non-crustal elements (Cu, Zn, Pb and Cd). These results suggest that the W Mediterranean Sea is profoundly influenced by human activities (which is directly linked to its proximity to industrial countries of Europe), but less impacted by crustal sources (consistent with its relatively long distance from the Saharan dust source region). While the majority of trace elements of anthropogenic sources previously observed in the NW of GoA (Eilat) have been attributed

1000

W Mediterranean

Khamaseen Dust

Aqaba

E Mediterranean

Eilat

10 No Data

EF

100

1

0.1 Fe

Mn

Cr

Cu

Zn

Pb

Cd

Fig. 2. The enrichment factors (EF) relative to average upper crust for trace elements in dry deposition over the GoA, compared to previously published data for Eilat (NW GoA) (Chen et al., 2008), Khamaseen dust (originated from Sahara desert) collected in Jordan (Abed et al., 2009), the eastern Mediterranean Sea (Herut et al., 2001) and the western Mediterranean coast (Keyse, 1995).

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to European air masses (Chen et al., 2008), local non-crustal sources are likely. The GoA is affected by a mix of local influences from harbor activities and nearby urban sources in Eilat and Aqaba, where the potential impacts from metals are generally restricted to locations adjacent to major cities or industrialized areas. Among others, emissions of phosphate (from the phosphate loading) and, mineral dusts (from fertilizer and cement factories) are potential contributors to Cd and Pb in the GoA (Abu-Hilal et al., 1998; Abu-Hilal and Badran, 1990; Abu-Hilal, 1993). The relatively higher EF values of Cd estimated over the Gulf (which are comparable to those calculated for the eastern Mediterranean Sea) (Fig. 2) could be attributed to phosphate loading activities at the GoA port (and in Eilat), where large quantities reach the air while loading. However, the non-crustal Cd to W Mediterranean sea (highly enriched in Cd) was probably related, among others, to emissions of motor vehicles (Chen et al., 2008) and nonferrous industries. Cu which is typically associated with anthropogenic sources, also remains within the group of enriched elements based on its EF values for the GoA (Fig. 2). Non-crustal Cu in the air often comes from nonferrous industries (Venkataraman et al., 2002). Higher EF value of Zn reported in the eastern and western Mediterranean Sea compared to the GoA (Table 3), were probably originated from Europe (particularly through smelting and incinerating operations (Huang et al., 2001)). In addition to the influence of air masses from Europe, the relatively high fluxes of Zn observed in the GoA, could be of local origin (the industrial activities in Aqaba and Eilat, or the neighboring Saudi Arabia and Egypt). Dry deposition to the GoA and the neighboring Mediterranean coasts was highly enriched in Pb and is related to the burning of fossil fuel (believed to originate from the local and Arabian regions as well as from the European source). Herut et al. (2001) observed higher enrichment factors of Cd and Pb in European-derived air masses flowing over the Mediterranean coast and the GoA. Khamaseen dust collected in Jordan (originated from North African Sahara) (Abed et al., 2009) showed EF values for Fe, Mn and Cr that were somewhat similar to those calculated in the present study. It also showed lower enrichment values for Cu, Pb and Cd, but higher for Zn relative to those estimated for the GoA. Abed et al. (2009) argued that highly enriched Khamaseen dust in Cd and Zn was not only related to human activities, but also attributed to phosphorite deposits in North Africa (and the Eastern Mediterranean). In addition, they explained that because neither Jordan nor the source area of the Khamaseen dust (and its path) are really industrialized, a possible source of the higher Cd and Zn was the phosphate fertilizers added continuously to the soils and blown by winds. Abed et al. (2008) identified that Cd and other potentially toxic trace metals are enriched in the DAP fertilizer (Diammonium phosphate) by a factor of about 2 and a factor of 3 in the phosphoric acid. Pesticides and similar materials may be another source for elements such as Zn Cr, As, Cu and Se (Cornejo et al., 2008). Unlike the GoA, the EF values for Cu and Pb in Khamaseen dust indicate that they were of crustal origin, rather than from anthropogenic sources. This is closely linked to distant location of Saharan desert (the source region of Khamaseen dust) from the anthropogenic impacts of European countries. The relatively elevated EF values of Pb in Khamaseen dust is likely related to Pb emissions from gasoline vehicles, where several major cities are located along the path of the Khamaseen dust in eastern Libya, northern Egypt and the eastern Mediterranean (Erel et al., 2006). Similarly, Cu in Khamaseen dust is probably related to human activities (non-ferrous industries) along the dust pathway and/or from Europe (as the Sahara desert still receives low levels of anthropogenic emissions from Europe).


6


The EF values of Ca showed highly enriched levels (EF = 22.38) compared to non-enriched values (EF < 10) for the previously calculated Ca over Eilat (Chen et al., 2008). The higher Ca/Al ratio observed is probably related to the wide distribution of calcite and dolomite in the region. The EF values calculated in the present study and those previously reported for the NW GoA (Eilat) and the adjacent eastern Mediterranean coast showed similar enriched and non-enriched groups of elements, where Fe, Mn and Cr remain within the group of crustally dominated elements, while the remaining elements are of anthropogenic origin, with some variations in EF levels. Acknowledgments The authors wish to thank Yarmouk University for funding this Project. Thanks are due to Department of Earth and Environmental Sciences at Yarmouk University for providing all necessary facilities for the chemical analyses. References Abed, A.M., Al Kuisi, M., Abul Khair, H., 2009. 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High reproductive synchrony of Acropora (Anthozoa: Scleractinia) in the Gulf of Aqaba, Red Sea.

Reproductive strategies of the coral Turbinaria reniformis in the northern Gulf of Aqaba (Red Sea).

Phytoplankton dynamics in the Gulf of Aqaba (Eilat, Red Sea): a simulation study of mariculture effects.

The elemental composition of demospongiae from the Red Sea, Gulf of Aqaba.

Impact of Aeolian Dry Deposition of Reactive Iron Minerals on Sulfur Cycling in Sediments of the Gulf of Aqaba.

Dataset for metatranscriptome analysis of Prochlorococcus-rich marine picoplankton communities in the Gulf of Aqaba, Red Sea.

Occurrence and dry deposition of organophosphate esters in atmospheric particles over the northern South China Sea.

Offshore Evidence for an Undocumented Tsunami Event in the 'Low Risk' Gulf of Aqaba-Eilat, Northern Red Sea.

Status of trace metals in surface seawater of the Gulf of Aqaba, Saudi Arabia.

Fractionation of trace elements in total atmospheric deposition by filtrating-bulk passive sampling.

A comparative study between the fluxes of trace elements in bulk atmospheric deposition at industrial, urban, traffic, and rural sites.

Storm-induced transfer of particulate trace metals to the deep-sea in the Gulf of Lion (NW Mediterranean Sea).

Monitoring of coastal coral reefs near Dahab (Gulf of Aqaba, Red Sea) indicates local eutrophication as potential cause for change in benthic communities.

Concentrations of trace elements in the kidney, liver, muscle, and skin of short sea snake (Lapemis curtus) from the Strait of Hormuz Persian Gulf.

Field measurements of the atmospheric dry deposition fluxes and velocities of polycyclic aromatic hydrocarbons to the global oceans.

Peatland Microbial Communities as Indicators of the Extreme Atmospheric Dust Deposition.

Health effects from exposure to atmospheric mineral dust near Las Vegas, NV, USA.

Use of scleractinian corals to indicate marine pollution in the northern Gulf of Aqaba, Jordan.

Study of road dust magnetic phases as the main carrier of potentially harmful trace elements.

An Artificial Turf-Based Surrogate Surface Collector for the Direct Measurement of Atmospheric Mercury Dry Deposition.

The content of nine mineral elements in raw and cooked mature dry legumes.

Influence of ashing techniques on the analysis of trace elements in biological samples : II. Dry ashing.

The mineral dust diseases.

Atmospheric deposition of trace elements around point sources and human health risk assessment. II. Uptake of arsenic and chromium by vegetables grown near a wood preservation factory.