- Email: [email protected]
A Reassessment of Trace Metal Budgets in the Western Mediterranean Sea
PII: S0025-326X(01)00065-0
Marine Pollution Bulletin Vol. 42, No. 8, pp. 623±627, 2001 Ó 2001 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0025-326X/01 $ - see front matter
A Reassessment of Trace Metal Budgets in the Western Mediterranean Sea FRANC GUIEUà and NICHOLAS H. MORLEY§ ß OISE ELBAZ-POULICHET *, CECILE UMR Hydrosciences, CNRS-IRD-University Montpellier II, CCMSE, F-34095 Montpellier Cedex 5, France àLaboratoire de Physique et Chimie Marines, University of Paris VI, CNRS-INSU, La Darse, BP8, 06230 Villefranche-sur-mer, France §Department of Oceanography, Southampton Oceanography Center, University of Southampton, SO14 3ZH Southampton, UK This paper presents inputs and output ¯uxes of dissolved metals (As, Cd, Co, Cu, Fe, Mn, Ni, Pb and Zn) into and out the Western Mediterranean. These ¯ux estimates are based on the most recently published concentrations and ¯uxes for the atmosphere, the rivers and the straits. Comparison of the dierent sources shows the predominance of the inputs through the straits over other sources. The river input is smaller than the atmospheric input except for As. For all elements except Fe, output ¯ux and input ¯ux are balanced; iron budget indicates transfer from the dissolved to the particulate phase. Ó 2001 Elsevier Science Ltd. All rights reserved.
Introduction Trace metal pro®les in the Mediterranean Sea are homogeneous with higher concentrations in surface waters than those found in open oceanic waters (Spivack et al., 1983; Copin-Montaigut et al., 1986; Sherell and Boyle, 1988; Morley et al., 1997). These enrichments have been attributed to external sources such as runo, atmosphere and the Atlantic, important vertical mixing and insucient removal by organisms (Boyle et al., 1985; Van Geen et al., 1988; Martin et al., 1989; Ruiz-Pino et al., 1990; Dorten et al., 1991; Van Geen et al., 1991). The previous ¯uxes reported by these authors do not compare inputs and outputs and rely upon a limited data set and a restricted number of metals. However, during the last 10 years numerous data have been published on atmospheric input (Guieu et al., 1993, 1997; Migon et al., 1993, 1997; Ridame et al., 1999), river input (Dorten et al., 1991, Guieu et al., 1991) and inputs through the straits Morley et al., 1997; Elbaz-Poulichet et al., 2001). In addition, the contribution of the dierent sources has changed due to reduction of the *Corresponding author. Tel.: +33-4-6714-39-31; fax: +33-4-671447-74. E-mail address: [email protected] (F. ElbazPoulichet).
atmospheric emissions in Europe. For example, the Pb concentrations in the atmospheric fallout have decreased (Migon et al., 1993; Ridame et al., 1999) as a result of reductions in Pb in petrol. In this context it was particularly interesting to make a new assessment of dissolved metal inputs to the Western Mediterranean Sea and to compare them to dissolved outputs through the straits using updated data. The scope of metals under consideration (As, Cd, Co, Cu, Fe, Mn, Ni, Pb and Zn) has been broadened.
Description of the Model The models generally presented for ¯ux calculations incorporate two horizontal boxes in order to include vertical transfers (Ruiz-Pino et al., 1990; Sarthou and Jeandel, 2001). Our study does not consider the internal ¯uxes as our aim was to evaluate the relative importance of input and output ¯uxes. This alternative implies a one-box model (Fig. 1) which incorporates inputs from the straits of Gibraltar and Sicily, rivers and atmospheric fallout. The measured output is through the straits (Gibraltar and Sicily). The water exchanges through the straits of Gibraltar and Sicily are well described by two layer models (e.g., Bethoux, 1979). In the case of the Strait of Gibraltar the in¯ow forms the upper layer with a deep export while the opposite situation is found in the Strait of Sicily.
Results and Discussion Input and output ¯uxes are reported in Tables 1 and 2, respectively. River input The global river water input to the Western Mediterranean basin is 10:5 1010 m3 yr 1 (Martin et al., 1989). Owing to the lack of data for small rivers especially for the African coast (Meybeck and Ragu, 1999), the mean river concentration has been established from the mean of Rh^ one and Ebro concentrations (Guieu 623
Marine Pollution Bulletin
et al., 1997). These rivers represent 70% of the total river discharge to the Western Mediterranean basin. The river ¯ux is comparable to that of Martin et al. (1989) and represents the smallest source of metals at the scale of the basin (Fig. 2). Atmospheric input The dissolved atmospheric fallout represents the dissolved ¯ux in wet deposition (rain) and the soluble part of dry deposition. The value has been established by correcting the total ¯ux for the North-Western Mediterranean basin given by Ridame et al. (1999), using the distribution coecients between dissolved and particulate phases determined by Guieu et al. (1997). As the soluble fraction of the aerosol is highly variable and depends on the origin of the aerosol (Guieu et al., 1997), a range is given for the atmospheric ¯ux. Due to the lack of data in the South Mediterranean basin, this ¯ux has been extended to the entire Western Mediterranean basin. According to Guieu et al. (1997), this probably
Fig. 1 One-box model of the Western Mediterranean basin. AIW: Atlantic in¯ow waters; SSOW: Sicilian strait out¯ow waters; MOW: Mediterranean out¯ow waters; SLIW: Sicilian levantine intermediate waters.
TABLE 1 Dissolved metal inputs (t yr 1 ) to the Western Mediterranean basin (w: winter; s: summer). Atmospherea
Mn Fe Ni Co Cu Zn As Cd Pb
2600±3300 4200±22 700 150±350 17±190 180±560 1300±3900 95±132 25±40 180±500
Riversb
360 1000 160 7 230 130 200 3 8
Gibraltarc
Sicilyd
Total inpute
Total straits
w
s
w
s
w
s
w
s
1240 630 2020 80 1420 1220 29 000 60 250
8340 1880 2370 145 3220 7300 30 000 145 720
1500 11 300 10 000 100 4000 18 500 57 000 260 830
740 2600 8400 100 3400 7400 57 000 250 450
2700 12 000 12 000 180 5400 19 700 86 000 320 1100
9100 4500 10 700 250 6600 15 000 87 000 400 1200
5700±6300 17 000±36 000 12 300±12 500 200±350 5800±6200 21 000±24 000 86 300 350±370 1260±1600
12 000±13 000 10 000±28 200 11 000±11 300 270±450 7000±7400 16 000±18 700 87 300 420±440 1360±1690
a Calculated using the total ¯ux of Ridame et al. (1999) and the partition coecient of Guieu et al. (1997). Surface of the Western Mediterranean basin: 840 000 km2 . b Calculated using the mean Rh^ one and Ebro concentrations (Elbaz-Poulichet et al., 1996; Guieu et al., 1997). River discharge to the Western Mediterranean basin: 10:5 1010 m3 s 1 (Martin et al., 1989). c Elbaz-Poulichet et al. (1999). d Calculated using the concentrations of Morley et al. (1997) and of Van der Weijden et al. (1990) for As. Water ¯uxes through the Strait of Sicily: 38 1012 m3 :yr 1 (Bethoux, 1981). e Martin et al. (1989).
TABLE 2 Dissolved metal outputs (t yr 1 ) in the Mediterranean basin (w: winter; s: summer). Sicilyb
Gibraltara w Mn Fe Ni Co Cu Zn As Cd Pb a b
1170 890 3730 70 1350 6870 33 300 190 220
4300 4300 7100 280 4300 10 700 57 000 250 1000
Total output s 6800 2800 5200 210 3300 4700 57 000 210 730
w 5430 5200 10800 350 5700 17 600 90 300 440 1220
Elbaz-Poulichet et al. (2001). Metal concentrations from Morley et al. (1997), As concentrations (Van der Weijden et al., 1990). Water ¯uxes: 38 1012 m3 yr
624
s 8000 3700 9000 280 4600 11 600 90 300 400 1000 1
(Bethoux, 1981).
Volume 42/Number 8/August 2001
Fig. 2 Comparison of the inputs to the Western Mediterranean basin through river, atmosphere and straits. The bars on the diagram represent the dierence between the maximum and minimum value.
overestimates the ¯ux for the pollution derived elements (e.g., Cd, Pb, Zn) and inversely minimizes the ¯ux for the elements derived from Saharan dust such as Fe. The atmospheric Cu, Cd and Pb ¯uxes are lower than previously published ¯uxes (Bergametti, 1987; Martin et al., 1989; Remoudaki, 1990; Guieu et al., 1997; Migon et al., 1997). This decrease results from the combination of two factors: (1) the actual decrease of the atmospheric concentrations in relation with the reduction of emissions (Ridame et al., 1999); (2) the occurrence of local/ regional contamination for these metals at some monitoring sites (Ridame et al., 1999). According to Ridame et al. (1999), the total atmospheric Pb ¯ux has decreased by at least a factor of 6 between 1983 and 1992, in relation with the decrease of leaded fuels. As a result, the Pb concentrations in the upper water column of the Western Mediterranean Sea have diminished by a factor of 2 during the same period (Nicolas et al., 1994; Migon and Nicholas, 1998). Despite the decrease of the atmospheric fallout for pollution derived metals, our results con®rm the predominance of the atmospheric ¯ux over the river ¯ux published by Guieu et al. (1997). Strait input The metal concentrations are seasonally variable particularly in the Strait of Gibraltar where the concentrations are maximum in June and minimum in September (Morley et al., 1999; Elbaz-Poulichet et al., 2001). This variability is attributed to the contribution of metal-enriched Spanish Shelf Water (SSW) originating from the Gulf of Cadiz. Metal concentrations in the waters of the Strait of Sicily are apparently maximum in winter and minimum in summer but the mechanism that produces such variations remains enigmatic and the data are not conclusive (Morley et al., 1997). As seasonal concentrations display opposite variations in the two straits (Gibraltar and Sicily), the total
Fig. 3 Comparison of the inputs through the straits of Gibraltar and Sicily. Bars as in Fig. 2.
strait input evolves in a narrow range for most elements. As shown in Fig. 2, it is the major source for Ni, Cu, Cd and Zn in the Western Mediterranean basin. For Fe and Mn the strait input remains in the range de®ned for the atmospheric input (Fig. 2). Although inputs through the Strait of Gibraltar are aected by contamination from a highly mineralized adjacent region (Nelson and Lamothe, 1983; ElbazPoulichet and Leblanc, 1996), inputs through the Strait of Sicily are generally similar or greater with the ex-
Fig. 4 Comparison between the input and output ¯uxes in the Western Mediterranean basin: (a) winter; (b) summer. Bars as in Fig. 2.
625
Marine Pollution Bulletin
ception of Mn (Fig. 3). The comparatively elevated input through the Strait of Sicily could simply result from the evaporation which takes place in the eastern basin. However, after normalizing to salinity (36.4 for AIW and 38.74 for SLIW) which diminishes the eect of evaporation, metal ¯uxes are equivalent. This con®rms an occurrence of metal sources in deep eastern basin waters as previously suggested by Morley et al. (1997). Strait output The Strait of Sicily output (Table 2) is higher than the Strait of Gibraltar output. As shown in Fig. 4, the total output ¯ux is balanced by the input ¯ux for all elements, except Fe. Assuming equilibrium conditions, this may suggest that exchange processes with sediments are negligible with regards to the magnitude of error. Alternatively the removal and release may be of the same order as indicated for Cd by Ruiz-Pino et al. (1990). The Fe output ¯ux is lower than the input. The difference, evaluated at 7±36 mg m 2 yr 1 , may represent the net transfer from the dissolved to the particulate phase. Indeed Sarthou and Jeandel (2001) calculated that the removal processes predominate over the release of Fe from particulate phase.
Conclusion The ¯uxes reported in this study simply represent an order of magnitude. Indeed transfer mechanisms are still poorly documented and trace metal data are relatively scarce in the Strait of Sicily. Due to the lack of data for the South-Western Mediterranean basin, the atmospheric fallout and the river ¯ux, measured on the northwest coast, have been extrapolated to the whole western basin. Nevertheless, this budget extends ¯ux knowledge to new elements and updates inputs and outputs to the Western Mediterranean basin. This update was necessary because previous ¯uxes did not include the reduction of the emissions into the atmosphere. This budget clearly indicates that inputs through the straits constitute the main source of dissolved metals to the Western Mediterranean basin. At a basin scale, the second source of metals is the atmosphere. The rivers represent a minor source. From the data presented here it is apparent that the overall import and export ¯uxes are near equilibrium, dissolved outputs balance dissolved inputs, except for Fe which sediments in the basin. This research was partly supported by the European Commission (DGXII) under contract TOROS (ENV4-CT96-0217), Environment and Climate Program (ELOISE) and CANIGO under contract MAS3PL95-0443, MAST. Bergametti, G. (1987) Apports de matiere par voie atmospherique a la Mediterranee Occidentale: aspects geochimiques et meteorologiques. Ph.D. thesis, University ParisVII, 296 pp. Bethoux, J. P. (1979) Budgets of the Mediterranean Sea. Their dependance on the local climate and on the characteristics of the Atlantic waters. Oceanology Acta 2, 157±163.
626
Bethoux, J. P. (1981) Le phosphore et l'azote en mer Mediterranee, bilans, fertilite potentielle. Marine Chemistry 10, 141±158. Boyle, E. A., Chapnick, S. D., Bai and Spivack X. X. (1985) Trace metal enrichments in the Mediterranean Sea. Earth and Planetary Science Letters 74, 405±419. Copin-Montaigut, G., Coureau, P. and Nicholas E. (1986) Distribution and transfer of trace elements in the Western Mediterranean. Marine Chemistry 18, 189±195. Dorten, W. S., Elbaz-Poulichet, F., Mart, L. and Martin, J. (1991) Reassessment of river input of trace metals to the Mediterranean Sea. Ambio 20, 2±6. Elbaz-Poulichet, F. and Leblanc, M. (1996) Transferts de metaux d'une province miniere a l'ocean par les ¯euves acides (Rio Tinto, Espagne), C.R. Academy of Science Paris, 322, Serie 2A, 1047± 1052. Elbaz-Poulichet, F., Garnier, J. M., Guan, D. M., Martin, J. M. and Thomas, A. J. (1996) The conservative behaviour of trace metals (As, Cd, Cu, Ni and Pb) in the surface plume of strati®ed estuaries: example of the Rhone river (France). Estuarine and Coastal Shelf Science 42, 289±310. Elbaz-Poulichet, F., Morley, N., Beckers, J. M. and Nomerange, P. (2001) Dissolved metal ¯uxes through the Strait of Gibraltar: the in¯uence of the Tinto-Odiel rivers. Marine Chemistry 73, 193± 213. Guieu, C., Mouchel, J. M., Noel, M., Guan, D. M. and Martin, J. M. (1991) Flux and behaviour of metals in the Ebro delta, Spain. Water Pollution Research Report 21, 293±307. Guieu, C., Zhang, J., Thomas, A., Martin, J. M. and Brun-Cottan, J. C. (1993) Signi®cance of atmospheric fallout on the upper layer water chemistry of the North-Western Mediterranean. Journal of Atmospheric Chemistry 17, 45±60. Guieu, C., Chester, R., Nimmo, M., Martin, J. M., Guerzoni, S., Nicolas, E., Mateu, J. and Keyse, S. (1997) Atmospheric input of dissolved and particulate metals to the northwestern Mediterranean. Deep-Sea Research II 44, 655±674. Martin, J. M., Elbaz-Poulichet, F., Guieu, C., Loye-Pilot, M.D. and Han, G. (1989) River versus atmospheric input of material to the Mediterranean Sea: an overview. Marine Chemistry 28, 159±182. Meybeck, M. and Ragu, A. (1999) River discharges to the oceans: an assessment of suspended solids, major ions and nutrients. Environment Information and Assessment Document, UNEP, Nairobi, 243 pp. Migon, C., Alleman L., Leblond N. and Nicolas E. (1993) Evolution of atmospheric lead over the northwestern Mediterranean between 1986 and 1992. Atmospheric Environment 27A, 2161±2167. Migon, C., Morelli, J., Nicolas, E. and Copin-Montegut, G. (1997) Evaluation of total atmospheric deposition of Pb, Cd, Cu and Zn to the Ligurian Sea. Science of Total Environment 105, 135±148. Migon, C. and Nicholas, E. (1998) Eects of antipollution policy on anthropogenic lead transfers in the Ligurian sea. Marine Pollution Bulletin 36, 775±779. Morley, N. H., Burton, J. D., Tankere, S. P. and Martin, J. M. (1997) Distribution and behaviour of some dissolved trace metals in the western Mediterranean Sea. Deep-Sea Research 44, 3±4, 675± 691. Morley, N. H., Elbaz-Poulichet, F. and Nomerange, P. (1999). Trace metals in the waters of the Straits of Gibraltar. Oral presentation. 24th General Assembly of the European Geophysical Society in The Hague, 19±23 April 1999. Journal of Geophysics Research Abstract 2, 402. Nelson, C. H. and Lamothe, P. J. (1983) Heavy metal anomalies in the Tinto and Odiel river and estuary system, Spain. Estuaries 16, 495± 511. Nicolas, E., Ruiz-Pino, D., Buat-Menard, P. and Bethoux, J. P. (1994) Abrupt decrease in lead concentration in the Mediterranean Sea: a response to antipollution policy. Geophysics Research Letters 21, 2112±2122. Remoudaki, E. (1990) Etude des processus controllant la variabilite des ¯ux atmospheriques de polluants et de poussieres minerales en Mediterranee Occidentale. Ph.D. thesis, University Paris VI, 224 pp. Ridame, C., Guieu, C. and Loye-Pilot, M. D. (1999) Trend in total atmospheric deposition ¯uxes of aluminum, iron, and trace metals in the northwestern Mediterranean over the past decade (1985±1997). Journal of Geophysics Research 104, D23, 30 127± 130, 139.
Volume 42/Number 8/August 2001 Ruiz-Pino, D. P, Jeandel, C., Bethoux, J. P. and Minster, J. F. (1990) Are trace metals balanced in the Mediterranean Sea? Paleogeography, Paleoclimatology, and Paleoecology 82, 369±388. Sarthou, G. and Jeandel, C. (2001) Seasonnal variations of iron concentrations in the Ligurian Sea and iron budget to the Western Mediterranean basin. Marine Chemistry 74, 115±129. Sherell, R. and Boyle, E. (1988) Zinc, chromium, vanadium and iron in the Mediterranean Sea. Deep-Sea Research 35, 1319±1334. Spivack, A., Huested, S., Boyle, E. (1983) Copper, nickel, and cadmium in the surface waters of the Mediterranean. In Trace Metals in Seawater, eds. C.S. Wong et al., pp. 505±512. Plenum Press, New York.
Van der Weijden, Middelburg, J., de Langue, G., Van der Sloot, H., Hoede, D., Woittiez, J. (1990) Pro®les of redox-sensitive trace elements As, Sb, V, Mo and U in the Tyro and Bannock Basins (eastern Mediterranean). Marine Chemistry 31, 167±186. Van Geen, A., Rosener, P., Boyle, E. A. (1988) Entrainment of trace metal-enriched Atlantic shelfwaters in the in¯ow to the Mediterranean Sea. Nature 331, 423±426. Van Geen, A., Boyle, E. A., Moore, W. S. (1991) Trace metal enrichments in waters of the Gulf of Cadiz, Spain. Geochimica Cosmochimica Acta 55, 2173±2191.
627
Marine Pollution Bulletin Vol. 42, No. 8, pp. 623±627, 2001 Ó 2001 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0025-326X/01 $ - see front matter
A Reassessment of Trace Metal Budgets in the Western Mediterranean Sea FRANC GUIEUà and NICHOLAS H. MORLEY§ ß OISE ELBAZ-POULICHET *, CECILE UMR Hydrosciences, CNRS-IRD-University Montpellier II, CCMSE, F-34095 Montpellier Cedex 5, France àLaboratoire de Physique et Chimie Marines, University of Paris VI, CNRS-INSU, La Darse, BP8, 06230 Villefranche-sur-mer, France §Department of Oceanography, Southampton Oceanography Center, University of Southampton, SO14 3ZH Southampton, UK This paper presents inputs and output ¯uxes of dissolved metals (As, Cd, Co, Cu, Fe, Mn, Ni, Pb and Zn) into and out the Western Mediterranean. These ¯ux estimates are based on the most recently published concentrations and ¯uxes for the atmosphere, the rivers and the straits. Comparison of the dierent sources shows the predominance of the inputs through the straits over other sources. The river input is smaller than the atmospheric input except for As. For all elements except Fe, output ¯ux and input ¯ux are balanced; iron budget indicates transfer from the dissolved to the particulate phase. Ó 2001 Elsevier Science Ltd. All rights reserved.
Introduction Trace metal pro®les in the Mediterranean Sea are homogeneous with higher concentrations in surface waters than those found in open oceanic waters (Spivack et al., 1983; Copin-Montaigut et al., 1986; Sherell and Boyle, 1988; Morley et al., 1997). These enrichments have been attributed to external sources such as runo, atmosphere and the Atlantic, important vertical mixing and insucient removal by organisms (Boyle et al., 1985; Van Geen et al., 1988; Martin et al., 1989; Ruiz-Pino et al., 1990; Dorten et al., 1991; Van Geen et al., 1991). The previous ¯uxes reported by these authors do not compare inputs and outputs and rely upon a limited data set and a restricted number of metals. However, during the last 10 years numerous data have been published on atmospheric input (Guieu et al., 1993, 1997; Migon et al., 1993, 1997; Ridame et al., 1999), river input (Dorten et al., 1991, Guieu et al., 1991) and inputs through the straits Morley et al., 1997; Elbaz-Poulichet et al., 2001). In addition, the contribution of the dierent sources has changed due to reduction of the *Corresponding author. Tel.: +33-4-6714-39-31; fax: +33-4-671447-74. E-mail address: [email protected] (F. ElbazPoulichet).
atmospheric emissions in Europe. For example, the Pb concentrations in the atmospheric fallout have decreased (Migon et al., 1993; Ridame et al., 1999) as a result of reductions in Pb in petrol. In this context it was particularly interesting to make a new assessment of dissolved metal inputs to the Western Mediterranean Sea and to compare them to dissolved outputs through the straits using updated data. The scope of metals under consideration (As, Cd, Co, Cu, Fe, Mn, Ni, Pb and Zn) has been broadened.
Description of the Model The models generally presented for ¯ux calculations incorporate two horizontal boxes in order to include vertical transfers (Ruiz-Pino et al., 1990; Sarthou and Jeandel, 2001). Our study does not consider the internal ¯uxes as our aim was to evaluate the relative importance of input and output ¯uxes. This alternative implies a one-box model (Fig. 1) which incorporates inputs from the straits of Gibraltar and Sicily, rivers and atmospheric fallout. The measured output is through the straits (Gibraltar and Sicily). The water exchanges through the straits of Gibraltar and Sicily are well described by two layer models (e.g., Bethoux, 1979). In the case of the Strait of Gibraltar the in¯ow forms the upper layer with a deep export while the opposite situation is found in the Strait of Sicily.
Results and Discussion Input and output ¯uxes are reported in Tables 1 and 2, respectively. River input The global river water input to the Western Mediterranean basin is 10:5 1010 m3 yr 1 (Martin et al., 1989). Owing to the lack of data for small rivers especially for the African coast (Meybeck and Ragu, 1999), the mean river concentration has been established from the mean of Rh^ one and Ebro concentrations (Guieu 623
Marine Pollution Bulletin
et al., 1997). These rivers represent 70% of the total river discharge to the Western Mediterranean basin. The river ¯ux is comparable to that of Martin et al. (1989) and represents the smallest source of metals at the scale of the basin (Fig. 2). Atmospheric input The dissolved atmospheric fallout represents the dissolved ¯ux in wet deposition (rain) and the soluble part of dry deposition. The value has been established by correcting the total ¯ux for the North-Western Mediterranean basin given by Ridame et al. (1999), using the distribution coecients between dissolved and particulate phases determined by Guieu et al. (1997). As the soluble fraction of the aerosol is highly variable and depends on the origin of the aerosol (Guieu et al., 1997), a range is given for the atmospheric ¯ux. Due to the lack of data in the South Mediterranean basin, this ¯ux has been extended to the entire Western Mediterranean basin. According to Guieu et al. (1997), this probably
Fig. 1 One-box model of the Western Mediterranean basin. AIW: Atlantic in¯ow waters; SSOW: Sicilian strait out¯ow waters; MOW: Mediterranean out¯ow waters; SLIW: Sicilian levantine intermediate waters.
TABLE 1 Dissolved metal inputs (t yr 1 ) to the Western Mediterranean basin (w: winter; s: summer). Atmospherea
Mn Fe Ni Co Cu Zn As Cd Pb
2600±3300 4200±22 700 150±350 17±190 180±560 1300±3900 95±132 25±40 180±500
Riversb
360 1000 160 7 230 130 200 3 8
Gibraltarc
Sicilyd
Total inpute
Total straits
w
s
w
s
w
s
w
s
1240 630 2020 80 1420 1220 29 000 60 250
8340 1880 2370 145 3220 7300 30 000 145 720
1500 11 300 10 000 100 4000 18 500 57 000 260 830
740 2600 8400 100 3400 7400 57 000 250 450
2700 12 000 12 000 180 5400 19 700 86 000 320 1100
9100 4500 10 700 250 6600 15 000 87 000 400 1200
5700±6300 17 000±36 000 12 300±12 500 200±350 5800±6200 21 000±24 000 86 300 350±370 1260±1600
12 000±13 000 10 000±28 200 11 000±11 300 270±450 7000±7400 16 000±18 700 87 300 420±440 1360±1690
a Calculated using the total ¯ux of Ridame et al. (1999) and the partition coecient of Guieu et al. (1997). Surface of the Western Mediterranean basin: 840 000 km2 . b Calculated using the mean Rh^ one and Ebro concentrations (Elbaz-Poulichet et al., 1996; Guieu et al., 1997). River discharge to the Western Mediterranean basin: 10:5 1010 m3 s 1 (Martin et al., 1989). c Elbaz-Poulichet et al. (1999). d Calculated using the concentrations of Morley et al. (1997) and of Van der Weijden et al. (1990) for As. Water ¯uxes through the Strait of Sicily: 38 1012 m3 :yr 1 (Bethoux, 1981). e Martin et al. (1989).
TABLE 2 Dissolved metal outputs (t yr 1 ) in the Mediterranean basin (w: winter; s: summer). Sicilyb
Gibraltara w Mn Fe Ni Co Cu Zn As Cd Pb a b
1170 890 3730 70 1350 6870 33 300 190 220
4300 4300 7100 280 4300 10 700 57 000 250 1000
Total output s 6800 2800 5200 210 3300 4700 57 000 210 730
w 5430 5200 10800 350 5700 17 600 90 300 440 1220
Elbaz-Poulichet et al. (2001). Metal concentrations from Morley et al. (1997), As concentrations (Van der Weijden et al., 1990). Water ¯uxes: 38 1012 m3 yr
624
s 8000 3700 9000 280 4600 11 600 90 300 400 1000 1
(Bethoux, 1981).
Volume 42/Number 8/August 2001
Fig. 2 Comparison of the inputs to the Western Mediterranean basin through river, atmosphere and straits. The bars on the diagram represent the dierence between the maximum and minimum value.
overestimates the ¯ux for the pollution derived elements (e.g., Cd, Pb, Zn) and inversely minimizes the ¯ux for the elements derived from Saharan dust such as Fe. The atmospheric Cu, Cd and Pb ¯uxes are lower than previously published ¯uxes (Bergametti, 1987; Martin et al., 1989; Remoudaki, 1990; Guieu et al., 1997; Migon et al., 1997). This decrease results from the combination of two factors: (1) the actual decrease of the atmospheric concentrations in relation with the reduction of emissions (Ridame et al., 1999); (2) the occurrence of local/ regional contamination for these metals at some monitoring sites (Ridame et al., 1999). According to Ridame et al. (1999), the total atmospheric Pb ¯ux has decreased by at least a factor of 6 between 1983 and 1992, in relation with the decrease of leaded fuels. As a result, the Pb concentrations in the upper water column of the Western Mediterranean Sea have diminished by a factor of 2 during the same period (Nicolas et al., 1994; Migon and Nicholas, 1998). Despite the decrease of the atmospheric fallout for pollution derived metals, our results con®rm the predominance of the atmospheric ¯ux over the river ¯ux published by Guieu et al. (1997). Strait input The metal concentrations are seasonally variable particularly in the Strait of Gibraltar where the concentrations are maximum in June and minimum in September (Morley et al., 1999; Elbaz-Poulichet et al., 2001). This variability is attributed to the contribution of metal-enriched Spanish Shelf Water (SSW) originating from the Gulf of Cadiz. Metal concentrations in the waters of the Strait of Sicily are apparently maximum in winter and minimum in summer but the mechanism that produces such variations remains enigmatic and the data are not conclusive (Morley et al., 1997). As seasonal concentrations display opposite variations in the two straits (Gibraltar and Sicily), the total
Fig. 3 Comparison of the inputs through the straits of Gibraltar and Sicily. Bars as in Fig. 2.
strait input evolves in a narrow range for most elements. As shown in Fig. 2, it is the major source for Ni, Cu, Cd and Zn in the Western Mediterranean basin. For Fe and Mn the strait input remains in the range de®ned for the atmospheric input (Fig. 2). Although inputs through the Strait of Gibraltar are aected by contamination from a highly mineralized adjacent region (Nelson and Lamothe, 1983; ElbazPoulichet and Leblanc, 1996), inputs through the Strait of Sicily are generally similar or greater with the ex-
Fig. 4 Comparison between the input and output ¯uxes in the Western Mediterranean basin: (a) winter; (b) summer. Bars as in Fig. 2.
625
Marine Pollution Bulletin
ception of Mn (Fig. 3). The comparatively elevated input through the Strait of Sicily could simply result from the evaporation which takes place in the eastern basin. However, after normalizing to salinity (36.4 for AIW and 38.74 for SLIW) which diminishes the eect of evaporation, metal ¯uxes are equivalent. This con®rms an occurrence of metal sources in deep eastern basin waters as previously suggested by Morley et al. (1997). Strait output The Strait of Sicily output (Table 2) is higher than the Strait of Gibraltar output. As shown in Fig. 4, the total output ¯ux is balanced by the input ¯ux for all elements, except Fe. Assuming equilibrium conditions, this may suggest that exchange processes with sediments are negligible with regards to the magnitude of error. Alternatively the removal and release may be of the same order as indicated for Cd by Ruiz-Pino et al. (1990). The Fe output ¯ux is lower than the input. The difference, evaluated at 7±36 mg m 2 yr 1 , may represent the net transfer from the dissolved to the particulate phase. Indeed Sarthou and Jeandel (2001) calculated that the removal processes predominate over the release of Fe from particulate phase.
Conclusion The ¯uxes reported in this study simply represent an order of magnitude. Indeed transfer mechanisms are still poorly documented and trace metal data are relatively scarce in the Strait of Sicily. Due to the lack of data for the South-Western Mediterranean basin, the atmospheric fallout and the river ¯ux, measured on the northwest coast, have been extrapolated to the whole western basin. Nevertheless, this budget extends ¯ux knowledge to new elements and updates inputs and outputs to the Western Mediterranean basin. This update was necessary because previous ¯uxes did not include the reduction of the emissions into the atmosphere. This budget clearly indicates that inputs through the straits constitute the main source of dissolved metals to the Western Mediterranean basin. At a basin scale, the second source of metals is the atmosphere. The rivers represent a minor source. From the data presented here it is apparent that the overall import and export ¯uxes are near equilibrium, dissolved outputs balance dissolved inputs, except for Fe which sediments in the basin. This research was partly supported by the European Commission (DGXII) under contract TOROS (ENV4-CT96-0217), Environment and Climate Program (ELOISE) and CANIGO under contract MAS3PL95-0443, MAST. Bergametti, G. (1987) Apports de matiere par voie atmospherique a la Mediterranee Occidentale: aspects geochimiques et meteorologiques. Ph.D. thesis, University ParisVII, 296 pp. Bethoux, J. P. (1979) Budgets of the Mediterranean Sea. Their dependance on the local climate and on the characteristics of the Atlantic waters. Oceanology Acta 2, 157±163.
626
Bethoux, J. P. (1981) Le phosphore et l'azote en mer Mediterranee, bilans, fertilite potentielle. Marine Chemistry 10, 141±158. Boyle, E. A., Chapnick, S. D., Bai and Spivack X. X. (1985) Trace metal enrichments in the Mediterranean Sea. Earth and Planetary Science Letters 74, 405±419. Copin-Montaigut, G., Coureau, P. and Nicholas E. (1986) Distribution and transfer of trace elements in the Western Mediterranean. Marine Chemistry 18, 189±195. Dorten, W. S., Elbaz-Poulichet, F., Mart, L. and Martin, J. (1991) Reassessment of river input of trace metals to the Mediterranean Sea. Ambio 20, 2±6. Elbaz-Poulichet, F. and Leblanc, M. (1996) Transferts de metaux d'une province miniere a l'ocean par les ¯euves acides (Rio Tinto, Espagne), C.R. Academy of Science Paris, 322, Serie 2A, 1047± 1052. Elbaz-Poulichet, F., Garnier, J. M., Guan, D. M., Martin, J. M. and Thomas, A. J. (1996) The conservative behaviour of trace metals (As, Cd, Cu, Ni and Pb) in the surface plume of strati®ed estuaries: example of the Rhone river (France). Estuarine and Coastal Shelf Science 42, 289±310. Elbaz-Poulichet, F., Morley, N., Beckers, J. M. and Nomerange, P. (2001) Dissolved metal ¯uxes through the Strait of Gibraltar: the in¯uence of the Tinto-Odiel rivers. Marine Chemistry 73, 193± 213. Guieu, C., Mouchel, J. M., Noel, M., Guan, D. M. and Martin, J. M. (1991) Flux and behaviour of metals in the Ebro delta, Spain. Water Pollution Research Report 21, 293±307. Guieu, C., Zhang, J., Thomas, A., Martin, J. M. and Brun-Cottan, J. C. (1993) Signi®cance of atmospheric fallout on the upper layer water chemistry of the North-Western Mediterranean. Journal of Atmospheric Chemistry 17, 45±60. Guieu, C., Chester, R., Nimmo, M., Martin, J. M., Guerzoni, S., Nicolas, E., Mateu, J. and Keyse, S. (1997) Atmospheric input of dissolved and particulate metals to the northwestern Mediterranean. Deep-Sea Research II 44, 655±674. Martin, J. M., Elbaz-Poulichet, F., Guieu, C., Loye-Pilot, M.D. and Han, G. (1989) River versus atmospheric input of material to the Mediterranean Sea: an overview. Marine Chemistry 28, 159±182. Meybeck, M. and Ragu, A. (1999) River discharges to the oceans: an assessment of suspended solids, major ions and nutrients. Environment Information and Assessment Document, UNEP, Nairobi, 243 pp. Migon, C., Alleman L., Leblond N. and Nicolas E. (1993) Evolution of atmospheric lead over the northwestern Mediterranean between 1986 and 1992. Atmospheric Environment 27A, 2161±2167. Migon, C., Morelli, J., Nicolas, E. and Copin-Montegut, G. (1997) Evaluation of total atmospheric deposition of Pb, Cd, Cu and Zn to the Ligurian Sea. Science of Total Environment 105, 135±148. Migon, C. and Nicholas, E. (1998) Eects of antipollution policy on anthropogenic lead transfers in the Ligurian sea. Marine Pollution Bulletin 36, 775±779. Morley, N. H., Burton, J. D., Tankere, S. P. and Martin, J. M. (1997) Distribution and behaviour of some dissolved trace metals in the western Mediterranean Sea. Deep-Sea Research 44, 3±4, 675± 691. Morley, N. H., Elbaz-Poulichet, F. and Nomerange, P. (1999). Trace metals in the waters of the Straits of Gibraltar. Oral presentation. 24th General Assembly of the European Geophysical Society in The Hague, 19±23 April 1999. Journal of Geophysics Research Abstract 2, 402. Nelson, C. H. and Lamothe, P. J. (1983) Heavy metal anomalies in the Tinto and Odiel river and estuary system, Spain. Estuaries 16, 495± 511. Nicolas, E., Ruiz-Pino, D., Buat-Menard, P. and Bethoux, J. P. (1994) Abrupt decrease in lead concentration in the Mediterranean Sea: a response to antipollution policy. Geophysics Research Letters 21, 2112±2122. Remoudaki, E. (1990) Etude des processus controllant la variabilite des ¯ux atmospheriques de polluants et de poussieres minerales en Mediterranee Occidentale. Ph.D. thesis, University Paris VI, 224 pp. Ridame, C., Guieu, C. and Loye-Pilot, M. D. (1999) Trend in total atmospheric deposition ¯uxes of aluminum, iron, and trace metals in the northwestern Mediterranean over the past decade (1985±1997). Journal of Geophysics Research 104, D23, 30 127± 130, 139.
Volume 42/Number 8/August 2001 Ruiz-Pino, D. P, Jeandel, C., Bethoux, J. P. and Minster, J. F. (1990) Are trace metals balanced in the Mediterranean Sea? Paleogeography, Paleoclimatology, and Paleoecology 82, 369±388. Sarthou, G. and Jeandel, C. (2001) Seasonnal variations of iron concentrations in the Ligurian Sea and iron budget to the Western Mediterranean basin. Marine Chemistry 74, 115±129. Sherell, R. and Boyle, E. (1988) Zinc, chromium, vanadium and iron in the Mediterranean Sea. Deep-Sea Research 35, 1319±1334. Spivack, A., Huested, S., Boyle, E. (1983) Copper, nickel, and cadmium in the surface waters of the Mediterranean. In Trace Metals in Seawater, eds. C.S. Wong et al., pp. 505±512. Plenum Press, New York.
Van der Weijden, Middelburg, J., de Langue, G., Van der Sloot, H., Hoede, D., Woittiez, J. (1990) Pro®les of redox-sensitive trace elements As, Sb, V, Mo and U in the Tyro and Bannock Basins (eastern Mediterranean). Marine Chemistry 31, 167±186. Van Geen, A., Rosener, P., Boyle, E. A. (1988) Entrainment of trace metal-enriched Atlantic shelfwaters in the in¯ow to the Mediterranean Sea. Nature 331, 423±426. Van Geen, A., Boyle, E. A., Moore, W. S. (1991) Trace metal enrichments in waters of the Gulf of Cadiz, Spain. Geochimica Cosmochimica Acta 55, 2173±2191.
627