Anthropogenic metal contamination and sapropel imprints in deep Mediterranean sediments

Marine Pollution Bulletin 62 (2011) 1041–1052

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Anthropogenic metal contamination and sapropel imprints in deep Mediterranean sediments M.O. Angelidis a,⇑, O. Radakovitch b, A. Veron b, M. Aloupi a, S. Heussner c, B. Price d a

Department of Environment, University of the Aegean, Lofos Panepistimiou, 81100 Mytilene, Greece CEREGE – CNRS UMR6635, Université Aix-Marseille III, Europôle de l’Arbois BP 80, 13545 Aix-en-Provence Cedex 4, France c CEFREM, University of Perpignan, 52 Alduy Ave., 66860 Perpignan Cedex, France d Department of Geology and Geophysics, Kings Building, West Mains Road, Edinburgh EH16 5NS, UK b

a r t i c l e Keywords: Mediterranean Pollution Sediments Metals Lead isotopes Sapropels

i n f o

a b s t r a c t Sediment cores from the deep Balearic basin and the Cretan Sea provide evidence for the accumulation of Cd, Pd and Zn in the top few centimeters of the abyssal Mediterranean sea-bottom. In both cores, 206Pb/ 207Pb profiles confirm this anthropogenic impact with less radiogenic imprints toward surface sediments. The similarity between excess 210Pb accumulated in the top core and the 210Pb flux suggests that top core metal inventories reasonably reflect long-term atmospheric deposition to the open Mediterranean. Pb inventory in the western core for the past 100 years represents 20–30% of sediment coastal inventories, suggesting that long-term atmospheric deposition determined from coastal areas has to be used cautiously for mass balance calculations in the open Mediterranean. In the deeper section of both cores, Al normalized trace metal profiles suggest diagenetic remobilization of Fe, Mn, Cu and, to a lesser extent, Pb that likely corresponds to sapropel event S1. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction It is well known that atmospheric input plays a key role for the transport of polluted particles to the Mediterranean basin (Guieu et al., 1993; Migon, 1993; Bethoux et al., 1999), while riverborne anthropogenic metals are mostly stored on continental shelves (Martin et al., 1989; Guieu et al., 1991; Dorten et al., 1991; Palanques and Diaz, 1994; Roussiez et al., 2006). Guieu et al. (1993) and Migon (1993) estimated that at least 50% of Cd, Pb and Zn transported to the offshore environment of the Western Mediterranean are of atmospheric origin. However, it is very difficult to assess the importance of atmospheric vs riverine inputs in the long term because of the limited number of data of trace metal concentrations in the atmosphere and their high temporal variability. Marine sediments provide a proxy for such determination (Ng and Patterson, 1982; Veron et al., 1987; Ferrand et al., 1999; Oktay et al., 2000; Santschi et al., 2001; Masque et al., 2003; Roussiez et al., 2006; Miralles et al., 2006). Land-based natural and anthropogenic sources both supply trace metals to the land-locked Mediterranean Sea. The anthropogenic imprint is clearly evidenced in most of the Mediterranean near-shore sediments (Nolting and Helder, 1991; Marin, 1998; Ferrand et al., 1999; Miralles et al., 2006; Palanques et al., 2008) where atmospheric deposition, riverine dis⇑ Corresponding author. Present address: UNEP/MAP, 48, Vas. Konstantinou Ave., 11635 Athens, Greece. Tel.: +30 2107273132. E-mail address: [email protected] (M.O. Angelidis). 0025-326X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2011.02.030

charges and lateral transport of suspended particulate mater (SPM) from continental margins contribute to enhanced trace metal concentration (Migon et al., 1991; Guieu et al., 1997; Guerzoni et al., 1999; Alleman et al., 2000). Also there is evidence for pollutant’s enrichments in deeper parts of the Western Mediterranean (Fernex et al., 1992, 2001; Martin et al., 2009). However, the flux of anthropogenic metals accumulated in the sediment is less known, and the only available budgets for metals were determined from the continental margins and its slopes (Marin, 1998; Ferrand et al., 1999; Miralles et al., 2006). We do not know how much of this contamination has been accumulated in pelagic sediments, and how much is due to atmospheric deposition. Mass balance outcomes are limited by uncertainties on atmospheric deposition, since there are few direct long-term records for atmospheric inputs and they are generally limited to the past 20 years. These uncertainties are even greater with pollutant metals of which accumulation is generally transient in time in marine sediments (Chow et al., 1973; Bruland et al., 1974; Ng and Patterson, 1982; Veron et al., 1987; Finney and Huh, 1989; Hamelin et al., 1990; Farmer et al., 1996; Ferrand et al., 1999; Marcantonio et al., 2002). For example, while sediment inventories of anthropogenic Pb in the Gulf of Lion seem to faithfully record atmospheric deposition at least on the slope (Ferrand et al., 1999; Miralles et al., 2006), there is no such evidence for open sea sediments. Furthermore, the evaluation of these anthropogenic inputs in the sediment is rather complicated by the fact that, in deep section of sediment cores, trace metals can display variations that rely on diagenetic transformations of the sediment

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or on particular deposits, like the sapropel events usually observed in the Eastern Mediterranean (Cramp and O’Sullivan, 1999; Rohling et al., 2002; Casford et al., 2003). The influence of such processes has to be evaluated for a correct estimation of anthropogenic inputs. Our main objectives in this study are to assess recent deep-sea accumulation of anthropogenic trace metals from atmospheric origin in order to establish a reliable centennial atmospheric deposition budget in the open sea. Answers to these questions depend very much on (1) the choice of a remote little-disturbed abyssal plain where direct atmospheric deposition and changes in water column biogeochemistry can be identified in top sediment cores and (2) the use of reactive transient and/or radioactive tracers allowing to date recent sediment deposition and characterize the anthropogenic impact. To resolve these questions, two experimental sites were chosen in the Western (deep Balearic basin) and Eastern (the Cretan Sea) Mediterranean (Fig. 1), both regions known to receive little particulate advective input from continental slopes. Therefore, trace metals accumulated in the sediment of the central Balearic basin and the Cretan Sea might mainly originate from direct atmospheric deposition rather than advection from other basins. Recent sapropel events were also observed in both cores and their influence on the natural trace metal concentrations was also discussed. Among all trace metals, we focused more particularly on Pb which is the most efficient long-term tracer for anthropogenic metal contamination because of its well known transient emissions and its isotopes. Stable and radioactive isotopes of Pb are being used to characterize accumulated sediments for the past 100 years because of the 210Pb radioactive period of 20.3 years (Ng and Patterson, 1982; Ferrand et al., 1999; Miralles et al., 2006; Martin et al., 2009) and the isotopic imprint of Pb aerosols released from industrial activities (Chow et al., 1975; Sturges and Barrie, 1987; Veron et al., 1999; Simonetti et al., 2000; Bollhofer and Rosman, 2001). Lead has 4 stable isotopes (204Pb, 206Pb, 207 Pb, and 208Pb) of which the last three are final members of the natural U-Th decay chains. These isotopes display distinct abundances depending on the age and original U-Th content of Pb ores (see Doe, 1970 and Ref. there in). Because of the extensive use of these ores in industry for the past 200 years (non ferrous alloys, additive in gasoline, paints. . .), anthropogenic Pb has been introduced to the troposphere and to surface waters of the Mediterranean (Martin et al., 1989; Nicolas et al., 1994; Guieu et al., 1997; Migon et al., 2008), where its residence time is short (days to months) as compared to air and water exchange between the Mediterranean and other oceanic basins. Therefore not only anthropogenic Pb is expected to have reached the deep abyssal reservoirs of the Mediterranean as in the Atlantic (Veron et al., 1987;

Hamelin et al., 1990), but also its isotopic composition and well known transient emissions allow to clearly distinguish between anthropogenic and crustal natural input in this semi-enclosed basin (Ferrand et al., 1999; Miralles et al., 2006). The U-Th decay chain also produces 210Pb that is an efficient tracer of sediment accumulation and mixing thanks to its well known atmospheric deposition and in situ production from 226Ra. Sediment dating is usually established with models based on the activity of atmospherically derived 210Pbxs found in excess of in situ 210 Pb produced in sediment (e.g. Robbins and Eddington, 1975; Appleby and Oldfield, 1983). Marine sediment accumulation rates are often overestimated due to frequent bioturbation and physical mixing (e.g. Robbins and Herche, 1993). In this case a maximum sedimentation rate can be however determined from a two-layer model (Anderson et al., 1987) as it has been done for various sites of the Mediterranean sea (Radakovitch et al., 1999; Sanchez-Cabeza et al., 1999, 2000; Miralles et al., 2005, 2006). The multi tracer approach offered by Pb and its isotopes therefore provides an efficient tool to assess to what extent sediment inventories in the open Mediterranean Sea do record anthropogenic imprints and whether or not this imprint faithfully reflect long-term atmospheric deposition of metal pollutants in this pelagic region. This investigation was conducted as part of the ADIOS EEC program, under the work package ‘‘accumulation and impact of pollutants and key elements in deep sea Mediterranean sediments and organisms’’. 2. Materials and methods Undisturbed sediment cores were collected by a multicorer or boxcorer in March 2001 (western site, stations: WA, WB and WC, depth 2850 m) and April 2001 (eastern site, stations EA and EB, depth 2800 m). Each station was located at the bottom of a sediment-trap mooring line deployed for one year during the ADIOS project (Fig. 1). The stations were 25 km apart from each other within each site. Cores were opened and sliced immediately onboard into sections of 0.5 cm (from surface down to 5 cm depth), 1 cm (from 5 to 20 cm depth) or 2 cm (below 20 cm depth). The samples were freeze-dried, homogenized and sub-samples were separated for the various analyses. Pb isotopes (including 210Pb), and metals were analyzed on the same sample, whereas artificial radionuclides were measured on a specific core, generally taken from the same multicorer cast. 210 Pb activities were measured by alpha spectrometry of its granddaughter 210Po. Samples were dissolved in a mixture of HCl, HNO3 and HF in the presence of 209Po as a yield tracer. Po was plated spontaneously from 1.5 N HCl solution onto Ag disks. Supported 210Pb was estimated following the method of Binford

Fig. 1. Location of ADIOS sediment core sampling in the Balearic basin (WA, WB and WC) and the Cretan Sea (EA and EB).

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et al., 1993 and was subtracted from the total 210Pb to obtain excess 210Pb (210Pbxs). Uncertainties were calculated by standard propagation of the 1 sigma counting errors of samples and blanks. Samples for stable Pb isotopes analyses were oxidized using HNO3, HF, HCl and were purified through AG1X8 anionic resins in dust clean laboratory. Pb isotopic ratios were determined by thermo-ionization mass spectrometry (FIN MAT 262) at CEREGE. Precision on 206Pb/207Pb and 208Pb/206Pb ratios was better than 0.01% per a.m.u. Mass fractionation was corrected with the SRM981 NIST standard. Trace metal concentrations were determined using a Perkin– Elmer 5100ZL Atomic Absorption Spectrometer with Zeeman background correction following oxidation in a microwave oven of 200 mg of dried sediment with aqua regia and HF, (Loring and Rantala, 1992). Copper and Zn were determined by Flame Atomic Absorption Spectrometry, while Cd and Pb were measured by Graphite Furnace Atomic Absorption Spectrometry with a mixture of 50 lg NH2H2PO4 and 3 lg Mg(NO3)2 as a matrix modifier (Angelidis and Aloupi, 1997). Analytical accuracy was controlled with the use of Reference Materials of the National Research Council of Canada (BCSS-1 marine sediment, PACS-1 harbor sediment) and International Atomic Energy Agency (SDM2TM marine sediment).

Major elements (Al, Fe, Mn, P, K, Ca, Si, Ti, Na and Mg) were analyzed by X-ray fluorescence with a Philips PW 2400 sequential wavelength dispersive X-ray spectrometer on 0.3 g bulk sediment aliquots, homogenized with 5.7 g of lithium tetraborate. Prior to the analyses, sub-samples were castled into fused beds in an induction oven at 1150 °C by addition of 5 mg of a tensoactive compound. 3. Results 3.1. Sediment composition In both western and eastern basin, sediments were mainly calcareous pelitic muds. A thorough sedimentological description of the western basin cores can be found in Zuniga et al. (2007a) who identified five main sedimentological units (U1–U5) in all cores, but at different depths within each core. The characteristic layers are U5 (0–1 cm) rich in pteropods, U3 (7–12 cm on site A; 8–19 cm on site B and 7–14 cm on site C) corresponding to a turbidite layer and U2 (12–13 cm; 19–20 cm and 14–15 cm in cores A, B and C, respectively) enriched in pteropods like U5. U1 and U4 are yellowish brown foraminifer-pteropod oozes. While such detailed

(a) Fe/Al 0.30

0.50

0.00

0.70

Cd/Al 0.02

Cu/Al 0.04

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Mn/Al

K/Al

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10.0

20

25

25

30

30

30

35

35

35

(c)

5.0

Zn/Al

15

25

(b)

Pb/Al

(d)

Fig. 2. Lithological units (a) and metal to Al profiles (b–d) in the western core WB (Cd/Al, Cu/Al, Pb/Al and Zn/Al  104).

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M.O. Angelidis et al. / Marine Pollution Bulletin 62 (2011) 1041–1052 Mn/Al

Depth (cm)

0.00 0

Fe/Al 0.60

Cd/Al

Cu/Al

1.20

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5

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Zn/Al 20.0

30.0

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25

(a)

Pb/Al 10.0

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Depth (cm)

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(b)

(c)

Fig. 3. Lithological units (a) and metal to Al profiles (b, c) in the eastern core EA(Cd/Al, Cu/Al, Pb/Al and Zn/Al  104).

sedimentological description was not conducted on our WB core owing to the sampling procedure, each of these sedimentological layers was clearly identified (Fig. 2). The pteropod enriched sequences U5 and U2 were observed at 0–1 cm and 15–16 cm, respectively within core WB. The turbidite layer U3 (7–15 cm in core WB) could be determined from changes in major elements profiles as noted in Zuniga et al. (2007a) with high Fe/Al and K/Al ratios (Fig. 2). In the eastern basin, cores consisted of light-brown muddy sediment from surface down to 19 cm depth including two layers enriched in pteropods at 0–1 cm and at 12–13 cm in EA (15–16 cm in EB) (Fig. 3). Below 19 cm, the sediment was a pale and uniform grey carbonate. In both cores (EA and EB) a black enriched organic layer was identified at 24–28 cm (EA) and 20– 24 cm (EB). It likely corresponds to the S1 sapropel layer previously observed at similar depths in this area and dated between 9 and 5.2 kyr BP (Thomson et al., 1995; Van Santvoort et al., 1996).

37 Bq/kg, respectively for core WA, WB and WC with excess 210 Pb being restricted to the first three centimeters of the sediment (Fig. 4). Core WA and WB show regular profiles decreasing exponentially with depth, whereas the profile of core C is disrupted, with high activities at 1.25 and 3.25 cm depth (the level 3–3.5 cm was duplicated and the two data are in perfect agreement) and a low value at 1.75 cm. Furthermore, excess 210Pb is observed until 4.5 cm depth at this station, but the activities are very low below 3.5 cm. These observations indicate that core C could be affected by non diffusive bioturbation of the surface sediment (Boudreau, 1986). Garcia-Orellana et al. (2008) recently published 210Pb, 137Cs and 239 + 240Pu profiles from cores collected on the same multicorer cast. Our data agree perfectly with their profiles and the very small differences observed are likely due to the use of different cores and different analytical technique (gamma counting for Garcia-Orellana et al., 2008).

3.2. Metal content

3.4. Stable Pb isotopes

Metal content is presented for Cd, Cu, Pb, Zn, Mn, Fe and Al in core WB and EA (Table 1). All metals but Al, Mn and Fe display higher concentration in the first few cm. Since metals from both natural and anthropogenic sources normally accumulate together mostly in the fine-grained sediment fractions, examination of the potential enrichment first requires normalization to the grain size and mineralogical effects on the metal variability. The most usual normalization method is the expression of metal concentrations as ratios to a proxy of the detrital sedimentary component, normally Al (Calvert and Pedersen, 1993; Wedepohl, 1995). Aluminum is assumed to represent the abundance of aluminosilicates in the sediment and its content is not perturbed by biogenic activity, authigenic enrichment or diagenetic mobilization. It is currently used in sapropel and other deep sea sediment studies (Arnaboldi and Meyers, 2007). Here we use ratios of metal to Al to characterize the anthropogenic imprint for each metal as well as biogeochemical processes that could affect metal distribution or be recorded in the sediments (Figs. 2 and 3).

The ratio of 206Pb to 207Pb is generally used to discuss the anthropogenic vs. natural imprint of Pb in sediments owing to its precision and its long-term usage (e.g. Chow et al., 1973; Ng and Patterson, 1982). Western and Eastern sediment cores display typical isotopic profiles from higher to lower 206Pb/207Pb ratios downward (Table 2, Fig. 5).

3.3.

210

Pb activities

In the western basin, the three cores exhibit similar profiles for Pb activities (Fig. 4). Supported 210Pb activities are 34, 37 and

210

4. Discussion 4.1. Sedimentation rates Based on 210Pb activities data and using the CFCS model (Anderson et al., 1987), maximum sedimentation rates for WA and WB are 0.0241 and 0.0227 cm y1 (or 0.022 and 0.0225 g cm2 y1) respectively. These rates are five times higher than the average rate of 4.5 cm ky1 calculated on site C by Zuniga et al. (2007a,b) from 14 C datation, suggesting that the apparent 210Pb distribution is due to mixing. This mixing is confirmed by Garcia-Orellana et al. (2008) who find artificial radionuclides reaching the same depth as the 210 Pbxs . Using a negligible sedimentation rate (S = 0 cm yr1), the maximum mixing rate (diffusive coefficient) calculated with a CFCS model is 0.016 cm2 yr1 for the two stations. According to the model of Miralles et al. (2006) and the 14C sedimentation rate of

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M.O. Angelidis et al. / Marine Pollution Bulletin 62 (2011) 1041–1052 Table 1 Trace metal concentrations in sediment cores WB (Western basin) (a) and EA (Eastern basin). Depth (cm)

Al (%)

Fe (%)

Mn (%)

Cd (mg/kg)

Cu (mg/kg)

Pb (mg/kg)

Zn (mg/kg)

(a) Core WB (Western basin) 0.5 5.42 1 7.01 1.5 6.95 2 6.96 2.5 6.94 3 6.88 3.5 6.91 4 7.07 4.5 6.79 5 6.80 6 6.78 7 6.61 8 6.30 9 6.36 10 6.33 11 6.29 12 6.29 13 6.28 14 5.96 15 5.90 16 5.62 17 6.47 18 6.12 19 6.14 20 6.21 22 5.85 24 5.98 26 6.08 28 6.36 30 6.60 32 6.71 34 5.85 37 5.88

2.68 3.45 3.41 3.39 3.38 3.35 3.38 3.35 3.33 3.33 3.34 3.25 3.14 3.18 3.18 3.16 3.13 3.14 2.93 2.84 2.46 2.91 3.02 3.11 3.20 2.97 2.99 3.06 3.23 3.40 3.51 2.76 2.81

0.125 0.160 0.161 0.157 0.150 0.149 0.149 0.143 0.145 0.144 0.134 0.119 0.095 0.097 0.107 0.119 0.138 0.150 0.156 0.156 0.064 0.068 0.065 0.068 0.064 0.054 0.075 0.099 0.091 0.128 0.164 0.122 0.069

0.147 0.165 0.155 0.117 0.097 0.091 0.103 0.095 0.104 0.103 0.088 0.093 0.096 0.105 0.107 0.083 0.077 0.084 0.078 0.069 0.068 0.075 0.074 0.067 0.081 0.063 0.072 0.084 0.091 0.098 0.093 0.084 0.067

36.1 41.9 45.4 44.3 43.1 40.1 45.8 42.9 42.8 46.6 45.6 41.7 37.1 36.4 29.1 31.0 28.9 30.1 30.2 32.8 38.5 44.9 39.5 27.2 32.2 43.5 45.2 41.1 35.1 36.5 36.2 37.5 36.8

32.2 38.4 35.8 29.8 24.2 20.0 24.8 22.4 21.7 23.5 22.7 20.6 18.3 18.2 15.6 15.4 16.2 15.8 15.5 19.6 14.8 17.2 21.3 17.7 17.6 15.8 14.5 14.1 16.2 17.5 18.6 18.6 15.0

67.7 82.6 81.4 75.1 71.1 65.1 70.7 67.9 66.7 74.7 67.3 67.2 62.6 65.1 58.2 52.7 60.2 55.1 56.1 54.8 50.5 53.1 60.8 54.8 65.7 60.0 57.4 56.5 62.1 68.1 70.6 63.2 66.7

(b) Core EA (Eastern basin) 0.5 4.29 1 5.04 1.5 4.33 2 4.20 2.5 4.01 3 4.14 3.5 4.05 4 3.85 4.5 4.33 5 4.43 6 4.55 7 4.38 8 4.15 9 4.11 10 3.91 11 3.67 12 3.54 13 3.56 14 3.66 15 3.99 16 4.00 17 3.83 18 3.73 19 3.97 20 4.40 22 4.71 23 4.74 24 4.78 25 4.70 26 4.62 27 4.67 28 4.71

2.48 2.92 2.51 2.43 2.29 2.37 2.32 2.20 2.46 2.52 2.61 2.55 2.36 2.37 2.29 2.16 2.10 2.11 2.19 2.45 2.56 2.55 2.64 2.88 3.38 3.89 4.18 4.48 4.64 4.80 3.95 3.10

0.112 0.136 0.118 0.116 0.104 0.113 0.125 0.131 0.108 0.106 0.108 0.106 0.094 0.095 0.098 0.110 0.136 0.203 0.536 1.118 2.221 1.695 0.548 0.332 0.345 0.502 0.580 0.667 0.360 0.049 0.040 0.034

0.260 0.275 0.127 0.120 0.121 0.155 0.122 0.126 0.151 0.130 0.088 0.121 0.106 0.114 0.135 0.148 0.115 0.209 0.204 0.301 0.265 0.189 0.153 0.110 0.097 0.088 0.084

52.3 60.0 50.9 53.3 50.0 51.8 52.0 52.5 49.2 54.9 45.9 49.3 48.4 50.1 49.0 45.6 47.7 53.7 60.7 68.1 78.7 83.0 48.2 37.5 47.5 48.5 63.5

19.9 19.9 14.8 15.1 13.2 14.0 14.9 15.3 18.0 18.9 15.1 13.6 11.6 11.7 11.2 9.9 10.8 11.3 12.0 11.6 11.4 12.3 11.5 12.0 13.0 13.2 14.3

45.5 52.4 43.9 41.3 39.2 40.8 41.7 42.0 40.6 43.8 40.1 42.6 42.5 43.8 41.3 36.4 37.6 36.9 39.8 45.2 56.0 54.3 40.7 45.4 49.4 50.6 54.6

0.098 0.240 2.345 1.243

79.6 72.1 83.1 62.9

11.9 11.7 11.2 14.4

60.2 58.5 55.2 57.9

Zuniga et al. (2007a,b), the real value of mixing rate is estimated at 0.013 cm2 yr1. The similarity between cores WA and WB (and to a lesser extent WC) indicates that they are representative of the mean sedimentation-mixing processes occurring in this abyssal plain. This is confirmed by the very similar excess 210Pb inventories

obtained for the 3 (2834 ± 56, 2806 ± 54 and 2676 ± 53 Bq m2 corresponding to a mean 210 Pbxs flux of 86 ± 5 Bq m2 yr1). These inventories are in agreement with those of Garcia-Orellana et al. (2008) (2603, 2238 and 2682 Bq/m2 for WA, WB and WC, respectively). 210Pb profiles alone do not allow to distinguishing between

M.O. Angelidis et al. / Marine Pollution Bulletin 62 (2011) 1041–1052

0

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5 Depth (cm)

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10 WA WB WC

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Pb total activity (Bq/kg)

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100 210

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Pb total activity (Bq/kg)

Depth (cm)

Depth (cm)

EA

15

EB

20

Fig. 4.

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400

2

3 EA 4

500

Pb excess activity (Bq/kg)

5 0

EB

50

100 210

150

200

250

300

Pb excess activity (Bq/kg)

Pb profiles (total and excess activities) in the western WA, WB, WC and Eastern EA, EB sediment cores.

sedimentation and bioturbation processes in such slowly accumulating sediments (Crusius and Kenna, 2007), but the depth of 210 Pbxs penetration (i.e. 3 cm, Fig. 4) provides an age constraint of 100–150 years (5–7 half lives) for particles accumulated within the top sequence of the cores. The distribution of total 210Pb activities with depth in the eastern basin is more complex (Fig. 4). Activities rapidly decrease from 0 to 2 cm where it reaches constant values that could be associated with supported 210Pb. Meanwhile, below this surficial layer, we observe an increase of 210Pb concentration, reaching a maximum at 16–17 cm in EA. This trend is likely to be related to a variation of 226Ra or 238U activities (producing 210Pb in equilibrium) rather than to an important mixing. In this case, the best value for supported 210Pb in sub-surface layers can be estimated according to the method of Binford et al. (1993). Supported 210Pb values of 32 ± 1 and 36 ± 3 Bq kg1 were calculated for station EA and EB, respectively (between 1 and 5 cm) that are similar to those from the western basin and slightly higher than those found by Thomson et al. (1995) in the same area and for the same water depth (average 27 Bq kg1). Excess 210Pb are restricted to 1.5 and 1.0 cm depth in cores EA and EB, respectively. Activities in the first centimeter of core EA are quite constant, clearly suggesting mixing, either from bioturbation or during coring. Our calculations are consistent with Garcia-Orellana et al. (2008) findings for the same core casts. Maximum 210Pb sedimentation rates are 0.017 and 0.006 cm yr1, and maximum mixing rates are 0.0057 and 0.0009 cm2 yr1 for station EA and EB. These mixing rates are in general good agreement with those found in nearby cores by Basso et al. (2004) (0.005 cm2 yr1) and about an order of magnitude lower than those by Thomson et al. (1995) (0.026 and 0.01 to 0.03 cm2 yr1). The same authors observe a thicker surface mixed layer (i.e. 2 cm). Excess 210Pb inventories in eastern cores (2397 ± 45 and 1194 ± 57 Bq m2 for station EA and EB) are 15–55% lower than in the western basin. Such difference could

be explained by a lower production rate or a higher decay flux in the water column of the eastern basin where 210Pb inventories reported by Garcia-Orellana et al. (2008) are respectively 2450 and 1779 Bq m2. 4.2. Trace metal sediment contamination At the western site, normalized concentrations (i.e. ratios to Al) of Cd, Pb and Zn are relatively constant in deep layers but increase from 3 cm upward (Fig. 2). Cu does not exhibit the same pattern: normalized concentrations fluctuate in the deep layers and are more constant near the surface. The similarity in the upper few centimeters between Cd and Pb and, to a lesser extent, Zn profiles probably reflects analogies in their environmental fate, in terms of origin, deposition and diagenesis into the sediment. The recorded Cd, Pb and Zn maxima in the surface may result either from input of anthropogenically contaminated particles and/or re-deposition of upward fluxes of previously deposited metals released by diagenetic mobilization of Fe and Mn oxides. This later process would imply Fe and Mn oxide dissolution in sub-oxic sub-surface sediment layers and the migration of their dissolved cations upward, where they are re-precipitated under oxic conditions (Klinkhammer et al., 1982; Thomson et al., 1993). In our case, both 210 Pbxs profiles and Pb isotopic ratios argue for a direct anthropogenic input. 210 Pbxs profiles reveal that the increasing trend of normalized concentrations is observed on the surface layer directly affected by mixing and corresponding to particles deposited during the past 100–150 years. Pb isotopic imprint also show that Pb accumulated in this layer has an anthropogenic origin derived from industry and gasoline emissions with less radiogenic 206Pb/207Pb ratios (Fig. 5). The purpose of the isotopic analysis was to accurately define the anthropogenic incursion and its penetration depth, so only the most accurate ratio (i.e. 206Pb/207Pb) was used. The radiogenicity of anthropogenic lead used in countries

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M.O. Angelidis et al. / Marine Pollution Bulletin 62 (2011) 1041–1052 Table 2 Ratios 206Pb/204Pb,

208

Pb/206Pb and 206

206

Pb/207Pb in western (a) and eastern (b) cores. sd

208

(a) Core WA (Western basin) 0.5 18.374 1 18.471 1.5 18.787 2 18.541 2.5 18.615 3 18.652 3.5 18.678 7 18.729 10 18.984

0.005 0.009 0.006 0.004 0.004 0.002 0.004 0.004 0.035

Core WB (Western basin) 0.5 1 1.5 2 2.5 3 3.5 5 6 7 8 11 12 13 14 17 19 30 36

18.428 18.485 18.530 18.587 18.664 18.672 18.680 18.731 18.708 18.738 18.785 18.876 18.815 18.826 18.860 18.717 18.738 18.857 18.817

(b) Core EA (Eastern basin) 0.5 1 1.5 2 3 4 5 7 9 13 19

18.604 18.670 18.732 18.697 18.812 18.812 18.780 18.837 18.831 18.861 18.857

Depth (cm)

Pb/204Pb

sd

206

2.0850 2.0860 2.0860 2.0820 2.0780 2.0730 2.0780 2.0700 2.0840

0.0010 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0020

1.1784 1.1814 1.1815 1.1852 1.1895 1.1929 1.1919 1.1967 1.1965

0.0001 0.0001 0.0001 0.0001 0.0001 0.0000 0.0001 0.0001 0.0005

0.003 0.006 0.004 0.005 0.004 0.006 0.006 0.006 0.004 0.015 0.005 0.041 0.011 0.007 0.007 0.050 0.009 0.003 0.022

2.0889 2.0882 2.0857 2.0822 2.0814 2.0769 2.0746 2.0792 2.0734 2.0704 2.0703 2.0714 2.0654 2.0659 2.0694 2.0802 2.0760 2.0628 2.0702

0.0001 0.0001 0.0002 0.0005 0.0003 0.0001 0.0002 0.0003 0.0003 0.0002 0.0001 0.0004 0.0002 0.0004 0.0001 0.0005 0.0002 0.0001 0.0007

1.1788 1.1812 1.1837 1.1875 1.1897 1.1925 1.1936 1.1926 1.1954 1.1975 1.1984 1.2001 1.2016 1.2017 1.2006 1.1933 1.1950 1.2038 1.1991

0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0002 0.0001 0.0002 0.0001 0.0001 0.0001 0.0003 0.0001 0.0001 0.0002

0.012 0.007 0.027 0.071 0.020 0.005 0.135 0.038 0.008 0.009 0.011

2.0803 2.0792 2.0754 2.0728 2.0736 2.0702 2.0686 2.0663 2.0680 2.0675 2.0652

0.0002 0.0003 0.0003 0.0004 0.0005 0.0002 0.0008 0.0005 0.0001 0.0003 0.0002

1.1890 1.1911 1.1971 1.1968 1.2006 1.2001 1.2004 1.2024 1.2026 1.2043 1.2031

0.0001 0.0001 0.0002 0.0005 0.0002 0.0001 0.0008 0.0003 0.0001 0.0001 0.0001

0

5

depth (cm)

10

15

20

West A

25

West B

30

East A

35

1,175

1,182

1,189

1,196

1,203

1,210

206Pb/207Pb Fig. 5. Pb isotopic imprint (206Pb/207Pb) in western (WA, WB) and eastern (EA) Mediterranean basins.

surrounding the Mediterranean basin is significantly lower than that of crustal lead (see Hopper et al., 1991; Grousset et al., 1994; Alleman et al., 2000; Bollhofer and Rosman, 2001; Erel

Pb/206Pb

Pb/207Pb

sd

et al., 2007) allowing the 206Pb/207Pb ratio to be used as a reliable marker for pollutant lead incursion. The penetration of the radioactive 210Pb isotope corroborates the usefulness of the 206Pb/207Pb ratio, and both tracers allow to defining more accurately the recent contamination of anthropogenic metals. The pattern shown in Fig. 5 is explained by a transient input of pollutant Pb with less radiogenic imprints than natural derived Pb from crustal origin. 206 Pb/207Pb ratios in surface sediment of both western cores (=1.178) are slightly less radiogenic than most imprints encountered in the Golf of Lions (e.g. Ferrand et al., 1999; Miralles et al., 2006) suggesting less mixing with local crustal particles. Below 10 cm, the isotopic signature varies around 1.20, a typical geochemical background reached in other cores of the Gulf of Lions. Two less radiogenic excursions are observed within this background at 16–18 cm and, to a lesser extent, 35 cm in Western core B that could reflect input from a specific source such as the Saharan dust, known as less radiogenic (Grousset et al., 1994). Indeed, nonlocal mixing processes could not be invoked to explain these shifts since 210Pb activities are not affected. It should also be noted that Pb isotope signatures reach the natural background at about 10 cm, twice as much deeper than excess 210Pb, indicating that pollutant Pb has clearly invaded the bottom of the deep Western Mediterranean basin for more than 100 years. The 206Pb/207Pb ratios versus (1/Pb) concentration plots show two mixing lines (with correlation factor r2 better than 0.8) for both the western and eastern cores (Fig. 6) that allow to define

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M.O. Angelidis et al. / Marine Pollution Bulletin 62 (2011) 1041–1052

The observed Pb peak around 6 cm is not matched by sudden changes in Pb isotopic ratios (Fig. 5) whereas the increasing concentrations of Pb in surface corresponds, (as in the western basin) to changes in Pb source emissions with 206Pb/207Pb ratios shifting from 1.20 at 3 cm to less than 1.19 at the surface of the core.

1.210

207Pb/207Pb

1.200

4.3. Metal inventories in the deep Mediterranean basins 1.190

2

West y=1.170+0.48x (r =0.84) 2

1.180

East y=1.175+0.33x (r =0.89)

1.170

0

0.025

0.05

0.075

0,1

1/Pb 206

Fig. 6. Pollutant isotopic imprint ( lated from f(1/Pb) = 206Pb/207Pb).

Pb/207Pb ratios) in cores WB and EA (calcu-

anthropogenic end-member 206Pb/207Pb ratios comprised between 1.170 and 1.175. These isotopic ratios are consistent with the expected atmospheric Mediterranean imprints as defined from contaminated aerosols and top soils (Maring et al., 1987; Hopper et al., 1991; Grousset et al., 1994; Erel et al., 1997, 2007; Veron et al., 1999; Bollhofer and Rosman, 2001; Teutsch et al., 2001; Miralles et al., 2004) and confirm the direct atmospheric impact of anthropogenically derived aerosols on deposited sediments in both deep basins. As for Pb, Cd and Zn in these surface layers are likely issued from anthropogenic inputs as well. While Cd enrichment could be anticipated from the current large anthropogenic contribution (>99%) of Cd to the total atmospheric deposition in the western Mediterranean (Migon and Caccia, 1993), elevated crustal Zn content in sediments generally prevents to clearly determine the contribution of anthropogenic input. Here, Pb isotopes help defining the penetration of recent anthropogenic perturbation into the sediments and therefore calculate the contribution of anthropogenically derived Zn and Cd to the deep ocean basin. In contrast to other trace metals, Cu profile does not show any clear enhancement in the upper 3 cm of the core, whereas fluctuations are found in the deeper layers (Table 1). In particular, a clear decrease in Cu normalized concentrations occurs within the turbidite layer followed upwards by an increase at the current redoxicline (at 8–9 cm depth). Anthropogenically derived Cu does not seem to be accumulated in the deep Mediterranean sediments in contrary to observations by Fernex et al. (1992). This might be explained by its distribution in sediment where Cu is less attached to particulate phases than other metals and therefore more prone to mobility (Chester, 1990). Guieu et al. (1997) have shown that 60% of total dissolved input of Cu to the Northwestern Mediterranean area is associated with atmospheric input, compared to 80–100% for Zn, Pb and Cd. These results are consistent with a calculated atmospheric input 2–3 times higher than the riverine one for dissolved Pb, Zn, and Cd into the Western Mediterranean basin (Elbaz-Poulichet et al., 2001) whereas they are similar for dissolved Cu. This difference could partly explaine why anthropogenic Cu is not clearly enriched in our sediment cores where atmospheric deposition is expected to be the main source for trace metal inputs. At the Eastern Mediterranean site, while Al normalized metal ratio do not show marked trend in surface sediment, a slight enrichment of Pb, Zn and especially Cd is however recorded in the first cm of the core, i.e. within the surface mixed layer (as defined by 210 Pbxs profiles) (Fig. 3). Changes in Cu, Zn and Pb concentration are also observed between 3 and 6 cm depth (Table 1),

Inventories for pollutant metals deposited into the deep Mediterranean basins can be inferred from concentration measured in our top cores. While atmospheric anthropogenic sources are evidenced in these cores, their direct non-recycled (from turbidites, deep boundary currents or diagenesis contribution) atmospheric origin needs to be clearly demonstrated in order to validate pollutant inventories. 210Pb activity is an efficient tool to answer this question. Not only 210Pb allows defining the top section of the sediment where solid material has accumulated for the past 100 years but also to determine whether or not these particles mostly originate from direct atmospheric deposition or not using mass balance calculation. If the flux of excess 210Pb (210 Pbxs ) corresponding to 210 Pbxs inventories determined in top sediment cores only originates from direct atmospheric deposition, then it should match the scavenging of 210Pb in the overlying water column as determined from the following equation (with F denoted ‘‘flux’’):

FS ¼ FA þ FP  FD where FS: 210 Pbxs deposited in sediment; FA: 210Pb deposited from the atmosphere; FP: 210Pb produced in the water column from 226Ra; FD: decay of 210Pb in the water column. The mean 210 Pbxs flux corresponding to the inventories of the western basin is 86 ± 5 Bq m2 yr1. The flux deposited from the atmosphere in the northwestern Mediterranean Sea is estimated to 91 ± 16 Bq m2 yr1 (Radakovitch et al., 2003). The flux of 210 Pb produced by 226Ra decay can be calculated from dissolved 226 Ra activities reported by Van Beek et al. (2009) at the Dyfamed station. This station located in the northern Mediterranean basin at 2350 m water depth is considered as an open-ocean station. Using their data collected in March and May 2003 and extending them to a 2900 m water column, the flux of 210Pb produced in the water column vary from 165 to 194 Bq m2 yr1 and can be taken as 179 ± 15 Bq m2 yr1. The 210Pb decay flux calculated from the 210 Pb dissolved activities reported by Zuniga et al. (2007b) for this area is 184 ± 4 Bq m2 yr1. This leads to a 210 Pbxs flux available for scavenging of 86 ± 22 Bq m2 yr1 of which the uncertainty is due to estimated atmospheric deposition and in situ production of 210 Pb. In spite of possible water mixing associated with deep water convection, boundary currents, gyres and forcing from extreme atmospheric events (Gascard, 1978; Schott and Leaman, 1991; Mertens and Schott, 1998, Millot, 1999; Castellari et al., 1998, 2000), this ‘‘theoretical’’ inventory is similar to that calculated from our Western core (86 ± 5 Bq m2 yr1). This result suggests that Pb atmospheric deposition to the open Western basin can be reasonably recorded into deep sea pelagic sediments. Inventories of anthropogenic metal accumulated in the sediment can be calculated as for 210 Pbxs using:

I¼

zX ¼1

qðxÞ  CðxÞdx

z¼o

where q(x) (g cm2) is the dry bulk density, dx is the sample thickness, and C(x) is the anthropogenic metal concentration (lg g1). The latter was determined by subtracting in each layer (from 0 to 3 cm depth in the west and 0 to 1.5 cm in the east) the median pre-anthropogenic background level (i.e. natural) to the total metal

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M.O. Angelidis et al. / Marine Pollution Bulletin 62 (2011) 1041–1052 Table 3 Pollutant trace metal inventories (lg.cm2) within the past 100 years in sediment cores WB (Western basin) and EA (Eastern basin).

Pollutant Pb inventory (µg.cm -2)

160 Western Basin WB Eastern Basin EA

Pbxs

Znxs

Cdxs

25.0 7.70

23.7 5.60

0.09 0.11

content. Because of significant variation in metal profiles, the median of the concentrations in the lower section was assumed to represent the average metal content of the sediments. Median values of the metal/Al ratio and 210 Pbxs profiles were used to define the depth of the anthropogenic perturbation corresponding to the past 100 years. Inventories for Pb and Zn are four times higher in the western basin (Table 3) where trace metal concentrations in aerosols are also 2–5 times more elevated than in the eastern basin (Chester et al., 1990; Guieu et al., 1991, 1997; Gullu et al., 1998). On the other hand Cd inventories are similar in both basins. While larger trace metal emissions in Western Europe (Pacyna et al., 1984) likely explain differences in Pb and Zn inventories, it is very dubious to clarify why Cd inventories would be the same in both basins. There are no clear emission records for this metal that could be compared to deposition in the deep sea.Lead inventory from the deep Balearic basin can be compared to pollutant Pb emission and deposition inventories from coastal atmospheric deposition, the Gulf of Lions slope-deep-sea fans and the deep Ligurian Sea in the Western Mediterranean Sea. Not only Pb transient emissions are well known from the Western Mediterranean regions, but also its atmospheric concentration and inventories have been measured in several coastal environments that can be compared to our abyssal record. Pollutant Pb inventories calculated from the deep Ligurian Sea (21.4 lg.cm2, Martin et al., 2009), the Gulf of Lions (slopes 110 ± 10 lg cm2 and deep-sea fans 80 ± 5 lg cm2, Ferrand et al., 1999; Miralles et al., 2006) and coastal soils (Camargue, southern France 99 ± 7 lg cm2, Miralles et al., 2004) are reported in Fig. 7, along with long-term atmospheric deposition in coastal southern France (145 ± 44 lg cm2). The later is determined from 1980’s and 1990’s atmospheric Pb concentrations as measured in southern France (Martin et al., 1989; Remoudaki et al., 1991; Migon et al., 1993; Guieu et al., 1997, 2009; Ridame et al., 1999) to which are applied Pb transient emission trends for France and the Mediterranean region (Pirrone et al., 1999; Ferrand et al., 1999). Such calculation is made possible because of Pb short residence time in the troposphere (less than a week, Moore et al., 1973; Turekian et al., 1977) that causes an almost instantaneous response of the Mediterranean Sea to changes in Pb emission (Nicolas et al., 1994). Accumulated pollutant Pb decreases from land-based determination, to the deep Gulf of Lions and the deep Mediterranean Balearic and Ligurian basins (Fig. 7). Similar inventories in the very geographically distinct Ligurian and Balearic basins suggest that atmospheric deposition in the open Mediterranean Sea is quite uniform and represents only 20 to 25% of coastal continental Pb deposition as determined from the Gulf of Lions sediment proxies (Fig. 7). Inventories in the Mediterranean open sea could even represent only 10 to 20% of coastal deposition when compared to the calculated atmospheric inventory in coastal zones (145 ± 44 lg cm2) (Fig. 7). While this atmospheric inventory shows large uncertainty, it does support the discrepancy between coastal and offshore inventories. These results strongly suggest that coastal inventories cannot be used directly to estimate long-term atmospheric deposition and mass balance calculations in the pelagic basins of the Mediterranean basin. 4.4. Paleo-surface sediment layers The composition of deep-sea sediments reflects climatic/surface productivity and/or ocean circulation at the time of deposition

120

80

40

0 Sed BB

Sed Lig

Sed DSF Sed slope

Soils

Atm calc

Fig. 7. Comparison of our pollutant Pb inventories in the deep Balearic basin (‘‘Sed Bal’’) to that of the Gulf of Lion slopes (Sed slope’’, Ferrand et al., 1999; Miralles et al., 2006) and deep-sea fans (Sed DSF, Ferrand et al., 1999), the deep Ligurian basin (‘‘Sed ligure’’, Martin et al., 2009). Long-term atmospheric inventories are also calculated from (1) coastal soil (‘‘Soil Camargue’’, Miralles et al., 2004) and (2) aerosol/rain measurements and transient emission estimates (‘‘Atm calc’’, Remoudaki, 1990; Remoudaki et al., 1991; Migon et al., 1993; Guieu et al., 1997, 2009; Ridame et al., 1999; Pirrone et al., 1999; Ferrand et al., 1999; Miralles et al., 2006).

(Kolla et al., 1979; Hoogakker et al., 2004). The late Pleistocene to Holocene sedimentary records of the Mediterranean are characterized by dark colored, organic rich laminated layers known as sapropels (Cramp and O’Sullivan, 1999). Recent sapropels (ca. 5.5–9.5 kyr) have been well described in the more isolated wellstratified eastern Mediterranean (Meyers and Arnaboldi, 2005) with Total Organic Carbon (TOC) content of 2%, up to 30% (Kidd et al., 1978; Hilgen, 1991). Elevated TOC suggests either the preservation of organic matter owing to periods of low oxygen availability in bottom waters, and/or increased productivity in surface waters (Bouloubassi et al., 1999; Martinez-Ruiz et al., 2003). Both are generally driven by increased productivity and limited deep water formation (Rohling and Gieskes, 1989; Rohling, 1991). Meanwhile sapropels are not easily evidenced in the western Mediterranean basin with TOC contents generally lower than 1% (Murat, 1999). Here, most recent sapropels could also be associated with the Atlantic inflow and wind-driven mesoscale gyres (Murat, 1999; Pierre et al., 1999). Redox-sensitive trace elements in sapropel rich layers are expected to migrate (Pruysers et al., 1991; Thomson et al., 1995; Warning and Brumsack, 2000; Arnaboldi and Meyers, 2007). The potential for such diagenetic change to help evidence sapropel layers could be investigated with the most recent and well evidenced sapropel event (S1) in the eastern Mediterranean. We expect this event to cause a redistribution of redoxsensitive trace elements (such as Mn, Fe) that would result in their accumulation above or below the present S1 (Thomson et al., 1995). The Mn/Al profile in our core EA is typical of several sediment cores recovered in the eastern Mediterranean (Fig. 3), where the sapropel S1 has been recognized (Pruysers et al., 1991, 1993; Thomson et al., 1995, 1999; De Capitani and Cita, 1996; Van Santvoort et al., 1996; de Lange et al., 1999; Krom et al., 1999; Rutten and de Lange, 2003), showing the characteristic double peak of non-steady state diagenesis at 16–24 cm depth (Fig. 3). The upper Mn peak marks the location of the oxic front developed at the time of the deposition of S1, although the process of its formation remains controversial (Thomson et al., 1995). This peak also represents the upper limit of the initial sapropel layer upon its deposition, since subsequent oxidation has lead to the removal of its upper part (Pruysers et al., 1993; Higgs et al., 1994). The lower peak indicates the position of the active oxidation front (for a review of the geochemical evidence aiming to the interpretation of diagenetic processes at sapropel S1 see Thomson et al., 1999). Both

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M.O. Angelidis et al. / Marine Pollution Bulletin 62 (2011) 1041–1052

peaks are formed by Mn oxyhydroxides (Rutten and de Lange, 2003). Consequently, the lower Mn peak along with Fe/Al and Ba/Al profiles (Thomson et al., 1995; Van Santvoort et al., 1996) suggest that the active redox front in core EA is located at 24 cm, i.e. at the top of the visible sapropel layer. The Fe(II)/Fe(III) redox boundary in EA is located below the Mn(II)/Mn(III,IV) front, i.e. at 26 cm depth, in accordance to its location in other cores (Van Santvoort et al., 1996; Rutten and de Lange, 2003). Normalized Cd, Cu, Pb and Zn to Al profiles near the depth of S1 in core EA should display specific variation depending of the redox-sensitivity of the element. The Al normalized Cu and Zn profiles in core EA display two peaks at depths that are similar to Mn and Fe maxima (Fig. 3). Such trends for these metals have already been observed where a progressive oxidation front evolves close to the oxic/ post-oxic boundary. This similarity is attributed to the high sorptive capacity of Fe and Mn oxyhydroxides towards these metals leading to their co-precipitation (Pruysers et al., 1991, 1993; Thomson et al., 1993, 1995). Below this level, high Cu and Zn concentrations in the remaining S1 are likely due to either (1) association with organic matter (Rutten and de Lange, 2003) or (2) sulfides (Thomson et al., 1995), while a significant contribution of aluminosilicate minerals could also been involved (Pruysers et al., 1991; Rutten and de Lange, 2003). The Al normalized Cd profile in EA follows a different pattern from Cu and Zn. A large sharp peak, corresponding to a fifteen-fold enrichment in comparison with Cd levels in the sediment above S1, is found within the visible sapropel, while a slighter enrichment is encountered in the vicinity of the upper Mn peak, in the oxic zone (Fig. 3). Cd is usually accumulated into sub-oxic to anoxic sediments (Thomson et al., 1995; Arnaboldi and Meyers, 2007) due to co-precipitation with pyrite or formation of metal sulfides (Calvert and Pedersen, 1993; Rinna et al., 2002). An important Cd enrichment has been reported in the S1 and other Holocene and late Pleistocene sapropels from different eastern Mediterranean sites (Pruysers et al., 1991; Thomson et al., 1995), although much higher Cd content has been found in older (i.e. Pliocene) sapropels (Warning and Brumsack, 2000; Arnaboldi and Meyers, 2007). It seems that the inferred partial oxidation of the initial S1 in EA has resulted in the remobilization of the labile fraction of the metal that has formed the observed peak in the oxic zone in association with Mn oxides, whereas a much stronger downwards flux has lead to its enrichment within the post-oxic S-rich sapropel unit (Thomson et al., 1995). In contrast to Cd, Cu and Zn, Al normalized Pb profile does not evidence prominent diagenetic redistribution as expected from Pb reactivity in Mediterranean sapropel layers (Mercone et al., 2001). Consequently, its variability thorough the core (except for the first cm) is controlled by lithological changes in detritical input to the eastern Mediterranean during S1 times (Krom et al., 1999) rather than diagenetic processes. Trace metal enrichments (versus Al) are also observed in our western Mediterranean cores (Fig. 2). Zuniga et al. (2007a) evidenced a clearly distinguishable turbidite layer within cores collected at the same ADIOS stations, in the deep central part of the balearic abyssal plain. This layer shows variable thickness and is observed between 8 and 19 cm at station WB. Because geochemical and sedimentological analyses at station WB were obtained in different cores, we decided to use the same criteria than Zuniga et al. (2007a,b) to identify the turbidite layer in our core, i.e. the K/Al, Ti/Al (Price, pers. comm.) and Mn/Al, Fe/Al profiles. Our Al normalized profiles match those presented by Zuniga et al. (2007a) (Fig. 2). Zuniga et al. (2007a) suggested that the disruption of the surface sediment by the turbidite was minimal, (density and low turbulence conditions). The Mn/Al and Fe/Al, and to a lesser extent Cu/Al profiles display an abrupt increase at the bottom of the turbidite layer (15 cm). The Mn/Al profile displays a decreasing trend up to 8 cm (Fig. 2), similar to the K/Al profile. This pattern

likely reflects a gradual mineralogical change within the layer, which, according to Zuniga et al. (2007a), mainly consists of zeolitized volcanoclastic material and clearly differs from the intercalated hemipelagic units. The Pb/Al profile also displays slight changes within and below the turbidite layer that are correlated to slight changes in 206Pb/207Pb ratios (1.192–1.193 instead of 1.200–1.201 in the overlying layer) (Fig. 5) and could be indicative of mineralogical variation within the turbidite layer. Both Al normalized Mn, Fe and, to a lesser extent, Pb ratios, show a shift around 35 cm (Figs. 2 and 5). Considering 14C dating and accumulation rates in this western core (Zuniga et al., 2007a), this layer could correspond to the sapropel S1 event in the western Mediterranean (around 8 kyr, Murat, 1999; Pierre et al., 1999) that occurred just after the Younger Dryas cold episode. Of course such layer should be confirmed by TOC content, oxygen and carbon isotopes, i.e. paleoproductivity trends and therefore remains tentative in our investigation.

5. Conclusions Cores collected in the deep Balearic basin and the Cretan Sea show the incursion of anthropogenic metals. The extent for such contamination in the deep Mediterranean Sea is well constrained by Pb radioactive and stable isotopes of which signatures and inventories allow characterizing the atmospheric imprint. In particular, 210 Pbxs mass balance calculations suggest that the deep Balearic basin faithfully recorded pollutant metal long-term atmospheric deposition. Pollutant Pb input to this deep Western basin represents 20–25% of the coastal long-term atmospheric inventories implying that coastal inventories should be used cautiously when establishing mass balance calculations in remote pelagic basin of the Mediterranean Sea. Variation of Al normalized metal ratios in the Balearic basin cores reveal trace element redistribution that could be associated with either sapropel and/or turbidite events. While more comprehensive data would be needed to better characterize those events, trace metal profiles clearly show diagenetic and/or mineralogical changes due to productivity/ocean circulation changes or bottom sediment dynamics. Specifically we evidence changes in the mineralogy and trace metal distribution likely related to the S1 sapropel event in both the Cretan Sea and the Balearic basin, while a significant turbidite event is well characterized in the western basin as shown by trace metal remobilization. These findings shall complement marine and atmospheric results obtained during the ADIOS European Community MAST program (Atmospheric Deposition and Impact of Pollutants) in order to assess biogeochemical cycles for pollutant metals and, most particularly, their scavenging kinetics and characteristics as well as their fate into the deep marine geological and biological reservoirs. Acknowledgements This work has been supported by the European community in the framework of the ADIOS MAST program (EVK3-CT-200000035, Atmospheric deposition and impact of pollutants on the open Mediterranean Sea). References Alleman, L., Hamelin, B., Veron, A.J., Miquel, J.C., Heussner, S., 2000. Lead sources, transfer in the coastal Mediterranean: evidence from stable lead isotopes in marine particles. Deep-Sea Res. II 47, 2257–2279. Anderson, R.F., Schiff, S.L., Hesslein, R.H., 1987. Determining sediment accumulation and mixing rates using the 210Pb, 137Cs and others tracers: problems due to postdepositionnal mobility or coring artefacts. Can. J. Fish. Aquat. Sci. 44, 231– 250.

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