evaluation of sediment trace metal records as ... · evaluation of sediment trace metal records as...

Evaluation of sediment trace metal records as paleoproductivityand paleoxygenation proxies in the upwelling center off Concepción, Chile (36°S)

Praxedes Muñoz a,b,⇑, Laurent Dezileau c, Carina Lange b,d, Lissette Cardenas d, Javier Sellanes a,b,Marco A. Salamanca d, Antonio Maldonado e

aDepartamento de Biología Marina & Centro de Estudios Avanzados en Zonas Áridas (CEAZA), Universidad Católica del Norte, Larrondo 1281, Coquimbo, ChilebCentro de Investigación Oceanográfica en el Pacífico Sur-Oriental (FONDAP-COPAS), Casilla 160-C, Concepción, Chilec Laboratoire Géosciences Montpellier (GM), Bâtiment 22, 1er étage, Université de Montpellier 2, Place Eugène Bataillon, 34095 Montpellier cedex 05, FrancedDepartamento de Oceanografía, Universidad de Concepción, Casilla 160-C, ChileeCentro de Estudios Avanzados en Zonas Áridas (CEAZA), Departamento de Biología, Facultad de Ciencias, Universidad de La Serena, Casilla 599, La Serena, Chile

a r t i c l e i n f o

Article history:Available online xxxx

a b s t r a c t

This study analyzes the records of several trace metals sensitive to redox conditions in continental shelfsediments off Concepción, Chile (36°S). The continental margin off Concepción (36°S; 73°W) lies beneathan important upwelling center characterized by high primary production rates and, consequently, highfluxes of organic matter. In spring and summer, this material settles to the seafloor where it decays, pro-ducing periods of very low oxygen content in bottom waters (<1 mL Lÿ1). In addition, an oxygen mini-mum zone develops at �100–400 m water depth, where dissolved oxygen levels are <0.5 mL Lÿ1. Thissituation changes during strong El Niño events, when dissolved oxygen at the bottom increases drasti-cally (>1 mL Lÿ1).The goals of this study were to determine the input of trace metals to the sediment and to decipher

how this information can be used to reveal variations in primary productivity or bottom oxygenation.Gravity cores collected at two stations – VG06-2 over the mid-shelf station (88 m water depth, upperboundary of the oxygen minimum zone) and VG06-3 over the outer shelf (120 m water depth, withinthe oxygen minimum zone) – were sampled for high resolution profiles (1 cm) of trace metals, biogenicopal, stable isotopes, and total organic carbon. The results suggest that the variability in the trace metaldistribution on the continental shelf off Concepción is determined by redox conditions and the organiccarbon flux to the bottom. Some sections of the sediment cores from the outer shelf showed appreciableauthigenic enrichment of U, Cd, and Mo (EF: 5–10, 2–5, and 10–16 respectively) along with heavier valuesof d15N, suggesting periods of suboxic conditions. During these periods, fluxes of organic material to thebottom were higher, as indicated by elevated TOC and opal contents. Alternating periods of higher andlower trace metal contents were not observed mid-shelf as they were on the outer shelf. Rather, themid-shelf samples showed authigenic enrichment of U, Cd, and Mo (EF: 1–6, 4–5, and 10–20, respec-tively) throughout the core except in a 10-cm-thick gray layer. In general, authigenic enrichment of U,Mo, and Cd occurred at both sites, coincident with olive green layers in the cores. These layers were asso-ciated with periods of elevated primary productivity and suboxic conditions. Such periods did not seemto last as long as the oxygenated periods, which had higher inputs of refractive detrital material, coinci-dent with the occurrence of distinct gray sediment layers.

Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Several studies of trace metal (TM) geochemistry in deep sedi-ments influenced by hypoxic waters have been carried out along

the margins of the NE Pacific, the Arabian Sea, and the SE Pacific(Klump, 1999; Nameroff et al., 2002; Pailler et al., 2002; Böninget al., 2004, 2005, 2009; Van der Weijden et al., 2006). These workshave been used to reconstruct past variations in productivity andbottom water oxygen content since hypoxic zones occur mainlybeneath areas that have high surface productivity, where upwell-ing is most intense, increasing the consumption of dissolvedoxygen (DO) by the degradation of organic matter and creatinga mid-water oxygen minimum zone (OMZ) (Wyrtki, 1962;Kamykowski and Zentara, 1990). This process is strongly coupledwith the extent of oxygen penetration into the pore waters below

0079-6611/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.doi:10.1016/j.pocean.2011.07.010

⇑ Corresponding author at: Departamento de Biología Marina & Centro deEstudios Avanzados en Zonas Áridas (CEAZA), Universidad Católica del Norte,Larrondo 1281, Coquimbo, Chile. Tel.: +56 51 20 9802; fax: +56 51 20 9812.

E-mail addresses: [email protected] (P. Muñoz), [email protected](L. Dezileau), [email protected] (C. Lange), [email protected] (J. Sellanes), [email protected] (M.A. Salamanca), [email protected] (A. Maldonado).

Progress in Oceanography xxx (2011) xxx–xxx

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Please cite this article in press as: Muñoz, P., et al. Evaluation of sediment trace metal records as paleoproductivity and paleoxygenation proxies in theupwelling center off Concepción, Chile (36°S). Prog. Oceanogr. (2011), doi:10.1016/j.pocean.2011.07.010

the sediment–water interface (Morford and Emerson, 1999), whichis the main factor controlling metal speciation in the environment(Chester, 1990). Trace metals in sediments can be authigenicallyenriched (at concentrations above the Earth’s crust composition)in different ways. Such enrichment may be associated with morereduced conditions in the environment related to the settling fluxof metabolizable organic matter linked with high biological pro-ductivity. Some TM (i.e., Cd, Co, Zn, Ni) are closely related to pri-mary productivity due to the fact that they are biologicallyessential elements scavenged to the sediments during organic mat-ter sedimentation (Chaillou et al., 2002; Saito et al., 2002; Calvertand Pedersen, 2007 and references therein). Others (such as Ba)are not known to possess biological function but are adsorbed orincorporated into organic particles (shells or debris), thus the fluxof such TM to the sediments is closely related to organic carbonfluxes and, hence, primary productivity (Dymond et al., 1992;Dymond and Collier, 1996; Paytan and Griffith, 2007 and refer-ences therein). In reduced sediments, nutrient-type TM could forminsoluble metal sulfides and/or be incorporated into pyrite(Huerta-Diaz and Morse, 1990, 1992), whereas Ba is remobilizedfrom the sediments in suboxic-anoxic environments (Torreset al., 1996).

Other TM such as U and Mo are conservative elements in thewater column but are affected by the environmental redox condi-tions, precipitating in euxinic environments and revealing suboxicor sulfidic conditions in the bottom water (Sohrin et al., 1999;Erickson and Helz, 2000; Zheng et al., 2000; Lyons et al., 2003;Siebert et al., 2003). Dissolved U(VI) is supplied to the sedimentsby diffusion across the sediment/water interface and reduced toU(IV) close to the Fe(III) to Fe(II) reduction zone (Klinkhammerand Palmer, 1991). The reduced U within the sediments is also con-trolled by the settling flux of metabolizable organic matter, whichreduces the oxygen content at the bottom, thereby lowering theconcentration gradient of dissolved U and increasing the rate ofreduction in the suboxic zone (Calvert and Pedersen, 2007 and ref-erences therein). Besides, the direct flux of non-lithogenic particlescould also contribute significantly to the accumulation of authi-genic U within the sediments (Zheng et al., 2002). In this sense,in some environments, U could also be considered to be an indica-tor of primary productivity. Mo is present in the water column asmolybdate (MoO2ÿ

4 ), and its accumulation within the sedimentsis related to its adsorption onto Mn-oxyhydroxides in surface sed-iments and its release into the pore waters during Mn reduction.The formation of thiomolybdates probably causes the Mo to re-main within the sediments. Thiomolybdates react with particlessuch as Fe sulfides and organic molecules via S bridges (Helzet al., 1996). Although Mo is an essential element, the role of or-ganic matter deposition and its degradation in Mo accumulationwithin the sediments is not known. Authigenic Mo enrichment re-quires the presence of sulfides (�100 lM) normally related to lowDO (<10 lM) in bottom waters and high carbon fluxes and, hence,this element can be used for paleoxygenation reconstructions(Zheng et al., 2000).

Central-southern Chile (�35–38°S) has an important upwellingcenter due to the effects of local topography and the predominanceof southwesterly winds (Arcos and Wilson, 1984; Figueroa andMoffat, 2000), with high primary productivity rates in spring-summer (19.9 g C mÿ2 dÿ1; Daneri et al., 2000) and high sedimenta-tion of organic material to the bottom. Local upwelling generatessurface sediments with chlorophyll-a (Chl-a) concentrations(9–110 lg gÿ1; Farías et al., 2004; Muñoz et al., 2007) that are oneorder of magnitude higher than those reported for other OMZs(Levin et al., 1991, 2000). Moreover, high contents of biogenic opal(5–11%) and organic carbon (4–5%) have been also reported inupwelling areas (Contreras et al., 2007; Muñoz et al., 2007). Theremineralization of the deposited organic material generates a

reduced environment (Thamdrup and Canfield, 1996; Ferdelmanet al., 1997), establishing favorable conditions for trapping TM –especially those elements associated with redox changes – withinthe sediments.

Here, a low-oxygen fringe develops between �100 and 400 mwater depth (O2 < 0.5 mL Lÿ1), defined as the OMZ, extending overthe shelf. Unusual summer oxygenation was reported during the1997–1998 warm El Niño (EN) event (Gutiérrez et al., 2000; Neiraet al., 2001; Sellanes et al., 2007). During this period, the visualappearance of the sediments was less reduced, with oxidized layersreaching a depth of 10 cm in some cases and positive potential re-dox values at the surface (Muñoz et al., 2004a). After this EN, the DOgradually decreased to its normal low concentrations (<0.5 mL Lÿ1),dropping well below 0.25 mL Lÿ1 in 2003 and 2004. Seasonal oxy-genation also occurs over the shelf in winter, but conditions atthe bottom are suboxic (defined as 0.2 > [O2] > 2 mL Lÿ1; Tysonand Pearson, 1991) most of the year. The COPAS research center(Universidad de Concepción, Chile, www.copas.cl) maintains amid-shelf time-series observation (Fig. 1A) of bottom-water DOthat reveals this seasonality.

This setting offers an ideal scenario in which to study the tem-poral distribution of TM during hypoxic and oxic conditionsthroughout the sedimentary record. Our goals were (i) to deter-mine the magnitude of the inputs of selected TM and (ii) to evalu-ate the downcore TM records as proxies for revealing historicvariations in primary productivity or bottom oxygenation. Toachieve these goals, we established the relationship between TMand carbon flux to the sediment and/or authigenic enrichment.Other elements related to primary production fluxes but not sensi-tive to redox conditions (Ba, Siopal) were also considered in order todetermine the relevance of the organic carbon fluxes in the TM dis-tributions. Furthermore, we analyzed Fe, Mn, Al, total organic car-bon (TOC), and stable isotopes (d13C, d15N) in order to establish theoxidative state of the depositional environment and the organicand detrital inputs to the shelf. This study offers complementaryproxies that contribute to our understanding of the processes oper-ating on interdecadal or centennial scales (i.e., ENSO cycle) andfluctuations in the strength of the OMZ along the SE Pacific margin,establishing the role (sink or source) of the OMZ for these elementsand their implications in biogeochemical cycles.

2. Methods

2.1. Sampling

Sediment samples were obtained with a gravity corer in August2006 on board the Chilean Navy vessel AGOR Vidal Gormáz at twostations located over the shelf off Concepción between 95 and120 m depth (Fig. 2): VG06-2 on the mid-shelf (upper OMZ bound-ary; core length = 220 cm; 88 m water depth) and VG06-3 on theouter shelf (within the OMZ; core length = 170 cm; 120 m waterdepth). The cores were sliced into 1-cm sections and subsampleswere separated for TM, biogenic opal, C and N stable isotope signa-tures (d13C, d15N), and TOC analyses. 14C and 210Pb were analyzed atselected sediment levels. The samples were kept frozen (–20 °C)until analysis. Salinity, temperature, and oxygen profiles were ob-tained from both outer shelf and slope stations (VG06-3 andVG06-5) using a Sea-Bird 25 CTDO (Fig. 1B).

2.2. Chemical analyses

2.2.1. Trace metal analysesTrace metals were measured in an Inductively Coupled Plasma-

MS Agilent 7500ce at the University of California Davis. Al and Fewere measured in an Atomic Absorption Spectrometer AAnalyst

2 P. Muñoz et al. / Progress in Oceanography xxx (2011) xxx–xxx


700 Perkin Elmer at the Universidad Católica del Norte. The sedi-ment digestions were prepared using strong acids (HNO3, HCl,HClO4, HF) until total dissolution in several steps, obtaining a finalsolution with suprapure HNO3 (2%). The cleaning procedure forvials and glassware, done according to Kremling (1999), alsoinvolved several steps. Blanks in all procedures were done using18.0 MX deionized water. The accuracy and precision of the

measurements were assessed by analyzing reference material(MESS-3). The precision obtained (n = 4) was between 0.3% and7% for all metals except Mo and Sr, for which it was 10%. The accu-racy was in general <12%, which is in the 95% confidence range,although Cd showed a higher average value than the standard(14%). The U concentration in the standard is only a recommendedvalue, and we obtained consistently lower concentrations with

Fig. 1. (A) Time-series of dissolved oxygen (DO) in mL Lÿ1 on the mid-shelf off Concepción (data from COPAS Center, Universidad de Concepción, Chile), and (B) CTDO profilesfrom the shelf and slope (St. VG06-3, VG06-5) showing the water properties in the area.

P. Muñoz et al. / Progress in Oceanography xxx (2011) xxx–xxx 3


high precision (1%) (Table 1). Since we were interested in observingthe variability of the concentration along the sediment cores, thiswas not expected to greatly affect the results and conclusions.

2.2.2. TOC, d15N, d13CTOC and stable isotope (d15N and d13C) analyses were per-

formed at Washington State University. The samples were driedat 80 °C for 24 h, milled to a fine powder, and acidified to removecarbonates. Dry material (0.5–2 mg) was placed into tin capsulesand combusted in an elemental analyzer Eurovector (Milan, Italy).The resulting N2 and CO2 gases were separated by gas chromatog-raphy and admitted into the inlet of a Micromass (Manchester, UK)Isoprime isotope ratio mass spectrometer (IRMS) to determine15N/14N and 13C/12C ratios. Typical precision of analysis was±0.5‰ for d15N and ±0.2‰ for d13C using atmospheric nitrogen asa standard in the first case and Peedee belemnite (PDB) in the sec-ond. Egg albumin was used as a daily reference material.

2.2.3. Biogenic silica (SiOPAL)Biogenic opal was determined according to the methodology of

Mortlock and Froelich (1989). Silica was extracted with an alkalinesolution (1 M NaOH) and the concentration of dissolved silica wasdetermined by spectrophotometry using the modified molybdate-blue method (Hansen and Koroleff, 1999); the values were ex-pressed as %SiOPAL. We used four to five dilutions of sodiumhexafluorosilicate (Sigma) to determine the concentrations of themeasured absorbances (nm). The linearity of data was 99%. Noreplicates of biogenic opal were done, but the historical standarddeviation of this analysis was �6%.

2.3. Geochronology (210Pb and 14C)

210Pb was determined in the surface sediments of the gravitycores and compared with 210Pb data from short cores obtainedwith a mini multicorer at the same sites in 2002 and 2003 (stations26B and 18, corresponding to our stations VG06-3 and VG06-2,respectively; Muñoz et al., 2004b, 2007) to estimate the surfacesediment sections affected during the core sampling. 210Pb activi-ties were quantified by alpha spectrometry of its daughter 210Poin secular equilibrium with 210Pb, using 209Po as a yield tracer(Flynn, 1968).

Radiocarbon measurements were performed in selected sam-ples of the gravity cores. The surface sediments between 35° and38°S were almost free of planktic foraminifera, most probablydue to carbonate dissolution at the sediment–water interface(Mohtadi et al., 2005); therefore 14C was analyzed using fish scalesin sections of the cores with sufficient amounts (4–8 mg). The sam-ples were submitted to the National Ocean Sciences AMS Facility(NOSAMS) of the Woods Hole Oceanographic Institution (WHOI).Fraction Modern (Fm) was corrected by the d13C content, and ageswere calculated using 5568 (yrs) as the half-life of radiocarbon. Theages were converted to calendar years before the present using thecalibration curve Calpal2007_HULU (Jöris and Weninger, 1998)and considering an age reservoir effect of 400 years (Mohtadiet al., 2008 and references therein) (Table 2). The time scale wasobtained according to the best fit of curves of 210Pbxs and 14Ccontrol points (Fig. 3). The age of surface sediments (from 210Pbxsinventory data; Turekian et al., 1980) was transformed to yearsbefore present (Appendix A).

2.4. Estimation of the authigenic enrichment factor (EF)

We estimated the authigenic enrichment factor of TM accordingto Böning et al. (2009):

EF ¼ ðMe=AlÞsample=ðMe=AlÞdetrital

where (Me/Al)sample is the bulk sample TM concentration normal-ized to the Al content and the denomination ‘‘detrital’’ indicates alithogenic background.

Fig. 2. Study area showing the position of sampling stations. Sediment samplingwas done on the mid- (VG06-2) and outer shelf (VG06-3). Bathymetry is given inmeters.

Table 1

Analysis of Standard Reference Material (National Research Council Canada) byinductively coupled plasma mass spectrometer (ICP-MS). Fe and Al were measured byFlame Atomic Absorption Spectrometry (FAAS). Average values (n = 4) are presentedin ppm, except Fe and Al, which are in %.

Element Mess-3

Measured Certified

Fe 4.21 ± 0.30 4.34 ± 0.11Al 8.99 ± 0.15 8.59 ± 0.23V 228 ± 3 243 ± 10Cr 106 ± 6 105 ± 4Mn 289 ± 5 324 ± 12Co 12.9 ± 0.3 14.4 ± 2Ni 46.5 ± 2.2 46.9 ± 2.2Cu 30.9 ± 1.6 33.9 ± 1.6Zn 149 ± 9 159 ± 8Sr 129 ± 13 129 ± 11Mo 2.73 ± 0.2 2.78 ± 0.07Cd 0.28 ± 0.06 0.24 ± 0.01Ba 967 ± 3 –Pb 20.5 ± 0.3 21.1 ± 0.7U 3.1 ± 0.04 4a

a Reported value only.



Detrital concentrations ([Me]detrital and [Al]detrial) were estab-lished considering the local TM abundance, which was moreaccurate than using mean Earth crust values (Van der Weijden,2002). We used the average TM concentrations reported forthe sediments along the Bío Bío Canyon axis, where continentalinputs were better represented: 61% of the particulate materialcame from the Andes and 39% from coastal ridge erosion

(Pineda, 1999). The TM concentrations in the 3-to-10 cm intervalwere considered in order to avoid the potential effect ofanthropogenic sources along the riverside. For Sr and U, we usedthe values reported for the central Chilean Andes (35–37°S;López-Escobar et al., 1981; Vergara et al., 1999), whereas forBa, we used the values reported for the Bío Bío River (Klump,1999) (Table 3).

Table 2

List of AMS 14C dating points from cores VG06-2 and VG06-3 discussed in the text, converted to calendar ages using the program CALPAL 2007-Hulu (Jöris and Weninger, 1998).

Station Core depth (cm) NOSAM accession # Sample type 14C age (yrs BP)a ±SD (yr) Reservoir (yrs) Calendar age (cal yr BP) ±SD (yr)

VG06-2 41 OS-66613 Fish scales 850 85 400 455 9054 OS-66616 Fish scales 1480 80 400 1020 8479 OS-66622 Fish scales 2820 120 400 2516 154

VG06-3 53 OS-66619 Fish scales 2630 130 400 2241 166123 OS-66630 Fish scales 4300 110 400 4330 158141 OS-66129 Fish scales 5330 110 400 5708 127

a BP = 1950 AD.

Fig. 3. Geochronology estimated from 14C at selected points and 210Pb in the surface sediments of cores VG06-2 and VG06-3. The age obtained with 210Pb corresponds to theage transformed to BP years at the maximum depth reached by the excess inventory (29 and 15 cm for VG06-2 and VG06-3, respectively).



3. Results

3.1. Hydrographic conditions and general characterization of thesediments

The structure of the water column over the shelf showed a ther-mocline around 40 m. At the surface, the temperature varied be-tween 12.20 and 12.03 °C, declining abruptly below 30 m andreaching values of 10.94 °C at the bottom. Salinity increased regu-larly with depth, ranging from 33.47 (surface) to 34.58 (bottom), inagreement with density. The DO profiles showed the presence ofan OMZ between �60 and 450 m water depth, reaching minimumvalues of 0.98 mL Lÿ1 at the bottom of the shelf station VG06-3 and0.45 mL Lÿ1 at 270 m depth at the slope station VG06-5 (Fig. 1B).

Layers of different colors were found in the sediment cores(Fig. 4), especially those from the outer shelf, which is permanentlyunder the influence of the OMZ (except during strong El Niñoyears). The upper 23–26 cm at both sites (mid- and outer shelf)were dark olive green in color. Mid-shelf, the intensity of the colorchanged gradually to olive green and extended downcore, exceptbetween �79 and 89 cm depth, where the color changed drasti-cally to gray. On the outer shelf, the layers below the surface sed-iments alternated between gray and olive green. The distinctiveolive green layers coincided with lower bulk density values(�0.6–0.8 g cmÿ3), whereas the gray layers matched higher bulkdensities (�1–1.3 g cmÿ3) (Fig. 4). The gray layers were thick andshowed some fine bands of olive green and brown (i.e., 113–138 cm). From 138 to 163 cm depth, the color changed drastically

Table 3

Continental composition of the Bío Bío Region. Metal concentrations and Me/Al ratios (�10ÿ4) from different sites are presented. The bold values were selected for calculations ofthe enrichment fraction (EF).

Trace metal concentrationsLocation V Cr Mn Co Ni Cu Zn Sr Mo Cd Ba Pb U Fe Al

Bio Bio Rivera 72.1 27.6 827.4 17.7 22.5 39.1 53.5 0.4 9.9 31.1 44.3Bio Bio Riverb – – – – – – – – – – – – – – –Central Andes (35–36°S)d 234.6 9.4 1800.0 23.2 8.2 45.6 97.8 249.4 178.2 82.6Central Andes (37°S)e 0.9 96.8Upper crustf 107.0 83.0 600.0 17.0 44.0 25.0 71.0 1.5 0.1 550.0 2.8 80.4

Trace metal/AI ratios �10ÿ4

Location V Cr Mn Co Ni Cu Zn Sr Mo Cd Ba Pb U Fe

Bio Bio Rivera 16.26 6.22 186.59 3.99 5.07 8.82 12.07 0.10 2.23 7003

Bio Bio Riverb 16.60 4.86 78.30 1.91 1.24 5.24 9.06 0.07 0.01 1.56 0.23Bio Biio Riverc 35.00

Central Andes (35–36°S)d 28.41 1.14 217.98 2.81 0.99 5.52 11.84 30.20 21.58Central Andes (37°S)e 0.09

Upper crust (average)f 13.31 10.32 74.63 2.11 5.47 3.11 8.83 0.18 0.01 68.41 0.35

a Pineda, 1999 (sediment).b Böning et al., 2009 (suspended particles).c Klump (1999).d Vergara et al. (1999).e López-Escobar et al. (1981).f McLennan (2001).

Fig. 4. Sediment characterization (age, color, dry bulk density) on the mid- (VG06-2) and outer shelf (VG06-3) off Concepción. DOG = dark olive green, OG = olive green,BG = brownish green, G = gray, POG = pale olive green.



to olive green, followed by a pale olive green color down to the endof the core.

At both sites, organisms in the sediments were scarce, and gen-erally very few benthic foraminifers and some fish debris (scalesand vertebrae) were observed in the olive green layers.

3.2. Geochronology

The 210Pb activities determined at the surface of the gravitycores were close to the unsupported activities found in deeper sec-tions of the multicores. We estimated matches between the longand short cores of around 23 and 26 cm for the mid- and outershelf, respectively. The chronology established for the short sedi-ment cores from the mid- and outer shelf (see Section 2, AppendixA) allowed us to determine the ages of the most recent sediments,which covered the last 185 and 204 years AD, respectively. Therecent sedimentation rates for these cores were 0.27 and0.14 cm yrÿ1 respectively, (Muñoz et al., 2004b, 2007), one orderof magnitude higher than for the longer cores (0.021 and0.025 cm yrÿ1 for stations VG06-2 and VG06-3, respectively); thisdiscrepancy precluded establishing a good lineal regression be-tween the ages calculated from the 210Pb and 14C data. Table 3shows the calibrated ages BP (before present = 1950) in detail.The chronology for longer cores was estimated using the old agesof the multicores: 140 ± 49 and 152 ± 55 year BP at 29 and15 cm, respectively, and the ages from the radiocarbon controlpoints, obtaining a good fit to the curves (r2: 0.99–0.98, p < 0.05)(Fig. 3). We obtained reasonable ages for longer cores that weremore accurate for station VG06-3 (outer shelf) than for stationVG06-2 (mid-shelf); in the former, the extrapolation of the linearregression matched year 0 with 1950 years AD (7 cm core depth;Fig. 4).

3.3. TOC, stable isotopes, C/Nmolar ratio, and SiOPAL distribution in thesediment cores

Figs. 5 and 6 show the distributions of TOC, stable isotopes, C/Nmolar ratios, and SiOPAL at the mid- and outer shelf stations. Theaverage TOC content was higher mid-shelf (2.01 ± 0.54%) than onthe outer shelf (0.72 ± 0.54%), with respective minimum/maximumvalues of 0.19/3.15% and 0.08/2.85%. The higher values of TOC cor-responded to relatively heavier d13C (�ÿ20‰) and d15N (>5‰) sig-natures and lower bulk densities (olive green layers), whereas thelower TOC values corresponded to lighter d13C (<ÿ25‰) and d15N

(ÿ2‰ to 0.5‰) signatures and higher bulk densities (gray layers),as clearly observed in core VG06-3 from the outer shelf (Figs. 4–6).

The C/Nmolar ratios were higher in the gray layers and extremelyhigh at station VG06-3. The values in the gray layers ranged be-tween �15 and 60, and unusually high values (�100–200) werealso measured in some sections of the core. In the olive green lay-ers, the values fluctuated between �8 and 13.

The average SiOPAL content (Figs. 5 and 6) was slightly highermid-shelf (�10%) than on the outer shelf (�8%) and the maximumvalues were similar at both sites (�13%). Mid-shelf, the lower val-ues were observed in the gray layer (�5–7%). On the outer shelf,maximum values (11–13%) were coincident with olive green layersin two sections of the core (58–67 cm and 97–105 cm depth).

In the mid-shelf core, the most conspicuous variations in bulkdensity, SiOPAL, TOC, and stable isotopes occurred in the gray layer(�79–89 cm). However, no good correlation was observed be-tween these proxies; SiOPAL, TOC, and d13C were correlated nega-tively with the bulk density (Spearman R: ÿ0.17, ÿ0.33, ÿ0.27,respectively, p < 0.05–0.01), and although the profile of d15N wassimilar to that of TOC and d13C, the former was not correlated withbulk density. On the outer shelf, better correlations were observedbetween TOC, stable isotopes, and bulk density (Spearman R:ÿ0.70 to ÿ0.58, p < 0.01), but not with the SiOPAL distribution(Appendix A).

3.4. Trace metal distributions in the sediment cores

Figs. 7 and 8 show the TM distributions normalized to the Alcontent (Me/Al). At the mid-shelf station VG06-2, the Me/Al distri-butions did not display a clear pattern, as was observed at the out-er shelf station VG06-3. In some sections, the fluctuations in theTM ratios were similar to the variations in the distribution of or-ganic compounds and bulk density. However, low correlationswere observed between the TM distribution and organic com-pounds (stable isotopes, TOC, SiOPAL; Spearman R: 0.16–0.41,p < 0.01–0.05; Appendix A).

The TM contents of the cores differed in relation to the gray andolive green layers. At the mid-shelf station (Fig. 7), some elementsshowed distinct lower Me/Al ratios in the gray layer, particularlyCd, Mo, and U (0.002–0.004) and somewhat less obviously Pb, Cr,and Zn. These low ratios coincided with the lowest values of SiOPAL(5.4%) and lighter stable isotopes (ÿ26‰, and 1‰ for d13C andd15N, respectively). Other elements had higher Me/Al ratios inthe gray layer (Mn: 8, Cu: 1, Co: 0.2, Sr: 5 and less obviously V:

Fig. 5. Total organic carbon (TOC) profile, stable isotope signatures (d13C and d15N), C/Nmolar ratio, and biogenic opal (SiOPAL%) at coring station VG06-2 located on the mid-shelf (OMZ upper boundary) off Concepción. G layer = gray layer.



2), corresponding with the lighter stable isotope signatures andlower SiOPAL values. Finally, Fe and Ba showed no changes in thegray layer, but increased notably below 136 cm depth (Ni in-creased less obviously). Mn, Cu, Co, and Sr also increased at thisdepth (Figs. 5 and 8).

At the outer shelf station VG06-3, Me/Al (Fig. 8) showed alter-nating periods of higher and lower concentrations along the cores.At this site, ratios of Cr (>0.9), Cd (>0.02), Mo (>0.07), and U (>0.03)were conspicuously higher in the olive green layers (0–26, 52–54,65–71, 97–104, 138–161 cm) than in the gray layers (0.001–0.009).Other elements (Mn, Fe, Pb, V, Ni, Zn, Sr, Ba) showed similar pat-terns but with less prominent variations between these layers.Finally, Cu and Co showed lower ratios in the olive green layers(�0.5 and 0.15, respectively). In general, good correlations wereobserved between elements at this station, especially between V,Mn, and Ba (Spearman R: 0.93–0.88, p < 0.01), and between U,Cd, and Mo (Spearman R: 0.84–0.91, p < 0.01; Appendix A). Highcorrelations were observed between Cu and Co, and low or no cor-relations were found with the other trace metals, TOC, opal, andstable isotopes. In contrast to the mid-shelf station VG06-2, the

TM at the outer shelf station VG06-3 showed better correlationswith bulk density (or color changes along the core), TOC, and stableisotope distributions.

3.5. Authigenic enrichment factor

The results indicated higher enrichment (EF) for U > Mo >Cd > Cr in the olive green layers, especially mid-shelf (Fig. 9), andno enrichment in the gray layers except for Sr, which was slightlyenriched mid-shelf (EF: �1.5). No enrichment was observed fornutrient-type elements (Cu, Zn, Ni, Co). In general, the EFs of themid-shelf cores were higher, but TM concentrations at this sitedid not show the changes in EF observed on the outer shelf. Table3 shows the different values that could be considered for the detri-tal source. Our estimated enrichment profiles did not differ signif-icantly from the values proposed by Böning et al. (2009). The majordifferences lie in the magnitudes of Cd and U (extremely higherand lower than our EF values, respectively), whereas Zn, Ni, andCu were slightly enriched throughout the whole core (in both olivegreen and gray layers), which does not seem feasible since these

Fig. 6. Total organic carbon (TOC) profiles, stable isotope signatures (d13C and d15N), C/Nmolar ratio, and biogenic opal (SiOPAL%) at coring station VG06-2 located on the mid-shelf (OMZ upper boundary) off Concepción. OG layer = olive green layer.

Fig. 7. Downcore trace element (Me/Al) distributions (�10ÿ3) in sediment core VG06-2 from the mid-shelf (OMZ upper boundary) off Concepción.



elements are not expected to be trapped efficiently in thesediments.

4. Discussion

4.1. General settings

The CTDO profiles clearly depicted the presence of a suboxicwater mass between �90 and 400 m water depth (Fig. 1B); thiswas the regional OMZ, one of the largest hypoxic areas described

in the world (Helly and Levin, 2004; Fuenzalida et al., 2009). Theseasonal nature of local upwelling leads to variations in the DOat the bottom throughout the year, especially mid-shelf (Fig. 1A),and the variable organic particle fluxes to the seafloor, oxygen con-sumption, and TM fluxes to the sediments also reflect this season-ality (Molina et al., 2004; González et al., 2007; Muñoz et al., 2007).During the sampling period, the DO at the bottom was normal forthe spring season (�0.98 mL Lÿ1).

The dominant lithological composition of the sediments washemipelagic clayey mud. The large supply of siliciclastic sediment

Fig. 8. Downcore trace element (Me/Al) distributions (�10ÿ3) in sediment core VG06-3 from the outer shelf (within the OMZ) off Concepción.

Fig. 9. Downcore trace metal enrichment fraction (EF) in sediment core (A) VG06-2 (mid-shelf) and (B) VG06-3 (outer shelf). G layer = gray layer. OG layer = olive green layer.



observed came from the Bío Bío and Itata rivers, which drain themountainous regions of the Andes and the Coastal Range, and fromthe ‘‘immature’’ bulk mineralogical assemblage resulting from re-duced chemical weathering (Lamy et al., 1998; Hebbeln et al.,2000). Differences in the appearance of sediments (e.g., alternatinglayers of olive green and gray) were observed mainly on the outershelf (Fig. 4). The dark olive green hemipelagic mud at the surfacewas followed by olive green or gray clayey mud. These layers werereported previously from the GEOB 7161-7 station, described inthe RV Sonne cruise report (SO-156, Hebbeln and cruise partici-pants, 2001), which coincides with our VG06-3 station and showssimilar lithology.

4.2. Organic contents in the sediment and their implications for thetemporal reconstruction of bottom-water oxygenation

In general, the observed TOC contents (0.1–2.5%; Figs. 5 and 6)were in the range of values reported previously by Contreras et al.(2007) for mid-shelf surface sediments (2.7–5.2%). The outer shelfsediments had the lowest TOC values and high downcore variations,concomitant with highly variable stable isotopes and consistentwith the intercalated olive green layer. The C/Nmolar ratios of the ol-ive green layers were within the range of those previously observedin the surface sediments (7–11) (Muñoz et al., 2007; Sellanes et al.,2007), suggesting that these layers had less degraded material thanthe gray layers, which showed the highest C/N ratios (�20–40 mid-shelf and �30–200 on the outer shelf) associated with a highlydegraded (or refractory) organic matrix. Nitrogen-rich compounds(e.g., proteins) degrade faster than nitrogen-deficient ones (carbo-hydrates, lipids). Thus, higher C/N ratios, regardless of the origin ofthe organicmatter, generally indicate amore advanced state of deg-radation (Cauwet, 1978). The organicmatter remineralization rate isalso strongly dependent on the bottom oxygen content (Gutiérrezet al., 2000; Molina et al., 2004; Sellanes et al., 2007), and bottom-water oxygenation can vary seasonally or episodically (during ElNiño years) in the study area. According to the degradation index(DI) reported for the mid-shelf, during intense upwelling periodsthe DI value could be two times lower than during oxygenated peri-ods such as EN events (DI: �0.5 and 1.2; Contreras et al., 2007).Moreover, oxygenation during these periods lasts longer than dur-ing normal seasonal variability and so, has a broader effect on thesediment’s early diagenetic processes (Neira et al., 2001; Sellaneset al., 2007). Thus, given the increased organic matter degradationrates during oxygenated periods, the C/N ratios should also increase.A similar situation was found for the differences in stable isotopesbetween the olive green and gray layers: d15N values were typicallyaround 10‰ in the olive green layers and below 5‰ in the gray lay-ers (Figs. 5 and6). The values in the olive green layers decreased dur-ingmore oxygenated periods (�8‰) but were quite similar to thoseobserved in surface sediments during suboxic conditions (�11‰)(Contreras et al., 2007), suggesting that differences in the downcoredistribution of the stable isotope signatures could represent differ-ences in bottomwater oxygen conditions. Besides, heavier N signa-tures in the sediments were usually attributed to denitrificationprocesses in thewater columndue to the prevalence of suboxic con-ditions (Altabet et al., 1999, 2002; Ganeshram et al., 2000; Sigmanand Casciotti, 2001). This process has been extensively describedoff the Peru and Chile margins associated with the OMZ (Libes andDeuser, 1988; Martínez et al., 2000; De Pol-Holz et al., 2007; FaríasandCornejo, 2007). Therefore, heavier isotopic signatures of this ele-ment suggest suboxic conditions.

The downcore d13C distribution revealed a similar pattern, withheavier values in the olive green layers (ÿ20‰, indicating marineorigins) intercalated with lighter values (<ÿ25‰) in the gray lay-ers, suggesting that these sections possess a different organic mat-ter composition, probably due to the reduced preservation of the

marine particles deposited on the bottom (Figs. 5 and 6). On theother hand, the light isotope signatures are close to the terrestrialend-member values considered in other studies (d13C: ÿ30‰ toÿ26‰; d15N: ÿ1‰ to 1‰) with moderately high C/N ratios(�20–60) (Ogrinc et al., 2005; Arnaboldi and Meyers, 2006), imply-ing that past relevant terrestrial inputs occurred in an oxygenatedenvironment.

Variations in the biogenic opal contents alternated betweenlower values in the gray layers and higher values in the olive greenlayers at both sites. The highest values in the olive green layerswere similar to those reported for upwelling periods (9–11%),whereas the lower values corresponded to periods of lower pro-ductivity (e.g., El Niño years) or winter (<9%) (Contreras et al.,2007), indicating the close relationship between SiOPAL in the sed-iments and primary productivity in the water column.

In synthesis, the olive green layers suggest the occurrence ofperiods of higher primary productivity in the water column andprobably higher oxygen consumption. Moreover, the shelf sedi-ments seem to have been under different oxygenation regimes inthe past, with the oxygenated periods lasting longer than the sub-oxic conditions. Evidence of periods of higher/lower inputs of ter-restrial material was also inferred from the presence of layers withhigh densities and from the higher C/N ratios (refractory material)in the gray layers.

4.3. Distribution of trace metals associated with suboxic conditionsand organic/inorganic particle fluxes to the sediments

The Me/Al downcore distribution suggests a relevant correla-tion with the sedimentary organic composition; most evidentwas a marked increase of several elements in the olive green lay-ers. On the contrary, other elements showed higher concentrationsin the gray layers, suggesting a link to elevated non-marine detritalinputs (Figs. 7 and 8).

At the mid-shelf station VG06-2 (Fig. 7), the most evident graylayer (highly refractory material as explained in the previous sec-tion) could correspond to the rapid deposition of allochthonous in-puts, probably from the outer shelf or slope. This layer containedMe/Al ratios of Mn, Cu, Co, and Sr that were even higher than thosein the outer shelf gray layers, probably due to adsorption onto set-tling particles (Calvert and Pedersen, 2007). Since these gray layersmay be the result of higher detrital inputs, the very low ratios ofCd, Mo, and U in these layers could imply that the continental in-puts were relevant for several elements in the area, but not for Cd,Mo, and U. This would agree with previous studies by Böning et al.(2005, and references therein), who suggested the dilution oforganic carbon fluxes by terrigenous material. Mid-shelf, these ele-ments showed lower ratios due to the prevalence of oxic condi-tions within the sediments, as indicated by Mn, which could co-precipitate with other elements such as V, Cu, Co, and Sr, beingstrongly influenced by Mn–Fe cycling (Calvert and Pedersen,1993, 2007). Iron contents were not higher in the gray layer, butfollowed a pattern similar to that of Mn and V below 136 cm depth(Figs. 7 and 8).

The increase of Mn, Fe, Cu, Co, Sr, Ba, and Mo below 136 cmdepth coincided with a slight decrease in TOC and SiOpal, interca-lated with lighter values of d13C down to �150 cm depth; the lattercould be related to refractory material of terrestrial origins (Figs. 5and 7). This pattern was also observed for Sr, which could be con-sidered to be an indicator of terrigenous input. In this case, the in-crease of Mo in this section could be associated with adsorptiononto Mn oxyhydroxides (Shimmield and Price, 1986). On the con-trary, in the next depth section (below 150 cm), the concentrationsof Mn, Fe, Cu, Co, Sr, Ba decreased (but remained higher than inprevious sections), coinciding with a slight increase of TOC.Moreover, the high Mo, Cd, and U ratios suggested the prevalence



of a reduced condition in which sulfides removed the Cd and Mo(through the formation of thiomolybdates) from pore waters(Fig. 7). Usually, U, Mo, and Cd are immobilized in reduced sedi-ments where sulfate reduction is intense (Crusius et al., 1996; Mor-ford and Emerson, 1999). The accumulation of these elementswithin the sediments should not be affected considerably by sea-sonal oxygenation. Probably, the high sedimentation rate at thissite (0.27 cm yrÿ1) precludes important oxygen penetration withinthe sediments. In general, the TM content of the mid-shelf coreshowed higher concentrations of Cr, Zn, Ba, Cd, Mo, and U thanthe outer shelf core (Figs. 7 and 8), but the EF values suggested thatonly Mo, U, and Cd were accumulated authigenically (Fig. 9); thedetrital inputs from the two main rivers in the area (Bío Bío andItata River) probably diluted the accumulation of TM from biogenicsources.

A different situation was observed on the outer shelf (VG06-3,Fig. 8). Several elements showed a good relationship with organicfluxes to the bottom (Appendix A). Previous studies in the areaindicated enriched Cd and Mo related to the reduced conditionwithin the sediments, which was in turn produced by TOC precip-itation (Böning et al., 2005). The elevated U concentrations couldbe related to both low oxygen conditions and high organic carbonfluxes to the sediments (Shaw et al., 1994; Mangini et al., 2001;Morford et al., 2005, 2007) since U correlated positively with ele-ments related to organic fluxes (Ni, Zn, Cd, Ba) and others relatedto oxygen changes (V, Cr, Mo).

Cd is considered to be a good indicator of sulfide productionfrom sulfate reduction, even at low sulfide concentrations(Rosenthal et al., 1995; Chaillou et al., 2002). The downcoredistribution of this element was similar to that of U, however itis independent of sulfide authigenesis and begins to precipitatewhen the reduction of reactive Fe (III) occurs (Chaillou et al.,2002; Sundby et al., 2004). Both Cd and U suggested suboxicconditions. Also, the correlation between U and Fe (Spearman R:0.70, p < 0.01) indicated that the high iron concentrations shouldbe a consequence of reduction and subsequent pyrite formation(otherwise they would have a negative correlation since reducedFe is soluble). This suggests that sulfate reduction predominatedwithin the sediments, consistent with periods of higher organiccarbon fluxes (Figs. 6 and 8). Likewise, Cd and Mo also showedstrong correlations (Spearman R: 0.91; p < 0.01); the latteraccumulates within the sediments at low sulfide concentrationsvia the formation of organic thiomolybdate compounds or byassociation with pyrite (Zheng et al., 2000; Sundby et al., 2004).In this case, higher concentrations of this element suggest theprevalence of suboxic conditions apparently not strongly affectedby seasonal oxygenation.

The EF of nutrient-type elements (i.e., Cu, Ni, Zn) did not differsignificantly from the crustal composition in the area (Fig. 9;Table 2); the seasonality of the oxygen condition could preventthese elements from being trapped within the sediments.Mid-shelf, less reducing conditions could extend down to 10 cmduring oxygenated periods, thereby promoting organic matterdegradation and the consequent release of nutrient-type ele-ments into pore waters. However, seasonal oxygenation did notseem to affect U, Cd, or Mo distributions, all of which wereenriched at both sites, especially mid-shelf; no strong effectwas shown over the shelf.

At both stations, good correlations were observed between Ba,Fe, and Mo (Spearman R: 0.63–0.77; p < 0.01; Appendix A). Ba isindependent of the oxidative changes within the sediments andclosely related to primary productivity fluxes to the bottom(Dymond et al., 1992; Sternberg et al., 2005). Reactive Fe couldform pyrite in reduced sediments, as is the case for the shelfoff Concepción, where pyrite formation is Fe-limited and highlydependent on the metabolizable TOC within the sediments

(Böning et al., 2005). Thus, both Fe and Ba should be related toincreased downward fluxes of organic carbon to the sediments,although neither element showed authigenic enrichment.However, this interpretation must be received with caution sinceorganic carbon is not well preserved in sulfate-reducing sedi-ments (Balakrishnan Nair et al., 2005; Paytan and Griffith,2007), and important inputs of Ba (and Fe) derived from thecontinental inputs could be potentially relevant along coastalmargins (Shaw et al., 1998; Klump, 1999), obscuring the biogenicBa deposition on the bottom. In general, TM enrichment washigher for elements associated with suboxic conditions such asU, Mo, and Cd in the olive green layers, all of which were relatedto organic inputs to the bottom, as suggested by the elevatedTOC contents in the same sections.

An accurate TM/Al detrital ratio for the area was difficult toestablish and certainly should be better assessed, as suggestedby Böning et al. (2009). Some EF could be underestimated, aswere Cu, Co, Ni, and Zn. Normally, these elements could be fixedas sulfides during organic matter degradation or could be incor-porated into pyrite (Tribovillard et al., 2006 and references there-in). Since these elements did not show relevant differencesbetween higher and lower organic fluxes to the sediments, it ispossible that their sedimentary record was not well preserved.This was also supported by the fact that they did not show evi-dent changes along the core as did the U, Mo, and Cd profiles,which certainly reflected the oxidative changes that occurredwithin the sediments.

Sedimentation is faster on the inner shelf than on the outershelf, resulting in different TM records. In the core VG06-2 (mid-shelf), periods of suboxic–oxic conditions were not observed asclearly as on the outer shelf. The most conspicuous characteristicof the mid-shelf core was the presence of a gray layer that, accord-ing to the radiocarbon dates, could have been formed at 2.4 Ka.Moreover, increments in some Me/Al ratios below 136 cm depthwere associated with detrital fluxes but also with the authigenicenrichment of Cd, U, and Mo that occurred during these continen-tal inputs. The TM distribution at this station could not be matchedwith the outer shelf core since no measurements of 14C data wereavailable below 80 cm depth.

On the outer shelf, four periods of suboxic conditions wereidentified at the bottom: 1.85–1.93, 2.38–2.62, 3.68–3.96, and5.35–6.28 Ka. These were shorter in time, lasting between 0.08and 0.93 Ka. These records fall within the overall humid phase ofthe late Holocene, which started at 5.7 Ka or at 4.0 Ka (Lamyet al., 2001; Latorre et al., 2007; Marchant et al., 2007 and refer-ences therein). The resolution established in these studies couldnot help constrain paleoceanographic interpretations for explain-ing the differences in the length of the suboxic periods.

The information supported by these cores (<2 m long) estab-lished several periods of lower and higher oxygen conditions onthe bottom within the last �6 Ka. This was interpreted from theTM distributions (i.e., Mo, U, Cd) and their authigenic enrichment.The contents of TOC, biogenic opal, and the C and N stable isotopesalso suggested high fluxes of organic material over the shelf. Thesefluxes were, in turn, related to periods of lower or higher bottomoxygen conditions.

Acknowledgments

We thank the captain and crew of the Chilean Navy AGOR‘‘Vidal Gormáz’’ for support at sea during the SeepOx cruise. Wewould also like to express our gratitude to Silvio Pantoja and theCOPAS Center, who provided the facilities at Dichato MarineBiology Station, University of Concepción, Chile. We also thankall the colleagues, technicians, and students who helped during



sample collection and analysis. Funding was provided by FONDE-CYT #1061214 and DGIP2008 projects to P.M. Additional supportfor ship time was provided by FONDECYT Project No. 1061217 toJ.S., and Scripps Institution of Oceanography through a NOAAOcean Exploration program Grant #NOAA NA17RJ1231 to Lisa A.Levin. We also thank the Gordon and Betty Moore Foundation forthe purchase of Sub Boiling duoPur MILESTONE equipment, whichpermitted the processing of sediment samples for ICP-MS analysis.

Appendix A

Tables A1–A3.

Appendix B. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.pocean.2011.07.010.

Table A1210Pb activities in excess and inventories measured in a short sediment core obtained at St. 18 (COPAS time-series) corresponding to our station VG06-2.

St.18 = VG06-2Depth (cm) Bulk density (g cmÿ3) 210PbXS (dpm gÿ1

ash) 1r Total inventory (dpm cmÿ2) 1r Age (yr) 1r 1r

0–0.5 0.11 12.09 1.09 45.79 0.75 0.45 0.75 2003 10.5–1.0 0.25 12.98 0.93 45.15 0.75 1.19 0.76 2002 21.0–1.5 0.31 14.50 1.09 43.52 0.74 1.69 0.77 2000 21.5–2.0 0.36 14.81 1.16 41.30 0.72 2.15 0.78 1998 32.0–2.5 0.38 16.00 0.87 38.64 0.69 2.66 0.81 1995 42.5–3.0 0.44 16.38 0.88 35.58 0.67 3.48 0.84 1992 53–4 0.41 18.76 1.76 31.94 0.64 4.18 0.81 1988 64–5 0.40 17.57 1.01 28.06 0.53 4.30 0.83 1983 65–6 0.38 14.73 1.38 24.56 0.49 3.91 0.81 1979 76–7 0.41 13.74 0.84 21.76 0.42 4.51 0.83 1975 87–8 0.40 11.92 0.83 18.92 0.38 4.35 0.85 1971 98–9 0.40 10.60 0.73 16.54 0.34 4.43 0.86 1966 109–10 0.41 9.29 0.64 14.42 0.31 4.57 0.89 1962 1110–11 0.41 7.80 0.10 12.51 0.28 4.40 0.97 1957 1211–12 0.44 6.32 0.55 10.92 0.28 4.41 0.99 1953 1312–13 0.47 5.19 0.44 9.52 0.25 4.42 1.02 1948 1413–14 0.50 4.06 0.30 8.30 0.23 4.16 1.08 1944 1514–15 0.56 2.97 0.22 7.30 0.21 3.90 1.14 1940 1615–16 0.58 2.87 0.22 6.46 0.20 4.47 1.22 1936 1716–17 0.59 2.77 0.22 5.63 0.19 5.05 1.32 1931 1817–18 0.59 2.63 0.24 4.81 0.18 5.63 1.43 1925 2018–19 0.57 2.56 0.24 4.04 0.17 6.42 1.57 1919 2119–20 0.56 2.49 0.24 3.31 0.15 7.59 1.77 1911 2320–21 0.55 2.40 0.21 2.62 0.14 9.33 2.10 1902 2521–22 0.56 1.80 0.19 1.96 0.12 9.54 2.53 1892 2822–23 0.54 1.20 0.17 1.46 0.11 8.09 2.95 1884 3123–24 0.51 0.60 0.15 1.13 0.10 4.65 3.15 1880 3424–25 0.52 0.60 0.20 0.98 0.10 5.58 3.14 1874 3725–26 0.52 0.56 0.15 0.83 0.08 6.25 3.32 1868 4026–27 0.50 0.70 0.10 0.68 0.07 9.69 4.16 1858 4427–28 0.50 0.76 0.15 0.50 0.06 15.36 5.50 1843 5028–29 0.54 0.38 0.10 0.31 0.05 25.05 10.28 1818 60

Unsupported value: 0.87 ± 0.3 dpm gÿ1 estimated from the exponential decay of activities (r2: 0.99, p < 0.02) and considering sediment compaction (Christensen, 1982).

Table A2210Pb activities in excess and inventories measured in a short sediment core obtained at St. 26 (COPAS time-series) corresponding to our station VG06-3.

St.26 = VG06–3Depth (cm) Bulk density (g cmÿ3) 210PbXS (dpm gÿ1

ash) 1r Total inventory (dpm cmÿ2) 1r Age (yr) 1r 1r

0–0.5 0.32 28.54 0.84 77.21 1.10 0.00 0.66 2002 10.5–1 0.34 25.58 0.70 72.64 1.08 1.97 0.66 2000 11–2 0.37 15.59 0.39 68.26 1.07 2.01 0.68 1998 22–3 0.39 27.17 0.77 62.44 1.05 2.88 0.71 1995 33–4 0.42 26.24 0.46 51.75 0.94 6.06 0.74 1989 34–5 0.43 24.56 0.40 40.83 0.84 7.65 0.80 1981 45–6 0.43 20.46 0.35 30.29 0.73 9.63 0.90 1972 56–7 0.45 13.42 0.23 21.45 0.59 11.14 0.99 1961 67–8 0.47 13.34 0.50 15.41 0.50 10.66 1.14 1950 78–9 0.50 6.78 0.24 9.10 0.28 16.99 1.09 1933 89–10 0.53 2.54 0.14 5.70 0.23 15.08 1.36 1918 1010–11 0.54 1.99 0.15 4.37 0.21 8.59 1.62 1909 1111–12 0.54 2.77 0.13 3.30 0.19 9.06 1.89 1900 1312–13 0.56 2.08 0.11 1.80 0.17 19.62 2.99 1881 1613–14 0.56 0.89 0.08 0.64 0.15 33.21 7.46 1847 2414–15 0.55 0.25 0.07 0.14 0.14 49.10 32.12 1798 56

Unsupported value: 1.4–1.11 ± 0.05 dpm gÿ1 for the surface and 0.8–1.0 ± 0.04 dpm gÿ1 at the bottom (Muñoz et al., 2004a,b)



Table A3

Spearman rank order correlations. Significant values are highlighted in bold.

Station VG06-2V/AI Cr/AI Mn/AI Co/AI Ni/AI Cu/AI Zn/AI Sr/AI Mo/AI Cd/AI Ba/AI Pb/AI U/AI Fe/AI d13C d15N TOC SiOPAL Bulk density

V/AI 1.00 0.31* 0.93* 0.80* 0.49* 0.82* 0.62* 0.71* 0.16** 0.27 0.16** 0.07 0.09 0.52* ÿ0.08 ÿ0.23* 0.03 ÿ0.33* ÿ0.01Cr/AI 1.00 0.24* 0.25* 0.70* 0.22* 0.58* 0.22* 0.65* 0.60* 0.49* 0.53* 0.55* 0.55* 0.34* 0.36* 0.14 0.19** ÿ0.03Mn/AI 1.00 0.83* 0.41* 0.81* 0.53* 0.83* 0.01 0.13 0.14 ÿ0.02 ÿ0.04 0.50* ÿ0.13 ÿ0.23* ÿ0.09 ÿ0.43* 0.09Co/AI 1.00 0.55* 0.93* 0.20** 0.87* 0.32* 0.14 0.39* ÿ0.08 ÿ0.09 0.67* ÿ0.18** ÿ0.12 0.16** ÿ0.31* 0.39Ni/AI 1.00 0.58* 0.32* 0.42* 0.66* 0.44* 0.41* 0.17** 0.34* 0.55* 0.17** 0.19** 0.08 0.14 0.13Cu/AI 1.00 0.22* 0.80* 0.29* 0.14 0.24* ÿ0.12 ÿ0.04 0.54* ÿ0.22* ÿ0.19** ÿ0.11 ÿ0.30* 0.30*

Zn/AI 1.00 0.21* 0.15 0.56* 0.15 0.52* 0.41* 0.36* 0.20** ÿ0.02 0.27* ÿ0.09 ÿ0.46*

Sr/AI 1.00 0.17** 0.05 0.39* ÿ0.10* ÿ0.04 0.65* ÿ0.13 ÿ0.04 ÿ0.19** ÿ0.30* 0.37*

Mo/AI 1.00 0.64* 0.72* 0.34* 0.46* 0.58* 0.22* 0.38* 0.21* 0.41* 0.12Cd/AI 1.00 0.51* 0.57* 0.36* 0.47* 0.20** 0.09 0.36* 0.35* ÿ0.31*

Ba/AI 1.00 0.31* 0.09 0.77* 0.10 0.26* 0.22* 0.27* 0.25*

Pb/AI 1.00 0.38* 0.32* 0.18** 0.16** 0.17** 0.17** ÿ0.28*

U/AI 1.00 0.16** 0.35* 0.43* 0.14 0.35* ÿ0.22*

Fe/AI 1.00 ÿ0.07 0.17** 0.00 0.04 0.29*

d13C 1.00 0.37* 0.18** 0.28* ÿ0.27*

d15N 1.00 ÿ0.10 0.29* 0.07TOC 1.00 0.19** ÿ0.33*

SiOPAL 1.00 ÿ0.17**

Bulk density 1.00

Station VG06-3V/AI 1.00 0.83* 0.93* 0.24* 0.81* ÿ0.04 0.84* 0.71* 0.69* 0.68* 0.88* 0.64* 0.81* 0.79* 0.65* 0.54* 0.51* ÿ0.09 ÿ0.48*

Cr/AI 1.00 0.72* ÿ0.12 0.84* ÿ0.41* 0.83* 0.73* 0.78* 0.80* 0.87* 0.64* 0.87* 0.68* 0.79* 0.67* 0.59* ÿ0.13 ÿ0.64*

Mn/AI 1.00 0.37* 0.72* 0.10 0.77* 0.70* 0.53* 0.54* 0.79* 0.54* 0.66* 0.78* 0.52* 0.39* 0.39* ÿ0.14 ÿ0.29*

Co/AI 1.00 0.08 0.83* 0.08 0.14 ÿ0.31* ÿ0.32* 0.08 ÿ0.15 ÿ0.10 0.30* ÿ0.25* ÿ0.33* ÿ0.32* 0.04 0.28*

Ni/AI 1.00 ÿ0.18** 0.83* 0.55* 0.69* 0.72* 0.75* 0.70* 0.86* 0.78* 0.63* 0.60* 0.58* 0.10 ÿ0.67*

Cu/AI 1.00 ÿ0.22* ÿ0.16 ÿ0.40* ÿ0.43* ÿ0.22** ÿ0.31* ÿ0.32* ÿ0.02 ÿ0.44* ÿ0.49* ÿ0.49* 0.09 0.50*

Zn/AI 1.00 0.67* 0.60* 0.65* 0.85* 0.66* 0.80* 0.82* 0.67* 0.54* 0.55* ÿ0.12 ÿ0.61*

Sr/AI 1.00 0.45* 0.50* 0.86* 0.44* 0.62* 0.65* 0.63* 0.33* 0.29 ÿ0.39 ÿ0.38Mo/AI 1.00 0.91* 0.63* 0.62* 0.79* 0.53* 0.69* 0.65* 0.60* ÿ0.05 ÿ0.54*

Cd/AI 1.00 0.67* 0.72* 0.84* 0.53* 0.73* 0.72* 0.65* ÿ0.07 0.62*

Ba/AI 1.00 0.64* 0.81* 0.77* 0.77* 0.55* 0.51* ÿ0.23* ÿ0.61*

Pb/AI 1.00 0.71 0.56 0.56 0.62 0.57 ÿ0.03 ÿ0.63U/AI 1.00 0.70* 0.79* 0.70* 0.66* 0.02 ÿ0.75*

Fe/AI 1.00 0.55* 0.43* 0.47* ÿ0.07 ÿ0.49*

d13C 1.00 0.68* 0.51* ÿ0.18** ÿ0.70*

d15N 1.00 0.62* 0.10 ÿ0.59*

TOC 1.00 0.03 ÿ0.58*

SiOPAL 1.00 ÿ0.13Bulk density 1.00

* p < 0.01.** p < 0.05).

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