Biogenic barium in surface sediments of the European Nordic Seas

Marine Geology 250 (2008) 89 – 103 www.elsevier.com/locate/margeo

Biogenic barium in surface sediments of the European Nordic Seas M. Pirrung a,⁎, P. Illner a , J. Matthiessen b a

b

Institute for Geosciences, F. Schiller University, Burgweg 11, D-07743 Jena, Germany Alfred Wegener Institute for Polar and Marine Research, P.O. Box 120161, D-27515 Bremerhaven, Germany Received 2 November 2006; received in revised form 22 November 2007; accepted 6 January 2008

Abstract Barium in marine terrigenous surface sediments of the European Nordic Seas is analysed to evaluate its potential as palaeoproductivity proxy. Biogenic Ba is calculated from Ba and Al data using a conventional approach. For the determination of appropriate detrital Ba/Al ratios a compilation of Ba and Al analyses in rocks and soils of the catchments surrounding the Nordic Seas is presented. The resulting average detrital Ba/Al ratio of 0.0070 is similar to global crustal average values. In the southern Nordic Seas the high input of basaltic material with a low Ba/Al ratio is evident from high values of magnetic susceptibility and low Al/Ti ratios. Most of the Ba in the marine surface sediments is of terrigenous and not of biogenic origin. Variability in the lithogenic composition has been considered by the application of regionally varying Ba/Al ratios. The biogenic Ba values are comparable with those observed in the central Arctic Ocean, they are lower than in other oceanic regions. Biogenic Ba values are correlated with other productivity proxies and with oceanographic data for a validation of the applicability in paleoceanography. In the Iceland Sea and partly in the marginal sea–ice zone of the Greenland Sea elevated values of biogenic Ba indicate seasonal phytoplankton blooms. In both areas paleoproductivities may be reconstructed based on Ba and Al data of sediment cores. © 2008 Elsevier B.V. All rights reserved. Keywords: Nordic Seas; surface sediments; Ba/Al ratio; biogenic barium; productivity

1. Introduction The European Nordic Seas (ENS) is one of the key areas for the global thermohaline circulation, as most of the North Atlantic Deep Water is formed by sinking of cooling water masses in the Greenland and Iceland seas (e.g. Swift, 1986). Therefore the knowledge about recent and past productivity in this area is important. However, the estimation of primary and export productivity from the particle flux in sediment traps, from shipboard measurements or satellite data (e.g. Schlüter et al., 2000; Ramseier et al., 2001; Sakshaug, 2004; Bauerfeind and von Bodungen, 2006) is a complex problem. On one hand, seasonal and interannual changes in the phyto- and zooplankton composition are highly variable, especially in the marginal sea–ice zone. On the other hand, the temporal and spatial resolution of shipboard data, the short deployment time of sediment traps and difficult weather and sea–ice conditions restrict information about long-term changes in productivity. Further complications result from the ⁎ Corresponding author. Tel.: +49 3641 948644; fax: +49 3641 948622. E-mail addresses: [email protected] (M. Pirrung), [email protected] (J. Matthiessen). 0025-3227/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.margeo.2008.01.001

dilution of in situ-produced biogenic particles by seasonally varying meltout of biogenic particles from sediment-laden sea ice (Nürnberg et al., 1994), and from lateral transport of plankton by surface and deeper water currents (Schröder-Ritzrau et al., 2001). The reconstruction of past productivity based on proxies in sediment cores is even more complex in this area due to dilution of biogenic components by bottom current transport of terrigenous material (e.g. Boltovskoy, 1994), sediment redistribution (Paetsch et al., 1992), bioturbation (Trauth et al., 1997), varying sedimentation rates and instability of biogenic material (TOC, calcitic and opaline microfossils, see e.g. Risebrobakken et al., 2006). Some paleoceanographic studies focussed on organic-walled microfossils (e.g. De Vernal et al., 2000), which are less susceptible to dissolution respectively degradation. Only few studies analysed combinations of various planktonic microfossil groups (e.g. Hass et al., 2001; Matthiessen et al., 2001). An alternative to proxies based on degradable or soluble material is biogenic barium (Babiogenic, also named Baexcess), which is preserved as barite that is characterized by a high stability under oxic conditions (e.g. Dymond et al., 1992). Babiogenic has been successfully applied as a proxy for paleoproductivity in open ocean settings that are characterized by biogenic sediments (e.g.

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Dymond et al., 1992; Nürnberg et al., 1997; Fagel et al., 2002; Nürnberg and Tiedemann, 2004; Nürnberg et al., 2004; Anderson and Delaney, 2005). Only some studies analysed Babiogenic in the more terrigenous sediments of continental margins (e.g. McManus et al., 1999, 2002; Fagel et al., 2004; Borchers et al., 2005; Plewa et al., 2006), where a separation of detrital from biogenic Ba is problematic. Most studies calculated Babiogenic from Ba and Al or (less frequently) Ba and Ti data, assuming a constant detrital (or terrigenous, lithogenic) Ba/Al or Ba/Ti ratio (Boström et al., 1973; Dymond et al., 1992; Kryc et al., 2003). However, these ratios are

influenced by changes in the composition of the terrigenous material (e.g. Klump et al., 2000). The knowledge of detrital Ba/Al or Ba/Ti ratios is especially important in the terrigenous sediments of the high northern latitudes (Nürnberg, 1996). The aim of this study is to test the potential of Babiogenic calculated from Ba and Al data as a proxy for (paleo)productivity in the terrigenous surface sediments of the ENS. For an adequate correction of the detrital Ba components regionally varying correction factors were determined by a compilation of Ba/Al ratios of rocks and soils in the catchment areas, by Al/Ti ratios and by

Fig. 1. Locations of marine surface sediments analysed for this study with references for published Ba and Al data and some oceanographic parameters of surface water masses in the European Nordic Seas (after Swift, 1986; Divine and Dick, 2006). For the catchment areas a simplified lithological map is included compiled after Dallmann et al. (2002); Escher and Pulvertaft (1995); Jóhannesson and Sæmundsson (1988); Koistinen et al. (2001).

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magnetic susceptibility of marine surface sediments indicating lithological variations. The resulting Babiogenic values are compared with estimations of primary and export productivity from satellite, shipboard and sediment trap data. Areas that may be suitable for the analysis of past Babiogenic variability are discussed. 2. Regional setting The surface water masses of the ENS are characterized by a northward transport of relatively warm and saline Atlantic Water within the Norwegian and Westspitsbergen currents and by a southward transport of cold and low saline Polar Water masses within the East Greenland Current (Fig. 1). Polar Water is covered with sea ice nearly year-round, whereas Atlantic Water is free of sea ice year-round. Cool and saline Arctic Surface Water originates from recirculation and cooling of Atlantic Water and mixing with Polar Water between the Polar and Arctic fronts (e.g. Johannessen et al., 1994). Sea ice formed on the Siberian shelves is transported by the Transpolar Drift towards the Fram Strait, and biogenic and lithogenic particles are released into the water column of the ENS during ice melt (Wollenburg, 1993; Nürnberg et al., 1994; Lindemann, 1998). Only a minor part of the sea ice exits through the Denmark Strait (Ramseier et al., 2001). Due to low export production rates (e.g. Schlüter et al., 2000; Sakshaug, 2004) and proximity of the surrounding land masses the surface sediments in the Fram Strait and the Greenland Sea are terrigenous in composition. In the Norwegian Sea, surface sediments change towards the south from terrigenous to biogenic composition, with increasing carbonate contents (up to 60 wt.%), as well as in the Iceland Sea (Stein et al., 1996; Huber et al., 2000; Schröder-Ritzrau et al., 2001; Taylor et al., 2002; Kierdorf, 2006). Opal contents are generally low, they increase from the northern Greenland Sea (b 2 wt.%) towards the Norwegian and Iceland seas (b 5 wt.%; Knies et al., 2000; Lochte et al., 2000; Schlüter and Sauter, 2000; Heinze and Dittert, 2004; Bauerfeind and von Bodungen, 2006).

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3. Material and methods The investigated samples, methods and references are listed in Tables 1–3. In the following, only the determination of geochemical parameters is summarized. For the determination of major and trace elements by X-ray Fluorescence Spectrometry (XRF) 1 g of Wax C (Hoechst ©) was added to 6 g of freeze-dried ground material, stored over night at 105 °C, and pressed at 200 Mpa. For major element analysis 1 g of material was glowed at 900 °C for 2 h and hereafter 4 g Spectromelt (Merck ©) was added to 0.4 g of glowed sample material. The material was melted with a highfrequency induction oven (Lifumat ©). The analyses were performed with a sequential wave-length dispersive spectrometer WDXRF-PW 2400 (Philips ©) at the Institute for Geosciences, Friedrich Schiller University of Jena. From repeated measurements (N = 8) of a certified standard (JB-03, see the GeoRem Database of the MPI for Chemistry, Mainz, http://georem.mpchmainz.gwdg.de) the accuracy was determined as being better than 0.04 wt.% for TiO2, 0.21 wt.% for Al2O3 and 8 ppm for Ba. The precision was estimated from standard deviations as 0.01 wt.% for TiO2, 0.09 wt.% for Al2O3 and 5.6 ppm for Ba. Ba, Al, Ti, biogenic Ba, terrigenous fraction and magnetic susceptibility data are included in the electronic supplement and are stored in the PANGAEA information system, www.pangaea.de. 4. Results 4.1. Ba/Al ratios in marine surface sediments Ba/Al ratios are available from 150 samples of surface sediments in the ENS and adjacent areas of the Arctic Ocean, Barents Sea and North Atlantic (electronic supplement 1). 9 samples on the western Bear Island Trough (Bogdanov et al., 1996) revealed anomalously high Ba/Al ratios of 0.3–0.5 and were not further considered, as in other nearby samples no elevated values were observed. In different parts of the ENS average Ba/Al ratios range

Table 1 The data sources and methods for several parameters applied in this study are listed below Parameter

Method

Sediment samples analysed in this study

Box corers, Multi corers, 93 of a set of 427 marine surface samples (electronic supplement 1) and 4 sea-ice samples (electronic 0-2 cm sediment depth supplement 2) of the core repository of the Alfred Wegener Institute for Polar and Marine Research (AWI), Bremerhaven (http://www.awi-bremerhaven.de) XRD; ICP-AES; XRF XRF: Nürnberg, 1996; Paetsch, 1991; ICP-AES: Siegel et al., 2000; XRF and colorimetry: 9 samples of Bogdanov and colorimetry et al. (1996) were only initially considered; data source: Information system PANGEA (http://www.pangaea.de), Alfred Wegener Inst. for Polar and Marine Res. (AWI), Bremerhaven, Center for Marine Environmental Sciences (MARUM), University of Bremen (58 samples); this study (93 samples and 4 sea-ice samples) XRF; all Ba/Al ratios GeoRoc database, Max Planck Institute for Geochemistry, Mainz (http://www.mpch-mainz.de); data (1591 are weight ratios and samples) of the LITO-project database (assessment of geochemical data for Norwegian rocks, Geological not molar ratios. Survey of Norway, NGU, http://www.ngu.no/lito/); unpubl. data of recent riverine sediments (1°latitude-spaced mean values of 1270 samples, Geological Survey of Denmark and Greenland); publications cited in Table 3. Bartington MS2 Pirrung et al., 2002 (356 samples); this study (71 samples) susceptibility meter Determined from bottle U.S. National Oceanic and Atmospheric Administration (NOAA) data base (http://www.ngdc.noaa.gov), samples ewoce-Atlas (http://dss.ucar.edu/datasets/ds543.0/data/) Satellite images NASA SeaWiFS project (http://oceancolor.gsfc.nasa.gov/cgi/biosphere_globes.pl); Schlüter et al., 2000 Software Ocean Data R. Schlitzer, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, http://www.odv.awi.de View, V. 3.1.0, 2006 Statistics of Linear correlation coefficient after Pearson Microsoft Excel

Ba, Al, Ti concentrations of marine surface sediments

Ba, Al, Ti concentrations of catchment rocks and soils

Mass-specific magnetic susceptibility Chlorophyll concentration Chlorophyll concentration Distribution maps Correlation analysis

Reference

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Table 2 Average values and standard deviations resp. ranges of Ba/Al ratios in marine surface sediments of the European Nordic Seas (entire area and selected parts) and adjacent areas and in sediments entrained into sea ice Region

Al2O3 (%)

Ba (ppm)

Ba/Al

N

References

European Nordic Seas, entire area European Nordic Seas, marginal sea-ice zone East Greenland Shelf Spitsbergen Shelf W- and NW-Barents Sea Shelf Yermak Plateau Vöring Plateau Iceland Plateau and Shelf, Iceland-Faeroe-, Reykjanes and Kolbeinsey-Ridge Greenland Basin Norwegian Basin Laptev Sea Kara Sea Arctic Ocean Arctic sea ice sediments Arctic sea ice sediments

12.2 ± 2.8 12.9 ± 2.2 13.9 ± 3.0 13.7 ± 3.7 12.3 ± 2.2 14.8 ± 1.4 9.9 ± 2.4 10.7 ± 3.6

512 ± 177 518 ± 128 546 ± 103 447 ± 136 469 ± 67 615 ± 88 428 ± 118 424 ± 184

0.0074 ± 0.0016 0.0076 ± 0.0017 0.0076 ± 0.0014 0.0063 ± 0.0017 0.0073 ± 0.0014 0.0079 ± 0.0011 0.0082 ± 0.0018 0.0074 ± 0.0018

132 30 18 5 6 9 7 21

This study; Paetsch, 1991; Nürnberg, 1996; Siegel et al., 2000; This study; Paetsch, 1991; Nürnberg, 1996; Siegel et al., 2000; This study; Paetsch, 1991; This study; Siegel et al., 2000; This study; Nürnberg, 1996; This study; Nürnberg 1996; This study; Paetsch, 1991; This study; Paetsch, 1991;

11.9 ± 1.9 9.8 ± 2.5 Not given Not given 14.6 ± 1.7 Not given 15.6 ± 0.5

436 ± 122 384 ± 102 327-682 310-470 524 ± 50 634 ± 277 498 ± 21

0.0069 ± 0.0016 0.0076 ± 0.0020 0.0050-0.0140 Not given 0.0069 ± 0.0010 Not given 0.0060 ± 0.0004

27 18 53 54 45 12 4

This study; Paetsch, 1991; This study; Paetsch, 1991; Nürnberg 1996; Nürnberg 1996; Nürnberg 1996 and unpubl. data; This study; Wollenburg, 1993; This study;

In this table, the area of the Yermak Plateau is attributed to the Nordic Seas, although it forms part of the Arctic Ocean in its northern section.

from 0.0069 to 0.0082 (Table 2), however with significant variations (Fig. 2). The maximum and minimum Ba/Al ratios are 0.012 and 0.002, respectively. Areas with high Ba/Al ratios N 0.009 occur on the NE Greenland shelf, on the northern Iceland Plateau southwest of the volcanic island of Jan Mayen, on the Norwegian continental shelf and slope and in the western Norwegian Basin. Areas with low Ba/Al ratios b0.005 are limited to the fjords in East Greenland between 69 and 75° N and to the adjacent shelf areas, and to the Denmark Strait, the Iceland shelf, the vicinity of the Faeroe Islands and the Mohns Ridge between the Greenland and Norwegian basins. Isolated locations with Ba/Al ratios b 0.003 occur on the lower slopes of the western and eastern Greenland Basin.

In the surface sediments of the ENS significant correlations between Ba and other parameters are as follows: positively with Rb (R = 0.85), Al2O3 (R = 0.81), K2O (R = 0.79), Na2O (R = 0.71), negatively with CaO (R = −0.75) and calcite (R = −0.66). Other correlations between Ba and e.g. Ti, Fe, opal, TOC (total organic C) are not significant. 4.2. Ba/Ti and Al/Ti ratios in marine surface sediments The average Ba/Ti ratio for samples in the ENS is 0.122 (Fig. 4a). Spots of high Ba/Ti ratios N0.2 occur on the southwestern slope of the Barents Sea, on the East Greenland shelf at 80° N and in the southwestern Greenland Sea. Areas with low Ba/Ti ratios b 0.1

Table 3 Ba/Al ratios in rocks (magmatic, metamorphic, and sedimentary) of different source areas around the European Nordic Seas Region

Al2O3 (%)

Ba (ppm)

Greenland, W′ 40° W

14.1 ± 3.6

400 ± 655 0.0052 ± 0.0089

Greenland, E′ 40° W

12.0 ± 3.6

E-Greenland, Geikie Plat.– Wollaston Forland Iceland Faeroe Islands W–N–NE–Scandinavia

13.9 ± 1.9

SE-Scandinavia Svalbard All regions

Ba/Al

N

References (listed only if N N 10)

613 GeoRoc; Kalsbeek and Taylor, 1985; Kalsbeek and Manatschal, 1999; Cadman et al., 2001; Mueller et al., 2002; Marks, 2003; Polat and Hofmann, 2003; Marks et al., 2003; Komiya et al., 2004; Mayborn and Lesher, 2004; Taubald et al., 2004; 480 ± 286 0.0079 ± 0.0041 1812 GeoRoc; GSDG; Moorlock et al., 1972; Kalsbeek, 1995; Curewitz and Karson, 1999; Bernstein et al., 2000; Hald and Tegner, 2000; Kalsbeek et al., 2001; Pedersen et al., 2002; Thrane, 2002; Peate and Stecher, 2003; Lassen et al., 2004; 224 ± 319 0.0031 ± 0.0042 191 GeoRoc; Hald and Tegner, 2000; Peate and Stecher, 2003;

14.6 ± 1.5 13.5 ± 1.4 14.4 ± 3.3

179 ± 237 0.0024 ± 0.0031 1093 GeoRoc; 70 ± 71 0.0010 ± 0.0011 77 GeoRoc; Holm et al., 2001; 667 ± 666 0.0092 ± 0.0142 2430 GeoRoc; LITO; Dypvik, 1979a; Emmett, 1989; Alapieti et al., 1990; De Haas et al., 1993; Persson et al., 1995; Hageskov, 1997; Cotkin, 1997; Rockow et al., 1997; Brewer and Menuge, 1998; Markl, 2001; Skår, 2002; Alirezaei and Cameron, 2002; Austrheim et al., 2003; Auwera et al., 2003; Barnes et al., 2003; Bingen et al., 2003; Bogaerts et al., 2003; Bolle et al., 2003; Gilmour et al., 2003; Rehnström, 2003; Slagstad, 2003; Brewer et al., 2004; 13.2 ± 3.2 507 ± 340 0.0070 ± 0.0044 1389 GeoRoc; Reimann, 2000; 14.8 ± 3.8 599 ± 431 0.0083 ± 0.0069 195 Dypvik, 1978; Dypvik, 1979b; Dypvik, pers. comm.; Gee et al., 1995; Carlsson et al., 1995; Johansson et al., 2000; Johansson et al., 2004; 13.7 ± 12.8 492 ± 505 0.0070 ± 0.0093 7653

GeoRoc = GeoRoc database, MPI for Geochemistry, Mainz, http://georoc.mpch-mainz.gwdg.de/georoc/; LITO = LITO-Project, Geological Survey of Norway, http://www.ngu.no/lito/; GSDG = Geol. Survey Denmak and Greenland, http://www.geus.dk/geuspage-uk.htm, unpubl. Data of recent river sediments. N = number of analyses.

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Fig. 2. Ba/Al ratios in marine surface sediments and in rocks and C-horizons of soils in the landmasses surrounding the European Nordic Seas. Catchment data were compiled from the references given in Table 3, for references of marine data see Fig. 1. The major part of the data in the catchment areas was retrieved from the GeoRoc database (http://www.mpch-mainz.de) and the PANGAEA information system (http://www.pangaea.de). Offshore assumed detrital Ba/Al ratios are indicated, which were estimated with respect to average Ba/Al ratios of onshore rocks and that were used for the calculation of biogenic Ba in Fig. 6.

extend from Scoresby Sund in East Greenland to the southern Iceland Plateau and into the Denmark Strait. Areas of high Ba/Al ratios correspond to those with high Ba/Ti ratios. Ba/Al and Ba/Ti ratios are significantly positively correlated (R= 0.76). Ba/Ti ratios are negatively correlated with TOC (R = −0.61). In the ENS, Al/Ti (weight) ratios (Fig. 4b) are elevated (N25) on the Jan Mayen Fracture Zone and on Mohns Ridge between the Greenland and Norwegian basins, and low values (b10) occur offshore Scoresby Sund and around Iceland. 4.3. Magnetic susceptibility in surface sediments The magnetic susceptibility of sediments originates primarily from the concentration of certain ferrimagnetic minerals (Evans and Heller, 2003). In the ENS the ferrimagnetic fraction of Holocene and late Pleistocene sediments is dominated by titanomagnetite (e.g. Frederichs, 1995; Ballini et al., 2006). The massspecific magnetic susceptibility of surface sediments is a suitable parameter to characterize compositional variations of the terrigenous fraction in the high northern latitudes (e.g. Pirrung et al., 2002; Watkins and Maher, 2003). In the ENS, high mass-specific magnetic susceptibility values N1000 ⁎ 10− 9 m3 kg− 1 occur within and offshore Scoresby Sund and on the Iceland–Faeroe Ridge (Fig. 4c), where maximum values N 3500 ⁎ 10− 9 m3 kg− 1 are present. The mass-specific magnetic susceptibility measured on bulk sediments reveals a significant positive correlation with TiO2 (R = 0.71). If mass-specific susceptibility is calculated for the terrigenous fraction (using water content, TOC, calcite and opal values from the PANGAEA information system) in order to

exclude dilution effects by biogenic material, then the correlation of magnetic susceptibility of the terrigenous fraction with TiO2 is high (R = 0.91), and a positive correlation with Al2O3 (R = 0.80) and a negative correlation with Al/Ti (R = −0.65) results. 4.4. Biogenic barium There exist several approaches for the calculation of biogenic Ba (Babiogenic) from geochemical analyses. A relatively timeconsuming method is the direct measurement of the barite content by a sequential leaching technique (Eagle et al., 2003; Reitz et al., 2004; Eagle Gonneea and Paytan, 2006), by Inductively Coupled Plasma Optical Emission Spectrometry of separated barite dissolved in ethylene diamine tetra acetic acid (Averyt et al., 2003) or by barite determination using a Scanning Electron Microscope (Robin et al., 2003). Most calculations of Babiogenic have in common the subtraction of detrital (terrigenous, lithogenic) Ba (Badetrital) from total Ba values (Batotal) assuming constant or (rarely) regionally varying Ba/Al- or Ba/Ti-ratios of the terrigenous fraction (Ba/Aldetrital resp. Ba/Tidetrital). The biogenic portion of total Ba has frequently been calculated from total Ba and Al by the formula of Boström et al. (1973): Babiogenic = Batotal − Badetrital = Batotal − Alsample ⁎ (Ba/ Aldetrital). For the calculation of Babiogenic, in a first step a (conventional) approach was based on the assumption of a constant Ba/Aldetrital ratio of 0.0070, which corresponds to the average Ba/ Al ratio compiled for catchment rocks surrounding the ENS (Table 3). These initial results (Fig. 4d) revealed a region with elevated Babiogenic values on the southern Yermak Plateau (average 66 ppm), high values around Jan Mayen (average 113 ppm),

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and relatively low values on the Iceland Plateau and the Kolbeinsey Ridge (average 37 ppm). However, this approach disregards compositional variations of the detrital fraction, which must be assumed due to the heterogeneity of the catchment rocks and strong regional variability of Al/Ti values in the terrigenous surface sediments (Fig. 4b). In a second step, regional variability of Ba/Aldetrital ratios has to be investigated. A promising approach might be the analysis of coastal samples with primarily detrital composition (see e.g. Nürnberg et al., 1997; Klump et al., 2000). Eight samples from fjords in East Greenland (70–75° N) have an average Ba/Al ratio of 0.0068 corresponding to onshore Ba/Al data, but carbonate contents up to 17% demonstrate that these samples are of limited use for estimations of Ba/Aldetrital ratios. Therefore, an estimation of Ba/Aldetrital based on the average Ba/Al ratios of the nearby catchment regions (Table 3) was applied for the coastal and shelf areas (indicated in Figs. 2 and 5). Towards the deep sea basins the Ba/Aldetrital ratios should converge towards the average Ba/Al ratio of 0.0070 for the catchment rocks, as redistribution of detrital material through bottom currents and ice-rafted debris should lead to an increase in lithological homogeneity. In addition to the consideration of Ba/Al ratios of nearby catchment rocks, the applied regional Ba/Aldetrital ratios were also based on the Al/Ti ratios (Fig. 4b) and magnetic susceptibility (Fig. 4c). Where massspecific magnetic susceptibility is higher than 1000 ⁎ 10− 9 m3 kg− 1 the existence of basaltic debris is plausible and if these values exceed 1500 ⁎ 10− 9 m3 kg− 1, then a significant content of basaltic components has to be assumed (Pirrung et al., 2002). On the Iceland–Faeroe Ridge and on the southern Iceland Plateau SE of Scoresby Sund, as well as in the Denmark Strait, mass-specific magnetic susceptibility is higher than the latter value. In this zone a lower than average Ba/Aldetrital ratio of 0.0050 was assumed. On the Iceland Plateau and the Kolbeinsey Ridge resulting Babiogenic values (133 ppm) are higher than with a constant Ba/Aldetrital approach. The resulting distribution of Babiogenic (Fig. 5) shows elevated values N 100 ppm on the Iceland Plateau, along the marginal sea–ice zone (Divine and Dick, 2006) on the East Greenland shelf between 70° and 75° N, and in the central Fram Strait. In contrast, in the central part of the ENS no Babiogenic is present. There is neither a significant general dependence of Babiogenic with water depth nor with the distance to the shore. 5. Discussion 5.1. General aspects The database of recent and past primary and export productivity is still relatively sparse in the area of the European Nordic Seas (ENS). As other proxies for paleoproductivity based on organic matter or carbonatic or siliceous microfossils are influenced by degradation and dissolution, biogenic Ba may provide important information on present and past productivity in the ENS. The organisms that incorporate Ba in their siliceous or carbonaceous skeletons or tests (e.g. Bernstein and Byrne, 2004; Hall and Chan, 2004) and the processes that lead to the precipitation of barite (e.g. Rushdi et al., 2000; Fagel et al., 2004; Anderson and

Winckler, 2005) are not yet fully understood. There are indications that a significant portion of barite forms during the decay of organic matter by sulfate release (Reitz et al., 2004). In surface water masses of the Arctic seas, depletions of Ba are connected to seasonal phytoplankton blooms (Guay and Falkner, 1997, 1998). However, in surface and deep water masses of the ENS barite concentrations are below saturation, as in most oceanic regions (Monnin et al., 1999). Estimations for the preservation factor of barite range at about 30% for Atlantic Ocean sediments (Dymond et al., 1992), which is much higher than that of organic carbon. In this study, calculations of biogenic Ba were based on Ba and Al data (e.g. Dymond et al., 1992) and not on Ba and Ti data (e.g. Eagle et al., 2003; Kryc et al., 2003). Al is a component of common silicate minerals. In contrast, the compatible element Ti is enriched in specific mafic minerals (e.g. in titanomagnetite, ilmenite), which are typical components in basic magmatic rocks. The average Ba/Ti ratio (Fig. 4a) for samples in the ENS is 0.122, which is close to the average value of 0.14 for the upper continental crust (Wedepohl, 1995). Extensive areas surrounding the SW part of the ENS are dominated by basaltic rocks, which are strongly enriched in Ti (1.6% TiO2 on average, N = 188; GeoRoc, http://georoc.mpch-mainz.gwdg.de/georoc/) compared to the average of the upper continental crust (0.52% TiO2; Wedepohl, 1995) and depleted in Ba (average Ba/Ti ratio of 0.005 in basalts of Greenland, Iceland, Faeroe Isles and Hebrides, N = 265, references given in Table 3). There is no significant correlation between Ti and Al (R = 0.28) in marine surface sediments of the ENS. As a consequence of these observations, the calculation of the terrigenous fraction of Ba by normalizing to Ti is not useful in this area. Several assumptions must be made if Babiogenic is calculated from Ba and Al data following the formula given by Boström et al. (1973), for a discussion see Eagle et al. (2003), Reitz et al. (2004): 1. all Ba not associated with terrigenous aluminosilicates is related to carbon export, 2. all Al is terrigenous, 3. the water column and sediments are oxic, 4. the assumed Ba/Al ratio is representative for each sample, 5. the anthropogenic input of Ba has to be considered. The validity of these assumptions will be discussed for the area of the ENS. 5.2. Origin of biogenic Ba 1. Ba present in organic matter (b 60 ppm Ba) and opal (c. 120 ppm Ba; Eagle Gonneea and Paytan, 2006) can be neglected due to the low concentrations of TOC (b 1.5% in the ENS, on average 0.6% for the samples used for the calculation of Babiogenic) and opal (1–6%, on average 2.5% for the samples used in this study) in the ENS. However, carbonate (c. 30–200 ppm Ba; Eagle Gonneea and Paytan, 2006) is more important (on average 14.6% for the analysed samples) and may contribute to the Ba values in the southern ENS, where carbonate contents are up to 60 wt.% (which could contribute up to 120 ppm Ba), but this is of minor importance in the northern parts of the ENS. 5.3. Origin of detrital Al Aluminosilicates have been detected in opaline skeletons and valves (e.g. Gehlen et al., 2002), but the low opal contents in the

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ENS suggest that this is without significance. In open oceanic areas with b5 wt.% lithogenic particle flux, the scavenging of a minor fraction of Al and Ti by adsorption to particulate matter has been observed (Kryc et al., 2003). However, with respect to the high terrigenous fraction of the sediments in the ENS (on average 86% for the analysed samples), such influences can be neglected. The authigenic formation of aluminosilicates (see e.g. Dixit et al., 2001) may be of importance in those areas where a high portion of reactive volcanic ash is present, like in the southern Iceland Sea and around Jan Mayen Island. However, to the knowledge of the authors such studies were not conducted in the ENS. 5.4. Redox conditions For the well oxygenated bottom water (Schlüter et al., 2000; Swift, 1986) and the intensely bioturbated surface sediments of the ENS (Romero-Wetzel, 1989; Trauth et al., 1997), barite dissolution, which has been observed under anoxic conditions (McManus et al., 1998; Lepland et al., 2000), is less likely. In anoxic pelagic sediments S and U are enriched and Ba concentrations are reduced due to barite dissolution and sulfide formation (McManus et al., 1998). In the 93 surface sediments of the ENS measured in this study, there is a not significant negative correlation of Ba with S (R = 0.2), perhaps a slight positive correlation of Ba with U (R = 0.45). Obviously, both Ba and U are predominantly terrigenous. In contrast, if redox conditions were driving the relationship, a negative correlation might be expected. As there is no correlation between Fe and S, in these surface sediments sulfide formation cannot be significant.

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0.014 in acid magmatic rocks and even to values greater than 0.5 in carbonatite (Fig. 3). Granites in Greenland are the rock type with the highest average Ba/Al ratio of 0.0135 in the catchment area of the ENS. Granitic rocks and alkalic gneisses occur further inland in the East Greenland Caledonides north of Scoresby Sund between 69° and 74° N (Escher and Pulvertaft, 1995). This is however not apparent from Ba/Al ratios of sediments on the adjacent East Greenland shelf, as the granitic rocks do not continue to coastal areas (Fig. 1). Granites and gneisses are also widespread in the Norwegian Precambrian orogenic belts (e.g. Bingen et al., 2003) and the Norwegian Caledonides (e.g. Austrheim et al., 2003). The relatively high Ba/Al ratios of these rocks are well reflected by high Ba/Al ratios in the surface sediments on the Norwegian continental margin (Fig. 2). Granitoids of limited extent exist on NW and central Spitsbergen and on NW Nordaustlandet (Dallmann et al., 2002), and detrital input of such rocks is evident in elevated Ba/Al ratios of offshore sediments on the southern Yermak Plateau. Recent riverine sediments in Northeast Greenland are also characterized by high Ba/Al ratios (Fig. 3; GSDG data, Steenfelt, pers. comm.), highest values of 0.010 occur in a region west of Jøkel Bugten dominated by Proterozoic granulitic gneisses (Fig. 2; Escher and Pulvertaft, 1995) and on the adjacent shelf high Ba/Al ratios are present. Ba/ Al ratios of Scandinavian riverine sediments are equal to those in East Greenland (Fig. 3) and result from the high portion of acid magmatic and metamorphic rocks in the Scandinavian Shield. Anomalously high Ba/Al ratios of N 0.5 are limited to Al-poor

5.5. Detrital Ba/Al ratio Most studies of Babiogenic used a global ratio for Ba/Aldetrital of c. 0.0070 (e.g. Dymond et al., 1992; Nürnberg et al., 1997) and a constant ratio of 0.0065 has been applied for surface sediments of the Arctic Ocean and the northeastern ENS by Nürnberg (1996). The average Ba/Al ratio of 0.0070 for catchment rocks around the ENS compiled in this study (Table 3) is close to the average value of 0.0074 for marine surface sediments in the ENS (Table 2). Both values lie within the wide range of estimated values (0.0037 to 0.010) for the average composition of the upper continental crust (Wedepohl, 1995; Reitz et al., 2004). This indicates that the major part of Ba in the terrigenous surface sediments of the ENS should be detrital and not biogenic in origin. A high variability in the composition of terrigenous detritus in the ENS is apparent from Al/Ti ratios (Fig. 4b) and magnetic susceptibility (Fig. 4c) of surface sediments. This limits the use of Babiogenic calculated with a constant Ba/Aldetrital ratio of 0.0070 (Fig. 4d) in this area. Therefore, the regional Ba/Aldetrital ratio of the terrigenous fraction in the ENS has been assessed from the compilation of bulk analyses of potential catchment rocks. Examples for areas with high- and low-Ba/Al ratios in the catchment rocks and offshore sediments are described in the following. As Ba is a lithophile element, the Ba/Al ratios of magmatic rocks increase with progressive differentiation, as Ba substitutes K in K-feldspar. There is a large range of average Ba/Al ratios of catchment rocks around the ENS from 0.001 in mafic rocks to

Fig. 3. Average values and standard deviations for Ba/Al ratios in rocks of the catchment areas around the European Nordic Seas. Shown are the main rock types and some frequent lithologies. For comparison, the presented basaltic rocks belong to the North Atlantic Large Igneous Province of Cretaceous to recent age, Paleozoic or Precambrian basalts are not included. Carbonatite rocks are shown as a Ba-rich endmember only, their distribution is very limited.

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rocks rich in calcite: in Norwegian marmor (LITO-Project, http:// www.ngu.no/lito/) and in silicocarbonatite in Southwest Greenland (Fig. 3; Taubald et al., 2004). Outcrops of these rocks are of limited extent and can be neglected as potential source of detritus in the ENS, whereas sedimentary carbonatic rocks are widespread in North Greenland (Higgins et al., 1991). Apparently, elevated Ba/Al ratios on the NE Greenland shelf, around Spitzbergen including the southern part of the Yermak Plateau, and in the SE Norwegian Basin result from the input of Ba-rich terrigenous detritus. In these areas the existence of biogenic Ba remains uncertain. The same holds for the area around the volcanic island of Jan Mayen, where Neogene and Quaternary basic and acid volcanics crop out, with a Ba/Al ratio of 0.009 (only one basalt analysis; Dallmann et al., 2002; GeoRoc). In contrast, catchment areas with extensive outcrops of basaltic rocks are characterized by low Ba/Al ratios. In Mid-Ocean Ridge Basalts (MORB) Ba contents are lower than in continental flood basalts (Wilson, 1989). On Iceland, which is the most important source for basaltic detritus in the ENS, lowest Ba/Al values b 0.001 occur in MORB of the Pleistocene and Holocene Neovolcanic Zone in Northwest Iceland and in the central Iceland Rift

Zone (Jóhannesson and Sæmundsson, 1998). In East Greenland, Paleogene flood basalts on the Geikie Plateau, and to a smaller extent on Jameson Land and Wollaston Forland (Escher and Pulvertaft, 1995), have Ba/Al ratios of c. 0.003 (Table 3). Further areas with Paleogene and Neogene basalts are located on the Faeroe Islands, on the outer Hebrides (Mason and Brewer, 2004) and on the eastern Svalbard archipelago (Harland et al., 1997; Dallmann et al., 2002), but they are of limited extent. This is also valid for Archean metabasalts on the Island of Skye (Scarrow et al., 2000), Mesozoic dolerites on the eastern Svalbard archipelago (Dallmann et al., 2002), as well as further to the east on Franz Josef Land (Trelnikov, 1985), gabbroic intrusives in southern and western Norway (e.g. Alirezaei and Cameron, 2002), and mafic metavolcanic rocks in Northeast Greenland southeast of Peary Land (Escher and Watt, 1976; Escher and Pulvertaft, 1995). Outcrops of submarine basalts in fracture zones of the ENS or on the Gakkel Ridge in the Arctic Ocean (e.g. Michael et al., 2003) may be a local source of detritus. As a consequence of detrital input of basaltic rocks, fjord and shelf sediments in East Greenland between 69° and 75° N and shelf sediments around Iceland are characterized by low Ba/Al ratios.

Fig. 4. Distribution of several parameters in surface sediments of the European Nordic Seas. a) Ba/Ti ratios, data were measured during this study or by Nürnberg (1996), Paetsch (1991), Siegel (2002); b) Al/Ti ratios, same references as a. c) Mass-specific magnetic susceptibility after Pirrung et al. (2002), with additional measurements of this study. d) Biogenic Ba calculated with a constant Ba/Aldetrital ratio of 0.0070 corresponding to the average Ba/Al ratio compiled for catchment rocks around the European Nordic Seas.

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Fig. 5. Biogenic Ba in surface sediments calculated with regionally varying Ba/Aldetrital ratios. On the western Yermak Plateau and in the southwestern Iceland Sea biogenic Ba was averaged from Ba and Al as well as Ba and Ti values to account for granitic and basaltic source rocks, respectively. For references see Fig. 2.

Greater than 15% of Icelandic glass fragments are present in surface sediments of the southern ENS to the SW, S and SE of Jan Mayen Island (Bond et al., 1997), corresponding to low Al/Ti ratios (Fig. 4b) and high values of magnetic susceptibility (Fig. 4c). A more distal source region with mafic rocks is the Siberian Putoran Massif (Fig. 1) with extensive Triassic flood basalts, which have an average Ba/Al ratio of c. 0.004 (e.g. Zolotukhin and Al'Mukhamedov, 1988). Through the large Siberian rivers Ob, Yenissei, Anabar and Khatanga basaltic detritus is transported to the shelves of the eastern Kara Sea and the western Laptev Sea (Stein et al., 2004). On the shallow shelf regions, this material is incorporated into sea ice and transported to the Fram Strait via the Transpolar Drift (Wollenburg, 1993; Lindemann, 1998; Schoster, 2005). Sediments from ‘dirty sea ice’ contribute to the sedimention in the ENS by meltout especially in the marginal ice-zone. In four samples of sediment-laden sea ice, collected in the western Lapev Sea and NWof Franz Josef Land, lower than average Ba/Al ratios of 0.006 correspond to values observed in marine surface sediments of the Laptev and Kara seas (Table 2), in sediments of the Ob (0.0064) and Yenisey estuaries (0.0046). In sea–ice sediments collected in the Siberian seas the presence of detritus from basaltic rocks is indicated by high smectite contents (Wollenburg, 1993). For the lower continental slopes and the deep sea basins in the ENS, the mixing of material from different rock types, source regions and different types of erosion, transport, and deposition processes will contribute to a higher homogeneity of the terrigenous material. Therefore, the application of the overall averaged Ba/Aldetrital ratio of 0.0070 seems adequate in the Norwegian and Greenland deep sea basins. The occurrence of 59 samples with negative Babiogenic values (Figs. 5 and 6), resulting from the application of regional values for Ba/Aldetrital based on catchment rock lithology, reflects small-scale lithogenic heterogeneity, which

is also evident in Ba/Ti, Al/Ti and magnetic susceptibility data (Fig. 4). Negative values could be avoided by the use of lower regional Ba/Aldetrital values than the (conservative) estimations applied in this study, or by regional correction values based on the lowest observed Ba/Al ratio in each specific marine region. The latter approach would however lead to unrealistically low Ba/ Aldetrital and too high Babiogenic values in the entire area of the ENS. Single Babiogenic values based on regionally varying Ba/Aldetrital ratios presented in Fig. 5 should not be interpreted too far unless other samples in the immediate vicinity show similar values. There is still one area to discuss, where there occur mean Ba/Al ratios of 0.0076 in marine sediments that clearly exceed Ba/Al ratios in the surrounding catchment areas: the region between the Iceland Plateau and the Kolbeinsey Ridge. The predominantly

Fig. 6. Biogenic Ba calculated with regionally varying Ba/Aldetrital ratios correlated with export productivity estimations based on satellite, sediment trap and shipboard data (Schlüter et al., 2000). Only those stations were selected where nearby sediment trap data were available or if high biogenic Ba values were calculated.

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basaltic catchment rocks in Iceland and on the Geikie Plateau have Ba/Al ratios of c. 0.003. If a regional Ba/Aldetrital ratio of 0.005 is applied, under the assumption that one half of the detrital fraction comes from local basaltic rocks and the other half was transported by bottom currents or ice-rafting from more distant catchments with the overall average Ba/Al ratio of 0.007, then this results in average Babiogenic values of 132 ppm. In this area a significant (c. 1/3) part of the total Ba must be of biogenic origin, whereas in most other areas the primary source of Ba is terrigenous detritus. 5.6. Anthropogenic Ba Barite has been used as a tool for monitoring the impact of oil drilling platforms (e.g. Hartley, 1996), as barite is a major component of drilling fluids. Lepland et al. (2000) attributed elevated Ba contents in near surface sediments of the Skagerrak, deposited since the 1960s, to hydrocarbon drilling in the North Sea. An influence of barite discharged from oil drilling platforms may be important along the Norwegian continental margin, but the sample coverage of this study is too low to detect such an influence. In the almost absence of exploration drillings and considering the few drillings of the Ocean Drilling Program in the northern ENS, this influence can largely be excluded for the areas in the Greenland Sea and the Fram Strait, where elevated values of Babiogenic occur. 5.7. Comparison of biogenic Ba in the ENS with other areas The average Babiogenic for the ENS and the adjacent Atlantic sector of the Arctic Ocean is very low: 14 ppm calculated with a constant Ba/Aldetrital ratio of 0.0070, 37 ppm calculated with regionally varying Ba/Al ratios, or 68 ppm calculated with a constant Ba/Aldetrital ratio of 0.0065, which has been applied by Nürnberg (1996) on the Yermak Plateau and the Barents shelf. All of these values are lower than in most other oceanic regions. Some examples for studies of Babiogenic in continental margin areas are listed in the following: surface sediments in the central Arctic Ocean almost no Babiogenic (Nürnberg, 1996), deep sediment traps in the N-Atlantic on the northern Iberian margin c. 200 ppm (Fagel et al., 2004) and in the Bay of Biscay c. 290 ppm (Dehairs et al., 2000), deep sediment traps in the Ross Sea c. 400 ppm (McManus et al., 2002), surface sediments in the Amundsen and Bellingshausen seas c. 700 ppm (Hillenbrand et al., 2003). The low values of biogenic Ba in the ENS certainly result from the dilution of organic material by terrigenous detritus and by the high sedimentation rates. At most locations in the ENS the uppermost cm of sediments accumulated over the last 2.5– 10 kyr with ages b3 kyr at the majority of locations (e.g. Ritzrau et al., 2001; Nørgaard-Pedersen et al., 2003). During Marine Isotope Stage I linear sedimentation rates in the ENS were highly variable (e.g. Paetsch et al., 1992; Voelker, 1999; Vogelsang et al., 2001; Risebrobakken et al., 2003; Nørgaard-Pedersen et al., 2003; Weinelt et al., 2003) ranging from b2 cm kyr− 1 (in the central Fram Strait and in the central Greenland and Norwegian basins) to N10 cm kyr− 1 (western slope of the Yermak Plateau, lower slope of the Vöring Plateau). These rates are higher than in most open ocean regions.

5.8. Comparison of biogenic Ba with productivity Correlations of Babiogenic with other productivity proxies (Information system PANGAEA) like TOC or calcite (Taylor et al., 2002; Kierdorf, 2006), opal (Schlüter and Sauter, 2000), or δ13C of planktic foraminifers (Köhler, 1992; Simstich et al., 2003) did not result in significant correlations. Due to intense degradation of particulate organic matter in the water column, only a minor fraction (2–4% of the primary production) of organic C is exported to the seafloor (Schlüter et al., 2000; Noji et al., 2001). A varying portion of the organic C in sediments of the ENS is terrestrial in origin (Birgel and Hass, 2004; Kierdorf, 2006). Studies based on the faunal composition and/or isotopic composition of planktonic or benthic calcitic (e.g. Wollenburg and Kuhnt, 2000; Nørgaard-Pedersen et al., 2003; Simstich et al., 2003; Risebrobakken et al., 2006) or siliceous microfossils (e.g. Koc et al., 1999; Bjørklund and Kruglikova, 2003; Cortese et al., 2005) are influenced by carbonate and opal dissolution, especially in the northern part of the ENS and during glacial periods. Primary production in the ENS is characterized by distinct contrasts between the colder and warmer water masses. Recent satellite images of the NASA SeaWiFS Project (http://www.snake. ne.jp/~yama/nph-docomo.cgi/010000A/http/oceancolor.gsfc. nasa.gov/SeaWiFS/) reveal relatively high chlorophyll concentrations in surface waters during spring around Iceland, in the marginal sea ice-zone of the Greenland Sea, on the southern part of the Yermak Plateau and in the western Barents Sea, and generally low concentrations in the central part of the ENS. The relatively good coincidence of enhanced Babiogenic values with the marginal icezone points to efficient drawdown of organic carbon during phytoplankton blooms and formation of barite during the degradation of organic matter. The sample coverage of shipboard chlorophyll data measured during the spring and early summer retrieved from the NOAA database is not sufficient for a comparison with the Babiogenic data, as no values on the East Greenland shelf are included. High rates of pelagic production of c. 160 g C m− 2 yr− 1 are estimated for ice-free polynyas NE of Greenland (Walsh, 1995; Kattner and Budéus, 1997). In sediment traps enhanced fluxes of particulate organic matter have been observed in the marginal icezone of the Greenland Sea, especially during the spring and early summer (Ramseier et al., 2001). These blooms are driven by high seasonal insolation, delayed development in zooplankton, upwelling of nutrient rich meltwater from glaciers in East Greenland, from the release of dissolved and particulate organic and from nutrient-rich terrigenous material enclosed into the sea ice. In general, high primary production rates (100–200 g C m− 2 yr− 1) prevail in the Iceland Sea (Sakshaug, 2004), lower rates (c. 70–150 g C m− 2 yr− 1) occur in the eastern Greenland Sea and in the Norwegian Sea (Schlüter et al., 2000; Sakshaug, 2004; Richardson et al., 2005; Bauerfeind and von Bodungen, 2006) and low rates have been observed in permanently ice-covered areas on the East Greenland shelf (Bauerfeind et al., 2005). This trend is also indicated by the Babiogenic values, where the highest values occur on the Iceland Plateau and the Kolbeinsey Ridge (Fig. 5) and low values occur in the central part of the ENS.

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In contrast to the relatively high primary production, the export production (rain rate of particulate C to the seafloor) is very low (c. 0.60–0.65 g C m− 2 yr− 1) in the deep sea basins of the Norwegian and Greenland seas and low (c. 2–6 g C m− 2 yr− 1) in continental margin areas (Schlüter et al., 2000). A comparison of export production versus biogenic Ba calculated with variable Ba/ Aldetrital ratios is shown in Fig. 6. There is a positive correlation between both parameters (R = 0.76). This relatively moderate correlation results from 1. the uncertainties related to the estimation of export productivity from sediment trap and shipboard data and chlorophyll estimations from space, which integrate over shorter time periods compared to the surface sediments, and 2. from spatial and temporal variations in the ice-rafted debris composition at an individual location, which depends on drift paths of icebergs or sea-ice floats. Therefore, the interpolation of Babiogenic data (Fig. 5) gives a better approximation of local export production than Babiogenic data of an individual site. 6. Conclusions Most previous calculations of biogenic Ba (Babiogenic) from Ba and Al data were based on assumptions about the average crustal Ba/Al ratio (Ba/Aldetrital), which is appropriate in open ocean areas. For the application of this approach in ocean basins with significant terrigenous material transport, like those of the high northern and southern latitudes, the determination of a regional Ba/Aldetrital ratio is essential. In this study the regional Ba/Aldetrital ratio of 0.0070 for the European Nordic Seas (ENS) was determined by a compilation of Ba/Al ratios in potential catchment rocks around the ENS. However, in areas offshore of catchments with a dominance of Ba-rich granitoid resp. Ba-poor basaltic rocks a regional Ba/Aldetrital ratio leads to an over- resp. underestimation of Babiogenic. In the ENS, Al/Ti ratios and magnetic susceptibility are efficient tools to trace transport pathways of basaltic material and to establish regionally varying Ba/ Aldetrital ratios for a more precise calculation of Babiogenic. The similarity between the Babiogenic distribution in surface sediments of the ENS with phytoplankton blooms along the sea– ice margin during spring and the positive correlation with estimated export production (Schlüter et al., 2000) indicate that Babiogenic is a promising proxy to estimate paleoproductivity, and hence to reconstruct the location of the spring sea–ice margin. In contrast to other proxies, Babiogenic is relatively insensitive to early diagenetic dissolution or degradation. Therefore, this proxy should be investigated in future studies of high-resolution sediment cores from the Nordic Seas. The sites that are most probably suitable for the analysis of paleoproductivity from Ba and Al data in sediment cores are those located in the Iceland Sea and along the marginal sea–ice zone in the Greenland Sea, where the highest Babiogenic values appear. For future applications of Babiogenic a normalization to the nearly constant flux of 230Th scavenged from seawater (Francois et al., 2004) would be desirable, as temporally varying sediment accumulation ratios play a major role in the ENS. A cluster analysis of trace elements in catchment rocks and marine sediments might further improve the correction for the terrigenous fraction of Ba values.

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Acknowledgements Christoph Kierdorf, STATOIL, Stavanger, provided samples from expeditions with RV Polarstern, and TOC and carbonate data for statistical analysis. Michael Ude, Institute of Geosciences, Univ. Jena, performed the XRF measurements. The captain and crew members of RV Polarstern, RV Meteor, RV Planet are thanked for their support at sea. We thank Åke Johannsson, Swedish Museum of Natural History, Stockholm, and Sally Gibson, Department of Earth Sciences, Univ. Cambridge, for the sending of reprints. For providing unpublished data we highly appreciate Henning Dypvik, Institute for Geology, Univ. Oslo (unpublished whole-rock analyses from Svalbard), Dirk Nürnberg, Leibniz Institute for Marine Sciences IFM-GEOMAR, Kiel (Ba-Al-data of marine surface sediments), Trond Slagstad, Geological Survey of Norway, Trondheim (Ba and Al data of the LITO Project, NGU) and Agnete Steenfelt, Geological Survey of Denmark and Greenland, Copenhagen (unpublished whole-rock analyses of recent river sediments, GSDG). The staff of the information system PANGAEA, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, and Centre for Marine and Environmental Sciences, Univ. Bremen, and the staff of the GeoRoc database, Max Planck Institute for Geochemistry, Mainz, are acknowledged for their kind assistance during data retrieval. The authors greatly appreciate the funding of the Deutsche Forschungsgemeinschaft (DFG, Pi 429/2-2). Nathalie Fagel and an anonymous reviewer gave valuable and detailed comments for the improvement of a previous version of this article, which we highly appreciate. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.margeo.2008.01.001. References Alapieti, T.T., Filén, B.A., Lahtinen, J.J., Lavrov, M.M., Smolkin, V.F., Voitsekhovsky, S.N., 1990. Early Proterozoic layered intrusions in the northeastern part of the Fennoscandian shield. Mineral. Petrol. 42, 1–22. Alirezaei, S., Cameron, E.M., 2002. Mass balance during gabbro–amphibolite transition, Bamble Sector, Norway: implications for petrogenesis and tectonic setting of the gabbros. Lithos 60, 21–45. Anderson, L.D., Delaney, M.L., 2005. Middle Eocene to early Oligocene paleoceanography from Agulhas Ridge, Southern Ocean (Ocean Drilling Program Leg 177, Site 1090). Paleoceanography 20. doi:10.1029/2004PA001043. Anderson, L.D., Winckler, G., 2005. Problems with paleoproductivity proxies. Paleoceanography 20. doi:10.1029/2004PA001107. Austrheim, H., Corfu, F., Bryhni, I., Andersen, T.B., 2003. The Proterozoic Hustad igenous complex: a low strain enclave with a key to the history of the Western Gneiss Region of Norway. Precambrian Res. 120, 149–175. Auwera, J.V., Bogaerts, M., Liégois, J.-P., Demaiffe, D., Wilmart, E., Bolle, O., Duchesne, J.C., 2003. Derivation of the 1.0–0.9 Ga ferro–potassic A-type granitoids of southern Norway by extreme differentiation from basic magmas. Precambrian Res. 124, 107–148. Averyt, K.B., Paytan, A., Li, G., 2003. A precise, high-throughput method for determining Sr/Ca, Sr/Ba, and Ca/Ba ratios in marine barite. Geochem. Geophys. Geosyst. 4. doi:10.1029/2002GC000467. Ballini, M., Kissel, C., Colin, C., Richter, T., 2006. Deep-water mass source and dynamic associated with rapid climatic variations during the last glacial stage in

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