Regional distribution of manganese, phosphorus, heavy metals, barium and carbon in sea-bed sediments (0-2 cm) from the northern part of the Norwegian Skagerrak

Regional distribution of manganese, phosphorus, heavy metals, barium and carbon in sea-bed sediments (0-2 cm) from the northern part of the Norwegian Skagerrak

OLA M.SAOTHER,GJERTFAYE,TERJETHORSNES,LEIFRISE,ODDVARLONGVA&REIDULV B0 E

Seet her,O.M.,Faye, G.,Thorsnes,T.,Rise,L.,Longva O.&Bee,R.1996:Reg io naldistri bution of manga nese,pho spho- rus,heavy met als,barium,andcarbon insea-bed sediments(0-2cm)from thenorthernpart of theNorweg ian Skag errak.Nor. geol. unders.430,103-112.

Thereg io nal distribution of manganese,phosp hor us,heavy metals, bariu m and organic carbon insea-bed sedi- ments(0-2 cm)from the northernpartoftheNor weg ian Skagerrak hasbeenmap ped and theresultsdiscussedin thelightof dispersionprocessesfrom natu raland humansources.Similar distri b ut io n patternsare foundformang- anese (M n), pho sphorus (P)and theheavymetalsCr,Cu,Ni,Pb,VandZnwhich allint ercorrelatewell.Thehigh est levelsof these eleme ntsoccu r inthedeepest partsofthe Skage rrak Basin.Barium (Ba)isconce nt rate datstations located in theshallo w erwate rsintheso ut hern part of theinvest iga tedarea.Mercury(Hq),on thecont rary,hasa bim od al dist rib ut io n,being enr ichedin the northernmost area andalo ng theNor w eg ian sout hcoast.The high est co ncent ratio ns oftota lcarbon andorgan iccarbo nare foundatint ermediatewater dept hsaroundthe perimeterof the deep Skagerrak Basin. Acco rdingtothe StatePolluti on Aut ho rity's (StatensForu rensn ingstilsyn1993)classifica- tio n ofthe cond it io nofsedim entsbasedonconcentr ationsof heavymet als(Cat eg ory I=Good,11=Fair,lIl=Poor,lV

=Bad,V=Very bad) ,the sea-bedsedi m entsin the northernpart of theNorwegianSkag errakfall inCategory11 wit h respectto NiandPb andinCategoryI with respectto Cr.Cu and Zn.

Ola M.Seether, GjertFaye,Terj eThorsnes,LeifRise,OddvarLongva&Reidulv Bee,Geological Survey ofNorway,Postboks 3006 Lode,N-7002Trondheim,Norway

Introduction

The Geological Survey of Norway, in cooperation with the University of Bergen and several other scientificinsti t uti- ons, has had responsibility for coordinating geochemical, geological and geophysical mapping of the sea-bed and its immediate subsurface in the Norwegian part of the Skagerrak.The Skagerrak is one of three principalareasin the North Sea (the other two are the Wadden Sea and the German Bight) where deposition of natural and anthro- pogenic suspended matter occurs today. In this contribu- tion we present the results of the geochemical mapping of sea-bed samples collected during the 1992 and 1993 cruises with emphasis on the lateral distribution of mang- anese, phosphorus, heavy metals,barium, and totaland organic carbon in the top0-2cm. These parameters have been chosen because some of them are perturbed by anthropogenic activity and are indicators of pollution by man.In addition,some of them act as activeadsorbates or sinks for the heavy metals investi gated and thus affect their distribution.These data reflect the effect of trans- port and depositional processes on the distributio n of contaminants,and give importantinformati on about the current extent of sedimentpollution wit hin thiskey area of the NorthSea.

The bathymetry of the Skagerrak is characterisedby a

600-700 m deep, elongated trough, the Norwegian

Trench,with its long axisoriented northeast-southwest (Holtedahl 1986) (Fig.1).Several currents merge in the Skagerrak.The Baltic Current drains brackish water north-

wards through the Kattegat and into the eastern part of the Skagerrak(St igebrandt 1983)where it converges with the northeasterly longshore Jutland Current,which swe- eps the western side of the Jutland Peninsulaand is fed by some of the largest rivers in northwestern Europe(e.g.

the Elbe, Ems,Meuse, Rhine,Thames and Weser).Water masses from the northeast Atlantic Ocean, which enter the Skagerrak basin at depth from the west (Danielsen 1991),are high in nutrient elements and total dissolved solids.The influx of water massesis balanced by water leaving the Skagerrak in a southwesterly direction as the Norwegian Coastal Current (Larsson&Rohde 1979,van Weering 1981).The coalescence of these major currents causes an increase in sediment transport capacity and subsequent sedimentation in the deeper,central parts of the Skagerrak.However, the sedimentation processes are complex because of stratification of the water masses, resuspension of bottom sediments duringextreme weat- her conditions,and a mixture of anthropogenic and natu- ralsources.The provenance of the sediments isthus by no means straightforward.

The highest sedimentation rates within the studied area are measured in the southern and northeastern parts(Eisma&Kalf 1981,van Weering 1981).The sedi- ments withinthe Skagerrak are transported by suspensi- on and consistmainly of clay and silt,but samples from the southern most stations(64,65and66,see Fig.1)and single stations close to the Norwegian mainland (Eisma 1981,van Weering 1981, van Weering et al. 1987,1993, Eisma&Kalf 1987,B0e et al. thisvolume)consistof a sig-

104 010M. $a:rher,Gjerr Faye,Terje Thorsnes,ieiiRise,OddvarLongva& ReidulvBee GU-BULL 430,1996

•

Norway..Denmark median line

-L._ -

N

L

NORWAY

... ___ · ·..·· 7 __

^~

- __ __ .. ____ __ -_ _ , _ .

Fig.I.Samplingstations(numbered2-75)and bathymetry(contourinterval 100m)of thenorthern parrofrheNorwegianSkagerrak.

nifican tporti on of fineand very finesand,

Cores of accumulated bottom sedime nt s from the Skagerrakshould give the bestindicati on of the general trends inNo rthSeawat er qualityover time and parti cu- larly ofthecon t amin ant contentof the suspended parti- cu late matter in the water masses (Turre ll 1992).Earlier geochemicalworkon sedimentsfromthe Skage rrak has focused on a wide range of dispersion processes and sources which might have caused the present vertical andlateral distributionof heavymetals(Anton etal. 1993, Forstne r&Reineck1974,Dominiket al. 1978,Kuijpers et al. 1993,Kunzendorfet al. thisvolume),Attemptsto esti- mate the enric hmentfactorsof heavy metals in Skagerrak sediments have been made by Cato (1977, 1986), Erlenkeuser & Pederstad (1984), Muller & Irion (1984), Holtedahl(1986) and Pederstad et al.(1993).

Sampling and analytical methods

Sediment cores were collected dow n to a sedim ent dept h of about 50cmusing a Niemistb®corer(Niemistb 1974)at eachof the 74 sampling stati ons(numbered 2-55 and 56-75 fo rst atio ns sampled during the 1992an d 1993 cruises,respectiv ely) (Fig.1).Sub-samples for geochemi- cal analyseswere collected onboard bycutting the sedi- ment core into ten2cm-thick slices downto 20 cm depth andthen at 25-27cm,35-37 cm,45-47 cm and 55-57cm depth below the sediment/wate r interface.The sliced geochemical sampleswereim med iat ely frozen at -18"(

and later freeze-dried.The inorganiccompon ents were extracted with 7N HN0₃in anaut oclaveat 120°Cfor one hour in the laboratory (Norsk Standard 1980).The ele- ment contents were determined by using inductively coup led plasma(ICP-AES)for barium (Ba),chrom ium(Cr),

NGU-BULL430,1996 010M.Seetber,Gje rt Faye,TerjeThorsnes,LeifRise,OddvarLongva&Reidulv80e 105

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M n P Pb Cr C u N i Z n V Hg Ba TC T OC

Fig.2. Scatter diagrams and correlati on coefficients calculatedon log1a-transfor- medconcentrationsoftheanalysedpara- meters in top 0-2cm related todep th(m) below sea level.

copper (Cu), manganese (Mn), nickel (Ni),phosphorus (P), lead (Pb),vanadium (V)and zinc (Zn) (0degihd 1987),and by cold vapour atomic absorption spectroscopy (AAS) for mercury (Hg) (Hatch&Ott 1968).In addition, total carbon (TC) and total organic carbon (TOC) were determined by ignition using a LECO®stove.

Results and discussion

Co-variations betweenparameters

A correlation matrixfor the logl o-transformed data and a scatter-diagram with the linear data, all plotted versus water depth,are shown in Fig.2.The positive correlation (r>0.50) between the heavy metals Pb,Cr,Cu, Ni,V, Zn, and partially TC and TOC,with Mn and P,suggests some similaritieswith regard to source and fatein thisenviron- ment.Between this group of elements and Hg or Ba there is no significant correlation.Nor is therea significant cor- relationbetween Hg and Ba.Thisindicates that theseele- ments have separate sources and modes of occurrence.

Manganese correlates very well with water depth (r=0.87),V (r=O.90)and P (r=O.82)and fairly well with Zn (r=O.7l), Cu (r=0.56), Cr (r=0.50) and Pb (r=0.70).

Vanadium correlates very well with Mn (r=O.90) and P (r=0.86),with the heavy metals Pb (r=0.80),Cr (r=0.76),Cu (r=O.77), Ni (r=0.94)and Zn (r=O.88),and with water depth (r=0.84).Vanadiumeo-precipitateswith Mn during diage- nesis,and shows a more linear increase in concentration as a function of water depth than manganese (see Fig. 2).

Thisprobably reflects the property of V to appear in seve- ral oxidation states (+11, +111,+IV and+V), e.g.it is the key transition metal in homogeneous catalytical respiration ofsome lower marine biota(Hagg 1966);and the oxidati- on state of vanadium is also sensitive to the periodically reduced oxidising conditions in the water column and the reducing conditions interstitiallyin the sedimentsjust below the sediment/waterinterface.Thiscould possibly be associated with a gradually diminishing transport capacity of the water currents with respect to particulate matter, including vanadium-bearing particles,as a result of increased water depth or an increased f1occulation with depth of Mn-particles scavenging vanadium and

106 010 M.Seetbet,GjertFaye,TerjeTbotsnes.LeifRise,OddvarLongva&Reidulv Bee NGU-BULL 430,1996

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Fig.3.Theconcentration in surfacesediments (0-2 cm)ofa)Mn,b)P,c)Pb,d)Cr,e)Cui,f)Ni,g)V,h)Zn,i)Hg,j)Ba,k)TC and/)TOCThe symbols on the maps arechosenaccordingto proceduresdevelopedforExploratoryData Analysis (EDA)asshownby Tukey(1977)and Hoaglinetal.(1983).The symbolsarelinked to a boxplot showing the concentration level for the<25(0),25-75(.)and>75(+)percentiles,Thebar-line in the box-plotindicatesthe50%-value.Larger open circles(0)and solidsquares )are chosenas symbolsfor samples withextremely low and extremely highconcentrations asindicatedin thelegend in the lower rightcorner.

NGU-BULL 430,1996 010M.Sonhet, Gjerr Faye,Terje Tbotsnes, LeifRise,OddvarLongva & ReidulvBee 107

II ⁺

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Mercury

Total Carbon

k ^{0 -}

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Te % I

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0 -

^0.89

T OC %

108 010M.Seetber,GjerrFoye,TerjeTborsnes,LeifRise,OddvarLongva&Reidulv B0e NGU-BULL 430,1996

, , { " } - " j

Pl

40 60 80 100 120 140 160 180 5

35

25 30

15 10

950 1050 1150 5

o

+""t~=R++-t++-++-rl--+-i 450 550 650 750

15

10

1600 2000 p

8000 1200 4000

20 30

10

O-+-+--HH~~-f=:+:~~

Mn

⁰

50 40

45 35

40

35 30

30 25

25 20

20 15

15 10

10

5 5

0 0

Cr ^{20 2530 354045 50 5560 6570 75 8085 90} Cu ⁶

20 18 16 14 12 10 8 6 4 2

o

-t--"H-t--+-+-H-+-+-+-+-!H -l

10 14 18 22 26 30 34 38 42 Ni 1416 18202224262830323436 384042

5

2

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40 50 60 70 80 90100 110120 130 140150 V 40 60 80 100 120 140 160 180 30

20 25

15 10 20

25 35 30

15

H

5 25 20 30

15 10 45

40 35 30 25 20 15 10 5

O-H~~~~~--+--W--R o#~4-I-+-U-W~~'r"""T"""1

TC 1.8 2.2 2.6 3.0 3.4 3.8 4.2 4.6 TOC0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 5

20 25

15 10

o

+-I-+-I--.J-+-J--.l--.jP;=t~""I""t:=I=I=:;:::+:1

Ba 60 100 140 180 220 260300340380420

Fig.4.Histoqram andfrequency distrlbution of elements mapped in Fig.3.

NGU-BULL 430,1996 010M.Seetbet,GjertFaye,TerjeThorsnes,LeifRise,OddvarLongva&ReidulvBee 109

other heavy metals.The heavy metals Pb,Cr, Cu, Ni and Zn show,except for a few outlying values, a nearly log- linear positive dependency with water depth. The con- centration of Hg decreases as a function of water depth, whereas Ba, TC and TOC are enriched at intermediate water depths (Fig.2).

Regional distributionofelement contents

The regional distributions of Mn, P, Pb,Cr, Cu,Ni, V, Zn, Hg, Ba,TC and TOC in the sediments 0-2 cm below the sediment/water interface are presented in the geochemi- cal maps shown in Fig. 3. This sequence of presentation is chosen because of the link between Mn and P with Cr,Cu, Ni, V and Zn revealed by the correlation analysis. The dis- tributions of Hg,Ba and TCITOC are each distinctly diffe- rent.

Manganese (Mn)

5ediments with the highest concentrations of mangane- se are found in the deeper parts of the investigated area at more than 500 meters of water depth.At these depths the concentration of manganese in the sediments is abo- ve 5,000mg/kg with a maximum value of 21,300 mg/kg.

The median level of manganese is 1,250 mg/kg for the whole dataset,reflecting the positive skewness of its fre- quency distribution(FigA ). Manganese is of considerable interest in this study, because it is widely used in industry and also affected by diagenetic processes. The latter take place when manganese in the sediments is mobilised by reducing processes and transported by diffusion to the sediment/water interface where it is oxidised and precipi- tates with iron as Fe-Mn-oxy-hydroxides. Moreover, these processes affect the concentration of other heavy metals like Cu, Ni, V and Zn, which are scavenged by the oxy- hydroxides (Jenne 1976).

The high concentrations of manganese at stations with water depths greater than 500 m partly reflect the redu- cing conditions in the sediments immediately below the water/sediment interface. This situation has probably been stable for many centuries.However, the general redox state of the local environment should be monito- red in the future,especially with respect to indicators of chemical processes leading to the decomposition of organic matter, such as: 1) oxygen consumption, 2) nitra- te reduction, 3) sulphate reduction and 4) methane for- mation (Berner 1971). Stagnant conditions leading to decomposition of organic matter and mobilisation of tra- ce metals have only been reported from uncontaminated fjords in which circulation is hindered by sills at the outlet (Piper 1971,Skei 1983),and from fjords with an unusually heavy anthropogenic load.

Phosphorus(P)

Phosphorus shows a similar distribution to that of mang- anese with concentrations ranging from about 500

mg/kg in the northeast and southern parts of the investi- gated area and along the south coast of Norway to above 1,000 mg/kg in the deeper(more than 400 m depth)parts of the basin(compare with Fig.1).However, although the areal distributions of these two elements coincide and as it is known that P is incorporated in Mn-oxyhydroxides (Cronan 1976),the factors influencing the distribution of phosphorus are thought to be more of a biological and sedimentological nature than diagenetic. Since a major source of phosphorus is sewage effluent,it is most likely associated with fine particulate matter,e.g.dead algae, which settles in the deeper parts of the basin where the currents are weak.Another possible anthropogenic sour- ce of unknown magnitude is effluent from the producers of fertilizers for agricultural purposes.

Lead (Pb)

Lead is enriched in the deeper parts of the investigated area and ranges from 24 to 177 mg/kg; with a median value of 58 mg/kg; which is well above the average of 23 mg/kg cited for siltstone (Lovering 1976) and the 25-30 mg/kg shown on maps of the concentration of Pb in overbank deposits in southeastern Norway (Bogen et al.

1992). However,the measured values are comparable to the median 60 and maximum 240 mg/kg reported for 100 argillaceous bottom sediments from the Atlantic Ocean and the Carribbean Sea(Ericson et al. 1961).

Lead has been used by man over the last three mille- nia, but a significant increase in lead emissions to the atmosphere has occurred in this century,and in Europe especially since the 1950'swhen lead alkyl compounds were added to petrol as an anti-knock agent. During this process it is injected into the air by car exhaust as minute elemental or oxide particles and dispersed in the lower atmosphere until it precipitates with rain or snow. Worldwide consumption of leaded petrol peaked at c.

253,000 tonnes in 1970-71 (Nriagu 1990).Other uses of lead, e.g. in car batteries, as a component in anti-corrosi- on boat coating, and in ammunition both for hunting and for military purposes (World War I and 11), might directly or indirectly have been the sources for some of the lead measured in these sediments. Air pollution is probably the dominant source of lead not bonded in the crystallat- tice of silicate minerals in these sediments (Pacyna,pers.

comm.1995).

Chromium (Cr),copper (Cu),nickel (Ni),vanadium (V)and zinc (Zn)

The regional distributions of the elements Cr,Cu,Ni, V and Zn are very similar to those of manganese,phospho- rus and lead, as is to be expected from the correlation analysis.The frequency distribution (Fig. 4)of these ele- mentsis unimodal with a fairly narrowran g e around the mean,except for V which seems to have two modes.This could reflect a clastic and diagenetic or biological mode of occurrence, or a separate anthropogenic source in

110 010M.Senber:GjertFaye,Terje Thotsnes.LeifRise,OddvarLongva& ReidulvBee IGU-BULL430.1996

addition to the nat ural ones.Chromiumand copperhas, asis the casefor lead,distinct outlying values,possibly reflectingthe natural and anthropogenicsources.

In general,the lowest concentrations are measuredat the northernmost and southern most stati ons where the water dept hs aresmall.At morethan about400 mdepth, the con centrations of the metalsin the sediment sare slightly higher than the median valuewit hthe high est concentra t ions present in the deepest part of the Skagerrak.

Mercury(Hg)

Mercury is presentat ratherlow concentrations throug- hou tthe investi gated area andrangesfrom 0.02to0.10 mg/kg with amedian value of 0.06mg/kg. The highest values arefound in the nort hernmost part of thestu dy area (stat ions 2-10), where the sed iment at ion ratesare the high est (Bee et al. this volume),and alon gthe sout h coast of Norwayat thesam plingstation s19,30,37,48, 59,60,71 and 72which are located at relatively shallow depths(see Fig. 1).Mercury shows adist inctbimoda ldis- tribution suggesting that theremig ht be atleast two dif- ferent modes of orig in (Fig.4).One oftheseisprobably the chlor-alkaline industry located along the Swed ish west coast(Cato 1977, 1986)andalongthe Glom ma River at Sarpsbo rg andin the Langesundfjordareain southeas- tern Norway. Mercury hasalso been used in the paper industrytoprotect tim ber frominfestati on andinagricul - tureto protect cerealseedsfrom decay beforespr out ing.

A thirdgeneralsour ce ofmercuryis public sewage con- tainin g contribu t ion s from dental office s.This amounted to a releaseofabout onetonneHg/yr in the mid-1980 's (5t atensForurensningst ilsyn(SFn 1990).Emissions ofHg to the atmosphere from point sources in sou theast ern Norway have beenestimate dto be at 55 tonnes Hg in the period 1940-1980(Anderson etal. 1987).

Barium(Ba)

Although Ba is not a heavy metal with prove n toxic effects,it is of interest in thisst udy because barit e (BaS0₄ with a density of 4.48 q/c rn') isabundantly used as an addit ive todrilli ng mudin the offshore industry. Barium

as barite maythus act asa tracerofdrilllinq for pet roleum offshore.The concentration sof barium in thesediment s range from about69 mg/kg to a maximumof433 mg/kg . In the southern mostpart of the sam pledareait occurs in concentrations of more than 200 mg/kg and is clearly associated with the coarser sediments(Bee et al.1995).

Using ascanningelectronmicroscope(JEOL)wit h a back- scatter imagi ng capability, we have proven that, at Statio ns 53,54,65,66 and 67,bariumoccursas discrete grainsof barit e.Thebarite grains in thesesamplescould be eitherdiagenet icordetrital. Barite is virtuallyinsoluble inwater. To whatexten t Bais affected bydiff usion pro- cesses and diageneticenrichment in the top of these sea- bed sediments is not known.A diageneticformation of barit e crystals wouldpresumablyleadtoaut higenic,well crystallisedmineralgrains.Since the barite grainsobser- ved inthesesamples seem to be pseudo sphericalwit h about 10 urn diameter,Le.smaller thanthemedian dia- meterofthe sediment grains in these samples,we assu- methey aredet rit al,prob ably deriv edfrom drilling muds used by the offshore indust ry in the North Sea. In the shallow er watersalong the coast and in the northern- most areaswherethesedim entation ratesare high,the concentratio nofBa is below100 mg/kg .

Totalcarbon(TC) andtotalorganic carbon (TOO

Totalcarbo nandtotal organiccarbon cor elatevery well (r=0.91) and exhib it sim ilar dist ribution patterns, which are distinctly different fro m those of manganese and phosphorus.The highestvaluesarefound atintermed ia- te water depths in the sou th ern partof the investig ated areaand aroundthe perimeterof the basin.The C/Nrati o of the organic matter in the sedirnents from the Skagerrak isbetween2 and 14(Olausson 1975)indicati ng mainly amarine origin. According to van Weering et al.

(1987) 400-600,000tonnesof organiccarbo naccumulate eachyearin theSkagerrak.

Comparison with pollution standards

The statisticsof our results arelistedinTable 1 together with the limitsused for classificatio n into five categories

Table 1.Min im um,medianand maximumconcentratio nsof manganese,pho sphoru s,heavy metals,bariumandcarboninsea-bed sediments(0-2cm) fromthe northernpart of the NorwegianSkagerrak com paredtoclassification limi t s(ClassI-V)givenbytheStatens Forurensning stilsyn(1993).

Min Median Max 11 III IV V

Mn 163 1250 21300

P 463 937 1200

Pb 24 58 177 <30 30-120 120-600 600- 1500 >1500

Cr 22 48 86 <70 70-300 300-1500 1500-5000 >5000

Cu 6 17 42 <35 35-150 150-700 700-1500 >1500

Ni 15 32 42 <30 30- 130 130-600 600-1500 >1500

Zn 45 105 148 <150 150-700 700-3000 3000-10000 >10000

V 41 108 173

Hg 0.Q2 0.055 010 <0.15 0.15-0.6 0.6·3 3·5 >5

Ba 69 136 433

TC 1.91 3.68 4.42

TOC 0.89 2.17 2.70

NGU-BULL 430,1996 010M.Ssn het,Gjert Faye,Terje Thotsnes,LeifRise,OddvarLongva&Reidulv Bee 111

(Category I

=

Good, 11

=

Fair, III

=

Poor, IV

=

Bad,V

=

Very bad) of the general condition of sediments with respect to their contamination of heavy metals (Statens Forurensningstilsyn 1993), Because of the unknown effect of different mineralogical compositions and appli- ed analytical methods, a direct comparison should be car- ried out only with caution.However, if one compares the median value of our samples with that of each class, it seems as if these sediments are at least contaminated according to the levels in Category 11 with respect to Ni and Pb (except for at Stations 63 and 64, which have hig- her concentrations of lead and belong to Category 111), and Category I with respect to Cr,Cu and Zn. The levels of Hg are all below the upper limit of CategoryI.

Conclusions

The distribution of the heavy metals Cr, Cu, Ni, Pb, Vand Zn in the top 0-2 cm of sea-bed sediments from the nor- thern part of the Norwegian Skagerrak seems to be strongly dependent on water depth,and on the distribu- tion of manganese and phosphorus.A regional dispersi- on pattern with deposition in the deeper parts of the basin seems to be dominant for most of these heavy metals.There is a widerange of both natural and anthro- pogenic sources for the heavy metals in these sediments and an assessment of the contributions from different natural and anthropogenic sources is part of a separate study. The distribution of Hg is different from the other heavy metals and probably reflects the contribution from several anthropogenic sources in addition to the natural ones.One ofthese is the industrial activity in the northern and eastern areas outside the investigated area,and a second source is public sewage effluent from towns along the south coast of Norway (St at ens Forurensningstilsyn 1990).Barium is not a heavy metal, but shows an enrichment as detrital grains of barite in sediments in the southern part of the studied area, where the coarsest sediments occur. The source of this barite is thought to be drilling mud used in the offshore industry.

The general level of contamination in the investigated area ought to be monitored in the future with reference to the data presented here. Compared to the State Pollution Authority's (St at ens Forurensningstilsyn 1993) classification (I-V)of the generalcondition of the conta- minationlevel of sediments based on theirconcentration of heavy metals,the sea-bed sediments (0-2 cm) in the northern part of theNorweg ian Skagerrakfall int o cate- gory 11 with respect to Niand Pb and in category Iwith respect to Cr,Cu and Zn.No classification isavailabl e for the other parameters discussedin thispaper.

Acknowledgemen ts

R. T.Ottesen,M.Paetzel,e.Reimann and H.Schrader arethan kedfor construct ive sugg estionsfor imp rovem ent sinanearlierversionofthis manuscript.

References

And ersson , T"Nilsson, A.,Hakanson,L.&Brydste n,L. 1987:Kvicksilveri sven skasjoar.StatensNa tu rvc'ird sverk,Rapport3291,92pp.

Anton,K.K.,Liebezeit,G.,Rudolph,e.&Wit h,H.1993:Origin, distributi- onandaccum ulat ionof organiccarbon in theSkag err ak. Mar. Geol.

111,. 287-297.

Bern er,RA 1971:Principlesofchem ica lse dimentology.McGraw Hill,New York,240pp.

Bog en, J.,Belvik en,B.&Ottesen,R.T.1992:Environm ent alstudiesin WesternEuropeusingoverba nksediment.InBog en,J"Walling,D.E.

& Day, T. (ed s.): Erosion and Sediment Transport Monitoring Programmesin RiverBasins.Pro ceed ingsofthe Oslo Symposium, August 1992.IAHSPubl.No,210.

Bee, R,Rise,L.,Thorsnes,T.&de Haas,H.,Saet her,O,M,&Kunzendo rf,H:

Sea bed sediments and sediment accumulation rat es in the Norwegian part of theSkagerrak (t h is volume).

Cato,I. 1977:Recent sedime nto logicalandgeochemicalcond itions and poll ut ion pro b lemsin tw omarin e areas insouth-w esternSweden. Striae6,158pp,

Cato,I.1986: Sedime nt ens belastn ing avtungmetall erochnarsalteri Gbtebor g s skarga rd 1982, samt forandrin qar efte r 1966. Univ.

Gothenborq,Dept.of MarineGeology,Rep .2,94 pp.

Cron an,0.5.1976: Manga nesenodu lesand ot he r ferro-m ang anese oxi- de deposits. In Riley, J.P. & Chester, R. (eds.): Chemical Oceanography.2ndEdit ion,Academic Press,5,.217-26 3.

Dahl, F.E. 1978:On the exist enc e of a deep counter-current to the Norw eg ian coastal curre ntin Skagerrak.Tellus 30,552-556. Domi nik,J.,Fbrstner,U,Mang ini,A.&Reineck,H.E.1978:Pb-210andCs-

137 chronolgy ofheavymetal pollutionin a sediment core fromthe German Bight(Nort hSea).Senckenb ergianaMarit ima 10,213-227. Eisma,D.1981:Supplyand depositi on ofsuspended matterin the Nort h

Sea.In Nio, S. D., Schiittel helm &van Weering,T.e. E.(eds.):

HoloceneMarineSedime nta tion in theNort h SeaBasin.Spec. Publ.

Int. Asso c. Sedi m ento l. 5,415-428.

Eisma,D.&Kalf,J.,1987:Dispersal,conce nt rat ionand dep osition ofsus- pended matterin the NorthSea. Jour. Geol.Soc.Lon don144,16 1- 178.

Ericson,D.B.,Ewing,M.,Woll in,G.&Heezen,B.e.1961:Atl an ti c deep-sea sedi me ntcores.Bull.Geol. Soc. Amer.72,193-285.

Erlen keu ser,H.&Ped erstad, K.1984: Recentsed ime ntaccu m ulatio n in the Skagerrak as dep icte d by 210Pb dating.Nor.Geol.Tid sskr.64, 135-152.

Fbrstner, U. & Reine ck, H.E. 1974: Die Anreic heru ng von Spurenelemente nin denrezen ten Sed imen t en einesProfi lkerne s ausder DeutschenBucht.SenckenberqianaMarit.6, 175-184. Hatch,W.R&Ott,W.L.1968:Determina t ionofsub- microgram quant iti-

esof mercury by atomicabsor ptionsect rophot om etry. Analytical Chem.40,2085-2087.

Hag g, G. 1966: Allm an ochoorganisk kemi.4th Edition, Almquist &

Wiksell,764 pp.

Hoagli n,

o.c ,

Moste ller,F.&Tuk ey,J.w.1983: Understa ndi ngRobustand Exploratory DataAna lysis,JohnWiley,New York, 447pp.

Holte dah l, H. 1986:Seafl oo r morphol og y and Late Quate rnary sedi- mentssouthof Langesundsfj ord, nort heasternSkagerrak.Nor.Geol.

Tidsskr.66,311-323 .

Jenne,EA 1976:Trace elemen tsorption bysed imentsandsoils-sites and processes.InChap pell,W.&Pet erson,K.(eds.):Symposi umon Molybden um.Vol. 2.Marcel Dekker,New York,425-553.

Kuij pers,A.,Denneqard,B.,Albinsson,Y.&Jensen,A. 1993:Sediment transport path ways inthe Skagerrakand Kattegat asindicatedby Chern obyl radi oactivity and heavy metal concentrati ons.Marine Geol.111,231-244.

Kunzend orf,H.,Longva,O.&Paetzel,M.1996:Recent sedimentat io n rat esacro sstheNorw eg ian Troug h(thisvolume).

Larsson,A.M. &Rohde,J.1979:Hydr og rap hical andchemicalobservati- ons in the Skag errak 1975-1977. Repor t 29. Oceanographiska lnst itutionen,Goteborq Universitet,Gothe nb urg,Swed en,170 pp. Lovering,T.G.1976:Abundance of lead in sedimentary rocks, sedi-

merits, and fossil fuels. In Loverin g, T.G. (ed.): Lead in the Enviro nment.U.S.Geol.Surv.Prof.Paper957,31-34.

Niemisto, L. 1974: A gravity corer for st udies of soft sedi ments.

Meretutkiuslait.JultJHavforskningsin st.Skr.238,33-38.

112 010M.Seetbet,GjerrFaye,TerjeTboisnes,LeifRise,OddvarLongva& ReidulvBee I~GU-BULL430,1996

Norsk St and ard1980:Vannu ndersokelse. Met allerivann,slam og sedi- ment er.Norsk Standard P193,NS4770, 243-251.

Nriagu,J.O.1990:The rise and fall of lead ed gasoli ne.Science Total Environment,992,13-28.

Muller,P.J.&Irio n,G.1984 :Chronologyof heavymet alcontaminati on from the Skagerrak.Mitt.Geol-Pataontot.Inst.Univ.Hamburg56, 413-42 1.

Olausson,E.1975:Man-made effect on sed iments from Kat te gat and Skagerra k.Geo/.Foren.Stockh.Forh.97,3-12.

Ped erstad,K.,Roaldset,E.&Ronningsland,T.M. 1993:Sedi ment ati o n and enviro nm ent al conditio ns in the inner Skagerrak-outer Oslofjord.Marine Geol.111,245-26 8.

Piper,D.Z.1971:The dist ribu t io nofCo, Ci,Cu,Fe,Mn,Ni,and Zn in Framvaren,a Norwegiananoxicfj ord.Geochim.Cosmochim. Acta35, 531-550.

Skei,J.1983:Geochemicaland sedi ment olo gic al considerat ion s ofa perma nent ly anoxic fjord-Framvaren,SouthNorw ay.Sed.Geo/.36, 131-145.

State nsForur ensning stilsyn(Sf'T)1990:Mat erialst ro msanalyseav kvikk- solvholdigavfall,SFT100ITA688,30pp.

St at ens Forur ensni ng stilsyn(Sm 1993:Klassifi seri ng avmiljokvalitet i fj or de r ogkystfarv an n.Generelldel.SFT-veiledning nr.93:03

Stig ebrand t,A.1983:A model for theexchangeof waterand salt betwe- entheBaltic andthe Skagerrak.Jour.Phys.Oceanography 13,411- 427.

Tukey,J.w.1977:ExploratoryDataAnalysis.Add ison-Wesley,Readi ng.

MA,506pp.

Turrell,W.R.1992:New hypothesescon cerningthl!circulation of the northernNorthSea andit s relatio n toNort h Seafish stockrecruit- ment.ICESJour.MarineSci.49,107-123.

van Weering,T.CE.1981:Recentsedim ents and sediment transportin thenorthern North Sea:surfacesedi m entsof the Skagerrak.lnNio, S.D., Shu t te nhelm. R.T.E. &van Weeri ng T.CE. (ed s.): Holocene MarineSedimentat ion intheNorth SeaBasin,Spec. Pub l.Int.Ass.

Sedi men t.5,335-360.

van Weering,T.C E.,Berger,GW.&Kalf,J.1987:Recentsedim ent accu - mulat ionin theSkagerr aknorthea stern Nort hSea.Neth.Jour.Sed.

Res.21,177-189.

van Weering,T.CE.•Rum ohr,J.&Liebezeit,G.1993:Holocenesedimen- tatio nin theSkagerrak:a review.MarineGeo/.tt ;379-39 1.

0degard.M.1981:The useofinduc tivelycou pled argonplasm a(ICAP) atom ic emission sp ect rosco pyin theanalysis ofst ream sediments.

Jour.Geochem.Explor.14,119-130.

Manuscript received May1995;revised versionacceptedJanuary 1996.