Recent changes in environmental conditions in the south­ western Kattegat, Scandinavia

CHRISTIAN CHRISTIANSEN, HELMARKUNZENDORF, MARIO J.e. LAIMA, LARSe. LUND-HANSEN& ANETTE M. PEDERSE N

Christiansen, C, Kunzendorf, H., Laima, MJ.c.. Lund -Hansen, L.e. & Pedersen, A.M. 1996: Recent changes in envi ron­ mental condi tions in th e southwestern Katte gat, Scandinavia. Nor. geol. unders. Bull. 430, 137-144.

Short cores (20-30 cm) we re taken from two sites in the southweste rn Kattegat at similar wate r depths «20 m; under the pycnocline) but wi th different exposures and resuspen sion rates (gross sedime ntati on rates: 34 19 and 6275 g m-2 y-l , net sedimentation rates: 469 and 479 g m-2 v'. respect ively). They were dated by 210Pb and analy ­ sed for their content of organic matter, bulk density, forami nifera, selected elements and grain-size distribut io n. Drastic change s in the foraminiferal fauna (from a nearly 100% agglutinated to about 75% hyaline fauna ) as well as in bulk sediment density and contents of especia lly Ba (0.7-0.2%), Ca (0.8-4.0%), K (1.2-2.4%). Ti (0.3-0.5%) and Zr (0.3-0.16%) were ob served in detail along one of the cores, at levels dated to the early 1970'ies. Mo re summary fo r­ aminiferal and element analyses of two other core s taken belo w the pycnocline corroborate these observations. In contrast, there were no clear changes in the foraminiferal and elemen t co nte nt s in a much mo re sandy core taken above th e pycn ocline. Durin g th e past 30 years, daily win d observat ions and salinity measureme nts have show n a chang e in th e local w ind regime to a higher freq uency of st rong wi nds fo llowed by an increase in salinity. Mo nt hly oxyge n measurements take n since 1976 have also shown a decline in the botto m-water oxygen concentration s. The presen t observations of down-core changes are explained by changes to more advec t ion and a smaller local water mass oxygen content .

Christian Christiansen, Mario l .C. Laima, Lars C. lund-Hansen & Anette M. Pedersen, Department of Earth Sciences, Univ ersity of Aarhus, Ny Munkegade Build. 520, 8000 Arhus C, Denmark. Helmar Kunzendori, Rise National Laboratory, DepartmentofEnvironmental Science and Technology, Postboks 49, 4000 Roskilde, Denmark.

Introduction Additionally, sediments enriched in Mo are often regar­ ded as indicative of anoxic conditions, e.g., as observed in Paleoenvironmetal reconstruction and information on the central and most H2S-enriched parts of the Baltic Sea paleocirculation are commonly based on biological indi­ (Wedepohl 1978). cators (see Nordberg (1991), for a review of paleo-ocean­ In this paper we present the results of studies on short ographic conditions in the Skagerrakl-Kattegat over the sediment cores from the southwestern Kattegat. We then last 8000 years). Similarly, Conradsen (1993), Conradsen discuss both the biological and the non-biological evi­ et al. (1994) and Alve (1994) have used foraminifers to dence of near-recent to recent changes in environmental infer sub-recent and recent environmental cond itions. conditions in the southern Kattegat. A number of non-biological indicators have, however, also been used to infer paleosalinity, i.e., to dist inguish between freshwater and marine sediment deposition. Study area Berner et al. (1979) showed good correlations between sediment FeS/FeS ratios and overlying water salinities. The st udy area in the southwestern Kattegat (Fig. 1) is Also, Berner & Raiswell (1984) devised a C/S method to situa ted in the transition zone between inflowing bottom distinguish between freshwater and marine sediments, water of high density (normal salinity) from the North Sea and C/N ratios were normally fou nd to be much high er in and outflowi ng low den sity (Iow salin ity) surface water terrestrial sedime nt s tha n in marine sedim ents. from the Baltic. The background concentration of suspen­ Emelyanov (1982) showed that Na is generally fixed in lar­ ded matter in the study area is lower than in the North ger quantities in marine t han in freshwater sediment s Sea and hig her than in the Baltic. Therefore, the concen ­ and that Mn, Ba and P contents in especially Baltic Sea tration of suspended matter and the rate of sedimentati­ sediments may serve as indicators for changes from on in the western part of the southern Kattegat are both lacustrine to marine environments. Recently, Christiansen highest when the area is dominated by an inflow of North et al. (1994) suggested that the relatively high Ca content Sea water (Lund-Hansen et al. 1993). in Kattegat surface sediments may be caused by inflows Because of the circulation, the water column has a from the SkagerraklNorth Sea .In line with such a sugges­ strong pycnocline at a depth of 10-20 m in spring and tion, Christiansen & Kunzendorf (1995) found that high summer (Stigebrandt 1983), whereas it is generally less contents of Ca in Baltic Sea sediments correlated with stratified during autumn and winter. known periods of strong inflow to the Baltic Sea . Water depths vary between 10 and 15 m in the western and northern parts of the study area and between 20 and 138 Christian Ctuistiansen,Helmar Kunzendorf,Mario l.C. l.aima, Lots C. i und-Hansen & AnerreM.Pedersen NGU-BULL 430, 1996

Fig. 1. Location map showing sampling positions and localit ies mentioned in the text.

25 m in its central part. Becauseof this depth distribution, t ions by a factor of 2-3 for Zn, Cd and Pb, and 4-9 for Hg as wave-induced resuspension of the sedimen ts is more fre­ compared to pre-1850 samples. Olausson (1975) also quent in the western and northern than in the central documented an increase in Cu, Ni, Zn and Po4-P du ring part (Floderus 1989, Christiansen et al. 1993).This results recent decades. in pronounced depth-dependent grain-size distri buti ons In the Kattega t there is a north to south decreasing of sedim ents (Skov & Natur-styrelsen 1992). The tidal gradient in the content of Ca in th e water colu mn. range is small « 0.4 m), and the se relatively small sea­ Bernard &Van Grieken (1989), in their study of suspended level variati ons are by far exceeded by meteorologically matter from th e Skagerrak to the Ba ltic Sea, fou nd that induced variat ions wh ich may amo unt to 1.7 m above th e North Sea acts as a source of CaC0 3 for the Balt ic Sea . and 1.5 m below mean sea-level (Christiansen et al. 1981). On th e ot her hand,Ingri et al. (1990) observed a rise in Wind -indu ced mixi ng and resuspension are important th e suspended matter conte nt of Ba in a profile fro m the facto rs in the nutrient cycling of the study area. Balti c Sea to t he Danish Belt area. An increase in the concentration of organic matter (OM) in the youngest sediment (<300 yrs. BP) is common­ ly observed in cores from the Kattegat (Nordberg & Methods Bergsten 1988, Christiansen et al. 1993). Seidenkrantz (1993) explained the OM increase in the eastern part of Four short (20-30 cm) cores were obtained by a 'Haps' the Kattegat as a result of anthropogenic activity, and corer (Kanneworff & Nicolaisen 1973). Gamma-spectro­ found th at the distribu tion of foraminifers also was affec­ met ric measurements of 210pb, 137CSand 226Ra were carri­ ted. Madsen & Larsen (1986) show ed that surface sedi­ ed out on two of the cores using a reverse-electr ode coa­ ments were generally enriched in trace metal concent ra- xial Ge-detector (10% reI. efficiency) with energy resoluti- NGU-BULL430, 1996 Chris tian Christiansen, He/mar Kunzendorf.Mariol.C Laima, tars C. Lund-Hansen &AnerreM.Pedersen 139

o on values of 640 eV (at 5.9 keV) and 1.7 keV (at 1332 keV). "'. _: :: ~ Subt racting 210 pb-supported activity, Le.an amount equi­ valent to the 226Ra activi ty, the unsupported activity 210Pbunsup is used to estimate linear sedimentation rates -50 for the cores using the constant initial concentration (ClC) model of interpretation. Historical profiles were construc­ ted using petrophysical core data and the constant rate <, ? of supply (CRS) model for lead-21O. - - ';I'. ,/- I - l OO Ti - ...B Q. The uppermost 15 cm of core 7082 were sliced into 1 f- "- -/ . .r cm samples, and the foram iniferal content quantitatively o, W A I analysed according to standard methods (Meldqard & o I l' ."---- Knudsen 1979). Eachsample (70-80 g) was washed in sie­ K_ -150 " ves with mesh-sizes 0.1 mm and 1.0 mm, a minimum of -" \ --- \ 300 specimens were counted and th e material screened \ \ \ for additional species. Paleoecological parameters such \ \ \ as the number of specimens in a 100 g wet sample, the 1I - 200 .:j.,..."';"",.,...,.,.,...,.,.,...,.,.,...,."";:'rrrrrrrrnrrnrrn..-rr...,."..-rT..-rTTTl percentages of agglutinated/calcareous species and the o 200 400 600 800 1000 foraminiferal accumulation rates have been used to inter­ CO NCENTRATiO N (0 /00) pret the ecological conditions. The other cores were only Fig. 3. Down-core variations in Ca, Ti, Zr and Ba concentrations (Station analysed at 4 levels down the cores. 7082). Note thestrong changesin thecore at 80 mm depth. Salinity has been measured daily in Middelfart since 1930 (Fig. 1). Data from this time series since 1950 were filtered by a 12 month moving average in order to elimi­ 210 Pb dating yields a sedimentation rate of 3 mm y-l nate seasonal salinity variat ions and detect possible long­ which is equivalent to a net deposition rate of469 g m-2y­ term changes. Wind directions and velocities were mea­ 1(CIC model). This is much less than the gross dep osition sured every three hours at the Vesborg lighthouse (Fig. rate 3419 g m-2y'l measured in sediment traps 4 m above 1). The concentration of dissolved oxygen in the water the bottom, suggesting a significant amount of resuspen­ column has been measured monthly in the study area sion. There is a bend in the dating curve (CRS model, Fig. since 1970 by Vejle County as part of a mon itoring pro­ 2) situated at a level of about -80 mm down-core, which gramme. corresponds to the beginning ofthe 1970'ies.The bend is associated with a significant change in sediment bulk density. The bulk density is on average 1.4 g cm-3 below Results the -80 mm level and less th an 1.2 g cm-3 above th e -80 mm level (Fig. 2). Also observed is a high content of orga­ Sediment changes nic matter increasing from about 10% at the -75 mm level to about 14% at the surface. At the same time t he grain Sediment changes were st udied in four cores taken size (88-92 % < 63m) does not change with dept h. below the pycnocline. Results presented here are mainly From the -80 mm level upward, there are also signifi­ from station 7082, but summary results from the other cant changes in the concentrations of a number of ele­ cores corroborate the findings from station 7082. The ments (Fig. 3). There is an increase in the content of Ca (from 0.8 to 4.2 %), K (1.2 to 2.4 %) and Ti (0.3 to 0.5 %). In contrast to this, Ba (0.7 to 0.2 %) and Zr contents (0.3 to 0.2 %) decrease. Other elements such as Fe, Zn, Rb, Sr and .. .~ -~ ~._ eaa _• • _ ._. _ • • •• •• •• •/ . : .. .. Yhave also been analysed, but no significant changes in 0.45 -DATING ~ : ~ thei r concentrations are observed in sediments from the : : : : ~~\/\':~:: : :: :: : : :: : :\ :: :: " :: . :::: ::::: ::: ~~ DENSrrY early 1970'ies. " One coarse-grained (16-20 % < 63m) core (station ...... ----.------: ~ ...••... _.. 0.3 _ 7677) with a significantly lowe r organic matter content \/: ~ . ------.. :-..---- .... 025 ~ (1.2-1.4 %) taken at a water depth of 14 m, which normal ­ ------, .. -- -- 02 ~ ly is above the pycnocline, showed no clear systematic changes in element concentrations (Fig. 4)...... - -- -\• -- ~ 0.15 <.i~ e-' eo en ...... ----..-- -..- - ~ 0.1 Foraminiferal changes --...... _------, . 0.05 e ·2001---=,..--.-~.--,---,.----.---,---+0 l ml~l~l~l~lml~l_~ The 15 analysed samples contain a total of 11 species, all YEAR benthonic. Five of th ese species have hyaline calcareous tests, while 6 species belong to agglutinated genera. Fig. 2. Down-coredatings(heavy line) ofthesediments(core7082).Alsoshown is thesediment bulk density asa function of time (dashed line). The analysed samples are divided into two zones; a 140 Christian Chtistiansen, Helmar Kunzendorf,Mario l.C.Laima, LarsC. Lund-Honsen & AnerreM.Pedersen NGU-BULL 430. 1996

...,'" • + i C • .. NLB52 ~ : :l A I .s. oof / ~ j + ~ U J / . ,e.001 \ 7677 _ ·1e,00"j 7677 NLB52 I 1 t- , -. • ~ " S . 00 ~ H O> \ ~"S.J o i o j +\ i '20 .oo J ..I 1 • • .20' ''''1 • 1 1 .25 .00 .1 · 25 . 00 .,...... ,.~~~~~~~~~~ 20.00 40 .'00 60.' 00 . 80 .'00 100 '.00 0 .00 2Z. a0 40 .00 6e .OO 00. 00 13e . OO AG GLU TINAT ED FORAM . ( %) PE~ CE~T AGES < 0 .863 ~M e.0·1S+ e. 00 1D . .. . ., \ '5' ''''1 I I _ J + / ~ L' NLB52 • 1 + U, ' e. ",,~ / 7677 \ 1102 ",, ~ ~ j ::, ' e. / I 1+ 7677 NLB52 l i 11 02 t- _ ~ ~ " S''''' l ';001 i o , j -20 .00 1 • I\ •I . 20.00j + • Fig. 4. Down-core variations at stations 1 j 1702, nlbS2 and 7677 in A) Percentages of -2S . ~ . ~ ·25 ""~. --~__~ _ agglutinated foraminifera, B) Content of Ca, 1.00 2. 00 3 . 00 4. 00 5.00 0."" CO TE T OF Co ( %) C) Grain-size, and D) Organic matter.

lower zone (Zone I) with faunal assemblages consisting of probably th e same in this sample as in th e rest of the ana­ 60-99 % agglutinated specimens, and an upper zone lysed samples. (Zone 11 ) wit h a content of calcareous specimens increa­ sing to about 75% of the total fauna (Fig. Sa). The zonal Wind and hydrographica l changes boundary is placed at the -90 mm level, w here the calca­ reous content increases from about 10 % of the tota l fau­ An analysis of wind data from t he Vesborg lighthouse na to more than 30 %. However, the change to >50 % of (Fig. 6) shows t hat substantial change s in the freq uency calcareous specimens takes place at the -70 mm level. of strong winds have occurred especially dur ing th e last The 90-70 mm interval can thus be regarded astransitory. 20-30 years. The frequency of high-velocity win ds (>11 m Dissolut ion of calcareous tests commonly leaves s') has increased from less than 10% of th e year in th e behind a residue of free organ ic lini ngs from certain spe­ 1960'ies to more th an 15% of th e year in the 1980'ies. cies, and in the core 7082 all such linings appe ar to be During the same period of time, t he frequency of even from t he species Ammon ia batava . In Zone I, w here the stronger win ds (>19 m S-l ) has doubled from less than agglut inated species domi nate, the conten t of free orga­ 0.5% to about 1% per year. The average prevailing wind nic lining s is around 6 per sampl e (70-80 g wet sediment), direction has, how ever, remained around southwest. w hile imm ediately above the zonal boundary it rises to Southwesterly w inds may increase the magn itu de of the 25-30 linin gs per sample. Stratigraphically higher in t he Jutland Current in t he North Sea (Bolding 1991) and the y core the conten t of free organ ic linings declines, and abo­ may also favour the inflow of more highly saline bottom ve th e -60 mm level t hey disappear. As t he free organic water into the Kattegat (Aarkrog 1988). lini ngs are not counted as calcareous specimen s, t hissug­ Average salinities in th e stud y period (Fig. 7) also show gests t hat the faun istic change fro m mainly agglut inated a rising tendency, from 19.5 psu in the 1950'ies to 20 psu to mainly calcareous, in reality was less gradual th an the at present. It is evident from Fig. 7 that strong fluctuati­ range-chart (Fig. Sa) indicates. The apparent ly t ransitory ons in salinity prevailed up to 1970, but since 1970 salini­ interval, 90-70 mm, is thus included in Zone 11. ty fluctuations have becom e smaller. The total number of species in each of th e samples is The average oxygen conte nt of the August-O ctober fairly constant, between 7 and 10, and, except for the water colum n has gradually declined from about 8 mg 1-1 130-140 mm sample, both t he total num ber of specimens in 1970 to abo ut 3 mg 1-1 at present. Oxygen deficiencies per 100 g wet samp le and t he to tal flux may also be con­ « 4 mg 1-1) in the study area have also become more sidered as constant (Figs. SA and 5B). The faunal assem­ increasingly common and widespread since 1970 blage in th e 130-140 mm sample consists of 91% small, (Schwae rter et al. 1990). probably ju venile specimens of Egg erelloides scabrus, and th e fo raminiferal biomass at the time of deposit ion was NGU-BULL430, 1996 Christian Cbristiansen, Helmar Kunzendorf,Moria l .C. Loima, Lars C. Lund-Hansen& Anette M. Pedersen 141

A

Core % O FT OTA L FA U:-; ,\ 7082 \ o t l ota l t oco'lll'l l n i teral f aun a: Agglutin'lh.·d < 1·'.

• 1 - 2-'. ~ e, c-" E E , o ~ ~ e :; s: " ~ 'E , .§ ~ . ~ ~ ~ ~ ~ l .~ ~ § 6 - 10',• ti , e ~ ~ ~ - .., -g '"c '"] Tl: -, . 1.2 ~ ::" 0< Z 11- 20-'. " < '-' ~ ~ ~ 0 ~ . ~ ~ E . ~ " ~ < '"~ ~ .2 '? ~ E ~ E 0 0 0 ~ 2 1- 4 0 -,. ]. 0 0 0 E . ~ E B 0 E 0 < < ~ ! o 1 1 < 1 9 ~ yea r '" '" I 4 1 - 6 0 -,. 1990

I1 1980 Fig. 5 (A). Range chart showing each foram i­ niferal species and th e combined agglutina­ ted species as percentages ofth e total fauna , 1970 The figur e also contains th e age of th e sam­ ples, the total number of specimens in 100 g 10 sampl e, and the zonation. (8). Range chart 1960 t t showing the yearly flux of each foraminiferal 12 species, the combined agglutinated species, 13 and the combined calcareous species per m2. 1950 14 The figur e also shows th e age ofth e samples o • and th ezona tion.

B LEGE~D Fl u , Core F L r X o t l or .. mi nif U d l s pe c imen. 7082 m ' )( ye a rs Agg )ulin, lh:d 0 Culca rco u-, ~ ' ... o c 1 -a ,I, " ~ • , - 2 e 1~ , " ;; g 1 2 - 10 e 0, , , 0 ~ ;i~ = ~ < .c c e, ~ . ~ ~ E " ~ ~ c. -c ~ 2- 'j 10 - 3 0 0< " = = 0 ~ ~ -e ~ .2 ] e 0 ~ 'E S 3 0 - 50 ~ 0 0 ~ .., . ~ c, 0 ;;: :§ E " ~ 0 ~ ~ , s- s: ~ 0" o' ~ 5 0 - 100 E ~ E J ~ E j' ~ cc ;;: tx y ear cm < - < 9 9 - - - < - , 0 0 1 0 I I I I· I 10 0 - 30 0 I W · V- 0 0 0 I I 0 0 0 . 1 > 3 0 0 19 9 0 2 e-- 0 0 0 I . 1 I . 0 I 0 t-- 3 · 0 I 0 I I 0 I 0 r-, 4 , 0 I 0 i 1 I I I 0 I1 1980 ~ - ; 0 I · 0 I j III: 6 I I · 0 1 0 0 I ~ 7 I 0 · · . I I 0 970 8 I I · 0 0 0 1 0 I I I 9 I , 1 I: ·0 K I 0 0 I I I I 0 r-, 10 I I I 0 0 I I. 1960 r-, · I 0 1 " I I . 0 I 0 0 12 '1 I r--.. 0 0 0 0 I 0 0 0 13 I I V- I . . I 1950 ' 4 I · 1 /' 0 I I 0 . 0 , ~ 0 II 0 142 Christian Cntiuiansen: He/mar Kunzendorf, Mario l.C. Laima, LarsC. Lund-Hansen &Anette M. Pedetsen NGU·BULL 430. 1996

Vesborg Fyr -or 1931 · 1960 - 1961 ·1990 ° A 270 w /\ r-; ~.A <; 225° .. ... sw _- ~ X' .1 y,' . , ~ ," \\(' ,, 180° \ ' S V, ,, , 135° SE ", 90° E B 25 , . I 20 I , : 1\ ~ ( 'v\,,). -4 15 \ , \ -; ,," If? , - , , kf\ , 10 A \ , \ , \ ' , . \ rv: ; \r - ' \ - c " 17.&1------..) 51101 55104 59107 63110 68101 72104 76107 80/10 84/12 89103 YEAR % 1

Fig. 7. Long-term mo nt hly mean salinity variations in the period from 1950 1960 Janu ary 1951 (5 1/0 I) to Ma rch 1989 (89103). The dat a have been filte red 1900 1990 wi th a 12-month moving average to remove seasonal variations. Also shown is the long-term trend (bold solid line). Fig. 6. Annual average wind direction (A) and freque nciesofwind velocities exceeding 6 Beaufort (B)and 9 Beaufort (C).

Disc ussi on A constant calcareous content throughout the analy­ sed core would create a major change in flu x at the zonal All the 11 fora mini feral species found in the samples are boundary (Fig. 5b), but assuming that the Ammo nia/ known to tolerate a wide range of envi ronmental cond iti­ Elphidium rati o was the same in Zone I as in Zone 11 , Le. ons such as salinity, temperature , bottom substrate, about 1:1 0, the number of calcareous specimens in Zone I water-depth and oxygen content . Most of them are also may have been some 10-15 % higher than actually pre­ commonly used as ind icators of reduced (less than nor­ served. This assumpt ion is not unreasonable, and the mal-marine) salinity and/or ext reme conditions in cool, resulting increase in the flu x is not high enough to shallow water (Lutze 1965, Mu rray 1971, Olsson 1976, demand an explanation; but the percentage of calcare­ Alve & Nagy 1986, Alve 1990). Some, including th e most ous specimens would still be much low er in Zone I than abundant species Eggerelloides scabrus, are also known to above . It can therefore be concluded t hat the calcareous tolerate various kinds of pollution (Alve & Nagy 1986, species apparently did not thrive during the deposition Alve 1990). Thus, considering the high tolerance of both of Zone I. the calcareous and the agglutinated species, there is no One reason for t his may invol ve t he low Ca content in single obv ious explanation for the faunistic change at the the sediment of Zone I, as comp ared with that in Zone 11. zonal boundary. Only a mino r percentage of the chalk in the sedimen t was Faunal assemb lages containing all or most of the 11 bound in the foraminiferal tests, but it may still have been foraminiferal species have been fou nd in the Baltic Sea difficult for the calcareous species to find enough accessi­ (Lutze 1965) and also in estuaries in the ble calcite. A second possib le explanat ion may relate to Kattegat/Skagerrak area by, among others, Alve (1990). the high to lerance for po lluted environments by the The fauna l assemblages of Zone 11 are thus what could be strongly do minat ing Eggerelloides scabrus. The highe r expected, given the physical parameters. However, we cont ents of Ba and Zr in Zone I may suggest a different raise the quest ion as to why are there so few calcareou s kind of po llution befo re the 1970'ies. specimens in Zone 17 One possibility is post-mortem dis­ A th ird exp lanat ion could be a change in the general soluti on of the calcareous tests, and the presence of free hydrographic environment. In spite of th e high to lerance organic linings in Zone I indicates that some dissolution of all the species, the palaeoe nviron ment of Zone I may has indeed taken place. All the linings are from the speci­ be specificall y suited for Eggerelloides scabrus, thus enab­ es Ammonia batava, so apparently none of the Elph idium ling t his species almost comp letely to out-com pete the species produced preservable free organ ic linings. ot her species; until a slight change, perhaps a different or Accord ing to Boltovskoy & Wright (1976), dissolution strong er bottom current or a movement/ weakening of of calcareous tests takes place at pH < 7.8. The present the pycnocline, altered the situation in favour of the cal­ ph -values are about 7.8 throughout the ent ire analysed careous species. Such a change may be very slig ht, and sequence, but cou ld have been lower during, or shortly need not show in the measured physical parameters. after, the deposition of Zone I. The present interpretations of down-core change s in NGU-BULL 430, 1996 Christian Christiansen, HelmarKunzendarf, MoriaJ.c. Laima, Lars C. Lund-Hansen &AnetteM. Pedersen 143

element distributions may be impeded by bioturbation on environmental changes taking place during the effects. However, cores in which such effects could be 1970'ies. Furthermore, Schrader et al. (1994) observed seen were not considered here. Further, the study area is that, since 1900, chemical elements characteristic for the frequently struck by oxygen deficits, which places a limit North Sea sedimentary system have been displaced in on biological activity. Additionally, the abrupt down-core two steps from the southwestern Skagerraktowards the changes in Cacontent (Fig.3) are taken asindicating very north and east. Also, Neuman et al. (1995) observed, in limited bioturbation effects on our cores. the sedimentary record, an increasing frequency of Most of the changes in the concentrations of elements inflows to the Baltic Sea. Inflows at the beginning of the which occurred at the beginning of the 1970'ies may be 1970'ies were strongly reflected in geochemical changes. explained by advection. Bernard & Van Grieken (1989) To decide whether the 1970 changes discussed here showed that the North Sea acted asa sourcefor Cain sus­ were local, or whether they resulted from a single, more pended matter in the Kattegat and the Baltic. regional, environmental change, requires additional stu­ Christiansen et al. (1993) found a north to south decrea­ dies. sing gradient in bottom sediment Ca concentrations in the Kattegat. In a study from Arhus Bay, Christiansen et al. (1994) reported high concentrations of carbonate-C in Acknowledgments trapped sediments associated with the presence of high­ ly saline water in the bay.Thus,the upward increase in Ca We wish to thank Vejle County for placing salinity and oxygen data at in our core suggests a stronger influence in the study our disposal. The manuscript benefitted from constructive comments from the two referees, Dr. Nordberg and Dr. Alve. This paper is a contri­ area of water from the Skagerrak. The slight increase in Ti bution from the Marine Centre under the Danish Strategic in sediments may also indicate a stronger influence of Environmental Programme. Skagerrak water. There are no local sources for this ele­ ment but Schrader et al. (1994) have reported increased concentrations of Ti in the Skagerrak since about 1900. References Ingri et al. (1990) observed a rise in the content of Ba in suspended matter in a profile from the Baltic Sea to the Aarkrog, A. 1988: An examination of the dilution of waterborne polluti­ on from the German Bight to the Kattegat by means of radioactive Danish Belt area. Consequently, the decrease in Ba at the tracers. Ris0-M-2746. beginning of the 1970'ies indirectly suggests a relatively Alve, E. 1990: Variations in estuarine foraminiferal biofacies with dimi­ greater inflow from the Skagerrakthan outflow from the nishing oxygen conditions in Drammensfjord, SE Norway. In C Baltic. Hemleben et al. (eds.): Paleoecology, Biostratigraphy, Paleoceanography and Taxonomy of Agglutinated Foraminifera. There has been a rising trend in salinity in the southern Kluwer Academic Publishers, The Netherlands, 661-694. Kattegat since 1950, with fewer year to year fluctuations Alve, E. 1994: Foraminiferal evidence of environmental change in the since the 1970'ies.The salinity measurements were carri­ Skagerrak over the past six decades: surface assemblages of 1937 ed out in the top 0-5 m of the water column. The rising and 1992/93 compared with those from short cores. 5th Marskat Meeting,Abstracts, 1. trend could therefore indicate a reduced outflow of Baltic Alve, E. & Nagy, J. 1986: Estuarine foraminiferal distribution in water. However, there is no such long-term trend present Sandebucta, a branch of the Oslo Fjord. Jour. Forami. Res. 16,261­ in the outflow of Baltic water through the Danish straits. 284. The rising trend in surface-water salinity may also reflect Bernard, P.C & Van Grieken, RE. 1989: Geochemistry of suspended mat­ ter from the Baltic Sea.1. Results of individual particle characteriza­ more wind-induced entrainment of bottom waters into tion by automated electron microprobe. Mar. Chem. 26, 155-177. surface waters. However, the Middelfart site is situated in Berner, RA, Baldwin, T. & Holden, G.R 1979: Authigenic iron sulphides the northern part of the Lillebelt, where the water as palaeosalinity indicators. Jour.Sediment. Petrol.49, 1345-1350. column usually is vertically homogeneous due to strong Berner, RA & Raiswell, R 1984: C/S method for distinguishing freshwa­ ter from marine sedimentary rocks. Geology12,365-368. current-induced mixing. We therefore suggest that the Bolding, K. K. 1991: Denjyske kyststrem. Havforskning fra Milj0styrelsen observed rise in salinity is due to a general increase in Nr. 6. 58 pp. advection. In the deeper parts of the study area, below Boltovskoy, E. & Wright, R 1976: Recent Foraminifera. Dr. W. Junk Publishers, 515 pp. the pycnocline, e.g. at station 7082, this means that bot­ Christiansen, C, Christoffersen, H. & Lomholt, S. 1981: Hydrography, tom-water salinity must have increased.Suchan interpre­ sediments and sedimentation in a low energy embayment, Knebel tation is supported by the observed rise in the frequency Vig, Denmark. Geograf. 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Manuscript received February 7995; revised version acceptedJune 7995.