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Holocene climate in the subarctic fjord Malangen, northern Norway: amulti-proxy study

MORTEN HALD, KATRINE HUSUM, TORE O. VORREN, KARI GRØSFJELD, HENNING B. JENSEN AND ALLA SHARAPOVA

Hald, M., Husum, K., Vorren, T. O., Grøsfjeld, K., Jensen, H. B. & Sharapova, A. 2003 (December): Holo-cene climate in the subarctic fjord Malangen, northern Norway: a multi-proxy study. Boreas, Vol. 32, pp.543–559. Oslo. ISSN 0300-9483.

A Holocene sedimentary record from the deep-silled Malangen fjord in northern Norway reveals regional changesin sedimentary environment and climate. Down-core analysis of two sediment cores includes multi-core sensorlogging, grain size, x-radiography, foraminifera, oxygen isotopes, dinoflagellates, pollen, trace elements andradiocarbon datings. The cores are located just proximal to the submarine Younger Dryas moraine complex, andreveal the deglaciation after Younger Dryas and the postglacial evolution. Five sedimentary units have beenidentified. The oldest units, V and IV, bracket the Younger Dryas glacial readvance in the fjord between12700 cal. years BP and 11800 cal. years BP. This is followed by deposition of glaciomarine sediments (units IVand III) starting around 12100 cal. years BP. Glaciomarine sedimentation ceased in the fjord c. 10300 cal. yearsBP and was replaced by open marine sedimentation (units II and I). A rapid stepwise warming occurred during thePreboreal. Onset of surface water warming lagged bottom water warming by several hundred years. The �18Orecord indicates a significant, gradual bottom water cooling (c. 4°C) between 8000 and 2000 cal. years BP, a trendalso supported by the other proxy data. Other records in the region, as well as GCM simulations, also support thislong-term climatic evolution. Superimposed on this cooling were brief warmings around 6000 cal. years BP and2000 cal. years BP. The long-term change may be driven by orbitally forced reduction in insolation, whereas theshort-term changes may be linked to for example solar forcing, meltwater and NAO changes all causing regionalchanges in the North Atlantic heat transport.

Morten Hald (e-mail: [email protected]), Katrine Husum and Tore O. Vorren, Department of Geology,University of Tromsø, NO-9037 Tromsø, Norway; Kari Grøsfield, Geological Survey of Norway, NO-7491Trondheim Norway; Henning B. Jensen, Geological Survey of Norway, Polar Environmental Centre, NO-9296Tromsø, Norway; Alla Sharapova, St. Petersburg University, Division of Historical Geology, St. Petersburg199034, Russia; received 25th October 2002, accepted 20th March 2003.

The Norwegian fjords are potentially suitable locationsfor high-resolution Holocene studies. Most were degla-ciated after the Younger Dryas and have acted aseffective natural sediment traps (Holtedahl 1975;Syvitski et al. 1987; Aarseth 1997). Many of the fjordsthus contain thick sediment packages largely depositedduring the last deglaciation and the Holocene. Thedeep-silled fjords along the coast of Norway commu-nicate with the Norwegian Sea and may be consideredas extensions of the open ocean towards land (Wass-mann et al. 1996). A proxy record from such a fjordtherefore has the potential of reflecting regional climatictrends of the northern North Atlantic region (Mikalsenet al. 2001). In the present study, we investigated thesubarctic fjord Malangen in northern Norway. The innerparts of this fjord contain a deglacial-Holocene basininfill package that is approximately 150 m thick. Today,the water masses in this fjord are influenced by a mix ofAtlantic Water brought to the area by the NorwegianCurrent and fresher coastal water transported by theNorwegian Coastal Current (Gade & Edwards 1980).The bottom water is heavily influenced by AtlanticWater and thus linked to the North Atlantic heattransport (Gade & Edwards 1980; Normann 2001).The surface water is influenced by the Coastal Currentas well as local runoff from land. The sediments in thefjord may trace changes in these two main water

masses. The northward transport of Atlantic Water isa main conveyor of heat to the northern latitudes.Changes in routing or magnitude of this water mass inthe past are shown to have regional as well as globalclimatic implications. The purpose of the present articleis to elucidate natural variability in climate andenvironment of the northeastern North Atlantic and itscorrelation to climate changes on land. In this article wepresent millennial to century scale reconstructions ofHolocene sedimentary environment and palaeoclimatefrom two sediment cores recovered from the thickdeglacial-Holocene sediment package in Malangen.The reconstructions are based on detailed studies ofacoustic data as well as on the physical properties of thesediments, fossil assemblages of benthic foraminifera,dinoflagellates, pollen, oxygen isotopes and geochemi-cal trace elements. These proxies are suitable forreconstructing bottom water conditions (benthic for-aminifera and benthic �18O), surface water conditions(dinoflagellates), and local vegetation, atmosphericclimate and land ocean correlation (pollen).

Physical setting

The Malangen fjord is situated in Troms county,northern Norway (Fig. 1). The fjord is 6 km broad and

DOI 10.1080/03009480310004134 � 2003 Taylor & Francis

44 km long and consists of an inner and outer basin of c.250 and c. 450 m depth, respectively, separated by athreshold area at c. 160 m. In addition, a small basin, theAnsnes Basin with a depth of c. 200 m, is located justinside this threshold area. The investigated sedimentcores are located in the Ansnes Basin. Another thresh-old at 200 m separates the outer fjord basin fromMalangsdjupet further off shore, which is a glacialtrough located on the continental shelf. At the south-eastern fjord head, the large river Malselva discharges(Fig. 1B). The outer part of the fjord is located withinPrecambrian basement. Kambro-Silurian metasedi-ments overlying the Precambrian basement surroundthe middle and inner fjord. Acoustic data show that thefjord basins are partly filled with glaciomarine-marinesediments interpreted to be mainly of Late Weichselianand Holocene age (Larsen 1986; Wold 1998). Thevolume of these sediments is estimated to be c. 3.72 km3

(Wold 1998).The Norwegian Current (NC) transports relatively

warm (�8°C) and saline (�35�) Atlantic Water intothe region (Hopkins 1991) (Fig. 1A). It flows northalong the Norwegian coast together with the NorwegianCoastal Current (NCC) (Fig. 1A). The water masses ofthe NCC are characterized by a temperature between2°C and 13°C and a salinity between 32� and 35�(Hopkins 1991). These currents follow the Norwegian

coast before they enter the Barents Sea (Hopkins 1991).The NCC is wedge-shaped in cross section and duringthe summer it becomes broader and shallower (50–100 m water depth) than during winter (�200 m waterdepth) (Sætre et al. 1988). This allows the NorwegianCurrent to expand onto the shelf and gives way to aninflow of dense Atlantic Water to the fjord during latespring and summer (Sælen 1950).

The sources for the water masses in the Malangenfjord include (a) Atlantic Water, transported to the areaby the Norwegian Current (Fig. 1) and influencing thebottom water of the fjord, (b) Coastal Water, trans-ported to the area by the Norwegian Coastal Current(Fig. 1) and influencing the intermediate and surfacewater of the fjord, and (c) Local runoff, in particularfrom the Malselva river (Fig. 1). Both temperature andfresh water supply to the fjord vary seasonally. Highestsurface temperatures are reached during summer(August) and highest bottom water temperatures arereached in November (Normann 2001). The lowestbottom temperatures (5°C) are reached during latewinter and early spring (Svendsen 1995). Stratificationof the upper water layer develops at the beginning ofsnowmelt in May–June to September. Stratificationdecreases in late fall and winter (Wassmann et al. 1996)and is most pronounced in the inner fjord towards theriver mouth (Fig. 2). Instrumental measurements of late

Fig. 1. Location map. A. Surface water masses in the Nordic Seas; frame indicates the study area. B. Bathymetry (in metres) of the Malangenfjord and adjoining shelf showing location of the sediment cores in the Ansnes Basin. C. Index map; frame indicates area shown in B.NC = Norwegian Current, NCC = Norwegian Coastal Current.

544 Morten Hald et al. BOREAS 32 (2003)

summer (September) bottom water at the core locationshow salinity and temperature fluctuations between5.6°C and 6.9°C and 34.4� and 34.8�, respectively,for the past 20 years (Normann 2001). By comparinginstrumental temperature and salinity data from thefjord and the open Norwegian Sea outside the fjord, aclose relationship becomes evident. Thus, from anoceanographic point of view a deep-silled fjord suchas Malangen may be considered as an extension towardsland of the Norwegian Sea.

Material and methods

We investigated two sediment cores, JM98-1 andMD99-2298, located in the Ansnes Basin at 69°29.9�Nand 18°23.6�E, with a water depth of 213 m (Fig. 1). Thelocation of the sediment cores was based on severalhigh-resolution seismic surveys using 3.5 kHz penetra-tion echo-sounding and Sparker during the 1980s and1990s. Sediment core JM98-1 is 7.6 m long and wassampled during a cruise with RV ‘Jan Mayen’ in 1998

using a piston corer. MD99-2298 is 36 m long and wassampled during the IMAGES-1999 cruise with RV‘Marion Dufresne’ using a modified piston coringsystem, a ‘Calypso-corer’, especially designed tosample long cores. The inner diameter of both cores is10 cm. The sealed cores were opened by being splitlongitudinally in two equal parts. One half was studiedwith regard to various geotechnical and sedimentologi-cal analyses, including multi-core logging, x-radi-ography and colour determination using the MunsellColour Charts. Furthermore, water content and shearstrength by the fall-cone test (Hansbo 1957) weredetermined for core JM98-1.

Total organic carbon (TOC) and total carbon (TC)were measured using a Leco induction furnace. TCcontent was obtained without any other pretreatment ofthe samples. The samples were combusted at 1350°C.TOC was obtained by HCl extraction of crushed samplematerial, assuming that the dissolved material wascarbonate carbon (CaCO3), and thereafter combusted inthe Leco furnace at 1350°C. The percentage of calciumcarbonate was calculated from values of the organic

Fig. 2. Salinity and temperature transects from the Malangen fjord. The transect is located along the longitudinal axis of the fjord andadjoining trough on the continental shelf. The hydrographic stations are indicated with arrows. Data have been provided by the NorwegianCollege of Fishery Science from the project ‘Sea Environmental Data from northern Norwegian Fjords and Coastal Areas’. The wintertransect is based on measurements carried out on 18 January 1995. The summer transect were measured over the two days 9–10 August 1995.

BOREAS 32 (2003) Holocene climate in fjord Malangen, N Norway 545

carbon and the TC according to the formula: %CaCO3 = (TC-TOC)*100/12. Grain-size analysis wasperformed using a Coulter LS 200 instrument, whichmeasures the particle size in the 0.4–2000 �m grain-sizerange using laser diffraction.

A total of 64 samples were selected for geochemicalanalyses at the Geological Survey of Norway (GSN),except CaCO3, which was done at both GSN and theUniversity of Tromsø. The sediment samples were air-dried at ambient temperatures. The sediment grain-sizefraction less than 2 mm was used for analysis. Thefractionated samples were extracted in 7 N HNO3 acidin autoclave, according to the Norsk Standard NS 4770.The extracts were submitted to ion-coupled plasma–atomic emission spectrometry (ICP-AES) using aThermo Jarrell Ash ICP 61 instrument. The ICP-AEStechnique gives data for 30 elements in the periodictable, of which we present the main elements Al, Ca andFe.

Preparation of the foraminiferal samples mainlyfollowed the methods of Feyling-Hanssen (1958) andMeldgaard & Knudsen (1979). About 300 individuals ofbenthic foraminifera were identified from the �100 �mfraction using a binocular microscope.

Pollen analysis was carried out on 30–50 g wetweight samples with a vertical length of 1 or 2 cm. Ingeneral, treatment followed the methods described byGrychuk (1940). For each sample, 200–400 arborealpollen grains were counted in magnification �500; non-arboreal pollen and spores were tallied in addition.

A total of 58 samples were examined for dinofla-gellate cysts following standard procedures described inGrøsfjeld et al. (1999). A minimum of 300 dinocystspecimens was counted in each sample.

�18O measurements were performed on the benthicforaminifer Cassidulina neoteretis and C. reniforme atthe Norwegian GMS laboratory at the University ofBergen, using the Finingan MAT 251 mass spectro-meter. Reproducibility at this laboratory is 0.07� for�18O. The samples were prepared following theprocedures described by Shackleton & Opdyke(1973), Shackleton et al. (1983) and Duplessy (1978).Cassidulina neoteretis appears to precipitate its shell inequilibrium of the ambient water (Hald et al. 1991). C.reniforme calcifies its test in disequilibrium with anoffset of 0.13� �18O (Austin & Kroon 1996). Theplotted �18O are corrected for the global ice volumeeffect (Fairbanks 1989). Bottom water temperature wascalculated on the basis of the benthic �18O record usingthe following equation modified from Shackleton(1974): T (°C) = 16.9 � 4.0 *(�18Oforaminifer ��18Owater). The modern – �18Owater for the Malangenfjord is 0.2� (Mikalsen et al. in prep.) and was used forthe calculations. Temperature and salinity both controlthe �18O content in recent benthic foraminifera. Atemperature change of 1°C corresponds to a change in�18O of 0.23� (Shackleton 1974) and in the northernNorwegian fjords 1 unit (PSU) change in bottom water

salinity corresponds to a change in �18O of 0.44�(Mikalsen et al. in prep.). The changes in the instru-mental bottom water temperature and bottom watersalinity since AD 1980 at the core site (Normann 2001)imply a temperature effect on the �18O signal inforaminifera that is approximately two times largerthan the salinity effect. Furthermore, a parallel relationbetween salinity and temperature at this location(Normann 2001) implies that they influence �18O inthe foraminifera in opposite directions. From this weconclude that the variations in the �18O record arecaused mainly by temperature fluctuations (cf. Mikalsenet al. 2001, 2002).

Accelerator Mass Spectrometry (AMS) radiocarbondates were performed on bivalve tests (Table 1) inUppsala, Sweden (Tua) and Kiel, Germany (Kia). Forthe Tua dates, the targets were prepared at the Radio-carbon Laboratory in Trondheim, Norway and weremeasured at the The Svedberg Laboratory in Uppsala,Sweden (Table 1).

Seismic stratigraphy

The investigated Ansnes Basin is located just proximalto the Tromsø–Lyngen moraine (Andersen 1968; Fig.1). This moraine complex occurs as a 1500–2500 mbroad, northward convex ridge. The western andnarrowest part is deposited on top of the Skarpnesmoraine (Lysa & Vorren 1997). A high-resolution(boomer) seismic profile across the Ansnes Basin andthe Tromsø–Lyngen moraine complex into Straums-fjorden shows the following four main seismo-strati-graphic units (Fig. 3):

A) Above the bedrock in the SW part of the sectionthere is an erosional remnant of glaciomarine/marine sediments or a till.

B) An up to 200 ms (c. 150 m) thick sequence withacoustic laminated internal signature stretches fromthe proximal part into the Straumsfjord. On theproximal slope of the Tromsø–Lyngen moraine, thissequence is truncated by an erosional unconformitycaused by glacial erosion.

C) Above the seismic laminated sequence (unit B) aredeposits belonging to the Tromsø–Lyngen glacierre-advance. They show lateral facies change. In theproximal part, as well as in the ridges, they arecharacterized by a chaotic seismic signature.

D) Below the distal moraine ridge (unit C), clinoformsrepresenting foresets are observed. They indicate theexistence of an ice-contact underwater fan (Lønne1995). The foreset bedding continues gradually intodistal bottomset beds in Straumsfjord having alaminated seismic signature.

E) Superposing the glacial erosional unconformity areponded sediments, i.e. in the small Ansnes Basinproximal to the Tromsø–Lyngen moraine. Disrupted


reflectors witness a deformation/transport of thesediments by mass movement in the lower part ofthe sequence in the Ansnes Basin.

Lithostratigraphy

Five sedimentary units can be identified in the two coresbased on visual inspection of the sediment cores, multi-core sensor logging, x-radiography and grain-sizedistribution (Figs 4, 5). The sediment units representvarious sedimentary environments including openmarine sediments (units I and II), glaciomarine envir-onments (units III and IV) and reworked glacigenicsediments (unit V). In addition, several turbidite layershave been identified in units II–V (Fig. 5).

Unit V – deformed sediments

The 36–25.5 m interval in the lower part of core MD99-2298 defines a unit characterized by intervals showingdeformation structures such as folds and faults. Thesefeatures are most pronounced in the upper and lower-most parts of this unit. A few laminated intervals areobserved in the lower part. This unit is characterized byhigh variability in grain size and magnetic susceptibilityand a grey (5y–5/1) colour. The dominant texture ispelite with scattered clasts. The deformation is mostprobably due to mass wasting. The unit consists ofseveral fossil-barren intervals.

Unit IV – glacial marine clay

The IV unit is between 2203 cm and 2550 cm in coreMD99-2298 and consists of massive, silty and grey (5y–5/1) clay with scattered clasts (Fig. 5). This unit differsfrom the other glaciomarine unit (unit III) by lighterchroma and a finer matrix, as well as absence ofbioturbation structures and fossils. The main elementsAl, Fe and Ca all show elevated values (Fig. 5). Thescattered grains are interpreted to be rafted by icebergs.The fine matrix and lack of fossils and bioturbation mayreflect an environment with high sediment flux by fall-out from suspension. The unit is completely barren ofmacro and micro fossils.

Unit III – glacial marine mud

Unit III is between 1100 and 2203 cm in core MD99-2298 (Fig. 5) and is characterized by a grey (5y–5/1) todark grey (5y–4/1) massive pelite with scattered clasts�1 mm. The clasts are interpreted to be rafted byicebergs. The unit is bioturbated with scattered sulphurstreaks and bivalve shells and is cut by 4–5 turbidites ofvarying thicknesses.T

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Fig. 3. Upper panel: A high-resolution (boomer) seismic profile across the Ansnes basin and the Tromsø–Lyngen (Younger Dryas) morainecomplex into Straumsfjorden. Vertical scale in ms shows two-way travel time (TWT). For location, see Fig. 1. Lower panel: Interpretation ofthe profile shown in upper panel.

Fig. 4. Lithostratigraphy of core JM98-1. Details for the radiocarbon datings are given in Table 1. Magnetic susceptibility was measured at1 cm intervals.


Fig. 5. Lithostratigraphy of core MD99-2298. Details for the radiocarbon datings are given in Table 1. Magnetic susceptibility was measuredat 1 cm intervals.


Unit II – interglacial marine grey mud

Unit II constitutes the lower part of core JM98-1 (745–460 cm) (Fig. 4) and the interval (1073–500 cm) in coreMD99-2298 (Fig. 5). The unit is characterized by amassive, bioturbated mud with a grey to dark greycolour (5y–3/1 to 5y–4/1) and is interpreted to bedeposited in an open marine fjord setting with high fluxof silt and clay, partly by fall-out from suspension andpartly from bottom transport.

Unit I – interglacial olive-grey marine mud

Unit I constitutes the upper 460 cm of core JM98-1 andthe upper c. 500 cm in core MD99-2298. The boundaryto unit II below is sharp in core JM98-1 and apparentlycut by a turbidite in core MD99-2298. The unit ischaracterized by soft, bioturbated and olive grey (5y-4/2) mud (Figs 4, 5). The dominating grain size is silt(average 71.3%) followed by clay c. 21% and sand c.8.7%. Compared to unit II, unit I shows an increase insand, TOC, CaCO3 and Ca and a reduction in Al and Fe.We interpret the unit to be derived partly by fall-outfrom suspension and partly bottom transport from theadjoining shallow areas of the fjord (Fig. 1) as well bybiogenic production at bottom or in the water columnabove the core site. Compared to unit II below, this unitseems to be less influenced by detrital input, as reflectedby the reduction in Al and Fe, which are abundantelements in the surrounding bedrock.

Turbidite layers

Seven marked turbidite layers are identified in coreMD99-2298 (Fig. 5). Glacial marine units (units III andIV) bracket five of these. One turbidite is found in theupper part of the interglacial marine unit II and anotherwithin the deformed beds (unit V). The turbidite layersare characterized by a laminated fine to medium sand inthe lower part fining upwards to a mud (clay and silt).The upper part of the turbidites merge gradually into theoverlying sediments. The upper boundary of theturbidite layers is difficult to trace exactly and onlythe coarser lower part is indicated in Fig. 5. The threeuppermost turbidite layers appear to have greatestthickness (�25 cm). The basal sand layers within theturbidites are clearly depicted by maxima in themagnetic susceptibility (Fig. 5).

Chronology

The chronology of the sediment cores is based on 21AMS radiocarbon dates performed on mollusc bivalves(Table 1). Most of these bivalves were identified tospecies level. All the dates were corrected for areservoir effect of 440 years (Mangerud & Gulliksen1975). An age model was produced by converting the

dates to calendar years following the calibration modelof Stuiver et al. (1998) (Fig. 6). In this model, werejected the date of 9850 � 95 years at c. 1200 cm incore MD99-2298, which compared to overlying andunderlying dates is considered to be too old. Sedimenta-tion rates (mm/cal. years) for the lithological units werecalculated by linear interpolation between the dates,except unit III, which has many dates and an apparentuniform lithology (Fig. 5). In this case we applied athird-order polynomial fit, following Andrews et al.(1999). The age model implies sedimentation rates forunit I from 0.3 to 12.7 mm/year, and for unit II asedimentation rate between 23.5 and 16.4 mm/year. Ahiatus of c. 2300 cal. years between c. 7800 and10100 cal. years BP was found by extrapolating thesedimentation rates towards the sharp boundarybetween units 1 and 2 in core JM98-1 at 460 cm (Fig.4). A hiatus or marked turbidite layers at approximatelythe same time have been found in several fjords inwestern and mid-Norway (Sejrup et al. 2001; H. P.Sejrup, pers. comm. 2002) and is assumed to be a resultof sediment instability caused by the Storegga Tsunami.This tsunami (Bondevik et al. 1997) is interpreted tohave had a large impact on the hydrology and sedimentdynamics both in the coastal and fjord areas of Norway,including northern Norway. The tsunami is dated to c.8200 cal. years BP (Bondevik et al. 1997). Thus, weconsider that the hiatus in core JM98-1 is a time markerfor the Storegga Tsunami and adjusted the age modelfrom 7800 to 8200 cal. years at this level (460 cm) in thecore, implying that the hiatus represents c. 2000 cal.years. In the parallel core MD99-2298, the age control isless accurate, but the marked turbidite is found at theunit I/II boundary, suggesting that the Storegga Tsu-nami also influenced this record. The age modelindicates very high sedimentation rates for the glacio-marine unit III (Fig. 6), and for units IV and V (Fig. 5).

Foraminifera

The foraminiferal fauna is dominated by benthicforaminifera and a total of 82 species have beenidentified from lithological units III, II and I. We havegrouped the foraminferal fauna into arctic species(Cassidulina reniforme and Elphidium excavatum f.clavata) and boreal species (Trinfarina angulosa,Cassidulina laevigata, Cassidulina neoteretis and Mel-onis barleeanus) according to their modern distribution(cf. Sejrup et al. 1981; Feyling Hanssen 1983; Hald &Steinsund 1996). During the early deglaciation of theMalangen fjord (c. 12000–11400 cal. years BP), theforaminiferal abundance is low and the assemblage isdominated by arctic species (Figs 7, 8). There was amarked reduction in the arctic species and a firstimmigration of boreal species at 11400 years BP.Planktic foraminifera were generally rare, but showed aslight increase after c. 6000 cal. years BP. Boreal


species dominated the Holocene foraminiferal fauna inMalangen, but there was an increase in arctic speciesafter c. 3000 cal. years BP.

Oxygen isotopes

The oxygen isotope record is based on measurements ofbenthic foraminfera; the stratigraphy older than11300 cal. years BP is measured on C. reniforme andthe stratigraphy younger than 11300 cal. years BP ismeasured on C. teretis. �18O measured on benthicforaminifera from units III, II and I show largevariability during the earliest part of the Holocene, c.12000–10000 cal. years BP (Fig. 8). There was amarked �18O maximum around 11400 cal. years BPfollowed by depletion reaching minimum values around10500 cal. years BP. A second �18O minimum occurredaround 5700 cal. years BP, followed by a generalincrease to c. 1900 cal. years BP (Fig. 7), followed bya rapid decrease.

Dinoflagellates

A detailed Holocene dinocyst stratigraphy has currentlybeen established from units III, II and I, and a total of 20different taxa have been identified (Grøsfjeld et al. inprep.). In the present article we show three main taxa,Brigantedinium spp., Operculodinium centrocarpumand Spiniferites ramosus in addition to the dinocystflux, supporting the main palaeoenvironmental conclu-sions (Figs 7, 8). O. centrocarpum is a ubiquitousspecies, tolerating large fluctuations in temperature andsalinity. Because of the abilities to exploit suchenvironments, which are uninhabitable for other taxa,O. centrocarpum has an advantage before other taxa. Itis therefore one of the first taxons to establish during ashift in hydrography, and peak occurrence of O.centrocarpum is often a signal of hydrographic changes.Although it occurs in the Arctic Ocean it is particularlycommon to abundant in warm and cold-temperateregions (e.g. Matthiessen 1995; Rochon et al. 1999;de Vernal et al. 2001). A high abundance of Brigante-dinium spp., where most of the specimens representBrigantedinium simplex, is often associated with lowsurface water temperatures and meltwater flux (e.g.

Fig. 6. Age in calendar years versus sediment depth for core JM98-1 (A) and core MD99-2298 (B). The age model and calculation ofsedimentation rates are discussed in the text.


Grøsfjeld et al. 1999; Voronina et al. 2001). Brigante-dinium spp. strongly dominate the Early Holocenedinocyst assemblages in Voldafjorden (Grøsfjeld et al.1999).

Attempts were made to reconstruct climate par-ameters such as sea surface temperature (SST), sea iceand salinity using a transfer function (Grøsfjeld et al.1999) based on the partial least squares technique (cf.Birks 1995). However, the reconstructed summer SSTswere unrealistically high, suggesting that the modernanalogue dinocyst data set serving as a basis for thetransfer function (Grøsfjeld & Harland 2001), still lackssufficient numbers of reference sites from fjord en-vironments. For example, such high abundances of S.ramosus as recorded in Malangen have so far not beenrecorded in any modern sediments. None of the modernreference sites in the ‘n–677’ database of de Vernal etal. (2001) contain such a high percentage of this taxon.

The earliest Holocene dinocyst assemblages arecompletely dominated by Brigantedinium spp., lowdiversity and low cyst abundance, indicating fairly lowsurface water temperatures. The marked reduction inBrigantedinium spp. and the increase in Operculodi-nium centrocarpum at 11200 cal. years BP indicate an

abrupt hydrographic shift likely succeeded by amelio-rated surface water temperatures. O. centrocarpumshowed a general increase, reaching maximum around6000 cal. years BP, associated with a marked increase incyst abundance. These changes are interpreted to reflecta strengthening of the Norwegian Coastal Current. Adecline in O. centrocarpum and an increase in S.ramosus after c. 4000 years BP indicate a strong coolingof the surface water in the fjord.

Pollen

A detailed pollen and spores record has been establishedfor units II and I of the sediment record from theMalangen fjord. The older part of the stratigraphy (unitsV, IV and III) was barren in pollen and spores. In thepresent article we present only the percentage curves forPinus and Betula (Figs 7, 8) illustrating some of thecharacteristic shifts in the vegetation. The two specieshad a largely inverse relationship showing a stepwiseincrease of Pinus and decrease in Betula around 7800,6000 and 3200 cal. years BP. In general, the pollenrecord compares well with the other proxies (Fig. 7).

Fig. 7. Palaeoclimatic proxies during the Holocene plotted versus a calendar year time scale based on data from sediment cores MD99-2298and JM98-1.


The main flora shifts also correlate to pollen and sporeassemblages from nearby lake sediments on Andøya(K.-D. Vorren & Alm 1999) and Prestvannet, Tromsø(Fimreite et al. 2001), thus indicating that the marinesediments of the Malangen fjord also function as anarchive for this terrestrial proxy.

Discussion

Allerød–Younger Dryas

The bulk of the seismo-stratigraphic unit B, the acousticlaminated sequence (Fig. 3), was probably depositedduring the glacial recession that occurred during theAllerød. At that time the margin of the FennoscandianIce Sheet most likely receded into the inner Malangenfjord. Similar thick acoustic laminated sequences ofAllerød age are found in fjords in southern Troms(Vorren & Plassen 2002) and in Ullsfjord in northernTroms (Plassen & Vorren 2003). Unit B was glaciallyeroded during the Tromsø–Lyngen re-advance thatoccurred in Younger Dryas (Andersen 1968; Vorren

& Plassen 2002). During this re-advance the markedunconformity was shaped, and till (unit C) and the ice-contact underwater fan (unit D) were deposited on topof the acoustic laminated sequence along with the upperand distal parts of the acoustic laminated sequence.

The ponded sediments, comprising unit E, accumu-lated after the final withdrawal of the ice sheet. Data fromcore MD99-2298 support this. Lithostratigraphic unit Vcontains deformed sediments deposited by submarinemass movements. Unit V sediments must be representedby seismo-stratigraphic unit B or C or the early part ofunit E. The dated bivalves at 33 m (12700 cal. yearsBP = 10800 14C years BP) are probably derived fromseismo-stratigraphic unit C. This is considered to be areliable date, since it was performed on a paired shell ofYoldiella lenticula (Table 1). Following the sedimenta-tion of lithostratigraphic unit VI comes sedimentation ofunits III, II and I, filling in the upper 22 m or so of theAnsnes Basin. The oldest date of undisturbed sediment is10300 14C years BP (11800 cal. years BP), which is aminimum age for the withdrawal of the glacier from theTromsø–Lyngen moraine in the fjord (Fig. 1B). Thedates 10800 and 10300 14C years BP thus bracket the age

Fig. 8. Blow-up of the time interval 12500–10000 cal. year BP of the palaeoclimatic proxies based on data from sediment cores MD99-2298and JM98-1 (cf. Fig. 7). The �18O data are based on measurements performed on Cassidulina reniforme (older than 11300 cal. BP years BP)and Cassidulina teretis (younger than 11300 cal. years BP); shift in species is indicated by an arrow.


of the Tromsø–Lyngen re-advance in this area. This is inagreement with results from southern Troms (Vorren &Plassen 2002).

Preboreal oscillations

The unit V–IV boundary at c. 12100 cal. years BPmarks the transition from an unstable ice proximal lateYounger Dryas regime, with frequent mass wasting, toan Early Preboreal glaciomarine sedimentation indicat-ing a retreat of the ice margin away from the core site.The high sedimentation rates indicated for unit IV (Fig.6) may partly explain the lack of fossils by sedimentmasking. Additionally, high rates may have hamperedthe biogenic production due to turbid waters. However,in unit III, starting at c. 11900 cal. years BP, both macroand micro fossils are abundant and can be used fordetailed reconstructions of the bottom and surface watermasses of the fjord.

In general, early Preboreal is characterized by aglaciomarine environment with cold water fossils andfrequent iceberg rafting. Cool water masses at bothbottom and surface are indicated by a dominance ofarctic benthic foraminifera and dinoflagellates (Fig. 8).However, the benthic �18O values around 2.0� are atthe same or slightly lower level than the upper Holocene(Fig. 7) indicating bottom water temperature of 7–9°C.This estimate is obviously too high, considering theforaminiferal fauna that resembles the modern faunasliving near tide water glaciers in arctic fjords withbottom water temperatures between 3°C and 0°C (Hald& Korsun 1997; Korsun & Hald 1998, 2000). Thus, weconclude that the water masses during early Preboreal,prior to 11100 cal. years BP, were probably depleted in�18O at this time. One possible cause of this is influenceby light isotopic water from the melting fjord glaciersthat was mixed through the water column, e.g. assediment-laden meltwater or by brine formation. How-ever, after 11100 cal. years BP the fauna, flora and �18Oindicate temperatures as warm or warmer than atpresent.

Bottom water warming is indicated from 11800 to11200 cal. years BP by the marked rise in boreal speciesand reduction in arctic species. However, there was noparallel warming at the surface to the marked bottomwater event 11800–11200 cal. years BP. This majorbottom water warming therefore predated surface waterwarming by c. 200 years. We suggest that this evolutionreflects the influence of temperate Atlantic Water at thebottom of the fjord, while the surface was still cooled bydeglacial meltwater. A marked short-lasting increase inbenthic �18O at c. 11400 cal. years BP may, if attributedonly to temperature, reflect a cooling of the bottomwater of maximum 4°C. This correlates with theregional North Atlantic Preboreal cooling documentedin the Greenland ice cores (Johnsen et al. 1992),terrestrial records (Bjorck et al. 1996) and marinerecords (Hald & Hagen 1998).

Early/Middle and late Holocene

Between 11000 and 10300 cal. years BP, glaciomarineconditions still characterized the fjord, as reflected bythe scattered IRD in unit III (Fig. 5). The dinocystsindicate slightly warmer conditions than during thePreboreal, but not as warm as during middle and lateHolocene (Fig. 7). Abundances of boreal foraminiferawere high, indicating relatively warm bottom waterconditions. This is also supported by low �18O.However, the water masses were probably still influ-enced by low oxygen isotopic meltwater at this time.Thus the reconstructed bottom water temperatures (Fig.8) may be too high. Iceberg rafting ceased by 10300 cal.years BP. This is in agreement with timing of the retreatof tidewater glaciers from the Malangen fjord (Eilertsenet al. in prep.). The surrounding vegetation indicatesrelatively cold conditions. The peak values in Pinus areconsidered as long transported. However, the presenceof Betula compares well with pollen records fromnearby lake sediments on Andøya (Vorren & Alm 1999)and Tromsø (Fimreite et al. 2001), indicating thatimmigration of birch forest had started.

Owing to a hiatus in the core, assumed to be linked tothe Storegga Tsunami (Bondevik 1997), the periodbetween 10100 and 8200 cal. years BP is not repre-sented in this study. Climate, probably warmer thantoday, was reached around 8000 cal. years BP. This issupported by all the marine proxy data and by anincrease in the more thermophilic dinoflagellates andforaminifera. The rise in Ca (Fig. 4) may be attributed toincreased marine production and reduced detrital input.The latter is supported by the reduction in Fe and Al(Fig. 4). Also the atmospheric climate appears to berelatively warm around 8000 years cal. BP, as indicatedby a maximum birch forest expansion as well as a rise inPinus indicating a warmer and gradually dryer summerclimate. This warm period was followed by a long-term,gradual cooling of both the surface and bottom watermasses until 1900 cal. years BP, during which thebottom water temperatures were reduced from c. 10°Cto 6°C. Most of this cooling occurred after 5000 yearsBP. Around 1900 cal. years BP, bottom water tempera-tures similar or slightly cooler than the moderntemperatures in Malangen (6–7°C, Fig. 2) were reached.The �18O record indicates that centennial scale fluctua-tions are superimposed on this long-term cooling,including slightly warmer intervals around 5900–5700and just after 1900 cal. years BP and some coolerintervals around 7600, 6500, 4400 and 1900 cal. yearsBP. The warm intervals in general compare well withpeaks in Pinus vegetation, corresponding to pollenzones interpreted as ‘Holocene climatic optimum’.

Correlations

We compare the temperature record from the Malangenfjord (Fig. 9C) to high resolution marine and terrestrial


proxy records (Fig. 9A, B, D–I). All records haveindividual, independent, radiocarbon-based time scales.In Fig. 9 we correlate temperature data in a S–N profile(Fig. 11) along the Norwegian–Barents Sea–Svalbardmargin. These records reflect latitudinal temperaturegradients of the Atlantic Water in the NorwegianCurrent during the Holocene (Fig. 9A–F), and arecompared to the North Grip Ice core �18O recordreflecting air temperature over summit Greenland (Fig.9G; Johnsen et al. 2001) and summer insolation at 70°N(Fig. 9H; Berger & Loutre 1991). The U. mediterranearecord from the northern North Sea (Fig. 9A) (Klit-gaard-Kristensen et al. 2001), the benthic �18O recordfrom the eastern Barents Sea (Duplessy et al. 2001)(Fig. 9E) as well as the Malangen temperature curve(Fig. 9C) are all indicators of Atlantic Water bottomtemperatures in relatively shallow settings (�400 m ofwater depth). Thus, they may be compared to ‘true’ seasurface temperature proxy records such as the diatombased SST record from the Vøring Plateau (Fig. 9B)(Birks & Koc 2002) and intermediate depth proxiesrepresented by planktic foraminifera �18O from theWestern Svalbard margin (Hald et al. 1996) and St.Anna Trough, eastern Barents Sea (Hald et al. 1999)(Fig. 9D, F).

A major trend observed in all records, except in theeastern Barents Sea (Fig. 9E, F), is the gradual coolingthroughout the last c. 9000 years. Both diatom SST (Fig.

9C) and the present Malangen record quantify thiscooling to 3–5°C. The gradient between the twolocations throughout most of the time-span is onaverage around 3°C, which is similar to that of thepresent temperature gradient. The eastern Barents Searecords also show a temperature optimum during earlyHolocene (Fig. 9E, F). However, the mid and lateHolocene cooling is not reflected by increased �18O inthese records. A possible explanation is that mid andlate Holocene cooling in the eastern Barents Sea wascharacterized by increased influence of cool, low salineand �18O-depleted Arctic Water (Hald et al. 1999;Duplessy et al. 2001; Lubinski et al. 2001).

The major cooling trend is also recognized in some ofthe terrestrial records. In particular there is a closesimilarity between the Malangen fjord temperaturerecord and the proxy records for atmospheric tempera-tures based on timber lines in nearby Troms, northernNorway (Fig. 9I) (Vorren et al. 1999). Similar trends arealso observed in other proxy records in Fennoscandia,such as the �18OSi measured on diatoms in lakesediments from the Swedish Lapland (Shemesh et al.2001; winter precipitation curve from western Norway(Nesje et al. 2001)).

Superimposed on the large-scale cooling are smallerclimatic shifts with a millennial to decadal duration.Comparing the various proxy records in Fig. 9 revealsboth differences and similarities. A major difference is

Fig. 9. Comparison of ocean temperature proxy records (A–F) with the Greenland ice core record (G) and June insolation (H). The proxy dataare from: A. (Klitgaard-Kristensen et al. 2001). B. Birks & Koc (2002). C. The present article. D. Hald et al. (1996). E. Duplessy et al. (2001).F. Hald et al. (1999). G. Johnsen et al. (2001). H. Berger & Loutre (1991). I. Vorren et al. (1999). Location of the records is shown in Fig. 10.


observed regarding the development of warming duringthe early Holocene. Both the Malangen fjord tempera-ture record (Fig. 9C) and the atmospheric temperaturerecord from Troms, northern Norway (Fig. 9I) show thatmaximum Holocene temperatures were establishedduring late Preboreal (after 11100 cal. years BP),whereas other proxy records (e.g. Fig. 9A, B, F, G)indicate that maximum temperatures were reached, laterwarming, between 10000 and 9000 cal. years BP. Thetime difference seems to be too large to be explained bydating problems. Thus, it is either linked to uncertaintiesin the proxy data or transfer functions used, or it may bereal geographical differences in the timing of warming.If geographical difference is the case, the implication isthat both east–west and north–south gradients differedfrom the present, including a later warming of theeastern Barents Sea (Fig. 9F) and the Vøring Plateau(Fig. 9B). The latter would imply that the AtlanticWater was narrower and restricted closer to theNorwegian Coast between 11000 and 10000 years BP.

The major cooling around 11500 cal. years BP in theMalangen fjord is correlated to the Preboreal oscillation(PBO) and discussed in detail by Husum & Hald (2002).It relates to the PBO cooling in the ice core record and isassumed to be forced by meltwater hampering thethermohaline circulation in the Nordic Seas (Hald &Hagen 1998).

Most of the proxy records show a temperature

optimum during early-middle Holocene (Fig. 9). How-ever, there are differences in timing of this optimumwith respect to onset, termination and duration. Themore southerly located records (Fig. 9A, B) indicate aduration of several thousand years and onset of coolingstarting as early as around 7500 cal. years BP. Incomparison, the eastern Barents Sea appears to have ashorter and delayed temperature optimum between8000 and 7000 BP. In addition to this early to middleHolocene climatic optimum, there are several small,short-lasting climatic shifts. The correlation betweenthese shifts in the various proxy records is uncertain,partly because of uncertainties in the individual agemodels, and partly because of the different proxy dataand transfer functions used. Future studies should aim toimprove the comparison between the various proxymethods and improve the correlation between therecords by applying robust statistical tools, for cross-correlation, cyclicity and age-depth modelling.

The general trend shown by most of the recordscompares well with the high latitude summer insolation(Fig. 9H). This trend has previously been attributed toMilankovitch forcing (cf. Koc et al. 1993), explainingthe relatively early Holocene warm period as a result ofincreased insolation to the northern hemisphere, reach-ing as much as 10% more than present-day insolation(Berger & Loutre 1991). Recent GCM simulationssupport this, and indicate that late Holocene cooling in

Fig. 10. Location map of the proxy records shown in Fig. 9.


northern latitudes was most pronounced in the NorthAtlantic region (CAPE Project members 2001). How-ever, additional forcing mechanisms should be takeninto account in order to explain the changes on shortertime scales. For the Preboreal Oscillations, freshwaterforcing may be an important factor (Bjorck et al. 1996;Hald & Hagen 1998; Fisher et al. 2002). Instrumentalobservations of changes in the North Atlantic Oscilla-tion (NAO) indices show increased winter precipitationand flux of Atlantic Water into the Norwegian Seaduring positive NAO indexes and also an east–westinverse relationship within the Nordic Seas region.Thus, some of the shorter warmings and coolings mayreflect periods of phase-locking of the NAO index in thepositive or negative mode, respectively. Bond et al.(2001) suggested variations in the solar forcing mech-anism for the North Atlantic ‘1500-year’ cycle duringthe Holocene. However, further investigation of theproxy data (Fig. 9) is needed to explore this cyclicityfurther.

Conclusions

� The data provide a high-resolution reconstruction ofclimate and environment in the Malangen fjord fromthe Younger Dryas to the end of the Holocene (c.1500 cal. years BP).

� A glacial readvance during the Younger Dryas (theTromsø–Lyngen event) occurred between 12700 and11800 cal. years BP (10800–10300 14C years BP).

� Five postglacial lithostratigraphic units are identified.The Late Younger Dryas and/or Early Preboreal ischaracterized by deformed sediments (unit V) indi-cating an unstable sedimentary environment withsubmarine mass movements in a glacier proximalsetting. A high flux of glaciomarine sedimentationcharacterized the fjord between 12100 and 10300 cal.years BP (units IV and III) followed by open marinesedimentation (units II and I) and a reduction insedimentation rates.

� The paleoclimatic evolution is reconstructed frombenthic foraminifera, benthic foraminiferal �18O,dinoflagellates and pollen data. The water masses inthe Malangen fjord have cooled significantly duringthe last c. 8000 cal. years. Bottom water temperaturereconstructions indicate a cooling of c. 4°C. Due tothe deep sill of the outer Malangen fjord, and thusgood hydrographic communication with the Nor-wegian Sea, the sediment record reflects regionalchanges. This is supported by the good correlation toother proxy records from the North Atlantic region.

� A correlation to summer insolation at northernlatitudes supports the idea of Milankovitch long-term climatic forcing. Climate changes on shortertime scales may have other explanations, such as

freshwater forcing (Preboreal Oscillations), solarforcing and phase-locking of NAO.

Acknowledgements. – Funding was provided by the ResearchCouncil of Norway to the Strategic University Programme SPINOFand to nationally coordinated research project NORPAST, and by theUniversity of Tromsø and the Geological Survey of Norway. Wethank the crew of RV ‘Jan Mayen’ and chief scientists L. Labeyrieand E. Jansen and crew on board RV ‘Marion Dufresne’.Furthermore, we thank Jan P. Holm for computer drawings, EdelEllingsen and Steinar Iversen for technical assistance, GauteMikalsen for discussions, Hans Petter Serjup and an anonymousperson for reviewing the paper.

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