Postglacial relative sea-level change and stratigraphy of raised coastal basins on Kola Peninsula, northwest Russia

Global and Planetary Change 31 Ž2001. 155–177 www.elsevier.comrlocatergloplacha

Postglacial relative sea-level change and stratigraphy of raised coastal basins on Kola Peninsula, northwest Russia Geoffrey D. Corner a,) , Vasili V. Kolka b, Vladimir Y. Yevzerov b, Jakob J. Møller c a

Department of Geology, Faculty of Science, UniÕersity of Tromsø, N-9037 Tromsø, Norway Geological Institute, Kola Science Centre of RAS, 14 Fersman St., 184200 Apatity, Russia c Department of Geology, Tromsø Museum, UniÕersity of Tromsø, N-9037 Tromsø, Norway

b

Received 9 December 1999; accepted 23 May 2001

Abstract A relative sea-level curve for the Holocene is constructed for Polyarny on the Kola Peninsula, northwest Russia. The curve is based on 18 radiocarbon dates of isolation contacts, identified from lithological and diatomological criteria, in nine lake basins situated between 12 and 57 m a.s.l. Most of the lakes show a conformable, regressive I–II–III Žmarine–transitional–freshwater. facies succession, indicating a postglacial history comprising an early Ž10,000–9000 radiocarbon years BP. phase of rapid, glacio-isostatically induced emergence Ž; 5 cm yeary1 . and a later phase Žafter 7000 years BP,. having a moderate rate of emergence Ž- 0.5 cm yeary1 .. Three lakes together record a phase of very low rate of emergence or slight sea-level rise at a level of ; 27 m a.s.l., between 8500 and 7000 years BP, which correlates with the regional Tapes transgression. Pollen stratigraphy in the highest lake shows that the area was deglaciated before the Younger Dryas and that previously reconstructed Younger Dryas glacier margins along the north Kola coast lie too far north. q 2001 Elsevier Science B.V. All rights reserved. Keywords: sea-level change; postglacial uplift; isolation basin stratigraphy; radiocarbon dating; Russia

1. Introduction Reconstructions based on moraine chronology suggest that the northern coast of the Kola Peninsula in northwest Russia lay close to the eastern periphery of the Fennoscandian ice sheet during its retreat at the end of the last ice age ŽNiemela¨ et al., 1993; Holmlund and Fastook, 1993; Andersen et al., 1995;

) Corresponding author. Tel.: q47-776-44405; fax: q47-77645600. E-mail address: [email protected] ŽG.D. Corner..

Rainio et al., 1995; Landvik et al., 1998; Yevzerov, 1998.. The isostatic response of this region to glacial unloading has recently been documented through the construction of reasonably well-constrained relative sea-level curves for two areas: the Nikel–Kirkenes area along the Norwegian–Russian border ŽCorner et al., 1999. and the Dalnie Zelentsy area approximately 150 km farther east ŽSnyder et al., 1996, 1997.. The Nikel–Kirkenes area is located some 5–20 km inside the Younger Dryas end moraine zone, whereas the Dalnie Zelentsy area is likely located several tens of kilometres outside this zone ŽSollid et al., 1973; Marthinussen, 1974; Niemela¨ et al., 1993; Rainio et al., 1995. ŽFig. 1..

0921-8181r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 8 1 8 1 Ž 0 1 . 0 0 1 1 8 - 7

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Fig. 1. Location map of the investigated area near Polyarny, showing isobases for the mid-Holocene ATapesB shoreline Žafter Møller, 1987, 1989; Snyder, 1996., the position of the Younger Dryas end moraine zone Žslightly modified after Sollid et al., 1973; Niemela¨ et al., 1993; Rainio et al., 1995., and areas for which relative sea-level curves have recently been constructed Ždashed boxes.. Our results show that the Younger Dryas ice margin, traced eastwards, passes south of the Polyarny area.

The present paper presents a relative sea-level curve for the northern Kola coast at Polyarny, near Murmansk, which is located midway along the coast between the Nikel–Kirkenes and Dalnie Zelentsy areas. The relative sea-level curve is constructed using dated isolation contacts Žmarine–lacustrine transition. in cores from emerged coastal basins at nine localities in the area, situated between 12 and 57 m a.s.l. It is based on a total of 18 radiocarbon dates, supplemented by a pollen diagram from the highest lake. The study was carried out to provide a

better regional control on relative sea-level change eastwards from the better documented adjacent area of Norway and to gain a better understanding of postglacial relative sea-level change and isolation basin stratigraphy in this northern area.

2. Location and setting The study area is located near the town of Polyarny Ž69812X N, 33820X E., on the western side of

G.D. Corner et al.r Global and Planetary Change 31 (2001) 155–177

Kola fjord, 20 km north of Murmansk and about 15 km from the open coastline of the Barents Sea ŽFig. 1.. It comprises nine lake basins lying between 12 and 57 m a.s.l., located within a 6 = 10 km area ŽFig. 2.. The lakes occupy glacially eroded rock basins in a moderately sheltered area of undulating low relief, lying mostly below 100 m a.s.l. Bedrock comprises Archaean and Proterozoic igneous and metamorphic rocks, mostly granite and gneiss ŽGorbunov, 1981; Papunen and Gorbunov, 1985.. Vegetation comprises tundra and forest tundra ŽKremenetski, et al., 1997. with bog, heath and birch

157

woodland. Tidal range at the nearest tide station at Murmansk ŽEkaterininskaja Gavan. is 1.2, 2.6 and 3.9 m for neap, mean and spring tide levels, respectively. Mean January and July temperature and mean annual precipitation near Polyarny are y88C, 98C and 450 mm, respectively. The investigated lake basins range in size from 100 m to 2 km long Ž0.5–100 ha., ŽFig. 3, Table 1.. Their present maximum depth is between 1.5 and ) 20 m. Drainage into the lakes is by seepage or stream flow ŽTable 1.. Drainage from the lakes is by stream flow across rock thresholds, except for the

Fig. 2. Location map of the cored lake basins Ž1–9. near Polyarny, showing the distribution of streams, lakes, and areas over 100 m Žstipled.. Coring sites not centrally situated in the largest investigated lakes are shown by a cross.

158

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Fig. 3. Summary diagram of the investigated lake basins in the Polyarny area showing lake and threshold elevations, lake size and depth, coring location in each lake, sediment core stratigraphy, and radiocarbon dates. Bottom profiles in lakes 6 and 9 show the shallower part of these deep lakes. Note the scale difference for core 5.

Table 1 Physiography of the investigated lake basins at Polyarny and stratigraphy of the recovered cores

1

P-9

56r57 " 3.5 a

2

P-8

47.5r48.5 " 3.5

3

P-7

38.6r41 " 2.5 a b

a

L = W Žm . ŽArea, ha .

Drainage Max.rcored Core stratigraphy Unit thickness Comments ŽFacies units. Žcm . intorout depth Žm . Lithological succession Diatom assemblage of lake ŽS s stream s s seepage .

100 = 50 Ž0.5 . 125 = 75 Ž0.8 . 1750 = 650 Ž90 . 350 = 125 Ž4.5 . 150 = 100 Ž1.5 .

srs

1.5r1.5

I–II–III

60–20–80

srs

2r2

I–III

26–154

Unusual occurrence of plant detritus in II Abrupt, possible hiatus

Srs

) 20r9.4

I–II–III–II–III

SrS

10.1r10

I–II–III

10–3–6– 1–44 31–5–57

Lamination ŽII. at two closely spaced levels Normal regressive

srS

1.5r1.5

I–II–III–II–III

42–162–48– 22–170

Very thick; laminated Fluctuating in lower facies at two levels I–II part of succession ŽII-1, II-2 .. Disturbance at base of II-I Abrupt possible hiatus Mixed assemblage in I. Normal or reworked assemblage in III Normal, thick, Normal transition Ž Paralia sulcata abundant. regressive Normal regressive Normal transition Ž P. sulcata very abundant. Normal regressive Abnormal occurrence of freshwater diatoms in I

4

P-1

32.5r31 " 3

5

P-2

28.5r28.5 " 3.5

6

P-6

26r26 " 1.5

1750 = 200 SrS Ž35 .

20r7.5

I–III

11–50

7

P-3

22.5r22 " 1.5 c

srS

3.5r3.5

I– Ž –I T . –II–III

71–14–165

8

P-5

17r17 " 3

125 = 75 Ž0.8 . 300 = 70 Ž2 .

SrS

5.8r5.8

I–II–III

55–3–77

9

P-4

12r12 " 1

2000 = 800 SrS Ž100 .

27r9.9

I– Ž –I T . –II–III

33–3–24

Isolation contact

ŽNot analysed .

Lower part of II

Normal transition

Base of II or slightly older Base of II. Possible ingression at top of II Lower part of II

Fluctuating in II ŽNot analysed .

Lower part of II. Possible ingression at higher level At I–III boundary or missing owing to post-isolation disturbance Base of II Base of II

Base of II

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Loc. Field LakerThreshold no. elevation Žm a.s.l..

a

Outlet drainage by seepage through fractured bedrock. Artificially raised lake; estimated threshold precision " 1 m. Adjacent higher Ž33 m . and lower Ž28 m . lakes provide constraints on original lake elevation. Peat covered threshold.

b c

159

160

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three highest lakes, where lake levels were observed to lie 1–2.4 m below the threshold, implying seepage through fractured bedrock. Raised shorelines are not conspicuous in this inland area and no information could be obtained on the elevation of the marine limit. The mid-Holocene transgression maximum ŽTapes. shoreline is predicted to lie approximately 25 m a.s.l. according to reconstructed isobases for the north Kola coast ŽSnyder et al., 1996..

and previous work in an adjacent area ŽCorner et al., 1999. suggest that the map elevational data is reliable. Threshold depth or height relative to lake level was determined locally in the field, and subtracted from or added to lake elevation to give the threshold elevation. The estimated total error for each threshold elevation determination relative to sea level, calculated as the sum of probable field and map related errors, ranges between "1 and "3.5 m ŽTable 1.. Elevations refer to Russian datum at Murmansk, which corresponds approximately to mean sea level.

3. Field and laboratory methods 4. Diatoms and pollen analysis Sediment cores were retrieved from ice-covered lakes in April–May, 1995. Depth sounding, using a portable echosounder, was carried out at several places in each lake to find the deepest and presumed most suitable, flat-bottomed location for coring. Cores were taken from the deepest, central part of each lake, except in the three largest lakes Ž3, 6 and 9. where maximum depth exceeded the length of the coring equipment Ž15 m.. Coring in these lakes was carried out on the flat-bottomed or gently sloping floor of shallow embayments closer to shore. Cores were taken in 1-m lengths using a lightweight, hand-operated, 54-mm diameter piston corer. At each site, multiple, overlapping cores were taken from adjacent holes to obtain a complete composite record of the stratigraphy and sufficient material for sampling and dating. The correlation between adjacent cores was made by matching stratigraphic horizons, in addition to using the measured depth below the ice surface. Retrieved sediment cores were extruded on-site, split longitudinally to reveal structure, then described, photographed and sampled. Sediment slices, 1-cm thick, were collected for analysis of diatoms, pollen Žlake 1. and grain size. Sediment slices, 2- to 5-cm thick, were collected for radiocarbon dating. Sediment colour was determined on moist samples in the laboratory using a Munsell colour chart. Lake elevations were obtained from 1:25,000 scale maps, either directly from lake elevations given to the nearest decimetre on the map Ž3, 6 and 9., or indirectly from the altitude of nearby lakes and 5-m contours. Numerous trigonometric points on the map

Diatom analysis was carried out on closely spaced samples from the marine–lacustrine transition in all but two of the basins. The results are presented as summary diagrams in which diatoms have been classified into the following salinity classes, according to Hustedt Ž1957.: polyhalobous Žprefer salinity ) 30‰., mesohalobous Žsalinity 30–0.2‰., oligohalobous halophilous Žprefer slightly saline water., oligohalobous indifferent Žprefer freshwater, tolerate slightly saline water. and halophobous Žexclusively freshwater, salinity - 0.2‰.. Polyhalobous and mesohalobous are referred to as marinerbrackish, halophilous as brackishrfreshwater, and indifferent and halophobous as freshwater. Salinity values in coastal waters of neighbouring northern Norway range from 33‰ to 29‰ for fully marine water, through ; 29–3‰ for surface waters in fjords and sounds, to -; 0.4‰ in lakes ŽNordgard ˚ et al., 1982 and own measurements; cf. also Bøyum, 1970.. Marinerbrackish diatoms are thus characteristic of preisolation basins, whilst brackishrfreshwater and freshwater diatoms are characteristic of post-isolation basins. The marine–freshwater diatom transition, shown on the summary diagrams, corresponds to the transition from a dominantly polyhalobous and mesohalobous flora, to a dominantly indifferent and halophobous flora. Frequency percentage diagrams showing species occurring at frequencies ) 2% are also shown for two basin showing normal and abnormal marine–freshwater transitions, respectively. Pollen analysis was carried out on 27 samples from cores from the highest lying lake. The results

G.D. Corner et al.r Global and Planetary Change 31 (2001) 155–177

were published by Yelovicheva et al. Ž1998. and are discussed below in the context of basin isolation.

5. Radiocarbon dates 5.1. Dating procedure and calibration Samples for radiocarbon dating ŽTable 2. were taken primarily from laminated or partly laminated gyttja overlying marine mud at a level thought to correspond best with the isolation contact. The NaOH-soluble fraction was dated preferentially to avoid possible contamination by younger root material ŽKaland et al., 1984.. Additional samples were taken from gyttja at immediately higher or lower stratigraphic levels Žlakes 3, 5, 7, 8, and 9. and from plant fragments Žlakes 4 and 8. to provide a better control on isolation dates and dating reliability. The results are corrected for isotopic fractionation by normalising to y25‰ relative to PDB standard, using measured d13 C values. Calibration to calendar years Žcal. years. was made using the current calibration programme CALIB 4.1 ŽStuiver and Reimer, 1993., assuming a sample age span of 100 years. Dates in the text are quoted primarily in conventional radiocarbon years Žyears BP.. 5.2. Dating reliability Dates were obtained from two or three successive levels in cores from three lakes Ž7, 8 and 9. and from different fractions from the same sample in two lakes Ž7 and 8. to provide information on: Ž1. the marine reservoir age of gyttja close to the isolation contact; Ž2. the age difference between laminated Žtransitional. and overlying non-laminated Žlacustrine. gyttja; and Ž3. the reliability of dating bulk gyttja samples compared with plant macrofossils. 5.2.1. Marine reserÕoir age All samples of laminated or partly laminated gyttja, and some samples of non-laminated gyttja, contain marinerbrackish diatoms ŽTable 2.. They may therefore contain marine carbon and require a correction for some proportion of the marine reservoir age, which in this region is approximately 450 years ŽCorner et al., 1999.. Plotting d13 C values against

161

percentage marinerbrackish diatoms ŽFig. 4. shows that samples from laminated gyttja containing mostly marinerbrackish diatoms and situated low in the succession tend to have higher d13 C values than samples of non-laminated gyttja containing mostly freshwater diatoms and occurring higher in the succession. This suggests that the source of the organic material changes upwards in the succession. However, neither relatively high d13 C values nor a high content of marinerbrackish diatoms is necessarily indicative of marine carbon content because d13 C values in marine and terrestrial organic material overlap in the range shown in Fig. 4 Žcf. Gulliksen, 1980; Mook and Van de Plassche, 1986; Miller et al., 1999. and because much of the organic material deposited during isolation may comprise inwashed terrestrial material Žcf. Bondevik et al., 1999.. In lakes where we can compare dates from closely spaced samples of gyttja containing different proportions of marinerbrackish diatoms Žlakes 7 and 8, Table 2., we find reasonably close agreement Ž230– 750 and 25–60 years, respectively. without reservoir age adjustment, and clearly inverted age relationships using a reservoir age adjustment Žbased on the percentage content of marinerbrackish diatoms.. Therefore, a reservoir age adjustment seems inappropriate in these cases. Likewise, in lake 9, a radiocarbon date from gyttja close to the isolation contact appears to be too young, rather than too old, compared with pollen stratigraphic evidence Žsee Section 7.1.. In the light of these examples and reasoning presented above, we believe that a marine reservoir correction is unwarranted in most or all of our samples. 5.2.2. Age difference between laminated (transitional) and oÕerlying non-laminated (lacustrine) gyttja Dates from transitional laminated gyttja and immediately overlying lacustrine non-laminated gyttja in lakes 7, 8 and 9 show mean age differences of approximately 450, 50 and 1000 cal. years, respectively. Expected age differences based on calculated average sedimentation rates Ž0.25, 0.13 and 0.05 mm yeary1 . are 450, 350 and 950 cal. years. However, calculated expected differences may differ from actual differences for a number of reasons, including differential compaction and the possibility that accu-

162 Table 2 Radiocarbon-dated samples from lake basin sediment cores at Polyarny. Dating was carried out at the Radiological Dating Laboratory, NTNU, Trondheim ŽT-samples. and at the mass spectrometer dating laboratory in Uppsala ŽTUa-samples.

1

57

2 3a 3b 4a 4b 5a 5b 6 7a 7b

48.5 41 41 31 31 28.5 28.5 26 22 22

7c 8a 8b

22 17 17

9a 9b

12 12 a

Sample material Sample ŽL s laminated. depth ŽNL s non-laminated. Žcm.

0

Mud ŽNL.qPlant frags.qGyttja ŽL. y1 Gyttja ŽNL. y1 Muddy gyttja ŽL-NL. y1 Gyttja ŽNL-L. 0 Twig 0 Muddy gyttja ŽL-NL. y1 Gyttja ŽNL. y1 Muddy gyttja ŽL. 1.1 Gyttja ŽNL. 0.4 Gyttja mud ŽL. 0.4 Gyttja mud ŽL. 0.4 Gyttja ŽNL. 0.4 Muddy gyttja ŽL-NL. 0.4 Bark frag. Gyttja ŽNL. 0.2 Gyttja mud ŽL-NL. 0.2 Gyttja ŽNL.

90–100

Lab. dating ref.

Sample dry wt. d13 C totalrdated Žg.

T-12402A

173r6.3

y23.8

9150"55a

10,150–10,025

Isolation

50r– 36r– 21r– 0.71r– 11r1.2 54r36 66r10.3 7r– 50r2.6 46r4.1 r32.3 16r4.9 21r8.4 0.29r– 16r– 29r– 11r–

y23.3 15 y23.9 55 y24.0 50 y29.9 0 y21.6 y26.0 25 y25.6 75 y30.3 2 y20.0 100 y25.4 90 y21.9 y28.7 25 y27.4 45 y28.3 0 y28.8 y25.9 2 y25.7 0

9165"65 9185"75 9340"100 5415"75 b 6875"140 b 7790"100 c 8935"70 c 8140"65 5790"115 6310"130 5830"95 5560"130 4895"95 4835"65 4920"65 4130"55 3430"70

10,190–10,030 10,225–10,035 10,420–10,170 6295–6110 7800–7550 8610–8420 9990–9890 9195–8980 6740–6450 7310–7040 6755–6515 6470–6230 5720–5580 5645–5485 5715–5605 4815–4545 3735–3590

Isolation Isolation Isolation Post-isolation Isolation Post-isol.ringression? Isolation Žearly. Isol.rpost-isolation? Isolation Žearly. Isolation Žlate.

149–153 50–55 46–50 61–68 57–60 498–508 488–498 46–50 172–179 165–172

TUa-1608A TUa-1607A TUa-2383A TUa-2661 T-12394A T-12395A T-14127A TUa-1606A T-12396A T-14126A T-14126B 162–165 T-14125A 74–79 T-12398A 69–74 TUa-2658 TUa-2659A 22–27 TUa-1605A 17–22 TUa-2660A

Pollen stratigraphic correlation suggests this date is too young. Inverted dates caused by twig being drawn down during coring. c Inverted dates suggest unconformable succession. b

% mariner Laboratory 14 brackish C date Ž . diatoms % Žyears BP.

Calibrated Event C date Žyears BP "1 s .

14

Post-isolation Isolation Post-isolation Isolation Post-isolation

G.D. Corner et al.r Global and Planetary Change 31 (2001) 155–177

Laker Threshold Tilt sample elevation corr. Žm a.s.l.. Žm. loc.

G.D. Corner et al.r Global and Planetary Change 31 (2001) 155–177

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non-laminated Žfreshwater. gyttja may show a considerable age difference, justifying our strategy of preferentially dating the laminated unit. Individual dates should be treated with caution and, ideally, several dates should be obtained from each succession, preferably from different fractions, including terrestrial plant macrofossils, in order to verify the accuracy of the results ŽKaland et al., 1984; Lowe et al., 1988; Miller et al., 1999..

6. Facies types and interpretation

Fig. 4. Relationship between d13 C values and percentage marinerbrackish diatoms in gyttja and muddy gyttja samples of freshwater and inferred mixed marine–freshwater origin from isolation basins at Polyarny Žnumbered. and in the Nikel–Kirkenes area ŽCorner et al., 1999..

mulation may have been more rapid during the isolation phase. For example, in lake 7, which contains an exceptionally thick Ž14 cm. laminated unit, the estimated age difference is about 60 years Žrather than 450 years. if an annual origin for the laminae is assumed. 5.2.3. Age difference between bulk gyttja and plant macrofossils A date from bark fragments extracted from lacustrine gyttja in lake 8 was 85 years Ž70–120 cal. years. younger than the date from the bulk gyttja sample. To conclude, the dating results show generally close agreement Ž"200 years. between obtained and expected ages, but larger differences are found in some cases. We note a tendency for dates from laminated gyttja from the lowermost part of the isolation succession to appear to be too young. In lakes having a low sedimentation rate Že.g., lake 9., samples from laminated Žtransitional. and overlying

The stratigraphic succession in each basin is analysed with reference to three major genetic facies units, considered to reflect major or potentially significant differences in depositional environment, and identified primarily based on lithological character. These units are: I—marine Žminerogenic., II—transitional Žorganic or mixed organicrminerogenic, typically laminated. and III—freshwater lacustrine Žorganic.. Subunit I T , which occurs at the top of unit I and is clearly transitional to the overlying unit, is recognised in some basins. Major facies which are repeated in a succession are distinguished as stratigraphic units for descriptive purposes Že.g., II-1, II-2, III-1, III-2.. A further subdivision into subunits Že.g., II-1a, II-1b, II-a, II-b. is made as appropriate. Facies codes based on field characteristics of lithologic compositionrgrain size and structure are also used for descriptive purposes on the sedimentary logs ŽTable 3.. The general characteristics and an environmental interpretation of the three major genetic facies types in the investigated basins are given below.

Table 3 Lithofacies codes for isolation basin sediments Lithology Ždominant, subordinate)10%.

Structure

tO: Plant detritus l: laminated O, o: Gyttja, organic-rich lw: weakly laminated P, p: Mud Žpelite., muddy d: deformed S, s: Sand, sandy G, g: Gravel, pebbly Q, q: shell bed, shelly Example: pOl—laminated muddy gyttja Žgyttja) mud)10%.

164

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6.1. Marine facies unit I Marine facies unit I consists of minerogenic material: typically structureless olive grey to dark grey mud or sandy mud, often containing isolated shells or shell fragments and ice-rafted or seaweed-rafted pebbles. The upper 2 cm of unit I in two lakes shows weak lamination combined with slightly darker colour Žsubunit I T .. Diatoms in unit I comprise mostly polyhalobous and mesohalobous Žmarinerbrackish. species, with halophilous and indifferent Žbrackishr freshwater and freshwater. species appearing in the uppermost few centimetres in some lakes. In two lakes, samples from unit I contain an abnormally high content of indifferent species, most likely the result of resedimentation or transport into the lake. Facies unit I is interpreted as having formed under marine conditions up until a time when the basin no longer received regular replenishment of oxygenated marine water. 6.2. Transitional facies unit II Transitional facies unit II typically comprises olive grey or olive brown to very dark brown or black laminated or weakly laminated gyttja mud, muddy gyttja or gyttja. The lamination varies in appearance, ranging from rhythmic alternations of distinct, millimetre-thick, light and dark laminae ŽFig. 5., to diffuse horizontal or slightly irregular banding. This facies is the sole constituent of unit II in five lakes and occurs together with other facies Žstructureless gyttja mud, plant detritus, and deformed weakly laminated muddy gyttja. in two other lakes. Where present Žin seven of the nine lakes., unit II ranges in thickness from 1 to 14 cm, except in lake 5 where it is exceptionally thick Ž162 cm.. Laminated gyttja facies also occurs higher in the succession, within structureless gyttja Žunit III facies., in two lakes Ž3 and 5.. The marine to freshwater diatom transition occurs within or just above the top of unit II in a typical I–II–III succession. In such cases, unit II formed during the transition between marine and lacustrine phases, when the basin no longer received marine water across the threshold during high tide. During this phase, marine bottom water in the basin became anoxic or was subject to enhanced seasonal variability in oxygen content, bioturbation ceased, and diatom deposition gradually changed from domi-

Fig. 5. Photograph illustrating a marine–lacustrine transition Žregressive I–I T –II–III facies succession. in lake 7.

nantly marinerbrackish to freshwater. The laminated facies of unit II formed during this phase, possibly under meromictic Žsalinity stratified. conditions that may have persisted for some time after isolation ŽCorner and Haugane, 1993; Corner et al., 1999.. The isolation contact, which corresponds approximately to mean high-tide level, is accordingly placed at or near the base of the laminated unit. 6.3. Lacustrine facies unit III Lacustrine facies unit III typically comprises black, very dark grey, or very dark brown gyttja. Coarse detritus gyttja overlies fine detritus gyttja in some lakes. Unit III varies greatly in thickness Ž24– ) 170 cm, Fig. 3., depending strongly on local conditions and partly on elevation above sea levelr time elapsed since isolation. Indifferent Žfreshwater.

G.D. Corner et al.r Global and Planetary Change 31 (2001) 155–177

diatom species dominate in unit III, often together with a small component of halophilous Žbrackishr freshwater. and halophobous Žfreshwater. species near the base.

7. Basin stratigraphy and isolation history Three lakes Ž1, 4 and 8. show a succession in which all three genetic facies units are found as a regressive I–II–III facies sequence ŽTable 1.. Two lakes Ž7 and 9. also contain a transitional I T subunit as part of a regressive I–I T –II–III succession in which the sedimentary transition from marine to lacustrine environment is even clearer lithologically.

165

Two lakes Ž2 and 6. show an abrupt I–III succession indicating a rapid or unconformable marine–lacustrine transition, and two lakes Ž3 and 5. show a I–II–III–II–III succession which may be related to sea-level fluctuation at the threshold. A description of the succession in each basin and its interpretation in terms of relative sea-level change follows. 7.1. Lake 1 (South of Pala Bay; threshold 57 m a.s.l.) The stratigraphy comprises a I–II–III succession ŽFig. 6.. Pollen analysis of 27 samples spanning units I–III indicates a regional vegetation history extending back to the Allerød, with a dominance of

Fig. 6. Stratigraphy of lake 1 showing location of pollen samples, pollen assemblage zones according to Yelovicheva et al. Ž1998., and estimated ages of regionally recognizable levels based on a comparison with pollen diagrams from Varanger ŽPrentice, 1981, 1982..

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herbs and shrubs during deposition of unit II and the uppermost part of unit I, and a dominance of trees during deposition of unit III and the lower part of unit I ŽYelovicheva et al., 1998. ŽFig. 7.. A radiocarbon date of 9150 " 55 years BP from the lower half of unit II appears too young compared with the pollen stratigraphy. Key levels in the pollen diagram which can be correlated regionally ŽK.-D. Vorren, personal communication., are the BetularEricales shift in the upper part of unit II Žlocal pollen zones 7–8., and a rise in Artemisia in the upper part of unit I Žlocal pollen zones 3–4.. Comparing with well-dated pollen diagrams from two comparable lakes on the Varanger Peninsula, 160 km to the west ŽPrentice, 1981, 1982. suggests that these key levels have an age of approximately 9100–9400 and 11,000 years BP, respectively. The level for the latter date is uncertain given the sparse pollen content below assemblage zone 7. A rise in Larix in zone 3 suggests that the base of the Younger Dryas Ž11,000 years BP. may be placed at the base rather than the top of zone 3 as indicated by Yelovicheva et al. Ž1998.. The Younger Dryas–Preboreal transition Ž10,000 years BP., according to Yelovicheva et al. Ž1998., lies close to the base of unit II. Thus, on the basis of regional pollen stratigraphy, the lower half of unit II has an estimated age of approximately 9500–10,000 years BP, which is more than 500 years older than the obtained radiocarbon date. There is no evidence, either lithological or pollen stratigraphic, to suggest that the obtained cores contain other than a conformable succession. Equisetaceae appear in the pollen diagram in the lower part of unit III ŽFig. 7., suggesting that the dating discrepancy may be caused by contamination by rootlets of Equisetum fluÕiatile ŽK.-D. Vorren, personal communication.. On lithological evidence and in the absence of diatom data, the isolation contact would normally be placed at the base of the laminated gyttja Žsubunit IIc.. However, the sharp drop in frequency of pine pollen shown by the pollen diagram in the middle of unit IIc may indicate the end of a phase of marine overrepresentation of these pollen grains, which tend to collect in large quantities on the water surface in the littoral zone ŽKaland, 1984; Fægri et al., 1989.. We infer that regular marine incursion ceased at this level. The isolation contact is therefore placed between this level and the base of unit IIc. It has an

estimated age of about 9500 years BP, corresponding to mean high-tide level at the threshold. 7.2. Lake 2 (South of Pala Bay; threshold 48 m a.s.l.) The stratigraphy ŽFig. 8. comprises a I–III succession and shows a progressive change in diatom flora ŽFig. 9. from dominantly polyhalobous and mesohalobous Žmarinerbrackish. species in unit I Žmainly Plagiogramma staurophorum., to almost exclusively indifferent oligohalobous Žfreshwater; notably Pinnularia Õiridis . and halophilous Žbrackishr freshwater. species in the lower part of unit III. The absence of a transitional facies unit II and the progressive change in diatom flora from marinerbrackish to freshwater suggests a rapid transition rather than a hiatus. A radiocarbon age of 9165 " 65 years BP from the lowermost part of unit III corresponds to a time shortly after isolation and mean high-tide level slightly below the threshold. 7.3. Lake 3 (South of Pala Bay; threshold 41 m a.s.l.) The stratigraphy ŽFig. 8. comprises a complex I–II–III–II–III succession and a diatom flora that fluctuates from dominantly polyhalobous and mesohalobous species in the uppermost part of unit I and lowermost laminated unit ŽII-1., to dominantly indifferent oligohalobous Žmainly P. Õiridis . and then reverting to dominantly polyhalobous and mesohalobous species in structureless unit III-1. Paralia sulcata is the most abundant species amongst polyhalobous and mesohalobous diatoms. A shell bed in unit I most likely reflects the position of the coring site near the threshold, where tidal currents would be strong leading up to isolation. The laminated gyttja mud lithology of unit II-1 and increase in brackishrfreshwater diatoms from unit I to II-1 suggest that unit II-1 was deposited following isolation, perhaps under meromictic conditions. An increase in marinerbrackish diatoms in the overlying stuctureless gyttja Žunit III-1. and development of a thin laminated bed overlying it Žunit II-2. suggest subsequent re-establishment of meromictic conditions, possibly as a result of storm overtopping of the threshold. Radiocarbon dates of 9185 " 75 years BP and 9340 " 100 years BP from the lower and upper

G.D. Corner et al.r Global and Planetary Change 31 (2001) 155–177

Fig. 7. Relative pollen diagram for lake 1 Žanglicised after Yelovicheva et al., 1998.. Compare Fig. 6 for lithostratigraphy. Scale in percentage.

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part of the unit II-1 to II-2 succession, respectively, show an inverted age relationship and together give an approximate date for isolation of the basin Žinitial isolation and subsequent storm overtopping., corresponding to mean high-tide level close to the threshold. 7.4. Lake 4 (Olenja–Pala Bay; threshold 31 m a.s.l.) The I–II–III succession ŽFig. 8. appears to represent a conformable transition from a marine to a lacustrine environment. The isolation contact is placed at the base of the laminated bed in unit II. A twig having freshly broken Žunstained. ends, spanning the unit I–II boundary and dated to 5415 " 75 BP, was probably dragged downwards from unit III during coring and gives a minimum age for basin isolation. A radiocarbon age of 6875 " 140 years BP Žor slightly younger if a marine reservoir age correction is necessary. from the upper half of unit II dates a time shortly after isolation, corresponding to mean high-tide level slightly below the threshold. 7.5. Lake 5 (Pala Bay; threshold 28 m a.s.l.)

Fig. 8. Stratigraphy of lakes 2, 3, 4 and 6. Diatom salinity groups are: I — oligohalobous indifferent, HL — oligohalobous halophilous, M—mesohalobous, P—polyhalobous.

The stratigraphy ŽFig. 10. comprises an unusually thick I–II–III–II–III succession and highly variable diatom flora that fluctuates between dominantly polyhalobous to dominantly indifferent oligohalobous around the unit I–II contact. The indifferent species Aulacoseira alpigena and A. distans are abundant in the lowermost sample, but do not occur at higher levels, and P. sulcata is the dominant polyhalobous species. The fluctuating marinerbrackish to freshwater diatom flora in units I and II, the occurrence together of polyhalobous and halophobous diatoms, and evidence of deformational folding in unit II-1a, suggest that the lower part of the succession is not conformable. This is supported by radiocarbon dates which show an inverted age relationship: 7790 " 100 years BP in unit II-1a and 8935 " 70 years BP in unit II-1b. The isolation contact is placed tentatively at the base of laminated unit II-1b, above which level the frequency of freshwater diatoms increases relative to marinerbrackish diatoms. The occurrence of P. sulcata in the samples probably indicates the proximity of isolation rather than a strong marine influence ŽZong, 1997..

G.D. Corner et al.r Global and Planetary Change 31 (2001) 155–177 Fig. 9. Diatom diagram for lake 2 indicating a fairly normal, though possibly abrupt, transition from marine to freshwater environment. See Fig. 8 for lithostratigraphy and an explanation of the diatom salinity groups.

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Fig. 10. Stratigraphy of lake 5 showing the full succession and recovered core levels Žleft. and detailed stratigraphy around the unit I–II transition Žright.. See Fig. 8 for an explanation of the diatom salinity groups.

The great thickness Ž152 cm. of the lower, transitional, laminated unit ŽII-1b, II-1c. and the occurrence, 106 cm higher in the succession, of a second laminated unit ŽII-2., is unusual and may be explained by: Ž1. slumping causing thickening and repetition of units, Ž2. a low rate of emergence followed later by a minor ingression and new isolation Žcf. Kaland, 1984; Svendsen and Mangerud, 1990., or Ž3. seasonal variations in organic sediment deposition caused by factors unrelated to sea-level change Žcf. Peglar et al., 1984; Zolitschka, 1996; Card, 1997.. The second of these alternatives, combined with slumping in the lowermost part of unit II,

is favoured given the setting and character of the sediments. The older of the two dates obtained from the bottom of unit II-1 Ž8935 " 70 years BP. may represent a time close to initial isolation, corresponding to mean high-tide level near the threshold. 7.6. Lake 6 (Southeast of Sayda Bay; threshold 26 m a.s.l.) The I–III succession in this lake ŽFig. 8. suggests an abrupt transition from a marine to a freshwater environment, or the presence of a hiatus. The diatom flora ŽFig. 11. changes from dominantly mariner

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171

Fig. 11. Diatom diagram for lake 6 showing a likely unconformable succession and mixed Žresedimented. diatom assemblage. See Fig. 8 for lithostratigraphy and an explanation of the diatom salinity groups.

brackish species in the lower part of unit I, to dominantly freshwater species in the upper part of unit I and the lower part of unit III. It appears to be anomalous, however, on account of an unusually high content of indifferent oligohalobous species in unit I, and the occurrence of both polyhalobous and halophobous species in the same sample in units I and III. This suggests a mixed flora caused by reworking of previously deposited material. The isolation contact is either missing in this core or occurs in the lower part of unit III. A radiocarbon date of 8140 " 65 years BP from the lowermost part of unit III may postdate or correspond approximately to isolation of the basin, depending on whether the isolation contact is missing or not. 7.7. Lake 7 (Lesnaja Bay, Sayda bay; threshold 22 m a.s.l.)

The isolation contact is placed at the base of unit II, which may have formed wholly or partly during a meromictic lake phase. Samples from three successive levels in units II to III gave radiocarbon dates of 5790 " 115 years BP Žsample 7a, soluble fraction., 6310 " 130 years BP Žsample 7b, soluble., 5830 " 95 years BP Žsample 7b, insoluble. and 5560 " 130 years BP Žsample 7c, soluble., respectively. These dates compare reasonably well with each other based on estimated sedimentation rates Žbetween 60 and 450 years; see Section 5.2., although it appears that sample 7a may be too young or sample 7b may be too old. Averaging all four dates gives an age of 5870 years BP, which is taken as a reliable estimate of the age of unit II, immediately postdating the isolation contact, and corresponding to mean hightide level just below the threshold. 7.8. Lake 8 (Sayda Bay; threshold 17 m a.s.l.)

The stratigraphy ŽFig. 12. shows a well-developed I–I T –II–III succession and a gradual change in the diatom flora from exclusively polyhalobous and mesohalobous species in unit I and the lowermost part of unit II Ždominantly Paralia sulcata and P. quadratarea., to exclusively indifferent oligohalobous and halophobous species in unit III.

The stratigraphy ŽFig. 12. shows a typical I–II–III succession and change in diatom flora from dominantly polyhalobous Žnotably P. sulcata. and mesohalobous species in units I and II, to exclusively indifferent oligohalobous and halophobous species in the lowermost part of unit III. The isolation contact

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is placed at the base of unit II. Samples from successive levels in unit II and the lowermost part of unit III are dated to 4985 " 95 BP Žsample 8a., 4920 " 65 years BP Žsample 8b, bulk gyttja. and 4835 " 65 years BP Žsample 8b, birch bark fragments.. The age of the lowermost sample Ž8a. corresponds to a time immediately after isolation and sea level just below the threshold. 7.9. Lake 9 (Finsko, Lesnaja Bay, Sayda Bay; threshold 12 m a.s.l.) The well-developed I–I T –II–III succession ŽFig. 12. suggests a gradual transition from a marine to a lacustrine environment. The diatom flora, however, appears abnormal compared with other successions on account of a dominance of indifferent oligohalobous species Žparticularly A. distans . rather than marinerbrackish species near the top of unit I. This may be related to a high freshwater input or an associated depositional event prior to basin isolation. Above this, the diatom flora shows a normal transition, with dominantly indifferent and subordinate polyhalobous, mesohalobous and halophilous species in unit II and almost exclusively indifferent oligohalobous species in unit III. The isolation contact is therefore placed at the base of unit II. A radiocarbon date of 4130 " 55 BP from gyttja mud and gyttja spanning unit II and the lowermost part of unit III corresponds to a time shortly after isolation and mean high-tide level slightly below the threshold. A radiocarbon date of 3430 " 70 years BP from the lower part of unit III postdates isolation.

8. Relative sea-level curve

Fig. 12. Stratigraphy of lakes 7, 8 and 9. Radiocarbon dates marked A and B were obtained from the soluble and insoluble fractions, respectively. See Fig. 8 for an explanation of the diatom salinity groups.

Fig. 13 shows a relative sea-level curve constructed for the Polyarny area based on dated isolation contacts in each of the nine investigated lake basins. The curve, and the dates on which it is based, are plotted in both radiocarbon and calibrated years. All dates obtained from core samples are plotted in the diagram at a level corresponding to their respective lake threshold elevations, adjusted to compensate for differential uplift Žtilt. since isolation. The adjustment Žtilt correction. was made relative to centrally located lake 4 by measuring the distance of

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173

Fig. 13. Relative sea-level curve for the Polyarny area based on dated core samples taken from close to the isolation contact in nine raised coastal lake basins. The curve and data points are plotted in conventional radiocarbon years Žcontinuous line. and calibrated years Žshort-dashed line.. Dating uncertainty Ž"1 s . and estimated maximum elevation errors are indicated by symbol width and height, respectively. Arrows indicate data points interpreted as being clearly younger than the isolation contact. Threshold elevations have been adjusted for differential uplift since emergence, relative to the elevation of centrally located lake 4.

each lake from lake 4 perpendicular to the shoreline isobase direction ŽFig. 1. and multiplying this distance by the gradient of the shoreline corresponding to basin isolation age, estimated from shoreline diagrams for the adjacent region of Norway ŽMarthinussen, 1945, 1960; Sollid et al., 1973; Møller, 1989.. The relative sea-level curve therefore refers specifically to elevations at locality 4. The tilt correction, however, is relatively small Ž- "1 m, Table 2.. Because pollen stratigraphy in lake 1 shows local deglaciation during the Allerød, the relative sea-level curve is extended to the Younger Dryas datum at ; 80 m a.s.l., having an inferred age of 10,300– 10,500 years BP ŽMarthinussen, 1974; Snyder et al., 1997; Corner et al., 1999.. The relative sea-level history is reconstructed assuming that the isolation contact corresponds to mean high-tide level, situated ; 1.5 m above mean sea level. The following evaluations are made for sites where the elevation-age plot indicates the need for adjustment to provide internal consistency among data points. Ž1. Radiocarbon dates from lakes 1, 2 and 3 are too close considering the elevational difference

among these lakes, and the date from lake 1 is too young according to pollen stratigraphic evidence. The relative sea-level curve is therefore drawn less steeply for this portion of the curve to provide a smooth fit between higher and lower levels. Ž2. Lakes 4, 5 and 6 are closely spaced in elevation Ž26–31 m a.s.l.. yet show a wide range of dates from close to the isolation contact Ž8935 " 70 to 6875 " 140 years BP.. Considered together, the elevation-age data from these lakes, as well as the stratigraphic succession in at least one of them Žlake 5., indicate a stillstand or slight rise in relative sea-level. In lake 5, a complex I–II–III–II–III succession suggests both an ingression and a prolonged phase of isolation Žcf. Kaland, 1984; Krzywinski and Stabell, 1984; Bondevik et al., 1998.. The oldest date from this lake, from gyttja in unit II-1 Ž8935 " 70 years BP., probably gives an approximate age for initial isolation, whereas the youngest date, from disturbed, mixedrfreshwater gyttja in unit II-1 Ž7790 " 100 years BP., may postdate an ingression. The uppermost laminated unit ŽII-2. in lake 5 has an estimated age of 4000–4500 years BP, assuming a uniform rate of sedimentation. It may be older if the

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sedimentation rate was higher during the transition period, and it may represent a final phase of basin isolation, although both the origin and age of this unit are uncertain. In lake 6, an abrupt, probably non-conformable, I–III succession, yielding a date of 8140 " 65 years BP, is consistent with an ingression, or with slumping following isolation or an ingression. Lake 4, on the other hand, shows a normal, I–II–III, regressive succession and no evidence of an ingression. With an isolation age of slightly younger than 6875 " 140 years BP, it must be situated lower than lakes 5 and 6, which were isolated earlier. The relative sea-level curve is therefore drawn to show a small sea-level rise following initial isolation of lakes 5 and 6, and a fall in sea level starting just before isolation of lake 4.

9. Discussion The relative sea-level curve ŽFig. 13. shows a rapid Ž4–5 cm yeary1 . sea-level fall between 10,000 and 9000 years BP, a stillstand or slight rise between 8500 and 7000 years BP, and a moderate rate of fall Ž; 0.5 cm yeary1 . between 7000 and 4000 BP, slowing to 0.2–0.3 cm yeary1 after 4000 years BP. Tide gauge records show that present rates of emergence are 0.3 cm yeary1 ŽEmery and Aubrey, 1991.. The combined evidence from lakes 4, 5 and 6 suggests that relative sea level between 8500 and 7000 years BP lay approximately 27 m above present mean s.l. There is little difference between the curves plotted using conventional radiocarbon and calibrated years, apart from a generally lower gradient in the latter case. Fig. 14 compares the relative sea-level curve for Polyarny with curves constructed previously for adjacent areas: Dalny Zelentsy to the east ŽSnyder et al., 1997. and the Nikel–Kirkenes area to the west ŽCorner et al., 1999.. The curve for Nikel–Kirkenes was constructed using marine-reservoir-age corrected dates from gyttja containing marinerbrackish diatoms. A re-evaluation of these dates, following conclusions drawn in the present article, suggests that only one of these dates Žfrom a non-laminated gyttja containing marine fish bones. probably re-

Fig. 14. Relative sea-level curves constructed for three locations along the northern Kola coast: Dalnie Zelentsy ŽSnyder et al., 1997., Nikel–Kirkenes ŽCorner et al., 1999. and Polyarny Žpresent work.. Two curves are shown for Nikel–Kirkenes: the original curve Ždotted line., which was based on gyttja dates adjusted for a marine reservoir age, and a revised curve Žcontinuous line., in which only one gyttja date was adjusted for a marine reservoir age.

quires a significant reservoir age correction. A modified relative sea-level curve for Nikel–Kirkenes based on uncorrected gyttja dates is shown in Fig. 14, together with the original curve. The three relative sea-level curves for the northwest Kola Peninsula ŽFig. 14. show a pattern of uplift which conforms predictably with the position of each site relative to the margin of the retreating Fennoscandia ice sheet and the direction of tilt shown by the reconstructed postglacial isobases. The initial rapid postglacial emergence indicates pronounced glacio-isostatic rebound immediately following deglaciation. The innermost locality at Nikel–Kirkenes, just inside the Younger Dryas end moraine zone, shows the greatest amount of postglacial emergence, whereas the outermost locality at Dalnie Zelentsy, some distance outside this end moraine zone, shows the least. Pollen stratigraphic evidence from the highest lake ŽYelovicheva et al., 1998. suggests that the Polyarny area was deglaciated during the Allerød and Younger Dryas and that the area is situated north of the Younger Dryas end moraine zone rather than to the south of it as shown previously ŽNiemela¨ et al., 1993; Andersen et al., 1995; Rainio et al., 1995..

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The stillstand or relative sea-level rise around 7000 years BP correlates with the regional Tapes transgression ŽHolocene trangsression maximum. which is dated as peaking between 7000 and 6000 years BP in this northern area ŽMarthinussen, 1962; Donner et al., 1977; Corner and Haugane, 1983; Møller, 1989; Fletcher et al., 1993; Snyder et al., 1996. and elsewhere along the coast of Norway ŽSvendsen and Mangerud, 1987; Bondevik et al., 1998.. The transgression is predictably greatest at the outermost area, and appears to die out at the inner localities, at around 25–30 m a.s.l. This is similar to the pattern in northern Norway ŽCorner and Haugane, 1983; Tanner, 1930; Sollid et al., 1973; Marthinussen, 1945; Møller 1987, 1989; Snyder et al., 1996.. Less predictable features of the reconstructed relative sea-level histories shown by Fig. 14 include a mid-Holocene stillstand in the Nikel–Kirkenes area which appears to be approximately 5 m too low relative to the regional Tapes isobases ŽFig. 1., and a rather late age for the waning of this stillstand. Possible reasons for these differences, discussed by Corner et al. Ž1999., include errors in the regional isobases combined with complexity in the Tapes shorelines, neotectonics, or elevationrdating errors. It should be stressed that the reconstructed sealevel curves for Polyarny and Nikel–Kirkenes are smoothed curves which do not take into account possible, short-term Ž- 500 years. fluctuations in relative sea-level caused by eustatic–climatic factors ŽEmery and Aubrey, 1991; Fletcher et al., 1993; Morner, 1999. or neotectonics ŽDehls et al., 2000; ¨ Fjeldskaar et al., 2000.. At both Polyarny and Nikel–Kirkenes, lake stratigraphies were found indicating possible minor sea-level fluctuations, at approximately 40 and 35 m a.s.l., respectively. The cause and magnitude of these fluctuations are uncertain; at Polyarny Žlake 3. a storm-surge origin is postulated, whereas at Nikel–Kirkenes a more prolonged transition is recorded. Resolving questions raised above about regional differences in relative sea-level change and the importance of short-period variations or local tectonic factors would require considerably more work entailing detailed stratigraphic study of several lakes at critical levels, multiple datings from each lake, and precise elevation control.

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10. Conclusions Ž1. Radiocarbon dates from gyttja at different levels close to the isolation contact in raised coastal lake basins at Polyarny show a fairly close correspondence Ž"200 years. with expected ages in most cases and a greater deviation in a few cases. Samples from laminated gyttja containing mostly mariner brackish diatoms and situated close to the isolation contact tend to have higher d13 C values than samples of non-laminated gyttja containing mostly freshwater diatoms and occurring above the isolation contact. This suggests a change in the source of the organic material upwards in the succession. A reduction for marine reservoir age is considered to be unwarranted in most cases. Ž2. Of the nine investigated lake basins, five contain a I–II–III Žmarine–transitional–lacustrine. facies succession indicative of a single isolation event, two contain an abrupt I–III succession indicating a rapid or unconformable marine–lacustrine transition, and two contain a I–II–III–II–III succession suggesting slight ingression following initial isolation. One of the ingressive successions Žlake 5, postdating 8900–7800 years BP. is correlated with the regional Tapes transgression, the other Žlake 3, 9200 years BP. may be the result of a short-lived climatically induced overtopping of the threshold following isolation. Ž3. The reconstructed relative sea-level curve for Polyarny shows a rapid Ž4–5 cm yeary1 . rate of relative sea-level fall between 10,000 and 9000 years BP Žfrom 80 to 30 m a.s.l.., a stillstand or slight rise in relative sea-level at a level of approximately 27 m a.s.l. between 8500 and 7000 years BP, and a moderate rate of relative sea-level fall Ž- 0.5 cm yeary1 . after 7000 years BP. The inferred relative sea-level history indicates a glacio-isostatic response that is broadly intermediate between that shown by more distal and proximal localities along the margin of the retreating Fennoscandian ice sheet on the northern Kola coast. Ž4. Pollen stratigraphic evidence from the highest lake ŽYelovicheva et al., 1998. shows that the Polyarny area was deglaciated during the Allerød and Younger Dryas and that previously reconstructed Younger Dryas glacier margins along the north Kola coast lie too far north.

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Acknowledgements We thank Lyudmila Ya. Kagan ŽKola Science Centre-RAS, Apatity. for diatom analyses; Steinar Gulliksen ŽLaboratory of Radiological Dating, Trondheim. for discussion and help with calibrating dating results; Karl-Dag Vorren for advice on the pollen stratigraphy; Marit Berntsen and Mary Raste for grain-size analyses; and Tove Midtun and Jan Petter Holm for preparing the diagrams. Stein Bondevik, Steven Forman and an anonymous referee are thanked for constructive criticism of the manuscript. The work was supported by a grant from the Norwegian Research Council’s Barents Sea programme.

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