Sea-Level Fluctuations Imply That the Younger Dryas Ice-Sheet Expansion

ARTICLE IN PRESS

Quaternary Science Reviews 26 (2007) 2128–2151

Sea-level ﬂuctuations imply that the Younger Dryas ice-sheet expansion in western Norway commenced during the Allerød

Øystein S. Lohnea,Ã, Stein Bondevikb, Jan Mangeruda,c, John Inge Svendsena,c

aDepartment of Earth Science, University of Bergen, Alle´gaten 41, N-5007 Bergen, Norway bDepartment of Geology, University of Tromsø, Dramsveien 201, N-9037 Tromsø, Norway cThe Bjerknes Centre for Climate Research, Alle´gaten 55, N-5007 Bergen, Norway

Received 20 December 2005; received in revised form 11 April 2007; accepted 11 April 2007

Abstract

After the ﬁrst emergence following deglaciation, relative sea level rose by 10 m in western Norway and culminated late in the Younger Dryas (YD). The relative sea-level history, reconstructed by dating deposits in isolation basins, shows a sea-level low-stand between 13 640 and 13 080 cal yr BP, a 10 m sea-level rise between 13 080 and 11 790 cal yr BP and a sea-level high-stand between 11 790 and 11 550 cal yr BP. Shortly after the YD/Holocene boundary, sea level fell abruptly by 37 m. The shorelines formed during the sea-level low-stand in the mid-Allerød and during the sea-level high-stand in the YD have almost parallel tilts with a gradient of 1.3 m km1, indicating that hardly any isostatic movement has taken place during this period of sea-level rise. We conclude that the transgression was caused by the major re-advance of the Scandinavian Ice Sheet that took place in western Norway during the Lateglacial. The extra ice load halted the isostatic uplift and elevated the geoid due to the increased gravitational attraction on the sea. Our results show that the crust responded to the increased load well before the YD (starting 12 900 cal yr BP), with a sea-level low-stand at 13 640 cal yr BP and the subsequent YD transgression starting at 13 080 cal yr BP. Thus, we conclude that the so-called YD ice-sheet advance in western Norway started during the Allerød, possibly more than 600 years before the Allerød/YD transition. r 2007 Elsevier Ltd. All rights reserved.

1. Introduction the peak of the transgression (Lohne et al., 2004) supports this causative connection. The numerical simulations A 9–12 m relative sea-level rise during the Lateglacial indicated that the re-growth of the ice sheet slowed down constitutes a conspicuous feature of the Late Weichselian the rebound of the crust and the growing ice-mass sea-level history of western Norway (Krzywinski and attracted, by gravity, more seawater towards the coast Stabell, 1984; Anundsen, 1985; Lohne et al., 2004). The (Fjeldskaar and Kanestrøm, 1980; Anundsen and Fjelds- transgression was called the Younger Dryas (YD) trans- kaar, 1983). As a result of this ice-sheet advance the model gression, when it became clear that the most of the sea-level simulated a signiﬁcant transgression in western Norway rise occurred during this period (Anundsen, 1985). during the YD. These models experiments presupposed a Numerical simulations carried out in the 1980s suggested uniform eustatic sea-level rise through the Lateglacial that the transgression was caused by a major (450 km) YD (Shepard, 1963). More recently, however, it has been ice-sheet re-advance (Mangerud, 1977; Fjeldskaar and shown that the eustatic sea-level rise occurred more Kanestrøm, 1980; Anundsen and Fjeldskaar, 1983; Mangerud, stepwise with episodes of rapid sea-level rise, referred to 2004). A strong synchronicity between the maximum as meltwater pulses (Fairbanks, 1989). The best known of ice-sheet position (Bondevik and Mangerud, 2002) and these pulses is the Meltwater Pulse 1A (MWP-1A), which represents a 20 m rise in eustatic sea-level over a period of 500 years, centred at 14 000 cal yr BP (Peltier and ÃCorresponding author. Tel.: +47 55 58 33 60; fax: +47 55 58 36 60. E-mail addresses: [email protected] (Ø.S. Lohne), Fairbanks, 2006). Several studies have also found that [email protected] (S. Bondevik), [email protected] the rate of eustatic sea-level rise was signiﬁcantly reduced (J. Mangerud), [email protected] (J.I. Svendsen). or even halted during the YD (Edwards et al., 1993; Bard

0277-3791/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2007.04.008 ARTICLE IN PRESS Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151 2129 et al., 1996; Dullo et al., 1998; Lambeck et al., 2002; Zinke Stabell, 1984) was one of the ﬁrst to document the et al., 2003; Camoin et al., 2004). These recent results Lateglacial transgression in Western Norway. Many of strengthen the argument that the YD transgression in the basins were analysed in detail both for pollen and western Norway was caused by regional effects and not so diatoms. The curve has subsequently been revised by much by a global sea-level rise. In order to understand the correcting the basin elevations for differential uplift (tilt) transgression event better, more precise description of its and by using another interpretation of the chronostrati- three-dimensional extension and timing is required. Here graphy in some of the basins (Anundsen, 1985; Svendsen we present a well-dated sea-level curve from the island and Mangerud, 1987). We have now further improved the Sotra, 10 km west of Bergen (Fig. 1), which represents a Lateglacial part of this curve by collecting new cores from major step forward in achieving this objective. two of the previously studied basins and by analysing an In the late 1970s, a large number of isolation basins were additional basin. Together these basins record the Allerød studied at Sotra (Fig. 1) to construct a relative sea-level low-stand and the YD high-stand. Many samples of curve. The Lateglacial part of the curve (Krzywinski and terrestrial plant macrofossils have been dated and a solid

Fig. 1. Map showing locations of the studied sites in Hordaland, western Norway. The most important localities are named and given symbols. Other localities are numbered according to Table 4. Elevations of marine terraces are adjusted to mean sea level (see text). Late YD isobases (stippled inside the former ice sheet) with a direction 3511 are shown for every 10 m. Projection plane for an equidistant shoreline diagram (Fig. 11) is shown. The indicated ice front position is the Herdla Moraines (Aarseth and Mangerud, 1974) showing the maximum ice-sheet extension with a late YD age (Bondevik and Mangerud, 2002). The YD ice sheet margin in southern Norway (Mangerud, 2004) is indicated on the inset map. ARTICLE IN PRESS 2130 Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151 calendar year chronology for the Lateglacial sea-level changed by human actions (e.g. local road construction, changes has been established. The Holocene part of the curve farming, etc.) and an additional uncertainty of 70.5 m has has also been calibrated and re-evaluated (Krzywinski and therefore been added in these cases. Stabell, 1978; Stabell and Krzywinski, 1979), and here we A Russian peat corer was used to investigate the depth present a complete curve from Sotra on a calendar year and sediment infill in the basins along prescribed transects. time scale. Based on this survey, we selected the location for the main Contributing processes that may have caused such a core used for further laboratory analyses. The main cores transgression (isostasy, eustasy, gravity) would affect the were recovered using either a 110 mm diameter piston corer tilt of the shorelines differently. In order to resolve the or a 110 mm diameter Russian peat corer. connections, we construct the shorelines that correspond to Loss on ignition and magnetic susceptibility were the mid-Allerød low-stand and the high-stand in the late recorded for all of the cores. Samples of constant volume YD. To draw these shorelines, we combined the new sea- (1 cm3) were dried overnight at a temperature of 105 1C and level curve from Sotra with and other curve from Os than heated to 550 1C for 1 h. Loss on ignition was (Lohne et al., 2004) as well as the altitudes of a number of calculated as a weight percentage of the dried sample. marine limit terraces in the area (Fig. 1). Magnetic susceptibility and density were analysed using a In the present paper, we use the term ‘YD transgression’, GEOTEK Multi-Sensor Core Logger. even though our data suggests that the relative sea-level rise Diatom slides were prepared as smear slides and started during the preceding Allerød period. Note that the mounted with Mountex (RI ¼ 1.67). At least 300 diatom term is used to signify a vertical change of the shoreline, i.e. valves were identified (Hustedt, 1930, 1930–1966, 1957; a relative sea-level rise. Hendey, 1964; Krammer and Lange-Bertalot, 1986, 1988, 1991a, b; Witkowski et al., 2000) and counted on each slide, 2. Methods and the diatom distribution was plotted as percentages grouped by salinity preferences (Table 1) as determined Our main strategy in reconstructing former sea-level empirically (de Wolf, 1982; Denys, 1991/1992). changes has been to use the so-called isolation basin Radiocarbon dating was performed on terrestrial plant method (Hafsten, 1960; Svendsen and Mangerud, 1987). macrofossils in order to avoid hardwater effects and The basis of this method is that the stratigraphic boundary marine reservoir age problems (Mangerud and Gulliksen, between marine and lacustrine sediments in lakes corre- 1975; Barnekow et al., 1998). The plant fragments were sponds with the isolation of the lake from the sea, i.e. the carefully picked from sieved material larger than 250 mm. time when the sea level fell below the level of the outlet In order to establish a firm chronology on a calendar year threshold of the lake basin. Such a sedimentary boundary, time scale, a series of samples were 14C dated from each where marine sediments are overlain by lacustrine deposits, sequence and an age model developed for each dated is termed an isolation contact. When relative sea-level rises section. and inundates a lake, brackish/marine sediments start to Conversion to calendar year ages was based on analysis accumulate above the lacustrine sediments and this of each series of dates using the sequence function in the boundary is called an ingression contact. The isolation OxCal v3.10 calibration software (Bronk Ramsey, 2005) and ingression contacts are considered to reflect the period and the INTCAL04 calibration dataset (Reimer et al., when the altitude of the outlet threshold corresponds with 2004). This method takes advantage of Bayesian statistics, local high tide level. which allows prior information to be incorporated into the The basins investigated in the present study were levelled calibration process. In the case of stratigraphic sequences, to a survey control point tied to the national datum level the prior rule imposed is that ages have to increase with (NN1954). At a tide gauge in the city of Bergen, the depth (Blockley et al., 2004). The method generates what is NN1954 datum lies 1.5 cm above local mean tide level called prior and posterior probability distributions of (Olav Vestøl, Norwegian Mapping Authority, 2004, pers. calibrated ages for each sample. The prior (unconstrained) comm.). Uncertainties connected to the levelling and the distribution is simply the probability curve for the datum level are in the order of a few centimetres and are negligible in the present context. In the original Sotra study (Krzywinski and Stabell, 1984), the threshold elevation of Table 1 Diatom salinity groups after Hustedt (1957) the basins were measured from the upper growth limit of the brown algae Fucus vesiculosus that is considered to be Halobian group Salinity tolerance close to the mean tide level (Berge et al., 1978). We assume 7 Polyhalobous Marine water taxa (430% salinity) an uncertainty of 0.5 m for these measurements, corre- Mesohalobous Brackish water taxa (30–0.2% salinity) sponding to a site-specific determination of the Fucus Oligohalobous Taxa that can live in both brackish and fresh water, vesiculosus upper growth limit and its relation to the mean halophilous optimum in brackish water tide level. All basins have a bedrock threshold that has Oligohalobous Taxa that can live in both brackish and fresh water, undergone negligible erosion after isolation from the sea. indifferent optimum in fresh water Halophobous Fresh water taxa ( 0.2% salinity) Nevertheless, some of the basin thresholds have been o ARTICLE IN PRESS Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151 2131 calibrated age range for each single 14C date. The posterior LOI, magnetic susceptibility and the density. The dates (constrained) distribution is the result of constraining the and the lithostratigraphy indicate that this boundary calibrated probability distributions to ensure that all ages represents the Allerød/YD transition. The Vedde Ash increase with depth. The agreement index (A) expresses the Bed is present at a depth of 1178 cm and is recognised convergence between the prior and posterior distributions. as a thin, hardly visible lamina. A distinct gravelly layer An A-index is calculated for the entire sequence and for occurs at 1167 cm. At 1161–1158 cm, there is a distinct, but each individual date and can be used as a measure of the gradual transition to the overlying dark brown (Holocene) reliability of the imposed age model and for each date gyttja (Fig. 2). (Walker et al., 2003; Blockley et al., 2004). The ‘sequence The diatom record shows that nearly all the deposits in function’ in OxCal treats the radiocarbon dates as though the basin are lacustrine, except for an 8-cm interval of they were evenly distributed in the sequence, but has a marine/brackish sediments close to the YD/Holocene possibility for separating segments of better dated intervals transition. This interval is dominated by marine- and using so-called ‘boundaries’. The dates obtained for our brackish-water diatoms—both planktonic and benthic records are unevenly distributed, being concentrated close species, and dinoflagellate cysts (Fig. 2, Appendix A to the sea-level events of interest, and hence we tested and B). There are also many valves of different euryhaline models using boundaries. A test with unbound models Fragilaria taxa that are often associated with isolation produced only slightly different results (figure not shown). contacts (Stabell, 1985). The frequent occurrence of the The occurrence of the Vedde Ash Bed (Mangerud et al., Fragilaria taxa may indicate that only spring tides reached 1984) in all our cores provided a useful marker for both above the bedrock threshold of the basin at this time. Other correlation in the field and as a calendar year index lakes at Sotra that are located at a slightly higher elevation point with a date of 12 121757 ice core (GICC05) yr BP (e.g. Førekleivsvatn at 41.3 m a.s.l., Table 4) do not show (Rasmussen et al., 2006). When necessary the ash layer was any trace of a marine incursion. Thus, we infer that the identified by counting ash particles larger than 63 mm under threshold at Gardatjønn was slightly below (0–2 m) the a stereomicroscope sieved from samples of constant high tide sea level when the sediment with brackish/marine volume (1 cm3). The distinct rise in Betula (birch) pollen diatoms was deposited. which occurs close to the YD–Holocene boundary Radiocarbon ages show that the marine interval is (Kristiansen et al., 1988; Paus, 1989; Berglund et al., centred on the 10 000 14C yr BP plateau. The Vedde Ash 1994; Bondevik and Mangerud, 2002) also provided a Bed occurs at 1178 cm, 9 cm below the first occurrence of useful stratigraphical marker. At Os (Fig. 1) the Betula rise marine diatoms, and the rise of Betula (birch) pollen was is found stratigraphically slightly above the YD–Holocene found 2 cm below the upper boundary of the marine boundary and was estimated to be 20–40 years younger interval (at 1163 cm, Fig. 2). We used Bayesian analysis on than this boundary (Lohne et al., 2004). the 15 radiocarbon ages from the core, including the age of the Vedde Ash Bed. The resulting age model (Fig. 3) 3. The investigated basins suggests an age of ca 11 790 cal yr BP for the lower boundary of the marine interval (ingression contact) and 3.1. Gardatjønn (39.370.5 m a.s.l.) ca 11 550 cal yr BP for the upper boundary, i.e. the isolation contact (Table 3). This means that the high-stand sea level Gardatjønn (60117.680N–05105.200E) is a small in Gardatjønn lasted about 240 years (Fig. 3). Thus, the (75 75 m) lake located in the central part of the island high-stand occurred from the very late YD and lasted a Sotra (Fig. 1). The lake has a drainage/surface area ratio few decades into the early Preboreal (slightly after the of 16.3/0.6 ha. A road built across the outlet area has Betula rise). disturbed the former threshold of the lake. The given altitude of 39.3 m a.s.l. was measured on the bedrock 3.2. Hamravatn (29.170.5 m a.s.l.—tilt adjusted to surface in the outlet creek, and we believe the lake level 31.571.4 m a.s.l.) could not have been higher than this because tree trunks are rooted along the lake shores. The thickest Lateglacial Hamravatn (601 12.410N–051 05.130E) is a small deposits were located in a small area within the deepest (50 250 m) lake in the south-western part of the island part of the lake, from where the analysed piston core Sotra (Fig. 1), with drainage/surface area ratio of 41.3/ (505-27) was obtained. 0.6 ha. The stratigraphy of the basin was originally The base of the core (Fig. 2) consists of a diamicton, investigated by Krzywinski and Stabell (1984). We re- interpreted as a till. The units above the till (1206–1187 cm) examined the deposits in the lake using a Russian peat consist of a transitional silt and clay at the base with a corer and collected two overlapping cores with a piston gradual transition to a silty gyttja and the organic content corer from the central and deepest part of the lake, at is gradually increasing upwards in the succession (Fig. 2). 601 12.410N–051 05.130E. The new cores can easily be At 1187 cm, the lithology changes sharply to brownish grey correlated by lithology with the core presented in Fig. 14 gyttja silt with a lower content of organic matter. Across in Krzywinski and Stabell (1984). However, our radio- this boundary there is also recorded a distinct change in the carbon ages are about 200–300 years younger than ARTICLE IN PRESS 2132 Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151

Fig. 2. Stratigraphy of core 505-27, obtained from the small lake Gardatjønn at Sotra (Fig. 1). The grey shaded area highlights a short interval of marine/ brackish sediments close to the YD/Holocene boundary. Detailed pollen and diatom diagrams are shown in Appendices A and B, respectively.

Krzywinski and Stabell’s (1984) three 14C ages from gyttja (1312–1290 cm) and which shows that relative sea corresponding stratigraphical depths. Because their sam- level was below the outlet threshold for a period during the ples are of bulk sediments and the deposits have low Allerød. The lower boundary constitutes a sharp sedimen- carbon content (LOI values are low), we consider our dates tary change from a layer of homogenous greyish silt at the based on terrestrial plant fragments to be more reliable. base to a layer of finely laminated algae gyttja above. The The lithostratigraphy of our core is described in Fig. 4 and diatom stratigraphy also reveals a sharp transition from a it represents deposits from the deglaciation of the area marine to lacustrine assemblage across this boundary and (prior to 12 270 14C BP) to the early Holocene. The verifies the inferred position of the isolation contact. sediments and diatoms reflect a depositionary environ- Marine diatoms reappear in the sediments just above the mental succession from glacio-marine–marine–lacustrine upper boundary of the silty gyttja. The ingression contact (Allerød)–marine (YD)–lacustrine (Holocene). has been interpreted to coincide with the lithological Our main focus has been the lower lacustrine phase boundary at 1290 cm, even though species grouped as (Fig. 4) which coincides with the deposition of the silty freshwater indicators also occur above this boundary. ARTICLE IN PRESS Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151 2133

3.3. Sekkingstadtjønn (24.370.5 m a.s.l.–tilt-adjusted 29.471.1 m a.s.l.)

Sekkingstadtjønn (601 21.000N–041 59.660E) is a small (100 150 m) lake situated at the western part of the island of Sotra (Fig. 1). Two parallel Russian cores from the deepest part of the lake revealed a zone of densely laminated sediments (1303–1291 cm depth) about 65 cm below the Vedde Ash Bed between (Fig. 5). Such laminations are characteristic for brackish sediments deposited during the isolation of a basin (Kaland, 1984; Svendsen and Mangerud, 1987). However, Krzywinski and Stabell (1984) reported that no traces of lacustrine or brackish sediment were found in the Lateglacial sequence from this site. The partly laminated brownish silty gyttja is 12 cm thick with olive grey and reddish brown laminae (Fig. 5). The LOI values are distinctly higher than below and above. The lower boundary of the laminated zone is sharp with respect to visible lithology, colour and LOI. The diatoms show a similar pattern with a sharp transition from a marine dominated flora below 1303 cm to predominantly lacustrine/brackish species at the base of the overlying unit (Fig. 5, Appendix C). According to the diatoms, the lower boundary (at 1303 cm in Fig. 7) represents the time when the local sea level fell below the basin threshold, so that seawater only occasionally, at very high tides, flowed into the basin. At 1299 cm, about 90% of the diatom flora belongs to lacustrine/brackish species and probably sea- Fig. 3. Calibrated probability distributions for the 14C dates from Gardatjønn that were calibrated using Oxcal (Bronk Ramsey, 2005) and water entered the basin only at extreme high tides and/or the INTCAL04 data-set (Reimer et al., 2004). The Vedde Ash Bed is during storm surges. Above this level, the diatom flora is included and is assigned a calendar year date of 12 121757 cal yr BP gradually replaced by marine species and, 10 cm higher up (Rasmussen et al., 2006). The prior unconstrained probability distribu- (at 1289 cm), only scattered freshwater diatoms occur. It is tions are shown as clear curves. The posterior probability distributions, difficult to determine precisely the boundary representing shown as filled black curves, are constrained by the Bayesian probability assumption of age increase with depth. The agreement index is given when the basin became submerged during the subsequent (as %) for each sample and for the whole sequence, indicating the transgression because of very gradual changes of the reliability of the imposed model (see methods). The ages for the ingression diatom assemblages. In general, the signature of diatom and isolation contacts are weighted averages of the posterior probability assemblages at ingression contacts varies between basins distributions (Table 3). The lowermost date in the core is obviously too due to differences in the rate of sea-level change, exposure young (Fig. 2) and was omitted in the Bayesian analysis. to open marine waters, freshwater input, and the size and bathymetry of the basin. Sekkingstadtjønn has limited freshwater input from a small (16.1 ha) drainage area. We therefore suggest that the increasing amount of marine These are mainly euryhaline Fragilaria species (Appendix B) diatoms from 1299 cm upwards reflects increasing inci- that are often found close to isolation and ingression dences of spring tides entering the basin and that daily tides contacts (Stabell, 1985). first rose above the threshold of Sekkingstadtjønn at the From the upper part of the lacustrine gyttja and in the time corresponding with the horizon at 1291 cm, where succeeding marine silt, we dated five levels; the sample at marine diatoms become dominant (490%). The gradual the ingression contact between 1290 and 1292 cm has an increase of marine diatoms may suggest that relative sea- age of 11 080750 14C yr BP. However, from the first level rise at this time was somewhat slower than the sea- isolation of the lake we could only find material for one level fall at the transition from full marine to brackish sample, dated 12 090760 14CyrBP (Fig. 4). By using the environment that occur at the base of the laminated unit. Bayesian analysis (not shown) of the sequence of dates and The contacts below and above the brackish zone (at 1303 the stratigraphical position of the Vedde Ash Bed, the age and 1291 cm) are hereafter termed the isolation and of the isolation and the ingression contacts to ca 13 920 ingression contacts, respectively, even though we assume and 12 950 cal yr BP (Table 3), respectively. The model that the basin was not entirely isolated from the sea during generated an agreement index of 99.2%. this time span. The important result is that the brackish ARTICLE IN PRESS 2134 Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151

Fig. 4. Stratigraphy of core 505-19 from the small lake Hamravatn at Sotra (Fig. 1). Highlighted in grey shade is an interval of lacustrine sediment showing that the basin was above the contemporary sea level during the Allerød. Detailed diatom diagram is shown in Appendix C. See Fig. 2 for legend.

deposit demonstrates that the threshold of Sekkingstadt- and thus the sea-level low-stand lasted about 560 years in jønn precisely deﬁnes the sea level at the Lateglacial low- Sekkingstadtjønn (Fig. 6). stand and that the interpreted position of the ingression contact provides a reliable minimum age for the start of the 4. The sea-level curve from Sotra subsequent transgression. In order to derive a precise age for the low-stand, we Although the main focus of the present study is the dated terrestrial plant macrofossils at nearly every cm regional Lateglacial sea-level history, we have also included throughout the laminated unit (Fig. 5, Table 2). The radiocarbon ages of Holocene age obtained from other sequence of radiocarbon dates and the age estimates for published isolation and ingression contacts on Sotra the Vedde Ash Bed were analysed using the OxCal (Table 4) to produce a complete Lateglacial and Postglacial Bayesian algorithm (Fig. 6). The model estimate an age sea-level curve (Fig. 7). of ca 13 640 cal yr BP for the ﬁrst isolation contact and The basins at Sotra are located at different uplift ca 13 080 cal yr BP for the subsequent ingression contact isobases (Fig. 1). In order to combine them all into one (Table 3). According to this chronology, the brackish phase sea-level curve, the altitude of the basins are adjusted for ARTICLE IN PRESS Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151 2135

Fig. 5. Stratigraphy of core 505-102, obtained from Sekkingstadtjønn at Sotra (Fig. 1). Indicated in grey shading is an interval of brackish/lacustrine sediment, showing the sea-level low-stand during the Allerød. Detailed diatom diagram is shown in Appendix D. See Fig. 2 for legend. differential isostatic uplift. The sea-level curve has been started before the onset of the YD period, usually dated to constructed for an isobase through Gardatjønn with a have commenced at 12 900 cal yr BP (e.g. Hughen et al., direction of 351731 (see below, Table 4). The tilt gradient 2000). The marine/brackish sediments, dated between ca varies through time and the individual sea-level index 11 790 and 11 550 cal yr BP in Gardatjønn represent the points for the Lateglacial period have been adjusted peak of the YD transgression at 39.3 m a.s.l. Continuous according to shoreline gradients determined in the present lacustrine deposits occur in the 2 m higher basin at study (see below) and the Holocene points according to the Førekleivsvatn (Krzywinski and Stabell, 1984), marked as shoreline gradients from the diagram of Kaland (1984). site 4 at Fig. 7, supporting this interpretation. The sea-level The basins are distributed along the isobases over a curve indicates that the amplitude of the YD transgression distance of about 30 km (Fig. 1), which due to uncertainties was 9.771.6 m at Sotra and that the average sea-level rise of the isobase directions introduces uncertainties to the during the transgression was 7 mm yr1. projected position at the projection plane and therefore During the early Holocene the relative sea level fell add to the uncertainties in the tilt corrections (Table 4). rapidly from 40 m a.s.l. to below 5 m a.s.l. in 1500 years (Fig. 7). This major regression started soon after the rise in 4.1. Lateglacial and early Holocene sea-level changes Betula sp. (birch) pollen and is dated to about ca 11 550 cal yr BP at Gardatjønn. Also the pollen diagrams The stratigraphy and the 14C ages from the three basins (Krzywinski and Stabell, 1984) from basins slightly below Gardatjønn, Sekkingstadtjønn and Hamravatn precisely Gardatjønn (Kvernavatn 38.9 m a.s.l., Klæsvatn 34.9 m a.s.l., deﬁne the YD transgression (Fig. 7). The Allerød low- Hamravatn 31.3 m a.s.l.) support the conclusion that the stand is determined in Sekkingstadtjønn, at 29.6 m a.s.l., regression started after the ﬁrst distinct Betula rise. which also indicates a more or less stable relative sea level at this site for about 560 years between ca 13 640 and 4.2. Holocene sea-level changes and the Storegga tsunami 13 080 cal yr BP. After this still-stand, relative sea level started to rise and inundated the 2-m-higher Hamravatn ca Re-evaluation of the evidence from the basins that were 12 950 cal yr BP. Thus, it is evident that the transgression affected by Holocene sea-level changes indicates that ARTICLE IN PRESS 2136 Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151

Table 2 Radiocarbon dates obtained from the sequences investigated in this study. In the Gardatjønn sequence we have used plant material from a parallel 110 mm Russian core in addition to the plant material from the core 505-27 described in the text

Locality Core Depth (cm) Terrestrial plant material dated Submitted Laboratory 14C age sample no. (yr BP) weight (mg)

Gardatjønn 505-121 1144.5–1147.5 Leaf fragments, wood, moss stems 3.54 Poz-6368 9520750 Gardatjønn 505-121 1150.5–1152.5 Leaf fragments, twig, wood 4.48 Poz-6369 9780750 Gardatjønn 505-121 1153.5–1155.5 Leaves (3), leaf fragments, Rhacomitrium 6.66 Poz-6370 9890750 Gardatjønn 505-121 1155.5–1156.5 Leaf fragments (S. herbacea) 5.65 Poz-6371 10 080750 Gardatjønn 505-27 1158.5–1159.5 S. herbacea leaves (3), leaf fragments 6.08 Poz-5130 10 040750 Gardatjønn 505-121 1159.5–1160.5 S. herbacea and S. polaris leaves, Rhacomitrium 11.75 Poz-5129 10 050750 Gardatjønn 505-27 1160.5–1161.5 S. herbacea leaves, leaf fragments 5.12 Poz-5185 9980750 Gardatjønn 505-27 1161.5–1162.5 S. herbacea leaves 7.82 Poz-5133 10 090760 Gardatjønn 505-27 1167.5–1168.5 S. herbacea leaves (4), Rhacomitrium, leaf frag. 4.88 Poz-5134 10 060760 Gardatjønn 505-27 1168.5–1169.5 S. herbacea leaves (3), Rhacomitrium, leaf frag. 5.17 Poz-5135 10 170760 Gardatjønn 505-27 1169.5–1170.5 Twig, leaf fragments 3.90 Poz-6372 10 090750 Gardatjønn 505-27 1171.5–1172.5 Twigs (2), leaf fragments 5.10 Poz-5136 10 270750 Gardatjønn 505-121 1186.5–1187.5 Leaves and leaf fragment, Rhacomitrium 9.15 Poz-5184 10 940760 Gardatjønn 505-121 1187.5–1188.5 S. herbacea and S. polaris leaves, Rhacomitrium 7.49 Poz-5131 10 910760 Gardatjønn 505-121 1199.5–1200.5 Leaf fragments 5.30 Poz-5132 12 130760 Gardatjønn 505-27 1201.5–1203.5 Leaf fragments 4.24 Poz-5137 11 720760a Hamravatn 505-19 1278–1280 S. herbacea, Rhacomitrium 27.16 Poz-4811 10 370750 Hamravatn 505-19 1285–1287 S. herbacea, Rhacomitrium, twig 5.51 Poz-4812 10 820760 Hamravatn 505-19 1290–1292 Bud scales (2), Rhacomitrium, twig 8.07 Poz-4813 11 080750 Hamravatn 505-19 1292–1294 S. polaris , Rhacomitrium 22.64 Poz-4814 11 070760 Hamravatn 505-19 1294–1296 S. polaris, Polytrichum, Rhacomitrium 11.52 Poz-4815 11 090750 Hamravatn 505-19 1312–1314 Rhacomitrium, Polytrichum, twig 3.86 Poz-4817 12 090760 Hamravatn 505-19 1348–1350 Leaf fragments, mosses 2.56 Poz-4818 12 270770 Sekkingstadtjønn 505-102 1252.5–1253.5 Dryas and S. herbacea leaves, Rhacomitrium 11.72 Poz-4908 10 700760 Sekkingstadtjønn 505-102 1292.5–1293.5 Rhacomitrium, bud scale, leaf fragments 5.71 Poz-5095 11 320770 Sekkingstadtjønn 505-102 1293.5–1294.5 Rhacomitrium, Polytrichum, leaf fragments 16.11 Poz-5096 11 440770a Sekkingstadtjønn 505-102 1294.5–1295.5 S. herbacea leaves, twigs, Rhacomitrium, Polytrichum 6.13 Poz-4909 11 310760 Sekkingstadtjønn 505-102 1295.5–1296.5 Rhacomitrium, fragments of S. herbacea leaves 11.80 Poz-4910 11 310760 Sekkingstadtjønn 505-102 1296.5–1297.5 S. herbacea leaves (4), Rhacomitrium, leaf fragments 20.30 Poz-4911 11 450760 Sekkingstadtjønn 505-102 1297.5–1298.5 Rhacomitrium, S. herbacea leaves, leaf fragments 14.31 Poz-4912 11 430760 Sekkingstadtjønn 505-102 1298.5–1299.5 Rhacomitrium, Polytrichum, leaf fragments 11.39 Poz-4819 11 310760a Sekkingstadtjønn 505-102 1299.5–1300.5 Rhacomitrium, S. herbacea leaf, leaf fragments 16.61 Poz-4914 11 470760 Sekkingstadtjønn 505-102 1300.5–1301.5 Rhacomitrium, leaf fragments 12.52 Poz-4915 11 560760 Sekkingstadtjønn 505-102 1301.5–1302.5 Rhacomitrium, Polytrichum, leaf fragments 8.83 Poz-4821 11 720760 Sekkingstadtjønn 505-102 1302.5–1303.5 Rhacomitrium, Polytrichum, leaf stem 4.87 Poz-4922 11 830760 Sekkingstadtjønn 505-102 1319.5–1321.5 Rhacomitrium, leaf fragments 7.13 Poz-4823 12 040760

aNot used in age modelling.

several of the sediment sequences were interrupted by the Storegga tsunami (Table 4). Judged by the available hiatuses, massive sand beds and chaotic sediments, indi- descriptions (Indrelid et al., 1976; Berge et al., 1978; Stabell cating significant disturbance. These features have later and Krzywinski, 1978), the remaining basins used to date been shown to be characteristic for basins inundated by the the sea-level curve seem undisturbed near the isolation and Storegga tsunami (Bondevik et al., 1997a, b). The tsunami ingression contacts. However, the sediment descriptions occurred about 7300 14C yr BP, or ca 8150 cal yr BP (Bondevik are sparse and it is quite possible that traces of the Storegga et al., 2005) and was the result of the giant Storegga slide tsunami have been overlooked. According to our judge- offshore Norway (Haflidason et al., 2004). ment, two parts of the curve (Fig. 7) are uncertain for Tsunami deposits have been found in isolation basins this reason; the exact position of the low-stand at both below and above the shoreline of that time. Near 9500 cal yr BP and part of the subsequent relative sea- Sotra, the tsunami had a run-up of at least 3–5 m level rise (the mid-Holocene Tapes transgression), prior to (Bondevik et al., 1997a) and one would expect that it the Storegga tsunami impact at 8150 cal yr BP. inundated most of the basins that were isolated after The lacustrine sequence in Trollabotn shows that the sea 11 000 cal yr BP. When drawing the revised sea-level level in the early Holocene fell below 4.8 m a.s.l. (Fig. 7, curve, we have excluded basins where the relevant part of Table 4). The thickness of this sequence is 35 cm and, the stratigraphical sequence obviously was disturbed by according to the dates, this sequence accumulated during a ARTICLE IN PRESS Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151 2137 period of 510–1180 years (68.2% confidence limit, Table 4). the Storegga tsunami. The lacustrine sequence may there- In addition, the boundary to the overlying marine fore have been thicker and represented a longer time span. sediments is sharp and may represent a hiatus caused by We assume that the low-stand was slightly lower, but lacustrine sediments are yet not reported in lower basins. The effect of the tsunami cause problems for reconstructing the trend of the mid-Holocene Tapes transgression (Bondevik et al., 1997a, 1998). Before the AMS method was introduced, bulk samples of lacustrine sediments just below the ingression contact were dated. If the tsunami had eroded the top of this unit, the dates would yield ages that are too old. Two ‘‘ingression dates’’ (locs. 10 and 15, Table 4) have been omitted because massive sand beds indicating erosion were described on this boundary (Indrelid et al., 1976; Berge et al., 1978; Stabell and Krzywinski, 1978). In the other basins (locs. 9, 12 and 13, Table 4), the descriptions do not indicate erosion and these dates are therefore plotted and used to draw the dotted curve in Fig. 7. However, it is quite probable that erosion occurred even here and we have therefore drawn an alternative curve showing a slower transgression (stippled curve in Fig. 7), which is supported by recent observations (Skulstad, 2006). Stabell and Krzywinski (1979) interpreted thin horizons of greenish algae gyttja in two different basins to represent the maximum of the Tapes transgression (locs. 11 and 16, Fig. 6. Estimates of calendar year ages of the dates and events in Table 4). However, the oldest of these dates (loc. 11, Sekkingstadtjønn sequence derived using a Bayesian probability approach. The Vedde Ash Bed is assigned a calendar year date at 12 121757 cal yr BP Storevatn) is of Storegga tsunami age, and as chaotic (Rasmussen et al., 2006). Prior unconstrained probability distributions sediments occur frequently in the basin (Berge et al., 1978), (clear) and posterior probably distributions (black) (constrained by the this date is therefore rejected. The date from basin no. 16 assumption that age should increase with depth) are shown. The agreement (Torkevikstjønn) post date the Storegga tsunami and index (percentages) is shown for each sample and for the whole sequence, constrain the culmination of the Tapes transgression to indicating the reliability of the imposed model (see methods). Two dates obtained agreement indexes below 60% and is not included in the above 6900 cal yr BP (Stabell and Krzywinski, 1978). The last presented model. The ages for the ingression and isolation contacts are 6900 years is characterised by gradual lowering of relative weighted averages of the posterior probability distributions (Table 3). sea level.

Table 3 Calendar year estimates for events dated in the present study by series of terrestrial plant material 14C dates, listed in chronological order. The calibration and the Bayesian probability calculations were performed using the OxCal v3.10 software (Bronk Ramsey, 2005) and the INTCAL04 calibration data set (Reimer et al., 2004). The posterior probability distributions are calculated using the Sequence function in OxCal

Event Depth (cm) Number of radiocarbon OxCal-posterior ranges: OxCal-weighted average dates used in the Bayesian 68.2%/95.4% (cal yr BP) of posterior distribution model (cal yr BP)

Hamravatn: Isolation 1313 7 dates+Vedde ash bed 14 000–13 840 13 940 14 060–13 790 Sekkingstadtjønn: Isolation 1303 11 dates+Vedde ash bed 13 750–13 580 13 640 13 780–13 460 Sekkingstadtjønn: Ingression 1291 11 dates+Vedde ash bed 13 190–13 020 13 080 13 220–12 880 Hamravatn: Ingression 1290 7 dates+Vedde ash bed 12 990–12 910 12 940 13 030–12 880 Gardatjønn: Ingression 1169 15 dates+Vedde ash bed 11 890–11 700 11 790 11 950–11 640 Gardatjønn: Isolation 1161 15 dates+Vedde ash bed 11 620–11 480 11 550 11 700–11 420 ARTICLE IN PRESS 2138 Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151 kansson (1980) ˚ Krzywinski and Stabell (1984) Krzywinski and Stabell (1984) Krzywinski and Stabell (1984) Krzywinski and Stabell (1984) Krzywinski and Stabell (1984) Krzywinski and Stabell (1984) Krzywinski and Stabell (1984) Krzywinski and Stabell (1984) Krzywinski and Stabell (1984) Krzywinski and Stabell (1984) Krzywinski and Stabell (1984) Bondevik et al. (2006) Stabell and Krzywinski (1978) Stabell and Krzywinski (1978) Ha Stabell and Krzywinski (1978) Stabell and Krzywinski (1979) Stabell and Krzywinski (1978) Krzywinski and Stabell (1984) Krzywinski and Stabell (1984) Krzywinski and Stabell (1984) Bondevik et al. (2006) Event Reference Isolation c (95.4%-cal yr BP) 210 15 450–13 450120 Isolation 13 800–13195 000 13 150–12 630 Ingression 120 Ingression 12 450–11180 250 12 250–10180 750 Isolation 12 650–11100 150 Isolation 12 650–11130 450 Isolation 12 000–11120 150 Isolation 12 250–1190 250 Isolation 110 Isolation 11 750–11 150 11 200–1070 400 Isolation 70 Isolation 10 700–10 28095 10 975 Isolation 90 10 710–10 24085 11 150–10 400 Isolation 90 11 100–10 400 Isolation 140 10 800–10 250 Isolation 10 750–9900100 Isolation 10 650–10 150 Isolation Isolation 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 C age (yr BP) Calibrated age 14 deglaciation stand Lab. number ) 1 Tilt gradient (m km 0.49 1.30.56 1.30.64 No marine 1.3 sediments0.56 at base. Upper limit of T-2896A the sea 1.3 level0.49 at No lacustrine 1.3 Allerød sediments. 12 Lower 080 limit of the T-2895A Allerød low- 0.53 Lu-1552 1.30.49 11 320 1.30.56 10 870 T-2636 1.30.57 T-2892A 1.30.56 10 180 T-2889A 1.30.51 9980 Lu-1529A 1.30.37 10 150 T-2885A 1.3 10 260 0.64 T-2632 0.50.79 9970 Lu-1503A 0.50.79 10 130 T-2888A 0.50.25 9920 TUa-3242 0.50.38 9470 TUa-3242 0.50.39 9315 Lu-1353A 0.50.13 9315 Lu-1498A 0.50.29 9290 Lu-1581A 0.50.24 9460 Lu-1361A 0.5 9420 T-2886A 9340 Lu-1357A 9190 9150 0.02 1.3 No marine sediments. Upper limit of the YD transgression. 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 3.88 Distance baseline (km) 1.31.5 0.41 1.6 3.56 1.5 4.05 1.3 3.56 0.5 0.41 1.4 0.6 1.3 2.94 1.5 0.41 1.5 2.46 1.5 3.14 1.4 3.56 1.1 1.83 0.9 3.92 1 4.05 1 3.23 0.7 3.23 0.8 3.64 1.3 4.18 0.60.7 6.48 0.6 4.04 4.03 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 Tilt corr. elevation (m a.s.l.) 0.5 38.7 0.5 35.1 0.5 27.9 0.5 35.1 0.5 38.7 0.5 41.3 0.5 39.6 0.5 38.7 0.5 37.9 0.5 36.6 0.5 35.1 0.5 31.5 0.5 29.4 0.5 24.6 0.5 19.4 0.5 19.4 0.50.5 13 11.3 1.0 11.1 0.5 10.8 0.5 10.3 0.5 8.7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 9.2 7.6 8.5 6.9 Present elevation (m a.s.l.) 38.2 30.5 22.6 30.5 38.2 40.5 38.2 35.8 34.7 32.5 30.5 29.1 24.3 22.6 17.8 17.8 11.2 13.0 N, E N, E N, E N, E N, E N, E N, E N, E N, E N, E N, E N, E E N, E N, E N, E N, E N, E N, E N, E N, E N, E 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .0N, 0 15.8 10.9 17.7 12.4 21 10.9 25.4 25.4 21.2 14.2 14.4 14.9 11.8 11.8 22.6 12.1 22.6 23.1 23.2 11.8 02.9 03.5 03.2 03.5 02.9 04.6 04.1 02.9 00.5 59.7 03.5 05.2 03.4 58.8 58.8 02.2 59.3 10.8 58.7 02.0 01.8 22.6 59.6 14.9 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Geo-ref (lat, long) 60 60 60 60 60 60 60 60 05 05 05 05 05 05 05 05 05 04 05 05 05 04 04 05 04 05 04 05 05 04 Figs. a a a a a a a a ) Kaldavatn (12) 60 1 and 7 Table 4 Age calibrated and tilt-corrected sea-level index points fromLocality (no. other in studies at Sotra, listed chronologically Storevatn (3) 60 Kvernavatn (1) Førekleivsvatn (4) 60 Kvernavatn (1) Krokavatn (6) Tresstjønn (7) Klæsvatn (2) HamravatnSekkingstadtjønn 60 60 Storevatn (3)Kvaltjern (8) 60 Kvaltjern (8) 60 60 Einerhaugtjønn (10) 60 Storavatn (11) 60 Skittjønn (13)Klokkarvatnet (14) 60 60 Klæsvatn (2) Klæsvatn (2) Storetjønn (5) Kvernavatn (1) 60 Lommatjønn (9) 60 ARTICLE IN PRESS Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151 2139 kansson (1980) kansson (1980) ˚ ˚ Stabell and Krzywinski (1978) Stabell and Krzywinski (1978) Kaland et al. (1984) Kaland et al. (1984) Stabell and Krzywinski (1978) Stabell and Krzywinski (1979) Stabell and Krzywinski (1978) Kaland et al. (1984) Stabell and Krzywinski (1979) Kaland et al. (1984) Stabell and Krzywinski (1978) Stabell and Krzywinski (1979) Stabell and Krzywinski (1978) Stabell and Krzywinski (1978) Ha Stabell and Krzywinski (1978) Ha Stabell and Krzywinski (1978) Stabell and Krzywinski (1978) 70 7160–6740 Tapes max 60 4980–4610 Isolation 100 10 500–9750110 9490–900085 Isolation 110 9250–8600 Ingression 9150–850080 Ingression 100 8650–8370 Ingression 8330–800075 Ingression 8390–8010 Ingression 65 Tapes max 65 6440–612050 5750–5460 Isolation 5280–4850 Isolation 60 Isolation 60 5280–482055 4800–4200 Isolation 55 4090–3720 Isolation 55 3040–2760 Isolation 55 3170–2840 Isolation 2740–2360 Isolation Isolation 55 2350–2130 Isolation 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 0.90.9 0.50.13 0.4 T-2891A 0.40.29 T-2890A 0.40.38 9020 Lu-1360A 0.30.39 8260 T-2887A 0.30.25 8060 Lu-1497A 0.3 7950 Lu-1354A0.25 7720 Lu-1580A 0.20.38 7400 0.10.29 7330 Lu-1355A 0.1 Lu-1496A0.13 5490 T-2884A 0.10.24 4880 0.10.35 4410 Lu-1359A 0.10.53 Lu-1356A 0.10.35 4340 Lu-1583A 0.10.14 3990 Lu-1495A 0.1 3600 Lu-1582A 2790 Lu-1528A 2860 2490 0.69 0.1 Lu-1527A 2240 0.59 0.2 Lu-1553A0.27 6050 0.1 Lu-1358A 4260 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 3.88 3.25 3.46 ) and omitted in the sea-level curve. 10.9 1.78 0.6 1.78 0.6 6.48 0.7 4.04 1.2 4.18 0.60.7 3.64 0.5 4.2 0.6 3.64 0.5 4.18 0.5 4.04 0.5 3.9 0.5 6.48 0.5 4.03 0.50.5 3.94 0.5 6.81 0.5 3.06 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 0.5 12.3 Bondevik et al., 1997a 0.50.5 5.6 0.5 5.4 0.5 9.9 0.5 9.9 10.5 1.0 11.8 0.5 12.6 0.5 11.7 0.50.5 9.6 0.5 8.9 0.5 8.3 0.5 8.2 0.5 7.3 0.5 7 0.5 5.5 0.5 5.5 3.8 0.5 3.8 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 77 7 7 7 4.8 4.8 7.6 8.5 9.2 9.2 8.5 7.9 7.6 6.9 7.3 5.3 5.7 3.5 3.6 13.0 11.2 11.8 11.2 N, E N, E N, E N, E N, E N, E N, E N, E N, E N, E N, E N, E N, E N, E N, E N, E N, E N, E N, 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 22.7 15.7 14.9 15.8 26.6 15.8 14.4 14.9 23.3 21.2 14.4 14.6 14.9 14.4 14.5 24.4 26.6 21.2 14.2 59.9 59.9 58.7 02.0 59.3 02.2 10.8 58.5 02.2 59.3 02.0 0.02 58.7 01.8 10.0 59.0 10.2 58.4 59.3’E 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 , for visual reasons. 60 60 60 04 04 04 05 04 05 05 04 05 04 05 05 04 05 05 04 05 04 04 b Fig. 7 b b Probably affected by the Storegga tsunami ( Not plotted in Wiggle matched age. a b c Bakketjønn (19) 60 Skrubbisvatn (21) 60 Lommatjønn (9) 60 Kaldavatn (12) 60 Trollabotn (15) 60 Trollabotn (15) Kaldavatn (12)Skittjønn (13) 60 Einerhaugtjønn (10) 60 Lommatjønn (9)Storavatn (11) 60 Torkevikstjønn (16) 60 Einerhaugtjønn (10) 60 Skittjønn (13)Midtjønn (17) 60 60 Klokkarvatnet (14) 60 Vestretjønn (18) 60 Austretjønn (20) 60 Angeltveitvatnet (22) 60 ARTICLE IN PRESS 2140 Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151

Fig. 7. Relative sea-level curve for Sotra based on emerged lake basins covering the last 14 500 cal years. The curve is constructed along a baseline (351731) through Gardatjønn that represents the YD isobase direction (Fig. 1). The age intervals are plotted with a 95.4% conﬁdence level and the height includes uncertainties from both the determination of the present basin elevation and the projection of the localities within 731 off the baseline. The dotted curve during the Holocene (Tapes) transgression is drawn after the available observations from Sotra, but it is quite probable that all these are affected by the Storegga tsunami and are showing too high ages for the transgression and we have therefore drawn an alternative curve showing a slower transgression (stippled), which is supported by recent observations (Skulstad, 2006).

5. The YD transgression and its causes shoreline (see Section 5.2) indicates that any vertical faults were minor. Relative sea-level changes at a locality can be caused by a (2) The principal vertical sea-surface changes were due to number of processes that can be grouped into (1) vertical melting of the ice sheets, but also to variations in the movements of the crust (tectonic, glacio- and hydro- gravitational attraction of the combined mass of glacier ice isostasy) and (2) vertical movements of the sea surface and land. For the small area we analyse, all the sea-surface (glacio-eustasy and geoid modifications), both relative to can be regarded as movements of a horizontal surface. the centre of the Earth. These different types of movement In this section, we will describe the geographical are commented on below. extension of the YD transgression and compare the (1) In general, Scandinavia experienced emergence gradients of the mid-Allerød and late-YD shorelines during the last deglaciation, due to glacio-isostatic re- (formed before and after the YD transgression, respec- bound. The amount of glacio-isostatic uplift is propor- tively), then we will discuss the causal connections for the tional to ice thickness, which results in shorelines being YD transgression. tilted, rising towards the area where ice load was greatest. Hydro-isostasy leads to the same tendency due to increased 5.1. The geographical extent of the YD transgression and water loading along the coast relative to the land. The YD ice sheet isostatic deformation of the crust has mainly been in the form of flexure, but there may also have been faulting The YD transgression has been studied in several places caused by the increased crustal stress (Gudmundsson, on the south-western coast of Norway between Stavanger 1999; Anda et al., 2002). However, because of the sparse and Bergen (Anundsen, 1985; Lohne et al., 2004), (Figs. 1 sediment cover in western Norway it is difficult to identify and 8). To the north of Bergen (Sunnmøre and Trøndelag) any fault movements and presently no positive evidence for and to the south/east of Stavanger (western Sweden) Lateglacial and Postglacial faults have been found in this relative sea level fell during the YD, as reflected in the region (Olesen et al., 2004). The linear form of the YD isobase pattern (Fig. 8). For example, the 60 m YD isobase ARTICLE IN PRESS Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151 2141

ice sheet margin is shaded. This is roughly the same area where relative sea level rose during the transgression and it seems likely that there is a causal connection.

5.2. Comparison of the gradient of Allerød and YD shorelines

Shoreline gradients can provide useful clues to the casual factors of sea-level change (Fig. 9). If, for example, the transgression resulted from isostatic down-pressing, caused by the YD ice-sheet growth, then it should be shown as an increase in tilt between the Allerød shoreline and the YD shoreline (Fig. 9D). On the other hand, if the Allerød

Fig. 8. Map indicating the geographical extent of the YD transgression shown as 60 m isobase outside (west of) the Allerød 60 m isobase. The relative sea-level changes from mid-Allerød to late-YD are shown as numbers in boxes, ‘‘’’ for emergence and ‘‘+’’ for transgression. Three simpliﬁed shoreline diagrams are shown with the projection planes for each indicated by thick lines (based on Svendsen and Mangerud (1987) for Sunnmøre-Sør-Trøndelag and Bjo¨ rck and Digerfeldt (1991) for SW Sweden). The dotted line indicates the maximum extension of YD ice sheet. Large arrows and grey shading indicate the area where a major ice sheet re-advance during the YD, which advanced beyond the 12 ka 14CBP ice sheet margin (Mangerud, 2004).

crosses the 60 m Allerød isobase north of Bergen (in Nordfjord) and to south of Stavanger, probably some- where at the southern coast of Norway (Fig. 8). The same section of the coast that was transgressed during the YD also experienced the major YD ice-sheet re-advance. The magnitude of a glacier advance is often Fig. 9. Theoretical shoreline diagrams showing the hypothetical tilts of difficult to determine because glacial erosion removes most the Allerød and YD shorelines for different isostatic movements. Arrows of the older deposits during advance. However, based on indicate relative sea-level change. (A) The typical situation from a newly, findings of shell-bearing tills, the ice sheet appears to have deglaciated area, with tilted uplift and emergence. (B) Diagram showing re-advanced by at least 40 km in the Bergen area during the tilted uplift as in A, but with larger eustatic sea-level rise than uplift giving a transgression. (C) In this case there was a transgression without any Lateglacial (Mangerud, 1977, 1980; Andersen et al., 1995; tilting. (D) The lowest panel shows a case where increased glacial loading Mangerud, 2004). In Fig. 8, the area where the YD ice gave steeper YD shoreline compared to the Allerød shoreline and a 14 sheet re-advanced beyond the location of the 12 ka CBP transgression with or without a eustatic sea-level rise. ARTICLE IN PRESS 2142 Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151 shoreline has a steeper gradient than the YD shoreline then it indicates a continued isostatic rebound through the transgression period (Fig. 9B). The Allerød low-stand and the YD high-stand shorelines were reconstructed perpendicular to the isobase direction, in order to establish their maximum tilts. The reconstructions are based on three data sets; data obtained from the isolation basins studied at Sotra (this study) and Os (Lohne et al., 2004) and analysis of the marine terraces associated with the moraines formed in the late YD (Aarseth and Mangerud, 1974; Bondevik and Mangerud, 2002; Lohne, 2005), which we believe was concurrent with the YD high-stand. All previously reported altitudes of shoreline features and isolation marker horizons were adjusted to mean sea level. The marine diatoms from the isolation basins reflect the high tide level and the threshold altitudes are therefore adjusted downwards by the present astronomical tidal Fig. 10. Graph showing the coefficient of determination (R2) of the linear amplitude in Bergen of 0.9 m (Tidevannstabeller, 1998). trend surface calculated from the YD observations for different isobase The marine terraces have not been re-surveyed by us. The directions. The interval of best fits (R240.99) are illustrated by grey reported altitudes, as measured by a number of investiga- shading and centred at the best-fit value obtained for isobase direction of 3511. Calculated shoreline gradients are shown for both the YD and the tors during the past 100 years are used, which introduces Allerød shorelines. The best-fit isobase directions suggest shoreline some uncertainties due to divergence in the measuring gradients for the YD and Allerød shorelines of ca 1.2–1.4 m km1, but techniques and reference datums employed. However, how may indicate a slightly steeper gradient for the YD. the terrace surfaces relate to mean sea level at the time of their formation may introduce a much bigger uncertainty. Postglacial period (Kaland, 1984; Anundsen, 1985). To In northern Norway, the distal parts of modern delta plains test this assumption, we calculated isobases for the Allerød lie about 1.5–3 m below mean sea level (Corner, 1980). low-stand and YD high-stand for a larger area in western Adjusted for difference in tide amplitude (Bergen 0.9 m, Norway. In theory, this produces mean orientations that Tromsø 1.60 m), the corresponding figure for the Bergen possibly deviates from local orientation. Linear trend area should be about 0.85–1.7 m below mean sea level. The surfaces were fitted to the observations from Stavanger, data for marine terrace surfaces have therefore been Yrkje, Tau, Os and Sotra (Thomsen, 1982; Anundsen, adjusted upwards by 1 m and are considered to represent 1985; Flatekval, 1991; Lohne et al., 2004), where both the the mean sea level to within 71m. Allerød low-stand and the YD high-stand shoreline points The shorelines were constructed using following assump- are fairly well constrained. The best-fit results define planes tions: (1) that the direction of the isobases is known and (2) where the Allerød and YD isobases orientations differ by that the directions of the isobases did not change over the only 21. We therefore conclude that the Allerød and YD relevant period (Svendsen and Mangerud, 1987). The follow- isobases are essentially parallel. ing points suggest that these assumptions are reasonable. The resulting shorelines for the Bergen area are shown in (1) Aarseth and Mangerud (1974) and Anundsen (1985) Fig. 11. The YD shoreline is plotted as a linear regression estimated the direction of the YD isobases to 3471 and line after the observations are projected into the projection 3491, respectively, based on regional terraces data. How- plane, indicating a tilt of the YD shoreline of 1.34 m km1 ever, we have applied a simple linear trend surface analysis (Fig. 11). The Allerød shoreline, based on two points only, to both the isolation basin and terrace data (Davis, 1986); has a gradient of 1.30 m km1. However, the shoreline tilt is the best fit of the observations between Herdla and Hagen sensitive to the orientation of the isobases (Fig. 10) because (Fig. 1) shows a slightly more northerly (3511) direction. the observations are spread out along the isobases (Fig. 1). The plane fits the observations well (R2 ¼ 0.9926), with Small deviations in direction affect both the absolute individual deviations less than 2 m. Using a determination values and the ratio between the Allerød and YD shoreline coefficient better than 0.99, the isobase orientation is gradients. Within the isobase direction interval defined 351731 (Fig. 10). above (351731), the Allerød shoreline gradients varies (2) The altitude of the Allerød low-stand can be between 1.23 and 1.37 m km1 and the YD shoreline determined only at two locations in the study area and between 1.25 and 1.44 m km1(Fig. 10). The differences hence the isobase orientation cannot be established. are small and, for the time being, we therefore regard the Therefore, any change in the orientation between the Allerød and YD shorelines to be parallel, with a gradient of Allerød and YD isobases cannot be detected. However, about 1.3 m km1. earlier studies suggest only minor changes of the isobase The YD shoreline has been interpreted to have a directions in this area for the entire Lateglacial and curvilinear concave profile both in the Bergen area ARTICLE IN PRESS Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151 2143

Fig. 11. Shoreline diagram for the coastal area of Hordaland constructed along a projection plane through the site Gardatjønn (Fig. 1). The diagram shows shorelines for the YD high-stand and the Allerød low-stand. The YD shoreline is reconstructed by linear regression of the observations and showsa tilt of 1.34 m km1 (R2 ¼ 0.9927). The two observations of the Allerød shoreline indicate a tilt of 1.30 m km1.The diagram is constructed perpendicular to the isobase direction (3511) and the observations are projected along the isobases. Horizontal intervals indicate positions at the projection plane according to uncertainties in isobase directions of 351731. The observations are adjusted to show mean sea level, by subtracting 0.9 m from the height of the isolation basins and by adding 1 m to the marine terraces (see text).

(Anundsen, 1985) and in the northern part of Western curve has been subtracted from the reconstructed Sotra Norway (Svendsen and Mangerud, 1987). As discussed curve. This enables us to isolate the factors caused by local above, we found the observations in the Bergen area to fit a deglaciation. The resultant curve, referred to as the straight line, although a second-order polynomial regres- ‘residual curve’, estimates the combined effects of the sion of the YD-TM observations gives a very slightly better glacio-isostatic rebound and the geoidal changes (Fjeldskaar fit (R2: 0.9930 vs. 0.9926). However, the observations in and Kanestrøm, 1980). this area are confined to a narrow zone between the coast Sea-level curves from so-called far-field (relative to the and the YD ice sheet margin and the shorelines are ice sheets) sites roughly estimate the glacio-eustatic sea- therefore traced for a maximum of 30–40 km only (Fig. 11). level change (Fleming et al., 1998; Lambeck et al., 2000; It would be difficult to detect a curvilinear trend under Milne et al., 2002). We regard the Barbados curve (Peltier these constraints. The shoreline diagram of Svendsen and and Fairbanks, 2006) as sufficiently accurate for the Mangerud (1987), on the other hand, covers about 175 km calculations made in this section. On Fig. 12 are only and a curvilinear trend is therefore easier to detect. Model shown dates of the coral species, Acropora palmata with experiments also predict that the YD shoreline should depth errors of 0–5 m, because of the large and partly be curvilinear in Western Norway (Fjeldskaar and uncertain depth error for other species (Richard Fairbanks, Kanestrøm, 1981). 2006, pers. comm.). Our conclusion is that no tilting took place between the The residual curve reflects strong uplift directly after the mid-Allerød and the late YD. Indeed if there is any deglaciation, occurring at the same time as the MWP-1a difference, then the opposite appears to be the case with the (Fairbanks, 1989). This uplift suggests that the melting YD shoreline being slightly steeper than the Allerød one. of the Scandinavian Ice Sheet contributed to MWP-1a, This is an important inference as it indicates that the although it is agreed that most of the meltwater originated isostatic rebound ceased or possibly was slightly reversed from other areas (e.g. Clark et al., 1996, 2002; Weaver during this time span, which only can be explained by an et al., 2003; Peltier, 2005). increased ice load to the east the study area (see above). On The residual curve has a pronounced knick point in late the other hand, as the isostatic rebound is not distinctly Allerød, which is followed by a drop of 3–4 m (Fig. 12). reversed, the transgression must also have been caused by a This is in accordance with our conclusions from the eustatic sea-level rise (glacio and/or geoidal). shoreline configuration that there was no isostatic uplift between the Allerød low-stand and the YD high-stand 5.3. Causal connection and the Meltwater Puls 1a (Section 5.2, Fig. 11), combined with a geoidal rise of 3m (MWP1a) as modelled by Fjeldskaar and Kanestrøm (1980). Both these factors have been interpreted as a response to In order to resolve the factors causing the relative sea- ice-sheet growth. The Lateglacial part stands in sharp level changes observed at Sotra, a glacio-eustatic sea-level contrast to the Holocene trend. It appears from the ARTICLE IN PRESS 2144 Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151

the glacio-eustatic sea-level rise seems to be complete by 7000 cal yr BP and the recorded regression at Sotra from this time and onwards must have been caused by continued gradual uplift (Fig. 12).

6. When did the ice-sheet in western Norway start to re- advance?

The sea-level low-stand in Allerød and the 10 m sea level rise in YD were caused by the increased load from growth of the inland ice sheet. The sea-level low-stand was reached at 13 640 cal yr BP, lasted for about 560 years and was followed by a transgression that started 13 080 cal yr BP. Thus, the rate of isostatic uplift must have been consider- able reduced 700 years before the Allerød/YD transition (12 900 cal yr BP). We therefore suggest that the inland ice sheet over western Norway grew continuously from the early Allerød and throughout the YD. In the North Atlantic region, the Bølling–Allerød interstadial has been inferred to have been warmest in the first part followed by a gradual cooling until the abrupt climatic deterioration at the Allerød/YD transition (e.g. Grootes et al., 1993; Coope and Lemdahl, 1995). In western Norway, the transition has been reconstructed by biotic proxies to a decrease of only about 1–2 1C in July air temperature (Birks et al., 2004), probably as a result of relatively cool temperatures during the Bølling/Allerød in western Norway interval (Birks et al., 2004). It is evident that many cirque glaciers survived throughout the Bølling/ Allerød even at low elevations (Larsen et al., 1998), indicating that the equilibrium line on glaciers in western Norway was low throughout the Lateglacial. The YD transgression occurred slightly after the cold Gerzensee/ Killarney oscillation associated with reduced north-flowing Atlantic water and increased sea-ice cover (Lehman and Keigwin, 1992; Haflidason et al., 1995; Klitgaard-Kristensen et al., 2001). Probably this cold oscillation contributed to increased ice-sheet growth causing the transgression, even though the ice build-up probably started even earlier (during the early Allerød). The reduced length of the YD melt season may have reduced the summer melting and contributed to further the ice-sheet expansion. It is possibly the ice sheet expansion during the Allerød Fig. 12. The relative sea-level curve from Sotra (the upper panel), where the was triggered by increased precipitation in connection with grey bars indicate the periods of the Allerød low-stand, the YD transgression a cooling. Reconstructions based on plant macrofossils and the YD high-stand at Sotra. The lower panel shows the Barbados sea- from Blomøy (Fig. 1) suggest that the precipitation was level observations (Peltier and Fairbanks, 2006). Only Acropora palmate species with habitation depth range of 0–5 m are included because of the relative high during the Bølling/Allerød (Birks et al., 1994) large and partly uncertain habitation ranges for other species (R. Fairbanks, and that sufficient moisture for ice sheet growth was 2006, pers. comm.). A curve has been drawn through the mid-depth of therefore available during the Allerød. This is supported by habitation depth ranges of the samples in order to get a continuous eustatic the quantitative palaeoenvironmental reconstructions from sea-level curve. The lower panel also shows the ‘‘residual’’ curve constructed the ocean suggesting relatively warm (6–10 1C) summer by subtracting the Sotra curve from the eustatic curve. Note that the residual curve combines both geoidal change and uplift, and that a geoidal rise in this sea-surface temperatures and limited sea-ice cover in the curve will be reflected by a change to more negative values. sea west of Norway during the Bølling/Allerød (Koc- et al., 1993; Rochon et al., 1998; Klitgaard-Kristensen et al., residual curve that the Holocene (Tapes) transgression 2001; Birks et al., 2004). During the YD, the sea-ice cover can be explained by the rate of eustatic sea-level rise was more extensive and the summer sea-surface tempera- exceeding the (decreasing) rate of uplift (Fig. 12). Most of tures lower (Koc- et al., 1993; Rochon et al., 1998; ARTICLE IN PRESS Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151 2145

Klitgaard-Kristensen et al., 2001). However, there was still simultaneously with the rise in Betula pollen (Bondevik seasonal open water (Rochon et al., 1998) and climate and Mangerud, 2002), suggesting that the sea-level reconstructions based on plant macrofossils indicate cold response to the reduced load was slightly delayed. oceanic conditions (Birks et al., 1994). It is therefore The sea-level high-stand in the late YD formed the evident that moisture was available for ice-sheet growth marine limit in the area. The marine limit observations also during the YD, possibly as a result of strong and indicate an isobase direction of 351731 for the Bergen stable westerly circulation shown in model simulations area. (Renssen et al., 1996). The shorelines for the low-stand in Allerød and the We conclude that the critical temperature and moisture high-stand in YD are almost parallel with gradients threshold that would trigger ice-sheet expansion in western of about 1.3 m km1. This suggests that no crustal move- Norway was reached sometimes during the gradual cooling ment occurred during the transgression. The relative sea- in Bølling/Allerød before 13 100 cal yr BP and possible as level rise was mainly caused by a change in the geoid early as 13 600 cal yr BP, and that the climatic conditions from the increased gravitational attraction by the growing were suitable for ice-sheet expansion throughout the late ice sheet. Allerød and YD. Acknowledgements 7. Conclusions We are grateful to the following for their contributions Our new relative sea-level curve from Sotra shows: (a) a to the study: to Aage Paus who conducted the pollen falling sea-level from the deglaciation to 13 640 cal yr BP, analysis from Gardatjønn; to Herbjørn Heggen for (b) a sea-level low-stand in Allerød between 13 640 and assistance during fieldwork at Gardatjønn; to Haflidi 13 080 cal yr BP, (c) a 10 m sea-level rise from late Allerød Haflidason for assisting with the Multi-Sensor Core to late YD (13 080–11 790 cal yr BP)—the YD transgres- Logger; to Tomasz Goslar for the radiocarbon results; sion, (d) a sea-level high-stand in the late YD/early and to John Lowe, Antony Long, Bjørg Risebrobakken Holocene (11 790–11 550 cal yr BP) and (e) a 37 m sea- and two anonymous referees for improving the manuscript. level fall in the early Holocene (11 550–10 100 cal yr BP). Financial support was provided by The Norwegian The timing of the Allerød low-stand and the subsequent Research Council. This is a contribution to the ‘‘The Ice transgression indicates an increased load by an expanding Age development and human settlement in northern ice sheet well before the YD chronozone, possible in the Eurasia (ICEHUS)’’ project, led by John Inge Svendsen. early Allerød (13 600 cal yr BP). The YD transgression culminated very late in the YD and the sea-level high-stand took place within the Appendix A 10 000 14C yr BP plateau. Sea level remained at the high- stand until just after the rise in Betula (birch) pollen in early See Fig. A1. Pollen diagram from Gardatjønn, core Holocene. The retreat of the inland ice-sheet started 505-27.

cysts ) type tremula (cm type type x Depth Sediments Dates ChronozonesSUM TreesSUM ShrubsSUMSUM DwarfAlnus Herbs shrubsBetula PopulusJuniperusSali communisEmpetrumVacciniumArtemisiaCarex ChenopodiaceaeFilipendulaPoaceae RumexOxyria sect.Sedum acetosaUrticaPollen sum

1150 437 1150 9780 ± 50

9890 ± 50 10 080 ± 50

361 10 040 ± 50 1160 10 050 ± 50 HOLOCENE 314 1160 9980 ± 50 Isolation 10 090 ± 60 399 Betula rise 378

10 060 ± 60 312

10 170 ± 60 YD 1170 10 090 ± 50 20 40 60 80 0 0 10 20 30 40 0 0 0 10 0 0 0 10 0 10 00010 00 00 0 1170

Fig. A1. Pollen diagram from Gardatjønn, core 505-27. ARTICLE IN PRESS

2146 Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151

BRACKISH

MARINE/ n

521 656 461 320 349 305 340 325 378 394 411 368 351 307 190

Diatomsum

Halophobous

U Unknow SUM

Oligo.indifferent

SUM

UNKNOWN SUM U Oligo.halophilous SUM

U Mesohalobous SUM

U Polyhalobous SUM

Unidentified

spp.

inlrasuchlandtii Pinnularia

vulgaris Navicula 0

HALOPHOBOUS

Fragilaria

abellaria

fenestrate 0

abellaria

aiuaschmassmannii Navicula

aiuapseudoscutiformis Navicula

aiuacocconeiformis Navicula

0 cnnhsconspicua Achnanthes 0

interrupta acuminatum

tuoesanceps Stauroneis

Pinnularia

0 Gomphonema 0

rglravirescens Fragilaria

construens rglrapinnata Fragilaria 0

OLIGOHALOBOUS INDIFFERENT

rglracntun .venter f. construens Fragilaria

minuta

rglracntun f. construens Fragilaria 2

Cymbella

yltlasp 3 spp. Cyclotella

bacillum vitrea 0

yltlaspp. Cyclotella

Caloneis

MESO Anomoeoneis

0 pusilla HALOBOUS 40

Fig. B1. Diatom diagram from Gardatjønn, core 505-27.

Achnanthes

0 hungarica

cnnhsminutissima Achnanthes

exigua a

Nitzschia

aiuadigitoradiata Navicula

Mastogloia

0 odnköd group nordenskiöldi

POLYHALOBOUS

ilni didym Diploneis

ahni aspera rachyneis

Thalassiosira

hboeaminutum Rhabdonema

coarctata

inlraquadratarea Pinnularia

litoricola 0

taxa >3% occurence plotted

Nitzschia brevis

0 Navicula Only

0 Caloneis %- 0 Sediments cm Depth 1200 1160 1170 1180 1190 ARTICLE IN PRESS

Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151 2147

cysts

LACUSTRINE Chrysophyceae 0

431 470 309 478 487 461 339 238 308 UN-

itmsum Diatom

indifferent

KNOWN U Unkown SUM

HALO-

PHOBOUS Halophobous SUM 80

U Oligo. SUM

Mesohalob U lg.halophilous Oligo. SUM

Polyhalob

SUM SUM 0

conspicua

inlraspp. Pinnularia

subcostulata aiuaschmassmannii Navicula

Achnanthes

rhynchocephala 0

Navicula

0 perpusilla .

var

Navicula

0 minima aiuapupula Navicula

0 INDIFFERENT Navicula 0

OLIGOHALOBOUS

aiuagallica Navicula

aiuacryptocephala Navicula

0 virescens

Fragilaria

rglraulna Fragilaria

osresf construens f. construens

rglrapinnata Fragilaria

spp.

vitrea

Fragilaria

yblaminuta Cymbella

Cyclotella

Anomoeoneis

levanderi OLIGOHAL. pusilla Achnanthes 0

HALOPHILOUS

cnnhsminutissima Achnanthes

valdestriata

Achnanthes

0 Nitzschia 0

MESO izci frustulum Nitzschia 0

HALOBOUS

aiuahalophila Navicula

aiuaduerrenbergiana Navicula

aiuascutelloides Nacicula

izci sigma Nitzschia

scoticus 0

p.1 spp.

izci hungarica Nitzschia

gruppen 0 Hyalodiscus

Cyclotella Fig. C1. Diatom diagram from Hamravatn, core 505-19.

aspera

mhr proteus Amphora

cnnhshauckiana Achnanthes

Trachyneis

quadratarea 0

hlsisr nordenskiöldi Thalassiosira

0 phyllepta

POLYHALOBOUS

Pinnularia

palpebralis 0

Navicula

aiuadissipata Navicula

yoim prolongata Gyrosigma

subcincta

rglrosscylindrus Fragilariopsis

smithii

Diploneis

0 ambigua

p.1 spp.

ocni scutellum Cocconeis

0 Biremis

0 Amphora % - Only taxa >3% occurence plotted 0 Sediments cm Depth 1290 1300 1310 1320 ARTICLE IN PRESS

2148 Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151 BRACKISH

403 367 394 349 323 358 350 361 313 429 Unknown Diatomsum

UNKNOWN Halophobous

SUM

U Oligo.indifferent SUM

Mesohalobous U Oligo.halophilous SUM

SUM

spp.

U Polyhalobous SUM

Unidentified

Achnanthes

pupula 0

inlrainterrupta Pinnularia

INDIFFERENT venter 0 f.

OLIGOHALOBOUS

Navicula

pinnata

rglravirescens Fragilaria

construens

Fragilaria

brevistriata

rglracntun .construens f. construens Fragilaria

0 Fragilaria

0 OLIGOHAL. sinuta Cymbella 0

HALOPHILOUS

yblaminuta Cymbella

valdestriata

cnnhsminutissima Achnanthes

halophila hiopei abbreviata Rhoicosphenia

Nitzschia

0 cincta

Navicula

moniliformis a

Navicula

tumida 0 Diatom

MESOHALOBOUS

cnnhsdelicata Achnanthes

Scoliopleura

hpldamusculus Rhopalodia

digitoradiata izci hungarica Nitzschia

smithii

izci acuminata Nitzschia

proteus

Navicula

helenensis Mastogloia

Amphora

ahni aspera rachyneis

hboeaminutum Rhabdonema

inlraquadratarea Pinnularia

0 sulcata Fig. D1. Diatom diagram from Sekkingstadjønn, core 505-102.

POLYHALOBOUS

Paralia

izci coarctata Nitzschia

aiuaphyllepta Navicula

litoricola 0

aiuapalpebralis Navicula

dissipata 0

macilenta

Navicula

directa 0

Navicula

cylindrus 0

Navicula

Grammatophora

Fragilariopsis

smithii 0 spp

occurence plotted ilni subcincta Diploneis 0

>2%

Diploneis

0 Cosinodiscus

0 taxa ocni scutellum Cocconeis 0 Only %- Sediments cm Depth 1303 1304 1305 1306 1298 1299 1300 1301 1302 1293 1294 1295 1296 1297 1288 1289 1290 1291 1292 1286 1287 ARTICLE IN PRESS Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151 2149

Appendix B Bondevik, S., Mangerud, J., 2002. A calendar age estimate of a very late Younger Dryas ice sheet maximum in western Norway. Quaternary See Fig. B1. Diatom diagram from Gardatjønn, core Science Reviews 21, 1661–1676. 505-27. Bondevik, S., Svendsen, J.I., Johnsen, G., Mangerud, J., Kaland, P.E., 1997a. The Storegga tsunami along the Norwegian coast, its age and runup. Boreas 26, 29–53. Appendix C Bondevik, S., Svendsen, J.I., Mangerud, J., 1997b. Tsunami sedimentary facies deposited by the Storegga tsunami in shallow marine basins and coastal lakes, western Norway. Sedimentology 44, 1115–1131. See Fig. C1. Diatom diagram from Hamravatn, core Bondevik, S., Svendsen, J.I., Mangerud, J., 1998. Distinction between the 505-19. Storegga tsunami and the marine transgression in coastal basins deposits of western Norway. Journal of Quaternary Science 13, Appendix D 529–537. Bondevik, S., Mangerud, J., Dawson, S., Dawson, A., Lohne, Ø., 2005. Evidence for three North Sea tsunamis at the Shetland Islands between See Fig. D1. Diatom diagram from Sekkingstadjønn, 8000 and 1500 years ago. Quaternary Science Reviews 24, 1757–1775. core 505-102. Bondevik, S., Mangerud, J., Birks, H.H., Gulliksen, S., Reimer, P., 2006. Changes in North Atlantic radiocarbon reservoir ages during Allerød and Younger Dryas. Science 312, 1514–1517. References Bronk Ramsey, C., 2005. The OxCal radiocarbon calibration software, v. 3.10. Aarseth, I., Mangerud, J., 1974. Younger Dryas end moraines between Camoin, G.F., Montaggioni, L.F., Braithwaite, C.J.R., 2004. Late glacial Hardangerfjorden and Sognefjorden, Western Norway. Boreas 3, to post glacial sea levels in the Western Indian Ocean. Marine Geology 3–22. 206, 119–146. Anda, E., Blikra, L.H., Braathen, A., 2002. The Berill Fault—first Clark, P.U., Alley, R.B., Keigwin, L.D., Licciardi, J.M., Johnsen, S., evidence of neotectonic faulting in southern Norway. Norwegian Wang, H., 1996. Origin of the first global meltwater pulse following the Journal of Geology 82, 175–182. last glacial maximum. Paleoceanography 11, 563–577. Andersen, B.G., Mangerud, J., Sørensen, R., Reite, A., Sveian, H., Clark, P.U., Mitrovica, J.X., Milne, G.A., Tamisiea, M.E., 2002. Sea-level Thoresen, M., Bergstrøm, B., 1995. Younger Dryas ice-marginal fingerprinting as a direct test for the source of global meltwater Pulse deposits in Norway. Quaternary International 28, 147–169. IA. Science 295, 2438–2441. Anundsen, K., 1985. Changes in shore-level and ice-front position in Late Coope, G.R., Lemdahl, G., 1995. Regional differences in the Lateglacial Weichsel and Holocene, southern Norway. Norsk geografisk Tidsskrift climate of northern Europe based on coleopteran analysis. Journal of 39, 205–225. Quaternary Science 10, 391–395. Anundsen, K., Fjeldskaar, W., 1983. Observed and theoretical Late Corner, G.D., 1980. Preboreal deglaciation chronology and marine limits Weichselian shore level changes related to glacier oscillations at Yrkje, of the Lyngen-Storfjord Area, Troms, North Norway. Boreas 9, southwest Norway. In: Schroeder-Lanz, H. (Ed.), Late- and Post- 239–249. glacial Oscillations of Glaciers: Glacial and Periglacial Forms. A. A. Davis, J.C., 1986. Statistics and Data Analysis in Geology. Wiley, Balkema, Rotterdam, pp. 133–170. New York, 646pp. Bard, E., Hamelin, B., Arnold, M., Montaggioni, L., Cabioch, G., Faure, de Wolf, H., 1982. Method of coding of ecological data from diatoms for G., Rougerie, F., 1996. Deglacial sea-level record from Tahiti corals computer utilization. Mededelingen Rijks Geologische Dienst 36, and the timing of global meltwater discharge. Nature 382, 241–244. 95–98. Barnekow, L., Possnert, G., Sandgren, P., 1998. AMS C-14 chronologies Denys, L., 1991/2. A check-list of diatoms in the Holocene deposits of the of Holocene lake sediments in the Abisko area, northern Sweden— western Belgian coastal plain with a survey of their apparent ecological a comparison between dated bulk sediment and macrofossil samples. requirements. Professional Paper no. 246, 41pp. GFF 120, 59–67. Berge, J., Bostwick, L.G., Krzywinski, K., Myhre, B., Stabell, B., A˚gotnes, Dullo, W.C., Camoin, G.F., Blomeier, D., Colonna, M., Eisenhauer, A., A., 1978. Ilandføring av olje pa˚Sotra. De arkeologiske undersøkelser Faure, G., Casanova, J., Thomassin, B.A., 1998. In: Camoin, G.F., 1977. Vindenes. Historisk Museum, Universitetet i Bergen, 151pp. Davies, P.J. (Eds.), Morphology and Sediments of the Fore-slopes of Berglund, B.E., Bjo¨ rck, S., Lemdahl, G., Bergsten, H., Nordberg, K., Mayotte, Comoro Islands; Direct Observations from a Submersible, Kolstrup, E., 1994. Late Weichselian environmental-change in South- pp. 219–236. ern Sweden and Denmark. Journal of Quaternary Science 9, 127–132. Edwards, R.L., Beck, J.W., Burr, G.S., Donahue, D.J., Chappell, J., Birks, H.H., Paus, A., Svendsen, J.I., Alm, T., Mangerud, J., Landvik, Bloom, A.L., Druffel, E.R.M., Taylor, F.W., 1993. A large drop in 14 12 J.Y., 1994. Late Weichselian environmental-change in Norway, atmospheric C/ C and reduced melting in the Younger Dryas, 230 including Svalbard. Journal of Quaternary Science 9, 133–145. documented with Th ages of corals. Science 260, 962–968. Birks, H.H., Kristensen, D.K., Dokken, T.M., Andersson, C., 2004. Fairbanks, R.G., 1989. A 17,000-year glacio-eustatic sea-level record: Exploratory comparisons of quantitative temperature estimates over influence of glacial melting rates on the Younger Dryas event and the last deglaciation in Norway and the Norwegian Sea. In: Drange, deep-ocean circulation. Nature 342, 637–642. H., Dokken, T., Furevik, T., Gerdes, R., Berger, W. (Eds.), The Fjeldskaar, W., Kanestrøm, R., 1980. Younger Dryas geoid-deformation Nordic Seas: An Integrated Perspective Oceanography, Climatology, caused by deglaciation in Fennoscandia. In: Mo¨ rner, N.-A. (Ed.), Biogeochemistry, and Modelling. American Geophysical Union, Earth Rheology, Isostasy and Eustasy. Wiley, Chichester, UK, Washington, pp. 341–355. pp. 569–574. Bjo¨ rck, S., Digerfeldt, G., 1991. Allerød–Younger Dryas sea level changes Fjeldskaar, W., Kanestrøm, R., 1981. The isostatic process in Fennos- in southwestern Sweden and their relation to the Baltic Ice Lake candia and inferred lithosphere and mantle rheology. In: Fjeldskaar, development. Boreas 20, 115–133. W. (Ed.), Late-Glacial movements of sea-level and crust in Fennos- Blockley, S.P.E., Lowe, J.J., Walker, M.J.C., Asioli, A., Trincardi, F., candia. Dr. Scient. Thesis, University of Bergen, pp. 93–145. Coope, G.R., Donahue, R.E., Pollard, A.M., 2004. Bayesian analysis Flatekval, L.H., 1991. Strandforskyvning pa˚Tau, Rogaland. Lito- og of radiocarbon chronologies: examples from the European Late- biostratigrafiske undersøkelser av tre myrbasseng ved Norwerk, Glacial. Journal of Quaternary Science 19, 159–175. University of Bergen, Bergen. ARTICLE IN PRESS 2150 Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151

Fleming, K., Johnston, P., Zwartz, D., Yokoyama, Y., Lambeck, K., Western Norway. Review of Palaeobotany and Palynology 53, Chappell, J., 1998. Refining the eustatic sea-level curve since the Last 185–231. Glacial Maximum using far- and intermediate-field sites. Earth and Krzywinski, K., Stabell, B., 1978. Senglasiale undersøkelser pa˚Sotra. Planetary Science Letters 163, 327–342. Arkeo 1, 27–31. Grootes, P.M., Stuiver, M., White, J.W.C., Johnsen, S., Jouzel, J., 1993. Krzywinski, K., Stabell, B., 1984. Late Weichselian sea-level changes at Comparison of oxygen-isotope records from the Gisp2 and Grip Sotra, Hordaland, Western Norway. Boreas 13, 159–202. Greenland Ice Cores. Nature 366, 552–554. Lambeck, K., Yokoyama, Y., Johnston, P., Purcell, A., 2000. Global ice Gudmundsson, A., 1999. Postglacial crustal doming, stresses and fracture volumes at the Last Glacial Maximum and early Lateglacial. Earth formation with application to Norway. Tectonophysics 307, 407–419. and Planetary Science Letters 181, 513–527. Haflidason, H., Sejrup, H.P., Klitgaard, D., Johnsen, S., 1995. Coupled Lambeck, K., Yokoyama, Y., Purcell, T., 2002. Into and out of the Last response of the Late Glacial climatic shifts of NW-Europe reflected in Glacial Maximum: sea-level change during Oxygen Isotope Stages 3 Greenland ice cores: evidence from the northern North Sea. Geology and 2. Quaternary Science Reviews 21, 343–360. 23, 1059–1062. Larsen, E., Attig, J.W., Aa, A.R., Sønstegaard, E., 1998. Late-Glacial Haflidason, H., Sejrup, H.P., Nygard, A., Mienert, J., Bryn, P., Lien, R., cirque glaciation in parts of western Norway. Journal of Quaternary Forsberg, C.F., Berg, K., Masson, D., 2004. The Storegga Slide: Science 13, 17–27. architecture, geometry and slide development. Marine Geology 213, Lehman, S.L., Keigwin, L.D., 1992. Sudden changes in North Atlantic 201–234. circulation during the last deglaciation. Nature (London) 356, 757–762. Hafsten, U., 1960. Pollen-analytic investigations in South Norway. In: Lohne, Ø.S., 2005. Late Weichselian relative sea-level changes and glacial Holtedahl, O. (Ed.), Geology of Norway. Norges geologiske Under- history in Hordaland, Western Norway. Ph.D. Thesis, University of søkelse, Oslo, pp. 434–462. Bergen, Bergen, Norway. Hendey, N.I., 1964. An Introductory Account of Smaller Algae of British Lohne, Ø.S., Bondevik, S., Mangerud, J., Schrader, H., 2004. Calendar year Coastal Waters. Part V: Bacillariophyceae (Diatoms). Her majesty’s age estimates of Allerød–Younger Dryas sea-level oscillations at Os, Stationary Office, London, 317pp. western Norway. Journal of Quaternary Science 19, 443–464. Hughen, K.A., Southen, J.R., Lehman, S.J., Overpeck, J.T., 2000. Mangerud, J., 1977. Late Weichselian marine sediments containing shells, Synchronous radiocarbon and climate shifts during the last deglacia- foraminifera, and pollen, at A˚gotnes, Western Norway. Norsk tion. Science 290, 1951–1954. geologisk Tidsskrift 57, 23–54. Hustedt, F., 1930. Bacillariophyta (Diatomeae). In: Pascher, A. (Ed.), Die Mangerud, J., 1980. Ice-front variations of different parts of the Su¨ sswasserflora Mitteleuropas. Gustav Fischer, Jena. Scandinavian Ice Sheet, 13 000–10 000 Years B.P. In: Lowe, J.J., Hustedt, F., 1930–66. Die Kieselalgen Deutschlands, O¨ sterreichs und der Gray, J.M., Robinson, J.E. (Eds.), Studies in the Lateglacial of Schweiz. In: Rabenhorst, L. (Ed.), Kryptogramen-Flora von Deutsch- North–West Europe: Including Papers Presented at a Symposium of land, O¨ sterreich und der Sweitz. Akademische Verlagsgesellschaft, the Quaternary Research Association held at University College Leipzig. London, January 1979. Pergamon Press, Oxford, pp. 23–30. Hustedt, F., 1957. Die Diatomeenflora des Fluss-Systems der Weser im Mangerud, J., 2004. Ice sheet limits on Norway and the Norwegian Gebiet der Hansestadt Bremen. Abhandlungen Herausgegeben vom continental shelf. In: Ehlers, J., Gibbard, P. (Eds.), Quaternary Naturwissenschaftlicher Verein zu Bremen 34, 181–440. Glaciations—Extent and Chronology. Vol. 1. Europe. Elsevier, Ha˚kansson, S., 1980. University of Lund radiocarbon dates XIII. Amsterdam, pp. 271–294. Radiocarbon 22, 1045–1063. Mangerud, J., Gulliksen, S., 1975. Apparent radiocarbon ages of recent Indrelid, S., Myhre, B., Krzywinski, K., Sønstegaard, E., 1976. Ilandfør- marine shells from Norway, Spitsbergen and Arctic Canada. ing av olje pa˚Sotra. Historisk Museum, Universitetet i Bergen, Quaternary Research 5, 263–273. 181pp. Mangerud, J., Lie, S.E., Furnes, H., Kristiansen, I.L., Lømo, L., 1984. A Kaland, P.E., 1984. Holocene shore displacement and shorelines in Younger Dryas Ash Bed in Western Norway, and its possible Hordaland, western Norway. Boreas 13, 203–242. correlations with tephra in cores from the Norwegian Sea and the Kaland, P.E., Krzywinski, K., Stabell, B., 1984. Radiocarbon-dating of North Atlantic. Quaternary Research 21, 85–104. transitions between marine and lacustrine sediments and their relations Milne, G.A., Mitrovica, J.X., Schrag, D.P., 2002. Estimating past to the development of lakes. Boreas 13, 243–258. continental ice volume from sea-level data. Quaternary Science Klitgaard-Kristensen, D., Sejrup, H.P., Haflidason, H., 2001. The last Reviews 21, 361–376. 18 kyr fluctuations in Norwegian Sea surface conditions and implica- Olesen, O., Blikra, L.H., Braathen, A., Dehls, J.F., Olsen, L., Rise, L., tions for the magnitude of climatic change: evidence from the North Roberts, D., Riis, F., Faleide, J.I., Anda, E., 2004. Neotectonic Sea. Paleoceanography 16, 455–467. deformation in Norway and its implications: a review. Norwegian Koc-, N., Jansen, E., Haflidason, H., 1993. Paleoceanograpic reconstruc- Journal of Geology 84, 3–34. tions of surface ocean conditions in the Greenland, Iceland and Paus, A., 1989. Late Weichselian vegetation, climate, and floral migration Norwegian Seas through the last 14 ka based on diatoms. Quaternary at Liastemmen, North-Rogaland, south-western Norway. Journal of Science Reviews 12, 115–140. Quaternary Science 4, 223–242. Krammer, K., Lange-Bertalot, H., 1986. Su¨sswasserflora von Mitteleuropa, Peltier, W.R., 2005. On the hemispheric origins of meltwater pulse 1a. Band 2/1, Bacillariophyceae. 1. Teil Naviculaceae. Fischer, Stuttgart, Quaternary Science Reviews 24, 1655. 876pp. Peltier, W.R., Fairbanks, R.G., 2006. Global glacial ice volume and Last Krammer, K., Lange-Bertalot, H., 1988. Su¨sswasserflora von Mitteleuropa, Glacial Maximum duration from an extended Barbados sea level Band 2/2, Bacillariophyceae. 2. Teil Epithemiaceae, Bacillariaceae, record. Quaternary Science Reviews 25, 3322–3337. Surirellaceae. Fischer, Stuttgart, 596pp. Rasmussen, S.O., Andersen, K.K., Svensson, A.M., Steffensen, J.P., Krammer, K., Lange-Bertalot, H., 1991a. Su¨sswasserflora von Mitteleur- Vinther, B.M., Clausen, H.B., Siggaard-Andersen, M.L., Johnsen, S.J., opa, Band 2/3, Bacillariophyceae. 3. Teil Centrales, Fragilariaceae, Larsen, L.B., Dahl-Jensen, D., Bigler, M., Rothlisberger, R., Fischer, Eunotiaceae. Fischer, Stuttgart, 576pp. H., Goto-Azuma, K., Hansson, M.E., Ruth, U., 2006. A new Krammer, K., Lange-Bertalot, H., 1991b. Su¨sswasserflora von Mitteleur- Greenland ice core chronology for the last glacial termination. Journal opa, Band 2/4, Bacillariophyceae. 4. Teil Achnanthaceae, kritische Of Geophysical Research—Atmospheres 111, D06102. Erga¨ nzungen zu Navicula (Lineolatae) und Gomponema: Gesamtli- Reimer, P.J., Baillie, M.G.L., Bard, E., Bayliss, A., Beck, J.W., Bertrand, teraturverzeichnis Teil 1–4. Fischer, Stuttgart, 437pp. C.J.H., Blackwell, P.G., Buck, C.E., Burr, G.S., Cutler, K.B., Damon, Kristiansen, I.L., Mangerud, J., Lømo, L., 1988. Late Weichselian/early P.E., Edwards, R.L., Fairbanks, R.G., Friedrich, M., Guilderson, Holocene pollen- and lithostratigrahy in lakes in the A˚lesund area, T.P., Hogg, A.G., Hughen, K.A., Kromer, B., McCormac, G., ARTICLE IN PRESS Ø.S. Lohne et al. / Quaternary Science Reviews 26 (2007) 2128–2151 2151

Manning, S., Ramsey, C.B., Reimer, R.W., Remmele, S., Southon, Stabell, B., Krzywinski, K., 1979. Havniva˚endringer pa˚Sotra, Hordaland. J.R., Stuiver, M., Talamo, S., Taylor, F.W., van der Plicht, J., Arkeo 1, 12–15. Weyhenmeyer, C.E., 2004. IntCal04 terrestrial radiocarbon age Svendsen, J.I., Mangerud, J., 1987. Late Weichselian and Holocene sea- calibration, 0–26 cal kyr BP. Radiocarbon 46, 1029–1058. level history for a cross-section of western Norway. Journal of Renssen, H., Lautenschlager, M., Schuurmans, C.J.E., 1996. The atmo- Quaternary Science 2, 113–132. spheric winter circulation during the Younger Dryas stadial in the Thomsen, H., 1982. Late Weichselian shore-level displacement on Nord- Atlantic/European sector. Climate Dynamics 12, 813–824. Jæren, south–west Norway. Geologiska Fo¨ reningens i Stockholm Rochon, A., deVernal, A., Sejrup, H.P., Haflidason, H., 1998. Palynolo- Fo¨ rhandlinger 103, 447–468. gical evidence of climatic and oceanographic changes in the North Sea Tidevannstabeller, 1998. Tidevannstabeller for den norske kyst med during the last deglaciation. Quaternary Research 49, 197–207. Svalbard samt Dover, England 1999. Statens kartverk, Sjøkartverket. Shepard, F.P., 1963. Thirty-five thousand years of sea-level. In: Clements, Walker, M.J.C., Coope, G.R., Sheldrick, C., Turney, C.S.M., Lowe, J.J., T. (Ed.), Essays in Marine Geology in Honor of K.O. Emery. Southern Blockley, S.P.E., Harkness, D.D., 2003. Devensian Lateglacial environ- California Press, Los Angeles, pp. 1–10. mental changes in Britain: a multi-proxy environmental record from Skulstad, B., 2006. Sedimentology and stratigraphic facies analysis of raised Llanilid, South Wales, UK. Quaternary Science Reviews 22, 475–520. Holocene shoreline deposits in the Vestrefjæra coast of Herdla, offshore Weaver, A.J., Saenko, O.A., Clark, P.U., Mitrovica, J.X., 2003. Meltwater Bergen. Master Thesis, University of Bergen, Bergen, Norway. pulse 1A from Antarctica as a trigger of the bolling- allerod warm Stabell, B., 1985. The development and succession of taxa within the interval. Science 299, 1709–1713. diatom genus Fragilaria Lyngbye as a response to basin isolation from Witkowski, A., Lange-Bertalot, H., Metzeltin, B., 2000. Diatom Flora of the sea. Boreas 14, 273–286. Marine Coasts I. ARG Gantner Verlag K.G. Stabell, B., Krzywinski, K., 1978. Strandforskyvningsundersøkelsen. In: Zinke, J., Reijmer, J.J.G., Thomassin, B.A., Dullo, W.C., Grootes, P.M., Myhre, B. (Ed.), Statfjord Transportation System Project. Ilandføring Erlenkeuser, H., 2003. Postglacial flooding history of Mayotte Lagoon av olje pa˚Sotra. De arkeologiske undersøkelser 1978. Vindenes. (Comoro Archipelago, southwest Indian Ocean). Marine Geology 194, Historisk museum, Universitetet i Bergen, pp. 93–132. 181–196.