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Lithostratigraphic description of the Lake Bjarstrask sediment succession (see Fig. 4). Org. C and CaCO3 represent contents of organic carbon and calcium carbonate respectively. Depths are related to the water surface. CaCO3 values exceeding 100% are due to intrinsic error propagation in the determination of TIC and TOC. These values are within the margin of analytical error.

Figure 4 Lithostratigraphic description of the Lake Bjarstrask sediment succession (see Fig. 4). Org. C and CaCO3 represent contents of organic carbon and calcium carbonate respectively. Depths are related to the water surface. CaCO3 values exceeding 100% are due to intrinsic error propagation in the determination of TIC and TOC. These values are within the margin of analytical error.

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Local climatic and hydrological data valid for Lake Bjarstrask. Mean annual tem- perature and precipitation data refer to climate normals (SMHI, 1968—1997). Mean annual evapotranspiration and runoff were obtained from Jutman (1995) and refer to the period 1961-1990.
Local climatic and hydrological data valid for Lake Bjarstrask. Mean annual tem- perature and precipitation data refer to climate normals (SMHI, 1968—1997). Mean annual evapotranspiration and runoff were obtained from Jutman (1995) and refer to the period 1961-1990.
Fig. 1. Location of the study area and other records mentioned in the text. (A) Schematic representation of the Siberian High atmospheric centre and direction of the associated winds; 1 = GISP2. (B) Map of Fennoscandia showing the location of Gotland (C) and other sites referred to in the text: 2 = Lake Flarken (Seppa et al., 2005); 3 = Lake Igelsjon (Hammarlund et al., 2003); 4 = coring site 303610-12, Eastern Gotland Basin (Harff et al., 2011); 5 = Lake Kurjanovas (Heikkila and Seppa, 2010); Smedby meteorological station. (C) Location of Lake Bjarstrask on the island of Gotland, and Hemse, the closest meteorological station. (D) Topographic map of the investigation area showing catchment extent, the position of Lake Bjarstrask within the catchment and upstream water bodies. Fr = Lake Fridtrask; Ra = Lake Rammtrask; Sl = Lake Slottstrask; Br = Lake Brotrask. (E) Map of Quaternary deposits in the area based on data provided by the Geological Survey of Sweden.
Fig. 1. Location of the study area and other records mentioned in the text. (A) Schematic representation of the Siberian High atmospheric centre and direction of the associated winds; 1 = GISP2. (B) Map of Fennoscandia showing the location of Gotland (C) and other sites referred to in the text: 2 = Lake Flarken (Seppa et al., 2005); 3 = Lake Igelsjon (Hammarlund et al., 2003); 4 = coring site 303610-12, Eastern Gotland Basin (Harff et al., 2011); 5 = Lake Kurjanovas (Heikkila and Seppa, 2010); Smedby meteorological station. (C) Location of Lake Bjarstrask on the island of Gotland, and Hemse, the closest meteorological station. (D) Topographic map of the investigation area showing catchment extent, the position of Lake Bjarstrask within the catchment and upstream water bodies. Fr = Lake Fridtrask; Ra = Lake Rammtrask; Sl = Lake Slottstrask; Br = Lake Brotrask. (E) Map of Quaternary deposits in the area based on data provided by the Geological Survey of Sweden.
Fig. 2. (A) Monthly mean values of precipitation (histogram) and temperatures (line) at Hemse (SMHI, 1968-1997), 8.3 km SSE of Lake Bjarstrask, and (B) composite monthly values of 580 of precipitation (5'0,) from Smedby (Global Network of Iso- topes in Precipitation, 1975—1980), on the mainland ca 148 km SW of Lake Bjarsktrask. Black dots refer to individual monthly values and the solid line to monthly mean values of isotopic data. The weighted annual mean for the period 1975—1980 (horizontal line) is —11.3%,. The data were obtained from the International Atomic Energy Agency and the World Meteorological Organization.
Fig. 2. (A) Monthly mean values of precipitation (histogram) and temperatures (line) at Hemse (SMHI, 1968-1997), 8.3 km SSE of Lake Bjarstrask, and (B) composite monthly values of 580 of precipitation (5'0,) from Smedby (Global Network of Iso- topes in Precipitation, 1975—1980), on the mainland ca 148 km SW of Lake Bjarsktrask. Black dots refer to individual monthly values and the solid line to monthly mean values of isotopic data. The weighted annual mean for the period 1975—1980 (horizontal line) is —11.3%,. The data were obtained from the International Atomic Energy Agency and the World Meteorological Organization.
Correlation coefficients (r) for winter (DJF), spring (MAM), summer (JJA), autumn (SON) and annually, calculated between NAO Index (Hurrell et al., 2001) and observed Precipitation (P) and Temperatures (T) data from Hemse (SMHI, 1968— 1997).
Correlation coefficients (r) for winter (DJF), spring (MAM), summer (JJA), autumn (SON) and annually, calculated between NAO Index (Hurrell et al., 2001) and observed Precipitation (P) and Temperatures (T) data from Hemse (SMHI, 1968— 1997).
Radiocarbon dates obtained from the Lake Bjarstrask sediment succession (see Fig. 4). Bet. = fruits and/or catkin scales of Betula pubescens, Aln. = fruits and/or catkin scales of Alnus glutinosa, Que. = bud scales of Quercus robur, Pin. = seeds and needle fragments o Pinus sylvestris, Nym. = fruits of Nymphaea alba, Dry. = leaf fragments of Dryas octopetala Emp. = seeds of Empetrum nigrum. Depths are related to the water surface. Table 4
Radiocarbon dates obtained from the Lake Bjarstrask sediment succession (see Fig. 4). Bet. = fruits and/or catkin scales of Betula pubescens, Aln. = fruits and/or catkin scales of Alnus glutinosa, Que. = bud scales of Quercus robur, Pin. = seeds and needle fragments o Pinus sylvestris, Nym. = fruits of Nymphaea alba, Dry. = leaf fragments of Dryas octopetala Emp. = seeds of Empetrum nigrum. Depths are related to the water surface. Table 4
Fig. 3. (A) Plot of 5'80 versus 8°H values of modern water samples collected from Lake Bjarstrask and adjacent snow and groundwater between 1999 and 2012. November values were reported by Pettersson (2003). (B) Isotopic composition of water samples from other lakes in the catchment. The solid line represents the global meteoric water line (GMWL), while the dotted line refers to the local evaporation line (LEL), which was constructed by linear regression through available lakewater data (r? = 0.94). The hypothetical composition of steady-state terminal lakewater (Sss,) at Lake Bjarstrask, constructed using the Craig and Gordon (1965) model, is shown for reference. Our multi-component isotopic study, with parallel records of 3'80 and 8%C obtained on bulk carbonates and B. tentaculata opercula, enables assessment of palaeoenvironmental and palae- oclimatic changes through most of the Holocene. As outcrops of
Fig. 3. (A) Plot of 5'80 versus 8°H values of modern water samples collected from Lake Bjarstrask and adjacent snow and groundwater between 1999 and 2012. November values were reported by Pettersson (2003). (B) Isotopic composition of water samples from other lakes in the catchment. The solid line represents the global meteoric water line (GMWL), while the dotted line refers to the local evaporation line (LEL), which was constructed by linear regression through available lakewater data (r? = 0.94). The hypothetical composition of steady-state terminal lakewater (Sss,) at Lake Bjarstrask, constructed using the Craig and Gordon (1965) model, is shown for reference. Our multi-component isotopic study, with parallel records of 3'80 and 8%C obtained on bulk carbonates and B. tentaculata opercula, enables assessment of palaeoenvironmental and palae- oclimatic changes through most of the Holocene. As outcrops of
Values from May and November 2002 (*) were reported by Pettersson (2003). Modern water samples collected from Lake Bjarstrask and its catchment (see Fig. 3). Table 5 a 3rd degree polynomial. The oldest part of the model (before ca 10,700 cal. BP) was modified to incorporate the assumed effect of relatively rapid deposition of the silty sediments at the base (units 1-3). The inferred age of the onset of lacustrine sedimentation (ca 11,300 cal. BP) is in general agreement with the estimated age of the isolation of the basin from the Yoldia Sea (see above).
Values from May and November 2002 (*) were reported by Pettersson (2003). Modern water samples collected from Lake Bjarstrask and its catchment (see Fig. 3). Table 5 a 3rd degree polynomial. The oldest part of the model (before ca 10,700 cal. BP) was modified to incorporate the assumed effect of relatively rapid deposition of the silty sediments at the base (units 1-3). The inferred age of the onset of lacustrine sedimentation (ca 11,300 cal. BP) is in general agreement with the estimated age of the isolation of the basin from the Yoldia Sea (see above).
Fig. 4. Age model (thick line) based on calibrated radiocarbon dates of terrestrial macrofossils (Table 4). Approximate uncertainty envelopes, taking into account double standard deviations of individual calibrated dates, are indicated by the grey shading. The left-hand columns show the lithostratigraphic units and the total organic carbon content of the sediments (see Table 3).
Fig. 4. Age model (thick line) based on calibrated radiocarbon dates of terrestrial macrofossils (Table 4). Approximate uncertainty envelopes, taking into account double standard deviations of individual calibrated dates, are indicated by the grey shading. The left-hand columns show the lithostratigraphic units and the total organic carbon content of the sediments (see Table 3).
Fig. 5. Records of 5'80 and 8'°C obtained on bulk carbonates (thin lines), discrete calcitic Chara encrustations (open circles) and Bithynia tentaculata calcitic opercula (thick lines total organic carbon (TOC) content, CaCO3 content, and carbon/nitrogen (C/N) ratio, obtained from the Lake Bjarstrask sediment sequence, plotted against age. (Hammarlund et al., 1999, 2003), which together with data from Lake Geneva (Anadon et al., 2006) suggests that calcification of B. tentaculata opercula is not associated with any substantial isotopic vital effects. Millennial-scale variations in 8'C, on the other hand, likely reflect changes in lakewater uptake of 'C-enriched atmospheric carbon dioxide through changes in residence time (cf. Hammarlund et al., 2003). Potential contributions derive from changes in the supply of soil-derived 'C-depleted carbon dioxide in response to vegetation development in the catchment (cf. Reuss et al., 2010). Variations in primary productivity are unlikely to have played a role as dissolved inorganic carbon (DIC) is rapidly replenished in Lake Bjdrstrask due to the short lakewater residence time. Moreover, centennial-scale episodes of higher/lower 5!°C values generally do not correspond to increases/decreases in sediment TOC content (Fig. 5), which can be assumed to primarily reflect aquatic pro- ductivity. This decoupling would suggest transient episodes of increased flushing of 'C-depleted groundwater and runoff, which could have disturbed the Chara calcification process due to elevated suspension load (cf. Hammarlund et al., 2005). An alternative explanation is periodic methane formation, which may have
Fig. 5. Records of 5'80 and 8'°C obtained on bulk carbonates (thin lines), discrete calcitic Chara encrustations (open circles) and Bithynia tentaculata calcitic opercula (thick lines total organic carbon (TOC) content, CaCO3 content, and carbon/nitrogen (C/N) ratio, obtained from the Lake Bjarstrask sediment sequence, plotted against age. (Hammarlund et al., 1999, 2003), which together with data from Lake Geneva (Anadon et al., 2006) suggests that calcification of B. tentaculata opercula is not associated with any substantial isotopic vital effects. Millennial-scale variations in 8'C, on the other hand, likely reflect changes in lakewater uptake of 'C-enriched atmospheric carbon dioxide through changes in residence time (cf. Hammarlund et al., 2003). Potential contributions derive from changes in the supply of soil-derived 'C-depleted carbon dioxide in response to vegetation development in the catchment (cf. Reuss et al., 2010). Variations in primary productivity are unlikely to have played a role as dissolved inorganic carbon (DIC) is rapidly replenished in Lake Bjdrstrask due to the short lakewater residence time. Moreover, centennial-scale episodes of higher/lower 5!°C values generally do not correspond to increases/decreases in sediment TOC content (Fig. 5), which can be assumed to primarily reflect aquatic pro- ductivity. This decoupling would suggest transient episodes of increased flushing of 'C-depleted groundwater and runoff, which could have disturbed the Chara calcification process due to elevated suspension load (cf. Hammarlund et al., 2005). An alternative explanation is periodic methane formation, which may have
Fig. 6. Plot of 8'°C versus 3'°0 showing the isotopic composition of carbonate sample from Lake Bjarstrask, compared to corresponding data obtained on Cretaceous lime stone samples from the local bedrock (Samtleben et al., 2000).
Fig. 6. Plot of 8'°C versus 3'°0 showing the isotopic composition of carbonate sample from Lake Bjarstrask, compared to corresponding data obtained on Cretaceous lime stone samples from the local bedrock (Samtleben et al., 2000).
Fig. 7. Comparison of oxygen- and carbon-isotope records obtained on Bithynia tentaculata opercula (5'8Opi¢ and 5'°Cpit) from Lake Bjarstrask (thick lines) with selected regional proxy records (see Fig. 1) plotted against time: a = pollen-based mean annual temperature reconstruction from Lake Flarken, south-central Sweden (Seppa et al., 2005); b = pollen- based summer temperature anomaly reconstruction from Lake Kurjanovas, Latvia (Heikkila and Seppa, 2010); c = smoothed (200 yr) potassium ion record from the GISP2 ice-core, central Greenland (Mayewski et al., 1997), which is a proxy for the Siberian High (note inverse axis and log-scale); d = first principal component (PC1) analysis of XRF data from core 303610-12, eastern Gotland Basin (Harff et al., 2011). The black arrow in d indicates the transition from the Ancylus Lake stage to the Littorina Sea stage (Harff et al., 2011).
Fig. 7. Comparison of oxygen- and carbon-isotope records obtained on Bithynia tentaculata opercula (5'8Opi¢ and 5'°Cpit) from Lake Bjarstrask (thick lines) with selected regional proxy records (see Fig. 1) plotted against time: a = pollen-based mean annual temperature reconstruction from Lake Flarken, south-central Sweden (Seppa et al., 2005); b = pollen- based summer temperature anomaly reconstruction from Lake Kurjanovas, Latvia (Heikkila and Seppa, 2010); c = smoothed (200 yr) potassium ion record from the GISP2 ice-core, central Greenland (Mayewski et al., 1997), which is a proxy for the Siberian High (note inverse axis and log-scale); d = first principal component (PC1) analysis of XRF data from core 303610-12, eastern Gotland Basin (Harff et al., 2011). The black arrow in d indicates the transition from the Ancylus Lake stage to the Littorina Sea stage (Harff et al., 2011).
Fig. 8. (A) The GISP2 K+ record (light blue) together with first principal component analysis scores (black) of the Lake Bjarstrask 5'°0,;, and 5'°C, i, isotopic records (PC1pit), plotted as 200-yr-smoothed curves. Each record is displayed on its own independent timescale. The arrows show increasing winter precipitation and a stronger Siberian High, respectively. (B) Maximum Entropy Method (Ghil et al., 2002) spectral estimates of the PC1pit (black line) and the GISP2 K+ series (light blue line) as determined over N/2 lags. Periods are noted above individual peaks. The dashed lines represent the 99% confidence limits for the respective records. The percentage indicates the variance of PC1,i signal explained for periods higher than 520 yr (statistically significant above the 99% confidence limit). The peak at 1.43 ka (22% of the total variance explained) is comparable to the 1.45 ka periodicity observed in the GISP2 Polar Circulation Index (PCI) series, as discussed in Mayewski et al. (1997). (C) Wavelet analysis (Morlet function) (Torrence and Compo, 1998) of the PC1pit record showing the power of the cycles (greyscale) over the length of the time series. The hatched area shows the cone of influence. The black contour is the 99% confidence limit, using a red-noise AR (1) background spectrum. (D) Global wavelet power spectrum performed by using the online application of the Department of Atmospheric and Oceanographic Science at the University of Colorado at Boulder (http://paos.colorado.edu/research/wavelets/). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 8. (A) The GISP2 K+ record (light blue) together with first principal component analysis scores (black) of the Lake Bjarstrask 5'°0,;, and 5'°C, i, isotopic records (PC1pit), plotted as 200-yr-smoothed curves. Each record is displayed on its own independent timescale. The arrows show increasing winter precipitation and a stronger Siberian High, respectively. (B) Maximum Entropy Method (Ghil et al., 2002) spectral estimates of the PC1pit (black line) and the GISP2 K+ series (light blue line) as determined over N/2 lags. Periods are noted above individual peaks. The dashed lines represent the 99% confidence limits for the respective records. The percentage indicates the variance of PC1,i signal explained for periods higher than 520 yr (statistically significant above the 99% confidence limit). The peak at 1.43 ka (22% of the total variance explained) is comparable to the 1.45 ka periodicity observed in the GISP2 Polar Circulation Index (PCI) series, as discussed in Mayewski et al. (1997). (C) Wavelet analysis (Morlet function) (Torrence and Compo, 1998) of the PC1pit record showing the power of the cycles (greyscale) over the length of the time series. The hatched area shows the cone of influence. The black contour is the 99% confidence limit, using a red-noise AR (1) background spectrum. (D) Global wavelet power spectrum performed by using the online application of the Department of Atmospheric and Oceanographic Science at the University of Colorado at Boulder (http://paos.colorado.edu/research/wavelets/). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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PalaeoclimatologyEarth SciencesGeologyOceanographyHistory and archaeologyLake SedimentsAtmospheric CirculationQuaternary Science ReviewsSiberian high
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