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Lateglacial and early Holocene environmental dynamics in northern Lithuania: A multi-proxy record from Ginkūnai Lake ARTICLE in QUATERNARY INTERNATIONAL · SEPTEMBER 2015 Impact Factor: 2.06 · DOI: 10.1016/j.quaint.2014.08.036
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Lateglacial and early Holocene environmental dynamics in northern nai Lake Lithuania: A multi-proxy record from Ginku Migle_ Stan cikaite_ a, Vaida Seirien e_ a, *, Dalia Kisieliene_ a, Tonu Martma b, nas a zeika a, Petras Sink u Gra zyna Gryguc a, Rimante_ Zinkute_ a, Jonas Ma a b
Nature Research Centre, Institute of Geology and Geography, T. Sevcenkos 13, 03223 Vilnius, Lithuania Institute of Geology, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia
a r t i c l e i n f o
a b s t r a c t
Article history: Available online xxx
To reconstruct the Lateglacial and early Holocene palaeoenvironmental dynamics in the northern part of nai Lake was studied applying a multi-proxy approach, Lithuania, the sediment record from Ginku involving pollen, diatom, and plant macrofossil surveys as well as d18O, d13C, 14C and loss on ignition (LOI) measurements, together with geochemical investigations. The obtained data suggest the deglaciation of the area started at approximately 16,000e16,500 cal BP, followed by the formation of a tree-less tundra. The obtained palaeobotanical records indicate the scarcity of the vegetation cover and the flourishing of the non-arboreal taxa in the local flora, suggesting a severe climatic regime. After 13,700 cal BP, the Pinus-Betula predominating forest progressively expanded, although this process was partly reversed during the recurrence of a cold interval recorded from 13,000 to 13,100 cal BP. Since 12,600 cal BP, rapid aridification of the climatic regime reflected in the isotope record was accompanied by the formation of cold-adapted vegetation, including Picea stands, which acted as an intensive supply of allochthonous material into the basin, thereby decreasing the water level. The identified period of physical disturbance lasted until approximately 11,800 cal BP. Significant changes of the palaeoenvironmental regime subsequently occurred in the area and were manifested in most of the obtained proxies, i.e., changes in the sediment type, transformations of the vegetation cover, and fluctuations of the sedimentation regime. Isotope records along with the geochemical data indicate a major climatic turn in terms of the temperature and moisture after 11,500 cal BP. The rising productivity of the basin was coincident with the stabilisation of the soil layer and the formation of dense vegetation cover enriched by Corylus (ca 9800 cal BP) and Ulmus (ca 10,300 cal BP) during the early Holocene. After 10,800 cal BP, the investigated part of the basin changed to a peat bog. © 2014 Elsevier Ltd and INQUA. All rights reserved.
Keywords: Palaeobotany Stable isotope Environmental history Lateglacial Early Holocene Lithuania
1. Introduction Marked by rapid and pronounced climatic oscillations (Walker et al., 1994, 1999), the Weichselian Lateglacial period is especially important for describing climate history and the subsequent ecosystem response in the North Atlantic realm. Numerous studies based on multi-proxy data obtained from terrestrial, marine and ice archives have revealed and characterised post-glacial climatic episodes (Walker, 1995; von Grafenstein et al., 1999; Lowe et al., 2008; Brooks and Birks, 2000a,b) and the tree population dynamics (Huntley and Birks, 1983; Birks and Birks, 2004; Willis and van Andel, 2004; Giesecke, 2005; Latałowa and van der Knaap,
* Corresponding author. _ E-mail address:
[email protected] (V. Seirien e).
€liranta et al., 2006; Birks and Willis, 2008; Binney et al., 2009; Va 2011), in northern Europe. The existing data sets suggest a high synchronicity of the main climatic events and the associated environmental response in this region (Lowe et al., 2008), while some alterations, such as the delay of the early Holocene warming and the subsequent environmental shifts in the northeastern part of the continent, were fixed (Wohlfarth et al., 2002, 2007; Stancikaite_ et al., 2008, 2009). Increasing the number of chronologically well-supported high-resolution multi-proxy archives representing areas where the number of similar investigations is still low may aid in improving the understanding of the Lateglacial climatic evolution and the ecosystem reaction in the Northern Hemisphere. Situated in the southeastern sector of the Scandinavian Ice Sheet (SIS), the eastern Baltic region can be described as a key area for improved understanding of these relationships in the east-west
http://dx.doi.org/10.1016/j.quaint.2014.08.036 1040-6182/© 2014 Elsevier Ltd and INQUA. All rights reserved.
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M. Stancikaite_ et al. / Quaternary International xxx (2014) 1e14
nai Lake study site. Fig. 1. Location of the Ginku
transect. Although studies of the Lateglacial, i.e., the deglaciation history (Hausen, 1913), vegetation dynamics (Weber, 1902; Thomson, 1931), among others, started in the region over onehundred years ago many questions related to the particular episodes in palaeoenvironmental history, including the timing and spatial variations of the recorded changes, remains unclear. Only resent research in which the multi-proxy approach has been increasingly used has farther described the ice-recession pattern nas, 2011; Kalm et al., 2011; Zel (Bitinas, 2011; Guobyte_ and Satku cs et al., 2011), vegetation history (Stan cikaite_ et al., 2004, 2009; € et al., 2009; Saarse et al., 2009; Seirien e_ et al., 2006; Heikkila Amon and Saarse, 2010; Amon et al., 2010, 2012; Veski et al., 2012), changes of the lacustrine environment (Novik et al., 2010; Ozola et al., 2010) and chronology of particular climatic and environmental events (Rinterknecht et al., 2006, 2008) in the region. By increasing the temporal resolution, it has also been possible to correlate the results regionally. To further describe the Lateglacial and early Holocene palaeoenvironmental dynamics in the eastern Baltic, a sediment core nai Lake, northern Lithuania. As very few was obtained from Ginku records covering the above mentioned time interval are known from this relatively unexplored territory, these new data may contribute to the reconstruction of the spatial-temporal pattern of the palaeoenvironmental fluctuations, both in the eastern Baltic and elsewhere. The objectives of this multi-proxy investigation are a) to reconstruct the floral dynamics representing the vegetation responses to climatic oscillations of different scales; b) to describe the sedimentary environment of the investigated aquatic system; and c) to contribute to the understanding of the paleoenvironmental changes in the context of the regional and global ones. To achieve the above-mentioned objectives, the authors combined pollen, diatom, and plant macrofossil evidence as well as the results of stable isotope (d18O, d13C, 14C) measurements together with loss on ignition (LOI) and geochemical data.
2. Study site nai Lake, with the coring point (55 560 5300 N, 23 200 1900 E, Ginku Fig. 1), is situated in the territory characterized as the Middle Lithuanian ice-marginal ridge formed during the Last (Weichselian) Glaci nas, 2011). The sedimentary basin stretches ation (Guobyte_ and Satku in a depression surrounded by morainic hills reaching to 140 m a.s.l. The middle part of the investigated eutrophic lake is waterlogged area, dividing the lake into two parts: a 16 ha northern (107 m a.s.l.) and 56.2 ha southern one (103 m a.s.l.). The core was made in the northern basin (Fig. 1). Low lake shores are boggy, and the headwaters of Kulpe_ River are situated in the northern part of the investigated lake. Pastures and agriculture fields predominate northwards from the lake, and the outskirts of Siauliai Town stretch southwards. The study area belongs to a boreo-nemoral vegetation zone and is characterized by the dominance of Pinus sylvestris L., Picea abies (L.) Karst., Betula pubescens Ehrh. and Betula pendula Roth. (Natkevicaite-Ivanauskiene, 1983). In the northern part of Lithuania, the annual average air temperature is 6 C, with mean January temperature at 5 C and mean July temperature at approximately 16.5 C. The average precipitation is approximately 550 mm y1 (Bukantis, 1994). 3. Methods 3.1. Coring and sampling Four adjacent 715 cm depth cores situated in a distance of 1.5e2 m from each other were taken using a “Russian” peat sampler with 1 m length and a 5 cm inner-diameter chamber. Multiple, parallel, overlapping sediment cores were transported into the laboratory, described, and sub-sampled for further survey. Characteristic lithological limits were easily determined due to the sharp transition between layers. One sediment sequence was sub-
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sampled for pollen, diatom and 14C investigations, a second one for d18O and d13C ratio, LOI, and geochemical measurements, and the other two for plant macrofossil research.
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Alongside with the visual inspection, stratigraphically constrained cluster analysis (CONISS), a method of incremental sum-of-squares (with no data transformation) was used for the subdivision of the palaeobotanical diagrams into the local zones.
3.2. Loss on ignition 3.4. Diatom analysis The content of organic material, calcium carbonate (CaCO3) and terrigenous matter was determined by loss-on-ignition (LOI) survey. To ascertain the LOI, sediments covering 2e4 cm interval were dried at 105 C for 24 h and combusted at 500 C (4 h) and 900 C (4 h) to calculate organic matter, carbonate and mineral compounds respectively. In total, 78 samples were measured. 3.3. Pollen analysis Sub-samples of 2 cm3 covering 2 cm interval were prepared for pollen analysis using a standard procedure (Erdtman, 1936; Grichiuk, 1940) that includes the application of heavy liquid (CdI2 þ KI). In order to calculate pollen concentration Lycopodium spores were added (Stockmarr, 1971). The total pollen (SP) sum exceeds 500 specimens of arboreal (SAP) and non-arboreal (SNAP) taxa in 154 investigated samples. Pollen identification followed Moore et al. (1991). Pollen percentage values were expressed relative to the sum of arboreal (SAP) and non-arboreal (SNAP) taxa and plotted using TGView software (Grimm, 2007). This program was applied in construction of all palaeobotanical diagrams.
Diatom frustules were extracted from the 52 samples covering 2 cm intervals. The conventional technique described by Battarbee (1986) was applied along with the application of HCl to remove carbonates and 35% H2O2 to oxidize organic material. Diatoms were identified under NICON light microscope at 1000x magnification and more than 500 specimens counted per sample. Species identification primarily followed Krammer and Lange-Bertalot (1988, 1991a,b, 1997). 3.5. Plant macrofossil analysis A total of 86 samples (230 cm3 in volume) covering 5 cm intervals each were analyzed by macrofossil survey. The collected remains, which had been extracted from the sediment samples by wet sieving (screens with mesh sizes of 0.2 and 0.5 mm), were analyzed using a microscope (NICON SMZ 1500) at a magnification of 20e60. Identification of the collected material followed Grigas (1986), Berggren (1969, 1981), and Cappers et al. (2006) in combination with the reference collections. Botanical nomenclature
Fig. 2. Litho- and chronostratigraphical data with d18O (‰) and d13C (‰) isotope records.
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follows Gud zinskas (1999). The plant macrofossils are presented as various identified specimens/sediment volume and classified into groups (trees, aquatic plants, shore and wetland plants, other) to aid in the interpretation of vegetation history. 3.6. Radiocarbon (14C) dating The chronostratigraphy of the investigated core was confirmed by both conventional and AMS radiocarbon dates performed in the Kiev Radiocarbon Laboratory (Ukraine) and Poznan Radiocarbon Laboratory (Poland). Due to the absence of macrofossils adequate for radiocarbon dating in the investigated part of the core, bulk sediment samples were analyzed in both cases. For calibration of 14C dates, OxCal v4.2 software (Bronk Ramsey et al., 2010) and IntCal2013 calibration curve (Reimer et al., 2013) were used. The 14C age-depth model was developed using Bayesian sequence modeling implemented in the OxCal v4.2 programme (Bronk Ramsey, 2009). 3.7. d18O and d13C ratio analysis Sub-samples of bulk sediments were taken at a 2 cm increment of the core for a total of 167 samples. Powdered material was analyzed for carbon and oxygen stable isotopes composition by Thermo Fisher Scientific GasBench II coupled to a Delta V Advantage mass spectrometer in the Laboratory of Mass Spectrometry, Institute of Geology at the Tallinn University of Technology, Estonia. CO2 was produced by reacting 0.6e2 mg of bulk sample with 100% H3PO4 by 70 C. Results are reported, using the usual d-notation, as per mil deviation from the VPDB standard. The reproducibility of results is generally better than ±0.1‰. 3.8. Geochemical investigations The total contents of major elements (Al, Fe, Ca, Mg) in weight percentages and trace elements (Ag, B, Ba, Co, Cr, Cu, Ga, Y, Yb, La, Li, Mn, Mo, Nb, Ni, P, Pb, Sc, Sn, Sr, Ti, V, Zn, Zr) in mg/kg were determined by Atomic Optical Emission Spectrophotometry (AOES) in 91 sediment samples. The sampled intervals were 5 cm in the upper part of the sediment core (310e610 cm) and 4 cm in the lower part (610e718 cm). Measurements were carried out using DFS-13 equipment and an MD-1000 microdensitometer in the laboratory of the Nature Research Centre, Lithuania. 4. Results and discussion 4.1. Lithostratigraphy and age control nai The investigated part of the sediment sequence from Ginku Lake is classified into five lithostratigraphic units, three of which are Lateglacial (Fig. 2). Especially low representation of the organic matter (less than 10%) was recorded throughout the strata. The representation of CaCO3 increases up to 88% (605e520 cm) and 94.6% (436e310 cm) in particular intervals. Minerogenic constituent predominates in the lowermost unit (up to 63%, 718e605 cm) and in the upper part of unit 3 (up to 76.8%, 520e436 cm). The amount of organic constituent culminates (84%) in the uppermost part of the profile, unit 5. The chronological subdivision of the investigated sequence was based both on the results of 14C measurements (Table 1) and biostratigraphical data including that obtained on the regional scale. As calcareous sediments predominate along the largest part of the profile, overestimation of the identified age due to a “reservoir effect” cannot be excluded. To diminish possible mistakes, regional biostratigraphical information supported by the independent chronological scale (Stan cikaite_ et al., 2008, 2009;
Heikkil€ a et al., 2009; Veski et al., 2012) was involved in assessing the age of the environmental variations. The oldest date obtained from the lower part of the section (640e642 cm depth) places the deposition of the investigated sediments at about 16,650e15,750 cal BP (Poz-45735) or GS-2a Stadial (Lowe et al., 2008). The high amount of terrigenous matter recorded in unit 1 (605e718 cm) suggests rapid sedimentation during the initial stages of deglaciation, as formation of the Middle Lithuanian marginal nai Lake was dated to 17,000 cal BP (Ehlers et al., ridge with the Ginku 2004). Re-deposition of the investigated material is also confirmed by the high representation of thermophilous taxa i.e. Alnus, Corylus, Tilia, Quercus, and Ulmus in GP-1 pollen zone and presence of preQuaternary diatoms in GD-1. Two upper dates at a depth of 614e618 cm and 602e604 cm yielded 14,950e13,750 cal BP and €lling13,990e13,680 cal BP respectively (Fig. 2), i.e. onset of Bo € d interstadial (GI-1) (Lowe et al., 2008). The pollen record Allero indicates the formation of the open vegetation with the local stands of Pinus at the transition from GP-1 to GP-2 that is typical for the onset of the Lateglacial Interstadial in the largest part of the Lithuania territory (Stan cikaite_ et al., 2008, 2009). Simultaneously, the amount of organic content started to increase (Fig. 2). Sediment €d warming (GI-1c-b-a), with distinctly unit 2 encompasses Allero predominating pine forest in the region (Stancikaite_ et al., 2008, 2009; Zernitskaya et al., 2010). The top of this zone is inferred to be the transition from the Lateglacial Interstadial to the Stadial (GS1) as the most remarkable changes occurred in palaeobotanical (Figs. 3e5), isotope (Fig. 2) and geochemical (Fig. 6) data. The onset of zone GP-3 is marked by the strong decline of AP taxa, suggesting abrupt opening of the vegetation. Based on biostratiographical features onset of the Younger Dryas or GS-1 event sensu Lowe et al. (2008) i.e. the lower limit of lithological unit 3 (520 cm) dates back to approximately 12,600 cal BP in Lithuania (Stancikaite_ et al., 2008). The four dates representing the upper part of the section were consistent, suggesting ongoing sedimentation during the earliest stages of the Holocene (units 4 and 5). Establishment of Corylus and Ulmus dated to about 9800 cal BP and 10,300 cal BP in correlation with the regional pollen records (Gaidamavi cius et al., 2011).
Table 1 14 nai Lake. C measurements from Ginku 14
No.
Depth, cm
Reference laboratory
95.4%
68.2%
1 2 3 4
272e282 318e320 365e370 405e410
Ki-15546 Poz-45786 Ki-14733 Ki-14734
8570 8670 9100 9680
± ± ± ±
120 60 100 120
9950e9250 9820e9530 10,600e9900 11,350e10,650
5 6 7 8
470e472 602e604 614e618 640e642
Poz-45788 Poz-45791 Ki-15547 Poz-45735
11,090 11,960 12,270 13,590
± ± ± ±
60 70 150 90
13,120e12,890 13,990e13,680 14,950e13,750 16,650e15,750
9700e9440 9690e9540 10,420e10,180 11,220e110,60 (33%) 13,070e12,940 13,900e13,740 14,600e13,950 163,90e15,940
C yr BP
Calibrated time, cal yr BP
4.2. Stages of the ecosystem dynamics The results of lithostratigraphical, palaeobotanical, isotopic and nai Lake and geochemical investigations implemented in Ginku summarised in Fig. 7 enable the reconstruction of the depositional environment during the particular time-intervals.
4.2.1. Before 13,700 cal BP The calcareous silt lying at the bottom of the investigated sequence (unit 1, Fig. 2) contains an especially low amount of organic material (less than 4%) and a high amount or minerogenic
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nai Lake with the selected taxa presented. Grey shade pattern represent х 30 exaggeration of base curves. Fig. 3. Percentage pollen diagram of site Ginku
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nai Lake. The hollow bar pattern represent х 2 exaggeration of base bar. Number of recovered plant macrofossils per 230 cm3. Fig. 4. Plant macrofossil diagram of site Ginku Abbreviations: fr. e fruit, s-seed, os. e oospore, en. e endocarp.
constituents (up to 69%), suggesting low productivity of the catchment and intensive reorganisation of the surface. A particularly low pollen concentration and influx value confirm the scarcity of the vegetation cover with non-arboreal taxa (up to 35% GP-1, Fig. 3). The fruits of Betula nana L. were recorded in the sediments deposited shortly after 14,700 cal BP (GM-2, Fig. 4). Furthermore, the pollen evidence confirms the sporadic presence of Betula, most probably B. nana. As the presence of local birch dominating woodland could be indicated by the pollen curve exceeding 25% (Huntley and Birks, 1983), the value of 10e25% nai core suggests local growth of this plant recorded in the Ginku during the earliest stages of the post-glacial. For Pinus, only pollen values exceeding 50% indicate local dominance of the plant (Huntley and Birks, 1983), while the recorded number (30e50%) most likely confirms the presence of long-transport originated nai. Other pollen grains, exotic for the pollen grains in Ginku Lateglacial vegetation, i.e., Alnus, Tilia, Corylus and Ulmus, were presumably in-washed from the older interglacial deposits or were originated from long-distance, as was suggested in contemporaneous records representing the Eastern Baltic region (Veski et al., 2012). Although the presence of Alnus macrofossils in the final stages of the Late Glacial is known from the region
wka, 2006; Stan (Latałowa and Boro cikaite_ et al., 2008), establishment of this plant at the outset of the post-Glacial in the region is hardly possible. Most likely, these macrofossils as well as thermophilous pollen grains were derived from the interglacial _ 1996). In beds recorded in this part of Lithuania (Kondratiene, general, the number and variety of plant macrofossils deposited before 15,500 cal BP is especially scarce (GM-1, Fig. 4). According to the collected palaeobotanical data, very few pioneer species representing shrub/herb/grass vegetation migrated to the glacier forelands, thereby forming unstable treeless tundra vegetation cover with scattered stands of birch and possibly pine at about 13,700 cal BP. The diatom record (GD-1, Fig. 5) suggests the existence of a shallow oligotrophic transparent water body with a rich set of diatoms, including epiphytic forms of Fragilaria spp., especially Fragilaria construens f. venter, with a pH level of approximately 7.8, needed for Potamogeton praelongus Wulfen to prosper (Hannon and Gaillard, 1997), before 14,700 cal BP. The dominance of pioneer benthic Fragilaria species is a typical feature of early post-Glacial € and Weckstrom, 1999), as these are diatom assemblages (Seppa very competitive during nutrient limiting conditions typical of oxygen-rich, alkaline water with a high content of dissolved
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M. Stancikaite_ et al. / Quaternary International xxx (2014) 1e14 nai Lake with selected taxa presented. Grey shade pattern represent х 7 exaggeration of base curves. Symbol (þ) is used to describe the relative abundance (þrare, þþ occasional). Fig. 5. Percentage diatom diagram of site Ginku
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Fig. 6. Amount of particular chemical elements discovered in the lake sediments.
originated exclusively from the eroded interglacial sediments. The highest median content of Mn (520 ppm) in the lowermost geochemical unit GCh-1 (Table 2) as well as the distribution pattern of Mn in the sediments (Fig. 6) indicate that the depositional environment was oxic, because the geochemical-focusing of manganese in the lake sediments is a promising proxy indicator for the reconstruction of oxygen conditions during deposition (Schaller and Wehrli, 1996). However, some changes in the diatom record, such as the increasing concentration of diatom frustules, occurred after 14,700 cal BP, suggesting stabilisation of the sedimentation regime in the basin.
mineral salts and calcium (Miller, 1977). An increase in Fragilaria pinnata indicates the presence of Ca in the basin, which positively correlates with the results of the CaCO3 measurement (unit 1, Fig. 2) and the amount of Ca in the geochemical record (GCh-1, Fig. 6). The allogenic fraction (clastic mineral particles) plays a leading role in the formation of these sediments, pointing to high erosion rates and the absence of stable soil cover in the lake catchment (Engstrom and Wright, 1984). The pre-Quaternary spores along with some plant macrofossils and diatom species of the Pliocene age (Paralia sulcata) accompanied by taxa typical for a marine environment (broken frustules of Coscinodiscus spp.) may have
Table 2 Geochemical characterization of the distinguished intervals. Median contents Unit and number of samples
Ca, %
Fe, %
Al, %
Mn, ppm
Sr, ppm
Ba, ppm
B, ppm
Cu, ppm
Mo, ppm
Mg, %
TCH-4, n ¼ 31 TCH-3b, n ¼ 8 TCH-3a, n ¼ 8 TCH-2, n ¼ 15 TCH-1, n ¼ 28
32.0 22.0 30.5 17.0 17.0
0.003 0.340 0.115 1.75 1.50
