The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

Home , Pollen zone, Suess (Martian crater), Water caltrop

Department of Physical Geography

Nichola Strandberg

Master’s thesis NKA 188 Physical Geography and Quaternary Geology, 60 Credits 2017

Preface

This Master’s thesis is Nichola Strandberg’s degree project in Physical Geography and Quaternary Geology at the Department of Physical Geography, Stockholm University. The Master’s thesis comprises 60 credits (two terms of full-time studies).

Supervisor has been Martina Hättestrand at the Department of Physical Geography, Stockholm University. Examiner has been Stefan Wastegård at the Department of Physical Geography, Stockholm University.

The author is responsible for the contents of this thesis.

Stockholm, 26 June 2017

Steffen Holzkämper Director of studies

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

Abstract

Lina Mire, Gotland, is an area of archaeological significance and has a complex history of shoreline displacement. Archaeologists suspect that Lina Mire was once part of an important inland water system which connected the Littorina Sea with central Gotland. This study investigates vegetational and palaeoenvironmental changes of the Lina Mire area between 6900 – 400 BC (8850 – 2350 cal years BP) in order to better understand how the area has developed and how humans have impacted the vegetation. Pollen analysis, C/N ratios, organic matter and carbon content measurements were conducted. The chronology was based on 14C AMS dating of terrestrial macrofossils and bulk sediments. A transgression of the Littorina Sea at about 6550 BC (8500 cal years BP) inundated the Lina Mire basin, which was a lake at the time. The onset of cultivation was indicated by the presence of Hordeum (Barley or Wild Barley) during the Late Neolithic, 2630 BC (4580 cal years BP). Hordeum continued to grow during the Bronze Age when Cereals appeared at about 970 BC (2920 cal years BP). During the onset of cultivation during the Late Neolithic, the Lina Mire basin was a bay of the Littorina Sea. The Lina Mire basin remained connected with the Littorina Sea until isostatic uplift caused it to become isolated at about 1870 BC (3820 cal years BP). The lake overgrew and became a mire about 820 BC (2770 cal years BP).

Nichola Strandberg

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

Table of Contents

Abstract ...... 1 Introduction ...... 5 Aims ...... 6 Background ...... 7 Pollen and charcoal as anthropogenic indicators ...... 7 The Baltic Sea Stages ...... 8 Previous Research on the Vegetational Development of Gotland ...... 10 The Climate History of Gotland ...... 11 Holocene Plant Migrations and Declines ...... 12 The Archaeology of Gotland ...... 13 The Mesolithic 12,000 – 4000 BC (13,950 – 5950 cal years BP) ...... 13 The Neolithic 4000 – 1700 BC (5950 – 3650 cal years BP) ...... 14 The Bronze Age 1700 – 500 BC (3650 – 2450 cal years BP) ...... 15 Site Description ...... 17 Methods...... 18 Field Methods ...... 18 Laboratory Methods ...... 19 Radiocarbon Dating ...... 19 Organic Matter and Carbon Content ...... 21 Carbon-to-Nitrogen Ratios ...... 22 Pollen and Charcoal ...... 22 Results and Interpretations ...... 24 The Mire Stratigraphy ...... 24 Chronology ...... 27 Organic Matter and Carbon Content ...... 28 Carbon-to-Nitrogen Ratios ...... 29 Pollen and Charcoal Particle Concentrations and Accumulation Rates ...... 29 Pollen ...... 30 Pollen Zone One ...... 32 Pollen Zone Two ...... 32 Pollen Zone Three ...... 32

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Pollen Zone Four ...... 33 Discussion ...... 34 Chronology ...... 34 Quaternary Geology and Mire Stratigraphy ...... 36 Pollen ...... 40 Pollen Zone One ...... 42 Pollen Zone Two ...... 43 Pollen Zone Three ...... 44 Pollen Zone Four ...... 45 Pollen and Charcoal Taphonomy ...... 48 Conclusions ...... 51 The Baltic Sea Stages and Development of the Lina Mire Basin ...... 51 Vegetational Development around Lina Mire ...... 52 Acknowledgements ...... 52 References ...... 54 Appendix ...... 64

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

Introduction Since the beginning of the Neolithic period, around 7000 years ago, humans have been influencing vegetation cover in North Western Europe. Pollen records reflect how farming, including clearance of woodland and the introduction of new species, changed the landscape (Lowe and Walker, 2014). Palynology can therefore be used to identify human activities and periods of abandonment (Brun, 2011). Behre (1981) proposed a method which relies on the identification of some indicator taxa such as crop and weed taxa, which are associated with arable farming and ruderal taxa. These are associated with disturbed land. Behre based his understanding of prehistoric taxa on modern equivalents. The approach by Behre takes into account traditional farming techniques described by Oberdorfer (1970) and Ellenberg (1979) among others. In order to create a precise reconstruction there must be knowledge about the ecosystems associated with human activities such as cultivated and ruderal environments, grazing land and meadows. Palynology has been used to investigate when the earliest agriculture can be traced to in Europe as shown, for example, in Behre (2007; 2008) and Tinner et al., (2007). The use of indicator taxa for inferring prehistoric human impacts have been adapted to suit countries in northern Europe, such as Sweden (Berglund and Ralska-Jasiewiczowa, 1986), Norway (Vorren, 1986) and Finland (Hicks, 1988). Agriculture was first introduced in Scandinavia about 3950 cal years BP (Gron et al., 2015). The introduction of agriculture had huge implications for prehistoric humans. Large Mesolithic settlements were usually near to the coast and were only occupied seasonally. However, the introduction of agriculture meant that people relocated inland and founded farming settlements (Gron et al., 2015). Identifying pre-agrarian and early-agrarian human impacts is more complex than identifying the onset of agriculture itself. This is partly due to the fact that climate, edaphic and other ecological factors impacted the woodlands more than humans during the first half of the Holocene (Behre, 1988 and Hicks, 1992). However, humans as early as the Stone Age used the woodland resources to collect wood for fires and to build dwellings. The action of opening up woodland and producing waste meant that the conditions became more favourable for nitrophilous and light demanding herbs (Behre, 1981 and Berglund, 1985). People have been living on Gotland, the largest island in the Baltic Sea, for about 9000 years (Martinsson-Wallin and Wallin, 2010). The lifestyles of these people have been influenced by changes in culture brought about by the arrival of new groups of people and by changes in the natural landscape. Lina Mire, one of the largest mires on Gotland (Fig. 1), was the area of the first settlements on the island. This area has undergone extensive shore displacement which has created an ever-changing landscape. During the Mesolithic and Early Neolithic Lina Mire had a narrow connection with the sea and was a lagoon. Today, the mire is 5 kilometres distance away from the shoreline. This change in natural landscape has affected the human relationship with land use based on economic, social, emotional and cognitive aspects. Many important archaeological sites from different periods have been discovered around the mire, especially

Nichola Strandberg on the northern and western side. This area is thus of particular importance from an archaeological perspective. This study is part of a larger research effort which began in 2009 and was initiated by Helene Martinsson-Wallin from the Department of Archaeology and Ancient History at Gotland University. This research effort which later became a project ‘In the footsteps of Tjelvar’ aimed to explore cultural and environmental changes which have occurred on Gotland since the pioneer phase of the Mesolithic until the early medieval phase. The project name was derived from the fact that this area of Gotland has the largest concentration of stone ship settings. This includes Tjelvar’s grave; a well-known legendary figure who was thought to have founded Gotland (Nihlén, 1928). A holistic approach to understand the changes surrounding Lina Mire over the past 8000 years was needed and during 2011-2012 the project expanded and became multidisciplinary with archaeology, social geography, ecology and environmental elements. In 2013 Gotland University merged with Uppsala University to become Campus Gotland. Later collaboration on the project began with the Department of Physical Geography at Stockholm University. Within this collaboration, sediment cores were retrieved from Lina Mire in spring 2014 and an initial diatom analysis was performed (Martinsson-Wallin, 2017). In 2016, as part of an internship, further pollen and diatom analyses were carried out on the cores which were retrieved in 2013 and Yrla Hanström, Uppsala University, wrote her undergraduate thesis on a study of macrofossils from the core. In August 2016 further cores were retrieved from Lina Mire with the aim of more detailed pollen and diatom analyses being carried out. Preliminary investigations indicated that the shore displacement maps from SGU (Sveriges geologiska undersökning/Geological Survey of Sweden) were at odds with dating of archaeological findings in the area. In order to understand the archaeology of the Lina Mire area better, a more detailed understanding of the shore displacement and landscape development would be required. The project ‘In the footsteps of Tjelvar’ aims to conduct a detailed investigation of the mire, including dating, through analyses of sediment cores which will allow for a digital landscape reconstruction. The project also aims to review and incorporate archaeological data from previous excavations and engage with the local community and societies to provide information for local residents and tourists through interactive communication. The cores retrieved during August 2016 were used to investigate shore displacement. This was carried out by Aleftin Barliaev, Master’s student at Stockholm University, through diatom analysis. Field work, organic matter and carbon content measurements and carbon dating have been carried out in collaboration with Aleftin Barliaev. Aims The present study aims to, using the sediment cores collected in August 2016, investigate vegetational and landscape evolution through pollen and stratigraphic analyses. Given that the area surrounding Lina Mire is archaeologically and culturally important, focus is placed on understanding human impacts and when they become evident.

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

The main objectives of this study were to: 1. Investigate the stratigraphy of the mire and what different stratigraphic units represent. This was done to understand how the mire developed, how it may have been utilised in the past and to understand the depositional environment for pollen. 2. Identify and discuss vegetational changes based on the pollen record. 3. Detect what, if any, human impacts can be inferred and when they occurred. Background Pollen and charcoal as anthropogenic indicators When the samples have been taken from stratified sediments or accumulations pollen analysis will show the mixture of fossil pollen; this is the pollen assemblage. Once several depths or horizons have been analysed it is possible to compare the pollen assemblages. The changes in the pollen record indicate vegetational change. The pollen data can be displayed in a pollen diagram; one approach is to show pollen data as a percentage diagram. This is where each taxon is displayed as a percentage of the total pollen sum. However, the interpretation of the pollen diagram is not straightforward. To understand the pollen diagram there must be knowledge of pollen preservation, production and dispersal (Lowe and Walker, 2014). Iversen (1941; 1949) was the first to see the value of pollen diagrams for understanding human induced vegetation changes and was also the first to identify which pollen taxa were related to human activity (Behre, 1981). The problem for archaeologists was to identify where pastoral and arable farming occurred in different cultures and time periods. This approach to solving this problem relies on identifying the taxa which are indicators of human occupation and farming (Behre, 1981). Naturally, the best indicators of prehistoric human activities are cultivated crops. Some examples of taxa that may have been cultivated are Cerealia-type, Linum usitatissimum and Cannabis (Behre, 1981). For most for most of Europe cultivation started around the time of the beginning of the Neolithic 4000 BC (5950 cal years BP) (Lahtinen and Rowley-Conwy, 2013). However, there are also pollen species, other than cultivated species, which can indicate human activities. These are known as ruderal taxa. Plantago lanceolata is an important ruderal taxon which indicates undisturbed grassland and therefore ley farming (Burrichter, 1969). Plantago lanceolata also colonises abandoned land and is therefore an indicator of fallow land (Behre, 1981). It is important to note that nowadays in Europe there are sharp divisions between land areas which are devoted to different uses. However, prehistoric cultures had a more mixed approach to land use. Rotational farming systems with fallow years were more common (Vuorela, 1976). Plants can also be grouped into plant communities which can be useful indicators for land use. For example, Juniperus, Urtica and Rumex observed together with a peak in charcoal may indicate human activity. Another example of a plant community is Artemisia, Chenopodiaceae and Plantago, which together with prior knowledge about the site may indicate shoreline vegetation (Miller and Robertson, 1981).

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Charcoal fragments in sediments can be used to indicate fire history. Optical counting of charcoal fragments is a relatively easy and well used method of quantifying charcoal abundance (Clark, 1982). Changes in the fire history are related to climate changes and human activities. Charcoal from plant material often appears elongated, black, opaque and angular (Clark, 1982).Charcoal fragments can be microscopic and counted at the same time as pollen using a microscope or larger (>100 µm) and separated during wet sieving (Mooney and Tinner, 2011). Counting charcoal with pollen has been popular since the research carried out by Iversen (1941) and the method probably shows fires of all scales from local to regional (Clark, 1988a). The Baltic Sea Stages As the Fennoscandian Ice Sheet grew and then melted, the weight of the ice deformed the Earth’s crust. The Earth’s crust then began to rebound after deglaciation, which is known as isostatic adjustment (Lowe and Walker, 2014). Eustasy is the fluctuation of water volume in the oceans and can be affected by melting ice sheets (Lowe and Walker, 2014). The retreating Fennoscandian Ice Sheet, eustatic sea level rise and isostatic uplift created the Baltic Sea stages. The associated changes in relative sea level impacted where settlements were located and even influenced the diet of pre-historic humans. The Baltic has undergone different phases since the deglaciation of the Baltic basin which began 15,000-17,000 cal years BP and ended 11,000-10,000 cal years BP (Björck, 2008). Stroeven et al., (2016) put the general deglaciation of the Gotland area at around 15,000- 14,000 cal years BP. According to Svensson (1989), the deglaciation at Oskarshamn which is to the SW of Gotland on the Swedish mainland is dated to 14,500 cal years BP (12300 14C years BP) which is in agreement with Stroeven et al., (2016). Hughes et al., (2016) indicated that the ice margin over Gotland retreated at around 14,000 cal years BP. The melting of the Scandinavian Ice Sheet created an interglacial environment. The gradual melting of the ice sheet also led to differential glacio-isostatic uplift in the basin of 9 mm/yr to -1mm/yr; (Ekman, 1996). During the deglaciation of Fennoscandia there were also variations of the sill locations and depths and widths of the thresholds separating the Baltic basin and the marine waters of Kattegat-Skagerrak. A combination of isostatic uplift and sill location caused salinity and water exchange variations in the Baltic basin (Björck, 2008). Four main stages of the Baltic Sea, during and following the final deglaciation, have been identified. Following the rapid deglaciation of the southern Baltic basin a proglacial lake, the Baltic Ice Lake, was formed. Glaciolacustrine sediments were deposited as varves as the ice sheet retreated northwards (Björck, 2008). As the ice retreated a final drainage of the Baltic Ice Lake occurred at Mt. Billingen at 11,620 ± 100 cal years BP (Stroeven et al., 2015). When the Baltic Ice Lake was drained the Yoldia Sea phase began and lasted for about 900 years (Björck, 2008). The Ancylus Lake was the freshwater Baltic Sea stage which followed the Yoldia Sea and the Ancylus transgression was formed due to uplift of the outlets which became shallower. Some outlets were even raised above sea level. The two which remained functioning during this stage where the Göta Älv (today Göta Älv river) and the Otteid/Steinselva (today east of

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

Idefjorden on the Swedish- Norwegian border). Shallowing of the outlets resulted in sea level rise south of the isobases (south of the outlets) which led to a transgression. The Ancylus Lake transgressions started at about 10,700 cal years BP and lasted for about 500 years. Examples of this transgression are drowned pine forests that can be seen in Skåne, and raised Ancylus beaches on Gotland, Latvia and Estonia. A forced regression, which is caused by a fall in relative sea level, occurred about 10,200 cal years BP and it is assumed that the Ancylus Lake found a new outflow between the islands of Zealand and Funen in modern day Denmark (Björck, 2008). According to Berglund et al., (2005) the transition between the Ancylus Lake and Littorina Sea occurred 9800–8500 cal BP, although the first traces of marine influence have been seen about 9000 cal years BP in the Southern Baltic basin. It is thought that at this time the Öresund strait was inundated by seawater from the global transgression (Björck, 2008) and that eustatic sea level outpaced glacio-isostatic uplift. Saline water entered the basin and the southern Baltic basin experienced several transgressions during the first 2500-3000 years of the Littorina Sea stage (Björck, 2008). The Littorina transgression is actually the term given for a number of transgressions (Berglund et al., 2005). The Littorina Sea phase is not well defined on Gotland. However, a short regression has also been noted during the Littorina Sea, at about 8100 cal years BP. This was indicated by coastal sediments in Blekinge, Sweden. This marine regression has been correlated with a cold phase at 8200 cal years BP. The cold event was probably caused by a disturbance in the climatic regime in the North Atlantic (Berglund et al., 2005). The general development of the Littorina transgression is known but many details remain unknown (Björck et al., 2008) such as accurate timing and the chronological order in which the straits were flooded (Rößler et al., 2011). Most of the separate Littorina transgressions were caused by the sudden melting of the Antarctic Ice Sheet and ice shelves (Björck, 2008). Whereas the steady rising of the Littorina Sea up until around 6000 cal years BP was due to the gradual melting of the North American Ice Sheet, during this time the final remnants of the Labrador Ice Sheet melted (Björck, 2008). There are also inconsistencies, for example, several transgressions have been seen in Sweden and Denmark (e.g. Berglund et al., 2005; Christensen and Nielsen, 2008; Wohlfarth et al., 2008) however, in Finland evidence for only one uniform transgression has been seen (Eronen, 1974; Miettinen et al., 2007). Similarly, only one main transgression has been seen in Estonia (Raukas et al., 1995a, Saarse et al., 2009a). At Vääna lagoon, Estonia the Littorina transgression began about 8300 cal years BP and continued until c.7000 cal years BP. Once again, only one transgression was seen (Saarse et al., 2009a). On Saaremaa Island, Estonia, the Littorina Sea transgression began about 8300–8200 cal years BP and lasted up to about 7300 cal years BP (Saarse et al., 2009c). The Littorina transgression altered the coastline; it created sea arms, lagoons, small islands, suitable for dwelling (Saarse et al., 2009c). These discrepancies are difficult to interpret but one reason for the difference could be differential isostasy (Yu, 2003).

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The transgressive trend ended around 6000 cal years BP, although some minor transgressions possibly occurred up to 5000 cal years BP. Uplift rates around the Baltic basin were different, but eustatic sea level stopped rising. In Sweden, across from the north coast of Lithuania land uplift continued resulting in a regression whereas the transgression continued in the most southern parts of the Baltic Sea basin (Björck, 2008). Previous Research on the Vegetational Development of Gotland There has been much archaeological research done on Gotland and there have also been a few notable studies relating to geology and pollen stratigraphy on the island. Sernander (1894) was the first to research vegetational development on Gotland and presented his findings in a table. Munthe et al., (1925) published a study about Gotland’s geology in 1925. They described the geological layers and varves which were created during the period of the retreat of the inland ice; the Baltic Ice Lake, the Ancylus Lake, the Littorina Sea. In 1927, Thomasson described diatoms from the Lina Mire (Thomasson, 1927). In 1927 von Post made a pollen diagram from Stora Karlsö (Fig. 1) (von Post, 1927). This pollen diagram was later recalculated and redrawn by Königsson (1983) for a digitalisation project. Lundqvist (1928) described clayey gyttja taken from Lina Mire which contained marine diatoms and molluscs and interpreted this as a Littorina Sea deposit. In 1939, Sernander wrote a book entitled “Lina Myr”, which gave an account of the plant-ecologically of the mire, ditching, drainage, and nature conservation views (Sernander, 1939). Pettersson (1958) presented two pollen diagrams from Mobjärgssmyr, Linde and Rövät, Hejnum, Gotland (Fig. 1). Påhlsson (1977) produced two pollen diagrams from Broträsk, Lojsta central Gotland (Fig. 1), combined the diagrams cover a period from the Allerød to the Sub-atlantic chronostratigraphic divisions. No radiocarbon dating was done and the dating was based on correlations with other studies. Österholm (1989) later compared these pollen diagrams with knowledge of the archaeology on Gotland. A pollen diagram from Lina Mire has been described by Svensson (1989). The main aim of this study was to investigate shore displacement. Pollen analysis was used for a means of correlation between sites on Gotland. The most recent accumulations, the upper 2.2m of the stratigraphy, were not analysed in Svensson’s study. Beach ridges were used to indicate the Littorina Sea and Ancylus Lake shorelines. In 1992, Eriksson published pollen diagrams from Stora Karlsö (Eriksson, 1992).

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

Figure 1. The location of Lina Mire and other notable archaeological and research locations. The Climate History of Gotland Blytt-Sernander created a climatic scheme based on data from Scandinavian peat bogs (Lowe & Walker, 2014). Climate episodes were identified for Northern Europe which were the Pre- Boreal, Boreal, Atlantic, Sub-Atlantic, Sub-Boreal. This is the Blytt-Sernander climate scheme (Blytt, 1876 and Sernander, 1908) the scheme was linked to regional pollen zones. However, it became apparent that the relationship between the climate scheme and regional pollen zones was not straightforward and the scheme mostly fell out of use (Lowe and Walker, 2014). Since the scheme was widely used in previous pollen studies, for example, Svensson, 1989, it can be used here for comparisons. There are both internal and external factors which have affected climate change in the Baltic basin, variations in solar radiation, changes in the amount of greenhouse gasses in the atmosphere, variations in aerosols caused by volcanic activity, albedo changes and circulation changes caused by salinity variations (Borzenkova et al., 2015). Climate changes throughout the Holocene impacted vegetation around the Baltic basin, hydrology and human migration. A recent study by Borzenkova et al., (2015) combined proxy archives to summarise climate for the Baltic basin for the last 12,000 years. This was based on isotopes, insect remnants and continental lake level records. Three distinct climate zones were identified, the first, 11,000– 8000 cal year BP was a cold period related to deglaciation. The second climate period

Nichola Strandberg identified was a warm period 8000–4500 cal year BP. The climate was stable and summer air temperatures were 1.0–3.5 °C warmer than present day. The third climate period was for the last 5000–4500 years where the general trend was for decreasing temperatures and increased instability. One notable feature of the Early Holocene is the 8.2 ka cold event which lasted 160.5 ± 5.5 years (Thomas et al., 2007). It is thought that air temperatures fell 3 ± 1.1 °C (Thomas et al., 2007). Cooling occurred throughout the Baltic region (Borzenkova et al., 2015). Pollen data from both Estonia and in the southern Fennoscandian Peninsula confirms this climate decline and estimated a decrease of 1˚C. This was indicated by a drop in thermophilus taxa Corylus and Ulmus (Seppä et al., 2007). It is commonly thought that the cause of the 8.2 ka event was melt water from continental ice sheets changed the circulation of the North Atlantic Ocean (Borzenkova et al., 2015). The Holocene Thermal Maximum occurred between 7500 and 5500 cal year BP. Temperatures were 0.8 to 1.5 °C warmer than the present day (Borzenkova et al., 2015). Seppä and Birks (2001) described a decrease in Pinus pollen and fern spores in northern Finland relating to the temperature increase. In central Sweden thermophilus taxa such as Tilia and Quercus expanded after 7000 cal year BP (Borzenkova et al., 2015). The same trend was seen in Estonia between 7000 and 5000 cal year BP (Saarse and Veski, 2001). There is evidence for Late Holocene cooling around the Baltic region for the last 4500 years. The cooling is thought to be due to decreased insolation during summers (Borzenkova et al., 2015). One general trend is for thermophilus taxa such as Corylus to decline. For the last 1500-2000 years climate has been cooler and wetter across Fennoscandia (Esper et al., 2012). Seppä et al., (2009) described climate variability for the last 5000 years for Northern Europe. It is thought that there was a cold period 3800-3000 cal years BP and a warm period around 2000 cal years BP (Seppä et al., 2009). These climate variations were associated with humidity changes, with colder climate linked to more humid conditions Seppä et al., (2009). Holocene Plant Migrations and Declines The range of where plants are able to grow changes with varying glacial and interglacial cycles (Bennett, 1997). Plant migrations can be traced from the last glacial maximum to the present in pollen diagrams (for example Seppä, 2009). Early pioneers of the pollen diagram understood that values for certain taxa can be crowded out by the arrival of new taxa (von Post, 1916). It is therefore beneficial to understand migration patterns of plants as the arrival of new taxa can appear as a decrease in other taxa even if there was no real decrease in the plant population (Seppä, 2009). Pettersson (1958) noted that on Gotland that Ulmus and Corylus migrated during the Boreal period. According to Svensson (1989), who produced several pollen diagrams around Gotland including Lina Mire, early-Holocene vegetation was characterised by the migrations of tree species. Corylus expanded about 10,960 cal years BP (9600 14C BP) and Alnus expanded about 10,050 cal years BP (890014C BP). At around the same time Quercus and Ulmus appeared, although they expanded more slowly. Tilia and Fraxinus followed the

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC expansion of Quercus and Ulmus. During the Atlantic period 8900- 5730 cal years BP (8000- 500014C BP) Tilia, Fraxinus, Ulmus and Quercus became important tree species. According to Seppä (2009) Picea abies, which is now one of the most common trees in Eurasia, spread in a western direction when it migrated to Fennoscandia. The migration spread through eastern Finland around 6500 cal years BP, Eastern Sweden around 2700 cal years BP and reached Southern Norway by about 1000 cal years BP. However, Parducci et al., (2012) found that conifer trees survived in Scandinavia through the last glaciation in ice free areas and after the deglaciation may have spread from the west. Österholm (1989) said that Picea established itself on Gotland during the Boreal period. One major feature of pollen diagrams in north-western Europe of the Holocene has been the Ulmus decline. According to Skog and Regnell (1995) the cause of the Ulmus decline has been attributed to many factors including, climate change, human activity, deterioration of soil and disease (for example Birks, 1986). A study at Ageröds Mosse, in the very south of Sweden, dates the Ulmus decline occurred about 3770 BC (5720 cal years BP) and persisted for a few decades around this time. This decline is shown as a drop in percentage in Ulmus pollen from 7% to 2% (Nilsson, 1964). According to Österholm (1989) the onset of the Sub- Boreal is usually indicated in a decrease in Ulmus pollen. Ulmus was rare in the pollen record and therefore the decline was not very dramatic. A second small decrease in Ulmus was dated to 3200 BC (5150 cal years BP). Another feature of pollen diagrams is a decline in Tilia. Today Tilia is rare in forests in Sweden; however, it was once more common in Southern Sweden and across Northern Europe. One reason for the Tilia decline was thought to be colder and wetter climate conditions during the Bronze Age. According to Hultberg (2015), Tilia was abundant in Southern Sweden around 6000 cal years BP during the Holocene thermal maximum. Tilia then declined around 4000 cal years BP probably due to the climate deterioration that occurred around that time. Hultberg (2015) also linked Tilia decline with an increase in cereal pollen during the Bronze Age, probably related to agricultural management. The Archaeology of Gotland The Mesolithic 12,000 – 4000 BC (13,950 – 5950 cal years BP) Gotland was first populated about 9400 years ago by hunter-gatherers (Martinsson-Wallin et al., 2011). Human skeletal remains and artefacts have been found on Stora Karlsö in the mouth of Stora Förvar cave (Lindqvist and Possnert, 1999). This find indicates subsistence based on seal hunting and fishing. It is uncertain if the first Mesolithic people who settled on Gotland are the ancestors of Gotlanders (Österholm, 1989). According to Martinsson-Wallin et al. (2011) it is more likely that people arrived at different times and from different places, such as Scandinavia and the Baltic countries. The transition from Mesolithic hunter-gatherers to the domestication of animals and farming remains unclear (Martinsson-Wallin et al., 2011). Late Mesolithic stone axes have been found on Gotland, especially on the western side of the island (Martinsson-Wallin and Wallin, 2010). These stone axes have been interpreted as

Nichola Strandberg being linked to large scale forest clearance on Gotland, which is reflected in pollen diagrams done by Påhlsson (1977) from central Gotland the island (Österholm, 1989). During the Mesolithic and early Neolithic, Lina Mire would have been a lake or lagoon connected to the sea via narrow straits (Wallin, 2010). A settlement from the early Mesolithic at Svalings (RAÄ Gothem 202:1), was later submerged owing to the Littorina transgression (Seving, 1986). Flint fragments and Grey Seal bones found beneath gyttja are thought to be deposited during the Littorina Sea (Welinder, 1975). During the late Mesolithic and the Early Neolithic many axe settlements existed in the area (Wallin, 2010). Amongst these was an early Neolithic Funnel Beaker settlement at Ardags, Ekby (RAÄ Ekeby 47:1) a few kilometres west of Gothem (Österholm, 1989; Lund, 1996). The Neolithic 4000 – 1700 BC (5950 – 3650 cal years BP) The Early Neolithic 4000 – 3300 BC (5950 – 5250 cal years BP) By the Neolithic, the land surface of Gotland had increased. Isostatic uplift, which was greater in the north than the south would have, by this time, created land which would have been ideal for pasture and farming land (Martinsson-Wallin et al., 2011). About ten sites with funnel beaker pottery, from the Early Neolithic, have been found on Gotland. These were mainly situated on the western side of the island where it is thought that the soils were ideal for farming or pasture. Neolithic cultures, such as the megalith graves, were probably brought to the island by new groups which arrived during the Neolithic. Ceramics, with the imprints of wheat grains, have been found on Gotland which date from the Early Neolithic. The Funnel beaker culture has been found at Gräne (Martinsson-Wallin et al., 2011) so it is probable that wheat was being cultivated on the island at this time. Lina Mire has a rich archaeological history. A late Mesolithic to early Neolithic axe settlement (RAÄ Vallstena 156:1) has been found close to Lina Mire (Nihlén, 1927; Lithberg, 1914) (Fig. 2). Early Neolithic carbon residue from a cooking pit have been dated to 3575- 3535 BC (Martinsson-Wallin, 2014). According to Wallin (2010) Gothem, an area just a few kilometres to the east was highly resource productive during the Neolithic and Bronze Age. The Middle Neolithic 3300 – 2300BC (5250 – 4250 cal years BP) and the Late Neolithic 2300 to 1700 BC (4250 – 3650BP) During the middle Neolithic the salinity of the Littorina Sea increased and seal hunting and fishing resurged in popularity (Martinsson-Wallin and Wallin, 2010). A study of graves at Ajvide in Eksta Socken (Fig. 1), on the south west coast of Gotland, indicates that subsistence was mainly based on seal hunting and fishing during the late middle Neolithic. Some sheep, goat, cattle and pig remains from this time (Martinsson-Wallin et al., 2011) indicate there was also some dependence on terrestrially sourced food. However, no traces of crops have been found from this period (Palmgren and Martinsson-Wallin, 2015). An increase in archaeological remains during the middle Neolithic indicates that the islands population increased during this time (Palmgren and Martinsson-Wallin, 2015). A burial and a

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC settlement (RAÄ Gothem 120:1) from the Pitted Ware culture, of the middle Neolithic, was discovered at Västerbjers, Gothem (Sundberg, 2008) (Fig. 3). During the late Neolithic it is thought that people developed control over land resources and domesticated animals (Martinsson-Wallin et al., 2011). A late Neolithic death house, a building built upon graves, has also been discovered in the vicinity of Nygårdsrum (RAÄ Vallstena 73:1) (Hallström, 1971). The Bronze Age 1700 – 500 BC (3650 – 2450 cal years BP) During the Neolithic to Bronze Age transition, metal was introduced. Copper appears in graves during the late Neolithic (Martinsson-Wallin et al., 2011). Land use changed during the Bronze Age and both arable and pastoral agriculture was intensified. Later, during the pre-Roman Iron Age (5th to 4th century BC) fencing systems created private farming areas (Lindquist, 1974). One of the most notable archaeological features in the area is Gothemshammar (Fig. 2) which is located on a peninsula close to the entrance of the Lina Mire basin and east of the river Gothem (Wallin, 2010). There a 500 m wall of unknown age is located (RAÄ Gothem 131:4) (Fig. 3). Dating of the domestic materials found during excavations date the stone wall enclosure at a date of about 900 – 700 BC. It has been suggested that the wall ended at sea level which would indicate that sea level was 10m above the present day sea level. The wall, as well as the other archaeological sites, shows the importance of the Line Mire area for the inhabitants of Gotland and possible visiting traders.

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Figure 2. Archaeological sites around Lina Mire. A/ Majsterrojr (RAÄ Gothem 111:1). B and C/ Gothemshammar (RAÄ Gothem 131:4). D/ Tjelvar’s grave (RAÄ Boge 28:1). There is a large complex of stone arrangements and a cairn known as the “Majsterrojr” (RAÄ Gothem 111:1) (Fig. 2). This indicates early Bronze Age activity in the area 3 kilometres inland from the Gothemshammar. Bronze Age activities are further indicated by the amount of stone ships in the area, especially to the north of Lina Mire (Wallin, 2010). There is a stone ship a few hundred meters north of the “Majsterrojr” (RAÄ Gothem 134:1). There are around 380 stone ship settings on Gotland and they are usually located close to the shoreline (Wehlin, 2010). Approximately 70 of these have been excavated to some degree. It is thought that these stone ships date to about 1100 – 500 BC. These stones ships are thought to be graves (Wehlin, 2010). Stone ship settings can be found along the Ancylus Lake and Littorina Sea shorelines Hansson (1927). Tjelvar´s Grave (RAÄ Boge 28:1) is also a stone ship setting (see Fig. 2 and Fig. 3 for location). According to Wehlin (2010) around 15% of the stone ships on Gotland occur around Lina Mire. Ohlsson (1984) stated that there may have been a historical route which boats could have used leading inland in a north-east direction. The opening of this water way would have

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC begun at Vitviken (Fig. 3), a bay just north east of Lina Mire, and then led inland to where Lina Mire is today.

Figure 3. The Ancylus Lake and Littorina Sea shorelines were drawn after Svensson (1989). The contour lines and elevation were based on modern day values from SGU. Archaeological sites of importance around Lina Mire are shown; the archaeological data was downloaded from Riksantikvarieämbetet. Site Description Lina Mire (57.570°N 18.643°E) is one of the largest mires on Gotland at 8.5 km2 and located 21 kilometres south-east of Visby (Fig. 1). To the west of the mire is marl and further to the west till (Fig. 4). To the east of the mire, limestone bedrock is exposed. The whole of Gotland has surface bedrock which is Silurian (Hede, 1925a). The bedrock geology of the area is Halla Formation limestone (Laufeld, 1974). According to the previous investigations of Lina Mire (Svensson, 1989) there were approximately 4 meters of peat and gyttja, below which was a sand layer and at least 2.5 meters of clay. Lina Mire is downstream from Holm Mire; both of these mires drain into the north-east via the Gothem River. The Gothem River was straightened during the drainage of the mire in the 1940’s. Before the drainage of the mire, the mire surface was measured at 13.1 m a.s.l in the southern part of the mire (Generalstabs kartan) and 10.6 m a.s.l in the northern part. The elevation of the Lina Mire from 2009 or later is about 9 m a.s.l, (Fig. 4) meaning that the mire surface elevation has sunk about 1.6 m since the drainage of the mire during a period of six to seven decades. The maximum elevation of Gotland is around 89 m a.s.l at Lojsta Hed.

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Lina Mire is below the highest limit of the Littorina Sea which implies that the whole mire was submerged during the Littorina Sea phase (Lundqvist, 1928). The shorelines of the Littorina Sea and the Ancylus Lake, drawn after Svensson (1989), were based on beach ridges (Fig. 3).

Figure 4. Quaternary sediments and accumulations. The coring locations from 2016 are included and are shown in red. Coring location 7 was the master core, there were also 15 parallel cores taken from a 2x2m grid around the master core but these are not shown here. This map is based on data from Quaternary deposit maps downloaded from SGU (2017) and archaeological data downloaded from Riksantikvarieämbetet (2017). Methods Field Methods The field work was carried out between the 2nd and 5th of August 2016. Coring was carried out in three transects in order to investigate the stratigraphy of the mire. For this study a master core was required; this master core should be a representative example of the stratigraphy of the mire. This was interpreted as being the location with all stratigraphic units present and with the thickest accumulations of fen peat and gyttja. A Russian peat corer that was 1 m in length and had a diameter of 4.5 cm were used to retrieve the cores for the transects and the master core. All of the coring locations were retrieved from the fen peat surface, except one which was retrieved from the marl surface (Fig. 4). The modern day river and ditches are shown and the outlet of the mire is towards the north-east. The elevation in the area ranges between 60 m a.s.l in the north-west and 9 m a.s.l on the mire surface (Fig. 3). The mire has its outlet towards the north-east (Fig. 3).

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

Extra material was required in order to search for material to date. Thus, fifteen parallel cores were retrieved in a 2 x 2 m grid around the master core. A Russian peat corer which was 70 cm long and 7 cm in diameter was used to retrieve this extra material. The cores were wrapped, labelled and brought back to the cold room at the Department of Physical Geography at Stockholm University. The stratigraphy of the master core was investigated in the field and a more detailed description was made in the laboratory. The description was based on analysis of the material under a stereo microscope x25 magnification in petri dishes, using Munsell colour charts and based on loss on ignition. Laboratory Methods Dating of macrofossils, loss on ignition and XRF (X-ray fluorescence) were carried out in co- operation with Aleftin Barliaev. The XRF results are not presented in this study. Pollen analysis and preparation for C/N ratios were undertaken independently. The top 40 cm of the master core and the parallel cores was not subsampled for loss on ignition, pollen or radiocarbon dating as ploughing had mixed the top 40 cm of fen peat. The parallel cores were correlated to the stratigraphy of the master core.

Radiocarbon Dating The fifteen parallel cores were collected in August 2016 whereafter they were stored in a cold room. The subsampling for macrofossils to use for the radiocarbon dating began later in August 2016. In the laboratory the fourteen parallel cores were visually correlated by aligning accumulation boundaries and colour bands. Only fourteen of the extra cores were used as one of the cores was required for other analyses. Eleven depths were dated using AMS (Accelerator Mass Spectrometry) radiocarbon dating, in order to establish a chronology and to study possible changes in accumulation rate. Eight dates were based on terrestrial macrofossils. Finding terrestrial macrofossils to date was not possible in all parts of the stratigraphy. As not many macrofossils were found in the Littorina Sea gyttja, five bulk samples from this part of the stratigraphy were radiocarbon dated (Tab. 1). One bulk sample was dated at the same depth as a terrestrial macrofossil sample (201 cm depth), so that the reservoir age could be calculated and deducted from the other bulk samples.

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Table 1. Dating materials from fourteen correlated cores which were taken from a 2x2m grid surrounding the master core.

Depth Terrestrial Laboratory (cm) Macro- Stratigraphy Sample material number fossil 2 Carex seeds and 25 Cladium Ua-54489 41 X Fen peat mariscus 1 Betula and 7 Cladium Ua-54979 52 X Fen peat mariscus seeds Ua-54322 97 X Gyttja 2 Betula seeds Ua-54782 121 Gyttja Gyttja bulk sample Ua-54783 175 Gyttja Gyttja bulk sample Ua-54784 201 Gyttja Gyttja bulk sample Ua-54415 201 X Gyttja 4.5 Betula seeds Ua-54785 225 Gyttja Gyttja bulk sample Ua-54786 270 Gyttja Gyttja bulk sample Ua-55698 276 X Gyttja 3.5 Betula seeds Calcareous Ua-54319 309 X 9 Betula seeds gyttja Calcareous Ua-54320 325 X 13 Betula seeds gyttja Calcareous Ua-54321 339 X 15 Betula seeds gyttja

Over four weeks, 45 subsamples of 2 cm3 were taken at different levels of the parallel cores. All of the parallel cores were correlated with the master core and then subsampled. The subsamples from each depth were put in plastic beakers with 10% KOH and left overnight with the purpose of dissolving fulvic and humic acids (Mauquoy et al., 2010). The material from the beakers was then sieved through a sieve with a 250 μm mesh size, to remove small particles. The retrieved macrofossil material was thereafter stored in water for ease of handling. Portions of the material were put in a petri dish whereafter the macrofossils were analysed under a stereo microscope at x25 magnification. Identification of seeds was made using images in literature from Birks (2007). Soft tweezers were used to extract seeds which were later stored in distilled water in plastic containers. Initially it was deemed preferable to date terrestrial macrofossils rather than bulk sediments. Bulk sediment samples contain a reservoir age caused by the older carbon which exists in 14 marine water (Hedenström and Possnert, 2001). The oceans absorb atmospheric CO2 which 14 dissolves to H2 CO3. Slow circulation in the oceans means that ages appear older. This marine 14C is incorporated into marine macrofossils (Siegenthaler et al., 1980). However, bulk samples were used for carbon dating because of a scarcity of terrestrial macrofossils. Of the bulk samples which were subsampled from the gyttja, a 1 cm thick slice was taken from one of the cores. Only the soluble fraction of the bulk sediments was dated as this contains pure organic material. By the time sampling for bulk sediments began, much of the material was already used during subsampling for macrofossils. For this reason, cores from different holes were required for bulk sediment sampling. Correlation of the gyttja was

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC difficult as there were no stratigraphic boundaries for 228 cm of the cores length. The clearest way to correlate these cores was through dark sulphide laminations, but these were not always clearly visible. Since the extra cores for dating were retrieved in 70 cm long sections radiocarbon dates Ua- 54782 and Ua-54783 were from the same single core. Radiocarbon dates Ua-54784, which was used to calculate the reservoir age, and Ua-54785 were from another core. Radiocarbon date Ua-54786, was from another separate core. All of the bulk samples, which were assumed to be deposited in a brackish environment, had a reservoir age deducted from them before they were calibrated. The reservoir age was calculated based on a comparison between two dates at the same depth, Ua-54415 which was based on 4.5 Betula seeds and Ua-54784 from bulk sediment. The 4.5 Betula seeds were found in different cores from different holes. Since much of the material from the paralel cores was destroyed during subsampling the bulk date was also taken from a different core from a different hole. The difference between 14C age Ua-54784 and Ua-54415, 6018 ± 32 and 5567 ± 51 respectively was 451 years. The reservoir age was deducted from all of the bulk sediment 14C ages before calibration. Calibration and the age depth model were carried out in and Clam 2.2 and R Workspace using IntCal13. The reservoir age was subtracted from the bulk sediment 14C ages prior to calibration. Radiocarbon date Ua-54784 was then omitted from the age-depth model. The ages from the Blytt- Sernander climatic scheme were also calibrated in order to directly compare previous studies (for example Svensson, 1989) with the chronology in this study.

Organic Matter and Carbon Content Loss on ignition (LOI) was carried out as a measure of organic matter content which is a proxy for organic carbon (Heiri et al., 2001). LOI can provide information about the depositional environment such as for example the biological productivity of lakes (Lowe and Walker, 1997). LOI at 950˚C can be used to estimate carbonate content (Heiri et al., 2001). Subsamples of about 1 cm3 were cut from the cores and placed into crucibles and dried in an oven at 110˚C overnight. Dried samples were weighed into pre-weighed crucibles and burnt at 550˚C in a furnace for 4 hours. The samples were stored in a desiccator and then reweighed. The same samples were then burnt at 950˚C, left to cool in the desiccator and reweighed. Loss on ignition for 550˚C and 950˚C was calculated as a percentage. Since LOI values were very low at some depths in the clay (below 340 cm depth) a different measure for organic matter content was also used. For these samples carbon content was measured rather than organic matter. The samples were dried for 2h at 100˚C and then ground into a powder using a pestle and mortar. Dried samples were stored in desiccators to avoid the samples taking on moisture and between 150 mg and 200 mg of sample was weighed into porcelain boats. Samples were combusted in an Eltra CS-500 Carbon Sulfur determinator where pressurised oxygen passes through a combustion chamber. The names and weights of the samples were programmed into the display of the Eltra CS-500 Carbon Sulfur determinator. Each sample was combusted at 550˚C and 950˚C where a new sample was used for the second combustion at 950˚C. The CO2 generated was then measured by an infrared

Nichola Strandberg detector (Delteus and Kristiansson, 2000). Both the organic carbon and matter contents were measurement was recorded as percentage dry weight.

Carbon-to-Nitrogen Ratios The ratio of carbon-to-nitrogen is useful for indicating to source of organic matter (Rice and Hanson, 1984).Variations in the carbon-to-nitrogen ratio occur because algae are enriched in nitrogen and depleted in carbon compared with vascular plants (Tyson, 1995). C/N ratios of <8 typically indicate marine sediments (Bordovskiy, 1965). According to García-Alix et al., (2012) a C/N ratio of <10 indicates aquatic organic matter. A C/N ratio of 10–20 values indicates a mix of terrestrial and aquatic organic matter inputs and a C/N ratio of >20 signifies that terrestrial organic matter was predominant (Jones et al., 2013). Mackie et al., (2005) have said that C/N ratios are a reliable proxy for changes in salinity and therefore relative sea level in isolation basins. Forty subsamples spaced 7 cm apart at around 1 cm3 volumes were subsampled and placed into glass beakers. The subsamples were retrieved from the master core. No subsamples were taken from the fen peat as it is already known that this was a terrestrial deposit. No subsamples were analysed for the clay as it can be assumed this formed in deep water. However, the source of organic matter in the calcareous gyttja and gyttja was less obvious. The samples were then treated with 10% HCl and stirred in order to break up calcium carbonates. The samples were then dried overnight at 50ºC in an oven and were then ground into a powder in a pestle and mortar. A microbalance was used to weigh 100μgC-1mgC into LUDI SWISS φ9.0 mm height 10mm tin foil capsules and sealed with tweezers. The samples were stored in a plastic container with labelled separators. The C/N ratio measurement samples were sent to the Atmosphere and Ocean Research Institute, Tokyo University and processed there using a CHNS analyser. The error of the C/N ratio1 σ ranged between ±41 and ± 1.19.

Pollen and Charcoal Pollen and Charcoal Preparation Subsamples of approximately 4 g were taken from the core and weighed. Three to six tablets of Lycopodium were dissolved with 10% HCl and added to the samples (Lycopodium batch number 938934 and the average spore amount 10679). The Lycopodium spores were added in order to compare the amount of indigenous pollen and spores to Lycopodium and to calculate the amount of pollen per gram. The optimal ratio between the amount of added Lycopodium spores as indigenous pollen is 1:1 (Regal and Cushing, 1979). However, knowing how many Lycopodium spores to add to achieve a ratio is difficult. This was also complicated by the varying amounts of indigenous pollen in the stratigraphy, for example fewer pollen in peat than in gyttja. After the first batch of pollen samples was counted it became evident that three Lycopodium tablets were insufficient so more were added. The pollen was prepared according to Berglund and Ralkska- Jasiewiczowa (2003). Chemical treatments were performed under a fume hood. To break up calcium carbonates the samples were mixed with 10% HCl and heated in water a water bath at 100˚C. In order to remove the

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

HCl from the samples they were centrifuged at 4000 rpm for 5 minutes. The HCl was then decanted away and the samples were rinsed with distilled water once. The process of centrifuging a decanting before new chemicals were added was repeated after every step which followed during the pollen preparation. To remove fine organic fragments and humic acids the samples were treated with 10% NaOH for 5 minutes in a warm water bath at 100˚C. The samples were then rinsed with water, two to three times, until the water was clear. To remove minerals and to disperse the samples, 5%

Na4P2O7 was added. Thereafter the samples were heated for 15 minutes in a 100˚C water bath. After this the samples were rinsed with water once. The samples were then treated with 40% HF for 7-9 days. After the HF treatment the HF was poured off and 10% HCl was added. The samples were heated in a water bath for 2-5 minutes and rinsed once again with water. Three batches of twelve samples were prepared in total and 29 samples were counted. To further reduce non pollen organic material, acetolysis was done. To dehydrate the samples glacial acetic acid (CH3COOH) was added. The sample was then centrifuged and decanted.

Then the acetolysis solution, consisting of nine parts of acetic anhydride (CH3CO)2O and one part 95% H2SO4, was added and heated for 8-10min in a water bath at 100˚C. Further

CH3COOH was added to the samples, centrifuged and decanted. Then 10% NaOH was added. The samples were washed twice with distilled water. The obtained pollen samples were stored in 1:1 parts with distilled water and glycerine. The microscope slides were mounted with glycerine and the cover slips were sealed with nail varnish.

Identification of Pollen Grains A light microscope was then used to count samples; 400X magnification was used for scanning and 1000X for identification with immersion oil. Pollen types were identified using literature by Beug, (2004) and Moore et al., (1991). Pollen grains were identified to genus or species level. Pollen reference slides from Stockholm University were used to aid identification. A phase contrast microscope was used to aid identification and to discern surface texture. The target count for each depth was 300 grains. Owing to time restrictions this target was not met on all of the depths. A microscope was then used to count samples. Magnification 400X was used for identification of pollen grains, spores and charcoal. The magnification was increased to 1000X for the identification of problematic pollen grains in order to see the surface structure with more clarity. Pollen types were identified using Fægri and Iversen (1989), Beug, (2004) and Moore et al., (1991). Pollen grains were identified to genus or species level. Since there was a limited amount of pollen on each slide and time restrictions this target was not met on all of the depths. For example a slide from the peat from a depth of 50 cm only yielded 55 pollen grains despite 5 separate slides being counted. Charcoal particles were counted and identified in the pollen slides as opaque, black and angular fragments larger than 25 μm. The charcoal particles were counted across 11 evenly spaced transects on each slide (Wang et al., 1999).

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Diagram Construction, Calculations and Statistical Analysis Pollen diagrams were created in Tilia 2.0.41. CONISS, a cluster analysis technique which is included in Tilia, was used (Grimm, 1987). CONISS allows for different pollen assemblages which have similar pollen percentage data to be grouped together into zones. Only taxa with over 5% in abundance were included in the CONISS calculations. The CONISS output diagram was used to interpret the pollen data into different pollen assemblage zones; however, owing to the importance of some indicator taxa such as Hordeum-type and Plantago lanceolata zonation was also partly based on the occurrence of these taxa. The calculation of total pollen and charcoal concentration in each sample was calculated using the following equation: 푇푐 ( ) × 퐿푠 퐶푡 = ( 퐿푐 ) 푊푡푠

푇푐 Where Ct is the concentration of pollen or charcoal, is the ratio of taxa counts to 퐿푐 Lycopodium counts, Ls is the total number of Lycopodium grains added to the sample and

푊푡푠 is the sample weight. Results and Interpretations The Mire Stratigraphy Three transects were investigated across the mire and the vertical red lines represent the maximum depth which the corer reached (Fig. 5). The stratigraphy is generally similar all over the mire; the lowermost unit was a bluish clay. In one location in the southernmost transect a reddish clay was found to be underlying the blueish clay. A layer of sand overlays the clay, which indicates a high energy event. This probably means that some sediment in the stratigraphy is missing and could have been eroded during a higher energy event. Part of bluish clay was probably eroded, meaning there was a hiatus in the stratigraphic record. Above the sand there is a layer of calcareous gyttja which was up to 70 cm thick. Superimposed onto the calcareous gyttja was gyttja, which was generally the thickest sediment unit, around 2 m thick. Above the gyttja was a second layer of calcareous gyttja. This unit can also be interpreted as being formed in a freshwater lake. Here the term freshwater lake refers to a lake formed in the basin of Lina Mire, disconnected from the Baltic basin, rather than a lake freshwater stage of the Baltic basin such as the Ancylus Lake. It can be noted that the first occurrence of calcareous gyttja, i.e. the lower calcareous gyttja was usually thicker and more extensive than the upper calcareous gyttja (Fig. 5). Peat overlaid the upper calcareous gyttja, indicating that the freshwater lake infilled and became a bog. The uppermost part of the fen peat was later disturbed after the 1940’s by cultivation. Mixing of the soil by ploughing was evident in the field and these upper parts of the sediment sequence were not used for laboratory analysis. This means that the most recent period, from approximately 400 BC (2350 cal years BP) until present, could not be analysed.

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

Figure 5. Cross sections of Lina Mire based on transects with vertical red lines indicating the coring depth achieved.

A description of the master core (coring location 7) and some interpretations based on the stratigraphy is provided (Tab. 2). Coring location 7 was selected as the master core, as it was deemed to be representative of the mire stratigraphy, and close to the access road through the

Nichola Strandberg mire. The parallel cores which were retrieved for extra material for dating were correlated to the master core stratigraphy in table 2. Some images of the cores retrieved at coring location 7 can be seen below (Fig. 6). Images B and C show how the cores were correlated using stratigraphic boundaries and dark sulphide colourings.

Table 2. Description and interpretation of the stratigraphy within the master core (coring location 7). Depths Accumulation type Munsell colour chart code Interpretation (cm) 40-57 Fen Peat 25Y 2/0 Fen mire 57-79 Calcareous gyttja Laminated 6/2 with laminations of 3/2 Freshwater lake 79-307 Gyttja 3/2 with some darker bands of Littorina Sea 307- Calcareous gyttja Variations between 7/2 and 5/2 Freshwater lake 339 339- Relatively high Fine sand 5GY 4/1 348 energy event 348- 56/ 5/1 1a with sulphide precipitations Clay Ancylus Lake 352 380 352- Relatively high Coarse sand 5GY 4/1 354 energy event 354- 56/ 5/1 1a with sulphide laminations Clay Ancylus Lake 400 380

Figure 6. Images of core segments retrieved from Lina Mire in 2016. A/ Upper part of the stratigraphy, with fen peat and the upper calcareous gyttja. / B/ Gyttja with coloured bands which were used for correlation of the parallel core segments. C/ Lower part of the stratigraphy with the lower calcareous gyttja and bluish clay.

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

Chronology All the AMS radiocarbon dates are shown in the appendix. Carbon-14 dates, in calibrated years before present (1950) and AD/ BC ages, are provided. The dates reported in this study which are based on interpolations have been rounded up or down to the nearest 10. Prior to calibration the bulk sediment radiocarbon dates had a reservoir age of 451 years subtracted from them. All radiocarbon dates have been calibrated using Clam 2.2 with R version 3.2.2. A basic linear regression between neighbouring levels and the IntCal13.14C curve for the northern hemisphere terrestrial dates were used (Reimer et al., 2013). Dates are reported with 95% probability. The radiocarbon dates had errors of ±28-60 years. The transparent orange boxes in the age-depth model indicate dates from bulk sediments which have been corrected with a reservoir age of 451 years (Fig. 7). The calibrated AMS dates were between 400 BC (2350 cal years BP) for the youngest sediments and 7030 BC (8980 cal years BP) for the oldest. Sample number Ua54786 which was based on a bulk sample has been excluded from this model as an outlier as it appeared to be too young. Radiocarbon date Ua-54320 appeared to be older than the date below it in the stratigraphy therefore radiocarbon date Ua-54320 was removed as an outlier as it appeared to be older than the date (Ua-54321) above it in the stratigraphy.

Nichola Strandberg

Figure 7. Age-depth model Clam 2.2 and R Workspace IntCal 13.14C atmospheric curve for the Northern hemisphere (Reimer et al., 2013). The red points indicate outliers and the orange boxes indicate bulk dates which have had the reservoir age subtracted to them prior to calibration.

Organic Matter and Carbon Content Loss on ignition at 550˚C and 950˚C is shown for the master core (Fig. 8). The clay and sand, which was measured using the Carbon and Sulphur determinator, had relatively low loss on ignition (0.15% and 1.42% at 550˚c and 950˚C respectively) indicating low organic carbon content. The calcareous gyttja, which was burned in an oven along with the other samples, from 307 to 338 cm had relatively low organic matter (LOI of 6.8% at 550˚C) and relatively high calcium carbonate content (LOI of 28.29% at 950˚C) probably due to the occurrence of shells and perhaps owing to some recycled material from the limestone bedrock. The gyttja from 307 to 79 had stable LOI values however the organic matter content is lowest in the

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC lower parts and increases upwards until around 270 cm depth, were values become more stable. The average LOI for the gyttja was 26.58% at 550˚C and 3.46% at 950˚C. The upper calcareous gyttja between 79 and 57 cm had a LOI of 21.38% at 550˚C and 30.95% at 950˚C. The organic matter content of the upper calcareous gyttja was higher than for the lower calcareous gyttja. The organic matter content of the peat was relatively high (LOI of 84.32%) and the calcium carbonate content was relatively low (LOI of 2.33%).

Figure 8. Loss on ignition at 550˚C and 950˚C. Note that organic carbon and carbonate measurements from samples below 340 cm were calculated based on carbon and sulphur determination rather than oven burning. C/N ratios, pollen and charcoal particle concentrations for the wet weight and accumulation rates. The red dashed lines indicate the main stratigraphic boundaries, interpolated ages for the stratigraphic boundaries have been included.

Carbon-to-Nitrogen Ratios The C/N ratio was relatively high for the lower calcareous gyttja (C/N ratio between 17-11) indicating mixed sources of organic matter. The C/N ratio was highest for the lower calcareous gyttja prior to the first isolation of the basin. The ratio started to shift towards lower values (C/N ratio of 9) after the transition to gyttja, thought to be formed during the Littorina Sea. This indicated that there was more aquatic organic material; however, the ratio did not fall below 8, which would indicate predominance of marine organic matter. After the initial shift to lower C/N ratios in the gyttja the ratio shifted to a higher value of 12 and then again to a lower value of 9 a total of three times. These three shifts to lower values at 208, 173 and 117 cm depth in the stratigraphy may indicate increases in aquatic influence. The C/N ratio increased again to 25 with the boundary of the gyttja and upper calcareous gyttja deposits but then decreased again to 11 indicating a shift from terrigenous organic matter in the lake to a mixed source of organic matter. Pollen and Charcoal Particle Concentrations and Accumulation Rates Concentrations of pollen and charcoal particles per gram were calculated (Fig. 8). The peat had the lowest pollen concentrations (average 100 000 pollen/g) whereas the gyttja had the

Nichola Strandberg highest concentration of pollen (500 000 pollen/ g). Charcoal concentrations are similar in pattern to pollen concentration except for a peak at around 190 cm depth. Sediment and peat accumulation rates are shown on the right hand side of the diagram in cm/yr. These accumulation rates are based on interpolated dates from the age-depth model. Accumulation rates were highest in the peat and gyttja. The upper calcareous gyttja seems to have had relatively low accumulation rates. Pollen A pollen percentage diagram for Lina Mire is shown (Fig. 9). All cf. species or taxa, meaning those which could not be identified with certainty or any pollen with very low abundance (less than 1%), were excluded from the diagram. Varia means those pollen grains which could not be identified.

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

Figure 9. Pollen percentage diagram for Lina Mire.

Nichola Strandberg

Pollen Zone One Pollen zone one is between 330 cm and 260 cm depth, which corresponded to calcareous gyttja and Littorina Sea gyttja in the stratigraphy. According to the age-depth model the age of this zone spans a time period of about 1410 years between about 6900 and 5490BC (8850 – 7440 cal years BP) during the Mesolithic period. Arboreal taxa specifically Corylus, Pinus and Betula were predominant. Corylus peaked at 290 cm at 28.1% of the pollen sum and Betula peaked at 310 cm at 22.4% of the pollen sum. This was at the expense of Pinus which fell from 45% of the pollen sum at the onset of zone one to 28% by the middle. By the end of zone one Pinus seems to have recovered. There were low amounts of QM (Quercetum mixtum, Quercus, Tilia and Ulmus) taxa and some Equisetum. At 270 cm depth Polypodiaceae pollen first appeared in the pollen record at 7.9% of the pollen sum. There was very little charcoal and therefore no indication of increased burning. No Pediastrum were found despite the calcareous gyttja indicating a freshwater lake environment. Pollen Zone Two Pollen zone two is between 260 cm and 190 cm and corresponds to gyttja in the stratigraphy, with ages spanning around 1230 years between about 5490-4260 (7440-6210 cal years BP) also during the Mesolithic period. The main difference between zones one and two was that during zone two there were more occurrences of herbs and QM taxa. However, Pinus, Corylus and Betula were still the most dominant taxa. Poaceae, which were smaller than 40 μm and therefore deemed not to be from cultivated grass, reached 2.2% of the total pollen sum. Ericaceae, Cyperaceae, Artemisia, Chenopodiaceae, Ranunculaceae and Rumex appeared more frequently in the pollen diagram. Nuphar, a freshwater plant taxon, appeared in zone two which was somewhat conflicting with the stratigraphy which indicated a brackish water environment. The general trend was that tree pollen decreased in favour of shrub, dwarf shrub and herb taxa. There were charcoal fragments throughout zone two. Pollen Zone Three Pollen zone three is between 190 and 97 cm and coincides with the upper part of the gyttja. This pollen zone covers a time span of about 1530 years between 4260 and 2730 BC (6210 – 4680 cal years BP) during the latter part of the Mesolithic, the Early Neolithic and part of the Middle Neolithic. The upper boundary of zone three, according to CONISS, should have been around 86 cm which is perhaps somewhat linked to the change in stratigraphy at 79 cm. However, owing to the importance of indicator species such as Hordeum-type and Plantago lanceolata which were present at the onset of zone four the upper boundary was placed at 97 cm. Pinus, Betula, Corylus and Alnus were the most dominant taxa in this zone. Picea was first seen in the pollen record at 180 cm depth but only one grain was observed. A second Picea grain was observed at 110 cm depth. Poaceae was low during the first part of zone three but then increased at around 115 cm depth. Herbs such as Cyperaceae, Artemisia and Rumex were all fairly consistent throughout zone three, whereas Chenopodiaceae was more sporadic. Equisetum spores also appeared relatively consistent throughout zone three whereas

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

Polypodiaceae increased towards the end of zone three. Charcoal fragments were fairly constant throughout zone three. Pollen Zone Four Pollen zone four differed the most from the others. Zone four was between the depths of 97 and 40 cm, which includes some of the gyttja, the upper calcareous gyttja and the fen peat. The time interval of zone four was about 2330 years between 2730 and 400 BC (4680 – 2350 cal years BP). This spanned part of the Middle Neolithic, the Late Neolithic, the Bronze Age and the beginning of the Iron Age. Pinus, Corylus, Betula and Poaceae were the most abundant taxa in the pollen record. The onset of zone four was defined by the onset of the human impact indicator taxa Hordeum-type and Plantago lanceolata (Fig.10). Herbs, namely Poaceae and Cyperaceae began to increase in abundance at 75 cm and 45 cm respectively. Two pollen grains from the Poaceae family, which were larger than 40 μm in diameter, and not identified as Hordeum-type, were seen in zone four. These grains were identified as being Cerealia-type (Fig. 10), since it was not possible to identify them to a lower taxonomic level. During zone four, pollen from other herbs such as Saxifraga-type and Apiaceae appeared in the pollen record. Towards the top of zone four, the number of Polypodiaceae and Equisetum spores increased. Charcoal fragment observations remained relatively consistent within zone four. Observations of Pediastrum coincided with the upper calcareous gyttja in stratigraphy which was indicative of a freshwater environment.

Figure 10. Pollen grains under 1000X magnification. A/ Cerealia-type seen through phase contrast microscope. B/ c.f Hordeum-type. C/ Chenopodium. D/ Plantago lanceolata.

Nichola Strandberg

Discussion Chronology The age depth model followed a linear trend with most samples becoming younger in an upwards vertical direction within the stratigraphy. However, sample Ua-54786 did not fit this trend. The dating for this sample was based on bulk sediments. This date when corrected for the reservoir age affect and once calibrated appeared to be about 1000 years younger than expected. This could be due to bioturbation or reworking of the sediment. Downward penetration of roots can also be a source of contamination (Kaland et al., 1984) but since only the soluble fraction of the bulk sample was dated this should have been avoided. Younger humic acids which may percolate downwards may also contaminate bulk sediments (Björck and Wohlfarth, 2001). Another reason for the younger than expected date could be caused by poor correlation between cores. As previously stated, cores from different holes within the 2x2 m grid around the master core were needed in order to subsample for bulk sediments. The gyttja was difficult to correlate due to a lack of clear stratigraphic boundaries. However, the correlation of the gyttja, with an average accumulation rate of about 0.06 cm per year would have needed to be around 60 cm out which is unlikely. Bulk sediment dating of the calcareous gyttja was avoided as fragments of limestone would have resulted in an infinite age. Limestone can also be taken up by molluscs and foraminifera and could significantly increase 14C ages, this is known as the hard water effect (Grimm et al., 2009). Once calibrated and plotted with a 95% confidence interval, radiocarbon date Ua-54320 appeared to be older than the date Ua-54321, which was immediately below it in the stratigraphy (Fig. 7). Both dates Ua-54320 and Ua-54321 were derived from Betula seeds within the lower calcareous gyttja. Perhaps reworking of the sediment or re-deposition was the reason for sample Ua-54320 appearing to be older than sample Ua-54321. It was unclear which date should be omitted from the age depth model. However, date Ua-54320 was omitted from the age-depth model since the Betula seeds may well have been remobilized and redeposited. At the time of deposition of the Betula seeds used for radiocarbon date Ua- 54320, Lina Mire was a lake and older material may well have been redeposited by water flowing into the lake from streams, overland flow or erosion of the banks. Given to the fact that the calcareous gyttja was dense and full of shell fragments it is perhaps unlikely that Betula seeds could have penetrated downwards. The macrofossils for dating were originally removed from fourteen different parallel cores; these cores were spaced closely together within just a 2 x 2 m grid. However, due to the uneven bathymetry of the basin, the small discrepancy in dates could be due to poor correlation between lower calcareous gyttja in the parallel cores despite correlation of the lower calcareous gyttja was relatively strait forward. Another issue with the chronology was that bulk sediment radiocarbon date Ua-54784, which was used to calculate the reservoir age for the Littorina Sea at 201 cm depth, was subsampled from a different parallel core to the parallel cores in which the Betula seeds were retrieved at 201 cm. It would have improved accuracy to retrieve the terrestrial macrofossils from the same core as the bulk sediment was subsampled in order for a more direct comparison of

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC dates. However, terrestrial macrofossils were scarce; in many cases, subsampling from fourteen parallel cores resulted in no terrestrial macrofossils being found. In order to construct an age-depth model, the radiocarbon dates based on bulk sediment samples had a reservoir age subtracted from them prior to calibration. Since the Baltic shelf is highly influenced by freshwater river runoff the reservoir age can be discussed as an offset from IntCal09 (Lougheed et al., 2013) which is a terrestrial calibration curve for the Northern hemisphere. The reservoir age is affected by both marine water containing older carbon and river runoff containing relatively younger atmospheric 14C and terrestrial carbon giving “true” ages of when the organics grew on land and stopped growing. Both shelves and coastal locations are affected by these factors. The present day reservoir age of bulk sediments from the Baltic Sea has been calculated from dating macrophytes and mollusc shells with known ages, this reservoir age is 300-400 years (Olsson, 1996). However, reservoir ages of 650–850 years for surface sediments in the Baltic Sea have been determined by Erlenkeuser et al., (1973). These examples show that even calculating reservoir ages for the present Baltic Sea is not straightforward. According to Lougheed et al., (2012), who have carried out a study in the Gotland Basin, the reservoir age associated with Baltic sediments has decreased throughout the Holocene. This could be due to the shallowing of the Baltic basin and reduction in marine 14C. A collection, from a museum, of pre-bomb mollusc shells was used to calculate reservoir ages for the Baltic including coastal Gotland (Lougheed et al., 2013). A reservoir age of 866 years from a location 16 km north of Lina Mire was calculated(Lougheed et al., 2013). In a shore displacement study at Lake Lilla Harsjön, Eastern Sweden, Hedenström and Possnert (2001) determined reservoir ages varied over time. They calculated that bulk sediments from the coastal Littorina Sea had reservoir ages of 1100-700 years. The reservoir age decreased with time and was about 400 years after the isolation of the lake and close to 0 years in the freshwater sediments. This study of Lina Mire estimates the reservoir age of the Littorina Sea to around 451 years, which is significantly less than what Hedenström and Possnert, (2001) and Lougheed et al., (2013) calculated. However, the reservoir age for Lina Mire is only based on the comparison between four and a half Betula seeds and one bulk sediment sample at one level in the stratigraphy. Terrestrial macrofossils were scarce in the Littorina sea gyttja, ideally more terrestrial macrofossils would have been found so that bulk sampling was not required and the uncertainty of reservoir effect could have been avoided. The difficulty with reservoir ages calculated for the Littorina Sea at Lina Mire is that little is known about the proximity to the shoreline or of freshwater inputs from rivers at this time during the Littorina Sea. There has only been a limited amount of research into the coastal reservoir ages and the modification of these ages by freshwater runoff (for example Cage et al., 2006). Many studies have had to use regional estimates for reservoir age based on the open ocean which is far from ideal (Lougheed et al., 2013).

Nichola Strandberg

Quaternary Geology and Mire Stratigraphy Much of the natural history of the area of Lina Mire can be learned from the Quaternary accumulations map of the area surrounding Lina Mire (Fig. 4). The calcareous gyttja at the surface directly to the west of the mire was probably formed when Lina Mire was a freshwater lake. The calcareous gyttja at the surface shows the extent of the old lake which would have been formed during the earliest freshwater lake phase. When the transects (Fig. 5) are compared to the surface geology (Fig. 4) it appears that the first freshwater lake covered a larger surface area than the second lake. Till further to the west of Lina Mire was probably deposited during the last deglaciation as no Quaternary depositions older than that have been found on Gotland (Svensson, 1989). It is likely that the wave washed sediment and postglacial sand were reworked when the Lina Mire basin was a bay or lagoon. Svantesson (1976) has investigated the tills of northern Gotland which are calcium carbonate and clay rich but boulder poor and the distribution and depth of the till is uneven. The till is usually covered by younger deposits. Eriksson (1992) commented that most glacial deposits on Gotland have been reworked by wave action because the whole of Gotland has been submerged during the earlier Baltic Sea stages. The stratigraphy of the mire is complex and there was probably a hiatus in the record. Since the mire was once joined with the Baltic, the mire stratigraphy can be compared with other Quaternary deposits usually found in the Baltic basin. Different sediment types of the Baltic basin can usually be identified by the stratigraphic properties and by the diatom species they contain (Ignatius et al., 1981). The stratigraphic order of units in the Baltic basin are rather regular from the south of the Baltic Sea to the northern Gulf of Bothnia (Ignatius et al., 1981). The bluish clay, seen in the master core stratigraphy at 354-400 cm, was interpreted as clay from the Ancylus Lake. The Ancylus Lake shoreline, drawn after Svensson (1989) was based on beach ridges; these approximately follow the 30m contour line (Fig. 3). Lina Mire was, during the Ancylus Lake phase, below the highest shoreline. Ancylus clay is homogeneous, which indicates that the ice retreat was distant. It was not possible to radiocarbon date the clay as there were no macrofossils and very little organic carbon. According to Svensson (1989) Ancylus Lake deposits began to be deposited at Lina Mire at around 9500 cal years BP. Ignatius et al., (1981) stated that older Ancylus clay sediments tend to be sulphide rich whereas the younger Ancylus deposits tend to be homogenous grey or even bluish and can sometimes be faintly laminated. The reddish clay seen during the coring at site 14 on the most southerly transect was probably from the Yoldia Sea or Baltic Ice Lake. The Baltic Ice Lake formed as a proglacial lake after the retreat of the Fennoscandian Ice Sheet and was drained at about 11,600 cal years BP. The Yoldia Sea was formed after the drainage of the Baltic Ice Lake and lasted for about 900 years (Björck, 2008). Yoldia Sea clays can have a reddish tint but both Yoldia Sea clays and Baltic Ice Lake clays can be varved (Winterhalter, 1992). Without dating of the reddish clay it is impossible to say with any certainty when it was deposited.

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

According to Jerbo (1961) the boundary between the Ancylus Lake and the Littorina Sea deposits in the Baltic basin is usually sharp. However, at Lina Mire there were additional stratigraphical units inbetween the Ancylus clay and Littorina gyttja. There was coarse sand immediately above the Ancylus clay, then a thin layer of clay, and then fine sand. The sand layers represent high energy periods in the record. The sand could have been deposited by wave action. The sand in the upper part was finer; this indicates transgressive succession as finer grains are deposited in deeper water. However, it is known that the Ancylus Lake was generally in a regressive phase at this time. The sand layers could also have been deposited by longshore drift or storm events were sand from the till was reworked and sorted by wave action. It is possible that around the time the sand was deposited there was some erosion in the area. However, there are no dates from the clay or sand so it is impossible to tell if there is a hiatus in the record or how long the hiatus may represent. The Ancylus Lake regression was caused by a drop in eustatic level which occurred about 10,200 cal years BP (Björck, 2008). According to Svensson (1989) the Ancylus regression was rapid in the beginning (5-10 m) followed by a slow regression. It is thought that the Ancylus Lake found a new outlet between the islands of Zealand and Funen (Björck, 2008). At 307-339 cm depth there was calcareous gyttja in the master core stratigraphy. The C/N ratio indicated that the source of the organic matter was mixed. The C/N ratio was about 11; according to Jones et al., (2013) a C/N ratio between 10 and 20 indicates a mixed source between terrestrial and aquatic matter. The lower calcareous gyttja unit was dated with three radiocarbon dates, one of which has been omitted from the age-depth model. The lower calcareous gyttja formed relatively quickly during about 480 years and between about 7030 – 6550 BC (8980 – 8500 cal years BP). This was the first isolation of the basin to form a freshwater lake and it is indicated by an increase in organic carbon and calcium carbonates (Fig. 8). The C/N ratio indicated that organic matter originated from both aquatic and terrigenous sources. The lower calcareous gyttja was generally thicker and more widespread than the upper calcareous gyttja (Fig. 5). The isolation of the lake was probably not caused by gradual isostatic uplift but rather by a forced regression in sea level caused by a drop in eustatic sea level. Svensson (1989) said that the first isolation of the Lina Mire basin, after the Ancylus Lake stage, occurred around 6650 BC (8600 cal years BP), which is about 380 years later than seen in this study (which indicates the first isolation at around 7030 BC (8980 cal years BP). Since the present study has better dating control the older date of isolation, as presented in this study, is probably the more accurate date. The freshwater lake phase persisted until the Littorina transgression. According to (Björck, 2008) the onset of the Littorina Sea began around 6550 BC (8500 cal years BP). The Littorina Sea shoreline was drawn after Svensson (1989); some sections of this shoreline follow the 20 m contour line. The 20m contour line gives an approximation of how the bay may have looked during the Littorina Sea stage (Fig. 3). Lina Mire was below this shoreline and was probably a relatively sheltered bay throughout the Mesolithic and subsequent periods. This understanding of the environment is fundamental to understanding the pollen record and the depositional environment. The transport of pollen grains from the

Nichola Strandberg open sea would be very different from that of an enclosed bay. As previously stated, archaeological finds at Svalings (RAÄ Gothem 202:1) were covered with Littorina Sea deposits. This indicates that the Littorina Sea level reached beyond the present day 10 m a.s.l. contour level (Fig. 3). The contours are based on modern day elevation above sea level (Fig. 3). The elevation and accumulation thicknesses have changed over thousands of years. However, the countour lines give some indication of the extent of the Littorina Sea bay at Lina Mire. The first Littorina Sea sediments in the master core stratigraphy appear at 307 cm depth corresponding to an age of about 6550 BC (8500 cal years BP). Littorina gyttja is typically soft and greenish in colour and has a high organic matter content of about 10-15% (Ignatius et al., 1981). However, the organic matter content of the Littorina deposits in the present study is 26.58%, and therefore higher than expected. This higher than expected organic matter content is perhaps due to the proximity of the site to the coast and increased input of allochthonous from the land. According to Björck (2008), the onset of the Littorina Sea is usually seen as an increase in organic matter content in the sediment composition. Saline water entered the freshwater Ancylus Lake and the rapid increase in salinity caused flocculation and an increase in deposition of minerals which were suspended in the water (Winterhalter, 1992). The decrease in suspended mineral particles allowed light to penetrate further into the water and organic productivity increased due to the increase of the photic layer (Winterhalter, 1992). The onset of the Littorina transgression at Lina Mire is reflected in the organic matter content measurements as a slight increase in organic carbon. The organic matter content then decreased slightly after the initial peak and stayed relatively constant throughout the Littorina Sea phase. Variations in the C/N ratio prior to the transgression showed a shift towards terrigenous organic matter prior to the Littorina transgression. This was followed by a shift towards a lower C/N ratio which is due to there being more aquatic organic matter than terrestrial as the lake was joined to the Littorina Sea. The Littorina Sea phase persisted for about 4680 years at Lina Mire from 6550 BC (8500 cal years BP) until about 1870 BC (3820 cal years BP). The Littorina sediments end at 79 cm in the master core stratigraphy where gyttja was succeeded by calcareous gyttja. At this point the lake became isolated for a second time. Comparisons between different areas around the Baltic basin are not straightforward as uplift rates varied. From this study alone it is impossible to tell if there was one main transgression which began at about 6550 BC (8500 cal years BP) or if there were further transgressions following this initial transgression. However, the three shifts to lower C/N ratios could be caused by increases in aquatic organic matter related to a transgression. The resolution of the C/N ratios (7 cm) was not high enough to see variations in detail. Rather, only general shifts in the C/N ratio are observed. This study finds three shifts towards more terrestrial organic matter followed by shifts back to aquatic organic matter during the Littorina Sea after the initial transgression. C/N ratios may vary for other reasons than an increase in aquatic or marine organic matter. A comparison between diatoms and C/N ratios in isolation basins in Scotland by Mackie, et al., (2005) discussed how amounts of phytoplankton in marine sediments may vary. The variations in phytoplankton would in turn affect the C/N ratio.

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

Freshwater and marine phytoplankton show similar ratios of carbon-to-nitrogen so it is therefore not possible to tell if water was marine or freshwater purely from C/N ratios. According to Sampei and Matsumoto (2001) C/N ratios should not be used as an indicator for source material when the organic matter content is low (less than 1%), as inorganic nitrogen can lower the C/N ratio. However, the organic matter content of the measured samples was typically around 20%. The three shifts towards terrestrial carbon, which were followed by shifts back to more aquatic organic matter, during the Littorina Sea phase, could be caused by terrestrial organic matter entering the bay due to deforestation from human activities. Another reason for the increases in terrigenous organic carbon may have been that the bay almost became isolated due to isostatic uplift. As a semi enclosed bay terrigenous inputs of organic matter may have been more influential then aquatic sources. The shifts back to predominance of aquatic organic matter may have occurred when the bay was flooded by brackish water again. These three shifts towards aquatic organic matter during the Littorina Sea phase at Lina Mire occurred at about 4560 BC (6510 cal years BP), 4040 BC (5990 cal years BP) and 3220 BC (5170 cal years BP). According to Björck (2008) there was a steady transgression of the Littorina Sea until about 6000 cal years BP although some minor transgressions possibly occurred up to 5000 cal years BP. This steady transgression was caused by gradual melting of the North American Ice Sheet. According to Saarse et al., (2009c) the transgressive trend of the Littorina Sea at Saaremaa, Estonia began around 8300–8200 cal years BP and persisted until 7300 cal years BP. This study finds a general shift from aquatic organic matter at Lina Mire until around 3220 BC (5170 cal years BP) although there were variations in the C/N ratio. After that point there was a shift towards terrestrial organic matter. In order for more concrete conclusions to be drawn about the Littorina Sea transgressions a shore displacement study would be required. The second isolation of the basin was not well dated as terrestrial macrofossils were scarce. The scarcity of terrestrial macrofossils was interesting in itself, as terrestrial macrofossils were very abundant in the lower calcareous gyttja. This is perhaps an indication that the environment was more open this time which fewer trees, such as Betula, close to the lake. The C/N ratios indicate terrestrial organic matter during the isolation of the basin (C/N ratio of 25) and then a mixed source of organic matter. This indicates that the lake may have experienced high inputs of terrestrial organic matter during the isolation or that basin may have dried out allowing plants to grow on the surface. However, there was no evidence of the lake drying out in the stratigraphy and organic matter content actually declined around the time of the isolation. Perhaps one explanation for the relatively high C/N ratios during the second isolation was deforestation in the catchment. Deforestation may have led to an increase in allochthonous material entering the basin. Units above and below the upper calcareous gyttja were dated (Fig. 7). It can be said that this freshwater lake phase occurred between 79 and 57 cm depth in the master core stratigraphy, and lasted around 1050 years from 1870 to 820 BC (3820 – 2770 cal years BP). This freshwater lake phase persisted for more than twice as long as the first freshwater lake phase at Lina Mire. Lakes are dynamic and the size and shape of the lakes would have changed over

Nichola Strandberg time due to water level change and uplift. However, from the stratigraphy of the mire it can be assumed that the first freshwater lake in the Lina Mire basin was larger and deeper than the second lake stage despite existing for a shorter period of time (Fig. 5). The Quaternary deposits map (Fig. 4) also showed the extent of one of the previous lake phases, which was probably from the first lake phase. However, it is known that the mire has dried out and the surface elevation of the mire has decreased by about 1.6 m since it was drained in the 1940’s. It could be that the upper part of the mire has dried out more than the lower parts. It is therefore difficult to make comparisons between the two freshwater lake phases directly from transects of the mire. It is likely that isostatic uplift rather than a regression caused the second isolation of the basin. It is thought that the transgressive trend of the Littorina Sea ended around 6000 cal years BP and the eustatic sea level stopped rising (Björck, 2008). Land uplift created new land which humans could use. As previously discussed, there are numerous archaeological sites around Lina Mire which illustrate how important the area has been historically (Fig. 3). The isolation of the lake from the Littorina Sea may have put an end to the use of the inland water system as a sailing route. The apparent shift in C/N towards aquatic organic matter during the second lake phase could actually be a reflection of conditions in the lake becoming more eutrophic with increased abundances of phytoplankton. The lake began to infill and became a mire about 820 BC (2770 cal years BP). Fen peat probably accumulated from when the lake began to overgrow to until the mire was drained in the 1940’s and the water table was lowered. According to a comparison between modern elevation data and the levelled surface elevation of the mire before the drainage (Generalstabs kartan) the surface elevation of Lina Mire has reduced by about 1.6 m between the 1940’s and 2009 or after (Lantmäteriet, 2016). This reduction in elevation was caused by lowering of the water table, which in turn oxidised the fen peat. Compaction from agricultural vehicles has probably contributed to the reduced elevation of the mire. The accumulation rates for fen peat and gyttja at Lina Mire have been calculated (Fig. 8) as around 0.06 cm per year. However, these accumulation rates are probably inaccurate due to the 1.6m elevation reduction previously discussed. The fen peat probably accumulated at higher rates than shown in this study. Pollen The local pollen assemblage zones and Baltic Sea stages are compared with climate variations for the Holocene for the Baltic region by Borzenkova, et al. (2015), the Blytt- Sernander climatic scheme and Archaeological divisions after Stenberger (1979) (Fig. 11).

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

Figure 11. A summary of the Baltic Sea stages seen at Lina Mire, including the local pollen assemblage zones, the Blytt- Sernander Climatic Scheme with calibrated dates, a summary of Holocene climate shifts after Borzenkova et al., (2015) and archaeological divisions after Stenberger (1979).

Nichola Strandberg

Pollen Zone One Pollen zone one and two were within the Mesolithic timescale on Gotland. This was also during the, Boreal and all of the Atlantic climatic periods (Fig. 11). According to research by Borzenkova et al., (2015), this was a period of relatively cool climate around the Baltic region. From archaeological finds it is evident that there were people living close to Lina Mire while it was a bay connected to the Littorina Sea. The archaeological finds at Svalings (RAÄ Gothem 202:1) which were submerged during the Littorina transgression are an example of this. Pollen concentrations were generally low, perhaps owing to there being sparse vegetation or poor preservation. Charcoal concentrations were also low. Mesolithic people on Gotland were hunter-gatherers and probably had a limited impact on vegetation except for gathering wood. Pinus pollen was predominant throughout most of the pollen record for Lina Mire and the same can be said for zone one. However, there were variations in the Pinus pollen percentage. The decline in Pinus pollen during zone one coincided with the Littorina transgression. According to Österholm (1989) much of the Pinus that grew along the coastlines was buried by the earlier Ancylus transgression. The same mechanism could be the cause of the Pinus decline during the Littorina transgression. Alnus reacted in a similar way as Pinus decreased around the time of the Littorina transgression. Corylus increased where Pinus and Alnus decreased. However, Pinus pollen can be transported long distances and may not purely reflect local changes in vegetation (Birks et al., 1988). The predominance of Pinus at Lina Mire substantiate the research carried out by Sernander (1894), Pettersson (1958) and Påhlsson (1977) who postulated that there were mainly Pinus forests on Gotland during the Boreal period. Towards the end of pollen zone one Salix appeared in the pollen record. There was no clear evidence of human impacts in zone one. According to Pettersson (1958) Ulmus and Corylus immigrated to Gotland during the Boreal. Ulmus and Corylus were present throughout the whole pollen record in this study, perhaps because the earliest analysed samples were from the late Boreal. According to Påhlsson (1977), by the late Boreal stable forests began to occur on Gotland. Påhlsson (1977), who analysed pollen from Lojsta, central Gotland, described that towards the end of the Boreal period Betula expanded as Pinus decreased which can be attributed to wetter climate conditions which occurred just prior to the Atlantic phase. This study finds a similar trend. However there were relatively low pollen count of the sample from 270 cm depth (70 pollen grains) providing an unrepresentative picture of the pollen assemblage. Another cause of the perceived decrease in Pinus pollen during zone one could be suppression by Corylus pollen which peaks at the same depth in the stratigraphy. According to Österholm, (1989) there were well established Pinus forests around the coastline of Gotland during the Boreal phase. Betula was present where there was more fertile soil. Österholm (1989) also stated that Corylus, Ulmus and Quercus arrived on Gotland during the Boreal phase. This study shows that Corylus, Ulmus and Quercus were present on

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

Gotland during the Boreal phase but does not identify the timing of their migration to the island. These tree taxa probably arrived on Gotland in the earlier part of the Boreal period. Österholm (1989) stated that Tilia, Fraxinus and Ulmus migrated to Gotland during the Atlantic phase. This study finds the first instance of Fraxinus at Lina Mire about 5650 BC (7600 cal years BP) which was indeed during the Atlantic period. However, this study finds that Tilia and Fraxinus were present, if not in large quantities, as early as the Boreal. The decrease in Corylus pollen at the end of zone one is perhaps related to the 8.2 ka event. Seppä et al., (2007) found that Corylus and Ulmus, which are thermophilus taxa, decreased from 10-15% to 5% during the 8.2 ka event. This study finds that Corylus pollen decreased from 39% to 12% between 6610 – 5650 BC (8560 – 7600 cal years BP). However, the resolution of samples analysed around this period was not high enough to show the decline in detail. It is not possible to show how climate and migration patterns of taxa have impacted the vegetation of Gotland through analysis of just one core at one location. Polypodiaceae spores increased from 0% to 8% during the same time Corylus pollen decreased. Pollen Zone Two This zone spanned the Mesolithic archaeological period and Atlantic climate period. During pollen zone two, about 5490 – 4260 BC (7440 – 6210 cal years BP) there were more taxa in the pollen record. Generally, tree pollen decreased while Corylus and herb pollen taxa increased. Corylus pollen production typically depends on the environment in which the trees or shrubs are growing; if the area is open, then more pollen is produced than in a dense forest (Eriksson, 1992). This may indicate that the area around Lina Mire became more open or an actual increase in Corylus. Corylus is heliophytic and therefore prefers open environments to dense forest (QMUL, 2001). Therefore, peaks in Corylus within pollen diagrams may indicate forest clearance. According to Simmons (1996) Corylus is more resistant to fire than other taxa so peaks in Corylus seen with simultaneous peaks in charcoal may indicate Mesolithic human impacts of vegetation. However, no clear peak in charcoal was seen during zone two. The changes in the pollen record could be due to Late Mesolithic deforestation. Wallin (2010) discussed the link between a decline in tree pollen and a peak in charcoal, around the late Atlantic period, which coincided with the latter part of the Mesolithic, with axes found from that period. Deforestation may have resulted in more light being available and more herbs being able to grow. Increases in herb taxa pollen during zone two reflect vegetational changes rather than environmental changes as Lina Mire was a bay throughout this period. Some of the herb taxa which appeared during zone two were Poaceae, Artemisia, Chenopodiaceae, Plantago lanceolata, Rumex and Filipendula. Filipendula is a tall herb and may suggest vegetation change (Ralska-Jasiewiczowa and Rzętkowska, 1987). Rumex can indicate some human influence; however more concrete assumptions could be drawn if Rumex was accompanied by a clear peak in charcoal or other indicator taxa (Karlsson, 1992). When Artemisia, Chenopodiaceae and Plantago lanceolata occur together it can be indicative of coastline weeds (Miller and Robertsson, 1981). Plantago lanceolata can also indicate grassland or ley farming (Burrichter, 1969).

Nichola Strandberg

In a study of shore displacement and vegetation development on the south-eastern coast of Sweden (Yu et al., 2004) where Poaceae and Polypodiaceae spores occur together it indicated a meadow environment. According to Rannap et al., (2004) people around the Baltic region have been grazing animals in areas which have risen from the sea for thousands of years. This was advantageous as the land was already free from trees and no labour was required to deforest the area. This uplift of the land created a niche habitat for flora and fauna where light loving plants could flourish. However, it is perhaps unlikely that there was grazing as early as 6000 BC (7850 cal years BP) as humans were probably hunter-gatherers during the Mesolithic on Gotland. According to Österholm (1989), the Atlantic forests of Gotland were dense and dark and as such the growth of ground flora such as Poaceae and herbs was suppressed by the dense canopy. This would have been a poor habitat for grazing animals but well suited to wild boar. For hunter-gatherers there would have been a choice of diet but a marine diet was perhaps the most important. Another interpretation of the increase in Poaceae pollen in zone two may be that the pollen originated from Phragmites. Phragmites, an aquatic grass, is one of the only Poaceae types which is not associated with human impacts (Fægri and Iversen,1989). According to Fægri and Iversen (1989) Phragmites pollen are relatively small (typically about 26 μm) compared to other Poaceae pollen grains. Since all Poaceae pollen grains under 40 μm were grouped together Phragmites pollen grains are included in this total. This may indicate that the increase in Poaceae pollen in zone two may reflect Phragmites growing around the bay. Phragmites tolerate brackish water (Moeslundet et al., 1990) and can grow in a wide range of water depths (Hannon and Gaillard, 1997). There is a peak in freshwater aquatic taxa during zone two. During this time the bay was brackish as it was connected to the Littorina Sea. One explanation for the occurrence of freshwater aquatic taxa in a brackish water bay could be that pollen flowed into the bay from freshwater lakes and streams further inland. According to Campbell (1999) pollen redeposited into lakes can be a source of error. Charcoal fragments were present in zone two but no clear peak is shown. Quercus remained somewhat constant during zones two and three which was probably due to the more favourable climate conditions of the Atlantic period. According to Borzenkova et al., (2015) the Holocene thermal maximum occurred around the Baltic region between 5550 – 3550 BC (7500 and 5500 cal year BP). In a pollen diagram from northern Finland Pinus pollen and Polypodiaceae spores decreased due to the temperature increase (Seppä and Birks, 2001). At Lina Mire Polypodiaceae spores declined from around the same time 5650 BC (7600 cal years BP). During the same period Pinus pollen declined from 59% to 21% at 3860 BC (5810 cal years BP). In Sweden and Estonia Tilia and Quercus expanded after 5050 BC (7000 cal year BP) (Borzenkova et al., 2015). At Lina Mire Quercus showed no pronounced trend of increase but Tilia increased from 2-6% during the Holocene Thermal Maximum. Pollen Zone Three Pollen zone three encompassed the last part of the Mesolithic and most of the Neolithic period; Lina Mire was still a bay of the Littorina Sea at this time. This was also the time of

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC the Atlantic chronostratigraphic division until around 5000 cal years BP and then the Sub- Boreal phase. The climate was generally warm as this period was still during the Holocene climate maximum. Many of the same pollen taxa which first appear in zone two persist in zone three; however, there was a decrease in Salix, Poaceae and Cyperaceae pollen. There was an increase in Equisetum spores. The presence of Equisetum indicated a wetland environment (Veski et al., 2005a) and possibly the overgrowing of lake shorelines (Ralska-Jasiewiczowa and Rzętkowska, 1987). Alnus increased throughout zone three and peaked at 19%. Alnus usually grows by rivers, streams, lakes, fens or swamps (Karlsson, 1992). This supports the idea of an increase in wetlands or freshwater in the area. However, the decrease in Poaceae pollen, which as previously discussed may be from Phragmites is more difficult to explain. One explanation may be that the shoreline was displaced either further inland (a transgression) or was displaced outwards towards the Littorina Sea (regression). In this case the Phragmites may have followed the shoreline and disappeared from the Lina Mire basin. There were two Picea pollen grains found during zone three, the earliest corresponds to an age of 4130 BC (6080 cal years BP). Österholm (1989) stated that Picea was established on Gotland during the Boreal period, however at Lina Mire the earliest Picea was only identified from the Atlantic period. It could be the case that Picea existed on Gotland as early as in the Boreal, but was not represented in the Lina Mire pollen record. According to Hicks (1986), Picea does not produce much pollen; however, the pollen produced is well dispersed. Picea pollen can be transported long distances, even over open seas, and they can be found in pollen records from sites where there are no Picea trees. However, Sugita et al., (1999) explained that Picea pollen grains are heavy and may not contribute much pollen in terms of long distance transport. It could therefore be argued that the few Picea pollen grains found were transported long distances or rather that some scattered Picea trees have existed on Gotland since the Boreal period. There were also some Juniperus pollen grains identified during zone three. Juniperus can indicate openness and dry meadow conditions (Veski et al., 2005b). It is known that land was rebounding and that new land was being formed. Water systems upstream and further inland of Lina Mire would have been isolated before Lina Mire itself. These water systems and lakes may have been discharging freshwater into the Lina Mire bay. Reworked spores from Equisetum and aquatic taxa pollen may have washed into the bay from upstream lakes. Pollen Zone Four Pollen zone four is where human impacts are most likely to have affected the vegetation around Lina Mire. The time periods for this zone were the Late Neolithic, the Bronze Age and some of the Early Iron Age. This was during the Sub-Boreal and part of the early Sub- Atlantic chronostratigraphic divisions. The general temperature trend was declining during much of this period (Borzenkova et al., 2015). Throughout zone four, tree pollen decreased and Corylus also decreased from 48% at the onset of zone four to 4% at the end. Wind pollinated tree taxa, such as Pinus, Corylus and Alnus, typically produce more pollen than herb taxa, even compared to Rumex which produces large amounts of pollen (Traverse,

Nichola Strandberg

2007). Thus the shift in vegetation type during zone four reflects a real change in the vegetation; however it is unclear if the decrease in Corylus pollen percentage was suppression by an increase in herb pollen or an actual decrease in Corylus. Herb taxa increased and the most notable increase was Poaceae pollen which increased from 2% to 21%. The increase in Poaceae pollen may be partly driven by an increase in Phragmites pollen. As the land was gradually uplifted the shoreline was displaced in regressive trend. The shoreline vegetation would have migrated with the shoreline; this shoreline vegetation may have included Phragmites. As previously mentioned, Corylus is a thermophilus taxa (Seppä et al., 2007) and therefore some of the decline in Corylus throughout zone four could be attributed to the cooling trend throughout the last 4500 years of the Holocene. A pollen diagram from southern Sweden also showed this trend of declining Corylus (Jessen et al., 2005). This study finds no evidence of a decline in Tilia around 2050 BC (4000 cal years BP), perhaps owing to the relatively low pollen counts or to local factors on Gotland and the area Lina Mire. However, Tilia did decline from 3.6% to 0.5% between 1920 BC and 400 BC (3870 – 2350 cal years BP). This decline in Tilia could be linked to agricultural management (Hultberg, 2015). Similarly, no clear evidence of a sudden decline in Ulmus was seen at Lina Mire in this study. At Ageröds Mosse, Southern Sweden, the Ulmus decline occurred about 3770 BC (5720 cal years BP) (Skog and Regnell, 1995). Österholm (1989) stated that there was a relatively small decline in Ulmus on Gotland at about 3200 BC (5150 cal years BP). This study found a small decline in Ulmus pollen at Lina Mire from 2.6% to 0% between 3170 BC (5120 cal years BP) and 2800 BC (4750 cal years BP). This is in agreement with the Ulmus decline described by Österholm, (1989). However, the Ulmus decline at Lina Mire is not clear. This result could be explained by relatively low pollen counts, a higher resolution study would be needed to investigate the Ulmus and Tilia declines in more detail. The most important human impact indicators in zone four are the taxa which may have been cultivated. This is the Hordeum-type and the Cerealia-type pollen which first appeared in the pollen record at 2630 BC (4580 cal years BP) and 970 BC (2920 cal years BP) respectively. The Cerealia-type pollen grains found were not identified to a lower taxonomic level but were probably from either Avena-type or Triticum-type. As previously discussed, Lina Mire was still connected to the Littorina Sea around the Late Neolithic and Early Bronze Age. It is possible that Lina Mire was then part of an important inland water system. Gothemshammar has been found to be from 900 – 700 BC; Lina Mire would have been isolated from the Littorina at this stage. Gothemshammar was built around 1000 years after the isolation of the lake from the Littorina Sea. According to Badr et al., (2000) Hordeum vulgare was probably first cultivated in the fertile crescent about 10,000 years ago. Hordeum vulgare was probably first cultivated from Hordeum spontaneum, a wild variety of Barley. Barley was one of the first crops which came with agriculture to Europe during the 6th and 5th millennia BC (Jones et al., 2008). According to Jones et al., (2008) Wild Barley grows naturally in south-west Asia and Turkey. Wild Barley tends to flower early in the season in its native arid environment in order to avoid the hottest and driest part of the year. However, in Northern Europe the growing season

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC is much longer, thus in order for Barley to be more productive it would have to flower later in the year. A mutation found in Wild Barley which is grown in Iran could have enabled Wild Barley to flower later in the year in Northern Europe. This is contrary to the idea that Wild Barley mutated to flower later in the year as it spread northward with agriculture. Bogucki (1996) who studied the spread of agriculture through Europe suggested that agriculture spread to Scandinavia around 4000 BC (5950 cal years BP). The findings of this study indicated that cultivation of Hordeum started around 2630 BC (4580 cal years BP) around Lina Mire. However, cattle rearing activity was more difficult to identify than cultivation and may have started much earlier than cultivation. According to Sillasoo et al., (2009) some cereal type taxa belong to wild grass species. It is therefore difficult to separate what is natural and what is anthropogenic. For example, Glyceria fluitans of which the pollen belongs to the Hordeum group was used for food in western Russia and in Europe until the 19th Century. Hordeum itself is associated with natural, wet habitats (Kuusk et al., 1979). However, Estonia does not have many natural occurrences of cereal type taxa (Sillasoo et al., 2009). The earliest cereal type pollen was Avena and Hordeum-type at Mustjärve, Central Estonia about 4700 14C years (Veski, 1998) and Kõrenduse, Estonia about 3215 BC (5165 cal years BP) (Pirrus and Rõuk, 1998). Avena and Hordeum-type pollen were also the earliest cereal pollen types at Rõuge, southern Estonia at about 2630 BC (4580 cal years BP) (Poska et al., 2004). This evidence of Avena and Hordeum-type cultivation is supported by a charred Hordeum spontaneum grain from the Iru settlement in Estonia 2700 BC (4650 cal years BP) (Jaanits et al., 1982). In Finland, Barley (Hordeum vulgare) is also the earliest cereal pollen and was dated to about 1690 – 1270 BC (3640–3220 cal years BP 3200 ± 170 14C BP) (Vuorela and Lempiäinen, 1988). Similarly, Barley (Hordeum vulgare) is also the earliest cereal seen in Latvia and was found from the time of the late Neolithic about 2050 – 1550 BC (4000– 3500 cal years BP) (Rasiņš and Taurina, 1983). Later during the pre-Roman Iron Age, Barley and Emmer (Triticum dicoccum) were the most abundant cereals. Secale pollen is first seen in Estonia about 500 BC (2450 cal years BP) (Poska et al., 2004); (Niinemets and Saarse, 2006). According to Österholm (1989) Secale pollen was found from the end of the Bronze Age and the beginning of the Iron Age and in such amounts as to indicate cultivation of Secale. This study has not found Secale specifically but finds that cultivation was probably underway around Lina Mire during the Bronze Age and Iron Age. Hordeum is an autogamous plant and produces large amounts of pollen. However much of the pollen remains in the hulls and is therefore poorly distributed. It is therefore common that this pollen type is not found in the pollen records even if they are close to cultivated areas (Behre, 1981). However, if the site itself was once cultivated it is likely that threshing on the cereals resulted in large quantities of pollen being incorporated into the soil (Behre, 1976). Pollen from Hordeum is very poorly dispersed during flowering but is released when harvesting and threshing occurs. Pollen is also deposited along the route where the harvest is taken (Vuorela, 1973). A study by Welten (1967) in Switzerland at a Neolithic lake shore dwelling showed large differences in Cerealia pollen between sites only 13 metres apart. Pollen diagrams are therefore somewhat unreliable indicator for prehistoric human activities

Nichola Strandberg and additionally, the absence of Cerealia-type pollen does not mean that cultivation was not taking place (Behre, 1981). Franzén & Hjelmroos (1988) analysed snow from Southern Sweden and discovered Hordeum-type, Plantago lanceolata and Urtica pollen. It was of course not possible to identify where the pollen originated from with certainty but it was suspected that the origin was Denmark, over 200 km away. Pollen grains can also travel thousands of kilometres, for example Hjelmroos & Franzén (1994) found that pollen grains of Secale-type, Triticum-type and small mineral particles in Northern Sweden, close to the Arctic Circle, probably originated in Italy and North Africa. It is therefore important not to place too much emphasis on only a few pollen grains. It is not certain that Hordeum was cultivated close to Lina Mire as grains could have originated from wild plants or transported by the wind. It is a possibility that Hordeum was cultivated, threshed or transported by humans very close to Lina Mire. However, when Hordeum was first seen in the pollen record Lina Mire was a bay of the Littorina Sea. It may be the case that Hordeum was grown near to the bay or threshed close to the bay. It is interesting that Hordeum-type was not replaced by Cerealia-type in the pollen record but that both grew simultaneously during the Bronze Age. Is it difficult to say if humans preferred Cereals to Hordeum or if they cultivated both at the same time? Another perspective is that humans preferred to cultivate Cereals but Hordeum remained and grew as a weed. Taxa other than cultivated crops can act as indicators of human activity. Plantago lanceolata occurred at the same depths as Hordeum-type. In rotational cultivation perennial species are common (Burrichter, 1969). The most important of these indicators is Plantago lanceolata which usually indicates undisturbed grassland and an important ley farming taxa. Modern analogues also show that Plantago lanceolata recolonises abandoned agricultural land and is therefore an indicator of fallow land (Behre, 1981). It is not only the farming method, i.e. rotational or continuous farming which is important for understanding weed species. The implements used for farming are also important as some weeds are more resistant to some farming techniques. Some methods may rip apart the soil but not destroy penetrating organs; in that case the spread of perennial species such as grasses and Plantain family would be favoured (Behre, 1981). Pollen and Charcoal Taphonomy Charcoal concentration rates were calculated (Fig. 7) and the charcoal was also calculated as a sum normalised against pollen and shown in the pollen percentage diagram (Fig.9). It is known that people have lived in the area of Lina Mire since the Mesolithic. However, it is not clear if charcoal fragments relate to natural fires or human activity as there is no clear peak in charcoal. Charcoal was relatively constant in the whole pollen record. There are, as with pollen, many taphonomic factors which affect charcoal distribution, preservation and identification. Counting charcoal on the pollen slide is a convenient method of calculating the microscopic charcoal abundance. However, since pollen preparation and counting is a long process it is not always possible to have a contiguous or high resolution record (Mooney and Tinner, 2011). The resolution for parts of the stratigraphy at Lina Mire was very low, in the

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC upper part of the stratigraphy the resolution was every 2.5 or 5 cm whereas the lower part was every 20 or 30 cm. According to Gardner and Whitlock (2001) macroscopic charcoal does not travel as far as microscopic charcoal which can be viewed on a pollen slide. This means that it may be difficult to differentiate between local fires and regional fires. In theory microscopic charcoal can be transported over long distances (Clark, 1988a). This is especially the case with convection currents of which are generated during wildfires (Patterson et al., 1987). Microscopic charcoal could have originated from fires as far away as 20–100 km (Conedera et al., 2009), thus it is unclear if charcoal was from a local or regional scale. However, microscopic charcoal counted with pollen is within a size range which is difficult to lift, but once taken up into the air it is suspended for a long time before being deposited (Clark, 1984). Charcoal counted with pollen is also a size which is underrepresented near the burning site as it tends to be transported away by winds or convection currents (Clark, 1984). Due to aerodynamics and cohesion more charcoal stays on the ground than gets transported into lakes (Clark, 1984). This could mean that the charcoal was underrepresented in much of the stratigraphy. Even so, charcoal accumulation rates were relatively higher in the lake and Littorina bay phases than for the fen peat. Another issue with charcoal is that recent human activity could have remobilised allochthonous charcoal which was stored in the catchment (Mooney and Tinner, 2011). Handling during the pollen preparation may have resulted in a higher charcoal count as charcoal is brittle (Clark, 1984). There can be problems visually departing charcoal from other dark coloured material on the pollen slides (Patterson et al., 1987). There are questions about how representative microscopic charcoal is as a means of reconstructing fire history. In order for results from a single sediment core to be robust, the charcoal counts must be high enough (Finsinger and Tinner, 2005). According to Finsinger and Tinner (2005) charcoal fragment counts need to be 200-300 in order reduce errors in calculating charcoal concentration rates to less than 5%. The total sums of charcoal and added Lycopodium spores counted in this study would need to be far higher in order to show a more representative picture. The charcoal counts for this study are probably not relevant as so few charcoal particles were counted. It has been discussed how plant taxa are affected by climate, human activities and environmental change. One additional factor which has not been discussed so far is to what extent the limestone bedrock may have affected the soil makeup and which plants could grow on Gotland. According to Svensson (1989), who analysed pollen on Gotland and mainland Sweden, there were no major differences caused by the limestone bedrock as most of the taxa which appeared in the pollen record of indifferent to soil pH. Pollen can be affected by many factors between being released from the plant to being analysed. Probably the most important of these factors is the difference between different taxa in pollen production (Campbell, 1999). Entomophilous species produce less pollen than anemophilous species. This means that entomophilous species may be underrepresented in pollen diagrams (Lowe and Walker, 2014). Self-pollinating (autogamous) species such as Hordeum (Behre, 1981) produce very little pollen. Tilia however produce large amounts of pollen despite being insect pollinated. Fagus sylvatica, which does not grow wild on Gotland

Nichola Strandberg

(Nordstedt, 1920), is wind pollinated but only produces small amounts of pollen (Lowe and Walker, 2014). Differential deposition and redeposition are also factors which must be taken into account. Knowledge of the depositional environment is important, for example if the plant which produced pollen was likely growing around a lake margin, on the surface of a mire or further away (Lowe and Walker, 2014). At Lina Mire it has been revealed from the stratigraphy that the environment of deposition changed numerous times. Throughout most of the pollen record presented here, Lina Mire was a lake or an enclosed bay. The largest changes in the pollen record occurred as the freshwater lake infilled and became a mire, which occurred around 820 BC (2770 cal years BP). It is likely that change in the local environment has affected the pollen record and that perhaps the record shows a more local signal where there was fen peat. According to Tauber (1965), where there are forests, airborne pollen reaches the surface of a mire by two ways. These are from either raindrop impact or through the canopy of the forest between tree trunks. There are additional factors relating to the movement of pollen through the canopy, such as how dense the forest was, the thickness of the foliage, the size or shape of the mire or lake, the wind speed and what time of year the trees release pollen. It is possible to try to try to understand these factors by monitoring modern day pollen dispersal and deposition using pollen traps (Gosling et al., 2003). This has however, not been carried out for this study. According to Giesecke and Fontana (2008) the size of a lake will influence which scale the pollen record shows. For example, a large or an open lake or mire will receive pollen from the region whereas a small or enclosed lake or mire may show a more local signal. It could be assumed that the first freshwater lake phase of the Lina Mire basin shown in this study was larger and or deeper than the second stage. Therefore, pollen from the first freshwater lake phase represent vegetation on a more regional scale, as does also the pollen from the Littorina Sea phase (when the basin was a bay). As previously discussed, it is also important to consider pollen transported by streams (Brown et al., 2007). There are pollen that are remobilised and deposited into the stratigraphy later. Once deposited, mixing and bioturbation could redistribute the pollen grains (Lowe and Walker, 2014). In a similar way pollen grains can be redistributed if an edge of the lake or bay collapses, or if there is overland flow of water (Campbell, 1999). According to Clymo and Mackay (1987) there can be some redistribution of pollen grains on a mire surface. They state that larger pollen grains remain trapped whereas smaller pollen grains can migrate downwards. However, when compared to peat accumulation rates this movement is somewhat insignificant. Pollen grains and spores can show signs of damage due to chemical, physical or biological factors. Oxidation, which is exposure to air, can cause such damage to pollen grains. Polypodium spores are quite resistant to damage whereas some pollen grains can be completely destroyed, for example Urtica (Lowe and Walker, 2014). This means that some spores and pollen grains may be under-represented in the pollen record. As Lina Mire was drained and the accumulations became oxidised is likely that many grains have been damaged. At Lina Mire, the most damaged pollen grains occurred at around 100 cm depth; it is possible that these gyttja deposits have been oxidised.

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

During the analysis of pollen grains under the microscope there can be identification problems. In this study some pollen grains have been identified to the species level, for example Plantago lanceolata. Other grains have been identified to the generic level for example Betula. Poaceae and Cyperaceae have only been identified as far as the family level. This mixture of taxonomic levels means that an accurate reconstruction of the plant communities is not possible as within, for example, the family level of taxonomic identification, there is a large difference in ecological preferences (Lowe and Walker, 2014). In order to reduce the error, the pollen sum should be at least 500 arboreal pollen grains in forested areas and 500 pollen grains of arboreal and non-arboreal in open areas (Berglund and Ralska-Jasiewiczowa, 1986). However, when counting pollen where there have been human impacts they recommend a minimum count of 1000 pollen grains at each depth so that the important indicator species are not missed. They recommend a pollen count of 2000 for Late Holocene human impact pollen investigations. This study falls short of these suggested pollen sums owing to time restraints. Since the pollen sums were on average 250, and one pollen sum was as low as 70, some of the rarer indicator species may have been missed. When the added Lycopodium spores were included in the pollen sum added Lycopodium spores only made up an average of 5.85% of the total. In order for the pollen sum and Lycopodium sum to be comparable with the indigenous pollen it would have been preferable to have close to equal amounts of each so that half of the pollen and spores counted were added Lycopodium spores. It is likely that low Lycopodium spore counts mean that the pollen and charcoal concentrations (Fig.7) are somewhat unreliable. In hindsight it may have been beneficial to increase the amount of Lycopodium tablets added to all of the samples and reduce the weight of the subsample. For example, the fen peat had on average 127,000 pollen grains per gram of material, 12 Lycopodium tablets should provide a ratio of indigenous pollen grains to added Lycopodium spores close to 1:1. Since there were so few Lycopodium spores and the pollen concentrations per gram are calculated using Lycopodium spores, it would be best to increase the amount of tablets, added gradually, until the ratio became equal. Conclusions

The Baltic Sea Stages and Development of the Lina Mire Basin Lina mire was submerged during the Ancylus Lake phase. There was then a period of high energy and possibly some erosion around this time. The period of high energy was probably caused by wave action during the Ancylus regression. The regression was caused by a drop in the eustatic level of the Ancylus Lake. Between about 7030 – 6550 BC (8980 – 8500 cal years BP) a small freshwater lake was formed in the Lina Mire basin. The lake existed for about 480 years. At about 6550 BC (8500 cal years BP) the Littorina transgression reconnected the lake with the sea and the Lina Mire basin became a brackish water bay. This transgression was caused by an increase in eustatic sea level. Lina Mire became an enclosed bay with a narrow connection to the open sea; this persisted for about 4680 years at until about 1870 BC (3820 cal years BP).

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After about 1870 BC (3820 cal years BP) the basin was once again isolated, this time due to isostatic uplift. A freshwater lake existed for 1050 years until 820 BC (2770 cal years BP). The isolation of the basin meant that the area could not be used as an inland water system anymore. Gothemshammar was built around 1000 years after the isolation of the lake from the Littorina Sea. At about 820 BC (2770 cal years BP) the lake overgrew and infilled to become a mire. Fen peat accumulated until the mire was drained during the 1940’s. The mire surface elevation level fell by about 1.6 m in the north of the mire after the drainage as the water table was lowered.

Vegetational Development around Lina Mire Pollen zone one, 6900 – 5490 BC (8850 – 7440 cal years BP). During this time there was mainly Pinus forest around Lina Mire. There would have been little to no human impacts on vegetation as humans were hunter-gatherers during this time. Pollen zone two, 5490 – 4260 BC (7440 – 6210 cal years BP) is where conditions became more open. This shift to open conditions was perhaps caused by isostatic uplift creating new land or by forest clearance by humans. Pollen zone three, 4260 – 2730 BC (6210 – 4680 cal years BP) showed an increase in wetland taxa and aquatic taxa as the land surrounding Lina Mire was uplifted although the basin was still a bay of the Littorina Sea. Pollen zone four, 2730 – 400 BC (4680 – 2350 cal years BP). This was the period which was most likely to have been influenced by humans, the landscape was more open with fewer trees and shrubs and more herbs. Hordeum-type and the Cerealia-type pollen first appeared in the pollen record at 2630 BC (4580 cal years BP) and 970 BC (2920 cal years BP) respectively. The interpretation of these cereal types being cultivated was substantiated by occurrences of Plantago lanceolata, a ruderal taxon, within the same pollen assemblages. This indicates that cultivation around Lina Mire may have started during the Late Neolithic. Acknowledgements I would like to thank Helene Martinsson-Wallin from the Institute of archaeology and ancient history for inviting me to work on the project ‘I Tjelvars fotspår’ (In the Footsteps of Tjelvar). Thank you to Martina Hättestrand from the Department of Physical Geography, Stockholm University for her feedback on the manuscript, supervising me during laboratory work and the writing of my thesis. Thanks to Jan Risberg at the Department of Physical Geography, Stockholm University, for helping with the field work, laboratory work and writing. Many thanks to Erik Wallin and Anton Uvelius (Campus Gotland) for all their help with the field work; without their help it would not have been possible to collect all of the material required for dating. Thanks to Britta Sannel from the Institute of Physical Geography Stockholm University, for help identifying macrofossils. Also thanks to Elin Norström from the Department of Geological Sciences, Stockholm University, for advice on C/N ratios. Thank you to Yusuke Yokoyama from the Atmosphere and Ocean Research Institute, Department of Earth and Planetary Sciences, University of Tokyo for C/N ratio

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC measurements. Thanks to Sven Karlsson from the Department of Physical Geography, Stockholm University, for help with pollen identification and laboratory work. I would also like to thank Cecilia Bandh from the Department of Environmental Science and Analytical Chemistry, Stockholm University, for help with the microbalance. Thank you to Sofia Kjellman, master’s student, Stockholm University, for advice with the preparation of C/N ratios and help with software. Thank you to Erika Modig and Alexander Strandberg for proof reading the text and providing helpful feedback. Huge thanks to Taariq Sheik and Veronica Nord for useful discussions about pollen preparation methods and identification. Finally thanks to Aleftin Barliaev, master’s student, Stockholm University, who I have worked with on this project. I would also like to thank Stefan Wastegård who was my examiner and provided useful comments on the text. This study was funded by Institute of Archaeology and Ancient History, Uppsala University and by the Gerard De Geer Foundation 2016 stipend.

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Appendix

Table 3. Radiocarbon dates and calibrations; radiocarbon dates from bulk sediments have had the reservoir age subtracted prior to calibration.

Calibrated Calibrated 14C years BP years BC Laboratory Depth Stratigraphic Sample Reservoir age (IntCal13.14C) (IntCal13.14C) number (cm) unit material age years BP 95% confidence 95% confidence interval interval 2 Carex seeds and 2339 2317 -2384 435 – 368 86.1% 25 Ua-54489 41 Fen peat ± 28 - 86.1% 483 – 438 8.9 % Cladium 2387-2432 8.9% mariscus seeds 2360-2541 54.6% 1 Betula 592 – 411 54.6% 2631-2701 and 7 752 – 682 26.3% 2448 26.3% Ua-54979 52 Fen peat Cladium - 669 – 632 11.1% ± 29 2581-2618 mariscus 630 – 613 2.9% 11.1% seeds 2562-2579 2.9%

2 Betula 4142 2886 – 2575 Ua-54322 97 Gyttja - 4524-4835 95% seeds ± 60 95% 3377 – 3322 5271-5326 49.9% 49.9% 3220 – 3171 5120-5169 16% 16% 5406-5446 3497 – 3457 Gyttja 14.5% 14.5% 5030 Ua-54782 121 Gyttja bulk 451 5065-5112 3163 – 3116 ± 31 sample 13.6% 13.6% 5171-5182 0.9% 3233 – 3222 0.9 5220 -5220 % 0.1% 3271 – 3271 0.1%

4079 – 3973 68.6% 5922-6028 4169 – 4127 68.6% Gyttja 14.5% 5695 6046-6068 4.1% Ua-54783 175 Gyttja bulk 451 4227 – 4202 ± 32 6076-6118 sample 7.8% 14.5% 4119 – 4097 6151-6176 7.8% 4.1%

Gyttja 6018 4494 – 4337 Ua-54784 201 Gyttja bulk 451 6286-6443 95% ± 32 95% sample 4.5 5567 4493 – 4341 Ua-54415 201 Gyttja Betula 6286-6443 95% ± 51 95% seeds 5000 – 4833 Gyttja 6782-6949 6472 94.4% Ua-54785 225 Gyttja bulk 451 94.4% ± 33 4812 – 4809 sample 6758-6761 0.5% 0.5% Ua-54786 270 Gyttja Gyttja 6235 451 6499-6658 95% 4709 – 4550

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

bulk ± 32 95% sample 5845 – 5646 3.5 7595-7794 94.4% 6862 Ua-55698 276 Gyttja Betula - 94.4% 5869 – 5865 ± 51 seeds 7814-7818 0.6% 0.6%

Calcareous 9 Betula 7777 6682 – 6502 Ua-54319 309 - 8451-8631 95% gyttja seeds ± 43 95% 7186 – 7037 92.1% 8986 -9135 7252 – 7229 Calcareous 13 Betula 8111 92.1% Ua-54320 325 - 1.6% gyttja seeds ± 40 9178-9201 1.6% 7290 – 7272 9221-9239 1.3% 1.3%

7145 – 7018 73.9% 6883 – 6831 8967-9094 9.9% 73.9% 6971 – 6913 8780-8832 9.9% 8.3% Calcareous 15 Betula 8072 8862-8920 8.3% Ua-54321 339 - 7172 – 7151 1.9 gyttja seeds ± 38 9100-9121 1.9% % 8953-8963 0.9% 7014 – 7004 8935-8935 0.1% 0.9%

6986 – 6986 0.1%

Table 4. The coring location coordinates are provided in latitude and longitude All depths are (m) a.s.l. and empty values indicate that the stratigraphic layer was not present or that coring was not deep enough to find the layer.

57.579866 57.578143 57.577180 57.576246 Coordinates (m) 18.661445 18.664239 18.665471 18.667325 Coring location number (Northern 1 2 3 4 transect) Distance between coring locations 258.86 125.1 151.42

(m) west-to-east Fen peat surface 8.93 8.90 8.93 8.26 Upper calcareous 8.30 7.73 gyttja surface Gyttja surface 8.01 8.25 7.60

Lower calcareous 6.05 5.06 gyttja surface Sand surface 6.51 5.85 4.73

Bluish clay surface 6.48 4.68

57.575743 57.573402 57.572094 57.571150 Coordinates (m) 18.645268 18.650568 18.653005 18.655212 Coring location number (Middle 5 6 Master core (7) 8 transect) Distance between 415.27 200.89 167.60 coring locations

Nichola Strandberg

(m) west-to-east Fen peat surface. 9.35 9.59 9.07 9.01 Algae gyttja 8.79 surface Upper calcareous 8.62 8.64 8.61 gyttja surface Gyttja surface 8.9 8.39 8.33 8.31 Lower calcareous 7.5 6.74 5.97 4.46 gyttja Clay surface. 6.45

Sand surface 6.7 6.38 5.69

Bluish clay surface 6.32

57.574 57.572 57.569 57.569 57.568 57.567 57.566 57.564 57.564 551 077 858 311 287 422 717 888 100 Coordinates (m) 18.634 18.638 18.641 18.643 18.645 18.647 18.648 18.652 18.654 655 791 491 119 629 578 924 548 284 Coring location number 9 10 11 12 13 15 15 16 17 (Southern transect) Distance between 106.17 coring locations 364.21 291.20 110.98 189.83 158.80 299.74 136.03 3 (m) west-to-east Fen peat surface 9.39 9.28 9.27 9.58 9.47 9.12 9.16 8.92 8.83 Upper calcareous/Algae 8.79 8.48 8.81 8.9 8.92 8.27 8.66 8.07 7.71 gyttja surface Gyttja surface 8.43 8.52 8.83 8.22 7.921 8.41 7.77 7.27

Lower calcareous 6.88 6.77 6.71 6.52 6.17 6.86 gyttja surface Sand surface 8.59 6.39 6.32 6.13 5.98 5.62 6.31 5.02

Bluish clay 6.30 5.42 4.98 surface Reddish clay 5.07 surface

Table 55. C/N ratios

Sample Depth C/N Error name (cm) Ratio 227-01 61 11.18 ±0.53 227-02 68 11.27 ±0.53 227-03 75 15.11 ±0.71 227-04 82 25.2 ±1.19 227-05 89 11.26 ±0.53 227-06 96 11.38 ±0.54 227-07 103 11.36 ±0.54 227-08 110 10.77 ±0.51 227-09 117 10.41 ±0.49 227-10 124 12.38 ±0.58 227-11 131 11.21 ±0.53 227-12 138 11.44 ±0.54 227-13 145 10.99 ±0.52 227-14 152 10.82 ±0.51 227-15 159 10.63 ±0.5 227-16 166 10.65 ±0.5 227-17 173 9.76 ±0.46 227-18 180 10.2 ±0.48 227-19 187 12.48 ±0.59 227-20 194 11.57 ±0.54 227-21 201 10.59 ±0.5 227-22 208 9.84 ±0.46 227-23 215 10.44 ±0.49 227-24 222 10.85 ±0.51 227-25 229 12.19 ±0.57 227-26 236 9.96 ±0.47 227-27 243 9.67 ±0.46 227-28 250 9.62 ±0.45 227-29 257 9.58 ±0.45 227-30 264 10.64 ±0.5 227-31 271 9.59 ±0.45 227-32 278 10.66 ±0.5 227-33 285 13.38 ±0.63 227-34 292 15.05 ±0.71 227-35 299 14.03 ±0.66 227-36 306 16.21 ±0.76 227-37 313 17.48 ±0.82 227-38 320 17.29 ±0.81 227-39 327 11.36 ±0.54 227-40 334 15.04 ±0.71

Table 6. Trees, herbs, shrubs, dwarf shrubs, spores and aquatic taxa with Latin, English and Swedish name.

Trees

Abies Fir Ädelgran Acer Maple Lönn Alnus Alder Al Betula Birch Björk Carpinus Hornbeam Avenbok Cupressaceae Conifer/Cypress family Cypressväxter Fagus Beech Bok Fraxinus Ash Ask Larix Larch Lärk Picea Spruce Gran Pinus Pine Tall Quercus Oak Ek Salix Willow Pil Sambucus-type Elderflower Fläder Sorbus-type Rowan Rönn Tilia Linden or Lime Lind Ulmus Elm Alm

Shrubs

Corylus Hazel Hassel Juniperus Juniper En Dwarf Shrubs

Ericaceae Heather Ljung

Herbs

Apiaceae

Artemisia Mugwort et al., Malörtssläktet Aster-type Asters Astersläktet Cerealia-type Cereal Sädesslag Chenopodiaceae Goosefoot et al., Ogräsmållor Cyperaceae Sedges et al., Halvgräs Filipendula Dropwort et al., Älggrässläktet Hordeum-type Barley or wild barley Kornsläktet Lactuceae Dandelion et al., Maskrossläktet Linum austriacum Flax Klipplin Linum bienne Pale flax Linsläktet Lobelia Lobelias Lobelior Menyanthes Trifoliata Bogbean/Buckbean Vattenklöver Plantago Lanceolata Plantain/Lamb's tongue/ribleaf Svartkämpar Poaceae Grass Gräs Potentilla-type Cinquefoils Fingerörtssläktet Primula Farinosa Bird's-eye primrose Majviva

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

Ranunculaceae Buttercup Smörblomma Ranunculas Arvenis Corn buttercup Åkerranunkel Rumex Common sorrel Ängssyra Saxifraga-type Saxifrages Bräckesläktet Scheuchzeria palustris Pod grass Kallgräs Teucrium Germanders Gamandrar Utricularia Bladderworts Bläddresläktet Veronica Veronica Veronikasläktet

Spores

Equisetum Horsetail Fräkensläktet Polygonum Trampörtssläktet Polypodiaceae Polypod ferns Stensöteväxter Sphagnum Peat moss Vitmossor Aquatics

Elodea Waterweeds Vattenpester Nuphar Water-lily Gulnäckrossläktet Nymphaeaceae Water lilies Näckrosväxter Stratiotes aloides Water soldiers Vattenaloe Trapa natans Water caltrop Sjönöt Typha Bulrush Kaveldunssläktet