Reconstructing Holocene Climate Change in The

Reconstructing

Holocene climate

change in the

southern

hemisphere from

a Chilean Lake

Transect (CHILT)

Margo Eekhaut

Ghent University Supervisor: Dr. Elie Verleyen

Faculty of Sciences Co-supervisor: Prof. Dr. Wim Vyverman

Department of Biology Tutor: Evelien Van de Vyver Thesis submitted to obtain the degree of Research group: Aquatic ecology and

Master in Biology Protistology

© May 2010 Faculty of Sciences – Aquatic ecology and Protistology; All rights reserved. This thesis contains confidential information and confidential research results that are property to the UGent. The contents of this master thesis may under no circumstances be made public, nor complete or partial, without the explicit and preceding permission of the UGent representative, i.e. the supervisor. The thesis may under no circumstances be copied or duplicated in any form, unless permission granted in written form. Any violation of the confidential nature of this thesis may impose irreparable damage to the UGent. In case of a dispute that may arise within the context of this declaration, the Judicial Court of Gent only is competent to be notified.

Content

1 Introduction ...... 5

1.1 Present day climate of South America and Chile ...... 9

1.1.1 Wind patterns and present day climate ...... 9

1.1.2 El Niño Southern Oscillation (ENSO)...... 11

1.2 Multi-proxy reconstruction ...... 13

2 Aims ...... 15

3 Material and methods ...... 16

3.1 Research area ...... 16

3.2 Sediment core collection, transportation and storage ...... 20

3.3 Core subsampling ...... 20

3.4 Lithology and sedimentary structure ...... 21

3.5 Physical core properties ...... 21

3.6 Sedimentological analysis...... 22

3.7 Biological and biogeochemical proxies ...... 23

3.7.1 Fossil pigments ...... 23

3.7.2 Diatom composition ...... 24

3.8 Core dating ...... 26

3.9 Statistical analysis ...... 26

3.9.1 Cluster analysis ...... 26

3.9.2 Ordination analysis ...... 27

4 Results ...... 28

4.1 Laguna Parrillar ...... 28

4.1.1 Magnetic susceptibility ...... 28

4.1.2 14C dating ...... 29

4.1.3 Diatom analysis ...... 29

4.1.4 Pigment analysis ...... 30

4.2 Lago Villarrica ...... 31

4.2.1 Lithology ...... 31

4.2.2 Magnetic susceptibility and density ...... 31

4.2.3 Water content and Loss On Ignition (LOI) ...... 32

4.2.4 Si/Al and Si/Zr measurements ...... 34

4.2.5 14C dating ...... 35

4.2.6 Diatom analysis ...... 37

5 Discussion ...... 52

5.1 Laguna Parrillar ...... 52

5.2 Lago Villarrica ...... 52

5.2.1 Volcanic activity recorded in Lake Villarrica ...... 52

5.2.2 Paleoclimate reconstruction ...... 53

6 Conclusion ...... 60

7 Samenvatting ...... 61

8 Dankwoord ...... 63

9 References ...... 64

10 Appendix ...... 77

1 Introduction

The Earth’s climate undergoes significant changes, which are not yet fully understood. Some of the most spectacular anomalies are apparently out of phase between the northern and southern hemisphere, such as the temperature excursions during the last glacial-interglacial transition (Stocker 2003). There have been a number of studies which showed that the southern high latitudes are important for the regulation of the global climate (e.g. Ribbe 2004) and that they may have triggered some of these major climate changes. The latest models indicate that during the last two deglaciations, the southern oceans initiated abrupt warming in the northern hemisphere (Knorr and Lohmann 2003) possibly through melting of parts of the Antarctic ice sheet (Weaver et al. 2003).

There are two hypotheses that explain abrupt climate changes during the last glacial period (Broecker 2003). The first suggests a re-organization of the Atlantic thermohaline circulation, caused by the catastrophic release of glacial meltwater in the North-Atlantic Ocean (Knutti et al. 2004; Steig 2006; Stocker 2002). Swingedouw et al. (2009) demonstrated a direct link between the abrupt changes in the Atlantic meridional overturning circulation (AMOC) and the more gradual changes in the southern ocean. The input of fresh water diluted the salt content of the ocean surface waters and slowed down the formation of deep water; as a result the AMOC weakened. Modeling results showed that a decrease in the strength of the AMOC would result in an instantaneous decrease of northward heat transport. Based on comparisons between data from the northern and southern hemisphere, it has been proposed that cold events in the North correlate with warm events in the South (Andres et al. 2003; Blunier and Brook 2001). This has lead to the development of the bipolar seesaw hypothesis (Barbante et al. 2006; Severinghaus 2009). The second hypothesis proposes that changes in the tropical atmosphere-ocean system are responsible for an instant climate response (Broecker 2003). The evidence for the first hypothesis concerning the thermohaline ocean circulation is compelling and seems to be strong (Broecker 2003).

Many paleoclimate studies over the last decade have highlighted the extreme climate fluctuations of the last glacial interval, but little is known about climate variability during the Holocene and the mechanisms behind it. Although the Holocene has not experienced climate changes of the same magnitude as during the major Quaternary glaciations (last 1.7 million years), it has been marked by many, often rapid, global temperature and precipitation excursions (Gasse 2000; Mayewski et al. 2004; Rohling and Palike 2005). A detailed knowledge about Holocene climate variability is however

5 very important, particularly with the present and future global change, because these anomalies occurred during similar climate boundaries as those of today.

A compilation of proxy data has shown that there must be multiple processes controlling this Holocene variability (Mayewski et al. 2004). Different regions did not respond uniformly to Holocene climate events, although they have a nearly global character. Of all the potential climate forcing mechanisms, solar variability seems to be the most important one. During the mid-Holocene, for example, climate changes appear to be related to orbitally driven changes in the seasonal cycle of the solar radiation (Clement et al. 2000). The hydrological cycle that manages the latent heat distribution in the atmosphere through water vapor transport, clearly plays a major role in the distribution of Holocene climate variability, as indicated by the large fluctuations in lake levels, monsoon activity, and regional humidity registered in paleoclimate records (Mayewski et al. 2004).

Interestingly, in some regions of the southern hemisphere, past Holocene climate changes are completely out of phase with anomalies of the northern hemisphere (Verleyen et al. 2010). For example several glacier advances occurred in New Zealand during classic northern warm periods, which points to the importance of regional driving and/or amplifying mechanisms (Schaefer et al. 2009). Moreover, several studies have shown that well-known past climate anomalies in the northern hemisphere have no analogue in the southern hemisphere. For example, in the North Atlantic there has been a significant short-lived cooling called the 8.2 ka event (Alley et al. 1997). It also appears to have been a generally cool period over much of the northern hemisphere, as shown by major ice rafting and by strengthened atmospheric circulation over the North Atlantic and Siberia (Mayewski et al. 2004). According to Rohling and Palike (2005) the 8.2 ka event can be attributed to a freshwater outflow of Lake Agassiz. On the other hand, Clarke et al. (2009) modeled the climate impacts of the final drainage of Lake Agassiz during this cold event 8200 years BP. They argue that the preflood outflow from Lake Agassiz had a high concentration of suspended sediment which actively removed freshwater from the upper ocean. This would mean that the lake discharge did not contribute to the freshening of the North Atlantic Ocean. Moreover, the effect of winds and the wind-driven ocean circulation should not be overlooked (Clarke et al. 2009). In the southern hemisphere however, there is no evidence for a cooling period around 8200 years BP (Kim et al. 2002; Moreno 2004).

Similarly, the Medieval Warm Period (MWP) (950 – 1250 AD) is characterized by relatively warm conditions in the northern hemisphere, whereas regions in the southern hemisphere exhibit a

6 cooling trend (Haberzettl et al. 2005; Mann et al. 2009). The Little Ice Age (LIA), a cooling period recorded in the northern hemisphere between 1400 and 1700 AD (or 550 - 250 years BP), is apparently out of phase between the northern and southern hemisphere (Mann et al. 2009). To date, it is however difficult to test competing models about interhemispheric linkage in past climate variability because of the general lack of high resolution records from the high latitudes in the southern hemisphere (Kershaw et al. 2007). This region is however crucial as it forms the transition zone between the climate systems of both hemispheres (Knorr and Lohmann 2003; Turney et al. 2007). In other words, determining whether the southern high latitudes follow a North Atlantic or an Antarctic signal is essential to understand the mechanisms involved in the initiation and propagation of past (abrupt) climate anomalies (Ackert et al. 2008).

South America is a well-suited study area, because it is the largest land mass in the southern hemisphere and stretches from the tropics at 10°N to the mid- and high-latitudes at 55°S (Villalba et al. 2009). Past climate records from this region can be compared to ice cores and lake and marine sediment cores from Antarctica (Lowell et al. 1995; Sugden et al. 2005). South America is characterized by the presence of an ice sheet and is surrounded by an ocean, which plays an important role in redistributing energy and carbon (Kershaw et al. 2007). Moreover, the continuous distribution of lakes, containing excellent sedimentary archives (De Batist and Chapron 2008) makes the region well suited to investigate spatio-temporal patterns in past climate variability (De Batist et al. 2008).

Particularly southern Chile is a key site to understand past climate variations, because it is located windward’s from the Andes and at the northern limit of the influence of the southern Westerlies. The Westerlies are the dominant winds in South America and variations in their intensity and latitudinal position have been proposed as important drivers of global climate change due to their influence on deep-ocean circulation and changes in atmospheric CO2 (Rojas et al. 2009). In addition, the climate of South America is strongly influenced by the El Niño Southern Oscillation (ENSO), which has changed distinctly through the Earth’s history (Shulmeister et al. 2006), but its variability during the Holocene is weakly understood (Moy et al. 2002). Both modeling studies (e.g. Clement et al. 1999) and paleorecords (e.g. Moy et al. 2002) revealed a prominent shift in the ENSO activity at ± 5000 years BP. A further intensification of the ENSO was found at around 3000 years BP (Sandweiss et al. 2001).

The climate of South America during the Holocene is characterized by warming and cooling events and dry and more humid periods which differ in timing and onset between different regions along a latitudinal gradient.

In Central Chile (32 - 35°S) moisture increased progressively after 5700 cal. years BP and around 3200 cal. years BP modern humid conditions were established (Jenny et al. 2002). In North-Central Chile (30°S), dry conditions between 10000 and 5000 years BP and an increased humidity after ± 5000 years BP (Kaiser et al. 2008) was reported based upon plant-wax n-alkanes and alkenones in marine sediments. A study of the grain-size distributions and clay mineral composition of marine sediments from the continental slope off mid-latitude Chile (33°S) similarly recorded the arid conditions between 8000 and 4000 cal. years BP (Lamy et al. 1999). Another reconstruction of the sea surface temperature from marine sediments of the Southeast Pacific (Kim et al. 2002) revealed a striking warming at 8000 – 7500 cal. years BP and a decrease in the SST at ± 5000 cal. years BP.

In Northern Patagonia (39°S – 44°S) a diatom sequence from Lago Puyehue recorded a decrease in precipitation in the Mid-Holocene, culminating around 5000 cal. years BP. An increase in precipitation occurred between 3000 cal. years BP and the present-day period (Sterken et al. 2008). A similar early to mid-Holocene transition was reported in a pollen record from North-West Patagonia (Moreno 2004), with cooling events at 7600, 6900 and 5700 cal. years BP. These results strongly suggest the start of cool-temperate conditions, associated with an increase in humidity brought on by an equatorward shift and/or intensification of the Westerlies. The increase in precipitation peaked at circa 5000 cal. years BP. After a warm and dry phase between ± 2900 and 1800 cal. years BP, modern conditions were established at about 1800 cal. years BP. In a marine record from the continental slope of high-latitude Chile (41°S) more arid conditions were found between 7700 and 4000 cal. years BP and an increase in the humidity from 4000 years BP to the present (Lamy et al. 2001).The 1490–1700 A.D. wet period recorded in Lake Puyehue could be associated with the onset of the European Little Ice Age (LIA) (Bertrand et al. 2005).

Abarzua et al. (2004) also reported a phase of rising precipitation regimes between 7000 and 5800 14C years BP and modern precipitation levels since 4750 14C years BP in Laguna Tahui (43°S). These findings suggest a recovery of maximum westerly precipitation from a southward shift to modern values through distinct steps at 7000, 5800, and 4700 14C years BP. A tree ring reconstruction of summer temperatures in Northern Patagonia showed a warm period between 1080 to 1250 years

BP, followed by a long, cold-moist interval from 1270 to 1660 AD, peaking around 1340 and 1640 AD (Villalba 1994).

In Central and Southern Patagonia (44°S - 54°S), renewed glacial activity was reconstructed during between 5400 and 4900 cal. years BP (Porter 2000). A multi-proxy approach applied to the sediments of Laguna Potrok Aike (51°S) in Argentina registered the lowest lake level at 8650 cal. years BP. Since 7300 cal. years BP the lake level rose, which is consistent with a more humid period (Haberzettl et al. 2007). In summary, past climate changes during the Holocene show regional complex variability. Despite some dating uncertainties, most of the records displayed a climate shift around 5000 years BP.

1.1 Present day climate of South America and Chile

1.1.1 Wind patterns and present day climate

The climate and weather pattern in South America are influenced by the InterTropical Convergence Zone (ITCZ) and the SubTropic High Pressure (STHP) (Figure 1-1). On or near the equator, where the solar radiation is highest, air warms at the surface and rises, which creates a band of low air pressure centered on the equator known as the ITCZ. This low pressure zone draws in surface air from the subtropics. When this subtropical air reaches the equator, it rises into the upper atmosphere because of conversion and convection and then begins flowing horizontally to the poles. The rising air comprises one segment of a circulation pattern called a Hadley Cell, which eventually returns air to the surface of the earth, near 30° North and South. The descending portion of the Hadley Cell produces a band of high air pressure at these latitudes called the STHP (Engle 2003).

From the high pressure zone, the surface air travels in two directions. Winds generated between the Subtropic High and the ITCZ, move from the high surface pressure towards the low surface pressure. These winds are deflected by the Coriolis force from east to west as they travel towards the equator, and are called Trade Winds or Tropical Easterlies. The other portion of the surface air moves towards the poles from the Subtropical High zone. This air is also deflected by the Coriolis force, producing the Westerlies. Unlike the Trade Winds, the Westerlies are highly variable and produce stormy weather (Jaksic 1998). The position, intensity and associated climatology of the southern Westerlies remain subject of intensive research (Rojas et al. 2009).

Figure 1-1: Global belts of low and high atmospheric pressure (Engle 2003).

The North-South precipitation gradient is caused by the STHP and the Westerlies. Seasonal shifts in the latitudinal position of the westerly storm tracks result from meridional sea-surface temperature gradients and the interaction between the STHP and the polar low pressure belt (Miller 1976).

There is also a longitudinal gradient in the precipitation, which is the result of the Andes mountain range and the Föhn wind. This is a warm and dry down-slope wind and is called the Puelche wind in Chile. On the East side of the Andes the air is forced to rise and as it rises the air expands and cools down. Cool air can retain less moisture, which results in a great amount of precipitation on the windward slopes. When the wind flows down the Andes at the western side, it undergoes compression; the resulting air is warm and drier (Marc 2009). So, the highest level of precipitation is located at the cost and the lowest precipitation level can be found inland. There is also a maximum peak in the precipitation at the mountain tops of the Andes, because of the rain shadow effect. Puelche winds appearing in spring can cause fast snow melt in the Andes producing floods and reducing the albedo of glaciers (Meruane et al. 2005).

The West - East profile of precipitation at 40°S shows a gradient between ca. 1500 mm per year at the

Chilean coast and about 3500 mm at the top of the Andes, abruptly decreasing to ± 300 mm in the xeric Patagonian steppe, about 50 km to the east of the mountains (Miller 1976; Villalba et al. 2003). A similar profile can be found around 50°S, where annual precipitation totals can exceed 7000–8000

10 mm on the South Patagonian Ice Field but decrease to ± 200 mm per year at El Calafate, 70 km east of the Ice Field (Villalba et al. 2003).

Mean annual temperatures across the whole of Patagonia are mainly influenced by latitude and elevation. At 40°S along the Chilean coast mean annual temperatures vary around 12°C, but decrease to 6°C at ca. 53°S. Across Patagonia, the mean temperature for the coldest month (July) ranges between 0 and 4°C, whereas for the warmest month (January) it ranges between 10 and 16°C. The absolute minimum temperatures can be lower than –25°C (Miller 1976). The climate in Northern Patagonia (37°S - 43°S) is transitional between the Chilean Mediterranean climate, with cool dry summers and moderate wet winters, and the Southern Patagonian oceanic climate, with precipitation all year round (Laugénie 1982). Here we have seasonal, meridional changes of the Westerlies, whereas Southern Patagonia (48°S - 54°S) is under influence of the Westerlies whole year round.

1.1.2 El Niño Southern Oscillation (ENSO)

The El Niño Southern Oscillation (ENSO) is a disruption of the ocean-atmosphere system in the Tropical Pacific, having important consequences for weather and climate around the globe. ‘El Niño’ refers to the ocean and ‘Southern Oscillation’ refers to the atmosphere.

ENSO has two phases: a warm (El Niño) and a cold phase (La Niña). El Niño starts with a difference in atmospheric pressure between the eastern and western part of the Pacific. This difference is used to calculate the Southern Oscillation Index (SOI). When the value of the SOI is negative, the strength of the Westerlies is weaker. As a result, the warm water of the Equatorial Pacific moves eastwards instead of staying near the Indonesian Archipel. The upwelling of cold nutrient rich water at the coast of South America is slowed down (Figure 1-2). In case of an extreme El Niño event, the warm water can migrate all the way to the coast of South America (Jaksic 1998). The El Niño effect occurs every 1 to 11.5 years and its strength is even more variable (Rasmusson and Wallace 1983). The El Niño Southern Oscillation is responsible for the interannual precipitation variability in South America.

Because warmer water evaporates more easily, the atmosphere contains more water vapor during the El Niño state. As a result the atmosphere has a greater potential to precipitate. Rainfall shifts from the western Pacific towards the Americas, while Indonesia and India become drier (Rasmusson and Wallace 1983). In South America the rainfall increases dramatically along the coast. The inland extent of these precipitation events is limited, and normally the El Niño effect is muted eastwards of

11 the Andes. In some regions the response is opposite of that noted along the coasts of South America (Shulmeister et al. 2006), which is especially true for southern Chile. Here El Niño events are marked by a significant reduction in precipitation. El Niño is known to be associated with drier than normal summers at 38°S – 41°S, which are correlated with weaker Westerlies (Montecinos et al. 2000; Montecinos and Aceituno 2003).

La Niña is the exact opposite of El Niño. In South America in general La Niña is related with lower temperatures and less precipitation, but in southern Chile conditions become more humid. During the last several decades the number of El Niño events increased, and the number of La Niña events decreased. The question remains whether this is a random fluctuation or a result of global warming (Trenberth and Hoar 1997).

Figure 1-2: Schematics of Normal Conditions and El Niño Conditions in the equatorial Pacific Ocean and atmosphere. In the normal state, the thermocline is near the surface in the east, temperatures there are cold and the Westerlies are strong. The stronger winds pull the thermocline up and increase upwelling. This creates a more positive Southern Oscillation that drives stronger winds. In the El Niño state, the winds relax, the thermocline deepens in the east and warm state is reinforced. (Cane 2005)

The ENSO also has an effect on the occurrence of tropical cyclones. During El Niño events some major storms were reported in Chile between 30°S and 41°S (Montecinos and Aceituno 2003). Moreover the ENSO effects the community structure of marine phytoplankton (Jaksic 1998), through the slowing down the upwelling, which results in a reduction of the nutrient concentration. This in turn has an effect on the higher levels of the marine food chain.

1.2 Multi-proxy reconstruction

The only way to explore climate system dynamics beyond instrumental records is to study natural archives, e.g. lacustrine and marine sediments, ice, pollen. In the extremely windy region of southern South America, most terrestrial deposits are prone to unconformities. Only bog and lake sediments provide a unique opportunity for continuous terrestrial records to study late Quaternary and Holocene environmental changes. Multi-proxy analysis has proven to be a valuable approach to study past climate variability in southern South America (De Batist et al. 2008; Sterken et al. 2008; Villalba et al. 2009).

Fossil pigments have been used in many paleoclimate studies (e.g. Bianchi et al. 1999; Fietz et al. 2007) in different parts of the world (e.g. Europe, Antarctica, North America) but their use in South America remains limited. Elsewhere, fossil pigments were used to reconstruct lake acidification (Guilizzoni et al. 1992), changes in the physical structure of lakes (Hodgson et al. 1998) and UV irradiation (Hodgson et al. 2005). They are excellent climate indicators as they are preserved for a long time span in sediments (Brown 1969). In contrast to siliceous microfossils and pollen, fossil pigment composition enables scientists to reconstruct changes in the contribution of the different autotrophic algae to the primary production over a yearly cycle. In contrast diatoms generally form blooms during particular seasons (e.g. winter in Chile) when lake waters are well-mixed. A disadvantage of fossil pigments is their unstable properties. They break down or transform rather fast under high light- and oxygenconcentrations, high temperatures, pH extremes and enzymatic action (Smol et al. 2001). An advantage of this proxy is the simplicity and speediness of the method used to analyze the pigment composition.

Diatoms were shown to be good proxies to reconstruct environmental changes in Chilean lakes (Sterken et al. 2008). Diatoms respond much quicker to climate changes, than for example catchment vegetation. They often have species specific demands for their environments, for example a specific concentration of nutrients, temperature, salinity or pH (Round et al. 1990; Krammer and Lange- Bertelot 1991, 1997). Diatoms have an excellent preservation potential, with the exception of diatoms in salt lakes. Another benefit of this proxy is that they occur in many different habitats and

13 regions, from Antarctica to the high Arctic. We can conclude that diatoms are well-established indicators for changes in water condition (Winter and Duthie 2000) and for tracking past environmental changes (Smol and Cumming 2000). However little is known about the ecological preference of the diatom species found in South America. In this region, diatom stratigraphies are interpreted based upon some abundant indicator taxa (Sterken et al. 2008). Aulacoseira, Cyclostephanos and Melosira are generally considered to be indicators for high mixing levels and relatively high nutrient concentrations (Kilham et al. 1986; Urrutia et al. 2000), while Cyclotella and Discostella were used as indicators for warmer climate conditions associated with increased lake water stability (Reynolds 1997; Urrutia et al. 2000).

2 Aims

The main objective of this thesis is to reconstruct Holocene climate variability based upon lake sediment records along a North-South transect trough Chile, South America. To this end, we use a multi-proxy approach, by combining a fossil pigment and diatom analysis in lake sediments from Lago Villarrica and Laguna Parrillar. Our data are used to reconstruct changes in the El Niño Southern Oscillation and study possible teleconnections between South America and other parts of the world.

Our results will contribute to the growing network of paleoclimate studies in southern South America (Denton et al. 1999; Moreno et al. 1999; Lamy et al. 2004; Lowell et al. 1995; Sterken et al. 2008) and to the discussion of the Holocene evolution of ENSO-related climate events. More in particular this study will contribute to several international projects. The first being the CHILT project that tries to complete PEP-I transect (The Americas Transect) that stopped at the low latitudes of South-America. The second is the CACHE-PEP (Climate and Chemistry – Pole-Equator-Pole) project: Natural climate variability – extending the Americas paleoclimate transect trough the Antarctic Peninsula to the pole. Both projects are aimed at extending a North-South transect with well-dated records from South America and the Antarctic Peninsula in order to better understand the size, pattern and timing of regional (and global) climate changes. Combined with reconstructions from other lakes obtained within these projects, our data will be used to determine the relative position, strength and cyclicity of the Westerlies.

3 Material and methods 3.1 Research area

Patagonia can be divided into 3 study areas: Northern Patagonia or the Chilean Lake District (39°S – 44°S), Central Patagonia (44°S – 49°S) and Southern Patagonia (49°S – 54°S) (Figure 3-1). In Northern Patagonia lakes are located on the western side of the Andes, in Central and Southern Patagonia lakes are located on the eastern side of the Andes (Figure 3-1). The landscape of Patagonia is strongly impacted by recurrent, large earthquakes, which originate at the interface between the subducting Nazca Plate and the overlying South American Plate (Moernaut et al. 2009).

The selection of the lakes was based on a very good understanding of their limnology, sedimentary processes, complete stratigraphy as assessed using seismic profiles, and the geological evolution of the lake basin. The necessary preliminary research has been performed by the Renard Centre for Marine Geology (RCMG, UGent) as part of the CHILT-project.

Figure 3-1: The 3 research areas in Chilean Patagonia. The dots indicate the places where lakes are selected to collect cores for the CHILT project (De Batist 2009a)

The selected study sites are located in Northern and Southern Patagonia. Lakes in Northern Patagonia are in general medium- to large-sized, steep, deep and glaciogenic with high Holocene sedimentation rates due to active volcanism (De Batist 2009). The high sedimentation rate results in high resolution paleorecords. In this region Lago Villarrica (39°15’S; 72°02’W; 214 m a.s.l.), a large glaciogenic lake, was selected as a suitable coring site (Figure 3-2). The lake basin originated from glacial valley overdeepening and the formation of large frontal moraine ridges during the Late Quaternary glaciations (Moernaut et al. 2009). The Villarrica Volcano, one of the ten most active in the world, is situated to the South of the lake (Witter et al. 2004).

Figure 3-2: Shuttle Radar Topography Mission (SRTM) image of the northern part of the Chilean Lake district showing the location of Lago Villarrica (De Batist 2009a).

Morphologically, Lago Villarrica consists of a single, deep central basin (maximum depth of 167 m), and a shallower area with more morphological variability in the South-West part of the lake (Campos et al. 1983). Its catchment has a surface area of about 2650 km2, with the majority of land covered by Nothofagus forests. Aside from the Villarrica Volcano, the Quetrupillán Volcano and Sollipulli Volcano are also situated in the catchment area. Its main affluent is the Trancura River, the course and alluvial plain of which have been strongly influenced by lava flows and lahars from the Villarrica Volcano. The Toltén River, which cross-cuts the moraine ridges, constitutes the outflow of the lake towards the Pacific Ocean (Moernaut et al. 2009) (Figure 3-3).

The lake is regarded as monomictic, with vertical mixing during winter and has a mean Secchi depth of 11.0 m (Campos et al. 1983). Recently there has been a shift from oligotrophic to mesotrophic and even eutrophic conditions (Hauenstein et al. 1996) conditions in the lake, due to the expanding touristic centers in the catchment area. Based on data collected by (Campos et al. 1991), the total nitrogen to total phosphorus ratio (TN:TP) equals 5.3, indicating that nitrogen may be the most

17 limiting nutrient for algal growth. In case of cultural eutrophication, excessive loads of phosphorus will produce conditions that are nitrogen limiting (Butkus and Durán 2000) (Appendix 1). The phyto- and zooplankton communities of Lago Villarrica are described by (Campos et al. 1983). Diatoms are dominant in autumn-winter, and the Myxophyceae and Chlorophyceae in spring- summer. The pattern of annual variation of phytoplankton density coincides with that of the primary productivity. Maximum productivity was registered in summer.

Figure 3-3: Morphological setting of Lake Villarrica. Lake surrounding topography derived from SRTM data. (Moernaut et al. 2009)

The climate of the region of Lago Villarrica has been classified as tempered rainy, with mean annual rainfall above 1000 mm and mean monthly temperatures from 7°C during winter up to 16°C during summer (Meruane et al. 2005). Limnological studies of Lago Villarrica have shown that during strong

Puelche winds, the thermocline rises in the upwind end of the lake, defining conditions close to upwelling. After these events, the thermocline deepens about 15 m, with a subsequent seiching motion that oscillates with a period of about one day (Meruane et al. 2005).

Lakes in Southern Patagonia have been much less subject of limnological research. In this region Laguna Parrillar (53°24’S; 71°21’W) was selected as a suitable coring site. Laguna Parrillar is a large, oligotrophic body of freshwater located in the centre of the Brunswick Peninsula in the fjord area of Southern Patagonia (Figure 3-4). It has a surface area of 9.7 km² and a mean depth of around 20 m. The lake is surrounded by subpolar Nothofagus forests (Draggan 2007). The soils in this region have a good drainage, with peat accumulating in less drained areas with bogs and tundra vegetation (Blanco and de la Balze 2004). The lake lies in an area of cold steppe climate, with the mean annual temperature between -3 and 12°C. The total precipitation level is around 2000 mm/year, mostly in the form of snow. Laguna Parrillar is completely frozen during winter. The lake is under the influence of strong westerly winds all year long and due to this wind force the lake is polymictic without stratification. The ice sheet modeling indicates that this lake could have remained ice free during the LGM and that potentially a high resolution, pre-LGM paleorecord is preserved in the lake sediments (De Batist 2009).

Figure 3-4: SRTM image of the Brunswick Peninsula and surroundings showing the location of Laguna Parrillar (De Batist 2009).

3.2 Sediment core collection, transportation and storage

The sediment cores were retrieved in April 2009 for Laguna Parrillar (Van Daele et al. 2009) and in December 2007-January 2008 for Lago Villarrica (Heirman et al. 2008).

For Laguna Parrillar the bathymetry of the lake was measured in February 2007 and a 50 cm long Livingstone core was taken (see Appendix 2). In November 2007 a first attempt was made to obtain a long core from the lake, but bad weather conditions prevented this (2007-2008 was a strong La Niña year) (De Batist 2009). In April 2009 a 5 m long core was taken at 53°41’S; 71°27’W. The cores were transported, preserved frozen (-20°C) and protected from the light, hence conditions for fossil pigment preservation were kept optimal.

The sediment cores from Lago Villarrica were taken in the western part of the basin (39°26’S; 72°17’W) in which an undisturbed sedimentary sequence is preserved, as identified on seismic reflection data. A bathymetric map of the lake is presented in Appendix 3. The long sediment core was taken with an Uwitec piston corer, whereas the short sediment core was taken with an Uwitec gravity corer, both on an elevated platform. The cores from Lago Villarrica were not frozen, but refrigerated (7°C), so the fossil pigment content could not be analyzed.

3.3 Core subsampling

The frozen cores of Laguna Parrillar were slowly defrosted before opening. All the cores were cut in half and one half was kept as an archive while the other part was used for sampling. Every 10 cm, a sample was taken for the analysis of fossil pigments and diatoms. For Lago Villarrica the cores were sampled every 10 cm for diatom analysis. The samples for pigment analysis are approximately 1 cm3 and were taken with a clean spatula. They were stored at -80°C in eppendorfs and protected from light penetration. The samples for diatom analysis were stored in sterile falcon tubes at 5°C (Figure 3-5).

Figure 3-5: Sampling of the cores for pigment and diatom analysis.

3.4 Lithology and sedimentary structure

The lithology and sedimentary structures in the core of Lago Villarrica were visually described by Katrien Heirman (RCMG, UGent). The following variables were described: sediment color (using a Munsell color scale), texture (qualitative grain‐size, sorting, etc.), structures (discriminating between “natural” structures and those induced by the coring process) and laminae thickness. The tephras, a general term for all the fragmental material erupted explosively from a volcano (Smith et al. 2007), were also identified and their depth and grain size was described.

3.5 Physical core properties

The magnetic susceptibility (MS) is the degree of magnetization of a material in response to an applied magnetic field. It can be used as a proxy for terrigenous supply, because it is directly related to the mineral content of the sediment (Bertrand et al. 2005). The magnetic susceptibility can also be used as a method of correlation between multiple cores from the same site to establish age-depth curves, because the parallel susceptibility changes are synchronous from core to core (Thompson et al. 1975). MS can also serve to track tephra layers in the sediments, because volcanoes produce a high amount of magnetic materials. Variations of the MS signal can be used to infer variations in terrigenous supply. These variations are mainly linked to precipitation, but the volcanic eruptions may also influence the terrigenous supply (Bertrand et al. 2008).

The MS of the Parrillar cores was measured using a MS2 Surface Scanning Sensor and the software program Multisus 2.44 (Bartington Instruments Ltd, 2006) in collaboration with Katrien Heirman (RCMG, UGent), who measured the MS in the Villarrica cores. For the Parrillar cores point MS measurements were made with a 2.5 mm resolution and drift correction was applied every 20 readings (Figure 3-6). In the case of Lago Villarrica both the MS (0.5 cm resolution) and density point MS (2.5 mm resolution) analysis were measured.

Figure 3-6: The MS2 Surface Scanning Sensor to measure the magnetic susceptibility.

The density (g/cm3) is a proxy of volcanic activity, because the magnetic materials originated from the volcano are much heavier than other types of sediment. X-ray fluorescence (XRF) measurements were applied on the cores from Lago Villarrica using an AVAATECH XRF scanner (RCMG, UGent). They determine the elemental composition and enable us to obtain a first impression of variations in terrigenous supply (i.e. based on Si/Al ratio, Si/Zr ratio). Al is a proxy for terrigenous material, flushed in trough the river or as a source of volcanic ashes. Si could be originated from diatoms, but also from terrigenous matter. A higher log(Si/Al) value can point to higher diatom productivity and/or less translocation of terrigenous material, which can either be sand or clay. Zr, together with Si is typical for sandy sediments and its erosion products. Al, together with Si is a typical element of clayey sediments (Katrien Heirman, personal communication).

3.6 Sedimentological analysis

The Villarrica cores were sampled for water content and Loss On Ignition (LOI) by the RCMG (UGent). These sedimentological parameters are powerful tracers of changes in the terrigenous sediment input and precipitation, which in turn control lake productivity through variations in nutrient supply (De Batist et al. 2008). The LOI of the first 5 m was measured at 550°C and at 950°C to respectively estimate the organic matter and carbonate content. A common interpretation is to use the sediment organic content as an index of past temperature (Fortin and Gajewski 2009). This is based on a number of paleolimnological studies that have described a synchronicity between changes in the

22 organic content and climate changes trough time (Kaplan et al. 2002; Willemse and Tornqvist 1999). For Laguna Parrillar only the water content of the first 2 m was determined.

3.7 Biological and biogeochemical proxies

3.7.1 Fossil pigments

The pigments of Laguna Parrillar were analyzed according to the method described in (Leavitt and Hodgson 2001) with High Performance Liquid Chromatography (HPLC). Pigment extraction and HPLC analysis was done by Ilse Daveloose and Evelien Van de Vyver.

3.7.1.1 Extraction fossil pigments

Prior to pigment extraction, the wet weight of every subsample was determined with an analytical balance with a precision of 0.00001 g (AX205 DeltaRange NV Mettler Toledo SA). After 4 hours of storage at -80°C, the frozen subsamples were then lyophilized for a minimum of 12 hours and their dry weight was determined, in minimum light conditions.

For the extraction of the fossil pigments 2-3 mL HPLC-grade acetone 90% was added to the dried samples, which improves the extraction of highly polar chlorophyllides, scytonemin and some pheophorbide derivatives (Jeffrey et al. 1997). Next, the samples were sonicated using the Vibra cell Ultrasonic processor for a short period of 60 seconds with an amplitude of 40W, to avoid high temperature rises. 1.5 mL of the solution was filtered with a syringe trough a 0.20 µm pore nylon filter. The first 0.5 mL was discarded and only the remaining 1 mL was stored in 1.5 mL (32 x 11.6 mm) vials. The extraction of the pigments took place within 2 days after the lyophilisation, because dry samples are much more sensitive to oxidation (Leavitt and Hodgson 2001).

3.7.1.2 Pigment analysis

The pigment composition was analyzed using the protocol of (Van Heukelem and Thomas 2001). The HPLC system (Agilent Technologies 1100 series) was equipped with an autosampler at -10°C, a diode array spectrophotometer (400-700 nm), an absorbance detector and a fluorescence detector with excitation at 430 nm and emission at 670 nm (Figure 3-7). An Agilent Eclipse XDB- C8 column was used at 60°C. This column was coated with an apolar monomer or polymer, which forms the stationary phase. The mobile phase is variable polar and is made up out of 2 solvents: solvent A (methanol/TBA 28 mM 70/30 ratio) and solvent B (methanol).

Figure 3-7: HPLC system (Agilent Technologies, 1100 series)

Pigment detection happened at a wavelength of 450 nm (all chlorophylls and carotenoids) and at 665 nm (some chlorophylls). The identification occurred on the basis of retention times and the specific absorption spectrum that was measured continuously from 370 to 800 nm, compared with standards and with published spectra (Jeffry et al. 1997). The software LC/MSD Chemstation from Agilent Technologies (1990-2003) was used for the identification.

The concentration of the different pigments was calculated using the area under the peak in the chromatogram and the responsfactor (Rf). The responsfactor was calculated using standards with known concentrations. Rf =

3.7.2 Diatom composition

3.7.2.1 Diatom oxidation

The falcon tubes with the sample were put in an oven at 60°C to dry. The drying period varied from 3.5 days to 7 days, depending on the water content and the size of the sample. The dried samples were weighed with an analytical balance with a precision of 0.00001 g.

The organic material was oxidized by adding 2 mL of hydrogen peroxide (H2O2). When the oxidation reaction went too fast, the falcon tube was placed in an ice bath. To speed up the reaction the samples were placed in an oven at 60°C. Every two days another 2 mL H2O2 was added to the samples. The process was repeated until the oxidation reaction stopped. It took about 1 to 2 weeks to degrade all of the organic matter. In the next step each sample was rinsed with demineralized water. The samples were left for 2 days to settle down. The supernatans was removed with a vacuum

24 pump up to 4 cm; the remaining sample was rinsed with demineralized water. This procedure was repeated once again and 200 µL homogeneous diatom liquid was transferred into eppendorfs.

3.7.2.2 Preparation of diatom slides

Diatom slides were prepared with a mix of 400 µL demineralized water, 50 µL of diatom liquid and 20µL of microsphere solution. The latter consists of polystyrene microspheres (concentration: 4.38 x 10-6/L) and allowed for quantitative analysis (Battarbee and Kneen 1982). The samples of Lago Villarrica had to be diluted 5 times, while the samples from Lago Parrillar were not diluted because of the low amount of diatoms. 100 µL of the solution was transferred on the cover glass and left to dry on a heating plate. The samples were embedded in Naphrax® and dried in the oven at 60°C for 5 days.

3.7.2.3 Diatom and stomatocyst counting

Transects were scanned at a magnification of 10x 100x with a Leitz Diaplan and a Zeiss Axioplan II light microscope. A minimum of 400 valves, together with the microspheres, was counted per sample. Diatoms were identified to generic or specific level, based on general floras (e.g. Krammer and Lange-Bertelot 1991, 1997; Patrick and Reimer 1966, 1975; Round et al. 1990; Rumrich et al. 2000) and regional studies (e.g. Guerrero and Echenique 2002, 2006; Rumrich et al. 2000). Scanning electron microscopy (SEM) was used to improve diatom identification. Oxidized samples were fixed on aluminum stubs trough air-drying, which were sputter-coated with 50 nm of Au. A JEOL-5800LV SEM was used at 20 kV.

Chrysophyte cysts were counted separately from the diatoms, but there was no distinction made between different cyst types. Stomatocysts are siliceous resting stages of the Chrysophyta that are produced to survive unfavorable circumstances. A higher amount of cysts can point to a higher abundance of Chrysophyta, but can also indicate less favorable conditions. Most of the chrysophyte species are freshwater and most common in planktonic, oligotrophic conditions (Smol 1988). Cysts are formed by all chrysophyte taxa, therefore they can potentially supply us with a complete record of past chrysophyte communities (Duff et al. 1995). Stomatocysts have a wide variety of ornamentation and size, but can always be recognized by the presence of a single pore (Wilkinson et al. 2001). They range in diameter from 2 µm to more than 30 µm. They are commonly preserved in lake sediments and can be useful as paleolimnological indicators (Smol 1995). The ratio of chrysophyte cysts to diatoms valves can be used to track eutrofication trends in the lake. A decline in the cyst ratio can be interpreted as a consequence of eutrophic conditions, because

25 chrysophytes are less competitive in a nutrient rich environment (Smol 1985). According to Smol (1988) this ratio can also be useful to reconstruct lake ice cover and thus regional climate variability. It can also serve as a means to identify areas where diatom preservation might be a problem (Meriläinen 1969).

3.7.2.4 Absolute and relative abundance

The absolute abundance of the diatoms was calculated using the following formula:

DDW: Number of diatoms per gram dry weight MSL: Microsphere liquid (µL) D: Number of diatoms counted MS: Microspheres DL: Diatom liquid (µL) DW: Dry weight sample (g)

Diatom data were presented as abundances.

3.8 Core dating

The sediment cores of Lago Villarrica were dated with AMS 14C analyses on wood and bulk organic matter. An age-depth model was developed, based on 16 dates (Table 4-3 and Figure 4-8). Also 6 bulk sediment samples of Laguna Parrillar were dated (Table 4-1), but an age-depth model has not been developed. The dating of the samples was done by two institutes, the Woods Hole Oceanographic Institution (WHOI) and the Poznan Radiocarbon Laboratory.

3.9 Statistical analysis

3.9.1 Cluster analysis

The diatom diagrams were generated in TG View 2.0.2 (Grimm 2004) en Tilia 2.0.b.4 (Grimm 1991- 1993). A Cluster analysis was applied using CONISS (Constrained Incremental Sum of Squares) (Grimm 1987), where the depth of the samples and the diatom composition was taken into account.

3.9.2 Ordination analysis

For grouping samples according to their taxonomic composition without sample depth constraints, an indirect ordination in Canoco 4.5 (ter Braak & Smilauer) was applied on the relative abundance data of all samples. An initial Detrended Correspondence Analysis (DCA) with detrending by segments was applied on the log (x + 1) transformed data. If the length of gradient of the first axis is greater than 1.5, we have to carry out a Correspondence Analysis (CA); otherwise we have to apply a Principal Components Analysis (PCA).

4 Results 4.1 Laguna Parrillar

4.1.1 Magnetic susceptibility

Magnetic susceptibility (MS) data vary between 2.1 (319.75 cm) and 154 SI (79.25 cm) (Figure 4-1). The values remain fairly constant (33 SI) from the base of the record until around 230 cm, where a sudden shift in the magnetic susceptibility is present (54 SI on average). At 112 cm a peak (129 SI) is observed, another one at 79 cm (154 SI) and one at 71 cm (149 SI). From 30 cm to the top of the core, the magnetic susceptibility remains around the value of 31 SI. Some of the low values throughout the core might be the result of false contact between the scanner and the sediment.

Figure 4-1: The magnetic susceptibility measured in SI units for Laguna Parrillar (cores PAR2SC and PAR2A) 28

4.1.2 14C dating

The following 14C dates were provided by Katrien Heirman (RCMG, UGent). The top sediments have a 14C age of 1050 years BP and the total sediment core is about 41600 cal. years old (Table 4-1).

Sample Depth Institute Material 14C age + σ Calibrated age 2σ error range of cal. name (cm) (yr BP) (cal. yr BP) age PARSCI 0-1 0.0 WHOI bulk 1050 ± 30

PARSCIII-21 21.0 WHOI bulk 2670 ± 30 2796 2746 - 2845 PAR1A-I-46 53.0 WHOI bulk 5550 ± 40 6347 6287 - 6407 PAR1A-I-65 72.0 WHOI bulk 9150 ± 40 10353 10230 - 10476 PAR1A-III-94 288.3 WHOI bulk 30800 ± 310 35522 34759 - 36284 PAR1B-III- 694.8 WHOI bulk 36600 ± 570 41598 40685 - 42510 bottom

Table 4-1: Radiocarbon dates from the Parrillar sediment core (Katrien Heirman, RCMG, UGent).

The age-depth curve is discontinuous with a continuous sedimentation rate between 0 and 300 cm and a high sedimentation rate between 300 and 700 cm (Figure 4-2).

Figure 4-2: 14C dates of Laguna Parrillar provided by Katrien Heirman (RCMG, UGent).

4.1.3 Diatom analysis

A total of 23 genera were identified in the Parrillar cores. A screening of the slides revealed that only two samples of the short core PAR2A-SC contained enough diatoms enabling a microfossil analysis

(Figure 4-3). Only the taxa with a 2 % occurrence in at least one sample were plotted. At 46.5 cm the total diatom count was about 526 x 104 valves per g dry weight. A maximum diatom abundance of 619 x 104 valves per g dry weight was found in the surface sediments. The sample at 46.5 cm was characterized by a dominance of Aulacoseira (62.2 %) and a high abundance of Fragilaria s.l. (17.9 %). In the surface sample Fragilaria s.l. is the dominant genus (38.9 %) and Aulacoseira is less abundant (22.9 %).

Figure 4-3: Diatom composition of the Parrillar short core (PAR2SC). Diatom species are represented as relative abundances. Only the taxa with a two % occurrence in at least one sample are shown.

In the other core PAR2A only found debris and occasionally frustules of Aulacoseira, Cyclotella, Fragilaria and Eunotia were observed (see Appendix 4 – Plate 1).

4.1.4 Pigment analysis

The pigment concentrations in the cores PAR2A-SC and PAR2A were similarly too low (maximum 0.31 µg/L) for paleolimnological reconstructions. The largest part of the samples did not contain any

30 detectable pigments. The pigments identified are listed in Table 4-2; three pigments remained unidentified.

astaxanthin like zeaxanthin chlorophyll b like diadinoxanthin like lutein echinenone alloxanthin like lutein like chlorophyll a diatoxanthin canthaxanthin b carotene

Table 4-2: The identified pigments in the Parrillar cores.

4.2 Lago Villarrica

4.2.1 Lithology

Core VILL (first 920 cm) consists of finely laminated to homogeneous clayey-silty sediments. Thirty- five tephra layers with a mean thickness of 1.1 cm and a total thickness of 39.1 cm were macroscopically described. These tephras consist of sand and gravel. From 590 to 520 cm the sediments have different characteristics than the rest of the core. Between 590 cm and 570 cm a very thick tephra (medium brown to black sand) is present and from 570 to 540 cm clay sediments were found. Another tephra was described between 540 an 530 cm, composed of coarse sand to gravel. Between 530 and 520cm the sediments are jolted and do not form a nice sequence of sediment layers. These two tephra layers were added to the diatom composition diagram (Figure 4-9). Only the first 920 cm will be discussed for the MS, density, LOI and Si ratios, because the other samples were not available on the time of diatom analysis.

4.2.2 Magnetic susceptibility and density

The MS values vary around 100 SI units trough the core, except for tree distinct peaks. The first peak is quite wide and situated between ± 590 cm and 470 cm (300 – 1000 SI). The other, much narrower peaks were found at about 725 cm and 280 cm. The density data vary around 1 g/cm3, but a peak was also observed between 590 and 470 cm. The overall pattern is quite similar to that of the magnetic susceptibility (Figure 4-4).

Figure 4-4: The magnetic susceptibility and density measurements, respectively in SI units and in g/cm3 for Lago Villarrica. Data provided by Katrien Heirman (RCMG, UGent).

4.2.3 Water content and Loss On Ignition (LOI)

The water content ranges between 20 and 100 %, while the LOI 550°C ranges between 1 and 15 %. A minimum in these two proxies was observed between 590 and 520 cm and between 500 and 470 cm. The LOI 950°C data vary from 0 to 5 %, with a peak observed around 590 and 200 cm depth. All three proxies show low values around 150 cm depth (Figure 4-5).

Figure 4-5: The water content and Loss On Ignition measurements (LOI 550°C and LOI 950°C), in percentages. Data provided by Katrien Heirman (RCMG, UGent).

4.2.4 Si/Al and Si/Zr measurements

The log(SI/Al) data vary between 0.9 and 1.8, with lower values being observed between 590 and 470 cm. The log(Si/Zr) data range between 0.7 and 2 and shows similar but less pronounced low values between 590 and 500 cm. A minimum was also described for the Si/Zr ratio at about 430 cm depth. Beside these two exceptions, the two ratios follow a similar course (Figure 4-6).

Figure 4-6: Si/Al and Si/Zr measurements of Lago Villarrica provided by Katrien Heirman (RCMG, UGent)

4.2.5 14C dating

The calibrated dates are presented in Table 4-3 and Figure 4-7. The first 920 cm are ± 4800 cal. years old.

Sample name Depth Institute Material 14C age + Calibrated age 2σ error range (cm) σ (yr BP) (cal. yr BP) of cal. age VILL VCS1 0-0.5 0.0 Poznan bulk 225 ± 100

VILLSC02 68-69 68.0 WHOI wood 720 ± 25 641.5 573 - 710 VILL1-TEST-I 59-60 85.8 WHOI bulk 2350 ± 30 2144.5 1926 - 2363 VILL1-TEST-I 73-74 99.8 Poznan bulk 2600 ± 30 2483.5 2273 - 2694 VILL1-TEST-II 49-50 157.9 WHOI bulk 2670 ± 35 2537 2329 - 2745 VILL2B-I 102-103 275.5 WHOI bulk 3160 ± 35 3144.5 2929 - 3360 VILL1C-I 106-107 378.8 WHOI bulk 4140 ± 40 4456 4205 - 4707 VILL1C-II 56-57 435.6 WHOI bulk 4380 ± 35 4758.5 4510 - 5007 VILL1D-I 66-67 589.7 WHOI bulk 4530 ± 30 4990 4750 - 5230 VILL2D-II 57-58 742.7 WHOI bulk 6620 ± 35 7283.5 7076 - 7491 VILL1E-I W 12.2-13.6 755.1 Poznan wood 4445 ± 35 5082 4880 - 5284 VILL1E-II 32-33 866.1 WHOI bulk 5290 ± 50 5852 5602 - 6102 VILL1E-II 93-94 927.1 Poznan bulk 5450 ± 90 6005.5 5731 - 6280 VILL1F-I 89-90 1027.2 WHOI bulk 6560 ± 45 7223 7002 - 7444 VILL1G-I 7-8 1184.2 WHOI bulk 7370 ± 45 7964 7743 - 8185 VILL1G-II 93-94 1361.8 Poznan bulk 9330 ± 110 10348 9993 - 10703

Table 4-3: Radiocarbon dates from the Villarrica sediment core (Katrien Heirman, RCMG, UGent).

Figure 4-7: The 14C dates of Lago Villarrica cores, provided by Katrien Heirman (RCMG, UGent).

Based on these dates a preliminary age-depth model was developed (Figure 4-8). There are some indications that there was an inflow of old carbon into the lake, which makes the dating older than the sediment actually is. Possible sources are the inflow of Dissolved Organic Carbon (DOC) from the

14 catchment and CO2 gasses from volcanic activity. This influences the C uptake by plants, both terrestrial and aquatic, which results in a disequilibrium between the lake system and the atmosphere. Based on the dating of the top sediments (14C age of 225 years), a correction of 225 years was applied.

An additional correction of 1400 was applied from 742.7 cm depth because a piece of wood at 68 cm was dated at 640 cal. years BP, whereas the bulk sediments were 2350 years BP. In addition, based on marker horizons of historical earthquakes in a surface core of another location in Lago Villarrica we believe that the date of the fossil wood is correct. Another indication is the difference between the dating of the Pucón Ignimbrite eruption around 3700 cal. years BP (Parejas et al. 2010) in the core (4530 14C years BP) and a dating of this deposit on land (3635 14C years BP). Some more research has to be done on the reservoir effect to improve the age-depth model (Katrien Heirman, personal communication).

The age-depth model is discontinuous and constructed by 3 linear regressions, assuming continuous sedimentation rates between 0.0 and 426.1 cm, between 426.1 and 924.0 cm and between 924.0 and 1362.4 cm.

Figure 4-8: Preliminary age-depth model of Lago Villarrica (VILL) based on the 14C dating (Katrien Heirman, RCMG UGent).

4.2.6 Diatom analysis

4.2.6.1 Cluster analysis

A total of 42 diatom genera were identified. The relative abundance of the dominant taxa along the sampled gradient is presented in Figure 4-9. Only the taxa with a 2 % occurrence in at least one sample or the presence in at least 5 samples were plotted. Diatom assemblages were dominated by planktonic taxa. The cluster analysis was based on the relative abundance of the dominant taxa and was used to identify the Local Diatom Zones (LDZ). The most pronounced changes in the diatom composition are recorded in the genera Discostella and Aulacoseira. Discostella is an indicator of oligotrophic environments, with low mixing levels and a high stability of the watercolumn. Aulacoseira on the other hand is more abundant in well mixed, nutrient-rich waters.

Local Diatom Zone 1 (920.60 – 790 cm / ± 4797 – 4399 cal. years BP)

LDZ 1 is dominated by D. glomerata and D. pseudostelligera, with a mean relative abundance of 35.7 %, which is low compared to the other LDZ. LDZ 1 is also characterized by very high abundances of Aulacoseira granulata var. angustissima and of the other subspp. (respectively 5.3 and 24.2 %), which are taxa characteristic of well mixed waters (Kilham et al. 1986). Urosolenia, an indicator of nutrient-rich conditions, is relatively abundant (7.7 % on average) in this zone. Both Aulacoseira agassizii and Cyclotella meneghiniana practically disappear in LDZ 1. Discostella stelligera has a low

37 relative abundance (1.1 %), and occurs only sporadically in the other zones. A peak in the abundance of Aulacoseira herzogii was observed at 840 cm (1.4 %), while this species is absent in LDZ 2 and 3. Increased abundances of tychoplanktonic species, Fragilaria s.l. (4.7 %) and Nitzschia (11.5 %) were observed. Nitzschia cf. fonticola, a small species compared to the others, is the most abundant species of this genus (10 %). Another sub-dominant taxon is Gomphonema, a benthic genus with a relative abundance of 4.7 % on average. The relative abundance of D. glomerata and pseudostelligera, both oligotrophic indicators, rises suddenly from 31.2 % at 835 cm to 46.1 % at 790 cm. The shift is accompanied by a decline in Aulacoseira granulata, Urosolenia, Fragilaria s.l. and Nitzschia and a rise in Gomphonema. The mean absolute diatom abundance is 183 x 107 valves per g dry weight and shows little variation in this zone. The ratio of the planktonic to benthic taxa is quite low compared to LDZ 2. The cyst ratio rises from 0 % at 920.6 cm to 7.5 % at 790 cm.

Local Diatom Zone 2 (790 - 510 cm / ± 4399 – 3545 cal. years BP)

The taxonomic composition is very distinct from other zones and has a higher variability in LDZ 2. It is characterized by relatively high abundances of the oligotrophic D. glomerata and D. pseudostelligera (mean 67.5 %). The abundance of Aulacoseira granulata subsp. is slightly lower (mean 8.4 %) and Aulacoseira granulata var. angustissima has a very low abundance in LDZ 2, compared to LDZ 1 and LDZ 4. Aulacoseira agassizii, characteristic of a more stable watercolumn, has a relative mean abundance of 2 %. A distinct peak in this planktonic species was observed at 540 cm (8.7 %). Discostella stelligera is only sporadically present in LDZ 2 (mean 1.8 %). LDZ 2 has the lowest relative abundances of Urosolenia (3.8 %). The abundance of the benthic genus Gomphonema rises up to 760 cm (10.4 %) and declines very distinctly to very low values. Nitzschia cf. fonticola has a mean relative abundance of 8.7 % with a distinct peak at 520 cm (21 %). The tychoplanktonic taxon Fragilaria s.l. shows a small decline in its abundance, compared to LDZ 1 (3.4 % on average).

Also the absolute diatom abundances are highly variable in LDZ 2. The total diatom concentrations have a mean abundance of 216 x 107 valves per g dry weight and a range of 11 x 107 (551 cm) to 697 x 107 valves per g dry weight (640 cm). Between 580 and 570 cm the absolute diatom abundance is around 35 x 107 valves per g dry weight. Between 570 and 540 cm the mean diatom abundance is even lower, ± 29 x 107 valves per g dry weight. The P:B ratio shows 5 distinct peaks in LDZ 2, with values reaching 116.67. At 581.2 cm the chrysophyte cysts make up 21.1 % in relation to the total diatom present. A maximum of 35.73 % is present at 541 cm.

Local Diatom Zone 3 (510 – 200 cm / ± 3545 – 1557 cal. years BP)

LDZ 3 is characterized by the dominance of D. glomerata and D. pseudostelligera, which reach the highest mean abundance (74.5 %) throughout the entire core. The different Aulacoseira species have a relatively low abundance in LDZ 3, with A. granulata subsp. (5.4 %) and A. granulata var. angustissima (1.1 %) being most abundant. Discostella stelligera is absent in some parts of LDZ 3, but a peak of 4.2 % was observed at 320 cm. Cyclotella meneghiniana is practically absent in this zone, similar to LDZ 1. Urosolenia has a very low abundance (1.5 %) and Gomphonema has a mean relative abundance of 4.4 %, similar to that of LDZ 1 and 4. The tychoplanktonic species Nitzschia cf. fonticola reaches a lower mean abundance of 5.5 % in this zone. The other Nitzschia species also have a very low abundance in LDZ 3 (0.5 %). The relative abundance of Fragilaria s.l. declines compared to LDZ 1 and 2 (mean 2.4 %).

The total diatom concentration declines from ± 500 x 107 valves per g dry weight at 510 cm to ± 200 x 107 valves per g dry weight at 200 cm, with minima recorded between 290 and 280 cm depth. This decline is accompanied by an increase in the abundances of Aulacoseira granulata, Urosolenia and Gomphonema and a decrease in the abundances of D. glomerata and D. pseudostelligera. The P:B ratio has a peak around 380 cm. At 280 cm depth the cyst ratio (11.9 %) is maximal in this zone.

Local Diatom Zone 4 (200 – 5 cm / ± 1557 – 39 cal. years BP)

The most abundant taxa present in LDZ 4 are again D. glomerata and D. pseudostelligera, with a lower mean abundance than in LDZ 2 and 3 (60.8 %). The relative abundance of the benthic genus Gomphonema is similar to that of LDZ 1 (4.6 % on average). Aulacoseira agassizii has a mean abundance of 1 %, with a maximum of 2.9 % at 170 cm depth. Fragilaria s.l. shows the lowest relative mean abundance (2.1 %). Increased abundances of Nitzschia are present in LDZ 4, compared to LDZ 3 (mean 6.5 %).

At 110 cm depth the relative abundance of D. glomerata and D. pseudostelligera reaches a minimum of 35.4 %. At the same depth the relative abundances of Aulacoseira granulata and Urosolenia rise to a maximum (respectively 27.3 % and 10.5 %). The mean total diatom concentration in LDZ 4 is 174 x 107 valves per g dry weight, comparable to that of LDZ 1. A minimum in the P:B ratio is present at around 100 cm depth.

Local Diatom Zone 5 (5 – 0 cm / ± 39 – 0 cal. years BP)

LDZ 5 only contains one sample and is remarkably different in diatom composition from the other zones. It is marked by the appearance of Asterionella, while this genus, characteristic of eutrofied waters, is nearly absent in the other zones (mean 4.6 %). The dominant species is Aulacoseira granulata (33.6 %), with var. angustissima contributing up to 36 %. Aulacoseira distans has a high abundance (8.5 % on average), compared to other zones. D. glomerata and D. pseudostelligera and Urosolenia have a small relative abundance of respectively 20.8 % and 0.5 %. D. stelligera has a mean abundance of 3.6 %, which is higher than in the older zones. Fragilaria s.l. has a relative high abundance in this zone (23 %), while the other tychoplanktonic genus Nitzschia has very low abundances in LDZ 5 (1 %). All benthic species are absent or have a very low abundance, e.g. Gomphonema (0.7 %). The absolute diatom concentration in LDZ 5 is 126 x 107 valves per g dry weight and the P:B ratio is higher compared to LDZ 4.

Figure 4-9: Diatom composition of the Lago Villarrica cores (VILL2). Diatom species are represented as relative abundances. The CONISS analysis is only based on changes in the taxonomic composition. Only the taxa with a two % occurrence in at least one sample or a presence in at least 5 samples are shown. The green lines portray the Local Diatom Zone boundaries. The ratio of planktonic to benthic species and the ratio of Chrysophyte cysts to the total diatom count were added to the diagram. The shaded gray lines represent tephra layers larger than 5 cm.

4.2.6.2 Ordination analysis

A DCA revealed that the length of gradient of the first component was 1.177 (Table 4-4). Because this value is smaller than 1.5, we applied a PCA.

Axes 1 2 3 4 Total inertia

Eigenvalues: 0.068 0.047 0.026 0.022 0.416 Lengths of gradient: 1.777 1.262 0.739 0.876

Cumulative percentage variance of species data: 16.4 27.8 34.1 39.4

Sum of all eigenvalues: 0.416

Table 4-4: Results of the Detrended Correspondence Analysis (DCA). The PCA revealed that 65% of the variation was explained by the first 4 axes (Table 4-5).

Axes 1 2 3 4 Total inertia Eigenvalues: 0.303 0.146 0.111 0.089 1.000 Cumulative percentage variance of species data: 30.3 44.9 55.9 64.9 Sum of all eigenvalues: 1.000

Table 4-5: Results of the Principal Components Analysis (PCA).

The first ordination axis (Figure 4-11) distinguishes between more oligotrophic (negative side) and more nutrient rich conditions (positive side) as species that are typical for oligotrophic waters (e.g. Discostella glomerata and D. pseudostelligera) are situated along the negative side, while species are indicative of more nutrient rich conditions such as Aulacoseira granulata are situated along the positive side . LDZ 2 and 3 are similar in terms of species composition, due to the presence of Nitzschia cf. fonticola, which is an indicator of mesotrophic conditions (Figure 4-10 and Figure 4-11). The species composition of LDZ 5 is very different from all other samples, and is characterized by the presence of Asterionella, a genus typical for eutrophic conditions. The samples of LDZ 1 are relatively similar to those of LDZ 4, due to a relatively high abundance of Aulacoseira granulata, an indicator of high mixing levels and eutrophic conditions and a high abundance of Urosolenia, a mesotrophic taxon. The samples of LDZ 2 are quite spread out over the diagram, with most of them being situated at the negative side of the first ordination axis. Only 4 samples of zone LDZ 2 are situated on the positive side.

Figure 4-10: Principal Components Analysis (PCA) of the relative diatom abundances of Lago Villarrica with a presentation of the different depths (cm).

Figure 4-11: PCA of the relative diatom abundances of Lago Villarrica with a presentation of the identified species, with a 2 % occurrence in at least one sample or the presence in at least 5 samples. Each species arrow points in the direction of steepest increase of values for the corresponding species and the angles between them indicate correlations (or covariance) between the species.

4.2.6.3 Auto-ecological information of the main diatom taxa

Achnanthes (Bory de St. Vincent, 1982) Fig. 13 Achnanthes has a benthic1 life form, with most species being haptobenthic2, epilithic3 and/or epiphytic4. Nearly all Achnanthes species are subaerial5 (Antoniades and Douglas 2002; Round et al. 1990). In Canada these species were found to be generalists (Antoniades and Douglas 2002) and according to (Domitrovic and Maidana 1997) their trophic status is species-dependent. Achnanthes species are mostly abundant in meso- to oligotrophic environments (Urrutia et al. 2000) and in acidic lakes with a low turbidity and low buffer capacity. This genus was listed together with Planothidium, Eolimna and Kolbesia under Achnanthes s.l.

Asterionella (Hassal, 1950) Fig. 18 Asterionella is a common planktonic6 freshwater genus and its growth is related to the silica content of the water (Round et al. 1990). The species found in the Netherlands were alkaliphilous7 (Van Dam et al. 1994). Asterionella is a typical bloom former, brought on by an enhanced supply of nitrogen (Reynolds 1998; Saros et al. 2005). This genus generally dominates phytoplankton blooms in the spring or fall (Kilham et al. 1986). Asterionella formosa is a typical species of high nutrient waters (Clerk et al. 2000; Merilainen et al. 2000).

Aulacoseira (Thwaites, 1848) Aulacoseira is a planktonic genus that is found in fresh water (Round et al. 1990). The presence of Aulacoseira species suggests an increase in water turbulence, because they have a high sedimentation speed (Kilham et al. 1986). Four species were identified in the Lago Villarrica sediment cores.

1 Benthic: associated with the substrate. Benthic species can be epiphytic, epilithic, epipelic, haptobenthic or metaphytic. 2 Haptobenthic: associated with solid surfaces. 3 Epilithic: growing on rocks (Wetzel 2001). 4 Epiphytic: growing on other algae or aquatic plants for physical support, non-parasitic (Wetzel 2001). 5 Subaerial: under the air, living on stable exposed surfaces above the soil, like rocks. 6 Planktonic: floating or moving freely in the watercolumn (Wetzel 2001). 7 Alkaliphilous: thriving in alkaline environments (pH > 7) (Van Dam et al. 1994).

Aulacoseira agassizii Figs. 91-92 Aulacoseira agassizii is planktonic and has an intermediate requirement for light and phosphorous (Kilham et al. 1986). A. agassizii has a very large diameter relative to its length, which means that this species has a higher buoyancy even in low energy environments (O'Farrel et al. 2001). Aulacoseira distans Figs. 79-83 Aulacoseira distans, a smaller species has a planktonic life form, but has also been reported as being tychoplanktonic8 (Jenny et al. 2002). It is an indicator of oligotrophic conditions (Urrutia et al. 2000; Van Dam et al. 1994) and has a pH range of 6 - 8 (Velez et al. 2003). Aulacoseira distans is also halophobous9 (Krammer and Lange-Bertelot 1991) and acidophilous10 (Foged 1978; Van Dam et al. 1994). It grows under high light and has low phosphor requirements (Kilham et al. 1986), with the optimal phosphor content situated between 7.7 and 8 µg/L (Urrutia et al. 2000). A. distans has already been found in Chilean lakes (Sterken et al. 2008). Aulacoseira granulata Figs. 84-90 Aulacoseira granulata is a planktonic species, but has also been reported as being tychoplanktonic. It is a warm-season species that require high light levels coincident with abundant nutrients. This species is found in temperate and warm temperate, shallow freshwater lakes that have sufficient turbulence to keep the heavy cells suspended in the photic zone (Kilham et al. 1986). In Owens Lake this species implies hydrologic input or persistence of freshwater during the summer or fall even against a strong evaporation gradient (Bradbury 1997). Also in Lake Victoria is A. granulata associated with higher precipitation levels (Stager and Johnson 2000). Aulacoseira granulata can serve as an indicator for eutrophic and well mixed waters (Urrutia et al. 2000; Van Dam et al. 1994), but was also found in oligotrophic waters in South Chile (Jenny et al. 2002). As a result of these high mixing levels, a high abundance of A. granulata can point to increasing wind and precipitation levels and/or decreasing temperatures (Sterken et al. 2008).

Aulacoseira granulata becomes a better competitor when the Si/P ratio decreases (Kilham et al. 1986). It is an alkaliphilous and oligohalobous indifferent11 species (Domitrovic and Maidana 1997; Van Dam et al. 1994) and (Gasse 1986) found A. granulata in waters with a pH between 6.9 and 9.8.

8 Tychoplanktonic: circumstantially carried into the plankton, for example, by turbulence. 9 Halophobous: prefers a salinity below 0.2 %. 10 Acidophilous: thriving in a relatively acidic environment (pH < 6) (Van Dam et al. 1994). 11 Oligohalobous indifferent: tolerant to slightly saline waters.

Aulacoseira granulata was found in lakes in Chile, Argentina, Peru and other countries in South America (Domitrovic and Maidana 1997; Hassan et al. 2009; Sterken et al. 2008). In our samples of Lago Villarrica we found the variety angustissima. According to Van Dam et al. (1994) A. granulata var. angustissima is also alkaliphilous and eutrophic. Because of its small size and thus high surface to volume ratio this variety is more efficient in nutrient-rich waters (Gomez et al. 1995). Aulacoseira herzogii Fig. 93 Not so much is known about Aulacoseira herzogii, beside the fact that it is oligohalobous indifferent and pH circumneutral12 (Foged 1978).

Cavinula (Mann and Stickle ex Round et al., 1990) Figs. 19-20 Cavinula is a benthic, epipelic13 genus that contains freshwater species, found in oligotrophic lakes or in shady, moist subaerial habitats (Round et al. 1990).

Cocconeis (Ehrenberg, 1835) Figs. 23-25 Cocconeis has a benthic (epiphytic or epilithic) life form and contains both freshwater and marine species (Round et al. 1990). They are alkaliphilous and an indicator of eutrophic conditions (Van Dam et al. 1994).

Centronella (Voigt, 1902) Figs. 21-22 The status of Centronella has been disputed, with some arguing that it is no more than an aberrant form of Fragilaria. We identified the species Centronella reicheltii in our samples, from which there are two forms. Centronella reicheltii f. rostafinskii, the symmetric form can be found in oligotrophic to mesotrophic conditions (Echenique and Guerrero 2004). The asymmetric form, Centronella reicheltii f. reicheltii is more indicative of eutrophic to mesotrophic conditions (Echenique and Guerrero 2004). In our diatom slides we practically always found form rostafinskii.

12 pH circumneutral: thriving in neutral conditions (pH = ±7) (Van Dam et al. 1994). 13 Epipelic: living on or in fine sediments, such as mud or sand (Wetzel 2001).

Cyclostephanos (Round, 1982) Figs. 94-95 Cyclostephanos, a freshwater to brackish genus, is planktonic and characteristic for nutrient rich and turbid waters (Round et al. 1990). In comparison to smaller, oligotrophic indicator species, Cyclostephanos can thrive better in lower light environments (Kilham et al. 1986). We found the species Cyclostephanos patagonicus that was recorded in western Patagonia, Argentina and described by Guerrero and Echenique (2002).

Cyclotella ((Kützing) Brebisson, 1838) Fig. 96 Cyclotella contains mostly planktonic freshwater species (Round et al. 1990). In our samples of Lago Villarrica we found the species Cyclotella meneghiniana. Cyclotella meneghiniana has a planktonic life form and according to Van Dam et al. (1994) characteristic for freshwater to brackish/freshwater environments. This species requires more light and less nutrients than other diatom taxa, so it can be found in oligotrophic, deep and low energy environments (Reynolds 1997). This points to a higher summer stratification, which can be attributed to higher temperatures and lower precipitation levels (Sterken et al. 2008). C. meneghiniana was also found in eutrophic environments (Domitrovic and Maidana 1997; Van Dam et al. 1994). C. meneghiniana is oligohalobous halophilous14 and alkaliphilous (Domitrovic and Maidana 1997; Gasse 1986; Van Dam et al. 1994).

Cymbella (Agardh, 1830) Fig. 26 Cymbella is a benthic, freshwater genus, with most species being epiphytic and some epilithic or epipelic (Round et al. 1990). In Canada they found that Cymbella species are not habitat specific (Antoniades and Douglas 2002), but Tolotti (2001) defines Cymbella as an oligotrophic, acidophilous taxon. According to Van Dam et al. (1994) most Cymbella species are oligotrophic to slightly mesotrophic.

Diatoma (Kützing, 1844) Fig. 27 Diatoma is a planktonic genus, found in freshwater and slightly brackish environments (Round et al. 1990). Diatoma species are alkaliphilous and meso- to eutrophic (Van Dam et al. 1994). D. tenue var. elongatum has already been found in Lago Villarrica (Rivera 1983).

14 Oligohalobous halophilous: prefers slightly saline waters.

Discostella (Houk and Klee 2004) Discostella is a new genus that contains the former stelligeroid taxa of Cyclotella. The transfer of these species was based on the position of both fultoportulae15 and rimoportulae16 within the striae, in contrast to Cyclotella where these processes are located within the interstriae (Guerrero and Echenique 2006). Like Cyclotella, a high abundance of this oligotrophic genus points to a higher summer stratification, attributed to higher temperatures and lower precipitation levels (Sterken et al. 2008). Discostella glomerata and D. pseudostelligera Figs. 102-114 Discostella glomerata en D. pseudostelligera are very hard to differentiate based upon light microscopy, so both species were lumped as that they have a similar ecology. They are freshwater species and indicators of oligotrophic conditions (Urrutia et al. 2000). These planktonic species require more light and less nutrients than many other diatom genera, implying that they are often found in low energy environments (Reynolds 1997). Discostella stelligera Figs. 97-101 Discostella stelligera is a freshwater species that can be planktonic or littoral17 (Velez et al. 2003). It is an indicator of oligotrophic conditions and deep, low energy waters according to Urrutia et al. (2000), but Domitrovic and Maidana (1997) claims it as a eutrophic species.

Fragilaria s.l. (Lyngbe, 1819) Figs. 39-42 Fragilaria s.l. has a (tycho)planktonic and/or littoral life form, with species that are predominantly freshwater (Round et al. 1990). Other diatom studies found species that were both benthic and planktonic (Schmidt et al. 2004; Velez et al. 2003). Fragilaria species have a wide ecological range (Van Dam et al. 1994). Staurosira, a genus we included with Fragilaria s.l., can survive changes in osmotic stress and nutrient concentrations and is found in disturbed environments (Round et al. 1990). Previous studies have indicated that Staurosira species could reflect more humid, colder conditions (e.g. Laing et al. 1999). The species F. crotonensis has already been found during former studies of Lago Villarrica (Rivera 1983). It strongly responds to an addition of nitrogen, and is thus an indicator of eutrophic conditions (Saros et al. 2005).

15 Fultoportulae: portules that consist of a tube, which penetrates the silica framework and is supported internally by two or more buttresses. The tube almost always has a single external opening (Round et al. 1990). 16 Rimoportulae: portules that consist of a tube which opens to the inside of the cell by one (rarely two) slits and to the outside by a simple aperture or a tubular structure open at the apex (Round et al. 1990). 17 Littoral: associated with the littoral zone of the lake, near the shore (Wetzel 2001).

Gomphonema (Ehrenberg, 1832) Figs. 44-51 Gomphonema has a haptobenthic life form and is very common in freshwater communities according to (Round et al. 1990). Gomphonema is epiphytic (Hay et al. 2000) and has a wide ecological range (Van Dam et al. 1994).

Melosira (Agardh, 1824) Fig. 115 The common genus Melosira is planktonic and epiphytic, and contains both freshwater and marine species (Round et al. 1990). It is particularly abundant under eutrophic and turbulent conditions, much like Aulacoseira (Kilham et al. 1986). In our samples of Lago Villarrica we found Melosira agassizii.

Navicula (Bory de St. Vincent, 1822) Figs. 55-56 Navicula is a common genus that has a benthic (epipelic) life form and includes both freshwater and marine species. Navicula occurs in a wide range of ecological conditions (Van Dam et al. 1994).

Nitzschia (Hassall, 1845) Figs. 58-63 Nitzschia is a planktonic to epipelic genus (Round et al. 1990), which requires intermediate concentrations of silica and phosphor (Kilham et al. 1986). Some studies claim that Nitzschia species are tychoplanktonic (e.g. Bradbury 1997), but Velez et al. (2003) found species that were both benthic and planktonic. The required environmental conditions vary between species, but most Nitzschia spp. are common in brackish and/or polluted waters (Van Dam et al. 1994). In our samples a lot of Nitzschia cf. fonticola, a small species compared with other Nitzschia species, was encountered. N. fonticola is a periphytic18, alkaliphilous species that can be found in meso- to eutrophic environments (Van Dam et al. 1994) and is associated with calm, stable conditions (Kilham et al. 1986). N. acicularis and N. americana have been found in Chile, respectively in Lago Villarrica and between 18°S and 44°S (Rivera 1983). In Argentina they found only benthic Nitzschia species (Hassan et al. 2009). Hay et al. (2000) found that the smaller Nitzschia species are mostly epiphytic and part of benthic communities.

18 Periphytic: sessile organisms that live attached to surfaces projecting from the bottom of a freshwater aquatic environment.

Planothidium (Round and Bukhtiyarova, 1996) Figs. 67-70 Planothidium has a benthic life form and contains mostly small species that live on sand (epipsammic19) (Vilbaste and Truu 2003). Planothidium is an indicator for meso- to eutrophic environments (Urrutia et al. 2000). This genus is listed under Achnanthes s.l.

Rhopalodia (Müller, 1895) Fig. 77 Rhopalodia has a benthic life form (epilithic and/or epipelic). Rhopalodia species can be freshwater or marine (Round et al. 1990) and are found in oligotrophic to eutrophic waters (Van Dam et al. 1994). Most species are alkaliphilous (Van Dam et al. 1994)

Sellaphora (Merschkowsky, 1902) Fig. 71 Sellaphora is benthic (epipelic) and species occur predominantly in freshwater communities, but also in brackish and marine communities (Round et al. 1990).

Urosolenia (Round and Crawford, 1990) Fig. 78 Urosolenia, a freshwater genus, is planktonic and has very delicate cells that break quite easily (Round et al. 1990). This taxon has been found in eutrophic waters (Clerk et al. 2000; Merilainen et al. 2000).

19 Epipsammic: living attached to grains in sandy sediments (Round 1979).

5 Discussion 5.1 Laguna Parrillar

The cores from Laguna Parrillar are characterized by very low concentrations of fossil pigments and diatoms, suggesting a low primary productivity. Possibly, terrestrial input of Dissolved Organic Carbon (DOC) had a large impact on the light availability and hence the primary production as was recently shown in nutrient-poor lakes where colored terrestrial organic matter controls the key process for new biomass synthesis through its effects on light attenuation (Karlsson et al. 2009). Unfortunately, this core could not be used for paleoclimate reconstructions.

5.2 Lago Villarrica

The lake sediments in Lago Villarrica allowed us to reconstruct past changes in volcanic activity and past climate variability.

5.2.1 Volcanic activity recorded in Lake Villarrica

Thirty-five tephra layers were described in the core of Lago Villarrica. Some of the major eruptions and the subsequent tephra deposits had a large influence on the total diatom concentration and to lesser extent on the diatom composition (Figure 4-9). The narrow magnetic susceptibility peak described ± 725 cm depth corresponds to the description of a tephra layer at 726 cm. The tephra between 590 and 570 cm (± 3789 – 3728 cal. years BP) can be considered as an instantaneous deposit, hence these 20 cm were deposited in a few days time and thus expected contain a low amount of diatoms. Between 580 and 570 cm the absolute diatom abundance is indeed very low, around 35 x 107 valves per g dry weight. This tephra deposit is strikingly consistent with the age of the Pucón Ignimbrite event (around 3500 - 3700 years BP) (Parejas et al. 2010; Stern et al. 2007), so we can possible attribute the tephra layer to this major volcanic episode. The clay sediments between 570 and 540 cm (± 3728 – 3636 cal. years BP) are probably related to the period after the volcanic eruption, when the ashes which covered the whole catchment were transported into the lake. The suspended clays likely reduced the light penetration in the lake which resulted in very low absolute abundances of diatoms between 570 and 540 cm (29 x 107 valves per g dry weight) (Cuker et al. 1990).

Another tephra was found between 540 and 530 cm (± 3636 – 3606 cal. years BP), which is yet again an instantaneous deposit. The deformation of the sediments between 530 and 520 cm is probably

52 caused by a heavy earthquake. It is highly unlikely that the sediments originated from another location (Katrien Heirman, personal communication).

The lithological description is consistent with a peak in the magnetic susceptibility and in the density of the core between 590 and 510 cm. These peaks point to high supply of heavy, magnetic materials coming from a volcanic eruption. The water content and the LOI 550°C (organic matter content) both reach a minimum between 590 and 510 cm. The lower organic content suggests a lower paleoproductivity during this period. The log(Si/Al) graph shows low values between 590 and 510 cm, which can also point to a higher translocation of terrigenous material. The log(Si/Zr) values are only low between 590 and 570 cm, which means that this terrigenous material is mostly composed of sandy sediment. It is indeed made up out of medium brown to black sand, according to the description of the lithology.

The magnetic susceptibility and density values are higher between 510 and 470 cm, while a minimum is present between 500 and 470 cm for the water content and LOI 550°C. This could point to volcanic activity. The sediments are characterized by a mix of tephra and silt and thin silt layers can be interpreted as rapid depositional features associated with storms events (Katrien Heirman, personal communication). The magnetic susceptibility show a peak value of 820 SI at ± 280 cm, which is related to a tephra layer.

5.2.2 Paleoclimate reconstruction

A clear evolution in the diatom assemblages of Lago Villarrica over the last 4800 years is evidenced by the identification of five Local Diatom Zones based upon the cluster analysis (Figure 4-9).

5.2.2.1 Local Diatom Zone 1 (920.60 – 790 cm / ± 4797 – 4399 cal. years BP)

The period between 4797 and 4399 cal. years BP is characterized by cooler, windy and wet conditions as could be inferred based upon three lines of evidence present in the diatom composition and productivity. First, Lower temperatures are consistent with the relatively high abundance of the planktonic species Aulacoseira granulata. This species occurs in well mixed waters with relatively high nutrient conditions (Kilham et al. 1986). These limnological conditions occur when temperatures are relatively low and/or wind strength and precipitation levels are high. Higher abundances of A. granulata can be associated with a rise in the precipitation (Bradbury 1997; Stager and Johnson 2000). Higher precipitation usually means an increase in cloudiness which reduces solar radiation and consequently results in lower temperatures (Villalba 1990). Results from a

53 biochemistry model suggest that the Puelche winds induce mixing in the upper layers of the lake (Meruane et al. 2005).

Second, lower temperatures can be inferred by the high abundance of Gomphonema, which is a benthic genus possibly derived from littoral and riverine environments. Benthic diatoms become more important when the abundance of planktonic taxa decreases. A low ratio of the planktonic to benthic taxa points to high light levels, which can be attributed to less thermal stratification and lower temperatures.

Third, LDZ 1 can be interpreted as a cold period, because of a lower absolute diatom concentration (± 180 x 107 valves per g dry weight), compared to LDZ 2 and 3. The lower diatom productivity can be attributed to lower temperatures or to low nutrient levels, that is through direct precipitation or trough diminished river discharges. Because the high abundances of nutrient-rich indicators (e.g. Aulacoseira granulata and Urosolenia) we can assign these low diatom concentrations to lower temperatures in LDZ 1.

Higher nutrient levels can also be inferred from the relative high abundance of Aulacoseira granulata var. angustissima. Because of its small size and thus high surface to volume ratio this variety is more efficient in nutrient-rich waters (Gomez et al. 1995). Increased abundances of tychoplanktonic species, Fragilaria s.l. can possible be attributed to disturbed conditions. The higher nutrient concentrations are consistent with a relatively lower abundance of D. glomerata and D. pseudostelligera, which are generally found in oligotrophic waters. These high nutrient concentrations can be attributed to higher precipitation levels or to a higher supply of terrestrial material from the catchment. D. glomerata and D. pseudostelligera require lower nutrient levels than other taxa, so the sudden rise in their abundance at 835 cm (± 4536 cal. years BP) might point to more nutrient-poor conditions in Lago Villarrica. Similarly, towards the end of LDZ 1 a transition to less nutrient-rich conditions can be inferred from a slow rise in the cyst ratio.

According to Lamy et al. (2001, 2004) the Westerlies shifted southward from 41°S between 7700 and 4000 cal. years BP, which likely led to lower amounts of precipitation. In contrast, Moreno (2004) inferred a cool and wet period between 7600 and 4100 cal. years BP based upon a pollen analysis at 41°S, which is consistent with our data. The results from the diatom stratigraphy in Lago Puyehue are not in agreement with our findings. Lower precipitation levels culminating around 5000 years BP, were reconstructed based upon lowered diatom total abundances and a temporal disappearance of

54 epiphytic taxa. The humidity only starts rising at 3000 cal. years BP (Sterken et al. 2008). However, our findings are consistent with a multi-proxy study, which inferred a progressive increase in the effective moisture after 5700 cal. years BP (Jenny et al. 2002).

5.2.2.2 Local Diatom Zone 2 (790 - 510 cm / ± 4399 – 3545 cal. years BP)

We suggest a warmer and drier climate at 4399 cal. years BP and more nutrient-poor conditions in Lake Villarrica, because of a higher stability of the water column. The higher temperatures are possible related to an increased occurrence of El Niño events. Higher air and surface water temperatures led to an increase in D. glomerata and D. pseudostelligera abundances through an increased strength and duration of the summer stratification. D. glomerata and D. pseudostelligera require relatively low nutrient levels and replaced other taxa during late summer when nutrient availability was minimal. Higher temperatures caused by a higher solar radiation, through a decrease in cloudiness, which in turn can be attributed to lower precipitation levels (Villalba 1990). El Niño is known to be associated with a reduction in the precipitation levels, drier than normal summers and wetter winters between 38 and 41°S (Montecinos et al. 2000; Montecinos and Aceituno 2003), which is in accordance with the very high abundance of D. glomerata and D. pseudostelligera in LDZ 2 (and LDZ 3). Moreover, lower mixing and precipitation levels can be inferred by a lower abundance of Aulacoseira granulata and a higher abundance of Aulacoseira agassizii. A. agassizii has a very large diameter relative to its length, which means that this species has a higher buoyancy even in low energy environments (O'Farrel et al. 2001). A decline in the relative abundance of the benthic genus Gomphonema can point to a lower inflow of fluvial water or to an increase of the terrestrial organic matter input, which lowered the light penetration. A study in Pajep Njakajaure, Sweden suggests that the shift in P:B ratio may be caused by a stronger and/or longer thermal stratification induced by warmer temperatures and a longer ice-free season (Rosen et al. 2009). More oligotrophic conditions can be inferred by the higher cyst:diatom ratio.

The absolute diatom concentrations and the taxonomic composition are highly variable in LDZ 2, which is in agreement with several paleoclimate reconstructions in both tropical and mid-latitude Pacific regions, and is often attributed to increased frequencies and amplitudes of El Niño events in the late Holocene (e.g. Haberle and Bennett 2004; Moreno and Leon 2003; Moreno 2004). The ordination analysis also shows that the samples of LDZ 2 are relatively spread out over the diagram. In Lago Puyehue, the late Holocene was characterized by high centennial to millennial variability in both diatom total abundances (Sterken et al. 2008) and sedimentological proxies (Bertrand et al.

2008), which probably reflected enhanced climate variability. Lower precipitation levels can also be inferred from the low magnetic susceptibility values (Figure 4-4).

After the two large tephra depositions in LDZ 2, a rise in the total diatom concentration is observed. This is consistent with other studies which reported a positive effect of tephra layers on the diatom production (e.g. Telford et al. 2004). This study also reported a change in the diatom composition, namely Fragilaria spp. replacing Aulacoseira spp. in planktonic dominated communities. LDZ 2 is indeed characterized by a lower percentage of Aulacoseira, but the relative abundance of Fragilaria s.l. did not rise in this zone.

The timing of the end of the ENSO suppression is still highly debated, with ranges from ± 7000 –5000 14C yr. BP (Rodbell et al. 1999), 5800 –5400 14C years BP (Haug et al. 2001; Sandweiss et al. 1996) and 5400 – 5300 cal. years BP (Keefer et al. 2003). The analysis of mollusks from archaeological sites on the coasts of Peru indicated that between ± 5800 and 3200 – 2800 cal. years BP, El Niño events were less frequent than today (Sandweiss et al. 2001). These findings are inconsistent with our diatom composition data in LDZ 2. Our data are also in disagreement with marine records from the continental slope of mid- and high-latitude Chile (33°S and 41°S), which recorded more humid conditions from 4000 years BP to the present, coinciding with the onset of the modern state of the ENSO system (Lamy et al. 1999, 2001).

A Mid to Late Holocene warm period is also present in many Antarctic lake and coastal marine records. Although there are some differences in the regional timing of this warm period, it typically occurs somewhere between 4700 and 1000 years BP, which overlaps with a similar optimum found in Antarctic Peninsula records (Verleyen et al. 2010). For example warming from 4200 to 3800 cal. years BP occurred at South Georgia Island, the Antarctic Peninsula and Victoria Land (Ingolfsson et al. 1998). The warm period from ± 4400 cal. years BP, inferred from our data, is situated within the range 4700 - 1000 year BP.

5.2.2.3 Local Diatom Zone 3 (510 – 200 cm / ± 3545 – 1557 cal. years BP)

LDZ 3 can be further dived in two subzones: LDZ 3a (510 – 380 cm / 3545 – 2959 cal. years BP) and LDZ 3b (380 – 200 cm / 2959 – 1557 cal. years BP). LDZ 3a is characterized by a warm climate with very low precipitation levels, which be inferred by an increase of D. glomerata and D. pseudostelligera and high total diatom abundances. This could reflect an enhanced seasonality with increased winter precipitation levels, and drier summers, perhaps both accompanied by higher temperatures. The proposed enhanced seasonality and climate variability support the increased

56 occurrence of El Niño related climate events in the late Holocene as reported in studies in tropical South America (e.g. Moy et al. 2002). LDZ 3a has thus a similar climate as LDZ 2. The intensification of the El Niño is consistent with the decreasing wind and precipitation levels and/or increasing temperatures inferred from a decrease in the diatom biovolume, due to a lower percentage of the large Aulacoseira species. A drop in the relative abundances of Cyclostephanos patagonicus, a eutrophic indicator species (Kilham et al. 1986) support this. The re-appearance of the benthic genus Gomphonema can point to high light levels, which can be attributed to less thermal stratification and lower temperatures. The high abundances of D. glomerata and D. pseudostelligera combined with the high total diatom concentration point to the higher temperatures, which is inconsistent with the previous. Gomphonema, possibly derived from littoral and riverine environments, can also indicate a higher inflow of fluvial water, which seems more likely in this case. More stable conditions can be inferred by lower percentages of A. granulata and higher percentages of A. agassizii. The latter has a very large diameter relative to its length, which means that this species has a higher buoyancy even in low energy environments (O'Farrel et al. 2001). Lago Villarrica is characterized by more oligotrophic conditions, indicated by high abundances of the oligotrophic indicator species D. glomerata and D. pseudostelligera. LDZ 3a is also characterized by lower MS values which indicate lower precipitation levels (Figure 4-4).

LDZ 3b has a slightly colder climate with higher precipitation levels. The zone starts with a sudden decline in the total diatom concentration, which can be interpreted as a transition towards lower temperatures. The diatom productivity was suppressed by low levels of incoming nutrients (either through direct precipitation or by diminished river discharges), by low temperatures, or by a combination of both factors. Slightly higher mixing levels and an increase in the nutrient concentrations can be inferred from a slow rise in the relative abundance of Aulacoseira granulata and Urosolenia. Moreover, less stable conditions can be inferred by a decrease in the abundance of Aulacoseira agassizii. The abundance of D. glomerata and D. pseudostelligera shows a slow decrease, which can point to a rise in the nutrient concentration and a decreased seasonality with lower temperatures. This supports a lowered intensity and frequency of the ENSO.

Our diatom composition data is consistent with a multi-proxy study in Central Chile, which inferred the establishment of more humid conditions around 3200 cal. years BP, likely associated with a lowered frequency and amplitude of El Niño (Jenny et al. 2002). Moreno et al. (2009) also inferred an increased precipitation of westerly origin in South-West Patagonia between 2900 and 1900 cal. years BP. Some other South Chilean records observed similar conditions (e.g. Haberle and Bennett 2004; Moreno and Leon 2003; Moreno 2004). Sandweiss et al. (2001) described an intensification of the

ENSO around 3000 cal. years BP. Similarly, Sterken et al. (2008) suggested that the humidity rose after 3000 cal. years BP, which might have marked .These records are in disagreement with the diatom composition of Lago Villarrica, which points to an increase in El Niño related climate events at ± 4400 cal. years BP, culminating around 3000 cal. years BP. However, because the age depth curve still needs refinement, the chronological control of the inferred climate variability is low and hence the records should be cautiously interpreted.

5.2.2.4 Local Diatom Zone 4 (200 – 5 cm / ± 1557 – 39 cal. years BP)

This period between ± 1557 and 39 cal. years BP can be interpreted as rather wet with slightly lower temperatures, based on lower total diatom abundances, compared to LDZ 2 and 3. The diatom productivity was suppressed by low levels of incoming nutrients (either through direct precipitation or by diminished river discharges), by low temperatures, or by a combination of both factors. High mixing levels and more nutrient rich conditions can be inferred from the higher percentages of Aulacoseira granulata. Large Aulacoseira species are known to favor well-mixed and nutrient rich water and they thrive in lower light conditions (Kilham et al. 1986). The high nutrient levels are confirmed by the high relative abundance of Urosolenia, a eutrophic indicator taxon. Higher nutrient concentrations can also be inferred by the relative high abundance of A. granulata var. angustissima. The high surface to volume ratio of this variety makes it more efficient in nutrient-rich waters (Gomez et al. 1995). The lower abundances of the oligotrophic D. glomerata and D. pseudostelligera also point in a similar direction. We can conclude that the diatom productivity was probably suppressed by lower temperatures. Higher precipitation levels can be inferred from the increase in the A. granulata abundances.

Moreover, lower temperatures can also be inferred by the high abundance of Gomphonema, which is a benthic genus possibly derived from littoral and riverine environments. Benthic diatoms become more important when the abundance of planktonic taxa decreases. A low P:B ratio points to high light levels, which can be attributed to less thermal stratification and subsequently lower temperatures or to a lower supply of terrestrial material. The P:B ratio is the lowest between 110 and 90 cm (857 - 701 cal. years BP). At 110 cm (857 cal. years BP) the abundances of D. glomerata and D. pseudostelligera are lower, combined with an increase in the abundances of A. granulata (var. angustissima). A cold phase and higher mixing levels could be inferred between 857 and 701 cal. years BP.

A pollen study in the southern Lake District inferred cooler and humid conditions for the last 500 years, which is consistent with our data. An expansion of shrubs and grasses in the Nothofagus forest

58 was reported, based upon which more open forest conditions could be inferred (Vargas-Ramirez et al. 2008).

5.2.2.5 Local Diatom Zone 5 (5 – 0 cm / ± 39 – 0 cal. years BP)

LDZ 5 is remarkably different in diatom composition from the other zones (Figure 4-10). It is characterized by the eutrofication of Lago Villarrica, which can be inferred from the presence of Asterionella and a dominance of Aulacoseira granulata, both indicators of eutrophic environments. The high nutrient concentrations probably led to Asterionella blooms and the high abundance of Fragilaria s.l., a possible indicator of disturbed environments. This led to very low abundances of benthic species, e.g. Gomphonema. This is also reflected in the high P:B ratio compared to LDZ 4. Moreover, the high abundance of A. granulata var. angustissima, a variety with a high surface to volume ratio points to nutrient-rich waters.

These findings are consistent with a pollution study by Hauenstein et al. (1996) in which they showed that there has been a recent shift from oligotrophic to mesotrophic and even eutrophic conditions in the lake, due to the expanding touristic centers in the catchment area. The common occurrence of A. granulata in this sample possibly points to higher mixing levels in Lago Villarrica (Kilham et al. 1986).

6 Conclusion

A Holocene diatom stratigraphy from Lago Villarrica (39°15’S; 72°02’W) was studied and combined with sedimentological proxies in order to infer paleolimnological and paleoclimate changes in Northern Patagonia, Chile. The diatom communities were well preserved in the 920 cm long, 14C dated core of ± 4800 years old. We could infer some marked shifts in the diatom stratigraphy. However, because the age depth curve still needs refinement, the chronological control of the inferred climate variability is low and hence the records should be cautiously interpreted.

The period between 4797 and 4399 cal. years BP is characterized by cooler, windy and wet conditions as could be inferred based upon the diatom productivity and composition which is dominated by taxa favoring relatively well mixed surface waters. Drier conditions could be inferred between 4399 and 2959 cal. years BP. The higher temperatures led to an increase in the strength and duration of summer stratification, and are possible related to an increased occurrence of El Niño events (Montecinos and Aceituno 2003). From 2959 cal. years BP the climate is characterized by transition towards higher precipitation levels and slightly lower temperatures, which can be the start of a lowered intensity and frequency of the El Niño Southern Oscillation. A cold phase and higher mixing levels could be inferred between 857 and 701 cal. years BP. The recent decades are characterized by an eutrophication, likely the result of human activities in and around the lake.

7 Samenvatting

Momenteel is er een dringende nood aan paleoklimaatreconstructies van de hogere breedtegraden in het zuidelijk halfrond. Een groeiend aantal studies toonde immers aan dat de zuidelijke hoge breedtegraden belangrijk zijn geweest in de regulatie en initiatie van globale klimaatsveranderingen (e.g. Ribbe 2004; Stocker 2003). Bovendien zijn Holocene klimaatsveranderingen in het zuidelijk halfrond uit fase met goed bestudeerde anomalieën in de noordelijke hemisfeer (Verleyen et al. 2010). Bijvoorbeeld de vooruitgang van verschillende gletsjers in Nieuw-Zeeland gebeurt tijdens warme perioden in het Noorden, wat wijst op het belang van regionale mechanismen (Schaefer et al. 2009).

Zuid-Amerika is uiterst geschikt voor dergelijke paleoklimaatreconstructies, omdat het een latitudinale gradiënt bestrijkt van 10°N tot de aan de hogere breedtegraden op 55°Z (Villalba et al. 2009) en cruciaal is in het bestaand netwerk van reconstructies in o.a. Antarctica en de gematigde breedtegraden in de zuidelijke hemisfeer (Lowell et al. 1995; Sugden et al. 2005). Vooral Zuid-Chili is een belangrijk gebied om vroegere klimaatsveranderingen te bestuderen, want het bevindt zich aan de windzijde van het Andes gebergte en op de noordelijke limiet van de invloed van de zuidelijke Westenwinden. De Westenwinden zijn de dominante winden in Zuid-Amerika en belangrijk voor het globale klimaat (Rojas et al. 2009). Het klimaat van Zuid-Amerika wordt ook sterk beïnvloed door de El Niño Southern Oscillation (ENSO), die sterk veranderde doorheen de geschiedenis van de aarde (Shulmeister et al. 2006).

Deze studie heeft tot doel Holocene paleoklimaatsveranderingen te reconstrueren op basis van biologische proxies in lacustriene sedimentboorkernen van Lago Villarrica en Laguna Parrillar en zal bijdragen tot verschillende internationale projecten. Het eerste is het CHILT project dat probeert om het PEP-I transect (The Americas Transect) dat stopte aan de lage breedtegraden van Zuid-Amerika te vervolledigen. Als tweede is er het CACHE-PEP (Climate and Chemistry – Pole-Equator-Pole) project: Natural climate variability – extending the Americas paleoclimate transect trough the Antarctic Peninsula to the pole. Beide projecten proberen het Noord-Zuid transect uit te breiden met goed gedateerde records van Zuid-Amerika en het Antarctisch Schiereiland. Op die manier wil men de grootte, het patroon en de timing van regionale en globale klimaatsveranderingen beter begrijpen. De studie van Holocene klimaatvariabiliteit is erg belangrijk, vooral door de recente global change, want deze afwijkingen gebeuren binnen vergelijkbare klimaatsgrenzen.

De Laguna Parrillar sedimentboorkern liet wegens de lage concentratie aan diatomeeën en fossiele pigmenten geen paleoklimaatreconstructie toe. Een Holocene diatomee stratigrafie van Lago Villarrica (39°15’Z; 72°02’W) werd onderzocht en gecombineerd met geochemische proxies zoals magnetische susceptibiliteit (MS) en Loss On Ignition (LOI), om vroegere limnologische en klimaatsveranderingen in Noord-Patagonia, Chili te beschrijven. Diatomeeën reageren sneller op klimaatsveranderingen dan bijvoorbeeld vegetatie in het stroomgebied. Ze hebben vaak soortspecifieke eisen voor hun omgeving, zoals een specifieke nutriëntconcentratie, temperatuur, saliniteit of pH (Round et al. 1990; Krammer and Lange-Bertelot 1991, 1997). Hoewel het diepte- ouderdom model van de Lago Villarrica sedimentboorkern nog moet verfijnd worden op basis van nieuwe 14C dateringen kunnen we reeds een aantal preliminaire conclusies trekken.

De periode tussen 4797 en 4399 cal. jaar BP wordt gekenmerkt door koelere, winderige en natte condities, die konden worden afgeleid op basis van een lagere diatomeeënproductie en een samenstelling die gedomineerd werd door taxa die een goed gemengde waterkolom prefereren (e.g. Aulacoseira granulata). Vanaf 4399 cal. jaar BP heersten er drogere en warme condities. De hogere temperaturen leidde, waarschijnlijk tot een toename in de kracht en de duur van de zomerstratificatie en zijn mogelijk gerelateerd aan een toename van de frequentie en amplitude van El Niño gebeurtenissen (Montecinos and Aceituno 2003). De sterkere zomerstratificatie leidde tot een toename in de abundantie van Discostella glomerata en D. pseudostelligera, oligotrofe indicator soorten.

Vanaf 2959 cal. jaar BP wordt een overgang naar hogere precipitatie niveaus en lagere temperaturen geïnfereerd, mogelijk gerelateerd met een verminderde intensiteit en frequentie van de ENSO. Deze timing van de El Niño events komt overeen met die in andere paleoklimaat records (e.g. Jenny et al. 2002; Moreno 2004; Moreno et al. 2009). De periode tussen 857 and 701 cal. jaar BP wordt gekenmerkt door koudere omstandigheden die kunnen afgeleid worden uit de diatomeeënsamenstelling gedomineerd door soorten die een goed gemengde waterkolom prefereren. De recente decennia worden gekenmerkt door een eutrofiëring, afgeleid van de relatief hoge abundanties van soorten die hoge nutriëntconcentraties prefereren (e.g. Asterionella en Aulacoseira granulata). Deze eutrofiëring van Lago Villarrica is waarschijnlijk het resultaat van menselijke activiteiten in en rond het meer.

8 Dankwoord

Allereerst wil ik mijn promotor Elie Verleyen bedanken, voor het uitschrijven van dit thesisonderwerp, het aanreiken van nuttige lectuur en het nalezen van mijn vele schrijfsels. Ook mijn begeleider Evelien Van de Vyver wil ik bedanken om samen met mij preparaten te maken en diatomeeën te tellen. Ook je hulp bij het determineren en het opzoeken van soortinformatie was meer dan welkom. Tenslotte wil ik je nog bedanken voor je kritische oog bij het herlezen van mijn teksten en het aanbrengen van nieuwe ideeën. Prof. Wim Vyverman wil ik bedanken voor de steun en om ervoor te zorgen dat we een strak schema aanhielden. Prof. Koen Sabbe, bedankt voor de hulp bij het determineren van enkele diatomeeën soorten en het vinden van de juiste naslagwerken. Een speciale bedanking gaat uit naar Katrien Heirman, die mij voorzien heeft van heel wat geochemische proxies en de dateringen van de boorkernen. Ook heel erg bedankt voor al je antwoorden op mijn vele vragen over de interpretatie van deze geologische data.

De volgende in het rijtje zijn Ilse, Renaat en Annelien, die ik wil bedanken voor alle hulp bij het praktische labowerk en alle uitleg die jullie verschaften. Zonder jullie was het nooit gelukt. Ook Ines, heel erg bedankt voor al de vragen waarmee ik bij jou terecht kon en het delen van jouw handige schema’s. Iedereen op het bureau, bedankt dat ik een tijdje bij jullie mocht verblijven en voor de ontspannende intermezzo’s. Nog veel succes met jullie toekomstige sportactiviteiten.

Tenslotte wil ik nog familie en vrienden bedanken voor de steun en de vele babbels over de thesis. Mijn ouders en zus Jasmien, Ineke en natuurlijk mijn vriend Karel verdienen een extra bedanking; zonder hen had ik dit project niet tot een goed einde kunnen brengen.

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10 Appendix

Appendix 1: Levels of total phosphorus in Lago Villarrica (Butkus and Durán 2000; Campos et al. 1983; Campos et al. 1991)

Mean Water Column Total Phosphorus (µg/L) Statistic 1979 1991 Maximum 47.8 66.6 Median 14.0 17.6 Minimum 5.0 11.7

Appendix 2: Bathymetric map of Laguna Parrillar (based on the depth soundings of the February 2007 and November 2007 field campaign) with the location of the 5 short cores taken in November 2007 and the location of the Livingstone core taken February 2007. (De Batist 2009)

Appendix 3: Bathymetric map of Lago Villarrica showing the locations of the long core and the short cores taken at this lake (Heirman et al. 2008).

Appendix 4: Figures diatom taxa Laguna Parrillar and Lago Villarrica

Plate 1: screening of Laguna Parrillar core PAR2A Plate 2 - 7: pennate diatoms Plate 8 - 10: centricate diatoms Plate 11: Chrysophyte cysts