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Dissertation from the Department of Geological Sciences No. Lipid biomarkers and other geochemical indicators in paleoenvironmental studies of two Arctic systems: a Russian permafrost peatland and marine sediments from the Lomonosov Ridge. Rina A. Andersson Stockholm 2012 Department of Geological Sciences Stockholm University S-106 91 Stockholm Sweden A Dissertation for the degree of Doctor of Philosophy in Natural Sciences Department of Geological Sciences Stockholm University S-106 91 Stockholm Sweden Abstract The reconstruction of past environmental conditions is a fascinating research area that attracts the interest of many individuals in various geological disciplines. Paleoenvironmental reconstruction studies can shed light on the understanding of past climates and are a key to the prediction of future climate changes and their consequences. These studies take on special significance when focused on areas sensitive to climate change. The Arctic region, which is experiencing dramatic changes today in its peatlands and in its ocean, is prime example. The entire region plays a major role in global climate changes and has recently received considerable interest because of the potential feedbacks to climate change and its importance in the global carbon cycle. For a better understanding of the role of Arctic peatlands and the Arctic Ocean to global climate changes, more records of past conditions and changes in the region are needed. This work applies different geochemical proxies, with special emphasis on lipid biomarkers, to the study of a permafrost peat deposit collected from the Eastern European Russian Arctic and a marine core retrieved from the Lomonosov Ridge in the central Arctic Ocean. The results reported of this study show that molecular stratigraphy obtained from the analysis of lipid biomarkers in both peat and marine profiles, combined with other environmental proxies, can contribute significantly to the study of Arctic ecosystems of the past. ©Rina A. Andersson, Stockholm 2012 ISBN: 978-91-7447-382-7 Cover: Russian arctic plants in summer 2007 Printed by US-AB SU, Stockholm 2012 Lipid biomarkers and other geochemical indicators in paleoenvironmental studies of two Arctic systems: a Russian permafrost peatland and marine sediments from the Lomonosov Ridge. Rina A. Andersson This thesis consists of a summary and four papers refered to as Paper I-IV Paper I- Andersson, R. A., Kuhry, P., Meyers, P., Zebühr Y., Crill P., Mörth M. 2011. Impacts of paleohydrological changes on n-alkane biomarker compositions of a Holocene peat sequence in the eastern European Russian Arctic. Organic Geochemistry 42, 1065–1075. Paper II- Andersson, R. A., Meyers, P., Hornibrook, E., Kuhry, P., Mörth, M. Elemental and isotopic carbon and nitrogen records of organic matter accumulation in a Holocene permafrost peat sequence in the East European Russian Arctic. Submitted to Journal of Quaternary Science. Paper III- Andersson, R. A. and Meyers, P. Effects of climate changes on delivery and degradation of lipid biomarkers in a Holocene peat sequence in the Eastern European Russian Arctic. Submitted to Organic Geochemistry. Paper IV- Andersson, R. A., Jakobsson, M., Meyers, P., Löwemark, L. and Johansson C. Organic matter delivery to Quaternary sediments of Amundsen Basin, central Arctic Ocean. To be submitted. The work in this thesis has principally been carried out by the author, except for the collection of the analyzed peat material and marine sediments, the macrofossil analyses in peat (Pete Kuhry), radiocarbon analyses (Lund University) and the XRF core scanning (Ludvig Löwemark). The extraction and GC-MS analyses of all lipid biomarkers has been the complete responsability of the author, which has also prepared the samples for elemental and stable isotopic analyses kindly performed by Heike Sigmund in the Stabila Isotop Laboratorium (Stockholm University). The collection of forams for radiocarbon analyses was mostly done by Otto Hermelin and Carina Johansson. The interpretation of the data has been lead by the author with important inputs from co-authors in Papers I-III, especially Phillip Meyers and Edward Hornibrook. Interpretation of data in Paper IV has been a collaboration with co-authors, especially Martin Jakobsson and Phillip Meyers. Stockholm, November 2011 Rina A. Andersson Contents Page 1. Introduction 1.1. Climate changes in the Arctic ............................................................................................ 5 1.2. P alaeoclimate studies in Arctic systems: traditional methods and techniques and the role of geochemistry....................................................................................................................... 6 1.3. Lipid biomarkers................................................................................................................. 7 1.3.1. Biomarkers: origin and degradation................................................................................. 8 2. Methods 2.1. Preparation of lipid biomarkers for analysis by GC/MS....................................................... 10 3. Summary of results 3.1. Paper I................................................................................................................................ 10 3.2. Paper II............................................................................................................................... 11 3.3. Paper III............................................................................................................................. 11 3.4. Paper IV.............................................................................................................................. 12 4. Discussion and future studies 4.1. Arctic permafrost peat........................................................................................................... 13 4.2. Marine sediments from the Arctic Ocean............................................................................... 13 5. References................................................................................................................. 14 6. Acknowledgements................................................................................................... 16 Lipid biomarkers and other geochemical indicators in paleoenvironmental studies of two Arctic systems Lipid biomarkers and other geochemical indicators in paleoenvironmental studies of two Arctic systems: a Russian permafrost peatland and marine sediments from the Lomonosov Ridge. Rina A. Andersson Department of Geological Sciences, Stockholm University, S-106 91 Stockholm, Sweden 1. Introduction In recent decades several dramatic changes have been observed in this region, but these changes seem to be different from those that originated from natural variability. Instead, they are probably associated with the warming of global air surface temperatures as a consequence of fossil fuel burning (Lemke et al., 2007). 1.1. Climate changes in the Arctic The Arctic is a key part of the global climate system and influences it through different feedbacks that include physical, ecological and human systems (McGuire et al., 2006). For millions of years, the Arctic has been the scenario of major changes in climate. As one example, during the Eocene Thermal Maximum 2 (ETM2, ca. 53.5 Myr ago), high CO2 atmospheric contents and probably sea surface temperatures warmer by 3-5 ºC prevailed in the Arctic Ocean (Sluijs et al., 2009). Some studies suggest that even during the early Holocene (around 10,000 years ago), seasonal Arctic sea ice was strongly reduced with periods of ice-free summers (Jakobsson et al., 2010). Fig 2. Arctic sea ice in the Lomonosov Ridge area (Photo: Martin Jakobsson). The temperature increases in the Arctic have been substantial, especially in northwestern North America and central Siberia (Hansen et al., 2006). The sea ice extent has rapidly declined (Lemke et al., 2007). Nearly 40% of the sea ice area that was present in the 1970’s was lost by 2007, the record low year for summer sea ice (Serreze and Stroeve, 2009). The surface waters of the Arctic Ocean have been warming in recent years, consistent with the rapid retreat of ice (Lemke et al., 2007). Evidence exists that a sharp decrease in sea ice extent affects the organic carbon fluxes to the Arctic Ocean deep basins (Gobeil et al., 2001). Fig 1. Aerial view of Swedish icebreaker Oden and Russian nuclear icebreaker 50 Years of Victory during the Lomonosov Ridge of Greenland (LOMROG) Expedition 2007 (Photo: Martin Jakobsson). 5 Rina A. Andersson Ice reduction has in turn other implications for temperature patterns over high-latitude land areas; one of them is the hastening degradation of permafrost that leads to increased release of greenhouse gases (Serreze and Stroeve, 2009). Trends for increasing soil temperatures in Alaska and Siberia with permafrost temperatures approaching 0ºC in many areas have already been observed (McGuire et al., 2006; Lemke et al., 2007). Peat covers a large part of the land surface in high latitude regions. The Russian peatlands alone contain a carbon pool of approximately 163 Pg (Tarnocai et al., 2009), most of it stored in large areas of continuous and discontinuous permafrost. This huge carbon pool in the Eurasia region stored in permafrost has functioned as a carbon sink since the last deglaciation, and hastening degradation of permafrost can transform it into a carbon source. Fig 3. North of the tree line near the Rogovaya River in the Eastern European Russian Arctic. Summer 2007 (Photo: Rina Andersson). 1.2. Palaeoclimate studies in Arctic systems: traditional methods and techniques and the role of geochemistry. All changes mentioned above suggest a large regional impact on biota and humans that is projected to grow and have global consequences (Mitchell et al., 1995; McGuire et al., 2006). Our understanding of how these changes impact different biogeochemical systems and ultimately biota and humans is not complete. Some approaches to gain a better understanding about how the Arctic responds to climate changes are to study different records contained in ice cores, in marine sediments and in peat. Below is a short description of some traditional methods and techniques used for palaeoclimate reconstruction in the study of Arctic systems. Important to note is the great development introduced by recent geochemical techniques, especially stable-isotope and organic biomarker techniques. Fig 5. Arctic sea ice (Photo: Martin Jakobsson). Different properties in ice cores can be measured to obtain an approximate reconstruction of past climates, like the melt layers used as indicators of past summer climates (Koerner and Fisher, 1990) or the stable oxygen isotope records in the water molecules of an ice core that provides valuable data on the reconstruction of past ice surface-air temperatures (Dansgaard et al., 1982; Johnsen et al., 2001). In the case of marine sediments, different proxies in dated sediment cores have been exploited in the last decades for the reconstruction of past climate changes in the Arctic. Some examples are ice rafted debris (IRD) that provides information about icebergs or continental Fig 4. Rogovaya in the northeastern European Russian Arctic. Summer 2007 (Photo: Rina Andersson). 6 Lipid biomarkers and other geochemical indicators in paleoenvironmental studies of two Arctic systems erosion by ice (St. John and Krissek, 2002; Eldrett et al., 2007), quantitative and stable isotopic analysis of calcareous nannofossils and microfossils (Shackleton et al., 1984; Gard, 1993; Jakobsson et al., 2001), quantitative analysis of fossil ice-dependent diatoms (Stickley et al., 2009), ice-dependent ostracodes (Cronin et al., 2010), and driftwood (Häggblom, 1982). Inorganic chemistry studies have also been applied for the same purpose and even for the study of modern changes in Arctic environmental conditions, like the analyses of manganese and other elements that indicate past and modern changes in redox conditions in the Arctic Ocean (Jakobsson et al., 2000; Gobeil et al., 2001). sub-arctic peat plateaus (Sannel and Kuhry, 2009), peat humification as a measure of climate-sensitive organic decay (Blackford and Chambers, 1995), testate amoebae as a surface moisture proxy (Mitchell et al., 2008; Booth, 2010), and the analyses of pollen (van Geel and Aptroot, 2006). Peat and its components have also been analyzed for stable isotopes, mainly carbon and oxygen (Ménot-Combes et al., 2002). Results from stable isotopic analyses in sub-Arctic and Arctic peat deposits and other soils are still few (Zech et al., 2008; Kaislahti Tillman et al., 2010b, 2010a). Lipid biomarkers have more recently been analyzed in peat for reconstructions of past environmental conditions (Ficken et al., 1998; Baas et al., 2000; Nott et al., 2000; Pancost et al., 2002; Bingham et al., 2010). Not many studies have reported the analyses of lipid biomarkers in Arctic soils (Zech et al., 2010). Most of the geochemical proxy-climate research in peatlands has been carried out in northern Europe. Paleoreconstruction studies in peatlands and soils in the Arctic region merit more geochemical work. In recent years it is important to note the advances introduced with the increasing use of a molecular stratigraphic approach based on the analyses of lipid biomarkers for the study of the Arctic Ocean (Belicka et al., 2002; Yamamoto and Polyak, 2009; Belt et al., 2010), sometimes also combined with other modern techniques of elemental analyses like X-ray fluorescence scanning (XRF) (Sluijs et al., 2009). 1.3. Lipid biomarkers Brassell (1992) defines biomarkers as organic molecules occurring in geological materials (e.g., sediments, petroleum, coals) that possess structures that record their biological origin. They can be indicators of a broad group of organisms or of a specific genus or species and are relatively resistant to degradation (Brocks and Pearson, 2005). Biomarkers are therefore considered molecular fossils that can give important insights on the origin of organic matter (OM) and help in the reconstruction of past climate. Biomarkers may be many different kinds of molecules that can be studied in terms of the chemical or biochemical transformations of biological precursors to geological products (Brassell et al., 1986). During this transformation some structures may be intact, revealing their biological source, but others may be modified. This latter case reflects an important characteristic of biomarkers: the capacity to be related to their original biosynthetic forms by understanding their chemical alteration pathways (Brassell, 1992). Fig 6. Rogovaya. Summer 2007 (Photo: Rina Andersson). With regard to the study of peat, peat bogs are the most studied systems for reconstruction of past climate and environmental conditions (Barber, 1993; Chambers et al., 2011). These ombrotrophic bogs are totally dependent on precipitation for their supplies of nutrients and water. These systems are therefore particularly sensitive to climate change. Traditionally, the most common methods and techniques for palaeoclimate reconstruction in peat include plant macrofossil analyses (Hughes and Barber, 2004), whichalso been applied in studies of 7 Rina A. Andersson many different biological input sources like algae, bacteria and vascular plants that contribute to generate a complex assemblage of molecular species that accumulate with time. However, in all cases, biomarkers can potentially give evidence for their origin because they are particular components of specific biological sources. The discovery of new biomarkers makes it possible to distinguish between archaeobacteria (e.g. methanogens), other prokaryotes (e.g. bacteria) and eukaryotes (e.g. algae and vascular plants) (Brocks and Pearson, Fig 7. Plant epicuticular waxes organize as crystals. Wax on the surface of an Arabidopsis stem © Goodman and Samuels, http://www.botany.ubc.ca/people/lsamuels.html 1.3.1. Biomarkers: origin and degradation Biomarkers analyzed for the most common paleoreconstruction studies derive from membrane lipids of bacteria, algae or the epicuticular waxes of plants. Studies of climate reconstructions based on peat largely relay in the plant waxes. In the case of peat, different plant materials contribute to the formation of peat, notably the Bryophytes. However, vascular plants like Betula trees, or Ericaceae dwarf shrubs thrive in their acidic soils (Vitt, 2006). Plant-derived biomarkers typically include long-chain n-alkanes, n-fatty acids and n-fatty alcohols. However, lipids derived from microbial biomass like phospholipids and lipopolysaccharides can be abundant in soil lipids (Hedges and Oades, 1997). 5 µm Fig 8. Crystals of epicuticular waxes in Ericaceae (Barthlott et al., 1998) © W. Barthlott. In complex marine environments like the Arctic Ocean, biomarkers in sediments may originate from 8 5 µm Fig 9. Crystals of epicuticular waxes in mosses (Barthlott et al., 1998) © W. Barthlott. 2005). The preservation of OM depends in general on several factors. Organic matter must ‘escape’ oxidation and remineralization, avoid microbial alteration in aerobic or anaerobic processes, and survive the chemical and physical changes involved in the burial processes that can modify or degrade OM (Brassell, 1992). In arctic peatlands, factors like water-logged anoxic conditions and cold temperatures contribute to the accumulation and preservation of organic matter (Moore and Basiliko, 2006). In lakes and oceans the degradation of dead biomass proceds rapidly in the water column and continues in the surface layers of the sediments and just a small amount of the biological production of OM escapes remineralization and accumulates (Hedges and Oades, 1997). After millions of years most lipids undergo structural rearrangements and the products are geologically more stable hydrocarbon skeletons. In palaeoreconstruction studies it is important to note that in peat as in marine sediments, lipids represent just a small percentage of the total organic matter (Hedges Lipid biomarkers and other geochemical indicators in paleoenvironmental studies of two Arctic systems and Oades, 1997; Baas et al., 2000), and because of the processes described above, lipids may not completely represent the conditions that prevailed during organic matter production and deposition.Therefore, it is important to use them in a complementary way with other proxies. In spite of this, lipid biomarkers have been proved to be good palaeoenvironmental tools, and their use is constantly increasing. peat, Paper II deals exclusively with those results. All papers dealing with the study of peat included analyses of plant macrofossil residues because they proved to be a very good support to the molecular stratigraphy. On the other hand, the results of the marine molecular stratigraphy described in Paper IV, were accompanied by elemental X-ray fluorescence (XRF) core scanning. In order to establish a chronological framework, radiocarbon dates were obtained from bulk peat or selected plant macrofossil samples. For the analyses of marine sediments the chronological framework was based on radiocarbon dating of the shells of the planktonic foraminifera Neogloboquadrina pachyderma. More information is included below about experimental procedures for analyses of lipid biomarkers. Details regarding the methodology followed for elemental, isotopic and macrofossil rests analyses, can be found in the papers. 1. Methods Papers I, III and IV included in this work are in general focused on the use of lipid biomarkers as palaeoenvironmental proxies. However, for the support of the peat and marine biomarker records, those studies include elemental and stable isotopic C and N compositions from bulk organic matter. In the analysis of permafrost ASE free lipids Bond Elut® DCM/MeOH Aminopropyl bonded silica Al2 O3 Hexane Hydrocarbon Hexane/DCM Acid fraction el. 2% acid in diethyl -ether Aromatic neutral fraction el. DCM/ isopropanol DCM Ketone/wax BF3 in BuOH DCM/MeOH Alcohol Butyl-esters MeOH CH3 (CH2 )3 OOC(CH2 )nCH3 1% TMCS Polar GC/MS Fig 10. Workflow diagram followed for the analyses of lipid biomarkers in peat. 9 BSTFA TMS ethers GC/MS (CH3)3SiO(CH2)nCH3 Rina A. Andersson 2.1. Preparation of lipid biomarkers for analysis by GC/MS The approach for the analyses of biological markers in this study was to fractionate and assess the freely extractable amounts of n-alkanes, n-alkanoic acids, nalkanols, n-alkan-2-ones and sterols. During the experimental analyses of lipid biomarkers in peat and marine sediments, the freeze-dried samples were extracted using organic solvents (organic compounds dissolve better in organic solvents). All samples were extracted in an automated solvent extractor (ASE) used dichloromethane (DCM) and methanol (MeOH). ASE groups or to be further purified before being analyzed by gas chromatography-mass spectrometry (GC-MS). Figure 11 shows a workflow diagram followed for the analyses of peat samples that describes the general procedure from the extraction of lipid extracts until analyzable compounds were obtained. Figure 12 shows the general workflow diagram used in the analyses of lipid biomarkers in marine sediments. These experimental procedures are based on the works of Hallman et al. (2008), Nierop and Jansen (2009), van Dongen (2008) and Nott et al. (2000). 2. Results The main results reported in the papers included in this thesis are summarized in this section. DCM/MeOH Paper I Impacts of paleohydrological changes on n-alkane biomarker compositions of a Holocene peat sequence in the eastern European Russian Arctic. free lipids SiO2 Hexane Hydrocarbon Fig 11. Workflow diagram followed for the extraction and preparation of n-alkanes for GC-MS analyses for marine sediments. However, the lipid extracts (dark brown for peat and yellow for marine sediments) usually contain highly complex mixtures with thousands of compounds. In order to simplify further analyses, the lipid extracts were separated into fractions with different polarity by column chromatography or solid phase extraction (SPE). Some fractions were derivatized to remove polar functional 10 This paper is inspired by the pioneering publication of Ficken K, Barber K. and Eglington G. (1998). It is well accepted that plant macrofossil stratigraphy can provide the history of the succession of plant communities in a peat sequence and as a consequence, the history of the paleohydrological conditions that have influenced those assemblages because many plant communities have adapted to specific peatland environments based on the relative position of the water table level (Barber, 1993; Rydin et al., 2006). At the same time, important advances have been made in using biomarkers as proxies for plant inputs to peat environments (Baas et al., 2000; Nott et al., 2000; Pancost et al., 2002) and to associate changes in past vegetation to environmental changes (Pancost et al., 2003; Nichols et al., 2006; Nichols et al., 2009; Bingham et al., 2010). In this paper we analyze n-alkane biomarkers of a peat plateau deposit in the Northeast European Russian Arctic and compare the molecular record to the plant macrofossil stratigraphy to assess the effects of Lipid biomarkers and other geochemical indicators in paleoenvironmental studies of two Arctic systems past hydrology on the molecular compositions. The radiocarbon age analyses showed that the peat profile accumulated over approximately 9 kyr, and according to the macrofossil rests it recorded a succession of vegetation changes until the onset of permafrost in the late Holocene marked a transition from a wet fen to a relatively dry peat bog. The molecular stratigraphy suggested that the contribution of the n-C31 homologue from the rootlet layers of Betula - rich in fine and dark roots- to the n-alkane compositions is important and has to be taken into consideration in paleoreconstruction studies based in n-alkane analyses. We also found that the Paq and n-C23/n-C29 proxies commonly used in the reconstruction of past water table can lead to wrong interpretations in the assessment of past moisture at depths where Betula and Sphagnum fuscum are present in the profile. Both are types of plants that can thrive in drier conditions and are abundant in the n-C23 and n-C25 homologues, giving therefore high values for the Paq and n-C23/n-C29 proxies with a consequent false interpretation of the past water table. Finally, we also observed that the average chain length (ACL) provides a relatively reliable record of changes in moisture availability, giving the highest values at depths where vascular plants dominated under drier conditions. Paper II Elemental and isotopic carbon and nitrogen records of organic matter accumulation in a Holocene permafrost peat sequence in the East European Russian Arctic In this paper we continued exploring the same permafrost peat sequence as in Paper I, but this time our aim was to get more insights regarding past C and N cycling and try to characterize the effects of environmental changes on organic matter preservation. For this purpose, bulk elemental and isotopic compositions were used in combination with analyses of plant macrofossil residues. According to the macrofossil analyses peat initially accumulated in a wet fen that after the onset of perma- frost transformed into a peat bog in the late Holocene (~2,500 cal a BP). The geochemical proxies indicated that total organic carbon (TOC) and total nitrogen (N) contents were different in the bog peat and the fen peat, with lower values in the moss-dominated bog peat layers. The results show low concentrations of total hydrogen (H) associated with degraded vascular plant residues. The atomic ratios of bulk elemental parameters, H/Ca and C/Na, proved to be good indicators of the origin of organic matter and the dominant mechanisms of N allocation due to changes in vegetation. The results also suggest that mosses have a higher capacity than vascular plants to accumulate N and confirm that OM derived from mosses is more resistant to degradation than OM derived from vascular plants (Turetsky, 2003). Bulk isotopic compositions show positive shifts in both δ15N and δ 13C values concurrent with the onset of permafrost and the consequent frost heave of the fen peat. This change in the environment resulted in vegetation changes and aerated the underlying fen peat. Differences observed in δ13C values appear to be associated mainly with changes in the succession of vegetation rather than diagenesis, whereas δ15N values suggest N isotopic fractionation could probably have been driven by microbial decomposition. The presence of permafrost in the peat plateau stage and water-saturated conditions at the bottom of the fen stage appear to have resulted in better preservation of organic plant material. Paper III Effects of climate changes on delivery and degradation of lipid biomarkers in a Holocene peat sequence in the Eastern European Russian Arctic In this paper we continue analyzing the permafrost peat profile described in Papers I and II, but this time we analyzed distributions and abundances of n-alkanols, n-alkanoic acids, n-alkanes, n-alkan-2-ones and sterols 11 Rina A. Andersson in order to have more insights regarding the effects of degradation on their palaeoclimate proxy information. Our study showed surprising results. The pattern described by the n-alkanoic acid content is more complex than the patterns found in the n-alkane and n-alkanols abundances, probably as a consequence of the input of vascular roots and degradation effects. Our results confirm that these biomarkers are more sensitive to modification and degradation than n-alkanols and n-alkanes (Meyers and Ishiwatari, 1993). The abundances and kinds of the originally deposited n-alkanoic acids seem to be augmented and modified during diagenesis. Our results suggest that n-alkanoic acids can also be incorporated as secondary products from other lipid components. We also found that the values of the carbon preference index (CPI) of these biomarkers show different trends. The n-alkanoic acids and n-alkanols display a pattern that tends to increase with depth towards the fen peat area, while the n-alkane CPI trend diminishes with depth. The stanol/stenol ratio suggests together with n-alkanes CPI values progressive degradation of biomarkers in this system with depth. All these features are evidence of the complexity of the processes that take place during humification, and we discuss some of them in this paper. We also analyzed n-alkan-2-ones in this peat sequence. Our observations suggest that n-alkan-2-ones appear to be produced by a combination of oxidation of n-alkanes and decarboxylation of n-alkanoic acids. The ratios ketmax/F.A. and ket/alkmax that we use here as proxies for degradation of organic matter seem to record microbial activity in the rootlet layers of the bog peat. The abundances and distributions of all the biomarkers analyzed in this study described a complex history about their origin and degradation and show the importance of considerating microbial diagenesis and the input of roots in the interpretation of the lipid biomarker information. 12 Paper IV Organic matter delivery to Quaternary sediments of Amundsen Basin, central Arctic Ocean In this paper we analyzed the n-alkane compositions of a short marine core retrieved from the Lomonosov Ridge. In recent years several reports suggested high abundances of terrigenous derived organic matter in the Arctic Ocean (e.g. Stein et al., 2004; Benner et al., 2005; Yamamoto and Polyak, 2009). The aim of this paper was to study changes of terrigenous influx of organic matter with time. The molecular stratigraphy data was accompanied by stable isotopic and elemental analyses that include X-ray fluorescence (XRF) core scanning. The first challenge in this work was to establish an age model. According to radiocarbon analyses, this core may cover approximately the last 27,000 years. However, given the paucity of enough amounts of calcareous foraminifera in the marine core, there is a high uncertainty regarding the use of a proper age model. This implies that this core may not extend to the Last Glacial Maximum (LGM, ~20 000 years BP) but rather would yield an age of about 13 000 years BP at 30 cm core depth, given the reported ages of other marine sediments in the Lomonosov Ridge. Organic and inorganic geochemical parameters explored in this study provided complementary paleoenvironmental perspectives for the study of the delivery and deposition of marine sediments from the central Arctic Ocean. The n-alkane distributions and abundances of the vascular plant homologues suggest increased terrestrially derived organic matter with depth. These results are reinforced by the C/N ratios that suggested a mixed terrestrial and marine source with more terrestrial influx in the older section of the core and the estimations of the terrigenous fractions derived by N/C ratios (Perdue and Koprivnjak, 2007). The combination of organic and inorganic geochemical perspectives is shown to be a valuable tool in paleoenvironmental studies. Lipid biomarkers and other geochemical indicators in paleoenvironmental studies of two Arctic systems 4. Discussion and future studies 4.1. Arctic permafrost peat. The results of Papers I, II and III give just a small insight at a molecular level, on the complexity of the responses of an ecosystem under different environmental changes. However, peatland ecosystems are by themselves very complex systems that merit much scientific work from the community of geochemists. In terms of the use of lipid biomarkers as palaeoenvironmental proxies, there is an urgent issue to solve: the vegetation in Arctic peatlands has not yet been fully characterized in terms of their lipid compositions. Very few are the reports of lipid biomarker compositions of Arctic vegetation (e.g. Zech et al., 2010) and this impose serious limitations for palaeoclimate studies based on lipid biomarkers. Most biomarker studies have been focused in the analyses of vegetation of peatlands in Northern Europe and recently in Asia (e.g.Baas et al., 2000; Huang et al., 2011). Also important to note is that until now almost all lipid biomarker studies for palaeoclimate reconstruction purposes relay on the input of vegetation, however, the biodiversity in peatlands is enormous and little is known for example of the role of fungi in peatland ecosystems and their possible biomarker inputs. This is important because these organisms are probably the principal decomposers in peatlands (Thormann et al., 2002) and it has been suggested that they assume a more dominant role than bacteria in this sense (Thormann, 2006). Important to mention is that almost all peatland plants are mycorrhizal (Thormann et al., 1999), i.e., fungi and roots of vascular plants form mutualistic associations and we do not know yet clearly their input in terms of lipid compositions in peat material. More work focused in the biomarker inputs of roots and fungi is necessary. Methane (CH4) production in high latitude peatlands has been an issue of great concern because increments in CH4 fluxes from northern peatlands can trigger future climate. In terms of biomarkers there have been important progresses in this area. Archeal lipids seem to be promising biomarkers in studies of methane cycling (e.g. Pancost et al., 2011). In this area, biomarker work in permafrost peatlands has been conducted (Wagner et al., 2005) and more work is needed. Finally, it is worth to mention that until now, most of the palaeoclimate reconstruction research based on lipid compositions of peat material has been carried out in raised bogs (e.g. Pancost et al., 2002; Nichols et al., 2006). However, the Arctic peatland landscape is more complex, most of the Canadian and Russian Wetlands are bogs and fen peatlands. Furthermore, now days thermokarst ponds become more commonly found features in these regions when permafrost collapse (Oksanen et al., 2001). These other systems in the peatland landscape need more geochemical studies in order to better understand how peatlands in their complexity respond to climate changes. 4.2. Marine sediments from the Arctic Ocean The results reported in paper IV show just a glimpse of the high complexity of the carbon cycle in the Arctic Ocean. This region has very large shelves and receives enormous inflows of riverine discharges that together with complex circulation patterns for ice and water make difficult to specify the sources and processes that affect OM (Belicka et al., 2002; Stein et al., 2004). In the central Arctic Ocean the influx of terrigenous OM is strong and there are high abundances of dissolved organic carbon (DOC) in surface waters (Benner et al., 2005) even though this is a region with reduced productivity. However, the central Arctic Ocean is not a desert. According to Gosselin et al. (1997), the central Arctic supports an active biological community that contributes to a dynamic carbon cycle in the surface waters. In terms of the use of lipid biomarkers as palaeoenvironmental tool it is a challenge to differentiate marine productivity from terrigenous influx. The analyses of sterols have helped in the understanding of the role of marine productivity in the Arctic Ocean (e.g. Belicka et al., 2002) and the analysis of glycerol dialkyl glycerol tetraethers (GDGTs) combined with other paleoceanographic proxies show promising results in this region (Yamamoto and Polyak, 2009) but more work needs to 13 Rina A. Andersson be done. Other important challenge to face in paleoceanographic studies of this region is the discontinuous occurrence of calcareous fossils. Calcareous fossils in general help to establish the chronology through their radiocarbon content and their lack hinders paleoclimatic investigations (Backman et al., 2004). In this regard, important advances have been done in the study of Antarctic sediments by using molecular-level radiocarbon dating, specifically fatty acid ages (Ohkouchi et al., 2003; Ohkouchi and Eglinton, 2008). This approach could potentially be applied to sediments of the Arctic Ocean. 5. 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Acknowledgements I want to thank my supervisor Magnus Mörth for the support during all the time we worked together. Thank you so much Magnus for making things happen, for the freedom I had to decide important things and for your complete engagement with my work. It is fantastic to work with you. I also had the privilege to work with Phil Meyers. I just think with deep gratitude of you Phil. The last two years of working with you have been quite fruitful. We worked so well together! I have learned a lot from you and not only science. What a great blessing to work with you! I also want to thank Martin Jakobsson 16 Thormann, M.N., Currah, R.S. and Bayley, S.E. 2002. The relative ability of fungi from Sphagnum fuscum to decompose selected carbon substrates. Canadian Journal of Microbiology 48: 204-211. Turetsky, M.R. 2003. New frontiers in bryology and lichenology: The role of bryophytes in carbon and nitrogen cycling. 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Zech, M., Zech, R., Zech, W., Glaser, B., Brodowski, S. and Amelung, W. 2008. Characterisation and palaeoclimate of a loesslike permafrost palaeosol sequence in NE Siberia. Geoderma 143: 281-295. Zech, M., Andreev, A., Zech, R., Müller, S., Hambach, U., Frechen, M. and Zech, W. 2010. Quaternary vegetation changes derived from a loess-like permafrost palaeosol sequence in northeast Siberia using alkane biomarker and pollen analyses. Boreas 39: 540-550. for the unexpected opportunity to work with marine issues and for the good collaboration. How much I have learned in this last year thanks to you! I also want to thank those scientists (most of them I have never met) that answered my e-mails full of questions (sometimes big questions, sometime little ones). It was quite important for me because in this way I learned several things that slowly helped me to construct this work. First of all I have to thanks Guido Wiesenberg because his first e-mail was like a light that helped me to see more clearly the big challenge I had before me regarding the work with biomarkers. I also want to thank Håkan Rydin and Prof.Riks Laanbroek because they kind- Lipid biomarkers and other geochemical indicators in paleoenvironmental studies of two Arctic systems ly answered all my e-mails full of questions in areas I am most ignorant. Thanks to Michael Perdue, Simon Belt, Yongsong Huang, Appy Sluijs and Leonid Polyak. I also want to thank the people in the Department of Geological Sciences, especially Eve Arnold and Alasdair Skelton. I think with especial gratitude and happiness of two incredible girls that helped me to live the everydayworking-in-the-lab more easily: Klara Hajnal and Heike Sigmud. Thanks a lot to Monica Rosemblom and all the anonymous heroes that helped me and other students indirectly with their work and their words to the construction of all projects in the Department: Arne, Anders, Björn, Dan, Carina, Elisabeth. I also want to thank Patrick Crill for giving me the opportunity to work in 17 this Department and Volker Brüchert for the good discussions we had. Regarding people in other institutions of SU, I want to thank Peter Kuhry for the collaboration and for making possible the summer trip to Russia in 2007. Thanks to Örjan Gustaffson that allowed me to use some equipment in ITM necessary for my experimental work and to Yngve Zebühr for his help. With love and deep gratitude I want to thank all my dear family and friends in Mexico, Santo Domingo and Stockholm. Thank you, for your love and prayers for me and the good wishes regarding my life and work in these last 5 years. Sustinuit anima mea in Domino. Mariam, sedes sapientiae ad te confugi.