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
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
recon-struction studies can shed light on the understanding of past climates and are a key to the
predic-tion 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
be-cause 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
biomark-ers, 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
anal-ysis of lipid biomarkers in both peat and marine profiles, combined with other
environ-mental 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
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
paleo-hydrological 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
mat-ter delivery to Quamat-ternary 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),
radiocar-bon 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.
paleoenvironmental studies of two Arctic systems:
a Russian permafrost peatland and marine sediments
from the Lomonosov Ridge.
Rina A. Andersson
Contents
1. Introduction
1.1.
Climate changes in the Arctic ...1.2.
Palaeoclimate studies in Arctic systems: traditional methods and techniques and the role of geochemistry... 1.3. Lipid biomarkers... 1.3.1. Biomarkers: origin and degradation...2. Methods
2.1. Preparation of lipid biomarkers for analysis by GC/MS...
3. Summary of results
3.1. Paper I... 3.2. Paper II... 3.3. Paper III... 3.4. Paper IV...
4. Discussion and future studies
4.1. Arctic permafrost peat... 4.2. Marine sediments from the Arctic Ocean...
5. References...
6. Acknowledgements...
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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
1.1. Climate changes in the Arctic
The Arctic is a key part of the global climate sys-tem 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 con-tents 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 Holo-cene (around 10,000 years ago), seasonal Arctic sea ice was strongly reduced with periods of ice-free summers (Jakobsson et al., 2010).
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 vari-ability. Instead, they are probably associated with the warming of global air surface temperatures as a conse-quence of fossil fuel burning (Lemke et al., 2007).
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).
Fig 2. Arctic sea ice in the Lomonosov Ridge area
Rina A. Andersson
Ice reduction has in turn other implications for tem-perature 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 tures in Alaska and Siberia with permafrost tempera-tures 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 hasten-ing degradation of permafrost can transform it into a carbon source.
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 ap-proaches to gain a better understanding about how the Arctic responds to climate changes are to study differ-ent records contained in ice cores, in marine sedimdiffer-ents and in peat. Below is a short description of some tradi-tional methods and techniques used for palaeoclimate reconstruction in the study of Arctic systems. Impor-tant to note is the great development introduced by re-cent geochemical techniques, especially stable-isotope and organic biomarker techniques.
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 ox-ygen 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 3. North of the tree line near the Rogovaya River
in the Eastern European Russian Arctic. Summer 2007 (Photo: Rina Andersson).
Fig 4. Rogovaya in the northeastern European
Rus-sian Arctic. Summer 2007 (Photo: Rina Andersson).
6
erosion by ice (St. John and Krissek, 2002; Eldrett et al., 2007), quantitative and stable isotopic analysis of cal-careous 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 environ-mental 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).
In recent years it is important to note the advances introduced with the increasing use of a molecular strati-graphic approach based on the analyses of lipid bio-markers 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 tech-niques of elemental analyses like X-ray fluorescence scanning (XRF) (Sluijs et al., 2009).
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
depend-ent on precipitation for their supplies of nutridepend-ents and water. These systems are therefore particularly sensi-tive to climate change. Traditionally, the most common methods and techniques for palaeoclimate reconstruc-tion in peat include plant macrofossil analyses (Hughes and Barber, 2004), whichalso been applied in studies of
sub-arctic peat plateaus (Sannel and Kuhry, 2009), peat humification as a measure of climate-sensitive organic decay (Blackford and Chambers, 1995), testate amoe-bae 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 isotop-ic analyses in sub-Arctisotop-ic and Arctisotop-ic peat deposits and other soils are still few (Zech et al., 2008; Kaislahti Till-man 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;
Bing-ham 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.
1.3. Lipid biomarkers
Brassell (1992) defines biomarkers as organic mole-cules 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 spe-cies and are relatively resistant to degradation (Brocks and Pearson, 2005). Biomarkers are therefore consid-ered molecular fossils that can give important insights on the origin of organic matter (OM) and help in the re-construction of past climate. Biomarkers may be many different kinds of molecules that can be studied in terms of the chemical or biochemical transformations of bio-logical precursors to geobio-logical 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).
Rina A. Andersson
1.3.1. Biomarkers: origin and degradation
Biomarkers analyzed for the most common paleo-reconstruction 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, no-tably the Bryophytes. However, vascular plants like
Bet-ula 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 bio-mass like phospholipids and lipopolysaccharides can be abundant in soil lipids (Hedges and Oades, 1997).
In complex marine environments like the Arctic Ocean, biomarkers in sediments may originate from
many different biological input sources like algae, bac-teria and vascular plants that contribute to generate a complex assemblage of molecular species that accumu-late with time. However, in all cases, biomarkers can potentially give evidence for their origin because they are particular components of specific biological sourc-es. The discovery of new biomarkers makes it possible to distinguish between archaeobacteria (e.g. methano-gens), other prokaryotes (e.g. bacteria) and eukaryotes (e.g. algae and vascular plants) (Brocks and Pearson,
2005).
The preservation of OM depends in general on sev-eral 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 Basi-liko, 2006). In lakes and oceans the degradation of dead biomass proceds rapidly in the water column and con-tinues in the surface layers of the sediments and just a small amount of the biological production of OM es-capes remineralization and accumulates (Hedges and Oades, 1997). After millions of years most lipids un-dergo 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
5 µm
Fig 9. Crystals of epicuticular waxes in
mosses (Barthlott et al., 1998) © W. Barthlott.
5 µm
Fig 8. Crystals of epicuticular waxes in
Ericaceae (Barthlott et al., 1998) © W. Barthlott.
8
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
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 im-portant to use them in a complementary way with oth-er proxies. In spite of this, lipid biomarkoth-ers have been proved to be good palaeoenvironmental tools, and their use is constantly increasing.
1. Methods
Papers I, III and IV included in this work are in general focused on the use of lipid biomarkers as palaeoenvi-ronmental 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
peat, Paper II deals exclusively with those results. All papers dealing with the study of peat included analy-ses 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, ra-diocarbon dates were obtained from bulk peat or se-lected 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 re-garding the methodology followed for elemental, isotopic and macrofossil rests analyses, can be found in the papers.
Fig 10. Workflow diagram followed for the analyses of lipid biomarkers in peat.
free lipids
ASE DCM/MeOH
Acid fraction el. 2% acid in diethyl -ether BF3in BuOH CH3(CH2)3OOC(CH2)nCH3 Butyl-esters GC/MS DCM/ isopropanol neutral fraction el.
Al2O3 Hexane Hexane/DCM DCM DCM/MeOH MeOH Hydrocarbon Aromatic Ketone/wax Alcohol Polar BSTFA 1% TMCS TMS ethers (CH3)3SiO(CH2)nCH3 GC/MS B on d E lu t® Aminopropyl bonded silica
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 alkanes, alkanoic acids, n-alkanols, 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 com-pounds dissolve better in organic solvents). All samples were extracted in an automated solvent extractor (ASE) used dichloromethane (DCM) and methanol (MeOH).
However, the lipid extracts (dark brown for peat and yel-low for marine sediments) usually contain highly com-plex mixtures with thousands of compounds. In order to simplify further analyses, the lipid extracts were sepa-rated into fractions with different polarity by column chromatography or solid phase extraction (SPE). Some fractions were derivatized to remove polar functional
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 pro-cedure from the extraction of lipid extracts until ana-lyzable 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.
Paper I
Impacts of paleohydrological changes on n-alkane
biomarker compositions of a Holocene peat
se-quence in the eastern European Russian Arctic.
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 com-munities in a peat sequence and as a consequence, the history of the paleohydrological conditions that have influenced those assemblages because many plant com-munities have adapted to specific peatland environ-ments 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 environ-ments (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 Rus-sian Arctic and compare the molecular record to the plant macrofossil stratigraphy to assess the effects of
Rina A. Andersson
10
Fig 11. Workflow diagram followed for the extraction and preparation of
n-alkanes for GC-MS analyses for marine sediments.
free lipids ASE DCM/MeOH Hexane Hydrocarbon
SiO
2past hydrology on the molecular compositions. The radiocarbon age analyses showed that the peat profile accumulated over approximately 9 kyr, and accord-ing 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 stratigra-phy suggested that the contribution of the n-C31 homo-logue 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 paleorecon-struction 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 mois-ture 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) pro-vides 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 com-bination with analyses of plant macrofossil residues.
According to the macrofossil analyses peat initially ac-cumulated 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 lay-ers. The results show low concentrations of total hydro-gen (H) associated with degraded vascular plant resi-dues. 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
on-set 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 prob-ably have been driven by microbial decomposition.
The presence of permafrost in the peat plateau stage and water-saturated conditions at the bot-tom of the fen stage appear to have resulted in better preservation of organic plant material.
Paper III
Effects of climate changes on delivery and
degra-dation of lipid biomarkers in a Holocene peat
se-quence 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,
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 de-scribed 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 con-firm that these biomarkers are more sensitive to modi-fication 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 re-sults suggest that n-alkanoic acids can also be incorporat-ed 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 hu-mification, 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-al-kanes and decarboxylation of n-alkanoic acids. The ra-tios ketmax/F.A. and ket/alkmax that we use here as prox-ies 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.
Paper IV
Organic matter delivery to Quaternary sediments of Amund-sen 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. How-ever, given the paucity of enough amounts of calcare-ous foraminifera in the marine core, there is a high un-certainty 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 sedi-ments in the Lomonosov Ridge.
Organic and inorganic geochemical parameters ex-plored in this study provided complementary paleoenvi-ronmental 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 terres-trially 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 in-flux in the older section of the core and the estimations of the terrigenous fractions derived by N/C ratios (Per-due and Koprivnjak, 2007). The combination of organ-ic and inorganorgan-ic geochemorgan-ical perspectives is shown to be a valuable tool in paleoenvironmental studies.
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 environmen-tal changes. However, peatland ecosystems are by them-selves 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 veg-etation (e.g. Zech et al., 2010) and this impose serious limitations for palaeoclimate studies based on lipid bio-markers. Most biomarker studies have been focused in the analyses of vegetation of peatlands in Northern Eu-rope and recently in Asia (e.g.Baas et al., 2000; Huang
et al., 2011).
Also important to note is that until now almost all li-pid 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 de-composers 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). Im-portant 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 fu-ture climate. In terms of biomarkers there have been im-portant 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 fea-tures in these regions when permafrost collapse (Ok-sanen et al., 2001). These other systems in the peatland landscape need more geochemical studies in order to better understand how peatlands in their complexity re-spond 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 produc-tivity. However, the central Arctic Ocean is not a desert. According to Gosselin et al. (1997), the central Arctic supports an active biological community that contrib-utes to a dynamic carbon cycle in the surface waters. In terms of the use of lipid biomarkers as palaeoenvi-ronmental 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 paleoceano-graphic proxies show promising results in this region (Yamamoto and Polyak, 2009) but more work needs to
be done.
Other important challenge to face in paleoceanograph-ic 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 investiga-tions (Backman et al., 2004). In this regard, important advances have been done in the study of Antarctic sedi-ments by using molecular-level radiocarbon dating, spe-cifically fatty acid ages (Ohkouchi et al., 2003; Ohkouchi and Eglinton, 2008). This approach could potentially be applied to sediments of the Arctic Ocean.
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6.
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
for the unexpected opportunity to work with marine is-sues 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 ques-tions (sometimes big quesques-tions, 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 be-cause his first e-mail was like a light that helped me to see more clearly the big challenge I had before me re-garding the work with biomarkers. I also want to thank
Håkan Rydin and Prof.Riks Laanbroek because they kind-Rina A. Andersson
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 everyday-working-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 con-struction of all projects in the Department: Arne,
An-ders, Björn, Dan, Carina, Elisabeth. I also want to thank Patrick Crill for giving me the opportunity to work in
this Department and Volker Brüchert for the good discus-sions 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.
