dissertation from the department of geological sciences no. lipid biomarkers and other

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 2012Department of Geological Sciences

Stockholm UniversityS-106 91 Stockholm

Sweden

A Dissertation for the degree of Doctor of Philosophy in Natural Sciences

Department of Geological SciencesStockholm UniversityS-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 2012ISBN: 978-91-7447-382-7Cover: Russian arctic plants in summer 2007Printed 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 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), 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.

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, November 2011Rina 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. Methods2.1. 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...................................................................................................

Page

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678

10

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14

1313

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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

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).

5

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 (Photo: Martin Jakobsson).

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 tempera-

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 sediments

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

Fig 5. Arctic sea ice (Photo: Martin Jakobsson).

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 nutrients 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-Arctic and Arctic 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 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).

7

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 biomarkers 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.

9

free lipidsASEDCM/MeOH

Acid fraction el. 2% acid in diethyl -ether

BF3 inBuOH

CH3(CH2)3OOC(CH2)nCH3

Butyl-esters

GC/MS

DCM/ isopropanolneutral fraction el.

Al2 O3

Hexane

Hexane/DCM

DCM

DCM/MeOH

MeOH

Hydrocarbon

Aromatic

Ketone/wax

Alcohol

Polar

BSTFA

1% TMCSTMS ethers

(CH3)3SiO(CH2)nCH3

GC/MS

Bon

d E

lut® 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 n-alkanes, n-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. ResultsThe main results reported in the papers included in

this thesis are summarized in this section.

Paper IImpacts 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

ASEDCM/MeOH

HexaneHydrocarbon

SiO2

past 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/N

a, 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,

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 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 inorganic geochemical perspectives is shown to

be a valuable tool in paleoenvironmental studies.

12


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

13

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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16

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 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 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. Mari-am, sedes sapientiae ad te confugi.

17


dissertation from the department of geological sciences no. lipid biomarkers and other

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