Download Dissertation from the Department of Geological Sciences No. Lipid

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.
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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
16
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281-295.
Zech, M., Andreev, A., Zech, R., Müller, S., Hambach, U., Frechen,
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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.