Download Compositional clues to sources and sinks of terrestrial

Compositional clues to sources and sinks of terrestrial
organic matter transported to the Eurasian Arctic shelf
Emma Sofia Karlsson
Doctoral thesis
Environmental Science and Analytical Chemistry (ACES)
Stockholm University
Stockholm, 2015
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© Emma S. Karlsson, Stockholm University 2015
Cover photo by Emma Karlsson after photos by Alexander Charkin and Oleg Dudarev
ISBN: 978-91-7649-195-9 pp.1-40
Printed by Holmbergs, Malmö, Sweden 2015
Distributed by the Department of Environmental Science and Analytical Chemistry (ACES)
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Muostakh Island coastal ice complex 2008, photo by Alexander Charkin
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ABSTRACT
The amount of organic carbon (OC) present in Siberian Arctic permafrost soils is estimated at twice the
amount of carbon currently in the atmosphere. The shelf seas of the Arctic Ocean receive large amounts
of this terrestrial OC from Eurasian Arctic rivers and from coastal erosion. Degradation of this landderived material in the sea would result in the production of dissolved carbon dioxide and may then add
to the atmospheric carbon dioxide reservoir. Observations from the Siberian Arctic suggest that transfer
of carbon from land to the marine environment is accelerating. However, it is not clear how much of the
transported OC is degraded and oxidized, nor how much is removed from the active carbon cycle by
burial in marine sediment.
Using bulk geochemical parameters, total OC, 13C and 14C isotope composition, and specific molecular
markers of plant wax lipids and lignin phenols, the abundance and composition of OC was determined in
both dissolved and particulate carrier phases: the colloidal OC (COC; part of the dissolved OC),
particulate OC (POC), and sedimentary OC (SOC). Statistical modelling was used to quantify the relative
contribution of OC sources to these phases. Terrestrial OC is derived from the seasonally thawing top
layer of permafrost soil (topsoil OC) and frozen OC derived from beneath the active layer eroded at the
coast, commonly identified as yedoma ice complex deposit OC (yedoma ICD-OC). These carbon pools are
transported differently in the aquatic conduits. Topsoil OC was found in young DOC and POC, in the river
water, and the shelf water column, suggesting long-distance transport of this fraction. The yedoma ICDOC was found as old particulate OC that settles out rapidly to the underlying sediment and is laterally
transported across the shelf, likely dispersed by bottom nepheloid layer transport or via ice rafting.
These two modes of OC transport resulted in different degradation states of topsoil OC and yedoma ICDOC. Terrestrial CuO oxidation derived biomarkers indicated a highly degraded component in the COC. In
contrast, the terrestrial component of the SOC was much less degraded. In line with earlier suggestions
the mineral component in yedoma ICD functions as weight and surface protection of the associated OC,
which led to burial in the sediment, and limited OC degradation. The degradability of the terrestrial OC
in shelf sediment was also addressed in direct incubation studies. Molecular markers indicate marine OC
(from primary production) was more readily degraded than terrestrial OC. Degradation was also faster in
sediment from the East Siberian Sea, where the marine contribution was higher compared to the Laptev
Sea. Although terrestrial carbon in the sediment was degraded slower, the terrestrial component also
contributed to carbon dioxide formation in the incubations of marine sediment.
These results contribute to our understanding of the marine fate of land-derived OC from the Siberian
Arctic. The mobilization of topsoil OC is expected to grow in magnitude with climate warming and
associated active layer deepening. This translocated topsoil OC component was found to be highly
degraded, which suggests degradation during transport and a possible contribution to atmospheric
carbon dioxide. Similarly, the yedoma ICD-OC (and or old mineral soil carbon) may become a stronger
source with accelerated warming, but slow degradation may limit its impact on active carbon cycling in
the Siberian Shelf Seas.
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SVENSK SAMMANFATTNING
Organiskt kol lagrat i permafrostjordar i Sibiriska Arktis uppskattas till två gånger den mängd kol som just
nu finns i gasform i atmosfären. En stor del av detta kol transporteras från land till de intilliggande
kusthaven via stora floder, och genom erosion av flodbankar och kuster. Nedbrytning av detta terrestra
material skulle leda till bildning av koldioxid i havet, som i sin tur kan bidra till ökad mängd koldioxid i
atmosfären. Enligt studier ökar dessutom mängden landmaterial som transporteras till kusthaven i
Sibirien. Det är dock oklart hur mycket av materialet som bryts ned och oxideras till koldioxid, och hur
mycket som istället lagras och begravs i marina sediment.
Med hjälp av geokemiska parametrar - organisk kolhalt, kolisotopsammansättning 13C and 14C, och
specifika biomarkörer i bladvaxer och ligninfenoler - undersöktes sammansättningen av organiskt kol i
både lösta och partikulära bärarfaser: i kolloider (en del av det lösta organiska kolet), i partiklar och i
sediment. Statistisk modellering användes för att kvantifiera de relativa bidragen av organiskt kol i dessa
tre faser. Organiskt material från land kommer i huvudsak från det översta permafrostlagret som tinar
varje sommarsäsong (ytjord) och ifrån fryst material med stor isvolym under det aktiva lagret som
eroderas vid flodbankar och kuster och kallas yedoma. De här två varianterna av landbaserat kol
transporteras olika i den akvatiska miljön. Ytjord återfanns i löst och partikulärt kol både i Lenafloden
och i ytvattnet över kusthavet, vilket tyder på att ytjordsmaterial transporteras långa sträckor i ytvatten.
Yedoma återfanns i den partikulära fasen i vattnet, men endast nära land, och dominerade istället
ytsediment, vilket tyder på att yedoma också transporteras långra sträckor lateralt, men troligen via
bentisk transport eller genom infrysning och förflyttning i havsis.
De olika transportvägarna verkar resultera i olika stadier av nedbrytning. Ligninfenoler indikerade en
högst nedbruten komponent i kolloidfraktionen, som dominerades av ytjordsmaterial. I kontrast visade
samma markörer en mycket mindre nedbruten komponent i sediment, som domineras av yedoma. I
linje med tidigare förslag verkar mineraler i yedoma fungera som vikt och skydd mot nedbrytning till det
associerade kolmaterialet. Yedoma sjunker ut ur vattenkolonnen och begravs, och undergår sedan
begränsad nedbrytning i sedimentet. Nedbrytbarhet av yedoma undersöktes också genom inkubationer
av sediment. Molekylära markörer visade att materialet från marin produktion bröts ned i högre grad än
terrestert material. Nedbrytningen var också snabbare i sediment från Östsibiriska havet där den marina
fraktionen var högre än i sediment från Laptevhavet. Även om den terrestra komponenten bröts ned
saktare bidrog terrestert material till bildandet av koldioxid under nedbrytningen i inkubationerna.
De här resultaten bidrar till vår förståelse av vad som händer med landmaterial som transporterats till
havet från det Sibiriska Arktis. Mobiliseringen av ytjord förväntas öka i omfattning i samband med
klimatuppvärmning och fördjupad upptining av permafrost. Ytjordsmaterial var nedbrutet, vilket tyder
på att det bryts ned under (och/eller innan) transport. Ökad frisättning av detta material kan leda till
ökad halt koldioxid i atmosfären. På liknande sätt kan större mängder yedoma frisättas till havet med ett
varmare klimat, men begränsad nedbrytning av yedoma i sediment kan begränsa dess eventuella
omvandling till koldioxid i de Sibiriska kusthaven.
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ABBREVIATIONS and DEFINITIONS
carrier phases
COC
cryosphere
CPI
δ13C
Δ14C
DOC
ESAS
freeze-locked
GC-MS
HMW
ICD
LMW
OC
PF
Pleistocene
POC
SOC
topsoil OC
thaw-remobilized
TN
yedoma
The physical forms that facilitate the transport of OC (COC, and POC)
Colloidal organic carbon part of dissolved organic carbon pool that is
between 0.7 µm and 1 000 Dalton in size
The part of Earth in which water is frozen, e.g. permafrost, glaciers
Carbon preference index, tracer of terrestrial origin and degradation
Conventionally defined stable carbon isotope ratio - 13C to 12C
Conventionally defined radiocarbon isotope ratio - 14C to 12C
Dissolved organic carbon
East Siberian Arctic Shelf
Inaccessible to cycling due to being frozen, generally refers to material in
long-term permafrost deposits
Gas chromatography – mass spectrometer
High molecular weight
Ice complex deposit, see yedoma
Low molecular weight
Organic carbon
Permafrost
Geological epoch, between 2.6 million to 11 700 years ago
Particulate organic carbon
Sedimentary organic carbon, a particulate phase that has settled out
The relatively young surface layer of permafrost soils that is seasonally
thawed, part of the active layer
Exposed to active cycling, and has previously been freeze-locked
Total nitrogen
Organic-rich mineral-associated permafrost soil with high content of ice,
often in form of ice wedges, also called ice complex deposit, of late
Pleistocene to mid Holocene ages
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CONTENTS
ABSTRACT ..................................................................................................................................................... 4
SVENSK SAMMANFATTNING ....................................................................................................................... 5
ABBREVIATIONS and DEFINITIONS .............................................................................................................. 6
My CONTRIBUTION to the papers ............................................................................................................... 9
OBJECTIVES ................................................................................................................................................. 10
1. INTRODUCTION ...................................................................................................................................... 12
Cryosphere and freeze-locked carbon ................................................................................................... 12
Terrestrial matter in the aquatic environment ..................................................................................... 14
2. METHODS ............................................................................................................................................... 14
Study area ............................................................................................................................................... 14
Sample collection ................................................................................................................................... 15
Analytical work ....................................................................................................................................... 16
Bulk geochemical composition tools ................................................................................................... 16
Monte Carlo simulation in end-member mixing model analysis......................................................... 17
Molecular geochemical composition tools ......................................................................................... 18
Closed system incubations of sediment in microcosm ........................................................................ 19
3. RESULTS and DISCUSSION ...................................................................................................................... 22
Source apportioning of terrestrial OC ................................................................................................... 22
Transport and transportability .............................................................................................................. 25
Degradation state and degradability ..................................................................................................... 27
4. CONCLUSIONS ........................................................................................................................................ 30
5. PERSPECTIVES on FURTHER RESEARCH ................................................................................................. 31
Preservation of yedoma ICD-OC ............................................................................................................ 31
Role of oxygen ..................................................................................................................................... 31
Sorption of OC ..................................................................................................................................... 31
Heterogeneity and Hydrology ................................................................................................................ 32
Spatial and temporal coverage .............................................................................................................. 32
ACKNOWLEDGEMENTS .............................................................................................................................. 33
REFERENCES ................................................................................................................................................ 36
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List of PAPERS
Paper #1
Carbon isotopes and lipid biomarker investigation of sources, transport and degradation of
terrestrial organic matter in the Buor-Khaya Bay, SE Laptev Sea. Biogeosciences, 8, 1865–1879,
2011, doi:10.5194/bg-8-1865-2011. © Author(s) 2011. CC Attribution 3.0 License. Published by
Copernicus Publications on behalf of the European Geosciences Union.
Karlsson, E.S., A. Charkin, O. Dudarev, I. Semiletov, J. E. Vonk, L. Sánchez-García, A. Andersson, and
Ö. Gustafsson
Paper #2
Contrasting regimes for organic matter degradation in the East Siberian Sea and the Laptev Sea
assessed through microbial incubations and molecular markers. Published in Marine Chemistry,
170, 11-15, 2015, doi:10.1016/j.marchem.2014.12.005. 0304-4203/© 2014 Elsevier B.V. All rights
reserved.
Karlsson, E.S., V. Brüchert, T. Tesi, A. Charkin, O. Dudarev, I. Semiletov, and Ö. Gustafsson
Paper #3
Different sources and degradation state of dissolved, particulate and sedimentary organic matter
along the Eurasian Arctic coastal margin
Karlsson, E.S., J. Gelting, T. Tesi, B. van Dongen, I. Semiletov, A. Charkin, O. Dudarev, Ö. Gustafsson
(submitted manuscript)
Paper #4
Contrasting sources of dissolved and particulate organic matter along 62N-72N in the Siberian Arctic
Lena River
Karlsson, E.S., B. van Dongen, I. Semiletov, A. Charkin, O. Dudarev, Ö. Gustafsson (manuscript)
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My CONTRIBUTION to the papers
I, Emma S. Karlsson, contributed to the papers included in this thesis through the following:
Paper #1
Performed the laboratory work after the 2008 sampling campaign was planned and carried out
by colleagues. Interpreted the data and wrote the paper in close collaboration with the co-authors.
Paper #2
Had a major role in planning the experimental setup of incubations. Carried out the laboratory
work. Interpretations were done in collaboration with the co-authors. Had the main role in writing
the paper.
Paper #3
Performed a substantial part of the laboratory work, but the 2008 sampling campaign was planned
and carried out by colleagues. Interpretations of the data were done in collaboration with the coauthors. Took the leading role in writing the paper.
Paper #4
The 2008 sampling campaign was planned and carried out by colleagues. Prepared the samples for
analysis. Data interpretations were done in collaboration with the co-authors. Took the lead on
writing the paper.
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OBJECTIVES
The overall aim of this thesis was to improve our understanding of the sources and sinks of terrestrial
OC released from the Eurasian Arctic landscape to the adjacent shelf seas. Specifically the objectives of
the thesis were to determine:
I)
The sources of OC: What is the bulk and molecular geochemical composition of the major
carbon carrier phases, colloidal, particulate and sedimentary OC? This was investigated with
plant wax lipid and CuO oxidation reaction product biomarkers. What are the relative
contributions of the major terrestrial OC sources, topsoil OC and yedoma ICD-OC to these
carriers in the recipients, the Lena River and Eurasian Arctic shelf? This was quantified
through a dual carbon isotope, δ13C and Δ14C, end-member mixing model analysis.
II)
Transport modes: How far is topsoil OC and yedoma ICD-OC transported and is it dispersed
over the shelf? This was investigated by comparing the geochemical source proxies in the
different carrier phases of OC in the water column and in the underlying sediments in a
spatial context.
III)
Degradability: What is the degradation state and degradability of topsoil OC and yedoma
ICD-OC in the colloidal, particulate and sedimentary OC in different shelf sea areas and
regimes? This was investigated through molecular degradation state proxies and relative
degradation rates derived from closed system microcosm incubations.
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Figure 1. Schematic representation of carbon cycling processes in the Arctic shelf seas.
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1. INTRODUCTION
Cryosphere and freeze-locked carbon
Thaw release of long-frozen cryosphere carbon is one of the few processes potentially moving large
amounts of carbon from land to the atmosphere, on decadal to centennial time scales, as a response to
raised greenhouse gases (such as carbon dioxide and methane) concentrations. Such releases may
represent the largest future transfer of OC from the biosphere to the atmosphere (Koven et al., 2011).
More than a fifth of the world´s terrestrial area is underlain by permafrost. Most of this is situated in the
high Arctic and northern Siberia (Brown et al., 1997, Heginbottom et al., 1984, 2002; Figure 2). The
estimated amounts of organic carbon (OC) stored in these deposits are vast (~1100-1500 Pg; Tarnocai et
al., 2009; Hugelius et al., 2014). The dominant portion of this carbon is stored in perennially frozen
ground (~800 Pg), but a large share (~500 Pg) is repeatedly thawed and refrozen as part of the active
layer dynamics during seasonal cycling (topsoil). At the same time, these thermally vulnerable regions
are also experiencing global warming at an amplified strength (ACIA, 2004; Jefferies et al., 2014; Tingley
and Huybers, 2013; IPCC, 2013) causing dramatic changes in the cryosphere landscape.
Riverbanks and shorelines are subject to erosional processes which can be dramatically accelerated
through parallel climate warming induced effects. A longer ice free season, increased wave fetch, more
frequent storms and raised sea water temperatures (Barnhardt et al., 2014, Stroeve et al., 2014; IPCC,
2013) can act in concert to enhance erosion. Some coastlines – e.g. those dominated by ice rich
permafrost – are particularly vulnerable to such processes (Lantuit et al., 2011; 2012). These coastlines
exhibit very high erosional rates, five to seven times faster than ordinary permafrost coastlines. This
translates to annual shoreline retreats between 0.5 and 10 m (Grigoriev et al., 1993, 2004; Rachold et
al., 2004; Lantuit et al., 2011, 2012; Günther et al., 2013) and thus release of late Pleistocene carbon to
the marine environment (e.g., Vonk et al., 2012; Sanchez-Garcia et al., 2014).
The seasonal dynamics of the active layer in permafrost soils, the top part of the upper meter of a
permafrost landscape, which thaws each summer, can release OC in episodic or abrupt events, for
instance, through the formation of thermokarst lakes and ground subsidence. Thermokarst lakes are
thaw-depression lakes that form from meltwater when underlying ice disappears. In areas of sporadic or
isolated permafrost, deepening of the active layer also leads to lateral shrinkage. Areas of discontinuous
permafrost are therefore more vulnerable to warming and thus anticipated to disappear first
(Osterkamp et al., 1999).
In a frozen soil environment, microbial communities are without water, and thawing therefore releases
one of the physical constraints to microbial (or photochemical) degradation (Rothman et al., 2007).
Previously freeze-locked permafrost OC is thus potentially exposed to decomposition and a possible
subsequent conversion to greenhouse gases. The estimated feedback of permafrost OC to the
atmosphere ranges between 7 and 500 Pg by the year 2100 (Schaefer et al., 2011; MacDougall et al.,
2012; Schneider von Deimling et al., 2012).
There is often a decoupling between permafrost thaw location and site of emission (Vonk and
Gustafsson, 2013), and processing of old thaw-remobilized OC can take place at many niches in the
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landscape, and during transport (Fig. 1). Lateral transport of thaw-remobilized old permafrost OC is
highly dependent on the hydrological cycle, since water is the major vector for its transport. Although
transport can be wind-driven, aeolian deposition of terrestrial OC is comparatively small over the
Eurasian Arctic shelf (Shevchenko and Lizitsin, in Stein and MacDonald, 2004). The hydrological cycle has
also been predicted and observed to undergo marked changes with climate warming, such as increased
precipitation and runoff (Dickson et al., 2000; Peterson et al., 2002; Serreze et al., 2003). Peterson et al.
(2002) for example report a 7% increase in average annual river discharge between 1936 and 1999 from
six large Eurasian Arctic rivers. In a study of daily flow data from 111 northern rivers, Smith et al. (2007)
suggest an increase of groundwater supply as part of the reason for observed increased river discharge
rates reaching at least back to ~1985. They propose this to be a combined effect of the increase in
declined seasonal ground freezing and precipitation.
Permafrost thaw and remobilization processes are difficult to monitor off site, and remote sensing
techniques often have poor coverage at high latitudes, too low resolution, or are simply insensitive to
permafrost processes. Due to the high heterogeneity, local studies are also hard to upscale for
describing processes on a pan-Arctic scale. Therefore many questions remain about the northern
Siberian Arctic systems which, due to the harsh environments and the extensive areas, are inaccessible
and understudied.
Continuous PF (90-100%)
Discontinuous PF (50-90%)
Sporadic PF (10-50%)
Isolated PF (<10%)
No permafrost
Yedoma
Figure 2. Circum-Arctic permafrost coverage. Data from Brown et al, 1998.
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Terrestrial matter in the aquatic environment
One way to handle the large heterogeneities of the Eurasian Arctic landscape is to use an inverse
approach: to study the fate of land derived material through the signal of terrestrial OC in the recipient
aquatic environment. Terrestrial OC is transferred to the aquatic systems via streams, rivers, and erosion
of coastlines directly to the seas. We view the streams and adjoining shelf waters as integrators of
processes in their drainage basins, as well as potential reactors of the terrestrial OC. By studying
terrestrial OC in the aquatic environment, we learn about land processes on a broader scale.
The seas contain a mixture of terrestrial and marine OC, which creates a need for distinguishing
between these pools when studying the terrestrial OC. Although the fate of terrestrial OC on the
continental shelves has long been an active area of research, general discrepancies remain in closing the
marine OC budgets. While marine OC is often considered more reactive than terrestrial OC, marine OC
accounts for most of the sequestered OC in sediments (Burdige, 2005; Julies et al., 2010; Bianchi, 2011).
In other words, there has been a missing sink of terrestrial OC in the marine compartment (Hedges et
al., 1997). There are, however, growing indications of major portions of recalcitrant (unreactive and slow
or unlikely to degrade) terrestrial OC being recycled upon entry in shelf waters (Keil et al., 1997; Aller
and Blair, 2004).
This thesis comprises studies of molecular degradation and source apportionment of terrestrial OC in
the Siberian Arctic marine system through a range of geochemical tools. Radiocarbon age, for instance,
is a vital tool for distinguishing between carbon from modern biological processes, and long freezelocked Pleistocene carbon. Throughout this thesis we generalize and refer to the old mineral-associated
permafrost soil components from beneath the active layer as either yedoma ice complex deposits (ICD;
Fig. 2) in the eastern Siberian Arctic, or deep permafrost OC in the western part of the study area. The
aforementioned contemporary component of terrestrial OC is referred to as topsoil OC. Molecular
proxies are used to trace the terrestrial matter and identify the provenance of various OC pools. By
combining these tools, we seek to improve the current understanding of terrestrial OC as it passes over
the land-ocean interface. This, we hope, will lead to a more detailed picture of mechanisms that act to
mediate the potential transfer of OC from the biosphere to the atmosphere in the Arctic.
2. METHODS
Study area
The Eurasian Arctic continental shelf is the widest and shallowest of the world’s continental shelves
(Stein and Macdonald, 2004). It reaches from the Kara Sea in the west at 50°E, past the Laptev Sea and
the East Siberian Sea after which it meets the Pacific Ocean water near 165°E. Extending several
hundred km offshore it has a water column depth of only 50 m on average (Jakobsson et al., 2008). The
Eurasian Arctic shelf water receives fresh water and organic matter from several great Arctic rivers such
as the Ob, Yenisey, Khatanga, Lena, Yana, Pechora, Indigirka and Kolyma Rivers. The Lena River is one of
the largest rivers and its discharge is found far east as the major coastal currents and the Lena River
discharge plume flow predominantly eastwards via the Dmitry Laptev Strait (Steele and Ermold, 2004;
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Semiletov et al., 2005). River discharge mix with material from coastlines of the East Siberian Sea and
Laptev Sea that to varying extents are comprised of yedoma ice complex deposits (ICD) extensively
eroded during the open water season (Grigoriev et al., 1996; Lantuit et al., 2012; Günther et al., 2013).
Sample collection
The sample set used in this thesis was a collection of samples from the International Siberian Shelf
Study. The main campaign was a 45 day expedition on the R/V Yakob Smirnitskyi in 2008 (ISSS-08;
Semiletov and Gustafsson, 2009). There were three sub-campaigns to the ISSS-08. One conducted in the
Buor-Khaya Bay on-board the R/V TB0012. One on-board the R/V Orlan in the Lena River delta area, and
one on-board the passenger ship M/S Mechanic Kubilin along the main stem of the Lena River from
Yakutsk to the Lena Delta. The samples used for the thesis work include mainly three phases of organic
carbon and thus three types of samples: i) sediment, ii) particles from surface water and iii) colloidal
matter from surface water. The sum of the carbon in the water column derived from unfiltered water, is
referred to as the total OC (TOC) and is a combination of the dissolved, and particulate matter (Fig. 3).
The colloidal pool is part of the dissolved pool, and sediment is the deposited particulate pool.
Figure 3. Schematic relationship between
different OC compartments. Total OC (TOC)
consist of dissolved OC (DOC) and particulate
OC (POC). DOC is divided into truly dissolved
OC, and colloidal OC (COC). These pools are
operationally defined by sampling methods.
Sedimentary OC (SOC) is deposited POC found
on lake- or sea-floors.
Surface sediment samples were collected with a Van Veen grab sampler and used for paper #1, #2 and
#3. The top three centimetres were subsampled with stainless steel spatulas from the collected grab
samples and stored frozen in plastic containers. Samples were either freeze-dried for molecular analysis
(paper #1 and #3), or used wet in incubation studies (paper #2).
Particulate matter samples were retrieved through filtration of surface water (0-4 m depth) onto GF/F
filters and used in paper #1, #3 and #4. GF/F is a type of glass fibre depth filter with a nominal cut-off of
0.7 µm. Sample sizes of up to 1000 L were GF/F filtered to allow molecular and isotopic analysis on the
collected particles (high-volume GF/F filtration; Fig. 4). Particulate matter samples were freeze-dried
before analyses (paper #1, #3 and #4).
Filtrate from GF/F was filtered further onto membrane filters with a much smaller cut-off, at 1000 D.
This method is referred to as cross flow filtration (CFF), tangential flow or ultrafiltration. The material
collected is referred to as the colloidal pool or the high molecular weight dissolved pool. Through CFF
you collect a concentrated fraction of material in a smaller volume of water, typically 0.5 to 1 L (called
retentate) with concentration factors above 10. Colloidal samples were desalted (paper #3) and freezedried (paper #3 and #4) before analyses (Fig. 4).
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Figure 4. Photographs of sample types in this thesis. Colloidal OC (COC) in polycarbonate bottles during
two stages of freeze-drying, and particulate OC (POC) on GF/F filters in the stainless steel filter holder
used for sampling.
Analytical work
The samples chosen for this thesis were analysed with bulk and molecular geochemical tools – organic
carbon content, nitrogen content, stable carbon and radiocarbon isotopes, plant wax lipid and CuO
oxidation product biomarkers. The theory and use of these analytical methods as well as their main
limitations and value to this work are described in this section. An overview of the data collection and
type of analysis done on which type of OC compartment is found in table 1. The biomarkers include a
range of proxies which are given as an overview in table 2 and 3, where each proxy, its abbreviation(s),
source(s), main function(s) and common use can be found.
Bulk geochemical composition tools
Bulk measures represent combined values from sometimes quite different sources, but often give a
good indication of contributing sources or the dominant traits in mixed OC pools. Therefore, bulk
measures were considered in both colloidal, particulate and sedimentary samples through this work.
After freeze-drying and removal of inorganic carbon via acidification, samples were analysed for organic
carbon content (TOC, or often only OC), total nitrogen content (TN) and stable carbon isotopes (δ13C) at
either the Stable Isotope Facility at the University of California Davis (Davis, CA, USA) or at the Stable
Isotope Laboratory (SIL) at the Department of Geological Sciences, Stockholm University (IGV,
Stockholm, Sweden).
Organic carbon content was used through this work to normalise biomarker proxies, since this is the
fraction of the total carbon pool that many chemically hydrophobic markers such as lignin phenols and
plant wax lipids partition into. (In contrast, acids, bases and metals, with stronger polarity are better
16
represented on the dry weight basis). The ratio between TOC and TN reflects the relationship between
two of the three major constituents in living matter (phosphorus is the third, C:N:P; Redfield, 1959),
differing among organism groups. Higher terrestrial plants exhibit C/N ratios over 20 while marine
plankton commonly have C/N ratios of ~4-10 (Hedges et al., 1986; Meyers, 1994), although microbial
degradation can sometimes preferentially remove nitrogen from an OC pool. Therefore the C/N ratio
was used in conjunction with other proxies to distinguish terrestrial from marine sources. If samples
exhibit low OC content, are very sandy or clayey, interpretations of an OC/TN ratio have to be done with
regards to a potential inorganic nitrogen component in mind (Schubert and Calvert, 2001).
The stable carbon isotope 13C comprises 1.1% of all C on Earth, but the proportion of the stable isotope
13
C incorporated into an organism compared to the 12C isotope varies and can provide information on
different sources and processes. Fractionation, the preferential uptake or loss of 13C over 12C, occurs
during many biological processes, such as carbon dioxide uptake by plants during photosynthesis,
formation of marine carbonates, microbial degradation and photo-oxidation of organic matter. The ratio
of 13C/12C is expressed as δ13C (and measured in ‰). Typical values of δ 13C with respect to the standard
(Pee Dee Belemnite, PBD) were used in this thesis for source apportionment of different OC pools. A
non-capitalized delta is used for δ 13C because it refers to a standard that does not change, in contrast to
the capitalized delta in Δ14C, which is used because it refers to a changing value – atmospheric
concentration at time of sampling (Coplen, 2011).
Radiocarbon isotope Δ14C value is also a strong carrier of information, and was used in this work for
identification of reservoir ages and transport times, as well as for distinguishing old and contemporary
carbon pools. Samples for radiocarbon analysis were acidified for removal of inorganic carbon and sent
to the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility at Woods Hole
Oceanographic Institution (WHOI, Woods Hole, MA, USA). Frequent swab tests are performed in the
laboratory facilities were these samples were handled to prevent and avoid contamination. Age
estimates are derived through quantifying the amount of the radiocarbon isotope 14C remaining in a
sample compared to the concentration in the atmosphere at the time of sampling. Radiocarbon dating is
limited to 60 000 years back since the estimate builds on the half-life of 14C (~5 000 years). Older
material is said to be 14C-dead, and contemporary material is called modern if close to that of the
atmospheric levels in 1950 (as defined by the oxalic acid standard). Samples in this thesis ranged from
modern to 11 000 14C years.
Monte Carlo simulation in end-member mixing model analysis
In addition to qualitative source apportionment, statistical modelling was used to quantify the two main
sources of terrestrial OC. The relative contributions of topsoil OC and yedoma ICD-OC, as distinguished
from marine OC, were estimated using an end-member mixing model analysis (EMMA). This type of
EMMA separates three sources based on two variables. In this work dual-carbon isotope values (δ13C
and Δ14C) were used. Since all end-members represent a range of values, the input variability was
accounted for by a random sampling strategy, a Monte Carlo simulation. The numerical background of
the Monte Carlo EMMA simulation is provided in Andersson (2011). EMMA was applied for sediment OC
(paper #1 and #3), particulate OC (paper #1 and #3) and for colloidal OC (paper #3).
17
Table 1. Type of analysis performed on colloidal OC (COC), particulate OC (POC) and sedimentary OC
(SOC), from the sample collection in this thesis, divided into the papers they are used in. Organic carbon
content (OC), plant wax lipid biomarkers (lipids), CuO oxidation reaction products (CuO products), stable
carbon isotopes (δ¹³C) and radiocarbon isotopes (Δ¹⁴C).
Paper #1
POC
SOC
OC
13
26
δ¹³C
14
23
Paper #2
SOC
Incubations
11
CuO products
11
Paper #3
COC
POC
SOC
OC
12
12
12
Paper #4
COC
POC
OC
10
10
Δ¹⁴C
6
8
lipids
12
22
δ¹³C
12
12
11
Δ¹⁴C
12
9
8
lipids
12
12
12
δ¹³C
10
10
Δ¹⁴C
10
10
CuO products
12
7
Molecular geochemical composition tools
Physical and biological processes leave various chemical traces in the environment and through
extraction of molecular components one can derive information on these processes. Biomarkers are
thus measurable indicators of a biological state or condition. The presence of chlorophyll for example
indicate that at some point in time (related to the chlorophyll degradation time), a photosynthetic
organism has been present, or its remains have been transported there. Each biomarker carries
constraints and is useful within certain conditions. The suitability of each biomarker molecule to provide
information has to be taken into account for each sample type and environment they are applied to.
Plant wax lipids and CuO oxidation reaction products, such as lignin phenols, are common biomarkers in
marine geochemistry. I used both lipid and lignin markers as tracers of terrestrial matter, but also to
assess relative degradation state. Both lipids and lignin represent parts of the bulk material, lipids
commonly contribute 1% and lignin phenols 2-4% of the bulk OC in marine sediments, but their stability
and specificity make them useful tools to understand terrestrial OC dynamics. The specific lipid and CuO
oxidation product biomarkers are summarized in tables 2 and 3.
The solvent extractable plant wax lipids were derived through soxhlet extraction or accelerated solvent
extraction (ASE; 24 hours in dichloromethane and methanol, 2:1, v/v) resulting in a total lipid extract
separated with regard to chemical polarities over Bond Elut and aluminium oxide columns in a workup
protocol detailed in van Dongen et al., (2008). CuO oxidation reaction products were derived in alkaline
CuO oxidation where samples were extracted under pressure and heating to 80°C in a microwave
system following Goni and Montogomery (2000). For colloidal samples CuO oxidation was done with an
18
addition of glucose to avoid superoxidation (Louchcouarn et al., 2000). Measures were taken to avoid
contamination, mainly of lipids from rubber and plastic materials, and laboratory work was performed in
pre-combusted glass ware. Both plant wax lipids and CuO oxidation reaction products were analysed on
GC-MS.
High molecular weight (HMW) lipids are constituents of epicuticular waxes of higher plants (Eglinton,
1963) and are in principal absent from marine and freshwater plankton. During synthesis in higher
plants the n-alkanes derive a predominance of odd chain lengths over even chain lengths in the range
C24-C34 at a maxima around C27, C29 or C31 (Eglinton and Hamilton, 1967; Cranwell et al., 1973; Rieley et
al., 1991). Therefore, a high abundance of HMW lipids, as well as the odd-over-even chain length
pattern called the carbon preference index (CPI; Bray and Evans, 1961), is an indication of terrestrial
matter in the aquatic environment (Farrington and Meyers, 1975). However, since the CPI decreases
during degradation (Killops and Killops, 2005), it works also as a relative degradation state marker, in
which higher indices reflect less degraded material (Table 3). Plant wax lipids were extracted for
sedimentary OC (paper #1 and #3), particulate OC (paper #1, #3 and #4) and for colloidal OC (paper #3).
Lignin is a phenolic biopolymer derived from vascular plants and not present in phytoplankton (Sarkanen
and Ludwig, 1971; Stark et al., 1989), and was thus used for tracing terrestrial matter. The alkaline CuO
oxidation also yield other products useful to trace sources and degradation state (Goni and Hedges,
1990a, b, 1995; Otto et al., 2006). Several of these products are specific to certain sources, such as
marine plankton, angiosperm tissue, herbaceous tissue and Sphagnum (Hedges and Mann, 1979;
Spencer et al., 2008; Lobbes et al., 2000; Table 3). The preferential loss of aldehydes compared to acids
is the basis to also use lignin monomers to assess relative degradation state. The evaluation is done for
the ubiquitous vanillyl and syringyl phenols through the ratio of aldehydes to acids (Ad/Al), in which
lower indices reflect less degraded matter. Alkaline CuO oxidation was performed on sedimentary OC
(paper #2 and #3) and on colloidal OC (paper #3).
Closed system incubations of sediment in microcosm
In addition to estimates of relative degradation state, laboratory based microcosm incubations were
used to compare degradability in sediments from two contrasting areas. Microcosm is an artificial
simplified system used to simulate certain properties of natural systems. These direct incubations were
a simple closed system setup to measure the evolved carbon dioxide during anaerobic degradation of
bulk sedimentary matter. Frozen sediment and artificial sea water were added to serum bottles that
were sealed and flushed with N2-gas to remove oxygen. Three serum bottles were prepared for each of
the four time points which were distributed over three weeks (initial value, 1 week, 2 weeks and 3
weeks). Part of the overlying headspace was withdrawn for injection on GC-FID to analyse the carbon
dioxide concentration. A degradation rate was calculated from the carbon dioxide increase over the
three weeks. OC pools include fast and slow OC pools that will degrade at different rates and on
different time scales, and the calculated rate from this setup was derived from a fast pool degradation.
The incubations were performed on sediment from the Buor-Khaya Bay in SE Laptev Sea and the Kolyma
paleoriver canyon in the East Siberian Sea (paper #2).
19
Table 2. Source proxies derived from plant wax lipids and CuO oxidation reaction products.
Abbreviation
HMW
n-alkanes
LMW
n-alkanes
HMW/LMW
n-alkanes
Biomarkers
Main source
Reference
High molecular weight (HMW) nalkanes, C20-C34
Low molecular weight (LMW)
n-alkanes, C17-C19
High molecular weight
n-alkanes over low molecular
weight n-alkanes
vascular plants - epicuticular plant
waxes
Eglinton and Hamilton, 1967; Simoneit 1997
marine phytoplankton, bacteria
Schubert et al., 1997
V
Vanillyl phenols
C
Cinnamyl phenols
C/V
S
S/V
P/V
Pn/P
Cinnamyl over vanillyl phenols
Syringyl phenols
Syringyl over vanillyl phenols
p-Hydroxybenzenes over vanillyl
phenols
p-Hydroxyacetophenone over pHydroxybenzenes
Cut
Cutin acids
FA
Fatty acids from CuO oxidation
DA
Dicarboxylic acids from CuO
oxidation
B
Benzoic acids from CuO oxidation
terrestrial organic matter over
marine organic matter (see HMW
and LMW n-alkanes
gymnosperm and angiosperm cell
walls
cell walls of non-woody vascular
plants
herbivore proxy - high ratio = woody
material
cell walls of angiosperms
angiosperm proxy, a low ratio =
gymnosperm (e.g. coniferous forest)
typical of sphagnum, ratio > 6, else
plankton
ratio is high in mosses; particularly
sphagnum
vascular plants - epicuticular plant
wax leaf tissue
multiple sources, relatively abundant
in phytoplankton, soil (bacteria)
multiple sources, relatively abundant
in phytoplankton, soil (bacteria)
multiple sources, relatively abundant
in phytoplankton, soil (bacteria)
Eglinton and Hamilton, 1967; Schubert et al., 1997;
Simoneit, 1997
Ertel and Hedges, 1984; Hedges et al., 1988
Ertel and Hedges, 1984; Hedges et al., 1988; Hartley, 1973
Goni et al., 2000; Stark et al., 1989; Hedges and Mann, 1979;
Sarkanen and Ludwig, 1971
Ertel and Hedges, 1984; Hedges et al., 1988; Hartley, 1973
Goni et al., 2000; Stark et al., 1989; Hedges and Mann, 1979;
Sarkanen and Ludwig, 1971
Williams et al., 1998; Amon et al., 2012
Williams et al., 1998; Amon et al., 2012
Riley and Kolattukudy, 1975; Goni and Hedges, 1990a,b
Goni and Hedges, 1995; Otto et al., 2006;
Wakeham et al., 1984
Goni and Hedges, 1995; Wakeham et al., 1984
Ertel and Hedges, 1984; Goni and Hedges, 1995; Otto and
Simpson, 2006; Williams et al., 1998
20
Table 3. Relative degradation state proxies derived from plant wax lipids and CuO oxidation reaction products.
Abbreviation Biomarkers
n-alk CPI
n-acid CPI
HMW n-alkane carbon preference index (oddover-even-pattern), chain lengths C24-C34
HMW n-alkanoic acid carbon preference index
(even-over-odd-pattern), chain lengths C20-C32
n-acids/
n-alks
HMW n-alkanoic acids over HMW n-alkanes
3,5-Bd/V
3,5-Dihydroxybenzoic acid over vanillyl phenols
Ad/Al
Acid over aldehyde ratios, both valid for syringyl
and vanillyl phenols, i.e. Sd/Sl and Vd/Vl
Main source
Reference
leaf waxes of
vascular plants
leaf waxes of
vascular plants
leaf waxes of
vascular plants
vascular plants, 3,5Bd common in soil
Bassel and Eglinton, 1983;
Fahl and Stein, 1997
Bassel and Eglinton, 1983;
Fahl and Stein, 1997
vascular plants
Comment
high index = less degraded
high index = less degraded
Brassel et al., 1984
high index = less degraded
Prahl et al., 1994
low index = less degraded
Opsahl and Benner, 1995,
1998; Amon et al., 2012
low index = less degraded
21
3. RESULTS and DISCUSSION
The results of this thesis have been structured under three main themes. Sources, transport and
degradation. These themes mirror the objectives of this work and the results are presented as a joint
summary and discussion of the combined outcome from the included papers.
Source apportioning of terrestrial OC
Source apportionment was used in this work to identify terrestrial sources contributing to OC in the
aquatic environment. The source identification was done in two ways for each of the carbon carrier
phases.
1) Qualitative assessment and comparison of source proxies to distinguish
marine from terrestrial matter.
2) Quantitative assessment of the relative contributions of the main terrestrial
sources, topsoil OC and yedoma ICD-OC, in an end-member mixing model.
Qualitative assessment. Several of the markers used to differentiate the terrestrial versus the marine
OC pools indicated a heavy terrestrial dominance in OC over the Eurasian Arctic shelf. The δ13C values in
the qualitative assessment of bulk SOC, POC and COC suggested an overall high contribution of
terrestrial OC to the entire study area, indicated by relatively depleted δ13C values (mainly between -26
and -28 ‰). These δ13C values were in accordance with other bulk and terrestrial markers, namely
relatively high OC/TN ratios, high concentrations of lignin phenols, high HMW lipid concentrations and
high HMW/LMW n-alkane ratios. The high HMW/LMW n-alkane ratio also showed terrestrial OC
consistently dominating over marine OC in both COC, POC and SOC (Fig. 5a). The terrestrial dominance
was less pronounced in the very east, where Pacific-influenced water masses meets the East Siberian
Sea; the latter having higher δ13C values. The marine signal towards the east, detected more clearly in a
larger set of δ13C data (Vonk et al., 2012) is suggestive of a mixing trend between terrestrial OC with
marine OC eastwards. However, vascular plant sources are varying east-westerly over the Laptev Sea
and East Siberian Sea shelf region seen in a changing lignin phenol S/V ratio, and confirmed by a larger
data set of CuO oxidation reaction products in SOC for the same area (Tesi et al., 2014).
The terrestrial pool was further apportioned into sources derived from two different permafrost
systems, the topsoil OC and the yedoma ICD-OC. Radiocarbon age was used to discriminate between
them revealing regional east-westerly differences. The sediment in the eastern Siberian Arctic was much
older (Δ14C ~-700‰) than in the western Kara Sea area (Δ14C ~-200‰). The distribution of older
sediment ages in the eastern Eurasian Arctic margin support other reports of the same pattern (Guo et
al., 2004; Gustafsson et al., 2011; Feng et al., 2013). The trend with increasing age toward the east was
seen also in the colloidal pool, with ages varying from modern to 850 14C-years. The colloidal pool thus
incorporates some component from older OC deposits despite being mostly modern. These regional
radiocarbon differences likely reflect the high proportion of late Pleistocene yedoma ICD-OC in the
eastern watersheds (Δ14C ~-940 ‰; Fig. 2), and the slightly younger age of deep peat deposits in the
western Eurasian Arctic (Δ14C ~-530‰; Macdonald et al., 2006).
22
Figure 5. Source markers in colloidal OC (COC; white), particulate OC (POC; green) and sedimentary OC
(SOC; black) on the Eurasian Arctic shelf from July/August 2008. A). Radiocarbon (Δ14C) over stable
carbon (δ13C) isotope values. Also plotted are the end-member values for different sources derived from
literature data. Detailed description of end-members can be found in paper #3 methods section. Briefly:
The marine plankton end-member is split into two by geographical area, thus east and west of 165°E.
Old permafrost OC is also split in two by geographical area, where yedoma ice complex deposit OC (ICDOC) exist in the eastern Siberian Arctic, but as deep peat permafrost soil (Deep-PF OC) in the western
watersheds, i.e. for Kara Sea samples. Topsoil OC is split into the carrier phases dissolved OC (DOC) and
particulate OC (POC and SOC).
23
Figure 6. Concentration of lignin phenols over
radiocarbon isotope values (Δ14C) in colloidal OC
The lignin vascular plant derived markers in the
colloidal pool were however derived from a
younger source, seen in a lignin concentration
highly associated with young bulk age (Fig 6). The
bulk geochemical markers together demonstrate a
terrestrial OC dominated aquatic carbon cycle. The
terrestrial dominance is manifested throughout the
three studied carrier phases and reflects a high
contribution from varied vascular plant sources and
a marine influence in the east
Quantitative assessment. In the end-member mixing model, topsoil OC and yedoma ICD-OC were found
in different proportions in the water column compared to the underlying sediment (paper #1, #3, and
#4). The relative contribution of topsoil OC dominated both the colloidal (66%) and particulate phase
(62%) throughout the study area, with only minimal contribution from yedoma ICD-OC and other old
permafrost (9% and 13% respectively; paper #3; Fig. 7). These relative contributions reflect the buoyant
nature of the OC suspended in the water column, and the low density of humic aggregates and
vegetation debris that are derived from upper soil horizons and surface soils part of the topsoil OC
source. In contrast to the colloidal and particulate phases in the water column, the underlying sediment
contained a smaller contribution from topsoil OC (23%), and a dominant ICD-OC contribution (54%; Fig.
7). The dominant yedoma ICD-OC fraction in sediment likely reflect the nature of its mineral component,
which gives sinking properties to the OC rather than ability to stay suspended, explaining the high
proportion of the yedoma ICD-OC at the seafloor. These results highlight partitioning of sources as
highly dependent on physical properties, and imply that source contribution in the different carrier
phases are related to its vertical and lateral transport patterns.
Figure 7. Fractional contributions of topsoil OC (grey), yedoma ICD-OC plus deep PF-OC (red) and marine
OC (blue) to colloidal OC (COC), particulate OC (POC) and sedimentary OC (SOC) on the Eurasian Arctic
shelf from July/August 2008.
24
Transport and transportability
Dispersion patterns of the carbon carrier phases were used to derive how different sources have been
transported over the study area. Transport of topsoil OC and yedoma ICD-OC are closely coupled to their
physical properties, and were found to exhibit different spatial distributions throughout the data set,
thus both in the Lena River and the Eurasian Arctic continental shelf.
Figure 8. Surface plots of Δ14C (‰) in surface water particulate OC and surface sediment OC in Buor-Khaya
Bay, Laptev Sea from July/August 2008. Coastal erosion hotspot Muostakh Island denoted via text box.
The topsoil OC was found as young OC in all surface water samples, but was of lesser relative abundance
in the underlying sediment (paper #1, and #3; compare panel a and b in Fig. 8). The presence and
dominance of topsoil OC in surface waters far out on the shelf suggest that topsoil OC is more readily
advected than yedoma ICD-OC. In parallel, the topsoil OC only contributes a small fraction to surface
sediment OC (topsoil OC is young and less depleted in Δ14C), which indicates that topsoil OC mostly stays
suspended in the water column. Therefore, its fate is affected by lateral water movement and wind
patterns. The difference in topsoil OC contribution between water column and sediment (Fig. 8) could
be a sign of decomposition, or could reflect an input of yedoma ICD-OC to the seafloor from lateral
transport. The latter is more likely since there was a strong vertical export of yedoma ICD-OC from the
surface water, as seen in high but rapidly decreasing concentrations around coastal erosion hotspots
(paper #1 and #3; Fig. 8). A vertical transport of yedoma ICD-OC is thus rapid and must happen within a
few kilometres from the source. This is particularly evident in Buor-Khaya Bay where the fraction
yedoma ICD-OC was strongly and negatively correlated with water depth (paper #1; Fig. 9a). The high
near-shore concentrations of yedoma ICD in POC suggest that yedoma ICD-OC partitions into POC, but
sinks out rapidly after entering the water (paper #1, and #3). The yedoma ICD is a mineral-carbon matrix
with high density that rapidly sinks with the associated OC out of the water column. This means that
very little yedoma ICD-OC are transported long distances over the Eurasian Arctic shelf by advection in
surface waters.
25
Figure 9. The fraction OC contributed by topsoil OC (green triangles), yedoma ICD-OC (black squares) and
marine plankton OC (blue circles) plotted over water column depth. A) Particulate OC (POC) and B)
sedimentary OC (SOC) in Buor-Khaya Bay from July/August 2008.
26
Despite the presumed rapid settling of yedoma ICD-OC from water column to sediment, the stations far
offshore (~500km) also have large shares of yedoma ICD-OC in SOC (paper #1 and #3; Fig. 9b). These
large, relatively even and dominant contributions of yedoma ICD-OC to SOC also on stations far offshore
(paper #3) suggest that ICD-OC is laterally transported and dispersed near the seafloor. Benthic or
nepheloid layer transport (near-bottom transport; Fig. 1) has previously been reported to be a strong
carrier of seafloor material over the Eurasian Arctic shelf (Are et al., 2002; Dudarev et al., 2006; Charkin
et al., 2011) and is one of two possible carriers of yedoma ICD-OC. Such a near-bottom transport
mechanism could potentially disperse a mineral-heavy fraction like the yedoma ICD-OC over the seafloor
without it being spread to the overlying particulate or suspended OC pools. Near-bottom transport is
potentially high on the Eurasian Arctic shelf due to turbidity and shallow water column depths, but there
are other lateral transport mechanisms. A possible transport pathway of yedoma ICD-OC is the
incorporation in sea ice (called ice rafting; Fig. 1). Ice rafting, suggested to partly control sediment
distribution (Reimnitz et al., 1998; Viscosi-Shirley et al., 2003), particularly in ice export from the Laptev
and East Siberian Sea (Nürnberg et al., 1994; Eicken et al., 1997, 2000), could equally result in a wide
dispersal of yedoma ICD-OC as seen in this data from the shelf area.
Degradation state and degradability
Two different approaches were used to assess degradation of OC, one through the use of molecular
biomarker proxies and the other by closed system incubations of sediment. Degradation is often closely
linked to transport pathways and properties of the source material; therefore the connections between
sources, transport and degradation are also discussed here.
The topsoil OC and ICD-OC clearly have different behaviours, regarding both transport and degradation,
once released to the shelf waters of the Eurasian Arctic. The two pools exhibit differences in degradation
state closely connected to their respective tendencies for long-range transport. Plant wax lipid markers
show a clear decoupling of degradation states between surface water OC (POC and COC) and the
underlying SOC. The terrestrial OC component is more degraded in POC than in the SOC (paper #1, and
#3; Fig. 10). Similarly, the COC is more degraded than the SOC. Degradation state markers from CuO
oxidation (3,5-Bd/V, Sd/Sl and Vd/Vl; Table 2) indicate a highly degraded state of the terrestrial COC
fraction (paper #3). Lateral transport of COC, following the surface water movement is likely faster than
the near-bottom lateral transport of SOC. A shorter time frame which allows less time for degradation,
and yet terrestrial COC is more degraded than terrestrial SOC. However, the COC is suspended in the
water column and thus greater exposure, potentially to both aerobic-microbial and photo-oxidative
processes, during lateral waterborne transport, which could explain the higher degradation state.
The SOC displayed a less degraded terrestrial signal relative to both POC and COC (paper #1, and #3).
However, around coastal erosion hotspots POC was also less degraded (Fig. 10a and c). The POC around
erosion hotspots were at the same time old, as seen in the radiocarbon data (Fig. 8a), suggesting that
the yedoma ICD-OC is less degraded. This low degradation state, and the widespread dispersal of
yedoma ICD-OC in this data set, suggests that yedoma ICD-OC is degrading less and instead rather
accumulating on the seafloor of the Eurasian Arctic shelf.
27
Figure 10. Surface distribution plots of surface water particulate OC and surface sediment OC from BuorKhaya Bay, SE Laptev Sea in July/August 2008. A) and B) high molecular weight (HMW) n-alkanoic acids
over HMW n-alkanes. B) and C) HMW n-alkane carbon preference index (CPI).
An explanation for the rapid sinking and preferential preservation of yedoma ICD-OC is the mineral
matrix supplying protection against degradation. The mineral-carbon association could be a physical
protection that prevents enzymatic cleavages of the adsorbed OC, as seen for OC on continental margins
by many (e.g. Mayer et al., 1994; Keil and Mayer, 2013). In addition, burial in shelf sediment could cause
less efficient degradation of OC (e.g. Hartnett et al., 1998), potentially delaying or halting degradation of
yedoma ICD-OC.
Degradation was directly measured through the formation of carbon dioxide, in sediment dominated by
yedoma ICD-OC in closed system incubations. Comparison of carbon dioxide formation rates in
conjunction with the molecular markers and CuO oxidation reaction products revealed two contrasting
degradation regimes. Degradation rates correlated well with molecular markers of marine OC in the East
Siberian Sea and of terrestrial OC markers in the Buor-Khaya Bay area. Furthermore, the degradation
rate was six times faster for the East Siberian Sea samples than for the Buor-Khaya Bay samples (Fig. 11).
Marine OC, generally considered to be more labile than terrestrial OC, was more abundant in the East
Siberian Sea than in the Buor-Khaya Bay. However, the difference between the marine OC fractions was
not proportional to the difference in degradation rate, i.e. there was a higher carbon dioxide formation
28
rate than predicted from the marine OC fraction in the East Siberian Sea samples. In addition, the two
shelf systems had similar geochemical signatures of terrestrial OC, suggesting that differences in
terrestrial OC composition are not the cause of the higher degradation rates in the East Siberian Sea.
The differing degradation behaviour of sediment from the two areas may be a manifestation of many
mechanisms: selective protection could favour a certain OC pool, co-metabolism (priming) could cause
loss of more refractory terrestrial OC when marine OC is readily metabolized, and/or microbial
community efficiencies could differ.
Figure 11. Results from direct incubations of surface sediment OC (SOC) from Buor-Khaya Bay, SE Laptev
Sea and Kolyma Paleoriver Canyon in East Siberian Sea in July/August 2008. A) Typical patterns of
evolved CO2 (μmol CO2 g OC−1) illustrated by station #51 in LS-Buor-Khaya Bay (anaerobic, blue
triangles), and station #36 on the East Siberian Sea Kolyma Paleoriver Canyon (aerobic, white squares
and anaerobic, blue squares). B) Evolved CO2 at four time points (T0–T3 in consecutive order; shown by
bar graphs where lightest gray is T0, darkest gray T3) during anaerobic incubation of surface sediments
from Laptev Sea-Buor-Khaya Bay and East Siberian Sea-Kolyma Paleoriver canyon on the primary axis.
Scatter plot (blue diamonds) showing the anaerobic degradation rate (μmol CO2 g OC−1 day−1) of the
same incubations on the secondary axis.
29
When taking the results in this thesis together it is clear that the two terrestrial OC sources, topsoil OC
and yedoma ICD-OC, have different fates regarding both transport and degradation over the Eurasian
Arctic shelf system. Topsoil OC appears to be degrading more during waterborne transport in COC or
POC, during river transport, or in the surface waters of the Eurasian Arctic shelf, and to some extent also
transported over long distances suspended in surface water. In stark contrast, yedoma ICD-OC settled
out in the near vicinity of its source release site, and maintained a terrestrial component (preferentially
preserved) throughout transport over the East Siberian shelf sea floor.
4. CONCLUSIONS
From the results in this thesis, a set of conclusions can be drawn regarding sources, transport and
degradation of the terrestrial matter transported to the Eurasian Arctic shelf.
 The bulk and molecular geochemical composition of all the carbon carrier phases indicate the
marine environment of the Eurasian Arctic shelf is dominated by terrestrial OC. This terrestrial
dominance is manifested throughout the three studied carrier phases and reflects a high
contribution from varied vascular plant sources, and a marine influence where the East Siberian Sea
meets Pacific influenced waters near 165°E. This terrestrial dominance suggest that other processes
in these marine environments, (e.g. primary production, gas exchanges between sediment-oceanatmosphere, inorganic carbon dynamics, pH) are influenced by the degradation and translocation of
large amounts of terrestrial OC.
 The two main terrestrial sources throughout this data set, topsoil OC and ICD-OC, are transported
differently over the Eurasian Arctic shelf system. The effect of transport of topsoil OC and yedoma
ICD-OC is seen in their distributions in the three carrier phases. The end-member mixing model
suggests that topsoil OC and yedoma ICD-OC are present in different proportions in the water
column, as opposed to the underlying sediment. These proportions indicate that yedoma ICD-OC is
accumulating on the shelf in a relatively undegraded state suggesting that the Eurasian Arctic shelf
is a sink of yedoma ICD-OC.
 The observation that topsoil OC contributes mainly to the particulate and colloidal pools suggests
that topsoil OC is transported out on the shelf in the surface water. The fact that topsoil OC is
derived from low-density humic surface horizons of the active layer, indicates that it is easily
suspended in the water column. Long range transport in surface water and exposure to UV
radiation and microbial degradation may explain the highly degraded nature of the topsoil OC. This
could imply that there is emission of carbon dioxide during the transport of topsoil OC in the rivers
and during transport to the sea. It is not clear however whether the degradation is taking place
during the transport, or close to (or at the) source site.
30
 The distinct export out of the water column, and the dominance of yedoma ICD-OC in surface
sediment far out on the shelf suggests that yedoma ICD-OC is laterally transported and dispersed
over the shelf, likely through near-bottom transport or via ice rafting. The rapid export of yedoma
ICD-OC from the water column to the underlying sediment may explain the relatively undegraded
state of yedoma ICD-OC. The mineral matrix could provide protection to the associated OC, either
through its high density causing burial in shelf sediment, or through the sorption causing physical
hindrances to enzymatic cleavage and degradation. The undegraded state of yedoma ICD-OC, and
the slower degradation of sediment that correlated to terrestrial proxies in incubations, suggest
that yedoma ICD-OC may not be a strong source of atmospheric carbon dioxide on the Eurasian
Arctic shelf. The yedoma ICD-OC may instead be contained, redistributed and/or exported off the
shelf.
 The rapid formation of carbon dioxide in the incubation experiments suggests that sediment
dominated by yedoma ICD-OC is degradable. In addition, there was a higher carbon dioxide
formation rate than anticipated from the marine OC fraction in the East Siberian Sea compared to
in Laptev Sea, proposing that the two areas have different degradation regime. Potential
explanations to the different degradation regimes could involve selective preservation, microbial
community composition or co-metabolism. In the case of co-metabolism increased primary
production could enhance degradation of terrestrial ICD-OC in Eurasian Arctic shelf sediment.
5. PERSPECTIVES on FURTHER RESEARCH
In this section I present some observations and suggestions for future work that would continue or
strengthen the results obtained in this thesis.
Preservation of yedoma ICD-OC
Role of oxygen
Oxygen exposure is known to affect degradation processes of organic matter in continental margin
sediments (Hartnett et al., 1998; Keil et al., 2004; Burdige et al., 2007), and may play a particular role in
control of yedoma ICD-OC degradation. The high density mineral-association of yedoma ICD causes it to
sink out of oxygenated water into anoxic sediment layers where degradation is less efficient. This export
and subsequent burial may (temporarily) halt or delay degradation of yedoma ICD-OC. While oxygen
penetration depths may have been studied elsewhere, it would also be a natural step in this research
area to investigate oxygen penetration depths in Eurasian Arctic shelf sediments, and relate this to
penetration depths of mineral-associated yedoma ICD. This could for example be done through oxygen
microelectrode measurements in combination with age profiles in sediment. Understanding the role of
oxygen is relevant for quantifying long term storage processes, e.g. how long the shelf may be a sink of
yedoma ICD-OC.
Sorption of OC
Mineral-association have been suggested to provide protection to OC in marine sediments (Keil et al.,
1994b, Hedges et al., 1997, Mayer, 2004). However, the actual mechanisms behind mineral-associated
protection in yedoma ICD-OC are yet to be detailed. Work could be directed specifically towards testing
31
sorption properties in organo-mineral complexes in yedoma ICD-OC, both on the Eurasian Arctic
continental margins, or as sorption mechanisms in the yedoma ICD itself. Investigations of particular
sorption phases for yedoma ICD-OC could also be done, as in Kaiser and Guggenberger, (2000) where
sorption of DOM in soils related to aluminium and iron oxyhydroxides were investigated. Perhaps
surface areas of manganese, that have been seen to provide large active surface areas in sediment, can
play a role too. Additionally, different size fractions of the particulate (and sedimentary) pool could
perhaps show different sorption properties and loading of topsoil OC and yedoma ICD-OC connected to
surface area. Sorption processes may thus speed up or slow down degradation of yedoma ICD-OC
accumulated on the Eurasian Arctic shelf.
Heterogeneity and Hydrology
The yedoma ICD itself is quite heterogeneous. Subdividing yedoma ICD into several subpools has, for
example, been done to assess differences in reactivity (Dutta et al., 2006; Zimov et al., 2006). Yedoma
ICD that comprises ice-rich permafrost of varying OC content is intersected with large ice wedges
(Schirrmeister et al., 2002). Different amounts of ice included in incubations have been observed to
induce different rates of degradation (Vonk, J. personal communication). The dry environment of frozen
soil is not favourable to processing of organic material, and the onset of melt does not necessarily result
in a wet environment, despite the conversion of ice to water. This means that since microbial
communities are dependent on suitable hydrological conditions, thawing does not necessarily induce
microbial activity. These effects of heterogeneity and hydrology in permafrost soils suggest that
sampling strategies of yedoma ICD-OC likely play an important role in trying to quantify degradation
processes, and sampling procedures should therefore be carefully designed.
Spatial and temporal coverage
This thesis has shown how composition, source, and transport of terrestrial organic material can affect
the organic carbon composition of the Eurasian Arctic shelf environment, but there are many remaining
questions regarding its long-term fate. For instance, the shelf system appears to function as a sink for
yedoma ICD-OC, but it is unclear whether yedoma ICD-OC is buried on the shelf, degraded on a longer
time scale, or exported off the shelf to the slope and central Arctic basin. Additional research to address
these questions with studies of better areal coverage and temporal resolution is needed. Longer-term
monitoring, seasonal studies, details of spring flood signatures - especially of particulate OC, winter
carbon cycling - both coupled to inland ice and sea ice dynamics, as well as interannual comparisons
would all give a better understanding of the fate of terrestrial matter transported to the Eurasian Arctic
shelf.
32
ACKNOWLEDGEMENTS
I want to start with thanking my family
Tobias och Isak! Ni är de klokaste små människor jag känner. Tack för att ni funnits vid min sida under
alla doktorandåren. Tack för att ni skällt på mig när jag varit odräglig, för att ni skrattat med mig när livet
varit tungt, och för att ni stått ut med riktigt halvdassig mat, fler dammtussar i hörnen och färre
lekstunder när tiden varit knapp. Jag är så stolt över er!
Vill också säga tack till min övriga familj. Mamma, du ställer upp massor, och vad vi har skrattat, men jag
hör på dig när du är orolig. Linus min älskade bror, och kära Frida. Pappa, som alltid blir rörd och är stolt
över mig. Birthe vid hans sida.
Tänker ofta på min morfar Bengt Gunnar Ellström som min stora saknad. Tänker att han gett mig
inspiration, nyfikenhet och lugn. Han var forskare i försvaret i Halmstad. Vi var hans ögonstenar, och han
log alltid med ögonen. Sörjer min farmor som var mig kär, och gick bort väldigt nyligen. Hon var min allra
mest frekventa barnvakt, och den jag rymde till om det behövdes. Jag lovar att fortsätta sjunga dina
sånger och ställa fram Gröna marmeladkulor.
Brett. What can I say, the only one who dared visit with some groceries when I was down with the swine
flu. You are me very dear, and what are you? My discussion partner, my computer nerd, my life
philosopher, my greatest annoyance, my most time consuming but enjoyable friend. Thank you for
taking part.
The Arctic Carbon group at my department. Julia, what words to use? I am not sure. I shared a lot with
you. Queen of gossip, queen of joy, queen of action! I totally love you. Marc – hang in there. You are
great. Henry! <3 The wise and witty - let us share more time. August! Your laughter rings in my ears.
Keep at it. Teach me play violin? I will continue sharing bird nerd stuff. Anton – office mate to trust!
Martin my dear shift mate – we did a really good job, thanks! Lisa, Tommaso, Barbara, Nina, Pete. The
SWERUS Arctic ocean expedition preparations and onboard time. Ups and downs right? What an
adventure. Thanks for sharing it with me.
All the old ITM current ACES faces. Frida, Cissi, Karin N, Hanna G, Anna S, ni har alla varit känslomässiga
bollplank åt mig. Tack! Det har hjälpt. Yngve, tack för dansant sällskap, men också för all lab-hjälp. Alla
glada ansikten i korridoren. Behöver flera rader med namn. Tack.
Jorien och Laura – solvent extractable lipids right? Thanks for teaching me! Also for chats and bits during
my first year, when life was tough.
Johan Gelting. Min tidigare rumskompanjon. Du var ovanligt artig och trevlig att ha i samma rum. Tack
för alla pratstunder om viktiga ting både utanför och i jobbet.
Michael McLachlan. You said to me: there is no need to be this sad. Words that I carry with me. Thanks
for listening all those times.
Volker – min biträdande handledare. Tack mest av allt för att du tog dig tid för min skull trots
ansökningar, undervisning och annat här på sluttampen. Det var mycket värt! Only responsible for the
science right? ;) hahaha.
33
Örjan – vad skriver man om dig? Tack för att du kallat mig rising star, tack för att du sagt att jag gått från
klarhet till klarhet. Du har varit tuff att jobba med, men jag har lärt mig en hel del. Både om sociala ting
och om hur man gör forskning. Du har lämnat efter dig stora och små minnen som jag tar med mig. Jag
har sett – du jobbar oerhört intensivt, du är familjefar till tre, och du räcker inte alltid till. Är trots alla
turer imponerad av dig – för jag tror att det är ensamt på toppen, men du gör också ett oerhört bra
jobb. Kör på positiva linjen, den behövs.
I also want to thank our Russian collaborators. Spatsiba! It has been a pleasure to learn and be inspired,
much by your field work competence. Oleg! Yikes, how many times have you been at longer
expeditions? Over 30 - I am impressed. Also - thanks for helping me with “water catastrophy” at the
SWERUS expedition. Sasha Charkin. My reliable team mate for submersible pump action. Kseniya for
Russian poetry! Igor – also the night shift ;), and thanks for pointing out Cape Emma and Cape Sofia on
Bennet island.
Malin S och Karin på kommunikationssidan. Tack så hjärtligt för att ni visar att ni uppskattat/r min
förmåga att kommunicera vetenskap. Visst är det otroligt kul.
Who did I forget? Probably a lot of people. People that meant something for me through my life. I am
not listing you all here.
I do however want to thank all my friends outside of work! Now that I have my life back I will become
visible again. Haha.  All welcome to overdose me with texts, emails, chats, late evenings, long walks,
day trips and other. - Itaí min Itaí -. Katarina och Håkan. Cecilia Lindh. Petra och Niklas. Maria och Stefan.
Therese. Susanna. Bodil. Ulrica. Johan M. Pähr H. Marc Mathison. Gabriella-papp. Jakangänget. Maarit
my dear red rog. (No doors in Finland still?)
Next to last: Raymond Pierrehumbert. Ray you inspire me – people are rarely this humble and still dare
to act with power upon the will to make change to this world. I want to - hope to, and will somehow also
do so, to the best of my ability. Golden stars and rays of sun to you! (Everyone – listen to this man).
Lastly I want to thank myself. Great job Emma. You really achieved a lot in these years. I am proud of
you.
Vänligen
/hon-som-får-saker-gjort, isbjörnsmamman, polarfararen, pemmis, super-Emma.
34
The road not taken
Two roads diverged in a yellow wood,
And sorry I could not travel both
And be one traveler, long I stood
And looked down one as far as I could
To where it bent in the undergrowth;
Then took the other, as just as fair
And having perhaps the better claim,
Because it was grassy and wanted wear;
Though as for that the passing there
Had worn them really about the same,
And both that morning equally lay
In leaves no step had trodden black.
Oh, I kept the first for another day!
Yet knowing how way leads on to way,
I doubted if I should ever come back.
I shall be telling this with a sigh
Somewhere ages and ages hence:
Two roads diverged in a wood, and I —
I took the one less traveled by,
And that has made all the difference.
35
Muostakh Island coastal ice complex in winter 2007, photo Alexander Charkin
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Bolshoy Lyakhovskiy Island, photo Alexander Charkin
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