Late Quaternary Biostratigraphy and Paleoceanography of the central Arctic Ocean MEDDELANDEN från

MEDDELANDEN
från
STOCKHOLMS UNIVERSITETS INSTITUTION
för
GEOLOGISKA VETENSKAPER
No. 345
Late Quaternary Biostratigraphy and Paleoceanography
of the central Arctic Ocean
Daniela Hanslik
Stockholm 2011
Department of Geological Sciences
Stockholm University
106 91 Stockholm
Sweden
© Daniela Hanslik, Stockholm 2011
ISBN: 978-91-7447-311-7
Cover: Sunset over the Greenland Sea © Daniela Hanslik
A dissertation for the degree of Doctor of Philosophy in Natural Sciences
Department of Geological Sciences
Stockholm University
106 91 Stockholm
Abstract
The central Arctic Ocean is one of the least explored deep sea regions and long biostratigraphic
sediment records are sparse. The main focus of this thesis is the Arctic Ocean foraminiferal record and
its application to reconstruct paleoceanographic variations and summer sea ice cover changes between
late Quaternary interglacial periods. One of the studied cores was retrieved from the central Lomonosov
Ridge Intra Basin. This core contains a relatively high-resolution biostratigraphic record spanning
Marine Isotope Stages (MIS) 1–3, although with a hiatus encompassing the Last Glacial Maximum.
Radiocarbon age calibrations in this core show a decreasing trend of high marine reservoir ages of about
1400 years during the last deglaciation to 700 years in the late Holocene. The cores from the Lomonosov
Ridge off Greenland and the Morris Jesup Rise contain preserved calcareous microfossils further back in
time than most previously studied central Arctic Ocean cores. The calcium content estimated by X-ray
fluorescence scanning of these cores shows a distinct pattern of calcium rich intervals coinciding with
peaks in foraminiferal abundance in the sediment record of MIS 1–7. The calcium peaks originate from
material accumulated during interglacials, primarily through detrital carbonate and dolomite input from
the decaying North American ice sheet and secondarily from biogenic material. Intervals of calcareous
benthic foraminifera are found in pre MIS 7 sediments on both the southern Lomonosov Ridge and
Morris Jesup Rise. Their assemblage composition and stable carbon isotope data suggest increased
primary production and decreased summer sea ice cover compared to the Holocene central Arctic Ocean.
This is also suggested for an interval with high abundance of the subpolar planktic foraminifera species
Turborotalita quinqueloba on the southern Lomonosov Ridge with a proposed MIS 11 age.
Late Quaternary Biostratigraphy and Paleoceanography
of the central Arctic Ocean
Daniela Hanslik
This thesis consists of a summary and three papers refered to as Paper I – III. The summary also
includes preliminary results and discussion dedicated for a paper in preparation.
Paper I – Hanslik, D., Jakobsson, M., Backman, J., Björck, S., Sellén, E., O’Regan, M.,
Fornaciari, E., Skog, G., 2010. Quaternary Arctic Ocean sea ice variations and radiocarbon
reservoir age corrections. Quaternary Science Reviews 29, 3430-3441. Reprinted with
permission from Elsevier.
Paper II – Hanslik, D., Löwemark, L., Jakobsson, M. Biogenic and detrital carbonate rich
intervals in central Arctic Ocean cores identified using X-Ray fluorescence spectroscopy.
Submitted to Polar Research.
Paper III – Hanslik, D., Hermelin, O. Late Quaternary benthic foraminiferal assemblages from
the central Arctic Ocean. Submitted to Marine Micropaleontology.
The work of this thesis has principally been carried out by the author. All manuscripts were
predominantly written by me with the support, suggestions and discussion of Martin Jakobsson
and Jan Backman. I conducted all work associated with foraminifera analyses. For Paper I
the calcareous nannofossil data were provided by Jan Backman and Eliana Fornaciari and the
correlation of physical properties by Emma Séllen and Matt O’Regan. Radiocarbon dating was
done by Göran Skog and Svante Björk supported the discussion of the radiocarbon results.
The XRF scanning for Paper II was conducted by Ludvig Löwemark, data analyses by me
and the manuscript written by me in close collaboration with the co-authors. Otto Hermelin
provided support and suggestions to the assemblage interpretations for Paper III. The amino
acid racemization analyses discussed in the unpublished data of this thesis was performed by
Darrel Kaufman and the results regarding these were discussed in personal communication with
him.
Stockholm, June 2011
Daniela Hanslik
The sea, once it casts its spell, holds one in its net of wonders forever.
Jacques Yves Cousteau
Contents
1. Introduction
1
1.1 Aim of this study
2
2. Background
3
2.1 Foraminifera
3
2.2 Sea ice 5
2.3 Oceanography
6
2.4 Seafloor – physiography
7
2.5 Quaternary biostratigraphy
8
2.6 Chronology and dating
8
3. Material and methods
9
3.1 Material
9
3. 2 Core and sample preparation
10
3.3 Core chronologies 11
3.4 Stable oxygen and carbon isotopes
12
3.5 X-Ray Fluorescence (XRF)
12
4. Results and Discussion
13
4.1 Paper I 13
4.2 Paper II
14
4.3 Paper III
16
4.4 Unpublished Data
17
5. Conclusions
25
6. Acknowledgements
26
7. References
26
Late Quaternary Biostratigraphy and Paleoceanography
of the central Arctic Ocean
Daniela Hanslik
Department of Geological Sciences, Stockholm University, 106 91 Stockholm, Sweden
1. Introduction
Biostratigraphy – or the use of fossils for
correlation and relative age assignments of
sediment sequences – is a widely used tool
in the field of paleoceanography. In marine
biostratigraphic studies microfossils are commonly
used to constrain or construct age models as well as
to reconstruct paleoceanographic conditions. One
of the major marine calcareous microfossil groups
in paleoceanographic studies is foraminifera,
single-celled protists that live in the upper water
column (planktic) and on the sea floor (benthic).
For example, the global stable oxygen isotope
(δ18O) record is built on analysis of calcareous
benthic foraminifera to reconstruct the global ice
volume and deep sea temperatures. This stacked
record is the product of more than forty drill sites
of the Deep Sea Drilling Project (DSDP) and
Ocean Drilling Program (ODP) and is the single
most comprehensive paleoceanographic record
encompassing the entire Cenozoic Era (Zachos
et al., 2001). A higher resolution Pliocene to
Pleistocene δ18O stack exists back to 5.3 million
years ago (Lisiecki and Raymo, 2005) defining
Marine Isotope Stages (MIS) for a common
timescale and correlation. However, no such
continuous δ18O record exists from the central
Arctic Ocean because the occurrence of calcareous
microfossils is sporadic at best in most available
sediment cores. This has large consequences
for Arctic Ocean paleoceanographic studies, in
particular it has proven to be difficult to establish
reliable age models for the retrieved cores without
a continuous biostratigraphy (Backman et al.,
2004).
The Arctic Ocean is special in many respects:
it is the smallest of the World's Oceans, almost
landlocked, covered by sea ice, wich is considered
to be of major importance for the global climate.
The effects of recent climate change are most
pronounced in the Arctic region and are expected
to be amplified compared to lower latitude areas
(Anderson et al., 2006; IPCC, 2007; Serreze and
Francis, 2006), which also holds true for the
paleorecord as recently shown by Miller et al.
(2010). The importance of the high latitudes was
also expressed by the fourth International Polar
Year 2007-2008, with active involvent of more
than 60 countries, thousands of scientists and
numerous field campaigns and projects in both
the Arctic and Antarctic region. Melting glaciers
and ice sheets (ACIA, 2004; Krabill et al., 2004;
Thomas et al., 2006; Velicogna and Wahr, 2006),
decreasing sea ice cover (Comiso et al., 2008;
Kwok and Rothrock, 2009; Serreze et al., 2007;
Stroeve et al., 2007; Wang and Overland, 2009),
rising air temperatures (Johannessen et al., 2004;
Overland and Wang, 2005), declining snow cover
(ACIA, 2004), increasing precipitation (ACIA,
2004), rising river flows to the Arctic Ocean
(ACIA, 2004) and thawing permafrost (Kuhry
et al., 2009) are some evidence for the strong
warming. A negative ice/snow albedo feedback
through replacement of high reflective surfaces
of snow and ice by vegetation and open ocean
absorbing more energy causes further warming
(Chapin et al., 2005; Perovich et al., 2008). A key
indicator for climate change in the Arctic Oceans
is the sea ice cover. It has a strong influence on
albedo, ocean currents and marine life and is in turn
sensitive to air and ocean temperature changes.
The last three decades of satellite measurements
show a decline in both the sea ice extent (Comiso
et al., 2008; Rothrock et al., 1999) and also a
loss of multi-year ice (Kwok et al., 2009; Kwok
and Rothrock, 2009) which is faster than most
climate model predictions (Stroeve et al., 2007).
The upper ocean waters in the Arctic are also
expected to be influenced by inflow of warmer
Pacific and North Atlantic water. This has been
demonstrated by models and observations in the
last decades (Gerdes et al., 2003; Polyakov et al.,
2005; Shimada et al., 2006; Woodgate et al., 2006;
Zhang et al., 1998). Episodes of intensified North
Atlantic water inflow to the Eurasian Basin during
past interglacials have been demonstrated through
the record of dinoflagellate cysts (Matthiessen et
1
180°
160°W
160°E
Mendeleev
Ridge
NP 26
Eurasian
Basin
e
dg
Ri
Ga
sin
Kara Sea
Na
n
A
80°W
100°E
Severnya
Zemlya
se
n
Am
un
ds
en
Ba
sin
B
el
Alpha
Ridge
M
ak
ar
100°W
Canadian
Arctic
Archipelago
120°E
ov
Ba
Lo
sin
m
on
os
ov
R
id
ge
Canadian
Basin
Laptev Sea
Ba
120°W
140°E
East Siberian
Sea
kk
Amerasian
Basin
Northwind
Ridge
140°W
Chukchi
Plateau
Chukchi
Sea
80°E
Morris Jesup
Rise
°
80
Greenland
°
GC-02
Novaya
Barents Sea Zemlya
Svalbard
75
60°W
Yermak
Plateau
60°E
96/12-1pc
PS2185
PC-04
HLY0503-18TC/JPC
Amundsen
40°E
Basin
40°W
Makarov
Basin
PC-06
LOMROG 07
cores
20°W
ACEX
Intra Basin
20°E
PC-07
PC-08
PS2200-2/5
GC-10
0°
A
B
Lomonosov Ridge
Figure 1 Map of the central Arctic Ocean (IBCAO, Jakobsson et al., 2008) with the main ridges and basins.
Insert A shows the position of the LOMROG 07 cores and PS2200-2/5, insert B the central Lomonosov Ridge
with the position of core HLY0503-18TC/JPC in the Intra Basin, as well as the key cores 96/12-1pc, PS2185
and ACEX on the ridge crest. The red track line indicates the HOTRAX expedition transect and the yellow
track the line covered by the LOMROG expedition.
al., 2001).
In the search for new high resolution
paleoceanographic records, icebreaker expeditions
during the last two decades have reached many
previously unexplored areas of the Arctic Ocean
and retrieved longer sediment cores than those
taken from ice islands (e.g. T-3 or CESAR). This
thesis is based primarily on studies of sediment
cores retrieved during two of these expeditions; the
Healy-Oden Trans-Arctic Expedition (HOTRAX)
2005 (Darby et al., 2005) and the Lomonosov
Ridge off Greenland Expedition (LOMROG)
2
2007 (Jakobsson et al., 2008). HOTRAX was
the first expedition to take sediment cores along
a transect across the entire Arctic Ocean from
Alaska to Svalbard while LOMROG was the first
scientific icebreaker expedition to reach the more
or less uninvestigated southern portion of the
Lomonosov Ridge of Greenland.
1.1 Aim of this study
The overall aim of this study is to provide
another piece to the puzzle of the Arctic’s
b
a
BG
TPD
d
c
0
Pacific Halocline
200
Polar Mixed Layer
-2 to 0°C <34.4 Atlantic Halocline
σ=27.9
400
Arctic Intermediate Water
Depth (m)
600
< 0°C 34.4-34.9
800
σ=32.8
1000
Canadian Basin
Deep Water
2000
3000
4000
σ=37.5
Eurasian Basin
Deep Water
-0.6 to -1.0°C
-0.3 to -0.5°C
>34.95
34.93
Bering
Strait
Alpha
Ridge
Lomonosov
Ridge
Gakkel
Ridge
Fram
Strait
Figure 2 a) Mean sea ice extent at the end of the summer season (September) 1979-2000 (yellow) and the
minimum September ice extent in 2007 (red); b) surface water circulation of the Beaufort Gyre (BG) and
the Transpolar Drift (TPD) (white), the main inflow path of the North Atlantic water (red), the Pacific water
inflow (yellow) and the intermediate water circulation (orange); c) Map with a sea level -120 m as experienced
during peak glacial times; d) profile of water stratification and the most important water masses (adopted from
Aargard et al., 1985 and Macdonald & Brewers, 1996).
Quaternary chronostratigraphy as well as
paleoclimate and paleoceanography. Some of
the studies included in this thesis use traditional
chronostratigraphic tools, such as radiocarbon
dating and biostratigraphy, which are applied,
tested and improved using new core material
(Papers I and III). Radiocarbon calibrations
are addressed in Paper I. Only with good age
models can realistic interpretations of the
paleoceanographic record be made. Furthermore,
methods such as the relative dating by amino acid
racemization, will be employed (unpublished data,
this thesis) as well as X-ray fluorescence scanning
used for identification of calcium/microfossil rich
intervals for core-to-core correlation and strategic
sub-sampling (Paper II). Foraminifera are used
as the main proxy for paleoenvironmental
interpretations of, for example the variability of
the central Arctic Oceans sea ice cover and related
ocean circulation changes through the warm
stages of the late Quaternary.
2. Background
2.1 Foraminifera
Foraminifera are single celled protists that
inhabit all marine environments from the tropics
to the polar regions. They live either as planktics
3
2
1
*
5
6
9
4
3
10
*
7
8
11
12
Plate 1
1 - Neogloboquadrina pachyderma sinistral; 2 - 3 Turborotalita quinqueloba, scale bars 50 μm; 4 - Buliminia
aculeata; 5 - 6 Cassidulina neoteretis; 7 - 8 Epistominella exigua; 9 - 10 Pullenia bulloides; 11- 12 Oridorsalis
tener. Scale bars = 100 μm, * = 50 μm.
in the upper few hundred meters of the water
column or as benthics on the seafloor or within
the upper few centimeters of the sediments. They
build tests of calcium carbonate (benthics and
all planktics) or by agglutination of, for example
sand particles (only benthics). Calcareous
foraminifera comprise a major component of deep
sea sediments above the carbonate compensation
depth (CCD), while agglutinated species can be
preserved also in sedimentary environments that
are undersaturated in carbonate. Benthic species
range from the early Cambrian to the present,
whereas planktic species appear in the Middle
Jurassic. Since the pioneer works of d’Orbigny in
1826 and Brady’s illustrations in 1884 from the
Challenger voyage, foraminifera have been widely
used in paleoceanographic and paleoecological
studies because specific species are sensitive
to the oceanographic conditions they live in.
For example, variations of fauna composition
are interpreted to reflect water properties such
as salinity, temperature and in high latitudes
sea ice conditions. In addition, benthic species
are dependent on bottom substrate, oxygen
4
availability and surface water productivity.
Some of the first (non Russian) work
describing Arctic Ocean foraminiferal taxonomy
and ecology are by Loeblich & Tappan (1953),
Green (1960), Ericson (1964) and Herman (1964).
The majority of benthic foraminiferal studies
conducted in the Arctic Ocean have been focused
on the more easily accessible shallow shelf areas
and on analyses of living species, e.g. from the
Kara Sea (Polyak et al., 2002), the Laptev Sea
(Wollenburg and Kuhnt, 2000), the Beaufort Sea
and Shelf (Scott et al., 2008b) and the Canadian
Arctic Archipelago (Vilks, 1969) (for more
records see Paper III Table 1). Wollenburg and
Mackensen (1998b) showed that the vertical
distribution of living benthic foraminifera under
the permanent ice cover is usually restricted to
the uppermost centimeter of the sediment column
as a consequence of the low supply of organic
matter. The distribution of planktic foraminifera
in the Arctic is largely influenced by surface water
salinity and temperature, sea ice cover and food
availability (Carstens and Wefer, 1992; Volkmann,
2007) most likely exerted a critical influence on
both paleoceanography and physiography because
the Arctic’s huge shallow shelf areas more or
less disappear during the glacial sea-level stands
(Figure 2b). As the majority of acquired sediment
cores from the central Arctic Ocean do not reach
further back in time than the Quaternary, only this
time frame will be considered in this thesis.
2000). The only planktic foraminifera considered
to be a true polar species is Neogloboquadrina
pachyderma (Ehrenberg), which not only is able to
survive but also to reproduce in the high latitudes
(Darling et al., 2004). This species' abundance
distribution has been shown to vary depending
on sea ice cover and water mass properties
like temperature and salinity (Carstens et al.,
1997; Carstens and Wefer, 1992). During some
interglacials, the subpolar species Turborotalita
quinqueloba (Natland) is present in sediment
cores (Adler et al., 2009; Nørgaard-Pedersen et
al., 2007), but it is thought to be transported into
the Arctic Ocean by advection of warmer water
from the Nordic Seas rather than actually living
in the central Arctic (Bauch, 1994; Carstens and
Wefer, 1992; Hebbeln et al., 1994). Turborotalita
quinqueloba bears photosynthesizing symbionts
and is therefore restricted to live in the photic
zone (Bé, 1977; Hemleben et al., 1989) where
light is not obstructed by a permanent ice cover.
The geographic distribution of planktic and
benthic foraminifera is by and large influenced
by the sea ice distribution, oceanography and
seafloor physiography (Figure 1 and 2). These
environmental parameters have varied greatly
over the geological history. For example, the large
sea level variations throughout the Quaternary
glacial and interglacial cycles (Rabineau et al.,
Greenland
2.2 Sea ice
The Arctic Ocean is one of the least productive
parts of the World's Oceans, one of the reasons
being its most prominent feature: the sea ice cover
(Sakshaug, 2004). The distribution and abundance
of marine life in the Arctic Ocean is to a large
extent dictated by the sea ice distribution and also
acts as an agent for sediment transport from the
shallow shelf areas to the deep ocean (Bischof,
2000). Most sea ice forms during the winter
months over the Eurasian shelves and the ice drift
generally follows the motion of the surface water
circulation (Figure 2b). The surface circulation
and, thus, sea ice drift, are characterized by the
Beaufort Gyre and the Transpolar Drift (Kwok,
2008). The Transpolar Drift was first revealed by
the drift of the ship Fram which was frozen into
the pack ice during Fridtjof Nansen’s expedition
between 1893 and 1896 (Nansen, 1900-1905).
Fram Strait
1
Svalbard
30
ice covered
10
ice margin
Abundance
ratio
ice free
Water depth (m)
0
Polar
water
-1.5 - 0°C
100
Atlantic
water
200
Depth
distribution
0 - 5°C
Figure 3 Living planktic foraminiferal abundance in the Fram Strait in a profile from Greenland (left) to
Svalbard at 78° and 80°N, adopted from Castens et al., 1997
5
The thickest (>4 m) multi-year pack ice is located
off northern Greenland and the Canadian Arctic
Archipelago (Rothrock et al., 2003). Modern
satellite observations with monthly time series
of sea ice extent, defined as the area with at
least 15% ice coverage, are available since 1979
(Serreze et al., 2007). These data show that the
ice extent declined for every month 1979-2006
with the most rapid decrease occurring during
the end of the summer season in September
(Serreze et al., 2007), reaching the so far lowest
extension in 2007 (Figure 2a). Also the thickness
of Arctic sea ice has decreased during the past
few decades (Rothrock et al., 2008). These
changes have a potentially large influence on the
primary production during the summer season,
resulting in a prolonged phytoplankton growing
season, as was shown by Arrigo et al. (2008). The
highest phytoplankton production is observed
in the Chukchi Seas in regions with the least
ice cover (55-80 %) and decreases considerably
under the increasing ice cover of the central
Arctic (Gosselin et al., 1997). The distribution
of planktic foraminifera also depends on the ice
cover. In a study from the Fram Strait at 80°N,
it has been demonstrated that the abundance of
living planktic foraminifera was greatest at the ice
margin and thirty times less abundant under the
ice (Carstens et al., 1997) (Figure 3). A transect in
the Arctic Ocean from the Barents shelf through
the Nansen Basin conducted in 1987 showed the
highest concentration of N. pachyderma and T.
quinqueloba between 81° and 83°N (Carstens
& Wefer, 1992). Here the planktic foraminifera
prefered the habitat depth below the pycnocline
at ~100 m, whereas in the northern province
between A similar correlation between 83° and
86°N most individuals were present in the colder
and fresher upper 50 m of the water column. Also
seen was a pronounced decrease in the percentage
of subpolar specied towards the north. Correlation
between the standing stock of living benthic
foraminifera and food availability, which is higher
in seasonally ice free areas, was demonstrated by
Wollenburg and Mackensen (1998a).
Historic perspectives on the Arctic ice cover are
given by several recently published papers. Cronin
et al. (2010) reconstructed the sea ice history on
a sea-ice dwelling ostracode (Acetabulastoma
arcticum), suggesting minimal ice cover during
the last deglacial (16-11 ka) and the early
Holocene thermal maximum (11-5 ka) followed
by an increasing ice cover during the middle to
late parts of the Holocene. Similar sea ice changes
6
are also suggested by foraminiferal abundances
presented in Paper I of this thesis. A long term
sea ice perspective through the Cenozoic until
the present day warming is given by Polyak et al.
(2010), showing not only the sea ice variations
but also including driftwood and terrestrial data
from around the Arctic perimeter. Multibeam
swath bathymetry and subbottom profiles of
glaciogenic features with age constraints from
sediment cores demonstrate that a large marine
ice sheet complex existed in the Amerasian Arctic
Ocean during MIS 6 (Jakobsson et al., 2010). The
variability of Arctic Ocean sea ice over longer
time periods must therefore be echoed in the
abundance and composition of foraminifera as the
primary production is affected. A complete sea ice
lid over the central Arctic Ocean should not be a
particularly foraminifera friendly environment.
2.3 Oceanography
Planktic foraminifera in the Arctic Ocean
live in the upper water masses between 50 and
200 m, but might change their depth habitats
depending on sea ice cover, food supply (primary
production) and water temperature (Carstens et
al., 1997; Carstens and Wefer, 1992; Kohfeld
et al., 1996; Volkmann, 2000). Inflowing North
Atlantic water is also an agent for transport of subpolar foraminifera species and coccolithophorids
(Carstens and Wefer, 1992; Gard and Backman,
1990). Abundance changes of foraminifera
or coccoliths in sediments can therefore be
an indicator of variations in past Atlantic
water inflow as well as changes in water mass
characteristics. Though inflowing Pacific surface
water through the shallow Bering Strait (53 m
sill depth) enriches the Amerasian surface water
with nutrients (Anderson et al., 2010), it does not
seem to be a pathway for planktic foraminiferal
migration (Darling et al., 2007). In order to
properly interpret paleoceanographic conditions
from either planktic or benthic foraminiferal
studies, a good knowledge of the Arctic Ocean's
present oceanography is required.
The central Arctic Ocean can be divided into
three major water masses: upper waters extending
from the surface to a depth of about 200 m,
intermediate waters between ~200 and 800 m and
deep waters below 800 m. These water masses can
be further divided based on their more detailed
temperature and salinity characteristics (Figure
2d).
The upper waters are composed of the
Polar Mixed Layer between 0 and 30-50 m and
halocline water between 30-50 and 200 m, with
temperatures close to freezing (-2 to 0°C) and
low salinity (<34.4) (Ekwurzel et al., 2001).
The surface water circulation is, as previously
mentioned, characterized by two major current
systems: the Transpolar Drift largely extending
over the Eurasian Basin and flowing from the
Siberian shelves to Fram Strait, and the mostly
anticyclonic Beaufort Gyre over the Amerasian
Basin (Figure 2b). The halocline waters act as
a buffer, protecting the sea ice cover from the
underlying warmer intermediate water.
The Arctic Intermediate Water (AIW) or
Atlantic layer at depth between about 200 m and
800 m is characterized by temperatures above
0°C (Schlosser et al., 1995). This water mass has
its origin from inflowing relatively warm North
Atlantic water that enters the Arctic Ocean as
an extension of the North Atlantic-Norwegian
Current through two branches (Figure 2b). The
first branch flows west of Svalbard through the
Fram Strait and continues further along the slope
of the Barents-Kara Seas continental margin. The
other flows across Barents Sea to St. Anna Trough
where it joins the Fram Strait branch. The Barents
Sea branch is colder and less saline than the Fram
Strait branch (Rudels et al., 1994). The merged
flow of the two branches continues eastwards from
St. Anna Trough following the continental slope.
It then separates into two major flow paths north
of the New Siberian Island where the Lomonosov
Ridge adjoins the continental margin. One path
continues across the Lomonosov Ridge into the
Amerasian Basin while the other re-circulates
Atlantic water towards to the Fram Strait along the
Eurasian side of the Lomonosov Ridge. Atlantic
water circulates in a cyclonal pattern around the
Amerasian Basin to eventually flow across the
southern Lomonosov Ridge north of Greenland
in passing the Morris Jesup Rise to exit in the
western Fram Strait (Björk et al., 2010).
The Arctic Ocean deep water below 800 m
is separated by the Lomonosov Ridge into the
Eurasian Basin Deep Water (EBDW) and Canada
Basin Deep Water (CBDW). The CBDW is
slightly warmer and more saline (-0.3 to -0.5°C,
>34.95) than the EBDW (-0.6 to -1.0°C, 34.93)
(Cronin et al., 1995). Brine formation on the
shelves adds cold and saline water to the deep
water masses through sinking over the continental
margin into the deep basins (Aagaard et al., 1985).
Deep water formation rate is a significant
factor when considering isolation and ventilation
changes through the past. This rate is, in particular,
influenced by changing sea level through glacial
or interglacial times as this in turn changes the
physiography of the Arctic Ocean, a topic further
discussed below. Variation in isolation times are
possible to capture in radiocarbon age differences
between planktic and benthic foraminifera
samples (Adkins and Boyle, 1997; Broecker et
al., 2008).
2.4 Seafloor – physiography
Benthic foraminifera live at all depths of the
World's Oceans and the broad scale seafloor
physiography is an important component of
their habitat. The Arctic Ocean physiography is,
however, from several points of view rather unique
compared to the rest of the World's Ocean. First, it
is surrounded by continents and relatively shallow
shelves occupy ∼53 % of the total area, which is
the proportionally largest shelf component for
any of the World Oceans (Jakobsson, 2002). The
shelves are narrow along the North American
and Greenland side while broad on the Eurasian
side with mean water depths between 50 and 250
m. Second, ridges make up ∼16 % of the Arctic
Ocean area compared to 3 % of the entire World
Ocean area (Jakobsson et al., 2003b). The most
prominent Arctic Ocean ridge is the Lomonosov
Ridge that stretches from the slope of the East
Siberian Sea shelf via the North Pole to north
of Ellesmere Island/Northern Greenland. This
prominent ridge divides the Arctic Ocean into the
Eurasian and Amerasian Basin. In the Eurasian
Basin the slow spreading Gakkel Ridge further
subdivides this basin into the Amundsen and
Nansen Basin. The Alpha-Mendeleev Ridge
separates the Canada and Makarov Basins on the
Amerasian side. Two prominent features in the
Eurasian Basin are located opposite to each other
on both sides of the Fram Strait: the Morris Jesup
Rise north of Greenland and the Yermak Plateau
extending from Svalbard's north-eastern margin.
The majority of key cores described from the
central Arctic Ocean are from the elevated ridges
and plateaus which have higher sedimentation
rates, less pronounced carbonate dissolution
and no influence of turbidites (Backman et al.,
2004). Depths shallower than 1000 m, however,
may have been affected by iceberg grounding
during previous glacials, which is why specific
caution must be taken in order to avoid disturbed
stratigraphies (Jakobsson et al., 2010). In this
thesis sediment cores from the central Lomonosov
7
Ridge, the southern Lomonosov Ridge of
Greenland and the Morris Jesup Rise located
below the ice scoure depth have been analyzed.
Modern benthic foraminiferal communities
living in the different physiographic regions are
highly diverse (Osterman et al., 1999; Scott et
al., 2008a; Wollenburg and Mackensen, 1998a).
Some of the major differences are the often
higher amount of agglutinated specimens in
shelf areas and higher number of smaller sized
calcareous species like Stetsonia horvathi and
Bolivina arctica in the deep basins (Osterman
et al., 1999; Scott and Vilks, 1991; Wollenburg
and Mackensen, 1998a). The distribution of
other benthic species seems to be influenced by a
variety of factors. Some suggest that the benthic
assemblage distribution is largely controlled by
depth and water masses, for example Oridorsalis
tener more abundant at water depths >1300 m
whereas Cassidulina neoteretis is dominant in
water depths under the influence of the AIW
(Bergsten, 1994; Osterman et al., 1999). Others
postulate that the distribution is mainly due to food
availability ( Wollenburg and Mackensen, 1998a).
Besides for paleoecological interpretations, some
benthic foraminifera’s occurrence is also used for
stratigraphy.
2.5 Quaternary biostratigraphy
Central Arctic Ocean biostratigraphic record of
the Quaternary is characterized by low taxonomic
diversity and discontinuous occurrences of
microfossils (Spielhagen et al., 2004). Biosiliceous
groups are absent in Quaternary sediments
and calcareous micro- and nannofossils occur
sporadically and often show signs of dissolution.
The largest abundance of both planktic and
benthic foraminifera is confined to interglacial
and interstadial units while the sediment units
representing glacial or deglacial periods are
barren, leaving a discontinuous record (Figure 4).
In most sediment cores from the Northwind Ridge
(Poore et al., 1993), Mendeleev Ridge ( Adler et
al., 2009; Polyak et al., 2004) and Lomonosov
Ridge (Jakobsson et al., 2001; Spielhagen et al.,
2004), the foraminifera records extend back to
MIS 7 (Sellén et al., 2010). However, in some
cores calcareous microfossils only occur back
to MIS 3. This is shown in Paper I of this thesis
where the cores retrieved from the small local
basin in the Lomonosov Ridge near the North
Pole, referred to as the “Intra Basin” by Björk et
al. (2007), only have calcareous microfossils back
8
to MIS 3 (Figure 4). If foraminifera are present in
sediments older than MIS 7 they are usually few in
numbers and calcareous specimens show signs of
dissolution. The benthic assemblage experiences
a switch to agglutinated species at around MIS 7
to 9 (Cronin et al., 2008; Jakobsson et al., 2001).
Some cores retrieved in the 1960-70s from the
ice island T-3 on the Mendeleev Ridge (T3-673/-11/-12, Herman, 1974) were suggested to
contain foraminifera in sediments older than MIS
7. However, these results are difficult to verify
because the first established aged models are
based on sedimentation rates that have lately been
shown to need correction (Backman et al., 2004)
and these first paleoceanographic interpretations
must be re-evaluated (Sellén et al., 2010). This
will be further discussed.
2.6 Chronology and dating
It is difficult to establish age models in central
Arctic Ocean cores. The use of biostratigraphy
is hampered by the short and discontinuous
records of calcareous microfossils (foraminifera,
ostracods, pteropods) and calcareous nannofossils.
There is presently a high biological productivity
in the wide shelf areas, which in combination
with brine production during sea ice formation
brings decay products to the deep central basin
(Anderson et al., 2010). This causes low pH
and an undersaturation of calcium carbonate
already at intermediate depths. Furthermore,
silica undersaturation prevents siliceous plankton
species like diatoms and radiolarians for being
preserved in the sediment record.
The use of stable oxygen as well as carbon
isotopes in the central Arctic Ocean are limited
by the discontinuous occurrences of calcareous
microfossils, and the interpretation of the isotopic
data are complicated by large amounts of riverine
discharge and melt water events throughout the
Quaternary (Spielhagen et al., 2004).
Another widely used relative dating method
is paleomagnetics, the measurement of the
orientation changes of magnetic grains in
sediments. It has, however, recently been shown
that paleomagnetic polarity changes measured
in Arctic Oceans sediment cores not only follow
past known changes in the Earth’s magnetic field,
but also changes induced by oxidation processes
(Channell and Xuan, 2009). During oxidation of
the seafloor sediments, in the low sedimentation
rate environment of the Arctic Ocean, Channell
and Xuan (2009) propose that titanomagnetite is
96/12-1pc
NP 26
0
Sediment depth (cm)
0
100
HLY0503-18TC
PF*10 /g sed
BF /g sed
PF*1000/g sed
BF /g sed
5 00
0
10 00
1
100
2000
PC-08
PC-04
PF /g sed
PF /g sed
PF /g sed
0
4000
0
0
100
100
5000
10000
200
5
5000
15000
0
500
1000
1-3
5.1
B. aculeata
200
0
5.5
200
200
7
7
300
300
400
400
500
500
0
20
40
60
BF /g sed
600
0
1000
BF/g sed
3000
BF/g sed
Figure 4 Key cores of the central Arctic Ocean (NP 26 from the Mendeleeve Ridge, Polyak et al., 2004, and
96/12-1pc from the Lomonosov Ridge, Jakobsson et al. 2001) with foraminiferal abundances correlated to the
cores of this study HLY0503-18TC from the Lomonosov Ridge Intra Basin, LOMROG07-PC-04 from the
southern Lomonosov Ridge and PC-08 from Morris Jesup Rise.
transformed to titanomaghematite, causing self
reversals that are not resolved using standard
demagnetization techniques. Even if these selfreversals are not caused by polarity changes of
the Earth’s magnetic field, they appear to have
occurred in synchrony on a basin wide scale
(Sellén et al., 2010). The consistent paleomagnetic
pattern in Arctic Ocean sediment cores is probably
the main reason that the first occurring magnetic
polarity change down-core was interpreted to
be the Brunhes-Matuyama reversal at 781 ka
(Lourens et al., 2004), which introduced the
interpretation of an extremely low sedimentation
environment with rates of ~1mm per thousand
years (ka) or even less (Clark et al., 1980).
The low sedimentation model was challenged
by a study in the 1980s (Sejrup et al., 1984) using
amino acid epimerization to date foraminiferal
tests, and from nannofossil studies in the northern
North Atlantic and Arctic Ocean in the 1990s
(Baumann, 1990; Gard, 1993; Gard and Backman,
1990), which indicated that the model had to be
revised. Optically stimulated luminescence dating
measured on core 96/24-1sel (Jakobsson et al.,
2003a) and manganese cycles enriched during
well ventilated bottom waters presented from core
96/12-1pc (Jakobsson et al., 2000) added material
to the new cm/ka-scale. The new consensus with
sedimentation rates on elevated ridges in the
Eurasian Basin in the centimeter scale has resulted
in re-interpretation of old cores (Spielhagen et al.,
2004), and was summarized by Backman et al.
(2004). This new chronology outside the range
of the absolute dating from radiocarbon was also
9
Table 1 Summary of core details and analyses performed (X) on the main cores discussed in this thesis.
P = planktic foraminifer, B = benthic foraminifera.
Position
Water depth
Core length
HLY0503-18TC/JPC
88°27’ N 146°34’E
2598 m
12 m
LOMROG-PC-04
86°42’N 53°46’W
811 m
5.25 m
LOMROG-PC-08
85°19’ 14°52’W
1038 m
5.9 m
X
X
X
X
X
X
X
X
X
X
number
identification
identification
P
P+B
X
P+B
P
P+B
P
X
X
X
Physical properties
Coarse size fraction
Planktic forams
63-125 µm
Planktic forams
>125 µm
Benthic forams
>125 µm
Stable isotopes
Radiocarbon dating
Amino acid
racemization
XRF
applied for the papers presented in this thesis.
3. Material and methods
3.1 Material
The results presented in this thesis are based
on analyses of sediment cores retrieved during
two icebreaker expeditions to the central Arctic
Ocean. The first was conducted in 2005 as a joint
crossing of the Arctic Ocean basin between the
US icebreaker USCGC Healy and the Swedish
icebreaker Oden: the Healy-Oden Trans-Arctic
Expedition (HOTRAX) 2005 (Darby et al., 2005;
Darby et al., 2009). These icebreakers completed
together a transect from the Bering Strait to
Svalbard. The second expedition, referred to as
the Lomonosov Ridge off Greenland (LOMROG)
expedition, was carried out in 2007 with the
Swedish icebreaker Oden assisted by the Russian
nuclear icebreaker 50 Years of Victory (Jakobsson
et al., 2008). Its primary focus was to reach the
southernmost part of the Lomonosov Ridge north
of Greenland in order to collect sediments cores
and geophysical mapping data where no previous
data existed due to the severe sea ice conditions.
The presented data in this thesis are primarily
from three regions of the central Arctic Ocean:
the central Lomonosov Ridge, the southern
Lomonosov Ridge of Greenland and Morris
Jesup Rise (Figure 1). The HOTRAX cores were
retrieved with the Healy’s Jumbo Piston Core
(JPC) system (Table 1). This system is capable of
10
taking up to 21 m long cores from the Healy and
3 m long associated trigger weight cores (TC).
With the JPC-system, cores HLY0503-18TC/JPC
were retrieved during the HOTRAX expedition
from the central Lomonosov Ridge, in a local
basin formed in the ridge’s morphology, hereafter
referred to as the “Intra Basin” (Figure 1). The core
has a total length of 12.55 m and the associated
trigger weight core (TC) is 1.87 m. Microfossils
and calcareous nannofossils are solely present in
the upper 70 cm of the TC. Therefore, analyses
of foraminifera, coccoliths and stable isotopes as
well as radiocarbon dating are concentrated to the
TC (Paper I).
During the LOMROG 2007 expedition all
cores were retrieved using a 12 m long Stockholm
University piston coring system which has an
associated 1.5 m long trigger weight core. Cores
LOMROG07-PC-04 and PC-08 were chosen to be
studied in this thesis because they are the longest
apparently undisturbed records from the southern
Lomonosov Ridge and Morris Jesup Rise (Figure
1). Both cores were analyzed for their planktic
and benthic foraminiferal assemblages (Paper
III), X-ray fluorescence (XRF) scanning (Paper
II), stable isotopes on N. pachyderma sinistral
and C. neoteretis (unpublished data presented in
this thesis) (Table 1). In addition, 14C dating was
carried out on four planktic foraminiferal samples
of core LOMROG07-PC-04 and five of core
LOMROG07-PC-08 and amino acid racemization
was analyzed on N. pachyderma sinistral in cores
HLY0503-18TC and LOMROG07-PC-08 (this
thesis).
3. 2 Core and sample preparation
The cores were logged directly after coring
onboard the ships using a Geotek MultiSensor Core Logger. The core logger measured
bulk density, p-wave velocity and magnetic
susceptibility. In Paper I, the bulk density data of
core HLY0503-18TC/JPC was used for core-tocore correlation. The split cores of the LOMROG
expedition were scanned with the Itrax XRF core
scanner prior to sub-sampling. Core HLY050318TC was sub-sampled in 2 cm thick slices,
and LOMROG-PC-04 and PC-08 in 1 cm thick
slices. The freeze dried samples were sieved with
63 µm sieves. The samples were dry sieved with
125 µm sieves for foraminiferal analyses and if
necessary split to count 300 specimens of planktic
and benthic foraminifera per sample. The benthic
species were identified using the literature cited in
Paper III. Digital light microscope and scanning
electron microscope pictures of the most important
species mentioned in this thesis are displayed on
Plate 1. For an extended benthic foraminiferal list,
see Paper III.
3.3 Core chronologies
The chronology of cores HLY0503-18TC/JPC,
LOMROG-PC-04 and PC-08 was established
through radiocarbon dating, amino acid
racemization and unique benthic foraminiferal
marker events. Additional cores from the
LOMROG expedition and their XRF results were
used for correlation and are presented in Paper II.
3.3.1 Core-to-core correlation
Gamma density data from HLY0503-18TC/
JPC were used to correlate this Intra Basin core
with 96/12-1pc retrieved during the Arctic Ocean
96 expedition (Jakobsson et al., 2001), as well as
with the cores from the Arctic Coring Expedition
(ACEX) (Backman et al., 2006; O’Regan et al.,
2008). Both the 96/12-1pc and ACEX sites are
located on the crest of the Lomonosov Ridge
further towards the Siberian margin from the Intra
Basin between approximately 87°N and 88°N
(Figure 1).
The planktic foraminiferal abundance curve of
core LOMROG-PC-08 from Morris Jesup Rise
was correlated to that of PS2200-2/5 (Spielhagen
et al., 2004) from the Arctic 91 expedition
(Fütterer, 1992). Some modifications were made
to the chronology due to the benthic foraminiferal
markers (see chapter 3.3.2). LOMROGPC-04 was correlated to PC-08 by the planktic
foraminiferal abundances, benthic marker events
and calcium intensity peaks measured with the
Itrax X-ray fluorescence scanner (see chapter 3.5).
These calcium intensity peaks were also used for
correlation of the remaining LOMROG cores.
3.3.2 Biostratigraphic events
Benthic foraminiferal species that occur only
in short stratigraphic intervals throughout the
central Arctic Ocean are useful in biostratigraphy
and core-to-core correlations. Among these
species are Bulimina aculeata (Plate 1, no. 4)
which occurs in MIS 5.1 (Backman et al., 2004;
Nørgaard-Pedersen et al., 2007; Polyak et al.,
2004), Epistominella exigua (Plate 1, no. 7, 8)
described as contrained to MIS 5.5 (Jakobsson
et al., 2001; Polyak et al., 2004), and Pullenia
bulloides (Plate 1, no. 9, 10) as an indicator for
MIS 7 (Backman et al., 2004; Jakobsson et al.,
2001; Nørgaard-Pedersen et al., 2007). In Paper
III we revise the occurrence of E. exigua with the
new core material from the LOMROG expedition.
The new data show that E. exigua is abundant also
in older sediments (Figure 8), and that it has its
last occurence in MIS 5.5.
Another biostratigraphic marker event is the
cross-over in calcareous nannofossil abundance
between Emiliania huxleyi and Gephyrocapsa
spp. This cross-over was originally suggested by
Thierstein et al. (1977) to have occured in MIS 5.2
to 5.1 in lower latitudes with time-transgression
towards younger ages in higher latitudes (MIS
4). New Arctic Ocean core material made a more
precise placement in the upper part of MIS 3
possible (Backman et al., 2009) (Figure 5).
3.3.3 Radiocarbon dating and calibration
Radiocarbon dating is a frequently used
method to date late Quaternary sediments, but
large uncertainties concerning marine reservoir
ages make calibration and therefore comparison
to terrestrial records a challenge (Bondevik et
al., 2006; Mangerud et al., 2006; Stuiver and
Braziunas, 1993). This appears to be a particularly
difficult case for the central Arctic Ocean where
modeling experiments suggest reservoir ages of
1400 years in present day simulation runs and
around 2500 years in glacial simulations for a
surface water mass with inhibited gas exchange
11
with the atmosphere and water mixing under
the sea ice cover (Butzin et al., 2005, pers. com.
2008). This approach to receive and use reservoir
age obtained by modeling for areas with no other
constraints is addressed in Paper I. Radiocarbon
dating was performed at the Lund University
Radiocarbon Dating Laboratory with the single
stage accelerator mass spectrometer (SSAMS),
using sample volumes of 50-1000 μg C. In core
HLY0503-18TC sixteen planktic foraminifera
samples (using N. pachyderma) and six benthic
foraminifera samples (using Cassidulina
wuellerstorfi and mixed species samples were
analyzed. Four samples were dated in core
LOMROG-PC-04 and five in PC-08, using N.
pachyderma. The results for the two LOMROG
cores are shown in Table 2 and Figure 9 of this
thesis. The radiocarbon dates of the HOTRAX
core are one of the main topics discussed in Paper
I. Differences in uncalibrated planktic to benthic
ages derived from the same samples are used to
suggest significant changes in ocean ventilation
since the last deglaciation.
3.3.4 Amino Acid Racemization (AAR)
Amino acids undergo an interconversion
(racemization) from the left (L – levo) chiral
usual form in living organisms to a mixture
of left and right (D – dextro) after death until a
mixture of 50:50 is reached. This conversion is
a function of time and temperature experienced
by the fossil since burial. AAR is interpreted in
terms of relative age and absolute dates can be
inferred through calibration for a study area using
samples of known age. AAR was first used in the
Arctic Ocean in the 1980s, but the interpretation
of the data was ambiguous. Sejrup et al. (1984)
AAR measurements implied high sedimentation
rates, against the low sedimentation rate theory
(Clark et al., 1980), whereas Macko and Aksu
(1986) suggested that their data supported the
slow sedimentation. The two studies are based
on the rate of isoleucine epimerization and were
calibrated against dated samples from the North
Atlantic. The shortcomings of this approach
are, according to Kaufman et al. (2008), the
temperature difference between the Arctic and
the North Atlantic, analyses of single samples
instead of replica and that isoleucine is not the
ideal amino acid since it reacts more slowly and
has a lower temporal resolution. In a new study by
Kaufman et al. (2008), aspartic acid and glutamic
acid were used which provide an enhanced age
12
resolution in low temperature regimens and are
most abundant in foraminiferal protein. The results
were calibrated against the new Arctic Ocean
chronostratigraphic framework with radiocarbon
ages and biostratigraphic marker events from the
central Arctic.
The AAR samples of this study were analyzed
at the Northern Arizona University by Darrell
Kaufman on 50 individual tests of N. pachyderma
sinistral per sample for 13 samples of core
HLY0503-18TC and 21 samples of LOMROGPC-08. To convert the measured D/L-rations of
aspartic and glutamic acid results into ages, we
used the age equation developed by Kaufman et
al (2008) calibrated for the last 150 ka (Table 3).
3.4 Stable oxygen and carbon isotopes
Stable oxygen and carbon isotope analyses of
planktic and benthic foraminifera were carried
out on samples weighing ~100 μg and containing
ca 20 specimens each of N. pachyderma and C.
neoteretis. Isotopic results have been shown to be
influenced by different foraminifera morphotypes
(Healy-Williams, 1992), secondary calcite crusts
(Volkmann and Mensch, 2001) and size fractions
of N. pachyderma (Hillaire-Marcel et al., 2004).
Therefore, mainly four-chambered, sinistral,
encrusted quadrate specimens of the 125-250
μm size fraction were used for the analyses of
38 samples in core LOMROG07-PC-04 and 57
samples in PC-08, and 23 samples picked from
the >150 μm fraction of core 18TC. The benthic
isotope analyses were performed on the infaunal
species C. neoteretis >125 μm, as this was the
only benthic species represented throughout the
LOMROG cores. Altogether, 87 samples in core
LOMROG07-PC-04 and 49 samples in PC-08
were analyzed (Figures 9 and 10).
Oxygen and carbon isotopes were measured
using a Finnigan MAT 252 mass spectrometer
connected to a Kiel carbonate device at the
Department of Geological Sciences, Stockholm
University for core 18TC and at MARUM,
University of Bremen, Germany, for the
LOMROG cores. Oxygen and carbon isotopes
were calibrated to the Vienna Pee Dee Belemnite
standard (VPDB) at the Stockholm laboratory and
the Solnhofen Limestone calibrated against NBS
19 as internal standard at MARUM and converted
to conventional delta notation (δ13C and δ18O)
(Coplen, 1996). Analytical precision is better than
0.1 ‰ for both δ13C and δ18O at Stockholm and
the long-term standard deviation of the MARUM
1
4000
A
11.7
plankt. 14C ka BP
2.7
PF /g sed
>125 µm
3
7.2 8.8 10.2 11.5 11.9
23
12.5
>42
>38
26
41
>42
>42
3000
40
2000
20
1000
pl. forams
bent. forams
0
B
Coccoliths %
100
Number of
coccoliths
60
BF /g sed
>125 µm
MIS
0
E. huxleyi
Gephyrocapsa
C. pelagicus
50
0
C
3000
1500
0
0
10
20
30
40
50
60
70
Sediment depth (cm)
Figure 5 A – Planktic and benthic foraminiferal abundance (>125 µm) with radiocarbon ages (uncalibrated),
B – relative abundance of calcareous nannofossils and C – number of coccolith per 1.24mm2 .
internal standard is <0.05‰ for δ13C and <0.07‰
for δ18O.
3.5 X-Ray Fluorescence (XRF)
The working halves of the LOMROG cores
were measured with the Itrax XRF core scanner at
Stockholm University core processing laboratory.
A detailed description of the Itrax core scanner is
provided by Croudace et al. (2006). Measurements
were done with a molybdenum tube operated at
30 kV and 25 mA with a sampling resolution of
0.1 cm and a 4 second exposure time or 0.5 cm
resolution and 20 second exposure time with data
output in counts rather than element concentration.
In this thesis the calcium counts (Ca) are the main
focus. Ca counts were normalized aby incoherent
and coherent scatterin and plotted with a running
mean over 3 cm.
4. Results and Discussion
The following chapter presents a summary
of the main results and discussion of the printed
Paper I on radiocarbon age corrections and sea
ice variations, the submitted Paper II on the
connection between XRF scanning results and
microfossil rich intervals and the submitted Paper
III on benthic biostratigraphic marker events and
paleoceanographic interpretations on an extended
benthic foraminiferal record. Also presented are
unpublished results intended for an additional
manuscript on morphological differences in
Turborotalita quinqueloba, as a possible new
chronostratigraphic marker, stable oxygen and
carbon isotope data, and amino acid racemization
as a potential dating method beyond the range of
radiocarbon ages.
4.1 Paper I
Quaternary Arctic Ocean sea ice variations and
radiocarbon reservoir age corrections, 2010,
QSR
This paper is focused on the 1.87 m long
sediment core HLY0503 - 18TC retrieved from
2598 m water depth in the Intra Basin formed in
13
ΔR=1000
ΔR=650
ΔR=300
ΔR=0
6.6 ±0.21
7.0 ±0.20
7.4 ±0.15
7.7 ±0.17
7.2 ±0.08
1.2 ±0.16
1.6 ±0.19
2.0 ±0.21
2.4 ±0.23
2.7 ±0.07
convent.
8.2 ±0.20
8.7 ±0.26
9.1 ±0.25
9.4 ±0.22
8.8 ±0.09
10.0 ±0.30
10.4 ±0.22
10.9 ±0.27
11.3 ±0.33
10.2 ±0.10
11.6 ±0.40
12.3 ±0.40
12.7 ±0.28
13.0 ±0.17
11.4 ±0.11
12.4 ±0.39
12.7 ±0.33
13.1 ±0.19
13.3 ±0.25
11.9 ±0.12
12.6 ±0.30
13.0 ±0.17
13.1 ±0.23
11.7 ±0.12
13.0 ±0.18
13.4 ±0.24
13.7 ±0.25
14.0 ±0.32
12.5 ±0.11 23.2 ±0.35
30
1600
1200
20
800
BF >125 µm /g sed
Younger Dryas
11.7 - 12.8 ka
2000
PF >125 µm /g sed
12.1 ±0.62
10
400
plankt. forams
bent. forams
0
0
0
5
10
15
20
25
30
35
40
Sediment depth (cm)
Figure 6 Radiocarbon calibration with different marine reservoir ages (ΔR=0, ΔR=300, ΔR=650, ΔR=1000)
and placement of the Younger Dryas cold event in relation the foraminiferal abundance. Black boxes around
the calibrated ages indicate the favored value for each time interval.
the central Lomonosov Ridge. Paleoceanographic
variations in the central Arctic Ocean are
interpreted from planktic foraminifera and
calcareous nannofossils with specific emphasis on
the Holocene evolution of the Arctic sea ice cover.
In addition, Arctic Ocean marine radiocarbon
reservoir ages are addressed and discussed. Over
an interval of ca 58 cm, 22 radiocarbon dates were
acquired from planktic and benthic foraminifera.
These radiocarbon dates divide the core into two
distinct parts with finite 14C ages in the upper part
and infinite ages in the lower (Figure 5). These
14
C dates, together with correlations between core
HLY0503 - 18TC and other Lomonosov Ridge
cores using measured sediment bulk density,
show that the upper 65 cm of the sediments in
the core were accumulated during MIS 1-3, but
that a hiatus exists encompassing the Last Glacial
Maximum (LGM). The ca 30 cm thick late glacial
to Holocene sequence of core HLY0503 - 18TC
suggests sedimentation rates ranging between 7.0
and 9.4 cm/ka for the late glacial and 1.3-3.3 cm/
ka for the Holocene time interval. This indicates
that the Intra Basin is an environment with higher
sedimentation rates than most other previously
cored areas near the North Pole. In order to
compare this relatively high resolution central
Arctic Ocean paleoceanographic record with
results from ice cores and other terrestrial paleoarchives, a calibration of the radiocarbon ages must
be carried out. We used four reservoir corrections
(ΔR=0/300/650/1000) of which the first is based
on the global model ocean reservoir age as
implemented in Marine04 (Hughen et al., 2004)
14
and the other three on numerical ocean circulation
simulations by Butzin (2005). A reservoir age of
1400 years (ΔR=1000) for the Lateglacial (14.7 –
11.7 ka BP) is inferred assuming that the Younger
Dryas cold event 11.7-12.8 ka (Muscheler et al.,
2008; Walker et al., 2009) was a colder and less
productive period reflected in the abundance
of foraminifera, while a reservoir of 700 years
(ΔR=300) was adopted for the Holocene (11.7 ka
BP – present) (Figure 6).
Interestingly, the MIS 3 interval is
characterized by an exceptionally high abundance
of foraminifera and about one order of magnitude
higher nannofossil abundance compared to other
Lomonosov Ridge cores (Backman et al., 2009)
(Figure 5). This is proposed to be caused by
different paleoceanographic conditions during
MIS 3 compared to MIS 1. The varying microand nannofossil abundances are generally
interpreted to reflect changes in summer sea ice
coverage and variations in inflow of subpolar
North Atlantic water. The radiocarbon calibration
exercise suggests marine reservoir ages of 1400
years in the central Arctic Ocean, or even more, at
least during the last deglaciation. Paired benthicplanktic radiocarbon dated foraminifera samples
show a slow decrease in age difference between
surface and bottom water from the late glacial
(~1200 years) to the Holocene (~250 years)
indicating progressive circulation and related
ocean ventilation changes.
PC-04
0
0
BF/g PF/g
BF/g PF/g
3000
0
2000 4000 6000 8000
0
1000
PS2200-2/5
PC-08
BF/g PF/g
2000
400
800
1200 1600 0
500 1000 1500
8000 16000 0
4000 8000 12000
4000
0
1-2
1-3
3
3.1
4
5.1
100
B. aculeata
5.1
T
T
5
5.5
E. exigua
5.5
Sediment depth (cm)
200
6
7
P. bulloides
T. quinqueloba
peak
300
7.1
7.3
7.5
400
500
600
0
0.5
1
1.5
0
Ca
0.5
1
1.5
Ca
Figure 7 Planktic (red) and benthic (blue) foraminiferal abundance (>125 µm) for cores LOMROG07-PC-04
and PC-08 and their correlation to core PS2200-2/5 (Spielhagen et al., 2004). The gray shaded areas show the
calcium intensity measured with the Itrax XRF. For the biostratigraphy used benthic foraminiferal markers
Bulimina aculeata (MIS 5.1), the last occurrence of Epistominella exigua (MIS 5.5) and Pullenia bulloides
(MIS 7) are indicated by green bares. Also shown is the abundance peak of Turborotalita quinqueloba (>125
µm) in core PC-04.
4.2 Paper II
Biogenic and detrital rich intervals in central
Arctic Ocean cores identified using X-Ray
fluorescence scanning, submitted, Polar
Research
A thorough analysis of calcareous microfossil
content in a sediment core is time consuming and
requires sometimes large amount of sediments that
may be difficult to reuse for other analyses. These
are some of the reasons that microfossil studies
are commonly concentrated to selected key cores.
However, selecting cores is not always straight
forward, particularly not in the central Arctic
Ocean where calcium carbonate preservation
varies both temporally and spatially (Backman et
al., 2004). In this Paper II, we show that intervals
with high calcium intensity measured by XRF
scanning of cores from the central Arctic Ocean
15
generally correlates well with intervals rich in
calcareous microfossils. The XRF scanning thus
provides a useful firsthand indication of the
potential stratigraphic positions of calcareous
microfossil-rich layers allowing strategic subsampling for microfossil analyses.
All cores retrieved during the LOMROG
2007 expedition were scanned with the Itrax
XRF installed at Stockholm University core
processing laboratory. The XRF results from
six of the LOMROG 2007 cores are presented
in Paper II. In addition, planktic and benthic
foraminiferal abundance estimations were made
in cores LOMROG07-PC-04 from the southern
Lomonosov Ridge and LOMROG07-PC-08 from
Morris Jesup Rise (Figure 1).
The element showing the most prominent
pattern in the XRF results is calcium, which
displays a distinct and almost cyclic pattern of
high intensity peaks in the upper 2.5 to 3 m of
all the cores in order to become more irregular
and less pronounced further downcore (Figure 7).
Even if some of the intensity peaks are linked to
detrital carbonate deposited through the input of
ice rafted debris, nearly all of the peaks coincide
with relatively high abundance of calcareous
microfossils .The Itrax-measurements of Ca are
thus able to provide a relatively reliable first proxy
for calcareous foraminiferal abundance variations
and aid when correlating Arctic Ocean sediment
cores from MIS 7 to the present. However, the Ca
signal is significantly less clear below MIS 7 with
more frequent lower intensity peaks occurring
in the studied cores. The planktic foraminifera
are few or absent in samples investigated below
MIS 7. The mass of calcium by the continued
presence of calcareous benthic foraminifera
alone is apparently not large enough to be picked
up by the XRF. The extremely low, or complete
disappearance of, calcium carbonate below MIS
7 is characteristic for central Arctic Ocean cores
(Backman et al., 2004).
In conclusion, the XRF detected calcium
content in the studied LOMROG 2007 cores is
a combination of biogenic and detrital calcium
carbonate/dolomite input. However, the Itrax
XRF scanning alone cannot be used to distinguish
whether the carbonate is of biogenic origin or
deposited as detrital carbonate from terrigenous
sources. On the other hand, there seems to be
a common paleoceanographic or geochemical
mechanism behind the preservation of especially
planktic foraminifera and the input of detrital
carbonate.
16
4.3 Paper III
Late Quaternary benthic foraminiferal
assemblages from the central Arctic Ocean,
manuscript
This study continues from Paper II by presenting
the benthic foraminiferal biostratigraphy of cores
LOMROG-PC-04 and PC-08 from the southern
Lomonosov Ridge and Morris Jesup Rise,
respectively (Figure 1). Extending beyond MIS
7, the benthic foraminiferal records of these cores
comprise some of the oldest calcareous microfossil
records from the central Arctic Ocean. The benthic
assemblages provide new insights into the late
Quaternary Arctic Ocean paleoceanography and
summer sea ice extent.
Five
different
benthic
foraminiferal
assemblages were identified in both cores. In
addition, a sixth assemblage was identified
downcore of assemblage five in core LOMROGPC-04 (Figure 8). The most abundant species in
all samples containing calcareous foraminifera
is Cassidulina neoteretis, whereas the accessory
species vary and determine the division into
the different assemblages. The benthic species
Bulimina aculeata, Epistominella exigua and
Pullenia bulloides were observed in discrete
intervals and used as chronological markers
following previous studies (Backman et al., 2004;
Jakobsson et al., 2001; Nørgaard-Pedersen et al.,
2007; Polyak et al., 2004). However, our record
shows that E. exigua, which previously has been
used as an indicator for MIS 5.5 (Jakobsson et
al., 2001; Nørgaard-Pedersen et al., 2007; Polyak
et al., 2004), occurs in older sediment units and
may therefore have its last occurrence in MIS
5.5. The biostratigraphic age indications together
with radiocarbon dating suggest that sediments
of MIS 2 age are absent or highly condensed in
both studied cores. A hiatus encompassing MIS
2 was observed in core HLY0503-18TC studied
in Paper I and has previously also been observed
in other central Arctic Ocean cores (Polyak
et al., 2004; Poore et al., 1999). Furthermore,
our chronology suggests that MIS 6 sediments
are nearly absent from core LOMROG-PC-04.
This core was retrieved from the crest of the
Lomonosov Ridge at about 800 m water depth.
Large marine ice sheet complexes, including deep
drafting ice shelves, appear to have existed during
MIS 6 (Jakobsson et al., 2010). Geophysical
mapping and coring show that deep drafting
icebergs from these ice complexes have grounded
and eroded physiographic features shallower than
.
5 0
15 0
0
15 0
15 0
.
As
se
m
rs
he
ot
15
30
1
100
Sediment depth (cm)
30 0
l.
ea
15
30 0
Ag
g
ac
ul
er
en
15
0
va
ria
ta
sp
p
in
cu
l
lo
ue
15 0
a
cu
l
15
Tr
ilo
Q
ui
nq
rc
ti c
a
e
30 0
.
a
in
15
V.
a
C.
re
n
i fo
rm
es
sp
p
P.
b
ul
lo
id
m
es
iu
id
id
El
ph
do
ici
30 0 15 30 45 0
B.
15
Ci
b
ici
de
s
ua
30 0
Ci
b
ex
ig
15
.
sp
.
sp
p
50 100 0
O
.t
0
E.
C.
n
eo
te
re
t
is
sp
p
.
PC - 04
2
3
200
4
5
300
400
6
500
Figure 8 Relative benthic foraminiferal abundance of the main species of core LOMROG07-PC-04. The for
paleoceanographic interpretations important species (C. neoteretis (green) as the most abundant and O. tener
(blue)) and biostratigraphic marker species (red) B. aculeata, E. exigua and P. bulloides are indicated.
approximately 1000 m present water depth all over
the central Arctic Ocean, including the southern
Lomonosov Ridge (Jakobsson et al., 2010). This
may explain why no distinct sediment unit of MIS
6 age is found in core LOMROG-PC-04.
The benthic foraminiferal assemblages, in
particular the occurrence of Oridorsalis tener,
suggest
paleoceanographic
environments
dominated by perennial sea ice cover from MIS
5.1 to the Holocene. O. tener is adapted to live
in oligotroph conditions and commonly occurs in
sea ice covered areas of the present central Arctic
Ocean (Osterman et al., 1999; Wollenburg and
Mackensen, 1998a). It should be noted that none
of these two studied cores have millennial-scale
age resolutions. This implies that it is not possible
to resolve variations within the Holocene, which
prevents a direct comparison with the results in
Paper I. However, the appearance of E. exigua
from MIS 5.5 and further downcore may indicate
a general change in sea ice conditions. This
species is described from North Atlantic studies
as opportunistic and phytodetrital exploiting
(Gooday, 1988, 1993). If E. exigua exhibits the
same food preferences in the Arctic Ocean as in the
North Atlantic, a higher primary production than
at present is required. This suggests considerably
less summer ice cover in the central Arctic Ocean
during MIS 5.5 and may indicate the importance of
not only substrate and deep water mass properties
but also surface water conditions for the benthic
environment and species composition.
4.4 Unpublished data
4.4.1 Turborotalita quinqueloba (Natland) Morphological comparison between MIS 5 and
11
The presence of the subpolar species
Turborotalita quinqueloba in the Arctic Ocean
is considered to be due to the influx of warmer
Atlantic water entering through the Fram Strait and
across the Barents Sea (Carstens and Wefer, 1992;
Volkmann, 2000). The species is present in areas
with seasonally sea ice free conditions (Carstens
and Wefer, 1992). In the Holocene to MIS 3
central Arctic Ocean sediments, T. quinqueloba is
only present either in low numbers or not at all
(Adler et al., 2009; Hanslik et al., 2010; NørgaardPedersen et al., 2007). However, T. quinqueloba
has commonly been observed in sediment of MIS
5 age, in the size fraction between 63 and 150
μm (Adler et al., 2009; Nørgaard-Pedersen et al.,
2007).
Core LOMROG07-PC-04 from the southern
Lomonosov Ridge was originally analyzed for
the foraminiferal content in the >125 μm fraction.
17
1
5
2
6
9
3
7
4
8
10
Plate 2
1 – 8 Turborotalita quinqueloba, scale bars 50 μm, 1 – elongated last chamber, PC-04, 120-121 cm, 63-125
μm, close-up of surface structure (scale bare 10 μm); 2 – ’normal’, PC-04, 120-121 cm, 63-125 μm, close-up of
surface structure (scale bare 5 μm); 3 – smooth last chamber, PC-04, 288-289 cm, >125 μm, close-up of surface
structure (scale bare 20 μm); 4 – ’normal’, PC-04, 288-289 cm, >125 μm, close-up of surface structure (scale
bare 10 μm); 5 – ’normal’, PC-04, 288-289 cm; 6 – kummerform last chamber, PC-04, 288-289 cm; 7 – smooth
last chamber, PC-08, 415-416 cm; 8 – smooth last chamber, PC-08, 415-416 cm; 9 – 10 Neogloboquadrina
pachyderma sinistral, scale bars 50 μm, 9 – non-encrusted test, PC-04, 0-1 cm, close-up of surface structure
(scale bare 20 μm); 10 – slightly encrusted test, PC-04, 120-121 cm, 63-125 μm, close-up of surface structure
(scale bare 5 μm).
In three of the four intervals with high planktic
foraminiferal abundances, N. pachyderma is the
major species. These intervals belong to MIS
1-3, 5.1 and 5.5 (Figure 7). The fourth interval
of high planktic foraminiferal abundances occurs
between 280 and 310 cm core depth. This interval
is primarily characterized of T. quinqueloba.
High relative abundance of T. quinqueloba is also
present in the two peaks of MIS 5.1 and 5.5, but
only in the 63-125 μm size fraction.
In addition to a difference in the test size of
T. quinqueloba between these high abundance
18
intervals there are also some morphological
differences. The appearance of T. quinqueloba
in the upper, younger interval corresponds well
to most pictures displayed in the literature (e.g.
Kennett and Srinivasan, 1983), with remnants of
spines, 4-5 chambers in the last whorl and about
50 % showing an elongated last chamber (Plate
2, fig. 1-2). The T. quinqueloba specimens in the
lower older interval have remnants of spines, 4-5
chambers in the last whorl, but seem to have a
less recrystallized surface and about 20-30 % of
the specimens are kummerforms, specimens with
a smaller and smooth last chamber without any
spine remnants (Plate 2, fig. 3-8). T. quinqueloba
in the smaller size fraction in this interval show
the same pattern as the larger individuals.
Specimens with an elongated last chamber and
those displaying a kummerform are not observed
in the same samples.
Similar morphological differences and
an abundance peak of T. quinqueloba have
previously been described from a core from the
Mendeleev Ridge (Herman, 1974). There, the
morphotype of T. quinqueloba is referred to as
Globigerina exumbilicata n. sp. (Herman, 1974),
later changed by Herman (1980) to Globigerina
quinqueloba egelida following Cifelli and Smith
(1970). Even though the chronostratigraphy
published for this core is not in accordance with
the one used today, the ”kummerform interval”
may well be synchronous with the one observed
at the southern Lomonosov Ridge. If we are able
to find the kummerform of T. quinqueloba in more
cores with constrained age models, this interval
could be used as a chronostratigraphic marker.
The predominance of T. quinqueloba points
towards a different paleoceanographic setting
during this time period compared to present day
conditions. The proposed time period for this
dominance is MIS 11 (374 - 424 ka, (Lisiecki
and Raymo, 2005), a ~50 ka interglacial which
showed a warmer climate on Greenland with a
reduced ice sheet volume and development of a
pine forest (de Vernal and Hillaire-Marcel, 2008).
The species T. quinqueloba is subpolar and
prefers higher water temperatures than the central
Arctic Ocean presently provides and is through
the utilization of symbionts also dependent on
sufficient light availability (Bé, 1977; Hemleben et
al., 1989). The high abundance of T. quinqueloba
in this material could indicate a period when
T. quinqueloba lived and even reproduced in
the area. This suggests reduced summer sea ice
cover compared to present conditions, but most
specimens show at the same time signs of stress,
expressed through phenotypical differences
relative to specimens present in MIS 5 or in the
North Atlantic (Bauch, 1994). The high number
of T. quinqueloba can also be a result of lower
input of clastic sediments due to less sea ice that
could transport sediment to this area during that
time interval.
4.4.2 Stable oxygen and carbon isotopes
As
described
in
previous
chapters,
interpretations of the isotopic signal recorded by
foraminifera are challenging and do not conform
to other deep sea ocean basins. Therefore, mainly
relative differences within the investigated cores
are described here. In core LOMROG-PC-04 from
the southern Lomonosov Ridge the δ18O values of
the benthic record display less variability than the
planktic record, and the benthic values in MIS 1 to
5 are slightly heavier (mean 4.6 ‰) compared to
those further downcore (mean 4.2 ‰) (Figure 9).
The δ13C values are lighter in the benthic record
downcore from MIS 5 with an average of -0.5 ‰
compared to 0.6 in MIS 1 to 5.1. A larger difference
in planktic to benthic δ13C values can be observed
from MIS 5 downcore (>0.7 ‰) compared to
relatively stable difference during MIS 1-3 (<0.5
‰). A peak of high δ13C values and high δ18O can
be seen in both the planktic and benthic record at
around 12.5 cm (Figure 9). This peak has a 14C age
of approximately 37 ka (Table 2).
The stable isotope record of core LOMROGPC-08 from Morris Jesup Rise shows less
pronounced changes which may, at least partly,
result from a lower sample resolution (Figure
10). No clear trends are visible in the planktic and
benthic δ18O records. Three peaks with lighter
values of δ18O, one each in MIS 1, 5.1 and 5.5, can
possiblybe seen as the result of warmer climate
conditions or increased freshwater influx. The
benthic δ13C record shows higher values from MIS
1 to MIS 5 with an average of 0.2 ‰ and lighter
values averaging -0.5 ‰ below MIS 5 similar
to the trend observed in core LOMROG-PC-04.
In contrast to the latter core the δ13C difference
between the planktic and benthic record is not
visible. The heavy δ13C and heavy δ18O excursions
observed in LOMROG-PC-04 can also be seen in
PC-08 at 8.5 cm sediment depth (Figure 10). In
this core the 14C age is 32.9 ka (Table 2).
The oxygen isotope record of deep sea benthic
foraminifera has been used to build a composite
record over the past 5 million years (Lisiecki and
Raymo, 2005). Changes reflect the variation in
continental ice volume and temperature through
time, and Shackelton (1967) first identified the
storage of light oxygen isotopes in continental
ice sheets as the main factor for the global
glacial to interglacial isotope variations. Studies
of living planktic foraminifera, core top and
late Quaternary sediments have shown that the
oxygen isotope record in the Arctic Ocean is in
addition to the continental ice volume to a large
degree influenced by 18O depleted freshwater
from meltwater and river runoff inflow (Bauch et
19
11
7
5.5
5.1
4
1
3
MIS
3
2
1
1
3
δ18O
5
4
0
0
600
500
400
300
200
100
0
0
4000
Planktic/g
1000 3000
8000
5
-1
δ18O
1
3
0
4
1
2
2
-1
0
1
2
5
4
3
2
1
0
0.8
1.6
0
δ18O
difference
δ13C
difference
δ18O
Benthic / Planktic
δ13C
Benthic / Planktic
δ13C
Planktic
δ13C
Benthic
Benthic/g
PC-04
Sediment depth (cm)
Figure 9 Stable oxygen (δ18O) and carbon (δ13C) isotopes measured on N. pachyderma sinistral (planktic) and
C. neoteretis (benthic) for core LOMROG07-PC-04, and the isotopic difference between planktic and benthic
values (last two plots to the right).
20
7
5.5
5.1
4
1
3
MIS
3
2
difference
1
1 .6
Benthic / Planktic
3
4
5
1
Benthic / Planktic
0
0.8
difference
0
δ18O
δ13C
δ18O
3
4
δ18O
600
500
400
300
200
100
0
0
Planktic/g
4000 8000 16000
1000
500
0
Benthic/g
-1
5
0
δ C
13
4
1
0
13
δ18O
δ C
1
-1
0
δ13C
Planktic
Benthic
PC-08
Sediment depth (cm)
Figure 10 Stable oxygen (δ18O) and carbon (δ13C) isotopes measured on N. pachyderma sinistral (planktic) and
C. neoteretis (benthic) for core LOMROG07-PC-08, and the isotopic difference between planktic and benthic
values (last two plots to the right).
21
al., 1997; Spielhagen et al., 2004; Spielhagen and
Erlenkeuser, 1994; Stein et al., 1994). The living
depth of N. pachyderma is around 150 m in the
southern Nansen Basin and around 80 m in the
northern part (Carstens and Wefer, 1992). The
average calcification depth is 100-200 m deeper
than the average habitat depth (Bauch et al., 1997).
This implies that N. pachyderma cannot be used
for surface condition reconstructions, but records
an integrated δ18O signal of the upper water
column. It is therefore a good indicator for water
mass change since it is not solely influenced by
regional or seasonal near surface signals (Bauch
et al., 1997). The δ18O values are variable in the
Eurasian Basin, displaying a north-south gradient
with lightest values towards the North Pole and
highest in the southern Nansen Basin, associated
with saline Atlantic water entering through Fram
Strait (Spielhagen and Erlenkeuser, 1994). The
δ18O changes are large and in contrast to low
salinity changes which suggests an increasing
influence by freshwater discharge towards the
Lomonosov Ridge and Amerasian Basin as the
main reason for the regional variations.
The modern Arctic Ocean shows low δ18O and
high δ13C values (Spielhagen and Erlenkeuser,
1994). The high δ13C values are interpreted as
evidence for well ventilated surface waters with a
balanced input of CO2 by the atmosphere to CO2
fixation through primary production and export
to the deep sea (Spielhagen and Erlenkeuser,
1994). The increased gradient between planktic
and benthic samples in core LOMROG-PC-04
in the sediments from MIS 5.5 downcore may
indicate relative δ13C enrichment in the upper
water column and at the same time δ13C depletion
in the bottom water as a product of increased
export productivity. It is possible that the same
gradient prevailed in the sediments older than
MIS 5, as suggested by the low benthic δ13C
values, but a comparison is impossible due to
the lack of planktic foraminifera in this interval.
An often observed distinct δ13C minimum occurs
together with δ18O depletion near 15.7 ka, and is
considered to be the product of large amounts of
meltwater released to the Arctic Ocean (Stein et
al., 1994). This minimum has not been observed
in Morris Jesup Rise core PS2200 (Stein et al.,
1994), or in the cores of this study. Stein et al.
(1994) concluded that the meltwater cover did not
reach into this part of the central Arctic Ocean so
early in the deglaciation phase.
4.4.3 Amino acid racemization
The long term thermal and geochemical
stability of deep sea depositional environments
are ideal for amino acid chronology. A calibrated
numerical age equation has been developed that
relates the extent of racemization of aspartic and
glutamic acids on the basis of a least square linear
regression (Kaufman et al., 2008). The equation
is based on radiocarbon dating and correlation
of cores from the Northwind, Mendeleev
and Lomonosov ridges using lithological
characteristics, foraminiferal abundances and
benthic foraminiferal events and should apply
to samples younger than 150 ka (Kaufman et al.,
2008).The calculated AAR ages are in relatively
good agreement with 14C ages throughout the
range of 14C dating for both the cores from the
central Lomonosov Ridge and Morris Jesup
Rise (Figure 11, 12 and Table 3). The core from
Morris Jesup Rise comprises sediment beyond
the range of 14C dating where ages were inferred
from benthic foraminifera marker events for MIS
5.1, 5.5 and 7 as described in chapter 3.3.2 of
this thesis and correlation to core PS2200 with
Table 2 Radiocarbon ages from cores LOMROG07-PC-04 and PC-08
14
Core depth (cm)
Lab no
C age
0–1
LuS 9047
6625 ± 55
LOMROG-PC-04
8–9
LuS 9046
31450 ± 300
16 – 17
LuS 9045
42050 ± 700
24 – 25
LuS 9044
*32600 ± 600
0 – 0.5
LuS 9043
6720 ± 50
LOMROG-PC-08
3–4
LuS 9042
14715 ± 90
7–8
LuS 9041
32950 ± 400
10 – 11
LuS 9040
37100 ± 5000
14 – 15
LuS 9039
> 47000
* The radiocarbon age is suspected to be too young due to low cathode current (too small sample
volume).
22
PC-08
D/L
Chronology
100
0
200
0 .2
0 .4
0
t.
based on
800 1600 0
R
800 1600 0
0
Age (ka)
PF*10 / g
BF / g
es
PF*10 / g
AA
PS2200-2/5
1-2
3
50
AAR age
Glu
estimated age
Asp
3
4
Sediment depth (cm)
B. aculeata
4
100
5
E. exigua
150
5
200
6
P. bulloides
250
6
7
300
350
Figure 11 Amino acid racemization results for core LOMROG07-PC-08 in relation to radiocarbon and
estimated ages based on biostratigraphic markers and the different chronological interpretations depending on
the dating method. D/L ratio is of glutamic acid (Glu) is plotted in red circles and aspartic acid (Asp) in blue
squares.
0
0 .1
0 .2
based on
0 .3
0
0 .4
R
60
C
40
14
20
AA
0
Chronology
D/L
Age (ka)
Glu
Asp
10
AAR age
cal 14C age
1 1
Sediment depth (cm)
20
30
2
40
3
50
3
60
70
0
2000
4000
PF >125 µm /g
Figure 12 Amino acid racemization results for core HLY0503-18TC in relation to calibrated radiocarbon ages
and the different chronological interpretations depending on the dating method.D/L ratio is of glutamic acid
(Glu) is plotted in red circles and aspartic acid (Asp) in blue squares.
23
Table 3. Amino acid racemization results of aspartic and glumatic acid and their conversion to ages. For
comparison the ages based on radiocarbon dating and estimated relative ages based on benthic
foraminifera markers and correlation. n = number of replica.
HLY0503-18TC
Depth
(cm)
n
Aspartic Acid
D/L
stdev
0.9
7.7
15.7
21.7
25.7
27.7
29.7
31.7
33.7
35.7
43.7
51.7
61.7
4
5
5
4
5
5
4
3
3
5
3
4
3
0.060
0.100
0.111
0.122
0.122
0.115
0.168
0.185
0.201
0.203
0.235
0.255
0.285
0.002
0.008
0.005
0.006
0.002
0.015
0.019
0.012
0.006
0.011
0.008
0.004
0.031
Glutamic Acid
D/L
stdev
0.018
0.031
0.031
0.037
0.036
0.035
0.052
0.060
0.071
0.067
0.089
0.093
0.110
Asp
0.001
0.003
0.002
0.002
0.002
0.005
0.010
0.002
0.004
0.007
0.004
0.003
0.012
1.4
4.7
6.0
7.5
7.5
6.6
15.7
19.5
23.6
24.1
33.9
40.7
52.8
Glutamic Acid
D/L
stdev
Asp
AAR age (ka)
Glu
average
2.5
5.7
5.8
7.7
7.4
6.9
13.2
16.9
21.9
19.8
31.2
33.7
44.1
2.0
5.2
5.9
7.6
7.4
6.7
14.4
18.2
22.7
22.0
32.5
37.2
48.4
14
C age
calib. (ka)
2.0
7.4
10.9
12.4
13.0
27.4
30.9
>38
>42
LOMROG-PC-08
Depth
(cm)
n
Aspartic Acid
D/L
stdev
2.5
4.5
7.5
9.5
11.5
14.5
20.5
85.5
95.5
105.5
115.5
125.5
140.5
150.5
160.5
200.5
245.5
255.5
265.5
275.5
4
6
6
4
6
3
6
5
3
6
5
3
3
6
5
4
4
4
3
4
0.123
0.169
0.188
0.208
0.243
0.237
0.206
0.279
0.329
0.354
0.343
0.321
0.377
0.386
0.350
0.434
0.406
0.402
0.439
0.435
14
* C age
0.006
0.013
0.005
0.009
0.027
0.003
0.013
0.006
0.008
0.021
0.026
0.009
0.029
0.008
0.017
0.052
0.018
0.010
0.010
0.007
0.045
0.063
0.073
0.087
0.095
0.101
0.075
0.117
0.141
0.164
0.167
0.141
0.165
0.186
0.151
0.223
0.201
0.180
0.224
0.231
0.006
0.007
0.004
0.005
0.017
0.006
0.011
0.005
0.005
0.018
0.013
0.009
0.022
0.007
0.012
0.031
0.007
0.009
0.020
0.004
10.6
18.2
23.0
30.0
34.6
38.6
24.0
48.6
65.5
83.5
85.9
65.8
84.6
102.4
73.3
136.2
115.1
96.4
137.8
144.4
9.1
17.0
21.6
27.7
35.6
36.5
24.4
49.4
69.4
85.0
83.1
67.6
92.3
104.0
79.0
137.3
116.8
106.3
140.0
141.8
est. age
(ka)
12.0**
17.4**
32.9*
35.7**
38.6**
>47*
50.0
75.0
79.0
82.0
85.0
96.0
119.0
123.0
127.0
200.0
213.0
226.0
240.0
14
** age based on linear extrapolation of C ages
a previously published age model (Spielhagen
et al., 2004). The AAR ages are in reasonable
agreement with estimations based on other proxies
until about 85 ka. Beyond about 85 ka, there is a
progressively increasing age discrepancy between
24
7.6
15.7
20.1
25.4
36.5
34.3
24.8
50.3
73.2
86.5
80.4
69.3
100.1
105.6
84.6
138.4
118.6
116.2
142.1
139.2
AAR age (ka)
Glu
average
calculated AAR ages and estimated ages based on
the benthic foraminiferal events. For the interval
estimated to belong to MIS 7 in core LOMROGPC-08 the AAR age suggests this sequence to be
100 ka younger. Difficulties already experienced
by Kaufman et al. (2008) is that the aspartic acid
D/L-ratio seems to reach a plateau above 0.4 and
the uncertainties in the chronologies of the used
sediment cores. Assuming that the last occurrence
of E. exigua is a chronostratigraphic marker
for MIS 5.5, then the AAR results suggest that
deepwater temperature at this site during MIS 5
was lower than at the other central Arctic Ocean
sites studied previously. Alternatively, the D/L
values indicate that the E. exigua occurrence is
younger than elsewhere, closer to 105 ka. The D/L
values from the P. bulloides marker event during
MIS 7 are beyond the range of applicability of
the existing age model of 150 ka (Kaufman et
al., 2008). More work is needed to determine the
temperature dependency of the rate of AAR in
N. pachyderma and to assess the bottom-water
history of core sites in the central Arctic Ocean.
5. Conclusions
Sediment cores from previously unsampled
areas of the central Arctic Ocean have been
analyzed in this thesis for the main purpose of
reconstructing late Quaternary paleoceanographic
conditions. The studied cores include one
retrieved from the central Lomonosov Ridge
Intra Basin. Radiocarbon dating of foraminifera
in this core yield late glacial sedimentation rates
as high as 7.0-9.4 cm/ka. These sedimentation
rates are higher than previously known to exist
anywhere in the central Arctic Ocean away
from the continental shelves. The relatively high
resolution of this Lomonosov Ridge core provides
new insights into the central Arctic Ocean late
glacial to Holocene paleoceanographic evolution,
specifically concerning variations in sea ice cover.
The other studied cores in this thesis are from a
previously neither cored nor mapped part of the
southern Lomonosov Ridge north of Greenland
and from the little explored Morris Jesup Rise.
These cores reveal calcareous foraminiferal
assemblages in sediments older than MIS 7. The
main conclusion from the core studies in this
thesis are summarized in following points:
(1) Variations in calcareous foraminiferal and
nannofossil abundance during MIS 1 and
MIS 3, as recorded in the Lomonosov Ridge
Intra Basin core, are proposed to be related
to changes in central Arctic Ocean summer
sea ice cover and inflow of subpolar North
Atlantic water. Less summer sea ice likely
caused more favorable conditions for planktic
and benthic foraminifera and thus higher
productivity.
(2) Radiocarbon calibration, using modeled
reservoir ages by Butzin (2005) and the
microfossil abundance records from this
study, suggests central Arctic Ocean reservoir
ages of > 1400 years during the deglaciation
after LGM. This high reservoir age positions
the Younger Dryas cold event (11.7 – 12.8 ka)
in the Lomonosov Ridge Intra Basin core to
an interval of low foraminiferal abundance.
Ventilation changes are recorded by a
progressive decrease in planktic to benthic
age difference from 1200 years during the
deglaciation to 700 years in the mid Holocene
and 250 in the late Holocene.
(3) Comparison
between
the
calibrated
radiocarbon ages and those derived from
amino acid racemization in the Intra Basin
core shows gradually larger discrepancies with
older ages beginning from early Holocene.
(4) Calcium data generated by XRF-scanning of
cores from the southern Lomonosov Ridge
and Morris Jesup Rise show patterns of
distinct high calcium intensity peaks separated
by intervals where the calcium content in
the sediment is close to zero, or below the
XRF detection limit. This signal appears to
be caused by the presence of both detrital
carbonate/dolomite, deposited by ice rafting,
and high planktic foraminiferal abundances.
This suggests that while ice rafting of
carbonate/dolomite debris occurred the
paleoceanographic conditions were generally
favorable for planktic foraminifera and also
permitted calcium carbonate preservation in
the sediments.
(5) The XRF calcium intensity peaks can be
used as a proxy for core to core correlation
as well as an aid to strategic sub-sampling for
microfossil analyses.
(6) Benthic foraminiferal assemblages north of
Greenland provide information about food
supply and sea ice cover. The presence of the
phytodetrital species Epistominella exigua in
sediments from MIS 5.5 and older suggests
increased primary production and less summer
ice cover.
(7) The occurrence of the subpolar planktic
foraminifera Turborotalita quinqueloba
in an interval older than MIS 7 suggests
25
changed ocean circulation patterns compared
to the modern setting and considerably less
sea ice. Morphologic and size differences
are visible among the specimens of this
interval, which probably represents MIS 11,
and the specimens observed in the smaller
size fraction during MIS 5. The altered
morphotype of T. quinqueloba could provide
a new biostratigraphic and biochronologic
marker.
(8) Stable carbon isotopes measured on the
benthic foraminifer Cassidulina neoteretis
show lighter values in the sediments from MIS
5.5 and older. A larger gradient of planktic to
benthic δ13C values with 12C depletion in the
surface and enrichment in the bottom waters
suggest a more efficient export of primary
productivity from the surface to the deep sea.
The combined results from the core studies
in this thesis suggest that the paleoceanographic
conditions in the central Arctic Ocean were
generally characterized by a different regime
prior to MIS 5. A transition towards more
modern oceanographic conditions began during
MIS 5.5. The older paleoceanographic regime is
manifested by: 1) low detrital carbonate input, 2)
absent to rare preserved planktic foraminifera, 3)
occurrence of calcareous benthic foraminifera,
4) presence of the phytodetrital benthic species
Epistominella exigua, 5) a peak of Turborotalita
quinqueloba tentatively assigned an age of MIS
11, and 6) generally lower δ13C measured on
benthic foraminifera.
Taken together, the biostratigraphy and studied
proxies seems to suggest less summer sea ice
cover and more bottom ventilation during the
interglacial periods prior to, and to some extent
during, MIS 5.
6. Acknowledgements
I can’t believe that this day has finally come.
First, I have to thank the persons who have
supported and encouraged my all my life, my
parents. Therefore, I will continue in german for a
while before I come back to the rest of you guys.
Mama und Papa, ihr habt keine Ahnung wieviel ihr
mir bedeutet. Ich bin euch so unendlich dankbar
für alle Unterstützung auch wenn ich mich mit
meinem Dickkopf mehr als einmal dagegen
gewehrt habe. Danke, dass ihr wie niemand
26
anderes immer an mich geglaubt habt und immer
da wahrt mit einem offenem Ohr für alle meine
Problemchen und alle meine Glücksmomente.
I would like to thank my supervisor Martin
Jakobsson and co-supervisor Jan Backman for
giving me the great opportunity of this project and
their support the writing this thesis and papers.
I am grateful to everyone assisting me with
the lab work, especially Åsa Wallin for sieving
all those samples and Klara Hajnal for the
isotope analyses. Marianne Ahlbom and Katerina
Karlsson for their patient help with the SEM and
telephone support on Saturday mornings. Matteo
Mellquist and Ludvig Löwemark for generating
the XRF data, and Matteo for one day coming into
your office and giving the inspiration for Paper
II with one of his plots. And not to forget Heike
Siegmund for watering my plants while I was
away on expedition.
To my office mates and friends Emma,
Benjamin and Moo, thanks for all the scientific
and, almost more important, all other talks.
Emma, do you remember how often we stood
in front of the Arctic map in our office, pointing
and wondering about ocean circulation? Thanks
Beni for not getting frustrated when I asked for
the tenth time how to save my figures and posters.
And Moo always happy and concerned about how
I felt. My proof readers and dear friends Verity
and Johanna, thanks for bearing with me during
these last month. I owe you big time.
Thanks to Otto Hermelin, Helen Coxall,
Michal Kucera and Karen-Luise Knudsen for
sharing their foraminiferal knowledge with me.
And all the open doors of colleagues and friends
at the department and all the people I forgot to
mention.
Thanks to Team Awesome and everybody who
was part of it for all the heated discussion and all
the fun we had.
My PhD position was financed by the
Department of Geological Sciences. Financial
support for some analytical work was granted by
the Ymer 80 foundation and the Swedish Society
for Anthropology and Geography (SSAG). I also
gratefully received travel funding by Bert Bolin
Climate Research School (BBCC), Stockholms
Marine Research Centre (SMF), C.F. Liljevalch’s
foundation, L&E Kinanders foundation and K &
A Wallenberg foundation.
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