PreprintPDF Available

Confusion and contamination of 8.2 ka cold climate records caused by the Storegga tsunami in the Nordic Seas

Authors:

Abstract and Figures

Since the end of the last ice age, no cold snap rivals the one dated to 8200 years ago. Its oceanic response has been reconstructed in part from sediments in the Norwegian Sea and North Sea. Here we show that these sediments have been reworked by currents generated by the Storegga tsunami, dated to the coldest decades of the 8.2 ka event. From a new simulation of the Storegga tsunami we calculated the maximum flow velocity to be 2–5 m/s on the shelf offshore western Norway and in the shallower parts of the North Sea, and up to about 1 m/s down to a water depth of 1000 m. We re-investigated sediment core MD95-2011, from which a large and abrupt 8.2 ka cooling had been inferred, and found the cold-water foraminifera to be re-deposited and 11,000 years of age. Oxygen isotopes of the recycled foraminifera and the content of sand grains, thought to be dropped from ice bergs, might have led to an interpretation of a too large and dramatic climate cooling. Our simulations imply that large parts of the sea floor in the North Sea and Norwegian Sea might have been reworked by currents during the Storegga tsunami.
Content may be subject to copyright.
Confusion and contamination of 8.2 ka cold climate
records caused by the Storegga tsunami in the
Nordic Seas
Stein Bondevik ( Stein.Bondevik@hvl.no )
Western Norway University of Applied Sciences
Bjørg Risebrobakken ( bjri@norceresearch.no )
NORCE Climate & Environment, Bjerknes Centre for Climate Research
Steven Gibbons ( steven.gibbons@ngi.no )
Norwegian Geotechnical Institute https://orcid.org/0000-0002-7822-0244
Tine Rasmussen ( tine.rasmussen@uit.no )
UiT the Arctic University of Norway
Finn Løvholt ( nn.lovholt@ngi.no )
Norwegian Geotechnical Institute
Article
Keywords:
Posted Date: September 26th, 2023
DOI: https://doi.org/10.21203/rs.3.rs-3082245/v2
License: This work is licensed under a Creative Commons Attribution 4.0 International License. 
Read Full License
Additional Declarations: There is NO Competing Interest.
1
Confusion and contamination of 8.2 ka cold climate
records caused by the Storegga tsunami in the Nordic
Seas
Stein Bondevik1, Bjørg Risebrobakken2, Steven J. Gibbons3, Tine L.
Rasmussen4 and Finn Løvholt3
1 Department of Environmental Sciences, Western Norway University of Applied
Sciences, P.O. Box 133, NO-6851 Sogndal, Norway.
2 NORCE Climate & Environment, Bjerknes Centre for Climate Research, Bergen,
Norway.
3 Norwegian Geotechnical Institute (NGI), P.O. Box. 3930 Ullevål Stadion, N-0806
Oslo, Norway.
4 Department of Geosciences, UiT the Arctic University of Norway, Tromsø,
Norway.
Corresponding author:
stein.bondevik@hvl.no
Keywords
8.2 ka event, Storegga tsunami, climate change, marine geology,
Norwegian Sea
Abstract
Since the end of the last ice age, no cold snap rivals the one dated
to 8200 years ago. Its oceanic response has been reconstructed in part
from sediments in the Norwegian Sea and North Sea. Here we show that
these sediments have been reworked by currents generated by the
Storegga tsunami, dated to the coldest decades of the 8.2 ka event. From
a new simulation of the Storegga tsunami we calculated the maximum
flow velocity to be 2–5 m/s on the shelf offshore western Norway and in
the shallower parts of the North Sea, and up to about 1 m/s down to a
water depth of 1000 m. We re-investigated sediment core MD95-2011,
from which a large and abrupt 8.2 ka cooling had been inferred, and
found the cold-water foraminifera to be re-deposited and 11,000 years of
age. Oxygen isotopes of the recycled foraminifera and the content of sand
2
grains, thought to be dropped from ice bergs, might have led to an
interpretation of a too large and dramatic climate cooling. Our
simulations imply that large parts of the sea floor in the North Sea and
Norwegian Sea might have been reworked by currents during the
Storegga tsunami.
3
Introduction
Tsunamis can disturb the seabed and rework offshore sediments.
Investigations after the 2011 Tohoku tsunami in Japan showed
redeposited mud and sorted sand layers on the Sendai shelf down to
~100 m water depth (Ikehara et al., 2021). Resuspended sediments were
also carried offshore and continued down the slope to deep water, as
turbidity currents (Arai et al., 2013). The Storegga slide in the Norwegian
Sea (Bryn et al., 2005) triggered a giant tsunami (Bondevik et al., 2005).
Deposits from this tsunami have been extensively mapped onshore in
Scotland (e.g. Dawson et al., 1988; Smith et al., 2004), Norway (e.g.
Bondevik et al., 1997), Shetland (Bondevik et al., 2003; Smith et al.,
2004), and the Faroe Islands (Grauert et al., 2001). Most likely, currents
in the Storegga tsunami must also have disturbed the seabed and
reworked offshore sediments, but to what extent?
For long wave tsunamis, such as the one generated by the Storegga
Slide, the currents are uniform from the surface to near the
water/sediment interface at the sea floor and are a function of surface
elevation (wave amplitude) and water depth. The maximum horizontal
flow velocity,
umax,
in a propagating tsunami can then be approximated to
the maximum surface elevation
ηmax
through the expression:
u
max
=
η
max
d
g
d
where
d
is water depth and
g
is the gravitational constant. If the
maximum sea surface elevation is 5 m and the water depth is 250 m, the
maximum horizontal velocity will be approximately 1 m/s. According to
the classical diagram of Hjulström (1935), that relates flow speed to
erosion, transportation and deposition of different grain sizes, a velocity
of 1 m/s will erode and entrain a wide range of grain sizes, from very fine
silt to fine pebbles (5μm to 7 mm).
The Storegga tsunami has been dated to the coldest decades of the
8.2 ka climatic event. Radiocarbon measurements of green moss
fragments, picked out of the onshore tsunami deposits, were dated to
4
7300±20 14C years BP (Bondevik et al., 2012) and calibrated to 8080–
8180 cal yr BP (8140±30 years ago, see age calibration in Supplementary
Information). The moss had still small amounts of intact chlorophyll, and
thus must have been killed during the tsunami. According to the
correlation with the Greenland ice cores, the date assigns the Storegga
tsunami to the coldest part of the 160-year-long interval of the 8.2 ka
event (Bondevik et al., 2012).
Here we ask the following question:
Could the 8.2 ka cold event, as
reconstructed from marine sediment cores in the North Sea and
Norwegian Sea, be contaminated or confused with sediments re-
deposited by the Storegga tsunami?
We answer by simulating the
maximum flow velocity of the Storegga tsunami in the Norwegian Sea
and North Sea and re-investigate a sediment core from the Vøring
plateau, about 200 km offshore Norway in a water depth of 1048 m – one
of the few North Atlantic marine sediment cores that recorded a distinct
and dramatic cooling, the 8.2 ka event (Risebrobakken et al., 2003;
Tegzes et al., 2014). Our short answer to the question is yes.
Results
Computer simulations of the Storegga Slide and tsunami
We obtained flow velocities generated by the Storegga tsunami in the
North Sea and Norwegian Sea from computer simulations of the landslide
and ensuing tsunami using a linear shallow water model (e.g. Bondevik et
al., 2005; Harbitz, 1992). The Storegga Slide was modelled as a cohesive
clay-rich debris flow. The following tsunami waves were simulated from
the time-dependent changes in water depth caused by the moving
landslide (Løvholt et al., 2017). We chose parameters of the landslide
rheology that best matched the run-out of the landslide and the observed
run-up heights of the tsunami deposits (Kim et al., 2019) (See methods for
details).
The simulated maximum flow velocity of the Storegga Slide tsunami
reflects the maximum wave amplitude and water depth. On the
5
Norwegian shelf and in the North Sea we calculate maximum velocities
larger than 1 m/s at depths shallower than 250 m (Fig. 1, Supplementary
Figs. 1a, b, d). On the shallowest shelves, around Shetland, the Faroe
Islands and in Western Norway, maximum velocities are between 2 and 5
m/s. At many places with depth down to 1000 m we also simulated
velocities above 1 m/s, especially in vicinity of the Storegga Slide (Fig 1).
The strongest simulated currents were due to the initial drawdown of
water from the Norwegian shelf towards the backwall of the Storegga
Slide; the currents here reached 5–10 m/s and the sea surface waters
lowered by 15–30 m (Supplementary Fig. 1b).
6
Fig. 1| Maximum flow velocity of the Storegga tsunami as
calculated for each grid point during the 10 h simulation time.
White triangles show location of marine sediment cores of the “8.2
event”. Purple triangles (a, b, c and d) are additional locations of
simulated time series (Supplementary Fig. 1). The white outline of the
Storegga Slide is the run-out of landslide debris (Haflidason et al., 2004),
the continuation of turbidites is not shown. Pixels in red-brown have
maximum velocity > 5 m/s and < 20 m/s. Green circles are onshore
locations of Storegga tsunami deposits (Bondevik, 2019). Depth contours
are paleo-bathymetry used in the simulations. Countries are shown with
their present-day coastlines.
7
Re-investigation of the 8.2 ka cold event layer in the Norwegian Sea
We re-investigated sediment core MD95-2011 that had revealed very
distinct changes identified as a response to the 8.2 ka climatic event
(Risebrobakken et al., 2003; Tegzes et al., 2014). The core was retrieved
from the inner part of the Vøring plateau on the slope towards the shelf
break (Fig. 1), in an area of high sedimentation rates (Rumohr et al.,
2001). Currents at the core location are at present too weak (< 1cm/s) to
influence the bottom sediments (Voet et al., 2010). However, during the
Storegga tsunami the simulations show a current speed of 39 cm/s
corresponding to a wave amplitude of 3.8 m (Fig. 2a).
The proxies of the sediment core show a well-defined anomaly
dated to around 8100 years ago. The anomaly, in a two-centimeter-thick
layer, from 533–535 cm, shows a significant change in grain size, in the
number of foraminifera, in the species of foraminifera, and in oxygen
isotope values (Fig. 3).
The mixture of foraminiferal species in this layer indicates re-
sedimentation. The abundances of both the cold polar species,
Neogloboquadrina pachyderma
and the warm Atlantic species
Neogloboquadrina incompta
increase 12–14 times (Fig. 3b). We also find
a large number of benthic foraminifera that belong to environments of
shallower water and stronger currents than presently found at the core
site (Fig. 3c) (Mjelde, 2002). Oxygen isotope values 18O) of
N.
pachyderma
increase from 2.25 to 2.95 ‰ at this level (Fig. 3d) which
would indicate a cooling of 3oC of the surface ocean water. This anomaly
is not seen in the oxygen isotopes of
N. incompta
(Risebrobakken et al.,
2003).
8
Fig. 2 | Simulation of wave height (blue line) and flow velocity
(dotted) during the Storegga tsunami at the location of marine
sediment cores with an 8.2 ka layer. Paleo-water depths in brackets.
For core locations, see Fig. 1. a Core site MD95-2011 at the Vøring
plateau in the Norwegian Sea. b Core site LINK14 east of the Faroe
Island and c Core site Troll, 28-03 in the Norwegian channel.
9
TABLE 1. RADIOCARBON MEASUREMENTS OF PLANKTONIC FORAMINIFERA OF THE
«8.2 ka EVENT» LAYER IN CORE MD95-2011
Depth
(cm)
Species
Weight
(mg)
δ13C
(‰
PDB)
14C age BP
(yr)
Calibrated yr
BP
(2 σ-range)*
Above the 8.2 ka layer
531–
532
N. incompta
0.7
–3.80
7810 ± 100
7980–8500
531–
532
N.pachyderm
a
0.7
–1.26
7600 ±
140
7710–8350
Within the 8.2 ka layer
533–
534
N.
pachyderma
1.0
–2.55
10,220 ±
140
10,990–
11,880
534–
535
N.
pachyderma
8.3
1.0§
9900 ± 60
10,690–
11,170
533–
534
N. incompta
5.0
8530 ± 160
8670–9520
534–
535
N. incompta
8.1
1.0§
8375 ± 55
8680–9190
Below the 8.2 ka layer
536–
537
N. incompta
0.7
–2.88
7860 ± 110
8010–8580
536–
537
N.pachyderm
a
0.67
–2.32
8080 ± 100
8290–8900
* Radiocarbon ages were calibrated to calendar years with the dataset Marine20
(Heaton et al. 2020) using a local marine reservoir correction of R = –145 ± 35.
Not used in the age modelling. Measured on the leached fraction of the foraminifera
sample, main fraction too small to measure.
§ Assumed value.
We radiocarbon-dated the planktonic foraminifera in the 8.2 ka
layer and found them to be much older than 8200 yr BP (Table 1). From
the lowest centimeter of the layer (534–535 cm) we dated the cold-water
species
N. pacyderma
to 10,690–11,170 cal yr BP and the warm-water
species
N. incompta
to 8680–9190 cal yr BP (Table 1 and Fig. 3b). From
the next cm up-core, within the layer,
N. pacyderma
was dated to 10,990–
11,880 and
N. incompta
to 8670–9520 cal yr BP. All these ages are older
than the radiocarbon dates below the layer, and especially the dates of
N.
pachyderma
are about 2500–3000 years older than 8200 year BP. The
high δ18O value of this species (2.95 ‰) is comparable to the Early
10
Holocene or Younger Dryas values in the same core (Risebrobakken et
al., 2003) and in agreement with their radiocarbon ages.
11
Fig. 3| Data from core MD95-2011 plotted according to age. a
Percentage of grains > 63 μm and the number of grains > 150 μm per
gram sediments. b Number of planktonic foraminifera, the blue line is for
the cold-water species
Neogloboquadrina pachyderma
and the red line is
12
for the warm-water species
Neogloboquadrina incompta.
New 14C dates
(this study) are plotted. c Percentage of benthic foraminifera that could
indicate re-deposition, shelf species
Trifarina angulosa
and
Elphidium
excavatum
(Mjelde, 2002)
.
d Oxygen isotopes of
Neogloboquadrina
pachyderma
. e Green curve shows the modelled distribution of the ages
of onshore green moss fragments within the Storegga tsunami, grey
curve is the original distribution (Bondevik et al., 2012). (See
Supplementary Information for age modelling).
The 8.2 ka layer fines upwards and has an erosive lower boundary.
The radiocarbon dates show a jump in ages across the layer and this jump
indicates a time gap in the stratigraphy. We thus included a hiatus at the
lower boundary (535 cm) in the age-depth modelling. The best fit shows a
time gap or hiatus of 400 years (Supplementary Fig. 5). According to the
sedimentation rates this corresponds to as much as 20 cm of erosion
(stippled lines in Fig. 3 a–d). The counts of mineral grains > 150μm, grain
size and amounts of foraminifera, both planktonic and benthic (Fig. 3a,
b), shows that the lowest centimeter (534–535 cm) is coarser grained
than the next centimeter higher up (533–534 cm), indicating that the
layer is normally graded.
All data support the hypothesis that the 8.2 ka layer in MD95-2011
is a turbidite. The erosive lower boundary, the upward fining of grains,
the large amounts of redeposited older foraminifera and especially the
high number of benthic foraminifera that thrive in shallower water
confirm our suggestion that this layer is a fine grained turbidite deposited
from the shelf break. Although the core site experienced currents directly
from the propagating tsunami (Fig. 2a), we conclude that the 8.2 ka layer
was deposited from a turbidity current released from sediments eroded
and transported to the shelf break in the tsunami backwash.
Discussion
Layers similar to the sand layer in MD95-2011 were found offshore
Japan after the Tohoku tsunami in 2011. A fine-grained soft sediment
layer covered wide areas of the deep sea outside the Sendai shelf after
13
the Tohoku tsunami (Ikehara et al., 2021; Usami et al., 2017). Evidence of
the turbidity currents came from an ocean bottom pressure sensor,
deployed at a water depth of 1052 m. The sensor was caught in the
turbidity current and transported 1 km downslope three hours after the
earthquake (Arai et al., 2013). The interpretation is that the tsunami
backflow carried sediments to the shelf and this cloud of suspended
sediments rushed down the slope because of excess density. The moving
suspension cloud grew into turbidity currents incorporating sea floor
sediments and the ocean bottom pressure sensor. After 1 km downslope
movement the 60 cm wide, 42-kilogram, sensor settled and, when the
cloud came to rest, the sediments settled: sand first followed by finer
grains. We think it is possible that similar sheet-like turbidity currents
could have been initiated along the shelf areas in the Norwegian Sea due
to suspension induced by the Storegga tsunami backwash.
Sediment core (LINK14) from a trough on the eastern shelf of the
Faroe Islands (Fig. 1, Supplementary Table 1), has an ‘8.2 ka layer’
interpreted by Rasmussen and Thomsen (2010) as deposited directly from
the Storegga tsunami currents. A fine sand layer (63–150 μm) between
114 and 116 cm core depth, shows an increase in larger-sized planktic
and benthic foraminifera. Small planktic species are absent. The peculiar
composition of the fauna, indicative of warmer sea surface temperatures,
led the authors to conclude that this layer was subject to some kind of
sorting effect, possibly from currents in the Storegga tsunami. Our
tsunami simulations show that the sediment core site would experience
quite strong currents of 1.2 and 1.75 m/s (Fig. 2b). These currents could
transport sand from the shallower banks into the trough. Both
Hjulström's diagram (Hjulström, 1935) and Weiss (2008) show that such
strong currents would erode sediments with grain sizes of fine silt to fine
pebbles.
Core 28–03 in the Norwegian Channel (Fig. 1; Supplementary Table
1) also show a distinct and sudden 8.2 ka event (Klitgaard-Kristensen et
14
al., 1998) that we think could be contaminated from currents in the
Storegga tsunami. The layer assigned to the 8.2 ka event is 3–4 cm thick
(~341–344 cm core depth), of clay-rich silts, and the age of the upper
boundary is ca. 8200 cal yr BP (Supplementary Information). The
strongest simulated currents are 0.7 m/s (Fig. 2c) and are aligned parallel
to the Norwegian Channel (Fig. 1). According to Hjulström (1935) these
currents could stir up fine-grained sediments (clayey silts) in the trench
(Klitgaard-Kristensen et al., 2002) and possibly rework and redeposit the
foraminifera.
The simulations also reveal strong currents on the shelf around
Iceland (Supplementary Figs. 1 and 2). Andrews and Giraudeau (2003)
found high amounts of reworked Neogene (Late Tertiary) coccoliths in a
sediment core from a shallow basin at 164 m depth, dated to 8.2 ka BP.
The peak of coccoliths was a unique signature of the 5.5 m long sediment
core and was inferred to be the result of erosion of Neogene outcrops and
re-sedimentation. Farther off the Icelandic coast, at 440 m water depth,
there might also be indications of re-sedimentation in core MD99-2275
(Supplementary Figs. 2 and 3). Knudsen et al. (2008) found a distinct
minimum in magnetic susceptibility followed by a peak of the epifaunal
foraminifera
Cibicides lobatulus
between 8200 and 8000 cal yr BP.
Radiocarbon ages of
C. lobatulus
are about 1500 years older than the
molluscs (Knudsen pers. comm., 2023). The authors suggested that the
peak in
C. lobatulus
might be due to reworking. We think it is possible
that this erosion and reworking was caused by the Storegga tsunami.
Conclusion
Large parts of the ocean floor between Norway, Iceland, and Greenland
could have experienced Storegga tsunami currents strong enough to
rework and move sediments. According to our simulations, a maximum
flow velocity of 25 cm/s or larger, capable of moving grains up to 1 mm,
was simulated down to about 1000 m water depth between 58° and 74° N
15
(Supplemental Fig. 3). In addition, turbidity currents could have been
released from the shelf breaks forming turbidites – as demonstrated for
core MD95-2011 at the Vøring plateau.
The previous climate reconstructions of a large and abrupt 8.2 ka
cooling from marine sediment cores in this area are thus faulty and
should be discarded. Instead, sea floor sediments showing a strong 8.2 ka
anomaly with evidence of re-working should rather be considered as a
deep-water Storegga tsunami deposit.
Methods
Computer simulations
Estimating critical velocity for erosion
We estimated the critical velocity for erosion at the two sediment
core sites LINK14 and 28-03 (Fig. 1). First, we plotted the maximum
simulated current velocities for each site in the Hjulström's diagram
(Hjulström, 1935), to see if the current velocities where higher than the
threshold for erosion of the grain sizes in the 8.2 ka layer. Secondly, we
used the procedure described by Weiss (2008) based on Shields diagram
(Yalin, 1977), and solved numerically the non-linear equation 3 in Weiss'
paper for the critical velocity for setting grains in motion. We noted that
the critical velocity for erosion were slightly higher using Hjulström's
diagram than Shields diagram (Weiss, 2008). Both methods estimated
higher velocities than the threshold for erosion of the grain sizes in the
8.2 ka layer at the two sediment core sites.
Computer simulation of Storegga slide and tsunami
The tsunami generated by the Storegga slide is modelled in two
stages. First, the dynamics and time-evolution of the slide itself are
simulated using the two-layer depth-averaged BingCLAW model (Kim et
al., 2019), developed for cohesive clay-rich landslides. Secondly, the
tsunami propagation, driven by the time-dependent changes in the water
16
depth modelled by BingCLAW, is simulated using the GloBouss tsunami
model (e.g. Løvholt et al., 2008; Løvholt et al., 2010; Løvholt et al., 2015).
The simulations used ocean depths as derived by Hill et al. (2014) that
account for changes in bathymetry since 8150 yr BP, covering a region
from 12.5°W to 16.6°E and 53.3°N to 70.0°N on a grid with
approximately 2 km spacing. Both landslide and tsunami simulations
were run for a duration of 10 hours which was deemed sufficient to
capture the evolution of the water wave over all geographical regions of
interest.
The landslide dynamics and runout are controlled by several
parameters describing the rheology of the flow. We chose the landslide
parameters that gave the best match to the observed tsunami run-up
heights (Bondevik et al., 2005), as guided by the sensitivity study of Kim
et al. (2019). The landslide simulation in the current study uses a volume
of 3200 km3, an initial yield strength,
τ
i
, of 12 kPa, a residual yield
strength,
τ
r
, of 3 kPa, a remoulding coefficient, Γ, of 0.0005, and an
added mass parameter,
c
m
, of 0.1. All other parameters are held to the
fixed values employed by Kim et al. (2019).
In this study we have used a landslide volume of 3200 km3, close to
the original volume estimate (Haflidason et al., 2004). Recently Karstens
et al. (2023) suggested that the volume of the Storegga slide should be
reduced to 1300–2300 km3. We emphasize that such a reduced volume is
not expected to change the conclusions found herein for the following
reasons: Firstly, the simulated waves and currents are calibrated towards
observed tsunami run-up heights (e.g. Bondevik et al., 2005). The
landslide is strongly linked to the properties of the slide material at the
time, which are uncertain (Kim et al., 2019). By reducing the strength
properties of the slide material, we can likely reproduce the same
amplitudes and currents of the tsunami with such a smaller landslide
volume. Secondly, the wave generation is dominated by the slide material
from farthest up the slope, in shallow water. In the study by Karstens et
17
al. (2023) the location of the slide material is not much altered compared
to the original reconstruction.
Data availability and Resources/Acknowledgements
The source code for the BingCLAW program that computes the evolution
of the viscoplastic debris flow is available from
https://github.com/norwegian-geotechnical-institute/BingCLAW_5.6.1
(last accessed 2023/08/23). BingCLAW requires the CLAWPACK software
library and all its dependencies. CLAWPACK is available for download
from http://www.clawpack.org/ (version 5.6.1 required: last accessed
2023/08/23). The source code to the GloBouss software for calculating
the tsunami is found on https://github.com/geirkp/geirkp.github.io (last
accessed 2023/08/23). Details of the implementation of the numerical
model are found in the document
https://github.com/geirkp/geirkp.github.io/blob/master/SUP/globouss/rap
port.pdf
We are grateful to Jon Hill for providing a file of the paleobathymetry
from his 2014 paper on which the tsunami simulation was calculated.
The map of the output from the tsunami simulation is generated using
GMT software (Wessel et al., 2019) available from https://www.generic-
mapping-tools.org/ (last accessed 2023/08/23).
References
Andrews, J. T., and Giraudeau, J., 2003, Multi-proxy records showing
significant Holocene environmental variability: the inner N. Iceland
shelf (Húnaflói): Quaternary Science Reviews, v. 22, no. 2, p. 175-
193.
Arai, K., Naruse, H., Miura, R., Kawamura, K., Hino, R., Ito, Y., Inazu, D.,
Yokokawa, M., Izumi, N., Murayama, M., and Kasaya, T., 2013,
Tsunami-generated turbidity current of the 2011 Tohoku-Oki
earthquake: Geology, v. 41, no. 11, p. 1195-1198.
Bondevik, S., 2019, Tsunami from the Storegga Landslide,
in
Meyers, R.
A., ed., Encyclopedia of Complexity and Systems Science: Berlin,
Heidelberg, Springer Berlin Heidelberg, p. 1-33.
Bondevik, S., Løvholt, F., Harbitz, C., Mangerud, J., Dawson, A., and Inge
Svendsen, J., 2005, The Storegga Slide tsunami—comparing field
observations with numerical simulations: Marine & Petroleum
Geology, v. 22, no. 1/2, p. 195-208.
Bondevik, S., Mangerud, J., Dawson, S., Dawson, A., and Lohne, Ø., 2003,
Record-breaking height for 8000-year-old tsunami in the North
Atlantic: Eos, Transactions American Geophysical Union, v. 84, no.
31, p. 289.
Bondevik, S., Stormo, S. K., and Skjerdal, G., 2012, Green mosses date
the Storegga tsunami to the chilliest decades of the 8.2 ka cold
event: Quaternary Science Reviews, v. 45, p. 1-6.
18
Bondevik, S., Svendsen, J. I., Johnsen, G., Mangerud, J., and Kaland, P. E.,
1997, The Storegga tsunami along the Norwegian coast, its age and
runup: Boreas, v. 26, no. 1, p. 29-53.
Bryn, P., Berg, K., Forsberg, C. F., Solheim, A., and Kvalstad, T. J., 2005,
Explaining the Storegga Slide: Marine and Petroleum Geology, v.
22, no. 1–2, p. 11-19.
Dawson, A. G., Long, D., and Smith, D. E., 1988, The Storegga Slides:
Evidence from eastern Scotland for a possible tsunami: Marine
Geology, v. 82, no. 3–4, p. 271-276.
Grauert, M., Björck, S., and Bondevik, S., 2001, Storegga tsunami
deposits in a coastal lake on Suouroy, the Faroe Islands: Boreas, v.
30, no. 4, p. 263-271.
Haflidason, H., Sejrup, H. P., Nygård, A., Mienert, J., Bryn, P., Lien, R.,
Forsberg, C. F., Berg, K., and Masson, D., 2004, The Storegga
Slide: architecture, geometry and slide development: Marine
Geology, v. 213, no. 1–4, p. 201-234.
Harbitz, C. B., 1992, Model simulations of tsunamis generated by the
Storegga Slides: Marine Geology, v. 105, no. 1–4, p. 1-21.
Hjulström, F., Studies of the morphological activity of rivers as illustrated
by the River Fyris1935, Volume 25, Bulletin of the Geological
Institute University of Uppsala, p. 221-527.
Ikehara, K., Irino, T., and Saito, Y., 2021, The 2011 Tohoku-oki tsunami-
induced sediment remobilization on the Sendai shelf, Japan, from a
comparison of pre- and post-tsunami surface sediments: Scientific
Reports, v. 11, no. 1, p. 7864.
Kim, J., Løvholt, F., Issler, D., and Forsberg, C. F., 2019, Landslide
Material Control on Tsunami Genesis—The Storegga Slide and
Tsunami (8,100 Years BP): Journal of Geophysical Research:
Oceans, v. 124, no. 6, p. 3607-3627.
Klitgaard-Kristensen, D., Fetter Sejrup, H., and Haflidason, H., 2002,
Distribution of recent calcareous benthic foraminifera in the
northern North Sea and relation to the environment: Polar
Research, v. 21, no. 2, p. 275-282.
Klitgaard-Kristensen, D., Sejrup, H. P., Haflidason, H., Johnsen, S., and
Spurk, M., 1998, A regional 8200 cal. yr BP cooling event in
northwest Europe, induced by final stages of the Laurentide ice-
sheet deglaciation?: Journal of Quaternary Science, v. 13, no. 2, p.
165-169.
Knudsen, K. L., Søndergaard, M. K. B., Eiríksson, J., and Jiang, H., 2008,
Holocene thermal maximum off North Iceland: Evidence from
benthic and planktonic foraminifera in the 8600–5200 cal year BP
time slice: Marine Micropaleontology, v. 67, no. 1, p. 120-142.
Løvholt, F., Bondevik, S., Laberg, J. S., Kim, J., and Boylan, N., 2017,
Some giant submarine landslides do not produce large tsunamis:
Geophysical Research Letters, v. 44, no. 16, p. 8463-8472.
Mjelde, E., 2002, Paleoseanografi og paleoklimatologi i De nordiske hav
siste 11 600 år, basert på studier av planktoniske og bentiske
foraminiferer i marine kjerner fra Vøringplatået [Cand. scient:
Universitetet i Bergen.
19
Rasmussen, T. L., and Thomsen, E., 2010, Holocene temperature and
salinity variability of the Atlantic Water inflow to the Nordic Seas:
The Holocene.
Risebrobakken, B., Jansen, E., Andersson, C., Mjelde, E., and Hevrøy, K.,
2003, A high-resolution study of Holocene paleoclimatic and
paleoceanographic changes in the Nordic Seas: Paleoceanography,
v. 18, no. 1.
Rumohr, J., Blaume, F., Erlenkeuser, H., Fohrmann, H., Hollender, F.-J.,
Mienert, J., and Schäfer-Neth, C., 2001, Records and Processes of
Near-Bottom Sediment Transport along the Norwegian-Greenland
Sea Margins during Holocene and Late Weichselian (Termination I)
Times,
in
Schäfer, P., Ritzrau, W., Schlüter, M., and Thiede, J., eds.,
The Northern North Atlantic: A Changing Environment: Berlin,
Heidelberg, Springer Berlin Heidelberg, p. 155-178.
Smith, D. E., Shi, S., Cullingford, R. A., Dawson, A. G., Dawson, S., Firth,
C. R., Foster, I. D. L., Fretwell, P. T., Haggart, B. A., Holloway, L.
K., and Long, D., 2004, The Holocene Storegga Slide tsunami in the
United Kingdom: Quaternary Science Reviews, v. 23, no. 23–24, p.
2291-2321.
Tegzes, A. D., Jansen, E., and Telford, R. J., 2014, The role of the
northward-directed (sub)surface limb of the Atlantic Meridional
Overturning Circulation during the 8.2 ka event: Clim. Past, v. 10,
no. 5, p. 1887-1904.
Usami, K., Ikehara, K., Jenkins, R. G., and Ashi, J., 2017, Benthic
foraminiferal evidence of deep-sea sediment transport by the 2011
Tohoku-oki earthquake and tsunami: Marine Geology, v. 384, p.
214-224.
Voet, G., Quadfasel, D., Mork, K. A., and Søiland, H., 2010, The mid-depth
circulation of the Nordic Seas derived from profiling float
observations: Tellus A, v. 62, no. 4, p. 516-529.
Weiss, R., 2008, Sediment grains moved by passing tsunami waves:
Tsunami deposits in deep water: Marine Geology, v. 250, no. 3-4, p.
251-257.
Acknowledgements
Maarten Blaauw answered questions about the age-depth modelling.
Morten Hald suggested us to radiocarbon date the foraminifera at the 8.2
ka spike. Radiocarbon measurements were supported by Research
council of Norway, project no. 325333.
Author contributions
S.B. conceived the idea of the paper and wrote the first draft of the
manuscript. B.R led the re-investigation of sediment core MD95-2011 and
picked foraminifera for radiocarbon dating. S.G. simulated the currents
and surface elevation of the Storegga tsunami under the guidance of F.L.
20
T.L.R picked foraminifera for new radiocarbon dates in sediment core
LINK14. All authors contributed to the final version of the paper.
Supplementary information
The online version contains supplementary material available at https://
Supplementary Files
This is a list of supplementary les associated with this preprint. Click to download.
SupplementaryInformationBondeviketal.pdf
ResearchGate has not been able to resolve any citations for this publication.
Article
Full-text available
Tsunamis are generally considered to disturb the seafloor, rework surface sediments, and change seafloor environments. However, the response of the seafloor to such extreme wave events has not been fully elucidated. Herein, we compare the surface sediments before and after the 2011 Tohoku-oki tsunami on the Sendai shelf and demonstrate that both sandy and muddy sediments were significantly reworked on the shelf. Muddy sediments (> 10 cm thick) were redeposited as graded mud with no or little bioturbation, characterizing the offshore muddy tsunami deposit, while well-sorted sand was found as the sandy tsunami deposit. This redeposited layer could also be retained in the shelf mud sequence. The results imply that the high friction velocity of the tsunami wave and its long-term effect on Sendai Bay might contribute to the large sediment reworking. Part of the resuspended mud moved offshore to the slope area as turbidity currents. Thus, the tsunami is an important mechanism not only for shelf sedimentation but also for deep-sea sedimentation along active plate margins. The detection of 134Cs derived from the Fukushima Daiichi Nuclear Power Plant accident in the redeposited mud indicates that the suspended shelf water state was maintained for some days after the tsunami.
Article
Full-text available
Tsunami generation from subaqueous landslides is controlled by landslide kinematics, which in turn is governed by the material properties of the slide mass. Yet the effect of the material properties on tsunami genesis is poorly understood. Geomorphological observations of landslide runout put constraints on the landslide dynamics. In addition, observations of tsunami runup heights can improve our understanding of how the landslide material transforms from initiation to final runout. The giant prehistoric Storegga Slide off the mid‐Norwegian coast caused a well‐documented ocean‐wide tsunami that offers a unique setting for coupling landslide material models to tsunami generation models. In this study we simulate the dynamics of the Storegga Slide and tsunami using the depth‐averaged landslide model BingClaw, which implements visco‐plastic rheology and remolding, and couple it to a standard tsunami propagation model. A broad sensitivity study varying the landslide material strength parameters in BingClaw shows that the initial soil yield strength and remolding rate are most important for the tsunami genesis but that the residual strength determined the final runout distance. BingClaw parameters were further optimized to obtain the observed runout distance and to minimize the relative error of the tsunami runup heights. As detailed time‐dependent three‐dimensional representations of landslide parameters cannot be determined through a field investigation of the landslide itself, these simulations of the Storegga Slide and tsunami can help in the selection of plausible parameter ranges for prognostic modeling in quantitative hazard assessments.
Article
Full-text available
Landslides are the second-most important cause of tsunamis after earthquakes, and their potential for generating large tsunamis depend on the slide process. Among the world's largest submarine landslides is the Storegga Slide that generated an ocean-wide catastrophic tsunami, while no traces of a tsunami generated from the similar and nearby Trænadjupet Slide have been found. Previous models for such landslide tsunamis have not been able to capture the complexity of the landslide processes, and are at odds with geotechnical and geomorphological data that reveal retrogressive landslide development. The tsunami generation from these massive events are here modeled with new methods that incorporate complex retrogressive slide motion. We show that the tsunamigenic strength is closely related to the retrogressive development, and explain for the first time, why similar giant landslides can produce very different tsunamis, sometimes smaller than anticipated. Because these slide mechanisms are common for submarine landslides, modeling procedures for dealing with their associated tsunamis should be revised.
Article
Full-text available
The so-called "8.2 ka Event" has been widely regarded as a major climate perturbation over the Holocene. It is most readily identifiable in the oxygen-isotope records from Greenland ice cores as an approximately 160 yr-long cold interval between 8250-8090 yr BP. The prevailing view has been that the cooling over Greenland, and potentially over the northern North Atlantic at least, was triggered by the catastrophic final drainage of the Agassiz-Ojibway proglacial lake as part of the remnant Laurentide Ice Sheet collapsed over Hudson Bay at around 8420 ± 80 yr BP. The consequent freshening of surface waters in the northern North Atlantic Ocean and the Nordic Seas resulted in weaker overturning, hence reduced northward heat transport. Here we present proxy records from site JM97-MD95-2011 on the mid-Norwegian Margin indicating a (sharp) decline in the strength of the eastern branch of the Atlantic Inflow into the Nordic Seas immediately following a uniquely large drop in (sub)surface ocean temperatures coeval with the lake outbursts. We propose that the final drainage of Lake Agassiz-Ojibway was accompanied by a major iceberg discharge from Hudson Bay, which resulted in the cooling of the northward-directed northern Gulf Stream-North Atlantic Drift-Norwegian Atlantic Current system. Since our current-strength proxy records from the mid-Norwegian Margin do not evidence an exceptionally strong reduction in the main branch of the Atlantic Inflow into the Nordic Seas at the time, we argue that a chilled northward-directed (sub)surface-current system and an already colder background climate state could be the main factors responsible for the 8.2 ka climate perturbation.
Article
Full-text available
Piston core LINK14 from 346 m water depth on the eastern shelf of the Faroe Islands in the Faroe-Shetland Channel has been investigated in order to reconstruct temperature and salinity changes of the Atlantic surface Water during the Holocene. We have analyzed the distribution of benthic and planktic foraminifera, stable isotopes and calculated by transfer functions absolute surface, subsurface and bottom water temperatures and salinities. The summer sea surface temperature (SST) shows a stepwise decrease from an early-Holocene warm phase 10 300—8300 yr BP with temperatures around 12°C, over a mid-Holocene cooler phase 8300—4000 yr BP, to a late-Holocene relatively cool phase with SST around or slightly below 11°C. Bottom water temperatures at 346 m water depth show much less variation than the SST. The late-Holocene sea surface cooling was probably caused by increase in the influence of the polar East Icelandic Current. A distinct decrease in the subsurface salinity from about 8300 to 6800 yr BP is probably also due to a stronger East Icelandic Current. The benthic faunas indicate strong bottom current activity during the entire period. A single exceptional disturbance dated to approximately 8300 yr BP was probably caused by extraordinary high bottom current velocities. The event is marked by a significant coarsening of the sediments and a sorting by size of the foraminifera. The event is close in time to the 8.2-ka cooling event, but more likely correlates with the Storegga slide event.
Article
Benthic foraminiferal assemblages within turbidites recovered from two upper slope stations off Sendai Bay, northeast Japan, have been analyzed to estimate the source area of the turbidites resulting from the 2011 Tohoku-oki earthquake and tsunami. The turbidite at one station (St. 5; 893 m water depth) is composed of a surface layer that contains foraminiferal species living on the outer shelf or inner bay, and a lower part with bathyal species. In the turbidite at the second station (St. 6; 1446 m), the assemblage consists of only bathyal species (living in 800–1000 m). The composition of the St. 6 assemblage gradually changes from the base to the top of the turbidite, consistent with the upward-fining graded structure (i.e. thin-walled, tiny species are increased in the upper layer). The lower part of the turbidites at both sites, St. 5 and St. 6, are considered to have originated from turbidity currents triggered by earthquake shaking. In contrast, the most probable generation mechanism for the turbidity current that formed the surface layer at St. 5 is the tsunami-related agitation of sediment in shallow water. The relatively good preservation of benthic foraminiferal tests in the turbidites suggests transport processes with minimal internal friction and/or collision of grains within the turbidity current. These results show that benthic foraminifera are useful in turbidite paleoseismology.
Chapter
Acoustic mapping and sampling of Holocene and Late Weichselian deglacial sediments combined with oceanographic measurements in the sediment source and accumulation areas on the eastern continental margin of the Norwegian-Greenland Sea provide evidence that episodic transport towards high-accumulation areas is primarily downslope and gravity driven. Triggered by various hydrographic conditions, the runoff repeatedly followed the local gullies and channels of the seafloor. In contrast, sedimentological and oceanographic data from a topographic sediment trap on the Vøring Plateau at the Norwegian Sea margin indicate upslope sediment transport in the bottom nepheloid layer. Less comprehensive data from the Greenland Sea margin suggest that the prerequisites to sediment advection in terms of oceanographic structure, availability and sources of sediment differ from those of the eastern margin. The resulting near-bottom sediment transport is less pronounced. Advected sediments reaching the continental rise and the abyssal plain follow an old channel system. The forcing mechanisms of sediment advection changed dramatically from Late Weichselian to Holocene times due to changes in sea level, sediment availability, and water-mass stratification.
Article
Over the last 50yr the N. Iceland margin has seen dramatic changes in temperature and salinity associated with the relative dominance of warm Atlantic water versus cold Arctic or Polar waters. We report a study of Holocene environmental changes to assess the sensitivity of this area on a longer timescale. We present sedimentologic, isotopic, and biotic (coccolith) proxies from a 5.5m piston core, B997-330PC, that was retrieved from a small basin on the inner N. Iceland shelf. Seven AMS dates indicate a relatively constant rate of sediment accumulation which averaged 55cm/kyr. Sampling resolution of our proxies varied between 16 and 90yr/sample. Our data indicate substantial variability in environmental conditions over the last 10,000calyr. Total carbonate content and coccolith concentrations track each other and indicate that the early Holocene was a time of low net carbonate accumulation. Net accumulation of carbonate reached maximum values in the mid- to late Holocene (4–2calka) but there has since been a substantial decrease with a minima during the Little Ice Age. North Atlantic Drift coccolith species show peaks in accumulation rates at 2 and ∼8calka, and low influx between 3.5 and 6calka. Reworked Neogene coccoliths occur also ∼8ka and coincide with light δ18O values in the epifaunal foraminifera Cibicides lobatulus. Principal component analysis indicates considerable covariance between biotic, isotopic, and sedimentological parameters. Three axes explain 84% of the variance in the data set and define three groups of interrelated variables. A major change occurs ca. 5calka after which conditions become more variable with a 1.5kyr cyclicity.