doi:10.3402/polar.v35.23104


R E S E A R C H / R E V I E W A R T I C L E

Sedimentary environments in the south-western Barents Sea
during the last deglaciation and the Holocene: a case study
outside the Ingøydjupet trough
Mauro Pau1 & Øyvind Hammer2

1
Physics of Geological Processes, University of Oslo, PO Box 1048, Blindern, NO-0316 Oslo, Norway

2 Natural History Museum, University of Oslo, PO Box 1172, Blindern, NO-0318 Oslo, Norway

Keywords

Deglaciation; Barents Sea ice sheet;

sediment cores; lithofacies; biozonation.

Correspondence

Mauro Pau, Physics of Geological

Processes, University of Oslo, PO Box 1048,

Blindern, NO-0316 Oslo, Norway.

E-mail: mauro.pau@fys.uio.no

Abstract

A lithological and foraminiferal study of newly acquired sediment cores outside

the Ingøydjupet (Ingøy Deep) trough has been carried out to improve

constraints on the last deglacial history in the south-western Barents Sea.

Three lithofacies and three foraminiferal facies were identified. The lowermost

lithological unit is a diamicton interpreted as glacial till. It contains a low-

abundance, ecologically mixed foraminiferal assemblage, presumably resulting

from glacial reworking. Above the diamicton, a layer of ice-rafted debris

(IRD), likely associated with intensive iceberg production, marks the initial

destabilization of the marine-based ice sheet. At this time, ca. 15.6�15.0 Ky B.P.,
opportunistic foraminiferal species Nonionellina labradorica and Stainforthia spp.

reached peak abundance. During the south-western Barents Sea ice-margin

retreat, presumably corresponding to the Bølling interstadial, a sequence of

glaciomarine laminations was deposited conformably on the layer of IRD.

Sedimentation rates were apparently high (estimated about 0.4 cm per year)

and the foraminiferal fauna was dominated by Elphidium spp. and Cassidulina

reniforme, species common for glacier-proximal environments. A hiatus at the

top of the deglacial unit is likely linked to the high bottom-current activity

associated with a strengthened inflow of Atlantic water masses into the Barents

Sea. The uppermost lithological unit is represented by the Holocene marine

sandy mud. It contains a high-abundance, high-diversity foraminiferal fauna

with common cassidulinids, Cibicides spp., Epistominella pusilla and planktic

species.

To access the supplementary material for this article, please see the

supplementary file under Article Tools, online.

Increasing attention has been paid over the past decade

to the dynamics of marine-based ice sheets, which are

ice sheets grounded below sea level (e.g., Grosfeld &

Sandhäger 2004; Svendsen et al. 2004; Heroy & Anderson

2007; Smith et al. 2011; Bigg et al. 2012; Hillenbrand et al.

2012). Interest stems from the fact that these bodies

of ice are inherently unstable; a minor retreat could

trigger a destabilization of the entire ice sheet, leading to

its collapse (e.g., Hughes 2011). Two major examples of

late Quaternary marine-based ice sheets are the Barents�

Kara and the West Antarctic ice sheets. At present,

collapse of the West Antarctic ice sheet threatens to

increase global sea levels (Joughin & Alley 2011 and

references therein). In addition, understanding the beha-

viour of the Greenlandic marine-terminating glaciers

is of importance for the assessment of future sea level

(Nick et al. 2009). Insights into the dynamics of these

modern marine-terminating ice margins can be gained by

using the palaeo-ice sheet that covered the Barents and

Kara seas as an analogue (Ingólfsson & Landvik 2013).

Polar Research 2016. # 2016 M. Pau & Ø. Hammer. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0
International License (http://creativecommons.org/licenses/by-nc/4.0/), permitting all non-commercial use, distribution, and reproduction in any medium, provided the
original work is properly cited.

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Several studies addressed the issue of defining the

extent and timing of the ice sheet in the Barents Sea

region during Late Weichselian time (e.g., Elverhøi et al.

1993; Lambeck 1996; Landvik et al. 1998; Ottesen et al.

2001; Olsen 2002; Ottesen et al. 2005; Sejrup et al. 2005).

There is a general agreement that the ice sheet extended

to the shelf break along the western Barents Sea margin

(Fig. 1) at least twice: before 22 Ky B.P. and after 19 Ky

B.P. (Vorren & Laberg 1996). The ice-sheet margin then

retreated rapidly by iceberg calving within the deeper

troughs, which served as outlets for fast-flowing ice

streams (Vorren & Laberg 1996; Landvik et al. 1998).

The deglaciation was coeval with rising sea level (Clark et al.

2009) and was greatly influenced by the influx of Atlantic

water masses (e.g., Chistyakova et al. 2010; Junttila et al.

2010). It was, however, punctuated by periods of ice

margin stability and readvances, as evidenced by a series

of ice-marginal deposits (Andreassen et al. 2008; Ottesen

et al. 2008; Winsborrow et al. 2010). The rates of retreat

were particularly high in Bjørnøyrenna (Bear Island

Trough), the largest trough in the western Barents Sea

(Fig. 1), where Winsborrow et al. (2010) estimate retreat

rates of 60�275 m year�1. By 16 Ky B.P., Bjørnøyrenna
was almost entirely ice-free, while by 15 Ky B.P. the ice-

sheet margin had retreated onshore in all areas of the

western Barents Sea (Winsborrow et al. 2010). This made

ice loss by calving no longer possible, and the rate of

retreat slowed significantly (Winsborrow et al. 2010).

The focus of this article is on the last deglaciation of the

south-western sector of the Barents Sea shelf (Fig. 1). The

glacigenic sediments in this region have been investiga-

ted mainly with the aid of two- and three-dimensional

seismic data, sub-bottom profiling and/or multibeam

bathymetry (Vorren & Kristoffersen 1986; Vorren et al.

1990; Andreassen et al. 2008; Bellec et al. 2008; Ottesen

et al. 2008; Winsborrow et al. 2010; Rebesco et al. 2011;

Rüther et al. 2011; Bjarnadóttir et al. 2012). The studies

based on the analysis of sediment cores (Hald et al. 1989;

Ivanova et al. 2002; Aagaard-Sørensen et al. 2010;

Chistyakova et al. 2010; Junttila et al. 2010) have focu-

sed on sites of high sedimentation rate such as the

Ingøydjupet (Ingøy Deep) trough (Fig. 1). The present

work provides new sediment-core data from the area just

outside Ingøydjupet to better constrain the history of the

last deglaciation in the south-western Barents Sea at

shallower water depths. The specific objectives were to (1)

Fig. 1 Regional bathymetry of the south-western Barents Sea, showing the main troughs and banks (Andreassen et al. 2008). Also indicated are the

approximate locations of the cores used in the present and previous studies. Bathymetry from the Norwegian Hydrographic Service (www.mareano.

no).

Abbreviations in this article
CT: computerized tomography

IRD: ice-rafted debris

Ky B.P.: thousand calendar years before 1950

MS: magnetic susceptibility

SEM-EDS: scanning electron microscopy with energy-

dispersive x-ray spectroscopy

SI: International System of Units

Sedimentary environments in the south-western Barents Sea M. Pau & Ø. Hammer

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identify major lithofacies, (2) distinguish foraminiferal

assemblage zones and (3) reconstruct sedimentary envir-

onments during and after the last deglaciation. By

combining x-ray tomography, gamma density, MS, grain

size analysis, SEM-EDS, biostratigraphy and radiocarbon

dating, this study could hold promise for improving

constraints on deglacial events in other areas of the

Barents Sea via stratigraphic correlation.

Data and methods

Multibeam swath bathymetry of the study area (Fig. 2)

was acquired by the Norwegian Defence Research Esta-

blishment in 2009 with a Kongsberg Maritime EM710

multibeam echosounder. The data have a resolution of

1�2 m and 0.1�0.2 m in the horizontal and vertical
directions, respectively.

Four gravity cores (Table 1, Fig. 2) were collected with

the Norwegian Defence Research Establishment’s RV

H.U. Sverdrup II in 2010. The cores are each 60 mm in

diameter and were sampled outside of pockmarks.

Recovery ranged from 142 to 165 cm. Accurate locations

of the coring sites were recorded using a hydroacoustic

position reference system.

Lithological analyses included x-ray tomography,

gamma density and MS measured with a multi-sensor

core logger, coarse grain size (Figs. 3, 4), as well as SEM-

EDS (Supplementary Fig. S1).

X-ray tomography was carried out with a Siemens

Somatom whole-body CT scanner at the Norwegian

University of Life Sciences in Ås, Norway, at a resolution

of 1 mm. X-ray density estimated after Boespflug et al.

(1995) is expressed in CT numbers averaged over the 40

central pixels of the image with a 3-point running

average.

After splitting, the cores were scanned for gamma ray

attenuation and MS (given following SI conventions) at

the Department of Earth Science, University of Bergen,

Norway, at a resolution of 1 cm.

Grain size analyses were performed on 5-cm-long

sections. The samples were freeze�dried, weighed and
wet-sieved at 63 mm. The coarser fraction was dried in an
oven at 408C and sieved at 2000 mm. The relative content
of gravel (�2000 mm) and sand (63�2000 mm) is given as
a dry weight percentage of the total sample weight.

SEM-EDS was performed on a limited number of

samples in core LU10-06 at the Natural History Museum

of the University of Oslo, Norway, in order to investigate

the nature of some particles suspected to have ferrimag-

netic behaviour.

The total number of foraminifera per unit weight of

dry sediment was evaluated in core LU10-01 (Fig. 5),

while the remaining cores were used to estimate rela-

tive abundances (Figs. 6, 7). Benthic foraminifera were

counted in the �63 mm fraction for every 5-cm slice
of the cores. The fine mesh was used in order not to

miss small specimens. However, most of the identified

foraminifera are larger than 100 mm, meaning that our
results can be compared with those of other studies using

larger meshes. The only exception is Epistominella pusilla

(see taxonomical note and Supplementary Fig. S2 in the

Supplementary File), which has a large variation

in size including some very small specimens. Therefore,

previous articles using 100 or 125 mm sieve size may
have underestimated its abundance slightly. However,

Risebrobakken et al. (2010) and Chistyakova et al. (2010),

using 100 mm sieve size, counted E. pusilla up to 40 and
57%, respectively, in the upper part of their Barents Sea

cores, similar to our numbers. Whenever possible, 300

specimens were counted, but in low-abundance samples

smaller counts were accepted. Relative abundances of the

most abundant and/or stratigraphically informative taxa

are reported as percentages of the total fauna (Fig. 6).

A simplified taxonomy was used with 25 taxa identified

mainly to the species and genus level. Specimens of

Elphidium were counted as a genus, although several

W
a
te

r 
d
e
p
th

 (
m

)

100m 375

374

373

372

371

370

369

Fig. 2 Bathymetry of the study area with the coring sites. See Fig. 1 for

location in the south-western Barents Sea. Note the occurrence of several

pockmarks, appearing as circular depressions (Pau et al. 2014). Multibeam

bathymetry acquired by the Norwegian Defence Research Establishment.

Table 1 Length, water depth and position (WGS84) of the Lundin

Petroleum 2010 (LU10) cores.

Core ID Length (cm)

Water

depth (m) Latitude Longitude

LU10-01 164 372 728 05.159? N 208 30.714? E
LU10-04 165 373 728 05.109? N 208 30.687? E
LU10-05 142 371 728 05.107? N 208 31.031? E
LU10-06 155 372 728 05.212? N 208 30.402? E

M. Pau & Ø. Hammer Sedimentary environments in the south-western Barents Sea

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species were probably present. An exception was made

for the distinct, often very large form E. bartletti.

Cassidulinids were mostly counted on the family level,

but with Cassidulina reniforme identified as a separate taxon.

The relative abundances of C. neoteretis and Islandiella spp.

were noted qualitatively. Minor taxa not presented here

include Pullenia bulloides, Fissurina sp., Lagena spp. (mainly

L. distoma), Uvigerina sp., Lenticulina sp. and Bulimina

marginata (in some core-bottom samples). Most of these

taxa were found only in the Assemblage Zone A (see

below), but Lagena spp. also occurred in Zone C. Bulimina

marginata was found only in Zone C.

Planktic foraminifera were also counted in the �63

mm fraction. Since they were scarce, we merged pairs of

samples to obtain acceptable sample sizes (n�30), giving

10-cm vertical resolution. The following forms were

counted in core LU10-06 (Fig. 7): Neogloboquad-

rina pachyderma, N. incompta, Turborotalita quinqueloba,

Globigerinita uvula and Globigerina bulloides. Other species

of planktic foraminifera were very rare. Studies using 100

or 125 mm sieve size may have underestimated the
abundance of the relatively small species T. quinqueloba

and G. uvula.

The biostratigraphic divisions were validated by cluster-

ing the foraminiferal assemblages (Supplementary Fig. S3)

using stratigraphically constrained unweighted pair group

method with arithmetic mean with the Bray�Curtis
distance measure, in PAST ver. 3.0 (Hammer et al. 2001).

Fig. 3 CT image, lithological units (dashed lines) and subunits (dotted lines), x-ray and gamma density, MS and grain size (gravel, �2000 mm; sand,
63�2000 mm) for the investigated cores. Average ages (Ky B.P.) of the dated intervals are indicated. Details of the CT images are illustrated in Fig. 4.

Sedimentary environments in the south-western Barents Sea M. Pau & Ø. Hammer

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Seven
14

C radiocarbon dates (Table 2) were obtained

from macroscopic shell material and collections of

foraminifera. The analyses were carried out by means

of accelerator mass spectrometry at the Radiocarbon

Dating Laboratory of Lund University, Sweden. The

radiocarbon dates were calibrated using the Calib v. 7.0

software (Stuiver & Reimer 2014) with the Marine13

calibration curve (Reimer et al. 2013), which operates

with a standard reservoir correction of 400 years

(DR �0). The employed total reservoir age was 467941
years (DR �67941), which is considered representa-
tive for the waters off northern Norway (Mangerud &

Gulliksen 1975; Reimer & Reimer 2001).

Results

Visually, the sediments appeared as grey mud for most

part of the cores, with the top 10�20 cm often showing
a brownish colour. The top 1 cm was rich in sponge

spicules. Gravel particles were occasionally visible and

were interpreted as iceberg dropstones. Almost no well-

preserved macroscopic shells were encountered.

Inspection of the CT images revealed significant details

of the internal structure of the cores (Figs. 3, 4) and

provided the basis to identify the lithological units des-

cribed below. The x-ray and gamma density logs were

rather consistent with each other (Fig. 3), with density

slightly increasing downcore as a result of sediment

consolidation. Because of variation in the thickness of

the split cores, however, the calibrated gamma density

values are not considered to be fully reliable. MS (Fig. 3) is

controlled by density and mineralogy; local variations may

therefore be influenced by the content of sand and gravel

(a)

LU10-01

(b)

LU10-04

(c)

LU10-05

(d)

LU10-06

(e) (f) (g) (h)

(i) (j) (k) (l)

(m) (n)

0

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)
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)
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)
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cm

)

5

10

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95

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Fig. 4 Detailed views of the CT images: (a�d) Holocene marine
sediments (Lithological Unit I); (e�h) glaciomarine laminated sediments
(Lithological Unit II, Subunit IIb); (i�l) IRD layer (Lithological Unit II, Subunit
IIc); (m) and (n) glacial till (Lithological Unit III). Columns from left to right

refer to cores LU10-01, LU10-04, LU10-05 and LU10-06. The yellow line in

(c) marks the contact between Lithological Unit I and the IRD layer

topping Lithological Unit II (Subunit IIa), while in (e) it marks the erosion

surface between Subunit IIa and the underlying laminations (Subunit IIb).

A

B

C

I

II

III

IIa

IIb

IIc

C
o
re

d
e

p
th

(c
m

)

Count/gram dry sediment

0 100 200 300

0

20

40

60

80

100

120

140

Fig. 5 Total number of foraminiferal specimens per unit weight of dry

sediment (histogram) in core LU10-01. Assemblage Zones A, B and

C (shades of grey), Lithological Units I, II and III (dashed lines) and

Lithological Subunits IIa, IIb and IIc (dotted lines) are marked.

M. Pau & Ø. Hammer Sedimentary environments in the south-western Barents Sea

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minerals, which possess higher values than clay minerals,

and by authigenic formation of ferrimagnetic minerals.

Lithostratigraphy

Three lithological units are distinguished based on the CT

images, and with the support of the density, grain size

and MS logs (Figs. 3, 4).

Lithological Unit III. This unit is observed at the

bottom 20�30 cm of cores LU10-01 and LU10-06. The

unit appears in the CT images as a diamicton (Figs. 3,

4m�n). The coarsest fraction is composed of rounded to
angular particles, typically 2�3 cm in size (Fig. 4m�n).
Sand content is around 15%, while MS values are

generally lower than 2 �10�4 (Fig. 3).

Lithological Unit II. Near the bottom of the unit, a

10-cm-thick layer (Subunit IIc) is observed with the

brightest intensity in the CT images. Its depth varies from

98 to 123 cm in the different cores (Fig. 4i�l). This layer is
dated to 15.6 Ky B.P. in core LU10-05, whereas the age

I

II

I

II

III

I

II

I

II

III

IIa

IIb

IIc

IIa

IIb

IIc

IIb

IIc

IIa

IIb

IIc

IIa

A

B

A

B

A

LU10-01

LU10-04

LU10-05

A

B

C

C

B

LU10-06

20

0

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60

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200 40 60 0 20 40 60 80 0 10 20 30 0 10 20 30 0 20 40 0 10 20 30 0 10 20 0 10 20 0 5 10 15 0 10 20 30 40

40

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200 40 60 0 20 40 60 80 0 10 20 30 0 10 20 30 0 20 40 0 10 20 30 0 10 20 0 10 20 0 5 10 15 0 10 20 30 40

40

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200 40 60 0 20 40 60 80 0 10 20 30 0 10 20 30 0 20 40 0 10 20 30 0 10 20 0 10 20 0 5 10 15 0 10 20 30 40

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200 40 60 0 20 40 60 80 0 10 20 30 0 10 20 30 0 20 40 0 10 20 30 0 10 20 0 10 20 0 5 10 15 0 10 20 30 40

4782
2211

2648

15422

14971

15601

0?

Elphidium spp. C. reniforme N. labradoricaE. pusilla Stainforthia spp. Cibicides spp. M. barleeanus E. bartlettiCassidulinids Planktic fauna
C

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cm

)
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cm

)
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cm

)
C

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cm

)

Fig. 6 Frequency distribution (%) of the main benthic foraminiferal taxa and the total planktic fauna in the �63 mm fraction in the studied cores.
Assemblage Zones A, B and C (shades of grey), Lithological Units I, II and III (dashed lines) and Lithological Subunits IIa, IIb and IIc (dotted lines) are

marked. Ages (Ky B.P.) are also indicated.

Sedimentary environments in the south-western Barents Sea M. Pau & Ø. Hammer

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obtained just below it in core LU10-04 is 15.0 Ky B.P.

(slightly overlapping error ranges, Table 2). Subunit IIc

has maximal density values and contains a high amount

of coarse material, with sand content up to 30�40% and
gravel content of over 10% (Fig. 3). The coarsest particles

reach 3 cm in size (e.g., in core LU10-01, Fig. 4i). MS in-

creases up to a peak of about 11 �10�4 in core LU10-05
(Fig. 3).

Further up, Lithological Unit II exhibits a 70�80-cm-
thick layer with laminated sediments (Subunit IIb), dated

to 15.4 Ky B.P. in core LU10-01 (Table 2). The laminae,

deposited in a rhythmic fashion, are about 0.2 cm thick

and are formed by brighter fine-sand bands alternating

with darker mud bands (Figs. 3, 4e�h). A disconformity,
illustrated in Fig. 4e, separates this laminated sediment

from an overlying gravelly layer. Rare clasts are present,

usually under 1 cm in size (e.g., Fig. 4h). Sand content,

averaged over the muddy and the sandy laminae, does

not exceed a few percent (Fig. 3). Density in Unit II

gradually decreases upcore (Fig. 3). The MS logs show

two distinct, correlatable peaks at ca. 70�80 cm depth
in core LU10-04 and around 30�40 cm depth in core
LU10-05 (Fig. 3). These peaks probably correspond to

a single peak just below 70 cm depth in core LU10-01

and at 60 cm depth in core LU10-06 (Fig. 3). SEM-EDS

analysis of grainy, black particles with reddish weathering

rims found exclusively at these levels (Supplementary

Fig. S1) revealed high abundances of iron and sulphur.

The Fe:S ratio of 0.75:1 measured on the black particles

(Supplementary Fig. S1b) is consistent with the presence

of authigenic greigite (Fe3S4), which may form at

relatively shallow depths within the sediment in areas

where methane hydrates are common (e.g., Larrasoaña

et al. 2007). The reddish grains (Supplementary Fig. S1c)

exhibit an Fe:S ratio of 2:1, probably due to sulphur loss

as a result of weathering.

At the top of Lithological Unit II, a ca. 10-cm-thick

layer (Subunit IIa) is observed with brighter appearance

in the CT images, coarser grain size, and slightly en-

hanced density and MS in comparison with sediments

above and below (Figs. 3, 4c). The age of 4.8 Ky B.P.

obtained for this layer from core LU10-01 (Table 2)

appears anomalously young and is interpreted to origi-

nate from a burrowing bivalve. The coarse fraction is

generally less abundant than in Subunit IIc. Sand con-

tent varies between 10 and 25%, while gravel content is

2�3% (Fig. 3). Gravel particles of up to 1 cm can be
identified in the CT images (for instance, in core LU10-05

below 12 cm core depth, Fig. 4c). In core LU10-04, MS

shows a peak of over 5 �10�4 (Fig. 3).

Lithological Unit I. This unit is found in the top 30�40
cm of most cores (Fig. 3). It is composed of homoge-

neous, somewhat sandy mud with irregular burrows.

The age of 2.6 Ky B.P. obtained at 15�20 cm depth in
core LU10-06 (Table 2) dates the unit to the Holocene;

however, the age of its bottom remains unconstrained.

Density rapidly decreases upcore in the top ca. 20 cm

of the unit. Sand content is 15�20% (Fig. 3), mostly
bioclasts. MS is around 2�3 �10�4, with peaks reaching
6 �10�4 in core LU10-04 and over 15 �10�4 in core
LU10-06 (Fig. 3). Lithological Unit I is thinner, about

12 cm, in core LU10-05 (Figs. 3, 4c). This is attributed to

the vicinity of this site to a pockmark (Fig. 2), where the

Holocene sediment cover is likely to be reduced (Chand

et al. 2012; Pau et al. 2014).

LU10-06

A

B

C

20

0

40

60

80

100

120

C
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re

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cm

)

140

N. incompta T. quinquelobaN. pachyderma G. bulloidesG. uvula

0 5 15 0 10 200 20406080 0 204060800 4 8

I

II

III

IIa

IIb

IIc

Fig. 7 Relative abundances of planktic foraminifera in core LU10-06

(percentages of the total planktic fauna). Assemblage Zones A, B and C

(shades of grey), Lithological Units I, II and III (dashed lines) and

Lithological Subunits IIa, IIb and IIc (dotted lines) are marked.

Fig. 8 Biostratigraphic correlations among the cores (solid lines).

Assemblage Zones (A, B and C; shades of grey), lithological units

(I, II and III; dashed lines) and subunits (IIa, IIb, and IIc; dotted lines) are

marked. Ages (Ky B.P.) are also indicated.

M. Pau & Ø. Hammer Sedimentary environments in the south-western Barents Sea

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Biostratigraphy

Three foraminiferal assemblage zones with relatively

sharp boundaries could be defined (Figs. 5�8, Supple-
mentary Fig. S3). Total abundance per unit weight of dry

sediment generally increases upcore, with higher abun-

dances in Zone B than in C, and higher in A than in B

(Fig. 5).

Assemblage Zone C. This assemblage is found in

Lithological Unit III. It is characterized by the presence

of cassidulinids other than C. reniforme, but in contrast to

Zone A there is a considerable proportion of Islandiella

spp. (Fig. 6). Elphidium spp. and C. reniforme are common,

but not as dominant as in Zone B. Planktic foraminifera

are common, with N. pachyderma predominating (�90%,

Fig. 7).

Assemblage Zone B. This zone is ca. 100 cm thick and

is found in Lithological Unit II. Total foraminiferal

abundance per unit weight of dry sediment shows a

peak around 70�80 cm depth in core LU10-01 (Fig. 5),
within Subunit IIb (laminated package). The zone is

marked by the presence of Elphidium spp. together with

C. reniforme (Fig. 6). Elphidium is generally dominant and

can reach almost 100%, but the top and/or bottom of the

zone may also contain peaks of Nonionellina labradorica,

Stainforthia and Cibicides. Cassidulinids (apart from C.

reniforme, Fig. 6) and planktic foraminifers (Fig. 7) are

absent or rare. A sparse planktic fauna dominated by

T. quinqueloba is found in the 40�60 cm interval in core
LU10-06 (Fig. 7).

Assemblage Zone A. This zone is found in Lithological

Unit I, presumably representing the Holocene sediment

cover. Total foraminiferal abundance per unit weight of

dry sediment increases suddenly from Zone B to Zone A

(Fig. 5). Zone A is dominated by Epistominella pusilla with

subsidiary Cibicides spp., Cassidulina neoteretis and Melonis

barleeanus, and abundant planktic foraminifers (Fig. 6).

Elphidium spp. and C. reniforme are notably absent. The

fauna is both abundant and species-rich, with minor

taxa including Stainforthia spp., P. bulloides, Fissurina sp.,

Lagena spp. and Uvigerina sp. The planktic component

is dominated by N. pachyderma, but with N. incompta, T.

quinqueloba, G. uvula and G. bulloides also common (Fig. 7).

Sponge spicules can be very abundant, especially in the

upper part of the unit.

Discussion

Environment prior to the deglaciation

The oldest lithological unit encountered (Unit III, Figs. 3,

4m, n) is a diamicton and is interpreted as glacial till.

This interpretation is supported by the lack of stratifica-

tion and the quite homogeneous abundance of gravel

particles across the cores (Licht et al. 1999). The scarcity

of datable material did not allow us to obtain a radio-

carbon age for the unit, but it must be older than the

15.6 Ky B.P. obtained near the base of the overlying

Lithological Unit II (Table 2, Fig. 8). The foraminiferal con-

tent (Zone C, Figs. 6, 7) may be glacially reworked. Rare

Bulimina marginata in Zone C are opaque and abraded.

Hald et al. (1990) reported B. marginata at 10�12 m core
depth in core 7120/06-01 in the Ingøydjupet area, in a

clearly disturbed sequence with reversed radiocarbon

dates, and interpreted this occurrence as reworked. If in

situ, the benthic foraminifera (Elphidium and Cassidulina

reniforme) would likely indicate a glaciomarine setting

(see below), while the planktic fauna could be inter-

preted as full marine but cold water, dominated by

Neogloboquadrina pachyderma. This diamicton may be

correlated with one described from the southern part of

Ingøydjupet and interpreted as a subglacial till (Unit 6,

Junttila et al. 2010). Similar diamictons have been

reported elsewhere from the Barents Sea, and some of

them were suggested to have undergone compression by

Table 2 Results from accelerator mass spectrometry 14C radiocarbon dating and calendar (cal.) year calibrations. The error in 14C age (not reservoir

corrected) is given as 91s. The analyses were conducted at the Radiocarbon Dating Laboratory, Lund University, Sweden. The dates were calibrated
into calendar years before 1950 (years B.P.) using the Marine13 calibration curve (Reimer et al. 2013) and are given as 95% confidence intervals. A

standard reservoir correction of 400 years with an additional reservoir correction DR � 67941 was employed.

Core ID Depth range (cm) Material C weight (mg)

14
C age91s

(years)

Cal. age, 2s ranges
(years B.P.)

Cal. age 92s
(years B.P.)

LU10-01 0�5 Astarte sp. 1.74 445950 living?
LU10-01 30�40 Collection of C. lobatulus 0.54 26159100 2503�1919 22119292
LU10-01 35�40 Bivalve debris 0.82 4655950 4969�4595 47829187
LU10-01 55�60 Collection of E. bartletti 0.57 13 360975 15 702�15 141 15 4229281
LU10-04 125�135 Collection of N. labradorica 0.72 13 120970 15 313�14 629 14 9719342
LU10-05 95�105 Collection of N. labradorica 0.66 13 510980 15 913�15 289 15 6019312
LU10-06 15�20 Mixed shell fragments 0.31 2985970 2865�2431 26489217

Sedimentary environments in the south-western Barents Sea M. Pau & Ø. Hammer

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glacial load (e.g., Unit IV, Ivanova et al. 2002). Unit III

can be related to the Stage 1 of the Late Weichselian

events in the south-western Barents Sea described by

Winsborrow et al. (2010). This period corresponds to

the glacial maximum after 19 Ky B.P., with ice streams

operating in Bjørnøyrenna and other troughs such as

Ingøydjupet.

Early deglaciation

The beginning of the deglaciation is marked by the de-

position of coarse material with abundant gravel particles

(�2000 mm) in the 10-cm-thick layer at the bottom
of Lithological Unit II (Subunit IIc, Figs. 3, 4i�l). This
material is interpreted as IRD resulting from increased

calving of icebergs from the marine ice-sheet margin

(Aagaard-Sørensen et al. 2010), which was mainly

triggered by sea-level rise (Winsborrow et al. 2010).

Glacial unloading and rising seawater temperatures dur-

ing the early deglaciation destabilized methane hydrate

deposits, leading to free gas release through the seafloor

and the formation of the pockmarks visible in the study

area (Fig. 2; Chand et al. 2012; Nickel et al. 2012; Pau

et al. 2014).

During the deposition of Subunit IIc, Nonionellina

labradorica reached peak abundance in all cores investi-

gated, marking the base of Assemblage Zone B (Fig. 6).

This species often peaks within the later stages of the

Late Weichselian deglaciation in the north-east Atlantic

(Knudsen and Austin 1996). Another noteworthy for-

aminifer peaking at the base of Zone B is Stainforthia

(Fig. 6). This is a highly opportunistic genus (e.g., Alve

2003), often dominating in areas of rapid environmental

change. In the Arctic region, Stainforthia is typically abun-

dant in areas with seasonal sea-ice cover or sea-ice

margins (Seidenkrantz 2013).

The timing of the IRD event of Subunit IIc is cons-

trained between 15.6 and 15.0 Ky B.P. (Table 2, Figs. 3, 8).

The age of 15.0 Ky B.P. is in line with the results pub-

lished by Pau et al. (2014), who correlate it with the base

of Lithological Unit II. Part of the discrepancy with the

age of 15.6 Ky B.P. may result from large uncertainty

in the radiocarbon calibration curve at the beginning

of the Bølling warming (Reimer et al. 2013) related to

rapid and uneven sea-level rise resulting from meltwater

pulses (e.g., Deschamps et al. 2012). Two deglacial IRD

events were found in Ingøydjupet, of which the older

one is estimated to have occurred at 15.1 Ky B.P. (Period

I, Aagaard-Sørensen et al. 2010). This IRD event can

possibly be correlated with our Subunit IIc. Junttila et al.

(2010) report a shift from diamicton to IRD abundance in

Ingøydjupet (Units 5 and 4), dating it to 15.0 Ky B.P.

Based on a peak in N. labradorica similar to that found in

the present study, Chistyakova et al. (2010) estimate the

deglaciation to have commenced in Ingøydjupet between

14.2 and 13.8 Ky B.P. Age variations between different

sites might reflect a difference in time for the position of

the ice margin, but more ages are needed to evaluate this

pattern. Winsborrow et al. (2010) assign the age of ca.

16 Ky B.P. to the onset of glaciomarine conditions in the

south-western Barents Sea (Stage 3) and ca. 15 Ky B.P. to

the complete loss of the ice cover in the region (Stage 4).

The laminated package immediately above the IRD

layer (Lithological Subunit IIb, Figs. 3, 4e�h) likely
documents high sedimentation rates in a glaciomarine

environment (e.g., Ó Cofaigh & Dowdeswell 2001 and

references therein). The fauna is dominated by Elphidium

spp., typical of ice-marginal settings, and C. reniforme,

a cold-water indicator (Fig. 6). Furthermore, the absence

of planktic foraminifera in the lower part of Zone B (Figs.

6, 7) is consistent with a glaciomarine environment (see

also the barren planktic zone PFZ-0 of Aagaard-Sørensen

et al. 2010). The age of 15.4 Ky B.P. in the upper part of

the laminated sediment (core LU10-01) is within the

error range of the age from the preceding IRD event in

adjacent cores (Table 2, Figs. 3, 8), possibly in relation to

high sedimentation rates. The lamination has a grada-

tional basal contact with the IRD layer and is character-

ized by planar and parallel laminae, occurrence of iceberg

dropstones and no bioturbation, probably due to the

negative effect of high sedimentation rate on macrofauna

(Fig. 4e�h). These features correspond to diagnostic
criteria for the deposition of laminae by suspension-

settling in an ice-proximal environment (Ó Cofaigh &

Dowdeswell 2001). The thickness of the laminae of about

0.2 cm (Fig. 4e�h), however, is not high enough to imply
a direct proximity to the ice edge (Ó Cofaigh &

Dowdeswell 2001). The alternating sand and mud

laminae may represent annual couplets reflecting sea-

sonally variable meltwater discharge, in which case they

can be classified as glaciomarine varves (Ó Cofaigh &

Dowdeswell 2001). A similar interval of laminated

sediments is reported from Ingøydjupet by Aagaard-

Sørensen et al. (2010) and Junttila et al. (2010), where

the timing of their deposition is related to the Older Dryas

(ca. 14.6�14.5 Ky B.P.). In the central part of the Barents
Sea, Ivanova et al. (2002) also describe a laminated

sequence overlying sediments with abundant IRD (Unit

II and III, respectively). They relate the deposition of the

laminae to glacier meltwater discharge, following an

initial phase of ice-sheet disintegration.

The peak in the total number of foraminiferal speci-

mens per unit weight of dry sediment found in Zone B

of core LU10-01 (Fig. 5) could be due to increased

M. Pau & Ø. Hammer Sedimentary environments in the south-western Barents Sea

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foraminiferal productivity along with a local ecological

change. Since the laminae do not show a decrease in

thickness, this peak is not explainable in terms of reduced

sedimentation rate. Moreover, considering Zone B is

barren of planktic foraminifera, we cannot relate it to

the peak abundance of planktic species found in similar

facies by Aagaard-Sørensen et al. (2010) and Junttila

et al. (2010). Ivanova et al. (2002) report no such peak

from the central Barents Sea either.

In core LU10-06, there is an interval near the top

of Lithological Unit II (40�55 cm core depth, Fig. 7) with
an initial, moderate influx of planktic foraminifera domi-

nated by the subpolar species T. quinqueloba. This indicates

a warmer surface water pulse terminating the glaciomar-

ine environments. For a comparison, in the Fram Strait

area T. quinqueloba predominates close to the sea-

ice margin in water masses influenced by the Atlantic

Water (Volkmann 2000). In contrast to a similar, but ap-

parently younger (base Holocene) peak of T. quinqueloba

found by Aagaard-Sørensen et al. (2010) in Ingøydjupet,

the accompanying benthic foraminiferal community

(Elphidium spp. and C. reniforme) is still distinctly glacio-

marine in core LU10-06. Moreover, the near-absence

of C. neoteretis indicates no considerable Atlantic Water

influence on the benthic fauna at this time. The 63-mm
sieve size used in the present study may have enabled

detection of this planktic faunal event, which studies

based on a larger mesh size (e.g., Aagaard-Sørensen et al.

2010, 100 mm) would fail to detect.

Late deglaciation

The disconformity at the top of the laminated sediments

(Fig. 4e) appears to be a result of bottom-current erosion.

Readvance of grounded ice as an agent of erosion is

unlikely, especially in the context of well-preserved

pockmarks in the study area (Fig. 2). We hypothesize

that the intensification of bottom currents was linked to a

climatic deterioration and the associated sea-surface cool-

ing and sea-ice formation, hence increased production of

brines, possibly during the Older Dryas (ca. 14.6�14.5 Ky
B.P.). Evidence for intense brine formation in a Svalbard

fjord coinciding with the Older Dryas (Rasmussen &

Thomsen 2014) supports this interpretation.

The coarse-grained material deposited on top of the

disconformity is interpreted as IRD (Subunit IIa, Figs. 3,

4e, c). Although less prominent than in Subunit IIc,

this IRD likely represents a second pulse of enhanced

iceberg production from the decaying ice sheet and can

be tentatively correlated with the Allerød interstadial

(ca. 14�13 Ky B.P.). Both the erosion event and the

deposition of Subunit IIa occurred subsequent to the

onshore retreat of the ice margin (Winsborrow et al.

2010, Stage 4, ca. 15 Ky B.P.).

No dates are available for the interval contained

between 15.0 and 4.8 Ky B.P. (Table 2), likely indicating

a major hiatus at the bottom of the Holocene (Fig. 4c),

probably due to erosion by bottom currents. No such

hiatus is reported from Ingøydjupet (Aagaard-Sørensen

et al. 2010; Chistyakova et al. 2010; Junttila et al. 2010);

nonetheless, the authors provide micropaleontological evi-

dence for high-energy bottom environments in the Early

Holocene (Aagaard-Sørensen et al. 2010; Chistyakova

et al. 2010). The difference in water depth between the

present study area and Ingøydjupet corresponds to about

50 m, suggesting topography-controlled local variations

in the hydrodynamic regime. Aagaard-Sørensen et al.

(2010) and Chistyakova et al. (2010) link the increased

bottom-current activity to a strengthening of the Atlantic

current, consistent with a regional trend for the Barents

Sea (Hald et al. 2007; Risebrobakken et al. 2010).

Near the boundary between Assemblage Zones A

and B, the investigated cores exhibit intermittent absence

of planktic foraminifera, together with a very low-

abundance benthic fauna. This thin, barren interval

could possibly reflect the Younger Dryas cold event dated

in Ingøydjupet to 12.70�11.65 Ky B.P. by Aagaard-
Sørensen et al. (2010) and to 12.8�11.3 Ky B.P. by
Chistyakova et al. (2010).

Late Holocene

The Holocene sedimentary record recovered is character-

ized by deposition of marine mud with an abundant

bioclastic component (Lithological Unit I, Figs. 3,

4a�d). The earliest date that can be provided for the
Holocene material is 4.8 Ky B.P. (Table 2). This age,

obtained on fragments of a thin-shelled bivalve from the

top of the underlying Assemblage Zone B (Fig. 8),

presumably represents the age for the bottom of Zone A

as bivalves may move vertically up to a few tens of

centimetres in their burrow. Mixed shell fragments re-

covered from the middle of Lithological Unit I/Assemblage

Zone A are of late Holocene age (2.6 Ky B.P., Table 2,

Figs. 3, 6, 8).

The hiatus between Units II and I is marked by a

relatively abrupt change in the taxonomic composition of

the foraminiferal assemblage, accompanied by a signifi-

cant increase in the species richness and abundance

(Assemblage Zone A, Figs. 5�7). The latter is explainable
in terms of reduced sedimentation rate in the Holocene,

and probably also downcore dissolution of the carbonate

Sedimentary environments in the south-western Barents Sea M. Pau & Ø. Hammer

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tests. The abundance of planktic foraminifers (Figs. 6, 7)

indicates full marine conditions. The increased influ-

ence of Atlantic Water is illustrated by a common occur-

rence of Cassidulina neoteretis (Mackensen & Hald 1988).

Furthermore, high abundance of Cibicides spp., with a

peak dated to ca. 2.2 Ky B.P. in one of the cores (Table 2,

Fig. 6), suggests high bottom-current velocities. A similar

faunal change, found elsewhere in the western Barents

Sea, has been explained by the influence of Atlantic water

masses and increased bottom currents (Ivanova et al.

2002; Aagaard-Sørensen et al. 2010; Chistyakova et al.

2010). The topmost 20�30 cm interval in some cores
under this study is characterized by a reduction in

C. neoteretis, with Epistominella pusilla becoming dominant,

reaching 70% at the core top. A similar development in

benthic foraminifers during the Holocene was noted in

Ingøydjupet by Chistyakova et al. (2010). The increase of

E. pusilla reflects warm Atlantic Water, increasing bottom

currents and unstable flux of organic matter to the seafloor

(Rasmussen et al. 2007; Chistyakova et al. 2010).

Conclusions

Based on a lithological and foraminiferal investigation of

sediment cores retrieved in the south-western Barents

Sea, three lithofacies and associated foraminiferal assem-

blage zones were identified. This stratigraphy represents a

transition from subglacial to glaciomarine and marine

depositional environments. Based on the available
14

C

ages, deglaciation of the study area began prior to ca.

15.6�15.0 Ky B.P. An IRD layer was deposited during the
initial disintegration of the ice sheet, possibly correspond-

ing to the inception of the Bølling interstadial. Overlying

laminated glaciomarine sediments were likely deposited

in proximity to the retreating ice-sheet margin. A major

depositional hiatus, loosely bracketed by the ages of

15.0 and 4.8 Ky B.P., separates deglacial and Holocene

sediments. The hiatus presumably indicates high bottom-

current activity, probably linked to a strengthening of the

inflow of Atlantic Water into the Barents Sea with the

onset of Holocene environments.

Acknowledgements

Harald Brunstad and Lundin Petroleum Norway are

warmly thanked for financial support and for providing

the cores. For the excellent support during the expedi-

tion, a sincere gratitude goes to Arnfinn Karlsen, Helge

Jubskås, Martin Syre Wiig, Kjetil Bergh Ånonsen and

Jon Otto Buer from the Norwegian Defence Research

Establishment, as well as to the officers and crew of RV

H.U. Sverdrup II, Johnny Remøy (captain), Terje Haugen,

Erling Olsen, Henning Bergsnes, John Johnsen, Bernt

Nilsen and Liv Sørensen. Arnfinn Karlsen is thanked

also for the logistical assistance. Haflidi Haflidason at

the University of Bergen is gratefully acknowledged for

the assistance with core logging. Knut Dalen at the

Norwegian University of Life Sciences is thanked for

assistance with CT scanning, and Mufak Naoroz at the

University of Oslo for support with grain size analysis.

The article benefited from comments and suggestions by

Leonid Polyak and other reviewers.

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