A deglacial–middle Holocene record of biogenic sedimentation and ...

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A deglacial–

middle Holocene record of biogenic sedimentation
and paleoproductivity changes from the northern Norwegian
continental shelf
Jochen Knies,
1
Morten Hald,
2
Hanne Ebbesen,
2
Ute Mann,
3
and Christoph Vogt
4
Received 4 December 2002;revised 29 April 2003;accepted 15 August 2003;published 18 December 2003.
[
1
] The relative proportions of marine organic carbon and biogenic carbonate in a high-resolution record froma
glacial trough on the northern Norwegian continental shelf were used to decipher changes in biogenic
sedimentation and paleoproductivity from the last deglaciation to the middle Holocene.Decadal-scale to
century-scale oscillations in biogenic sedimentation and surface ocean productivity recorded in the Andfjorden
sediments are synchronous with abrupt climate changes in open oceanic and atmospheric regimes of the high
northern latitudes.Following several fluctuations during the Bølling-Allerød interstadial,the most dramatic drop
in marine organic carbon and biogenic carbonate proportions occurred during the Younger Dryas.However,
many short-term and low-amplitude events during the Preboreal and the Holocene have also affected biogenic
sedimentation in the outer Andfjorden.Apparently,these abrupt changes in biogenic sedimentation were caused
by the suppression of a potential upwelling center in the outer Andfjorden by variable Atlantic Water inflow
over the past 14,000 years.The adjustment of decadal high-productivity coastal systems to freshwater-forced
multiple cooling events during the late glacial to middle Holocene highlights the impact of global climate
changes on the climate-sensitive local ecosystems off coastal Norway.
I
NDEX
T
ERMS
:4267 Oceanography:General:
Paleoceanography;4219 Oceanography:General:Continental shelf processes;4279 Oceanography:General:Upwelling and
convergences;4863 Oceanography:Biological and Chemical:Sedimentation;K
EYWORDS
:paleoceanography,organic sedimentation,
Norwegian continental shelf
Citation:Knies,J.,M.Hald,H.Ebbesen,U.Mann,and C.Vogt,A deglacial –middle Holocene record of biogenic sedimentation and
paleoproductivity changes from the northern Norwegian continental shelf,Paleoceanography,18(4),1096,
doi:10.1029/2002PA000872,2003.
1.Introduction
[
2
] Glacial troughs on the continental shelf provide
ideal sites for studying climate records on decadal to
centennial timescales [Vorren and Plassen,2002].High
sedimentation rates preserve short-term paleoclimatic fluc-
tuations over timescales appropriate to understand climate
change.The sediments delivered to the troughs contain
both paleoenvironmental information on environmental
changes of the hinterland and paleoceanographic variabil-
ity on the adjacent continental margins and shelves
through water mass exchange.Moreover,marine biogenic
sedimentation on the shelf mirrors local as well as global
influences on the environment.Hence sediments accumu-
lating in glacial troughs offer an excellent opportunity for
studying land-ocean interactions and can provide ultra
high-resolution records of local responses to short-term
variability in Earth’s climate [e.g.,Hald and Hagen,
1998].
[
3
] The Andfjorden,a glacial trough located on the
continental shelf off Troms,northern Norway (Figure 1),
for example,has been intensively investigated for local,
regional and global climatic changes occurring over the past
15,000 years.Much of these data have been synthesized in
the studies of Vorren et al.[1984],Hald and Vorren [1984,
1987],and Vorren and Plassen [2002,and references
therein].The area is well suited for studying paleoenvi-
ronmental patterns because (1) the influences of iceberg
ploughing and bottom current erosion on sedimentation
were low [Vorren et al.,1983],(2) very high sedimentation
rates (up to 400 cm ka
1
) allow detailed investigations with
a very high resolution,and (3) the location adjacent to an
area influenced by the Norwegian Atlantic Current (NAC)
contributing to the formation of North Atlantic Deep Water
in the Nordic seas was potentially sensitive to abrupt
climate changes during the late glacial-middle Holocene
[Koc¸ Karpuz and Jansen,1992;Lehman and Keigwin,
1992;Hald et al.,1996;Hald and Hagen,1998].
[
4
] In this paper,we investigate the biogenic sedimenta-
tion in the Andfjorden with a resolution of up to 10 years
per sample.Instead of focusing on absolute proxy values for
estimating productivity changes such as organic carbon,
carbonate,biogenic opal,trace metals as well as faunal and
floral assemblages [e.g.,Berger et al.,1989;Fischer and
Wefer,1999],we show that relative proportions of marine
organic carbon and terrigenous-free (biogenic) carbonate
PALEOCEANOGRAPHY,VOL.18,NO.4,1096,doi:10.1029/2002PA000872,2003
1
Geological Survey of Norway,Trondheim,Norway.
2
Department of Geology,University of Tromsø,Tromsø,Norway.
3
SINTEF Petroleum Research,Trondheim,Norway.
4
Department of Geosciences,University of Bremen,Bremen,Germany.
Copyright 2003 by the American Geophysical Union.
0883-8305/03/2002PA000872$12.00
20 -
1
may be better indicators of changes in paleoproductivity in
high-accumulation areas off coastal Norway.This approach
has been successfully used by Gardner et al.[1997]
reconstructing time-space maps of terrigenous-free carbon-
ate,opal,and organic carbon to investigate changes in
biogenic sedimentation along the eastern boundary of the
California Current.However,it has never been tested in
deglacial/interglacial glaciomarine environments of the Nor-
dic seas so far.Here,we show that by using relative
proportions of marine organic carbon and biogenic carbon-
ate in high-accumulation areas off coastal Norway,decadal
to centennial oscillations in biogenic sedimentation attrib-
uting to surface-ocean biological productivity changes may
be synchronous with rapid changes in atmospheric temper-
atures,reduced Atlantic water inflow and corresponding
North Atlantic deep water formation [e.g.,Lehman and
Keigwin,1992].
2.Climate History and Oceanographic Setting
[
5
] Vorren and Plassen [2002] recently reviewed the
glacial history and paleoclimate in the Andfjorden during
the last deglaciation.On the basis of earlier studies from the
1970s and 1980s [Vorren and Plassen,2002,and references
therein] and recently retrieved seismic and core data,they
described eight main glacial events between 24 to
10.7 ka in the fjord area.The final deglaciation from the
shelf break at the end of the last glacial period started at
17.4 ka.The accompanying meltwater flux into the
northern Norwegian Sea contributed to the formation of
Figure 1.(a) Simplified map of surface waters in the Nordic seas.Blue arrows indicate the pathway of
the East Greenland Current.Red arrows indicate the pathway of the North Atlantic Current.Broken
arrows show the Norwegian Coastal Current.(b) Detailed bathymetric map of the Andfjorden area
including the core locations of JM99-1200 and T79-51/2.(c) Simulated primary productivity (in
g C cm
2
yr
1
) along the northern Norwegian continental margin [Slagstad et al.,1999].Black arrow
marks the inflow of the Norwegian Atlantic Current (NAC).White stippled lines indicate the 500 m and
200 m water depth isoclines.The JM99-1200 core position is displayed.See color version of this figure
at back of this issue.
20
-
2 KNIES ET AL.:NORWEGIAN SHELF BIOGENIC SEDIMENTATION
the early deglacial low oxygen isotopic (meltwater) event
(LOE 1) in the Nordic seas [e.g.,Jones and Keigwin,1988;
Koc¸ and Jansen,1994;Sarnthein et al.,1995;Hald et al.,
1996;Bauch et al.,2001].Vorren and Plassen [2002]
suggested atmospheric warming as the main trigger mech-
anism for melting the ice sheets.On Andøya,near the
Andfjorden area (Figure 1),pollen-derived paleoclimatic
reconstruction indicates two episodes of prominent atmo-
spheric warming prior to the onset of the last deglaciation
[Alm,1993].Thus orbitally forced warming at the end of the
last glacial period was already under way before melting of
the ice sheets started [Hald et al.,1996].A sea-ice-free
corridor opened along Norway at 16 ka based on diatoms
[Koc¸ et al.,1993].The initial intrusion of Atlantic water into
the study area during the last deglaciation is suggested to
occur at 14.3 ka [Hald and Aspeli,1997].According to
Vorren and Plassen [2002],glaciers in northern Norway
receded during the Bølling climate amelioration from14.7
to 14.1 ka [Bjo¨rck et al.,1998] contributing to the global
sea level rise of melt water pulse 1A(MWP 1A) [Fairbanks,
1989;Hanebuth et al.,2000].However,the ice rapidly
readvanced at 14.1 ka possibly triggered by the MWP 1a
and the subsequent cooling phase [Clark et al.,2001].After
ice recession to the fjord heads or even farther inland during
the Allerød,the Younger Dryas glacial advance commenced
at the end of the Allerød.According to Vorren and Plassen
[2002],the advance may have been initiated by the cold
climate during the intra-Allerød cold period (IACP)
[Lehman and Keigwin,1992].The first phase (11.7 to
11.3 ka) of a two-step surface ocean warming during the
Younger Dryas-Preboreal transition terminated the glacia-
tions of the Andfjorden and caused a sudden retreat of the ice
sheet toward the inner fjords [Hald and Hagen,1998;Vorren
and Plassen,2002].A surface ocean temperature maximum
off northern Norway was recorded between 10.7 and
8.9 ka [Hald et al.,1996].
[
6
] Two water masses,the Atlantic water of the NAC and
the coastal water of the Norwegian Coastal Current (NCC)
dominate the oceanographic regime in the study area
(Figure 1).The warm (>2C) and saline (>35%) NAC
[Hopkins,1991] flows northward adjacent to and beneath
the less saline (32–35%) NCC by following the bathym-
etry of the northern Norwegian shelf.The shelf topography,
which is dominated by relative shallow to intermediate
glacial troughs,strongly steers the inflow and outflow of
both water masses [Moseidjord et al.,1999].Almost half of
the shelf water flow makes a right turn into the Andfjorden
along the western slope and flows out again on the eastern
slope [Nordby et al.,1999;Slagstad et al.,1999].When
hitting the northward flowing NAC along the shelf break
again,the flow is forced to change direction,which causes a
topographically steered upwelling via vertical mixing
[Slagstad et al.,1999].The upwelling leads to primary
production rates of up to 190 g C m
2
yr
1
in the outer
Andfjorden by supplying nutrient-rich waters to the eupho-
tic zone (Figure 1) [Slagstad et al.,1999].On the other
hand,the influence of continental input with regard to
nutrient supply and biogenic production is rather small in
northern Norway [Wassmann et al.,1996].By studying a
sediment core (JM99-1200) obtained from the upwelling
area,changes in past productivity patterns on the shelf off
northern Norway and its relation to paleoceanographic
changes may be documented.
3.Material and Methods
[
7
] Piston and box cores were retrieved from Andfjorden
aboard the research vessel ‘‘R/V Jan Mayen’’ in November
1999.Sediment core JM99-1200 (Figure 1;6915.95
0
N;
1625.09
0
E;476 mbsf;11 m core length) was described
with respect to texture,color and sedimentary structure and
stored at in situ temperatures (5C) until analysis.The
sediment core was routinely sampled at 5 cm resolution.
Samples were freeze-dried and carefully ground prior to
geochemical and sedimentological analysis.
3.1.Geochemical Analysis
[
8
] One set of subsamples was analyzed for weight
percentages (wt %) of total carbon (TC) and total organic
carbon (TOC) using a LECO CS 244 analyzer.For the TOC
analyses,aliquots (200 mg) of the samples were treated
with 10%(vol.) hydrochloric acid (HCl) and heated to 60C
to remove carbonate,and then washed with distilled water
to remove all traces of HCl.We caution the reader that the
possible loss of organic material by acid leaching is not
taken into account.The samples were dried overnight
(50C) and then analyzed.The carbonate content (wt %)
was calculated as CaCO
3
= (TC  TOC)  8.33.The
reproducibility of TC and TOC analyses are ±0.1% and
±10%,respectively.
[
9
] Detrital carbonates were studied by means of X-ray
diffraction analysis of the powdered bulk sample at a Philips
X’Change with Cu radiation and fixed divergence (0.5).
Measurements of unoriented nontextural specimens ranged
from 3 to 85 2 theta with a 0.03 2 theta/3 s mode.The
dolomite content equals the peak intensities of the 2.89
A
˚
ngstro¨m (A
˚
) peak divided by the sum of calcite (3.03 A
˚
)
and dolomite (2.89 A
˚
) peak intensities times the carbonate
content [Vogt,1996].
[
10
] Lipid biomarkers were extracted by means of the
Soxthec technique.Briefly,an aliquot (3–4 g) of freeze-
dried and homogenized sediment was extracted for 3 hours
(1 hour boiling and 2 hours rinsing at 80C) using 50 ml
of a dichloromethane/methanol (97:3) mixture.Squalane
was added as internal standard.The sample was then
saponified with 6% potassium hydroxide in methanol.
Neutral lipids were obtained by extraction with hexane
(2 ml  3) and cleaned with 1 ml deionized water.The
dissolved neutral fraction was treated with bis-trimethyl-
silyl-trifluoroacetamide (BSTFA) (60C,30 min) prior to
gas chromatography/mass spectrometry (GC/MS) analysis.
Neutrals were analyzed by performing GC/MS analysis
with a Hewlett-Packard 6890 GC-FID/HP 5973 MSD,and
equipped with a Chrompack CP-Sil 5 CB Low bleed,
50 m  0.25 mm ID  0.25 mm.The injector (280C)
operated in the splitless mode (40 ml/min for 2.0 min).The
column oven temperature was programmed from 90C
(1 min) –10C/min–180C–6C/min–320C (30 min).
The MS was operated at 70 eVunder full scan mode.Helium
was used as carrier gas.Concentrations of n-alkanes and
KNIES ET AL.:NORWEGIAN SHELF BIOGENIC SEDIMENTATION
20
-
3
isoprenoids were calculated from extracted ion chromato-
grams,m/z 57.The reproducibility was better than 10%.
[
11
] Ten samples were analyzed for biogenic opal (per-
cent) by molybdate-blue spectrophotometry on ground bulk
samples using an automated leaching technique [Mu¨ller and
Schneider,1993] at the Alfred Wegener Institute for Polar
and Marine Research,Bremerhaven,Germany.The relative
precision is about 4–10% for samples with less than 10%
biogenic opal [Bonn et al.,1998].Percent biogenic opal was
obtained by following the extrapolation procedure of
DeMaster [1981] with a precision better than 0.5%.A
threshold of 1–2% biogenic opal is assumed to be an
artifact due to partial leaching of clay minerals [Bonn et
al.,1998].
3.2.Isotopic Analysis
[
12
] Stable carbon isotope ratios of the organic fraction
(d
13
C
org
) were determined on decarbonated (10% HCl)
samples using a PDZ Europa elemental analyzer isotope
ratio mass spectrometer (EA-IRMS,Iso-Analytical Limited,
UK).The d
13
C
org
results are in per mil notation.20%of the
samples were analyzed in duplicate with an average stan-
dard deviation of 0.06% (n = 18).The reference material
was Iso-Analytical Ltd.working reference standard IA-
Flour with a d
13
C
org
value of 26.43% versus Vienna-
PDB.Along with IA-Flour,NBS-1577a (Bovine Liver,d
13
C
org
= 21.68%versus Vienna-PDB) was analyzed as a
quality control check during analysis of the sediments.
[
13
] Accelerator Mass Spectrometry (AMS) radiocarbon
dates of bivalves (Table 1) were obtained at the Radiocar-
bon Laboratory of Uppsala,Sweden,and at the Leibniz
Labor fu¨r Altersbestimmung,Kiel,Germany.The precision
of the ages ranges between ±50 and ±100 years (standard
deviation).The
14
C dates were d
13
C-normalized and cor-
rected for an average global ocean reservoir effect of
400 years,with a regional delta R value of 64 ± 35 years
for northern Norway [Stuiver et al.,1986,1998].The
radiocarbon ages were converted into calendar ages by
using the INTCAL-98 calibration data set [Stuiver et al.,
1998].All ages are given in calendar years unless otherwise
stated.
3.3.Sedimentological Analysis
[
14
] Grain size analyses of total sediment were obtained
from laser diffraction techniques (Coulter LS 2000) (for
details,see Xu [2000,and references therein]).The mea-
surement range is 0.4 mm to 2000 mm.The grain size
distribution is determined on volume basis with an uncer-
tainty of ±3%,by assuming the same density of the
materials.
[
15
] Density (g cm
3
) was determined using a GEOTEK
TM
multisensor track instrument (MST).Densities were used to
calculate dry bulk density (DBD) (g cm
3
) by following
the procedure described by Weber et al.[1997].Mass
accumulation rates (g cm
2
ka
1
) of bulk sediment
(ARbulk) were calculated from linear sedimentation rates
(cm ka
1
;based on calibrated ages;cf.Table 1) and DBD
data [van Andel et al.,1975].Accumulation rates of
different components (ARcomp) were calculated according
to the equation ARcomp (g cm
2
ka
1
) = (COMP/100) 
ARbulk,where COMP is the amount of a single component
(e.g.,TOC wt %).
4.Results and Discussion
4.1.Age Model and Sedimentation Rates
[
16
] The age/depth model for JM99-1200 was constructed
by linear interpolation between 7 calibrated AMS
14
C ages
(Table 1).They cover the period from 6.3 to 14.1 ka.The
core base is tentatively estimated to be roughly 14.8 ka by
assuming constant sedimentation rates from the last age fix
point to the base.However,this older part of the record is
not further explored because of the age uncertainties.Age/
depth relations in JM99-1200 indicate linear sedimentation
rates ranging from 120 to 280 cm ka
1
during the last
deglaciation with maximum values up to 620 cm ka
1
(13 ka) and a significant drop to values of about
40 cm ka
1
during the early to middle Holocene
(Figure 2).The distinct increase in linear sedimentation rates
from200 to 620 cmka
1
at 13.1 ka appears very large
and abrupt;however,there is no evidence for lithological
disturbances such as a hiatus or mass flow transport in this
part of the core.Without more detailed age dates for JM99-
1200,bulk and constituent accumulation rates simply follow
the jumps in sedimentation rates and may therewith distort
quantitative estimation of paleoproductivity fromthe organic
carbon data (see discussion below).
4.2.Carbonate Time Series
[
17
] Two independent processes mainly control the per-
centages of carbonate in Andfjorden sediments:Carbonate
production/advection in surface water masses and dilution.
Carbonate dissolution is considered to be of minor impor-
tance as indicated by foraminiferal studies on surface sedi-
Table 1.Accelerator Mass Spectrometer (AMS) Radiocarbon Dates in JM99-1200
a
Core
Number
Depth,
cm
14
C Age
Before
Present
Carbon
Source Laboratory
Calendar Ages
Calendar
Age Before
Present Used
Sedimentation
Rate,
cm kyr
1
2s
Maximum Intercepts
2s
Minimum
JM99-1200 59 5965 ± 60 Cylichna alba TUa 6447 6295 6179 6295 9.37
JM99-1200 281.8 10,130 ± 50 Nuculana pernula KIA 11,595 11,078 10,479 11,078 46.58
JM99-1200 511 11,460 ± 85 Nuculana pernula TUa 13,476 12,939 12,648 12,939 123.16
JM99-1200 655.5 11,830 ± 85 Bathyarca glacialis TUa 13,786 13,171 13,003 13,171 622.84
JM99-1200 723.5 12,160 ± 80 Bathyarca glacialis TUa 13,850 13,491 13,060 13,491 212.5
JM99-1200 788 12,425 ± 55 Bathyarca glacialis KIA 14,292 13,834 13,432 13,834 188.04
JM99-1200 855 12,575 ± 100 Bathyarca glacialis TUa 15,133 14,070 13,450 14,070 283.89
a
A global ocean reservoir correction of about 400 years with an regional delta R-value of 64 ± 35 for northern Norway has been used to calculate
calendar ages.The radiocarbon dates have been calibrated with the INTCAL-98 data set [Stuiver et al.,1998] Tua,Laboratory of Uppsala,Sweden;KIA,
Altersbestimmung,Kiel,Germany.
20
-
4 KNIES ET AL.:NORWEGIAN SHELF BIOGENIC SEDIMENTATION
ments and Holocene sections [Hald and Vorren,1984].
Detrital carbonate such as dolomite is of subordinate im-
portance.Average values of 1.0% do not disturb the
overall trend of the carbonate record (Figure 2).Carbonate
dominates JM99-1200 (up to 38%) at lower sedimentation
rates <48 cmka
1
,whereas carbonate decreases (2–10%) at
sedimentation rates between 120–680 cm ka
1
(Figure 2).
A similar trend is observed at the nearby site T-79-51/2
[Hagen,1995].Hence this first-order trend from rather low
carbonate values during the late deglaciation (until 11.1 ka)
to higher values during the Holocene is possibly caused by
noncarbonate dilution effects governed mainly by variable
input of glaciomarine sediments during deglaciation
[Plassen and Vorren,2002].
[
18
] Superimposed on this long-term trend,short-term
fluctuations in carbonate percentages may indicate that other
processes were involved.Hald and Vorren [1984] observed
carbonate fluctuations during the last deglaciation in several
records from the Andfjorden and suggested a variable input
of detrital carbonate by glacial erosion.This is not confirmed
by our data (Figure 2).Instead,a cross plot between the
carbonate percentages and the abundance of planktic fora-
minifera/per gram sediment shows a highly significant cor-
relation (R
2
= 0.94) in nearby core T-79-51/2 (Figure 3).
This relationship strongly suggests a close linkage between
production of planktic foraminifera and carbonate sedimen-
tation in Andfjorden.Henrich [1998] concluded that
changes in the oceanic regime in the Norwegian Sea are
well recorded by the sedimentary carbonate content.This is
evidently controlled by the enhanced production of calcar-
eous plankton under water masses of NAC affinity.How-
ever,using the carbonate record for paleosurface water
reconstructions on the Norwegian continental shelf is too
simplistic.Unfortunately,the high degree of correlation
Figure 2.Compilation of total accumulation (g cm
2
kyr
1
) (solid line) and sedimentation rates
(cm kyr
1
) (shaded),total organic carbon (wt %),d
13
C isotopic composition (%),calcium carbonate
(wt %),biogenic opal (wt %),and coarse fraction (% greater than 63 mm) from core JM99-1200 against
calendar years before present.Corresponding lithostratigraphic units for Andfjorden [Vorren et al.,1983]
are displayed.Black arrows show calibrated AMS
14
C datings (in calendar years).Three stippled lines
mark prominent coarse-grained layers resulting in distinct TOC minima.
KNIES ET AL.:NORWEGIAN SHELF BIOGENIC SEDIMENTATION
20
-
5
between carbonate and planktic foraminifera in T-79-51/2 is
based on an exponential rather than linear function (Figure
3).Excluding carbonate dissolution and detrital carbonate
input as potential reasons,the exponential function possibly
displays the effect of highly variable sedimentation rates
(10–500 cm kyr
1
) [Hagen,1995] in Andfjorden,where
relatively high sedimentation rates strongly dilute the car-
bonate and planktic foraminifer production and vice versa.
This certainly prevents the use of the JM99-1200 carbonate
record as a simple proxy for changes in the oceanic regime
and surface water productivity in Andfjorden.To avoid
dilution effects in the interpretation of the carbonate varia-
tions,the relative contribution of biogenic (terrigenous-free)
carbonate in the biogenic components of the sediment will
be used.This requires the calculation of the other biogenic
component groups,biogenic opal and marine organic car-
bon [e.g.,Gardner et al.,1997].
4.3.Biogenic Opal Time Series
[
19
] The time series of biogenic opal in JM99-1200
mirrors the general pattern in the Nordic seas and shows
no glacial-interglacial variations (Figure 2).As in JM99-
1200,biogenic opal contents in Nordic seas surface sedi-
ments do not exceed 2% in general [Schlu¨ter and Sauter,
2000;Schlu¨ter et al.,2001;Matthiessen et al.,2001].
Considering the relative abundance of carbonate and opal
in the sediments,a strong predominance of the carbonate
flux is evident for the Nordic seas [Peinert et al.,2001].The
low biogenic opal abundance is most likely due to dissolu-
tion processes [von Bodungen et al.,1995],suggesting an
almost negligible contribution to the burial of biogenic opal
in Nordic Sea sediments [Schlu¨ter et al.,2001].In contrast
to the Southern Ocean,where biogenic opal records were
used to estimate changes in paleoproductivity [e.g.,Bonn et
al.,1998],small-scale fluctuations of biogenic opal in the
Nordic seas are not easily related to primary production in
the photic zone.Values of less than 2% in JM99-1200
(Figure 2) are close to the detection limit of the applied
technique [Bonn et al.,1998].Consequently,to estimate
terrigenous-free,relative proportions of biogenic carbonate,
we regard the biogenic opal content in JM99-1200 as
insignificant.
4.4.Organic Carbon Time Series
[
20
] The TOCvalues vary between 0.5 and 0.8%with a
gradual increase during the deglaciation and more or less
constant values during the early/middle Holocene (Figure 2).
Three prominent minima during the late glacial coincide
with (slightly) larger input of coarse-grained material,
possibly turbidities (Figure 2).The trend from slightly
lower TOC values during deglaciation to more or less
constant values during the middle Holocene possibly
mirrors the average changes in the magnitude of the sedi-
mentation rates from 300 cm ka
1
(max.600 cm ka
1
)
to 40 cm ka
1
and may suggest differences due to clastic
dilution [Mu¨ller and Su¨ss,1979;Johnson-Ibach,1982;
Stein,1986;Betts and Holland,1991].However,variable
input of marine and terrestrial organic carbon may also
explain the trends in %TOC in JM99-1200.Organic carbon
contribution as a result of freshwater supply seems to be of
negligible importance,as indicated by dinoflagellate cyst
assemblages in selected samples (K.Grøsfjeld,personal
communication,2002).
[
21
] A simple two-component mixing model was applied
to the bulk organic carbon isotopic (d
13
C
org
) data to estimate
the proportions of marine and terrestrial organic carbon in
the core [e.g.,Wagner and Dupont,1999;Schubert and
Calvert,2001].In general,marine organic carbon has
heavier d
13
C
org
values than terrestrial C
3
(Calvin-Benson
Cycle) plant material.Admixture of C
4
(Hatch-Slack) plant
debris in these higher latitudes is of minor importance [Teeri
and Stowe,1976].C
3
plant derived terrestrial organic
carbon has depleted d
13
C
org
values between 25.5 and
29.3%,with an average end-member signature of
27% [e.g.,Tyson,1995].However,interpreting d
13
C
org
values of high-latitude phytoplankton requires caution.Very
light plankton d
13
C
org
values (24.0 to 30.0%) have been
observed in the Southern Ocean [Fischer,1991;Rau et al.,
1992].In contrast,phytoplankton from high northern lat-
itudes,comparable to our core location (64–71N) shows
d
13
C
org
values from 18.4 to 23.3%,with an average of
20.9%[Rau et al.,1982].A more secure method is to use
paired analyses of specific organic biomarker compounds
and the d
13
C
org
signatures of contemporaneous sedimentary
organic matter in order to determine marine organic carbon
isotopic end-members [Jasper and Gagosian,1990].For
this purpose we used the sum of long-chain (C
27
,C
29
and
C
31
) n-alkanes (mg/g TOC),a specific biomarker indicative
of vascular plant debris [Eglinton and Hamilton,1963].The
correlation between d
13
C
org
values and long-chain n-alkanes
is significant (R
2
= 0.66) (Figure 4).This suggests that
climatically modulated mixing of C
3
terrestrial/reworked
and marine organic carbon mainly controls fluctuations in
the d
13
C
org
record (Figure 2).As the sum of n-alkanes
approaches zero,a d
13
C
org
value of 20.3% may be
Figure 3.Cross plot of total carbonate content (wt %) and
the total amount of planktic foraminifera (numbers/g
sediment) in core T-79-51/2.Data are adapted from Hagen
[1995].Note the high correlation coefficient of R
2
= 0.94.
20
-
6 KNIES ET AL.:NORWEGIAN SHELF BIOGENIC SEDIMENTATION
considered as the marine d
13
C
org
end-member (Figure 4).
This value agrees with observations by Rau et al.[1982]
and is consistent with several studies from near coastal and
shelf environments with marine d
13
C
org
end-member values
of 20.7 and 20.4%,respectively [Wada et al.,1987;
Cifuentes et al.,1988].The simultaneous use of lipid
biomarker and d
13
C
org
values allows model calculations of
terrigenous and marine organic concentrations by a simple
end-member mixing model [cf.Jasper and Gagosian,1990;
Schubert and Calvert,2001]:
f mð Þ ¼
d
13
C
org
sð Þ d
13
C
org
tð Þ
d
13
C
org
mð Þ d
13
C
org
tð Þ
;ð1Þ
where F (m) is the marine fraction of total organic carbon,
d
13
C
org
(s) is the d
13
C
org
value of a given sample,d
13
C
org
(t)
is the literature based terrestrial d
13
C
org
end member
(27%) for C3 plant debris,and d
13
C
org
(m) is the
calculated marine d
13
C
org
end-member (20.3%).Down-
core changes in % marine organic carbon are shown in
Figure 5.A predominance of marine organic carbon
(>50 rel.%) occurs throughout the record,and changes in
its abundance are highly correlated with biogenic carbonate
content (see discussion below).
4.5.Relative Proportions of Carbonate and Marine
Organic Carbon as Paleoproductivity Indicators
[
22
] In a first approach,we estimate the surface water
paleoproductivity in Andfjorden from the marine organic
carbon content in JM99-1200 by applying equation (2)
published by Knies and Mann [2002].Equation (2) is based
on studies by Mu¨ller and Su¨ss [1979],Betzer et al.[1984],
Johnson-Ibach [1982],Stein [1986,1991],and Betts and
Holland [1991].Three main processes may control the
marine organic carbon sedimentation in oxic environments
and are therefore considered in the equation:(1) the primary
productivity of marine organic matter and its flux through
the water column;(2) its dilution by inorganic components;
(3) its decomposition/preservation during burial (burial
efficiency).These factors are numerically expressed as
Organic Carbon Flux Dilution
##
MOC ¼
0:409PP
1:41
z
0:63
10
 
100
DBDLSR
 
Burial Efficiency
#
0:54 0:54
1
0:037LSR
1:5
þ1
  
;
ð2Þ
where MOC is marine organic carbon (in %),PP is the
primary productivity (in g C m
2
yr
1
),z is the water depth
at the time of deposition (in m),DBD is the dry bulk density
of sediment (in g cm
3
),and LSR is the linear sedimenta-
tion rate (in cm ka
1
).
[
23
] Solving equation (2) for PP allows the estimation of
the primary paleoproductivity of the overlying surface water
from sediment data:
PP ¼
MOC 0:378 DBDLSR z
0:63
1 
1
0:037LSR
1:5
þ1
  
8
>
>
<
>
>
:
9
>
>
=
>
>
;
0:71
:ð3Þ
Figure 5 shows rather low productivity values (100–
120 g C m
2
yr
1
) during early to middle Holocene,
whereas values between 200 and 280 g C m
2
yr
1
(max.values about 700 g C m
2
yr
1
) prevailed during
the last deglaciation.These results closely follow changes
in the bulk accumulation rates (Figure 2).Obviously,
accumulation rates of MOC in JM99-1200,the prerequi-
site for estimating paleoproductivity in this classical
approach [Stein,1991],are heavily affected or even
controlled by LSR because LSR variations are often
higher and more variable in coastal and shelf settings
than the concentration of a given component (e.g.,MOC).
Hence the paleoproductivity estimates in our study area
seem not to be indicative for any kind of higher-
resolution variability in surface water productivity changes,
Atlantic water inflow or deglaciation patterns (Figure 5).
Indeed,reestimation of paleoproductivity based on mass
fluxes and burial rates of marine organic carbon in
extremely variable and high-accumulating shelf areas
makes only sense if a well-constrained and high-
resolution age model is available.This is not given for
JM99-1200.Accordingly,the use of linear,highly
variable (40 to >600 cm ka
1
) sedimentation rates
over relatively longer time periods (>1 kyr) in glacio-
marine environments with rather low percentages of
Figure 4.Cross plot of the sum of long-chain (C
27
,C
29
,
C
31
) n-alkanes (mg/g TOC) and the d
13
C isotopic signature
of the total organic matter (d
13
C
org
) in JM99-1200.By
approaching the regression to zero,we estimated a d
13
C
org
marine end-member of 20.3%.
KNIES ET AL.:NORWEGIAN SHELF BIOGENIC SEDIMENTATION
20
-
7
biogenic components reflects only a very rough trend or,
even worse,falsifies reestimation of paleoproductivity.
[
24
] Instead,the use of relative proportions of terrigenous-
free biogenic carbonate and marine organic carbon based on
the d
13
C
org
end-member mixing model is here proposed to
reflect paleoproductivity changes in surface water masses
and biogenic sedimentation on the shelf off northern Nor-
way.The calculation of the biogenic (terrigenous-free)
proportions of the total sediment is based on the assumption
that carbonate and marine organic carbon are the principal
contributors to the biogenic sedimentation.As already
mentioned above,biogenic opal content is negligible.We
Figure 5.Paleoproductivity estimates based on equation (2) (in g C m
2
yr
1
),relative proportions of
marine organic carbon,and relative biogenic (terrigenous-free) carbonate percentages shown against
calendar years.Black arrows mark available AMS
14
C datings.Multiple cooling events during the last
deglaciation and the early/middle Holocene are marked.IBCP,Intra Bølling Cool Period;IACP,Intra
Allerød Cool Period;PBO,Preboreal Oscillation.
20
-
8 KNIES ET AL.:NORWEGIAN SHELF BIOGENIC SEDIMENTATION
calculate percentages of the terrigenous-free biogenic car-
bonate using the equation
Rel:%CaCO
3
terrigenous freeð Þ
¼
%
CaCO
3
%
CaCO
3
þ
%
bioOpalþ
%
MOC
ð Þ
100;
ð4Þ
where %CaCO
3
is the total carbonate fraction,1.8%
biogenic opal is used as an average background value and
%MOC represents the amount of marine organic carbon of
the total organic carbon fraction.Figure 5 indicates that the
biogenic carbonate dominates (>60%) the entire biogenic
fraction in JM99-1200.However,the fluctuations in the
biogenic carbonate record are not related to any changes in
surface water settings,but to the mutual dilution by marine
organic carbon after the effect of terrigenous dilution has
been removed.The interpretation of relative proportions of
biogenic carbonate alone might be therefore rather arbitrary.
However,a cross plot with three independent proxies,i.e.,
the d
13
C
org
derived relative proportions of marine organic
carbon,the total weight percentages of carbonate,and the
terrigenous-free (biogenic) percentages of carbonate illus-
trate a close coupling with both clastic dilution and primary
(marine organic carbon) and secondary (biogenic carbonate)
production (Figure 6).The exponential correlation between
d
13
C
org
-derived marine organic carbon and total percentage
of carbonate (R
2
= 0.78) still reflects the clastic dilution
effect with rather low carbonate values (<10%) at moderate
relative marine organic carbon values (50–60 rel.%).In
contrast,the linear correlation between the terrigenous-free
(biogenic) percentages of carbonate and d
13
C
org
-derived,
relative proportions of marine organic carbon is significant
(R
2
= 0.8) and may reflect the direct response of biogenic
carbonate production to surface water paleoproductivity
changes (Figure 6).Hence,rather than focusing on absolute
proxy values indicating biogenic sedimentation,we
hypothesize that the relative proportions of marine organic
carbon and terrigenous-free (biogenic) carbonate calculated
independently from each other may be useful indicators of
changes in paleoproductivity and biogenic sedimentation in
high-accumulation areas off coastal Norway.
4.6.Paleoceanographic Implications
[
25
] Broecker et al.[1989] and recently Clark et al.
[2001] have suggested that abrupt,high-amplitude climate
changes during the last deglaciation are plausibly related to
melt water diversion from North America.Melt water
discharge from the retreating Fennoscandinavian ice sheet
[Hald and Hagen,1998],including the Baltic ice lake
[Bjo¨rck et al.,1996;Bode´n et al.,1997] and the Arctic
Ocean [Spielhagen et al.,1998;Fisher et al.,2002],may
have further amplified the freshening in the Nordic Sea
during the last deglaciation and this may have inhibited the
strength of the North Atlantic heat conveyer [e.g.,
Broecker et al.,1988,1990].The striking similarities
between ocean records in the North Atlantic and North
Sea [Lehman and Keigwin,1992;Haflidason et al.,1995;
Klitgaard-Kristensen et al.,2001] and southeastern Nor-
wegian Sea [Koc¸ Karpuz and Jansen,1992],and the ice
core records from Greenland [e.g.,Johnsen et al.,1997;
Stuiver and Grootes,2000] point to a tight response of
variable Atlantic inflow and air temperature changes to
episodic melt water supply from retreating ice sheets in
high latitudes [Clark et al.,2001].
[
26
] Decadal-scale to century-scale climate oscillations in
those records correlate well,within a deviation of less than
100 years to GRIP ice core,with the abrupt changes in
relative proportions of marine organic carbon record in the
Andfjorden (Figure 7).The relative percentages of biogenic
carbonate largely follow the trend,albeit with a lower
amplitude.The initial warming during the onset of the
Bølling-Allerød interstadial complex (14.4–12.7 ka) was
not recovered in JM99-1200.Assuming that the climate
history of Greenland is in phase with changes in North
Atlantic circulation [Kroon et al.,1997],multiple cooling
events detected in several terrestrial and marine records
during the interstadial,i.e.,the Intra Bølling Cool Period
(IBCP),the Older Dryas (OD),and the Intra Allerød Cool
Period (IACP),are indicated by distinct fluctuations in
relative marine organic carbon input (Figure 7).The IACP
or Killarney Oscillation [Levesque et al.,1993] is preceded
by another short-termcooling spell (here defined as pIACP),
which is indicated by the parallel return of N.pachyderma
sinistral in the North Sea record [Klitgaard-Kristensen et
al.,2001] and a significant drop in the relative proportions
of marine organic carbon (Figure 7).The two major lows of
marine organic carbon closely correspond to the ODcooling
(13.8 ka) and the IACP (13.0 ka) [Lehman and Keigwin,
1992;Koc¸ Karpuz and Jansen,1992;Kroon et al.,1997].
The lows may be due to a significantly higher contribution
of terrestrial organic carbon forced by glacial erosion in the
Andfjorden [Vorren and Plassen,2002].Vorren and Plassen
suggested that ocean cooling subsequent to MWP1a
[Fairbanks,1989] at possibly 14.6–14.3 ka [Hanebuth
et al.,2000] might have triggered the small-scale
ice advance in the Andfjorden during the Older
Dryas (Figure 7).The relatively short duration (<150 years)
of Older Dryas glacial activity in high northern latitudes
was explained by the rather low impact of MWP1a on
Figure 6.Cross plot of the d
13
C
org
-based relative propor-
tions of marine organic carbon (rel.%),the total amount of
calcium carbonate (wt %),and the relative proportions
biogenic (terrigenous-free) carbonate (rel.%),respectively.
KNIES ET AL.:NORWEGIAN SHELF BIOGENIC SEDIMENTATION
20
-
9
thermohaline circulation [Clark et al.,2002] and thus
Atlantic water inflow.Surprisingly,glacier advances in
the Andfjorden during the IACP has not been distin-
guished so far (Figure 7) [Vorren and Plassen,2002].
The whole time span of 1000 years for these multiple
cooling events may be too short to be resolved separately
by the existing records in the Andfjorden.The IACP in
JM99-1200 resembles the pattern of the Older Dryas
with an abrupt drop of relative marine organic carbon
input to higher terrestrial organic proportions (Figure 7).
Together with a maximum in total accumulation rates (up
to 1000 g cm
2
ka
1
) during the IACP (Figure 2),this
may be an indication for another glacial readvance in the
Andfjorden area.A significantly higher contribution of
terrestrial organic carbon could be forced by glacial
advance,whereas the maximum in accumulation rates
points to a short-term pulse of erosional products during
rapid retreat.
[
27
] The parallel lows in relative percentages of marine
organic carbon may reflect the accompanied reduction in
Atlantic water inflow and enhanced sea ice formation in the
Norwegian Sea during both cooling events (Figure 7) [Koc¸
Karpuz and Jansen,1992;Koc¸ et al.,1993;Haflidason
et al.,1995;Klitgaard-Kristensen et al.,2001].A more
likely reason could be changes in a topographically
steered local upwelling system in the outer Andfjorden
that acts today as a chimney where water,rich in
nutrients,is supplied to the euphotic zone [Slagstad et al.,
1999].The westward flowing current out of the
Andfjorden that meets the northward flowing North
Figure 7.Comparison between qualitative and quantitative proxy records from the eastern Nordic Sea
and the Andfjorden with the oxygen stable isotopes (d
18
O) record obtained from the GRIP ice core
[Johnson et al.,1997].On the basis of the relatively low age deviations (<100 years) between the
multiple cooling events in JM99-1200 and the GRIP ice core record,we assume a time equivalence
indicated by the stippled lines.(a) Klitgaard-Kristensen et al.[2001] published the Neogloboquadrina
pachyderma sinistral (%) record from Troll core 8903/28-03 (North Sea;6052
0
N,0344
0
E).(b) Diatom-
based sea surface temperature reconstruction in cores HM79-6/4 (Norwegian Sea;6258
0
N,0242
0
E;
6306
0
N,0233
0
E;adapted fromKarpuz and Jansen [1992]).(c) Vorren and Plassen [2002] compiled the
glacial history in the Andfjorden area and compared the waxing and waning of the ice sheet with the
glacial meltwater discharge from the Sunda continental shelf (dotted line) and U/Th ages from Barbados
(solid line),respectively (adopted from Hanebuth et al.[2000]).
20
-
10 KNIES ET AL.:NORWEGIAN SHELF BIOGENIC SEDIMENTATION
Atlantic Current along the shelf break force this upwelling
[Slagstad et al.,1999].Assuming the existence of this
upwelling system since the Bølling-Allerød interstadial,
we propose that during freshwater-triggered cooling
events [Clark et al.,2001] and a simultaneous reduction in
Atlantic water inflow,upwelling activity in the outer
Andfjorden was suppressed.Simultaneous increase
in planktic foraminiferal assemblages dominated by
N.pachyderma sin.in the northern North Sea [Haflidason
et al.,1995;Klitgaard-Kristensen et al.,2001] and the
abrupt drop in sea surface temperatures in the southeastern
Norwegian Sea [Koc¸ Karpuz and Jansen,1992] indicating a
distinct drop in NAC intensity support our model (Figure 7).
The suppression of an upwelling centre in the outer
Andfjorden should have triggered a significant lowering in
biological productivity and thus marine organic carbon and
carbonate sedimentation.
[
28
] Dramatic changes in biogenic sedimentation and
surface water productivity on the shelf off northern Norway
occurred parallel to the onset of the Younger Dryas period
(Figure 7).The sudden drop in both relative percentages of
marine organic carbon (20 rel.%) and biogenic carbonate
(30 rel.%) tentatively coincide with the abruptness and
amplitude of high-latitude climate changes during this cold
spell [Alley,2000].The duration of low production in
JM99-1200 is about 1200 years (12.7–11.5 ka) indicating
a very good match with the GRIP chronology for the
Younger Dryas [Johnsen et al.,1997].Considering huge
melt water pulses on both sides of the North Atlantic and
the Arctic Ocean as a plausible forcing mechanism for the
Younger Dryas [e.g.,Bode´n et al.,1997;Spielhagen et al.,
1998;Clark et al.,2001],the waning/decrease of the
thermohaline circulation and enhanced sea ice formation
in the study area during this time [Hald and Aspeli,1997;
Sarnthein et al.,1995,2001] may have triggered a severe
reduction in local upwelling and thus biogenic sedimenta-
tion in the outer Andfjorden.A major glacial advance in the
Andfjorden occurred simultaneous between 10.7 and
10.3
14
C ka (12.7–12.0 ka) (Figure 7) [Vorren and
Plassen,2002].The sudden increase in biogenic sedimen-
tation follows almost exactly the restart of the thermohaline
circulation amplifying the close linkages between regional
coastal environments off northern Norway and global cli-
mate changes (Figure 7) and support our general model of
an abrupt response of highly vulnerable,coastal ecosystems
to rapid freshwater-enforced changes in oceanic regimes
during the last deglaciation.
[
29
] Multiple cooling continues toward the early and
middle Holocene,although with lower amplitudes and
resolution.In general,the climate amelioration in the
Andfjorden during the early Holocene described by Hald
et al.[1996] is recorded by the gradual increase in the
relative proportions of marine organic carbon and biogenic
carbonate.Short-term decreases,however,point to abrupt
changes in surface ocean conditions at least during four
phases.Two prominent lows in marine organic carbon may
correlate with the Preboreal Oscillation (PBO;11.17–
11.05 ka) [Bjo¨rck et al.,1996],and the Greenland 8.2 ka
cold event [Alley et al.,1997].Both events may have been
triggered by freshwater pulses,which disturbed thermoha-
line circulation in the northern North Atlantic [Hald and
Hagen,1998;Klitgaard-Kristensen et al.,1998;Barber et
al.,1999;Fisher et al.,2002],However,few dates and
poorer resolution prevent a closer inspection of Holocene
climate changes in JM99-1200 so far.
[
30
] In summary,we show that coastal regimes off north-
ern Norway closely follow the abrupt frequencies and
amplitudes of changing sea surface conditions in the Nordic
seas during the last deglaciation.The possibility that coastal
upwelling systems responded with little delay to changes in
Atlantic water inflow during the last deglaciation and
probably the Holocene highlight the complex interactions
of rapid atmospheric and oceanic changes to ecological
variables in coastal ecosystems.
5.Conclusions
[
31
] Absolute values of calcium carbonate and total
organic carbon cannot be used as proxies for paleoceano-
graphic reconstruction in high-accumulation areas off
coastal northern Norway.Instead,we find that relative
percentages of (terrigenous-free) biogenic carbonate and
marine organic carbon are useful indicators for deciphering
biogenic sedimentation and surface water productivity.
Sudden drops in relative proportions of biogenic carbonate
and marine organic carbon reveal multiple cooling events
during the last deglaciation.The abruptness closely follows
changes in atmospheric and oceanic regimes.Prior to the
most prominent drop in biogenic sedimentation and surface
productivity during the Younger Dryas cold spell,indica-
tions of four short-term cool precursors possibly time
equivalent with the Intra Bølling Cold Period,the Older
Dryas,and the Intra Allerød Cold period (pIACP and IACP)
were detected.These precursors point to a highly dynamic
and unstable ecosystem off coastal northern Norway,where
the variable inflow of Atlantic water masses is suggested to
be the major controlling mechanisms for the biogenic
sedimentation.Depending on its intensity during the last
deglaciation and,with less amplitude,during the early/
middle Holocene,a potential upwelling system controlling
surface water productivity and thus biogenic sedimentation
in the outer Andfjorden were either suppressed (during
cooling) or enforced (during warming).The local coastal
response of rapid global climate changes and variable
Atlantic water inflow not only documents the complex
environmental interactions during the last deglaciation and
the Holocene,but also elucidates potential effects on coastal
human societies and economy.
[
32
]
Acknowledgments.Steven Brookes (Iso-Analytical Limited,
Cheshire,UK) are greatly acknowledged for providing the d
13
C
org
results.
Anne Nordtømme and Wieslawa Koziel (Geological Survey of Norway,
Trondheim,Norway) were responsible for the LECO and Coulter analyses.
We sincerely thank Kristin Lind and Torun Vinge for support in the
geochemical labs at SINTEF Petroleum Research,Trondheim,Norway.
Thomas Wagner is gratefully acknowledged for useful comments to an
earlier draft of the manuscript and two anonymous reviewers for the formal
review.J.K.was funded by Total Fina Elf and the German Research
Foundation (DFG),grant KN527/1.M.H.and H.E.were funded by the
University of Tromsø,the Norwegian Research Council (NORPAST and
SPINOF) and VISTA.The data set will be available from the German
paleoclimate data repository PANGAEA,Alfred Wegener Institute for Polar
and Marine Research,http://www.pangaea.de.
KNIES ET AL.:NORWEGIAN SHELF BIOGENIC SEDIMENTATION
20
-
11
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H.Ebbesen and M.Hald,Department of
Geology,University of Tromsø,N-9037 Tromsø,
Norway.(morten.hald@ig.uit.no;hanne.
ebbesen@ig.uit.no)
J.Knies,Geological Survey of Norway,
N-7491 Trondheim,Norway.( jochen.knies@
ngu.no)
U.Mann,SINTEF Petroleum Research,
N-7465 Trondheim,Norway.(ute.mann@
iku.sintef.no)
C.Vogt,Department of Geosciences,Univer-
sity of Bremen,Klagenfurter Strasse,D-28359
Bremen,Germany.(cvogt@min.uni-bremen.de)
KNIES ET AL.:NORWEGIAN SHELF BIOGENIC SEDIMENTATION
20
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Figure 1.(a) Simplified map of surface waters in the Nordic seas.Blue arrows indicate the pathway of
the East Greenland Current.Red arrows indicate the pathway of the North Atlantic Current.Broken
arrows show the Norwegian Coastal Current.(b) Detailed bathymetric map of the Andfjorden area
including the core locations of JM99-1200 and T79-51/2.(c) Simulated primary productivity (in
g C cm
2
yr
1
) along the northern Norwegian continental margin [Slagstad et al.,1999].Black arrow
marks the inflow of the Norwegian Atlantic Current (NAC).White stippled lines indicate the 500 m and
200 m water depth isoclines.The JM99-1200 core position is displayed.
KNIES ET AL.:NORWEGIAN SHELF BIOGENIC SEDIMENTATION
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