Quaternary Science Reviews 19 (2000) 619}631
The N and W Iceland Shelf: insights into Last Glacial Maximum ice
extent and deglaciation based on acoustic stratigraphy
and basal radiocarbon AMS dates
John T. Andrews!,*, JoH runn HardardoH ttir!,", GudruH n HelgadoH ttir#, Anne E. Jennings!,
AD slaug GeirsdoH ttir", AD rny E. SveinbjoK rnsdoH ttir$, Stephanie School"eld!,
GreH ta B. KristjaH nsdoH ttir$, L. Micaela Smith!, Kjartan Thors%, James P.M. Syvitski!
!Institute of Arctic and Alpine Research and Department of Geological Sciences, University of Colorado, Box 450 Boulder, CO 80309 USA
"Department of Geosciences, University of Iceland, 101 Reykjavn& k, Iceland
#Jardfr~distofa Kjartans Thors Borgartu& n 18, 105 Reykjavn& k, Iceland
$Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavn& k, Iceland
%Marine Research Institute of Iceland, Sku& lagata 4, 101 Reykjavn& k, Iceland
Abstract
We present 32 AMS radiocarbon dates collected from sediments obtained during cruises of CSS Hudson (1993), RV Jan Mayen
(1996), and Bjarni Saemundsson (1997). The radiocarbon dates were obtained on samples from the basal part of sediment cores
collected across an area between 64 and 673N and 18}293W. Core sites were based on 3.5 kHz acoustic subbottom surveys. The
3.5 kHz subbottom pro"les indicate that several of the troughs contain*30 m of Quaternary sediment. At many sites, the acoustic
surveys suggest the presence of one or more strong re#ectors which can be traced over extended areas ('100 km) of the sea#oor.
These may represent large-scale volcanic ash falls, such as the Vedde ash and its correlatives, as well as other regionally signi"cant
tephras. We report dates from seven areas; (1) Northern troughs * Eyjafjardarall, Huna#oadjup, and Reykjafjardarall: (2) Huna#oi
area and inner shelf and fjords; (3) DjuH paH ll area; (4) Isafjardardjup area ; (5) KolluaH ll; (6) western shelf break and slope; and 7)
JoK kuldjuH p. The dates range in age from Marine Isotope Stages 3}1. Five cores have basal dates*16 ka and thus provide information
on the timing and environments during the deglaciation. Several dates of &12 ka indicate that the inner shelf may have been largely
ice-free by that time. Estimates of average sediment accumulation rates vary between 4 and 90 cm/kyr, with modal estimates of
30}40 cm/kyr. ( 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction
Until recently, the only records from the west Iceland
shelf were the undated faunal and isotope study of
HelgadoH ttir (1984) from JoK kuldjuH p in western Faxa#oH i
(Fig. 2A). Thus, critical questions, such as the extent of
glacial ice on the Iceland shelves, dates of deglaciation of
the shelves, changes in marine conditions during the
Holocene, and land/ocean correlations, have been addressed with some di$culty because of the lack of solid
basis in marine core and seismic stratigraphic research
* Corresponding author. Tel.: 001-303-492-5183; fax; 001-303-4926388;
E-mail address: [email protected]. (J.T. Andrews).
(IngoH lfsson, 1991; IngoH lfsson et al., 1997). In 1996 and
1997 the Norwegian research vessel Jan Mayen (cruise
JM96-) and Marine Research Institute of Iceland's
trawler Bjarni S~mundsson (cruise B9-97, HelgadoH ttir,
1997), respectively, recovered a series of gravity and/or
piston cores from the Iceland slope, shelf, and fjords
(Table 1). Radiocarbon dates from CSS Hudson cruise
HU93030 (Asprey et al., 1994) and from Icelandic cores
in DjuH paH ll (e.g. Smith et al., 1996) were earlier described
in Manley and Jennings (1996). These cruises were a part
of an Iceland/USA `Paleoclimate of Arctic Lakes and
Estuaries (PALE)a investigation of the Iceland continental margin. The dates are from sediment cores
with lengths that vary between 0.5 and 5.5 m (Fig. 2B,
Table 1). The cores ended in sediments which ranged
from muds to diamictons.
0277-3791/00/$ - see front matter ( 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 2 7 7 - 3 7 9 1 ( 9 9 ) 0 0 0 3 6 - 0
01.0N/223 48.0
16.4N/223 51.4W
16.51/223 51.674W
16.62N/223 50.53W
643 46.559N/243 29.14W
663
663
663
663
643 17.06N/243 12.42W
A
643 04.5N/243 19.3W
643 16.479N/243 01.39W
633 55.7N/243 28.9W
oK kuldjuH p
193030}006LCF
A
97}348PC
97}350PC
97}347PC
Western shelf and slope
96}1227GGC
653 47N/263 19.5W
JM96}1221GGC
653 07.9N/273 32.2W
96}1220GGC
653 00.0N/273 30W
96}1222GGC
653 25.0N/283 25W
ID safjardardjuH p region
97}339PC2
97}311PC
97}342PC
97}341PC
KolluaH ll
97}343GGC
A
!332
!239
!321
!247
!198
!483
!514
!1045
!268
!104
!100
!94
!96
!183
!239
!215
!388
663 25.04N/233 37.06W
66341.207N/24310.698W
663 37.1N/243 00W
663 20.1N/183 39.04W
97}320PC
!373
!92}456GCC
97}335PC
96}1232GGC
663 38.49N/203 51.793W
97}327PC
!418
!282
!349
!480
!422
!1047
!223
!242
66326.829N/18350.24W
66331.42N/2139.13W
663 34.545N/213 00.19W
663 53.47N/183 58.46
663 26.53N/183 51.06
97}319GGC
97}324PC1
97}325PC
97}321PC
97}319PC2
!494
673 01.2N/253 09.1W
663 35.15N/233 58.8W
663 41.2N/243 09.7W
66335.27N/18351.9W
97}317PC
!397
DjuH paH ll
96}1229GGC
96}1234GCC
97}336PC
66350.78N/20313.64W
97}323PC1
!357
!108
!165
!94
66356.29N/1936.5W
Northern troughs
97}322PC
Water depth
(m)
Northern fjords and inner shelf
97}332PC
663 08.059N/21338.42W
97}330PC
653 52.0N/213 04.9W
97}328PC
653 57.4N/213 33.1W
Latitude/longitude
Area Core ID
16
*12
*10
*20
A
10
*15
*15
*20
*7.5
*10
*15
'10
*15
*12
*30
*15
*30
*20
*10
&11
*7
*30
*33.5
*30
'7.5
*7
*10
NA
*7.5
'7m
*7.5
*7.5
Estimated
sediment
thickness (m)
491
430
480
1235
A
56
185
187
68
154
527
328
440
220
150
427
265
259
501
530
540
422
327
330
192
300
271
300
227
*245
292
161
Sample
depth (cm)
CAMS-44861
AA-29211
CAMS-44860
AA-12896
AA-20736
CAMS-42012
CAMS-44858
CAMS-44857
AAR-3517
AA-27761
AA-26518
CAMS-44862
AA-31748
AA-29210
AAR-3707
AA-27760
AAR-3515
CAMS-44859
CAMS-46527
CAMS-42013
CAMS-44871
CAMS-44864
CAMS-44863
AA-29185
CAMS-44870
AA-29184
AAR-3888
CAMS-44869
CAMS-44872
AAR-3886
AAR-4209
CAMS-27763
AAR-3887
Laboratory no.
12,280$50
10,747$75
10,730$100
13,105$85
12,810$205
36,050$560
18,240$80
18,090$80
15,690$110
3985$50
10,405$85
9,140$50
9,270$80
2,980$55
12,250$120
10,350$80
9,060$7010.7
31,310380
15,720$70
13,680$70
10,330$60
9,400$60
4,680$50
3,880$65
4,560$50
12,100$110
9,720$110
9,380$50
7,540$40
6,440$80
12,270$100
25,330$640
42,600$3050
Age (14C
years BP)
41.6
7.1
3.5
4.2
4.0
19.9
7.1
15.5
12.0
9.7
16.6
11.1
22.8
7.5
4
9.2
C. lobatulus
7.8
6
6.3
5.6
7.9
232
13.8
9.3
9.0
5.7
10.8
11.2
5.8
5.1
6.1
7.2
Weight
(mg)
lobatulus
pachyderma s
pachyderma s
pachyderma s
N. Labradoricum
E. excavata
forma clavata
Nuculana pernula
N. Labradoricum
mixed planktic &
benthicforams
C.
N.
N.
N.
Melonis zaandamae
Nuculana buccata
Nucula tenuis
Yoldia spp.
Nucula tenuis
N. pachyderma s
Mixed benthics
Axinopsis orbiculta
bivalve
Mixed benthics
C. lobatulus
30.8
N. labradoricum
N. labradoricum
Yoldia bivalve
Mixed benthic
& planktic forams
Mixed benthic and
planktic forams
N. labradoricum and
C.teretis
Mixed benthics
Mixed benthics
N. labradoricum
Scaphopod
Globobulimina
auriculata
Globobulimina
auriculata
Globobulimina
auriculata
Material dated
40.0
40
44.8
95
A
1.6
10.1
10.3
4.3
38.7
52.7
35.9
47.3
73.8
12.7
43
8.6
16.5
37.3
53.3
60
98.6
84.3
72
15.9
30.9
30.2
42
35.2
20.2
11.7
3.8
Average sediment
accumulation rate
(SAR cm/ky)
Table 1
Uncorrected basal radiocarbon dates from Iceland shelf and slope cores (see Fig. 1). Sites in brackets are from earlier cruises, where appropriate (e.g. HU93030-00). Basal dates are arranged from oldest to youngest within each area
(see also Manley and Jennings, 1996; Smith et al., 1999). PC"piston core; GGC"giant (10 cm diameter) gravity core
620
J.T. Andrews et al. / Quaternary Science Reviews 19 (2000) 619}631
J.T. Andrews et al. / Quaternary Science Reviews 19 (2000) 619}631
621
in North Atlantic marine sediments (Bond and Lotti,
1995; Bond et al., 1997; Labeyrie et al., 1998). Furthermore, high-resolution studies of Icelandic o!shore sediments have just recently been initiated (cf. Eiriksson et al.,
1998; Hagen 1995; Jennings et al., 1996, 1999).
2.1. Bathymetry
Fig. 1. Present-day oceanographic setting of Iceland in the
North Atlantic Region. Black arrows represent relatively warm ocean
surface currents, whereas grey arrows indicate relatively cold surface
currents.
The purpose of this paper is to present our radiocarbon results on basal marine core sediments from Iceland
shelf and fjord locations (Figs. 1 and 2A) in order to
assess the extent of ice during the LGM and to pave the
way for future high-resolution studies of these cores (e.g.
Jennings et al., 1999). We discuss our dates on the basis of
their location, relationship to glacial limits, and sediment
accumulation rates (SAR, cm/kyr). This paper presents
the "rst survey of dates of Icelandic shelf sediments for
the region west of 183 W and between 643 and 673N.
2. Background
The oceanographic and climatic location of Iceland, at
the boundary of water masses with `polara and `Atlantica characteristics (Malmberg, 1969, 1985; Johannessen,
1986) (Fig. 1) gives it an obvious importance to marine
paleoenvironmental research (cf. Ruddiman and McIntyre, 1981a,b). Their work was carried out in cores from
the southern part of Denmark Strait (V28-14) (Fig. 1) (see
also Kellogg, 1984; Ruddiman et al., 1994). Given the
contrast in the severity of marine conditions across Denmark Strait (Malmberg, 1985), it is suprising that there
are more published paleoceanographic papers from the
East Greenland continental margin than there is for
Iceland (Williams et al., 1995; Stein et al., 1996; Andrews
et al., 1996, 1997). In the last few years, however, attention is being directed toward the glacial history of Iceland because of the identi"cation of ice-rafted sediments
(often associated with Heinrich events) of Icelandic origin
Bathymetric maps indicate that Iceland is fringed by
a shallow shelf, which is traversed by a series of crossshelf troughs. These troughs are relatively shallow and
frequently increase in depth seaward. However, in some
cases the troughs are silled. This is particularly the case
for the large troughs west of 183W o! N Iceland. EyjafjardaraH ll (Fig. 2A), for example, which is the deepest
trough within the study area, has a maximum water
depth of 670 m whereas the sill to the north has a depth
of 425 m. The origin of the troughs is most likely in part
tectonic, and in part attributable to glacial erosion.
Given the high present rates of glacial erosion in Iceland
(Boulton 1979; Boulton et al., 1988; BjoK rnsson, 1996) it is
interesting that the Iceland fjords and o!shore troughs
are relatively shallow compared to fjords and troughs o!
Greenland, Norway, and NE Canada (Syvitski et al.,
1987). Seismic pro"les indicates that this cannot be simply attributable to the in-"lling by glacial marine and
post-glacial sediments, as sediment thicknesses are modest (see later, Table 1, Fig. 3). Recent studies by Bentley
and Dugmore (1998) indicate that landslides survived
glaciation in parts of northern Iceland, again indicative
of only moderate rates of glacial erosion. Previous research on bathymetry and seismic stratigraphy indicated
that large ridges occur on parts of the Iceland shelf.
In Fig. 2B we show the location of features which
have been identi"ed as moraines (e.g. OD lafsdoH ttir, 1975;
Eglo! and Johnson, 1979; Syvitski et al., 1999). The
mapping of these features provides some constraints on
the extent, but not the timing of glaciation on the Iceland
shelf.
3. Methods
On both the JM96 and B9-97 cruises, core sites were
selected on the basis of 3.5 kHz acoustic subbottom records. They were chosen to obtain either the longest
temporal record possible, given the lengths of the coring
system, or the highest resolution. We used the 3.5 kHz
records, with an estimated velocity of sound through
water and sediment of 1500 m/s, to derive preliminary
estimates of sediment thickness at each coring locale
where we had survey data (Table 1).
On the JM96 cruise, an 11 cm diameter `giant gravity
corera (GGC) was used. On the B9-97 expedition we
mainly employed a 7 cm diameter `BenthosTMa medium weight piston corer, complemented by a WHOI
622
J.T. Andrews et al. / Quaternary Science Reviews 19 (2000) 619}631
Fig. 2. Map showing location of cores and the seven areas discussed in the text. (B) Basal radiocarbon ages (not corrected for ocean reservoir e!ect) as
introduced in Table 1. Possible ice margin limits based on bathymetric and seismic surveys (see text) are also shown.
J.T. Andrews et al. / Quaternary Science Reviews 19 (2000) 619}631
623
Fig. 3. Selected 3.5 kHz subbottom pro"les from some of the core sites. The `apparenta basement at the core sites is shown, although in many
instances a clear re#ection from the underlying bedrock was not obvious. The depth scale is based on a two-way travel of 1500 m/s. The horizonal axis
is estimated on the basis of the ship speed and is approximate.
`suitcasea gravity corer with a 11 cm barrel. On board
both ships, whole-core magnetic susceptibility (WCMS)
was obtained at 3 cm intervals using a Bartington MS
meter and an appropriate loop. Units are dimensionless
SI units (]10~5) (Thompson and Old"eld, 1986). Sediments from the core catchers were collected and washed
through a '63 lm screen, and then inspected via a binocular microscope. Whole marine bivalves were selected
for radiocarbon dating, if available, as they are frequently
considered to be more reliable than dates on foraminifera, but otherwise we attempted to obtain 4 mg or more
of benthic and/or planktonic foraminifera (Table 1). Nine
samples were dated at the University of Arizona's NSF
AMS Facility (Slota et al., 1987; Donahue et al., 1990)
and are identi"ed by the AA-pre"x (Table 1). Seven
samples were submitted via the Science Institute, University of Iceland, and processed into targets and dated at
the AMS Laboratory, As rhus University, Denmark
(AAR-). The remaining samples (15) were processed at
the INSTAAR Target Preparation Laboratory, and age
determinations were made at the Lawrence Livermore
Accelerator Facility (CAMS-). The samples are reported
after correction for d13C and listed as reported from the
laboratories (Table 1). All dates refer to 14C yBP (i.e.
before 1950 AD). The present day reservoir correction in
Icelandic waters has been listed as 365$20 years BP
(Ha> kansson, 1983). We have applied a 400 year ocean
reservoir correction; these corrected dates are listed in
brackets with a ka notation. We are aware that this
correction is not invariable with time (e.g. Bard et al.,
1994), and o! northern Iceland (Voelker et al., 1998) this
correction varied between 400 and 1600 yr. At this time
we have not corrected our dates to sidereal years (Stuiver
and Braziunas, 1993; Stuiver and Reimer, 1993), therefore
our calculations of SAR (cm/kyr) overestimate the rates
of sediment accumulation (Table 1).
624
J.T. Andrews et al. / Quaternary Science Reviews 19 (2000) 619}631
Fig. 4. Downcore logs of magnetic susceptibility from selected cores and their uncorrected basal radiocarbon dates (Table 1). The stippled line shows
the 1000]10~5 SI unit value.
J.T. Andrews et al. / Quaternary Science Reviews 19 (2000) 619}631
625
4. Results
In Table 1 we report only basal dates. For several cores
we have multiple dates that have been obtained for
various research projects (School"eld, 1998; KristjaH nsdoH ttir et al., 1998). These will be published in the next
INSTAAR Date List (Smith and Licht, 1999; e.g. Manley
and Jennings, 1996). We discuss the dates in terms of
seven areas (Fig. 2) and illustrate some aspects of individual core sites based on 3.5 kHz records (Fig. 3) (cf.
HelgadoH ttir, 1997) and WCMS logs (Fig. 4) (Andrews
and Stravers, 1993; Andrews et al., 1995). Glacial marine
sediments that date from the period of deglaciation have
WCMS values '1000]10~5 SI, whereas during the
Holocene values are (500]10~5 SI (Fig. 4). If we
compare the basal dates with the basal WCMS there is
a strong overall positive trend (Fig. 5). When the data are
plotted for the seven areas (Fig. 5) this association is
maintained for all areas with dates that extend into
Marine Isotope Stage 2 or beyond.
4.1. Northern troughs area-EyjafjardaraH ll, HuH nayoH adjuH p,
and ReykjafjardaraH ll
Fig. 5. Graph of the relationship between basal core age and the
median whole core magnetic susceptibility values in the lowermost
15 cm of the core for the entire set of data (Table 1, Figs. 2B and 4). The
data are plotted for the six areas (Area 5 has only one date). The dashed
line lies at 10.4 uncorrected radiocarbon years BP. Notice that the
tendency for older sediments to have higher WCMS values pertains to
three of the six areas.
The extent of ice o! northern Iceland during the last
glacial maximum (LGM) has not been determined, although Hoppe (1968,1982) observed glacial striations on
the island GrmH msey (Fig. 2A) ca. 40 km from the current
coastline of Iceland and related them to the LGM. Based
on the presence of the Vedde ash in proglacial lake
sediments above EyjafjoK rdur (Norddahl and Ha#idason,
1992; Ashwell, 1996) the extent of ice during the Younger
Dryas Chronozone is mapped as "lling the fjords and
extending to the coast (Norddahl, 1991; IngoH lfsson and
Norddahl, 1994; IngoH lfsson et al., 1997). However, lake
sediment records from Skagi Peninsula to the west of
EyjafjoK rdur indicate that the peninsula was deglaciated
prior to 11 ka (Rundgren, 1995). O!shore geological research has been mainly restricted to seismic surveys of
various kinds (e.g. McMaster, et al., 1997; Thors, 1982;
Thors and Boulton, 1991) with some focus on structure
and evidence for faulting. Ha#idason (1983) determined
sediment accumulation rates (SAR) in EyjafjoK rdur based
on the recognition of tephra horizons associated with
eruptions of the volcano Hekla in southern Iceland (H-1,
H-3 and H-4) which gave long-term SAR estimates of
around 200 cm/kyr (Ha#idason, 1983p. 137).
We obtained cores from twelve sites in the northern
troughs and to the west of 183W (Fig. 2), namely B9-97316 to !327 (HelgadoH ttir, 1997). The easternmost sites
are close to cores collected in 1995 by EirmH ksson et al.
(1998). The 3.5 kHz survey indicated one or more regional subbottom re#ectors (Fig. 3), which could be
traced for 10's}100's km. A cross-pro"le of EyjafjardaraH ll
implies that some of the re#ectors are faulted; Thors
(1982) also noted evidence for Quaternary faulting in an
area immediately to the east of this area. Sediment
thickness, assuming a velocity of 1500 m/s, varied, but
within the main troughs thicknesses of*30 m are estimated (Table 1).
Basal dates have been obtained from ten cores
(Table 1; Fig. 2A and B). The AMS 14C dates from these
sites vary from ca. 4000 to 42,000 BP (Table 1). There is
a signi"cant di!erence in the basal ages between the
outermost core in EyjafjardaraH ll and the outermost cores
in ReykjafjardaraH ll. The date from the base of B9-97321PC is only 7540$40 (7.1 ka, 300 cm), whereas the
dates on -322PC2 and -323PC1 are 42,600$3050
(42.2 ka; 161 cm) and 25,330$640 (24.93 ka; 292 cm)
(Fig. 2). The di!erences in ages are in keeping with the
di!erences in basal lithofacies, as indicated by the
WCMS (Figs. 4 and 5). The basal dates from B9-97323PC1 and -322PC2 of ca. 25 and 42 ka suggest that we
have retrieved at least two records that span the LGM.
One basal date (6440; 6.04 ka) from the core catcher of
B9-97-319PC2 appears to be in error (Table 1). This date
occurs in sediment with WCMS glacial marine values of
'1000]10~5 SI.
Average sediment accumulation rates (SAR, cm/kyr),
based on the premise (tested for some cores, i.e. B9-97317PC1, -319GGC, -319PC2, -321PC), that the surface
sediments are close to modern ()500 BP) vary widely
from 4 to 84 cm/kyr. These are minimum rates as no
allowance is made for the fact that we know that the
some core tops (e.g. JM96-1221GGC) are `olda, i.e. of the
order of 8ka. Within the main troughs, the SAR during
626
J.T. Andrews et al. / Quaternary Science Reviews 19 (2000) 619}631
the latest Pleistocene or Holocene is around 30 cm/kyr
indicating a relatively constant SAR across the deep
basins of the northern shelf.
4.2. HuH nayoH i area and inner shelf and fjords
The second area (Fig. 2; Table 1) includes ReykjarfjoK rdur, IngoH lfsfjoK rdur, and adjacent inner shelf basins. There
is no published work that we are aware of on the marine
geology of this area, and the extent and deglacial history
of the last glaciation across the easternmost NW peninsula of Iceland is undetermined (IngoH lfsson, 1991; IngoH lfsson and Norddahl, 1994). The 3.5 kHz pro"les show
that at sites B9-97-329, -330, and -332 there is a major
seismic re#ector below the sea #oor (bsf) at a depth of
10}20 m bsf within the basins, but rises to within a few
meters of the surface on bathymetric highs (Fig. 3B}D).
This re#ector may be caused by changes in sediment
properties associated with deposition of volcaniclastic
sediments. The likely candidates are tephra layers associated with the numerous complex Icelandic volcanic
eruptions coinciding with the deglaciation of Iceland.
These tephras are correlated with Ash Zone I of the
North Atlantic (Ruddiman and Glover, 1972; Sejrup
et al., 1989; BjoK rck et al., 1992; Norddahl and Ha#idason,
1992), dated between 9 and 11 ka (Birks et al., 1996). Our
coring strategy at B9-97-329, !330, and !332 was to
select a site where this re#ector might be penetrated by
the piston corer ((6 m sediment thickness) (Fig. 3}D).
Acoustically penetrable sediment at sites !330 and
!332 is 6 and 11 m, respectively, although ca. 18 m of
acoustically laminated and transparent sediments "ll the
central basins.
We dated the base of three cores. The oldest date
comes from IngoH lfsfjoK rdur (B9-97-332PC) where we obtained a basal age of 10,330$60 (9.93 ka). Our longest
core (540 cm) is from ByrgisvmH kurpollur (Table 1) with
a basal date of 9400$60 (9.0 ka) (B9-97-330PC) and
thus with SAR of 60 cm/kyr. As might be expected, near
the head of ReykjarfjoK rdur (B9-97-328PC), the SAR is
higher at 99 cm/kyr.
There are pronounced changes in the WCMS logs
from this area (Fig. 4). The upper 3 m in cores B9-97330PC and -332PC show relatively low SI values
((300]10~5 SI). The much higher basal MS values in
-332PC, compared to -330PC, support the approximately 1 ka di!erence in basal age (Table 1; Fig. 4). Core
B997-330PC should have penetrated the prominent re#ector (Fig. 3C), however, the ship may have drifted away
from the precise site by 100 m or more.
4.3. DjuH paH ll area (NW Iceland)
DjuH paH ll is a long shallow trough ()300 m wd) that
trends NW from IsafjardardjuH p to the Iceland slope
north of Denmark Strait (Fig. 2). We dated cores JM96-
1229, -1232, and -1234, and B9-97-335PC and -336PC.
The Marine Research Institute of Iceland collected cores
from the inner part of DjuH paH ll in 1992, some of which
have been dated (A9-92-456; Table 1) (Smith et al., 1996;
Manley and Jennings, 1996).
Although Thors (1974) studied the sur"cial marine
geology of this area, the history of glaciation of the NW
Peninsula of Iceland is poorly known (Hjort et al., 1985;
IngoH lfsson, 1991). It is thought that an independent
ice cap may have covered this area, although the
locations of the ice margins are unmapped. Seismic
surveys have identi"ed possible terminal moraines in
a variety of locations along the trough (Fig. 2; HelgadoH ttir and Thors, 1998 and unpublished data). A large ridge,
which is crossed approaching IsafjardardjuH p, may
mark the LGM, or it might be a late-glacial recessional
moraine. The 3.5 kHz records from DjuH paH ll suggest
that part of the #oor of the trough is mantled by a `driftlikea deposit with marked re#ectors that pinch out toward the margin of the trough (Fig. 3D). At least 35 m of
sediment mantles the #oor of the trough along its central
axis.
In DjuH paH ll, the basal date of 13,680$70 (13.28 ka) for
-336PC3, and the WCMS log for -336PC3 and -335PC
(Fig. 4), suggest that the transition from high to more
modest WCMS values occurs close to the base of 335PC, or at 10,350$80 (9.95 ka). Farther landward,
core JM96-1234GGC (Table 1; Fig. 2) had an initial date
from the core catcher of ca. 11 ka, but dating of
foraminifera above this level resulted in a much older
sequence of 14C dates; at 265 cm we obtained a date of
15,720$70 (15.32 ka) (Fig. 4). Our basal dates from
DjuH paH ll range between 9000 and 16,000 ka implying an
average SAR of close to 30 cm/kyr (Table 1). O! DjuH paH ll
the upper slope is devoid of sediment but sediment has
accumulated below ca. 700 m wd. JM96-1229GGC has
a basal date of 31,310$380 (30.91 ka) (SAR"
8.6 cm/kyr) (School"eld, 1998).
4.4. ID safjardardjuH p area
The extent of ice cover during the LGM across NW
Iceland is unknown but, as noted earlier, the ice may
have extended onto innermost DjuH paH ll. Our data from
Area 3 above does, however, indicate that glacial ice had
retreated from the outer and mid-trough by '15 ka.
HelgadoH ttir and Thors (1998) have undertaken extensive
seismic surveys in parts of this large fjord complex (Area
4) and obtained basal radiocarbon dates from several
gravity cores ((3 m length).
We collected six cores and have dated four (Table 1).
We cored three sites in JoK kul"rdir (B9-97-311PC,
-341PC, and 342PC) close to the major river discharge
from DrangajoK kull; an ice cap which occupies the uplands of the NW Peninsula. Site -311PC is close to
a location where a prominent re#ector approaches the
J.T. Andrews et al. / Quaternary Science Reviews 19 (2000) 619}631
surface. Site B9-97-339PC2 is located farther in the fjord
system where SkoK tufjoK rdur enters the main trunk fjord.
The 3.5 kHz system shows sediment re#ectors with variable sediment thickness over `apparent basementa but
with thicknesses in excess of 20 m at some sites. Based on
the WCMS data (Fig. 4) a turbidite was deposited at ca.
1 m depth in core-339PC2.
The basal dates of between 9 and 10 ka (Table 1)
from -311PC,-342PC, and 339PC2 indicate that the
SAR is between 36 and 53 cm/kyr. However, at site
-341PC3 within JoK kul"rdir, the low and relatively
monotonous WCMS log (Fig. 4) is in keeping with
a `non-glaciala Holocene date for the base. The
basal date of 2880$55 (2.48 ka) indicates a rapid rate
of sediment accumulation in parts of JoK kul"rdir
(70 cm/kyr), a rate much higher than at the nearby sites
(Table 1).
4.5. KolluaH ll
KolluaH ll is a 300 m deep trough which parallels the
Snvfellsnes Peninsula and extends toward the western
shelf of Iceland (Syvitski et al, 1999). Because of heavy
seas we were unable to deploy the piston corer in 1997,
and obtained only four, relatively short, gravity cores
(HelgadoH ttir, 1997).
The seismic stratigraphy of this trough has been discussed in part by Syvitski et al. (1999) based on data
collected in 1993 on CSS Hudson. Our 3.5 kHz data
reveal at least 15 m of sediment. The single date we have
obtained of 3985$50 (3.59 ka) indicates a SAR of
around 38 cm/kyr (Table 1).
4.6. West Iceland shelf and slope
This area (Fig. 2) includes a large morainal ridge, "rst
described by OD lafsdoH ttir (1975), and surveyed in more
detail by Syvitski et al. (1999). Eglo! and Johnson (1979)
described the sediments below the shelf break on the
basis of seismic surveys. Large drifts were identi"ed and
called the `Snorri Drifta (McCave and Tuscholke, 1986).
We collected seismic data across the W Iceland slope in
1988, 1993, and 1996 (e.g. Syvitski et al., 1999). In 1996 we
obtained a series of gravity cores from the upper slope,
and one from the shelf (Fig. 2) and obtained four dates
(Table 1). These cores sampled between 50 and 200 cm of
the uppermost sur"cial sediments. The sediments from
these cores show large oscillations in the WCMS (Fig. 4)
with peaks '1000]10!5 SI.
Radiocarbon dates indicate that the basal sediments of
JM96-1220GGC and -1221GGC date from the LGM at
ca. 18 ka. This implies an average SAR of 10 cm/kyr. The
date of 36,050$560 (35.65 ka) at the base (55 cm) of
JM96-1227GGC was taken from a site close to the distal
side of the morainal ridge (Syvitski et al., 1999; OD lafsdoH ttir, 1975). The date was obtained on specimens of
627
Cibicides lobatulus (Table 1), and there was nothing in the
foraminifera assemblage to suggest reworking nor an ice
proximal glacial marine environment. Nevertheless, caution should be exercised in the interpretation of this date
until others are obtained from this short core or from
adjacent sites. These dates from the upper slope in Area
6 (Fig. 2) do not necessarily con"rm nor deny the presence of ice at the moraine during the LGM. However,
compared to other slope sites, for example across Denmark Strait at HU93030-007 (Cooper, 1995; Andrews
et al., 1998), the SAR is relatively modest (14 versus 32
cm/kyr), which may imply that the W Iceland ice sheet
margin was not a major contributor of sediment to the
upper slope. Alternatively, this area was by-passed by
various downslope sediment transport processes during
the LGM (e.g. Syvitski et al., 1999). However, rates of
sediment accumulated on the #oor of Denmark Strait,
south of the sill, are only 10 cm/kyr (Kellogg, 1984; Bond
and Lotti, 1995).
4.7. JoK kuldjuH p
A broad trough runs from Faxa#oH i to the SW; the
feature has depths '200 m and is called JoK kuldjuH p
(Fig. 2). HelgadoH ttir (1984) studied the foraminifera assemblages in 1}2 m long gravity cores from the landward
portion of the trough and showed marked changes in
benthic faunal composition. Aspects of the sea#oor morphology and seismic stratigraphy have been outlined in
several publications (Thors, 1978; HelgadoH ttir, 1984;
Syvitski et al., 1999; Jennings et al., 1999a). Considerable
research has been undertaken on the terrestrial deglacial
history of SW Iceland; these studies indicate that the ice
retreated to the present coastline between 12 and 13 ka
(IngoH lfsson, 1988; EirmH ksson et al., 1991, 1997; GeirsdoH ttir
and EirmH ksson, 1994). Evidence for postglacial changes in
sea level, associated with the glacial isostatic recovery of
Iceland and global changes in the ocean volume, have
also been documented for this area of Iceland (Thors and
HelgadoH ttir, 1991).
A series of cores were obtained from that area in 1993
(HU93039-003, -004, 006; Asprey et al., 1994; Hagen,
1995; Jennings et al., 1999; Jennings et al., 1999). The
basal dates from HU93030-006 of 13,105$85
(12.705 ka) and 12,810$205 (12.41 ka) (Table 1; Manley
and Jennings, 1996) were obtained very close to a seismic
boundary marking the transition from glacial marine to
glacial sediments (Syvitski et al., 1999; Jennings et al.,
1999). These dates are nearly identical to 14C dates
obtained on shells from raised marine sediments in
W Iceland (IngoH lfsson, 1985,1988; EirmH ksson et al., 1997)
implying that ice retreat across the shelf must have been
extremely rapid during the B+lling/Aller+d interstadial.
The 3.5 kHz records from B9-97-350PC (Fig. 3H)
show about 15 m or more of acoustically massive sediment lying above a prominent re#ector. At B9-97-348PC
628
J.T. Andrews et al. / Quaternary Science Reviews 19 (2000) 619}631
there is an additional re#ector lying close to the sea#oor,
at approximately 4}5 m bsf (Fig. 3G). The date for this
re#ector must be*12,280$50 BP (11.88 ka) given the
basal date at 491 cm depth in core -348PC. Hence, the
temporal relationship to the distinct re#ector in
HU93030-006, which is associated with the Vedde ash
(Jennings et al., 1996; 1999), is ambiguous. Ash shards
bearing a$nities to the Vedde Ash (ca. 10,300 BP, Birks
et al., 1996) were also noted in the base of -347PC (Fig. 2).
Geochemical analyses of these ash shards and other
tephra layers are underway. Average SAR for these three
sites are close to 40 cm/kyr, whereas at HU93030-006 the
average rate is twice as high. The WCMS records indicate substantial variations in the magnetic susceptibility
signal along the 60 km transect (Fig. 4). The WCMS
values from all cores are (1000]10~5 SI and all show
a progressive upward decrease in susceptibility.
5. Discussion and conclusion
Our goal has been to present the preliminary chronological framework for seven selected areas (Fig. 2). Our
data provide important constraints, but no absolute answers, to long-standing questions about the extent of ice
during the LGM, dates of deglaciation of the shelf, and
the rates of sediment accumulation from fjords seaward
to the continental slope. Histograms of basal dates and
average sediment accumulation rates (Fig. 6) show a peak
in radiocarbon dates centered on 10 ka; about 30% of the
sites have a SAR of between 30 and 50 cm/kyr (Fig. 6).
This is about twice the SAR from the more heavily
glacierized polar margin of East Greenland between
653}683 N (Andrews et al., 1996). Thus, these relatively
high average SARs indicate that downcore studies of
Icelandic marine sediments will result in high-resolution
(decadal) time series.
We have obtained radiocarbon dates '15 ka from
seven sites (Fig. 2B, Table 1), and these serve to identify
locations where longer cores will extract evidence of
variations in glaciation and oceanography back to Marine Isotope Stage 3 and beyond. Our inspection of the
3.5 kHz records indicates that in most instances there is
considerable sediment thickness beyond the range of the
coring equipment used on the 1996 and 1997 cruises
(Table 1; Fig. 6). Our results, and the work of Syvitski
et al. (1999), suggest that in places `olda (pre-LGM)
sediments exist on the W and N Iceland outer shelf. We
cannot exclude the possibility that the western shelf moraine (Fig. 2A and B) (OD lafsdoH ttir, 1975) dates from preLGM time, because the date on JM96-1227GGC, and
the low SAR from the adjacent slope sites, may indicate
that a major sediment source (an ice cap) was not located
at the shelf break during the LGM. In N Iceland we
suggest that the ice limit probably lies landward of cores
B9-97-322PC and -323PC as both have basal
dates*25 ka. O! N. Iceland the high WCMS values
(Figs. 4 and 5) for sites with basal dates of ca. 12 ka
indicates that glacially derived sediment was still reaching the inner to mid-shelf during the B+lling/Aller+d
interstadial, however, in JoK kuldjuH p (Fig. 2A and 4)
at about the same time WCMS values were (1000]
10~5 SI units suggesting more open marine conditions
(cf. Jennings et al., 1999). The location of the ice
margin o! the NW Peninsula of Iceland is not well
de"ned, but our dates from JM96-1234GGC indicates
that the mid- to outer part of DjuH paH ll was ice free by at
least &15 ka
Our estimates of sediment thicknesses at core sites
(Table 1) is biased toward lower values because we frequently chose sites so as to maximize the time covered by
a core (see Fig. 3). In addition, the 3.5 kHz systems are
not designed for surveys of thick basin "lls, and the
`apparent basementa in our records may not always
necessarily represent bedrock. Nevertheless, our estimates (Fig. 6) indicate that sediment thickness varied
between 5 and *35 m. Thors (1982) surveyed an area
between 17 and 183 W o! N Iceland with a Sparker
seismic system and showed (Thors, 1982, pp. 108}109)
that the troughs contain 50}100 m of Quaternary sediments. Thus our results indicate the potential for recovering several additional 1000'yrs of paleoenvironmental
records with longer coring systems. Fig. 6D shows
a naive estimate of the basal age of sediment "lls based on
our estimates of SAR and sediment thickness. This calculation suggests that many sites will contain sediments that
span the last 20}40 ka. The potential of these Icelandic
sites will be tested in 1999 during the IMAGES V cruise to
the northern North Atlantic (Labeyrie et al., 1997).
Acknowledgements
We wish to thank the captain, crew, and scienti"c sta!s
of the Hudson, Jan Mayen, and Bjarni S~mundsson for
their considerable assistance. The R/V Jan Mayen cruise
was largely "nanced by a grant from the Norwegian
Science Foundation to Dr. Morten Hald, University of
Troms+. Support for the 1997 Bjarni S~mundsson cruise
was principally from the Marine Research Institute of
Iceland. The University of Colorado's participation in
the 1996 Jan Mayen cruise was supported by grants from
the National Science Foundation OPP-9707161 and
ATM-9224554, and in the 1997 B9-97 cruise by ATM9531397. KristjaH nsdoH ttir's and HardardoH ttir's participation in the B9-97 cruise was supported by a grant from
the Icelandic Research Council to Dr. AD slaug GeirsdoH ttir. Dates designated by CAMS- were provided with
major support from the PALE Steering Committee,
whereas dates from As rhus University, Denmark, were
provided through an agreement with the Iceland Science
Institute and Dr. Arny Sveinbjornsdottir. Dates from the
J.T. Andrews et al. / Quaternary Science Reviews 19 (2000) 619}631
629
Fig. 6. Histograms of data: (A) Basal radiocarbon dates; (B) Core length; (C) Sediment accumulation rates (SAR); and (D) Estimated ages of basal
sediment "lls.
University of Arizona AMS Facility were subsidized by
funds from NSF. We are indebted to Nancy Weiner for
picking most of the foraminifera samples that are listed in
Table 1. Furthermore, we thank Dr. Charles Hart for
fauna identi"cation and Dr. Karl GroK nvold for tephra
analysis. We thanks Drs. O. Ingolfsson and S. Bjorck for
their constructive comments and assistance in preparing
the "nal draft. PALE contribution No. 134.
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