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Holocene paleoclimate change in the Antarctic Peninsula: evidencefrom the diatom, sedimentary and geochemical record
F. Taylora,*, J. Whiteheadb, E. Domacka
aDepartment of Geology, Hamilton College, Clinton, NY 13323, USAbAntarctic Co-operative Research Centre/Institute of Antarctic and Southern Ocean Studies, GPO Box 252-80, Hobart 7001,
Tasmania, Australia
Received 7 December 1999; revised 2 July 2000; accepted 10 July 2000
Abstract
Holocene, marine deposition in Lallemand Fjord, Antarctic Peninsula, is reinterpreted using statistical analyses (cluster
analysis, analysis of variance, nonmetric multidimensional scaling and multiple regression) to compare diatom assemblages
and the primary sedimentological proxies. The assemblages have been deposited in a variable sea ice zone over the last ca.
10,500 yr BP in response to a climate change. In the Late Pleistocene/early Holocene (10,580±7890 yr BP), a sea ice diatom
assemblage was deposited in the presence of a retreating ice shelf at the head of the fjord. In the mid Holocene (7890±3850 yr
BP), an open water assemblage was deposited and sea ice cover was at a minimum. We associate the assemblage with climatic
warming, which characterizes much of the Antarctic Peninsula during this time. A second sea ice assemblage, different from
that deposited in the early Holocene, has been deposited in Lallemand Fjord since the late Holocene (,3850 yr BP). The
assemblage re¯ects Neoglacial cooling, an increase in sea ice extent and/or an advance of the MuÈller Ice Shelf. q 2001 Elsevier
Science B.V. All rights reserved.
Keywords: Holocene; Antarctica; paleoclimate; diatoms; sedimentology; statistical analysis
1. Introduction
Sedimentary diatom assemblages have been used
successfully in numerous studies as a proxy for
Antarctic marine paleo-reconstructions (e.g. Truesdale
and Kellogg, 1979; Pichon et al., 1987; Leventer et al.,
1996; Cunningham et al., 1999). Many of these
studies include statistical techniques to reconstruct
Quaternary glacial history, but few incorporate a
subjective, multi-disciplinary approach. In the present
study, we incorporate diatom, sedimentological and
geochemical data with classi®cation and indirect
ordination analyses to interpret the Holocene paleo-
environment of Lallemand Fjord on the western
Antarctic Peninsula.
Climate records from both Hemispheres demonstrate
increasingly that the Holocene (,11,500 yr BP, after
Roberts, 1998) has been a period of rapid and variable
climate change (Domack and Mayewski, 1999;
Rosqvist et al., 1999). Marine sediment cores from
the Antarctic Peninsula revealed multi-century and
millennial-scale variations in primary production
(Leventer et al., 1996; Shevenell et al., 1996;
Marine Micropaleontology 41 (2001) 25±43
0377-8398/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved.
PII: S0377-8398(00)00049-9
www.elsevier.nl/locate/marmicro
* Corresponding address. Antarctic Co-operative Research
Centre/Institute of Antarctic and Southern Ocean Studies, GPO
Box 252-80, Hobart 7001, Tasmania, Australia. Tel.: 161-3-
6226-7888; fax: 161-3-6226-2973.
E-mail addresses: ®ona_taylor72@hotmail.com (F. Taylor),
jm_whitehead@hotmail.com (J. Whitehead),
edomack@hamilton.edu (E. Domack).
Rosqvist et al., 1999; Domack et al., 2000), and
similar patterns have been observed in Prydz Bay,
East Antarctica (e.g. Taylor, 1999). Yet the circum-
Antarctic marine paleoenvironmental record, as a
whole, remains poorly understood with regard to
rapid climate change (Domack and Mayewski,
1999). Given that the Antarctic Peninsula has under-
gone one of the most dramatic and rapid periods of
climatic warming in recent history (Smith et al.,
1999), the identi®cation and interpretation of paleo-
climatic events in this region is integral in under-
standing its response to predicted global climate
change. To investigate this, we provide a new,
detailed analysis of down-core diatom assemblages
from Lallemand Fjord, and compare the assem-
blages statistically to sedimentary and geochemical
variables. This builds upon the work commenced by
Shevenell et al. (1996).
2. Physical setting
The Lallemand Fjord is located on the Antarctic
Peninsula's west coast (Fig. 1), between 66850 0±
67820 0S and 66830 0W. It is the largest embayment
on that side of the peninsula and it lies close to the
northern limit of the polar climatic regime (Domack
and McClennen, 1996). Mean annual temperatures
range from 25.08 to 26.08C (Reynolds, 1981). The
fjord is within the Antarctic sea ice zone (SIZ),
which consists mostly of ®rst-year ice that melts
each season. The SIZ is a complicated, mobile
mixture of open water and ice of different types and
thickness (Allison and Worby, 1994) in a constant
state of ¯ux and rapid change (Foster, 1984). The
structure of the sea ice margin varies with wind
strength and direction. It may be a compact zone
that has a distinct boundary with the open water;
there may be a transitional zone between close pack
and open water that is several hundreds of meters
wide, or an even broader, loose pack zone kilometers
wide (Foster, 1984). In Lallemand Fjord, sea ice inter-
annual variability differs greatly and land-fast ice
often persists until late summer (Shevenell et al.,
1996).
Ocean circulation patterns along the western side of
the Antarctic Peninsula are poorly known (Domack and
Ishman, 1993). In Lallemand Fjord, oceanographic
F. Taylor et al. / Marine Micropaleontology 41 (2001) 25±4326
PalmerDeep
LarsenIce
Shelf
b
GC1
66û30'
67û00'
67û10'
67û20'
c
67û45'
Antar
ctic
Peninsula
Müller IceShelf
LallemandFjord
a
Fig. 1. Location of Lallemand Fjord and MuÈller Ice Shelf in relation to the Antarctic continent.
conditions appear generally uniform and bottom
waters are dominated by Circumpolar Deep Water
(Ishman and Domack, 1994). Water column data
suggest that this warm (.18C) water mass intrudes
into the Lallemand Fjord to cause sub-ice shelf melt-
ing and in¯uence the distribution of suspended
organic matter (Brandon, 1998).
At the head of the fjord, two low-pro®le valley
glaciers feed the MuÈller Ice Shelf. At least three
other major tidewater glaciers also empty into the
fjord and, combined, provide a total drainage
surface area of ca. 1290 km2 (Domack and
McClennen, 1996). Several deep, steep-sided basins
are present within the Lallemand Fjord. The largest
and deepest (.1500 m) occurs in the outer reaches
of the fjord system (Domack and McClennen,
1996). Sediment characteristics are controlled by
proximity to the glaciers at the head of the fjord
(Frederick et al., 1991). Sand and magnetic suscept-
ibility (MS) decrease with distance from its head; total
organic carbon (TOC) content increases with distance
from terrigenous sources (Domack and McClennen,
1996).
3. Materials and methods
3.1. Core description
PD92-II-01 GC1 (GC1) is a 550 cm-long gravity
core recovered from near the head of the Lallemand
Fjord (67810.765 0S, 66847.822 0W, Fig. 1) in a water
depth of 630 m. It consists of olive gray (5Y 5/2) clay
at the top, grading into olive gray (5Y 4/2), sandy clay
at the base. Dark yellowish brown (10Y 4/4) staining
occurs from 0 to 9 cm. Moderate disturbance occurs
from 0 to 12, 50 to 91, 244 to 276 and 328 to 335 cm,
and slight disturbance over 107±110 and 276±
328 cm. At 535 cm, one olive gray (5Y 4/2), sandy
lamination is present. Clasts of irregular-shaped,
sandy mud occur at 541, 542 and 545 cm.
Subrounded, coarse, granitic pebbles are scattered
throughout the core, at 37±39, 354±355, 357±360,
390±391 and 441±442 cm. Angular, ®ne basaltic
pebbles occur at 132±132.5 and 461±461.5 cm. A
whole scaphopod (Class: Mollusca) is present at
467 cm. Shell orientation, lack of coarse in®ll sedi-
ment in the shell and presence of a burrowing ®lter
strongly suggest that it is in situ (Shevenell et al.,
1996). Other sedimentological characteristics are
summarized in Shevenell et al. (1996).
3.2. Radiocarbon dates
Radiocarbon dating was conducted at the Univer-
sity of Arizona's Accelerator Mass Spectrometer
laboratory. A modern marine reservoir age of
1460 ^ 60 yr (Lab. #AA29182) was obtained from a
living scaphopod recovered from a surface sediment
grab sample (LMG98-02 G8) at the head of the MuÈller
Ice Shelf. The in situ scaphopod removed from GC1 at
456±460 cm has been radiocarbon dated previously at
9360 ^ 70 yr (Shevenell et al., 1996).
3.3. Sample preparation for diatom analysis
The core was sub-sampled at 10 cm intervals, and
samples stood for 24 h in distilled water to which
10 ml of 30% H2O2 had been added. Two drops of
HCl (2 N) were then added to remove organic carbo-
nate, and samples allowed to stand for another 24 h.
They were then centrifuged three times at 2500 revo-
lutions21 for 5 min; samples were washed in distilled
water to remove chemical residue and salt crystals
between centrifuging. Washed samples were diluted
in 10 ml distilled water and ,1±3 drops of the diluted
solution pipetted onto a glass cover-slip and dried on a
hotplate at 508C. Permanent, qualitative slides were
mounted in Norland Optical Adhesive 61 (refractive
index 1.56) and cured under a UV light for at least
5 min.
Diatoms were identi®ed and counted at 1000 £magni®cation using a phase contrast Zeiss Standard
25 phase contrast light microscope. Each slide was
traversed horizontally until at least 400 valves were
counted. To avoid counting the same specimen
twice, only valves that were .50% intact were
counted. For elongate species that are rarely preserved
intact, such as Trichotoxon, Thalassiothrix and
Pseudonitzschia, only end pieces were counted and
divided by two. Valves that could not be identi®ed,
due to orientation or obscuring debris, were class-
i®ed as ªmiscellaneous centricsº or ªmiscellaneous
pennatesº. Due to the high abundance of Chaetoceros
resting spores (spores, hereafter) in all samples
(.50%, Fig. 2), slides were re-counted, excluding
Chaetoceros. This allowed the background abundance
F. Taylor et al. / Marine Micropaleontology 41 (2001) 25±43 27
of ecologically important species, which may have
been otherwise masked by Chaetoceros spores, to be
determined.
We have chosen to split Thalassiosira antarctica
var. antarctica resting spores into separate varieties
as two morphological types were observed (Plate 1).
Resting spore type 1 (T. antarctica T1) has a ®ner
areole structure than resting spore type 2 (T. antarc-
tica T2), and the valves were often smaller in
diameter. Thalassiosira antarctica T2 appears similar
to that described by Fryxell et al. (1981), with distinct
ªshoe-likeº projections around the valve margin.
Large occluded processes in the margin are some-
times visible also in T. antarctica T2. Neither of
these characteristics was obvious in T. antarctica
T1. Similar morphological variation between T.
antarctica spores has been observed in surface
sediment samples from the Ross Sea and Antarctic
Peninsula (Leventer, pers. comm.) and Palmer Deep
(Sjunneskog and Taylor, submitted). Detailed taxo-
nomic work beyond the scope of this study is required
to de®ne the two varieties.
In addition to diatoms, the Parmales species Penta-
lamina corona was counted. Parmales is a group of
Chrysophyte with siliceous cell wall plates. They have
been observed in abundance in surface waters surface
sediment of Prydz Bay, East Antarctica, (Marchant,
1993; Franklin and Marchant, 1995; Taylor et al.,
1997) and the Weddell Sea (Zielinski, 1997). All
suggest that Parmales are useful indicators of sea ice
environments.
3.4. Statistical analyses
Diatoms and Parmales were expressed as a percen-
tage of the total number of cells counted per sample
(excluding Chaetoceros spores). Rare species (rela-
tive abundance ,2%) were removed prior to analysis
as they are not present in suf®cient abundance to be
signi®cant statistically (Katoh, 1993). The remaining
data were logarithmically transformed �log10x 1 1� to
reduce the score and bias of other abundant species
that may have otherwise masked the effect of less-
abundant species (Field et al., 1982). Data transforma-
tion does not alter zero values.
Data were analyzed using Bray±Curtis cluster
analysis, the student Newman±Keuls multiple range
test (SNK), non-metric multidimensional scaling
(NMDS), and multiple regression, following the
method outlined in Taylor et al. (1997). Down-core
cluster analysis was conducted similar to the method
of Whitehead (1996). Eight core variables were
compared to the diatom data by multiple regression:
MS, d 13C, percent TOC, clay, ®ne-medium silt and
coarse silt, sand and mean grain size. Methods for data
collection of individual variables (except d 13C) are
described in Shevenell et al. (1996).
3.5. d 13C analysis
Sediment samples for analysis of total organic
carbon 13C/12C ratios were dried (608C), powdered
and 10±20 mg weighed into silver foil envelopes.
Weighed samples were acidi®ed in situ with 6%
sulfurous acid to remove calcium carbonate. Carbon
stable isotopic composition was determined using a
F. Taylor et al. / Marine Micropaleontology 41 (2001) 25±4328
50.0 60.0 70.0 80.0 90.0 100.00
50
100
150
200
250
300
350
400
450
500
0
1000
3000
5000
7000
8000
10000
9000
3000
4000
6000
% Chaetoceros Spores
Dep
th(cm
)
Ag
e(yr
BP
)
Fig. 2. Relative abundance (%) of Chaetoceros spores from GC1.
Carlo Erba NA1500 elemental analyzer/Con¯o II
device and a Finnigan Delta Plus mass spectrometer
at Stanford University. Carbon isotopic reproducibil-
ity, as determined by replicate analyses of NBS-21,
is 0.08½.
4. Results
4.1. Chronology
Using a marine-reservoir correction factor of
F. Taylor et al. / Marine Micropaleontology 41 (2001) 25±43 29
Plate 1. Key indicator taxa in GC1; 1 Ð Fragilariopsis curta; 2 Ð Fragilariopsis kerguelensis; 3 Ð Eucampia antarctica (a) intercalary
winter valve, (b) terminal winter valve; 4 Ð Thalassiosira gracilis var. expecta; 5 Ð T. gracilis var. gracilis; 6 Ð Thalassiosira antarctica T2;
7 Ð T. antarctica T1; 8 Ð Thalassiosira lentiginosa.
1460 ^ 60 yr, based on the living scaphopod, the
uncorrected radiocarbon age of 9360 ^ 70 from
the in situ shell at 456±461 cm was calibrated to
8844 calendar years (yr BP) after Stuiver and
Reimer (1993). Based on this, and assuming a
constant deposition rate, a sedimentation rate of
0.052 cm yr21 is calculated over the entire length of
the core.
4.2. Statistical analyses
Twenty-eight taxa with an abundance of .2%
(excluding Chaetoceros spores) were observed in
the 55 core samples (Table 1). One outlier sample
was identi®ed in the preliminary cluster analysis and
removed from further analysis. The sample (from
440 cm) was observed to have an unusually high
abundance of Thalassiosira gracilis var. gracilis and
Thalassiosira gracilis var. expecta. Three cluster
groups were identi®ed in the subsequent analysis
(Fig. 3), at 34.4% dissimilarity and with a cophenetic
correlation of 0.65 (0.00 indicating no match with the
original data; 1.00 indicating a perfect match). Signif-
icant differences in species abundance between cluster
groups were identi®ed by SNK (Table 1).
Cluster group 1 characterizes the upper 160 cm
(,3080 yr BP). Between 190 and 220 cm (3650±
4230 yr BP), this group alternates with cluster group
2. One sample from cluster group 1 occurs at 340 cm
(6540 yr BP). Thalassiosira antarctica T1 is dominant
(28.3%) in cluster group 1; T. antarctica T2 (19.9%)
and Fragilariopsis curta (15.7%) are subdominant.
Also common (2±10% abundance) are Fragilariopsis
cylindrus, Navicula spp., T. gracilis var. gracilis, and
the Chrysophyte Pentalamina corona. Five taxa are
identi®ed by the SNK test as indicators of the assem-
blage: F. rhombica, Pseudonitzschia turgiduloides,
Rhizosolenia spp., ªmiscellaneous centricsº and P.
corona.
Cluster group 2 characterizes the mid-section of
the core. Between 170 and 210 cm (4420±7880 yr
BP), the cluster group alternates with group 1.
Between 230 and 410 cm (4420±7880 yr BP),
cluster group 2 forms a continuous unit (with an
exception at 340 cm). Cluster group 2 is also
present at 460 cm (8850 yr BP). Thalassiosira
antarctica T2 (35.0%) dominates the assemblage;
T. antarctica T1 (19.7%) and Eucampia antarctica
(17.5%) are subdominant. Common species are
Fragilariopsis curta, Fragilariopsis kerguelensis
and Fragilariopsis cylindrus. Unique abundance
indicator taxa are Achnanthes spp., F. kerguelensis,
Stellarima microtrias and Thalassiosira lentiginosa.
Cluster group 2 can be distinguished further from
cluster group 1 by a signi®cantly greater abundance
of T. antarctica T2 and a signi®cantly smaller
abundance of T. antarctica T1.
Cluster group 3 occurs below 420 cm (.8080 yr
F. Taylor et al. / Marine Micropaleontology 41 (2001) 25±4330
Table 1
Mean arithmetic abundance (%), analysis of variance (F) and SNK
multiple range tests of dominant (.2%) species in cluster groups.
Analyses were carried out on log10�x 1 1� transformed abundance.
Degrees of freedom� 2.54. ANOVA P values: n.s. not signi®cant,
* , 0.05, ** , 0.005, *** , 0.0005. Bold: species with signi®cant
differences in mean abundance. Underlined: species with signi®-
cantly higher abundance in a cluster group
Species Mean abundance
(%) per cluster
group
F P
1 2 3
Achnanthes spp. 0.9 1.3 0.6 4.33 *
Actinocyclus actinochilus 0.3 0.4 0.8 5.37 *
Cocceneis spp. 0.3 0.9 0.7 8.34 **
Eucampia antarctica 1.1 17.5 20.6 43.63 ***
Fragilaria spp. 0.2 0.0 0.4 3.74 **
Fragilariopsis curta 15.7 10.1 25.5 9.91 ***
Fragilariopsis cylindrus 10.4 2.2 9.8 71.86 ***
Fragilariopsis kerguelensis 1.8 3.8 2.3 13.43 ***
Fragilariopsis obliquecostata 0.9 1.6 2.0 6.62 ***
Fragilariopsis rhombica 1.3 0.6 1.0 6.81 **
Fragilariopsis sublinearis 0.2 0.1 0.0 2.85 n.s.
Fragilariopsis vanheurckii 0.9 0.7 3.7 20.35 ***
Navicula spp. 2.5 0.4 1.6 42.74 ***
Odontella spp. 0.3 0.9 2.9 21.11 ***
Pentalamina corona 2.3 0.3 1.8 27.73 ***
Pseudonitzschia turgiduloides 1.2 0.1 0.2 29.02 ***
Rhizosolenia spp. 1.6 0.7 0.9 10.09 ***
Stellarima microtrias 0.2 0.7 0.3 6.09 **
Synedra spp. 1.6 0.7 0.5 11.58 ***
Thalassiosira antarctica T1 28.3 19.7 1.5 62.62 ***
T. antarctica T2 19.9 35.0 13.7 21.92 ***
Thalassiosira gracilis var.
gracilis
2.2 1.5 2.0 1.33 n.s.
T. gracilis var. expecta 1.1 0.6 2.6 13.09 ***
Thalassiosira lentiginosa 0.2 0.9 0.4 13.38 ***
Thalassiosira tumida 0.1 0.1 0.7 3.12 n.s.
Thalassiosira sp. A 0.0 0.8 0.6 5.62 *
Miscellaneous pennates 0.6 0.5 0.9 3.34 *
Miscellaneous centrics 0.7 0.2 0.0 11.01 ***
BP). The diatom assemblage is dominated by Fragi-
lariopsis curta (25.5%) and Eucampia antarctica
(20.6%). Thalassiosira antarctica T2 is subdominant
(13.7%), but signi®cantly less compared to that in
cluster groups 1 and 2. Common taxa are F. cylindrus,
F. kerguelensis, F. vanheurckii, Fragilariopsis obli-
quecostata, Odontella spp., T. gracilis var. gracilis
and T. gracilis var. expecta. Three unique indicator
F. Taylor et al. / Marine Micropaleontology 41 (2001) 25±43 31
0cm20cm40cm
80cm140cm120cm30cm10cm
90cm150cm160cm100cm180cm220cm70cm60cm50cm
190cm130cm110cm
310cm300cm260cm250cm270cm240cm230cm210cm200cm170cm340cm
410cm390cm290cm330cm320cm280cm360cm380cm350cm370cm
430cm540cm470cm490cm500cm510cm480cm520cm530cm450cm
460cm400cm
420cm
Gro
up1
Gro
up2
Gro
up3
% Dissimilarity
20.010.0 30.0 40.00.0
Fig. 3. Dendrogram illustrating sample af®nities, based on diatom abundance. Cluster group 1� dense sea ice assemblage; cluster group 2�seasonally open water assemblage; cluster group 3� loose sea ice assemblage.
00.
10.
20.
30.
4
Axis
Str
ess
1 432
Fig. 4. Nonmetric multidimensional scaling (NMDS) ordination axis versus stress. Two axes were selected as best ®tting the data, based on the
point of maximum change in direction of the curve (from Kruskal and Wish, 1978).
taxa are present: Actinocyclus actinochilus, Fragi-
laria spp. and F. vanheurckii.
Two NMDS ordination axes were chosen as best
summarizing the data (Fig. 4). Stress values
converged after 10 iterations at a value of 0.1202,
indicating a good ®t with the original data (Hosie,
1994). The NMDS results are illustrated in Fig. 5.
There is good agreement between NMDS and cluster
analysis, visible when the cluster groups are circled on
the NMDS plot (Fig. 5). Using the ordination scores,
multiple regression analysis compared the diatom data
with the eight core variables. Three variables are
signi®cantly correlated with the data (Table 2), and
the direction of maximum correlation for each (Table
3) is illustrated in Fig. 5. (In Fig. 5, arrow length
represents the signi®cance of the correlation between
the diatom data and core variable, i.e. the longer the
arrow the greater the correlation with that variable,
and arrow direction indicates the direction in which
the variable is most correlated to the data.) Percent
TOC accounts for 54.9% of the variance observed in
the data; MS for 38.6% of the variance, and percent
®ne-medium silt for 30.7% of the variance. d 13C is
slightly less signi®cant, accounting for 22.3% of the
variance. The signi®cant variables and cluster groups
2 and 3 are clearly separated. Arrow length and
direction (Fig. 5) indicate the direction of maximum
correlation between the core variables and cluster
groups. Cluster group 2 is closely associated with
high TOC values, a high abundance of ®ne-medium
F. Taylor et al. / Marine Micropaleontology 41 (2001) 25±4332
Fig. 5. Ordination plot of samples, based on diatom species abundance (%). Arrows indicate direction of maximum correlation for signi®cant
multiple regressions between ordination scores and core variables. Cluster groups identi®ed in Fig. 3 are superimposed. Cr silt� coarse silt;
FM silt� ®ne-medium silt.
Table 2
Multiple regression analysis between dependent variables (physical
properties) and NMDS scores for a two-dimensional ordination.
Degrees of freedom� 2.48. ANOVA P values as for Table 1. Radj2 �
adjusted coef®cient of determination, which gives the fraction of
variance accounted for by the explanatory variable (Jongman et al.,
1987)
Dependent
variable
Direction cosine Radj2 F P
x y
d13C 1.778 21.213 0.223 8.190 **
MS 31.048 390.505 0.386 17.331 ***
TOC 0.740 20.420 0.549 33.247 ***
Clay 5.480 7.633 0.059 2.655 *
FM Silt 21.230 214.868 0.307 12.719 ***
Coarse silt 1.603 5.389 0.058 2.644 *
Sand 25.853 1.846 0.003 1.072 n.s.
Mean Grain Size 28.017 0.749 0.006 1.153 n.s.
silt and high d 13C; group 3 is closely associated with
high MS (Fig. 5). There is little or no signi®cant
association between the cluster groups and percent
clay, coarse silt, sand or mean grain size (Table 2).
5. Discussion
5.1. Chaetoceros abundance
Chaetoceros spores are the dominant taxa in GC1,
forming .50% of frustules counted in all samples
(Fig. 2). Abundance is high, but variable, in the
upper 520 cm of the core, and ranges from 66.8 to
95.1%. High concentrations of Chaetoceros spores
in Antarctic sediment are considered to be indicative
of high primary production in the water column
(Donegan and Schrader, 1982; Leventer, 1992;
Leventer et al., 1996). During spring diatom blooms,
surface waters can become so nutrient-depleted that
diatom growth is limited (Nelson and Smith, 1986;
McMinn et al., 1995) and spore formation is induced
(Davis et al., 1980). They remain dormant at the
sediment±water interface until favorable conditions
induce germination. Chaetoceros spore abundance
decreases relative to other diatom taxa below
520 cm, reaching a minimum of 53.1%. The decrease
suggests reduced primary production. The abundance
of Chaetoceros spores may also have been diluted by
higher siliciclastic deposition, although this is less
likely as there is no increase in gravel abundance in
this section of the core (Shevenell et al., 1996).
5.2. Diatom assemblages
Excluding Chaetoceros spores, cluster analysis and
NMDS identify three cluster groups (representing
diatom assemblages). The assemblages are interpreted
to have been deposited within the complex SIZ, where
studies have indicated that the different sea ice types
contain different algal assemblages (e.g. Garrison et
al., 1986; Scott et al., 1994; Leventer and Dunbar,
1996). Based on the dominant and indicator taxa
with known ecological af®nities in the present study
(Fig. 6 and Plate 1), the diatom assemblages discussed
are interpreted to represent different sub-environ-
ments within the SIZ.
5.2.1. Cluster group 3 (sea ice associated)
Cluster group 3 dominates the lower third of GC1
(550±420 cm; Fig. 7). Fragilariopsis curta and
Eucampia antarctica are the most abundant species;
Thalassiosira antarctica T2 is subdominant (Table 1).
Based on the known ecology of the abundant and
indicator taxa in cluster group 3, the diatom assem-
blage is described as sea ice associated.
Fragilariopsis curta occurs commonly in ice edge
and within-ice algal assemblages (Scott et al., 1994;
Leventer and Dunbar, 1996) and in meltwater-
strati®ed surface water layers associated with retreat-
ing sea ice (Garrison et al., 1987). Leventer and
Dunbar (1996) hypothesized that the high abundance
of F. curta within the water column and surface
sediment of the Ross Sea is due to its being seeded
into the water column from fast ice during the spring
ice recession. In surface sediment diatom assemblages
from Prydz Bay and the Ross Sea, F. curta occurs
in high abundance where sea ice often persists
throughout summer (Taylor et al., 1997; Cunningham
and Leventer, 1998).
Eucampia antarctica is also widely considered to
F. Taylor et al. / Marine Micropaleontology 41 (2001) 25±43 33
Table 3
Cosine and acosine values (using NMDS axes 1 and 2 coef®cient values) used to determine direction of maximum correlation in Fig. 5
Variable Coeff1 Coeff2 Cos1 Cos2 Acos1 Acos2
d13C 1.778 21.213 0.826 20.564 34.303 124.303
MS 31.048 390.505 0.079 0.997 85.454 4.546
TOC 0.740 20.420 0.870 20.494 29.578 119.578
Clay 5.480 7.633 0.583 0.812 54.324 35.676
FM Silt 21.230 214.868 20.082 20.997 94.729 175.271
Coarse Silt 1.603 5.389 0.285 0.958 73.434 16.566
Sand 25.853 1.846 20.954 0.301 162.495 72.495
Mean Grain Size 28.017 0.749 20.996 0.093 174.663 84.663
F. Taylor et al. / Marine Micropaleontology 41 (2001) 25±4334
Fig. 6. Relative abundance (%) of key indicator taxa in GC1.
F.
Ta
ylor
eta
l./
Ma
rine
Micro
paleo
nto
logy
41
(2001)
25
±43
35
Fig. 7. Core log, core variables, sedimentary units (dashed horizontal line) and diatom assemblages from GC1. Diatom assemblages in relation to cluster groups are: dense sea ice
(cluster group 1); seasonally open water (cluster group 2); loose sea ice (cluster group 3). Sedimentary units from Shevenell et al. (1996). December solar insolation from Berger
(1978).
be a sea ice diatom (Burckle et al., 1990), although
Zielinski and Gersonde (1997) suggest that it should
not be de®ned as such. They have noted that E.
antarctica is most abundant where surface waters
are 22±08C and 2.5±5.58C, indicating that it is
related to surface waters in the Antarctic and the
Polar Front Zone of the Southern Ocean (Zielinski
and Gersonde, 1997). This discrepancy in distribution
may be attributable to the two varieties of Eucampia
that Fryxell and Prasad (1990) identify. One variety is
a truly Antarctic, ice edge organism (E. antarctica
var. recta), and the other is subpolar (E. antarctica
var. antarctica). Abundance of E. antarctica in
surface sediment assemblages has been interpreted
to indicate reworking and/or current winnowing
(Truesdale and Kellogg, 1979; Taylor et al., 1997;
Cunningham and Leventer, 1998). The high abun-
dance (up to 46%) of E. antarctica in cluster group
3 is not attributed to reworking mechanisms, however.
Reworked and current winnowed assemblages typi-
cally contain a high abundance of other heavily
silici®ed, robust, often extinct, taxa, and lack small
and fragile taxa that have been removed by dissolution
or strong water currents. In contrast, the assemblage in
GC1 contains fragile taxa, such as Fragilariopsis
cylindrus and the Chrysophyte Pentalamina corona,
in comparable, if not greater, abundance to the other
diatom assemblages observed in the core.
Less abundant, but statistically signi®cant, indica-
tor taxa in cluster group 3 are underlined in Table 1.
Planktic pennates, such as Fragilariopsis obliquecos-
tata and F. vanheurckii, are considered to be ice asso-
ciated (Garrison and Buck, 1985; Medlin and Priddle,
1990). F. obliquecostata has been observed in sub-ice
microalgal strands under coastal fast ice (Watanabe,
1988), but Cunningham et al. (1999) report it to be
open water associated. The planktic, centric Actino-
cyclus actinochilus is considered a typical Antarctic,
neritic species (Kozlova, 1966) that occurs in the ice
edge zone (Medlin and Priddle, 1990). It is one of the
characteristic species found in the ªSouth Weddellº
diatom assemblage described in surface sediment by
Pichon et al. (1987), which is associated with an area
where sea ice is absent for only ,2 months.
Odontella spp. are also important statistically in
cluster group 3 and reach a maximum abundance of
10.2%. There is little documentation of the ecology
of this spore-forming genus, although Odontella
weis¯oggii (Janisch) Grunow is considered endemic
to the Southern Ocean and occurs in Antarctic near-
shore regions where water temperatures are between
22 and 58C (Zielinski and Gersonde, 1997).
Froneman et al. (1997) report it to be a temperate,
neritic species that probably gets transported into
Antarctic waters by unusual, southern intrusions of
subantarctic surface waters. The ecology of Thalas-
siosira gracilis var. expecta and the benthic taxa
(Cocconeis, Fragilaria, Navicula) are also amongst
the less-well-documented taxa. Zielinski and
Gersonde (1997) observe that T. gracilis (no variety
speci®ed) reaches maximum abundance in Antarctic
surface sediment that occurs below relatively warm
waters with a temperature 20.5±28C, but should be
considered a taxon with no de®nitive relation to envir-
onmental parameters. Due to the generally low abun-
dance of the above taxa and ecological uncertainties,
these species have not been used to interpret the
assemblage's paleoecology.
5.2.2. Cluster group 2 (seasonal open water)
Cluster group 2 characterizes the mid-section of the
core (Fig. 7). The most abundant taxon is Thalassio-
sira antarctica T2 (54.4%). T. antarctica T1 and
Eucampia antarctica are subdominant. Fragilariopsis
curta is relatively common, but it is signi®cantly less
abundant compared to cluster groups 1 and 3. The
presence of species such as Fragilariopsis kergue-
lensis and Thalassiosira lentiginosa suggests that the
diatom assemblage was deposited in a seasonally
open water environment (discussed below). F.
kerguelensis attains a maximum abundance of 6.5%
in cluster group 2. Whilst this does not rank it amongst
the most common species in the group, the abundance
is signi®cantly higher compared to groups 1 and 3,
and it forms a unique indicator of the assemblage.
Fragilariopsis kerguelensis is a valuable paleo-
indicator, used to identify open marine deposition.
Today it is dominant between 52 and 638S (Burckle
et al., 1987), where summer surface water tempera-
tures are .08C (Krebs et al., 1987). Abundance is also
known to be negatively correlated with sea ice
(Burckle et al., 1987), and to increase with distance
from the Antarctic continent in both surface water
(Kozlova, 1966) and sedimentary assemblages
(Leventer, 1992; Harris et al., 1998). Similar observa-
tions have been made of Thalassiosira lentiginosa,
F. Taylor et al. / Marine Micropaleontology 41 (2001) 25±4336
suggesting that it is an equally valuable indicator of
open water (Zielinski and Gersonde, 1997). In cluster
group 2, T. lentiginosa is numerically rare (maximum
abundance 2.5%), but its abundance is signi®cantly
high and it forms a unique indicator in the assemblage.
The high abundance of Eucampia antarctica in
cluster group 2 also supports the hypothesis that this
species is not solely a sea ice indicator (Zielinski and
Gersonde, 1997). We have not distinguished between
the two varieties of Eucampia identi®ed by Fryxell
and Prasad (1990), and demonstrated to have different
geographical distributions and to inhabit different
environments (Fryxell and Prasad, 1990; Kaczmarska
et al., 1993), but suggest this in future analyses. E.
antarctica var. antarctica has a subpolar distribution,
whilst E. antarctica var. recta is restricted to cold,
polar waters associated with sea ice cover (Fryxell
and Prasad, 1990; Kaczmarska et al., 1993).
The genus Thalassiosira is widespread in Antarctic
waters, where it generally occurs in open water. It is
uncommon in sea ice (Fryxell and Kendrick, 1988;
Leventer and Dunbar, 1996; Zielinski and Gersonde,
1997), which Fryxell et al. (1987) attribute to its
inability to survive the low light intensity beneath,
and within, sea ice. The observation that Thalassiosira
antarctica is a member of some sea ice samples (e.g.
Villareal and Fryxell, 1983; Leventer and Dunbar,
1996), however, has led to the suggestion that it
may be associated with coastal sea ice and zones of
lose platelet ice (Cunningham and Leventer, 1998).
Indeed, some Thalassiosira species are sea ice related.
A bloom of Thalassiosira tumida, for example, is
reported in slush ice forming near the Ronne Ice
Shelf (El-Sayed, 1971), and Thalassiosira australis
Peragallo 1921 is observed amongst the dominant
species beneath snow-free fast ice in Ellis Fjord
(Vestfold Hills, East Antarctica), and McMurdo
Sound (McMinn, 1996; McMinn, 1999). Taylor
(1999) suggests that the formation of T. antarctica
spores could be triggered by the low light intensities
that occur beneath developing pack and platelet ice.
Reduced wind mixing below the sea ice may also
induce spore formation.
As in cluster group 3, the ecology of many of the
rarer, but statistically signi®cant diatoms is ambigu-
ous. Stellarima microtrias, for example, is reported as
being restricted to the Antarctic Zone south of the
Polar Front, in waters 22±18C (Zielinski and
Gersonde, 1997). Hasle et al. (1988) ®nd S. microtrias
benthic on or in sea ice and planktic in waters in¯u-
enced by sea ice Ð a paradox that they suggest may
be explained by its ability to produce spores. Along
with the benthic taxa (Achnanthes and Cocconeis), the
species whose ecology is poorly documented and
whose ecological af®nity is uncertain are not used
for paleoenvironmental interpretation.
5.2.3. Cluster group 1 (sea ice associated)
Cluster group 1 is present in the upper 200 cm
of GC1 (Fig. 7). Thalassiosira antarctica T1 is
signi®cantly more abundant (up to 47.6%)
compared to that in cluster groups 2 or 3. T.
antarctica T2 and Fragialriopsis curta are subdo-
minant members of the assemblage (with an aver-
age of 28.3 and 15.7%, respectively), but both are
signi®cantly less abundant compared to abundance
in cluster group 2. The diatom assemblage of
cluster group 1 is interpreted to represent deposi-
tion in a sea ice-associated environment, but is
statistically different from the sea ice diatom
assemblage of cluster group 3. Each probably
represents deposition within a different zone of
the seasonal sea ice zone, but we ®nd it dif®cult
to distinguish these differences based on diatoms
alone.
The subdominant and common taxa in cluster
group 1 are of mixed ecological preference. As
discussed previously, the genus Thalassiosira tends
to be associated with open water deposition, but rest-
ing spore formation may be induced by sea ice. Fragi-
lariopsis curta is a member of sea ice assemblages
where ice retreat has created a melt-water, strati®ed
surface water layer. Fragilariopsis cylindrus has been
observed amongst the dominant taxa in pack and fast
ice (Garrison and Buck, 1989; Scott et al., 1994) and
ice edge blooms (Kang and Fryxell, 1992), and has
been also found in open water (Garrison et al., 1987;
Leventer et al., 1993). The ecology of the Chrysophyte,
Pentalamina corona, is not well known, although
evidence suggests that Parmales inhabit ice edge and
pack ice environments. Silver et al. (1980) report
ªsiliceous cystsº (now known to be Parmales) in low
abundance in sea ice samples from the Weddell Sea, and
Brandon (1998) has found one species in water column
samples from in front of the MuÈller Ice Shelf. Three
of the ®ve indicator species in the cluster group
F. Taylor et al. / Marine Micropaleontology 41 (2001) 25±43 37
(Fragilariopsis rhombica, Pseudonitzschia turgidu-
loides and P. corona) are indicators of ice-associated
and ice-edge diatom assemblages in the surface sedi-
ments of Prydz Bay where multi-year ice frequently
persists (Taylor et al., 1997). Grouped genera such as
Navicula, Rhizosolenia and Synedra are statistically
signi®cant but numerically rare in the cluster group.
5.3. Multiple regression
The direction of maximum correlation for TOC,
®ne-medium silt and d 13C corresponds with cluster
group 2 (Fig. 5). High TOC and d 13C values in
sediment samples containing this diatom assemblage
indicate that it is associated with high primary produc-
tion. The abundance of ®ne-medium sized silt
particles (4±31 mm), which are within the size range
of most diatom frustules, could be used to indicate that
diatoms were the main primary producers. The direc-
tion of maximum correlation for MS corresponds with
cluster group 3 (Fig. 5). This suggests that terrigenous
input, relative to biogenic particle ¯ux, during deposi-
tion of the diatom assemblage was higher. Simulta-
neously, TOC and ®ne-medium silt deposition are
low.
5.4. Paleoecological interpretation
5.4.1. Late Pleistocene±Early Holocene (10,580±
7890 yr BP)
The ice-associated diatom assemblage from cluster
group 3 corresponds with the sedimentological unit III
of Shevenell et al. (1996) in GC1 (Fig. 7). The unit
contains laminated, gray, silty mud, overlain by struc-
tureless, gray, silty mud. It is characterized by an
upward increase in TOC, and a decrease in MS and
mean grain size (Fig. 7). The sedimentological struc-
ture is inferred to represent a transition from ice
proximal to open marine deposition as Late Pleisto-
cene±Early Holocene deglaciation occurred in the
fjord (Shevenell et al., 1996). This is supported by
the presence of the ice-associated diatom assemblage
of cluster group 3, which was deposited from at least
10,580 to 8080 yr BP (assuming a constant sedimen-
tation rate based on 0.052 cm yr21). The increasing
TOC and d 13C values suggest increasing primary
production, although TOC remains relatively low
compared to mid Holocene values (Fig. 7) and may
re¯ect dilution of this signal due to increased sili-
clastic sedimentation (as would occur in close
proximity to a receding glacier). Based on the diatom
taxa, their preferred ecological habitat, and sedimen-
tology, sea ice cover is thought to have been in the
form of loose sea ice that expanded and contracted
seasonally over water exposed by the retreating
MuÈller Ice Shelf.
Deposition of the loose sea ice assemblage was
interrupted brie¯y at 8850 and 8460 yr BP. During
both times, seasonally open water and unusual
Thalassiosira gracilis-dominated assemblages were
deposited (Figs. 6 and 7). The latter assemblage
formed an outlier in cluster analysis and was excluded
from further analysis. We suggest that both assem-
blages represent deposition in an environment asso-
ciated with windy, cool climatic episodes, which
interrupted the deglaciation phase, resulting in more
open water conditions in comparison to that during
deposition of the ice-associated assemblage. The
open water conditions may have been associated
with a polynya that may have formed due to high
winds pushing sea ice offshore. This follows the
hypothesis of Leventer and Dunbar (1988), who
suggest that a relative increase in abundance of
Thalassiosira spp., compared to Fragilariopsis
curta, approximately 350 yr BP in McMurdo Sound
is the result of more persistent and/or strong katabatic
and synoptic winds. Increased winds would reduce the
amount of near-shore sea ice cover and allow for
higher primary production.
A century-scale, globally distributed, cooling event
to support our hypothesis has been identi®ed in the
Taylor Dome (Antarctica) and GISP2 (Greenland) ice
core records between 8400 and 8200 yr BP (Alley et
al., 1997; Stager and Mayewski, 1997). It is inferred to
have been synchronous with global cooling of
approximately half the amplitude of the Younger
Dryas. A cooling event has also been identi®ed in
sediments from the nearby Palmer Deep (Fig. 1),
following the Last Glacial Maximum's deglacial
episode (Domack et al., 2000). On South Georgia, in
the sub-Antarctic Southern Ocean, a short-lived cold
event is recorded in age-calibrated lake sediments
between 7800 and 7400 yr BP (Rosqvist et al.,
1999). If these events are correlated with the age
calibrated data from GC1, increased wind associated
with cooling in Lallemand Fjord 8800 yr BP could
have reduced sea ice cover, allowing the deposition
F. Taylor et al. / Marine Micropaleontology 41 (2001) 25±4338
of the Thalassiosira antarctica T2-dominated assem-
blage. Increased primary production 8500 yr BP could
be inferred in GC1 where there is a peak in TOC
(discussed below) at 440 cm, correlating with the
Thalassiosira gracilis-dominated assemblage.
5.4.2. Mid Holocene (7890±3850 yr BP)
The cluster group 2 diatom assemblage, character-
ized by open water taxa, dominates the mid Holocene
in Lallemand Fjord between 7890 and 3850 yr BP
(Fig. 7). It corresponds with sedimentological unit II
that is characterized by silty mud. Scattered ice rafted
debris are present and decrease up-core. Total organic
content is generally high. It is suggested that climatic
warming, which caused deglaciation of the fjord in the
Early Holocene, created a more open marine, ice
distal, depositional environment with high biogenic
input and elevated primary production (Shevenell et
al., 1996). The observed maxima in d 13C over this
period (Fig. 7) further suggests high primary produc-
tion in which CO2 may have been limited in the photic
zone. Our results, combined with Shevenell et al.
(1996), support the hypotheses that the Antarctic
Peninsula experienced a climatic optimum during
the mid Holocene (e.g. Leventer et al., 1996; Hjort
et al., 1998; Rosqvist et al., 1999).
Lake sediment data from South Georgia (Birnie,
1990; Rosqvist et al., 1999) and James Ross Island
(BjoÈrck et al., 1996), and marine records from the
Ross Sea (Cunningham et al., 1999), suggest that
during the mid Holocene sea surface temperatures
were warmer and atmospheric temperatures were
warmer and/or more humid than present. Cunningham
et al. (1999) also show that, in contrast to our ®ndings,
mid Holocene diatom assemblages from the Ross Sea
contained a higher abundance of Fragilariopsis curta,
and fewer open water species, compared to modern
Ross Sea sediments. They suggest that sea ice melt
and water column strati®cation probably occurred
earlier than today in the Ross Sea, as a result of earlier
spring warmth. They speculate that earlier ice melt
allowed the spring bloom to be dominated by F.
curta seeded from the melting sea ice, rather than
for the bloom to be dominated by open water taxa.
Our data indicate that in the mid Holocene diatom
assemblage was characterized by signi®cantly fewer
F. curta than today, and more open water taxa. This
may indicate that less winter sea ice was present
during the mid Holocene and that during the spring
melt a signi®cant abundance of ice-associated diatoms
were not being released to seed the water column.
The variable TOC levels observed in Lallemand
Fjord during the mid Holocene probably re¯ect varia-
tions in primary productivity, which, in turn, re¯ects
variation in sea ice extent (Shevenell et al., 1996).
Low TOC values correspond with deposition of the
sea ice-associated assemblage 6730 yr BP. This event
occurs within the prolonged period of TOC minima,
between 7310 and 5390 yr BP, which was interpreted
by Shevenell et al. (1996) to indicate extensive sea ice
cover in the fjord. Low TOC and the sea ice assem-
blage may also be correlatable with a climatically cold
triple event (minima in solar irradiance; Stuiver and
Braziunus, 1989) documented in the GISP2 ice core
6200±5000 yr BP (O'Brien, 1995). The most variable
period of TOC accumulation in Lallemand Fjord
occurs between 4810 and 2880 yr BP, as indicated
by the ¯uctuating values (Fig. 7). During this time,
the diatom assemblages also undergo alternating
deposition of the seasonally open water assemblage
of cluster group 2, and the ice assemblage of cluster
group 1. The latter is deposited during periods of TOC
minima at the top of the core, supporting the hypoth-
esis that low TOC re¯ects increased ice cover.
5.4.3. Late Holocene (,3850 yr BP)
The cluster group 1 diatom assemblage has been
deposited from about 3850 yr BP. It was interrupted
brie¯y 3270 yr BP by redeposition of the seasonally
open water assemblage. From 2880 yr BP, cluster
group 1 corresponds with the core's sedimentary
unit I (Fig. 7). Cluster group 1 contains an ice-
associated diatom assemblage, and the onset of its
deposition is hypothesized to represent late Holocene
climatic cooling (the Neoglacial). Before discussing
this in detail, however, it is important to distinguish
how the ice-associated diatom assemblage of cluster
group 1 differs from the ice-associated assemblage of
cluster group 3. We ®nd it dif®cult to determine the
speci®c sea ice environments they each represent,
based on diatom abundance alone.
Cluster groups 1 and 3 both contain abundant
ice-associated diatoms, but the abundance of these
diatoms is signi®cantly different (Table 1). We
suggest that each cluster group represents a different
sub-environment within the SIZ, which is more
F. Taylor et al. / Marine Micropaleontology 41 (2001) 25±43 39
readily identi®ed by considering other data. Combin-
ing the diatom, sedimentary and geochemical data we
hypothesize that cluster group 1 (,3850 yr BP)
represents a period of more dense sea ice than that
associated with the loose sea ice-associated assem-
blage of cluster group 3 (deposited .7890 yr BP).
In sedimentary unit I, there is an overall decrease in
TOC, hypothesized to re¯ect decreased primary
production in response to the change in depositional
regime from an open marine environment with mini-
mal sea ice coverage to one with increased fast or
shelf ice (Shevenell et al., 1996). The tandem decrease
in d 13C also suggests that primary production
decreased in comparison to the mid Holocene.
Shevenell et al. (1996) also note an increase in the
siliciclastic (relative to biogenic) component of the
sediment, an increase in coarse silt and mean grain
size, and minimal ice-rafted debris and coarse-grained
terrigenous input, indicative of proximal ice shelf
deposition. These observations assist in differentiating
the depositional environments that the two signi®-
cantly different, but ice-associated, assemblages
were formed from. Based on these results, we also
suggest that the two varieties of Thalassiosira
antarctica resting spores have the potential to be
good paleo-indicators. Modern studies are required
to con®rm our hypothesis that T. antarctica T1 is
associated with dense sea ice, and T. antarctica T2
with less sea ice cover and more open water.
Domack and McClennen (1996) suggest that
climatic cooling in Lallemand Fjord, associated with
the Neoglacial, commenced sometime prior to
2000 yr BP. Based on the diatom record herein, it is
suggested that the transition from a seasonally open
water environment to one in¯uenced by more dense
sea ice commenced as early as 4420 yr BP. The
increased sea ice cover may have even been in the
form of compact pack ice, multi-year ice, or fast ice.
The latter dominates in the fjord today until late
summer. It is also possible that the ice shelf at the
head of Lallemand Fjord came into closer proximity.
The transition from a seasonally open water environ-
ment to an ice-associated environment is similar to the
®ndings of Sjunneskog and Taylor (submitted). They
mark the transition from the mid Holocene climatic
optimum to cooler Neoglacial conditions in the
Palmer Deep at 4420 yr BP, based on a decline in
total diatom abundance. Both results suggest that the
Neoglacial transition commenced approximately
1000 yr earlier than sedimentary data from the Palmer
Deep implies (Domack et al., 2000). Deposition of the
dense sea ice diatom assemblage of cluster group 1 in
Lallemand Fjord did not become well established
until 3080 yr BP. Prior to this, deposition oscillated
with the seasonally open water assemblage. This may
indicate that the environment ¯uctuated during the
transition from the mid Holocene climatic optimum
before stabilizing. Ciais et al. (1994) also suggest that
a stable average temperature has characterized the
Late Holocene with short-lived ¯uctuations from
4420 yr BP. From 3080 yr BP, the cluster group 1
assemblage has been deposited without major inter-
ruption.
Before concluding, we address the question: what is
the driving force behind Holocene variation in the
Antarctic Peninsula primary production? Variation
in solar insolation is regarded as one primary climatic
forcing mechanism (Nesje and Johannessen, 1992),
but we hypothesize it is not the mechanism in place
here. At polar latitudes (608S), summer insolation
reached a Holocene maximum ,2000 yr BP (Berger,
1978) (Fig. 7). This is well after the mid Holocene
climatic optimum, de®ned as terminating in Lalle-
mand Fjord 3850 yr BP based on the transition from
the seasonally open water to ice-associated assem-
blages. It seems likely that the changes in primary
production that we observe in Lallemand Fjord are
related more closely to shifts in water mass distribu-
tion (namely Circumpolar Deep Water) and sea
surface temperature.
6. Conclusion
This study indicates that detailed diatom analysis
highlights the variability of the transitions in paleo-
environmental reconstruction. Three diatom assem-
blages (two sea ice-associated and one seasonally
open water associated) are identi®ed in Lallemand
Fjord by cluster analysis and NMDS. The assem-
blages' association with down-core sedimentary and
geochemical variables are determined by multiple
regression. The assemblages have been deposited
within the SIZ since the Early Holocene, but each
re¯ects variations within this zone. In the Early
Holocene, Lallemand Fjord underwent deglaciation
F. Taylor et al. / Marine Micropaleontology 41 (2001) 25±4340
and we hypothesize that seasonal, loose sea ice was
present. The mid Holocene is characterized by more
open water and higher primary production. The Late
Holocene has undergone climatic cooling and
increased sea ice cover, in the form of compact pack
ice, multi-year ice, fast ice and/or closer proximity of
the MuÈller Ice Shelf. There is no association between
primary production and insolation in this sedimentary
record.
Acknowledgements
This work was supported by a grant from the
National Science Foundation's Of®ce of Polar
Programs (Grant OPP-9615053 to Hamilton College).
We wish to thank R. Dunbar for d 13C data, and
Leanne Armand, Amy Leventer and an anonymous
reviewer for critically reviewing the manuscript.
Appendix A. Taxonomic appendix
List of diatoms (Bacillariophyceae) cited in text.
Taxonomy is based on Johansen and Fryxell (1985);
Priddle and Fryxell (1985); Medlin and Priddle (1990)
and Roberts and McMinn (1999). Non-diatom
taxa (Chrysophyceae) are listed beneath the diatom
taxonomy. Chrysophyte taxonomy is based on
Booth and Marchant (1987).
Bacillariophyceae
Achnanthes Bory 1822
Actinocyclus actinochilus (Ehrenberg) Simonsen
1982
Chaetoceros (Ehrenberg) 1844 (spores)
Cocconeis Ehrenberg 1838
Eucampia antarctica (Castracane) Mangin 1915
Fragilaria Lyngbye 1819
Fragilariopsis curta (Van Heurck) Hustedt 1958
Fragilariopsis cylindrus (Grunow ex Cleve)
Helmcje & Krieger 1954
Fragilariopsis kerguelensis (O'Meara) Hustedt
1952
Fragilariopsis obliquecostata (Van Heurck)
Heiden in Heiden & Kolbe 1928
Fragilariopsis rhombica (O'Meara) Hustedt
1952
Fragilariopsis sublinearis (Van Heurck) Heiden
in Heiden & Kolbe 1928
Fragilariopsis vanheurckii (Peragallo) Hustedt
1958
Navicula Bory 1822
Pseudonitzschia turgiduloides (Hasle) Hasle
1995
Rhizosolenia Brightwell 1858
Stellarima microtrias (Ehrenberg) Hasle et Sims
1986
Synedra Ehrenberg 1832
Thalassiosira antarctica var. antarctica Comber
1896 (spores)
Thalassiosira gracilis var. gracilis (Karsten)
Hustedt 1858
Thalassiosira gracilis var. expecta (Van Land-
ingham) Fryxell et Hasle 1979
Thalassiosira lentiginosa (Janisch) Fryxell 1977
Thalassiosira tumida (Janisch) Hasle 1971
Thalassiosira sp. A
Chrysophyceae
Pentalamina corona Marchant 1987
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