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Global and Planetary Chang
Record of the early Holocene warming in a laminated sediment
core from Cape Hallett Bay (Northern Victoria Land, Antarctica)
Furio Finocchiaroa,*, Leonardo Langoneb, Ester Colizzaa, Giorgio Fontolana,
Federico Gigliob, Eva Tuzzia
aDipartimento Scienze Geologiche, Ambientali e Marine, Universita di Trieste, v. E. Weiss, 2-34127 Trieste, ItalybISMAR-CNR, Sezione Geologia Marina, Via Gobetti, 101-40129 Bologna, Italy
Received 16 September 2003; accepted 28 September 2004
Abstract
This paper presents an integrated multiproxy approach study (sedimentological, geochemical, preliminary smear-slides
diatom assemblages, and 14C ages analyses) performed on a sediment core collected in Cape Hallett Bay (Ross Sea, Antarctica).
Sediments record the early Holocene rapid climate changes: buried varved diatomaceous ooze on the base of core (N9.5–9.4 ka
BP) are linked to the early Holocene warming and open marine conditions. From 9.4 ka BP, the climate starts to cool (massive
mud). From 8.0 to 7.8 ka BP, sandy mud sediment suggests a rapid landward recession of the local/regional glaciers, with
relevant underflow inputs, together with the onset of seasonal sea-ice formation. The ages and the characteristics of the
youngest sediments are related to the changed oceanographic conditions linked to the retreat of the calving front of the Ross Ice
Shelf.
D 2004 Elsevier B.V. All rights reserved.
Keywords: Paleoenvironmental reconstruction; Laminated sediments; Early Holocene; Ross Sea; Antarctica
1. Introduction
Recently, research on paleoclimatic reconstruction
in Antarctic areas has focused on short-term climatic
changes during the Holocene. This period is crucial
for understanding the present climatic system and
0921-8181/$ - see front matter D 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.gloplacha.2004.09.003
* Corresponding author. Tel.: +39 040 5582025; fax: +39 040
5582048.
E-mail address: Finofu@univ.trieste.it (F. Finocchiaro).
predicting future global changes. Review of ice-core
data has identified two climatic optima during the
Holocene, the first between 11.5 and 9 ka BP, and a
second between 6 and 3 ka BP in the Eastern
Antarctic sector and between 7 and 5 ka BP for the
Ross Sea area (Masson et al., 2000). According to
Cias et al. (1992), the period of maximum Holocene
warmth in East Antarctica ice cores is between 10
and 7.5 ka BP; Siegert (2001) indicates a warm peak
at 9.4 ka BP in Southern Hemisphere. Timing of the
early climatic optimum coincides with a peak in
e 45 (2005) 193–206
F. Finocchiaro et al. / Global and Planetary Change 45 (2005) 193–206194
abundance of foraminifera in South Atlantic sedi-
ments (Hodell et al., 2001). Baroni and Orombelli
(1994) reported a mid-Holocene warm phase on the
basis of penguin rookery occupation along Victoria
Land coast.
The study of this restricted time interval needs
high-resolution geological records, and for marine
sediments, continuous and expanded sedimentary
successions. Marine successions characterized by
high-sedimentation rates in late Quaternary shelf
sediments around Antarctica have been found mainly
in embayments and fjords along the Antarctic
Peninsula coast. There, sedimentation rates are
Fig. 1. Location of core ANTA02-CH41. Bathymetric data and land morph
edited by U.S. Geological Survey.
higher than 100 cm ka�1 (Lallemand Fjord, Domack
et al., 1995; Palmer Deep, Leventer et al., 1996;
Domack et al., 2001) with maximum values of 1500
cm ka�1 (Brialmont Cove; Domack and McClennen,
1996). Recently, another site of very high accumu-
lation rate in laminated diatomaceous ooze (290 cm
ka�1) was found in George V Land continental shelf
(Harris et al., 2001). Marine sediments in this sector
also record two climatic optima: the first in the early
Holocene, the second one in the mid-Holocene
(Pudsey et al., 1994; Leventer et al., 1996; Domack
et al., 2001; Taylor et al., 2001; Taylor and McMinn,
2001; Presti et al., 2003; Goodridge, 1999–2000).
ology from map SS 58-60/2 (Cape Hallett), original scale 1:250,000,
F. Finocchiaro et al. / Global and Planetary Change 45 (2005) 193–206 195
Concerning the mid-Holocene optimum, authors are
not in agreement about exact timing and period of
this phase.
In the Ross Sea, information on Holocene
climatic changes based on the sediment record is
very scarce. Offshore basins of the Ross Sea
continental shelf show generally low sedimentation
rates: the highest values (ca. 20–24 cm ka�1)
characterize modern biogenic mud in the deepest
and central part of the Joides Basin (Frignani et al.,
1998; Finocchiaro et al., 2000). Only inside Granite
Harbor, where the thickness of diatomaceous ooze
can be at least 10 m (Domack et al., 1999), the
sedimentation rate is very high (up to 250 cm ka�1,
DeMaster et al., 1996), reinforcing the observation
that bays and fjords have excellent potential to
preserve high-resolution sedimentary records.
Many authors recognized that the retreat of the
grounding line in the Ross Sea began about 14–13 ka
BP (Stuiver et al., 1981; Denton et al., 1989; Licht et
al., 1996; Brambati et al., 1997). The general ice
withdrawal was affected by minor climatic fluctua-
tions (Steig et al., 1998; Brambati et al., 1997; Orsini
et al., 2003). Recently, detailed studies on diatom
assemblages have identified a warmer period between
6 and 3 ka (Cunningham et al., 1999), while high
resolution in late Holocene paleoclimatic reconstruc-
tion has been obtained from Granite Harbor sediments
(Leventer et al., 1993).
Evidence of the early Holocene climatic warm
phase is herein reported based on results from a
gravity core (ANTA02-CH41) collected in Cape
Hallett Bay (Lat. 72817.49VS–Long. 170809.05VE;water depth: 416 m) during the 2001–2002 austral
summer (Fig. 1). The early Holocene time interval is
well documented due to very high sediment accu-
mulation rates at the coring site. A succession of
climatic events was tentatively reconstructed based
on paleoenvironmental inferences.
2. Material and methods
Cape Hallett is located along the northern Victoria
Land coast, about 110 km north of Coulman Island
(Fig. 1). The sediment core was collected at the
entrance of the Edisto Inlet, along the conjunction
between Cape Hallett and Cape Christie. Edisto Inlet
is a small bay, about 15 km long and 4 km wide,
deeper than 500 m and separated by a sill from the
larger Moubray Bay (USGS, 1968). The Edisto
Glacier is small and flows into the inner part of the
bay, whereas a saddle at only 800 m above sea level
separates (a few kilometers southward) the bay from
the terminal section of the Tucker Glacier.
The core site is seaward (north) of the sill, and a
SBP 3.5 kHz seismic reflection profile shows parallel
and subparallel reflectors of a stratified sequence about
8 m thick (Bussi et al., 2003). The 408-cm-long
sediment core was collected from the site using a 2.3-
ton gravity corer. The core was scanned for magnetic
susceptibility, split, X-radiographed, described, and
sub-sampled.
The upper 3 m of core are massive and were
sampled in 1-cm-thick slices taken at 10-cm intervals.
Below 3 m, the sediment has alternating dark and
light layers. Forty-two layers were sampled along this
interval. Samples were dried at 60 8C and then
slightly disaggregated for the following analyses.
Porosity was calculated based on water content
according to Berner (1971) and assuming a mineral
density of 2.55 g cm�3.
Particle size was determined after treatment with
H2O2 and wet sieving at 63 Am. Sandy samples were
then analyzed by a MacroGranometer sedimentation
balance and muddy samples by a Sedigraph 5100 ET
(Micromeritics). A Coulter Multisizer (100-Am ori-
fice tube) was used for very small muddy samples
from the laminated section.
Organic carbon content of each sample was
determined using a FISONS NA2000 Elemental
Analyzer (EA) after removal of the carbonate
fraction by adding HCl 1.5 N. The errors associated
with determinations are around 1%. Biogenic silica
content was determined through a progressive dis-
solution method (DeMaster, 1981), followed by
colorimetric analysis. We used NaOH 0.5 M as an
extractant in view of the significant concentrations of
biogenic silica usually found in Antarctic samples
(DeMaster, 1981).
Forty-three smear slide observations provided
preliminary information on diatom assemblages. The
chronology of the sediment core was defined by
means of 7 AMS 14C ages determined on the bulk
organic fraction at Geochron Laboratories (Cam-
bridge, MA, USA).
F. Finocchiaro et al. / Global and Planetary Change 45 (2005) 193–206196
3. Results
Preliminary data of core ANTA02-CH41 were
reported by Finocchiaro et al. (2003).
Two main lithological units can be recognized
in the core (Fig. 2). In the lower unit (Unit A,
408–207 cm), two subunits (A1 and A2) can be
distinguished.
Sub-Unit A1 (408–307 cm) is characterized by a
rhythmic sequence of parallel light and dark mud
laminae, from 0.5 to 19.5 mm thick (Fig. 3). Only
10% of laminae has a thickness between 10.5 and
19.5 mm, and we report them as dthick laminaeT,following the terminology of Reineck and Singh
(1973). Colors of laminae vary from black-gray to
several shades of olive (dark olive to pale olive). In
general, contacts between light laminae and over-
lying dark laminae are gradational, whereas the
contacts from dark to light laminae are sharp. From
preliminary observations of smear slides, light
laminae are almost entirely composed of diatom
frustules, whereas volcaniclastic silt is a subordinate
component of dark laminae. The compositional
difference between light and dark laminae is also
testified by the slightly higher values of organic C
Fig. 2. Core ANTA02-CH41: Lithostratigraphy and unit identification; m
content (%) on wet weight; concentration of organic carbon and biogenic
(0.85 vs. 0.73 wt.% for light and dark laminae,
respectively), but their biogenic silica values are
similar (34.1 vs. 33.3 wt.%).
The particle size of laminae of different color was
measured: dark laminae are poorly sorted with a
coarse-grained tail, whereas olive laminae have the
same modal diameter (12–15 Am), although it is
more leptokurtic. Pale olive laminae have better
sorting and a finer mode (6–7 Am; Fig. 4). The
different particle size distributions of light laminae
are probably related to different diatom assemblages.
Some light laminae (pale olive) show a bfluffyQtexture, very similar to the description of the
bcottonyQ layer found in cores from Granite Harbor
and MacRobertson Bay (Leventer et al., 1993;
Taylor and McMinn, 2001).
Number and thickness of laminae were measured.
Two hundred and sixteen laminae have been defined,
well recognizable by both direct visualization and
different X-ray beam attenuation in radiographs.
Total thickness of 108 pairs of laminae (light+dark
lamina couplets) varies from 3 to 23 mm (mean
value of 8.9 mm) with frequent oscillations, but the
trend is to thin upward (Fig. 5a). The light laminae
are generally thicker than those dark in color. The
ass magnetic susceptibility (from Finocchiaro et al., 2003); water
silica (wt.%).
Fig. 3. Photograph (left) and positive X-ray (right) of the parallel
laminated interval Sub-Unit A1. Scale in centimeters, from the core
top.
F. Finocchiaro et al. / Global and Planetary Change 45 (2005) 193–206 197
ratio between dark lamina and total thickness of
light–dark pair tends to increase upwards, due to
reducing thickness of the light laminae, whereas the
dark laminae remain almost constant in thickness
(Fig. 5b).
Sub-Unit A2 (307–207 cm) is a massive dark
olive-grey mud with wavy and irregular laminae
concentrated between 253 and 207 cm. In compar-
ison with Sub-Unit A1, organic carbon and biogenic
silica decrease (mean values 0.77 and 18 wt.%,
respectively), whereas the sand content increases.
Grain size of massive sediment shows a prevalence
of silt, with a modal diameter between coarse silt and
very fine sand (Fig. 4).
The upper unit (Unit B, 207–0 cm) is charac-
terized by sand (Figs. 2 and 4) with dispersed gravel
clasts as dropstones. Two subunits can be distin-
guished in this section: the lower subunit (Sub-Unit
B1, 70–207 cm) is a dark olive-grey muddy sand
with a sand content varying between 33% and 85%.
Organic carbon and biogenic silica contents of Sub-
Unit B1 are the highest of Unit B (mean values, 0.37
and 5 wt.%, respectively). The Sub-Unit B2 (0–70
cm) is very dark grey, slightly muddy sand, with
sand content varying from 68% to 70%, and the
lowest values of organic carbon (0.24 wt.%) and
biogenic silica (2%).
Preliminary diatom analyses show that Corethron
pennatum (=C. criophilum: Crawford et al., 1998),
Fragilariopsis curta, together with Chaetoceros rest-
ing spores account for up to 96% of the diatom
assemblages in the whole core. C. pennatum occurs
only in the laminated levels (Sub-Unit A1 and only
partially in Sub-Unit A2), whereas F. curta and
Chaetoceros r.s. are found in different percentages
throughout the core. F. curta becomes dominant in the
upper, coarse-grained Unit B.
Finally, we tried to determine if the total
thickness of the light+dark pair and dark/light
lamina ratio have cyclical trends through time,
considering each couplet as a 1-year deposit.
Although the autocorrelation and Fourier analyses
did not give statistically significant results, total
thickness data and dark/light thickness ratios show
11- and 13-year major periodicity cycles, respec-
tively. Standard Z statistics was applied on auto-
correlation coefficients for the lag=11 and 13
years, giving Z t(11 years) =1.60 and Z t(13
Fig. 4. Particle-size data: (a) Sub-Unit A1: average frequency curves of dark, pale olive and dark olive laminae measured by Coulter Multisizer;
(b,c,d) from Sub-Units A2, B1, and B2, respectively, frequency curves of samples, measured by sedimentation balance and Sedigraph.
F. Finocchiaro et al. / Global and Planetary Change 45 (2005) 193–206198
years)=1.85, slightly lower than 95% probability
limit (Zt=1.96).
4. Age model and sediment accumulation rates
Due to the absence of carbonate, it was necessary
to date the bulk organic matter in the sediment. Seven
radiocarbon dates of bulk organic matter (Table 1)
were used to set the chronological constraint (Fig. 6)
and estimate sedimentation rates (Fig. 7).
Radiocarbon ages from Antarctic material must be
interpreted with great caution because of the uncer-
tainty of several factors, such as: reservoir effect, vital
effect among different organisms, and other minor
effects (Domack et al., 1999). In addition, sediments
may be variably contaminated with reworked carbon
(Harris et al., 1996). In this regard, diatomaceous mud
and ooze units provide the most accurate determina-
tions of radiocarbon age, because the material has the
highest concentration of autochthonous organic matter
of all the lithofacies. Ages at or prior to the last glacial
maximum (LGM) are interpreted as mixed (Domack et
al., 1999). Most authors use a reservoir correction
ranging between 1.2 and 1.5 ka for the Ross Sea region
(Stuiver et al., 1981; Licht and Andrews, 1997;
Berkman, 1997; Licht et al., 1996, 1999) and for other
Antarctic shelf areas (Pudsey et al., 1994; Shipp and
Anderson, 1994; Gingele et al., 1997). Nevertheless,
the problems that plague radiocarbon dating and the
high spatial variability of surface sediment ages in the
Antarctic marine system mean that it is unlikely that a
reliable absolute age for a single-dated horizon within a
sediment core can be obtained (Domack et al., 1999).
Adjustments could be made by subtracting the age of
the organic matter at the sediment–water interface for
each core, but one needs to be certain that the
sediment–water interface has been recovered and
sediment mixing also must be evaluated (Domack et
al., 1999).
By comparing the magnetic susceptibility profiles
with a companion box-core collected in the same site
(data not shown), the uppermost 2 cm of the
sedimentary succession of core ANTA02-CH41 seems
to have been lost during coring operations. If a
sediment constant accumulation rate of 12.6 cm ka�1
is assumed between the levels 0–1 and 34–35 cm, then
interpolated age at the sediment–water interface is 1630
Fig. 5. Thickness variation of laminae of Sub-Unit A1 (307–408 cm) relative to: (a) 108 dark+light laminae couplets; (b) dark laminae, and (c)
light laminae.
F. Finocchiaro et al. / Global and Planetary Change 45 (2005) 193–206 199
years, which is very near to the most commonly used
value for reservoir corrections.
Radiocarbon results were consequently corrected by
subtracting the calculated age of the organic carbon at
the core top and the bias due to the top loss during core
sampling. According to the corrected data, the studied
core spans from early Holocene to the Recent. There is
a progression of ages down core, with the exception of
three dates measured in Sub-Unit A1, which are not
completely consistent with values above. Only part of
Table 1
AMS 14C ages of ANTA91-CH41 core, on bulk organic matter
Cruise Core Level Code 14C age (year BP) F(1r) d13C (x vs. PDB)
ANTA02 CH41 00–01 GX-29188 1790 40 �25.8
ANTA02 CH41 34–35 GX-30574 4490 50 �25.5
ANTA02 CH41 70–71 GX-29991 9400 40 �28.6
ANTA02 CH41 232 GX-29189 9970 50 �27.3
ANTA02 CH41 300 GX-29190 10,920 50 �26.7
ANTA02 CH41 369 CX-29992 9130 40 �31.9
ANTA02 CH41 402 GX-29191 10,070 50 �28.4
F. Finocchiaro et al. / Global and Planetary Change 45 (2005) 193–206200
the difference can be also accounted for by reproduci-
bility variability (Andrews et al., 1997, 1999). More
likely, the inversion could be due to the release of 14C
depleted glacial meltwater, a variable reservoir effect
through time (van Beek et al., 2002) or contamination
during subsampling. Alternatively, if the lamina
couplets are an annual record of surface productivity,
the Sub-Unit A1 comprises the sediment accumulating
in a very short time interval (about one century).
To overcome the problem of the lower three dates
and to calculate sediment accumulation rates, an age
model was developed.
For the uppermost 300 cm, ages of samples were
estimated assuming a constant sedimentation rate
Fig. 6. Age-depth model of the core ANTA02-CH41. Conventional14C dates were corrected for a reservoir age of 1630 years. The age
model was developed using an integrated approach: in the upper-
most part of the core (0–300 cm), ages were calculated based on a
constant sediment accumulation rate for each lithological unit; below
300 cm, an assumption was made that each couplet was a varve.
within each lithological unit. In detail, in the Sub-Unit
A2, a sediment accumulation rate of 71.6 cm ka�1 was
calculated based on corrected 14C dates measured at
232 and 300 cm. Then, the ages at the boundaries of
Sub-Unit A2 (207 and 307 cm) were extrapolated,
assuming for the whole subunit the same sedimentation
rate measured between 232 and 300 cm.
To calculate the sediment accumulation rate of Sub-
Unit B1, the measured and calculated ages of 70.5 and
207 cm depth, respectively, were used. Downcore, for
Sub-Unit A1 (307–408 cm), we assumed an annual
varved-like sedimentation (see previous discussion).
By assuming this age model (Fig. 6), we calculated
linear sediment accumulation rates and fluxes of bulk
mass, biogenic (organic carbon and biogenic silica) and
lithic components (Fig. 7).
In early Holocene, represented by Sub-Unit A1,
the linear accumulation rate is very high (926 cm
ka�1). Sediment accumulation rates decrease (71.6
cm ka�1) in Sub-Unit A2, increase again in Sub-Unit
B1 (615.7 cm ka�1), and then becomes low (9.3 cm
ka�1) during the last 7.8 ka�1 in Sub-Unit B2. A quite
different picture is obtained when we observe the
variation of mass accumulation rates with time (Fig.
7b) due to the different porosity and bulk dry density
between the sediment above and below 300 cm. In
fact, the mass accumulation rate shows the highest
values in Unit B1 (8.0–7.8 ka BP) and the lowest
(12.2 g cm�2 ka�1) in the last 7.8 ka BP (Unit B2).
However, the strong variability of sediment compo-
sition that characterizes the time interval between 9.5
and 7.8 ka results in a partition in three time intervals:
the oldest, equivalent to the laminated section (9.5–
9.4 ka), is characterized by the highest biogenic
fluxes of both organic carbon and biogenic silica (Fig
7c,d), whereas the youngest period (8.0–7.8 ka)
shows the highest fluxes of the lithogenic fraction
Fig. 7. (a) Linear (dashed line) and mass (solid line) accumulation rate vs. sediment depth (cm); (b) mass accumulation rate (g cm�2 ka�1) vs.
time (ka). Temporal variations of the mass accumulation rate (MAR) of biogenic silica (BSi), Corg and lithic fraction were plotted with more
detail between 10 and 7.5 ka BP, in (c), (d), and (e), respectively.
F. Finocchiaro et al. / Global and Planetary Change 45 (2005) 193–206 201
(Fig. 7e). The accumulation of both lithogenic and
biogenic components (Fig. 7c–e) are relatively low in
the intermediate time interval (9.4–8.0 ka).
5. Discussion and conclusions
5.1. Laminated sediments (Sub-Unit A1)
The most common stratigraphic succession on the
Ross Sea shelf has a basal diamicton unit of glacial
origin at its base (Anderson, 1999; Domack et al.,
1999; Brambati et al., 2002). Overlying facies are
composed of glacimarine silt and sandy intervals. The
uppermost portion of most cores collected in the Ross
Sea is a diatomaceous ooze (Dunbar et al., 1985; Licht
et al., 1996; Frignani et al., 1998; Langone et al.,
1998; Domack et al., 1999) interpreted as having been
deposited in seasonally open water conditions.
The presence of fine diatomaceous mud buried
under about 2 m of sandy sediment is peculiar of core
ANTA02-CH41, and indicates open marine condi-
tions during early Holocene. Despite the fact that
buried diatomaceous sediment was recently recog-
nized by Colizza et al. (2003) south of the Drygalski
basin, this stratigraphic sequence is quite rare in the
Ross Sea.
Fine-grained laminated sediments are widely
reported in Late Quaternary Antarctic sequences.
For example, highly laminated sediments characterize
the drift area of the Pacific margin of the Antarctic
Peninsula (Pudsey and Camerlenghi, 1998; Lucchi et
al., 2002), Palmer Deep and Gerlache Strait (Leventer
et al., 2002; Goodridge, 1999–2000), the MacRo-
bertson Shelf (Harris, 2000), the George V continen-
tal shelf (Wilkes Land Margin: Domack and
Anderson, 1983; Domack, 1988; Brancolini and
Harris, 2000; Presti et al., 2003), and outer slope
areas of the Ross Sea embayment (Bonaccorsi et al.,
2000). In the inner shelf of the Ross Sea, laminated
sediments are reported by Nishimura et al. (1998)
(north of Ross Island), Leventer et al. (1993) (Granite
F. Finocchiaro et al. / Global and Planetary Change 45 (2005) 193–206202
Harbour) and Colizza et al. (2003) (Wood Bay area).
In general, the preservation of parallel lamination in
marine sediment is considered a proxy for anoxic
conditions, that exclude the presence of a benthic
community, or a very high sedimentation rate in areas
characterized by upwelling or by favorable oceano-
graphic conditions (Grigorov et al., 2002; Cofaigh
and Dowdswell, 2001).
5.2. Facies interpretation and paleoenvironmental
reconstruction
Based on physical, geochemical, and biological
proxies, and using the age-depth model, a sequence of
depositional events driven by paleoclimate and
paleoenvironmental changes was tentatively recon-
structed. Particular attention was devoted to the early
Holocene, a time interval well preserved in sediments
of Cape Hallett Bay.
5.2.1. Sub-Unit A1 (N9.5–9.4 ka BP)
The high accumulation rate and high organic
carbon and biogenic silica contents in the Unit A
(about 2 m thick) of core ANTA02-CH41 suggest a
period of high biological productivity. Based on the
modern assemblage distribution (Cunningham and
Leventer, 1998), the Corethron occurrence is
associated with a well-stratified water column
linked to weak wind, thermal warming and/or sea-
ice meltwater (Leventer et al., 1996). The olive
laminae are mainly composed by Corethron and
Chaetoceros r.s. Few pale-olive, fluffy, thick lam-
inae contain a nearly monospecific Corethron
assemblage, which produces pulses of rapidly
sinking algal flocs during early spring blooms. In
the following dark lamina, the contribution of fine
glacial debris mainly from overflow plumes
increases through summer. Thus, the pair of
laminae depicts a varve-like sedimentation with a
seasonal alternation of productivity events (light
laminae) and deposition of terrigenous debris (dark
laminae).
All these proxies, together with the age model,
constrain the deposition of the lowest sedimentary
unit to the early Holocene warming.
Leventer et al. (1993) documented a layer of
Corethron ooze that was related to deposition during
the Medieval Warm Period.
5.2.2. Sub-Unit A2 (9.4–8.0 ka BP)
Climatic conditions were not constant during the
time of fine-grained sediment accumulation (Unit A):
the reduction of light lamina thickness in the upper
part of Sub-Unit A1 implies a general decrease in
productivity over the period, thus suggesting a
progressive climate cooling. The massive mud of
Sub-Unit A2 further indicates the end of the optimal
climatic conditions of the early Holocene. However,
the shifting is punctuated by several oscillations
marked by an alternation between massive and
irregularly laminated levels. In Sub-Unit A2, both
biogenic silica and sand contents show intermediate
values from the laminated interval and the Sub-Unit
B1, above.
The low lithic mass accumulation rate (about one
third of the Sub-Unit A1), together with the
significant increase of F. curta and Chaetoceros in
diatom assemblages, imply a climate cooling which
is likely to be associated to a more persistent sea-ice
covering. Subsequently, during a shorter and cooler
summer, a low amount of meltwater prevents the
formation of stratification along the water column; in
the same manner, fine sediment release from over-
flow plumes is sensibly lower than during the
Holocene warming.
The sedimentary signature is therefore given by the
superimposition of fine detrital material settled during
summer, arranged in amalgamated and structureless
(by bioturbation) layers, only occasionally interrupted
by laminated biosiliceous mud, typical of warmer
phases.
5.2.3. Sub-Unit B1 (8.0–7.8 ka BP)
The abrupt change at level 207 cm depth
(corresponding to 8.0 ka BP) can be related to a
dramatic environmental change. All paleoproducti-
vity markers decrease, particle-size becomes coarser
and consequently, the mass accumulation rate of
lithics exceeds the biogenics. Corethron disappears,
whereas F. curta becomes the prevailing diatom
species. High percentages of F. curta have been
associated with marginal sea-ice zones (Leventer et
al., 1996; Cunningham et al., 1999). The high
accumulation of the terrigenous sediment could
document the rapid landward recession of the local
and/or regional glaciers and the onset of seasonal sea-
ice formation.
F. Finocchiaro et al. / Global and Planetary Change 45 (2005) 193–206 203
In the Ross Sea region, the ice sheet retreated by 11
ka BP (Domack et al., 1999). A possible trigger of the
fast retreat of local glaciers could be linked to a
relative sea level rise following the regional retreat of
the East Antarctica Ice Sheet (EAIS). The rapid EAIS
retreat and related sea level rise may well have forced
instability of the local glacier grounding line pinned
on the morphological high at the entrance of Edisto
Inlet (Fig. 1). Consequently, the glacier grounding line
rapidly migrated to inner positions of the inlet.
In some cores from the continental shelf of the
Ross Sea, the transition from glacial (diamicton) to
glacimarine sediment and/or siliceous mud is marked
by a sorted muddy sand layer. The occurrence of this
layer was first pointed out by Kellogg et al. (1979)
and then described as a bgranulated faciesQ by
Domack et al. (1999). This coarse grained sediment
has been interpreted as a meltwater facies, related to
decoupling and lift-off of a recessional melting line of
the ice sheet. The depositional model interprets the
granulated facies as resulting from melting of basal ice
near the grounding zone, linked to strong bottom tidal
currents that have winnowed out the fine fractions,
thus increasing sand percentages and sorting (Domack
and Harris, 1998). The sandy level recognized at the
base of this subunit, may be the equivalent of the
granulated facies, representing the lift-off of local
glaciers in the Cape Hallett area.
Despite the moderate increase of the mud content,
the remnant upper part of the Sub-Unit B1 features
grain size distribution with marked sorting character-
istics (Fig. 4). These data, together with the high
sedimentary rates and increase in ice-rafted debris
(IRD), suggest a progressive landward recession of
the glacier front, which caused an abundant release of
dense underflow plumes. A new circulation pattern
inside the fjord, supported by high meltwater fluxes
and sea-level rise, is likely to be the main triggering
factor for bottom currents able to winnow and
transport sediments toward the deepest part of the
bay, far from the supply zone of coarse debris (glacier
margin subaqueous fan; Boulton, 1990).
5.2.4. Sub-Unit B2
Proxies at the base of Sub-Unit B1 (140–207 cm)
and in Sub-Unit B2 (0–70 cm) are quite similar,
suggesting that similar processes affected sedimenta-
tion processes, but the sedimentation rate dramatically
decreased to values typical of offshore Holocene
sediments of the Ross Sea: 9.1 cm ka�1 (Brambati et
al., 1997; Frignani et al., 1998) during the last 7.9 ka.
This difference may indicate the retreat of the calving
front of the Ross Ice Shelf over the study site at about
8.0 ka BP and the reduction of the glacial debris
supplied only by small glaciers flowing into the
Edisto Inlet.
Retreat of the ice sheet from most of the Western
Ross Sea area had as a consequence the onset of the
Ross Sea and Terra Nova polynyas and the formation
of High Salinity Shelf Water (HSSW), the densest
waters of the Ross Sea continental shelf. The HSSW
feeds bottom currents flowing out the Ross Sea along
the coast of the Victoria Land. Establishment of these
conditions also determined a more pronounced
intrusion of the Circumpolar Deep Water onto the
shelf (Denton et al., 1989) that, in turn, contributed to
raise to present-day levels the diatom productivity that
characterizes the southwestern Ross Sea and the
JOIDES basin.
The uppermost lithofacies (0–70 cm) of core
ANTA02-CH41 is a common feature in the north-
western Ross Sea. In fact, coarse sediment was also
observed in surficial sediments collected on the
continental shelf between Coulman Island and Cape
Adare (Melis et al., 2002), supporting the hypothesis
of a similar origin.
5.3. Concluding remarks
This study sheds new light on the sedimentary
record of rapid climatic changes affecting the early
Holocene in the Antarctic region. An integrated
multiproxy approach has allowed the documentation
of:
! A possible varved biogenic ooze, which implies a
recovery of the record of the early Holocene
warming in sediments of the Ross Sea. Sedimen-
tological and geochemical parameters, together
with floral assemblage observations, indicate this
time period (N9.5–9.4 ka BP) as being character-
ized by weak winds and thermal warming of the
strongly stratified upper water column. Biological
productivity was highly enhanced with substantial
early spring algal blooms, which produced epi-
sodic events of sediment deposition of rapidly
F. Finocchiaro et al. / Global and Planetary Change 45 (2005) 193–206204
sinking biogenic material. During the following
summers, thermal warming released a peak of fine
glacial debris. The result was the accumulation of
an annual couplet of alternating light and dark
laminae.
! Starting at 9.4 ka BP, the climate cooled. The algal
assemblages show more stressed environmental
conditions, and also, glacial melting diminished.
The shift to these conditions is quite well marked,
although interrupted by several short-lived warm
oscillations.
! From 8.0 to 7.8 ka BP, the sediment core records a
high flux of terrigenous material, coarse and well-
sorted at the beginning and finer at the end of this
time interval, which was interpreted as the product
of a rapidly receding glacier. The diatom assemb-
lages suggest that seasonally open marine con-
ditions were established, associated with marginal
sea-ice zones.
! The onset of the current general circulation system
of the Ross Sea was tentatively set at 7.8 ka BP, as a
consequence of the polynya and HSSW formation.
We demonstrate that the coastal bay near Cape
Hallett is a promising location to obtain detailed
paleoenvironmental records for paleoclimate recon-
structions. In this regard, the database should be further
improved: the sediment core did not recover the base of
the laminated layer, equivalent to the onset of the early
Holocene warming. Based on the SBP seismic profile,
the maximum thickness of the laminated sequence is
expected to be 4 to 5m thick. In addition, this study was
based on the analyses and interpretation of a single
sediment core. It is necessary to sample further sites in
the bay in order to understand to what extent of
confidence our paleoenvironmental interpretations can
be extrapolated on a spatial scale. Finally, our findings
have to be more closely integrated with regional
information from the Ross Sea.
Acknowledgments
Research carried out within the framework of
the Project 4.5 (P.I. Prof. A. Brambati) of the
Italian Programma Nazionale di Ricerche in Antar-
tide, and financially supported by ENEA. We thank
the crew and scientific party onboard R/V Italica
for their help with fieldwork during the ANTA02
cruise. The two referees Amy Leventer and Ross
D. Powell are fully acknowledged for the critical
review of the manuscript. The authors wish to
dedicate this paper to the seaman David Basciano,
who has left us too early. This is contribution No.
1434 of the ISMAR-CNR, Sezione Geologia
Marina di Bologna, Italy.
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