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JOURNAL OF QUATERNARY SCIENCE (2005) 20(4) 327–347
Copyright ß 2005 John Wiley & Sons, Ltd.
Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jqs.920
Holocene millennial/centennial-scale
multiproxy cyclicity in temperate eastern
Australian estuary sediments
C. GREGORY SKILBECK,1* TIMOTHY C. ROLPH,2 NATALIE HILL,2 JONATHAN WOODS1 AND ROY H. WILKENS3
1
Department of Environmental Sciences, University of Technology, Sydney, Australia
2
School of Geosciences, University of Newcastle, Callaghan, Australia
3
Hawai’i Institute of Geophysics, University of Hawai’i, Honolulu, USA
Skilbeck, C. G., Rolph, T. C., Hill, N., Woods, J. and Wilkens, R. H. 2005. Holocene millennial/centennial-scale multiproxy cyclicity in temperate eastern Australian
estuary sediments. J. Quaternary Sci., Vol. 20 pp. 327–347. ISSN 0267-8179.
Received 18 September 2003; Revised 17 December 2004; Accepted 14 January 2005
ABSTRACT: We have undertaken a comparative study of down-core variation in multiproxy
palaeoclimate data (magnetic susceptibility, calcium carbonate content and total organic carbon)
from two coastal water bodies (Myall and Tuggerah Lakes) in temperate eastern Australia to identify
local, regional and global-forcing factors within Holocene estuarine sediments. The two lakes lie
within the same temperate climate zone adjacent to the Tasman Sea, but are not part of the same
catchment and drain different geological provinces. One is essentially a freshwater coastal lake
whereas the other is a brackish back-barrier lagoon. Despite these differences, data from two sites
in each of the two lakes have allowed us to investigate and compare cyclicity in otherwise uniform,
single facies sediments within the frequency range of 200–2000 years, limited by the sedimentation
rate within the lakes and our sample requirements. We have auto- and cross-correlated strong periodicities at 360 years, 500–530 years, 270–290 years, 420–450 years and 210 years, and
subordinate periods of 650 years, 1200–1400 years and 1800 years. Our thesis is that climate is
the only regionally available mechanism available to control common millennial and centennial
scale cyclicity in these sediments, given the geographical and other differences. However, regional
climate may not be the dominant effect at any single time and either location. Within the range of
frequency spectral peaks we have identiﬁed, several fall within known long-term periodical ﬂuctuations of sun spot activity; however, feedback loops associated with short-term orbital variation, such
as Dansgaard–Oeschger cycles, and the relationship between these and palaeo-ENSO variation, are
also possible contributors. Copyright ß 2005 John Wiley & Sons, Ltd.
KEYWORDS: Holocene; multiproxy data; spectral analysis; estuarine sediments; palaeoclimate.
Introduction
The recognition of climate cyclicity in deep marine or nonmarine sediments is commonly accompanied by a regular
alternation of facies such as the carbonate/clay cycles of deep
ocean cores (e.g. Shackelton and Opdyke, 1973; Dean and
Gardner, 1985; Diester-Haass and Rothe, 1988; Diester-Haass,
1991), or the regular alternation of evaporite/epiclastites in salt
lakes (e.g. Kotwicki and Isdale, 1991) or other ‘closed’ systems
(e.g. Horiuchi et al., 2000) that directly or indirectly reﬂect climate-induced facies variation. In none of these situations do
* Correspondence to: C. Gregory Skilbeck, Department of Environmental
Sciences, University of Technology, Sydney, PO Box 123, Broadway, NSW
2007, Australia. E-mail: [email protected]
eustatic sea level rise and fall directly inﬂuence sediment accumulation, and the vertical sequences therefore represent continuous sedimentation across several Milankovitch cycles, at
least in the case of the deep marine sequences. Generally,
however, deep-ocean sedimentation rates are insufﬁcient to
allow sampling at rates high enough to deﬁne centennial or
millennial scale cyclicity. Facies alternations also occur in
coastal and shallow marine deposits, but as a direct consequence of sea-level rise and fall. In these settings sedimentation
is rarely continuous across several facies or sedimentation
cycles. For example, where highstand deposits are imbricately
stacked, there is little chance of a continuous record spanning
more than one sea level cycle being preserved in any one
place. This means that sequences in littoral settings usually
include non-depositional or erosional breaks at Milankovitch
frequencies. However, the coastal zone does provide a good
location in which to study cyclicity at sub-Milankovitch
328
JOURNAL OF QUATERNARY SCIENCE
frequencies. Drowned estuaries and coastal lakes contain
many sediment sinks where expanded Holocene (and other
highstand) sections can be examined in high-resolution (subMilankovitch) detail.
In order to assess the effects of external or regional controls
on sedimentation, we have analysed the sedimentary records
of two New South Wales (Australia) coastal lakes (Myall and
Tuggerah Lakes, Fig. 1). Both are located inboard of the Holocene highstand beach system and, on the basis of the 14C age
sequence and correlatable high-resolution magnetic susceptibility records, contain a stratigraphically continuous Holocene
estuarine sequence overlying either an earlier Pleistocene erosion surface, or lowstand late Pleistocene ﬂuvial deposits. The
estuarine sediments were deposited as sea level rose and
drowned the coastal areas following the last glacial maximum,
some 20 000 calibrated years ago. In this paper, we describe
and compare downhole variation in three parameters common
to our two studies, magnetic susceptibility, percentage calcium
carbonate (%CaCo3) and percentage total organic carbon
(%TOC) from the Holocene estuary sediments in the two lakes.
Temporal variation in these properties will reﬂect the changing
nature of the local environment, providing a signal of the ecosystem response to direct, or indirect (e.g. sea-level change) climate forcing functions. Time series analysis of these properties
demonstrates the potential for deciphering local and regional
controls on sedimentation and, potentially, on climate in temperate eastern Australia over at least the last 10 000 years.
Lake settings
The southeastern Australian coast is a wave-dominated sediment-deﬁcient stable passive margin (Roy and Boyd, 1996) that
formed during opening of the Tasman Sea 80–55 million years
ago (Weissel and Hayes, 1977). The Myall Lakes System
(which includes Myall, Broadwater and Boolambayte lakes,
Fig. 2) overlies irregular Carboniferous ( 320 Ma) basement
comprising rhyodacitic-to-basaltic forearc basin volcanics
and metasediments of the New England Fold Belt (Skilbeck
and Cawood, 1994). To the north and west, basement rocks
crop out around the lakeshores, and most of the small islands
within the lakes comprise basement outcrops. None of the
cores to date have intersected rocky basement and the pattern
of depth to bedrock is essentially unknown. On the seaward
side of the lakes, the Pleistocene and Holocene dunes
(Melville, 1984; Roy and Boyd, 1996, Fig. 2) link headlands
formed of Carboniferous basement outcrop. The minimum
topographic relief between Myall Lake and the adjacent ocean
is 20 m above mean sea level, meaning that this part of the system is essentially isolated from direct marine inﬂuence. The
maximum water depth approaches 5 m, although lake level is
known to ﬂuctuate up to 80 cm above sea level (D. Rissik, pers.
comm., 2001), mainly as a result of rainwater inﬂux, but at
equilibrium approximates local sea level. The lake system
has an indirect marine connection at Port Stephens, some
30 km to the southwest of the lake system (Fig. 1). Despite
this connection, and its proximity to the sea, Myall Lake
contains virtually fresh water (2–3 ppt TDS) and has no existing
tidal or external wave-current inﬂuences. This situation is
unique along the New South Wales coast where all other lakes,
including Tuggerah Lake, are either directly or periodically
open to the sea and contain widespread reworked marine sand
deposits.
Tuggerah Lake (part of the Tuggerah, Munmorah and
Budgewoi Lakes system) is a barrier estuary (Roy, 1984) formed
within a valley incised into the Triassic Narrabeen strata of the
foreland Sydney Basin (Glen and Beckett, 1997). Tuggerah
Lake has a maximum water depth of 3 m and fully saline to
brackish waters. It is semi-enclosed by a coastal sand barrier
but is in permanent communication with the Tasman Sea
through a microtidal inlet (The Entrance) located near the
southeastern end of the lake. Quaternary sediments are extremely variable in thickness having been deposited within and
adjacent to at least two incised channel systems, during multiple phases of sea level rise and fall (Weale, 2001).
The two lakes therefore have some attributes in common
(inter alia regional setting; area, water depth, geomorphology,
Tertiary history) and some that differ (inter alia provenance;
current marine inﬂuence). It is relevant to our study that the rivers feeding the two lakes drain distinctly different geological
provinces (Fig. 1), but because some of the units in the Sydney
Basin were derived from erosion of the New England Fold Belt
(Hamilton and Galloway, 1989), a common lithological provenance cannot be excluded when trying to assess regional and
local controls on sedimentation.
Sediment description
Figure 1 Map showing the location of the Myall and Tuggerah Lakes
systems along the eastern coast of Australia. Locations of core sites discussed in detail in this paper are indicated. The Hunter Thrust (heavy
dashed line) separates the Palaeozoic New England Fold Belt (to the
northeast) from the Permo-Triassic Sydney Basin
Copyright ß 2005 John Wiley & Sons, Ltd.
We have recovered 36 cores from Myall Lakes (referred to
herein as ML#) and 2 from Tuggerah Lake (Pelican 1 and
Chittaway 1), using a combination of vibrocoring (in 75 mm
diameter aluminium liner), push-piston and hammer coring
methods (range of 32 mm to 90 mm diameter plastic liner)
J. Quaternary Sci., Vol. 20(4) 327–347 (2005)
HOLOCENE MULTIPROXY CYCLICITY, EASTERN AUSTRALIA
329
Figure 2 Map and cross sections from Myall Lakes showing facies distribution in selected cores. Note that in the north of the lake (ML13, 12, 24) that
Holocene highstand estuary deposits overlie an erosion surface beneath which probable MIS 5e orange mottled estuarine clay subcrops. Downhole
logs adjacent to stratigraphic sections are low-frequency magnetic susceptibility (in cgs 106 units). For facies key refer to Fig. 4
Copyright ß 2005 John Wiley & Sons, Ltd.
J. Quaternary Sci., Vol. 20(4) 327–347 (2005)
75
75
75
75
32
32
32
90
90
90
90
90
90
1.3a
1.3a
2.6a
2.6a
0.5
3
3
2
5
5
2
5
5
(see Table 1 for summary of cores investigated in detail in this
study). Penetration ranges from 0.45 m (ML29, by vibrocore) to
10.77 m (ML34, push-piston core) in Myall Lakes, and up to
4.34 m (Pelican-1, hammer core) in Tuggerah Lake. Although
currently undated, the oldest sediments encountered in cores
in both lakes are interpreted to be highstand estuary deposits
emplaced during the last interglacial highstand (MIS 5e) and
subaerially exposed during the last glacial maximum (MIS 2).
These sediments are very similar in appearance to the Holocene estuarine muds described below, but are considerably
stiffer. The uppermost parts of these units have orange-brown
iron oxide mottles.
In the deeper basinal parts of both lakes the main facies is a
pale–medium grey (5GY/3; Munsell, 1975) silty clay containing mostly disseminated grains of ﬁne to medium-grained subangular-rounded quartz sand and irregularly distributed
fragmentary and rare intact bivalve shells (Fig. 3). This unit is
interpreted to be a highstand central basin estuarine facies that,
where depositionally complete, ranges in thickness up to
1.74 m in Tuggerah Lakes (Pelican-1), and up to 2.05 m
(ML07) in Myall Lakes. The facies is uniform in appearance,
although rare dark grey mottling may indicate some localised
bioturbation. Internal bedding is rare; in a few cores (ML14 and
19) sand is concentrated into thin laminae near the top of
the unit, and a 10 cm sandy silt layer is present in Pelican-1
in Tuggerah Lake. Common shell fragments and rarer whole
Copyright ß 2005 John Wiley & Sons, Ltd.
Uncompacted (1 cm and 2 cm respectively in core).
To maximum age of 10 k 14C yr BP.
b
a
Chittaway 1
Pelican 1
Myall 19B
Myall 19A
Myall 11B
Magnetic susceptibility
Magnetic susceptibility
TOC
CaCO3
Magnetic susceptibility
TOC
CaCO3
Magnetic susceptibility
TOC
CaCO3
Magnetic susceptibility
TOC
CaCO3
1603
1965
1965
1965
7560
7560
7560
3355
3355
3355
2022
2055
2055
9680
8125
8125
8125
12 508
12 508
12 508
7728
7704
7704
5002
5002
5002
8077
6160
6160
6160
2440b
2440b
2440b
4373
4373
4373
2980
2947
2947
3740
2640
2660
2660
1200
1200
1200
1800
1820
1820
1520
1560
1560
141
94
190
190
378b
378b
378b
81
202
202
108
271
271
107
118
58
58
27
27
27
89
36
36
56
22
22
V
V
V
V
P
P
P
H
H
H
H
H
H
Core diameter
(mm)
Proxy
Age min. (yr)
Age max. (yr)
Range (yr)
Tmax (yr)
Tmin (yr)
N
Core type
Sample
spacing (cm)
JOURNAL OF QUATERNARY SCIENCE
Core
Table 1 Core data and analytical parameters used in this study. ‘Age min.’ and ‘Age max.’ refer to the age range of the proxy in the given core; Tmax and Tmin are the range for which reliable frequency peaks can be
determined (given by SPECTRUM analysis); core type V ¼ vibrocore; P ¼ piston core, H ¼ hammer core
330
Figure 3 Photograph of core ML19A showing the uppermost gyttja
and estuarine clay (both Holocene in age) and the upper part of the latest Pleistocene sapropel facies). Note the gradational contacts between
facies. The close-up shows a shell horizon within the estuarine clay
J. Quaternary Sci., Vol. 20(4) 327–347 (2005)
HOLOCENE MULTIPROXY CYCLICITY, EASTERN AUSTRALIA
331
Figure 4 Downhole proxy data for Tuggerah and Myall Lakes; (a) Pelican 1, (b) Chittaway 1, (c) ML11B, (d) ML19A and (e) ML19B. Magnetic susceptibility data in all cores are low-frequency volume measurements. In Pelican 1 magnetic susceptibility reached a maximum of 443 cgs 106 units
near the base of the core. Ages in ML11B and ML19A are cal. yr BP with 2 range (95% conﬁdence). Correlation tie point of 0 m in ML19B shown on
Fig. 4(d); age tie points from ML19A shown on Fig. 4e
Copyright ß 2005 John Wiley & Sons, Ltd.
J. Quaternary Sci., Vol. 20(4) 327–347 (2005)
332
JOURNAL OF QUATERNARY SCIENCE
Figure 4 Continued
shells (Figs 3 and 4), dominantly of the bivalves Anadara sp.
and Notospisula trigonella, are present in many of the cores
in the middle part of the estuarine unit. Shell concentrations
within this zone produce layers up to 15 cm thick (e.g.
Chittaway-1), while in places the shell material appears to be
present in two or three poorly deﬁned bands (Figs 3 and 4)
mostly up to a few cm thick. Elsewhere shells and shell fragments are distributed irregularly and lack a preferred orientation. Magnetic susceptibility data, supported by 14C dates,
indicate that shell beds/layers do not correlate in age. Minor
components are variably scattered throughout the estuarine
facies, and include charophyte gyrogonites (in the upper part
of the unit, immediately beneath the gyttja facies), common
authigenic pyrite, and irregularly distributed wood and
charcoal fragments.
Along the landward side of both lakes, a combination of
sandy silt or silty sand is the uppermost sediment present, in
beds up to 30 cm thick. This unit represents progradation of ﬂuvial clastic sediments (bayhead deltas; e.g. Chittaway-1, Fig. 3).
Copyright ß 2005 John Wiley & Sons, Ltd.
The sediments comprise mainly lithic silty sand, with variable
amounts of mud and organic material. Along the seaward margin of both, well-sorted ﬁne to coarse-grained quartz sand and
silty sand, represents either ﬂood tidal deltas (e.g. Pelican-1,
Fig. 1) and/or aeolian dune migration (e.g. ML02, ML26,
Fig. 2). In both cases, the coarse-grained sand units are up to
3 m thick and contain shell material, ﬁbrous plant remains
and charcoal. Well-deﬁned vertical and horizontal burrows
are variably present. In all cases, the coarse-grained beds are
restricted to the margins of the lake. Nowhere have either ﬂuvial or marine sand bodies migrated completely over ﬁnergrained estuarine sediments in the central part of either lake.
In the central parts of Myall Lake, a layer of olive-yellow/
green amorphous organic matter (AOM), up to 1.6 m thick,
overlays the grey silty estuarine clay. This sediment, or
gyttja, is soupy (in the upper 40–60 cm) to gelatinous (downcore) in consistency. Its base has been dated at around
1110 140 cal. yr BP (OZD298, Table 2). It is the youngest unit
intersected in all cores away from the edges of Myall Lake. In
J. Quaternary Sci., Vol. 20(4) 327–347 (2005)
HOLOCENE MULTIPROXY CYCLICITY, EASTERN AUSTRALIA
333
Figure 4 Continued
all cases the boundary between the gyttja and the underlying
estuarine clay is gradational over 10–20 cm. Minor components include disseminated quartz and lithic sand-grains, relatively abundant charophyte remains, and subordinate black,
well-rounded faecal pellets. Much of the ﬂoor of the central
part of Myall Lakes is covered by weeds dominated by the
macroalgae Najas marina (prickly waternymph) and it is
thought that the breakdown of this material has contributed
most of the organic mass of the gyttja facies. Although this unit
is Late Holocene in age, we have excluded it from our analysis
because of highly variable sedimentation rates calculated at
different sites, mainly a result of highly variable amounts of
compaction.
Underlying the estuarine clay one of two facies types are
present:
1 Around the margins of Myall Lakes, and in the two
Tuggerah cores, the underlying facies is a grey silty clay
of similar appearance and composition to the Holocene
estuarine sediment described above, but with prominent
orange–reddish brown mottling, and a much stiffer consistency. Where this sediment is present, the boundary is
invariably sharp, and probably erosional. In Pelican-1 the
immediately overlying facies is a coarse, intra-formational
lag in which the clasts are composed of angular oxidised
clay pellets clearly derived from the underlying material.
Copyright ß 2005 John Wiley & Sons, Ltd.
In Chittaway-1 and in all Myall Lakes cores, however, the
lag deposit is absent and the younger, softer estuarine clay
immediately overlies the stiffer unit. We interpret this
underlying unit as an estuarine, central basin facies, probably accumulated during the MIS 5e highstand,
in environments similar to those existing today. The unconformity and reddish-brown staining indicate subaerial
exposure and probable erosion that we believe occurred
during the intervening MIS 5d-2 period, prior to the last
postglacial marine transgression.
2 In the central parts of Myall Lakes, the underlying facies is a
dark brown or grey to black, organic-rich (TOC up to 24%,
ML19) structureless silty clay, or sapropel. It has common to
abundant disseminated plant and woody material, much of
which is coated with iron monosulphides (Fig. 2). Disseminated quartz and lithic grains occur near the base of the
unit. Gypsum crystals and unidentiﬁed ?sponge spicules
of at least two types occur irregularly throughout. Rare, thin
oxidised horizons (e.g. ML11A) suggest periodic subaerial
exposure of the facies. The upper boundary varies from
sharp (e.g. ML01, 09, and 32) to gradational over 20–
70 cm (ML03, 11A,B, 22, 28) or mottled and bioturbated
(ML07, 19, 20, 21). We interpret this unit to represent overbank deposition in a semi-permanent ﬂuvial standing water
body such as a swamp, during the lowstand conditions that
would have dominated the area from MIS 5d-2.
J. Quaternary Sci., Vol. 20(4) 327–347 (2005)
Copyright ß 2005 John Wiley & Sons, Ltd.
ML19A
ML19A
ML19A
ML19A
ML19A
ML11B
ML11B
ML11B
ML11B
ML11B
ML11B
P1
P1
P1
C1
C1
P1
C1
OZD298
OZD299
OZD300
OZD301
OZD302
OZE430
OZE431
OZE434
OZE435
OZE432
OZE433
WK8741
WK8742
WK8743
WK8744
WK8745
WK10406
WK10407
40
60
140
160
180
100
118
245
284
170
196
231
363
406
108
235
328
229
Core
depth
(cm)
54
81
188
215
242
118
138
288
335
200
231
231
363
406
108
235
328
229
Uncompacted core
depth (cm)
1200.0
2228.2
8146.2
8832.0
8351.2
634.4
1357.4
7706.7
9076.2
4312.6
5563.7
3170.0
5840.0
8130.0
1860.0
5300.0
3545.0
3948.0
C age
(radiocarbon
years)
14
70.3
60.8
96.2
75.7
78.2
40.7
40.9
55.0
57.7
39.0
39.4
250.0
330.0
160.0
230.0
210.0
101.0
71.0
1
error
(yr)
b
a
60
60
80
100
60
20
20
50
40
130
120
280
360
180
260
200
150
150
Rounded
1
error
(cal. yr)
C laboratory, NZ.
14
1110
2210
9060
9890
9360
580
1280
8450
10 220
4420
5940
3380
6660
9030
1820
6090
3550
3910
Calibrated
ageb
(cal. yr BP)
OZ ¼ ANSTO AMS Laboratory, Lucas Heights, NSW, Australia; WK ¼ Waikato
Calibrated age rounded according to Stuiver and Polach (1977).
c
B ¼ bulk sediment sample; S ¼ shell.
d
I98 ¼ INTCAL98; M98 ¼ MARINE98.
Core
Laboratory
codea
0.815
0.790
0.649
0.658
0.584
0.664
0.931
0.911
0.935
1.000
1.000
0.928
0.980
0.784
1.000
0.954
1.000
1.000
% area
enclosed
by 1
probability
distribution
140
120
250
260
130
50
60
90
140
280
220
580
670
400
500
430
320
300
Rounded
2
error
(cal. yr)
1.000
0.990
0.887
0.985
0.854
1.000
0.889
1.000
0.990
1.000
1.000
0.992
0.986
0.983
1.000
1.000
1.000
1.000
% area
enclosed
by 2
probability
distribution
%
modern
C
86.4
75.9
36.3
33.3
35.3
93.0
84.7
38.2
32.2
58.5
49.9
67.4
48.3
36.3
79.3
51.7
63.5
61.2
13C
(per mil)
22.3
23.5
23.7
24.8
27.6
18.4
22.4
28.6
28.1
0.04
1.9
24.4
23.8
25.2
26.9
24.1
0.04
0.5
B
B
B
B
B
B
B
B
B
S
S
B
B
B
B
B
S
S
Sample
typec
I98
I98
I98
I98
I98
I98
I98
I98
I98
M98
M98
I98
I98
I98
I98
I98
M98
M98
Calibration
curved
—
—
—
—
—
—
—
—
—
7
7
—
—
—
—
—
7
7
R
(cal. yr)
Table 2 Radiocarbon sample data showing depth, calibration and reservoir correction factors used in this study. Uncompacted depth is the depth reconstituted from the actual penetration for vibrocores
—
—
—
—
—
—
—
—
—
86
86
—
—
—
—
—
86
86
R 1
error
(cal. yr)
334
JOURNAL OF QUATERNARY SCIENCE
J. Quaternary Sci., Vol. 20(4) 327–347 (2005)
HOLOCENE MULTIPROXY CYCLICITY, EASTERN AUSTRALIA
Lake stratigraphy
The Late Quaternary stratigraphy of Myall Lakes is relatively
well-known because of the number of cores available.
Tuggerah Lakes has been extensively drilled as part of a coal
exploration programme, but unconsolidated sediment, including the Late Quaternary, was only spot-sampled from drilling
ﬂuids during the exploration program. The two cores from
the current study remain the only continuous lithological samples from the Late Quaternary in Tuggerah Lakes. A study of the
sequence stratigraphy in Tuggerah Lakes from a 2D shallow
seismic survey was recently undertaken (Weale, 2001).
The stratigraphy of Myall Lakes is summarised in Fig. 4. It can
be seen that uppermost gyttja is present commonly across the
central, deeper parts of the lake where it is up to 1.63 m thick
(ML11B). Close to the margins of the lake, the uppermost facies
is sand, which along the southern margin is well sorted and
quartz-rich and represents the landward edge of the relict/modern dune complex. Core ML05 has penetrated through this
sandy facies, showing that the sand represents the prograded
distal fringes of the Pleistocene/Holocene dune complex and
that it is underlain by ﬁner-grained facies. Along the northern
margin of the lake, the sand is poorly sorted and lithic, indicating its origin as a prograding ﬂuvial wedge derived from the
underlying Carboniferous sedimentary rocks. The volumetrically dominant facies in the lake is the estuarine grey silty clay
that is present in all cores, except ML13 located at the northern
shoreline of the lake. In the central parts of the lake, where it is
gradationally underlain by the sapropel facies and gradationally overlain by gyttja, this estuarine facies is consistently
between 1.60 and 2.05 m thick. Magnetic susceptibility data
(Fig. 2) suggest deposition has not been uniform across the
central part of the lake, despite the uniform appearance of
the facies, and the correlatable pattern indicates either that
there has been little or no bioturbation, or that the magnetic
signature is post-depositional in nature.
The strike of the palaeosubstrate, as indicated by the facies
distribution described above, is approximately northeast–
southwest, parallel to the current long axis of the lake. Marine
and estuarine facies have clearly prograded towards the north
during recent evolution, but the absence of recent estuarine
clay in ML13 suggests the lake has never extended farther to
the north than its current limit.
Dating and sedimentation rates
Chronologies and sediment accumulation rates have been
established using conventional (Tuggerah) and AMS (Myall)
radiocarbon dating. The conventional analyses were carried
out by the Waikato Radiocarbon Dating Laboratory, while
the AMS ages were obtained from the Australian Nuclear
Science and Technology Organisation (ANSTO) ANTARES
facility (Lawson et al., 2000). Results are given in Table 2.
The radiocarbon samples from the Tuggerah Lake cores were
approximately one-quarter core segments, 4 cm thick, providing between 50 and 100 g of dry weight; the Myall Lakes samples were approximately 1 cm3 in size over a 1 cm interval.
All ages cited herein have been converted to cal. yr BP where
possible (i.e. for ages <20 000 cal. yr BP), using CALIB Version
4.3 (Stuiver and Reimer, 1993; Stuiver et al., 1998), and have
been rounded according to the convention outlined in Stuiver
and Polach (1977). Ages are cited in the text and on Fig. 4 with
the 2 error determined from the probability distribution
Copyright ß 2005 John Wiley & Sons, Ltd.
335
(Method B in CALIB 4.3; see Table 2). The percentage probability distribution associated with both the 1 and 2 errors by this
method are also given in Table 2. The carbon in bulk sediment
samples derives from a mixture of terrestrial and estuarine plant
and freshwater algal material and hence the 14C ages were corrected using the atmospheric correction curve INTCAL98. The
shell samples from Tuggerah Lake were corrected using marine
calibration curve MARINE98, because this system is open to
the sea. Although Myall Lake is currently a freshwater system,
the bivalve fauna is estuarine in character and the marine
calibration curve MARINE98 has been used, with the eastern
Australian regional reservoir correction (Table 2). For all
Holocene AMS ages, the 13C values have been measured
(range 28.59 to 22.33% for bulk sediment samples and
1.89 to 0.44% for shells).
For the Tuggerah Lakes cores, age and proxy samples have
been obtained from the same core at each of the two locations,
whereas in Myall Lakes ages were obtained from cores ML11B
and ML19A and then correlated with adjacent cores from
which the proxy samples were collected (ML11A and ML19B
respectively) using high-resolution magnetic susceptibility
records and calculated sedimentation rates. The age sample
locations and tie points are shown on Fig. 4. The method is
comparable with that used by Moy et al. (2002) for their study
of palaeo-ENSO in the Andes.
Eighteen 14C ages are available from the Holocene estuarine
facies in four cores. The downhole plots of calibrated age
against uncompacted core depth are shown in Fig. 5. In both
Myall and Tuggerah Lakes, the ages determined on bulk sediment samples deﬁne consistent downhole sedimentation rates
for estuarine sediment where up to four ages are available in
one core (ML11A, ML19A; Fig. 5). In Myall Lake, the rates
range between 11 and 22 cm per thousand years (kyr), whereas
in Tuggerah Lake they are slightly higher at 30 cm kyr1.
From Fig. 5 it is clear that the bulk sediment samples deﬁne
consistent downhole sedimentation rates across the Holocene
interval, with high correlation coefﬁcients for the linear regression, but shell-derived ages plot well off these regression lines.
For the Myall Lake samples, the shells yield ages about 200 yr
older than their stratigraphic position suggests compared with
the bulk sediment ages, whereas in the Tuggerah cores the ages
are between 1500 and 2200 years younger than their stratigraphic position within the sequence of terrestrial dates would
indicate. These differences suggest that the average eastern
Australian reservoir correction of R ¼ 7 86 yr, is in error
by at least 200 yr, but also that a general reservoir correction
cannot be applied to littoral faunas. We consider the shell ages
to be unreliable and they have not been used for interpolating
ages for the spectral analysis.
Of the remaining 14 bulk sediment-derived ages, only
two require further discussion. The lowermost date of
9030 400 cal. yr BP (WK8743) at a depth of 4.06 m in Pelican
1 (Fig. 4) is of concern. The bulk sample was taken from the lag
layer at the very base of the Holocene section, which contains
clay rip-up clasts and thus could be contaminated by older
material. The sea level curve for eastern Australia (Thom and
Roy, 1985) indicates that sea level was between 6 and 9 m
below present sea level at this time so this age would yield
an index point that lies above the sea-level curve. In addition,
shell and wood material dated between 6800 and
8200 cal. yr BP in nearby Lake Macquarie and the Hunter River
estuaries, are present at depths of 9.7–16 m b.s.l. (Thom et al.,
1992; Roy, 1994; Walker, 1999). The younger terrestrial ages
in the Pelican-1 and Chittaway-1 cores are consistent with
the data of Thom and Roy (1985) indicating that present sea
level was reached at 6500 cal. yr BP. Because of the uncertainties about this older Tuggerah date, we have ignored it for
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Figure 5 Depth versus calibrated age (in cal. yr before 1950) showing regression ﬁts for ages in (a) Myall Lake and (b) Tuggerah Lake. Linear regression and Pearson correlation coefﬁcient from MS Excel 2002. See text for explanation of shell-derived ages
the purposes of the frequency analysis and used instead an age
extrapolated from the two overlying Holocene dates. These
yield an extrapolated basal age for the Holocene estuarine
sediments of 7730 cal. yr BP and a sedimentation rate of
40 cm kyr1 across the Holocene interval, marginally higher
than that calculated from the linear regression shown on Fig. 5.
In ML19A, the lowermost Holocene ages of 9890 260cal. yr BP (OZD301) and 9360 130 cal. yr BP (OZD302),
both lie within the upper part of the sapropel layer underlying
the estuarine clay facies and are out of chronostratigraphic
order relative to each other. The older age yields a sedimentation rate of 32 cm kyr1 for the lowermost part of the
Holocene section, and is supported by the three other ages
across the Holocene section. In contrast, the younger of the
two out-of-sequence ages yields a sedimentation rate of
154 cm kyr1 for the same interval. As the lower of the two
rates rate falls well within the range determined by Roy
(1994) for Holocene estuarine sedimentation in eastern
Australia, and is supported by all other ages determined in this
study, the 9360 130 cal. yr BP age has been disregarded for
interpolation of multiproxy data.
With the above two exclusions, sedimentation rates for the
Holocene estuarine section in Myall Lakes range between 18
Copyright ß 2005 John Wiley & Sons, Ltd.
and 32 cm kyr1, whereas in Tuggerah Lakes they are slightly
higher at between 37 and 49 cm kyr1. Both fall within the
ranges discussed above, and in addition support the more isolated location with respect to ﬂuvial detrital sediment input of
Myall Lake compared with Tuggerah Lake. Ages from the lower
parts of the sapropel facies in Myall Lake (Fig. 4) suggest initiation of this unit during the MIS 3 interstadial, whereas the upper
parts of this facies yield early Holocene dates. This chronology
implies intermittent accumulation during MIS 2, and this interpretation is supported by sedimentological evidence such as
thin oxidised layers of periodic subaerial exposure of this unit.
Analytical methods
The main factors that can cause changes in down-core sediment characteristics are: (1) changes in the nature of the
material entering the water body; (2) authigenic production
of sediment components; and (3) alteration of sediment components within the water body or after deposition. These factors
will respond on a regional basis directly, or indirectly, to
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337
Figure 6 Power spectra for autocorrelation functions from SPECTRUM for (upper left) ML11B, (upper right) ML19B, (lower left) Pelican 1 and (lower
right) Chittaway 1. The x-axis is log10 of the period (yr). Asterisked time series are plotted against the right axis; all other time series results are plotted
against the left axis. Indexed peaks are in yr
climate change; the crux of the interpretive procedure is to
identify the driving mechanism of a particular sediment parameter. Part of this process is to analyse the power spectrum
of the various data and identify common spectral peaks that
can be associated with known climate cycles.
The data sets common to both lakes are percentages of total
organic carbon (TOC), calcium carbonate and water content
and (volume) magnetic susceptibility ().
Total organic carbon–calcium carbonate
determinations
In Tuggerah Lakes, TOC and %CaCO3 were determined using
the method of Dean (1974) by % wt LOI at 550 C and 1000 C
respectively, after evaporating free interstitial water at 105 C
for 12 hours. Organic matter content was converted to organic
carbon using a multiplication factor of 0.58, the average range
of the weight fraction of carbon in dry peat and lignite (Maher,
1998). In the high resolution Myall samples, these parameters
were measured using a Rosemount Dohrmann catalytic combustion chamber in which CaCO3 was determined by difference between TOC and total carbon after the removal of
carbonate by acid digestion. TOC and carbonate data determined from LOI are also available for ML19A. The sample spacing of 10 cm does not yield useful results in the 200–2000 yr
band of interest in the frequency analysis, so these have not
been incorporated into our spectral study, but the results do
conﬁrm the downhole trends in the higher resolution ML11
data (Fig. 4).
Copyright ß 2005 John Wiley & Sons, Ltd.
Magnetic susceptibility
In three of the four cores (Pelican-1, Chittaway-1 and ML11B)
volume magnetic susceptibility was measured using a Bartington
MS2B dual-frequency sensor attached to a Bartington MS2
meter, and the low-frequency data were used for spectral analysis. Data for core ML19B were measured on a Geotek multisensor core logger using an MS2C loop attached to a Bartington
MS2 meter. All other magnetic susceptibility data were collected using a high-resolution MS2E surface scanning sensor
attached to a Bartington MS2 meter. In both of the latter cases,
the values reported are volume determinations measured at a
low frequency and are directly comparable with the low-frequency readings of the dual-frequency sensor. Values of magnetic susceptibility in both lakes are reported in cgs 106
units and are uniformly low, except where iron oxide staining
is visible in the cores. In order to conﬁrm that the downhole
magnetic susceptibility trends shown in Fig. 4 are real, we conducted multiple runs at varying sample spacings (10, 2 and
1 cm) using both high (10 second count, 0.05 cgs 106 units)
and low (1 second count, 0.5 cgs 106 units) resolution measurement settings.
In addition to the proxies in common, magnetic parameters
ARM (anhysteretic remanent magnetisation) and SIRM (saturation isothermal remanent magnetisation) were obtained for the
Tuggerah Lake cores and ML11B, whereas P-wave velocity,
density and major and trace element geochemistry were
obtained from selected Myall Lake cores, including ML19B.
Further discussion and spectral analysis is limited to the
common parameters %TOC, %CaCo and volume magnetic
susceptibility.
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Figure 7 Power spectra for the cross-correlation functions from SPECTRUM for (upper left) ML11B, (upper right) ML19B, (lower left) Pelican 1 and
(lower right) Chittaway 1 data sets. ‘Mag sus’ ¼ magnetic susceptibility. The x-axis is log10 of the period (yr). Asterisked time series are plotted against
the right axis; all other time series results are plotted against the left axis. Indexed peaks are in yr
Sediment properties (proxies) and driving
mechanisms
The organic carbon content of the sediments will be related to
the type/source of organic matter and its rate of accumulation
(both absolute and with respect to the remainder of the sediment load) and degradation. In estuaries and lakes, the organic
matter load is a combination of allochthonous organic matter
brought in by rivers and autochthonous production within the
water body. The former is dominated by more refractory terrestrial organic matter comprising material from vascular plants
that is at least partially oxidised. Conversely, autochthonous
organic matter comprises both vascular material (e.g. bottomrooted emergent plants), and more labile non-vascular (e.g.
algae) material. Mineralisation of the organic matter is accomplished through processes mediated by aerobic and anaerobic
bacteria; the efﬁcacy of mineralisation depending on the proportion of refractory to labile components and relative importance of the aerobic to anaerobic pathways (Westrich and
Berner, 1984; Hedges et al., 1988; Canﬁeld et al., 1993;
Canﬁeld, 1994; Kristensen et al., 1995; Hedges and Kiel,
1995; Hulthe et al., 1998). The relative importance of the anaerobic pathway will depend on the exposure time of the organic
matter to aerobic conditions before transport below the oxic/
anoxic boundary (redoxocline). Typically the redoxocline is
located just below the sediment–water interface, so exposure
time to aerobic conditions will relate to the water depth, rate
of burial, resuspension effects and bioturbation (Canﬁeld,
1994; Aller, 1994; Meyers and Ishiwatari, 1995; Kristensen,
2000). The carbonate content of the sediments will largely
Copyright ß 2005 John Wiley & Sons, Ltd.
reﬂect the abundance of intact and fragmentary micro- and
macrofossil shell material. Other mechanisms that could affect
the carbonate content include photosynthesis in the surface
water, which can deplete CO2 levels to the point where calcite
supersaturation occurs and calcium carbonate is precipitated
(Kelts and Hsu¨, 1978), and the post-depositional diagenetic dissolution and precipitation of carbonate minerals within the
sediment (Berner, 1980).
The quantity, particle-size and type(s) of magnetic minerals
entering the water body will determine the initial magnetic
properties of the sediments. Changes in the magnetic input
may occur through variable catchment erosion and/or changes
in the magnetic properties of catchment soils due, for example,
to ﬁre (Rummery et al., 1979) or to variations in pedogenic
intensity (Tite and Linington, 1975). Subsequent modiﬁcation
within the subaqueous sediments may occur through microbially mediated reductive diagenesis, authigenesis and biomineralisation (Stoltz et al., 1986; Canﬁeld and Berner, 1987;
Karlin et al., 1987; Karlin, 1990; Tarduno and Wilkison,
1996). Based on the ARM data, reductive diagenesis has probably modiﬁed the magnetic minerals in the Tuggerah Lakes
cores as indicated by the jump in magnetic susceptibility at a
depth of 180 cm (Fig. 4, Chittaway 1). Mineralisation of
organic matter in the anoxic sediment has led to the dissolution
and pyritisation of primary magnetic minerals and the formation of secondary magnetic minerals. This alteration potentially
obscures the primary depositional signal replacing it with a signal related to the intensity of suboxic or sulphidic diagenesis.
Consequently, the magnetic data from the Tuggerah cores provides, at least partly, a record of environmental processes that
postdate the deposition of the sediment in which that change is
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Figure 8 Autocorrelation (above) and cross-correlation (below) power spectra for magnetic susceptibility data for the cores indicated. Note that
ML19A has been included as an extended time series for ML19B. ‘P1’ ¼ Pelican 1; ‘C1’ ¼ Chittaway 1. The x-axis is log10 of the period (yr). Asterisked
time series are plotted against the right axis; double-asterisked curves are plotted against the far right scale in the upper diagram. All other time series
results are plotted against the left axis. Indexed peaks are in yr
recorded. Spectral analysis of the Tuggerah magnetic data must
therefore be viewed with caution.
Spectral analysis
We have carried out auto- and cross-correlation spectral analysis of the interpolated time series for volume magnetic susceptibility, total organic carbon and carbonate spectral data
for each of the two sites in the two lakes studied (Pelican 1,
Chittaway 1 from Tuggerah Lake; ML11A/B and ML19A/B from
Myall Lake). Temporal record length and sample spacing for
each site, and the analytical parameters these affect, are listed
in Table 1. Because of the limitations inherent in the study, the
combination of site location (which affects the type of facies
present) and the sample spacing (which controls the temporal
resolution of the data), we have only been able to investigate
spectral content in the range 200–2000 yr for the data available. We have employed two different Fourier transform
Copyright ß 2005 John Wiley & Sons, Ltd.
analytical methods, (i) the Blackman–Tukey method (BT),
undertaken using the wave analysis software package Igor
Pro# from Wavemetrics, and (ii) the Lomb–Scargle method,
using the freeware SPECTRUM package (Schultz and Stattegger,
1997). The latter method has the advantage of not requiring
evenly- (for a single time series), and evenly- and equallyspaced time data (for pairs of data sets in cross-spectral analysis). Interpolation of data to produce this condition leads to a
predictable decline in amplitude at successively higher frequencies (‘red noise’) according to Schultz and Stattegger
(1997; see inter alia this paper, and Xanthakis et al. (1995),
for discussion and comparison of various spectral analysis
methods as applied to palaeoclimate records). The results from
SPECTRUM include an estimation of the reliable frequency
range, the maximum period for which analysis identiﬁes at
least two cycles within each analytical segment of the data
set (i.e. the low-frequency limit, Tmax), and an average (because
the data are not equally spaced) Nyquist frequency (i.e. the
minimum resolution, Tmin). On the other hand, IgorPro provides considerably more control over analytical parameters,
and in particular, the smoothing algorithms which are used
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to remove high-amplitude, low-frequency spectral content,
beyond the reliable frequency range. In at least some of our
data, these are introduced because of boundary effects at the
upper and lower stratigraphic contacts of the estuarine clay
facies. In most of our data, the sedimentation rate (i.e. the thickness of the Holocene sequence) and dependent sampling frequency have resulted in time series with less than 100 data
points. This is less than ideal for the statistical estimations, particularly at levels of conﬁdence above 90%, which accompany
individual spectral analysis. We suggest, however, that the use
of the multiproxy data and four different sites, and the use of
two different analytical methods, allows us a robust crosscheck of the signiﬁcance of the results.
Our study comprised spectral analysis of (i) autocorrelated
time series for each available parameter at each site; (ii)
cross-correlation of the time series for each of the three different parameters at each coring site; and (iii) cross-correlation of
the time series of each common parameter at all sites, using
‘raw’ data in SPECTRUM. The analytical parameters, which
were common throughout, are given in Table 3. The results
are shown diagrammatically in Figs 6 to 10 which show
Table 3 Analytical parameters used in the SPECTRUM analysis of all
time series data (see Schultz and Stattegger (1997) for explanation)
Parameter
Value
OSFC
HIFAC
Segments with 50% overlap
Window type
Level of signiﬁcance
Subtract trend from data segments
Use logarithmic dB scale
Unit of time
Maximum frequency to plot
4.0
1.0
1.0
Hanning [3]
0.10 [2]
Y
N
Ka [2]
Nyquist HIFAC [1]
stacked normalised power spectra for the above combinations
of data, converted to log10 age (period) space, rather than the
more common frequency space, for ease of visual inspection.
We then carried out spectral analysis of the same data sets
using IgorPro to remove or reduce the low-frequency content
of the data beyond the 2000 yr limit. Although this operation
Figure 9 Autocorrelation (above) and cross-correlation (below) power spectra for CaCO3 data for the cores indicated. ‘P1’ ¼ Pelican 1;
‘C1’ ¼ Chittaway 1. The x-axis is log10 of the period (yr). Asterisked time series are plotted against the right axis; all other time series results are plotted
against the left axis. Indexed peaks are in yr
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341
Figure 10 Autocorrelation (above) and cross-correlation (below) power spectra for TOC data for the cores indicated. ‘P1’ ¼ Pelican 1;
‘C1’ ¼ Chittaway 1. The x-axis is log10 of the period (yr). Asterisked time series are plotted against the right axis; double-asterisked plots
in the lower diagram are plotted against the far right axis. All other time series results are plotted against the left axis. Indexed peaks
are in yr
can be carried out automatically in SPECTRUM (via the harmonics menu), IgorPro offers more control over the analysis.
Removal of low-frequency information was achieved by applying a 15-point Gaussian smoothing window to the raw data,
subtracting these smoothed values from the raw input data,
and applying a Fourier transform to the residual curve. The procedure is shown graphically for ML11B carbonate data,
together with the resulting variation in the power spectra, in
Fig. 11 and the power spectra for the autocorrelation analysis
for the time series from the remaining three cores in Fig. 12.
Modelling of ideal data sets containing up to four weighted
and unweighted sine waves with both SPECTRUM and IgorPro
has shown that the relative amplitude of spectral power peaks
is a function of both the relative amplitudes of the various frequencies in the original data (and the number of actual points
deﬁning these), as well as the combination of parameters used
for the analysis (such the number of points in the analytical segments). In order to minimise the potential effect of spectral
amplitude not being tied to peak signiﬁcance in terms of its
geological importance, we have additionally undertaken a simple frequency distribution of all unweighted spectral peaks
Copyright ß 2005 John Wiley & Sons, Ltd.
from all of the SPECTRUM-analysed data sets. The resulting frequency histogram is plotted in Fig. 13. While this procedure
weighs the data at the higher end of the frequency spectrum
more heavily than at the lower end, it still allows us to identify
the most common frequencies as peaks in various parts of the
overall 200–2000 yr range.
The standard fast Fourier transform algorithm in IgorPro
requires a minimum of between three and ﬁve cycles to be present in the raw time series, in order produce reliable determination of their recurrence period. While this limitation is
supposed to be partly reduced by the Lomb–Scargle method
(to the two cycles deﬁned by the reliable frequency range),
we have still chosen to restrict our analysis to the period range
200–2000 yr discussed above. The other potentially critical
factor which has not yet been incorporated in our analysis, is
the condition of stationarity in the time-series data. We are
aware that non-stationarity is present in the magnetic susceptibility data from Pelican-1 in Tuggerah Lake, probably because
of diagenetic alteration, and as yet it cannot be excluded from
other data sets. However, overall the procedure has still
yielded useful results.
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Figure 11 Down-core time series data for CaCO3 in ML11B showing raw, smoothed (15 point Gaussian window) and residual ( ¼ raw smoothed)
(upper panel). Lower diagram shows the power spectra of the raw (heavy line)) and the residual time series, plotted as frequency (1/period) on the xaxis. The period of the cyclicity represented by the peaks are labelled (yr) on the residual power spectral curve. The diagram shows how removal of the
low-frequency content of the time series by smoothing enhances the peaks at higher frequencies in the range being investigated (200–2000 yr). Analysis from IgorPro
Results
In our analysis of the results we are most concerned with frequencies that are common between sites and proxies, rather
than in the dominant frequencies. Inspection of the results of
the SPECTRUM analyses (Figs 6 to 10) has enabled us to identify between four and six quasi-frequency/period peaks which
are relatively consistent across the majority of our multiproxy
data sets. These are, in chronological order, at 210 yr,
250 yr, 350–370 yr, 420 yr, 500–530 yr and 1250–
1450 years. One additional, but less clearly deﬁned frequency,
at 1800 yr, shows up at the low end of the study range. In
identifying these peaks we have relied not only on the actual
position (frequency) of the peak, but also on the pattern of
the power spectra for the time series. This similarity in spectral
pattern but actual frequency mismatch is not unexpected
because of the relatively few age tie points available, and
resulting small-scale variations in sedimentation rates that
could not be accounted for. Overall, the repeatability of the
spectral patterns gives us conﬁdence that the data are real.
Interestingly, there are no clearly common or coherent frequencies in the range 530–1000 yr. A number of peaks in this
Copyright ß 2005 John Wiley & Sons, Ltd.
range probably represent local cyclicity in various individual
parameters.
The longest record available to us at the highest resolution for
all proxy data was obtained from ML11B, in the eastern part of
Myall Lake (time series range 6160 yr [1965–8125 yr]; n ¼ 118
for magnetic susceptibility and n ¼ 58 for TOC and CaCO3;
Tmin ¼ 94 yr, Tmax ¼ 2640 yr for magnetic susceptibility). Not
surprisingly, the highest coherency was obtained for auto- and
cross-correlation of the records from this core within the 200–
2000 yr analytical range. We identiﬁed strong common peaks at
all of the frequencies mentioned above from the auto- and
cross-spectra for the multiproxy time series (Figs 6 and 7), and
one additional peak at around 1000 yr which is strongly present
in the carbonate data and as a slight shoulder peak in the carbonate–magnetic susceptibility cross correlation data.
Auto- and cross-spectral analyses of the same proxy data
from the other sites (Figs 6 and 7) support the commonality of
the mid-300 yr (in the range 340–370 yr) peak, with the exception of the data from ML19B (where the record only covers the
early part of the Holocene) and the magnetic susceptibility data
from Chittaway-1 (which is affected by diagenetic alteration,
but has a slight shoulder in the mid-300 yr range). However,
a periodicity of 360 yr is subordinately present in the
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Figure 12 Left: Plots of the residual time series data from (a) ML11B, (b) ML19B, (c) Pelican 1 and (d) Chittaway 1 for each of the data sets indicated.
Magnetic susceptibility plotted against the left axis in each case, carbonate plotted against the near right axis and TOC data plotted against the far right
axis. Right: Power spectra for each of the adjacent time series, plotted with the x-axis as log10 of the period (yr). The period of the cyclicity represented
by the peaks are labelled (yr). Analysis from IgorPro
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Figure 13 Frequency distribution histograms using a class interval of 20 yr (upper) and a base 10 exponent of 0.02 (lower). In each case the curve is
the ﬁve-point moving average of all peaks appearing on the power spectra for all auto- and cross-correlation functions used in this study. Power
spectra derived from SPECTRUM using raw data
magnetic susceptibility record of ML19A which spans in excess
of 8000 yr of the Holocene. This peak is the also one of three
that are common to all residual data sets (Fig. 12).
The ML11B data contain three peaks in the 200–300 yr range
( 210, 240–260, 275–280 yr) with the 250 yr peak being the
strongest, and the only one present in all three proxy data sets.
Most data sets from other sites have one, or more commonly
two, peaks in this range, and in all cases it is the mid-200 yr
peak which is present. The exception is the TOC and CaCO3
data in Chittaway-1 where the Nyquist frequency (Tmin on
Table 1) is 271 yr.
There are indications of two or three peak periods in the
range 1000–2000 yr in most of the data sets. The most common
of these are in the ranges between 1000 and 1100 yr, and
1300–1500 yr. In both cases peaks are present at all sites in
at least one data set, although in some (e.g. a minimal shoulder
in the Pelican-1 carbonate data), they are suppressed in the BT
data from Igor analysis. The 1300–1500-yr period is strongest
in the longest time series (ML11B and ML19A), and in the carbonate and TOC cross-correlation data. It is not present in any
of the magnetic susceptibility cross-correlation, which is a
manifestation of the lowish Tmax values in Pelican and Chittaway cores (Table 1).
Discussion
The presence of periodic signals that have an intra- and interlake commonality must indicate a driving mechanism, or
Copyright ß 2005 John Wiley & Sons, Ltd.
mechanisms, with at the very least a regional expression.
Palaeoenvironmental research in the last two decades has identiﬁed variability in the Holocene climate at millennial, and
shorter, periods (for reviews see Adams et al., 1999; Chambers
et al., 1999; Overpeck and Webb, 2000). Suggested driving
mechanisms include solar cycles (periodicities of 2200,
210 (Suess cycles), 80 (Gleissberg cycles), 22 and 11
(Schwabe cycles) yr; e.g. Chambers et al., 1999; Perry and
Hsu¨, 2000) and thermohaline circulation (Dansgaard–
Oeschger (D/O) cycles; 1500 yr quasi-periodicity; e.g. Bond
et al., 1997). Periodicities of 779 yr and 206 yr in monsoon
rainfall intensity have been resolved in the 18O record
obtained from a stalagmite collected from Oman (Neff et al.,
2001) and a 770-yr periodicity is present in marine sea surface
salinity records in the South China Sea (Wang et al., 1999) and
at ODP Site 658 (Kutzbach and Guetter, 1986) where it is
attributed to Asian and African monsoon activity respectively.
North Atlantic sediments have yielded periodicities in sediment colour (a proxy for North Atlantic deep water circulation)
centred at 550 yr and 1000 yr (Chapman and Shackleton,
2000). Plant cellulose from peat deposits in northeastern China
has signiﬁcant 18O periodicity at around 207, 245, 311, 590,
820 and 1046 yr (Hong et al., 2000), while organic matter content in a Scottish lake shows a quasi-periodicity at 200–
225 yr (Battarbee et al., 2001). A compilation of peat bog studies from northwest Europe (Chambers and Blackford, 2001)
lists centennial-scale cycles with lengths of 200–210, 260,
360, 450, 520 and 800 yr. One possible explanation for the
non-obvious expression of the 1500-yr cycle is the minimal
amplitude expression of this phenomenon during interglacials,
J. Quaternary Sci., Vol. 20(4) 327–347 (2005)
HOLOCENE MULTIPROXY CYCLICITY, EASTERN AUSTRALIA
as is recorded in the GISP2 ice-core signature over the interval
550–5000 yr BP (Schulz et al., 1999), but it could also be a
manifestation of the variable frequency of Dansgaard–Oeschger cycles, that range between 1000 and 2000 yr over the Late
Pleistocene (MIS 2, 3 and 4).
Of particular interest to temperate and tropical eastern Australia is the long-term variability (and existence) of the El Nin˜o–
Southern Oscillation (ENSO) climate phenomenon. Stott et al.
(2002) have concluded from a study of Mg/Ca and 18O in the
western Paciﬁc warm pool that a ‘super’ ENSO oscillating in
phase with stadial/interstadial (i.e. D/O cycles) has operated
in the Paciﬁc region over the past 70 kyr, and a similar conclusion was reached by Moy et al. (2002) from a study of Holocene Andean lake sediments. Many workers have found that
ENSO had a reduced intensity over the period from 15 000 to
about 6 000cal. yr BP (Sandweiss et al., 1996; Clement et al.,
1999; Rittenour et al., 2000; Koutavas et al., 2002; Moy
et al., 2002). Bond et al. (2001) proposed a solar forcing
mechanism for at least the Holocene part of the North Atlantic
1500-yr cycle, although more recently Schulz and Paul (2002)
have called the existence of a 1400–1500-yr North Atlantic
cyclicity into question for the Holocene.
Although there are clearly no shortage of candidates with
which to match the periodicities obtained from the present
study, we are left with essentially uniform, massive Holocene
estuarine deposits in at least two coastal lake/lagoonal systems,
containing at least three proxies which yield common periodicities matching global or semi-global forcing factors at centennial and millennial scale (for instance, solar or deep ocean
thermohaline circulation). Whilst we are unable to prove a
direct cause and effect relationship between the variables
and the climate factors, and are unable to elucidate relationships such as coherency or lag between these at this stage,
we must speculate that global climate factors are inﬂuencing
the accumulation of one or more components of the sediment
system along the NSW coast. It may be that the common periodicities seen in our data and the proxy monsoon records,
Chinese peat cellulose accumulations and long-term ENSO
variability support the suggestion that trans-equatorial air
streams driven by the monsoon and trade winds can link the
climate of the two hemispheres (An, 2000).
Our most intriguing result is that the most consistent cyclicity
in our records, the 340–360-yr period, is present in the pollencount data from the northwest European peat bogs (Wijmstra
et al., 1984; Oliver et al., 1997), where it is attributed
by Wijmstra et al. to sun-spot cycles. Whether our data
reﬂect a local response to solar variability is uncertain,
although a link between solar variability and the strength of
ENSO impacts has been suggested for Australia and North
America (Franks, 2001).
Comparison of our data with existing Australian records is
hampered by a lack of published information on Holocene
cyclicity at millennial and centennial scales. The Holocene climate of southeast Australia has been the subject of two recent
reviews (Dodson, 1998; Schulmeister, 1999). There is a consensus on the rapid amelioration of climate between
11 500 and 8500 cal. yr BP followed by a climatic optimum,
at least in effective precipitation, between 7000 and
5000 cal. yr BP. The last 5000 yr appears more equivocal, with
Dodson (1998) inferring a cooler drier climate, but with an
increase in effective precipitation after 3000 cal. yr BP, while
Schulmeister (1999) infers a sharp reduction in effective precipitation after 5000 cal. yr BP. However, there is a dearth of published information regarding Holocene climate cyclicity for the
region. The penultimate cold period seen in the northern hemisphere ( 3100–2400 yr; e.g. O’Brien et al., 1995) coincides
with changes in peat accumulation at Barrington Tops, NSW
Copyright ß 2005 John Wiley & Sons, Ltd.
345
(Dodson, 1987), southeast Australian lake levels (Bowler and
Wasson, 1984), and a 1-m sea level fall at Port Hacking,
NSW (Baker and Haworth, 2000), although at least some of
the coastal sea level variation can be attributed to hydroisostasy. However, there needs to be a concerted effort to generate Holocene climate records from the Australian continent
that have sufﬁcient resolution and chronological control to
address inter-hemispheric climate links and the question of the
global nature of Holocene climate cyclicity (e.g. Charles et al.,
1996; Broecker, 2001). This will be the target of our future investigations of southeast Australian Holocene sediments.
Conclusions
Our data suggest it is possible to identify meaningful periodicities in down-core data sets where there are less than an ideal
number of discrete data points for frequency analysis, using a
multiproxy approach. We have demonstrated strong Holocene
global climate periodicities within our data over the analytical
range 200–2000 yr at 210 yr, 250 yr, 350–370 yr, 420 yr,
500–530 yr and 1250–1450 yr, and possibly at around
1800 yr. All of these periods have been identiﬁed in other
palaeoclimate studies of stratigraphic data where they have
manifested in both deep marine and non-marine environments
and can be attributed to variations in solar insolation or perturbations in orbital cycles brought about by feedback loops.
Our study shows that even in otherwise uniform, single
facies sediments, it is possible to measure and meaningfully
analyse down-core variation in relatively easy-to-measure physical and chemical parameters. In order to pursue the study to
decade scale resolution, and to allow us to address the statistical signiﬁcance of individual spectral analyses, we must either
seek Holocene sections in excess of 6 m thick (for bi-decadal
resolution, or undertake multiple hole coring at our current
sites. The former option is the more attractive because it does
not involve the need for detailed and accurate correlation.
Acknowledgements We would like to thank the Australian Nuclear
Science and Technology Organisation (ANSTO) through the Australian
Institute of Nuclear Science and Engineering (AINSE) granting scheme
(grants number 97/195R and 99/124) for the provision of carbon-14
dating. The research has been supported by the Australian Research
Council (Small Grant 97/311). Brian Jones and Colin Murray-Wallace
provided comments on the original manuscript.
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