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Influence of Agulhas forcing of Holocene climate change in South Africa’s southern Cape

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This paper analyses a series of high-quality continuous records from southeastern Africa to study the spatiotemporal pat-terning of Holocene hydroclimatic anomalies in the region. Results indicate dominant frequencies of variability at millen-nial time scales, and a series of anomalies broadly common to all records. Of particular interest, data from the southern Cape coast exhibit periods of wetter/drier conditions that are out of phase with the sites less than 150 km away in the adjacent interior, but in phase with sites in tropical regions over 1000 km to the northeast. To explain such spatial patterns and gradients, we propose that the Agulhas Current may be a critical vector by which tropical climatic signals are propagated along the littoral zone, exerting a dominant, highly localized influence on near-coastal environmental conditions. Limitations in the data available do not allow for a detailed examination of the climatic dynamics related to these phenomena, but this paper highlights a series of avenues for future research to clarify the spatial extent and stability of the patterns observed.
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Quaternary Research (2018), 17
Copyright © University of Washington. Published by Cambridge University Press, 2018.
doi:10.1017/qua.2018.57
Inuence of Agulhas forcing of Holocene climate change in South
Africas southern Cape
Brian M. Chase
a
*, Lynne J. Quick
b,c
a
Centre National de la Recherche Scientique, UMR 5554, Institut des Sciences de lEvolution-Montpellier, Université Montpellier, 34095 Montpellier,
Cedex 5, France
b
Department of Environmental and Geographical Science, University of Cape Town, South Lane, Upper Campus, 7701 Rondebosch, South Africa
c
Centre for Coastal Palaeoscience, Nelson Mandela University, Port Elizabeth, Eastern Cape 6031, South Africa
(RECEIVED February 23, 2018; ACCEPTED May 14, 2018)
Abstract
This paper analyses a series of high-quality continuous records from southeastern Africa to study the spatiotemporal pat-
terning of Holocene hydroclimatic anomalies in the region. Results indicate dominant frequencies of variability at millen-
nial time scales, and a series of anomalies broadly common to all records. Of particular interest, data from the southern
Cape coast exhibit periods of wetter/drier conditions that are out of phase with the sites less than 150 km away in the adja-
cent interior, but in phase with sites in tropical regions over 1000 km to the northeast. To explain such spatial patterns and
gradients, we propose that the Agulhas Current may be a critical vector by which tropical climatic signals are propagated
along the littoral zone, exerting a dominant, highly localized inuence on near-coastal environmental conditions. Limita-
tions in the data available do not allow for a detailed examination of the climatic dynamics related to these phenomena,
but this paper highlights a series of avenues for future research to clarify the spatial extent and stability of the patterns
observed.
Keywords: Southern Africa; Palaeoclimate; Holocene; Agulhas Current
INTRODUCTION
Southern African climatic variability is determined by the
inuence of two primary circulation systems: (1) the tropical
easterlies, which advect moisture to the continent from the
Indian Ocean, and (2) the southern westerlies and associated
storm track (Tyson and Preston-Whyte, 2000). Precipitation
across most of the subcontinent is related to the tropical
easterlies and falls primarily in the summer months (the
summer rainfall zone[SRZ]; sensu Chase and Meadows,
2007), when evaporation and convective potential are high-
est. In contrast, the southwestern Cape receives the bulk of its
rainfall in the winter months (the winter rainfall zone
[WRZ]), when the westerly storm track shifts equatorward.
This seasonal dynamic has been widely applied as a model to
understand and explore Quaternary climatic dynamics, with a
coeval inverse relationship being proposed wherein summer
(winter) rainfall systems are relatively more invigorated
during interglacial (glacial) periods (van Zinderen Bakker,
1976; Cockcroft et al., 1987; Chase and Meadows, 2007).
In recent years, focused efforts to test and rene this model
have shown that, while it may be applicable in broad terms
(Chase et al., 2017), there exists a much greater degree of
spatiotemporal complexity than was previously predicted.
Evidence indicates, for example, that the eastern SRZ cannot
be treated as a homogeneous region, as there exist at least two
(southern-central and northern) subregions (Chevalier and
Chase, 2015), and that climatic variability across much of the
interior is driven by the interaction between temperate and
tropical systems, rather than by either system in isolation
(Chase et al., 2017). It has also been suggested that the
inuence of the tropical easterlies has at times been a key
determinant of climatic variability not only in the SRZ, but in
parts of the modern WRZ as well (Chase et al., 2015b), and a
comparison of records from sites along the interface between
the SRZ and WRZ seem to suggest that strong dipoles may
exist over very short distances (<100 km) (Chase et al.,
2015a, 2015b).
In this paper, we apply a selection of recent data sets to
explore the spatiotemporal distribution of millennial-scale
hydroclimatic anomalies during the Holocene in the southern
*Corresponding author at: Centre National de la Recherche Scientique,
UMR 5554, Institut des Sciences de lEvolution-Montpellier, Université
Montpellier, Bat.22, CC061, Place Eugène Bataillon, 34095 Montpellier,
Cedex 5, France. E-mail address: brian.chase@um2.fr (B.M. Chase).
1
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Cape of South Africa. This region receives precipitation from
both tropical and temperate systems (in what is referred to
here as the aseasonal rainfall zone[ARZ]; cf. YRZ
denition of Chase and Meadows, 2007) and is further
inuenced by the warm Agulhas Current, which may induce
either localised precipitation (Jury et al., 1993) or may con-
tribute to the development of larger regional convective
systems (Tyson and Preston-Whyte, 2000). As such, the
southern Cape is recognised as being a climatically complex
region, and while it is currently one of the most mesic regions
in South Africa, it may also be one of the most sensitive to
change as a result of perturbations in any one of the elements
that comprise its climatic system.
SITE SELECTION
For this study, we consider sites from the central and eastern
SRZ and both the interior and coastal zones of the southern
Cape (Fig. 1). As we focus on identifying millennial-scale
hydroclimatic anomalies, we have selected only those
records that (1) are continuous, (2) have sampling intervals
that are a consistently less than 500 yr, and (3) can be related
with reasonable certainty to changes in precipitation and/or
aridity. Underpinning our analyses at the regional scale are
the northern and southern-central SRZ (N-SRZ and SC-SRZ,
respectively) summer precipitation reconstructions of Che-
valier and Chase (2015) (Fig. 2a and e). These reconstruc-
tions (1) include data from the best-resolved fossil pollen
records from eastern southern Africa, (2) analyse the data
using the CREST software (Chevalier et al., 2014) to obtain
quantied estimates of past precipitation, and (3) allow for
the identication the N-SRZ and SC-SRZ as two largely
distinct regions based on differences observed between the
records considered (see Chevalier and Chase [2015] for more
details). To explore the extent of the climatic anomalies
observed in these regional reconstructions and the inuence
of the dominant climatic systems, we consider four additional
records (Fig. 1). The rst, a δD record recovered from a
marine core off the coast from the Zambezi River mouth
(Schefuß et al., 2011), is of relatively low resolution, but as
an indicator of rainfall amount/intensity it provides informa-
tion regarding the northern extent of the patterns observed.
Along the southeastern African coastal margin, Holocene
pollen records have been recovered from Lake Eteza (Neu-
mann et al., 2010) and the Mfabeni Peatland (Finch and Hill,
2008), but the resolution of these records is too low (sampling
intervals exceed 500 yr in some portions of the records) for
the level of analysis undertaken in this study. We instead use
the δ
13
C record from the Mfabeni Peatland, which provides a
higher-resolution measure of C
3
(primarily trees and shrubs)
versus C
4
(primarily tropical drought-adapted grasses)
vegetation and has been interpreted as relating to general
changes in humidity during the Holocene (Baker et al., 2014).
While general, this index of vegetation change is similar to
the interpretive basis of the Mfabeni and Lake Eteza pollen
records, and the patterns of change observed in the records
are similar. From the southern Cape coast, the high-resolution
pollen record from Eilandvlei provides valuable insight into
regional hydroclimatic conditions, with changes in afrotempe-
rate taxa being strongly linked to changes in humidity (Quick
et al., 2018). Inland of Eilandvlei, 130 km to the northwest in
the Groot Swartberg mountains, rock hyrax middens from
Seweweekspoort have provided a detailed δ
15
Nrecord,
reecting changes in hydroclimate over the last 22,000yr
(Chase et al., 2013, 2017). While other records do exist from
this region of southern Africasuch as those recovered from
Groenvlei (Martin, 1968) and Rietvlei-Stillbaai (Quick et al.,
2015)and results do share similarities with the Eilandvlei
record (see Quick et al., 2018), their continuity, resolution,
chronologic control, and/or signicance in terms of hydrocli-
matic variability limit their suitability for this study (see Deacon
and Lancaster [1988], Chase and Meadows [2007], and Scott
et al. [2012] for further information).
18
18
20
20
22
24
26
16
12
16
18
12
WRZ
ARZ
SRZ
RI
TW
WK
TV
MF
EV
ZB
FL
SW
BL
EQ
BR ET
10°E 15°E 20°E 25°E 30°E 35°E 40°E
45°S
40°S
35°S
30°S
25°S
20°S
15°S
A
g
u
l
h
a
s
C
u
r
r
e
n
t
Figure 1. Map of southern Africa showing sea-surface temperature
isolines (°C), the extent of the southern African winter rainfall zone
(WRZ), aseasonal rainfall zone (ARZ), and summer rainfall zone
(SRZ) (sensu Chase and Meadows, 2007), and the location of the
sites considered in this study. They are: the palaeoenvironmental
sites used for the reconstruction (Chevalier and Chase, 2015) of
northern summer rainfall zone climates (Tate Vondo [TV; Scott,
1987a], Wonderkrater [WK; Scott, 1982], Tswaing Crater [TW;
Scott, 1999; Metwally et al., 2014], and Rietvlei [RI; Scott and
Vogel, 1983]); southern-central summer rainfall zone climates
(Braamhoek [BR; Norström et al., 2009], Florisbad [FL; Scott and
Nyakale, 2002], Equus Cave [EQ; Scott, 1987b], and Blydefontein
[BL; Scott et al., 2005] according to Chevalier and Chase [2015]);
the GeoB9307-3 marine core (ZB; Schefuß et al., 2011); Mfabeni
Peatland (MF; Baker et al., 2014); Lake Eteza (ET; Neumann et al.,
2010); Eilandvlei (EV; Quick et al., 2018); and Seweweekspoort
(SW; Chase et al., 2017). Sites are colour coded to reect
similarities in climatic variability phasing, and regions (as dened
by these ndings) are described by shaded areas. (For interpretation
of the references to color in this gure legend, the reader is referred
to the web version of this article.)
2B.M. Chase and L.J. Quick
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0
Age (cal ka BP)
25810134679
0
Age (cal ka BP)
25810134679
Seweweekspoort
composite δ15N (‰)
2
1
0
3
4
5
Frequency (years)
1600
400
100
200
(f)
800
6.75-6.75
SC-SRZ PWetQ
(detrended, normalised mm)
-2
0
1
-1
Frequency (years)
1600
400
100
200
(e)
800
4.5-4.5
Eilandvlei afrotemperate forest
pollen (%)
4
8
12
16
Frequency (years)
1600
400
100
200
(d)
800
7.6-6.6
-1
Mfabeni δ13C (‰, normalised)
0
1
Frequency (years)
1600
400
100
200
(c)
800
4.5-4.5
-1
Zambezi Basin δD
(‰, detrended, normalised)
0
2
1
Frequency (years)
1600
400
100
200
(b)
800
2.75-2.75
N-SRZ PWetQ
(detrended, normalised mm)
-2
0
1
-1
Frequency (years)
1600
400
100
200
(a)
800
4-4.5
2
Frequency (years)
1600
400
100
200
(a)
800
3.7-6.3
Frequency (years)
1600
400
100
200
(b)
800
2.7-7.3
Frequency (years)
1600
400
100
200
(c)
800
4.3-5.7
Frequency (years)
1600
400
100
200
(d)
800
5.7-4.5
Frequency (years)
1600
400
100
200
(e)
800
4.4-5.7
Frequency (years)
1600
400
100
200
(f)
800
5.5-4.5
1
Figure 2. (color online) Comparison of the records considered for this study: (a) the northern summer rainfall zone (N-SRZ) and (e)
southern-central summer rainfall zone (SC-SRZ) summer precipitation stacks (Chevalier and Chase, 2015), (b) the δD record from the
GeoB9307-3 marine core (Schefuß et al., 2011), (c) the δ
13
C record from the Mfabeni Peatland (Baker et al., 2014), (d) the Eilandvlei
afrotemperate forest pollen record (Quick et al., 2018), and (f) the Seweweekspoort δ
15
N composite record (Chase et al., 2017). Each
record has been analysed using continuous Morlet wavelet transforms. Panel 1 shows the local wavelet power spectrum for each record,
with black lines indicating the cone of inuence to show where boundary effects are present and the regions of greater than 95%
condence using a white-noise model. Panel 2 highlights the real-value signal power at different time scales. In this paper, we are
considering the common millennial-scale variability identied at >1600 yr frequencies, which highlights an antiphase relationship between
tropical and coastal sites (panels ad) and those from the interior (panels e and f). Each record has been oriented according to
interpretations of aridity, with wetterconditions towards the top of the graph and with higher real-value signal power.
Inuence of Agulhas forcing of Holocene climate change in South Africas southern Cape 3
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DEFINING MILLENNIAL-SCALE CLIMATIC
VARIABILITY IN THE STUDY REGION
As we are concerned here with the mechanistic relationships
between sites/regions, we focus primarily on the direction
and timing of change rather than amplitude. To highlight this
clearly, we have removed low-frequency multimillennial/
orbital-scale trends (cubic polynomial) from the SRZ stacks
and the Zambezi Basin record, as they are dominated by a
signal linked to direct insolation forcing during the Holocene
(Schefuß et al., 2011; Chevalier and Chase, 2015). For this
study, we have also removed the pollen records from the
coastal sites of Lake Eteza and the Mfabeni Peatland from the
SC-SRZ stack, as dened by Chevalier and Chase (2015), to
more clearly differentiate between coastal and interior sig-
nals. Chronologies for all records presented were established
by the original authors using Bacon (Blaauw and Christen,
2011) and the SHCal13 (Hogg et al., 2013) or Marine13
(Reimer et al., 2013) calibration data. We have updated the
Mfabeni Peatland and Zambezi Basin records using these
same calibration data to ensure comparability.
To identify patterns of millennial-scale climatic variability
within the Holocene, we have used continuous Morlet wavelet
transforms (Torrence and Compo, 1998) (Fig. 2). Before
analysis, each record was linearly interpolated to a common
100 yr resolution for analytical purposes, but the differing
sampling resolutions limit the scope of robust comparisons
to lower, millennial-scale frequencies. While the variable
sampling resolutions result in the appearance of signicant
bands at different frequencies, we focus here on the common
bands of high signicance in the 1600 to 2400yr frequencies
to distil millennial-scale variability (Fig. 2, panel 1).
Real-value wavelets show positive or negative oscillations in
the data, and strength of the anomalies at these frequencies
(Fig. 2, panel 2). These results indicate that common cycles of
variability are identiable in records from across the study
region, and anomalies can be seen to manifest between
approximately 01.2 cal ka BP, 1.23 cal ka BP, 35.2 cal ka
BP, 5.27.2 cal ka BP, and 7.29.3 cal ka BP. These signals
have been isolated in Figure 3, which plots the average signal
strength and sign for the 1600 to 2400yr frequencies for each
record across the Holocene.
DISCUSSION
When considered together, records from the study region
indicate a strong antiphase relationship between the N-SRZ
and the SC-SRZ over millennial time scales (Figs. 2a and e,
and 3), and the pattern exhibited in the SC-SRZ extends well
into the ARZ. It has been proposed that this latter phenom-
enon may be determined by the interaction between tempe-
rate and tropical systems to create composite synoptic
systems such as tropicaltemperate troughs (Chase et al.,
2017).
Of particular interest is the strong dipole that has been
revealed to exist within the ARZ between Eilandvlei (Quick
et al., 2018) on the southern Cape coast and Seweweekspoort
(Chase et al., 2013, 2017) (Fig. 2). Considering their position
and proximity, it would be expected that they share similar
climatic histories. Instead, for most of the Holocene, the
progression of hydroclimatic anomalies are strongly opposed
between the sites. The differences between these sites are
unlikely to be related to Seweweekspoorts position closer to
the WRZ, as a similarly antiphase relationship can be
observed between the Eilandvlei record and the SC-SRZ
stack (Figs. 2 and 3).
We propose that the similarities in phasing between
Eilandvlei and the N-SRZ are the result of the transport of
warm waters along the east coast via the Agulhas Current,
which, by modifying the surface heat ux and the onshore ow
of moist air (Jury et al., 1993, 1997), effectively propagates a
tropical climate signal along its zone of inuence. As sug-
gested earlier, the inuence of this vector is apparently both
strong and highly localized. While its resolution precludes it
from the methods of analysis employed here, analyses of the
Lake Eteza pollen record indicate distinct similarities with the
Eilandvlei data, supporting this nding (Fig. 4).
The consideration of the interior-coastal dipole may thus
be critical when either (1) extrapolating results from coastal
sites to understand broader palaeoenvironmental conditions
across the subcontinent or (2) drawing on data from non-
coastal sites to establish a context for the rich archaeological
sites of the southern Cape coastal region (Klein, 1975; Hen-
shilwood et al., 2002; Marean, 2010). However, at this stage,
the observation of this phenomenon is restricted to those
few records of sufcient resolution and palaeoclimatic
0
Age (cal ka BP)
25810134679
Tropical and coastal signal strength
(average of 1600-2400 yr frequencies)
0
1
2
-1
-2
N-SRZ
Zambezi
Mfabeni
Eilandvlei
r2=0.923
r2=0.870
r2=0.782
r2=0.625
(a)
Interior and temperate signal strength
(average of 1600-2400 yr frequencies)
0
1
2
-1
-2
SC-SRZ
Seweweekspoort
(b)
Figure 3. (color online) Comparison of millennial-scale signals
(16002400 yr frequencies) from (a) the northern summer rainfall
zone (N-SRZ; Chevalier and Chase, 2015), Zambezi Basin
(Schefuß et al., 2011), Mfabeni Peatland (Baker et al., 2014), and
Eilandvlei (Quick et al., 2018); and (b) the southern-central
summer rainfall zone (SC-SRZ; Chevalier and Chase, 2015) and
Seweweekspoort (Chase et al., 2017). In panel a, correlations are
calculated relative to the N-SRZ signal, which is considered to be
most representative of tropical variability in the region.
4B.M. Chase and L.J. Quick
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signicance that have been recovered from the southern Cape
coastal region. Thus, several key questions await the recov-
ery of suitable records:
1. What is the spatial extent of the dominant Agulhas
inuence? Similarities between records from Mfabeni
(Baker et al., 2014) and Eilandvlei (Quick et al., 2018)
(Figs. 2, 3, and 4) may indicate that the Agulhas has a
strong inuence along the whole of the southeastern
South African coast, but conrmation will require the
recovery of further records from the region between
these sites. Further, it may be predicted that the signal
observed at Eilandvlei will diminish to the west of
Eilandvlei, towards the zone of Agulhas Current retro-
ection and the cooler waters of the Benguela Current
(Lutjeharms and Van Ballegooyen, 1988; Jury et al.,
1993), but better-resolved records from the southwestern
Cape coast will be required to test this hypothesis.
2. Is the dominance of the Agulhas Current restricted to
specic climate states? Even within the Holocene there
are some indications that the localized inuence of the
Agulhas Current and the establishment of the coastal-
interior dipole may be restricted to specic global
boundary conditions. As an example, the strong relation-
ship between the Eilandvlei and N-SRZ records at
millennial time scales appears to break down over the
last 2000 yr (Fig. 3). Recent work has shown that the
dominant drivers of millennial-scale climate change
across the interior may have changed signicantly as
global climates evolved from glacial to interglacial states
(Chase et al., 2017). Considering changing spatial
relationships in the earliest Holocene and the last
millennium (Fig. 2), it may be that the coastal-interior
dipole did not exist during the last glacial period, and it
may not exist in the future. Here again, more records
from the region are required to study these possibilities.
3. How might changes in sea-surface temperatures versus
changes in the position, strength, and/or extent of
Agulhas Current ow combine or counteract each other
to modulate the degree of Agulhas inuence on
terrestrial environments? To some degree, a positive
relationship exists between the temperature of the
Agulhas Current and the strength and extent of its ow
along the southern Cape coast. During glacial periods,
the source regions for the Agulhas Current were cooler
(Bard et al., 1997; Sonzogni et al., 1998; Caley et al.,
2011) and the westward ow of the Agulhas may have
been restricted as the subtropical front shifted equator-
ward (Rau et al., 2002; Peeters et al., 2004; Bard and
Rickaby, 2009). At ner spatiotemporal scales, however,
the relationship between temperature and ow, and the
inuence on the climates of the subcontinent may be
signicantly more complex (Cohen and Tyson, 1995),
and it remains to be seen to what extent changes in the
Agulhas Currents sea-surface temperatures may be
applied as a proxy for coastal-zone humidity during
periods not covered by the available records. To date, no
sea-surface temperature records of sufcient resolution
have been recovered from the region to adequately
explore these dynamics.
CONCLUSIONS
Recent data from South Africa highlight the existence of a
strong dipole in hydroclimatic conditions between interior
and coastal regions of the southern Cape during the Holo-
cene. The coastal signal appears to be highly localized, and
observations of its spatial extent suggest that the Agulhas
Current is a strong determinant of Holocene coastal climatic
variability, operating to propagate climate change signals
from the tropics to the southern Cape coast. Consideration of
this mechanism is critical for understanding the extent to
which data from interior or coastal sites may be extrapolated
to understand or predict change in other regions of the sub-
continent. Research targeting coastal and marine sites with
the goal of obtaining high-resolution hydroclimatic and sea-
surface temperature records extending into the last glacial
period will allow for a clearer understanding of the stability
and dynamics of the relationship observed during the Holo-
cene. This is ISEM contribution no. 2018-112.
ACKNOWLEDGMENTS
This study was funded in part by the European Research Council
under the European Unions Seventh Framework Programme (FP7/
2007-2013)/ERC Starting Grant HYRAX, grant agreement no.
258657, and by the German Federal Ministry of Education and
Research through the collaborative project Regional Archives for
Integrated Investigations, which is embedded in the international
research program Science Partnership for the Assessment of Com-
plex Earth System Processes. We would like to thank Nicholas
Lancaster, Tyler Faith, and Claude Hillaire-Marcel for their thought-
provoking comments.
REFERENCES
Baker, A., Routh, J., Blaauw, M., Roychoudhury, A.N., 2014.
Geochemical records of palaeoenvironmental controls on peat
Eilandvlei afrotemperate forest
pollen (%)
4
8
12
16
Lake Eteza PCA2
4
2
0
-2
-4
0
Age (cal ka BP)
25810134679
Lake Eteza PCA1
4
2
0
2
4
Figure 4. (color online) Comparison of Eilandvlei afrotemperate
pollen percentages (Quick et al., 2018) with PCA1 and PCA2
from the Lake Eteza pollen record (Neumann et al., 2010). Each
record has been oriented according to interpretations of aridity,
with wetterconditions towards the top of the graph.
Inuence of Agulhas forcing of Holocene climate change in South Africas southern Cape 5
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forming processes in the Mfabeni peatland, Kwazulu Natal, South
Africa since the late Pleistocene. Palaeogeography, Palaeocli-
matology, Palaeoecology 395, 95106.
Bard, E., Rickaby, R.E.M., 2009. Migration of the subtropical front
as a modulator of glacial climate. Nature 460, 380383.
Bard, E., Rostek, F., Sonzogni, C., 1997. Interhemispheric
synchrony of the last deglaciation inferred from alkenone
palaeothermometry. Nature 385, 707710.
Blaauw, M., Christen, J.A., 2011. Flexible paleoclimate age-depth
models using an autoregressive gamma process. Bayesian
Analysis 6, 457474.
Caley, T., Kim, J.H., Malaizé, B., Giraudeau, J., Laepple, T.,
Caillon, N., Charlier, K., et al., 2011. High-latitude obliquity as a
dominant forcing in the Agulhas current system. Climates of the
Past 7, 12851296.
Chase, B.M., Boom, A., Carr, A.S., Carré, M., Chevalier, M.,
Meadows, M.E., Pedro, J.B., Stager, J.C., Reimer, P.J., 2015a.
Evolving southwest African response to abrupt deglacial North
Atlantic climate change events. Quaternary Science Reviews 121,
132136.
Chase, B.M., Boom, A., Carr, A.S., Meadows, M.E., Reimer, P.J.,
2013. Holocene climate change in southernmost South Africa:
rock hyrax middens record shifts in the southern westerlies.
Quaternary Science Reviews 82, 199205.
Chase, B.M., Chevalier, M., Boom, A., Carr, A.S., 2017. The
dynamic relationship between temperate and tropical circulation
systems across South Africa since the last glacial maximum.
Quaternary Science Reviews 174, 5462.
Chase, B.M., Lim, S., Chevalier, M., Boom, A., Carr, A.S.,
Meadows, M.E., Reimer, P.J., 2015b. Inuence of tropical
easterlies in southern Africas winter rainfall zone during the
Holocene. Quaternary Science Reviews 107, 138148.
Chase, B.M., Meadows, M.E., 2007. Late Quaternary dynamics of
southern Africas winter rainfall zone. Earth-Science Reviews 84,
103138.
Chevalier, M., Chase, B.M., 2015. Southeast African records reveal
a coherent shift from high- to low-latitude forcing mechanisms
along the east African margin across last glacialinterglacial
transition. Quaternary Science Reviews 125, 117130.
Chevalier, M., Cheddadi, R., Chase, B.M., 2014. CREST (Climate
REconstruction SofTware): a probability density function (pdf)-
based quantitative climate reconstruction method. Climates of the
Past 10, 20812098.
Cockcroft, M.J., Wilkinson, M.J., Tyson, P.D., 1987. The applica-
tion of a present-day climatic model to the late Quaternary in
southern Africa. Climatic Change 10, 161181.
Cohen, A.L., Tyson, P.D., 1995. Sea surface temperature uctuations
during the Holocene off the south coast of Africa: implications for
terrestrial climate and rainfall. Holocene 5, 304312.
Deacon, J., Lancaster, N., 1988. Late Quaternary palaeoenviron-
ments of southern Africa. Clarendon Press, Oxford.
Finch, J.M., Hill, T.R., 2008. A late Quaternary pollen sequence
from Mfabeni Peatland, South Africa: reconstructing forest
history in Maputaland. Quaternary Research 70, 442450.
Henshilwood, C.S., dErrico, F., Yates, R., Jacobs, Z., Tribolo, C.,
Duller, G.A.T., Mercier, N., et al., 2002. Emergence of modern
human behavior: Middle Stone Age engravings from
South Africa. Science 295, 12781280.
Hogg, A.G., Hua, Q., Blackwell, P.G., Niu, M., Buck, C.E.,
Guilderson, T.P., Heaton, T.J., et al., 2013. SHCal13 Southern
Hemisphere Calibration, 050,000 Years cal BP. Radiocarbon
55, 18891903.
Jury, M., Rouault, M., Weeks, S., Schormann, M., 1997. Atmo-
spheric boundary layer uxes and structure across a land-sea
transition zone in southeastern Africa. Boundary-Layer Meteor-
ology 83, 311330.
Jury, M.R., Valentine, H.R., Lutjeharms, J.R.E., 1993. Inuence of
the Agulhas Current on summer rainfall along the southeast coast
of South Africa. Journal of Applied Meteorology 32, 12821287.
Klein, R.G., 1975. Middle Stone Age mananimal relationships in
southern Africa: evidence from Die Kelders and Klasies
River mouth. Science 190, 265267.
Lutjeharms, J.R.E., Van Ballegooyen, R.C., 1988. The retroection
oft the Agulhas Current. Journal of Physical Oceanography 18,
15701583.
Marean, C.W., 2010. Pinnacle Point Cave 13B (Western Cape
Province, South Africa) in context: the Cape Floral kingdom,
shellsh, and modern human origins. Journal of Human
Evolution 59, 425443.
Martin, A.R.H., 1968. Pollen analysis of Groenvlei Lake sediments,
Knysna (South Africa). Review of Palaeobotany and Palynology
7, 107144.
Metwally, A.A., Scott, L., Neumann,F.H.,Bamford,M.K.,Oberhän-
sli, H., 2014. Holocene palynology and palaeoenvironments in the
Savanna Biome at Tswaing Crater, central South Africa. Palaeo-
geography, Palaeoclimatology, Palaeoecology 402, 125135.
Neumann, F.H., Scott, L., Bousman, C.B., van As, L., 2010.
A Holocene sequence of vegetation change at Lake Eteza, coastal
KwaZulu-Natal, South Africa. Review of Palaeobotany and
Palynology 162, 3953.
Norström, E., Scott, L., Partridge, T.C., Risberg, J., Holmgren, K.,
2009. Reconstruction of environmental and climate changes at
Braamhoek wetland, eastern escarpment South Africa, during the
last 16,000 years with emphasis on the PleistoceneHolocene
transition. Palaeogeography, Palaeoclimatology, Palaeoecology
271, 240258.
Peeters, F.J.C., Acheson, R., Brummer, G.-J.A., de Ruijter, W.P.M.,
Schneider, R.R., Ganssen, G.M., Ufkes, E., Kroon, D., 2004.
Vigorous exchange between the Indian and Atlantic Oceans at the
end of the past ve glacial periods. Nature 430, 661665.
Quick, L.J., Carr, A.S., Meadows, M.E., Boom, A., Bateman, M.D.,
Roberts, D.L., Reimer, P.J., Chase, B.M., 2015. A late
PleistoceneHolocene multi-proxy record of palaeoenvironmen-
tal change from Still Bay, southern Cape Coast, South Africa.
Journal of Quaternary Science 30, 870885.
Quick, L.J., Chase, B.M., Wündsch, M., Kirsten, K.L., Chevalier,
M., Mäusbacher, R., Meadows, M.E., Haberzettl, T., 2018.
A highresolution record of Holocene climate and vegetation
dynamics from the southern Cape coast of South Africa: pollen
and microcharcoal evidence from Eilandvlei. Journal of Qua-
ternary Science (in press). https://doi.org/10.1002/jqs.3028.
Rau, A.J., Rogers, J., Lutjeharms, J.R.E., Giraudeau, J., Lee-Thorp,
J.A., Chen, M.-T., Waelbroeck, C., 2002. A 450-kyr record of
hydrological conditions on the western Agulhas Bank Slope,
south of Africa. Marine Geology 180, 183201.
Reimer, P.J., Bard, E., Bayliss, A., Beck, J.W., Blackwell, P.G.,
Bronk Ramsey, C., Grootes, P.M., et al., 2013. IntCal13 and
Marine13 radiocarbon age calibration curves 050,000 years cal
BP. Radiocarbon 55, 18691887.
Schefuß, E., Kuhlmann, H., Mollenhauer, G., Prange, M., Patzold,
J., 2011. Forcing of wet phases in southeast Africa over the past
17,000 years. Nature 480, 509512.
Scott, L., 1982. A late Quaternary pollen record from the Transvaal
bushveld, South Africa. Quaternary Research 17, 339370.
6B.M. Chase and L.J. Quick
https://www.cambridge.org/core/terms. https://doi.org/10.1017/qua.2018.57
Downloaded from https://www.cambridge.org/core. Port Elizabeth University, on 15 Aug 2018 at 07:54:55, subject to the Cambridge Core terms of use, available at
Scott, L., 1987a. Late Quaternary forest history in Venda,
Southern Africa. Review of Palaeobotany and Palynology 53,
110.
Scott, L., 1987b. Pollen analysis of hyena coprolites and sediments
from Equus Cave, Taung, southern Kalahari (South Africa).
Quaternary Research 28, 144156.
Scott, L., 1999. Vegetation history and climate in the Savanna
biome South Africa since 190,000 ka: a comparison of pollen data
from the Tswaing Crater (the Pretoria Saltpan) and Wonderkrater.
Quaternary International 5758, 215223.
Scott, L., Bousman, C.B., Nyakale, M., 2005. Holocene pollen from
swamp, cave and hyrax dung deposits at Blydefontein (Kikvors-
berge), Karoo, South Africa. Quaternary International 129,
4959.
Scott, L., Neumann, F.H., Brook, G.A., Bousman, C.B., Norström,
E., Metwally, A.A., 2012. Terrestrial fossil-pollen evidence
of climate change during the last 26 thousand years in
southern Africa. Quaternary Science Reviews 32, 100118.
Scott, L., Nyakale, M., 2002. Pollen indications of Holocene
palaeoenvironments at Florisbad spring in the central Free State,
South Africa. Holocene 12, 497503.
Scott, L., Vogel, J.C., 1983. Late Quaternary pollen prole from the
Transvaal Highveld, South Africa. South African Journal of
Science 79, 266272.
Sonzogni, C., Bard, E., Rostek, F., 1998. Tropical sea-surface
temperatures during the last glacial period: a view based on
alkenones in Indian Ocean sediments. Quaternary Science
Reviews 17, 11851201.
Torrence, C., Compo, G.P., 1998. A practical guide to wavelet
analysis. Bulletin of the American Meteorological Society 79,
6178.
Tyson, P.D., Preston-Whyte, R.A., 2000. The weather and climate
of southern Africa. Oxford University Press, Cape Town.
van Zinderen Bakker, E.M., 1976. The evolution of late Quaternary
paleoclimates of Southern Africa. Palaeoecology of Africa 9,
160202.
Inuence of Agulhas forcing of Holocene climate change in South Africas southern Cape 7
https://www.cambridge.org/core/terms. https://doi.org/10.1017/qua.2018.57
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... Further integrative works i.e., Chase and Meadows (2007), Chase et al. (2013), Chase et al. (2020) and Chase and Quick (2018), have sought to summarize the Quaternary variability in both ocean and atmospheric circulation systems and their impact on southern African climate. Long-term macro-scale climatic influences include a variety of forcing mechanisms e.g., precession or extent of Atlantic sea ice (Berger and Loutre, 1991;Street-Perrott and Perrott, 1993;Nielsen et al., 2004;Fischer et al., 2007;Chase et al., 2013). ...
... Long-term macro-scale climatic influences include a variety of forcing mechanisms e.g., precession or extent of Atlantic sea ice (Berger and Loutre, 1991;Street-Perrott and Perrott, 1993;Nielsen et al., 2004;Fischer et al., 2007;Chase et al., 2013). Recently, Chase and Quick (2018) argued that in contrast to the adjacent interior, the primary driver of climatic change in the southern coastal zone, was the localised coastal influence of the Agulhas Current. Subsequently, Chase et al. (2020) presented further evidence for a coastal-continental interior Fig. 1. A. Vegetation types with numbers 1 to 6 indicating the locations of modern surface pollen samples (see Supplementary Material 1) location of the KMR site (rectangle covers B). ...
... Indeed, the increase in succulent pollen at KMR is consistent with reduced moisture availability (i. e. aridity) associated with such a temperature increase, as might be the reduced palatability/availability (for hyraxes) of (C 4 ) grasses (Chase et al., 2020).Considering regional climatic drivers, the KMR sequence can be viewed in terms of the hypothesis of Chase and Quick (2018), which emphasises the role of the warm Agulhas current in driving climatic variability in the southern coastal region, in direct contrast to drivers and trends in the relatively nearby southern interior areas. The Seweweekspoort record c. 80 km from the coast (Chase et al., 2017;Chase and Quick, 2018) provided evidence to support this hypothesis, while the Baviaanskloof record, if differing in detail, provides some further support for this coastal-interior dichotomy. ...
Article
To address long-standing questions concerning Southern Hemisphere climate dynamics and palaeoecological change in southern Africa, a Late Glacial-Holocene alluvial sediment sequence from the relatively dry interior year-round rainfall zone in South Africa was investigated. The study site borders the Fynbos biome and Succulent Karoo biome ecotone, and comprises a rare stratified sequence of sandy and organic-rich silt deposits, shown to span the last 14,000 years. A high resolution multi-proxy record of ecological change was derived using pollen, phytoliths and organic geochemical analyses. For the period 14–11 ka, significant valley aggradation occurred under relatively drier conditions, followed, during the early and middle Holocene, by alternating phases of humid and dry events with higher stream energy, slower accumulation or subtle seasonality changes. A transition from relatively humid to more arid conditions at 4–3 ka is identified and is consistent in timing with several interior year-round rainfall zone records. Results revealed alternations of fynbos and karroid elements and C3/C4 grasses throughout the last fourteen thousand years, but did not suggest large-scale biome shifts. The record joins a growing number of sites contributing to debate over the complex atmospheric-oceanic drivers of palaeoclimate in this region. These data broadly fit to the regional pattern for the southernmost interior of South Africa in showing alternating influences from the westerly winter rain systems in the early Holocene, with a greater contribution from subtropical summer rain system during the middle and later Holocene.
... Most of those studies use rather discontinuous sediment records, leading to a contrasting interpretations of South Africa's hydrological evolution during the Late Quaternary; interpretations further complicated by the use of various indirect paleohydrological proxies (e.g. Chase and Meadows, 2007;Chase and Quick, 2018;Cockcroft et al., 1987;Reinwarth et al., 2013;Singarayer and Burrough, 2015;Wündsch et al., 2016;Zhao et al., 2016). ...
... Seweweekspoort , might be independent. Thus, these new data add further weight to the proposed steep climate response gradient between coastal and uplands sites in the southern Cape region (Chase et al., 2020;Chase and Quick, 2018). However, to provide more detailed information about those landsea interactions, there is a need for more continuous highresolution quantitative sea-surface and terrestrial temperatures at South Africa's southern Cape coast. ...
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The Late Quaternary climate history of South Africa and, in particular, potential changes in atmospheric circulation have been subject to considerable debate. To some extent, this is due to a scarcity of natural archives, and on the other hand the available indirect hydrological proxies are not suited to distinguishing between precipitation originating from temperate Westerlies and tropical Easterlies. This study presents a paleoenvironmental record from Vankervelsvlei, a wetland located on the southern Cape coast in the year-round rainfall zone of South Africa. A 15 m long sediment record was retrieved from this site and analysed using a multi-proxy approach. This includes, for the first time in this region, analysis of both compound-specific δ²H and δ¹⁸O from leaf wax-derived n-alkanes and hemicellulose-derived sugars, respectively, to investigate hydrological changes during the Late Quaternary. Our data suggest the driest conditions of the past ∼250 ka likely occurred from MIS 6 to MIS 5e, which still caused sediment deposition at Vankervelsvlei, and MIS 2, during which time there was an absence of sedimentation. Moist conditions occurred from MIS 5e to 5a and during parts of MIS 3, while drier conditions prevailed between MIS 5a and early MIS 3 and at the transition from MIS 3 to MIS 2. Besides changes in the amount and proportional contribution of precipitation contributions from Westerlies during glacial and Easterlies during interglacial periods, relative sea-level change affected the continentality of Vankervelsvlei, with a distinct impact on the sites hydrological balance. High-resolution analyses of the Middle- and Late-Holocene parts of the record show moist conditions and increased Easterly/locally-derived summer precipitation contributions from 7230 ⁺¹⁶⁰/−210 to 4890 ⁺²⁸⁰/−180 cal BP and after 2840 ⁺³⁵⁰/−330 cal BP. Dry conditions, accompanied by the reduction of Easterly/locally-derived summer rainfall and increased seasonality occurred from 4890 ⁺²⁸⁰/−180 to 2840 ⁺³⁵⁰/−330 cal BP. Our findings highlight that source and seasonality of precipitation play a major role in the hydrological balance of the southern Cape coastal region. By comparing the Vankervelsvlei record to other regional studies, we infer a coherent trend in the overall moisture evolution along South Africa's southern Cape coast during the Late Quaternary.
... CC BY 4.0 License. 2012;2019), mammal bone assemblages (Klein, 1983;Avery, 1982;Faith, 2013;Cruz-Uribe, 2016, 2000;Nel and Henshilwood, 2016;Nel et al., 2018;Forrest et al., 2018), microwear patterns and stable isotopes of fossil teeth (Copeland et al., 2016;Sealy et al., 2016;Hodgkins et al., 2020;Williams et al., 2020), charcoal (Cartwright and 35 Parkington, 1997;Cowling et al., 1999;Cartwright, 2013;Parkington et al., 2000), phytoliths (Esteban et al., 2018; and pollen (Meadows and Sudgen, 1991;Chase and Meadows, 2007;Scott and Woodborne, 2007a;2007b;Meadows et al., 2010;Quick et al., 2011;Valsecchi et al., 2013;Chase and Quick, 2018;Scott and Neumann, 2018). The list is by no means comprehensive. ...
... CC BY 4.0 License. the south coast is contributed by cut-off-lows (16% of annual rainfall), ridging high pressure systems (46%) and tropicaltemperate troughs (28%). In addition, the Agulhas Current would have influenced the coastal area propagating climate signals 100 from the tropics to the southern Cape coast (Chase and Quick, 2018). ...
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The flora of the Greater Cape Floristic Region (GCFR) of South Africa is a biodiversity hotspot of global significance, and its archaeological record has contributed substantially to the understanding of modern human origins. For both reasons, the climate and vegetation history of south-western South Africa is of interest to numerous fields. Currently known paleo-environmental records cover the Holocene, the last glacial-interglacial transition and parts of the last glaciation but do not encompass a full glacial-interglacial cycle. To obtain a continuous vegetation record of the last Pleistocene glacial-interglacial cycles, we studied pollen, spores and micro-charcoal of deep-sea sediments from IODP Site U1479 retrieved from SW of Cape Town. We compare our palynological results of the Pleistocene with previously published results of Pliocene material from the same site. We find that the vegetation of the GCFR, in particular Fynbos and Afrotemperate forest, respond to precessional forcing of climate. The micro-charcoal record confirms the importance of fires in the Fynbos vegetation. Ericaceae-rich and Asteraceae-rich types of Fynbos could extend on the western part of the Palaeo-Agulhas Plain (PAP), which emerged during periods of low sea-level of the Pleistocene.
... Despite the challenges of conducting Quaternary paleoenvironmental studies in arid-semi-arid areas (see Chase and Meadows, 2007), considerable progress has been made over the last decade in terms of the generation of high-resolution palaeoclimatic records for the southwestern and southern Cape regions (e.g., Neumann et al., 2011;Stager et al., 2012;Chase et al., 2013Chase et al., , 2015aChase et al., , 2019aChase et al., , 2020Valsecchi et al., 2013;Quick et al., 2018;Wündsch et al., 2018;Kirsten et al., 2020). This emerging regional data set is enabling a more refined understanding of the spatial and temporal complexity of climate and vegetation responses to a range of forcing mechanisms and suggests that substantial variability in inferred climatic trends/trajectories occurs across relatively short distances (e.g., Chase et al., 2015aChase et al., , 2017Chase et al., , 2020Chase and Quick, 2018). Even though more-and indeed more detailed-records are now available, most of these records only cover the Holocene (11.7-0 cal ka BP) or portions thereof. ...
... However, when considered in the context of other comparable records from the region, a pattern of marked spatial heterogeneity is observed (Chase et al., 2015a(Chase et al., , 2019a, particularly between coastal and interior sites Quick et al., 2018). Furthermore, the mid-Holocene in the Cape is a period of significant climatic variability, and while efforts have been made to establish diagnostic patterns of change that can be used to infer specific drivers (Chase et al., 2017Chase and Quick, 2018), the Pearly Beach record currently lacks the requisite resolution to draw meaningful conclusions in this regard. It is evident that there are significant changes in the overall vegetation composition at Pearly Beach between the deglacial and Holocene, with a clear shift from ericaceous fynbos in the late Pleistocene to other structural types of fynbos (proteoid, restioid, and asteraceous) in the middle and late Holocene. ...
Article
Full-text available
The southwestern Cape of South Africa is a particularly dynamic region in terms of long-term climate change. We analysed fossil pollen from a 25,000 year sediment core taken from a near-coastal wetland at Pearly Beach that revealed that distinct changes in vegetation composition occurred along the southwestern Cape coast. From these changes, considerable variability in temperature and moisture availability are inferred. Consistent with indications from elsewhere in southwestern Africa, variability in Atlantic Meridional Overturning Circulation (AMOC) was identified as a strong determinant of regional climate change. At Pearly Beach, this resulted in phases of relatively drier conditions (~24–22.5 cal ka BP and ~22–18 cal ka BP) demarcated by brief phases of increased humidity from ~24.5–24 cal ka BP and 22.5–22 cal ka BP. During glacial Termination I (~19–11.7 ka), a marked increase in coastal thicket pollen from ~18.5 to 15.0 cal ka BP indicates a substantial increase in moisture availability, coincident, and likely associated with, a slowing AMOC and a buildup of heat in the southern Atlantic. With clear links to glacial and deglacial Earth system dynamics and perturbations, the Pearly Beach record represents an important new contribution to a growing body of data, providing insights into the patterns and mechanisms of southwestern African climate change.
... There has been a reticence to apply CREST and CRACLE to pre-Quaternary scenarios, despite being recommended by DeepMIP (Hollis et al., 2019). CREST has been used in paleoclimate reconstructions of the Holocene of North and South Africa Chase & Quick, 2018;Chevalier et al., 2017;Cordova et al., 2017;Nourelbait et al., 2016), South Korea (Yi et al., 2020), Europe (Cheddadi et al., 2016), and the Pleistocene of South Africa Lim et al., 2016;Scott, 2016), Africa (Chevalier et al., 2020) and Turkey (Chevalier, 2019). CRACLE has been applied to the Holocene of North America (Lora & Ibarra, 2019) and the Pliocene of Arctic Canada (Fletcher et al., 2019). ...
Article
Full-text available
Neogene sediments in the UK are ideally situated for understanding the early development of hydrological dynamics and atmospheric circulation that led to the modern oceanic climate of northwest Europe. Onshore Neogene fossiliferous deposits in the UK are limited to the solution pipe fills at Trwyn y Parc in Anglesey (Middle Miocene), the Brassington Formation of Derbyshire (Serravallian‐Tortonian), and the Coralline Crag Formation (latest Zanclean‐earliest Piacenzian) and Red Crag Formation (Piacenzian‐Gelasian) in southeast England. Palynoflora from these localities can be used to provide snapshots into the climate at the time of deposition, however, palaeobotanical‐based reconstructions are typically lacking in their poor estimation of error. Therefore, we present the first pre‐Quaternary application of two terrestrial climate reconstruction techniques: CREST (Climate Reconstruction SofTware) and CRACLE (Climate Reconstruction Analysis using Coexistence Likelihood Estimation), that use Bayesian and likelihood estimation probability respectively to generate a new palaeoclimate reconstruction, and compare this to Co‐existence Approach reconstructions from the UK and continental Europe. Our study shows how Mean Annual Temperature (MAT) declines by 3°–6°C, Mean Annual Precipitation (MAP) declines by 480–600 mm and Precipitation Seasonality approximately halves throughout the Neogene. CREST and CRACLE reconstructions overlap with the Co‐exisence Approach and have the advantage of providing uncertainty, rather than ranges. The UK appears to have had a milder, wetter, and less seasonal climate than continental Europe. This is likely due to the buffering effects of the Atlantic Ocean and North Sea ameliorating the UK Neogene climate despite regional and global changes in atmospheric and oceanic circulation.
... To expand on the theory outlined in Chase and Quick (2018) that a strong dipole in hydroclimatic conditions exist between the coast and interior during the Holocene, and that the Agulhas Current acts as a vector for the propagation of tropical southeast African climate signals to the southern Cape, more data is required. For a clearer understanding of the spatiotemporal dynamics of this hypothesized relationship additional high-resolution records extending into the last glacial period are needed from both the interior and coastal subregions of the southern Cape as well as from offshore (i.e. ...
... Further complicating this research is the recognition that prevailing conceptual models for regional climate change only have limited predictive capabilities, and that significant variability is the result of more complex processes (e.g. Chase et al., 2017), resulting in substantially greater spatiotemporal heterogeneity in signals of environmental change (Chase et al., in press;Chase et al., 2019a;Chase and Quick, 2018;Chevalier and Chase, 2015). This paper reviews: 1) the general framework of the southern African climate systems that are considered to have driven the major trends in environmental variability during the late Quaternary, and 2) how mechanisms both external (i.e. ...
Article
Southern Africa hosts regions of exceptional biodiversity and is rich with evidence for the presence and activities of early humans. However, few records exist of the concurrent changes in climate that may have shaped the region's ecological evolution and the development and dispersal of our ancestors. This lack of evidence limits our ability to draw meaningful inferences between important changes in the global and regional climate systems and their potential influence in shaping the region's natural and cultural history. This paper synthesises the data currently available to define a general empirically-based conceptual model of the spatio-temporal dynamics of climate change as they relate to changes in the earth's orbital configurations. The goal is to identify mechanistic links between orbital forcing, which can be calculated continuously over the past several million years, and environmental responses to related changes in the major atmospheric and oceanic circulation systems influencing southern Africa. Once identified, these relationships can be used to infer the most likely trends and patterns of climate variability for periods and regions for which proxy evidence is not available. Findings indicate that coherent patterns of change can be observed at wavelengths associated with ∼400-kyr and ∼100-kyr cycles of orbital eccentricity. In southeastern Africa, the ∼2400-kyr grand cycle in eccentricity may have had an influence long-term patterns of aridification and humidification, and the stronger ∼400-kyr eccentricity cycle has a significant influence across inter-tropical Africa, through changes in hydroclimate and monsoon circulation. The attribution of the ∼100-kyr cycle to specific orbital controls depends on location, as it can be determined by eccentricity-modulated direct insolation forcing or through the combined orbital parameters and earth system responses that drive the evolution of Pleistocene glacial-interglacial cycles. Following the onset of the mid-Pleistocene transition (c. 1250–700 ka), the increasing development of substantial polar ice sheets influence the nature of high-latitude drivers in southern Africa. In southwestern Africa, records indicate an evolution in climate and circulation systems strongly correlated with the global benthic δ¹⁸O record, suggesting a particular sensitivity to high latitude forcing. The close correlation between ∼100-kyr eccentricity and glacial-interglacial cycles makes it difficult to determine whether high- or low-latitude drivers dominate in southeastern Africa, but the spatio-temporal patterning of environmental variability in many records are generally considered to indicate a degree of high-latitude influence. Records from southeastern and southernmost Africa also indicate that the influence of low latitude forcing, expressed through the local precessional cycle, is – at least over the last glacial-interglacial cycles - dependent on eccentricity. Periods of reduced eccentricity, particularly during periods of extensive high-latitude ice sheet development, result in diminished influence in direct forcing and an increase in the expression of high latitude forcing, and an increasingly positive correlation between the northern and southern tropics at these wavelengths. In general, the records available allow for a simple conceptual model of the relationship between orbital parameters and regional climates to be defined, with the strongest relationships existing at longer timescales, such as the ∼400-kyr eccentricity cycle. At finer spatio-temporal timescales, the data indicate degrees of complexity that are not readily predicted, but the expansion of the regional dataset will continue to allow for refinements to the conceptual model described.
Article
Full-text available
The Greater Cape Floristic Region (GCFR) of South Africa is a biodiversity hotspot of global significance, and its archeological record has substantially contributed to the understanding of modern human origins. For both reasons, the climate and vegetation history of southwestern South Africa is of interest to numerous fields. Currently known paleoenvironmental records cover the Holocene, the last glacial–interglacial transition and parts of the last glaciation but do not encompass a full glacial–interglacial cycle. To obtain a continuous vegetation record of the last Pleistocene glacial–interglacial cycles, we studied pollen, spores and micro-charcoal of deep-sea sediments from IODP Site U1479 retrieved from SW of Cape Town. We compare our palynological results of the Pleistocene with previously published results of Pliocene material from the same site. We find that the vegetation of the GCFR, in particular fynbos and afrotemperate forest, responds to precessional forcing of climate. The micro-charcoal record confirms the importance of fires in the fynbos vegetation. Ericaceae-rich and Asteraceae-rich types of fynbos could extend on the western part of the Paleo-Agulhas Plain (PAP), which emerged during periods of low sea level of the Pleistocene.
Article
Full-text available
South Africa is a key region to reconstruct and understand past changes in atmospheric circulation, i.e. temperate westerlies and tropical easterlies. However, due to the scarcity of natural archives, South Africa's environmental evolution during the late Quaternary remains highly debated. Many available sediment archives are peri-coastal lakes and wetlands; however, the paleoenvironmental signals in these archives are often overprinted by sea-level changes during the Holocene. This study presents a new record from the coastal wetland Voëlvlei, which is situated in the year-round rainfall zone of South Africa on the southern Cape coast. It presents an ideal sedimentary archive to investigate both sea level and environmental changes. A 13 m long sediment core was retrieved and analysed using a multi-proxy approach. The chronology reveals a basal age of 8440 +200/-250 cal BP. Paleoecological and elemental analyses indicate marine incursions from ca. 8440 to ca. 7000 cal BP with a salinity optimum occurring at 7090 +170/-200 cal BP. At ca. 6000 cal BP, the basin of Voëlvlei was in-filled with sediment resulting in an intermittent (sporadically desiccated) freshwater lake similar to present. In contrast to previous investigations which used indirect proxies for hydrological reconstructions, here we apply a combined biomarker–sedimentological approach that allows the potential identification of precipitation sources, in combination with relative estimates of moisture availability. Increasing moisture is observed throughout the record starting from 8440 +200/-250 cal BP with contributions from both westerlies and easterlies from ca. 8440 to ca. 7070 cal BP. Westerly-derived rainfall dominates from ca. 7070 to ca. 6420 cal BP followed by a distinct shift to an easterly dominance at ca. 6420 cal BP. An overall trend to westerly dominance lasting until ca. 2060 cal BP is followed by a trend towards an easterly dominance to the present, but both phases show several intense, short-term variations. These variations are also evident in other regional studies, highlighting that the source and seasonality of precipitation has varied distinctly on the southern Cape during the Holocene. Comparison of the Voëlvlei record with other regional studies suggests a coherent trend in the overall moisture evolution along the southern Cape coast during the past 8500 years.
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South Africa is a key region for paleoclimate studies reconstructing and understanding past changes in atmospheric circulation, i.e., temperate Westerlies and tropical Easterlies. However, due to the scarcity of natural archives, the environmental evolution during the late Quaternary remains highly debated. Many archives that are available are peri-coastal lakes and wetlands and sea level changes during the Holocene often overprinted the paleoenvironmental signals in these archives. This study presents a new record from the coastal wetland Voёlvlei, which is an intermittent lake situated in the year-round rainfall zone (YRZ) of South Africa at the southern Cape coast. It presents an ideal archive to investigate both sea level and environmental changes. A 13 m-long sediment core was retrieved from Voёlvlei and analysed using a multi-proxy approach. The chronology reveals a basal age of 8,440+200/−250 cal BP. Paleoecological and elemental analyses indicate marine intrusions from 8,440 to 7,000 cal BP with a salinity optimum at 7,030+150/−190 cal BP. Since 6,000 cal BP, silting up has been causing an intermittent freshwater lake. Inferred from changes in allochthonous input, δ13Cn-alkane and δ2Hn-alkane increasing moisture is observed from 8,440+200/−250 cal BP. The δ2Hn-alkane record provides new evidence in contribution of different precipitation sources throughout the record with contributions from both Westerlies and Easterlies from 8,440 to 7,070 cal BP. Westerlies dominate from 7,070 to 6,420 cal BP followed by a distinct shift to an Easterly-dominance at 6,420 cal BP. An overall trend to a Westerly-lasting until 2,060 cal BP is followed by a trend towards an Easterlies-dominance, but both phases show several climatic spikes. Those spikes are also evident in other regional studies highlighting that the source and seasonality of precipitation has a mayor role for the hydrological balance. By comparing the Voёlvlei record with other regional studies, a similar trend in the overall moisture evolution along the southern Cape coast is inferred during the past 8.500 yrs.
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