The African landscape is recognized as important to hominin development and therefore 454
understanding the mechanisms driving vegetation dynamics on a variety of timescales is of interest.
455
Pleistocene vegetation records reveal highly variable conditions across the African continent. A 456
compilation of West African marine pollen records indicates that despite strong fluctuations, the 457
latitudinal arrangement of biomes has been conserved through the past three or four climate cycles 458
(Dupont, 2011). There is some tendency toward increased forest vegetation during interglacials while 459
during glacials an equatorward savanna shift into the modern rain forest area is suggested (Dupont, 460
2011). At elevated areas open mountainous scrubland was widespread during the glacials, 461
alternating with phases in which mountain forests expanded, with Podocarpus maxima falling mostly 462
between the extremes of full glacials or full interglacials (Dupont 2011).
463
At Lake Malawi (11º S) multi-proxy records including pollen indicate a “megadrought”, 464
occurring during MIS 6 and persisting for 18,000 years (Lane et al., 2013; Beuning et al., 2011; Scholz 465
et al., 2007; Cohen et al., 2007). During the megadrought, the volume of water in Lake Malawi was 466
21
reduced by at least 95% (Scholz et al., 2007) and grass-dominated vegetation was limited, implying 467
extreme aridity and suggesting conditions that would have been inhospitable to humans in the 468
region (Beuning et al., 2011). Our Limpopo basin vegetation records contrast significantly as we find 469
no evidence of the megadrought (Figure 4) suggesting that the extreme aridity was confined to more 470
tropical sites. In MD96-2048, the proportion of EM1, reflecting mainly humid mountainous 471
Podocarpus forest, is relatively high at this time (Dupont et al., 2011) while no significant changes in 472
the C31/(C29+C31) ratio or 13Cwax are observed (Figure 4). Although glacial-interglacial changes in the 473
vegetation of southern East Africa are observed, notably woodland/forest pollen persists throughout 474
the entire record (Dupont et al., 2011) (Figure 4). The continued presence of trees on the landscape 475
indicates substantially less variability in the vegetation of southern East Africa in comparison to the 476
Lake Malawi region. Beuning et al. (2011) noted consistency between Lake Malawi and West African 477
pollen records (Angola and Congo basins) and suggested that large scale vegetation changes were 478
not controlled by SST but rather by changes in Hadley circulation or ITCZ position, which would be 479
sensitive to precession. However, we find that SW Indian Ocean SST variability, driven by obliquity, 480
exerted the main control on southern East African vegetation. Dupont (2011) concluded that while 481
the representation of tropical rain forest fluctuated with summer insolation and precession, the 482
subtropical biomes showed more obliquity variability or followed the pattern of glacial and 483
interglacials.
484
The emerging picture is that Pleistocene environments of the southern African continent 485
were more stable in contrast to those of tropical Africa. In recent years the southern African 486
continent has received an increasing amount of attention as a region critical to hominin evolution 487
and the appearance of modern behavior (Compton, 2011). Our results support the hypothesis that 488
the southern African continent provided suitable living environments for hominins and fauna 489
22
throughout the Pleistocene, which may have been especially important at times when tropical 490
Eastern Africa experienced extreme aridity.
491
492
5. Conclusions 493
Paired analyses of plant leaf waxes and pollen assemblages reveal insights into Pleistocene 494
vegetation change in southern East Africa. We find that while the Limpopo River basin did not 495
experience major glacial-interglacial changes in C3 vs. C4 vegetation, n-alkanes chain lengths are 496
sensitive to varying inputs of open mountain vegetation, which is closely tied to SW Indian Ocean 497
SST. In turn, the SST of the SW Indian Ocean largely reflects changes in high-latitude obliquity. Our 498
leaf wax records indicate a clear response of the southern East African vegetation to glacial-499
interglacial climate variability as well as to the MBE. Differences between pre- and post-MBE 500
vegetation and climate of southern East Africa are attributed to shifts in the position of the STF, and 501
associated changes in the strength of the Agulhas leakage and AMOC may have been important for 502
transmitting the MBE outside of the southern high latitudes. Overall, our vegetation records indicate 503
that while glacial-interglacial changes in vegetation assemblages occurred, and a long-term shift 504
took place over the past 800 ka, in general landscapes of subtropical southern East Africa were 505
relatively stable compared to those of tropical East Africa. The relatively stable Pleistocene 506
environments of southern East Africa may have provided an important refuge for early hominins and 507
fauna at times when inhospitable conditions occurred in tropical East Africa.
508
509
Acknowledgements 510
We thank Michiel Kienhuis, Monique Verweij, Marianne Baas, Ellen Hopmans and Jort Ossebaar for 511
analytical assistance. Qiuzhen Yin is especially acknowledged for examining her model output from 512
23
Yin (2013) to investigate the movement of the subtropical front during pre- and post-MBE 513
interglacials. We are grateful to Dr. Jessica Tierney and an anonymous reviewer for insightful 514
comments that helped clarify and improve the manuscript. The Netherlands Organization for 515
Scientific Research (NWO) is thanked for financial support through a VICI grant to S. Schouten. Core 516
MD96-2048 was collected during the MOZAPHARE cruise of the RV Marion Dufresne, supported by 517
the French agencies Ministère de l’Education Nationale de la Recherche et de la Technologie, Centre 518
National de la Recherche Scientifique (CNRS), and Institut Paul Emile Victor (IPEV). This work was 519
supported by the "Laboratoire d'Excellence" LabexMER (ANR-10-LABX-19) and co-funded by a grant 520
from the French government under the program "Investissements d'Avenir", and by a grant from the 521
Regional Council of Brittany (SAD programme).
522
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33 Figure Captions
704
Figure 1: Map of the southern African continent with core locations and major surface currents 705
drawn based on Caley et al. (2011). The locations of marine cores 2048 (this study), MD96-706
2077 (Bard and Rickaby, 2009) and ODP Site 1082 (Jahn et al., 2003) are shown. The Zambezi and 707
Limpopo River basins are outlined by the light and dark gray shading, respectively. The black line 708
drawn on southern region of the continent indicates the location of the Great Escarpment. The 709
location of Maputo (M) is given by the white dot and the approximate location of drill core MAL05-710
1c from Lake Malawi is indicated (Scholz et al., 2007; Cohen et al., 2011; Beuning et al., 2011). The 711
Agulhas Current (AC), Agulhas Return Current (ARC), Benguela Current (BC) are the major surface 712
currents in the region and are shown by the labelled arrows. Sites of retroflection and recirculation 713
are noted. The approximate location of eddies of the Mozambique Channel (Moz.), East Madagascar 714
Current, and the Agulhas Rings, which transport heat and salt into the Atlantic Ocean, are indicated.
715
The dashed line indicates the location of the subtropical front (STF). B) The plant geographical 716
regions of southern Africa (figure modified from Dupont et al. (2011), which is based on White, 717
1983). The five regions relevant for our study are Zambezian (tropical, mainly savanna and 718
woodland), Zanzibar-Inhambane (tropical, mainly forest), Highveld (subtropical grassland), 719
Tongaland-Pondoland (subtropical forest) and Afromontane (White, 1983).
720
721
Figure 2: MD96-2048 n-alkane data. a) The concentration of the nC27, nC29, nC31 and nC33n-alkanes.
722
The C31n-alkane is the most abundant of the long-chain n-alkanes (mean concentration of 0.10 μg g 723
sed-1) followed by the C33 n-alkane (mean concentration of 0.09 μg g sed-1) and the C29 n-alkane 724
(mean concentration of 0.05 μg g sed-1). b) The mass accumulation rate (MAR) of long-chain n -725
alkanes (sum of C27 to C33; black circles) and c) the MAR of total branched glycerol dialkyl glycerol 726
34
tetraethers (GDGTs; open gray triangles). d) The average chain length (ACL). e) The carbon isotopic 727
composition of the C31 n-alkane (13Cwax). f) The C31/(C29+C31) n-alkane ratio. In D, E and F the 728
horizontal lines plot the mean values for the 800-430 ka and 430-0 ka intervals. The vertical dashed 729
line at 430 ka indicates the MBE. The Marine Isotope Stages (MIS) are indicated by the numbers at 730
the top of panel E.
731
732
Figure 3: Summary of paleoclimate records during the past 800 ka. a) The carbon isotopic 733
composition of the C31n-alkane (13Cwax). The thick green line represents the smoothed data (5 point 734
running mean). Higher (less negative) values indicate increased inputs from C4 vegetation. b) 735
Average chain length (ACL). Higher ACL values occur at times of lower SST and thus are likely mainly 736
reflecting changes in aridity. c) The C31/(C29+C31) n-alkane ratio. The y-axis is reversed. Higher values 737
suggest increased inputs of grasses (C31) and likely reflect arid conditions. d) The SST record of core 738
MD96-2048 based on the stacked record of the UK’37 Index, Mg/Ca ratios of G. ruber s.s., and TEX86. 739
Data from Caley et al. (2011). In b, c, and d, the straight gray line indicates the overall trend over the 740
past 800 ka. e) The global benthic oxygen isotope (18O) stack is shown for comparison (Lisiecki and 741
Raymo, 2005). Marine Isotope Stages (MIS) are indicated by the gray boxes and numbers at the 742
bottom and top of the graph. The vertical blue bars and roman numerals at the top indicate glacial 743
terminations. With the exception of SST (d), all y-axes are reversed.
744
745
Figure 4: Comparison between n-alkane parameters and pollen assemblage data for the past 350 ka.
746
All pollen data are from Dupont et al. (2011). In a, b and c the results of end-member modeling of 747
the pollen assemblages are displayed (note the reversed y-axes). EM3 is plotted in a) and represents 748
a complex assemblage of different biomes with woodland and forest taxa combined with coastal 749
35
vegetation. EM1 is plotted in b) and represents humid mountainous Podocarpus forest and 750
woodland taxa. EM2 is plotted in c) and represents open mountain vegetation dominated by 751
ericaeceous scrubs. d) The SST record of MD96-2048 from Caley et al. (2011). e) The carbon isotopic 752
composition of the C31n-alkane (13Cwax). The black line is the 5 point running mean. f) The 753
C31/(C29+C31) n-alkane ratio. g) The percent of woodland and forest pollen in core MD96-2048. It is 754
notable that woodland/forest pollen is present throughout the entire record. The Marine Isotope 755
Stages (MIS) are indicated by the gray boxes and numbers at the bottom and top of the graph. Note 756
the relationships between EM2, SST and the C31/(C29+C31) n-alkane ratio, supporting that SW Indian 757
Ocean SST is a main control on the vegetation of southern East Africa.
758
759
Figure 5: Cross-spectral analysis between the SST stack (Caley et al., 2011) and the C31/(C29+C31) 760
ratio from site MD96-2048. a) power spectra (log-scale) showing the SST record in black and the 761
C31/(C29+C31) ratio in gray, b) coherence with the 80 and 95% confidence intervals indicated by the 762
dashed lines, and c) phase in degrees. Strong 41 kyr cyles are noted in the SST and C31/(C29+C31) 763
ratio supporting the role of obliquity in driving SW Indian Ocean SST and vegetation change in 764
southern East Africa.
765
766
Figure 6: Box and whisker plots highlighting the differences between pre- and post-MBE intervals in 767
MD96-2048. In all plots the bottom and top of the box indicate the first and third quartiles while the 768
solid line inside the box indicates the median (the second quartile). The dashed line inside of the box 769
indicates the mean, which in a few cases plots on top of the median line. The tips of the whiskers
indicates the mean, which in a few cases plots on top of the median line. The tips of the whiskers