https://doi.org/10.1177/0959683617744259
The Holocene
1–11
© The Author(s) 2017
Reprints and permissions:
sagepub.co.uk/journalsPermissions.nav
DOI: 10.1177/0959683617744259
journals.sagepub.com/home/hol
Introduction
South Africa is positioned between the warm western boundary
Agulhas Current and the cool nutrient-rich eastern boundary Ben-
guela Current and influenced by both tropical and temperate
water masses and climate systems (Chase and Meadows, 2007;
Chase et al., 2013; Shannon and Nelson, 1996; Tyson et al., 1996).
Tropical systems bring summer rainfall to the northern and east-
ern parts of the summer rainfall zone (SRZ), where moisture from
the Indian Ocean is the dominant source of precipitation (Chase
and Meadows, 2007; Chase et al., 2015). In contrast, the winter
rainfall zone (WRZ) (indicated in Figure 1), the smaller, south-
western section, is affected by temperate climatic influences. Pre-
cipitation here occurs as a result of seasonal northward shifts of
the rain-bearing Southern Hemisphere Westerlies (SHW) over the
southernmost tip of Africa (Stager et al., 2012; Tyson and Pres-
ton-Whyte, 2000). Climatic changes in the WRZ were suggested
to be indicative of large-scale shifts in tropical and temperate cli-
mate zones (Carr et al., 2006; Chase and Meadows, 2007) with
large shifts over glacial–interglacial timescales (Chase and Mead-
ows, 2007; Chase and Thomas, 2007) and smaller shifts over mil-
lennial timescales (Hahn et al., 2015; Stager et al., 2012; Tyson
et al., 2002).
At present, there is, however, a limited understanding of the
climate dynamics in this region, particularly during the past ~2000
years, a time period that is relevant to future climate predictions
(McGregor et al., 2015). A record of this time period would set an
important benchmark for the region regarding its response to mil-
lennial and centennial climatic changes in the late Quaternary,
including the major global climate phases such as the ‘Little Ice
Age’ (LIA; 1350–1800 CE; Mann et al., 2002) and the Medieval
Climate Anomaly (MCA; 950–1250 CE; Mann et al., 2009).
The linkage between the Benguela upwelling system (BUS; an
oceanic system comprising the Benguela Current, its upwelling
cells and filaments, the west coast mud belt, and the poleward
undercurrent) and the continental rainfall in the Southern African
Late-Holocene dynamics of sea-surface
temperature and terrestrial hydrology in
southwestern Africa
Robyn Granger,
1
Michael E Meadows,
1,2
Annette Hahn,
3
Matthias Zabel,
3
Jan-Berend W Stuut,
3,4
Nicole Herrmann
3,5
and Enno Schefuß
3
Abstract
Southwest Africa is an important region for paleo-climatic studies, being influenced by both tropical and temperate climate systems and thus reflecting the
interplay of variable controls. The aim of this study was to unravel the interaction of sea-surface temperature (SST) changes in the southernmost Benguela
upwelling system with precipitation changes in South Africa’s winter rainfall zone (WRZ) during the late Holocene. Therefore, a marine sediment core
from the southernmost Benguela upwelling system was investigated to reconstruct climate changes in this region for the past ~2000 years. Grain size and
geochemical analyses were conducted to reconstruct changes in fluvial sediment discharge and weathering intensity, while SST changes were estimated
using alkenone paleo-thermometry. Results show that the southernmost Benguela behaves distinctly in comparison with the rest of the Benguela system
reflecting amplified SST changes. Decreasing SSTs accompanied increasing river discharge during times of increased precipitation in the WRZ, reflecting
northerly shifted westerly winds during austral winter. We infer a control of past SST changes by processes not analogous to modern processes driving
seasonal SST changes by changes through upwelling intensity. The findings suggest that late-Holocene SST changes in the southernmost Benguela upwelling
system and the precipitation in the WRZ were both driven by latitudinal shifts of the austral westerly wind belt and associated changes in advection of
cold sub-Antarctic waters and/or changes in Agulhas leakage of warm Indian Ocean waters.
Keywords
late Holocene, river runoff, sea-surface temperature, South Africa, winter rainfall zone
Received 4 September 2016; revised manuscript accepted 11 October 2017
1
Department of Oceanography, University of Cape Town, South Africa
2
School of Geographic Sciences, East China Normal University,
Shanghai, China
3
MARUM–Center for Marine Environmental Sciences, University of
Bremen, Germany
4
Royal Netherlands Institute for Sea Research (NIOZ) and Utrecht
University, Texel, The Netherlands
5
Now at Institute for Geology, University of Hamburg, Germany
Corresponding author:
Robyn Granger, Department of Oceanography, University of Cape
Town, University Avenue, Rondebosch 7701, Cape Town, South Africa.
Email: grnrob016@myuct.ac.za
744259HOL 0 0 10.1177/0959683617744259The HoloceneGranger et al.
research-article 2017
Research paper