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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.

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... In addition, in terms of nutrient and CO 2 budgets, water entering through the Agulhas leakage significantly contributes preformed nutrients that contemporaneously render South Benguela a sink for atmospheric CO 2 . Concerning the centennial variability of upwelling over the period 1600-1900, Granger et al. (2018 reasoned from their analysis of grain size and SST changes derived from marine sediment records that the inflow of Agulhas water into the South Benguela upwelling system is stronger when westerlies are located further to the south and SSTs are cooler during northernmost positions of the westerlies. ...
... During the 16th century, a particularly cold century during the Little Ice Age (LIA) between the 15th and the 19th centuries, the westerlies significantly weakened and shifted equatorward. This is supported by the studies by Hahn et al. (2017), Stager et al. (2012), and Granger et al. (2018), who also found that the winds shifted equatorward during cooler and poleward during warmer periods. Nevertheless, the position of Southern Hemisphere westerlies during the LIA is still under debate and seems to depend on the region, as studies of the African, South American, and Australian sector provide varying results (Chase and Meadows, 2007). ...
... This agrees with the proxy-based findings of Granger et al. (2018) for the late Holocene. They found that during a northward shift of the westerlies, SSTs were lower in South Benguela, not caused by intensified upwelling but due to changes in the advected water masses. ...
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The westerlies and trade winds over the South Atlantic and Indian Ocean are important drivers of the regional oceanography around southern Africa, including features such as the Agulhas Current, the Agulhas leakage, and the Benguela upwelling. Agulhas leakage constitutes a fraction of warm and saline water transport from the Indian Ocean into the South Atlantic. The leakage is stronger during intensified westerlies. Here, we analyze the wind stress of different observational and modeled atmospheric data sets (covering the last 2 millennia, the recent decades, and the 21st century) with regard to the intensity and position of the southeasterly trades and the westerlies. The analysis reveals that variations of both wind systems go hand in hand and that a poleward shift of the westerlies and trades and an intensification of westerlies took place during the recent decades. Furthermore, upwelling in South Benguela is slightly intensified when trades are shifted poleward. Projections for strength and position of the westerlies in the 21st century depend on assumed CO2 emissions and on their effect relative to the ozone forcing. In the strongest emission scenario (RCP8.5) the simulations show a further southward displacement, whereas in the weakest emission scenario (RCP2.6) a northward shift is modeled, possibly due to the effect of ozone recovery dominating the effect of anthropogenic greenhouse forcing. We conclude that the Agulhas leakage has intensified during the last decades and is projected to increase if greenhouse gas emissions are not reduced. This will have a small impact on Benguela upwelling strength and may also have consequences for water mass characteristics in the upwelling region. An increased contribution of Agulhas water to the upwelling water masses will import more preformed nutrients and oxygen into the upwelling region.
... Instead, the physical mechanisms linking variations in strength and position of the wind systems to SST in the South Atlantic is the Agulhas leakage, 20 which modulates the advection of warm Indian Ocean water into the South Atlantic and into the Benguela upwelling system. This agrees with proxy-based findings of Granger et al. (2018) for the late-Holocene. They found that during a northward shift of the westerlies, SSTs have been lower in South Benguela, not caused by intensified upwelling but due to changes in the advected water masses. ...
... Both wind systems, westerlies and trade winds, are stronger when located further south in most of the centuries and vice versa. Furthermore, the northward shift and weakening of the westerlies during the cooler Little Ice Age in the 16th century in these simulations is consistent with evidence from sediment cores for the same period (Granger et al., 2018), of a weak Agulhas leakage during periods of cooler climate. ...
... During the 16th century, a particularly cold century during the Little Ice Age between the 15th and the 19th centuries, westerlies 5 significantly weakened and shifted equatorward. This is supported by the studies byPeeters et al. (2004) andGranger et al. (2018), who also found that the winds shifted equatorward during glacial periods.The MPI-ESM simulations for the historical period(1850( -2005 and the future (2006-2100 CE) reveal the same coherences of westerlies and trades as the other data sets (NCEP1,COREv2, JRA-55, ERA20C, and ECHAM6XR). However, a significant difference is that the intensity of trades and westerlies are not correlated in the model results of the rcp4.5 and rcp8.5 10 scenarios. ...
Article
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The westerlies and trade winds over the South Atlantic and Indian Ocean are important drivers of the regional oceanography around Southern Africa, including features such as the Agulhas current, the Agulhas leakage and the Benguela upwelling. The Agulhas leakage is the transport of warm and saline water from the Indian Ocean into the South Atlantic. The leakage is stronger during intensified westerlies and probably also when the wind systems are shifted poleward. Here we analyzed the wind stress of different observational and modelled atmospheric data sets (covering the last two millennia, the recent decades and the 21st century) with regard to the intensity and position of the south-easterly trades and the westerlies. The analysis reveals that variations of both wind systems go hand in hand. A poleward shift and intensification of westerlies and trades took place during the recent decades. Furthermore, the upwelling in South Benguela slightly intensified and the characteristics of the water masses fed into the upwelling region changed with a poleward shift of the trades. Projections for strength and position of the westerlies in the 21st century depend on assumed CO2 emissions. In the strongest emission scenario a further southward displacement will occur, whereas a northward shift is modelled in the weakest emission scenario, possibly due to the dominating driving effect of ozone recovery. Thus, the Agulhas leakage has intensified during the last decades and is projected to increase if greenhouse gas emission are not reduced. This will have a small impact on Benguela upwelling strength, but will have consequences for water mass characteristics in the upwelling region. An increased contribution of Agulhas water to the upwelling feed water masses will import more preformed nutrients and oxygen into the upwelling region.
... It has been demonstrated that the Agulhas leakage, besides its impact on the ocean circulation and global climate change, has strong local effects on the Benguela system. The Alkenone-derived sea surface temperatures (SST) together with grain size data and element ratio in the southernmost Benguela region suggests an influence of the Agulhas leakage during the late-Holocene (Granger et al., 2018;Hahn et al., 2016). Coccolithophore data from the same core were obtained to reconstruct surface water conditions such as water temperature and nutrient availability (Weiser et al., 2016). ...
... Different calibrated ages were reported by Hahn et al. (2016) and Granger et al. (2018), although with minor differences. Table 1. ...
... The age-depth model show a basal age of 268 BCE. The alkenonederived SSTs, grain size (Granger et al., 2018), and coccolithophore data (Weiser et al., 2016) were also plotted on the new age model. Because of the limited number of radiocarbon ages, there is about a 500 year range for the 95% probability in the age-depth model, which should be regarded with caution. ...
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The southern Benguela upwelling system near the St Helena Bay has been proposed to be affected by various factors, while few investigations about the late-Holocene oceanic conditions has been carried out in this area. To determine the oceanic variability and its forcing mechanisms in the southern Benguela region during the late-Holocene, we examined organic-walled dinoflagellate cyst (dinocyst) records from two marine sediment cores located in the southernmost and central Benguela upwelling system. We compare our results with other proxies including alkenone-derived SSTs, grain size, and coccolithophore assemblages from the same samples. The results indicate a distinctive behavior between the southernmost Benguela system and the central Benguela area. We infer that the oceanic conditions in these two regions are primarily governed by an interplay of wind-induced upwelling, fluvial discharge, and advection of cold sub-Antarctic waters, which is consistent with the current understanding of the paleoclimate conditions in this area. However, the findings also suggest that the southernmost Benguela system also receives additional effects of warm and saline waters via the Agulhas leakage, which has a clear influence on the oceanic conditions in this area.
... The most depleted dD values and the most enriched d 13 C values of the record can be found from~600 tõ 300 cal yr BP, indicating that this interval was particularly humid, even more than the preceding MCA. The time frame corresponds roughly to the LIA chronozone and is recorded as a humid phase throughout the South African WRZ (Kirsten and Meadows 2016;Granger et al., 2017;Hahn et al., 2015 (Fig. 4g);Meadows et al., 1996;Benito et al., 2011;Stager et al., 2012;Weldeab et al., 2013;Wündsch et al., 2016;Quick et al., 2018) (Fig. 6 panel b). Most regional studies associate this increase in rainfall with a northward shift of the SHW (as suggested in the LIA compilation studies by Tyson and Preston-Whyte (2000) and Chase and Meadows (2007)). ...
Article
Mpondoland on the South African east coast is a particularly dynamic region in terms of climate change as it is influenced by both temperate and tropical circulation and climate systems. We present a sediment record that indicates regional climatic change and anthropogenic influence during the last ~5500 yr. Catchment data allow an understanding of signal transmission from the catchment to the site of the marine core. Plant-wax isotope distributions and elemental composition, as well as palynological, burned phytolith and micro-charcoal data, are used to infer paleoclimatic shifts and reconstruct past human activity. Whereas previous studies have often disregarded early anthropogenic drivers of environmental change, our study provides palynological evidence of human impacts and geochemical evidence of increased erosion starting as early as ~1500 years ago. Downcore proxy analysis suggests that particularly humid conditions persisted from ~900 to ~300 cal yr BP, encompassing both the Medieval Climate Anomaly and the Little Ice Age. We suggest that humidity during the Medieval Climate Anomaly was sourced from a poleward shift of the Southern Hemispheric Westerlies and the South African high�pressure cell, allowing for the southward expansion of the Southern Indian Ocean Convergence Zone. During the Little Ice Age, the equatorward movement of the Southern Hemispheric Westerlies probably brought increased rainfall to areas that are normally beyond the northern limit of the Southern Hemi�spheric Westerlies. Comparison of our record to available regional archives of centennial-scale late Holocene climate variability in South Africa demonstrates that Mpondoland is located at a transition zone of tropical and sub-tropical climatic influences.
... Palaeoenvironmental investigations in the southwestern Cape and adjacent oceanic environment have revealed that the region has experienced some major fluctuations in climate, sea level and ocean dynamics during the Holocene (Compton, 2001;Granger et al., 2018;Kirsten and Meadows, 2016;Miller et al., 1995). Climate variability is primarily attributed to the strength and positioning of the SWW and southeast trade winds, but also to external forcing, such as from solar variability (Kirsten et al., 2018). ...
Article
We present a diatom record from a well‐dated 15.25 m composite sedimentary core from Verlorenvlei, a shallow coastal lake on the west coast of South Africa. We show that fluctuations in the diatom record occur in response to changes in sea level, ocean–atmosphere interactions and latitudinal shifts in the wind belts. During the early to mid‐Holocene, the system primarily responds to sea level changes. A marine community that favours high nutrients is evident, particularly during 9200–8000, 7420–7000 and 6200–5600 cal a bp, corroborating periods of Benguela upwelling linked to fluctuations in the southeast trade winds. Increases in bioproductivity (%TOC, C/N) and fresher‐water diatoms are associated with wetter conditions over the region and the northward migration of the southern westerly wind belt, most notably between 8000 and 7500 cal a bp and over the last 700 years. The latter trends are concomitant with changes in the extent of Antarctic sea ice and availability of moisture in southern South America. During the late Holocene, as sea levels stabilised to modern levels, climate variability is more strongly evident. The body of evidence further reveals the sensitivity of the region to high‐latitude atmospheric mechanisms, but also showcases the significance of the southeast trade winds.
... This dry phase detected in the proxies of Princessvlei coincide with the driest phase registered between 2250 and 2000 yr BP in the hydrological variations in the southwest river catchments within the winter rainfall zone interpreted as the result of a poleward migration of the Southern Hemisphere Westerlies (Granger et al., 2018). This dry phase is not clear in the d 18 O diatom record, as the only value shows a moderate enrichment (38.4‰) at 2450 cal yr BP, which would be more suggestive of wet conditions due to the incidence of westerlies (Harris et al., 2010). ...
Article
A multi-proxy approach conducted on a sediment core from a small lake in the Cape Flats (Princessvlei, South Africa), supported by five AMS dates, reveals the paleoenvironments over the last 3900 years. Despite some gaps in the records, phytoliths, diatoms, δ¹⁸Odiatom, pollen, coprophilous fungus spores, microscopic charred particles (micro-charcoal), and burnt-grass phytoliths, indicate vegetation disturbances caused by climatic changes, anthropogenic influences, fire, and herbivore activity. Pollen spectra indicates a moist period (3600-2600 cal yr BP), which co-occurs with an increase in fires, possibly due to greater biomass fuel loads coupled with the moderate presence of large herbivores. Subsequently, a dry period (2600-1900 cal yr BP) saw a rapid increase of large herbivores probably congregating around the lake, a contention supported also by the occurrence of nutrient-rich waters. This dry period saw reduced fires and a decline of C3 grasses in favor of C4 grasses. The arrival of herders in the Cape after 2000 cal yr BP is not immediately apparent in the multiple records, except for minor vegetation changes and regional fires c. 1200–1400 cal yr BP. However, a more consistent presence of livestock in the immediate area of Princessvlei occurs only after c. 600 cal yr BP, when peak frequencies of coprophilous spores coincide with changes in vegetation composition and occurrence of more eutrophic waters in the lake. The introduction of exotic flora, fire suppression, and a reduction of herding activities, characterizes the period of European settlement (c. 300 BP to present).
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Sediments are the most important source of Late Quaternary palaeoclimate information in southern Africa, but have been little studied from a geochemical perspective. However, recent advances in analytical techniques that allow rapid and near-continuous elemental records to be obtained from sedimentary sequences has resulted in the increasing use of elemental indicators for reconstructing climate. This paper explores the diverse information that can be acquired from the inorganic component of sediments and reviews some of the progress that has been made over the last two decades in interpreting the climatic history of southern Africa using elemental records. Despite the general scarcity of elemental records, excellent examples from the region exist, which provide some of the longest and most highly resolved sequences of environmental change currently available. Records from Tswaing crater and marine deposits on the southern KwaZulu-Natal coastline have provided rare glimpses into hydroclimate variability over the last 200 000 years, suggesting that summer rainfall in the region responded predominantly to insolation forcing on glacial-interglacial timescales. Over shorter timescales, lakes and wetlands found in the Wilderness embayment on the southern Cape coast and along the Maputaland coast in north-eastern South Africa have yielded highly-resolved elemental records of Holocene environmental change, providing insight into the changing interactions between tropical (e.g., El Niño-Southern Oscillation) and temperate (e.g., mid-latitude westerlies) climate systems affecting rainfall variability in the region. The examples discussed demonstrate the multiple environmental processes that can be inferred from elemental proxies and the unique insight this can provide in advancing our understanding of past climate change on different timescales. The interpretation of geochemical data can be complicated by the complex nature of sedimentary environments, various proxy assumptions and analytical challenges, and the reliability of sediment-based climate reconstructions is substantially enhanced through multi-proxy approaches.
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Introduction The core of this book is the vegetation map of the region which is the culmination of many years of work by many people. The vegetation units described become far more useful when they are made spatially explicit and the dimensions, distribu¬tion and shapes of each vegetation unit cannot adequately be described by text alone. Also the relationships between adjacent vegetation types as well as interdispersion patterns become clear through the device of the maps presented in this atlas. The atlas is presented here as a systematic series of A4 maps. These depict 435 of the vegetation types of our subcontinental region. Not depicted in this edition is AZm 1 Cape Kelp Beds that is described in the text. The map of the vegetation types of the subantarctic Marion and Prince Edward Islands is to be found in Chapter 15. The mapping in this chapter corresponds closely to the large 1:1 000 000 map sheets of Mucina et al. (2005) and is also printed at this convenient scale. In this atlas a grey outline to polygons has been added to help differentiation between adjacent vegetation units. The A4 map pages include an area of overlap at the edges with the maps on overleaf pages and contain navigational arrows to adjacent sections of the 26° map. The series of maps is preceded by an index map to page numbers of the maps of the atlas, followed by the legend to the vegetation types with colours and codes of the vegetation types. Given the large number of colours required for the atlas, the codes provide the definitive identity of vegetation types. For convenience this legend is reprinted as a separate booklet in a sleeve within the back cover of the book. Geographical names as approved by the South African Geographical Names Council are as gazetted before 1 January 2005. A compact disc (CD) containing the electronic shape files of the map is placed in a sleeve within the front cover of the book. This CD also contains the software ArcReader suitable for view¬ing the map on computer. This is a particularly valuable and effective means of zooming in to view very small polygons and intricately divided vegetation types that are difficult to see on the printed maps. Some attributes are displayed when click¬ing on a polygon in the electronic map. These are Code used in the book, Name of the vegetation type, Conservation tar-30° get, Percent of the vegetation type that is protected, Percent of the vegetation type that is unaltered, Conservation status and Protection status of the vegetation type, Area in square kilometres of the vegetation type, Area in square kilometres of the specific polygon, Code without space used on the map, Sort order (using numbers for biome, bioregion and vegetation type), Codes and names for biome, group and bioregion, and IDs for vegetation type, biome, group and bioregion used for linking data tables. The maps of biomes and bioregions at much less detailed scales are to be found in Chapter 3. Credits of work done are detailed in the individual major chap¬ters (Chapters 4 to 14) and are therefore not repeated here. Reference Mucina, L., Rutherford, M.C. & Powrie, L.W. (eds) 2005. Vegetation Map of South Africa, Lesotho and Swaziland, 1:1 000 000 scale sheet maps. South African National Biodiversity Institute, Pretoria.
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In order to calibrate radiocarbon ages based on samples with a marine carbon component it is important to know the marine carbon reservoir correction or ΔR value. This study measured the ΔR on both known-age pre-bomb marine shells and paired marine and terrestrial samples from two regions on the west coast of South Africa: the southwestern Cape and Namaqualand. Pooling the data by region produces ΔR values that are similar enough to use a west coast weighted mean ΔR of 146 ± 85 14C years to correctly calibrate marine shell or mixed marine and terrestrial 14C ages. There are however temporal differences in ΔR throughout the Holocene, which we compare with proxy data for upwelling and sea surface temperatures.
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1] We present a dust plume source inventory for southern Africa. In order to locate and track the local, short-lived plume events, source and frequency data have been derived from Meteosat Second Generation (MSG) thermal infrared composite data (4 km data using 8.7, 10.8, and 12.0 μm) and Moderate Resolution Imaging Spectroradiometer (MODIS) visible composite data (0.25 km data utilizing 0.620 – 0.670 μm, 0.545 – 0.565 μm, and 0.459 – 0.479 μm). Between January 2005 and December 2008, a total of 328 distinct daytime dust plumes more than 10 km in length were detected. These plumes were attributed to 101 distinct point sources, consisting largely of ephemeral inland lakes, coastal pans as well as dry river valleys in Namibia, Botswana, and South Africa. These data also provided sub-basin scale source observations for large basins such as Etosha and Makgadikgadi Pans. Citation: Vickery, K. J., F. D. Eckardt, and R. G. Bryant (2013), A sub-basin scale dust plume source frequency inventory for southern Africa,
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The IntCal09 and Marine09 radiocarbon calibration curves have been revised utilizing newly available and updated data sets from 14C measurements on tree rings, plant macrofossils, speleothems, corals, and foraminifera. The calibration curves were derived from the data using the random walk model (RWM) used to generate IntCal09 and Marine09, which has been revised to account for additional uncertainties and error structures. The new curves were ratified at the 21st International Radiocarbon conference in July 2012 and are available as Supplemental Material at www.radiocarbon.org. The database can be accessed at http://intcal.qub.ac.uk/intcal13/. © 2013 by the Arizona Board of Regents on behalf of the University of Arizona.
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The western continental margin of South Africa is a dynamic environment. It is a site of intense upwelling and high productivity, as well as a repository for large quantities of terrigenous sediment delivered by wind and rivers, most notably by the Orange River. Essential to understanding the complex dynamics of sedimentation on this margin is an accurate, robust age model. Here we present 32 radiocarbon ages of mollusc shells and foraminifera tests recovered from Holocene organic-rich mud deposits on the middle-inner shelf (the mudbelt), and from calcareous ooze on the continental slope. Sedimentation rates of between 0.25 and 2.4 mm/year are recorded in the Holocene mudbelt, whereas slope cores have average sedimentation rates of between 0.04 and 0.22 mm/year. Low sedimentation rates in the mudbelt correspond to increases in the coarse-silt fraction, associated with periods of winnowing. In the north, the mudbelt sediments have been deposited since 11 thousand years before present (11 ka), whereas sedimentation in the southern mudbelt was initiated at around 2 ka. From changes in sedimentation rate and the southward younging of the deposit, we infer that the mudbelt depo-centre has shifted during the Holocene in response to changes in sea level and accommodation space on die shelf. Holocene carbonate ooze on the slope contains 20 to 40 weight % terrigenous material, indicating significant off-shelf transport. Onshore Orange River palaeoflood deposits provide a terrestrial record spanning 12 ka. Linking high-resolution continental and marine records will allow for the comparison of oceanographic and climatic changes in southern Africa during the Holocene.
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We present alkenone-derived Sea Surface Temperature (SST) records from three marine cores collected within the southern Benguela Upwelling System (BUS) spanning the last 3 ka. The SST evolution over the last 3 millennia is marked by aperiodic millennial-scale oscillations that broadly correspond to climatic anomalies identified over the North Atlantic region. The BUS SST data further suggest cooling and warming trends opposite to the temperature evolution in the Moroccan upwelling region and in Antarctica. In contrast, the last decades are marked by a cooling of unprecedented magnitude in both the Benguela and Moroccan upwelling systems, which is not observed in the Antarctic record. These contrasted responses in Atlantic upwelling systems triggered by natural and anthropogenic forcings shed light on how different climatic mechanisms are mediated by ocean-atmosphere interactions and transmitted to the geological records of past and present climate changes.
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The CORTEX (Corescanner Texel) is a non-destructive XRF system for the logging of split sediment cores. It is a seaworthy instrument that remains active during heavy weather conditions. The scanner produces reliable counts for K to Sr, highly correlated with concentrations measured with atomic absorption spectrometry (AAS). The option to scan Al, Si, and elements heavier than Sr is in preparation. A core section of 1 m can be scanned at 2-cm intervals within an hour. A maximum resolution of 1 mm can be achieved. At present, each region and sedimentary environment requires separate calibration. In the nearby future the generator settings will be standardized, which may result in the development of a standard calibration procedure. Because of the high resolution of its semi-quantitative records, the CORTEX is a useful tool for detailed time-series analysis, inter-core correlation, and shipboard analysis.
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A climatology of satellite-derived sea surface semperature (SST) and surface chlorophyll a concentration (Ch1), and their associated variability at time-scales from weeks to years, was constructed for the Benguela and Agulhas ecosystems. Global area coverage data at 4.5 km spatial resolution from both AVHRR and SeaWiFS sensors were used to assemble the climatology, from weekly and 5-day time-series respectively. The SST data series spanned 18 years (1982-1999), the Ch1 data the period September 1997-April 2002. The dominant pattern in the annual SST is the cold upwelled water on the western continental shelf of South Africa and Namibia. SST was high at the Angola-Benguela Front (15-17degreesS) and on the Agulhas Bank, the northern and southern extremities of the upwelling region. Monthly SST variability was high in both regions, except for the Luderitz and Cape Columbine-Cape Peninsula upwelling zones, where variability was low. The western Agulhas Bank exhibited a clear seasonal pattern of warm surface water in summer and cool surface water in winter, with an amplitude of 2.5degreesC. A band of high Ch1 (>5-10 mg m(-3)) was apparent close to the coast from the Angola-Benguela Front to Cape Town, but there was a well-defined relative minimum at Luderitz. On the South Coast, highest Ch1 (>3 mg m(-3)) was between Cape Agulhas and Port Elizabeth, in the form of a plume moving offshore. In contrast to SST, Ch1 variability was mainly at intramonthly intervals, although variability was particularly high north of the Angola-Benguela Front in summer, and at various upwelling sites in winter.
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A field program to study the circulation of the Benguela Current and its extension into the southeastern Atlantic Ocean has completed the survey and instrument deployment phase. We report here new observations of three Agulhas rings north and west of Cape Town, South Africa. Three mesoscale anticyclonic rings initially identified by means of TOPEX/POSEIDON altimetry were surveyed with expendable bathythermographs, conductivity-temperature-depth-oxygen profiles, direct current measurements from a lowered acoustic Doppler current profiler, a hull-mounted acoustic Doppler current profiler, and satellite-tracked surface drifters. Characteristics of the rings are presented, and their origins are discussed. Two are typical Agulhas rings surveyed at different times after their generation; the third Agulhas ring has an anomalous water mass structure whose most likely origin is the Subtropical Front.
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The Agulhas Current is the major western boundary current of the Southern Hemisphere [Lutjeharms, 2006] and a key component of the global ocean “conveyor” circulation controlling the return flow to the Atlantic Ocean [Gordon, 1986]. As such, it is increasingly recognized as a key player in ocean thermohaline circulation, with importance for the meridional overturning circulation (MOC) of the Atlantic Ocean. Unusual dynamics pervade the motion of this warm-water current—as it moves west around the southern tip of Africa, it is retroflected back east by the Antarctic Circumpolar Current. Not all waters are captured by this sudden diversion of course—parts of the Agulhas Current leak away into the South Atlantic Ocean (Figure 1).
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The development of suitable reference states for ecosystem-based management requires documentation of changes in structure and functioning of marine ecosystems, including assessment of the relative mportance of bottom-up and top-down processes as drivers of change. We used monitoring data available from St Helena Bay, the most productive bay and an important nursery area situated on the west coast of South Africa, during 1950–2010 to reveal changes in the abiotic and biotic components. St Helena Bay in the 1950s showed similarities to 2000–2010 in terms of wind patterns, hydrology and phytoplankton. Upwelling, oxygen and nutrient concentrations in subthermocline water displayed pronounced decadal-scale variability. Primary production in St Helena Bay is variable, but consistently higher than that on the adjacent Namaqua shelf. Zooplankton size composition and biomass in August have changed markedly since the 1950s. During 2001–2010, mesozooplankton biomass in autumn was considerably lower than in summer, probably due to predation by small pelagic fish. Pelagic fish catch patterns and distributions have altered dramatically. Conservation measures, implemented to reverse past negative human impact, have benefitted marine mammals, the abundance of which has increased in the area, but additional conservation measures are necessary to reverse the decline in African penguins Spheniscus demersus. St Helena Bay shows a muted response to long-term change in the southern Benguela, with marked decadal variability but no clear long-term trend in oceanography and biogeochemistry. Changes in ecosystem boundary conditions and fishing pressure cannot be ignored as important drivers of change in the southern Benguela since the 1950s.
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The hydrogen isotope composition of plant leaf wax (δDwax) has been found to record the isotope composition of precipitation (δDp). Hence, δDwax is increasingly used for palaeohydrological reconstruction. δDwax is, however, also affected by secondary factors, such as vegetation type, evapotranspiration and environmental conditions, complicating its direct application as a quantitative palaeohydrological proxy. Here, we present δDwax data from soils along vegetation gradients and climatic transects in southern Africa to investigate the impact of different environmental factors on δDwax. We found that δDwax correlated significantly with annual δDp (obtained from the interpolated Online Isotopes in Precipitation Calculator data set) throughout the eastern and central South Africa, where the majority of the mean annual precipitation falls during the summer. We found evidence for the effect of evapotranspiration on δDwax, while vegetation change was of minor importance. In contrast, we found that δDwax did not correlate with annual δDp in western and southwestern South Africa, where most of the annual precipitation falls during winter. Wide microclimatic variability in this topographical variable region, including distinct vegetation communities and high vegetation diversity between biomes as well as a potential influence of summer rain in some locals, likely compromised identification of a clear relationship between δDwax and δDp in this region. Our findings have implications for palaeoenvironmental investigations using δDwax in southern Africa. In the summer rain dominated eastern and central region, δDwax should serve well as a qualitative palaeohydrological recorder. In contrast, the processes influencing δDwax in the winter rain dominated western and southwestern South Africa remain unclear and pending further analyses potentially constrain its use as palaeohydrological proxy in this region.
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This paper highlights some of the main developments to the radiocarbon calibration program, OxCal. In addition to many cosmetic changes, the latest version of OxCal uses some different algorithms for the treatment of multiple phases. The theoretical framework behind these is discussed and some model calculations demonstrated. Significant changes have also been made to the sampling algorithms used which improve the convergence of the Bayesian analysis. The convergence itself is also reported in a more comprehensive way so that problems can be traced to specific parts of the model. The use of convergence data, and other techniques for testing the implications of particular models, are described.
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The Benguela is one of four major eastern boundary current regions of the World Ocean. The oceanography off the west coast of southern Africa is dominated, like the regions off California, Peru and North West Africa, by coastal upwelling; but the Benguela is unique in that it is bounded on both the equatorward and poleward ends by warm water regimes. In this paper we build on review articles which were published during the 1980s by highlighting the main advances in the conceptual understanding of the system since 1985. A large amount of research on this eastern boundary domain has been conducted in recent years by the institutes to which the authors are affiliated. This has given clear definition to four aspects of shelf dynamics, these being poleward flow at depth across the shelf and out into the slope region, the existence of baroclinic shelf-edge jets in the vicinity of the shelf break, barotropic shelf waves and the importance of variation in wind rather than constant strength of wind as a factor controlling upwelling. Short discussions of some, as yet, unpublished findings supplement published works by ourselves and other authors. Of particular importance are the events such as Benguela Ninos in the north and intrusions of Agulhas water in the south. The latter, which can take the form of filaments or rings, influences the oceanography of the region of the “Greater Agulhas Current”, with interactions between Agulhas rings and Benguela shelf waters.
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We use the Total Ozone Mapping Spectrometer (TOMS) sensor on the Nimbus 7 satellite to map the global distribution of major atmospheric dust sources with the goal of identifying common environmental characteristics. The largest and most persistent sources are located in the Northern Hemisphere, mainly in a broad "dust belt" that extends from the west coast of North Africa, over the Middle East, Central and South Asia, to China. There is remarkably little large-scale dust activity outside this region. In particular, the Southern Hemisphere is devoid of major dust activity. Dust sources, regardless of size or strength, can usually be associated with topographical lows located in arid regions with annual rainfall under 200-250 mm. Although the source regions themselves are arid or hyperarid, the action of water is evident from the presence of ephemeral streams, rivers, lakes, and playas. Most major sources have been intermittently flooded through the Quaternary as evidenced by deep alluvial deposits. Many sources are associated with areas where human impacts are well documented, e.g., the Caspian and Aral Seas, Tigris-Euphrates River Basin, southwestern North America, and the loess lands in China. Nonetheless, the largest and most active sources are located in truly remote areas where there is little or no human activity. Thus, on a global scale, dust mobilization appears to be dominated by natural sources. Dust activity is extremely sensitive to many environmental parameters. The identification of major sources will enable us to focus on critical regions and to characterize emission rates in response to environmental conditions. With such knowledge we will be better able to improve global dust models and to assess the effects of climate change on emissions in the future. It will also facilitate the interpretation of the paleoclimate record based on dust contained in ocean sediments and ice cores.
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Cross-shelf distributions of temperature, salinity, water masses, and dissolved oxygen in St Helena Bay revealed substantial vertical and seasonal variations. In the surface layers, near-shore and offshore temperature and salinity patterns differed, with bay-scale variability linked to upwelling dynamics and coastal processes, while the offshore region was influenced by solar insolation. Spectral analysis revealed that an annual signal prevailed at most stations, and corroborated contrasting patterns between the offshore and near-shore regions, with phase differences suggesting shoreward propagation of the offshore temperature signal. The shelf was dominated by Modified Upwelled Water (MUW) and Subantarctic Mode Water (SAMW), which comprised the primary source of upwelled water. Clear zonation of MUW was evident across the shelf, resulting from seasonal variations in locations of the oceanic and bifurcated shelf-break fronts. Dynamics within St Helena Bay consistently differed from those further offshore, due to the influences of the shelf-break front, Cape Columbine upwelling plume, and cyclonic recirculation, which appeared to be associated with an intra-annual signal with a periodicity of 3-4 months. Persistent hypoxia in the bottom waters suggested the occurrence of a permanent reservoir of Low Oxygen Water (LOW). Seasonal shoreward and offshore expansion of LOW occurred throughout the upwelling season, with maximum extent reached during summer and autumn, due to the coupled effects of advection and local phytoplankton decay. While wind mixing ventilated the water column at near-shore stations in winter, and the onset of upwelling during spring introduced oxygen-richer water from further offshore, hypoxia persisted in the centre of the Bay. This article is protected by copyright. All rights reserved.
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Preface Acknowledgments 1. The Oceans 2. Basic Equations 3. Boundary Conditions at the Air-Sea Interface 4. Geostrophic Flow 5. Planetary Boundary Layers 6. Barotropic Ocean Circulation 7. Baroclinic Ocean Flows 8. General Circulation of a Baroclinic Ocean with Bottom Topography 9. Surface Gravity Waves 10. Inertial Motions 11. Astronomical Tides 12. Vorticity Appendices References Recommended Books Index
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All Agulhas rings that were spawned at the Agulhas retroflection between 1993 and 1996 (a total of 21 rings) have been monitored using TOPEX/Poseidon satellite altimetry and followed as they moved through the southeastern Atlantic Ocean, decayed, interacted with bottom topography and each other, or dissipated completely. Rings preferentially crossed the Walvis Ridge at its deepest parts. After having crossed this ridge they have lower translational speeds, and their decay rate decreases markedly. Half the decay of long-lived rings takes place in the first 5 months of their lifetimes. In addition to the strong decay of rings in the Cape Basin, about one third of the observed rings do not seem to leave this region at all but totally disintegrate here. The interaction of rings with bottom topography, in particular with the Vema Seamount, is shown frequently to cause splitting of rings. This will enhance mixing of the rings' Indian Ocean water into that of the southern Atlantic. This localized mixing may well provide a considerable source of warm and salty Indian Ocean water into the Atlantic overturning circulation.
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Quantitative provenance analysis based on high-resolution bulk-petrography and heavy-mineral data on beach and dune sands, integrated with detrital-zircon geochronology and chemical analyses of pyroxene, garnet and staurolite, demonstrates that sand derived from the Orange River is carried by powerful and persistent longshore currents as far as northern Namibia and southern Angola, 1750 km north of its mouth. This is the longest cell of littoral sand transport documented so far. Compositional forward modeling indicates that ≥ 80% of dune sand in the Skeleton Coast is Orange-derived, the remaining ≤ 20% being supplied by slow erosion of the Damara Orogen chiefly via the Swakop River. A decrease in basaltic rock fragments and pyroxene with relative enrichment in garnet, staurolite, tourmaline and other metamorphic minerals north of Walvis Bay indicates that only one-third of beach sand in the 350 km dune-free gap between the Namib and Skeleton Coast Ergs is Orange-derived, the remaining two-thirds being supplied largely by the Swakop River draining the Damara Orogen. Although volcanic gravel becomes dominant in beaches of the Skeleton Coast north of the Uniab mouth, detritus from Cretaceous Etendeka lavas accounts for only 4% of beach sand, reflecting limited sand generation in the arid catchment. Contributions from the Kunene River to either dune or beach sands is ruled out, indicating that gem diamonds found in placer deposits along the coast of Namibia are all derived from the Orange River.
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We have analysed alkenones in 149 surface sediments from the eastern South Atlantic in order to establish a sediment-based calibration of the U37K′ paleotemperature index. Our study covers the major tropical to subpolar production systems and sea-surface temperatures (SST’s) between 0° and 27°C. In order to define the most suitable calibration for this region, the U37K′ values were correlated to seasonal, annual, and production-weighted annual mean atlas temperatures and compared to previously published culture and core-top calibrations. The best linear correlation between U37K′ and SST was obtained using annual mean SST from 0 to 10 m water depth (U37K′ = 0.033 T + 0.069, r2 = 0.981). Data scattering increased significantly using temperatures of waters deeper than 20 m, suggesting that U37K′ reflects mixed-layer SST and that alkenone production at thermocline depths was not high enough to significantly bias the mixed-layer signal. Regressions based on both production-weighted and on actual annual mean atlas SST were virtually identical, indicating that regional variations in the seasonality of primary production have no discernible effect on the U37K′ vs. SST relationship. Comparison with published core-top calibrations from other oceanic regions revealed a high degree of accordance. We, therefore, established a global core-top calibration using U37K′ data from 370 sites between 60°S and 60°N in the Atlantic, Indian, and Pacific Oceans and annual mean atlas SST (0–29°C) from 0 m water depth. The resulting relationship (U37K′ = 0.033 T + 0.044, r2 = 958) is identical within error limits to the widely used E. huxleyi calibrations of Prahl and Wakeham (1987) and Prahl et al. (1988) attesting their general applicability. The observation that core-top calibrations extending over various biogeographical coccolithophorid zones are strongly linear and in better accordance than culture calibrations suggests that U37K′ is less species-dependent than is indicated by culture experiments. The results also suggest that variations in growth rate of algae and nutrient availability do not significantly affect the sedimentary record of U37K′ in open ocean environments.
Article
We reexamine the relationship between circulation, bathymetry, and surface chlorophyll in the Southern Ocean, using new high-resolution maps of the frontal structure of the Antarctic Circumpolar Current (ACC) derived from satellite altimetry. The maps reveal that the ACC consists of multiple filaments or jets. By averaging surface chlorophyll measurements along streamlines, we show that the fronts define the limits of zones with similar concentrations and seasonality of surface chlorophyll. The overall pattern of surface chlorophyll is consistent with strongest upwelling of nutrient-rich deep water south of the Polar Front (PF). However, the distribution of chlorophyll in the Southern Ocean is concentrated in a number of persistent blooms, observed downstream of islands and bathymetric features. In contrast to previous studies, we find little evidence that the fronts of the ACC are associated with enhanced productivity, at least where the fronts are distant from topography. Rather, we find that most regions of elevated chlorophyll in the open Southern Ocean can be explained by upwelling of nutrients (both macronutrients and micronutrients) where the ACC interacts with topography, followed by downstream advection. The upwelling is shown to be the consequence of the bottom pressure torque established by the large-scale flow, rather than being due to small-scale instabilities of the jets. The interaction of the flow with the topography therefore establishes both the large-scale dynamical balance of the ACC and determines the productivity of the open Southern Ocean.
Article
The Holocene lithostratigraphy and geochronology of sediments on an inner continental-shelf mudbelt off the west coast of southern Africa is presented. Based on a study of seven large gravity cores, numerous grab samples and two vibracores, two distinctive sections of the mudbelt have been identi” ed. The northern section is associated with the Orange River prodelta, and is dominated by laminated clay-rich sediments, while the southern section off Namaqualand is associated with more homogeneous muds. AMS radiocarbon ages of 31 samples from these cores are problematic due to the absence of expected modern material at the sedimentocean interface and numerous age reversals and inconsistencies in some of the cores. Possible mechanisms to explain the apparently anomalously old surface and near-surface samples are suggested. Most likely expla nations appear to lie in a combination of sediment-retrieval problems, the periodic loss of ” ne particulate organic carbon from within the water column, the sampling of possible relic sediments and, most likely of all, the incorporation into the sediments of 14C-depleted terrigenous organic matter. The age reversals are especially evident in the laminated sediments, and the entrainment of ‘old’ carbon from the terrestrial source of these sediments is offered as the most parsimonious explanation. Stable carbon isotope analyses and a single lumi nescence age support the contention that radiocarbon date inconsistencies are a consequence of terrestrial inputs of carbon which is non-contemporaneous with the actual time of sedimentation. In studies of offshore accumulations of terrigenous material, the marine-derived organic fraction may therefore prove a more reliable measure of radiocarbon chronology.
Article
Models of southern African palaeoclimate implicate surface atmospheric circulation anoma lies as forcing large-scale changes during the Late Quaternary. The available proxy data are insufficient to test the models since they provide information about temperature and rainfall rather than surface circulation. A conceptual model is proposed which links coastal ocean temperatures with atmospheric circulation and allows a history of surface circulation to be inferred from sea-temperature data. A Holocene sea-surface temperature (SST) record was constructed by measuring the oxygen isotope composition of marine mollusc shells preserved in an archaeological cave deposit on the coast of the eastern Agulhas Bank, southern Africa. Radiocarbon-dating of individual shells allowed definition of the timing and timespan of events in the record. By serially sampling along the growth axis of each shell, information was obtained about intra-annual variability as well as millennial-scale trends. During the early Holocene, the sea surface on the eastern Agulhas Bank was colder than it is at present. Maximum summer and winter temperatures obtained 5800 years ago, exceeding by more than 2°C those recorded in the region today during non-El Nino years. On average, temperatures remained high for the following 1500 years but dropped again during the Late Holocene. At 650 BP, at the start of the 'Little Ice Age' in southern Africa, the surface waters on the eastern Agulhas Bank were colder during both winter and summer.
Article
Several sedimenit cores ai-ounid the coastal lake of Verlorenvlei, Westem Cape, have thus far revealed important details of the development of this semi-arid winter-rainfall environment during the late Quatemary. Complex interplay between climate change, sea-level fluctuation and human activities have characterized the Verlorenvlei record and suggests that these environments have been subject to high degrees of disturbance over time. However, due to the discontiniuous nature of the sedimentary record, the Holocene record has remained fragmentary. Investigation of a 6 in vibracore sequence at Klaarfontein (32&dgr;25′26″S; 18&dgr;29′40″E). an artesian spring site some 18 km inland of Eland's Bay. facilitates a more complete Holocene palaeoenivironmental reconstruction. Pollen concentrations in 37 spectra distributed through the 6 m core vary with organic content, but at all depths are stufficient to facilitate interpretation of vegetation history and reveal a high degree of dynamism in the local and regional environments. The lower sediments are characterized by elements strongly indicative of more xeric conditions and the catchment appears to have been dominated by drought-resisting woody shrubs. Local vegetation in the mid-Holocene is consistent with the occurrence of two sealevel transgressions resulting in each case in the development of a salt marsh at the site. The uppermost pollen spectra are all relatively modern (post 200 BP). Grass pollen declines from 1900 BP, possibly as a result of the occupation of the area by pastoralists, although climate change cannot be ruled out. A decline in pollen diversity towards the surface is associated with a further reduction in grass pollen and ani increase in the proportion of succulents, hence offerinig support for the hypothesis of significant colonial and post-colonial disturbance of the vegetation. The evaluation of the pollen sequence at Klaarfontein supports previous palaeoenvironmental reconstructions and at once reveals new insights regarding the complex Holocene limnology, hydrology and geomorphology of the Verlorenvlei system.
Article
The Cederberg Mountains (Western Cape Province, South Africa) are located within the Fynbos Biome, which exhibits some of the highest levels of species richness and endemism in the world. The region’s post-glacial vegetation history, however, remains largely unknown. Presented here is a high resolution pollen and microcharcoal records spanning the last 15,600 years obtained from the De Rif rock hyrax midden from the Driehoek Valley of the central Cederberg. In this region, previous pollen studies have shown muted variability in vegetation community composition during periods of globally marked climatic variability (e.g. the last glacial-interglacial transition). In our record, however, significant changes in vegetation composition are apparent. Most notably, they indicate a shift from ericaceous/restioid fynbos (present from 15,600 to 13,300 cal yr BP) to a brief, but prominent, development of proteoid fynbos at the beginning of the Holocene around 11,200 cal yr BP. This vegetation shift is associated with increased moisture at the site, and coincides with reduced fire frequency as indicated by the microcharcoal record. At 10,400 cal yr BP, there is a marked reduction in Protea-type pollen, which is replaced by thicket, characterised by Dodonaea, which became the dominant arboreal pollen type. This shift was likely the result of a long relatively fire-free period coupled with warmer and wetter climates spanning much of the early Holocene. A brief but marked decrease in water availability around 8500-8000 cal yr BP resulted in the strong decrease of Dodonaea pollen. The vegetation of the mid- to late Holocene is characterised by the increased occurrence of Asteraceae and succulent taxa, suggesting substantially drier conditions. These data give unprecedented insight into the vegetation dynamics across a period of substantial, rapid climate change, and while they confirm the presence of fynbos elements throughout the last 15,600 years, the results highlight significant fluctuations in the vegetation that were triggered by changes in both climate and fire regimes.
Article
The combined analysis of hydrographic, kinematic, and dynamic data collected during the 1997–1999 KAPEX (CAPe of Good Hope EXperiments) reveals a quasi-stationary meandering pattern of the Agulhas Retroflection Current east and upstream of the Southwest-Indian Ridge. The current meanders between 38°S and 40°S in a spatially and temporally continuous fashion and has a core width of approximately 70km with an associated transport of 44±5×106m3s−1 in the upper 1000m. Peak surface velocities decrease from 2.1ms−1 near the Agulhas Retroflection to 1.1ms−1 around 32°E. Meander troughs (northward extremes) are found predominantly near 26.8°E, 32.6°E and 38.9°E, while crests (southward extremes) are located with high probability near 29.7°E, 35.5°E and 42.9°E, resulting in a typical wavelength of 500km. Cold eddies are shed along the northern boundary of the current from meander troughs into the recirculation regime between the Agulhas Current proper and the Agulhas Return Current. Strongest cyclonic eddies are preferably shed in austral autumn. The cyclonic eddies so formed propagate westward at an average phase-speed of 5.4cms−1, with, however, a variability of at least the same magnitude. Subsequently, the cyclones are absorbed by the next meander trough located upstream and to the west of the shedding trough.
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We examined near-surface, late Holocene deep-sea sediments at nine sites on a north-south transect from the Congo Fan (4°S) to the Cape Basin (30°S) along the Southwest African continental margin. Contents, distribution patterns and molecular stable carbon isotope signatures of long-chain n-alkanes (C27-C33) and n-alkanols (C22-C32) are indicators of land plant vegetation of different biosynthetic types, which can be correlated with concentrations and distributions of pollen taxa in the same sediments. Calculated clusters of wind trajectories and satellite Aerosol Index imagery afford information on the source areas for the lipids and pollen on land and their transport pathways to the ocean sites. This multidisciplinary approach on an almost continental scale provides clear evidence of latitudinal differences in lipid and pollen composition paralleling the major phytogeographic zonations on the adjacent continent. Dust and smoke aerosols are mainly derived from the western and central South African hinterland dominated by deserts, semi-deserts and savannah regions rich in C4 and CAM plants. The northern sites (Congo Fan area and northern Angola Basin), which get most of their terrestrial material from the Congo Basin and the Angolan highlands, may also receive some material from the Chad region. Very little aerosol from the African continent is transported to the most southerly sites in the Cape Basin. As can be expected from the present position of the phytogeographic zones, the carbon isotopic signatures of the n-alkanes and n-alkanols both become isotopically more enriched in 13C from north to south. The results of the study suggest that this combination of pollen data and compound-specific isotope geochemical proxies can be effectively applied in the reconstruction of past continental phytogeographic developments.
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The Holocene climate of the Southern Ocean is not well understood, mainly because of the lack of high-resolution reconstructions of ocean surface properties. Here we present a 12,500-yr-long, decadal-scale record of Holocene sea-surface temperatures and sea- ice presence from the Polar Front of the East Atlantic Southern Ocean. The record shows gradual climate change, with no abrupt Neoglacial cooling, and an unprecedented late Holocene warming. The dominant forcing factor appears to be precessional insolation; Northern Hemisphere summer insolation correlates to at least the early to middle Holocene climate trend. Spectral analysis reveals centennial-scale cyclic climate changes with periods of 1220, 1070, 400, and 150 yr. The record shows good correlation to East Antarctic ice cores and to climate records from South Georgia and Bunger Oasis. However, the record shows out-of-phase behavior with regard to climate records from the western Antarctic Peninsula and the Peru-Chile Current; such behavior hints at a climatic divide through Patagonia, the Drake Passage, and between West and East Antarctica.
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Mineral dust sources were identified in Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) images along the south‐west coast of Africa. Up to 150 dust plumes were observed over a 3 year period, and these are linked to sources that are either salt pans or dry river beds in the Namib Desert. This demonstrates that dust supply is maintained by fluvial landforms and associated hydrology. This paper highlights the need to look in more detail at source areas around the globe, as this will further our understanding of dust‐production processes.
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A series of sediment cores extracted from what is today a large freshwater coastal lake, Verlorenvlei, has been sub-sampled, radiocarbon-dated and subjected to a range of palaeoenvironmental techniques, in particular pollen analysis, sedimentology and geochemistry. A mid-late-Holocene higher sea level is evident in the cores indicating the rapidity with which sea level change can occur and invoke other forms of environmental response. Following a hiatus in sedimentation, most probably around 3800BP, the marine conditions at the site were replaced by fresh water as the dominant hydrological and ecological influence. Laminated organic sediments in some of the cores suggest that, around 300years ago, a fresh water lake characterised Verlorenvlei. Since then, the picture revealed by high-resolution palynology is one of progressive levels of human disturbance both in and around the study area. Sedimentological and palaeoecological analyses of additional cores from the vlei, two from the distal (inland) and one from the proximal (coastal) end of the system, serve further to elucidate the precise nature of sea level change in the late Holocene and facilitate the construction of a refined Holocene sea level curve for the region. Environmental changes in the late Holocene are shown to be especially dynamic.