Southern Hemisphere anticyclonic circulation drives oceanic and climatic conditions in late Holocene southernmost Africa

Hahn, Annette; Schefuß, Enno; Andó, Sergio; Cawthra, Hayley C.; Frenzel, Peter; Kugel, Martin; Meschner, Stephanie; Mollenhauer, Gesine; Zabel, Matthias

doi:10.5194/cp-13-649-2017

Cited by 37 publications

(15 citation statements)

References 80 publications

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“…The Benguela upwelling system is divided into two distinct subsystems, north and south, separated by the Lüderitz upwelling cell at 27 • S (Hutchings et al, 2009). Upwelling in South Benguela varies seasonally, with the strongest upwelling in austral summer (December-February) (Tim et al, 2015), when the South Atlantic subtropical high has moved southward to induce trade winds parallel to the coast.…”

Section: Introductionmentioning

confidence: 99%

Analysis of the position and strength of westerlies and trades with implications for Agulhas leakage and South Benguela upwelling

et al. 2019

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Abstract. 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.

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Section: Introductionmentioning

confidence: 99%

Analysis of the position and strength of westerlies and trades with implications for Agulhas leakage and South Benguela upwelling

et al. 2019

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“…δ 2 Hn-alkane and δ 13 Cn-alkane from marine sediments recovered off the mouth of the Gouritz River (GeoB18308-2; Fig. 1) show a very similar pattern to Voёlvlei over the past 4,000 cal BP (Hahn et al, 2017) (Fig. 7).…”

Section: Paleoenvironmental and -Climate Evolutionmentioning

confidence: 85%

“…However, the terrestrial climate signals in these coastal archives are often overprinted by marine water intrusions induced by relative sea level change during the Holocene (Martin, 1959(Martin, , 1968Reinwarth et al, 2013;Wündsch et al, 2018;Wündsch et al, 2016a) or anthropogenic impact (Haberzettl et al, 2019). Further paleoenvironmental information from this area is available from e.g., peatlands (Quick et al, 2016;Strobel et al, 2019) and speleothems (Braun et al, 2018;Braun et al, 2020;Talma and Vogel, 1992), rock hyrax midden (Chase et al, 2019;Chase et al, 2017;Chase et al, 2015) and marine sediments (Hahn et al, 2017) (Fig. 1 A).…”

Section: Introductionmentioning

confidence: 99%

Holocene sea level and environmental change at the southern Cape – an 8.5 kyr multi-proxy paleoclimate record from lake Voёlvlei, South Africa

Strobel¹,

Bliedtner²,

Carr³

et al. 2020

Preprint

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Abstract. 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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“…Meteor, with promising spots identified from the subbottom profiling surveys. Details of these sampling campaigns are given in Ekau et al (2014), Cawthra et al (2016), Hahn et al (2017) and Zabel et al (2017).…”

Section: Offshore Field Mappingmentioning

confidence: 99%

The chronological, sedimentary and environmental context for the archaeological deposits at Blombos Cave, South Africa

Jacobs

Jones

Cawthra

et al. 2020

Quaternary Science Reviews

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The site of Blombos Cave (BBC) is well known for archaeological remains that have advanced our understanding of the development of modern human behaviour during the Middle Stone Age (MSA). Occupation of the cave occurred against a backdrop of landscape-scale environmental and sedimentary processes that provide the broader context for finer-scale interpretations of the site-formation history and archaeological patterns detected in the cave deposits. Aeolian and palaeosol sequences are abundant in the vicinity of BBC and these provide a partial view of the past landscapes available to the inhabitants of the cave. An important extension to the palaeo-landscape around BBC currently lies submerged on the Agulhas Bank, as sea levels were lower than at present for the entire period of human occupation of BBC. In this paper, we revisit the optically stimulated luminescence (OSL) chronology for the full sequence of sediment deposition inside BBC, increasing the number of dated samples to a total of 40 and revising the period of MSA occupation to between 97.7 ± 7.6 and 71.0 ± 5.7 ka (uncertainties at 95.4% probability). We describe the geological successions at four main areas around BBC, estimate the time of sediment deposition using OSL, and describe and interpret three seismic profiles on the Agulhas Bank, offshore of BBC. By correlating these onshore and offshore geological sequences with the sedimentary deposits inside BBC, we place the archaeological record within a landscape-scale chrono-stratigraphic framework to examine how environmental changes may have regulated the presence or absence of humans in the cave and surrounding terrain between about 100 and 70 ka.

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Southern Hemisphere anticyclonic circulation drives oceanic and climatic conditions in late Holocene southernmost Africa

Cited by 37 publications

References 80 publications

Analysis of the position and strength of westerlies and trades with implications for Agulhas leakage and South Benguela upwelling

Analysis of the position and strength of westerlies and trades with implications for Agulhas leakage and South Benguela upwelling

Holocene sea level and environmental change at the southern Cape – an 8.5 kyr multi-proxy paleoclimate record from lake Voёlvlei, South Africa

The chronological, sedimentary and environmental context for the archaeological deposits at Blombos Cave, South Africa

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