Variability in the Benguela Current upwelling system over the past 70,000 years

Summerhayes, Colin; Kroon, Dick; Rosell‐Melé, Antoni; Jordan, Richard W.; Schrader, Hans; Hearn, Ruth; Villanueva, Joan; Grimalt, Joan O.; Eglinton, G.

doi:10.1016/0079-6611(95)00008-5

Cited by 141 publications

(103 citation statements)

References 66 publications

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“…Indeed, northern Benguela SSTs were lower during glacial than interglacial stages (Kirst et al 1999). SST-records from the eastern Walvis Ridge and the upper continental slope off Walvis Bay also support the notion that upwelling was generally more intense during glacials (Oberhånsli 1991;Summerhayes et al 1995). Cohen & Tyson (1995) propose a valuable model, which predicts the response of coastal SSTs around South Africa to the displacement and intensification of the atmospheric circulation features associated with extended, i.e.…”

Section: Pathway Atmospherementioning

confidence: 74%

“…Owing to several ODP-expeditions on the continental slope off southwest Africa, the Pleistocene evolution of upwelling is relatively well known, (e.g. Diester-Haas et al 1988;Oberhånsli 1991;Summerhayes et al 1995;Kirst et al 1999;Berger & Wefer 2002;Kim et al 2002). In contrast, only few studies (e.g.…”

Section: Introductionmentioning

confidence: 98%

“…1). Following this assumption, the cooling of the southern Benguela during the Younger Dryas and oxygen isotope stages 2-4 has been ascribed to slackened thermohaline overturn and a correspondingly reduced input of warm Agulhas Water (Cohen et al 1992;Summerhayes et al 1995).…”

Section: Pathway Oceanmentioning

confidence: 99%

“…Holmes et al 1999). In fact, Quaternary-age sediment cores from the continental slope off Walvis Bay display a close negative correlation between AR TOC and SST (Summerhayes et al 1995;Kirst et al 1999). …”

mentioning

confidence: 99%

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Nutrient regime and upwelling in the northern Benguela since the middle Holocene in a global context - a multi-proxy approach

et al. 2011

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The last 5500 years of climate change and environmental response in the northern Benguela Coastal Upwelling are reconstructed by means of three sediment cores from the inner shelf off central Namibia. The study is based on nutrient (delta(15)N, delta(13)C) and productivity proxies (accumulation rates of total organic carbon; AR(TOC)). Reconstructed sea surface temperatures (alkenone-derived SST) and temperatures at subsurface depths (T(delta 18O); based on tests of planktonic foraminifers) reflect the physical boundary conditions. The selection of proxy indicators proved a valuable basis for robust palaeo-climatic reconstructions, with the resolution ranging from multi-decadal (NAM1) over centennial (core 178) to millennial scale (core 226620). The northern Benguela experienced pronounced and rapid perturbation during the middle and late Holocene, and apparently, not all are purely local in character. In fact, numerous correlations with records from the adjacent South African subcontinent and the northern hemisphere testify to global climatic teleconnections. The Holocene Hypsithermal, for instance, is just as evident as the Little Ice Age (LIA) and the Roman Warm Period. The marked SST-rise associated with the latter is substantiated by other marine and terrestrial data from the South African realm. The LIA (at least its early stages) manifests itself in intensified winds and upwelling, which accords with increased rainfall receipts above the continental interior. It appears that climate signals are transferred both via the atmosphere and ocean. The combined analysis of SST and T(delta 18O) proved a useful tool in order to differentiate between both pathways. SSTs are primarily controlled by the intensity of atmospheric circulation features, reflecting changes of upwelling-favourable winds. T(delta 18O) records the temperature of the source water and often correlates with global ocean conveyor speed due to varying inputs of warm Agulhas Water. It seems as though conveyor slowdown or acceleration not only affected the temperature of the source water but also its nutrient content. This relationship between source water quality and conveyor speed is already known from glacial times

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Section: Pathway Atmospherementioning

confidence: 74%

Section: Introductionmentioning

confidence: 98%

Section: Pathway Oceanmentioning

confidence: 99%

mentioning

confidence: 99%

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Nutrient regime and upwelling in the northern Benguela since the middle Holocene in a global context - a multi-proxy approach

et al. 2011

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“…The candidates are shelf-edge upwelling processes (Barange and Pillar 1992;Summerhayes et al 1995b;Holmes et al 1998;Pichevin et al 2005), nitrogen fixation in the outer fringes of the coastal upwelling cell (for which there is no independent evidence), or advection of particulate nitrogen with low d 15 N from outside the upwelling system. An indication for the latter process may be the cluster of low ratios found around 20°S, in water depths around 500 m, because this feature cannot be fuelled by upwelling nitrate from the coastal cells.…”

Section: Nutrient Utilisation and Denitrification Intensity From D 15 Nmentioning

confidence: 99%

Variability in upwelling intensity and nutrient regime in the coastal upwelling system offshore Namibia: results from sediment archives

Emeis

Struck

Leipe

et al. 2007

Int J Earth Sci (Geol Rundsch)

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The coastal upwelling system offshore Namibia is ideally suited to address a focal question of the Integrated Marine Biogeochemistry and Ecosystem Research Programme: what are the mechanisms that drive long-term changes in ecosystems? Considerable interannual variability in climatic forcing is indicated by long time series of meteorological and remote sensing observation; these accompany considerable interannual to interdecadal changes in the upwelling intensity over the last 100 years, as well as a centennial trend. On longer time scales, the only archives available are sediment records spanning the late Holocene. To decipher the sediment record, we mapped surface-sediment patterns of proxies for physical (sea surface temperature/SST from alkenone unsaturation indexes) and nutrient (d 15 N on bulk sedimentary N) variables. Their present-day surface-sediment patterns outline the coastal upwelling cells and filaments and associated high productivity area. Analysed in an array of dated sediment cores, the spatial patterns of SST suggest long-term ([100 years) variability in the location and intensity of individual upwelling cells. The patterns of d 15 N outline an area of intense denitrification near the coast, and advection of water with low-oxygen concentrations in the undercurrent from the North. d 15 N exhibits considerable downcore variability, in particular over the last 50 years. The variability appears to be governed by differences in extent of denitrification and thus of the shelf oxygen balance, which appears to have deteriorated in the last 50 years. Together, the data suggest that SST and denitrification conditions have remained in the narrow bounds outlined by today's patterns in surface sediments, but that spatially small variability in upwelling intensity and make-up of upwelling feed waters induced considerable changes in the lower trophic levels of the coastal upwelling ecosystem over the last 6,000 years. Attempts to correlate proxy records from sediments with observational time series and regional climate reconstructions were not successful, possibly because annual to interannual environmental signals are erased in the process of sediment formation.

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The interplay between the surface and bottom water environment within the Benguela Upwelling System over the last 70 ka

et al. 2016

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The Benguela Upwelling System (BUS), located between 30 and 20°S, is one of the fundamental high-productivity systems of the world ocean. The BUS has previously been studied in terms of primary productivity and ecology over glacial-interglacial timescales; however, the response and coupling with the benthic environment have received little attention. Here, for the first time, we present a high-resolution reconstruction of the BUS highlighting the link between surface and benthic productivity and their response to climatic and oceanographic changes over the last 70 ka. The study is based on benthic foraminiferal faunal analysis together with analyses of diatom assemblages, grain size of the terrigenous fraction, and stable O and C isotopic and bulk biogenic components of core GeoB3606-1. We reveal significant shifts in benthic foraminiferal assemblage composition. Tight coupling existed between the surface and bottom water environment especially throughout marine isotope stages 4 and 3 (MIS4 and MIS3). Due to the high export production, the site has essentially experienced continuous low oxygen conditions; however, there are time periods where the hypoxic conditions were even more notable. Two of these severe hypoxic periods were during parts of MIS4 and MIS3 where we find an inverse relationship between diatom and benthic foraminifera accumulation, meaning that during times of extremely high phytodetritus export we note strongly suppressed benthic productivity. We also stress the importance of food source for the benthos throughout the record. Shifts in export productivity are attributed not only to upwelling intensity and filament front position, but also, regional-global climatic and oceanographic changes had significant impact on the BUS dynamics.

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Variability in the Benguela Current upwelling system over the past 70,000 years

Cited by 141 publications

References 66 publications

Nutrient regime and upwelling in the northern Benguela since the middle Holocene in a global context - a multi-proxy approach

Nutrient regime and upwelling in the northern Benguela since the middle Holocene in a global context - a multi-proxy approach

Variability in upwelling intensity and nutrient regime in the coastal upwelling system offshore Namibia: results from sediment archives

The interplay between the surface and bottom water environment within the Benguela Upwelling System over the last 70 ka

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