Holocene variability in climate and oceanic conditions in the winter rainfall zone of South Africa—inferred from a high resolution diatom record from Verlorenvlei

Abstract

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. Figure 4. Downcore percentage abundance of key diatom species of the VER14 composite core relative to age (cal a BP) and depth (cm) based on salinity preferences. Where: Aulacoseira group = A. granulata, A. granulata v. angustissma, A. ambigua; Fragilaria sensu lato (= Staurosirella pinnata, Pseudostaurosira elliptica); Diploneis (agg) (= Diploneis crabro, D. caffra and D. interrupta); and Coscinodiscus species (= C. nodulifer, C. perforatus, C. radiatus). The community is subdivided into three biological zones based on CONISS. [Color figure can be viewed at wileyonlinelibrary.com]

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

“…The proxies used in this study generally support the assumed sea-level evolution at the southern Cape coast of South Africa (Kirsten et al, 2018b;Marker and Miller, 1993;Reddering, 1988;Wündsch et al, 2018Wündsch et al, , 2016a. In (supra-)regional comparison, these results are also in line with studies from the west coast of South Africa (Baxter and Meadows, 1999;Carr et al, 2015;Kirsten et al, 2020) and Namibia (Compton, 2006), as reviewed in Cooper et al (2018), showing a rapid sea level rise to a maximum of +3.8 m a.s.l. (ca.…”

An uncertainty-focused database approach to extract spatiotemporal trends from qualitative and discontinuous lake-status histories

“…The Verlorenvlei catchment occupies 1890 km 2 , comprising the Verlorenvlei River, its tributaries, extensive marshes, and a coastal lake, and is distinctive both topographically and geologically (Kirsten et al, 2020). Shifting sands and dune building during the late Holocene led to a southward migration of the mouth and the near isolation of the valley from the sea, forming a narrow, 2.5 km long estuarine channel.…”

“…Information on Verlorenvlei's lake-status history is sourced from Kirsten et al (2020). The record covers the last ~10,000 years but a strong proportion of marine taxa is visible from the diatom abundance diagram, which suggest full marine conditions at Verlorenvlei during most of the Holocene.…”

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

“…Africa (Baxter and Meadows, 1999;Carr et al, 2015;Kirsten et al, 2020) and Namibia (Compton, 2006), as reviewed in Cooper et al (2018) showing a rapid sea level rise to a maximum of +3.8 m a.sl. (~7,600 -5,800 cal BP), followed by decrease to +1 m a.sl.…”