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

Abstract

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.

A comparison of benthic foraminiferal Mn / Ca and sedimentary Mn / Al as proxies of relative bottom-water oxygenation in the low-latitude NE Atlantic upwelling system

“…Inset: location of the study area off coastal NW Africa. Modified after Romero et al (2008). inates the foraminiferal fauna during very high diatom input (Caralp, 1984;Filipsson et al, 2011;McKay et al, 2014McKay et al, , 2015. Therefore E. exilis, being present (albeit in considerably varying abundance) throughout the GeoB7926-2 record, is an ideal candidate to record oxygen changes in the environment in which they lived and also provide an opportunity to test if export productivity is causing low-oxygen conditions as opposed to the dominance of this species merely being a fresh phytodetritus diet signal (Caralp, 1989).…”

Refining the planktic foraminiferal I/Ca proxy: Results from the Southeast Atlantic Ocean

“…Ocean deoxygenation has been observed in large areas of the Southeast Atlantic Ocean in the past five decades (Schmidtko et al, 2017). Previous studies reconstructed glacial-interglacial histories of sea surface temperature (SST) (e.g., Farmer et al (2005); Mollenhauer et al (2003); Pichevin et al (2005a)) and primary productivity (e.g., Mollenhauer et al (2002); Romero et al (2015)), but few studies focused on reconstructing water column oxygenation (e.g., McKay et al (2016)). Information on glacial-interglacial changes in oceanic oxygenation may help inform us on the extent of and controls on potential future ocean deoxygenation.…”

Nutrient utilization and diatom productivity changes in the low-latitude SE Atlantic over the past 70 kyr: Response to Southern Ocean leakage

“…• 05 E, 1785 m water depth), providing an exceptionally high-resolution paleoclimatic archive of nutrient conditions, productivity, and sea surface temperature (SST) variations off Namibia for the past 70 kyr (McKay et al, 2016;Romero et al, 2015Romero et al, , 2003Romero, 2010;Shukla and Romero, 2018, Supplemental Material). The robust age model for core GeoB3606-1 has been published elsewhere (Romero, 2010;Romero et al, 2015), with additional radiocarbon dates from McKay et al (2016). The published conventional 14 C ages have been converted to calendar ages.…”

“…The published conventional 14 C ages have been converted to calendar ages. High-resolution counts of diatom valves, bulk biogenic components, planktonic and benthic foraminifera stable isotopes and alkenone-based SST have been previously published (Romero, 2010;Romero et al, 2015;McKay et al, 2016). At site GeoB3606-1, diatoms are the main contributors to the opal fraction.…”