Regional and global impact of CO2 uptake in the Benguela Upwelling System through preformed nutrients

Claire Siddiqui; Tim Rixen; Niko Lahajnar; Anja K Van der Plas; Deon C Louw; Tarron Lamont; Keshnee Pillay

doi:10.1038/s41467-023-38208-y

Regional and global impact of CO₂ uptake in the Benguela Upwelling System through preformed nutrients

Nat Commun. 2023 May 4;14(1):2582. doi: 10.1038/s41467-023-38208-y.

Authors

Claire Siddiqui¹, Tim Rixen^{2

3}, Niko Lahajnar³, Anja K Van der Plas⁴, Deon C Louw⁵, Tarron Lamont^{6

7

8}, Keshnee Pillay⁶

Affiliations

¹ Leibniz Centre for Tropical Marine Research - ZMT, Fahrenheitstrasse 6, 28359, Bremen, Germany. claire.siddiqui@leibniz-zmt.de.
² Leibniz Centre for Tropical Marine Research - ZMT, Fahrenheitstrasse 6, 28359, Bremen, Germany.
³ Institute of Geology, Universität Hamburg, Bundesstrasse 55, 20146, Hamburg, Germany.
⁴ National Marine Information and Research Centre, PO Box 912, Swakopmund, 13001, Namibia.
⁵ Debmarine Namibia, 10 Dr Frans Indongo Street, Windhoek, 10005, Namibia.
⁶ Oceans & Coasts Research Branch, Department of Environment, Forestry and Fisheries, PO Box 52126, Victoria & Alfred Waterfront, Cape Town, 8000, South Africa.
⁷ Marine Research Institute & Department of Oceanography, University of Cape Town, Rondebosch, South Africa.
⁸ Bayworld Centre for Research & Education, 5 Riesling Road, Constantia, Cape Town, 7806, South Africa.

Abstract

Eastern Boundary Upwelling Systems (EBUS) are highly productive ecosystems. However, being poorly sampled and represented in global models, their role as atmospheric CO₂ sources and sinks remains elusive. In this work, we present a compilation of shipboard measurements over the past two decades from the Benguela Upwelling System (BUS) in the southeast Atlantic Ocean. Here, the warming effect of upwelled waters increases CO₂ partial pressure (pCO₂) and outgassing in the entire system, but is exceeded in the south through biologically-mediated CO₂ uptake through biologically unused, so-called preformed nutrients supplied from the Southern Ocean. Vice versa, inefficient nutrient utilization leads to preformed nutrient formation, increasing pCO₂ and counteracting human-induced CO₂ invasion in the Southern Ocean. However, preformed nutrient utilization in the BUS compensates with ~22-75 Tg C year^-1 for 20-68% of estimated natural CO₂ outgassing in the Southern Ocean's Atlantic sector (~ 110 Tg C year^-1), implying the need to better resolve global change impacts on the BUS to understand the ocean's role as future sink for anthropogenic CO₂.