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

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.

Unveiling Profound Seasonal and Spatial Dynamics of Greenhouse Gases (CO2, CH4, N2O) in the Northern Benguela Upwelling System Unnamed Article

“…An increase in organic carbon burial is associated with factors such as enhanced primary production, shallower water depths, and amplified oxygen depletion in bottom waters during the autumn and summer seasons, in contrast to the winter season was also underscored previously (e.g. Santana-Casiano, et al, 2009;Siddiqui, et al, 2023).…”

“…In these regions, waters enriched in nutrients and GHG are brought close to the surface, triggering both phytoplankton blooms and the release of these gases to the atmosphere (Capone and Hutchins, 2013). Yet, the ocean's contribution to the atmospheric budget of these GHG is associated with a large range of uncertainty due to limited in-situ measurements and large intrinsic heterogeneity, whereby seasonal variability due to coastal upwelling is the dominant factor (Weber et al, 2019;Yang et al, 2020;Siddiqui et al, 2023). The Benguela upwelling system (BUS) comprises one of the most productive marine ecosystems worldwide and it is one of the four major global coastal upwelling regions.…”

“…Certain regions within the BUS were previously recognized as carbon sinks, characterized by elevated rates of primary production and sedimentary organic carbon. However, in other areas, there has been a transition to becoming CO 2 sources, primarily attributed to the upwelling of mineralized organic compounds (e.g., Carr, 2002;Mollenhauer et al, 2002;Siddiqui et al, 2023). This shift from carbon sinks to sources is influenced by temporal oscillations, highlighting the dynamic nature of these ecosystems (Zhang et al, 2022).…”