Organic carbon sequestration is insensitive to variability in surface productivity in the Subantarctic Zone: implications for enhancing the biological carbon pump for climate mitigation

[Geoengineering News]

https://essopenarchive.org/users/621328/articles/1368681-organic-carbon-sequestration-is-insensitive-to-variability-in-surface-productivity-in-the-subantarctic-zone-implications-for-enhancing-the-biological-carbon-pump-for-climate-mitigation

Authors: Cathryn Ann Wynn-Edwards, Xiang Yang, Scott D Nodder, Elizabeth H. Shadwick

12 December 2025

Abstract

The efficiency and stability of the biological carbon pump (BCP) set the ocean’s capacity to sequester carbon on climate-relevant timescales. Despite its importance, the BCP is difficult to observe directly making quantification of its efficiency challenging. Here, we present multi-year sediment trap records from two sites in the iron-limited Subantarctic Zone (SAZ): the Southern Ocean Time Series (SOTS; south of Australia) and the Subantarctic Mooring (SAM; east of Aotearoa New Zealand). Particle fluxes are combined with satellite-based net primary production (NPP) to investigate the links between variability at the surface and the delivery of material to depth. Despite higher NPP at SAM, annual particulate organic carbon (POC) flux was not significantly different at the two sites. Interannual anomalies in NPP are much smaller than POC flux anomalies and are weakly correlated with POC flux. At the SOTS site, the correlation between BSi and POC flux suggests that silicifying phytoplankton are important for the delivery of material to depth. By contrast, ballasting material has very little predictive value for annual POC flux at the SAM site. These results show that carbon sequestration is not necessarily related to short-term surface variability, implying limited leverage of productivity-enhancement strategies (e.g., iron fertilization) for enhancing the BCP in the SAZ. This underscores the need to distinguish carbon export near the surface from carbon retained at depth in order to quantify baseline variability in the BCP prior to evaluating the feasibility of proposed climate mitigation strategies that aim to enhance deep ocean carbon sequestration.

Source: ESS Open Archive