Monteiro, PMSBoyd, PWHauck, JMongwe, PNicholson, Sarah-AnneThomalla, Sandy JWard, BMeredith, MPMelbourne-Thomas, JGarabato, ACNRapheal, M2026-03-072026-03-072025978‑1‑032‑52081‑0978‑1‑032‑50086‑7978‑1‑003‑40647‑1DOI: 10.4324/9781003406471-5http://hdl.handle.net/10204/14723The Southern Ocean (SO) plays a critical role in the earth’s carbon–climate– biogeochemistry nexus through its mediation of both anthropogenic and natural carbon fluxes as well as the earth’s energy imbalance and nutrient supplies that support 75% of ocean primary production outside the SO (Sarmiento et al., 2004; Frölicher et al., 2015). In the industrial period, these links are dominated by the two large negative feedback fluxes of the CO2 sink (±0.75PgCy−1; ±40% of the ocean CO2 sink: 1985–2018) and heat uptake (±70% of the energy imbalance) (Frölicher et al., 2015; Hauck et al., 2023). The sensitivity and complexity of these strong SO–Earth System (ES) carbon and climate feedback links are emphasized by recent work, which suggests that the elimination of the NH aerosol impact on shortwave radiation may rebalance the magnitudes of the SO carbon and heat sinks (Williams et al., 2024). These two negative feedback fluxes are the core of the strong links between the SO and the ES (Frölicher et al., 2015; Menviel and Spence, 2024). The SO is linked to the ES through both the relatively fast atmospheric forcing (1–10 years) and the slow (10–100s years) MOC in the ocean, with the mixed layer (ML) as the connection between them (Figure 5.1). Both drive and are influenced by the feedback of CO2 , heat, and wind (Figure 5.1; see Chapters 3 and 4 for atmosphere and ocean physics, respectively). The fluxes link across these three domains and the resulting feedback provides the context to understand and project the past, present, and future role of the SO in the ES (Chikamoto and DiNezio, 2021; Katavouta and Williams, 2021; Roy et al., 2021; Menviel and Spence, 2024). Here, we outline these links and then characterize the carbon and climate ocean processes that explain the large carbon and heat sinks and their feedback at global and regional SO scales (Figure 5.1).FulltextenSouthern Ocean carbon cycleAnthropogenic CO₂ sinkOcean heat uptakeMeridional Overturning CirculationMOCEarth system biogeochemistryBookN/A