The Heat and Carbon Characteristics of Modeled Mesoscale Eddies in the South–East Atlantic Ocean

Abstract

Mesoscale eddies provide critical links between the atmosphere and the ocean interior modulating the exchanges of key climatic tracers across the air‐sea and mixed‐layer interface. Mesoscale eddies, widespread in the Southern Ocean, are unresolved by Earth System Models; to what extent they modify contemporary and future heat and CO2 uptake remains unknown. The missing contribution of mesoscale eddies and their effects on properties and fluxes of heat and CO2 are investigated in the South‐East Atlantic using a mesoscale resolving (1/12°) physical biogeochemical model. Unsupervised Self‐Organizing Maps are used to separate anticyclonic and cyclonic eddies into distinct sub‐categories based on spatial characteristics in relative vorticity. Thermal drivers dominated over non‐thermal on partial pressure of ocean CO2 (pCO2sw) leading to a weaker CO2 sink in anticyclonic eddies and a stronger CO2 sink in cyclonic eddies relative to the climatological mean. Magnitudes and depth extents of tracer anomalies scale with eddy size but are also dependent on background tracer gradients. Resolving only the largest (>50 km radii) eddies leads to underestimations in total magnitude of heat storage by 52% and 77%, and underestimations of 61% and 77% in dissolved inorganic carbon (CT) storage for anticyclonic and cyclonic eddies respectively. The inclusion of smaller eddy features (<50 km) also offsets the asymmetry in heat and CT storage between anticyclonic and cyclonic eddies. Resolving eddies explicitly or improvements in existing parameterizations that fail to sufficiently include eddy effects are crucial to improving estimates of heat and CO2.

The Role of Ocean Mesoscale Variability in Air‐Sea CO2 Exchange: A Global Perspective

“…Note, however, that in our analysis, F <2°C O 2 includes not only the large-scale eddies, but also smaller-scale features. Although large coherent eddies have been shown to dominate mesoscale-related CO 2 fluxes in the South Atlantic (T. Smith et al, 2023), the smaller-scale features may contribute some net source/sink not accounted for in Ford et al (2023) analysis. Although the overall magnitude of the globally integrated net mesoscale-related CO 2 uptake is small (on the order of 10 5 tC per year) in comparison to the ocean's total capacity for carbon absorption (of order 10 3 MtC per year), mesoscale processes may still exert a significant influence on the ocean carbon budget.…”

“…Recent observational evidence on regional ocean scales suggests that coherent mesoscale eddies can significantly modify local air-sea CO 2 exchange (e.g., Ford et al, 2023;Kim et al, 2022). However, a consensus has yet to be reached on whether mesoscale eddies with specific polarity and anomalous seawater properties act as a sink of CO 2 to the ocean (Ford et al, 2023;Jones et al, 2017;T. Smith et al, 2023) or a source of CO 2 to the atmosphere (Chen et al, 2007;Kim et al, 2022;Pezzi et al, 2021).…”