Immediate and Long‐Lasting Impacts of the Mt. Pinatubo Eruption on Ocean Oxygen and Carbon Inventories

Abstract

Large volcanic eruptions drive significant climate perturbations through major anomalies in radiative fluxes and the resulting widespread cooling of the surface and upper ocean. Recent studies suggest that these eruptions also drive important variability in air‐sea carbon and oxygen fluxes. By simulating the Earth system using two initial‐condition large ensembles, with and without the aerosol forcing associated with the Mt. Pinatubo eruption in June 1991, we isolate the impact of this volcanic event on physical and biogeochemical properties of the ocean. The Mt. Pinatubo eruption forced significant anomalies in surface fluxes and the ocean interior inventories of heat, oxygen, and carbon. Pinatubo‐driven changes persist for multiple years in the upper ocean and permanently modify the ocean's heat, oxygen, and carbon inventories. Positive anomalies in oxygen concentrations emerge immediately post‐eruption and penetrate into the deep ocean. In contrast, carbon anomalies intensify in the upper ocean over several years post‐eruption, and are largely confined to the upper 150 m. In the tropics and northern high latitudes, the change in oxygen is dominated by surface cooling and subsequent ventilation to mid‐depths, while the carbon anomaly is associated with solubility changes and eruption‐generated El Niño—Southern Oscillation variability. We do not find significant impact of Pinatubo on oxygen or carbon fluxes in the Southern Ocean; but this may be due to Southern Hemisphere aerosol forcing being underestimated in Community Earth System Model 1 simulations.

How Does the Pinatubo Eruption Influence Our Understanding of Long‐Term Changes in Ocean Biogeochemistry?

“…One of the key findings from this study is that, while the Pinatubo climate perturbation influences the distribution of preindustrial carbon, it has no discernible impact on the externally forced changes in the anthropogenic carbon distribution. This finding agrees with previous studies that find an important role for Pinatubo in preindustrial carbon variability (Eddebbar et al., 2019; Fay et al., 2023; McKinley et al., 2020), and gives us additional confidence that observation‐based estimates of changing anthropogenic carbon distribution (e.g., Gruber et al., 2019; Müller et al., 2023); (also Müller , Jens Daniel , Gruber , Nicolas , Carter , Brendan R ., Feely et al ., Decadal Trends in the Oceanic Storage of Anthropogenic Carbon from 1994 to 2014 , in preparation for Authorea ) are relatively unaffected by the Pinatubo climate perturbation. This confidence, however, is only valid to the extent that the methods employed can accurately separate anthropogenic carbon from the much larger preindustrial component.…”

“…By investigating the externally forced (ensemble mean) evolution of multiple ocean variables in the decade following the eruption, we can begin to understand how Pinatubo altered key tracers of physical and biogeochemical processes and use this to understand how Pinatubo influenced the observed decadal changes in these properties. Pinatubo drove decadal‐scale increases in AOU in the subpolar North Atlantic, likely due to an increase in ventilation following the eruption (Fay et al., 2023). In the subtropical Atlantic thermocline, Pinatubo‐driven decadal‐scale increases in both AOU and preindustrial carbon are likely a result of post‐eruption cooling and solubility driven increases in dissolved oxygen and carbon (Fay et al., 2023).…”

“…Pinatubo drove decadal‐scale increases in AOU in the subpolar North Atlantic, likely due to an increase in ventilation following the eruption (Fay et al., 2023). In the subtropical Atlantic thermocline, Pinatubo‐driven decadal‐scale increases in both AOU and preindustrial carbon are likely a result of post‐eruption cooling and solubility driven increases in dissolved oxygen and carbon (Fay et al., 2023). These increases are pronounced in the Atlantic, likely due to its connection with the global thermohaline circulation.…”

“…The increased ventilation in the North Atlantic that was caused by Pinatubo also affected p CFC‐12 below the main thermocline for multiple decades. In the Pacific, CESM responds to the Pinatubo climate perturbation by producing El Ni$$\tilde{\mathrm{n}}$$o‐like conditions (Eddebbar et al., 2019; Fay et al., 2023). This causes reduced upwelling of carbon‐rich and oxygen‐poor waters, reducing both AOU and preindustrial carbon concentrations.…”

Air‐Sea Fluxes of CO2 in the Indian Ocean Between 1985 and 2018: A Synthesis Based on Observation‐Based Surface CO2, Hindcast and Atmospheric Inversion Models

“…Recently Fay et al. (2023) reported high oxygen and carbon anomalies associated with Pinatubo volcanic eruptions for several years in the northern and tropical Pacific and tropical Indian Ocean but an insignificant impact is noticed in the Southern Ocean. The models used in this study also suggest an impact of the Pinatubo volcanic eruption on the Indian Ocean CO 2 fluxes around 1991–1992 most pronounced in the EIO region (Figure 7).…”