Search for: All records

Abstract The strength and variability of the Southern Ocean carbon sink is a significant source of uncertainty in the global carbon budget. One barrier to reconciling observations and models is understanding how synoptic weather patterns modulate air-sea carbon exchange. Here, we identify and track storms using atmospheric sea level pressure fields from reanalysis data to assess the role that storms play in driving air-sea CO₂exchange. We examine the main drivers of CO₂fluxes under storm forcing and quantify their contribution to Southern Ocean annual air-sea CO₂fluxes. Our analysis relies on a forced ocean-ice simulation from the Community Earth System Model, as well as CO₂fluxes estimated from Biogeochemical Argo floats. We find that extratropical storms in the Southern Hemisphere induce CO₂outgassing, driven by CO₂disequilibrium. However, this effect is an order of magnitude larger in observations compared to the model and caused by different reasons. Despite large uncertainties in CO₂fluxes and storm statistics, observations suggest a pivotal role of storms in driving Southern Ocean air-sea CO₂outgassing that remains to be well represented in climate models, and needs to be further investigated in observations. 

Abstract In the tropical Pacific, weak ventilation and intense microbial respiration at depth give rise to a low dissolved oxygen (O₂) environment that is thought to be ventilated primarily by the equatorial current system (ECS). The role of mesoscale eddies and vertical mixing as potential pathways of O₂supply in this region, however, remains poorly known due to sparse observations and coarse model resolution. Using an eddy resolving simulation of ocean circulation and biogeochemistry, we assess the contribution of these processes to the O₂budget balance and find that vertical mixing of O₂, which is modulated by the surface wind speed and the vertical shear of the eddying currents, contributes substantially to the replenishment of O₂in the upper equatorial Pacific thermocline, complementing the advective supply of O₂by the ECS and meridional circulation at depth. These transport processes vary seasonally in conjunction with the wind: mixing of O₂into the upper thermocline is strongest during boreal summer and fall when the vertical shear and eddy kinetic energy are intensified. The relationship between eddy activity and the downward mixing of O₂arises from the modulation of equatorial turbulence by Tropical Instability Waves via their impacts on the vertical shear. This interaction of processes across scales sustains a local pathway of O₂delivery into the equatorial Pacific interior and highlights the need for adequate observations and models of turbulent mixing and mesoscale processes for understanding and predicting the fate of the tropical Pacific O₂content in a warmer and more stratified ocean. 

Abstract Pinatubo erupted during the first decadal survey of ocean biogeochemistry, embedding its climate fingerprint into foundational ocean biogeochemical observations and complicating the interpretation of long‐term biogeochemical change. Here, we quantify the influence of the Pinatubo climate perturbation on externally forced decadal and multi‐decadal changes in key ocean biogeochemical quantities using a large ensemble simulation of the Community Earth System Model designed to isolate the effects of Pinatubo, which cleanly captures the ocean biogeochemical response to the eruption. We find increased uptake of apparent oxygen utilization and preindustrial carbon over 1993–2003. Nearly 100% of the forced response in these quantities are attributable to Pinatubo. The eruption caused enhanced ventilation of the North Atlantic, as evidenced by deep ocean chlorofluorocarbon changes that appear 10–15 years after the eruption. Our results help contextualize observed change and contribute to improved constraints on uncertainty in the global carbon budget and ocean deoxygenation.