The Deep Ocean's Carbon Exhaust

Area of Science:

• Oceanography
• Climate Science
• Biogeochemistry

Background:

• The deep ocean stores significant amounts of pre-industrial carbon dioxide (CO2).
• Southern Ocean upwelling releases this CO2, counteracting carbon uptake elsewhere and influencing global climate.
• Understanding these CO2 fluxes is crucial for predicting atmospheric CO2 levels and anthropogenic CO2 uptake.

Purpose of the Study:

• To identify the source and characteristics of CO2 release from Southern Ocean upwelling.
• To investigate the factors controlling the partial pressure of CO2 (PCO2) in these waters.
• To assess the sensitivity of Southern Ocean CO2 fluxes to future upwelling changes.

Main Methods:

• Utilized year-round profiling float measurements to track CO2 release.
• Employed ship-based measurements to analyze subsurface water chemistry.
• Characterized the Indo-Pacific Deep Water (IPDW) and its CO2 properties.

Main Results:

• Identified a specific zonal band of upwelling between the Subantarctic Front and sea-ice edge responsible for CO2 release.
• Found that Indo-Pacific Deep Water (IPDW) has a high partial pressure of CO2 (PCO2), exceeding atmospheric levels.
• Determined that decreasing temperatures and increasing alkalinity limit CO2 outgassing from deeper waters.

Conclusions:

• Southern Ocean CO2 release is linked to IPDW upwelling and its unique carbon chemistry.
• Vertical profiles of remineralization and dissolution significantly influence CO2 outgassing.
• Future changes in Southern Ocean CO2 fluxes will depend on subsurface carbon chemistry and upwelling dynamics.