Regional Wind Variability Modulates the Southern Ocean Carbon Sink

Area of Science:

• Oceanography
• Climate Science
• Carbon Cycle Research

Background:

• The Southern Ocean plays a critical role in global carbon dioxide (CO2) uptake, absorbing about half of the annual oceanic CO2. Its capacity as a carbon sink is known to fluctuate significantly over various timescales.
• Understanding the drivers of this variability is crucial for predicting the future oceanic carbon uptake and its role in mitigating anthropogenic CO2 emissions.

Purpose of the Study:

• To investigate the recent trends and drivers of carbon variability in the Southern Ocean carbon sink.
• To determine the influence of climate modes, such as the Southern Annular Mode (SAM), and other regional climate shifts on Southern Ocean carbon uptake.

Main Methods:

• Analysis of mapped sea-air CO2 fluxes derived from upscaled surface ocean CO2 measurements.
• Statistical analysis of historical data spanning 35 years to assess correlations between carbon sink variability and climate indices like the Southern Annular Mode (SAM) and regional sea level pressure patterns.

Main Results:

• The Southern Ocean carbon sink has weakened since approximately 2011, contrasting with a strengthening trend observed in the 2000s.
• While the Southern Annular Mode (SAM) shows regional impacts on carbon uptake, its net effect on overall Southern Ocean carbon sink variability over 35 years is found to be negligible due to opposing regional influences.
• Regional shifts in sea level pressure, associated with zonal wavenumber 3 (ZW3) and subsequent changes in surface winds, are identified as significant contributors to inter-annual to decadal variability in the Southern Ocean carbon sink.

Conclusions:

• The Southern Ocean's role as a carbon sink is dynamic and influenced by complex regional climate dynamics rather than solely by large-scale modes like the SAM.
• Recent weakening of the Southern Ocean carbon sink highlights the need for improved climate models that incorporate regional atmospheric and oceanic drivers for accurate future projections.