Southern Ocean Sulfate Aerosol Sources Quantified From Sulfur Isotopes in Antarctic Ice Cores

[Geoengineering News]

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025GL118622

Authors: U. A. Jongebloed, T. P. Fischer, P. R. Kyle, L. Kang, Y. A. Bhatti, B. Alexander

First published: 22 January 2026

https://doi.org/10.1029/2025GL118622

Abstract

The Southern Ocean has emerged as a key region for constraining aerosol-climate interactions due to its relatively low anthropogenic influence. Sulfate is an important aerosol over the Southern Ocean, and models suggest dimethyl sulfide (DMS) is the largest source of sulfate during summer. However, sulfur isotopes of sulfate (δ34S(SO42−)) in Antarctic ice cores suggest a significant contribution from a previously unexplained non-DMS source. Here we show that the fractional contribution from passive volcanic degassing (fvolc) explains observed δ34S(SO42−), and that a global chemical transport model underestimates fvolc across Antarctica. Underestimated fvolc implies that the model mischaracterizes sulfate sources in this important region. The discrepancy between observed and modeled sulfate sources can be reconciled by increasing passive volcanic sulfur degassing emissions and decreasing DMS emissions. Our results imply that current biases in emissions inventories could bias assessments of aerosol-cloud interactions in the Southern Ocean region and globally.

Plain Language Summary

Sulfate aerosols are small particles in the atmosphere that have a cooling effect on global climate. The Southern Ocean, which encircles Antarctica, is of great interest to climate scientists because this pristine region shows how aerosols interact with clouds in conditions largely unaffected by anthropogenic pollution. We examine sulfate in Antarctic ice cores to determine how much each source of sulfur contributes to sulfate aerosols in the atmosphere. Possible sulfate sources are volcanic gas emissions, marine plankton, and other minor sources. By comparing our ice core constraints to a state-of-the-art global model, we find that the model both underestimates sulfur emissions from passive (i.e., non-eruptive) volcanic degassing while overestimating sulfur emissions from plankton. These biases are important because sulfur emissions strongly influence how climate models simulate and project future climate.

Key Points

Sulfur isotopes in ice cores quantify how much sulfate over the Southern Ocean comes from passive volcanic degassing versus phytoplankton

A global chemical transport model underestimates the volcanic fraction of sulfate observed in the southern high latitudes

Increasing passive volcanic degassing and decreasing Southern Ocean DMS emissions corrects the discrepancy and constrains model bias

Source: AGU