Articles | Volume 23, issue 2
ACP Letters
 | Highlight paper
01 Feb 2023
ACP Letters | Highlight paper |  | 01 Feb 2023

Natural marine cloud brightening in the Southern Ocean

Gerald G. Mace, Sally Benson, Ruhi Humphries, Peter M. Gombert, and Elizabeth Sterner


Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-571', Anonymous Referee #1, 07 Sep 2022
    • AC1: 'Reply on RC1', Gerald Mace, 03 Nov 2022
  • RC2: 'Comment on acp-2022-571', Anonymous Referee #2, 09 Sep 2022
    • AC2: 'Reply on RC2', Gerald Mace, 03 Nov 2022

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
AR by Gerald Mace on behalf of the Authors (03 Nov 2022)  Author's response   Author's tracked changes   Manuscript 
ED: Publish subject to minor revisions (review by editor) (14 Nov 2022) by Barbara Ervens
AR by Gerald Mace on behalf of the Authors (17 Nov 2022)  Author's response   Author's tracked changes   Manuscript 
ED: Publish as is (22 Nov 2022) by Barbara Ervens
ED: Publish as is (22 Nov 2022) by Martina Krämer (Executive editor)
AR by Gerald Mace on behalf of the Authors (02 Dec 2022)  Manuscript 
Executive editor
The Southern Ocean can be considered a region exhibiting pristine conditions as during the pre-industrial time. Thus, any changes in radiative forcing in this region can be attributed to natural factors. Feedbacks of ocean biological activity on Earth’s radiation budget have been put forward as the CLAW hypothesis (Charlson et al., 1987, It implies that emissions of biogenic sulfur-containing compounds result in the formation of cloud condensation nuclei, which lead to higher cloud droplet number concentrations. Such clouds are more reflective and thus lead to a cooling effect. The current study provides satellite-based evidence of the increase droplet number concentrations and cloud reflectivity (‘albedo’) triggered by chlorophyll emissions, as a proxy for biological activity. Specifically, it demonstrates for the first time the extent to which the cloud albedo is modulated by biological factors as a function of latitude along the Antarctic shelf. While the study does not extend to discussing the subsequent feedbacks of cloud reflectivity to biological activity, it clearly demonstrates how biological ocean activity affects cloudiness above the Southern Ocean and thus may regulate temperature.
Short summary
The number of cloud droplets per unit volume is a significantly important property of clouds that controls their reflective properties. Computer models of the Earth's atmosphere and climate have low skill at predicting the reflective properties of Southern Ocean clouds. Here we investigate the properties of those clouds using satellite data and find that the cloud droplet number and cloud albedo in the Southern Ocean are related to the oceanic phytoplankton abundance near Antarctica.
Final-revised paper