Preprints
https://doi.org/10.5194/egusphere-2023-3050
https://doi.org/10.5194/egusphere-2023-3050
22 Dec 2023
 | 22 Dec 2023

Assessing heat and freshwater changes in the Southern Ocean using satellite-derived steric height

Jennifer Cocks, Alessandro Silvano, Alice Marzocchi, Oana Dragomir, Noémie Schifano, Anna E. Hogg, and Alberto C. Naveira Garabato

Abstract. The Southern Ocean plays a central role in regulating the global overturing circulation, ventilating the deep ocean, and driving sea level rise by delivering heat to Antarctic ice shelves. Understanding heat and freshwater content in this region is key to monitoring these global processes and identifying multiyear changes; however, in-situ observations are limited, and often do not offer the spatial or temporal consistency needed to study long-term variability. Perturbations in steric height can reveal changes in oceanic heat and freshwater content inasmuch as they impact the density of the water column. Here, we show for the first time that the monthly steric height anomaly of the Southern Ocean south of 50° S can be assessed using altimetry and GRACE gravimetry data from 2002 to 2018. Steric height anomalies are validated against in-situ Argo float and CTD data from tagged elephant seals. We find good agreement in the ice-free ocean and parts of the seasonal ice zone, but that the uncertainty of steric height increases on the Antarctic continental shelf and within the permanent ice zone due to leakage error and anti-aliasing in GRACE. The open-ocean steric height anomalies exhibit spatio-temporally coherent patterns that: (i) capture the expected seasonal cycle of low (high) steric height in winter (summer); and (ii) reflect interannual anomalies in surface heat and freshwater content and wind forcing associated with positive and negative phases of the two major modes of Southern Hemisphere climate variability (the El Niño – Southern Oscillation and Southern Annular Mode).

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Jennifer Cocks, Alessandro Silvano, Alice Marzocchi, Oana Dragomir, Noémie Schifano, Anna E. Hogg, and Alberto C. Naveira Garabato

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Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-3050', Anonymous Referee #1, 11 Feb 2024
  • RC2: 'Comment on egusphere-2023-3050', Anonymous Referee #2, 22 Apr 2024
Jennifer Cocks, Alessandro Silvano, Alice Marzocchi, Oana Dragomir, Noémie Schifano, Anna E. Hogg, and Alberto C. Naveira Garabato
Jennifer Cocks, Alessandro Silvano, Alice Marzocchi, Oana Dragomir, Noémie Schifano, Anna E. Hogg, and Alberto C. Naveira Garabato

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Short summary
Heat and freshwater fluxes in the Southern Ocean mediate global ocean circulation and abyssal ventilation. These fluxes manifest as changes in steric height: sea level anomalies from changes in ocean density. We compute the steric height anomaly of the Southern Ocean using satellite data and validate it against in-situ observations. We analyse interannual patterns, drawing links to climate variability, and discuss the effectiveness of the method, highlighting issues and suggesting improvements.