the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 30 Apr 2025
Satellite-based regional Sea Surface Salinity maps for enhanced understanding of freshwater fluxes in the Southern Ocean
Abstract. This paper presents newly developed Sea Surface Salinity (SSS) products for the Southern Ocean (SO), derived from SMOS (Soil Moisture and Ocean Salinity) measurements by the Barcelona Expert Center (BEC). The primary challenges in retrieving SSS from L-band brightness temperature (TB) measurements in the Southern Ocean include degraded sensitivity in cold waters, radiometric signal contamination near sea ice edges and low variability in SSS across the region. To address these challenges, significant improvements were made to the retrieval algorithms. The BEC SO SSS product v1.0 delivers 9-day SSS maps on a 25 km EASE-SL grid, generated daily. The time series spans from February 1, 2011, to March 31, 2023, with spatial coverage south of 30° S (https://doi.org/10.20350/digitalCSIC/15493).
The product shows high accuracy farther than 150 km from sea ice edges, with nearly zero bias and a standard deviation of 0.22 (compared to marine mammal data) and 0.25 (compared to TSG data from research vessels). Larger errors are observed within 150 km from the ice edges, due to residual sea-ice contamination and sampling-related errors in these dynamic areas. The product effectively captures seasonal and interannual variability, in line with the SOSE regional model. Although differences between satellite-derived and in situ salinity are more pronounced in these regions, the satellite product successfully reproduces the dynamics near ice edges.
This product will significantly contribute to the understanding of processes influenced by upper-ocean salinity, including ice formation and melt, the reduction of Antarctic sea ice extent, and the opening of offshore polynyas.
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Status: open (until 12 Jun 2025)
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RC1: 'Comment on essd-2025-212', Giuseppe M.R. Manzella, 08 May 2025
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Comment on paper ESSD-2025-212
General comment
This is one of many papers that researchers clustered around BEC submit to journals and in particular to ESSD. This is a list (for sure not complete one)
- Improved BEC SMOS Arctic Sea Surface Salinity product v3.1 - https://doi.org/10.5194/essd-14-307-2022
- First SMOS Sea Surface Salinity dedicated products over the Baltic Sea - https://doi.org/10.5194/essd-14-2343-2022
- New SMOS SSS maps in the framework of the Earth Observation data For Science and Innovation in the Black Sea - https://doi.org/10.5194/essd-2021-364
- Nine years of SMOS Sea Surface Salinity global maps at the Barcelona Expert Center - https://doi.org/10.5194/essd-13-857-2021
It is normal that ‘general’ algorithms need to be adapted to the particular marine environments, but the dispersion of applications in different papers is not useful to the researchers interested in using SMOS products for several small seas and analyze the differences and possibly make further adjustments. The potential proliferation of articles for each single basin risks being of little use to research.
At the extreme north and south of the global ocean, important common problems are (1)Low sensitivity of brightness temperatures (TB) to salinity in cold waters, (2) Land–sea contamination (LSC) and ice–sea contamination (ISC), (3) Lack of sufficient in situ measurements. It would have been appropriate to discuss in a single publication the different peculiarities of the waters in these environments and what the appropriate solutions are. Same concept for the Baltic and Black Seas.
It is understood that in practice articles are written on the basis of collaborations that are built over time and therefore the practice of the authors is acceptable, but each article should highlight and point out the differences much more accurately. In particular, I would have expected a discussion after line 52 of the introduction on what has been done in the Arctic Sea and what needs to be done differently in the Southern Ocean.
In the remaining part of the article, the work for the geophysical corrections and for the analyses of the various SST products is appreciable. The validation and intercomparison are also very appreciable.
The paper itself is well written and practically complete and can be published after minimal corrections.
Specific comments
Introduction lines 14-15 - understanding of processes influenced by upper-ocean salinity, including ice formation – explain how it is possible to study the formation when SMOS resolution is large enough and the distance from the ice edge is more than 150 km, while within 150km there is high noise?
Figures 5, 7, 18 show very noisy areas near the continent. What does this mean for studies on the potential applications of the product: understanding of processes influenced by upper-ocean salinity, including ice formation and melt, the reduction of Antarctic sea ice extent, and the opening of offshore polynyas. It is not necessary to go into depth on the oceanographic issues, but to give a general indication of the limits of the product for the listed applications.
Citation: https://doi.org/10.5194/essd-2025-212-RC1
Data sets
BEC Southern Ocean SSS Product Description (V.1.0) Verónica González Gambau et al. https://doi.org/10.20350/digitalCSIC/15493
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