Science

27 mars 2025

New Sea Surface Salinity Record Extended To End Of 2023

Version 5.5 Reduces Uncertainties at High Northern Latitudes and Radio Frequency Interferences Contaminations

An updated global Sea Surface Salinity (SSS) data record, derived from satellite observations has been released by researchers contributing to the ESA Climate Change Initiative. This new product, now in its fifth iteration (version 5.5), covers the period 2010-2023 and integrates L-band Microwave Radiometer measurements from ESA’s Soil Moisture and Ocean Salinity (SMOS), NASA’s Aquarius and Soil Moisture Active Passive (SMAP) satellite missions into one globally consistent record.

Version 5.5 offers enhanced accuracy and global consistency and is now extended by a year in comparison to version 4.41. It is available as both a weekly and monthly product, sampled on a 0.25° grid, at ~50km spatial resolution. Improvements made include, SMOS L2 SSS data have been reprocessing with the most up-to-date forward models (i.e., new dielectric constant). In addition, SMAP SSS v5.3 data have been used, Radio Frequency Interference (RFI) mitigation on SMOS SSS has been extended globally, a global quality check flag is now available (SSS_qc), and the absolute calibration of SSS north of 65°N has been improved.

Comparison of the space-based salinity record with in-situ measurements in the validation exercise indicates:

• Version 5 products show better performance than version 4, in particular the systematic underestimation in 2010 and the issue linked to SMAPv5.0 between April to August have been resolved;
• No systematic biases against reference data;
• Global precision (STDD) against reference gridded data is of 0.14 practical salinity scale (PSS);
• Remaining seasonal oscillation of CCI SSS differences against reference (< 0.05 pss) in the Northern Hemisphere (> 40°N);
• Uncertainties provided in the CCI salinity product are in good agreement with observations (within 30%);
• Mesoscale features in Tropical Atlantic are coherent between CCI v5 and Thermosalinograph (TSG) transects up to a wavelength of 250-300km (resolving features of ~150km);

Exploring Sea Surface Salinity: A Key Indicator of Ocean Health

Sea Surface Salinity is an Essential Climate Variable (ECV) that plays a crucial role in the density-driven global ocean circulation, the water cycle and climate. Salinity, or saltiness, at the sea surface is an important driving force behind the conveyor-belt-like ocean circulation patterns that transport heat and carbon around the globe. Tracking this variable is critical for assessing the state of the ocean and also for understanding and forecasting climate phenomena such as the Pacific’s El Niño Southern Oscillation (ENSO) which can disrupt ecosystems, economies and human health.

Use of data: Improving El Niño Forecast

By combining sea-surface salinity data with ocean or atmospheric models, this new salinity record will allow the scientific community to more precisely assess the current state of the ocean and its coupled dynamics, as well as to investigate the relationship with various elements of the water cycle, such as evaporation/precipitation, continental runoff and sea-ice formation/melting. Combining these data with observations of other climate variables, such as sea surface temperature, improves the ability to predict El Niño events. For example, model predictions using salinity information are useful for seven months, whereas without this information they are useful for only four months.

Evolution of the salinity fields around the globe, depicting areas of high salinity and low salinity from 2010-2023

Dataset Highlight Table

"The new SSS data set takes climate monitoring to a new level. It is available for various scientific applications thanks to its longer time duration and reduced systematic uncertainties “– CCI Salinity project science leader, Jacqueline Boutin of the Laboratoire d'Océanographie et du Climat (LOCEAN), France.

About ESA

ESA CCI is dedicated to producing robust satellite Climate Data Records (CDR) explicitly tailored to climate applications. All data are fully validated and uncertainty characterised into a consistent long-term record to address GCOS requirements and meet the key requirements that climate scientists take into account when selecting data to incorporate into models used to predict future change.

Dataset citable as:

Boutin, J.; Vergely, J.-L.; Reul, N.; Catany, R.; Jouanno, J.; Martin, A.; Rouffi, F.; Bertino, L.; Bonjean, F.; Corato, G.; Gévaudan, M.; Guimbard, S.; Khvorostyanov, D.; Kolodziejczyk, N.; Matthews, M.; Olivier, L.; Raj, R.; Rémy, E.; Reverdin, G.; Supply, A.; Thouvenin-Masson, C.; Vialard, J.; Sabia, R.; Mecklenburg, S. (2025): ESA Sea Surface Salinity Climate Change Initiative (Sea_Surface_Salinity_cci): Weekly and monthly sea surface salinity products from L-band, v5.5. NERC EDS Centre for Environmental Data Analysis, 03 March 2025. doi:10.5285/7294d93479654c139770f13fae4142d1. https://dx.doi.org/10.5285/7294d93479654c139770f13fae4142d1

Learn More: http://catalogue.ceda.ac.uk/uuid/7294d93479654c139770f13fae4142d1/