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This study assesses the capability of Surface Quasi-Geostrophy (SQG) to reconstruct the three-dimensional (3D) dynamics in four critical areas of the Arctic Ocean: the Nordic, Barents, East Siberian, and Beaufort Seas. We first reconstruct the upper ocean dynamics from TOPAZ4 reanalysis of sea surface height (SSH), surface buoyancy (SSB), and surface velocities (SSV) and validate the results with the geostrophic and total TOPAZ4 velocities. The reconstruction of upper ocean dynamics using SSH fields is in high agreement with the geostrophic velocities, with correlation coefficients greater than 0.8 for the upper 400 m. SSH reconstructions outperform surface buoyancy reconstructions, even in places near freshwater inputs from river discharges, melting sea ice, and glaciers. Surface buoyancy fails due to the uncorrelation of SSB and subsurface potential vorticity (PV). Reconstruction from surface currents correlates to the total TOPAZ4 velocities with correlation coefficients greater than 0.6 up to 200 m. In the second part, we apply the SQG approach validated with the reanalysis outputs to satellite-derived sea level anomalies and validate the results against in-situ measurements. Due to lower water column stratification, the SQG approach’s performance is better in fall and winter than in spring and summer. Our results demonstrate that using surface information from SSH or surface velocities, combined with information on the stratification of the water column, it is possible to effectively reconstruct the upper ocean dynamics in the Arctic and Subarctic Seas up to 400 m. Future remote sensing missions in the Arctic Ocean, such as SWOT, Seastar, WaCM, CIMR, and CRISTAL, will produce enhanced SSH and surface velocity observations, allowing SQG schemes to characterize upper ocean 3D mesoscale dynamics up to 400 m with higher resolutions and lower uncertainties.

Ocean Sciences Meeting (OSM), 16-21 February 2020, San Diego, CA, USA.- 1 page, 7 figures, This study focus in the Arctic Ocean, identified as a hotspot of climate change. Hotspot regions refer to most responsive regions to climate change based on the changes of regional mean and interannual variability of precipitation and air temperature (Giorgi 2006). In the Arctic Ocean, adding satellite SSS information could potentially provide better estimates of surface currents, as SSS dominates surface buoyancy in specific seasons and therefore density, as they both are inversely proportional to each other.
Salinity has a major importance in the regional dynamics in the upper Arctic Ocean, where the hydrography is changing as seen in observational and modeling studies (Haine 2015). An increment of the global mean annual temperature should induce an increase in the discharge of Arctic rivers (Mulligan 2010). In particular, an increase of liquid freshwater content over both the Canadian Basin and the central Arctic Ocean has been observed (Rabe 2014). However, the precise impact of an increase of the Arctic freshwater runoff remains unclear.
SMOS SSS maps developed at Barcelona Expert Center at high latitudes (Olmedo 2018) are used to study the correlation between SST, SSH and SSS anomalies. We analyse the effective spatial and temporal resolutions of the different satellite variables, in order to better understand the dynamical processes that are being described by each one. We asses where and when SSS has a key role in ocean dynamics and would allow to provide better estimates of ocean currents. We demonstrate how the information of SSS enhance our understanding of the dynamics in the Arctic Ocean, where fresh water fluxes are of major importance.
Giorgi, F. 2006. Climate change hot-spots, Geophys. Res. Lett. 33, L08707.
Haine, T. et al. 2015. Arctic freshwater export: Status, mechanisms, and prospects, Global and Planetary Change, 125, 13 – 35.
Mulligan, R. P., et al. 2010. Dynamics of the Mackenzie River plume on the inner Beaufort shelf during an open water period in summer, Estuarine, Coastal and Shelf Science, 89(3), 214 – 220.
Rabe, B., et al. 2014. Arctic Ocean basin liquid freshwater storage trend 1992- 2012, GRL, 41(3), 961–968.
Olmedo, Estrella, et al. 2018. Seven Years of SMOS sea surface salinity at high latitudes: Variability in Arctic and Sub-Arctic Regions. Remote Sensing 10.11 (2018): 1772, Marta Umbert is funded by Marie Skłodowska-Curie Individual Fellowship Career Restart Panel. PROJECT DYNACLIM: Ocean DYNAmics reconstruction using remotely sensed variables in two CLIMate hotspots (MSCA-IF-EF-CAR Number 840374). DURATION: Sept. 2019- Sep. 2022 The Barcelona Expert Center is a joint initiative of CSIC and UPC funded by the Spanish Ministry of Education and Science through the National Program on Space. www.smos-bec.icm.csic.es, Peer reviewed

Special issue Remote Sensing of the Polar Oceans.-- 29 pages, 9 figures, 2 tables 1 appendix, The overall volume of freshwater entering the Arctic Ocean has been growing as glaciers melt and river runoff increases. Since 1980, a 20% increase in river runoff has been observed in the Arctic system. As the discharges of the Ob, Yenisei, and Lena rivers are an important source of freshwater in the Kara and Laptev Seas, an increase in river discharge might have a significant impact on the upper ocean circulation. The fresh river water mixes with ocean water and forms a large freshened surface layer (FSL), which carries high loads of dissolved organic matter and suspended matter into the Arctic Ocean. Optically active material (e.g., phytoplankton and detrital matter) are spread out into plumes, which are evident in satellite data. Russian river signatures in the Kara and Laptev Seas are also evident in recent SMOS Sea Surface Salinity (SSS) Arctic products. In this study, we compare the new Arctic+ SSS products, produced at the Barcelona Expert Center, with the Ocean Color absorption coefficient of colored detrital matter (CDM) in the Kara and Laptev Seas for the period 2011–2019. The SSS and CDM are found to be strongly negatively correlated in the regions of freshwater influence, with regression coefficients between −0.72 and −0.91 in the studied period. Exploiting this linear correlation, we estimate the SSS back to 1998 using two techniques: one assuming that the relationship between the CDM and SSS varies regionally in the river-influenced areas, and another assuming that it does not. We use the 22-year time-series of reconstructed SSS to estimate the interannual variability of the extension of the FSL in the Kara and Laptev Seas as well as their freshwater content. For the Kara and Laptev Seas, we use 32 and 28 psu as reference salinities, and 26 and 24 psu isohalines as FSL boundaries, respectively. The average FSL extension in the Kara Sea is 2089–2611 km2, with a typical freshwater content of 11.84–14.02 km3. The Laptev Sea has a slightly higher mean FSL extension of 2320–2686 km2 and a freshwater content of 10.15–12.44 km3. The yearly mean freshwater content and extension of the FSL, computed from SMOS SSS and Optical data, is (as expected) found to co-vary with in situ measurements of river discharge from the Arctic Great Rivers Observatory database, demonstrating the potential of SMOS SSS to better monitor the river discharge changes in Eurasia and to understand the Arctic freshwater system during the ice-free season, M. Umbert was funded by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Individual Fellowship Career Restart Panel (MSCA-IF-EF-CAR Number 840374). R. Gonçalves-Araujo has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Grant Agreement No. 839311. This research was funded by the Spanish government, through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Peer reviewed

This work represents a contribution to the CSIC Thematic Interdisciplinary Platform PTI-POLARCSIC and PTI-TELEDETECT.-- Special Issue Remote Sensing Techniques for Ocean Dynamics: State of the Art, Present and Future Applications.-- 29 pages, 13 figures, 2 tables, This study assesses the capability of Surface Quasi-Geostrophy (SQG) to reconstruct the three- dimensional (3D) dynamics in four critical areas of the Arctic Ocean: the Nordic, Barents, East Siberian, and Beaufort Seas. We first reconstruct the upper ocean dynamics from TOPAZ4 re- analysis of sea surface height (SSH), surface buoyancy (SSB), and surface velocities (SSV) and validate the results with the geostrophic and total TOPAZ4 velocities. The reconstruction of upper ocean dynamics using SSH fields is in high agreement with the geostrophic velocities, with correlation coefficients greater than 0.8 for the upper 400 m. SSH reconstructions outperform surface buoyancy reconstructions, even in places near freshwater inputs from river discharges, melting sea ice, and glaciers. Surface buoyancy fails due to the uncorrelation of SSB and subsurface potential vorticity (PV). Reconstruction from surface currents correlates to the total TOPAZ4 velocities with correlation coefficients greater than 0.6 up to 200 meters. Due to a lower stratification of the water column, the performance of the SQG approach is better in fall and winter than in the spring and summer. In the second part, we apply the SQG approach validated withthe reanalysis outputs to satellite-derived upper ocean currents and validate the results against in-situ measurements. Our results demonstrate that using surface information from SSH or surface velocities, combined with information on the stratification of the water column, it is possible to effectively reconstruct upper ocean dynamics in the Arctic and Subarctic Seas up to 400 meters. Future remote sensing missions in the Arctic Ocean, such as SWOT, Seastar, WaCM, CIMR, and CRISTAL, will produce enhanced SSH and surface velocities observations, allowing SQG schemes to characterize upper ocean 3D mesoscale dynamics up to 400 meters with higher resolution and lower uncertainties, M. Umbert received funding from H2020 Marie Skłodowska-Curie Actions under Grant Agreement No. 840374. E. De Andres received funding from Margarita Salas fellowship un-´ der Next Generation EU Grant Agreement No. UP2021-035. This work has also been funded by the AEI with the ARCTIC-MON project (PID2021-125324OB-I00). [...] We also received funding from the Spanish government through the ”Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928-S) and from the ESA Arctic+Salinity project (AO/1-9158/18/I-BG), Peer reviewed

The Vendée Globe is the world’s most famous solo, non-stop, unassisted sailing race. The Institute of Marine Sciences and the Barcelona Ocean Sailing Foundation installed a MicroCAT on the One Ocean One Planet boat. The skipper, Dídac Costa, completed the round trip in 97 days, from 8 November 2020 to 13 February 2021, providing one measurement of temperature and conductivity every 30 s during navigation. More than half of the ship’s route was in the sub-Antarctic zone, between the tropical and polar fronts, and it passed through areas of oceanographic interest such as Southern Patagonia (affected by glacier melting), the Brazil–Malvinas confluence, the Southern Pacific Ocean, and the entire Southern Indian Ocean. This sailing race gave a rare opportunity to measure in-situ sea surface salinity in a region where satellite salinity measurements are not reliable. Due to the decreased sensitivity of brightness temperature to salinity in cold seas, retrieving sea surface salinity at high latitudes remains a major challenge. This paper describes how the data are processed and uses the data to validate satellite salinity products in the sub-Antarctic zone. The sailing race measurements represent surface information (60 cm depth) not available from drifters or Argo floats. Acquiring measurements using round-the-world sailing races would allow us to analyse the evolution of ocean salinity and the impact of changes in the ice extent around Antarctica, This work has been carried out thanks to European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 840374, Temperature and salinity of the ocean surface, Peer reviewed

VII Encuentro de Oceanografía Física (EOF) - Expanding Ocean Frontiers Conference, VIII International Symposium on Marine Sciences, 6-8 July 2022, Las Palmas de Gran Canaria, España, We have assessed the capability of Surface Quasi-Geostrophy (eSQG) to reconstruct the three-dimensional (3D) dynamics in two key areas of the Arctic Ocean: the Nordic and the Beaufort Seas. We reconstructed the upper ocean dynamics from sea surface height (SSH), surface buoyancy (SSB) and surface velocities and validated the results with the classical geostrophic and original TOPAZ reanalysis velocities. When compared to geostrophic velocities, the results demonstrated that the reconstruction of upper ocean dynamics using SSH fields is in high agreement, with correlation coefficients greater than 0.8 for the upper 400 m. SSH reconstructions outperforms surface buoyancy reconstructions also in places near freshwater inputs from river discharges, melting sea ice and glaciers. Surface buoyancy fails due to the uncorrelation of SSB and subsurface potential vorticity (PV). Reconstruction from surface currents correlates to TOPAZ velocities with correlation coefficients greater than 0.5 up to 200 meters. Due to a deeper thermocline and halocline, the performance of the eSQG approach is better in the fall and winter than in the spring and summer. Our results demonstrate that using only surface information from SSH or surface velocities, it is possible to effectively reconstruct upper ocean dynamics in the Arctic and Subarctic Seas up to 400 meters. Future remote sensing missions in the Arctic Ocean, like Seastar, WaCM, CIMR, and CRISTAL, will give improved and enhanced SSH and surface velocities observations, allowing SQG schemes to characterize upper ocean 3D dynamics, This work has been carried out thanks to European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 840374. We also received funding from the Spanish government through the “Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928-S), Peer reviewed

WOC User Consultation Meeting, 10-12 October 2022, Frascati, Italy.-- 1 page, 4 figures, This work has been carried out thanks to European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No.
840374. We also received funding from the Spanish government through the “Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928-S)

This work represents a contribution to the CSIC Thematic Interdisciplinary Platform PTI POLARCSIC and PTI TELEDETECT.-- Ocean Salinity Conference, 6-9 June 2022, New York, USA, This work has been carried out thanks to European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 840374. We also received funding from the Spanish government through the “Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928-S), Peer reviewed

13 pages, 7 figures, 2 tables.-- Code availability: Underlying research code can be accessed at https://github.com/martaumbert/Ocean-Science-2024 (De Andrés et al., 2024).-- Data availability: Underlying research data are available at https://doi.org/10.6084/m9.figshare.c.7084813.v1 (Umbert, 2024), The hydrography of the Arctic Ocean has experienced profound changes over the last 2 decades. The sea ice extent has declined by more than 10 % per decade, and its liquid freshwater content has increased mainly due to glaciers and sea ice melting. Further, new satellite retrievals of sea surface salinity (SSS) in the Arctic might contribute to better characterizing the freshwater changes in cold regions. Ocean salinity and freshwater content are intimately related such that an increase (decrease) in one entails a decrease (increase) in the other. In this work, we evaluate the freshwater content in the Beaufort Gyre using surface salinity measurements from the satellite radiometric mission Soil Moisture and Ocean Salinity (SMOS) and TOPAZ4b reanalysis salinity at depth, estimating the freshwater content from 2011 to 2019 and validating the results with in situ measurements. The results highlight the underestimation of the freshwater content using reanalysis data in the Beaufort Sea and a clear improvement in the freshwater content estimation when adding satellite sea surface salinity measurements in the mixed layer. The improvements are significant, with up to a 70 % reduction in bias in areas near the ice melting. Our research demonstrates how remotely sensed salinity can assist us in better monitoring the changes in the Arctic freshwater content and understanding key processes related to salinity variations that cause density differences with potential to influence the global circulation system that regulates Earth's climate, This project was funded by Marie Skłodowska-Curie grant agreement no. 840374. Eva De Andrés is funded by Margarita Salas grant no. UP2021-035 under the NextGenerationEU program and supported by the MCIN/AEI project PID2020-113051RB-C31. We also received funding from the AEI with the ARCTIC-MON project (PID2021-125324OB-I00) and from the ESA Arctic+ Salinity project (AO/1-9158/18/I-BG) and Arctic+ SSS CCN (4000125590/18/I-BG). This research was supported by the European Union's Horizon 2020 research and innovation program under grant agreement no. 101003826 via the project “CRiceS – Climate Relevant interactions and feedbacks: the key role of sea ice and Snow in the polar and global climate system”, With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Peer reviewed