Abstract. The mean dynamic topography (MDT) is a key reference surface for altimetry. It is needed for the calculation of the ocean absolute dynamic topography, and under the geostrophic approximation, the estimation of surface currents. CNES-CLS mean dynamic topography (MDT) solutions are calculated by merging information from altimeter data, GRACE, and GOCE gravity field and oceanographic in situ measurements (drifting buoy velocities, High Frequency radar velocities, hydrological profiles). The objective of this paper is to present the newly updated CNES-CLS22 MDT. The main improvement of this new CNES-CLS22 MDT over the previous CNES-CLS18 MDT is in the Arctic, with better coverage, no artifacts and a more realistic solution. This is due to the use of a new first guess estimated with the CNES-CLS22 MSS and the GOCO06s geoid to which optimal filtering has been applied, as well as Lagrangian filtering at the coast to reduce the intensity of normal currents at the coast. Improvements also include updating the drifting buoy and T/S profile databases, as well as processing to obtain synthetic mean geostrophic velocities and synthetic mean heights. In addition, a new data type, HF radar data, was processed to extract physical content consistent with MDT in the Mid Atlantic Bight region. The study of this region in particular has shown the improvements of the CNES-CLS22 MDT, but that there is still work to be done to obtain a more physical solution over the continental shelf. The CNES-CLS22 MDT has been evaluated against independent height and velocity data in comparison with the previous version, the CNES-CLS18. The new solution presents slightly better results, although not identical in all regions of the globe.

An unusually large positive salinity anomaly was observed across the eastern Gulf of Maine (GoM) in winter 2017-2018. Buoy measurements in Jordan Basin found this anomaly extended down to at least 100 m, the deepest mixing observed in the past 19 years. Similarly, this is the strongest positive regional salt anomaly in sea surface salinity (SSS) satellite observations. To determine the source waters driving this event and to diagnose the relative importance of forcing processes, passive tracer adjoint sensitivity experiments are performed using a data assimilating version of the Regional Ocean Modeling System. The model shows that northeastward Scotian Shelf wind anomalies cause a dramatic decrease in freshwater transport to Jordan Basin, which leads to an early winter upper water column salinity surplus. This salinity change weakens the normally haline-controlled vertical stratification across the eastern Gulf. Modeled upper ocean density and vertical diffusivity from 2007-2021 both show a maximum in January 2018. Winter 2017-2018 is the only period where the enhanced winter mixing extends below 100 m. Thus, anomalous vertical entrainment of saltier subsurface Gulf water is the major factor driving the extreme positive satellite-observed SSS anomaly across the eastern Gulf including Jordan Basin. Other factors, including a modest increase in wind-forced slope water transport, and positive fall 2017 salinity anomalies on the Scotian Shelf and Slope Sea appear to play lesser roles in the observed salinification. The adjoint sensitivity analysis demonstrates its utility for back tracing transport pathways for periods of several months.