Sea surface salinity (SSS) is a key variable for ocean–atmosphere interactions and the water cycle. Due to its climatic importance, increasing efforts have been made for its global in situ observation, and dedicated satellite missions have been launched more recently to allow homogeneous coverage at higher resolution. Cross-shore SSS gradients can bear the signature of different coastal processes such as river plumes, upwelling or boundary currents, as we illustrate in a few regions. However, satellites performances are questionable in coastal regions. Here, we assess the skill of four gridded products derived from the Soil Moisture Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP) satellites and the GLORYS global model reanalysis at capturing cross-shore SSS gradients in coastal bands up to 300 km wide. These products are compared with thermosalinography (TSG) measurements, which provide continuous data from the open ocean to the coast along ship tracks. The comparison shows various skills from one product to the other, decreasing as the coast gets closer. The bias in reproducing coastal SSS gradients is unrelated to how the SSS biases evolve with the distance to the coast. Despite limited skill, satellite products generally agree better with collocated TSG data than a global reanalysis and show a large range of coastal SSS gradients with different signs. Moreover, satellites reveal a global dominance of coastal freshening, primarily related to river runoff over shelves. This work shows a great potential of SSS remote sensing to monitor coastal processes, which would, however, require a jump in the resolution of future SSS satellite missions to be fully exploited.
This study assessed the extremes of wave conditions for past (1979–2005) and future (2026–2045 and 2081–2100) time slices in the Gulf of Guinea (GoG). The ensemble produced from eight General Circulation Models under different Representative Concentration Pathway (RCP) emission scenarios (RCP4.5 and RCP8.5) was subjected to linear regression analysis and Mann–Kendal test for their trends and significance, respectively. Results showed an increase in the extreme of significant wave height (Hs) and mean wave period (Tm) between 1979–2005, 2026–2045, and 2081–2100 with few exceptions. The average values of annual and seasonal Hs and Tm range from 1.26–1.62 m and 10.37 s–10.86 s, respectively, for 1979–2005. These Hs values are projected to increase by 0.1 m (0.05 m) to 1.72 m (1.67 m) and the Tm will increase by 0.29 s (0.24 s) to 11.15 s (11.10 s) by the end of the century (mid-century) time slices, respectively. The mean wave direction (Dm) (201.89°–206.27°) showed an anticlockwise shift (−29.2 × 10−3 degrees per year) for 1979–2005 which is projected to become more southwesterly with an increase up to 2.2° (0.5°) by end (mid) century in 2100 (2045), respectively. Future work will be on the impacts of changing wave on longshore sediment transport along the GoG.
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