North-Atlantic Ocean Subtropical Gyre: New perspective and mechanisms of low-frequency Variability

Using Argo based recent ocean analysis together with historical dataset going back to the 1960s, we diagnosed the low-frequency variability of the North-Atlantic Ocean Subtropical Gyre stratification key components: the Eighteen Degree Water (EDW), the permanent pycnocline and the Gulf Stream Extension. We have found a 2005-2015 quasi-decadal trend of reduced EDW heat content due to a combined reduction of its volume and temperature. These changes are explained by modified EDW formation region properties and wind-driven reduced overturning circulation. We will put these recent changes into a more historical context of multi-decadal trends of the North-Atlantic Western Boundary system determined using a new statistical approach based on un-supervised classification of profiles. The robustness of the signal will be discussed using an ensemble approach. This work is part of the CNRS/LEFE SOMOVAR and OST/ST PIRATE projects.