Using ARGO/Gyroscope float data, we describe the SubPolar Mode Waters (SPMW) properties and their seasonal and interannual variability, and we investigate the SPMW formation processes. The floats display a substantial data set of high quality salinity and temperature measurements. The space-time sampling allows us to interpolate the data on pressure and potential density levels throughout the mid-latitude North Atlantic Ocean via an objective analysis. Comparison with previous studies shows the consistency of the interpolation method and the ability of the data set to observe the SPMW.

We confirm the presence of several varieties of SPMW in the North East Atlantic, quite unequally distributed and being set apart by the density ranges they occupy. They are distributed around the outer periphery of the North Atlantic subpolar gyre in extended patches north of the North Atlantic Current (NAC) and in small patches south and near Newfoundland. South of the NAC density jumps are detected between the different varieties of SPMW. The analysis helps us distinguish recently ventilated SPMW from subducted SPMW. Those varieties can coexist in the same geographical area at different depths. A significant variability has been observed in regard to previous data sets.

Mode waters are formed in late winter when mixed layers reach their deepest depth. Our observations suggest that the deepening of the mixed layers occurs during a 2 month temporal window and that the deepest mixed layers appear in very restricted areas in the subpolar Gyre. The local nature (in time and space) of the late winter deep mixed layers may explain the discontinuous aspect of the properties of the different SPMWs.

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Poster