The transformation of internal waves on continental shelves is important to processes such as mass transfer, nutrient replenishment and heat transfer. We present one month of in situ summer-time measurements to describe the internal tide and NLIW on the southeast continental shelf of the Bay of Biscay. The data set includes through water column observations of temperature and currents at the outer- (150 m depth) and inner-shelf (60 m depth). The internal tide and mode-1 NLIW generated currents more than three times the barotropic tidal current. The background double pycnocline stratification at the inner-shelf was modulated by wind-driven circulation, modifying the NLIW response. When the inner-shelf stratification was characterised by a stronger near-surface pycnocline, we observed polarity transformation of a wave of depression train coming from offshore. Whereas when the inner-shelf stratification was characterized by a stronger near-bed pycnocline, regular trains of elevation waves resulted from internal tide steepening. Under these conditions we also observed depression NLIW travelling on the near-surface pycnocline within the same internal tide phase as elevation NLIW. The NLIW of opposite polarity were propagating either at similar or different propagation speed and therefore interacted. We observed modification of the elevation wave as a faster travelling depression wave interacted with it.
