Mass transport in the Bay of Biscay from an inverse box model

Abstract

Mass transports in the Bay of Biscay for thermocline, intermediate and deep water masses are estimated from a box inverse model applied to hydrographic data from a quasi‐synoptic survey carried out in August 2005. The model obeys conservation statements for mass in a volume of ocean bounded by 43 full depth CTD stations in the horizontal, and neutral density layers in the vertical. It permits advective exchange between layers and an adjustment of the Ekman transport and the freshwater flux divergences. Bay of Biscay has a thermocline transport of −8.0 ± 0.7 Sv with an anticyclonic recirculation of +6.9 ± 0.6 Sv. An equatorward flow of +0.5 ± 0.4 Sv is attributed to the slope current close to the northwestern Spanish coast. The mean wind stress curl for the region corresponds with a clockwise upper layer flow which produces a downwelling of −0.6 ± 0.4 Sv. The surface circulation pattern agrees with the obtained with the Jason‐1 altimeter. Intermediate waters follow the same surface pattern of the thermocline waters as a subsurface eastern boundary current with an eastward flow of −7.9 ± 1.0 Sv and a southwestward flow of +8.0 ± 1.0 Sv. Finally, our results show that deep waters also flow into the box with a net transport of −3.6 ± 2.0 Sv and flow out of the box with a net transport of 2.3 ± 2.0 Sv.