Geothermal Heating in the Panama Basin. Part II: Abyssal Water Mass Transformation

Diabatic upwelling of abyssal waters is investigated in the Panama Basin employing the water mass transformation framework of Walin [1982]. We find that, in large areas of the basin, the bottom boundary layer is very weakly stratified and extends hundreds of meters above the sea floor. Within the weakly stratified bottom boundary layer (wsBBL) neutral density layers intercept the bottom of the basin. The area of these density layer incrops increases gradually as the abyssal waters become lighter. Large incrop areas are associated with strong diabatic upwelling of abyssal water, geothermal heating being the largest buoyancy source. While a significant amount of water mass transformation is due to extreme turbulence downstream of the Ecuador Trench, the only abyssal water inflow passage, water mass transformation across the upper boundary of abyssal water layer is accomplished almost entirely by geothermal heating.