Geothermal Heating in the Panama Basin. Part II: Abyssal Water Mass Transformation. Issue 10 (21st October 2018) - Banyte, D.
Abstract: 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, 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. Plain Language Summary: This study investigates how abyssal waters become lighter with the focus on geothermal heating effect. We find that in the Panama Basin, geothermal heating dominates the upwelling across the upper boundary of abyssal waters. Nevertheless, high turbulence at the abyssal water inflow passage contributes significantly to lighten the densest waters. Finally, most of the upwelling is found in the weakly stratified bottom boundary layer, which is hundreds of meters thick, contrary to the common assumption of it being just meters to 10s of meters thick. Key Points: Geothermal heating is the strongest water mass transformation process for abyssal waters inside the Panama Basin Almost all abyssal water mass transformations occur within the weakly stratified bottom boundary layer (wsBBL) hundreds of meters thick The thickness of the wsBBL may be used to differentiate the basin walls form the basin bottom