Geothermal heating and the properties of bottom water in Cascadia Basin

Abstract

A new compilation of CTD data sheds light on the circulation and properties of bottom water within Cascadia Basin. A relatively high salinity water mass is revealed in a region of likely bottom water inflow east of the Blanco Fracture Zone. Water mass distributions and the deep geostrophic shear field are consistent with a general cyclonic circulation within the basin and suggest a northward‐flowing boundary current next to the deep continental slope. Shifts in temperature‐salinity relationships are consistent with a vertical transition from waters of northern origin to waters of southern origin approaching the seafloor. This vertical water‐mass transition complicates the interpretation of temperature anomalies. We redefine the temperature anomaly due to geothermal activity and the thickness of the layer influenced by seafloor heating. Simple heat budget calculations lead to a residence time of about one year for the bottom water, shorter than suggested by previous studies.