Circulation, hydrography, and transport over the summit of Axial, a deep volcano in the Northeast Pacific

Abstract:

A numerical model of ocean flow and transport is used to extrapolate observations of currents and hydrography and infer patterns of material flux in the deep ocean around Axial Volcano, a destination node of NSF's Ocean Observatories Initiative's Cabled Arrays. Using an inverse method, the model is made to approximate measured deep ocean flow around this site during a 35-day time period in the year 2002. The model is then used to extract month-long mean patterns and examine smaller-scale spatial and temporal variability around Axial. Like prior observations, model month-long mean currents flow anti-cyclonically around the volcano's summit in toroidal form at speeds of up to 7 cm/s. Temperature and salinity iso-surfaces sweep upward and downward on opposite sides of the volcano with vertical excursions of tens of meters. As a time mean, the temperature (salinity) anomaly distribution takes the form of a cold (briny) dome above the summit. Passive tracer material continually released at the location of the ASHES vent field exits the caldera primarily through its southern open end before filling the caldera. Once outside the caldera, the tracer circles the summit in clockwise fashion, fractionally re-entering the caldera over lower walls at its north end, while gradually bleeding southwestward during the modeled time period into the ambient ocean. Another tracer release experiment using a source of only two day duration inside and near the northern end of the caldera suggests a residence time of the fluid at that locale of 5-6 days.