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

Abstract

A numerical model of ocean flow, hydrography, and transport is used to extrapolate observations of currents and hydrography and infer patterns of material flux in the deep ocean around Axial Seamount, a destination node of NSF's Ocean Observatories Initiative's Cabled Array. 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 anticyclonically around the seamount's summit in toroidal form with maximum speeds at 1500 m depth of 10–11 cm/s. 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 reentering the caldera over lower walls at its north end, while gradually bleeding southwestward during the modeled time period into the ambient ocean. A second tracer release experiment using a source of only 2 day duration inside and near the CASM vent field at the northern end of the caldera suggests a residence time of the fluid at that locale of 8–9 days.

Seasonal patterns in deep acoustic backscatter layers near vent plumes in the northeastern Pacific Ocean

“…Although it was not the purpose of this study to examine the circulation at Endeavour Ridge measured by the ADCPs, it is likely that currents play an active role in the zooplankton movement and distribution in the region. As noted previously, passive vertical displacements of up to 100 m due to semidiurnal tides generated over the abrupt ridge topography are expected based on earlier current meter measurements in the area (Mihaly et al 1998) and from numerical simulations of tidal motions over nearby Axial Seamount (Xu and Lavelle 2017). It is further likely that low-frequency currents modified by the ridge topography may be responsible for passive advection of the zooplankton within the study region.…”

“…Temperature and transmissometer profiles at the ridge, along with numerical simulations using nested-grid ocean circulation models (Thomson et al 2005(Thomson et al , 2009) reveal that the rising plumes in the axial valley, augmented by diffuse venting, spread laterally at their level of neutral buoyancy at around 1900-2100 m depth about 200 m above bottom (mab). Plumes drift both along and across the ridge axis with the prevailing currents (Thomson et al 2003(Thomson et al , 2005(Thomson et al , 2009Xu and Lavelle 2017). Plume remnants are also evident outside the confines of the axial valley and ridge complex, where water depths are much greater .…”

Volcaniclastic Dispersal During Submarine Lava Effusion: The 2012 Eruption of Havre Volcano, Kermadec Arc, New Zealand

“…Lateral dispersal in the model is driven by a simplified unidirectional current extending across the entire depth of the water column. Current profiles in the ocean are hard to model, especially in regions with significant bathymetric relief (i.e., seamounts) where interaction of tides, large ocean currents and the seafloor can produce temporally variable large eddies or localized currents along the seafloor (Wright, 2001;Xu and Lavelle, 2017). However, we believe that the assumption of a unidirectional current is an acceptable simplification due to the extensive evidence of preferential dispersal to the north west during the 2012 Havre eruption (Carey et al, 2014(Carey et al, , 2018.…”

Observation and Modeling of Hydrothermal Response to the 2015 Eruption at Axial Seamount, Northeast Pacific

“…After an initial 10-day spin-up, the model results show that ocean circulation averaged over a 29.5-day (i.e., one lunar cycle) period following the brine release features an anticyclonic (clockwise) toroidal circulation around the summit of Axial with a maximum speed of 10-11 cm/s at a depth of 1,500 m (Figure 8a). Xu and Lavelle (2017) attributed the presence of the clockwise circulation around Axial to the rectification of oscillatory flows at tidal and subtidal frequencies. Within the caldera, mean flow is from north to south in general with inflow from the northern end of the caldera and outflow at its southern end (Figure 8a).…”