Circulation near Axial Seamount

Abstract

Year‐long moored current measurements from 1987 to 1988 on the saddle (1860 m) between Axial Volcano and Brown Bear Seamount show an oscillating flow with a broadband frequency centered at about 4 days and a long‐term average flow of about 4 cm/s southward. The measurements at sill depth also suggest a possible alternating exchange of water north and south of the Cobb‐Eickelberg seamount chain with warmer water (0.05°C) coming from the north. However, measurements near the top of the volcano at about 1400 m show a weaker, but northward, mean flow, and the 4‐day oscillation barely exists. Conductivity, temperature, and depth (CTD) observations on the east side of the volcano infer possible intensification of southward flow adjacent to the Juan De Fuca Ridge, similar to that found with combined CTD and current meter observations about 100 km to the south. Southward flow is hypothesized along the entire east side of the ridge. On the west side the Axial‐Brown Bear saddle may be near a convergence zone between southward and northward currents which then flow westward. The highly energetic environment on the saddle suggests other gaps in the ridge, and seamount chains may be important in determining the fate of the hydrothermal effluents. The general oceanic flow at the top of the caldera, however, is more tenuous, and the depth of change between these two regimes cannot be determined.