The international project on ocean CO2 sequestration Ocean current measurements off Keahole Point, Hawaii, 5 August - 12 September, 1999

Abstract

The report presents data from an RDI ADCP and an Aanderaa RCM9 current meter deployed at ca. 800 m depth from August 5 - September 12, 1999, off Keahole Point on the Big Island of Hawaii. The measurements were part of the international project on ocean CO2 sequestration. The ADCP measured 3D currents from 763 m to 259 m depth in 85 separate cells, each of 6 m thickness. The recording interval was 40 minutes, while the RCM9 at 10 m above the bottom sampled at 10 min. intervals. Average speed measured by the ADCP increased upwards from ca. 4 cm/s near bottom to 5.5 cm/s at 500 m depth and 10.5 cm/s in the shallowest cell. Corresponding maximum currents were ca. 15, 17 and 45 cm/s. The RCM9 showed average and maximum speeds of 4 and 15 cm/s respectively. The main flow was along the NW-SE axis, with SE flow dominating the deeper layers and NW the shallower ones with a shear zone at around 500 m depth. Tides of diurnal and semi-diurnal period dominated the energy field, while shorter periods had peaks around 1 and 2 hours, corresponding to resonating, bottom modified internal waves.