The Subduction experiment : cruise report R/V Oceanus cruise number 250 legs 1 and 2 subduction 2 mooring deployment and recovery cruise, 25 January-26 February 1992

Abstract

Subduction is the mechanism by which water masses formed in the mixed layer and near the surface of the ocean find their way into the upper thermocline. The subduction process and its underlying mechanisms were studied through a combination of Eulerian and Langrangian measurements of velocity, measurements of tracer distrbutions and hydrographic propertes and modeling. An array of five surface moorings carrying meteorological and oceanographic instrumentation were deployed for a period of two years beginning in June 1991 as part of an Office of Naval Research (ONR) funded Subduction experiment. Three eight month deployments were planned. The initial deployment of five surface moorings took place during the third leg of R/V Oceanus cruise number 240. The moorings were deployed at 18°N 34°W, 18°N 22°W, 25.5°N 29°W, 33°N 22°W and 33°N 34°W. A Vector Averaging Wind Recorder (VAWR) and an Improved Meteorological Recorder (IMET) collected wind speed and wind direction, sea surface temperature, air temperature, short wave radiation, barometric pressure and relative humidity. The IMET also measured precipitation. The moorings were heavily instrumented below the surface with Vector Measuring Current Meters (VMCM) and single point temperature recorders. Expendable bathythermograph (XBT) data were collected and meteorological observations were made while transitting between mooring locations. This report describes the work that took place during R/V Oceanus cruise 250 which was the second scheduled Subduction mooring cruise. During this cruise the first setting of the moorings were recovered and redeployed for a second eight month period. This report includes a description of the instrumentation that was deployed and recovered, has information about the underway measurements (XBT and meteorological observations) that were made including plots of the data and presents a chronology of the cruise events.