U.S.-Australia Cooperative Study of the Northern Branch of the Antarctic Circumpolar Current.
The principal task of this cruise SW of Tasmania is to deploy approximately 40 seafloor instruments and 9 current meter moorings in an array spanning the northern (strongest) current jet associated with the Antarctic Circumpolar Current (ACC). The experiment is intended to provide a sufficiently dense three-dimensional array of measurements of currents and temperature to provide answers to questions concerning the important momentum and energy balances in the ACC. In addition, the experiment has several goals relating to the intensity and dynamics of the total zonal transport of water and heat through the array, which are relevant to WOCE objectives.
The seafloor instruments are lightweight, self-contained and free-falling, and will be recovered in 2 years by acoustic recall. They measure either the horizontal components of the ambient electric field, proxies for the magnitude and direction of total water column transport, or the seafloor to sea surface to seafloor acoustic travel time, which is inverted to provide information on the large-vertical-scale thermocline fluctuations. We will deploy a single line of 16 horizontal electrometers (HEMs) from about 48.9S, 144.2E, to about 53.1S, 142.1E, with approximately 32 km spacing. At about 26 km distance, on both sides of the middle two-thirds of this NNE-SSW linear array of HEMs, there will be linear arrays of inverted echo sounders (IESs). Along each line of IESs, the IESs will be separated by about 32 km.
Centered at about 50.7S, 143.4E, and imbedded in the linear arrays of HEMs & IESs, we will deploy 9 nearly-full-depth current meter moorings in a diamond-shaped array with principal axes parallel and perpendicular to the linear arrays of HEMs & IESs. Each mooring will carry 4 current meters and additional temperature sensors. The maximum separation between the outermost moorings will be about 104 km along the axis (WNW-ESE) of the ACC.
At 52 km beyond each of the two outermost moorings, we will deploy one additional HEM. Finally, at each of the four HEMs at the vertices of the overall 500 km by 200 km cross-shaped array, we will deploy a single bottom pressure gauge. At each of the 40 deployment sites, a bathymetric survey of the area will be performed prior to deployment.
Assuming all the deployments above are completed in a timely manner, we will revisit all the IES, mooring and HEM sites (in that order of priority), for the procurement of full-depth CTD profiles.
As secondary priority, we will be running the 150 kHz ADCP to/from Hobart and between instrument deployment sites. SEA BEAM data will be collected in an ancillary mode (funded under a DMA grant to Stu Smith) while the ship is underway, both to/from Hobart and between instrument sites. Smith also requested that we tow the magnetometer to/from Hobart and we will be happy to oblige.
Science party as of December 15, 1994 (19 to 23 people):