Making progress and Wanting More: One-year near-surface current measurements from a surface mooring in the Gulf Stream and other thoughts about long-term surface moorings

Recently, as part of the CLIMODE (CLIVAR Mode Water Dynamics Experiment) a surface mooring was placed at 38degN, 65degW, a location that was at times in the core of the Gulf Stream. The surface mooring survived the first year at this 5000 m deep site, and the second deployment failed after 2 months. Two Nortek current meters provide some of the first direct near-surface current time series from such a location, and represent progress in sustained sampling from surface moorings. At the same time, the ability to sustain surface moorings for a year at a time presents challenges for current meters. After one year, it is hard to escape biofouling and, at times, damage from fishing gear. Such concerns lead to using current meters with no moving parts, but the present trade off between sampling and power in most instruments typically constrains one to four samples per hour, not frequent enough to either match the sustained sampling rate of temperature and salinity now possible or to resolve high frequency processes of interest. Once per minute sampling and proven accuracy as can be obtained by a Vector Measuring Current Meter (VMCM) would be desirable for near-surface moored deployments.