Abstract: The present invention provides a subsurface instrument and a system for the collection and transmission of deep ocean data utilizing standard buoy mooring lines. The system includes a moored surface buoy and a submerged data collection instrument both inductively coupled to the buoy cable. The instrument has a transducer responsive to the characteristics of seawater. A slave modem is interconnected to the transducer through an A/D converter allowing analog transducer signals to be converted to standard telephone modem signals. The modem signals are inductively coupled into the mooring cable and received by a master modem located in the buoy. The buoy may contain a satellite transceiver allowing transmission of the signals to a remote location. The subsurface instrument is battery powered and battery life is extended by powering down when the instrument is not in use.