A New Tool for Probing Thermohaline Fine Structure in the Ocean: Seismic Reflection Profiling of the Labrador Current/North Atlantic Current Front

We present acoustic images of thermohaline structure in the ocean created from marine multichannel seismic reflection profiles across the major oceanographic front between the Labrador Current and the North Atlantic Current. The images show that distinct water masses can be mapped, and their internal structure imaged, using low-frequency acoustic reflections. The reflections are generated by sound-speed contrasts at interfaces across which temperature changes by up to 3 degrees C. Returns from reflection coefficients (RC) as low as 0.0001, corresponding to sound speed changes of 0.3 m/s (temperature changes of ~0.1 degrees C), can be imaged. The warm/cold front is characterized by strong (RC ~ 0.004; 12 m/s), east-dipping reflections generated by thermohaline intrusions in the upper 1000 m of the ocean. Regions away from the front show weaker undulating reflectors suggestive of internal waves in the thermocline and submesoscale eddies beneath the thermocline. Our results imply that standard low frequency marine seismic reflection techniques can provide excellent spatial resolution of important oceanic phenomena, including thermohaline intrusions, internal waves and eddies.