No, we’re not probing whales and dolphins, but we are probing their environment to learn more about their habitat. XBT is the acronym for EXpendable BathyThermograph – a one-time use instrument that collects temperature (thermo) and depth (bathy) data. It’s just one of the instruments we use to collect environmental information and although it is not a complicated instrument, it can tell us a lot about the medium in which whales, dolphins, and their food all live. For example, XBT data can reveal the depth of the thermocline (area where temperature changes rapidly and plankton are known to aggregate), and help resolve the boundaries of thermal fronts. Most importantly, XBTs can be launched while we are underway and do not detract from marine mammal observer effort.
XBT launches on this cruise are targeted for tracklines that cross the shelfbreak. These launches, every 3 to 5 nautical miles, will provide temperature profiles to supplement Conductivity, Temperature, Depth (CTD) data. In conjunction, these instruments will help us resolve the position of the Middle Atlantic Bight shelfbreak front, an oceanographic feature we think is an important part of the habitat for marine mammals in the area.
Below is a temperature profile of one XBT launch.
The type of XBTs we use – Sippican T-7s – only report data to 765 meters (2,510 feet) depth. The surface temperature is just above 20 oC (68oF ) and drops to approximately 10 oC (50oF) by 50 meters ( 164 feet) depth. Temperature then increases to about 13 oC (about 55oF) by 100 meters (328 feet) depth before starting to slowly decrease as the probe descends to its terminal depth.
Duke Marine Lab