Thermal profiles were measured in surficial sediments using Alvin’s 50 cm heat flow probe in Guaymas Basin, Gulf of California (111W 27N) in November 2018. Alvin dive numbers 4991-5001.
A Heatflow probe manufactured by the Woods Hole Oceanographic Institution (WHOI) was used to measure temperature profiles. This is a 0.6 m titanium tube containing a linear heater and five thermistors (type 44032, Omega Engineering, Inc.) at 10 cm intervals along the length of the tube (personal communication with Lane J. Abrams, WHOI). The thermistors have a tolerance of +/- 0.2 up to 40C, and +/- 1 C up to 200C.
The probe has thermal sensors every 10 cm, starting 5 cm under the attached plastic disk (the “puck”) that limits probe penetration and rests on the seafloor once the probe is inserted. After approx. 3 to 5 minutes, temperature readings stabilize and are recorded. The heat flow probe shorted at the beginning of Alvin dive 5000; instead, the thermosensor within the tip of the suction intake was inserted into the sediment at approx. 5 cm, 10 cm and 20 cm depth, and the temperature was recorded immediately.
The probe is considered fully inserted when a disk at the base reaches the sediment surface, and takes temperature readings at 0, 10, 20, 30 and 40 cmbsf. For additional resolution, 5 cm depth resolution was achieved by first inserting the probe 5 cm less than complete insertion and recording one profile, and then inserting the probe the rest of the way and recording a second profile, 5 cm offset from the first. Temperatures were recorded after the readings had stabilized for each of the five depths, usually after 3 to 5 minutes.
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