Dataset: Temperature Profiles AT15-40 and AT15-56
Deployment: AT15-40_Alvin_Dives

During Alvin dives 4483-4492 (Dec 6-17, 2008) and 4562-4573 (Nov 22-Dec 6, 2009) in the 2000 meters (m) deep Southern Guaymas trench, 113 temperature profiles were taken in sediments near and within Beggiatoa mats, at the hydrothermally active areas from 27°N00.30 to 27°N00.60, and 111°W24.65 to 111°W24.35. All temperature probe measurements, positions of the 139 probes in the mat, and penetration depths were checked with the Alvin dive videotapes that provide a continuous record of all dive operations. Of the 113 temperature profiles, 78 were measured in mats with both orange and white filaments to focus on the relationship between differently colored Beggiatoa.

A Heatflow probe manufactured by the Woods Hole Oceanographic Institution (WHOI) was used to measure 69 of the 78 temperature profiles. This is a 0.6 m titanium tube containing a linear heater and five thermistors (type 44032, Omega Engineering, Inc.) at 10-centimeter (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 40 degrees Celsius (C), and +/- 1 degree C up to 200 degrees C. It is considered fully inserted when a disc at the base reaches the sediment surface, and takes temperature readings at 0, 10, 20, 30, and 40 centimeters below seafloor (cmbsf).

For 28 profiles, 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. Occasionally, this technique resulted in channel formation, and the second set of readings was higher than the first. During dive 4490, one temperature profile was repeated three times, giving a range of sensor precisions from 1.0 to 4.1 C. A high-temperature probe was used to produce nine additional temperature profiles with varying depth intervals from the sediment surface down to 37.5 cmbsf. The high-temperature probe has a type-K thermocouple located at the tip, with a tolerance of +/-3 degrees C up to 400 degrees C. To measure temperature profiles with this probe, the tip touched the sediment surface for the first reading before inserting the probe sequentially to desired depths and taking readings.