Fluid flow or mud eruptions? Sediment temperature distributions on Hهkon Mosby mud volcano, SW Barents Sea slope

Hهkon Mosby mud volcano is located on the SW Barents Sea slope at a water depth of approximately 1250 m. In-situ temperature measurements using gravity corers equipped with autonomous temperature loggers and a short temperature lance operated by an ROV were collected during three cruises between 2003 and 2006, revealing an exceptionally high level of activity and a complex thermal structure of the mud volcano. Simple analytical models were applied to the measured data to estimate rates of specific discharge and to test the hypothesis of episodic mud eruptions. Strongly curved profiles from 4 to 16 m below the seafloor suggest fluid flow at rates from 1 m/year close to the limits of the central area to more than 4 m/year approaching the geometrical center. At the limits of the central area, the profiles show distinct maxima at sediment depths of about 10 to 15 m, which are interpreted as the result of lateral flow. Repeated measurements at shallow depths along a transect crossing the central area revealed a persistent pattern of temperature gradients, while changes in the absolute values point to temporal variability. Temperatures gradients of more than 40 °C/m within the upper half meter of the sediments close to the geometrical center suggest even higher rates of specific discharge than estimated from the deeper profiles. These high rates of fluid flow are most likely accompanied by frequent mud eruptions of small volume and limited local extent.