Another day, another heat flow measurement…

Rob Harris, Oregon State University

 The weather has cleared with incredibly calm seas given our location in the Southern Ocean.  We hope this good weather will continue for the remainder of our research cruise and the next cruise where seafloor instruments that have been deployed over the last year are scheduled to be recovered. 

We have successfully completed the seismic survey of the northern area and are now in the midst of a final scramble to finish our heat flow transects in this area before moving to the southern area. A figure of our current transect is shown below and as I write this we are working our way from west to east (going downhill) and have finished about 10 measurements.  We expect this transect to take about 48 hours to complete. 

 While the probe is on the seafloor it sends pings though the water column that allows us to assess its performance.  We monitor the probe tilt to make sure it has not fallen over, and the top, middle, and bottom thermistor.  Monitoring the thermistors allows us to determine whether the probe is fully inserted into the seafloor and gives a qualitative indication of the thermal gradient.  So far it’s all good.  Data for quantitative analysis is stored in the data logger that we only get access once the probe is recovered and the data is downloaded.

This is an exciting transect because we cross several interesting targets.  These targets include the location of a proposed scientific drill hole and faults near the deformation front.  The measurements across the fault zones will tell us whether significant quantities of fluid are moving up to the seafloor along these faults. We are also crossing two basement highs that are buried in sediment just east of the deformation front.  Significant variation in heat flow across these features will tell us about the magnitude of fluid flow through these features and conversely, a lack of variation will indicate that fluids are not advecting heat.  In both of these cases we are using heat as a tracer for fluid flow.  Measurements in front of the deformation front will be used to estimate the thermal structure of this subduction zone. 



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