### Measuring heat flow below the seafloor

posted Oct 28, 2017, 9:08 AM by Beth Orcutt
 You know the feeling when you’re too excited to fall asleep? Maybe the night before your birthday, or before the first day of school? I had that feeling last night, because today is the day for my science!   You may have already read about the types of experiments going on here. Kelle has been part of the team collecting crustal fluids, Annie taught you about CORKs, Rose is growing microbes from rocks she retrieved. I have been patiently waiting for my chance: I’m going to measure heat flow!  Here I am with the heat flow probe before loading it onto ROV Jason. Photo by Jackie Goordial.   Why am I so excited? Measuring heat flow is a tool that we can use that will tell us what the sediment and underlying rocks are like, and how water and heat might be moving through them. If we know how water moves through these places, we can better understand how microbes are surviving.   How does it work? Jason uses a heat flow probe, which is a long metal rod. Inside the rod are thermistors, or temperature sensors, and a small heater. There are two parts of this tool that provide information:   1: Jason sticks the probe into the sediment while the thermistors record temperature. The probe will heat up a tiny bit because of the friction from pushing the probe into the sediment. It takes about eight to ten minutes for the temperatures to cool back down. This is how we measure the natural temperature in the sediment!   2: Once the temperatures are stable, I command the probe from the ROV Jason control van to fire a heat pulse. For 20 seconds, the probe heats up. The thermistors then record how fast it cools down. This can tell us the thermal conductivity of the sediment. Thermal conductivity is a measure of how easy it is for the sediment to transfer heat, as in, how fast it can cool down or heat up.   Here we are comparing the results of two probes tested at the same time. The Jason control van shows us three different images so we can see exactly how the probes were inserted.   By combining 1 and 2, we can start to predict how heat and water might be transferred through the sediment. For example, if it cools down quickly after the heat pulse, that might mean that cold water from the bottom of the ocean is flowing through the sediment.   This graph shows temperature over time. Each color is a different temperature sensor. Notice how quickly the temperature cools after the peak.   I was up all day yesterday taking these measurements during our final dive of this cruise! Hopefully we’ll be able to learn a little bit more about how water and heat move through the rocks below the ocean.