Seafloor Geodesy and Salty Crabs

It’s not often that one gets to go to sea. It’s not often, either, when one finds a stowaway in their backpack.

Hello! Bonjour! My name is Jesse Hutchinson. I have a PhD from the University of Victoria, Canada, and I specialize in geophysics; specifically seismology. I am also a staff scientist at Ocean Networks Canada, a non-profit organization focused on marine science and outreach, where I have worked for over two years. Since 2012, I have lived in Victoria, BC with my wife, where we had two wonderful children, one of whom snuck the little stowaway, named Jelly, into my backpack for this expedition. I’m not often away from home for long, so it is nice having a little reminder of my family riding around in my pocket on a daily basis.

As a geophysicist with almost no experience at sea, this expedition appealed to me for several reasons. While I may normally be landlocked, the instruments I use for my work are located at the bottom of the ocean. These instruments include ocean-bottom seismometers (OBS) and GNSS-acoustic mirror transponders, known as FETCHs. I was curious about the operational procedures involved in deploying these instruments, as well as the combined effort of the scientists and crew required to make it all happen.

Yesterday, I participated in the efforts to deploy three FETCHs to replace three others that had run through their batteries. FETCHs are fairly simple in concept, they send an acoustic signal in response to receiving one. This can be done thousands of time to try and triangulate their location to a high degree of accuracy, allowing them to act like GNSS stations on the seafloor. Why is this done? To determine the rates of motion of tectonic plates beneath the ocean, specifically the Juan de Fuca plate in this case. Those plate motions enhance our understanding of how the tectonic plates are interacting, and also go towards informing hazard models for more accurate predictions to mitigate against disasters such as large earthquakes and tsunamis. Pretty important stuff!

Deployment of these instruments was only possible with the ROV Jason, which has been riding along with us on the R/V Atlantis since we left port on July 5th. Prior to putting Jason in the water, the three FETCHs were dropped overboard on an elevator, a buoyed platform which is used for a slow, controlled descent. Once ready, the Jason descended to the elevator to begin retrieving the FETCHs, one at a time, to ferry them to their respective sites, install them, and then return again to the elevator.

It was my job to log events and capture screenshots of what was happening. Despite the long journeys to each site, I found myself constantly searching over the screens to look for little critters crawling and swimming along the seafloor. These included rock fish, halibut, crabs (large and small), anemones, and more. The crabs ended up being of particular interest.

We had noticed that the benchmark at each site, which is a solid, secure foundation for the FETCHs to rest on, were beginning to erode along the edges. By them time we reached the third site, we saw that it was crawling with crabs. Further, it seemed that the crabs were responsible for chipping at the edges of the benchmarks, effectively eroding them from the outside in! Fortunately, they seem to be rather slow at their jobs, so the FETCHs should be safe for the coming years.

That’s it for now and bon voyage!