We completed deep-towing our second profile today and brought SUESI back on deck around lunch time. Samer told me that two days ago during the tow down the continental slope they had an unintended low altitude event on the Vulcan receiver that is towed on a tether 500 m behind SUESI, and that it likely had scraped the sea bottom. Sure enough, the Vulcan receiver came back up today with its nose electrode pushed in about three centimeters with the pipe full of seafloor mud. The acoustic relay transponder towed behind it also had a small fan shaped plant attached it. We haven’t seen any animal or plant life on the instruments yet other than jelly fish tentacles so it was nice to finally see evidence of life on the seafloor. We also discovered some corrosion on the back half of SUESI’s pressure case on the unpainted but anodized sections. Steve thinks something may have come loose inside and is shorting current to the pressure case; that current travels out the easiest paths, which are the non-painted parts of the pressure case, where it electrochemically corrodes the aluminum. This is the first time we’ve seen this on SUESI in its ten years of service, so we’re planning to switch to the spare SUESI for the final two planned deep-tows. Photos from today below.
We did it! Today we deep-towed SUESI to 5100 m deep in the Alaskan subduction zone, making this the deepest ever deep-tow of a controlled-source electromagnetic transmitter. Woohoo! Edit: the night team just pushed SUESI down to 5150 m! This beats our previous record of 5000 m set in 2010 at the Middle America Trench offshore Nicaragua.
This video shows what it was like in the deep tow control room for several hours today while the ship crept along in the fog.
We finished deploying all 42 (err, now 39) receivers at 10:55 AM and then headed 10 nautical miles up the profile so that when we turned back around to tow SUESI down the line, we would be getting nice deep-sensing long offset CSEM data on the first receiver. SUESI was in the water and transmitting by just past 2 PM, and the rest of the day has quite peaceful and relaxing, including sunny skies and a pod of whales spouting about a kilometer from the ship most of the evening. Jupiter is visible just about the horizon again too. Photos and a video from today below.
Around 3 AM last night we finished recovering the ocean bottom EM receivers deployed along our first profile and by 4:45 PM we were on the deep end of the second profile deploying receivers every with 30 minutes, with 20 already deployed as I write this at 1:45 AM. Some time after breakfast we should finish deploying the last receiver (39th) and then we will begin towing SUESI down the profile.
We have an awesome team of graduate students, postdocs, technicians and scientists that are doing a great job starting up data loggers, assembling and testing the receivers and making sure they get deployed safely down to the seafloor. BIG THANKS to all of you! Some photos and videos from today below.
Two days ago I got the dreaded early morning phone-call wakeup, with Samer on the line hysterical that the RV Sikuliaq had just run over a second, yes SECOND!!!!$#@!!@#$, of our receivers, which was now stuck in the ship’s propeller and the data logger was dangling out of the receiver frame and about to fall away into the abyss. Uggh. I came out on deck just about when they freed the remains of the instrument and were raising it back onto the deck:
Miraculously we got both data loggers (and importantly the data they contained) but we lost an acoustic transponder unit, an induction coil magnetometer, two electronic compasses, and lots of cables to the sea. The instrument frames were destroyed, and we lost several electrode arms. The glass floatation floats where banged around enough that we can no longer trust their suitability for deep deployments. One of the induction coil magnetometers (a marine version of the EMI BF4 sensor) that made it back on board the ship was severely bent (and destroyed):
Ship handling for instrument recoveries isn’t easy but I’ve only seen a ship completely run over an instrument and destroy it a couple of times in over twenty years of going to sea. So two instruments destroyed in the same day was super upsetting, to say the least, especially since this happened on instrument recoveries #2 and #6 out of 42 total, which meant there were 36 more chances for instruments to get munched by the Sikuliaq. Morale was super low and that made tensions high for the rest of the instrument recoveries that day.
But all is not lost. We put the carnage of the morning behind us and the ship worked hard at more precise and careful handling. Now two days later we have only about 10 more receivers to recover. We’ve had a few hiccups with some of the ORE acoustic units on the receivers that were deployed for the first time in deep water on the incoming plate, and one stubborn receiver has refused to release from the seafloor, likely due to a malfunctioning ORE acoustic unit. But we now have lots of good data in hand and are cruising along, so things are looking up.
We started on the deep end of the profile and are now moving up the continental slope. We should finish picking up the last few receivers, located in the shallow waters of the continental slope, later tonight.
Here’s a video of a receiver recovery from yesterday afternoon in what could be called a text-book recovery with slow and careful positioning by the ship and efficient and careful handling by the deck crew.
Today we completed deep towing our first profile. After bringing the SUESI transmitter back on deck we began recovering the seafloor EM receivers. First three are back on the ship and only 39 more to go. We are planning to release them in groups of 3-4 staggered every 30-60 minutes, so we should be done within another two days. Then we will transit to the next profile and repeat the whole process for another week. Then on to the 3rd and 4th profiles…but lets not get ahead of ourselves as there’s a lot of work ahead of us. Photos from the last day below.
When deep towing we often say boring is good. That means we’re stuck sitting at the deep tow station all day watching the transmitter’s data feed while the ship moves along at a mere 1.5 knots (about 0.7 m/s or walking speed). Alternative non-boring scenarios include winch drums freely unspooling, power transformers melting down, broken cable terminations shorting to seawater, torn transmitter electrodes or other things that would end our data collection. So yeah, boring is good. Photo and video from today below.
The last receiver went over the side of the ship around five this morning, completing the deployment of all 42 EM receivers in just 27 hours. We then beelined for the start of the deep-tow profile and managed to get the EM transmitter SUESI, its 300 m long antenna and towed-EM receiver (at 500 m offset) deployed before the weather kicked up in the afternoon. When we first fired up SUESI to full power we heard some loud rattling coming from the top-side power supply in the back lab and then SUESI’s telemetry data feed went bad, so we decided to power down and start it up again, but again the rattling came back at high power. So we decided to revert to the spare power supply unit. However when we powered that one up, SUESI would no long talk to us and that started to get us all worried . We switched back to the original power supply and again SUESI wouldn’t talk to us. Oh no! Fear and anxiety and thoughts of a failed experiment started coming to mind. One option was to beach SUESI and switch to the spare SUESI, but that would have required a few hours of deck work in increasingly poor weather. So we opted to test some other things in the lab first, just in case…We swapped out the deck unit and that didn’t work. Then Steve Constable had the brilliant idea to swap out the deck box’s communication cable since that was one of the components detached and then reattached we moving between the power supplies. Bingo! SUESI came back to life! Yay, no more failed experiment, at least for now! But we still had the problem with the rattling power supply in unit #1 so we went with the backup power supply and fired SUESI up to 250 A. Using the ship’s winch, we lowered it down at a rate of about 30 m of wire per minute to a tow altitude of about 100 m above the increasingly deepening seabed as we tow down slope into 5500 m deep trench along this stretch of the Alaskan subduction zone. If all goes well, we will complete our first CSEM profile in another two days. Photos and video from today below.
Thanks to good weather, good ship handling and our hard working science team, we were able to deploy 36 receivers today (well, now yesterday since I write this just past midnight local time). We have a lot of new people on the science team this cruise and many of them have never gone to sea before or have never worked with marine EM equipment. They all came up to speed quickly today. So big thanks to both the newbies as well as the old salts for making today go so smoothly. We have only six more receivers to deploy and then we will turn back around and head down the line to start deep-towing our controlled source electromagnetic transmitter system. Here are photos and movies from the marathon of receiver deployments.