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.
Christine Chesley, Eric Attias, Peter Miller and Jake Perez on the day shift in the deep tow station.
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.
Samer Naif happy with the new antenna roller system.Graduate student Christine Chesley at the helm of the deep-tow and winch control station.
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.
Check out the deployment list. After getting the more widely spaced first six receivers deployed, we were able to deploy the more closely spaced central receivers about every half hour.
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Chris Armerding working the acoustic deck box to test the receiver’s acoustic release system.Christine Chesley cleaning out the track on one of our concrete receiver anchors.Graduate student Janine Andrys about to pull the release rope for the pelican hook so that the ocean-bottom electromagnetic receiver can free fall to the seafloor.Eric Attias, postdoc from University of Hawaii
Since pushing off the dock at Seward around 13:00 yesterday, we’ve been transiting at 10-11.5 knots towards station 201, which we should reach around 3-4 a.m. tonight. During the transit, we’ve been getting our sea legs as the ship rolls and pitches in the moderate sea swell, eating tasty food that galley cooks Mark I and Mark II have been treating us to, and getting ourselves organized and prepared for the on-rush of deck work that will begin soon. Below are some photos from yesterday and today. Scroll to the end to get so see the bonus video of Dall’s porpoises!
View of Resurrection Bay as we left the dock at SewardMan-overboard rescue drill with observers on the stern pointing towards the dummy in the water as the Sikuliaq’s small boat motors in for the rescue.The dummy from the man overboard drill resting after being saved by the ship’s crew.Sikuliaq’s 1st Mate John Hamil gives us a safety briefing prior to our departure from Seward.As party of the safety briefing we got to try on our immersion suits, which are big floppy versions of dry-suits. They are designed to keep you buoyant and insulated and we were told you could survive for about a day floating in the cold water in one of those. Ideally, if the situation non-ideally arose, you would only need the immersion suit for when swimming from say a sinking vessel towards a life raft. Left to right: graduate students Christine Chesley, Tanner Acquisto, Brandon Chase and Scripps technician Jake PerezGraduate student Janine Andrys, ship’s tech Tony, graduate student Li Wei and EM technician Goran Boren ready to abandon ship during the safety drill yesterday.Marine tech Jake Perez explaining how to assemble an ocean-bottom EM receiver.Jake and Chris teaching the graduate students and cruise volunteers how to assemble an ocean-bottom EM receiver.Bosun Paul in the ship’s winch room pointing to the far drum holding about 9 km of the .680″ coax cable we will use with our deep-towed EM transmitter (the near drum holds the ship’s trawl wire). Out of view is a large level winder and a traction winch that are part of the winch system. The .680 cable goes off the drum, through the level winder and traction winch, then up to a block above the main deck and finlly out through a sheave attached to the A-frame on the stern.The .680″ coax cable drum. The cable holds a coaxial conductor, which we make electrical contact to through the slip rings in the small stainless steel cylinder on the right. The slip rings allow us to transmit power (in our case about 2000 V) from our top side power supply to the cable on the rotating drum by using brushes to make electrical contact with conductors on rotating rings. Power then goes through the cable and on down to the deep-tow transmitter system (which you will see in posts in a few days from now).
Here are some photos from yesterday showing the RV Sikuliaq and some of our science team preparing equipment. Right before leaving the ship for dinner in town, we were treated to a mother and baby humpback whale swimming around right next to the ship. Today we have some safety meetings in the morning and then will depart for sea sometime around lunch time.
We’ve all arrived in Seward, Alaska, and boarded the RV Sikuliaq today. We need to prepare the OBEM receivers, set up the lab, terminate the deep-tow cable and make other preparations before the ship pushes off the dock tomorrow. The map below shows our four planned controlled-source electromagnetic (CSEM and magnetotelluric (MT) survey profiles and some of the other past, present and upcoming geophysical surveys in this region.
Planned survey map showing four trench crossing EM profiles with 42 ocean bottom EM receivers (white dots) per profile. Grey lines show past active source seismic profiles and red lines show upcoming multichannel seismic profiles to be collected by another group this summer. Red circles show ocean-bottom seismometers currently deployed for the Alaskan Amphibious Community Seismic Experiment.
We’ve passed the halfway point with more than 22 of the 42 seafloor MT receivers now recovered. Here are some photos from the last few days, starting from when we left port.
The forecasted high winds and swell arrived last night, making the instrument recoveries a bit exciting as well as challenging. Here’s a video from this morning showing us recovering a seafloor magnetotelluric receiver in rough weather.
