OSU’s June Marion talks about being a tech aboard TTIDE
Good morning! The daytime watch awoke to a spectacular sunrise here aboard the R/V Revelle, stationed about 40 kms off southeastern Tasmania.
All 14 moorings are aboard and we have been settling in for the final few days of ocean observations. We have 48 hours left on this final leg and the TTIDE team is making as many “yoyo” and “towyo” operations as we can.
If losing an expensive package of scientific instruments on the bottom of the ocean is a painful fact of life for the sea-going oceanographer then finding something that was once lost is a glorious moment.
The TTIDE leg 2 team was unable to bring home one of their bottom mounted ADCP’s, lost somewhere off the northeast of Tasmania in about 80 metres of water. “ADCP” is an acronym for Acoustic Doppler Current Profiler, an instrument capable of measuring the velocity of ocean currents from the shelf floor to the surface. But something unexpected and disastrous occurred and a recovery float, the ADCP’s lifeline to the surface, became separated from its companions.
So for two nights on TTIDE leg 3 the R/V Revelle patrolled the last known position of the lost gear, dragging heavy trawl wire and grapples in a crisscross pattern. Last night at 2am, after many hours of searching, suddenly the tension on the line monitor jumped to over 1000 pounds. Was this just a spike in wire tension, a temporary snag? No, the tension was steady and that meant the TTIDE team had caught something significant. “You don’t imagine that you can actually collect this thing that has a tiny footprint of about 20 metres on the bottom,” said Amy Waterhouse, lead scientist at the time of the recovery.
If snagging the ADCP was impossibly improbable getting it back to the surface and on deck safely was potentially perilous. In what condition and orientation would this mess of anchor, grapple, wire, and technology arrive aft of the R/V Revelle? Slowly, over a operation carefully executed by the skillful resident technician Josh Manger, each part of the tangle was brought aboard step by step in the dark. Finally, two hours later the ADCP was lying on the deck surrounded by a happy bunch of TTIDE crew celebrating out on the Tasman Sea at 4 in the morning.
The R/V Revelle quickly set course south for the next task, the recovery of mooring “T7”.
As dawn broke off Tasmania’s Freycinet Peninsula the TTIDE team and crew of the R/V Revelle faced an increasingly angry sea and a challenging 72 hour weather forecast. Strong westerly winds, gusting up to 54 knots, make for demanding working conditions on the back deck. After a brief meeting on the bridge a decision was made to temporarily cancel mooring recovery operations and switch efforts into “yoyo” mode.
“Yoyo” is a term that refers to mounting a large number of scientific instruments on a specialised frame and hanging that frame off a powerful and capable winch system. This package of instruments is slowly lowered to great depth and then brought back to the surface taking measurements of the ocean’s properties. The up and down motion of the instrumentation package on the wire gives “yoyo” operations their name.
With great patience each up and down dip of the frame, known as a CTD cast, adds one snapshot of information about the internal state of the sea. Ideally we will stay on station for at least 24 hours to capture an entire tidal cycle, the beating pulse of the internal waves the TTIDE team is chasing.
With our CTD casts underway we have one eye on the winch and one eye on the weather. When we get a break in the storm force winds it will be back to our line of moorings to recover “T7”.
Thomas Moore, for the TTIDE team
Running a research program at sea involves the constant re-assessment of options: how to learn the most about the planet with the limited amount of time remaining in the cruise. As the time runs-down, the assessment effort intensifies. In every cruise a rather surreal moment is reached when one runs out of options: all remaining time is committed. The re-assessment process is history, the cards have been played and you get to see how much / whether you’ve won.
This happened for us last Sunday, at “Site 10” in 1100 m of water. The data coming in were just too interesting to walk away from. We decided to stay and keep the Fast CTD running until the “last-minute” of the cruise. Given our time requirements, the last minute was determined to be 03:00 Tuesday morning.
It’s a strange feeling to “turn off” a system that’s bringing in good data, providing an exciting view of the ocean 1000 m down. For the teams that kept the Fast CTD running 24-7 for the past three weeks it was almost like turning off the life-support system in a hospital setting. However, there’s nothing like extreme fatigue to minimize sentimentality and the morning watch got a three-hour break as the Revelle headed inshore to begin recovery of the T-SHELF mooring array.
The effort began at first light. Ominously, the surface float marking the position (and key to the recovery) of the inshore doppler current profiler (ADCP) was missing. We would have to come back and drag a grappling hook to try to pull this instrument up.
Working progressively offshore, subsequent moorings came up with varying degrees of drama. By Wednesday noon, all moorings were aboard and we returned to the inshore site to drag for the errant ADCP. By 16:00 our time was up. We reluctantly left the instrument and headed for Hobart.
Figure 2. Tough day at the office: strategizing the search for the ADCP .
In that final evening at sea, the mooring team was involved in a frenzy of opening instruments, downloading data to computers, and archiving results. As the process unfolded the results proved gratifying. Drew Lucas’ two Wirewalkers each achieved ~2500 profiles, with all instruments aboard functioning properly. Nicole Jones’ five surviving moorings all worked well, with the exception of three thermometers lost during the recovery.
The archiving and packing effort was still going strong as the Revelle sailed up the Derwent Estuary Thursday morning for an on-time arrival in Hobart. As the morning progressed data archiving continued, the Fast CTD winch and boom were dis-assembled and packed, the T-Shelf mooring gear was offloaded, and bunk-rooms and labs were cleaned and readied for the Leg III team.
Somewhat strangely given the pace of the preceding weeks, by lunch-time there were people looking for something to do. It was time to disband. We gathered that evening with the ship’s crew and Matthew Alford’s Leg III team at the Hobart Customs House Hotel for a party worthy of Leg II. While totally successful, the party was reconvened Friday night to handle “unfinished business” and further brief the arriving Leg III group.
The “briefing” process was clearly effective: in the early hours of Thursday 5 March, after successfully recovering many of the TTIDE moorings, Matthew’s team dragged up the wayward TSHELF ADCP. What an effort!!
I have to thank Capt. Murline and the Revelle crew, as well as the US and Australian Leg II participants, for an incredibly successful cruise.
Down here in the “roaring forties” Tasmanians have a saying for their typical weather patterns, “four seasons in one day”. It can be sunny and calm one moment and blowing a gale the next. After the R/V Revelle’s first few days of relatively calm weather we have what looks to be multiple cold fronts on the way, along with the roaring westerlies they can bring.
Luckily the TTIDE team and the R/V Revelle have been working like a well oiled precision timepiece and we are on schedule, the back deck currently abuzz with winches and gloves hauling in our seventh mooring for this the third and final TTIDE leg. Our promptness has also been a blessing as it has put us at our series of northern shelf moorings, up in shallower water near the coast of Tasmania and somewhat in the lee of the gale gusting to 45 knots.
In the lee of Tasmania the roaring forties have less “fetch” – the distance travelled by wind across open water – saving the TTIDE mooring recovery crew from having to perform their often tricky and sometimes dangerous work on a deck pitching and heaving in mountainous swells.
Mooring “T3” is coming in across the blocks as this post it being typed and with luck and skill the TTIDE team will wrestle back from the bottom four entire moorings today. A challenging feat – wish us well.
– Thomas Moore, for the TTIDE team
The ocean we are trying to better understand is always moving and changing, varying across great distances and depths as well as the passing days and seasons. It’s impossible for us to be everywhere all the time but with the help of special programmable gliders TTIDE scientists are learning more.
Gliders are a relatively new type of instrument platform, essentially ocean floats with wings and a robot brain, and they fill important gaps in our TTIDE shipboard and mooring observations. This is a very capable ocean science platform, some versions of which have been developed in house at the Scripps Institution of Oceanography, that can turn and change both their horizontal and vertical position within the water column. Gliders can literally fly through the sea and be programmed to record data like ocean temperature, salinity, velocity, and sometimes other more biologically important quantities such as oxygen levels and chlorophyll.
Another virtue of the glider platform over fixed moorings is that they regularly return to the surface and communicate back to base at Scripps. This allows very recent ocean measurements to be seen by an operator who then has the option to reprogram the glider and adapt to changing priorities. Oceanographers call this “adaptive sampling”.
We have so far successfully recovered two of these wandering ocean robots and their data will help provide a baseline for TTIDE scientists to better understand the complex dynamics of the internal wave pulses that cross this stretch of the Tasman Sea.
– Thomas Moore, for the TTIDE team
Words and photography: Thomas Moore
Latitude – 44.5 degrees south
Longitude – 152.3 degrees west
Ocean Depth – 4768m
The TTIDE team is back aboard the R/V Revelle and we are again plying the fickle waters of the Tasman Sea. This is the final cruise in our latest venture to better understand ocean mixing and how internal waves can influence both climate and the ecosystems that support marine life and our communities and industries back at home.
On the maiden cruise our team, a capable mix of veterans and first time volunteers, deployed fifteen moorings, towering strings of scientific instruments thousands of metres tall supported by giant floats and anchored to the seabed by hefty weights. Like 15 giant balloons tethered sky-high in a watery atmosphere, our moorings have swayed in the ocean currents for over a month recording characteristics like temperature, salinity, pressure, and the speed and direction of ocean currents. The TTIDE moorings have been listening carefully to the ocean for a long time but all that they have learned will stay a secret unless we can get them back safely aboard the Revelle and in one piece.
Hello, are you still there?
On our first day the Revelle steamed from Hobart, Tasmania roughly one third of the way to New Zealand to arrive at location “A1”, the tallest and most complicated of all our moorings at 4727 metres worth of wire, engineering, and technology. Mooring A1 is designed specifically to measure the energy in the beam of internal waves rolling towards Tasmania before that beam can be influenced by the bottom when it eventually travels into the shallower waters of the slope and shelf. Here the water is almost 5km deep and therein lies our first challenge. To get the mooring to rise to the surface we must “talk” across this underwater distance with sound waves, literally commanding it to return from the bottom. What if we speak but nobody is listening? It’s always the first unknown in a mooring recovery operation and on “A1” the TTIDE team had some anxious moments from the very start.
We carry aboard Revelle three different options for acoustically communicating with the mooring releases, the mechanical “hands” that grasp the bottom anchors on the sea floor. Each of these three communication units sends acoustic messages from the surface and receive back responses from the release units, or at least that is what is meant to happen. For much of the first operational hour of our twelve day cruise the science team sat huddled around the acoustic unit at first expecting, later hoping, and finally praying that we’d get a response. “Hello, are you still there”?
Mooring release failure is one of the worst situations a sea-going oceanographer can encounter. After sometimes years of proposals, funding, planning, construction, and deployment you now have a precious cargo of pricey scientific instruments and priceless oceanographic data that sits silent on the ocean floor – unresponsive, unmoving, stuck out of reach. If you talk to the deep but the deep is not listening you have but one extreme measure left to consider – dragging. Nobody wants to drag for their mooring.
Dragging for a mooring involves streaming many kilometres of heavy cables, weights, and hooks behind the ship in blind hope that you can literary rake the mooring off the seafloor and force it to the surface. It’s an arbitrary and highly destructive option reserved for the most desperate of situations. Luckily for the TTIDE team, after the failure of our first two acoustic units, we were all very happy to get a response from the mooring release on our third and final backup unit. A few minutes later there was immense relief when the top mooring float finally broke the surface about 300 metres away from our position. Now the team could get cracking bringing in over 4700 metres of wire and some sixty odd scientific instruments.
A day on the wire
Getting a 4700 metre mooring to the surface is just the start of the job and it took all the daylight hours we had on hand to get all the bits of wire rope, floats, and scientific instruments back aboard the Revelle.
The first day of mooring recovery on the back deck of any research ship is always somewhat unpredictable as a new group of veterans and volunteers gets into the rhythm of wire and winch. For our first day we were blessed with great weather, relatively calm seas, and a team that immediately hit their stride. Effective teamwork is the most vital component for success on a cruise with such an ambitious agenda of recovering 15 moorings in a short period of time. The operational tempo for TTIDE leg 3 over the next 11 days or so will necessarily remain extremely high for the whole crew and science team.
It was wonderful for us all to get mooring A1 back from the depths and onboard today. The instruments are cleaned and loaded into the labs aboard Revelle and in a few days all the data should be downloaded.
The deep does sometimes talk back when called upon.
TTIDE leg 3 team, aboard the R/V Revelle over and out for now.
– Thomas Moore, for the TTIDE team
TTIDE Leg II is entering the home stretch, with great weather & even better data coming in. Aside from a brief appearance to steal one of Capt. Dave’s fishing lures. Bruce the shark has been kind enough to stay away from our deep-profiling Fast-CTD fish. We spent last Tuesday doing a series of water sampling stations for Nicole Jones & the T-Shelf team and checking that Drew Lucas’ wave-powered Wirewalkers were indeed walking (No problem: 0-100 m every 6 minutes).
Then it was back to work with the Fast CTD, looking at deep internal waves propagating up the slope. This “work” has been a lot more fun, given the host of improvements to the system implemented by Mike Goldin and our technical team. In addition to a radical improvement in reliability and user-friendliness, the game-changing addition to the system is a newly created acoustic altimeter. This gadget is a cigar-sized version of a ships echo sounder , (Figure 2a). Shoe-horned into the tail of the fish, it can tell us the distance to the sea-floor as the fish plummets downward. We’re really interested in measuring as close to the bottom as possible, as the turbulence we’re hoping to measure can be strongly influenced by the friction of the sea-floor.
The altimeter can detect the bottom at distances up to 75 m, and we typically hit the brakes and reverse at 15-20 m, giving us a 5-10 second cushion before impact (Figure 2b).
Figure 2 a. The altimeter transducer being installed in the tail of the fish. b), The lab readout shows a noisy band at 80 m range. When the bottom gets within range, we get to watch the final approach. Here the fish is turned around 15 m above the seafloor, 1900 m down.
The precise turn-arounds, as well as all other aspects of the operation, have been achieved by a mixed team of tech-savvy veterans and young volunteers, with homes ranging from the University of Texas to the University of Suva. No two of the students were born in the same country. All are getting into watching the deep ocean evolve in real-time. Working 12 hours on-12 off, 7 days a week, this great group has collected roughly 2500 CTD profiles without (shark excepted) mishap.
Figure 3. A 36 hour record of the deep slope, with 1100 -1600 m depth zone sampled every ~10 minutes. The horizontal blue lines indicate the depths of constant density surfaces , as they are vertically heaved by the internal waves. Every 12 hours, a ~100m tidal crest passes, bringing cold waters from below up the slope. The red dots indicate locations where more dense water is found above less dense water: internal breakers. Massive breaking is found in the crests, but it initially occurs above the sea floor & works its way downward.
The view has been definitely worth the price of admission. A 36-hour record taken in 1630 m of water on the slope is shown in Figure 3. For classical internal waves in a flat-bottomed ocean, the biggest vertical motions are found in mid water column. At the sea-floor, vertical motion dies completely away. But if you add just a few degrees of tilt to the sea floor, as we have here on the Tasman Slope, suddenly the biggest vertical motions are found just above the bottom. The big excitement is associated with the 100 m tall tidal crests that take the form of up-slope propagating “hills” of cold water. There’s a lot of turbulence associated with these shoaling crests, and it has a somewhat unique behavior. Unlike a classical turbulent bore (e.g. wave run-up on the beach), where the turbulence is initiated by friction over the sea-floor, these shoaling crests first go turbulent well above the bottom. The turbulence then spreads downward to the sea-floor as the crest passes. Developing a dynamical understanding of this new phenomenon will be a priority of our post-cruise data analysis.
All lab activities have been presided over by our cruise mascot and in-resident Tasmanian Devil, Clarence, (Figure 4a) who was shanghaied onto the cruise by our Leg I predecessors. Attempts to enlist local fishermen to stand shark-watch for us have been unsuccessful: they’re just too laid back (Figure 4b).
Figure 4 a. Clarence and his demure companion Winnie the wombat preside over the lab. Clarence is proving to be somewhat of a party animal. He won’t get a real chance to strut his stuff(ing) till we get back to the beach. Rules are rules. b. Ground Hog Day, Tasman Sea style. Only six more weeks of winter this summer!
It’s never good news when the phone rings in the chief scientists cabin. It was 7:30 am on Tuesday. We had just lost electrical communication with our Fast-CTD fish. I arrived on the fantail to find the worst-case scenario unfolding. Fifty meters of wire were being coiled on the deck. There was no instrument on the end. The fish and 800 m of wire were lost.
It didn’t take long to see what had happened. Nearly 20 m of the cable was filleted by razor sharp cutters (Figure 1). Then a few meters of undisturbed wire…. then “Chomp”!
About once a cruise we have a deep encounter with a shark or big fish (Figure 2). Our recent cruises have been in the South China Sea or in equatorial waters, where sharks are expected. Only the depth of the encounters has been a surprise. Our old fish design had a lead nose, which over time got decorated with the gouge marks of sharks teeth (Figure 3). Once we brought up a tooth stuck in the lead. Off Tasmania, in the “Roaring Forties”, the waters are surprisingly warm, due to the south-flowing East Australia Current. As the local surfers confirm, there are sharks here too.
Figure 1. A close up of roughly 20m of “flossed” cable.
We were profiling between 1300 and 1900 m when the incident happened. “Bruce” (Nemo, Finding, W. Disney Inc, 2003), while swimming through the blackness at around 500 meters depth, apparently bumped into our wire. The instrument was near the top of its profile, 800 meters below. He struck at the moving wire, using the first 20m to floss his teeth. Then he bit down hard.
Figure 2. The nose of our 2012-vintage Fish showing the orange micro-conductivity cell, before (left) and after
(right) an encounter with a UFO (Unidentified Fishy Object).
It’s tough when you lose an instrument. In over forty years of playing this game, well over 100 thousand profiles, we have previously lost only one CTD. It’s part of the cost of doing business in field science, and the cost unfortunately is getting to be quite high. The value of this instrument is equivalent to the operational cost of our ship for roughly 12 hours.
Wasting time bemoaning lost equipment is expensive too. By 11 am we were ready to go again with our back-up CTD fish, using an old, well-worn, cable from a previous experiment. Hopefully we’ll learn a lot more about ocean mixing & no more about sharks as the cruise continues to unfold.
Figure 3. When the lead beneath the black tape is deeply gouged and there is a matching gouge on the opposite side of the fish, you know that you’ve failed the Bruce taste-test.