Monthly Archives: March 2015

Back to the barn // TTIDE ends in Hobart port

The R/V Revelle has headed “back to the barn” and has just docked in Hobart, Tasmania.

Back to the Barn. Photos: Thomas Moore

Back to the barn. Photos: Thomas Moore

All hands on deck are now in the usual post-cruise full-court-press to get all the remaining scientific gear packed, off the ship, and into containers for the return journey.

It’s a morning of mixed emotions, we’re all happy to be back in port and heading home but it’s bitter-sweet to be leaving behind the R/V Revelle, her Captain and crew, and our days on the Tasman Sea.

Albatross of the Tasman Sea. Photo: Thomas Moore

Albatross of the Tasman Sea. Photo: Thomas Moore

 

Good morning from the Tasman Sea

A special dawn for the R/V Revelle off southeastern Tasmania.  Photo: Thomas Moore

A special dawn for the R/V Revelle off southeastern Tasmania. Photo: Thomas Moore

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.

T-TIDE student profile: Madeleine Hamann

PhD student Madeleine Hamann from the Scripps Institution of Oceanography is aboard the R/V Revelle for the T-TIDE leg 3 cruise and here she talks about her work and how studying math, science, and engineering has opened up a world of opportunity for her.

The final countdown

The Final Countdown

Albatross fill the air, Tasman Island in the distance - the location for the TTIDE southern moorings.  Photo: Thomas Moore

Albatross fill the air, Tasman Island in the distance – the location for the TTIDE southern moorings. Photo: Thomas Moore

It’s the second weekend out here on the Tasman Sea for the TTIDE leg 3 crew aboard the R/V

Revelle. Today we are pushing hard to finish recovering all four remaining moorings still in the water.  If the team can make all that happen before darkness falls tonight that will keep the TTIDE project ahead of schedule and give the scientists extra time to conduct “yoyo” and “towyo” operations – filling important gaps in our view of the internal wave energy pulsing across the Tasman Sea.  There are only a few days left until the R/V Revelle steams “back to the barn” and for all aboard it’s starting to feel a bit like the final countdown.

Dawn broke gray and chilly but the howling westerly wind and the short, steep windswell it generated has mercifully laid down.  It was a great way to start the recovery of TTIDE “M4”, a 2300 metre tall mooring designed to capture the energy of internal waves breaking in the shallowing waters of the continental slope using two highly specialised McLane profilers.

The McLane profilers are “wire-crawlers”, programable robots that climb and descend the mooring line over and over and over again, one million metres worth of travel in every one of their large internal lithium battery packs.  These profilers come jammed with an array of instruments that

A McLane profiler breaks the surface.  Photo: Thomas Moore

A McLane profiler breaks the surface. Photo: Thomas Moore

measure pressure, temperature, salinity, and most importantly current velocity at a finer scale and across a longer vertical reach than any other tool in our oceanographic toolbox.

The McLane data are invaluable, they are costly acquire, and each profiler runs on hardware and software that takes great skill and experience to operate.  The McLane profiler, often abbreviated as “MP” in casual conversation on the back deck, is the star of the show and everybody quietly anticipates the outcome each time one of these yellow beasts breaks the surface of the sea under the tug of our winches.  Did the wire-crawler survive the pressures of the deep and what data will it hold for the TTIDE team?

Science, caught fresh from the sea

The MP’s have indeed brought a data harvest, fresh from the sea.  As moorings have been brought onboard the attached instruments are cleaned and logged before TTIDE team members get busy up forward in the analytical labs extracting the data onto a dizzying collection of hard drives.

the first analyses of MP data is underway

the first analyses of MP data are underway

Time is always short aboard ship but TTIDE scientists have started to look at the new MP data in the past 24 hours, building the initial analyses of what an underwater robot has learned from crawling a mooring wire for many months deep under the surface of the Tasman Sea.  This first look at the MP data shows the clear fingerprints of the daily tide, lunar cycle, and the passing of swirling mesoscale eddies as they swept over the slope 20 kilometres or so off St Helens, Tasmania.

When the TTIDE scientists finally return home* they will bring all the fresh science they have caught into their data kitchen and cook up a better understanding of our earth, climate, and ocean.

Thomas Moore, for the TTIDE team

Prof. Matthew Alford works on a MP back in the ship's lab.  Photo: Thomas Moore

Prof. Matthew Alford works on a MP back in the ship’s lab. Photo: Thomas Moore

* “home” means many things for the diverse TTIDE team, made up of experts from the University of Minnesota – Duluth, the University of Alaska – Fairbanks, Oregon State University, the University of Washington, and the Scripps Institution of Oceanography.

A needle in a giant haystack at the bottom of the sea

Dmitry Brazhnikov, Josh Manger, June Marion, Amy Waterhouse, and Matthew Alford celebrate with an ADCP selfie

Dmitry Brazhnikov, Josh Manger, Bex Dunn, Amy Waterhouse, and Matthew Alford celebrate with an ADCP selfie

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.

Night ops on the R/V Revelle.  Photo: Thomas Moore

Night ops on the R/V Revelle. Photo: Thomas Moore

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”.

Storm Force

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.

Storm force winds whip the Tasman Sea off Tasmania.  Photo: Thomas Moore

Storm force winds whip the Tasman Sea off Tasmania. Photo: Thomas Moore

“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

Matthew Alford, Captain Dave Murline, Eric Boget, and Gunnar Voet discuss weather options on the bridge of the R/V Revelle.  Photo: Thomas Moore

Matthew Alford, Captain Dave Murline, Eric Boget, and Gunnar Voet discuss weather options on the bridge of the R/V Revelle. Photo: Thomas Moore

Revelle Passing the Torch: Leg II Postscript

T_Tide_Logo_2015 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.

WW#1 returns from 2500 cyclesFigure(1) A Wirewalker profiler comes aboard early Tuesday morning.

Tough Day at the OfficeThe 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.Sun_Glint_Albatross

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.

 

Rob Pinkel

 

In the lee

Captain Dave Murline of the R/V Revelle keeps eyes out for a mooring rising to the surface.  Photo: Thomas Moore

Captain Dave Murline of the R/V Revelle keeps eyes out for a mooring rising to the surface. Photo: Thomas Moore

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. 

A 48" orange ball of syntactic foam - the top of mooring T3 - floats at a distance in a wind-blown Tasman Sea.  Photo: Thomas Moore

A 48″ orange ball of syntactic foam – the top of mooring T3 – floats at a distance in a wind-blown Tasman Sea. Photo: Thomas Moore

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

Undersea Gliding

Albatross, a glider of the southern skies. Photo: Thomas Moore

Albatross, a glider of the southern skies. Photo: Thomas Moore

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.

Bex Dunn with one of the two recovered gliders.  Photo: Thomas Moore

Bex Dunn with one of the two recovered gliders. Photo: Thomas Moore

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

scripps oceanography uc san diego