Category Archives: Falkor

Falkor: You, Me, and the Tasman Sea

Swirling, living ocean

I used to think the ocean felt vast – an endless empty expanse of water, deep and unchanging. Within a month of starting my graduate degree at the University of Washington School of Oceanography, I had learned that the ocean is neither empty nor static. The ocean is teeming with life, and not just `charismatic mega-fauna’ like whales and tropical fish, but also tiny single-celled photosynthetic phytoplankton. Plankton may seem insignificant, but there are billions and billions of them, and their combined effect is enough to change the amount of carbon stored in the deep ocean and the amount of oxygen available for us to breathe.

And the ocean water itself is alive with motion. It circulates slowly, for sure, especially compared to the atmosphere that gives us our ever-changing weather. The deep currents in the ocean travel across the sea-floor for hundreds of years, and surface currents skirting the edges of the continents move at a few miles per hour or less. The surface itself is a patchwork of eddies – a literal ocean of swirling vortices. And the internal tides we are studying criss-cross the ocean in a web of wave beams, spilling onto the slopes and breaking or bouncing off again.

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 Falkor cruise track overlaid on sea surface height map from satellite altimetry (AVISO), showing eddies in the survey region. Courtesy of Luc Rainville.

 

 

 

Our little patch of sea

So, the ocean is not empty and not quiet… but surely the ocean is huge? Surely it’s beyond our ability to ever fully understand, beyond our ability to change? You might think – floating out here on a ship with the same group of people for a month, with nothing in any direction but the endless rise and fall of the Tasman Sea – that the ocean would feel uncommonly big. I have found however, that at least for me, the opposite is true.

The longer I’m out here, the more this patch of ocean has begun to feel familiar, comprehensible, like a well-known neighborhood in the middle of a sprawling city. The Tasman Sea determines our days here – the science we can do, the measurements we can make, the birds and fish and plankton we come across, even how easy it is to sleep or shower. We are in constant motion with the waves beneath us. I feel connected to the ocean here, now that I know more about it – the creatures that live here, the moods of the weather, how to work with the Tasman Sea instead of against it.

Dissolving disaster

Truth is, we are all more connected to the ocean than we realize. And we have a greater impact on it than you might expect. Here’s a simple experiment: the next time you brush your teeth or wash your face, take a look at your toothpaste or face wash. Do you see any tiny colored specs? Chances are these rough little particles are actually plastic! They are great at polishing teeth and exfoliating skin, but they often end up in the ocean and are not so great for the plankton and other marine life, who cannot digest them and die. Here on the Falkor, Randall Lee is measuring the micro-plastics coming from Australia, from near Hobart where concentrations are higher to way out here in the Tasman Sea where the ocean is almost empty of plastic.

Microplastics aren’t the only threat facing sea critters, in fact they aren’t even the worst one. As we’ve mentioned here before, the ocean is taking up a lot heat, reducing the immediate impact of global warming. It’s also taking up quite a lot of CO2 – something like 30-40% of human emissions. This gas dissolves in the ocean at the surface, forming carbonic acid and making the ocean more, well, acidic.

‘Ocean acidification’ is a hot topic right now, with clear evidence of the problems it’s causing for everything from the corals in Australia’s Great Barrier Reef to the oysters on the West Coast of the United States. Many tiny sea creatures have shells made of calcium carbonate, and they are slowly dissolving away. It’s difficult to imagine the solution, especially to a problem that seems so huge.

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 Microplastic filtration system set up by Randall Lee on the Falkor. Photo credit: Judy Lemus.

Microplastic

 Simulation of microplastics released from a flood plume into Port Phillip Bay, and moved by the winds and tides, slowly spreading towards the Bay entrance. Courtesy of Randall Lee

 

Global connections

I imagine that it’s kind of like the ocean though. You start with what is right in front of you, you work to understand your little patch of the world and treat it with respect, and it will connect you to everything and everyone and everywhere else! And, just like our internal tides, spreading out across the globe, local changes often have an unexpected global ripple effect. We are working to understand one tiny part of the ocean in order to improve our understanding of the entire climate system. But it’s the everyday choices we all make that have the best chance of protecting it.

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 Sunrise over the Tasman Sea looking out past the A-frame, from the aft deck of the Falkor. Photo credit: Hayley Dosser.

 

 

 

 

 

– Hayley Dosser, Falkor

Falkor: Thanks for watching, part 2

We are all happy to be home, but had a great time doing science at sea on the Falkor. In the remaining hours of our T-Beam cruise, we were able to put together a video using one of our favourite songs: Tassie Whalers by The Overlanders (Pete’s uncle is one of the members!).

When not working, we were also hard at work trying to win the fitness challenge between the Revelle and Falkor crew. As the Revelle Leg-1 crew mentioned, it is important to keep healthy when at sea for such a long time. We tried our best and we even had a rowing competition with medals! Overall, the Falkor science and ship’ crew:

  • Ran 375km
  • Cycled 671km
  • Rowed 194.5km
  • Pullups 351
  • Pushups 7091
  • Situps 6347
  • Squats 1766
  • Dead lifts 70
  • Yoga 405mins
  • Burpees 850
  • Gun sculpting 23
  • Skipping 8400
  • Hoola hoop 30mins
  • Cheese 42
  • Bacon 20

Well done team!

 

Falkor: Back from the Tasman Sea

After 26 days at sea, the T-Beam crew has sailed back into port along the Derwent Estuary, and tied up on land. We never expected this work to be easy – battling with the constant barrage of storms headed directly from the southern ocean – the Tasman Sea did not disappoint. We did, however, have a successful cruise.

Our part of the T-TIDE experiment was tasked with identifying the internal tide beam as it races across the Tasman Sea, through a sea of eddies to understand what the beam looks like before it slams into the continental slope of Tasmania. After starting out with some coordinated operations with the Revelle at the beginning of our cruise, we headed east and set up camp in the middle of the Tasman Sea.

 

Gabi Pilo (right), Spencer Kawamoto and Ryan McDougall-Fisher taking instruments off the CTD-cage on a rare sunny day during the transit to Hobart. Credit: Judy Lemus

Gabi Pilo (right), Spencer Kawamoto and Ryan McDougall-Fisher taking instruments off the CTD-cage on a rare sunny day during the transit to Hobart. Credit: Judy Lemus

We conducted a set of nine 25-30 hour CTD profiling stations two different lines spanning the internal tide beam. Our CTD was equipped two ADCPs to get vertical profiles of horizontal velocity as well as chi-pods which are able to measure temperature (and turbulence) at a very high rate. T-TIDE PIs have been working tirelessly over the months & years leading up to these cruises to determine, to the best of their ability, where the internal tide beam might be. This has involved using satellite altimetry data as well as mathematical models designed to simulate what the internal tide characteristics look like and guided us in picking our CTD stations. Although our work has only just begun, and we will spend the next months (and years!) untangling the data set that we have obtained, our initial findings suggest that we found the beam!

Preliminary estimates of the internal tide energy flux (arrows) as measured from the Falkor. Pink triangles (F2-F9) are the locations of our CTD stations, and the red/grey arrows show our initial estimates of the semi-diurnal internal tide energy flux headed towards the Tasman slope right towards the T-TIDE moorings (blue circles). Credit: Sam Kelly, Luc Rainville and Amy Waterhouse.

Preliminary estimates of the internal tide energy flux (arrows) as measured from the Falkor. Pink triangles (F2-F9) are the locations of our CTD stations, and the red/grey arrows show our initial estimates of the semi-diurnal internal tide energy flux headed towards the Tasman slope right towards the T-TIDE moorings (blue circles). Credit: Sam Kelly, Luc Rainville and Amy Waterhouse.

Although we will all be scattering our separate ways very soon, there is really not enough that can be said about the incredible science crew on our T-Beam cruise. This includes the hard work of Captain Heiko and his ship’s crew. Everyone worked long hours and endured some of the worst weather – yet everyone was always ready for more, determined to get as much science as we could while being a great, fun group of people!

T-Beam science crew enjoying the last sunset on the RV Falkor. Credit: Danielle Mitchell
T-Beam science crew enjoying the last sunset on the RV Falkor. Credit: Danielle Mitchell

Hayley Dosser, a PhD candidate at UW-APL, interviewed the science party yesterday asking us simply ‘Why you study the ocean?’ After thinking for a few minutes, I realized that this is a very profound question. I study the ocean because I love it – I love the complex physical signals that lie beneath the ocean surface, and as scientists, I feel that we are responsible for doing our part in understanding how these complex signals will change or affect our changing climate. The internal tide in the Tasman Sea is a process that we need to understand in order to broaden our understanding and ability to predict the future ocean & climate, and with these small steps, such as the T-TIDE experiment, we are making that process.

Fair seas to the Leg-2 and 3 Revelle T-TIDE contingent who are still out on the slope! We are looking forward to your updates.

— Amy Waterhouse, Falkor

Falkor: Rollin’ in the Deep

This morning I was handed a small vial of water from the deepest reaches of the Tasman Sea (4800 meters deep, to be exact).  So what, you ask?  Well, this water has not seen the light of day for about 600 years.  That’s right, 600 years ago this water became very cold, salty, and dense, gradually sank to the bottom of the ocean in either the North Atlantic or the Southern Ocean and has not been in contact with Earth’s atmosphere since.  These water samples were collected by Pete Strutton on our last CTD profile – the Niskin bottles on the CTD were opened at 4800 meters and the cold, salty water poured in.  We’ve previously mentioned Pete’s work on nutrients in surface waters and the effect on phytoplankton.  In this case, he wanted to be able to compare the abundance of those nutrients at the surface with the very deepest water in the Tasman Sea (which would tell him a bit of how much the deep nutrients are getting mixed into the upper layers).  Back at the surface, Danielle Mitchell partitioned the samples out into vials as souvenirs for everyone on board.
Shrunken cups

Decorated Styrofoam cups brought down to 4000 meters deep become doll-sized due to the efects of pressure (the paper towels inside are helping them retain their shape until they dry). SOI/Judy Lemus
Deep water

A vial of water that has spent 600 years in the deep ocean. SOI/Judy Lemus

What goes down, must come up
Our retrieval of this deep ocean water gives me the opportunity to talk about the important role of deep water circulation around the globe and the water cycle.  The water that we brought up in our samples actually has a 50% chance of being either from the North Atlantic or the Southern Ocean (Matsumoto, 2007).  These two areas are responsible for creating the large masses of deep ocean water because the surface water in these two areas becomes very, very cold.  Water becomes more dense as it cools and therefore it starts to sink. In addition, the surface seawater may even freeze (especially in the Antarctic) and as it does, the dissolved salts precipitate out, making the seawater below even more salty, and even more dense. The sinking water masses, called “North Atlantic Deep Water” and “Antarctic Bottom Water”, initiate a deep ocean circulation pattern (called thermohaline circulation) that carries water from these two regions towards the equator where wind-driven upwelling brings it to the surface, gets warmed again, some of which is evaporated into the atmosphere, becomes clouds, and rains back down into the ocean again in higher latitudes.  Surface waters are entrained in large ocean gyres that move in a cyclonic fashion around the ocean basins in the northern and southern hemispheres.

A summary of the path of the thermohaline circulation. Blue paths represent deep-water currents, while red paths represent surface currents. This collection of currents is responsible for the large-scale exchange of water masses in the ocean. Figure by NASA
Chi-pod work

Working in the deep ocean means instruments must be constantly maintained.  Here Amy and Sam tend to one of the Chi-pod temperature sensors. SOI/Judy Lemus

The Dating Game
A familiar characteristic of the deep ocean is the immense pressure, due to the thousands of meters of water pressing down from above.  Students at Salmon Bay school in Seattle, WA will get a first hand demonstration of this pressure when the Styrofoam cups they decorated come back to them after being taken down to 4000 meters in a mesh bag attached to the CTD.  But what is ecologically important about the deep ocean is its storage capacity.  In addition to nutrient storage covered in a previous blog, the deep ocean can store a large amount of heat and carbon.  It is this storage of carbon, as dissolved CO2, that gives scientists the ability to know how long the water we collected on our CTD is about 600 years old.  The earth’s atmosphere has a very small amount of naturally occurring 14C, also called radiocarbon.  14C is an unstable form of carbon and undergoes radioactive “decay” (one of its neutrons becomes a proton and the molecule becomes a stable nitrogen atom, 14N).  This decay happens at a very predictable and measurable rate.  There is no source of 14C in the ocean, so all of the 14C in the ocean has come from the atmosphere.  Once 14CO2 is dissolved in seawater, any decay of the 14C can only be replaced by new 14C if the water remains in contact with the atmosphere.  So radiocarbon dating can tell us how long it has been since a particular sample of deep ocean water has been at the surface.  And that can give us an estimation of how long it takes for water to move through the “conveyor belt” of global thermohaline circulation.  From one small atom to a big picture of how the ocean affects Earth’s climate – science is pretty amazing.

– Judy Lemus, Falkor

The Tasman Tidal Dissipation Experiment//Supported by the National Science Foundation

Falkor: Using Nebula to Solve Nebulous Problems

Out here in the Tasman Sea, chasing the internal tide involves a lot of detective work, piecing together clues from water velocity, temperature, and density to determine where exactly the tide beam is heading.  Scientists know from 20 years of satellite altimetry (sea height) data where it is most likely to be, based on estimations of energy flux.  But there are a lot of factors that come into play that can affect the direction of the beam, including the physical characteristics and shape of the deep sea ridge where the internal tide is generated.

This is where mathematical modeling is again helpful. Modeling allows scientists to create a visualization of a complex phenomenon that integrates multiple sources of data with theoretical physics. The current state of the art model to describe ocean circulation, including internal waves, is called the MITgcm model (created at MIT in Boston, MA).  On board Falkor, Dmitry Brazhnikov is using this model to generate a hypothesis that will describe the pathway of the T-Tide beam after it is generated on the Macquarie Ridge.  Having an accurate picture of the direction of the beam is very important for understanding how it will interact with and reflect off of the Tasman Continental Slope. Starting with the satellite altimetry data to define one geographic section (domain) of the beam, Dmitry then began adding velocity and temperature data from this cruise into the model to re-prescribe the parameters of the MITgcm model to fit the specific conditions for the Tasman internal tide.  This process is called data assimilation and is extremely useful for improving the accuracy of numerical models, and for exploring the behavior of a system/phenomenon when you don’t have the luxury of making direct observations on every aspect of it.

Dmitry with clouds

Internal waves can occur in any medium where there is a strong difference in densities. Dmitry Brazhnikov admires the cloud formations created by an internal wave in the atmosphere. SOI/Luc Rainville

A Bending Beam
Although the weather has not been entirely cooperative, the T-Tide science team have still been able to collect a good amount of velocity and temperature data that offer a glimpse of where the T-Beam is.  As we mentioned previously, the highest water velocities at the depth we would expect to see the internal tide seem to be located somewhat north of where the original model using satellite altimetry data had indicated.  Dmitry is now using those data to create new simulations of the beam, and is getting some very interesting preliminary visualizations.  Rather than simply taking a more northward course directly from the point of origin, the model shows the beam “bending” toward the north as it progresses across the Tasman Sea. Physicists categorize waves into “modes” according to their vertical structure, which defines the energy, wavelength, and stability. Dmitry’s model shows that as the T-Beam wave moves toward and encounters the Tasman Shelf, the energy from the internal wave transitions from a long wavelength, stable mode 1 wave (which can be propagated over long distances), to a mode 2 wave (shorter wavelength and less stable) and then to a mode 3 wave (even smaller wavelength and stability).  The energy from the mode 3 wave is likely entirely dissipated on the continental shelf.

T-Beam model

Dmitry’s model illustrating the “bending” of the T-Beam across the Tasman Sea. Figure by Dmitry Brazhnikov
Model of beam reflection

This model shows the primary beam of the internal tide (mode 1: large energy with a major single direction) transitioning to a reflected wave that is mostly mode 2 (with some dispersed energy), and finally to mode 3 (dissipated energy without any general direction).  Figure by Dmitry Brazhnikov

Modeling the Future of Oceanography
None of these simulations would be possible during the course of a research cruise without the help of a “supercomputer”, which is essentially a computer with very high computing power and processing speed. This cruise, the T-Beam team is fortunate to be able to use the Nebula system, a cloud-based supercomputer recently installed on Falkor. Dmitry believes that supercomputers will help advance oceanographic research by allowing scientists to adapt a cruise plan while at sea, depending on what the real-time data are indicating.  This could have real implications for biological oceanography where scientists might want to predict the location of, say, zooplankton communities, over the course of a cruise.  Or use this dynamic modeling to help locate hydrothermal vents based on chemical and temperature signals in the water column.  In the future, there is the potential for substantial savings of time and money by being able to identify ocean features and phenomena while researchers are actually at sea, rather than waiting to analyze and visualize the data back in their laboratories.

Dmitry doesn’t just work with models at a computer – here he handles one of the tag line poles to recover the CTD. SOI/Judy Lemus

– Judy Lemus, Falkor

The Tasman Tidal Dissipation Experiment//Supported by the National Science Foundation

Falkor: Stormy weather

With most of our field work on the RV Falkor located in the middle of the Tasman Sea, we have had our fair share of rough weather. We were able to hunker down (or escape) the biggest storms that rolled through, but sometimes we had to stop collecting data for a few hours. Below is footage of one time we were glad not to be on deck.

– Sam Kelly & Amy Waterhouse, Falkor

The Tasman Tidal Dissipation Experiment // Supported by the National Science Foundation

Falkor: Engineering a Career in Ocean Science

As you may have noticed, there is a lot of high-tech experimental equipment and instruments on an oceanographic research cruise.  We are in an era of ocean exploration that sometimes rivals the technologies used in space exploration.  While research scientists may be involved in the design or concept of research equipment, the majority of this design work, along with the development, construction, assembly, and testing of the equipment, is done by ocean engineers, specifically folks known as development engineers.

A critical role

Development engineers are a critical element for oceanography cruises.  When an investigator has a question they want to ask, or some parameter they want to measure, that requires special equipment, they engage the help of a development engineer.  Unlike other engineering professions that tend to specialize, development engineers will often be involved in all aspects of creating a piece of equipment, which may include skills in mechanical, electrical, and program engineering.  Once the equipment is tested and ready for work, the development engineer still plays a key role – they accompany the researchers on the cruise to ensure things are set up properly, work as they should, and troubleshoot when they don’t.  So the job offers opportunities for both lab and field work – a bonus for people who love variety in their career.

Spencer tagline

Spencer Kawamoto mans one of the tag lines during a CTD/LADCP deployment.  SOI/Judy Lemus
Amy and Spencer testing LADCP

Amy and Spencer make sure the LADCP and computer are able to communicate with one another. SOI/Judy Lemus

Spencer Kawamoto is the development engineer on board Falkor for the T-Beam cruise.  He trained as an electrical engineer at UCSD after taking courses at a community college in Saratoga, CA.  Although he was already thinking about engineering (his dad is also an engineer), an early job placement course at West Valley CC confirmed his aptitude for the field and he set off on his path. “I always liked putting things together”.  As a development engineer, he has a lot of flexibility to explore many aspects of his discipline and teach himself new skills.

Multi-talented

Spencer got his start at Scripps Institution of Oceanography through an internship while he was still an undergraduate.  His specialty at that time was programming and he developed software that helped translate “machine language” (binary code) into scientific language (actual scientific units of measurement).  From there he was offered other jobs and then a permanent position at Scripps.  He’s worked on systems for a variety of projects, mostly related to climate, but ranging from low cost weather stations deployed in Yosemite, CA to moorings that measure mixing between the Pacific and Indian Oceans.

Installing LADCP

Amy and Randall help Spencer reinstall the LADCPs onto the rosette (note the custom brackets) after changing the internal batteries. SOI/Judy Lemus

 Spencer using the ADCP brackets for an alternative purpose – to build up his guns. SOI/Judy Lemus
Spencer’s specific role on the T-Beam cruise involves the LADCPs that have been providing all the data on the internal tide current velocities.  As we’ve mentioned, the CTD rosette has two of these instruments, one pointing up and one pointing down.  The challenge was that the ADCPs were coming from Scripps, and the CTD rosette lives on Falkor.  Each CTD rosette is slightly different so there is no “one size fits all” solution for attaching the instruments to the rosette.  So Spencer designed the brackets that would hold the LADCPs on the metal frame of the rosette.  These have to be strong enough to hold the instruments in place AND withstand possible high wave action, bumping and jostling, AND also be as light as possible.  Lucky for the T-Beam team, Spencer is very good at his job and the brackets have worked exactly as they should!

Engineers often get right into the science duties – in this case helping to recover the CTD (note the angle of the ship deck to the ocean!).  SOI/Judy Lemus

– Judy Lemus, Falkor

The Tasman Tidal Dissipation Experiment//Supported by the National Science Foundation

Falkor: It’s getting hot in here, let’s mix it up!

Last week, the great dark turquoise waves rolling past the ship in the dark looked impressive, at 15 feet tall or more, but they are nothing compared to their giant cousins below. As you know, the internal tide we are chasing across the surging Tasman Sea is hundreds of feet tall, heaving water deep below the ocean’s surface up and down by over 100 feet every twelve hours.

Waves from outer space

These waves may not be visible to us, standing on the deck of Falkor, but that doesn’t mean we don’t know roughly where they are. Satellite altimeters floating in the blackness of space have been measuring the height of the sea surface for the past 25 years. They can track the motion of the ocean caused by the tide and by the internal tidal beam that we are hunting; the surface of the ocean moves up and down by only a few inches, but that’s enough for a satellite!

In fact, satellite altimeters can even measure the gradual sea-level rise caused by global warming, currently estimated to be about 3 millimeters per year, about the height of two stacked pennies. This may not sound like much, but some small island nations may already be suffering from the effects of rising ocean levels, including some of the South Pacific islands near Australia. So what causes sea-level rise, and what does any of this have to do with T-TIDE?

Sunset

Surface waves roll past the Falkor at sunset, giving little clue to the 100 meter high wave below. SOI/Judy Lemus
Ryan XBT

Ryan McDougall-Fisher launches an XBT off the aft-deck of the Falkor. SOI/Luc Rainville

Expanding ocean

Let’s start with some simple physics, because hey, I love simple physics! If you want sea levels to rise, you need more ocean, which means you need a bigger volume of ocean water. There are two ways to increase volume – increase mass or lower density – and each one contributes about half of the total observed sea-level rise.

The first thing you can do to raise sea levels, if you are really keen on having a lovely ocean beach near your house in central Oregon, is to melt some ice to increase the total mass of water in the ocean. Sea-ice won’t work, because it’s already floating, but the Antarctic and Greenland ice sheets are perfect. Greenland alone has been losing hundreds of cubic kilometers of melt water – that’s like 100 times the amount of water in Lake Washington – each year!

The second way to increase sea levels, and turn Seattle into an expensive island chain, is to add a lot of heat to the ocean. Warm salt water is less dense than cold salt water, which means it expands and takes up more volume. This is called thermal expansion. Thermal expansion doesn’t happen equally everywhere in the ocean, because heat isn’t added evenly everywhere.

Satellite altimetry

Satellite altimetry map of the sea surface height associated with the internal tidal beam in the Tasman Sea. Zhongxiang Zhao, University of Washington, Applied Physics Lab.

All mixed up

And that is where T-TIDE comes in! As we’ve mentioned here before, one reason we are studying the internal tide is to better understand how internal waves cause mixing, so we can improve how that mixing is integrated into climate models. This is all mixed up (heh) with sea-level rise and thermal expansion because mixing is really good at moving heat through the ocean.

Heating the ocean is not as simple as warmer oceans = nicer swimming (although being from Seattle, I wish it worked like that). Ocean locations with more heat being added to the surface (like the sunny tropics where I secretly suspect the Revelle has been hanging out based on their photos) will experience more sea-level rise unless that heat is mixed or transported elsewhere. And while heat carried down into the deeper ocean may seem good in the short run, it also means that ocean water near the surface absorbs even more heat, resulting in higher seas in the long run.

Meltwater flows off the Greenland ice sheet, Credit: Roger J. Braithwaite, The University of Manchester, UK. Image Source: NASA.

The good news is that every day we learn more about the oceans and the Earth’s complicated climate, we get better at predicting what will happen in the future. That means we can plan for and adapt to a changing planet. So hopefully no one will have to be up to their ankles ocean waves unless they really want to be!

– Hayley Dosser, Falkor

The Tasman Tidal Dissipation Experiment//Supported by the National Science Foundation

Falkor: A Steep Slope

The continental shelf of Tasmania is pretty steep.  If you were on the bottom of the Tasman Sea, it would be like driving in a car across a desert and running into a mountain 4,000 meters high (13,000 feet).  The grade up this mountain road would be about 8%, the steepest of any interstate in the U.S. The mountains that generate the T-Tide over on the New Zealand side of the basin (called the Macquarie Ridge) are also steep, also about 4,000 meters high from the sea floor.  Scientists have observed that steep slopes generate larger internal tides with higher velocities than more gradual slopes.  Much like a larger stone (i.e., a bigger disturbance) generates larger ripples. So the 100 meter tall internal wave generated at Macquarie Ridge moves across the Tasman basin at a fairly fast velocity, as far as internal waves go, about 1.5 m/s (3.4 miles/hour).

It’s complicated

Scientists like Sam Kelly have studied and modeled internal tides and waves for several years.  Because internal tides are very regular and their locations are pretty well known from satellite data, scientists can use mathematical models to predict how a particular internal tide behaves once it is generated.  Waves of any kind will always follow well-understood principles of physical laws.  That’s the simple part.  The more difficult piece is that these waves will interact with all kinds of structures and processes in their path, some known but many unknown.  And that complicates things considerably. We’ve already mentioned how eddies might interact with the propagation of the T-Tide beam.  Other elements include seamounts, seasonal density differences in the water, and even interaction with other internal waves, such as the remnants of the T-Beam itself after it hits Tasmania.

Sam with tunicate

Sam Kelly with a pelagic tunicate (sea squirt) that got caught up on the small CTD rig one evening. SOI/Randall Lee
Model of reflectivity

Map figure showing modeled reflectivity of the T-Beam off the Tasman slope. The lines indicate different cross-sections of the continental slopes that were tested with the model. The color indicates the fraction of incoming energy that bounces off the slope without dissipating. The depth contours are every 1000 m. The black arrow indicates the angle of the incoming T-Beam.  Sam Kelly

Current models predict that even though the T-Beam may be partially refracted and dissipated by various processes, the majority of the wave’s energy still propagates all the way across the Tasman Sea to Tasmania.  So the question becomes, “What happens to it next?”.  There are two possibilities: 1) the wave is completely dissipated on the Shelf, much like a surface wave crashing on a beach; or 2) the wave is reflected off the Tasman Shelf, either at a different angle with somewhat less energy, or back into the pathway of the incoming internal wave.  In fact, both of these processes may occur for any given wave.

Seeing the reflection

Sam Kelly believes there is good evidence that reflection may be particularly prominent for the T-Beam. In the southern region of Tasmania around Hobart, the continental shelf is especially steep.  Remember that steep slopes can generate very high internal tides  – which means that they can also create high reflection of an internal tide as the wave bounces off the vertical face.  Data from underwater gliders (a type of autonomous vehicle) – built by Shaun Johnston at Scripps (and another T-Tide investigator) – collected over several months also indicate there is a lot of reflection of the internal tide around southern Tasmania.  That is, the wave patterns are similar to those created under controlled conditions when a primary wave is reflected off a vertical wall.  Further north, the picture changes and it appears that there may be more scattering of the wave, changing it from a wave with large energy and large wavelength (a “low mode” wave), to one with less energy and smaller wavelength (a higher mode), which then dissipates more quickly.

New locations

Google Earth image showing the cruise track of Falkor, as well as the previous transect line C1-C2 and location of new transect at which CTD/LADCP profiles will be conducted at sites F6 and F5.  Luc Rainville and Amy Waterhouse

After dodging some crummy weather over past two days (again), the data that we collect at our next site along the beam will hopefully give Sam and the rest of the T-Team a better picture of how strong the beam is closer to the Macquarie Ridge.  Then they can estimate any energy lost in the beam over the 100km distance between these two transects. Knowing that will get them one step closer to understanding the total energy budget (energy coming from the ridge + energy dissipated by eddies + energy coming back from Tasmania) of the T-Beam, and one step closer to understanding the role of internal tides in contributing to Earth’s climate.

Doing science is always a team effort.  Team Falkor gets it done. SOI/Judy Lemus

– Judy Lemus, Falkor

The Tasman Tidal Dissipation Experiment//Supported by the National Science Foundation

Falkor: Beginning a Research Career

For new comers to science, it is important that they begin their journey in some particular way. Some may embark on land based science or even pure laboratory work. I have started with something way out of my comfort zone… a research cruise. If you had of told me this time last year that I would be embarking on ship-based science I probably would have laughed and told you that would never happen. But here I am today, on Falkor doing science with Pete Strutton and the science crew from SCRIPPS and SOI.
I was very fortunate to be offered this opportunity by Pete, who at the time had been a supervisor for a mini research assignment in my undergrad unit looking at Marine ecology. He asked if I was graduating at the end of the year and whether an experience at sea is something that I would be interested in to gain some experience doing science in these crazy, unpredictable conditions.
CTD coming up

The CTD with water samples coming up after a 30 hour profile. SOI/Randall Lee

Ample downtime

So far my on-board experience has been wonderful and will certainly be an opportunity which I will never forget. I have met so many interesting people from both the science party and the ship crew. When science is on hold – whether it’s due to foul weather or waiting for the 30 hour CTD deployment – there is always someone around to have a chat, play a game, or watch the odd movie with. I have also learnt that it is possible to survive seasickness, even when it has set in for a few days.

My original expectations of ship-based research consisted of limited down time with insane sleep deprivation, yet the actual experience is totally different. I have been able to get enough sleep to function enough to perform accurate science and there has been a lot more down time than I had expected, which is most likely due to the horrible weather that we have had.

Sam with vegemite

Sam Kelly taking a break to talk science over a Vegemite sandwich. SOI/Danielle Mitchell
Krill

Krill caught in the screen Randall Lee is using to look for ocean plastics. SOI/Danielle Mitchell

Picking a research project

This trip has certainly been a learning experience, especially in terms of broadening my interest for investigating biological productivity. Biological productivity is the amount of biomass created in an ecosystem. It’s affected by both phytoplankton photosynthesis (primary productivity) and the zooplankton that feed on them (consumption). This is one aspect that I am hoping to conduct some research myself with a possible focus on zooplankton and their feeding rates over a day/night cycle. I have done some pilot studies looking at zooplankton feeding in the Spring time in Storm Bay, Tasmania and would really like to do a larger scale study in the same area to not only perfect my scientific skills but also broaden my knowledge on zooplankton and their influence on daily biological productivity. I have a strong interest in the lower levels of the food chain because without those tiny creatures many of the bigger charismatic creatures would not exist, and it is likely that humans would struggle to exist without these basis organisms. I think it’s important to study and understand these organisms so that we know their contribution to the ocean and their potential reactions to different climatic events as well as their response to human induced changes.

Pete analyzing chlorophyll fluorescence of phytoplankton in surface water.

Science and ship crew discussing options for deploying research equipment.

– Danielle Mitchell, Falkor

The Tasman Tidal Dissipation Experiment//Supported by the National Science Foundation

scripps oceanography uc san diego