Last week, the very first Gordon conference on ocean mixing took place in Andover, NH. 167 participants from all over the world learned about the state of the art of our field and its impact on other fields. It was enlightening, inspiring and a lot of fun!
We are currently looking for a postdoc to work with us on the Samoan Passage project. Research tasks include analysis of a dense 3D dataset of moorings and tows resolving hydraulically controlled flows, breaking internal waves, turbulent mixing and other processes in the Samoan Passage, a constriction in the abyssal Pacific Ocean. In addition, we have results from a very high resolution numerical model of the region at hand to help with the analysis.
For most of us in our daily lives we think of our world in three dimensions. We need to get up out of bed, across the floor, and through the door to the kitchen to make the coffee. But when it comes to observing the physical nature of planet earth what is happening at a given location in three-dimensional space is only half of the story.
As part of their training one of the fundamental skills an oceanographer learns is to think beyond three dimensions, to include time and the change at a given location over time in their scientific perspective. It’s not enough to go somewhere and have a look just once. Without gathering data and building computer models in this fourth dimension we wouldn’t know that the sea-ice at the very spot in the ocean we are floating on at the moment has changed rapidly over the past twenty years.
So scientists talk about things they are observing in terms of space and time, scales of ocean measurement that fundamentally define how rich or spare their digital libraries of data become. And how well sea-going oceanographers can see things over these scales are ultimately dependent on the scientific gadgets in their tool box and which ones they choose to put into water.
The research vessel Sikuliaq is a capable moving platform for our suite of custom ocean tools and her role is to take this technology all across the Beaufort Sea where it can best be put to use. But a ship can’t be everywhere in the Arctic at the same time and so there are gaps, blind spots, but we can help fill those by deploying what ocean researchers call a mooring.
A mooring is a towering string of scientific instruments thousands of metres tall supported by giant floats at the top and held to the seabed by a beefy weight. And on this mooring, this undersea science station, we put robots.
Deploying an ocean mooring in over 3000 meters of water is no mean feat, it is one of the bread and butter professional competencies that a group like the ArcticMix team must have and work relentlessly to maintain. A highly technical and often hazardous operation that can take many hours on the back deck of a ship like the Sikuliaq, mooring deployments are often exposed to whatever weather and waves the sea decides is right for the occasion.
This voyage the weather and seas were mostly kind and the ArcticMix mooring was happily fastened to the mud on the bottom of the Beaufort, its top float suspended in the ocean currents a bit like a giant balloon on a string swaying in a watery breeze.
Attached to this mooring are unique, recently developed ocean instruments called McLane profilers (MP’s). MP’s are “wire-crawlers”, programable robots that descend and climb the mooring wire over and over and over again, one million metres worth of travel in their large internal lithium battery packs.
These profilers come jammed with an array of instruments that measure pressure, temperature, salinity, and most importantly current velocity across a longer vertical reach than any other tool in our oceanographic toolbox. The following figure, calculated from MP data collected in the South China Sea in 2007, shows the kind of ocean current information that can be measured as time passes. Scientists call it a “time series”.
While the ArcticMix team aboard Sikuliaq spends the coming month exploring elsewhere, our mooring, fixed in one location, can observe ocean parameters over a long period giving us a base of consistent information to anchor the wider story of Arctic change.
[ by: Thomas Moore, for the ArcticMix team ]
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
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.
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.
[ by: Thomas Moore, for the TTIDE team ]
* “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.