Category Archives: Blog – news

CERMIT the tripod returns!

This May, the UW Sediment Dynamics Lab deployed a benthic tripod in the head of Astoria Canyon to measure canyon hydrodynamics and sediment flux. Over the summer, our tripod recorded minute-by-minute data, documenting the forces that move sediment through Astoria Canyon and into the deep water sediment record. This fall, it was time to recover our tripod from the seafloor. Andrea and Evan boarded the RV Rachel Carson, steamed out to the deployment site, and sent our tripod a signal to release its recovery float… After sleepless nights worrying about bottom-trawl fishing nets hauling away our tripod, we were relieved to discover it was intact and upright, just where we left it. Recovery went smoothly in low seas, and within the hour, our tripod was on deck. We spent a few hours cleaning sandy mud off its feet, scrubbing “biology” off of its sensors, and downloaded data from its instruments.

CERMIT the tripod, above water for the first time in four months.

This little crab was recovered with our tripod.

Although the tripod was safely on deck, our jobs were far from over–we had also set out to collect seismic profiles and sediment cores from the canyon! The USGS accompanied us aboard the RV Carson, and in collaboration with this project, they created a survey plan to map the geologic structure of Astoria canyon with seismic gear (CHIRP and multichannel). Together, the crew logged ten days of 24-hour seismic data collection, and through all that surveying, we managed to have some fun. We caught salmon and tuna, saw dozens of humpback and pilot whales, and had heated discussions over the best practices in coffee brewing. After returning to port, the USGS crew returned to Santa Cruz, reinforcements from UW’s Sed Lab arrived, and we boarded the vessel yet again for two final days of coring. Over this two day effort, the sediment lab collected 25 box cores in and around the canyon head and shelf rim, coring efficiently in spite of large swell and mechanical difficulties. 

USGS scientists deploy the CHIRP seismic package behind the boat, where it will be towed for the next week. This unit contains both the seismic source and receiver.

Aaron takes in the sunrise while steaming out to the first coring station of the cruise.

All told, three datasets were successfully collected from Astoria Canyon, and this is a big step forward in understanding what phenomena drive sediment from the continental shelf to the deep ocean. We’re excited to begin sharing results!

Aaron enjoying the little things on the ride home.

CERMIT the tripod has landed!

The sediment dynamics group has been thinking deep thoughts lately–170 meters deep, to be exact. This winter, the lab outfitted a new benthic tripod frame with instruments to quantify sediment transport in Astoria Canyon, the submarine counterpart to the Columbia River. Fast forward to this May, the lab hitched a ride on the RV Oceanus for a week and set our tripod in the head of the Canyon to record a summer of canyon events and processes. While the Oceanus pitched and rolled a few extra degrees with its heavy lift crane atop the second story, the ship and its crew were wonderful help in nestling our tripod safely into the narrow canyon head.

Both amphibious and gangly, we believe the acronym CERMIT will stick (Canyon Edge ReMote In-situ Tripod), though fans should feel free to write in with their suggestions. CERMIT is outfitted with a long list of additional acronyms: multiple ADCPs, OBSs, CTDs, an ABS, a LISST, and more. These instruments will tell us precisely where and how fast the water is moving, and the concentration of sediment along for the ride. This summer, with a bit of luck, we will catch a few of the sediment-gravity flows that travel through Astoria Canyon, and determine what caused them: earthquakes, dredging for fish, or the (less-and-less) mighty Columbia may be the culprits. This information, in turn, helps our lab and other geologists interpret sedimentary deposits nearby and across the globe.

Stay tuned for its recovery and results this September!

UW vans arrive at the Oceanus carrying the tripod (deconstructed for travel). After this photo was taken, we got to work assembling it in the sunshine!

After construction on the dock, a crane brings the tripod aboard the Oceanus.

On the morning of deployment, the tripod is moved under the A-frame for lowering.

The tripod sneaks overboard, with everyone thankful for small swell.

Goodbye for now, CERMIT!

Recent field work in Myanmar

The lab just finished a short, two-week trip to Myanmar. The primary goal of this trip was to discuss research with our Burmese colleagues. We participated in a conference at Yangon University, where we also heard presentations from American colleagues who have been working in the Gulf of Martaban.

Aaron preparing to discuss results with collaborators from VIMS and Yangon University

Next we presented our results at Pathein University, where we also led a data processing workshop and a short research trip on the Pathein River.

Filtering water samples doesn’t have to be boring!

We also managed to fit in two days of field work on the Yangon River with Myanmar Maritime University. During the winter period of dry weather, the river discharge decreases, and the amount of sediment in the water increases. During our previous trip, in March 2018, we measured as much as 15 grams of sediment per liter and our acoustic instruments didn’t work! This time, we came prepared for very high sediment concentrations. We were able to track the high concentrations during a full tidal cycle and also measure the river discharge. It’s very exciting to see such an extreme riverine environment!

Large vessels using the Yangon River. This one parked in the middle of our sampling location.

Improvised raft for measuring water flow.

Our Yangon River crew

Ocean Networks Canada Workshop: Seafloor collapse and submarine canyons

This month Ocean Networks Canada held a workshop in Victoria, BC focused on the “seabed and sediment in motion” at their observatory sites. They have cabled instruments on the seafloor that continually send data back to shore. The workshop focused on studies at two contrasting focus sites, one on the Fraser River delta, and the other in Barkley Canyon on the continental margin. Submarine canyons are dramatic features of continental margins throughout the world. They can be many kilometers deep and cut far into the shelf, like a Grand Canyon deep underwater. These canyons are hotspots of biological activity as well as conduits for sediment, nutrients, chemicals, and trash. Andrea Ogston attended the workshop to present collaborative research from Barkley Canyon and hear results from colleagues.

Map of a few of the instrumented ONC observatory sites in Barkley Canyon. Our margin off the west coast of the US/Canada is incised by numerous submarine canyons.

On the Fraser Delta, frequent mass failures of the seafloor and energetic gravity flows pose potential problems for the coastal port structures.  Dr. Gwyn Lintern, PGC, showed a dramatic data set from sensors that tumbled in a bottom flow recording velocities of 6-8 m/s, and eventually disconnected and disappeared!  In contrast, Barkley Canyon located off the coast of Vancouver Island has a very limited source of sediment at present, and dynamics are not as dramatic. However, Andrea Ogston showed two modes of particulate transport at ~1000 m water depth within the canyon axis:  1) relatively dense fine particles move down the canyon, carried by residual currents, and are at times pumped back up-canyon by tides, and 2) loose, fluffy phytodetritus (chunks of tiny organisms) from the surface ocean are mixed down into the canyon and during winter downwelling periods can be rapidly transferred to the deep ocean.  This winter process has the potential of adding significantly to the biological pump (which transports carbon to the deep sea). If you’re interested in reading more, check out Thomsen et al., 2017.

After a presentation and discussion of what can be done with the existing data on the Oceans Network Canada observatories, the workshop turned to needs and wants that could enable the next steps in the scientific discovery using the observatory data streams.  New, updated sensors and a reconfiguration of Barkley Canyon’s sensor array will be upcoming and will allow the scientific community to further explore the importance of the wintertime delivery of carbon to the deep sea.  Stay tuned for more on this exciting discovery!

Victoria BC at night during the ONC Seabed and Sediment in Motion Workshop

Wave Supported Gravity Currents – Flume Experiment

Experiments have started in the newly modified and improved “fluid-mud tank” located in Harris Hydraulics Lab.  Collaboratively with colleagues in the Environmental Fluid Mechanics group in CEE, we are studying the role of sand on the capacity to develop wave-supported sediment gravity flows in continental-shelf environments.  New to this set of experiments are detailed bed characterization studies along with improved observations of suspended-sediment concentration very close to the sediment-water interface.  We are using our x-radiography equipment to resolve bed structure through the flume wall, and have developed the smallest (flume-sized) coring device known to sedimentology!  Stay tuned for results!

link to EFM group: http://depts.washington.edu/uwefm/wordpress/

Fluid-mud tank at the Harris Hydraulic Lab (credit: A. Fricke).

New Particle Size Analyzer

The Sediment Dynamics Group is getting an upgrade! Specifically, the lab has purchased an LS 13-320 Beckman-Coulter particle size analyzer through the Student Technology Fee Grant. The STF “provides for capital investments in technology and projects that improve students’ educational opportunities.

Quantifying grain size distributions is key to understanding the transport and deposition of sediment in rivers and oceans. This new instrument will supplement the current set of Sedigraph grain size analyzers.  The laser-based LS 13 320 can measure particles from 0.017 µm to 2000 µm and can measure particles in small volume or dilute samples. These capabilities open new possibilities for measuring suspended sediment particle sizes. Characterizing suspended sediment is central to understanding sediment transport.

The LS 13-320 will also be used by students in Marine Geology and Geophysics to measure microplastics in Puget Sound and by students in Biological Oceanography to count and size phytoplankton. The instrument is available for any undergraduate or graduate research project, including research outside the School of Oceanography. If you are interested in using this instrument please contact Hannah: hglover@uw.edu.

Congrats to Dr. Dan!

Congratulations to Dr. Dan Nowacki!  Dan turned in his dissertation, entitled “Sediment dynamics in tidal environments spanning a range of fluvial influence”, over the winter break.  His dissertation research covers a wide range of environments from the shallow tidal flats of Willapa Bay, to the intertidal channel environments along the tidal Amazon River, to the distributary channels of the Mekong tidal river and estuary.  The next step for Dan is a prestigious Mendenhall Postdoctoral Research Fellowship.  In March, he moves to Woods Hole, Massachusetts to join the USGS Coastal and Marine Science Center.  Congratulations, Dan, on a job well done!

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