Posts by Amber Stronk
Deep-Ocean Vertical Structure
It is often assumed that, at frequencies below inertial, the vertical structure of horizontal velocity and vertical displacement can be reasonably described by a single dynamical mode, e.g. the lowest order flat-bottom baroclinic mode. This is appealing because it would mean that first-order predictions of deep-ocean velocity structure could be determined from knowledge of density and surface currents. However, there is a relative paucity of full ocean depth data to test this idea. A study by Toole et al. (2023) used full ocean depth data from five sites – four of which are Ocean Observatories Initiative (OOI) arrays (Station Papa, Irminger Sea, Argentine Basin and Southern Ocean) – to address the question “does subinertial ocean variability have a dominant vertical structure?”
Data analysis was challenging, because it involved working with gappy records as well as combining information from multiple instruments on different moorings. As noted by the authors, “no single OOI mooring sampled velocity, temperature and salinity over full depth.” Wire-following profiler data from Hybrid Profiler Moorings were combined with ADCP and fixed-depth CTD data from adjacent moorings. While the authors note that “depth-time contour plots of the velocity data from each OOI site clearly reveal the shortcomings of the datasets” they also recognized that despite the shortcomings, “these observations constitute some of the only full-depth observations of horizontal velocity and vertical displacement from the open ocean.”
It was possible to obtain 2-3 years (non-contiguous in some cases) of near-full ocean depth data from each site. Inertial and tidal variability was removed, and the data were filtered over 100 hr (~4 days). Empirical Orthogonal Function (EOF) decomposition was used to identify an orthogonal basis set that described horizontal velocity and vertical displacement. In addition, dynamical modes were determined for three cases: flat bottom, sloping bottom and rough bottom. Note that computing the dynamical modes requires the vertical density profile, which was taken as the mean over each deployment. Analysis was focused on the lowest modes, which accounted for the majority of the variance.
The results (Figure 32) showed that there is an EOF consistent with a dynamical mode at most sites. However, the appropriate dynamical mode is different for each site – no single dynamical accounted for a dominant fraction of variability across all sites. The authors note that differences in bathymetry, stratification and local forcing complicate the picture, with different dynamical processes dominating at different sites. Prior studies (not full ocean depth) that appear to show a “universal” vertical structure may be misleading
This project shows the potential for OOI data, with appropriate processing and analysis, to provide unique insights into ocean structure and dynamics. The researchers have made the combined vertical profile data available to the community on the Woods Hole Open Access Server. The dataset DOI (https://doi.org/10.26025/1912/66426) is also linked here: https://oceanobservatories.org/community-data-tools/community-datasets/.
[caption id="attachment_34586" align="alignnone" width="624"] Mode 1 EOFs for velocity (u, red; v blue; cm/s) and vertical displacement (black, decameters) for OOI arrays at (from left) Argentine Basin, Southern Ocean, Station Papa and Irminger Sea. Adapted from Toole et al., 2023.[/caption]
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References:
Toole, J.M, R.C. Musgrave, E.C. Fine, J.M. Steinberg and R.A. Krishfield, 2023. On the Vertical Structure of Deep-Ocean Subinertial Variability, J. Phys. Oceanogr., 53(12), 2913-2932. DOI: 10.1175/JPO-D-23-0011.1.
Read MoreSubsurface Acoustic Ducts in the Northern California Current System
Xu et al.’s analysis of the hydrographic data recorded along the U.S. Pacific Northwest coastline leads to the identification of a secondary subsurface acoustic duct. A numerical simulation based on the sound-speed field determined from OOI Coastal Endurance and APL-UW glider CTD data suggests that the presence of the duct has major impact on sound propagation at a mid-range frequency of 3.5 kHz in the upper ocean (Figure 31). Specifically, the ducting effect is evident in the trapping of sound energy and the consequent reduction in transmission loss within the duct. Glider observations show that the duct is a large-scale phenomenon that extends hundreds of kilometers from the outer continental shelf to regions offshore of the continental slope. The axis of the duct shoals onshore from between 80 and 100 m depth offshore of the continental slope to less than 60 m over the shelf. Analysis of the sound-speed profiles determined from glider CTD data suggests that the prevalence of the duct decreases onshore, from over 40% in regions offshore of the continental slope to less than 5% over the shelf. In addition, analysis of the long-term time series of sound-speed profiles determined from the CTD data recorded over the shelf slope off the Washington Coast suggests that the duct is more prevalent in summer to fall than in winter to spring. Furthermore, examination of concurrent OOI Coastal Endurance Array (Washington Offshore Profiling Mooring) observations of sound speed and flow velocity indicates that the duct observed over the shelf slope is associated with a vertically sheared along-slope velocity profile, characterized by equatorward near-surface flow overlaying poleward subsurface flow.
[caption id="attachment_34581" align="alignnone" width="462"] (adapted from Fig. 3 of Xu et al., 2024) (a) The sound-speed field obtained from the CTD data recorded by an OOI-CEA coastal glider during 06-16 October 2018. The contour lines are potential density (in kg/m3). The magenta dots mark the locations of the local sound-speed minima along the axis of the subsurface duct. (b) The trajectory of the Seaglider. The red dot marks the location of the OOI-CEA Washington Offshore profiler mooring. The bathymetry contour lines mark seafloor depths in 100 m increments between 10 and 500 m and then in 500 m increments between 500 and 3000 m. (c) The vertical sound-speed profile at 20 km along-track distance. The local sound-speed minimum at the axis of the duct is labeled.[/caption]
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References:
Guangyu Xu, Ramsey R. Harcourt, Dajun Tang, Brian T. Hefner, Eric I. Thorsos, John B. Mickett; Subsurface acoustic ducts in the Northern California current system. J. Acoust. Soc. Am. 1 March 2024; 155 (3): 1881–1894. https://doi.org/10.1121/10.0024146
Read MoreAxial Seamount: The Phoenix Rises
Regional Cabled Array live data feeds from the bottom pressure tilt, seismic, and temperature-resistivity instruments are capturing a marked increase activity at Axial Seamount with total seafloor uplift approaching the threshold depth for the 2015 eruption. As noted by W. Chadwick (OSU), whose website provides daily forecasts, the average differential inflation rate has almost doubled in the last six months. Bottom pressure tilt data at the Central and Eastern Caldera sites, show a marked increase in uplift beginning in April increasing from ~ 6 cm/yr to ~10 cm/year. The increase in uplift rates is coincident with a dramatic increase in seismic activity [viewable on daily plots of earthquakes accessible on W. Wilcock’s Axial Earthquake Catalogue (UW)] with >1000 earthquakes in a 24 hr period also occurring in April: seismic activity remains, high, but has not reached the 1000’s per day as detected prior to the April 2015 eruption (Wilcock et al, 2016). The hydrothermal system in the International District Hydrothermal Field, located on the eastern rift zone within Axial Caldera, is also responding to this increased activity. Fluid temperatures measured by the temperature-resistivity sensor in a parasitic orifice on the side of the hydrothermal vent Escargot show an increase in the past 6 months, with a marked change in the past 3 months (Courtesy of W. Ruef, UW). Excitement is building as we watch this dynamic volcano respond to melt migration 2 km below the seafloor – January 2025 is not far away.
[caption id="attachment_34576" align="alignnone" width="597"] RCA bottom pressure tilt data Central Caldera Axial Seamount[/caption]
Read More Off We Go – Will Axial Seamount Surprise Us?
– Deborah Kelley, School of Oceanography Director at UW & Principal Investigator, OOI
The UW Regional Cabled Array team from the School of Oceanography and the Applied Physics Laboratory will once again have an exciting summer in the NE Pacific maintaining the National Science Foundations’ Regional Cabled Array (RCA) underwater observatory. This summer’s 37-day expedition (August 6-September 11) is especially exciting because we will be spending significant time directly viewing the highly active submarine volcano off our coast ‘Axial Seamount’, which erupted in 2015 and is poised to erupt anytime between now and sometime in 2025 (see Dr. Bill Chadwick’s blog).
The volcano, >300 miles offshore Oregon and Washington and nearly 1 mile beneath the ocean’s surface, has woken up over the past three months. Over 1000 earthquakes occurred in a single day in April and this week daily numbers are spiking at several hundred events each day (e.g >600 July 23)(see Dr. William Wilcock’s earthquake catalogue). Over this same period, the summit of the volcano began inflating at a more rapid rate as melt migrates into the shallow magma reservoir beneath the volcano. The summit of the volcano has already reached the depth it was at when it erupted in 1998 and 2011 and is approaching that of the 2015 eruption. That eruption resulted in a >400 ft thick lava flow (equivalent to ~ 2/3 up the height of Seattle’s Space Needle) and detection of over 30,000 explosions as the lava issued onto the seafloor. Temperatures in the underwater hot springs we will be visiting during the cruise are also rising — all pointing towards an immanent eruption.
The cruise will use the remotely operated vehicle (ROV) Jason and the global class research ship the R/V Atlantis operated by Woods Hole Oceanographic Institution. Excitement is building as our equipment is fully tested, safely packed away, and next week on its way via numerous 48 ft-long trucks to Newport, Oregon where we will begin mobilizing the ship starting August 6th. We are very much looking forward to working with 26 US and international students who are joining us on the expedition, working side-by-side scientists, engineers, and the ship and ROV teams.
This cruise is highly complex including berthing for 72 RCA folks during the three Legs of the cruise. A diverse array of >100 instruments, seafloor substations (junction boxes), and instrumented pods on the Shallow Profiler Moorings will be recovered and reinstalled, and tested. The cruise will also include turning instrumented vehicles on Deep Profiler Moorings. The vehicles make daily trips spanning up to ~18,000 ft as they traverse from the near seafloor environment to ~ 300 ft beneath the ocean’s surface.
The ship will be “packed to the gills” on each of the three legs that make up this expedition, carrying everything from state-of-the-art mooring components to sharpies. In addition to the core Ocean Observatories Initiative (OOI) work, seven days of the cruise will be dedicated to special programs funded by NSF to research scientists that involve turning of specialized instruments on the cable, recovery instruments and sampling of methane seeps at Southern Hydrate Ridge, and sampling of hydrothermal fluids for shore-based investigation of microbes and viruses in the extreme environments at Axial Seamount.
You will be able to watch our underwater operations live through streaming video as the ROV Jason works 1) 5000 ft down at the summit of Axial Seamount where we will see astounding seascapes of lava and numerous deep-sea active hot spring deposits that are home to some of the most bizarre creatures on Earth; 2) offshore Newport, Oregon to depths of ~250 ft to 10,000 ft in some of the most biologically productive waters in the oceans; and 3) sedimented sites on the Cascadia margin where methane-rich plumes jet from the seafloor. Here, methane seeps support dense bacterial mats and giant clams that thrive in the absence of sunlight on gases migrating through the seafloor.
An enhanced, high-bandwidth satellite connection from the R/V Atlantis will allow you to experience in real-time our deep-sea operations through live video streams to shore and onto this website.
The satellite feeds will allow scientists onboard to see data as new instruments are connected to the seafloor submarine fiber optic cables that bring the Internet into the ocean. During the cruise, engineers from the Applied Physics Lab will utilize the RCA operations center in the School of Oceanography where they will communicate directly with the instruments as they are installed, turn power on and off, and command and control instruments from hundreds of miles away and far offshore (including a resident cabled high definition camera that streams video live of an underwater hot spring at the summit of from Axial Seamount throughout the year). All total, the system hosts 150 instruments that stream data at the speed of light in real-time to shore 24/7, where they are stored and visualized through the OOI Cyberinfrastructure system at Oregon State University.
As always, it will be great to be away from the dock, smell the salt air again, and work beneath the waves on some of the most advanced technology in the oceans. For many students, these expeditions have changed their lives.
Read MoreAwash with Data
Forty-seven professors from 13 states attended the Data Labs 2024 workshop in Wilmington to enhance their teaching by integrating raw oceanographic data from the NSF Ocean Observatories Initiative (OOI) into their curriculum.
Read MorePOGO Fellow Aditi Sharma Returns from Sea and Reflects on 17-Day Expedition
Partnership for Observation of the Global Ocean (POGO) Fellow Aditi Sharma has returned from a 17-day expedition aboard the R/V Sikuliaq to recover and deploy OOI’s Global Station Papa in the Gulf of Alaska. A PhD candidate at the National Institute of Oceanography India, Aditi was chosen from over 80 applicants for a shipboard training fellowship sponsored by POGO, WHOI, OOI, and the Nippon Foundation.
Back on land, Aditi is reflecting on her time at sea and her goals for the future.
How did you benefit from the training?
The training has been immensely beneficial as it provided me with a chance to engage in work and learn from the experts in the field. The hands-on operations of winch, deployment procedures, data downloading, and calibration techniques have given me confidence in practical skills essential for the fieldwork. These experiences are particularly relevant as I now intend to apply them to my current project at my parent institute, which involves monitoring diverse environmental variables in the coastal Bay of Bengal using advanced meteorological sensors on a fixed mooring buoy. This training has helped in enhancing my capability to contribute meaningful insights to the project. In addition to the scientific aspects, the training has provided me with an understanding of the operational challenges during expeditions. It has highlighted the need for improvisation in adverse weather conditions and emphasized collaborative work approaches. Additionally, it has instilled in me a strong sense of time management that I aim to apply both in my career and in my personal life.
What are your future aspirations?
I am currently working towards my PhD at the National Institute of Oceanography. Upon completing my PhD, I aim to pursue postdoctoral studies and collaborate with fellow scientists in my specialized field. This journey represents a vast ocean of knowledge that I am eager to explore, with a strong desire to effectively share and discuss my insights with peers.
[caption id="attachment_34524" align="alignnone" width="640"]
Aditi Sharma aboard R/V Sikuliaq[/caption]
Read More Opportunity to Add New Sensors/Equipment to Pioneer MAB Array
The U.S National Science Foundation (NSF) Ocean Observatories Initiative (OOI) is excited to report that the relocation of the Pioneer Array to the Mid-Atlantic Bight (MAB) is now complete and the OOI facility is again considering requests by Principal Investigators to add new sensors and/or equipment to the Pioneer MAB Array. The process for requesting additions to the Array is described here.
The MAB deployment is the culmination of a three-year, multi-tiered process to relocate the Pioneer Array from its former location off the New England Shelf to the MAB. The NSF and the OOI Facilities Board (OOIFB) hosted a series of workshops in 2021 to elicit community input on where a relocated Pioneer Array might best meet science and educational needs. Based on input from these community workshops, the NSF gave its approval to the MAB site and the process was launched. Data from most instruments is available in real-time from the OOI Data Explorer. All non-telemetered data will be available after instruments are recovered on Array maintenance cruises that occur at nominal six-month intervals (April, October).
“Completing installation of the Pioneer Array in the MAB was the culmination of a significant effort by the OOI Team,” said Al Plueddemann, who served as the Chief Scientist for the first deployment of the array in the MAB and is Principal Investigator for OOI’s Coastal and Global Scale Nodes. “The time is right for researchers to propose additional sensors or equipment be added to the array so its full data collection potential can be realized.”
Notes:
- The installation of some sensors, especially acoustic sensors, may be subject to compliance with NSF’s Memorandum of Understanding with the US Navy.
- While the requests must be made for any additions to the Array, OOI would appreciate notification on plans to deploy stand-alone instrumentation within the OOI footprint.
Pioneer MAB Layout[/caption]
Read More Graduate Students Apply Now for Endurance Fall Shipboard Experience
Upcoming cruise volunteer opportunity on NSF Ocean Observatories Initiative Coastal Endurance Array Expedition
When: Leave Newport, Oregon on October 4, 2024; return to Newport on October 20, 2024
Applications Due: August 30, 2024
There is an opening for a student volunteer in the Fall 2024 as part of the U. S. National Science Foundation Ocean Observatories Initiative (OOI) Coastal Endurance Array on R/V Sikuliaq. The Coastal Endurance Array team will deploy and recover oceanographic moorings, profilers and gliders off Washington and Oregon. Seven surface moorings will be deployed and recovered along with up to four profilers and six gliders. The team will also conduct CTD (Conductivity, Temperature, and Depth) casts, with bottle sampling, and collect underway ship data for comparison to data from deployed equipment.
The selected volunteer will have the opportunity to assist in the deployment and recoveries of moorings and water sample processing. They will also have opportunities to work directly with OOI data. The cruise will consist of two legs, each lasting about 8 days. Interested applicants can apply to participate on either or both legs. Domestic (within the USA) travel reimbursement is possible.
The primary goal of this program is to provide graduate students currently completing (or who have recently completed) a degree in a field of oceanographic research with the opportunity to participate in a research cruise. The participant will be a member of the scientific party and be involved in data collection and all other activities at sea. It is envisioned that the individual will be familiar with the science to be conducted at sea, and thus, form new collaborations and potentially develop new research directions. To be eligible to participate, the individual must either currently be studying at a U.S.-based institution or be a recent graduate, and have either a U.S. Passport or an applicable U.S. Visa.
Questions and application materials should be sent to Edward.Dever@oregonstate.edu. Application materials are:
- a CV or resume
- a one page letter of interest describing how this opportunity fits their professional and/or research interests
- contact information for two references.
For a first-hand view of what to expect at sea, check out this video.
[media-caption path="https://oceanobservatories.org/wp-content/uploads/2024/06/Sikuliaq-1.jpeg" link="#"]R/V Sikuliaq, University of Alaska Fairbanks.[/media-caption] Read More