Posts Tagged ‘Coastal and Global Scale Nodes Group’
Summer Science Tours: CGSN Engages Young Environmentalists
The U.S National Science Foundation (NSF) OOI Coastal and Global Scale Nodes (CGSN) Team at WHOI has had a busy summer of talks and tours. With the help of Mashpee Wampanoag WHOI Tribal Liaison and Native Land Conservancy (NLC) founding board officer, Leslie Jonas, CGSN hosted two notable sets of visitors in July and August 2024. The NLC is an Indigenous-led land conservation nonprofit based on Cape Cod that seeks to preserve land for future generations.
As a part of their Preserving Our Homelands (POH) summer science program, a group of students from the Mashpee Wampanoag tribe visited WHOI on 18 July. The POH program provides 6th, 7th, and 8th grade native students with hands-on science experiences in order to deepen their understanding of the environment from a western science perspective and its relationship to tribal culture, and traditional ecological knowledge. Their visit included a stop at the LOSOS facility, where CGSN team members talked about the scientific and technical aspects of the OOI program and provided an opportunity to see ocean observing technology up close. CGSN is grateful to WHOI engineer Ben Weiss and Sea Grant Marine Educator, Grace Simpkins, for organizing the visit and looks forward to ongoing interactions with the POH program.
Before the excitement from the POH tour had died down, a second group of visitors was hosted in early August. The group was made up of about 20 members of the Black, Indigenous, and People of Color (BIPOC) environmental science community. This included the NLC Executive Director, Diana Ruiz, and thirteen members of the Massachusetts Audubon Society and four NLC First Light Fellows. First Light is a paid summer fellowship program for rising Native American conservationists ages 18-25. With mentors from Mass Audubon, Fellows develop individual projects with topics in areas of ecological research, wetland restoration, water quality or land protection that build career skills and advance the NLC’s work. The fellowships combine indigenous culture, environmental sciences, and career development in order to open up career pathways. The four Indigenous Fellows who visited WHOI are studying at Brown, Yale, and Salish Kootenai College and got exposure to real-world instrumentation and engineering tools used to address pressing questions in ocean science research.
Read more about the NLC Fellows.
[caption id="attachment_34683" align="alignnone" width="640"]![](https://oceanobservatories.org/wp-content/uploads/2024/08/CSGN-1-640x311.jpg)
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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/.
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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 MoreWave Statistics from 3-Axis Motion Sensors on OOI Surface Buoys
The Ocean Observatories Initiative (OOI) Pioneer Array at the New England Shelf (Pioneer-NES) collected data for nine years from November 2013 through November 2022 across the shelf break. Of the three Surface Moorings in the array (Inshore – ISSM (40.37°N, 70.88°W); Central – CNSM (40.14°N, 70.77°W); Offshore – OSSM (39.94°N, 70.89°W), only CNSM was equipped with a surface wave sensor: the Axys Technologies Tri-Axys Directional Wave Sensor (WAVSS). This meant that observations on wave data were limited to a single location within the array. Recognizing that data from a single location could be restrictive for some types of analysis, the Coastal and Global Scale Nodes Group (CGSN) identified an opportunity to increase the number of surface wave observations and extend their geographic extent to the full cross-shelf span of the Pioneer-NES Moored Array. This was accomplished by using the engineering data collected by the MicroStrain 3-axis motion sensors (MOPAK) deployed on all three surface moorings. The data collected by the MOPAKs can be used to compute the bulk and directional wave statistics at each Surface Mooring in the array.
The MOPAK sensors collected triaxial acceleration, angular rate, and magnetic orientation for 20-minutes at 10 Hz once-an-hour. These data are used to compute the buoy displacements and velocities. A zero-crossing algorithm, which identifies the number of times the buoy vertical displacement (heave) crosses zero (indicative of wave motion), is used to calculate six bulk wave statistics: significant wave height (Hsig) and period (Tsig); wave height (H10) and period (T10) of the highest 10% of waves; and the mean wave height (Havg) and period (Tavg).
The wave power and cross-spectrums are used to compute five directional wave statistics: peak wave height (Hs) and period (Tp); mean wave direction and spread; and an alternative method for significant wave height (Hm0). The MOPAK-derived wave statistics were validated against, and showed excellent agreement with, both the WAVSS dataset from the CNSM mooring and wave datasets collected by National Data Buoy Center wave buoys 44097 (Block Island, RI – 40.97°N, 71.12°W) and 44008 (Nantucket, MA – 40.50°N, 69.25°W).
[media-caption path="https://oceanobservatories.org/wp-content/uploads/2023/10/Screenshot-2023-10-31-at-3.12.55-PM.png" link="#"]Figure 1. The significant wave height (Top) and mean wave period (Bottom) at the Pioneer-NES Central Surface Mooring for Deployment 11 (Apr. 2019 – Sept. 2019) as measured by the WAVSS (blue), calculated from the MOPAK (red), and from the two nearest located NDBC buoys – Nantucket (green) and Block Island (grey).[/media-caption]The Python code to process a MOPAK dataset into a wave dataset is available to users as the process_mopak.py module in the public OOI Data Exploration GitHub repository. The wrapper function calculate_wave_statistics in the module accepts a deployment’s worth of MOPAK data and returns a new dataset with the calculated wave statistics, including attributes, units, and associated metadata, which may be saved as a new netCDF file. This process triples the number of surface wave datasets at the Pioneer-NES Array, allows for validation of the existing WAVSS wave dataset, and opens new possibilities for studying the wind-wave field across the NES-break.
We encourage users to work with the MOPAK code to generate surface wave statistics, and to submit any questions to the OOI HelpDesk.
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