Ocean Observatory Initiative News Feed

News from Ocean Observatory Initiative

1. Salinification of the Cold Pool on the New England Shelf

   (Adapted from Taenzer et al., 2025) The continental shelf within the Mid-Atlantic Bight is cooled and mixed vertically in the winter. This relatively cold, fresh water is trapped below the seasonally-warming surface layer, retaining its properties as a subsurface “cold pool” throughout most of the spring and summer. The cold pool is important for regional ecosystems, serving as a cold-water habitat and a nutrient reservoir for the continental shelf. It is known that the cold pool warms and shrinks in volume as a result of advective fluxes and heat exchange with surrounding waters. A recent paper by Taenzer et al. (2025) shows for the first time that the cold pool is also subject to salt fluxes and increases significantly in salinity from April to October. The Pioneer New England Shelf (NES) inshore moorings (ISSM and PMUI) are positioned shoreward of the shelfbreak front and sample conditions on the outer continental shelf where the cold pool can be identified. The authors extracted data from these two moorings from a quality-controlled data set containing timeseries of hydrographic data (temperature, salinity and pressure) from all of the Pioneer NES moorings on a uniform space-time grid, covering the timeframe from January 2015 through May 2022 (Taenzer et al., 2023). The cold pool study used data from 2 m depth, 7 m depth, and 2 m above the bottom on ISSM and from roughly 28 m to 67 m depth on PMUI. Seven years of data from the Pioneer ISSM and PMUI moorings were used to create a composite annual cycle, which showed that subsurface salinity on the outer shelf consistently increases in the spring and summer. Evaluating the 67 m depth salinity record, and restricting the time period to when the moorings are in the cold pool, resulted in a salinification estimate of 0.18 PSU/month, or ~1 PSU over the six month period (Figure 34a). It was shown that this salinity change could not be explained by a seasonal change in the frontal position. Isolating the corresponding cold pool region within the New England Shelf and Slope (NESS) model (Chen and He, 2010), and computing a similar multi-year mean, showed a salinification trend nearly identical to that from the observations (Figure 34b). Using the model, it was possible to define a three-dimensional cold pool volume and estimate terms in the cold pool salinity budget. It was found that cross-frontal fluxes transport salt from offshore to the cold pool at a relatively steady rate throughout the year, and that along-shelf advection contributes little to the salinification process. It was argued that the cold pool exhibits two regimes that result in the seasonal salinification: During the winter, vertical mixing is strong, and the cold pool gets replenished with fresh water from the surface layer, which tends to balance the cross-shelf salt flux. During the spring and summer, surface stratification increases, vertical mixing is inhibited, the cold pool is effectively isolated from surface mixing, and the cross-shelf salt flux results in cold pool salinification. This project shows the importance of long-duration observations in key locations to isolate phenomena that would not be identifiable from a short-term process study. It is notable that the authors undertook a significant quality control effort and created a merged, depth-time gridded data set that was made publicly available. By combining the observations with a high-resolution regional model, the authors were able to examine the cold pool salinity budget and attribute the observed signals to ocean processes. [caption id="attachment_36391" align="alignnone" width="402"] Figure 34: The seven-year mean annual cycle of continental shelf cold pool salinity from a) Pioneer Array PMUI salinity at 67m depth, b) NESS model salinity for all waters below 10◦C along 70.875 W. The shaded envelope depicts one standard deviation of interannual variability. The salinification trend is from a linear fit during the stratified season (April-October). From Taenzer et al., 2025.[/caption] ___________________ References: Chen, K., & He, R. (2010). Numerical investigation of the Middle Atlantic Bight Shelfbreak Frontal circulation using a high-resolution ocean hindcast model. J. Physical Oceanog., 40 (5), 949 - 964. doi:10.1175/2009JPO4262.1 Taenzer, L.L., G.G. Gawarkiewicz and A.J. Plueddemann, (2023). Gridded hydrography and bulk air-sea interactions observed by the Ocean Observatory Initiative (OOI) Coastal Pioneer New England Shelf Mooring Array (2015-2022) [data set], Woods Hole Oceanographic Inst., Open Access server, https://doi.org/10.26025/1912/66379. Taenzer, L.L., K. Chen, A.J. Plueddemann and G.G. Gawarkiewicz, (2025). Seasonal salinification of the US Northeast Continental Shelf cold cool driven by imbalance between cross-shelf fluxes and vertical mixing. J. Geophys. Res., accepted.

2. Subsurface Temperature Anomalies off Central Oregon during 2014–2021

   Brandy T. Cervantes, Melanie R. Fewings, and Craig M. Risien Cervantes et al. (2024)  use water temperature observations from a stationary oceanographic platform located in 80 m water depth off Newport, Oregon to calculate variations from the long term mean temperature at the surface, near surface, and bottom from 1999 to 2021.  This site, known as NH-10, was occupied since 1999 successively by an Oregon State University National Oceanographic Partnership Program (OSU NOPP), GLOBEC Long Term Observation Program, Oregon Coastal Ocean Observing System (OrCOOS), NANOOS/CMOP.  Since 2015 it has been occupied by the NSF OOI Coastal Endurance Oregon Shelf mooring (CE02SHSM). The temperature observations from these different programs that have not previously been combined into one long time series. Of particular interest are the details of the marine heatwave (MHW) periods of 2014–2016 and 2019– 2020, which had widespread impacts on marine ecosystems. Strong deviations from the mean water temperature observed near the ocean bottom during late 2016 are the largest sustained warm anomalies in the time series. The 2019–2020 period shows warm anomalies in the summer and fall that are only observed near the surface. They also analyze the local winds during years with and without MHWs and find that spring/summer upwelling favorable, or northerly winds, which are important for bringing cold, nutrient rich water to the surface in coastal regions, interrupt MHW events and can lessen extreme heating during MHWs in coastal waters as illustrated in Figure 33. The three periods detailed in Figure 33 show warmer daily surface temperatures during the MHW years than the non‐MHW years and several days during 2014–2016 with surface and bottom anomalies greater than 4°C and during 2014–2016 and 2019–2020 with surface anomalies greater than 4°C (Figure 12a). During upwelling favorable winds (negative wind stress), the three periods follow similar patterns with colder surface temperatures typically associated with higher wind stress magnitudes. During downwelling‐favorable winds (positive wind stress), 2014–2016 is substantially warmer at the surface than the other periods at all wind stress values. [caption id="attachment_36388" align="alignnone" width="526"] Figure 33: 8‐Day low‐pass filtered surface temperature at NH‐10/CE02SHSM for (a) 1999–2000, (d) 2014–2015, and (g) 2019–2020; 8‐day low‐pass filtered along‐shelf surface velocity for (b) 1999–2000, (e) 2014–2015, and (h) 2019–2020; and NDBC 46050 wind stress vectors (thin light lines) and along‐shelf 8‐day wind stress (thick lines) (c) 1999–2000, (f) 2014–2015, and (i) 2019–2020. Events identified as surface marine heatwaves are shaded in gray. The thick black line in panels (a–b), (d–e), and (g–h) is the climatological mean computed over the full NH‐10 time series (Figure 33c), repeated twice, and the thin black lines are the 90th and tenth percentiles.[/caption] ___________________ References: Cervantes, B. T., Fewings, M. R., & Risien, C. M. (2024). Subsurface temperature anomalies off central Oregon during 2014–2021. Journal of Geophysical Research: Oceans, 129, e2023JC020565. https://doi.org/10.1029/2023JC020565

3. Soundscapes Spanning the Oregon Margin and 300 Miles Offshore

   [caption id="attachment_36382" align="alignnone" width="1430"] Figure 32: An example of a daily spectrogram generated by the RCA Data Team spectrogram viewer. A Humpback whale song is visible throughout the day at ~40-1000 Hz. A chorus of Fin Whale vocalizations is visible at 20-40 Hz. A weather event is visible at 0100, and a ship passage at 2200.[/caption] The Regional Cabled Array (RCA) operates six broadband hydrophones that continuously capture soundscapes across the Cascadia Margin (Oregon Shelf and Oregon Offshore - seafloor), near the toe of the margin (Slope Base -seafloor and 200 m water depth) and 300 miles offshore at Axial Seamount (Axial Base - seafloor and 200 m water depth). The hydrophones, operational since 2014, capture signals from 10-64,000 Hz, including vessel traffic, marine mammal vocalization, wind, surf, and seismic events. The RCA broadband acoustic archive currently contains forty years (350,000 hours) of acoustic data in miniSeed format. The RCA Data Team has developed a pipeline that can summarize and visualize a year of hydrophone data in 30 minutes. The spectrograms output (see Figure 32) by this pipeline are now easily accessible through an interactive viewer on the RCA’s Data Dashboard. The spectrogram viewer will make OOI-RCA broadband hydrophone data more searchable and accessible to data users and strengthen QA/QC of RCA acoustic data. Any day of hydrophone data, since 2014, will be viewable in minute/hybrid-millidecade resolution. The pipeline also enables users to convert RCA acoustic data to audio format (FLAC or WAV) in bulk. The spectrogram viewer was developed with input and guidance from the Ocean Data Lab at University of Washington and the Monterey Bay Aquarium Research Institute Soundscape team. It utilizes open source acoustic software tools - ooipy, pypam, and mbari-pbp.

4. Now Available from BCO-DMO: Time Series Water Sample Data from Four OOI Arrays

   OOI launched a collaboration in 2023 with the Biological & Chemical Oceanography Data Management Office (BCO-DMO) to make OOI water sampling data available via the BCO-DMO website and ERDDAP server. BCO-DMO curates publicly available research-ready oceanographic data in accordance with FAIR data principles. Advantages of distributing OOI data through BCO-DMO include concatenation of the cruise-by-cruise data into a single dataset with a Digital Object Identifier (DOI) and provisioning through ERDDAP, which provides both human and machine-to-machine interfaces. The BCO-DMO Dataset pages include descriptions of sampling and processing methods, and README files for each cruise. Currently BCO-DMO has data from the OOI Station Papa Array (Gulf of Alaska, annual cruises over 11 years), Irminger Sea Array (North Atlantic, 10 years), Southern Ocean Array (SW of Chile, 6 years) and Argentine Basin Array (South Atlantic, 4 years). You can access the datasets via this direct link or from the BCO-DMO home page: Click on Projects, then search for “OOI Discrete CTD and Water Sampling Cruise Data”. Figures 1 and 2 provide an example of the concatenated datasets using 10 years of data from the Irminger Sea Array. A Python script (implemented in a Jupyter Notebook available in https://github.com/WHOIGit/ooi-on-bco-dmo) was used to access the data from the BCO-DMO ERDDAP server, extract variables of interest, apply available quality control (QC) flags, and visualize the data.  Figure 1 shows profiles of selected variables for successive cruises to give a sense of the depth-time data coverage. Note that the sample depths are relatively sparse since the OOI sampling goal is to validate instruments on the moorings rather than collect comprehensive profile data. Figure 2 represents profile variability over time by an overplot color-coded by year. Even though constrained to “Acceptable” QC flags, some of the values plotted appear to be outliers, indicating the need for the user to consider further data quality assessment. Note that Discrete README files within the BCO-DMO dataset and CTD Cast Logs on OOI’s Raw Data Archive provide useful information. For example, the low values of oxygen in 2021are noted as inconsistent with oxygen from the CTD cast, whereas the high values of salinity in 2015 appear to be real, associated with a salinity maximum observed by the CTD. Since creating the Jupyter Notebook, data for two of the Irminger Sea cruises in OOI’s Raw Data Archive have been updated (including Nitrate for the 2021 cruise); these updates will be in the next version of the Irminger Sea dataset on BCO-DMO. For additional Python scripts to explore OOI Discrete CTD and Water Sampling Cruise Data as distributed by BCO-DMO, for example to plot a discrete parameter against its corresponding CTD sensed parameter, see notebooks available in https://github.com/WHOIGit/ooi-on-bco-dmo/tree/main/notebooks. [caption id="attachment_36331" align="alignnone" width="472"] Figure 1. Profiles of a) oxygen, b) salinity, and c) nitrate at the OOI the Irminger Sea Array from discrete bottle samples.[/caption] [caption id="attachment_36332" align="alignnone" width="532"] Figure 2. Temporal variability of a) oxygen, b) salinity, and c) nitrate over 10 years depicted as overlaid profiles.[/caption]

5. Miniboats, Major Impact: The Legendary Returns to Sea with OOI Roots

   In 2022, we shared a story of student-driven ocean exploration: a miniboat deployed from the R/V Neil Armstrong as part of the Educational Passages program, intersecting with the Ocean Observatories Initiative’s (OOI) Coastal Pioneer Array. That miniboat was one of many in a fleet of educational vessels aimed at engaging students in ocean science, data interpretation, and maritime technology. Today, we're excited to provide a scientific update on one of the program's longest-running vessels: The Legendary. Originally built in 2018 by elementary students in Manchester, NH, The Legendary was designed to foster early engagement in oceanography and to introduce students to the physical and observational tools of marine science. During its maiden voyage, the boat passed near the OOI Pioneer Array and students used this opportunity to correlate real-time OOI measurements—like sea surface temperature, salinity, and currents—with the miniboat's trajectory, deepening their understanding of ocean circulation and data-based prediction. After making landfall in Portugal in October 2019 during its second voyage, The Legendary became a catalyst for international STEM collaboration. Portuguese students adopted the vessel at Agrupamento de Escolas Diogo de Macedo, refurbishing it and connecting virtually with their peers in New Hampshire to continue its mission of oceanic discovery. In February 2025, The Legendary was finally relaunched into the Atlantic Ocean alongside another miniboat. Equipped with an upgraded GPS tracker, the vessel continues to serve as a student-driven observational platform. As it navigated wind and ocean currents, students tracked its progress, analyzing real-time environmental conditions, and drawing connections to large-scale oceanographic processes. After less than two weeks at sea, the boat made its way to Morocco, traveling nearly 600km. This new landing brings an opportunity for more students to come aboard the project, living up to its namesake: Legendary. This long-duration project illustrates the synergy between Educational Passages and the OOI. While OOI provides continuous, real-time measurements of physical, chemical, and biological parameters across key regions of the global ocean, Educational Passages offers a scalable, accessible pathway for students to interact with those data. Through these programs, students aren’t just learning about the ocean - they're participating in its observation and interpretation. To follow The Legendary’s current voyage and read more about its evolution, visit the Educational Passages feature article: Crimson Voyager and The Legendary Relaunched from Portugal. [caption id="attachment_36320" align="alignnone" width="640"] The Legendary landed on a sandy beach in Morocco, just south of Zaouiet Bouzarktoune. (c): Educational Passages[/caption] [caption id="attachment_36321" align="alignnone" width="360"] The Legendary (c): Educational Passages[/caption]