Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
• Data Files
• Supplemental Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Data collection is ongoing, with updates made semi-annually. For guidance on downloading data subsets, please refer to the BCO-DMO ERDDAP instructions here: https://guide.bco-dmo.org/access-and-reuse/erddap. Decadal subsets available for download from this ERDDAP service include the following download links:

• Hydro S CTD Data 1988-2000
• Hydro S CTD Data 2000-2010
• Hydro S CTD Data 2010-2020
• Hydro S CTD Data 2020-2023

CTD profiles at the Hydrostation S site have been collected since station cruise #60643 in October 1988 and although there have been some changes during the past thirty-two years as a result of new instrumentation or methodologies, the the general sampling procedures have been consistent with those detailed in the BATS method manual version #4 (Knap et al., 1997).

In summary, the CTD is operated as per SeaBird's suggested methods with data collection at the full scan rate of 24 Hz. The CTD is powered up and allowed to stabilize at 12 m prior to profiling and once stable  (typically 4 minutes) the CTD is brought back to the surface from which point the profile begins with typical descent rates of 0.7-1.0 m/s, depending on weather conditions. Water samples are collected on the upcast and prior to triggering bottles the CTD is kept at the desired depth for a minimum of 60 seconds to ensure that entrainment from the following wake has subsided. Once the water sample is taken the CTD immediately continues with the upcast at an ascent rate of 0.7-1.0 m/s. 

The basic system used to acquire CTD data is a Sea-Bird SBE 9plus CTD, with an internal Digiquartz pressure sensor, a Sea-Bird SBE-3F temperature sensor, a Sea-Bird SBE-4 conductivity cell and a Sea-Bird SBE-5 pump. Additional sensors include the Sea-Brid SBE-43 dissolved oxygen sensor, the WET Labs C-Star or Chelsea/Seatech
Transmissometer, the Chelsea Aqua 3 Fluorometer, and the Biospherical/Licor PAR/Irradiance sensor. Present configuration also includes a secondary temperature sensor, a Sea-Bird SBE-35 temperature sensor, a secondary conductivity sensor and pump, which are connected independently from the primary units. The temperature and conductivity sensors are connected by a standard Sea-Bird TC-duct (clear, low viscous type), which ensures that the same parcel of water is sampled by both sensors, improving the accuracy of the computed salinity. The dissolved oxygen sensor is connected downstream from the conductivity cell and the flow rate through this sensor configuration is maintained at a steady rate by the inertia balanced SBE-5 pump. 

Ship information:​

• R/V Weatherbird I (Jan 1983 - September 1989)
• R/V Weatherbird II (October 1989 - February 2005)
• R/V Atlantic Explorer (May 2006 - Present)

CTD data processing typically follows the procedures outlined in Knap et al., 1997 and can be divided into two major stages: (1) CTD signal conversion and dynamic sensor correction, and; (2) static drift corrections and empirical field calibrations. Stage 1 is performed using SeaBird's SEASOFT software and some Matlab scripts, while Stage 2 is performed completely in the Matlab environment.

The basic steps of Stage 1 are:

• preliminary CTD sensor quality check;
• determination of the dynamic coefficients associated with time alignment and thermal mass problems;
• application of pressure filter and velocity filter (0.3 m/s);
• application of digital filters for erroneous signal removal;
• and finally average to 2 Hz ready for stage 2 processing.

The processing steps in Stage 2 include:

• static drift corrections as determined from the sensor calibration history;
• empirical field calibration of the conductivity and oxygen sensors;
• final QC analysis; and bin average downcast data to 2 dbar.

Following experience of profiling with the SBE–35RT temperature probes, appropriate routines are being implemented to assess performance of the SBE–03f units against the SBE–35 and implement correction procedures. It should be noted that only downcast data are processed and reported, except for the marker data during bottle fires on the upcast.

Instrument calibration:
CTD sensor calibration: Temperature, conductivity and dissolved oxygen sensors are routinely returned to SeaBird every 6-9 months for routine calibration, while the pressure unit is calibrated following full service of the underwater SBE 9 unit every 18-24 months. Auxiliary instruments (fluorometer, tranmissometer, PAR) are sent for calibration every 12 months.

Quality control data access note:
Data fields that have a WHPO quality flag =3 hav been deemed questionable by the PIs, so any individual accessing the data should be aware that they are accessing data of questionable quality. Parameter quality flags defined as 1= unverified, 2= verified acceptable, 3= questionable, 4= bad, 9= no data

- imported all 805 CTD meta files into BCO DMO system
- concatenated all CTD meta files into one file
- imported all 805 CTD data files into BCO DMO system
- concatenated all CTD data files into one file
- imported all 805 CTD mask files into BCO DMO system
- concatenated all CTD mask files into one file
- replaced NaN and -999 with the fill value 'nd'.
- joined the data and mask files based on row number
- converted date and time to ISO UTC times for deployment and recovery
- converted longitude values to decimal degrees (multiplied degrees West by -1)
- created new fields for "Cruise_type", "Cruise_num", and "Cast" (extracted from ID column)
- modified parameter names to conform with BCO-DMO naming conventions and to be more consistent with other BATS data submissions

Hydrostation S (also known as Panulirus hydrographic station) is recognized as one of the most important sustained ocean time-series sites in the world.  Located about 25 km southeast of Bermuda in the North Atlantic Ocean, this site has oceanographic measurements dating back to 1954, when Henry Stommel and co-workers initiated repeat biweekly hydrographic observations. 

The most recent project awards and abstracts are listed below.  A detailed history of funding with summary of all project awards for Hydrostation S (Panulirus Hydrographic stations) can be found here (PDF format):
https://datadocs.bco-dmo.org/docs/305/Hydrostation_S/data_docs/Hydrostation_S_funding_history.pdf

Years 70-74:
NSF Award OCE-2122606 Abstract:

This project continues hydrographic observations at Hydrostation S, extending the time-series of ocean data to almost 70 years. Hydrostation S (formerly known as the Panulirus site), located about 25 km southeast of Bermuda in the North Atlantic Ocean, is one of the longest open-ocean hydrographic stations in the world. This program of repeat biweekly hydrographic observations began in 1954 and now, in its seventh decade, has proved to be the catalyst for numerous studies of ocean physics, biological processes and biogeochemistry. Sustained observations of the ocean, such as those from Hydrostation S, remain critically important to establish rates of change to provide quantitative empirical data for myriad regional and global ocean synthesis and modeling of ocean processes and future ocean change. Hydrostation S program and its data are considered as a service to the community, being openly distributed and subsequently have been an invaluable resource in understanding processes and patterns of variability in the ocean, as well as education, mentorship and outreach activities.

The major objective of the proposal is to continue Hydrostation S into the eighth decade with numerous questions related to warming and cooling, salinification and freshening, deoxygenation and insights on biogeochemical changes over time. This program constitutes frequent water column sampling of temperature, salinity, and dissolved oxygen (and indirectly, sampling of important ocean carbon time–series) of the North Atlantic subtropical gyre at the Hydrostation S site. Such work is complementary to other sustained observations such as the Bermuda Atlantic Time–series Study (BATS) and Ocean Flux Program (OFP). The project entails a similar sampling format that has been followed for the past 68 years. Hydrostation S also supports the longest global ocean CO2 and acidification time-series (from 1983 to present).

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Years 65-69:
NSF Award OCE-1633125 Abstract:
The physical properties of the ocean from the surface layers to the abyssal water masses are changing in concert with natural and anthropogenically influenced physical forcing and sustained observations of the ocean are critically important to establish these rates of change. One of the longest open-ocean hydrographic stations in the world is maintained at the Hydrostation S site (formerly known as the Panulirus site) located about 25 km southeast of Bermuda in the North Atlantic Ocean. This repeat biweekly hydrographic observations was initiated by Henry Stommel and co-workers in 1954. Now, in its seventh decade, it continues to be recognized as one of the most important sustained ocean time-series and provides an invaluable metric for the long-term state of the North Atlantic subtropical gyre in relation to the meridional overturning circulation, western boundary transport, and gyre recirculation. For example, the upper ocean warming trend has strengthened (about 0.8° C since the 1970's) while the deep Labrador Sea has cooled by a few tenths of a degree. The signature of deoxygenation has been observed at Hydrostation S in the upper ocean (about 7 micro-moles/kg/decade decrease in dissolved oxygen) as well as an intensification and expansion of the oxygen minimum zone. These changes suggest that the North Atlantic subtropical gyre is experiencing deoxygenation as in the Pacific Ocean as a result of increased upper ocean stratification and reduced solubility of oxygen in warmer waters. The Hydrostation S program and its data set are managed as a service to the ocean community, being openly distributed and used as a resource in understanding processes and patterns of variability in the ocean, as well as for education, mentorship and outreach activities. The Hydrostation S project will contribute to the research and training of six research specialists and research technicians at BIOS and contribute to the research projects of at least three Ph.D. students through on-going educational partnership with Princeton University and the University of Southampton in the U.K. The one-day Hydrostation S research cruises are an ideal platform for testing new sensors and for providing hand-on training to undergraduate students enrolled in summer programs.

The Hydrostation S project is designed to address the overarching hypothesis that the physical properties of the upper-ocean to deep-ocean are changing in concert with natural and anthropogenically influenced physical forcing. Sustained observations of the ocean, such as those from Hydrostation S, remain critically important to establish rates of change to provide quantitative empirical data for myriad regional and global ocean synthesis and modeling of ocean processes and future ocean change. The major objective of Hydrostation S into the seventh decade is to continue the frequent water column sampling of temperature, salinity, and dissolved oxygen (and indirectly, sampling of important ocean carbon time?series) of the North Atlantic subtropical gyre. Such work is complementary to other sustained observations such as the Bermuda Atlantic Time-series Study (BATS) and Ocean Flux Program (OFP). As for the past five years, two CTD profiles will be conducted to better capture the deep-water variability while maintaining all the previous discrete depths. The first CTD cast will profile to full ocean depth (3,200-3,500 m) while the second CTD cast will profile from the surface to 500 m to allow for biogeochemical instrumentation not rated for full ocean depth and to support ancillary studies of ocean physics, biological processes and biogeochemistry. A secondary objective will be to build upon the collaborative comparison of physical data collected as part of two autonomous sensor projects. In the latter stages of the project, as ocean glider deployment becomes more sustainable and reliable, collaborative and comparative efforts will be used to test the capability of ocean gliders to provide data of sufficient quality to detect long-term oceanic change in a "virtual" mooring time-series mode. The robust and highly accurate Hydrostation S data will be used to test the capability of emerging technologies over the next five to ten years.