Description of the WHOTS-19 Mooring Cruises
Contents
2. Description of the WHOTS-19 Mooring Cruises¶
2.1. WHOTS-19 Cruise: WHOTS-19 Mooring Deployment¶
The Woods Hole Oceanographic Institution Upper Ocean Processes Group (WHOI/UOP) with the UH group’s assistance, conducted the 19th deployment of the WHOTS mooring onboard the Oscar Elton Sette during the WHOTS-19 cruise between June 15 and June 22, 2023. The WHOTS-19 mooring was deployed at Station 50 on June 17, 2023, 02:59 UTC at 22°46.057’N, 157°53.964’W, and the WHOTS-18 mooring was recovered on June 19, 2023. The scientific personnel that participated during the cruise are listed in Table 2.1.
Name |
Title or function |
Affiliation |
|---|---|---|
Plueddeman, Albert |
Chief Scientist |
WHOI |
Bigorre, Sebastien |
Research Specialist |
WHOI |
Graham, Raymond |
Research Associate |
WHOI |
Llanos, Eduardo |
Research Technician |
WHOI |
Santiago-Mandujano, Fernando |
Research Associate |
UH |
Fitzgerald, Dan |
Marine Electronics Technician |
UH |
Rohrer, Tully |
Research Associate |
UH |
Maloney, Kelsey |
HIMB Housing Coordinator |
UH |
Adkison, Camille |
Research Assistant |
UH |
Dale, Elizabeth |
Research Technician |
WHOI |
The UH group conducted the shipboard oceanographic observations during the cruise. A complete description of these operations is available in the WHOTS-19 cruise report [Santiago-Mandujano et al., 2024].
A Sea-Bird CTD (Conductivity, Temperature, and Depth) system was used to collect temperature (T), salinity (S), and dissolved oxygen (O₂) profiles during CTD casts. The time, location, and maximum pressure for each cast are listed in {numref}table-2. A total of five CTD casts were conducted during the WHOTS-19 cruise between June 16 and June 19. CTD profiles were obtained at Station 20 (while in transit to the WHOTS mooring) and Station 52 (near the WHOTS-18 buoy). The cast at Station 20 reached a depth of approximately 1500 m and included three acoustic releases—two designated for the WHOTS-19 mooring and one backup—attached to the rosette frame for functional testing. Four CTD yo-yo casts were conducted at Station 52 to obtain repeated upper-ocean profiles for comparison with subsurface instruments on the WHOTS-18 mooring prior to its recovery. These casts were initiated approximately 0.25 nautical miles from the buoy and included multiple up-and-down cycles between the surface and depths of 200 to 215 meters, with varying drift during each cast. CTD modulo errors began to appear during casts 3 and 4, indicating intermittent communication issues between the CTD and the deck unit. The frequency of these errors increased substantially during subsequent casts near the WHOTS-19 mooring, ultimately leading to aborted casts. The issue persisted even after re-terminating the CTD cable and replacing the primary CTD with a spare unit, suggesting the fault likely resided in the CTD wire or the slip-rings. As a result, no CTD casts could be completed near the WHOTS-19 mooring.
Between 2 and 4 water samples were taken from all casts. These samples were to be analyzed for salinity at UH and used to calibrate the CTD conductivity sensors.
Station/cast |
Date |
In-water Time |
Location |
Maximum pressure (dbar) |
|---|---|---|---|---|
20/1 |
06/16/2023 |
07:01 |
21°28.052´N, 158°21.087´W |
1489 |
52/1 |
06/18/2023 |
16:05 |
22°40.680´N, 157°58.892´W |
215 |
52/2 |
06/18/2023 |
20:02 |
22°40.888´N, 157°58.803´W |
203 |
52/3 |
06/19/2023 |
00:05 |
22°40.707´N, 157°58.954´W |
202 |
52/4 |
06/19/2023 |
05:22 |
22°41.226´N, 157°58.574´W |
200 |
Also, continuous ADCP and near-surface thermosalinograph data were obtained while underway.
The R/V Oscar Elton Sette was equipped with a RDI Ocean Surveyor 75 kHz ADCP, set to function in broadband and narrowband configurations. The configuration information is shown in Table 2.3. The ADCP used input from a SAMOS gyrometer and Furuno GP 150, a GPS receiver, to establish the ship’s heading and attitude.
Parameters |
OS75BB |
OS75NB |
|---|---|---|
Sample interval (s) |
300 |
300 |
Number of bins |
80 |
55 |
Bin Length (m) |
8 |
16 |
Transducer depth (m) |
5 |
5 |
Blanking length (m) |
8 |
8 |
Near-surface temperature and salinity data during the WHOTS-19 cruise were collected using the thermosalinograph (TSG) system installed aboard the NOAA Ship Oscar Elton Sette. The system sampled seawater from the ship’s continuous intake line and included the following instruments: an SBE-21 thermosalinograph (SN 3168), an SBE-45 micro-thermosalinograph (SN 0290), and an external SBE-38 temperature sensor (SN 212). The SBE-21 and SBE-45 units, each equipped with internal temperature and conductivity sensors, were located in the ship’s chemistry lab, approximately 70 meters from the hull intake. The SBE-38 was mounted externally at the seawater intake, positioned on the starboard side of the bow, forward of the bow thruster, at a depth of approximately 3 meters. All sensors recorded data every second. The system included a flow meter located in the chemistry lab, which indicated a flow rate of approximately 1.1 liters per minute throughout the cruise. Among the instruments, only the SBE-45 was equipped with a debubbler. To validate and correct for potential drift in salinity measurements, seawater samples were collected from the chemistry lab exhaust line every 8 hours. These samples were stored in 0.25-liter glass bottles and analyzed post-cruise at the University of Hawai‘i laboratory.
2.2. WHOTS-20 Cruise: WHOTS-19 Mooring Recovery¶
The WHOI/UOP group carried out the mooring turnaround operations during the WHOTS-20 cruise, which took place from May 31 to June 8, 2024. The WHOTS-20 mooring was successfully deployed at Station 52 on June 2, 2024, at 03:54 UTC, at coordinates 22°40.08′N, 157°57.01′W. The WHOTS-19 mooring was recovered on June 6, 2024, at 18:50 UTC. The scientific personnel who participated in the cruise are listed in Table 2.4.
Name |
Title or function |
Affiliation |
|---|---|---|
Bigorre, Sebastien |
Chief Scientist |
WHOI |
Llanos, Nico |
Engineer |
WHOI |
Graham, Raymond |
Engineer |
WHOI |
Fitzgerald, Dan |
Marine Electronics Technician |
UH |
Santiago-Mandujano, Fernando |
Research Associate |
UH |
Rohrer, Tully |
Research Associate |
UH |
Shepherd, Merritt |
Research Assistant |
UH |
Maloney, Kelsey |
HIMB Housing Coordinator |
UH |
Jandial, Prajna |
Graduate Student |
UH |
Dirks, Jonah |
Graduate Student |
UH |
The UH group conducted the shipboard oceanographic observations during the cruise. A complete description of these operations is available in the WHOTS-20 cruise report [Santiago-Mandujano et al., 2024].
A Sea-Bird CTD (Conductivity, Temperature, and Depth) system was used to collect temperature (T), salinity (S), and dissolved oxygen (O₂) profiles during CTD casts. The time, location, and maximum pressure for each cast are shown in Table 2.5.
Nine CTD casts were conducted during the WHOTS-20 cruise between June 1 and June 6, 2024. CTD profiles were collected at Station 20 (en route to the WHOTS mooring), Station 50 (near the WHOTS-19 buoy), and Station 52 (near the WHOTS-20 buoy). The cast at Station 20 reached a depth of approximately 1500 m and included three acoustic releases—two intended for the WHOTS-20 mooring and one backup—secured to the rosette frame for functionality testing. This cast exhibited anomalous values in the primary temperature, conductivity, and oxygen sensors. Post-cast inspection revealed that the CTD pump cable had been pinched beneath a hose clamp on one of the Niskin bottles. The secondary sensor suite was unaffected. Four CTD yo-yo casts were conducted near the WHOTS-19 mooring prior to recovery to provide comparison profiles for the subsurface instruments, and three additional yo-yo casts were conducted near the WHOTS-20 mooring after deployment. All yo-yo casts began approximately 0.25 nautical miles from the buoys and consisted of five vertical cycles between 5 m and 205 m depth, with varying drift during each cast.
The first two yo-yo casts near the WHOTS-19 mooring (S50C1 and S50C2) displayed anomalous data at the start of each profile, likely due to air bubbles in the CTD plumbing system. These artifacts disappeared below 100 m. A Y-shaped plastic “de-bubbler” was subsequently installed in both CTD plumbing lines to mitigate this issue. All subsequent casts returned high-quality data.
One deep CTD cast was conducted approximately 2 nautical miles from the WHOTS-19 buoy to obtain a profile for comparison with the near-bottom MicroCAT sensors. This cast reached a maximum depth of nearly 4550 m. However, due to the absence of a functioning altimeter onboard, it was not possible to safely approach the depth of the deepest MicroCATs, located at approximately 4659 m.
Between four and five water samples were collected during each cast using 0.25 liter glass bottles. These samples were returned to the University of Hawai‘i for salinity analysis and were used to calibrate the CTD conductivity sensors.
Station/cast |
Date |
In-water Time |
Location |
Maximum pressure (dbar) |
|---|---|---|---|---|
20/1 |
6/1/2024 |
02:55 |
21°17.112′N, 158°19.541′W |
1529 |
50/1 |
6/3/2024 |
16:07 |
22°46.880′N, 157°55.793′W |
204 |
50/2 |
6/3/2024 |
20:04 |
22°46.221′N, 157°56.073′W |
202 |
50/3 |
6/4/2024 |
00:08 |
22°46.396′N, 157°56.165′W |
205 |
50/4 |
6/4/2024 |
04:02 |
22°46.339′N, 157°56.148′W |
202 |
52/1 |
6/4/2024 |
20:37 |
22°40.237′N, 157°59.375′W |
203 |
52/2 |
6/4/2024 |
23:58 |
22°40.237′N, 157°59.271′W |
202 |
52/3 |
6/5/2024 |
04:04 |
22°40.430′N, 157°59.022′W |
204 |
50/5 |
6/6/2024 |
00:09 |
22°47.311′N, 157°57.818′W |
4625 |
Also, continuous ADCP and near-surface thermosalinograph data were obtained while underway.
The NOAA Ship Oscar Elton Sette was equipped with a Teledyne RDI Ocean Surveyor 75 kHz Acoustic Doppler Current Profiler (ADCP), configured to operate in narrowband mode. The broadband mode was non-functional during this cruise. Configuration details are provided in Table 2.6. The ADCP relied on input from a SAMOS gyrometer and a Furuno GP-170 GPS receiver to determine the ship’s heading and attitude.
Parameters |
OS75NB |
|---|---|
Sample interval (s) |
300 |
Number of bins |
55 |
Bin Length (m) |
16 |
Transducer depth (m) |
5 |
Blanking length (m) |
8 |
Near-surface salinity data during the WHOTS-20 cruise were collected using the thermosalinograph (TSG) system installed aboard the NOAA Ship Oscar Elton Sette. The system sampled water from the ship’s continuous seawater supply and consisted of a Sea-Bird SBE-45 micro-thermosalinograph (SN 0290), equipped with internal temperature and conductivity sensors located in the ship’s chemistry lab, approximately 70 meters from the hull intake.
A second TSG unit, the Sea-Bird SBE-21, was installed but was non-functional throughout the cruise. Similarly, the SBE-38 remote temperature sensor, mounted at the water intake near the ship’s bow, was also inoperative. As a result, sea surface temperature data could not be collected during the cruise.
The SBE-45 recorded data at 1 Hz and included a built-in debubbler. The seawater intake is located at the bow of the vessel, forward of the starboard-side bow thruster, at a depth of 3 meters. Flow through the system was monitored via a flow meter in the chemistry lab, which registered a rate of approximately 1.5 liters per minute during the cruise.
To correct for potential drift in conductivity measurements, discrete salinity samples were collected every 8 hours from the exhaust line in the chemistry lab using 0.25-liter glass bottles. These samples were returned to the University of Hawai‘i laboratory for post-cruise salinity analysis.