Hawaii Ocean Time-series (HOT)
in the School of Ocean and Earth Science and Technology at the University of Hawai'i at Manoa
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Continuous near-surface salinity and temperature data were collected during every 2019 HOT cruise (HOT-309 through HOT-317) using Sea-Bird thermosalinograph and temperature sensors aboard R/V Kilo Moana and R/V Oceanus. The details of each thermosalinograph system varied from ship to ship. Still, each system consisted of a remote temperature sensor measuring near-surface temperature close to the intake of the ship's uncontaminated seawater supply in conjunction with a thermosalinograph sensor that measured both conductivity and temperature further down the seawater supply line. The salinity of seawater was then calculated using the internal temperature and conductivity as well as the internal pressure of the pump.
Thermosalinograph conductivities were calibrated using bottled salinity samples taken periodically (approximately every 4 hours) from the continuous seawater line outtake near the thermosalinograph. The data from each cruise were also compared with the CTD temperature and conductivity data collected simultaniously and from near the same depth as the seawater supply intake for a final data quality control.
The thermosalinograph system aboard the R/V Kilo Moana consisted of the SBE-38 external temperature sensor (SN 0150) in the bow-thruster chamber in the starboard bow close to the seawater intake. The intake depth was 8 meters below the surface, and the pump's internal pressure was approximately 6 dbar. An SBE-45 Seacat thermosalinograph (SN 0267) measuring internal conductivity and temperature was in the IMET lab at the ship's port bow. Data were acquired every second.
The thermosalinograph system aboard the R/V Oceanus comprised an internal SBE-45 Seacat unit (SN 0593) along with an SBE-3 external temperature sensor (SN 0607) located at the seawater intake situated at about 3 m below the sea surface. The external data were acquired once every four seconds but later interpolated to a one-second sample interval to match the thermosalinograph and navigation data time. The internal temperature and conductivity data were obtained every second.
These data were processed and calibrated against bottled salinity samples. Final data for 2019 from cruises aboard R/V Kilo Moana are derived from the SBE-45 thermosalinograph at 1-second intervals.
Thermosalinograph measurements of near-surface temperature (NST) and near-surface salinity (NSS), as well as navigation for the 2019 HOT cruises are presented in the Figures below. Thermosalinograph data recorded while on station can be compromised by ship effects such as temperature changes in the water due to the ship's hull and engine temperatures. Salinity can also be influenced by the ship when on station as the ship provides a potential source of contamination and disturbs the water being sampled.
In general, cooler near-surface temperatures and, in most cases, saltier near-surface salinities were observed at Station ALOHA compared to the data recorded near Oahu.