Hydrography
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To assist in the interpretation of the data, it can be displayed using the Hawaii Ocean Time-series Data Organization & Graphical System (HOT-DOGS©).

The majority of our sampling effort, approximately 60-72 h per standard HOT cruise, is spent at Station ALOHA. High vertical resolution environmental data are collected with a Sea-Bird CTD having external temperature (T), conductivity (C), dissolved oxygen (DO) and fluorescence (F) sensors and an internal pressure (P) sensor. A Sea-Bird 24-place carousel and an aluminum rosette that is capable of supporting 24 12-L PVC bottles are used to obtain water samples from desired depths. The CTD and rosette are deployed on a 3-conductor cable allowing for real-time display of data and for tripping the bottles at specific depths of interest. The CTD system takes 24 samples s^-1 and the raw data are stored both on the computer and, for redundancy, on VHS-format video tapes (prior to HOT-322) and as an audio signal on a laptop PC (HOT-322 - present).

In February 2006, before cruise 178, we replaced our 24 aging 12-L PVC rosette bottles with new 12-L bottles fabricated at the University of Hawaii Engineering Support Facility, using plans and specifications from John Bullister (PMEL).

CTD Profiling

Continuous measurements of temperature, salinity, oxygen, and fluorescence are made with a Sea-Bird SBE-9/11Plus CTD package with dual temperature, salinity, oxygen sensors, and fluorometer described in Tupas et al. (1995). In 2022 the CTD underwater unit #91361 was used during cruises HOT-335 through HOT-339. A new CTD #1487 acquired in February 2022 was used during the WHOTS-18 cruise.

Data Acquisition and Processing

CTD data were acquired at a rate of 24 samples per second. Digital data were stored on a laptop personal computer and for redundancy, the CTD signal was recorded using a USB sound card and Audacity® software on a separate laptop. Backups of CTD data were made onto USB storage cards and compact disks. The raw CTD data were quality controlled and screened for spikes described in Winn et al. (1993). Data alignment, averaging, correction and reporting were done as described in Tupas et al. (1993). Salinity spike rejection parameters were modified for some cruises in 2022 because of rough sea conditions. Spikes occur when the CTD samples the disturbed water of its wake; therefore, samples from the downcast are rejected when the CTD moves upward or when its acceleration exceeds 0.5 m s^-2 in magnitude.

Some cruises were conducted under relatively rough conditions. To relax the data rejection criteria and avoid eliminating excessive points, the CTD acceleration cutoff value had to be increased to between 0.55 and 1 m s^-2 for some casts. The World Meterological Organization (WMO) Sea State codes are as follows:

The data were additionally screened by comparing the temperature and conductivity sensor pairs. These differences permitted identification of problems in the sensors. Only the data from one set of T-C sensors and one oxygen sensor, deemed most reliable, are reported here.

Temperature is reported in the ITS-90 scale. Salinity and all derived units were calculated using the UNESCO (1981) routines; salinity is reported in the practical salinity scale (PSS-78). Oxygen is reported in µmol kg^-1. Chloropigment (Fluorescence) is reported in µg/l.