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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 pressure calibration strategy employed a high-quality quartz pressure transducer as a transfer standard. Periodic recalibrations of this lab standard were performed with a primary pressure standard. The transfer standard was used to check the CTD pressure transducers. The corrections applied to the CTD pressures included a constant offset determined at the time that the CTD first enters the water on each cast, and a pressure dependent offset, obtained from semi-annual bench tests between the CTD sensor and the transfer standard.

The transfer standard is a Paroscientific Model 760 pressure gauge equipped with a 10,000-PSI transducer. This instrument was purchased in March 1988, and was originally calibrated against a primary standard. Subsequent recalibrations have been performed every 2.5 years on average either at the Northwest Regional Calibration Center or at the Scripps Institute of Oceanography. The latest calibrations were conducted at the Scripps Institute of Oceanography in April 1999, May 2001, May 2003, July 2005, and July 2009.

CTD pressure transducer bench tests were done using an Ametek T-100 pump and a manifold to apply pressure simultaniously to the CTD pressure transducer and to the transfer standard. All these tests had points at six pressure levels between 0 and 4500 dbar, increasing and decreasing pressures.

Three Sea-Bird SBE-3-Plus temperature transducers #2454, #4448, and #2907 were calibrated at Sea-Bird. Sensor #2907 had its wein-bridge capacitors replaced at Sea-Bird in August 2008. Sensors #2454 and #4448 showed a sudden temperature difference offset of about 0.3m°C at 4600 dbar during the first deep cast of HOT-204, but it was not possible to identify which sensor was causing the offset. Both sensors were sent to Sea-Bird for calibration and paired again during HOT-205, when again they showed a temperature difference offset in the deep section of the deep cast (3600 dbar). Continued troubleshooting during 2009 cruises indicated that a similar problem occurred when sensor #2907 was installed. Eventually it was identified that the problem was with sensor #4448, and also with sensor #2907. These sensors were sent to Sea-Bird in September 2009, where they were opened, inspected, and had their O-ring replaced, this appeared to have solved the problem.

The history of the sensors, as well as the procedures followed to obtain the sensor drift from the Sea-Bird calibrations are well-documented in previous HOT Data Reports (Fujieki et al., 2010, 2008, 2007, 2006, 2005, Santiago-Mandujano et al., 2002, 2001, 1999, Tupas et al., 1993, 1994a, 1995, 1997, 1998, Karl et al. 1996) Calibration coefficients obtained at Sea-Bird for these sensors after 2007 and used in the drift estimates were used in the following formula that gives the temperature (in Deg C) as a function of the frequency signal (f):

For each sensor, the final calibration consists of two parts: first, a single "baseline" calibration is chosen from among the ensemble of calibrations during the year; second, for each cruise a temperature-independent offset is applied to remove the temporal trend due to sensor drift. The offset, a linear function of time, is calculated by least squares fit to the 0-30 Deg C average of each calibration during the year. The maximum drift correction in 2008 was less than 0.5 x 10^-3 Deg C for the data collected with these sensors, except for sensor #4448, which had a maximum drift correction of 1.39 x 10^-3 Deg C. The baseline calibration is selected as the one for which the trend-corrected average from 0-5 Deg C is nearest to the ensemble mean of these averages.

A small residual pressure effect on the temperature sensors documented in Tupas et al. (1997) has been removed from measurments obtained with our sensors. Another correction to our temperature measurements was for the viscous heating of the sensor tip due to the water flow. This correction is thoroughly documented in Tupas et al. (1997).

Dual sensors were used during each of the 2008 cruises. The temperature differences between sensor pairs were calculated for each cast to evaluate the quality of the data, and to identify possible problems with the sensors. Means and standard deviations of the differences in 2-dbar bins were calculated from the ensemble of all casts at Station ALOHA for each cruise. Both sensors performed correctly during the 2008 cruises, showing temperature differences within expected values. The mean temperature difference as a function of pressure was typically less than 1 x 10^-3 Deg C, with a standard deviation of less than 0.5 x 10^-3 Deg C below 500 dbar. The largest variability was observed in the thermocline, with standard deviation values up to 5 x 10^-3 Deg C.

Three conductivity sensors were used during the 2008 cruises #2959, #3162, and #2218. The history of the sensors is well documented in previous HOT Data Reports (Fujieki et al., 2010, 2008, 2007, 2006, 2005, Santiago-Mandujano et al., 2002, 2001, 1999, Tupas et al., 1993, 1994a, 1995, 1997, 1998, Karl et al. 1996). Dual sensors were used during each of the 2008 cruises.

For each sensor, the nominal calibrations were used for data acquisition, and a final calibration was determined empirically from salinities of discrete water samples acquired during each cast. Prior to empirical calibration, conductivity was corrected for thermal inertia of the glass conductivity cell as described in Chiswell et. al. (1990).

Procedures for preliminary screening of bottle samples and empirical calibration of the conductivity cell are described in Tupas et al. (1993, 1994a). For cruises HOT-199 through -206,the standard deviation cutoff values for screening of bottle salinity samples were: 0.0035 (0-150 dbar), 0.0048 (151-500 dbar), 0.0019 (501-1050 dbar), and 0.0010 (1051-5000 dbar).

A least squares fit (ΔC = b₀ + b₁C + b₂C²) to the CTD-bottle conductivity differences was used. No cruises during 2008 required a quadratic calibration. The calibrations were best below 500 dbar because the weaker vertical salinity gradients at depth lead to less error when the bottle and CTD pressures are slightly mismatched.

The final step of conductivity calibration was a cast-dependent bias correction as described in Tupas et. al. (1993) to allow for drift during each cruise or for sudden offsets due to fouling. Only 3 casts during 2008 required a cast-dependent bias correction.

Conductivity differences between sensor pairs were calculated the same as for the temperature sensors. The range of variability as a function of pressure was about ± 1 x 10^-4 Siemens m^-1, with a standard deviation of less than 0.5 x 10^-4 Siemens m^-1 below 500 dbar, from the ensemble of all the cruise casts. The largest variability was in the halocline, with standard deviations reaching up to 5 x 10^-4 Siemens m^-1 between 50 and 300 dbar.

During the 2008 cruises our three Sea-Bird SBE-43 oxygen sensors were used: #43262, #43918, and #43982. The history of these sensors is documented in previous HOT Data Reports (Fujieki et al., 2010, 2008, 2007, 2006, 2005). Sensor #43918 showed an offset between deep casts in two cruises before cruise 202, and it was sent to Sea-Bird for inspection in August 2008. The sensor's membrane was found punctured and it was repaired. The sensor's lid and membrane assembly were replaced, and its electrolyte reservoir was re-backfilled.

Water bottle oxygen data were screened and the oxygen sensors were empirically calibrated following procedures described previously (Winn et. al. 1991; Tupas et. al., 1993). The calibration procedure follows Owens and Millard (1985), and consists of fitting a non-linear equation to the CTD oxygen current and oxygen temperature. The bottle values of dissolved oxygen and the downcast CTD observations at the potential density of each bottle trip were grouped together for each cruise to find the best set of parameters with a non-linear least squares algorithm. Two sets of parameters were usually obtained per HOT cruise, corresponding to the casts at Station 1 and 2 (calibration coefficients from cast 2 are also used to calibrate the cast at station 6, 50 and 52). The calibration procedure for the Sea-Bird SBE-43 sensors is documented in Santiago-Mandujano et. al. (2001).

Dual sensors were used during cruises, but only the sensor whose data were deemed more reliable is reported.