Dear Mark, Thank you for your DQE evaluation of CTD data collected along WOCE section P18. We considered each of your suggestions and the following is an itemized explanation of what we did or didn't change in our data files, as well as answers to your questions. Kristy McTaggart and Greg Johnson *************************************************************************** STATION SUMMARY FILE (.sum) .sum files here were ammended to contain the same maximum pressure values for stations 25, 27, 32, 46, 61, and 78 as you listed. The PDR sound speed used for sounder readings was 1500 m/s. The readings were not corrected for transducer depth below the waterline. The depth of the transducer would've been about 5.5 +/- 0.6 m. We would prefer to use the PDR depths as listed and correct them using Carter's tables so that they serve as independent measurements and can be used as a check on CTD pressure. SALINITY Regarding suspicious CTD salinity data listed in Table 4: station 24 2-6 dbar flags not changed to 3 station 51 84 dbar flag changed to 3 station 52 74 dbar flag changed to 3 station 53 70 dbar flag changed to 3 station 55 flags not changed to 3 station 67 46 dbar flag changed to 3 'Scatter of salinity residuals' There is an incompatibility between the General Oceanics rosette sampler and the Sea-Bird 911plus CTD system that generates a spike in the data stream at the moment a bottle is confirmed as tripped. Because of this, upcast CTD burst data had to be averaged prior to the bottle confirm bit. Two-second averages were chosen over a longer interval because the CTD operators did not always let the package sit at bottle depth for at least 10 seconds before firing the rosette. Hence no changes were made. 'Biasing of CTD salinity data for individual stations' Of course one can seemingly make a (very slight) improvement in the CTD-bottle residual statistics by allowing more degrees of freedom in the fit as the DQE has suggested (that is, breaking up the fit into small station groupings). One could get the best statistics by individually fitting each station to its bottles, but most experts would argue that this would be a bad choice, because one would not be taking advantage of the CTD calibration as a way to average out station-to-station bottle salinity noise. We believe that the SBE-9/11 CTD conductivity slope drifts gradually, and is actually more stable than the day-to-day fluctuations in the autosal- inometer salinities owing to small temperature drifts in the laboratory and the fact that severe budgetary constraints on these cruises forced us to economize even on such things as standard sea water. We suspect that the "biasing of the CTD salinity data" mentioned in the DQE evaluations is actually noise in the bottle data. Somewhat suspicious is that the station groupings recommended by the DQE of the correct size (most often 3-5 stations per group) that they could easily be owing to daily drift problems in the autosalinometer. For our original calibrations we deliberately chose to model the conductivity slope adjustments of the entire data sets for P14S/P15S and P18 using 4th-order polynomial functions of station number to average out bottle salinity noise. We did this because we saw no obvious jumps in the CTD calibration for either cruise, just gradual drifts. Statistical support for our philosophy over that of the DQE is given by the following exercise: The 2oC potential isotherm is well within the oldest Pacific Deep Water, and has some of the tightest Theta-S relation- ships in the Pacific Ocean (and probably the world). For both P18 and P14S/P15S, we looked at the absolute values of station-to-station changes in CTD salinity on Theta=2.0oC (Figure 1) for our original calibration, creating a histogram of station-to-station differences for each cruise in 0.001 bins. We then applied the DQE's suggested ad-hoc calibrations for smaller station groupings to the data and conducted the same analysis. When the histograms are differenced (Figure 2), one can see that the Theta-S relations at 2oC after the DQE's corrections are noisier for both cruises. For P18, after the DQE's suggested correction there are four less station pairs in the 0.000 difference bin and one less in the 0.001 difference bin whereas there are three more in the 0.002 difference bin and two more in the 0.003 difference bin. For P15S/P15S there are four less stations in the 0.000 difference bin after the DQE's suggested correction, with one more in the 0.001 difference bin and three more in the 0.002 difference bin. Since the DQE's "corrections" actually introduce more noise in the CTD Theta-S relation at 2oC than our original calibration, we decline application of them. The small groups do not improve the calibraiton, they degrade, perhaps by introducing auto- salinometer drift noise. OXYGEN Rankings for stations as listed in Table 6 were complied with except for station 160, which is closer to a rating of 2 than 1 and was flagged as 3 not 4. A cutoff of 3750 dbar was used to reflag the deep data of stations 21 and 22; 3400 dbar for station 65; 3200 dbar for station 67; and 2200 dbar for station 85. Note all flags of 6, 7, or 8 were preserved in the reflagging. Poor oxygen data were owing to poor sensor performance not to the data processing or curve fitting. A few worst case groupings were reexamined using two sets of fit coefficients blended near the oxygen minimum as was done for P14S/P15S. However, there was no significant improvement. Unfortunately, only one oxygen module was available for this cruise due to severe budgetary constraints, and it was not a good one. Suspicious oxygen data listed in Table 5 were examined and near surface data were reflagged as 3 as suggested. Note that data files submitted before and after the DQE evaluation are 1 dbar averages, not the 2 dbar averages referenced. For suspicious oxygen data deeper in the water column, these were interpolated over and flagged as 6 (stations 30, 69, 70, 71-74, 128, 153, and 180). The shift in oxygen data between 2084 and 2384 dbar for station 188 was flagged as 3 and not interpolated over. Again, all flags of 6, 7, or 8 were preserved in the reflagging. Stations 26, 89 and 160 were viewed with adjacent profiles and their bottles. Station 26 and 89 oxygen profiles were flagged as 4 as suggested in Table 6. Station 160, however, looked to be closer to a rating of 2 than 1 and was flagged as 3 not 4. CTDOXY flags in the .sea file were changed to 4 for all the station samples you listed. Also, CTDOXY flags were changed to 4 where profiles were recently interpolated as a result of DQE suggestions: station 30 sample 121 70 107 73 108 180 111 TEMPERATURE There is a typo in the data report. The value of the drift for temperature sensor T1461 is -0.0006 C. Temperature calibrations were applied to the data using Seasoft processing module DATCNV which reads the sensor's .con file for coefficients. DESPIKING, INTERPOLATION AND FLAGS The flag value of 8 used near the surface in the .ctd files represent data that were continued to the surface from the first assumed good value. For P14S/P15S we used 7. For P18, this procedure was done in program POSTCAL where temp, cond, oxc and oxt were copied back and flagged as 8, then salinity was recomputed and flagged as 2 in most cases. Despiking done after POSTCAL changed some flags to 6. Flags of 8 were left in the data files for this cruise. As for the large blocks of interpolated data (mostly oxygen) listed in Table 2, we maintain that this is the best way to deal with these data from a poor and failing sensor. Flags of 6 (as well as 7 and 8) have been preserved even when reflagging the entire oxygen profile as suggested in Table 6. DENSITY INVERSIONS Original data submitted for P18 were not examined for small density inversions. In response to the DQE evaluation, program DELOOP, as applied to P14S/P15S, with an N^2 criteria of -3x10e-6 was applied to P18 profiles. Over 82% of the density inversions listed in Table 7 were interpolated over. Delooped 1 dbar averaged data files with all the changes noted above are resubmitted along with this reply to the DQE. DOCUMENTATION Again, the PDR sound speed was 1500 m/s, and the readings have not been corrected for transducer depth (5.5 +/- 0.6 m) below the waterline. Station groupings used for oxygen calibrations and final values of fit parameters are given in a separate oxygen calibration table. Oxygen calibration problems were owing to poor sensor performance. Temperature pre- and post-cruise calibration difference for sensor T1461 was a typo in the documentation and should read -0.0006 C. More frequent flagging of surface temperatures compared to surface salinities is explained in the previous section, DESPIKING, INTERPOLATION AND FLAGS. Data files submitted to the WOCE office were 1 dbar averages, not 2 dbar.