The Ocean Climate Laboratory (OCL) at the National Oceanographic Data Center (NODC) is supported by the NOAA Climate and Global Change program to produce scientifically quality controlled oceanographic databases. Work to date includes quality control of historical in situ temperature, salinity, oxygen, phosphate, nitrate, and silicate data and the preparation of one-degree latitude-longitude mean fields for each of these parameters using objective analysis techniques. Specifically, this project has produced four ocean atlases describing the global distributions of these parameters and two technical reports describing the quality control and processing procedures (see section 6 of this documentation for a listing of these publications). Observed and standard level profile data (along with quality control flags) used in the production of these atlases are being made available to the international oceanographic community on the World Ocean Atlas 1994 CD-ROM series (referred to herein as WOA94). In addition, the CD-ROM series contains the objectively analyzed one-degree latitude-longitude mean fields for each of the measured parameters, and two derived parameters (Apparent Oxygen Utilization and oxygen saturation), and five-degree square statistics of standard level values. Profile data on the CD-ROM series are recorded in ASCII format and sorted geographically, so they are easy to access and manipulate. The CD-ROMs are formatted in the ISO 9660 standard. The Ocean Climate Laboratory expresses its thanks to all those who provided us with their comments and helped us develop an improved product.
Data on the CD-ROM series includes the following flagged data:
Source: All data from NODC's low resolution CTD file (CTD profiles from the NODC Station Data file were transferred to this file)
Source: NODC MBT file (Includes NODC MBT data from the NODC Selected Bathythermograph (SBT) data file that contains data at selected depths)
The drop rate correction applied was:
zc = 6.733t - 0.00254t2
where
zc = the corrected depth
"t", the elapsed time since the instrument entered the ocean, is determined by:
t = 1498.14 - (2244447.430 - 462.963z0)1/2
where
z0 = originally calculated depth (Szabados, personal communication).
Table 1. Precision and number of profiles for each parameter. ---------------------------------------------------------------- Maximum stored # of Parameter Unit precision Profiles ---------------------------------------------------------------- Temperature degrees C xx.xxx 4,553,426 Salinity p.s.u. xx.xxx 1,254,771 Oxygen ml/l xx.xx 367,635 Phosphate micromolar xx.xx 184,153 Silicate micromolar xxx.x 110,413 Nitrate micromolar xx.x 75,403 ----------------------------------------------------------------Each parameter is identified in the data by a numeric code. The parameters and their associated codes are listed in Table 2.
Table 2. Numeric codes associated with each parameter -------------------------------------- Code Parameter -------------------------------------- 0 Depth 1 Temperature (in-situ) 2 Salinity 3 Oxygen 4 Phosphate 6 Silicate 8 Nitrate --------------------------------------
For many analysis purposes, it is necessary to interpolate from observed level to standard depth levels. The standard depth analysis levels selected for this study are listed in Table 3 and include the 30 NODC standard depths and three additional levels at 3500, 4500, and 5500 meters. There are additional standard level depth data in some of the standard level profiles (i.e., 6000, 6500, 7000, 7500, 8000, 8500, 9000 meters, numbered 34 through 40).
Table 3. Standard levels and depths (in meters) ------------------------------------------------ Level Depth Level Depth 1 0 18 900 2 10 19 1000 3 20 20 1100 4 30 21 1200 5 50 22 1300 6 75 23 1400 7 100 24 1500 8 125 25 1750 9 150 26 2000 10 200 27 2500 11 250 28 3000 12 300 29 3500 13 400 30 4000 14 500 31 4500 15 600 32 5000 16 700 33 5500 17 800 ------------------------------------------------The quality of the observed and standard level data were checked using the following procedures:
At the NODC:
Data were flagged for each quality control check. A datum or profile flagged as an outlier was excluded from further checks. A description of the flags can be found in Appendix 1. The quality control procedures have been documented in two NOAA Technical Reports (Boyer and Levitus, 1994; Conkright et al., 1994).
Table 4. Available objectively analyzed fields for each parameter. ---------------------------------------------------------------------- PARAMETER ANNUAL* SEASON** MONTH*** Temperature X X X Salinity X X X Dissolved oxygen X X Apparent Oxygen Utilization X X Oxygen saturation X X Phosphate X Nitrate X Silicate X *ANNUAL - composite of all data regardless of season or year **SEASON - data composite based on seasons following the Northern Hemisphere convention. The seasons are defined as: Winter (January - March) Spring (April - June) Summer (July - September) Fall (October - December) *** MONTH - data composite for each month. January through December analysis for 19 depth levels only (0-1000 m) ----------------------------------------------------------------------For all the files in Table 4, there are accompanying mask files. The mask file contains the number of grid points which contain data within the radius of influence surrounding each grid box. If a grid box contains three or fewer observations within its radius of influence, the mask value for that one-degree square will be zero. This file is used in plotting routines to "mask" or cover up areas with three or less observations (see maps in the World Ocean Atlases for fields plotted using these masks).
A. DOCUMENTATION DESCRIBING THE QUALITY CONTROL PROCEDURES: (a) Boyer, T.P. and S. Levitus. 1994. Quality control and processing of historical temperature, salinity and oxygen data. NOAA Technical Report NESDIS 81. U.S. Department of Commerce. Washington, D.C. 65 pp. (b) Conkright, M.E., T.P. Boyer and S. Levitus. 1994. Quality control and processing of historical nutrient data. NOAA Technical Report NESDIS 79. U.S. Departement of Commerce, Washington, D.C. 75 pp. B. DOCUMENTATION DESCRIBING THE ANALYSIS PROCEDURES AND THE DATA DISTRIBUTION AND ANALYSIS: (a) Conkright, M.E., S. Levitus and T.P. Boyer. 1994. World Ocean Atlas 1994 Volume 1: Nutrients. NOAA Atlas NESDIS 1. U.S. Department of Commerce, Washington, D.C. 150 pp. (b) Levitus S. and T.P. Boyer. 1994a. World Ocean Atlas 1994 Volume 2: Oxygen. NOAA Atlas NESDIS 2. U.S. Department of Commerce, Washington, D.C. 186 pp. (c) Levitus S., R. Burgett and T.P. Boyer. 1994b. World Ocean Atlas 1994 Volume 3: Salinity. NOAA Atlas NESDIS 3. U.S. Department of Commerce, Washington, D.C. 99 pp. (d) Levitus S. and T.P. Boyer. 1994c. World Ocean Atlas 1994 Volume 4: Temperature. NOAA Atlas NESDIS 4. U.S. Department of Commerce, Washington, D.C. 117 pp. C. DOCUMENTATION DESCRIBING THE NON-ARCHIVED NODC DATA USED: Levitus, S., R. Gelfeld, T. Boyer and D. Johnson. 1994e. Results of the NODC and IOC Oceanographic Data Archaeology and Rescue Projects. Key to Oceanographic Records Documentation No. 19, NODC, Washington, D.C. D. DOCUMENTATION DESCRIBING THE NODC ARCHIVED DATA USED: Levitus, S. and R. Gelfeld. 1992. NODC Inventory of Physical Oceanographic Profiles. Key to Oceanographic Records Documentation No. 18, NODC, Washington, D.C. Appendix 1. Description of flags used in the quality check of observed and standard level data. ERROR FLAGS WHOLE-PROFILE FLAGS (AS A FUNCTION OF PARAMETER) 0 - accepted profile 1 - failed annual standard deviation check 2 - two or more density inversions (Levitus 1982 criteria) 3 - flagged cruise 4 - failed seasonal standard deviation check 5 - failed monthly standard deviation check 6 - failed annual and seasonal standard deviation check 7 - failed annual and monthly standard deviation check 8 - failed seasonal and monthly standard deviation check 9 - failed annual, seasonal, and monthly standard deviation check FLAGS ON INDIVIDUAL DEPTHS AND OBSERVATIONS Depth Flags: 0 - accepted value 1 - error in recorded depth (same or less than previous depth) 2 - temperature inversion of magnitude > 0.3 degrees/meter 3 - temperature gradient of magnitude > 0.7 degrees/meter 4 - temperature gradient (of > 0.7 degrees/meter) followed closely by a temperature inversion (of > 0.3 degrees/meter) or vice versa Observed Level Flags: 0 - accepted value 1 - range outlier (outside of range check) 2 - density inversion 3 - failed range check and density inversion check Standard Level Flags: 0 - accepted value 1 - bullseye marker 2 - density inversion 3 - failed annual standard deviation check 4 - failed seasonal standard deviation check 5 - failed monthly standard deviation check 6 - failed annual and seasonal standard deviation check 7 - failed annual and monthly standard deviation check 8 - failed seasonal and monthly standard deviation check 9 - failed annual, seasonal and monthly standard deviation check EXPLANATION OF ERROR FLAGS A. CHECK FOR DEPTH INVERSIONS AND DUPLICATE DEPTHS Depth error flags: (1) If the second of two successive depths is shallower than the first (a depth inversion), the second depth will be marked with a flag value = 1. (2) If two successive depths are shallower than the first depth, every depth reading following the first will be marked with a flag value = 1. (3) If two successive depth readings are equal, the second reading will be marked with a flag value = 1. (4) All correct depths are marked with a flag value = 0. B. STANDARD DEVIATION CHECK ON STANDARD LEVEL DATA This check calculates the mean and standard deviation of five-degree square latitude-longitude boxes for annual (all parameters), seasonal (temperature, salinity, and oxygen), and monthly (temperature and salinity) periods. Data are flagged if (1) a value is five standard deviations away from the mean in coastal waters (defined as any five-degree grid box adjacent to a land grid point or any five-degree grid box with a bottom depth of less than 200 m); (2) a value is four standard deviations away from the mean in near coastal waters or near the ocean floor (defined as any one-degree grid point where the depth is equal to or less than the depth in an adjacent one-degree box) or any adjacent five-degree grid box is designated coastal; (3) a value is three standard deviations away from the mean in open ocean; (4) if a profile contains two or more standard deviation failures, the whole profile is flagged. C. DENSITY CHECKS FOR TEMPERATURE AND SALINITY PROFILES The criteria for an instability are described by Levitus (1982). Flags are assigned (1) for density inversions at the depths where they occur in the observed and standard level profiles; (2) when two or more density inversions (or instabilities) occur in a standard level profile. The entire profile is then flagged. [Note: Stability checks were performed on observed as well as standard level data. Observed level flags are included for information only, since they were not used to exclude any data from the profile data sets. Whole-profile flags for stability and standard deviation checks are for standard level data only. For informational purposes, if a standard level profile includes a whole profile density flag (or standard deviation flag), the observed level data will also include a whole profile flag.] D. CRUISE FLAGS Indicates all profiles from a cruise have anomalous data. E. BULLSEYE FLAGS Flags individual depths with anomalous data which cause ripple effects or "bullseyes" in the contoured objectively analyzed data.