Standard Depths for Ocean Measurements
From OceanWiki_EN
Oceanographic measurements have traditionally been taken at standard "nominal" depths, based originally on the length of wire cable that was let out from the ship to suspend the instrument or the sampling device. The word "nominal" means that it was always well known that the label placed on the sample was probably inaccurate due to the angle of the wire in the presents of currents. Thus, a "100-m" sample could have been taken at 99 or 98 m. Only during processing of the reversing thermometer data (or from physical measurement of the wire angle) was a final, correct depth assigned to the data. Nevertheless, oceanographers have always attempted to make their measurements at a set of standard depths, selected to capture the salient features of the stratified sea.
Other factors, including the move toward extensive use of electronic sensors (especially the CTD and its ancillary sensors), as well as the move toward use of pressure instead of depth as the Z-variable in ocean datasets, make the story of standard depths more complicated. We focus in OceanTeacher on the use of meters (as used in the World Ocean Database). These levels are often used in atlases as the depths of the variables to be analyzed. Standard Depths Table (m)
0
10
20
30
50
75
100 1000
125 1100
150 1200
200 1300
250 1400
300 1500
400 1750
500 2000
600 2500
700 3000
800 4000
900 5000
Additional Levels
To these levels, the World Ocean Atlas series adds 3500, 4500, 6000, 6500, 7000, 7500, 8000, 8500 and 9000 m. NOTE: During several recent major global programs, special measurements at other depths have been added to the "standard depths" in order to capture specific phenomena in the ocean. Data managers must always be aware that these additional depths may be present in the data.
Source: OceanTeacher.org, International Oceanographic Data and Information Exchange (IODE) Programme of the Intergovernmental Oceanographic Commission of UNESCO (IOC)
