From Ocean Teacher Library

Standard Depths for Marine Measurements

Contents 1 Background 2 Standard Depths (m) Table 3 Additional Levels 4 Subsections of this Article 5 Information about this article 6 Contact

Background

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 only 99 m or 98 m, for example. 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 (m) Table

0   100  1000
10  125  1100
20  150  1200
30  200  1300
50  250  1400
75  300  1500
    400  1750
    500  2000
    600  2500
    700  3000
    800  4000
    900  5000

Additional Levels

• 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.
• The World Ocean Atlas series uses these depths for its analyzed fields, plus 3500, 4500 and 5500m

Subsections of this Article

No subsections available

Information about this article

Short title: Standard Depths

Description: none

Expertise level: beginner

Author: Murray.Brown

Approval status: approved

Approved by: Murray.Brown

Last change: 2009-9-1

Subsection of: Marine Data Standards

Contact

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