3. EQUIPMENT AND INSTRUMENTS 



95 



should be taken directly or the data adjusted 

 by interpolation from the distribution at 

 other levels. The standard depths, in meters, 

 are: 0, 10, 20, 30, 50, 75, 100, 150, 200, (250), 

 300, 400, 500, 600, (700), 800, 1000, 1200, 

 1500, 2000, 2500, 3000, 4000, and thence at 

 1000 meter intervals to the bottom. The 

 depths in parenthesis are optional. Refer to 

 H.O. Pub. 607 for detailed instructions cov- 

 ering observation procedures. 



Several factors influence the spacing of 

 sample bottle depths, particularly in the up- 

 per layers, in turbulent water, and in areas 

 of upwelling or where temperature inver- 

 sions occur. It is desirable to determine the 

 temperature curve accurately from surface 

 to bottom. A BT lowering to maximum 

 depth should be made at each oceanographic 

 station. The BT trace will show temperature 

 gradients, disclose the existence of inver- 

 sions, and assist in selection of appropriate 

 depths for sampling. Steep gradients may 

 require closer spacing of the bottles. 



Because oceanographic data are assembled 

 from many sources on a nation-wide basis 

 and processed by machines, it is desirable 

 to use the International Standard Depths. 

 When serial temperatures and salinities are 

 observed for correction of soundings in rela- 

 tively small project areas and the register- 

 ing sheave is graduated in fathoms, observa- 

 tions should be taken at the following ap- 

 proximate depths: 0, 2, 10, 20, 30, 50, 75, 

 and 100 fathoms. 



3-117 Protected reversing thermometers. 



— Two types of protected reversing ther- 

 mometers are used by the Coast and Geodetic 

 Survey. One has a scale graduated to 0.2 

 degree C. and without an enclosed auxiliary 

 thermometer. It is used in a Tanner-Sigsbee 

 Reversing Frame. The second type is some- 

 what larger, is graduated to 0.1 degree C, 

 is accurate to a few hundredth of a degree, 

 and has an auxiliary thermometer enclosed 

 (Fig. 34). This is a more precise thermome- 

 ter and should always be used in Nansen 

 Bottle casts at oceanographic stations. Re- 

 quisitions for protected reversing thermom- 

 eters should state the type desired — that is. 



Figure 34. — Precision type deep sea reversing ther- 

 mometers, unprotected on left, protected on right. 



