WORK OF THE 'CARNEGIE' 115 



approximately at right angles to the Peruvian Current and may be termed cross-sections, 

 while two, from Sts. 50-45 and from 60-70, are almost parallel to the current and may 

 be called longitudinal sections. This observation may be considered open to question, 

 for the sections above described seem to be orientated respectively at right angles and 

 almost parallel to the intermediate Antarctic current, and not to the surface currents as 

 figured schematically. In relation to the latter, the sections tend to encircle the centre of 

 anticyclonic movement and in consequence to illustrate the surface current longi- 

 tudinally in some parts and transversely in others. The significance of these salinity 

 sections will therefore be better understood in relation to the Peru Current, when the 

 surface currents and the trend of the surface circulation have been defined for the year 

 in question : it will be possible then to decide the angle at which the several sections cut 

 across the current. 



The two sections which run more or less parallel to latitude show an increase of sur- 

 face salinity when departing from the coast. In the more northerly of the two sections 

 (Sts. 40-45), this is attributed to the presence of water from the Gulf of Panama (water 

 of the Equatorial Counter-current), lying close to the Ecuador coast. The rate of in- 

 crease is, however, very slow, which suggests that the section runs very much more with 

 the current than across its path. Westwards of 90° W long., the section may be taken 

 to represent the South Equatorial Current. 



In the next section (Sts. 70-80) the low surface salinity inshore may indicate that the 

 water has welled up from the lower layers near the coast of Peru. In this latitude the 

 salinity increase on departure from the coast is such that the surface drift may also be 

 inferred to have a marked westerly component, the concentration of surface salinity at 

 greater distances from the coast being brought about presumably by evaporation of the 

 surface layers. This section, which illustrates conditions in the Peru Current at much 

 greater distances from land than any of our own, will be referred to in greater detail 

 later (Fig. i). 



The other sections show an increase of surface salinity from south to north, but the 

 increase is less rapid near the coast (Sts. 60-70) than further west (Sts. 60-50). More- 

 over, as noted above, the surface salinity is of a lower order near the coast than in the 

 open sea. Sverdrup suggests that this is due to a constant transport of water of low 

 salinity from the south, but, in view of the westerly set noted above, this impoverishment 

 of surface salinity near the coast may be regarded as further evidence of upwelling. 



In January and February 1929 when the 'Carnegie' ran her line westwards of Callao 

 (Sts. 70-80, Fig. i), she recorded an increase in surface salinity from just over 35 °l^^ 

 at St. 70, at 80 miles or so ofi^shore, to more than 36 %o in 105° W long. The salinity 

 of the intermediate Antarctic layer is about 34-5-34-6 °j^^. At the western end of the 

 section, that is west of lOO' W long., a sharp salinity gradient separates the surface water 

 from water below 250 m. This sharp gradient exists betvYcen the isohalines of 36-0 and 

 34'7 °/oo ^^'^ constitutes a discontinuity layer. Above this layer the water seems to be 

 tropical. At the eastern end of the section no discontinuity layer is present, the isohalines 

 increasing gradually from the low value of 34-6 "/^^ in the intermediate Antarctic layer 



