UPWELLING 201 



depth, the minimum estimate may have been unduly lowered through mixture of the 

 upwelled water with its surroundings. This is shown to be probable by consideration 

 of the state of the hydrological conditions antecedent to our visit. Pichidanque Bay has 

 been shown to be a locality where upwelling had not been active for some time ; and at 

 Caldera mixing on a considerable scale would have been a natural consequence of the 

 eddy and the changes of wind noted on pp. 125-7. At Callao, upwelling was not only 

 allayed, but the inshore water might have been subsiding (p. 209). At these localities the 

 discrepancy between the minimum and maximum estimates may imply a capacity for 

 greater upwelling than was observed at the time of our visit. The homogeneity of the 

 upper layers off the Lobos Islands and Punta Aguja is also evidence that mixture had 

 been extensive, but whether at these localities upwelling was not at its height, is 

 uncertain. Thus we see that different depths are affected according to circumstances. 

 Upwelling brings up water from a depth of 40 m. at least, and more usually 100-130 m., 

 and depths of 180-360 m. may sometimes be touched (Table XVII). If the figures are 

 averaged, the mean upwelling depth is shown to be by temperature 123 m., and by 

 salinity 143 m., themselves giving a mean of 133 m. The mean minimum and mean 

 maximum upwelling depths are given in the table. 



Table XVII. Showing the estimated depth from which water wells up and the greatest depth 



affected by upwelling 



The minimum depth from which water wells up is judged by the depth offshore of the isotherm (and isohaline) corresponding 

 to the value of the inshore temperature (or salinity) at the surface. The maximum depth affected by upwelling is judged by the 

 greatest depth at which isohalines and isotherms show signs of rising up towards the shore from their normal depth. 



