9 
The average vertical distance is given between the neighbour water samples (Fig. 3). 
Historical profiles have generally a rather poor vertical resolution, with distances between 
samples exceeding 400 meters for depths below 1500 meters. Results depicted in Fig. 3 
were used to compromise on the maximum ’’gap” size between the bottles of the cast 
allowing a vertical interpolation of water properties. Most of the data were obtained between 
Number of Observations (*1 OOO) 
O 10O 200 300 400 500 600 700 
Fig. 3: Average spacing between observed levels versus sample depth. 
Fig. 4: Number of profiles per year (a) and per month (b). 
1960-1990 (Fig. 4a). An apparent decrease of the data acquisition rate during the last 
decade is explained by the lag between the data acquisition and its availability to the 
oceanographic community. The overall sampling is biased to the summer period of the 
Northern Hemisphere (Fig. 4b).