Distribution of planktonic Foraminifera in some Mediterranean sediments 205 



Aegean Sea. The depth of the surface-water layer in the Mediterranean is approxi- 

 mately 200 m or less. Although planktonic Foraminifera have been found living at 

 greater depths it is probable that they are most abundant in the upper layers (Phleger, 

 1954) and it is assumed here that the characteristics of the surface layer are those to 

 which they are adapted. 



The eastern and western basins of the Mediterranean are separated by a sill, 

 between Sicily and Tunis, having a maximum depth of about 400 m. The western 

 basin (Tyrrhenian Sea and Algiers-Provengal Basin) is separated from the Atlantic 

 by a sill depth of 320 m. Water enters the Mediterranean from the Atlantic and passes 

 from the western basin to the eastern basin by surface currents. In both cases water 

 flows westward at intermediate depths. A study of numerous sources of information 

 shows that the surface temperature variation in the western area is approximately 

 13" C to 24^ C, the warmest season being in July-August and the coldest in February- 

 March. Greater extremes are found at various near-shore areas, especially along the 

 coast of France. The temperature of the surface water just east of Gibraltar in 

 August, 1938, was 19-5° C rising to 24° C farther east (Rough, 1940). Surface 

 salinities vary from 36°j^^ at Gibraltar to 3^°Uo "^^r Sicily. Variable salinities are 

 often found at near-shore localities. In 1949-50 at Monaco there was a winter variation 

 from 36-8° ;, to 38-5°/„, and at Algiers 34-57,,. to 37-67'oo (Kruger, 1950). The 

 eastern basin (Ionian Sea and Levantine Basin) apparently contains surface water 

 derived chiefly from the west via the surface current through the Sicily-Tunis gap. 

 The deep water, according to Pollak (1951), is all derived from the Adriatic Sea. 

 Little is known at present about the influence of the Suez Canal, but it is probable that 

 any water derived from this source would quickly lose its identity. Surface tempera- 

 tures in this area vary from 16° C to 24° C in the western part and 16° C to 28' C in 

 the extreme east. Surface salinities vary from 38°/,, in the west to appro.ximately 

 39-5°/,, in the east but here again local variations may occur near shore. An example 

 of this is the comparatively low salinity of 30° ,, found ofi"Gaza, Israel, in September, 

 1947, due probably to the Nile flood (Oren, 1952). Surface currents enter the Aegean 

 Sea from the southeast and from the Black Sea. Surface temperatures vary from 

 13° C to 25° C and surface salinities from approximately 30° ,, near the Dardanelles 

 to 39°/,, just north of Crete. Due to the counter-clockwise surface circulation, 

 salinities on the eatern side are higher than those on the western. 



These data show that there are lower winter temperatures and somewhat lower 

 salinities in the western than in the eastern Mediterranean. In the Aegean there are 

 lower winter temperatures than in the eastern area and a complex salinity pattern 

 with comparatively low salinities in the northern part. 



Conditions in the Atlantic immediately west of Gibraltar are also of interest. 

 Here the surface temperature variation is somewhat less than in the Mediterranean, 

 16° C to 22' C. The surface salinity is somewhat less than that obtaining at Gibraltar. 



DISCUSSION OF PLANKTONIC POPULATIONS 

 The identifications of the planktonic species are in most cases the same as those 

 given by Phleger, Parker and Peirson (1954) in their study of Atlantic deep-sea 

 cores Some species groups, as defined here, contain forms recognized as species or 

 varieties by some authors. Their omission does not necessarily indicate that they are 

 believed to be invalid. Glohigerinoides rubra probably includes, or in some cases is 



