Depth-temperature evaluation of selected California and Mediterranean bathyal foraminifera

Abstract

The Mediterranean Sea is essentially a closed complex basin with maximum depths of about 4,600 m and a sill depth at Gibraltar of about 320 m. At similar depths, values for temperature, salinity, and oxygen content are significantly higher in the Mediterranean than in the sea off California. Prominent deeper bathyal foraminiferal zonation off southern California is not duplicated in the Mediterranean, probably because of the control of sill depth in the latter. Foraminifera common to the two areas may be categorized into isobathyal and heterobathyal groups. Isobathyal species, those with the same upper depth limits in various oceanic areas, provide some evidence of depth zonation in the Mediterrenean Sea which is common to California. It is postulated as follows: 100 m ± 50 m Hoeglundina elegans ( d'Orbigny) Uvigerina peregrina Cushman 200 m ± 50 m Gyroidina soldanii altiformis Stewart et Stewart 700 m ± 100 m Globobulimina pyrula spinescens ( Brady) Cibicides wuellerstorfi ( Schwager) occurs in the two areas with an upper depth limit of about 1,200 m; elsewhere it occurs as a rare species between depths of 500 and about 2,400 m, it is more characteristic of depths below 2,400 m. Additional sample control is needed in the Mediterranean and California regions to establish the precise zonation for this species. Heterobathyal species are those with different upper bathymetric limits in contrasting oceanic bodies; those common to the Mediterranean and the sea off southern California include some spinose buliminids, Stainforthia complanata ( Egger), and Sigmoilina tenuis ( Czjzek). Isobathyal species exhibit depth control rather than dependence upon temperature. Some heterobathyal species occur in shallow warm waters in one case and in deep colder waters in other cases, others occur in shallow cooler waters in one area and in deeper and warmer waters in other areas. Thus, both groups show little correlation with temperature.