Benthic foraminiferal evidence for reduced deep-water circulation during sapropel deposition in the eastern Mediterranean

Abstract

An analysis of deep-sea benthic foraminifera from six eastern Mediterranean piston cores was carried out to determine the faunal response to the deposition of sapropel S5, formed between 125,000 and 116,000 yrs B.P. The pre-S5 population is the most diverse, being composed of miliolids, Articulina tubulosa, Gyroidina spp., and various rotaliids. An assemblage found near the base and top of S5 is dominated by Chilostomella mediterranensis, Globobulimina affinis, and Bolivina spp, and the post-S5 fauna is dominated by A. tubulosa and Gyroidina spp. The faunal data are interpreted in terms of the microhabitat preferences of the fauna, based on living (stained) benthic foraminiferal data and associated morphological characteristics from the North Atlantic. Epifaunal species dominate pre-S5 and post-S5 sediments and are associated with low organic carbon values ranging from 0.1 to 0.4%. Infaunal species, occurring near or within sapropel layers, are found with organic carbon values of >0.7% and live in environments characterized by low dissolved oxygen levels. The dominance of epifaunal species within the pre-S5 and post-S5 sediments is interpreted to reflect low levels of food in a well-oxygenated environment, while the low abundance and dominance of infaunal taxa at the base and top of S5 reflects low food and low oxygen conditions. Although an increase in surface productivity may have occurred immediately preceding and during the deposition of S5, the critical factor in deposition of sapropel S5 is anoxia resulting from reduced ventilation of the deep waters. The similarity of the faunal patterns in the six cores suggests that bathyal environmental conditions were uniform in the eastern Mediterranean at depths ranging from 2042 to 3150 m during deposition of sapropel S5.