Calcareous nannofossil paleoecology in the sapropel S1 of the eastern Ionian sea: paleoceanographic implications

A high-resolution study performed by means of calcareous nannofossils on two box cores located in the South Eastern Ionian basin allowed recognition of fluctuations in the assemblage, which can be related to the climatic and paleoceanographic changes that occurred during the deposition of the Holocene Sapropel S1. This study reports a decrease of the coccolith abundance and of the genus Reticulofenestra in the S1 sapropel interval considered as whole with its Mn and Fe oxidized intervals. Florisphaera profunda shows an increase at the base of the dark Corg rich interval, while Helicosphaera carteri and Rhabdosphaera claviger show an increase in abundance within the Fe enriched interval of the oxidized sapropel. Braarudosphaera bigelowii is very rare in the interval studied as a whole, however, it shows a small but significant increase in abundance in the Mn enriched interval of the oxidized sapropel. Sapropel deposition is probably related to important climatic changes that influenced the abundance of the various nannofossil species as a function of their paleoecological preferences. Our results indicate that three different paleoceanographic phases exist in S1, suggesting eutrophication at the beginning of S1 deposition, followed by an intermediate stage characterized by nutrient depletion and, finally, by stagnation.