Simulations of ecosystem response during the sapropel S1 deposition event

A one-dimensional ecosystem numerical model is used to simulate the ecosystem changes that could have occurred in the open
ocean areas of the Eastern Mediterranean Sea during the Climatic Optimum interval (9500–6000 B.P., Mercone et al. [Mercone, D.,
Thomson, J., Croudace, I.W., Siani, G., Paterne, M., Troelstra, S., 2000. Duration of S1, the most recent sapropel in the eastern
Mediterranean Sea, as indicated by accelerator mass spectrometry radiocarbon and geochemical evidence. Paleoceanography 15,
336–347]). In this period the S1 sapropel was deposited. S1 is the most recent sapropel in the succession of organic carbon-rich
layers intercalated in normal Neogene sedimentary sequences. Different theories have been invoked in order to explain the
deposition of this peculiar layer. Our simulations seem to indicate that the modified thermohaline circulation, supplying oxygen
only in the first 500 m of the water column, is responsible for the sapropel deposition when higher productivity is allowed in the
euphotic zone. The model shows the importance in this process of bacteria that consume oxygen by decomposing the Particulate
Organic Matter (POM) produced in the upper water column. The sinking velocity of POM partially regulates the timescale of the
occurrence of anoxia at the bottom and in the whole water column, allowing the relatively rapid onset of sapropel deposition.

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