Surface water dynamics and phytoplankton communities during deposition of cyclic late Messinian sapropel sequences in the western Mediterranean

This succession shows similar characteristics in the four studied cycles, allowing us to interpret surface water dynamics in this region on orbital time scales. The top of the sapropel represents a warm, low salinity and well stratified episode under a situation of maximum insolation. A well developed pycnocline and oligotrophic conditions (moderate production of calcareous phytoplankton) coinciding with anoxic conditions at the bottom enhance the preservation of organic matter, and consequently generate a sapropel. Diatomites are deposited under a situation of unstable pycnocline that produce an increase in productivity in surface waters. Diatoms significantly deplete limiting nutrients, and consequently calcareous nannofossils start to be dominant again in the water column as result of a progressive stabilization of the pycnocline.