LA-ICP-MS analyses on coral growth increments reveal heavy winter rain in the Eastern Mediterranean at 9 Ma

Sediment particles incorporated into coral skeletons reflect variation in composition and amount of suspended material in ambient water during coral growth. They can be used to identify periods of enhanced storm frequency and associated freshwater discharge. Tortonian (Late Miocene) Porites corals from Crete (Aegean Sea, Eastern Mediterranean) show pronounced annual density bands in X-ray photographs. δ 18O compositional variability reflects the annual banding equivalent with a ~ 7 °C annual sea surface temperature (SST) cycle over a seven-year period. Fine sediment particles are concentrated in layers with skeletal porosity parallel to growth increments. Variations in the chemical composition of coral skeletons can result from changes in the environment. Therefore, variations in element concentrations with a spatial resolution of ~ 500 µm along a transect perpendicular to growth increments were measured using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Complementary X-ray diffraction, X-ray fluorescence and scanning electron microscope analytical techniques were applied in order to characterize the sediment particles. Besides Sr/Ca and U/Ca variability indicating SST seasonality, the alternation of layers of pure aragonite and layers of aragonite coated with sediment particles (e.g., kaolinite, montmorillonite, quartz) is reflected in systematic variations in major and trace element concentrations. This element pattern results from a seasonal environmental mechanism where periodically enhanced input of sediment particles into the coral reef environment causes high concentrations of non-lattice bound elements (e.g., Al, Mn, Mg). Potential sources for the non-lattice bound elements (i.e., elements related to the clay minerals) such as airborne Saharan dust, Nile-derived sediment suspension as well as volcanic ash fall can be excluded on the basis of chemical, mineralogical or geological evidence. In contrast, normalized element patterns indicate that the clay minerals represent weathering products of local rocks, e.g., ophiolites, which at present crop out on Crete in mountainous areas, and formed islands exposed to erosion during the Late Miocene. High concentrations of the non-lattice bound elements correlate with low SSTs of the winter months. The discrepancy in SST estimations between δ 18O and Sr/Ca seasonality suggests that fresh water originating from intense winter rain caused a reduction of the annual δ 18O amplitudes a