Archive | 2021
Climate and carbon cycle changes drive the hydrographic configuration of the eastern Mediterranean through the Tortonian-Messinian Transition
Abstract
The Late Miocene has been considered one of the most climatically stable periods of the Cenozoic, time span characterized by minor long-term cooling and ice growth. Especially, the TortonianMessinian Transition is recognized as a priority for paleoenvironmental reconstruction and climate modelling due to the significant paleoenvironmental changes preceding the Messinian Salinity Crisis (MSC; 5.97-5.33 Ma). Here, we present stable oxygen (δ 18 O) and carbon (δ 13 C) isotopes measured on benthic and planktonic foraminifera from Potamida section (Crete Island, eastern Mediterranean). The δ 18 O results indicate a decoupling between the surface and the bottom water column starting before the Tortonian-Messinian boundary. The difference between planktonic and benthic oxygen isotope signals (Δδ 18 O) further provides an estimate of the degree of water column stratification during that time. The δ 13 C data indicate a generally trend towards lighter values as an excellent illustration of the Late Miocene Carbon Isotope Shift (LMCIS; 7.6-6.6 Ma) due to progressive restriction of the Mediterranean basin, with the exception of the 7.38-7.26 Ma time interval where significantly heavier δ 13 C values are documented in both records. Such changes in carbon cycle seem to be most pronounced in the planktonic foraminiferal record (surface waters) through a 6-cycle development indicative of a cyclic productivity pattern during the latest Tortonian. The entire record is substantiated by sea surface temperature (SST) estimates based on TEX 86 biomarker based proxy. The reconstructed SST record shows that a warm phase characterized the late Tortonian sea surface (~270C), time followed by a strong, steady cooling starting with earliest Messinian, when the SSTs dropped to values as low as 200C. The outcome of the combined stable isotope and biomarker based SST data hint to increased salinity in the surface waters already before the Messinian, while at the Tortonian-Messinian Transition, the conditions in the surface waters changed towards cooler (~240C) and normal salinity conditions.