Late Miocene benthic stable isotopes in the Gibliscemi section (Sicily): Correlation to Mediterranean and open ocean stable isotope records

Abstract

During the Late Miocene, the earth’s climate was subjected to cooling through ice sheet expansion. In the Mediterranean this cooling phase happened together with restriction of inflow of surface water from the Atlantic Ocean causing rising salinities. These variations in salinity, temperature and ice volume of the bottom waters are recorded in the stable isotopes of benthic foraminifera. These longer term trends are modulated by shorter climate variations as Milankovitch cycles. Very little benthic stable isotopes studies are performed during the Late Miocene for both the Mediterranean and the open ocean. The Gibliscemi composite section (Sicily, Italy) with its independent age model is a good candidate for benthic stable isotope chemistry. This has not been done due to scarcity of benthic foraminifera, which is no longer a problem with present-day mass spectrometry. Here, a δ13C and δ18O record of the Gibliscemi A/B sections are presented from 9.7-7.2 Ma. In the Mediterranean, the records show that correlation between Metochia and Gibliscemi is possible, although the mechanisms of bottom water formation do differentiate. From the δ18O records the amount of δ18O increases caused by salinity could be calculated. The δ18O record of Gibliscemi shows similar forcing mechanism as open ocean records during the Late Miocene and Pliocene, with a dominating obliquity forcing, which can be correlated to other open ocean records, like ODP 926, 982 and 1085. These correlations show a normal phase relations, as observed in the Pliocene, up to 8.5 Ma. After 8.5 Ma, an anticorrelation is found with the obliquity solution, which is consistent with the open ocean records. Therefore, the obliquity or the values for tidal dissipation are incorrect. The correlations between the Gibliscemi section and the open ocean records are used to label individual δ18O excursion to a similar fashion as in the Pliocene. The Gibliscemi section, or other Mediterranean sections, or a combination of these can be used as a stratigraphic backbone, through their independent age models based on sapropel interference patterns, which gives a higher age model resolution. In combination with the δ18O labels the Gibliscemi δ18O record can contribute to more accurate age models and a consensus in Late Miocene isotope stratigraphy.