Late Glacial-Holocene transition in the southern Adriatic Sea: Coccolithophore and Foraminiferal evidence

摘要

A detailed micropaleontological analysis was performed in core SA03-01, recovered in the southern Adriatic basin, in the framework of the EC-project EUROSTRATAFORM. The results of an integrated study based on calcareous nannofossils and foraminifera, during the Late Glacial-Holocene transition, are here presented. This study reports high runoff input from the near Apennines during the lowermost phase of the Greenland Stadial 1 /Younger Dryas (GS-1 /YD), as well as the presence of cold and productive waters. More arid conditions and enhanced seasonality contrast are inferred upwards. The Pre-Boreal is marked by the initial development of the warm and oligotrophic coccolithophore group, reflecting an overall warming trend since the beginning of the Holocene. Within this warming, three short-lived cold and dry episodes have been detected in the foraminifer record. During the deposition of Sla equivalent (9.7 kyr), the coccolithophore and foraminifer records reflect a widespread temperature increase of surface waters and oligotrophic conditions. Moreover, the high development of Florisphaera profunda and the absence of the genus Globorotalia are indicative of strong water stratification, responsible for very critical oxygen conditions in the sea floor, which in turn allowed the formation of the sapropel layer. The SI interruption (8.6-8.2 kyr) is recorded by a general opposite behaviour of the coccolithophore species when compared to that exhibited during the previous phase. The unexpected peak of F.profunda may be explained by the wetter conditions associated to the cold and multicentennial 8.2 kyr event in Europe. However, the foraminifer data suggest that this period is characterized by moderate cooling and a slight increase of oxygenation in the sea floor. During the S1b eq. interval, the coccolithophore records suggest the reoccurrence of a shallow pycnocline, which may result of the presence of surface turbid and fresh waters. Based on foraminifer data, this second phase of the sapropel is relatively colder than the first one, even if its base is characterized by a slight temperature increase.