Late Quaternary paleoclimatic and paleoenviromental changes in Tyrrhenian Sea

Paleoclimatic and paleoenvironmental changes that occurred in the Tyrrhenian Sea during the last 26 kyr are investigated in this paper. Isotopic and micropaleontological studies on foraminifers, supported by radiometric and sedimentological analyses, are carried out in a high-resolution core from the upper continental Tyrrhenian slope, near the Ombrone River mouth. The location of the studied core allows us to obtain both paleoclimatic data and results concerning the transgression caused by the last deglaciation, while previous paleotemperature reconstructions are based on deep-sea, or on coastal proxies like coral reefs and spelean serpulids. Cumulative curves of cold and warm-water species presented were derived from Hierarchical Cluster Analysis (HCA). Comparing these curves with those of Globigerina bulloides delta O-18 and delta(13) C results on paleoclimatic events of the Late Quaternary were obtained. Faunal and isotopic proxies concur and were used to isolate seven climatic zones, corresponding to the well-known climatic episodes of the last glacial-post-glacial cycle. During the Late G(l)acial, three main climatic episodes were recognised: Last Glacial Maximum (LGM), centred at about 22.5 kyr BP, during which our proxies indicate the lowest temperatures; Bolling-Allerod, between 15.0 and 12.5kyr BP, characterised by rapid climatic fluctuations; Younger Dryas (YD), centred at about 11.4kyr BP, with Sea Surface Temperature (SST) not dissimilar to that of LGM. A brief time span of about only 500 years separates the YD climax from the first appearance of seasonality that is typical of Holocene. On the whole, the transition between glacial peak and full Holocene conditions spans about 1000 years. Foraminiferal, isotopic and sedimentological data agree in excluding important bathymetric changes during glacial times. A rapid sea-level rise is recorded at the onset of the Holocene, with a mean rate of about 23 mm/yr calculated between 10.9 and 8.3 kyr BP. Three distinct phases of water circulation regimes were evidenced in the course of Holocene. During Pre-boreal and Boreal chronozones (10.9-8.3 kyr BP) a marked seasonality has been recognised. It corresponded to a homogeneous. water column, favoured by efficient vertical mixing during the winter and by warm stratified water column and oligotrophic surface waters during the summer. Both faunal and isotopic record indicate, from 8.3 to 5.2 kyr BP, well-stratified water column with a low-salipity layer in surface waters, probably marking its climax at 6.2 kyr BP. Such conditions correspond to the deposition of sapropel S1 in the eastern Mediterranean Sea. The subsequent paleoceanography is characterised by the establishment of the winter convection and vertical mixing typical of the Modern Tyrrhenian Sea. (c) 2005 Elsevier Ltd. All rights reserved.