Palaeoclimate and the formation of sapropel S1: inferences from Late Quaternary lacustrine and marine sequences in the central Mediterranean region

Synchronous responses to climatic changes during the Late Pleistocene-Holoc ene transition are inferred from marine and lacustrine stratigraphic record s in the central Mediterranean region, New stratigraphic data are presented from well-dated sequences in the Meso-Adriatic Depression (MAD), two crate r lakes in the Lazio region, and in the Tyrrhenian Sea. The sequences all s pan the last termination and the Holocene, but we focus here on the evidenc e in each record for the time period during which sapropel S1 formed in the Mediterranean (ca, 9.0 to 6.8 cal kyr B.P.). The new records provide evide nce of palaeoenvironmental changes on land and sea that can be reconstructe d at a high temporal resolution, and which throw some light on the processe s which led to the formation of S1. The collective evidence indicates that: (i) organic-rich sediments occurred in both the marine and the crater lake sites during the time of formation of the S1 sapropel; (ii) there is evide nce of increased stratification and anoxia in the sea-water column during t he period of S1 formation; (iii) the S1 period in the study area is divisib le into two subphases (S1a and S1b), which reflect short-term variations in oceanographic conditions (stratification and anoxia); (iv) changes in stra tification in the marine column were contemporaneous with regional climate variations that are inferred from the terrestrial records. We conclude that the key factor that initiated the formation of S1 was increased discharge of freshwater into the Mediterranean following a change post-9.0 cal kyr B. P. to a warmer and wetter climate. Furthermore, the period of S1 formation was interrupted by a short-lived episode (ca. 500 years) of comparatively c ooler and drier conditions during the Early-Middle Holocene transition (EMH T). (C) 2000 Elsevier Science B.V, All rights reserved.