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

Abstract

Synchronous responses to climatic changes during the Late Pleistocene–Holocene transition are inferred from marine and lacustrine stratigraphic records in the central Mediterranean region. New stratigraphic data are presented from well-dated sequences in the Meso-Adriatic Depression (MAD), two crater lakes in the Lazio region, and in the Tyrrhenian Sea. The sequences all span the last termination and the Holocene, but we focus here on the evidence 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 evidence of palaeoenvironmental changes on land and sea that can be reconstructed at a high temporal resolution, and which throw some light on the processes 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 evidence of increased stratification and anoxia in the sea-water column during the period of S1 formation; (iii) the S1 period in the study area is divisible into two sub-phases (S1a and S1b), which reflect short-term variations in oceanographic conditions (stratification and anoxia); (iv) changes in stratification 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 cooler and drier conditions during the Early–Middle Holocene transition (EMHT).