Evidence for short-lived oscillations in the biological records from the sediments of Lago Albano (Central Italy) spanning the period ca. 28 to 17 k yr BP

We report the results of analyses of pigments (derived from algae and photo synthetic bacteria), diatoms and invertebrate fossil remains (ostracods, cl adocerans, chironomids) in two late Pleistocene sediment cores from Lago Al bano, a crater lake in Central Italy. The record contains evidence for osci llations in lake biota throughout the period ca. 28 to 17 k yr BP. The earl iest of these are contained in the basal 3.5 m of light olive-gray and yell owish-gray spotted muds sampled in core PALB 94-1E from 70 m water depth. T he later oscillations are best represented in the more extended sediment se quence recovered from a second core site, PALB 94-6B, in 30 m water depth. The sediments at site 1E, containing the earlier oscillations (ca. 28-24 k yr BP), predate any sedimentation at the shallower site, from which we infe r an initially low lake level rising to permit sediment accumulation at sit e 6B from ca. 24 k yr onwards. At site 6B, massive silts rich in moss remai ns are interbedded with laminated silts and carbonates. These sediments spa n the period ca. 24 to 17 k yr and are interpreted as representing, respect ively, times of shallow water alternating with higher lake stands, when the lake was stratified and bottom water was stagnant. A range of mutually ind ependent chronological constraints on the frequency and duration of the osc illations recorded in the lake biota indicate that they were aperiodic and occurred on millennial to century timescales. We interpret them as response s to climate forcing through its impact on lake levels and changing aquatic productivity. The time span they occupy, their frequency and their duratio n suggest that at least some of these changes may parallel both the Dansgaa rd-Oeschger events recorded in Greenland Ice Cores and the contemporary osc illations in North Atlantic circulation documented in marine sediment cores .