Sulfur isotope evidence for changing input of continental and marine aerosols in a 60,000-year sediment core from Lake Tulane, central Florida, USA

Abstract

Variations in sulfur isotope ratios in lacustrine sediments are used here to reveal regional aspects of past environmental change at Lake Tulane, Florida, USA. Earlier studies of this late-Pleistocene/Holocene lake sediment core provided the framework for assessing some of the underlying mechanisms of change in the paleolimnology of Lake Tulane. Prior research on the lake's history identified seven phases of Pinus-dominated vegetation, interpreted as periods with warm and wet climate; intervening times were relatively cool and dry. We hypothesized that variations in vegetation and climate, along with deepening of the lake, might lead to temporal changes in S cycling and in δ34S of sulfur delivered to the sediment.The stratigraphy is characterized by a wide range of δ34S values (+7 to +15‰V-CDT), and a sequence of four major, extended trends in δ34S within the 60,000-year period. Changes in the δ34S profile were statistically unrelated to five tested parameters (concentrations of S, organic matter, Al, and Fe, and local vegetation). Total sulfur concentration was positively correlated with organic matter; pyrite was not detected. The δ34S trends were more likely related to changes in the distance to sources of marine aerosols during the late Pleistocene and Holocene. Flux of marine aerosols (with more positive δ34S) would have been lowest at the Last Glacial Maximum, about 20–25,000calyrBP, when sea level was at least 120m lower than present and the shorelines east and west of Florida were as much as 200km seaward of the modern position. The δ34S lake sediment profile thus provides insights into past paleogeographic changes that are not evident in other geochemical or palynological data.