Early cenozoic glaciation, antarctic weathering, and seawater Sr-87/Sr-86:is there a link?

Stable and radiogenic isotopic and sedimentological data from sub-Antarctic deep sea sediment cores reveal a temporal link between changes in seawater Sr-87/Sr-86 ratios and major episodes of late Eocene-early Oligocene clima te change. The Sr-87/Sr-86 records show two major inflections, one at 38-39 Ma near the middle/late Eocene boundary, followed by another at 33.4 Ma. S imilarly, the oxygen isotope, ice-rafted debris, and clay assemblage record s indicate two important climatic events: the appearance of alpine glaciers and/or small ice-sheets on Antarctica in the late Eocene at 38-39 Ma, foll owed by a rapid transition to larger and more permanent temperate ice-sheet s in the early Oligocene at 33.4 Ma. Moreover, during the early Oligocene ( 30-33 Ma) three to four inferred peaks in glacial activity appear to coinci de with subtle steps in the Sr-87/Sr-86 record. The coupled variations in c limate and seawater Sr isotope ratios during the Eocene/Oligocene imply a s trong causal link between the two. Either changes in climate directly influ enced patterns of continental weathering and hence seawater chemistry, and/ or a tectonic event (e.g., uplift) as reflected in weathering and seawater chemistry triggered relatively abrupt changes in global climate. (C) 1999 E lsevier Science B.V. All rights reserved.