Detrital carbonate influences on bulk oxygen and carbon isotope composition of lacustrine sediments from the Mediterranean

Detrital carbonate contamination is one of the principal problems with the integrity of stable isotope data from authigenic lake carbonates. Here we investigate the origin and climatic implications of stable isotope data from carbonate minerals deposited in two Mediterranean lakes: Gölhisar Gölü (SW Turkey) and Lake Pamvotis (NW Greece). In Gölhisar Gölü the bulk carbonate oxygen and carbon isotope composition has previously been interpreted in terms of significant climate variation related to the lake's hydrological balance. However, the origin of the carbonates was not investigated even though phases of high magnetic susceptibility suggest that there were several periods of increased soil erosion from the karstic catchment which could bring detrital limestone in to the lake. SEM evidence suggests that the carbonates in Gölhisar Gölü sediments of Holocene age are predominantly derived from forms of authigenic calcite (i.e. platelets, prismatic crystals), although periods of inwash clearly occurred which may have influenced parts of the isotope stratigraphy during the last two millennia. For comparison we also looked at data of Late Pleistocene to Holocene age from Lake Pamvotis. Here, there is an excellent correlation between the bulk carbonate oxygen isotope and magnetic susceptibility data, but no significant correlation between the bulk carbonate isotope data and ostracod isotope data from the same levels. SEM analyses confirmed the presence of detrital carbonates and the lack of significant authigenic carbonate. While the Gölhisar record records aspects of climate in most of its isotope data, in the Pamvotis record only the ostracod data are likely to contain meaningful information.