Holocene climate change in southwest Turkey: a stable isotope record of lake response
by
Warren J. Eastwood
School of Geography and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.
Coauthors: Melanie J. Leng (NERC Isotope Geosciences Laboratory, British Geological Survey, Nottingham, UK)), Neil Roberts (Department of Geographical Sciences, University of Plymouth), John C. Tibby (Department of Geography and Environmental Sciences, Monash University), Jane M. Reed (Department of Geography, University of Hull)

Stable isotope, pollen, diatom and lithological data from Gölhisar Gölü (37º 8´N, 29º 36´E; elevation 930 m), a small intramontane lake located in Burdur Province, southwest Turkey, provide a 9500 yr record of changes in climate, lake productivity, catchment stability and vegetation. The modern oxygen isotope water data are used as a means of comparing present isotopic composition of the lake-water to the calculated (from ¹⁸O/¹⁶O ratios in photosynthetically mediated calcite precipitated in the summer months) oxygen isotope composition of the lake-water in the past. The modern data clearly establishes an evaporative relationship between marginal spring-water and lake-water, and therefore the palaeo-data can be interpreted in terms of changing precipitation/evaporation ratios.

Most of the calcite precipitated in Gölhisar Gölü during the Holocene was in water which was isotopically lighter (depleted in ¹⁸O) due to less evaporative loss of ¹⁶O in the past. If we assume the lake was originally filled with water with a composition similar to modern day marginal springs (-8.1‰), at the mean summer temperatures, the resultant calcite would have delta¹⁸O values between -9.1 and -10.1‰. These values do not occur in the core record and therefore there has never been a phase when lakewater was isotopically similar to modern spring water which suggests that the lake has always been responsive to changes in precipitation/evaporation. However, delta¹⁸O data throughout the Holocene show predominantly negative values indicating wetter (than today) climatic conditions. Particularly notable are isotopic fluctuations in the early to mid Holocene (8000-6000 ¹⁴C years BP) when mixed forest became established comprising oak, pine and juniper. Delta¹⁸O and delta¹³C data for this period show marked fluctuations suggesting oscillations between aridity and humidity. Pollen spectra for the later Holocene indicate a period of increased human impact which occurs shortly after the deposition of a volcanic tephra layer originating from the Minoan eruption of Santorini (Thera) radiocarbon dated to 3330±70 yr BP (Cal.  1600 BC). This period of human impact is comparable to the Beysehir Occupation (BO) phase recorded at other sites in southwest Turkey and involved forest clearance and the cultivation of fruit trees such as olive, walnut, sweet chestnut and vines together with arable cereal growing and pastoralism. The BO phase at Gölhisar Gölü came to an end around 1300 BP (Cal. AD  700) when pine became the dominant forest tree. Delta¹⁸O and delta¹³C data for this period are generally stable, although decreasing values through this phase suggest increased humidity towards the top of the BO phase. The modern trend towards aridity started about 1000 years ago during post BO times.

Date received: April 27, 2001

Copyright © 2001 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # cahi-29.