Investigation of paleoclimatic and geochemical changes in lake Akgöl(Terme,Samsun)during the late holocene

Abstract

In this study Lake Akgöl (Terme, Samsun, Türkiye) sediments are investigated for paleoenvironmental changes during the Late Holocene (<1500 years before present). The lake is located in the Black Sea and is declared a ''Wildlife Protection Area''.The purpose of this thesis is to examine paleoenvironmental changes that impacted the southern Black Sea margin based on a multi-proxy analysis of a 193-cm-long sediment core from Lake Akgöl (Terme, Samsun, Türkiye). Sediment description and analysis were performed in the East Mediterranean Centre for Oceanography and Limnology (EMCOL) Applied Research Center at ITU. Sediment properties that have been measured for a subsequent paleoenvironmental reconstruction include gamma ray density, magnetic susceptibility (MS), grain size composition, total organic carbon (TOC)/total inorganic carbon (TIC), X-ray fluorescence (XRF), and X-ray diffractometry (XRD). The chronology is based on sediment dating using AMS radiocarbon ages.From bottom to top the core indicates following changes based on XRF counting.Between 190-175 cm (~1350-1300 cal. yr BP) high XRF counts of in K, Fe, Si, Mn, and Ti are linked to a high abundance of detrital input. This is also supported by the high presence of fine-to-coarse silt, and fine to medium sandy layers in this interval.Between 175-160 cm (~1300-1200 cal. yr BP) XRF counts of the same elements have low counts.Between 160-140 cm (~1200-800 cal. yr BP) detritus- related XRF counts increase again and are paralleled by low TOC values.Above 130 cm (<800 cal. yr BP) TOC values increase reflecting a higher organic productivity at the site towards modern time. High Ca values in this core part are related to microfossil contents (e.g. ostracods, molluscs) instead of authigenic origin.The XRD analysis of the record shows that the lower core part is dominated by Quartz and Feldspars among others, whereas in the more fine-grained upper part Gypsum and Illite are prominent (among others).