Küçükçekmece Lagünü'nde (İstanbul) "Küçük Buzul Çağı" ve "Orta Çağ Ilık Dönemi" çökel kayıtları

This study focuses on the sedimentary records of climatic changes in the Kucukcekmece Lagoon over the last 1300 a. The main objective of the study is to investigate the envirenmental conditions in Istanbul during the Little Ice Age (LIA, 600-100 a BP) and Medieval Warm Period (MWP, 1000-600 a BP), which occurred in Europe during the last millenia. The Kucukcekmece Lagoon is situated on the northern shoreline of the Sea of Marmara, west of Istanbul. It has a surface area of 15 km 2 , maximum depth of 20 m and water volume of 145x10 6 m 3 . The lagoon is connected to Sea of Marmara via a 2 km long natural narrow channel. The main freshwater input is mainly from small sterams and groundwater springs (Altun el al., 2009). The Little Ice Age was a period of mountain glacier expansion during 16th–mid 19th century period during which European climate was strongly impacted (Bradley and Jones, 1993; Jones et al., 1998; Mann et al., 1998, 1999; Mann, 2002). This period begins with a trend towards enhanced glacial conditions in Europe following the warm conditions of the so-called MWP. The LIA terminated with a dramatic retreat of the Alpine glaciers during the 20 th century. During this period the temperature was 0.5-0.7 o C lower than 1950’s avarage. The previous Holocene climate studies in Turkey are rare and mostly confined to the Black Sea and Central Anatolia regions (e.g., Jones et al. 2006; Fleitmann et al, 2009; Kuzucuoglu et al, 2011 ) . In view of the variability of the present-day climate of Turkey mainly because of its geographic location and topography, and scarcity of data in NW Turkey, the recovery of late Holocene climate records from Kucukcekmece Lagoon (Istanbul) is very important. For this prupose we collected one short interface core (0.6 m) and one 4.5 m long piston core from the Kucukcekmece lagoon. The cores were analyzed for physical properties (magnetic susceptibilty: MS, gamma density, and resistivity) at 5 mm resolution using Multi Sensor Core Logger (MSCL), and multi-elemental analyis at 0.2 mm resolution using XRF (X-Ray Fluoresance) core scanner. The cores were then sampled at 50 mm intervals for total inorganic carbon (TIC), total organic carbon (TOC), and micropaleontological (ostracoda and benthic foraminifera) analysis. The micropaleontological analysis was made in the sand size fraction under binocular microscope. The ostracoda and benthic foraminifera individuals are identified. Suitable species of ostracoda (Loxoconcha sp.) and benthic foraminifera ( Ammonia sp .) were picked and analyzed for the stable oxygen and carbon isotope analysis. Four samples were dated using AMS 14 C analysis . The ages were calibrated to calendar year by CALIB 6.0 software using INTCAL 9.0 and MARINE 9.0 options . The short and long cores were correlated using the MS profiles and a continuous composite section was constituted. The lithology of the composite core section in general consists of homogenous olive green mud that rarely includes layers of plant remains and laminated intervals. The benthic foraminifera and ostracoda distribution suggests that the lagoon has been brackish over the last 1300 a. The age model was obtained from the calibrated AMS C-14 datings of two total bulk organic carbon and two plant remain layers . The multiproxy data were used to analyze the evaporation/precipitation changes in sediment cores. Increasing MS (SI), Ti (cps) values and decreasing of d 18 O- d 13 C (‰ VPDB), Ca/Ti, Sr/Ca ratio and TOC (%wt) values were interpreted to show wet conditions. We also modified the Leng and Marshall’s (2004) d 18 O- d 13 C model for the Kucukcekmece Lagoon . The multi-proxy physical properties, geochemical and stable O- and C-isotope data in Kucukcekmece Lagoon show that wet conditions prevailed during ca 220-70 a BP, 1300-750 a BP and dry conditions during ca 70- 0 a BP, 750-220 a BP. The late (250-100 a BP) and early episodes (600- 250 a BP) of the Little Ice Age period was wet and and dry, respectively. During the the Medieval Warm Period (1000-600 a BP) wet conditions occurred in the region. The climate records also show that decadal-scale wet periods occurred during 340-270 a BP and 680-610 a BP, and dry periods during ca 1050 – 1000 a BP, 1130-1080 a BP and 1260-1210 a BP. Climatic records of Kucukcekmece Lagoon shows similarity with European records in Little Ice Age and Medieval Warm Period . Keywords: Kucukcekmece Lagoon (Istanbul), Little Ice Age, Medieval Warm Period .