Bu çalışmada Batı Karadeniz havzasından çoklu karotiyer (multi-corer) sistemi ile alınmış toplam iki karotta jeokimyasal analizler uygulanarak, son 3000 yılda önemli ani oluşmuş doğal ve antropojen kökenli çevresel değişimler saptanmış ve bu değişimler 210Pb yöntemi ve yayınlanmış 14C verileri ile tarihlendirilmiştir. İki ayrı istasyonun 600 m (BS98-09) ve 1319 m (BS98-15) su derinliğinden alınan bu karotlarda 210Pb radyoizotopu kullanılarak tayin edilen toplam kütle birikim hızı (MAR) sırasıyla 171.5 ve 71.3 g.m-2. y-1 dır. Sedimantasyon hızı ise BS98-09 karotunda 72 cm.ky-1 ve BS98-15 karotunda ise 24 cm.ky-1 olarak bulunmuştur. Son 125 yıl içerisinde BS98-15 istasyonundan alınan karotta toplam organik karbon ve karbonatın ortalama MAR değerleri 1.56 ve 24.26 g.m-2.y-1olarak bulunurken, BS98-09 istasyonundan alınan karotta ise toplam organik karbon ve karbonatın ortalama MAR değerleri 13.4 ve 48.1 g.m-2.y-1 olarak bulunmuştur. Sapropel biriminin en üst kısmında ise toplam organik karbon ve karbonatın ortalama MAR değerleri 3.43 ve 13.54 g.m-2.y-1 olarak hesaplanmıştır. Metal (örneğin, Ba, Cu, Pb, Zn) konsantrasyonlarında son 80 yıl içerisinde çok hızlı bir artış gözlenmektedir. Baryum zenginleşmesinin her iki karotun üst kısmında, normal doğal seviyesinden 5-5.5 kat daha fazla olduğu ve bunun da Karadeniz’de artan ötrüfikasyondan kaynaklandığı sanılmaktadır. BS98-15 karotunun üst kısmında Zn, Cu ve Pb’nun zenginleşmesi normal doğal seviyelerinden sırasıyla 5, 2 ve 9 kat daha fazladır. BS98-09 karotun üst kısmında ise aynı elementler sırasıyla 3.6, 2.4 ve 2 kat daha fazladır. Anahtar Kelimeler: Karadeniz, kütle birikim hızı, organik karbon, karbonat, metaller. Geochemical studies of two cores from the western continental margin of the Western Black Sea Basin at water depths of 600 (BS98-09) and 1319 (BS98-15)m revealed naturally and anthropogenically driven environmental changes in the Black Sea over the last 3000 yr. These changes were dated using the 210Pb analysis of this study and published 14C data. The studied cores were obtained using a multi-corer during a cruise of the International Atomic Energy Agency (IAEA) in 1998. Mass accumulation rates (MAR) based on 210Pb dating are 171.5 g.m-2.yr-1 for BS98-09 and 71.3 g.m-2.yr-1 for Core BS98-15, respectively. The considerably high MAR value in Core BS98-09 is in agreement with its location being closer to the Danube delta than that of Core BS98-15. The average MARs of total organic carbon (TOC) and carbonate during the last 125 yr in Core BS98-15 are 1.56 and 24.26 g.m-2.yr-1, whereas the corresponding values in Core BS98-09 are 13.41 and 48.12 g.m-2.yr-1. The MARs of TOC and carbonate in the upper part of the sapropel unit are 3.43 and 13.54 g.m-2.yr-1 in Core BS98-15. Core BS98-15 includes a Coccolith Unit and the top of the underlying Sapropel Unit, whereas Core BS98-09 contains the Coccolith Unit only. The two units in Core BS98-15 have been deposited under anoxic conditions in the last 7500 yr BP (before present). The top of the Sapropel contains the ?first coccolith band?, marking the first entry of Emiliania huxleyi in the Black Sea during the Holocene. The Coccolith Unit is microlaminated and consists of alternations of white E. huxleyi and dark organic-rich clay laminae. The unit in the studied cores contains 57.3-62.7% wt total carbonate and 3.5-4.1% wt total organic carbon (TOC). High carbonate content of this unit is almost totally made up of calcitic E. huxleyi coccoliths. The Sapropel Unit is an organic-rich black mud containing 26.3-36.1% wt carbonate and 5.6-10.4 % wt TOC. The high MARCaCO3 value of the Coccolith Unit is caused by the presence of calcitic coccoliths and coccospheres of E. huxleyi. The average sedimentation rate, calculated for whole of the Coccolith Unit using the 2000 yr (corrected) 14C age of Coccolith/Sapropel boundary (Arthur and Dean, 1999) and assuming a linear sedimentation rate, was found to be 1.5 to 3 times lower than the sedimentation rates for the last 125 years computed from the 210Pb data. This indicates that the sedimentation rate has not been constant during the last 2000 years and that it increased drastically especially in the last few hundred years as a result of human impact in the form of deforestation and agricultural activities. The ?first coccolith band?, dated 2000 yr BP (present before) by Arthur and Dean (1999) and 2720 BP by Jones and Gagnon (1994), marks the first appearance of E. huxleyi in Holocene. This was an important event in the oceanographic and sedimentological history of the Black Sea, causing a large carbonate flux to the seafloor. Colonization of the Black Sea surface waters by E. huxleyi at about 2000 yr BP was most probably because of the increase in the sea surface salinity to a threshold value of 11? that is needed for the survival of these organisms (Paasche, 2002). A period of highest carbonate deposition, corresponding to high E. huxleyi production, was observed in both cores at different core depths. According to the 210Pb dating, these depths correspond approximately to AD 1700, with the carbonate peak widths corresponding to a period of about 100 years between AD 1750-1650. This time period can be correlated by the ?Late Maunder Minimum?, the coldest phase of the ?Little Ice Age?, which was characterized by glacier advances in Northern and Southern Hemispheres, average annual temperatures 1-2oC lower than the present, and an increased precipitation in most of Europe. Metals (Ba, Cu, Pb, Zn) show sharp increases in concentrations towards the top of the cores. Barium enrichment is 5-5.5 times the background values in both cores, attesting to the increased eutrophication of the Black Sea. Zn, Cu and Pb enrichments at the top of the cores are 5, 2 and 9 times the background values in Core BS98-15 and about 3.6, 2.4 and 2 times in Core BS98-09, showing the strong industrial metal pollution of the Black Sea sediments in the last 80 years. Keywords: Black Sea, holocene sediment, organic carbon, carbonate, metals
