itüdergisi (E-Journals - İstanbul Teknik Üniversitesi, Istanbul Teknik Uniersity., İTÜ)
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Karışık karbon kaynağı ortamının nişasta giderim performansı ve bakteriyel kompozisyon üzerine etkisi
Full text linkThe microbial processes have been extensively investigated for the efficiently design and operation of the activated sludge systems. The experimental studies have often focused on the single representative carbon source, although, microorganisms have to remove wastewater which is the mixture of several different type carbon sources. Under such conditions, bacteria often utilize one carbon source preferentially and other carbon sources are consumed only, when the preferred one is exhausted. The carbon source providing the best growth rate and/or growth yield is preferred, and the successive utilization of the substrates is often represented (Monod, 1942). In the environmental engineering point of view, it is important to understand the interaction between the removal mechanisms of different carbon sources which have a different degree of complexity. Although, recent studies have mainly focused on the biodegradation kinetics of the industrially produced starch as the only pollutant in wastewater, the simultaneous use of multiple substrates, such as the co-treatment of the industrially produced wastewater with the domestic wastewater produced in the facility, can lead to differences in biodegradation kinetics of any individual organic constituent as well as in the bacterial community. The researches with bacteria and higher organisms have revealed that selective carbon source utilization is common and that glucose is the preferred carbon source by many organisms. Moreover, the presence of glucose often prevents the use of other, secondary, carbon sources (Gorke and Stülke, 2008). In a study carried out under aerobic conditions with a mixture of similar type substrates (i.e. a mixture of acetic, lactic and propionic acid), a strong decrease in the removal rates of acetic and lactic acid was observed when treated in the presence of another substrate (Dionisi et al., 2004). This strong interaction among different substrates was explained with the interconnected pathways utilized by microorganisms for the removal of these substrates. Less clear evidences are available when dealing with mixtures of different type substrates, like volatile fatty acids and carbohydrates. Carta et al. (2001) reported that there were no differences in the uptake rate of acetate and glucose under mixed substrate environment compared to single substrate environment. In addition to the substrate uptake rates, the degradation kinetics and rates of the storage compounds were also reported as the same. In another study, when starch and acetate were treated together, slightly lower rates were observed in terms of individual carbon removal of acetate and starch, as well as respective storage of PHA and glycogen compared to treatment of substrate alone (Karahan et al., 2008). The fate of slowly biodegradable carbon source was evaluated in a SBR acclimated to starch as the sole carbon source and mixture of starch and acetate. The SBRs were operated with the same organic loading rate at two different sludge ages. Acetate, which is the one of the volatile fatty acid, was used as secondary pollutant as the volatile fatty acids have been reported as the main constituents of the domestic wastewaters. Although, the carbon source was fed to the SBRs in continuous mode throughout the cycle, the production of the storage polymer, namely glycogen, was observed in all SBRs. The relatively constant storage ratios were observed in SBRs fed with different carbon sources. The COD removal efficiency of the SBRs operated at the sludge ages of 8 days was significantly affected from the presence of acetate in the environment, although the COD removal efficiencies were constant at the sludge ages of 2 days independently from the presence of the secondary substrate. The bacterial characterization studies performed with fluorescent in situ hybridization (FISH) showed the decrease in the Actinobacteria phylum which was reported as the main starch consumer when the starch removal was performed in the multiple substrate environments at the sludge ages of 8 days. On the other hand, the detection of different groups at different sludge ages indicated the importance of the sludge age for evaluating treatment performance in activated sludge systems. Keywords: Starch; dual substrate; substrate removal kinetic; FISH, activated sludge system. Evsel atıksuların arıtımında yaygın olarak kullanılan aktif çamur sistemlerinin başlıca kirletici parametre olan karbon kaynağının giderim performansı açısından değerlendirilmesi, sistemin en uygun tasarım kriterlerinin belirlenmesi açısından büyük önem taşımaktadır. Bu konuda yürütülen çalışmalarda, evsel atıksuların içeriğini yansıtacak şekilde seçilen tek bir karbon kaynağı model substrat olarak kullanılmaktadır. Fakat farklı karbon kaynaklarının bir arada veya ayrı ayrı arıtılmaları mikrobiyal dinamikler doğrultusunda farklı giderim performansları elde edilmesine neden olabilmektedir. Bu kapsamda, çalışmanın amacı evsel atıksuların karbonhidrat içeriğini yansıtan ve hedef karbon kaynağı olarak ele alınan nişastanın, başka bir karbon kaynağı ile beraber aktif çamur sisteminde arıtılması durumunda, giderim veriminde ve bakteriyel komposizyonda oluşabilecek farklılıkların tespit edilmesidir. 2 farklı çamur yaşında işletilen sistemde, ikincil karbon kaynağı olarak evsel atıksu kompozisyonun büyük bir kısmını oluşturan uçucu yağ asitlerini temsilen asetat seçilmiş ve bu sayede farklı giderim mekanizmaları ile giderilen farklı yapıdaki karbon kaynaklarının birbirlerine etkileri araştırılmıştır. Elde edilen veriler, 8 gün çamur yaşında nişasta giderim performansının, ortamda asetatın bulunmasından etkilendiğini ancak, 2 gün çamur yaşında karışık karbon kaynağı ortamının nişasta giderim performansı bakımında önemli bir etkisi olmadığını göstermiştir. Farklı koşullarda işletilen reaktörlerde bulunan baskın türlerin Flüoresanlı yerinde hibritleşme tekniği (FISH) yöntemi ile analizi sonucunda, 8 gün çamur yaşında karışık karbon kaynağı ortamının sadece mikrobiyal aktivite üzerinde değil aynı zamanda mikrobiyal seleksiyon üzerinde de etkisi olduğunu göstermiştir. Ayrıca, deneysel sonuçlar, çamur yaşının sistem performansı ve bakteriyel kompozisyon üzerinde etkili bir parametre olduğunu ve bu nedenle aktif çamur tesislerinin tasarımında öncelikli olarak ele alınması gerektiğini ortaya koymuştur. Anahtar Kelimeler: Nişasta; karışık karbon kaynağı; karbon kaynağı giderim kinetiği; FISH; Aktif Çamur Sistemi. 
Benzo[a]anthracene'nin aktif çamur üzerine kronik etkisinin respirometrik incelenmesi
Full text linkIn this study, activated sludge taken from İstanbul ISKI Paşaköy Biological Treatment Plant, acclimated to synthetic peptone mixture for 6 months. Benzo[a]anthracene (B[a]A) was selected as model xenobiotic and the effect of B[a]A to the acclimated activated sludge was investigated. B[a]A is a toxic and carcinogen polycyclic aromatic hydrocarbon (PAH) and generated via cigarette smoke, diesel exhaust, commercial solvents etc. B[a]A is also listed in Environmental Protection Agency (EPA) priority pollutant list. In this study, 0.011 g/L B[a]A was added to the sequencing batch reactor (SBR). The chronic effect of B[a]A to activated sludge, were performed and monitored through respirometric studies as well as conventional parameters. The activated sludge operated 10 sludge ages for chronic effects. The chronic effect was estimated by using a multi-component model. 0.011 g/L B[a]A addition has no effect on COD removal. While biodegradation of peptone mixture, the B[a]A addition effects hydrolysis rate and PHA storage mechanism. The amount of B[a]A in activated sludge and supernatant monitored through high performance liquid chromatography (HPLC). PAHs, which are a class of xenobiotic, are unique contaminants in the environment because they are generated continuously by the inadvertently incomplete combustion of organic matter. PAHs include 70 natural and anthropogenic organic compounds constituted by aromatic rings, ranging between two and seven, and mainly derived from petroleum activities. In the 20th century there was a great increase of anthropogenic production of PAHs by combustion of fossil fuel. Beside of predominating anthropogenic sources e.g. road traffic and combustion of fossil fuels, there are also natural sources, e.g. volcanic eruptions and forest fires. PAHs consist of fused benzene rings in linear, angular or clustered arrangements and contain by definition only carbon and hydrogen atoms. However, nitrogen, sulfur and oxygen atoms may readily substitute in the benzene rings to form heterocyclic aromatic compounds, which are commonly grouped with the PAHs. Due to their toxicity, 16 PAHs were listed by U.S. Environmental Protection Agency (USEPA) as priority pollutants, which should be monitored in aquatic and terrestrial ecosystems. The increase in the hydrophobicity and electrochemical stability is associated with an increase in the number of benzene rings and angularity of a PAH molecule. The high molecular weight (HMW) PAHs are more persistent and recalcitrant than the low molecular weight (LMW) PAHs. The stability and distribution of the PAHs in the natural environment is influenced by the configuration of the aromatic rings, physico-chemical properties. PAHs are considered as important environmental pollutants since many of the compounds in this group are of major concern to environmental agencies and researchers worldwide due to their mutagenic, toxic, genotoxic and carcinogenic properties depending upon the number and configuration of the benzene rings and the presence and position of their substituents. Microorganisms, such as bacteria and fungi, may transform the PAHs to other organic compounds or to inorganic end products such as carbon dioxide and water. The latter process has been referred to as mineralization. Some PAH-degrading microorganisms, primarily bacteria, are capable to use the PAHs as a carbon and energy source, and may thus transform the contaminants into molecules that can enter the organisms’ central metabolic pathways. Other microorganisms have the capacity to degrade PAHs, while living on a widely available substrate. Such co-metabolism does not always result in growth of the microorganism, and sometime the cosubstrate, i.e. the PAH, is only transformed into another compound without any apparent benefit for the organism. Keywords: Xenobiotic, PAH, activated sludge, Benzo[a]anthracene, modeling, respirometer.Benzo[a]anthracene (B[a]A), toksik ve karsinojen bir polisiklik aromatik hidrokarbon (PAH) olup sigara dumanında, dizel araçların egzoz dumanında, yangın sonucu çıkan dumanlarda, ticari solventlerde vb. bulunmaktadır. B[a]A, Amerika’daki Çevresel Koruma Ajansı (Environmental Protection Agency - EPA) tarafından öncelikli kirleticiler listesinde yer alan 16 PAH’tan biridir. Bu çalışmada, benzo[a]anthracene (B[a]A), model zenobiyotik olarak seçilmiş ve B[a]A’nın sentetik pepton karışımına alışmış aktif çamur üzerindeki kronik etkisi incelenmiştir. Aklimasyon çalışmaları İSKİ Paşaköy İleri Biyolojik Atıksu Arıtma Tesisi’nden alınan biyokütle ile başlatılmış, hidrolik bekletme süresi 1 gün olan doldur-boşalt reaktörler çamur yaşı 10 gün olarak işletilmiştir. Kronik deneylere başlamadan önce sistem 3 ay süre ile organik madde olarak evsel atıksuyu en iyi temsil ettiği düşünülen sentetik pepton karışımı (600 mg KOİ/L) ile beslenmiştir. Kronik etkinin belirlenmesi için günde iki çevrim ile çalıştırılan çamur yaşı 10 gün olan bir ardışık kesikli reaktör (AKR) sistemi kullanılmıştır. Sadece sentetik pepton karışımı ile beslenen AKR sistemi, kronik etkinin belirlenmesi için 21 gün boyunca sabit miktarda B[a]A (0.011 g/L) eklenerek izlenmiştir. B[a]A’nın aktif çamur üzerine olan kronik etkisi, respirometrik yöntemin yanı sıra konvansiyonel parametreler ile de incelenmiştir. 0.011 g/L B[a]A eklemesinin KOİ giderimi açısından AKR sistemi üzerine bir etkisi olmadığı anlaşılmıştır. Yürütülen modelleme çalışması, respirometrik testler aracılığıyla Modifiye Edilmiş Aktif Çamur Modeli No. 3’teki kinetikler hakkında deneysel veri desteği ve bilgi sağlamıştır. Pepton karışımının biyolojik parçalanmasında B[a]A ilavesi hidroliz hızında bir artışa neden olmuştur. Bunun yanısıra sistemin depolama mekanizması üzerinde de bir etkisi olduğu görülmüştür. Anahtar Kelimeler: Zenobiyotik, PAH, aktif çamur, Benzo[a]anthracene, modelleme, respirometre
Endokrin bozucu dimetil fitalatın elektrokoagülasyon ve elektrokoagülasyon/Fenton prosesleri ile arıtımı
Full text linkPhthalic acid esters (phthalates) are frequently used as plasticizers for cellulosic and vinyl ester resins, but also in ceramic, paper, cosmetic, ink and paint industries. Phthalates are readily adsorbed through the skin and have negative impacts on human health and fertility. They have been detected in surface and groundwater in the ng/L-mg/L concentration range and associated with birth defects, organ damage, infertility, as well as testicular cancer, and are also known to be among the major endocrine disrupting compounds. The short-chained esters such as dimethyl phthalate (DMP), which mainly originate from industrial wastewater discharge and leaching and volatilization from plastic products during their usage and after disposal, are among the most frequently, identified phthalates in diverse environmental samples. Studies of DMP's biodegradation in fresh water, marine water, sediment, wastewater and sludge, have revealed a low degradation rate in the range of several days to a few months. Thus the destruction of these bio-recalcitrant organic pollutants requires the application of advanced treatment technologies such as electrocoagulation (EC) and electrocoagulation/ Fenton (EC/Fenton) processes. EC offers high removal efficiencies in compact reactors with simple equipments for control and operation of the process. In an EC reactor, the coagulant is generated in the reaction solution from a sacrificial electrode (e.g. iron, aluminum) leading to the in-situ formation of the respective metal hydroxides. A complex and yet not deeply understood reaction mechanism is thought to be involved in the EC process featuring a complex scheme of coagulation, particle entrapment, adsorption, absorption, flotation and redox reactions. In EC/Fenton process, strong oxidizing hydroxyl radicals (HO·) are generated in the solution by the well-known Fenton's reaction between H2O2 and electrochemically generated Fe2+ ions from sacrificial iron anodes. HO· is one of the most reactive free radical (oxidation potential: + 2.8 eV) and can indiscriminately degrade organic compounds. The number of parameter involved in the design and operation of the EC and EC/Fenton processes is relatively high and thus an efficient design and operation of the processes call for a detailed and careful evaluation and optimization. The main targets of the present study were: to assess the performance of EC and EC/Fenton processes in the treatment of aqueous solution of DMP selected as a model phthalate and to determine the most appropriate operating conditions for maximizing the processes performances. In this study, classical optimization method (a single-factor-at-a-time approach) and Central Composite Design (CCD) Response Surface Methodology (RSM) were used to optimize the treatment of aqueous DMP by EC and EC/Fenton with stainless steel electrodes, respectively. The effects of the key process variables such as initial DMP concentration (DMPo), current density (Jc), electrolyte concentration (NaCl) and treatment time (tr) and H2O2 dosage on DMP and total organic carbon (TOC) removals were evaluated. According to the second-order polynomial regression models, established for EC process by CCD-RSM, DMP and TOC removal efficiencies were affected by the process variables in the following decreasing order; Jc>tr>DMPo>NaCl (negative impact), tr>DMPo (negative impact)>Jc>NaCl (negative impact). Analysis of variance indicated that the experimental design models obtained for the EC treatment of aqueous DMP solutions in terms of the model pollutant and mineralization were statistically significant. For aqueous DMF concentration of 100 mg/L, current density of 13.5 mA/cm2, electrolyte concentration of 1250 mg/L NaCl and treatment time of 120 min were found to be as optimum conditions. At these conditions at the end of 120 minutes, 95% DMP and 7% TOC removals were obtained. The results of the present study also clearly indicated that the EC/Fenton process run with stainless steel electrodes is an effective treatment application for DMP destruction as well as mineralization. The optimum operational conditions for the EC/Fenton process were determined as follows: initial pH of 2.0, current density of 22 mA/cm2, an electrolyte concentration of 1500 mg/L NaCl, and H2O2 dosage of 40 mM for the treatment of aqueous DMP (100 mg/L). Under these conditions at the treatment time of 120 minutes 94% DMP and 71% TOC removal were obtained. Keywords: Dimethyl phthalate, endocrine disruptive substances, electrocoagulation process, electrocoagulation/Fenton process, response surface methodology.Fitalik asit esterleri (fitalatlar) endüstriyel uygulamalarda yaygın olarak kullanılan ve Dünya genelinde yıllık üretim miktarları 2.7 milyon ton gibi yüksek değerlere ulaşan, toksik özellik gösteren, kanserojen, endokrin bozucu ve birikim potansiyeline sahip maddelerdir. Bu çalışmada konvansiyonel yöntemlerle istenilen düzeyde arıtılamayan fitalat benzeri kirleticilerin gideriminde elektrokoagülasyon (EK) ve elektrokoagülasyon/Fenton (EK/Fenton) proseslerinin kullanımı araştırılmış ve bu iki prosesin verimleri ana madde ve toplam organik madde (TOK) giderimleri dikkate alınarak karşılaştırılmıştır. Her iki proses için en uygun işletme koşullarının belirlenmesi amacıyla optimizasyon çalışmaları yürütülmüştür. Her iki proses için en uygun işletme koşullarının belirlenmesi amacıyla optimizasyon çalışmaları yürütülmüştür. EK prosesinin optimizasyonu “Cevap Yüzey Yöntemi” metodolojisi kullanılarak, EK/Fenton prosesinin optimizasyonu ise geleneksel optimizasyon çalışmaları ile gerçekleştirilmiştir. EK/Fenton prosesi ile yürütülen çalışmalarda, 100 mg/L DMF sulu çözeltisi için optimum koşullar 22.5 mA/cm2 akım yoğunluğu, 1500 mg/L NaCl elektrolit konsantrasyonu, başlangıç pH’sı 2 ve H2O2 dozajı 40 mM olarak belirlenmiştir. Bu koşullarda 60 dakikalık reaksiyon süresi sonunda %100 DMF ve %90 TOK giderimi elde edilmiştir. EK prosesi için ise farklı giriş DMF konsantrasyonları (20-100 mg/L) için optimum işletme koşulları cevap yüzey yöntemi ile belirlenmiştir. 100 mg/L DMF sulu çözeltisi için optimum koşullar 13.5 mA/cm2 akım yoğunluğu, 1250 mg/L NaCl elektrolit konsantrasyonu ve başlangıç pH’sı 6 olarak belirlenmiş ve bu koşullarda 120 dakika sonunda %95 DMF ve %7 TOK giderimleri elde edilmiştir. Anahtar Kelimeler: Dimetil fitalat, endokrin bozucu maddeler, elektrokoagülasyon prosesi, elektrokoagülasyon/Fenton prosesi, cevap yüzey yöntemi
Van Gölü havzasının temel yapısal unsurları, tektonik ve sedimanter evrimi, Doğu Türkiye
Full text linkThe peculiar one of the wedge-basins in E-Turkey is orogen-parallel Lake Van trough that is the deepest basin of the rotated portions of EAAC and thrust-bounded region. This lake is emplaced at N-end of Bitlis-Pötürge Massive (BP-M) along Muş suture, separating EAAC from BP-M. Lake Van region is a place where no mantle lid exists and hot asthenosphere is doming, therefore, it has dome-shaped structure with the highest elevation (2 km), termed as Lake Van Dome. The domal pattern of the lake, in fact, is a morphological paradigm, well representing the surficial effects of delamination event, crustal consolidation and crust-forming process. Not surprisingly, outline anatomy of Lake Van Dome clearly exhibits an orogenic structure with its formation of the squashy basin and thus, both its morphological and limnological characteristics may imply basement reactivation and orogenic features of the Highlands rifting phenomena in the domal center of accretionary complex. Compared to other convergent lakes in major mountain ranges, such as Lake Baikal, Lake Van is not well studied, its geophysical characteristics are poorly documented and understood. An overall understanding of this lake as a complex highlands system is still lacking. This lack assumes utmost importance given the fact that Lake Van and surrounding highlands are prone to thinning convergent crust, decompressional melting magmatism and post-collisional opening of sutures, through which extensional magma propagates. These processes dictate how ascending magmatic materials are transported through the crust toward the surface and react with their surrounding environment within the volcanic or magmatic edifice. A sequential development of these events is focused on understanding the rich dynamics of multiple linked systems with weak basement coupling and with many internal variables that exhibit multiscale interactions beneath the lake. Multi-component approach into basement and basin margin weakening highlights the relative roles of upper crustal tectonics, magmatism and the role of delamination and break off events, just beneath the lake. This generates deep insights into upper crust-driven seismicity and its results in basin response and subsequent impact on anisotropic variability of the convergent crust. The focus and objectives of Lake Van basin research are to provide a better understanding and overview of tectonic and magmatic processes in accretionary orogens and their role in the formation and evolution of the continental crust. Understanding post-collisional dynamics of accretionary wedges beneath Lake Van and their effect on Lake Van basin formation is essentially needed in this study. Multi channel seismic reflection profiles with a length of 850 km across Lake Van basin are collected by International Contiental Scientific Drilling Program, (PaleoVAN 2004 Project). Seismic structural interpretation showed that Plio-Quaternary structural development of the Lake Van basin is the result of two separate stress regimes: a Paleotectonic period of collision-compression and a Neotectonic period of extension/strike-slip deformation. Older structural elements bordering the lake have undergone reactivation as sinistral and dextral strike-slip faults along the basin margins. The consequence of this stress reversal has been tectonic instability of accretionary wedges, a reactivation of convergent basement and a change in kinematic boundary conditions of the lake. As a result, during post-collisional period, Lake Van region has undergone basin block fragmentation and separation, implying an oblique opening of Muş suture, through which extensional magmatism propagated into the lake, intensely deformed lake sediments and created the huge magma-hydrothermal lacustrine system. The oblique opening of suture zone views the Highlands rifting phenomena in Lake Van, especially its S-margin. Based on the above observations, the structural form of the early compressional Lake Van basin is quite different from the present-day basin. An interplay of sedimentation and tectonics in Lake Van provided a new angle on basement reactivation, oblique motion of the upper crustal flakes and the strike-slip evolution of accretionary wedge basins in Turkic-type orogenic setting. Lake Van is the Highlands rifted basin produced by doming asthenosphere, hence, Lake Van basin should be evaluated in a concept of the Highlands dynamics of hot and younger accretionary and Turkic-type orogens. Lastly, Lake Van basin shows tectonics and sedimentary characteristics of the Highlands Turkic type orogeny and thus, opens a new paradigm. Keywords: Extensional mechanism, Turkic-type orogeny, Basement reactivation, Paleotectonics.Sismik yansıma verilerinin yapısal analizi ve yorumlanması Van Gölü havzasının batıdaki sınır fayının bükümlenme gösterdiği gerilmeli kenarında geliştiğini göstermiştir. Batıdaki transtansiyonel faylanma, transtansiyonel ve doğrultu atımlı sedimentasyon gösteren merkezi Tatvan havzasının gelişiminde ana kontrol mekanizması olarak davranmıştır. Sınır fayının büküm aşağı transtansiyonel hareketi aşamalı olarak, batıdaki bükümden uzağa doğru olmak üzere yatay bir harekete dönüşmüştür. Bu yapısal oluşum, merkezi Tatvan havzasında gelişen karakteristik doğrultu atımlı dizilim sekanslarını oluşturmuştur. Böyle bir yapısallık sonucu oluşan mekansal ve yersel boşluklar, faylanmalar boyunca gelişen doğrultu atımlı harekete ek olarak, hem batı ve güney kenarlardaki lokalize olarak gelişen yatay gerilme ve incelmeyi ve hem de kuzey kenardaki kısalma ve kalınlaşmayı gerektirmiştir. Kuzey marjini boyunca gelişen dik faylanma her ne ölçüde dik olarak gelişebilmişse, fay bükümlenmesine bağlı olarak gelişen gerilmeyi karşılamak için gerekli çökme o derece hızlı gerçekleşmiştir. Fay büküm yapısının gölün yapısal gelişiminde oynadığı rol öyle belirgindir ki, düşünülmesi gereken, havza asimetrisinin tektonik yapısından çok çökel merkezinin yatay taşınımına ve doğrultu-atım sedimentasyonuna havza asimetrinin etkisidir. Asimetrik havza yapısı ve gölün tek yönlü yapısal gelişimi aynı zamanda, güney marjinindeki sağ yanal transtansiyonun, daha önce var olan Muş suturunu izlediğini ve var olan tektonik rejimin eski bindirme faylarını reaktive ederek yeniden harekete geçirdiğini göstermiştir. Bu bindirme fayları çökel merkezinin yatay migrasyonunu karşılayabilmek için oblik olarak, hem gerilmeli ve hem de sıkışmalı bileşenler olarak, atım yapmışlardır. Anahtar Kelimeler: Genişlemeli mekanizma, Türkik tipi orojen, temel reaktivasyonu, Paleotektonik dönem
Zemin büyütmesi ve yerel koşulların spektral ivmeye etkisi
Full text linkOne of the most commonly encountered problems in geotechnical earthquake engineering is the evaluation of soil amplification. Soil amplification can be defined as the increase in the amplitudes of the earthquake waves. Soil amplification is mostly affected by the local soil conditions such as bedrock depth, the thickness and dynamic characteristics of the soil layers, the limited width of the soil layers and the topographical properties. The variation of ground motion is denoted as an amplification or de-amplification of amplitudes at all frequencies, which is dependent on many parameters. Some of them are inherent of the dynamic soil behavior and its physical properties such as shearing modulus, damping ratio, shear wave velocity, plasticity index etc., and others are related to the characteristics and the intensity of the incoming wave-field, geometrical features like surface/bedrock topography, lateral geological discontinuities etc. Site effects play an important role in the variation of ground motion intensity distribution during earthquakes and therefore they have to be evaluated correctly for the design of earthquake resistant buildings. In this study, in order to investigate the effects of the local soil conditions to the soil amplification, an idealized simple model consisting of a crest and basin geometry was selected. One (1D) and two-dimensional (2D) dynamic analyses were performed for the two different cases of the top basin layer as high plasticity clay and silty sand, and the obtained results were compared. Six bedrock acceleration records with different frequency content were used in the dynamic analyses. Within the scope of this study, EERA and Flushplus softwares were used in the 1D and 2D dynamic nonlinear dynamic analyses, respectively. Flushplus is a finite element dynamic analysis software that is based on equivalent linear method and it works in the frequency domain. Viscous dashpots that were calculated proportional to the shear and pressure waves of the relevant layers were set at the boundaries of vertical and horizontal layers in the 2D model. The variations of the soil amplifications with the surface geometry were investigated by the 1D and 2D dynamic analyses. The 2D/1D spectral acceleration ratios were calculated for different period values at the lowland and highland regions of the 2D model in order to understand the difference between 1D and 2D dynamic behaviors. It was understood that the peak acceleration value of the bedrock ground motion was amplified by twice in case the top basin layer was selected as silty sand and the soil amplification value reached to 4.5 for the case of top basin layer as high plasticity clay. When the top soil layer was high plasticity clay, the 2D/1D spectral acceleration ratios reached their maximum values for high frequencies at the basin edge section where X/D is between 0.5 and 0.75, while X indicates the horizontal distance and D is the depth. As approaching to the mid part of the basin, 2D/1D spectral acceleration ratios reached their maximum values at lower frequencies because of the wave transformations that occur at basin edges. The difference between the results of 1D and 2D dynamic analyses decreased for higher frequencies with the increasing distance from the edge of the basin. When the top layer was selected as sand, the 2D/1D spectral acceleration ratios showed similar behavior for the lower frequencies, but an increase in the 2D/1D values was noticed at higher frequencies mainly for the sections 0.75Because of the limited width of the soil layers in basin and vertical boundary conditions, the 2D predominant period of the model took a lower value when compared with the results of 1D dynamic analysis. As a result the spectral acceleration values obtained by the 2D dynamic analyses were different from the spectral acceleration values calculated by 1D dynamic analysis especially at higher frequencies. The peak surface acceleration values that were calculated by the 2D analyses approached to each other regardless of the basin geometry when the non-linear behavior became dominant at the top layers. Topographical effects were negligible for very low frequencies, while the effects became significant for high frequencies or low wavelengths comparable to the geometric characteristics of the model. The intensity of the bedrock acceleration and the variation of dynamic properties with soil type play an important role in the development of non-linear dynamic behavior. Keywords: Soil amplification, local conditions, 2D dynamic analysis, spectral acceleration ratio.Bir sahada yerel koşullara bağlı olarak oluşabilecek zemin büyütmesinin belirlenmesi, geoteknik deprem mühendisliğinin önemli konularından birini oluşturmaktadır. Anakaya seviyesinde bir kaynaktan açığa çıkan enerjinin oluşturduğu sismik dalgalar yayılımları sırasında, içinden geçtikleri ortamların özelliklerinden etkilenmekte; süre, frekans ve genliklerinde değişimler olabilmektedir. Deprem dalgalarının yüzeye yakın zemin tabakaları içinden geçerken genliklerinde meydana gelen artış zemin büyütmesi olarak tanımlanmaktadır. Zemin büyütmesi anakaya derinliği, zemin tabakalarının kalınlığı, cinsi ve dinamik özellikleri, tabakaların yanal süreksizliği ve topografik özellikler gibi yerel koşullardan etkilenmektedir. Bu çalışmada, yerel koşulların zemin büyütmesine etkisini incelemek amacıyla tepe ve ovadan oluşan bir model seçilmiş, ova bölgesinde zemin kesitinin en üstünde yüksek plastisiteli kil ve siltli kum tabakasının olması durumu için, altı anakaya depremi kullanılarak bir (1D) ve iki boyutlu(2D) dinamik analizler yapılmıştır. Yüzeyde 19 farklı noktada farklı depremler için elde edilmiş ivme zaman geçmişleri ve ivme spektrumlarının mesafeye bağlı değişimleri incelenmiştir. Anakaya ivmelerinin, üst tabakanın kum olması durumunda zemin yüzeyinde ortalama iki kat, üst tabakanın kil olması durumunda ise daha fazla arttığı belirlenmiştir. Üst tabakanın kil olması hali için özellikle anakaya dalımının ova tabanına ulaştığı bölgenin izdüşümünde yer alan kesimlerde, spektral ivme oranlarının yüksek frekanslarda en büyük değerini aldığı, ova ortasına doğru 1D ve 2D analiz sonuçları arasındaki farkın azaldığı belirlenmiştir. 1D analizlerde sonlu farklar yöntemine dayanan, eşdeğer lineer malzeme modeli ile çalışan EERA yazılımı, 2D analizlerde ise frekans ortamında çalışan Flushplus sonlu elemanlar programı kullanılmıştır. Anahtar Kelimeler: Zemin büyütmesi, zemin koşulları, 2D dinamik analiz, spektral ivme oranı
Conta bağlantılı PVC boruların deformasyon davranışının laboratuvar deneyleri ile belirlenmesi
Full text linkModelling of joints in pipelines is a critical issue influencing both the short and long term performance of these systems. Defects at pipe joints can contribute significantly to reduction of the overall performance of the pipe system. The most common problems attributed to joint defects are infiltration, exfiltration, and erosion of the soil surrounding the pipe that can ultimately produce pipe failure. Joints are known to be the source of a number of pipe failures or installation problems due to the fact that in many cases they are the weakest points along a pipeline. Many design variables affect joint performance and it is difficult to predict the behavior of joints in service. The interaction between the pipe and the gasket is a complex phenomenon and represents a challenging modeling problem. Although joints can have a major influence on the pipe performance, little research has been conducted in regard to their design.This research reports on preliminary comparisons of the FEA (finite element analysis) with pipe assembly experiments. In the FEA, the three dimensional response of a rubber-gasketed bell-and-spigot jointed PVC (polyvinyl chloride) pressure pipe was examined to develop an understanding of the effect of gasket modulus, friction coefficient, insertion length and joint rotation on the pipe-joint behavior. The numerical analyses were performed using ABAQUS version 6.7. The finite element analysis procedure was conducted in two steps representing the insertion of the spigot into the bell, and the bending of the pipe across the assembled joint. In the analyses, a pipe of SDR (standard dimension ratio) 28 and nominal size 135 mm has average internal diameter 133 mm, average wall thickness 5 mm, average external diameter 143mm, average bell depth of 100mm was modeled.In this research, the jointed pipe specimens which were modeled using ABAQUS in the former study were tested in the laboratory to investigate the behavior of the pipe-joint assembly during insertion and bending. Two types of insertion tests were performed representing the joint behavior in conditions with and without gasket lubrication. The results of the insertion tests showed that lubrication decreases the amount of force needed for the insertion of the spigot into the bell end of the pipe. The peak forces needed for the insertion of the lubricated and non-lubricated specimens correspond to an insertion distance where the outer surface of the cylindrical part of the spigot comes in contact with the gasket, and the gasket is fully compressed between the spigot and the bell. A similar trend was observed in the finite element analyses. The results of the laboratory tests confirm the general pattern of force versus displacement behavior calculated in the finite element analyses, though further work is needed to establish the exact constitutive characteristics of the gasket so that better direct comparisons can be made. In order to check the accuracy of the experimental work, testings were carried out on two different test machines (Zwick Z020, and Instron 8802 test machines). The comparison of the results of the Zwick and Instron tests showed that almost the same results were obtained by the Zwick and Instron tests for the non-lubricated samples. However, although the general shapes of the curves were the same for the lubricated samples, the magnitude of the forces needed for 6.0 cm insertion were seen to be very different. The difference in the magnitudes of the forces might be caused by uneven spreading of the lubricant or the pipe?s out of roundness, which are known to be very important parameters that may affect the insertion process for these pipes. The comparison of the results of the insertion tests for lubricated samples with the FEA results show that the best fit between the FEA and the experimental results was achieved for the lubricated sample tested in the Instron machine. The higher differences in the results of the other tests and the FEA are thought to be caused by some factors such as the pipe out of roundness, the change in the gasket stiffness along the spigot taper, and the experimental variability along spigot cylinder.The results of the bending tests showed that the joint behavior is highly variable. Therefore, it is difficult to determine if lubrication influences bending in jointed pipes. However, these experiments were undertaken 6 weeks after insertion and it is not clear how much of the lubricant remained. This behavior results because time after insertion in the field could also influence the effectiveness of the lubrication, so that short term bending response under construction loads, for example, could be different to those after extensive time periods. Keywords: PVC pipe, pipe joint, vertical deformation, bending deformation.Gömülü boru hatlarının bağlantı yerlerinde karşılaşılan hasarlar, tüm boru sisteminin davranışını olumsuz yönde etkileyebilecek önemli sorunlara yol açabilir. Hasarlı boru bağlantılarında meydana gelen su sızıntısı ve buna bağlı olarak boru etrafındaki zeminde meydana gelen erozyon, zamanla borularda göçmeye neden olan en yaygın problemlerden biridir. Bu nedenle, boru bağlantılarının tasarımı, boruların uzun ve kısa dönemli davranışını büyük ölçüde etkileyen önemli bir konudur. Ancak, boru bağlantılarının boru hattı boyunca en kritik noktalardan biri olmasına ve boru performansı üzerinde büyük bir etkiye sahip olmalarına rağmen, boru ve conta arasındaki etkileşimin modellenmesindeki zorluk nedeniyle bu konu üzerinde çok sınırlı sayıda çalışma yapılmıştır. Bu çalışmada, boru ve conta arasındaki sürtünme, boruların birbiri içine itilme boyu ve ek yerinde meydana gelen dönmenin boru davranışı üzerindeki etkilerini incelemek amacıyla conta bağlantılı bir PVC boru üzerinde laboratuar deneyleri ve sonlu elemanlar analizleri yapılmıştır. Deneyler, boruların birbiri içine itilmesi için gerekli itme kuvvetini ve boruların eğilme davranışını belirlemek amacıyla iki aşamada gerçekleştirilmiştir. Elde edilen sonuçlar, aynı geometri ve malzeme özelliklerine sahip PVC boruların ABAQUS sonlu elemanlar programı kullanılarak modellendiği üç boyutlu sonlu elemanlar analiz sonuçları ile karşılaştırılmıştır. Deney sonuçlarıyla sonlu elemanlar analiz sonuçlarının karşılaştırılması, analizlerin boruların çeşitli şartlar altındaki temel fiziksel davranışını modellemekte başarılı olduğunu, ancak borularda üretim hataları ya da saklama koşullarındaki dikkatsizlikler nedeniyle ortaya çıkabilen boru en kesitlerinin tam dairesel olmaması durumunun boru davranışı üzerindeki önemli etkisini incelemenin gerekliliğini ortaya koymaktadır. Anahtar Kelimeler: PVC boru, boru bağlantısı, düşey yer değiştirme, eğilme
Reappraisal of properties soils encountered in the Golden Horn
Full text linkHaliç üstünde inşa edilen ve edilmekte olan Haliç Köprüsü, Yeni Galata Köprüsü, Haliç Metro Geçiş Köprüsü sondajlarından ve yapım sırasında elde edilen bilgiler, bu bölgedeki zeminlerin özellikleri hakkında ayrıntılı bilgiler elde edilmesini sağlamaktadır. Membadan mansaba doğru bu köprüler Haliç Köprüsü, Haliç Metro Geçiş Köprüsü, Yeni Galata Köprüsü olarak sıralanmaktadır. Yeni Galata Köprüsü kazıklarının girdiği çakıl tabakası, yaklaşık 80 m derinliktedir. Haliç Metro Metro Geçiş Köprüsü ekseninde kaya tabakasının derinliği, Azapkapı tarafında 55 metreden, Unkapanı tarafında 80 metreye alçalmaktadır. Yeni Galata Köprüsü kazıklarının oturduğu çakıl tabakası, Haliç Metro Geçiş Köprüsü yerindeki kaya tabakasına göre yatay olarak kabul edilebilir. Buna karşılık, Haliç Metro Geçiş Köprüsü’nün Unkapanı tarafında taban kayasında derin bir çukur bulunmaktadır. Böyle bir çukurun varlığı, Haliç’te kaya yüzeyinin enine ve boyuna doğrultudaki genel eğimlerine uymayan bir durum oluşturmaktadır. Kaya tabakaları çok yumuşak, kalın kil/silt tabakaları ile örtülüdür. Kıyılarda kalın şehir dolgusu bulunmaktadır. Yumuşak tabakaların üst yüzü hemen hemen yataydır ve bu durum zeminin yüksek su muhtevasını yansıtmaktadır. Likit limit kıvamında tabakalar, bir çanak şeklindeki taban kayasını doldurmaktadır. Haliç’in büyük ekseni boyunca kaya tabakasının derinliği, Haliç’in ağız kısmına doğru büyük bir eğimle alçalmakta ve 80 m kadar derinliğe ulaşmaktadır. Anahtar Kelimeler: Haliç (Golden Horn), yumuşak killi zeminler, çatlaklı ayrışmış kayalar.The Golden Horn is a seven and half kilometres long natural inlet of Boğaziçi Strait. It has a maximum width of about 700 m near its entrance. At its deepest part its depth is 40 m. The Golden Horn divides historical part of the city from the rest. The geology of the Istanbul area has been studied by many investigators. Penck was first to recognize the shales and graywackes as the oldest of the formations encountered in the area. He named them as the Thrace series. Subsequent investigations indicated the existence of various lithological and paleontological zones in Thrace series, and it is concluded that they belonged to the Early Carboniferous Period of the same era. Over centuries, the detritus brought by Alibey, Kâğıthane, and other creeks, heavy industrial and domestic wastes, and uncontrolled fills have changed drastically almost the entire cross section of the Golden Horn. Along the shores, many valleys have been levelled off by generally uncontrolled fills, and comparatively large areas have been reclaimed.The thickness of the man-made fill is over 40 m along the south shore and over 30 m along the north shore on the axis of the New Galata Bridge. The thickness of the fill decreases with increasing distance from the shore. Man-made fill is underlain by sedimentary deposits consisting of sand, silt and clay in varying proportions. In general it is described as grey-dark organic silty clay of marine origin. On the Eminönü (South) site of the New Galata Bridge, the soft layers are underlain by a few meters thick weathered shale. Over the deeper part of the waterway and towards the Karaköy side soft layers is underlain by cobbly gravel. The design of new bridges over the Golden Horn was subject to severe constraints. The New Galata Bridge is founded on large diameter tubular steel piles. Piles were driven into limestone, diabase and sandstone origined gravel which is encountered between the depths of 76 m and 88 m. Most of the piles of the New Galata Bridge were driven into the shuttered rock bottom. The adoption of a closed end pile having a diameter as large as 2000 mm is well suited to the soil conditions and the design requirements – the damage of the pile tip is prevented, settlement criteria are satisfied. The piles of the New Galata Bridge were designed to carry high working loads (up to 12 000 kN) in end bearing and to comply with severe restrictions on allowable settlement. A box girder bridge carried on temporary supports was constructed over the test pile and was loaded by ingots. Four hydraulic jacks were placed on the head of the test pile to obtain a total reaction of 2000 tonnes. The composite piles of the Metro Crossing Bridge extended to depths over 100 m. They were designed to carry even higher loads (up to 47 000 kN). Osterberg type of loading tests was made on Metro Crossing Bridge. In general dynamic measurements are not considered as a reliable substitute to static pile loading test. On the Metro Crossing Bridge site, dynamic analysis (PDA) is carried out and dynamic response during pile driving is also recorded. Results are found consistent with the exploration data. Depth of water on the axis of Metro Crossing Bridge is about 34 m. Soil profile is overlain by very soft, almost at liquid consistency, silt clay layer. The thickness of clay layer varied between 30 m and 50 m. Very soft silty clay layer is underlain by sandstone, siltstone and mudstone layers. Depth of rock is 55 m at Azapkapı (North) and 80 m at Unkapanı (South) side of the Bridge. Sea bottom at Golden Horn Bridge site is very shallow. Depth of rock is more than 70 m and is overlain by a gravel layer. The depth of exploration at Metro Crossing Bridge site was well over 100 m. Special attention was given to ascertain the level and characteristics of a suitable stratum. Form the initial data indicated existence of weathered rocks and alternating strong and weak rock formations. Soil investigations and pile driving provided ample information about the rock bottom of the Golden Horn. Rock levels at the site of Golden Horn Bridge and at the site of New Galata Bridge are almost flat in comparison with that of the Metro Crossing Bridge. Furthermore transversal profile of the rock bottom at Metro Crossing Bridge contains a deeper section near Unkapanı (South). Existence of such depression is not confirming with the general slopes of the rock strata. Keywords: Golden Horn, soft clayey soils, soft rocks
Silindirik bir sıvı tankının oturma performansının belirlenmesi
Full text linkCylindrical tanks are usually used in petro-chemical industry to store water or chemical materials. When their diameters, heights are taken into account, excess stresses will be transferred to the soil that they would be built on. Therefore even if the soil is considered to have sufficient bearing capacity, under the loading conditions over a large area, there can be problems due to bearing capacity, settlements and deformations. When designing a tank, foundation engineering is an important factor to consider. In the design of these wide diameter and flexible based structures, built on the problematic soils, a need for soil improvement as it would be done for a wide area could be costly. Therefore in the geotechnical analysis for these structures, the limit and tolerable values for settlement criteria needs to be considered in terms of structural integrity performances. When wide cylindrical tank structures are built on the weak soils, the settlement performance needs to be considered along with the damages that can occur on the upper structure. Settlements can cause problems in the nearby structures and the pipe connections can be effected. Cylindrical tanks are usually built on compacted granular fill materials or ring foundations with filled granular materials in the middle. In the weak soil conditions, the appropriate soil improvement method is chosen and applied or pile foundation system is used. In this paper, a cylindrical tank constructed on a site where there could be geotechnical problems, is considered. The tank considered is 65m in diameter and has a height of 19m. The settlements that could be critical are compared with the allowable ones stated in literature. Types of settlements that a wide cylindrical tank undergo are; uniform, planar and non-planar rotation, dishing, rotation at the crust and the base of the tank, and settlement at the base of the tank. The settlement calculations done were based on Janbu's tangent modulus method developed in 1967. Uniform settlements occur where beneath the tank at every point similar settlements exist. Planar rotation occurs when there is a differential settlement between two points on the tank. Dishing occurs where differential settlements are observed between two points on the tank and the middle of the tank base settle more than expected. Under the base of the tank, if there is soil with different geotechnical properties, local settlements can occur. Due to different soil strata thickness and deformation modules at the crust of the tank non-planar deformations can happen. In the case considered here, settlement calculations are done for various points on the tank and the total settlement values changed between 32cm to 79.3cm. Therefore as the minimum values for the settlement of the structure is calculated, it is seen that uniform settlement will occur. The settlements that would occur due to dishing or rotation will make up the differential settlements. According to the settlement analysis done, dishing value of 9.6cm is calculated in the centre of the tank. The differential settlements will occur at the crust of the tank which was not within the limits suggested in literature. Settlements due to liquefaction of soil were calculated as well. With different thickness of the liquefiable layers settlement values varied in different parts of the tank. As the structure is flexible, in the case of floating roofed tank systems, due to earthquake loadings, there would be big displacements and deformations that could cause collapse of the structure or damage in the structural system. Therefore the cylindrical tanks that would be constructed in the earthquake zones, dampers can be placed in their foundations. Under the tanks that are big in diameter, differential settlements will occur. Soil improvement can be done to prevent these deformations. Stress distribution in the soil of these heavy structures attenuates at depth. Therefore site investigation needs to be done in detail and at depth. Bearing capacity can be sufficient and settlements can be within limits under static conditions. However when saturated soils are considered, under earthquake loadings, liquefaction analysis needs to be done. Excess settlements can occur due to liquefaction. Steel cylindrical tanks are usually filled with liquid. Depending on the level of fullness, the vibrating frequency of the tank changes and needs to be calculated and dampers can be used. Dynamic analysis needs to be done with considering the local soil conditions. Keywords: bearing capacity, cylindrical tanks, settlement.Geniş çaplı ve esnek taban özelliklerine sahip silindirik tank yapıların tasarımında, problemli zeminlerde iyileştirme gerekliliği ortaya çıkması durumunda, alanın genişliğine bağlı olarak ıslah maliyeti yüksek olmaktadır. Bu tip yapıların geoteknik açıdan analizinde, gerek taşıma gücü gerekse oturma kriterlerinde sınır değerler, yapısal bütünlük performansı yönünden ele alınması gerekmektedir. Tank oturmaları zeminin göçmeye karşı güvenliğine göre daha önemli ve esas tasarım koşuludur. Oturmalar aynı zamanda komşu yapıları ve boru bağlantılarını olumsuz yönde etkileyebilmektedir. Tank yapısı altında gerçekleşen oturmalara bağlı olarak üstyapı formunda deformasyonlar meydana gelmektedir. Deformasyon derecesine bağlı olarak yüzer çatılı sistemlerde, çatı sisteminin sıkışmasına ve sistemin çalışmamasına neden olabilmektedir. Zeminin sıvılaşmasına ve sıvılaşan tabaka kalınlığına bağlı olarak deformasyonlar meydana gelecektir. Yapının esnek olması nedeniyle, deprem yüklerine bağlı olarak, büyük deplasman ve deformasyonlar oluşacak yapıda yıkılma veya hasar oluşmasa dahi yapısal sistemde arızalar meydana gelebilecektir. Bu çalışma kapsamında, tank yapıları için özellikle kritik olabilen oturmalar ele alınmıştır. Literatürde silindirik tank yapıları için verilen, oturma limit değerleri ve bu değerler dikkate alınarak, siltli kil kum tabakalı bir zeminde yer alan silindirik tank yapısı için analiz yapılmıştır. Yapılan hesaplar sonucu oturmalar silindirik tankın bazı noktalarında izin verilebilecek değeri aşmaktadır. Ayrıca tank ekseni boyunca meydana gelen düzlemsel oturma, merkez noktada hesaplanan oturma ile karşılaştırılıdığında çanaklanmaya bağlı olarak oturma meydana gelmiştir. Meydana gelicek oturmaları önlemek için zemin iyileştirilmesi önerilebilinir. Anahtar Kelimeler: Silindirik tank, oturma, taşıma gücü
Küçükçekmece Lagünü'nde (İstanbul) "Küçük Buzul Çağı" ve "Orta Çağ Ilık Dönemi" çökel kayıtları
Full text linkThis study focuses on the sedimentary records of climatic changes in the Küçükçekmece 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 Küçükçekmece Lagoon is situated on the northern shoreline of the Sea of Marmara, west of İstanbul. It has a surface area of 15 km2, maximum depth of 20 m and water volume of 145x106m3. 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 20th century. During this period the temperature was 0.5-0.7ºC 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; Kuzucuoğlu 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 Küçükçekmece Lagoon (İstanbul) 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 Küçükçekmece 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 14C 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 d18O-d13C (‰ 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) d18O-d13C model for the Küçükçekmece Lagoon. The multi-proxy physical properties, geochemical and stable O- and C-isotope data in Küçükçekmece 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 Küçükçekmece Lagoon shows similarity with European records in Little Ice Age and Medieval Warm Period. Keywords: Küçükçekmece Lagoon (İstanbul), Little Ice Age, Medieval Warm Period.Küçükçekmece Lagünü çökellerinde Günümüzden Önce (GÖ) 1300 yıldaki iklim değişimleri ile Avrupa’da soğuk dönem olan Küçük Buz Çağı (GÖ 600-100) ve öncesinde yaşanan Orta Çağ Ilık Dönemi’in (GÖ 1000-600) İstanbul’daki koşulların karşılaştırmasını amaçlamaktadır. Bu nedenle Küçükçekmece Lagünü’nden uzunlukları 0.6 ve 4.5 m olan iki çökel karotunda; 5 mm çözünürlükle Çok Sensörlü Karot Logu Alıcısı (Multi Sensor Core Logger, MSCL) ile manyetik duyarlılık, P-Dalga hızı, yoğunluk ve öz direnç; 0.2 mm çözünürlükle XRF (X -Ray Fluorescence) tarayıcısı ile 25 elementin analizi ve 50 mm çözünürlükle toplam inorganik (TIC)–organik (TOC) karbon analizleri yapılmıştır. Ayrıca 50 mm aralıkla örnekler yıkanıp elenerek elde edilen çökeller içinden belirlenen ostrakod (Loxoconcha sp.) ve bentik foraminifer (Ammoniasp.) türleri toplanarak duraylı oksijen ve karbon analizleri yapılmıştır. Karotlar AMS 14C yöntemleri ile yaşlandırılmıştır. Elde edilen sonuçlara göre Küçük Buz Çağı’nın (GÖ 600-100) GÖ 250-100 yılları arasındaki son bölümünde yağışlı; ilk bölümünde (GÖ 600-250 yılları arası) ise bölgede kurak koşulların egemen olduğu anlaşılmıştır. Buna göre, Ortaçağ Ilık Dönemi (GÖ 1000-600 yılları) ve Karanlık Çağ Soğuk Dönemi’nin (GÖ 1500-1000 yılları) son evresini içeren GÖ 1200-600 yılları arasında yağışlı ve GÖ 1300-1200 yılları arasında ise kuraktır. Anahtar Kelimeler: Küçükçekmece Lagünü (İstanbul), Küçük Buz Çağı, Ortaçağ Ilık Dönemi
Son 20 000 yılda Karadeniz ve Marmara Denizi'nde oluşan paleo-çevresel değişimler
Full text linkThe connection of Marmara Sea and Black Sea with global ocean and between themselves are established via the Çanakkale and Istanbul straits. Because of the shallow sill depths of these straits, these connections were interrupted in during the late glacial period (LGM). As a result of these important paleoceanographic events, Marmara and Black Seas experienced significant sedimentological, biological and chemical changes. Despite the high scientific interest and large number of previous studies, the timing and nature of the interruptions and reconnections of the two basins with each other and with the world ocean are still matters of debate. This debate has stemmed from mainly the following shortcomings of the previous studies: a) confinement of the study in one basin, b) selection of unsuitable core locations, and/or c) use of inadequate sampling resolution and proxies. To overcome these difficulties, we analyzed organic (Corg) and inorganic carbon (total carbonate:Tkarb) and determined sedimentation rates for the different climatic stages in four chronostratigraphically well dated cores (two each) from the Black Sea and Sea of Marmara. As identified by the previous studies, three units are present in the Black Sea Cores GC-19 and SL-12 covering the period from the LGM to present. The uppermost unit is the Coccolith Unit that consists of microlaminated gray green mud containing alternations of coccolith-rich and clay-organic matter rich lamina. The unit started depositing when coccolithophore Emiliania huxleyi invaded the basin at 2720 a (calib.) BP and the present-day oceanographic conditions were established. The underlying unit is Sapropel Unit that consists of laminated dark gray mud with high (up to 21 wt %) Corg. The Lutit Unit deposited under lacustrine conditions that consists of gray clayey mud. The lake /marine transition is characterized by high total carbonate content (up to 80 wt %) in the Black Sea (C1 carbonate) and dated 9.3 ka (calib.) BP. The Sea of Marmara cores contain two lithostratigraphic units deposited in the last 20 ka. The upper unit (Unit 1) is a green marine mud that includes a dark olive green Sapropel with more than 1.5 % Corg. The lower unit (Unit 2) is banded gray mud that was deposited under lacustrine conditions. The lacustrine / marine transition occurred 14.7 ka BP. Unit 2 includes a rhyodacitic ash layer that is defined as the Y-2 ash-layer of Santorini origin, dated 22 ka (calib.) BP. Sedimentological and geochemical (Corg and Tkarb) analysis, together with the changes in the sedimentation rates in the cores show that the Black Sea and Sea of Marmara were disconnected to each other during the LGM but connected during the post-glacial Heinrich 1 (H1, 17.9-16.5 ka BP), Red Clay Layer (RL; 16.2-14.8 ka BP) and Younger Dryas (YD, 12.9-11.9 ka BP) cold periods when large inputs of freshwater and sediment occurred to the Black Sea and Marmara basins by the west and northwest European rivers, leading to one-way connection between the two basins. In between the post-glacial cold periods during the early Holocene (11.9-9.3 ka BP) and Bølling-Allerød (14.8-12.9 ka BP), carbonate-rich C2 and C3 units, predominantly of calcite composition, were deposited with low sedimentation rates respectively. During these carbonate depositional periods relatively warm and dry conditions with low water levels prevailed in the Black Sea and the Sea of Marmara, and no connection existed between the two basins. Another carbonate depositional event, this time predominantly of aragonite composition, took place in the Sea of Marmara and the Black Sea as during the lake/marine transition. The carbonate beds are dated 14.5-12.9 ka BP in the Sea of Marmara and 8.6-7.6 ka BP in Black Sea (C1); the event in the Sea of Marmara partly overlapping with the Bolling/Allerod (B/A). The carbonate deposition in both the basins took place as a result of mixing of lacustrine and marine waters leading to carbonate overstaturation. Sapropels were deposited in the Black Sea and in the Sea of Marmara Sea during 11.5-7.0 and 7.8-2.7 ka BP, respectively, when the Mediterranean waters poured sequentially into the lacustrine Sea of Marmara and Black Sea. Arrival of marine waters pushed up the nutrient rich deep waters up into the photic zone, thereby initiating high primary productivity and lead to water stratification, preconditioning the basins for the sapropel formation. The sapropel deposition was interrupted in the Sea of Marmara during YD and 8.2 ka BP cold periods as a result of increased deep water ventilation. Keywords: Black Sea, Sea of Marmara, Paleoceanography, Paleoclimatology, Sapropel.Karadeniz ve Marmara Denizi’nde yapılan sedimentolojik ve jeokimyasal çalışmalar son 20 bin yıl boyunca her iki denizde önemli iklimsel ve oşinografik değişimlere işaret etmektedir. Çökelme oranı ve çökel jeokimyası (organik ve inorganik karbon) buzul çağında iki deniz arasında bağlantı olmadığını; buzul çağı sonrası H1 (Heinrich 1), RL (kırmızı kil) ve YD (Younger Dryas) soğuk dönemlerinde ise bağlantı sağlandığını desteklemektedir. H1, RL ve YD Avrupa nehirleri ile Karadeniz ve Marmara Denizi’ne bol miktarda kırıntı girdisinin olduğu dönemlerdir. Bu soğuk dönemler arasında Karadeniz’de erken Holosen (C2) ve Bølling-Allerød (C3) dönemlerinde düşük çökelme oranları ve yüksek toplam karbonat değerleri izlenmektedir. Bu dönemlerdeki yüksek toplam karbonat değerleri ve düşük çökelme oranları havzada kurak ve ılıman bir iklimin hakim olduğunu ve her iki deniz arasında bağlantının kesik olduğunu göstermektedir. Marmara Denizi’nde G.Ö. 11.5-7.0 ve Karadeniz’de G.Ö. 7.8-2.72 bin yılları arasında yüksek organik karbon (Corg) ve düşük çökelme oranları ile temsil edilen Sapropel birimleri, göl ortamına deniz suyunun girmesi, su tabakalanması oluşması ile bunların biyojeokimyasal döngülerde değişimler oluşturması ile çökelmeye başlamıştır. Özellikle tuzlu ve yoğun Akdeniz sularının bu havzalardaki besin elementlerince zengin derin suları üste, fotik zona itmesi ile organik üretimi artırması sapropel çökelimini tetikleyen en önemli etken olmuştur. Akdeniz sularının Marmara Denizi’ne girmesi ile başlayan organik maddece zengin çökellerin depolanması YD ve 8.2 bin yıl soğuk dönemlerinde su dolaşımındaki hızlanma nedeni ile kesintiye uğramıştır. Anahtar Kelimeler: Karadeniz, Marmara Denizi, Paleoşinografi, Paleoiklim, Sapropel
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