Organic geochemical characterization of Early-Mid-Holocene swamp deposits near the Neolithic settlement in Yenikapı-Istanbul: Assessment of environmental variability and anthropogenic impacts

Abstract

During the archaeological excavations in the Byzantine Theodosian harbor (Istanbul) a Holocene dark gray to black clay sequence was uncovered. This clay unit was deposited under anoxic conditions in a small swamp. Both wooden artifacts from the Neolithic period, but also dispersed organic matter were perfectly preserved within this sequence. The aim of this study was the assessment of environmental changes and anthropogenic impacts with the help of organic geochemical and isotopic characterization of organic matter in this clay unit. The age model, based on ¹⁴C data, showed that the clay was deposited during a period about from 11,100 to 7500 cal. years BP. Hydrogen Index values lower than 100 mgHC/gTOC, n-alkane distributions with maxima at nC₂₉ or at nC₃₁, a predominance of long-chain n-alkanes (C₂₅–C₃₃) and δ¹³C_org values around −24‰ to −27‰ suggest a predominantly terrestrial origin of organic matter from C₃ plants. Obvious excursions of bulk δ¹³C_org and compound-specific δ¹³C and δD values of nC₂₇, nC₂₉, nC₃₁, and nC₃₃ are interpreted as indicators of changes in environmental and climatic conditions. Several shifts toward colder and warmer climatic conditions were identified and dated. Furthermore, two sudden changes in the hydrological regime were dated to 9000–8820 cal. years BP and to 8150–8050 cal. years BP toward wetter and drier conditions, respectively. Specific molecular organic geochemical indicators such as faecal sterols or a strong enrichment of δ¹⁵N caused by human impact could not be detected. Therefore, the swamp should not have been intensively affected by Neolithic people and/or respective indicators of their influence have been diluted due to the high sedimentation rate.

Keywords

climate changes 8.2 event geoarchaeology Holocene stable isotope geochemistry Istanbul-Turkey

Introduction

During the salvage excavations in the Byzantine Theodosian harbor, which is located at the southern coast of the so called “Old Town or Historical Peninsula” of Istanbul in the Yenikapı area (Figure 1) diverse archaeological objects, including 37 ship wrecks from VIth to XIth century of the Byzantine period have been discovered. As a result very important and new information on the cultural, social, technological, and commercial activities during these periods have been obtained (Akkemik and Kocabaş, 2014; Asal, 2010; Kızıltan, 2010; Kocabaş, 2010, 2015; Pulak, 2007; Pulak et al., 2014, 2015).

Figure 1.

The location of the excavation site in Yenikapı-Istanbul. The digital image has been generated from Google Earth 4.3 (modified from Algan et al., 2009).

In addition to this, the sedimentary sequence exposed during the excavations was studied from geological and geoarchaeological points of view in order to obtain new data on the Black Sea-Mediterranean connection and sea-level changes during the Holocene (Algan et al., 2009, 2010, 2011; Perinçek, 2010a, 2010b; Yalçın et al., 2019). From top to bottom a sequence consisting of soil and artificial fill, fluvial deposits, marine sediments, a dark gray to black clay at the eastern part of the excavation area, and late Miocene deposits underlying these units have been uncovered (Algan et al., 2007, 2009, 2011; Bony et al., 2011; Sezerer-Bulut et al., 2019; Yalçın et al., 2019). Lithological properties, age, thickness, and areal extension of this dark-colored clay unit, which is a new unit of the geology of the Istanbul area, were recently addressed by Yalçın et al. (2015). This unit is of Early-Mid-Holocene age and has a limited spatial extension in the Yenikapı area. Furthermore, characteristics of the depositional environment of the clay sequence, some aspects of the environmental conditions of the Istanbul area and temporal changes of them have been briefly discussed in the light of elemental composition and bulk organic geochemical properties of this sequence (Yalçın et al., 2015).

The relationship of the Neolithic settlement in Yenikapı, dated to 8500–7500 years before present (BP) with this clay unit and its depositional environment have also been addressed (Yalçın et al., 2015). Hereby, wooden and other type organic material, which was perfectly preserved under anoxic conditions in the swamp, helped very much deciphering this relationship. This swamp or the wetland occasionally dried out for considerable periods during which it has been intensively used for certain purposes such as burials, storage of grains, temporary settlements, etc. (Kızıltan, 2014; Kızıltan and Polat, 2013; Özdoğan, 2013; Yalçın et al., 2015; Yılmaz, 2011).

Not only wooden artifacts, but also dispersed organic matter was perfectly preserved within the clay sequence. It is evident that the study of the molecular and compound-specific isotopic compositions of organic matter constituents would help to define the environmental changes and probable anthropogenic influences, as already demonstrated at other archaeological sites (D’Anjou et al., 2012; Dubois and Jacob, 2016; Evershed, 2008; Karlik et al., 2018; Schwarzbauer et al., 2018). Although some basic bulk organic geochemical data of the clay unit are available and were used in the Yenikapı area, a detailed investigation of compound class fractions such as n-alkanes, fatty acids and alcohols, and their isotopic signatures are still missing.

The aim of this study is therefore to determine temporal changes of the environmental conditions and climate in Istanbul area during the Holocene by applying molecular organic and isotope geochemistry. Furthermore, we attempted to detect possible anthropogenic influences of the Neolithic community, which lived here for ca. 1000 years between 8500 and 7500 years BP (Kızıltan and Polat, 2013; Özdoğan, 2013). Such influences may be related to agricultural activities and/or to the usage of the swamp during dryer periods for different purposes.

Material and methods

In order to obtain fresh samples of the clay unit, a fully-cored borehole (Yenikapı-2) has been drilled at N 41°00′25.2″ and E 028°57′09.3″ in 2012. A rotary drilling device with corer equipment was used to obtain sediment cores. Cores were extruded in the field into plastic pipes lined with plastic film. In the laboratory, these were cut lengthways into two equal sections. One half was used for sampling and the other stored at 4°C as archive material for further investigations. The total depth of the borehole was 11.05 m. It started at the level of marine Holocene sequence which lies 1.40 m above the contact of marine Holocene and Holocene clay unit. The clay sequence continued until 7.22 m, where the boundary to the Miocene basement was penetrated (Figure 2). Hence a 5.82 m thick clay sequence was encountered. This sequence mainly consists of dark gray to black homogeneous clay without any sedimentary structures and bedding or lamination from the top until a depth of 4.00 m (Figure 2). Below this depth thin grayish green silt to fine sand intervals are intercalating with dark-colored clay (Figure 2). The interval from 7.22 to 11.05 m represents the Miocene basement.

Figure 2.

Lithostratigraphy of the Yenikapı-2 borehole.

Eighty-nine samples were taken from the clay unit representing a sequence between 1.67 and 7.19 m. Six samples from the interval between 7.28 and 7.65 m belong to the Miocene basement (Supplemental Table S1). The distance between two subsequent samples varied between 2.0 and 18.0 cm. Values higher than 4 cm are related in general to sandy intervals, which were washed out during drilling. The upper homogenous clay section was sampled at intervals of 2–3 cm. The mean sampling interval was approximately 6.5 cm. In a previous borehole (Yenikapı-1), which is very close to this borehole, a sedimentation rate of 1.73 mm/year was determined by Yalçın et al. (2015). Assuming the same sedimentation rate, sampling intervals of 6.5–3 cm would correspond to a temporal resolution between 37.5 and 17 years, respectively.

In this study bulk and molecular organic geochemical and isotopic characteristics of solid and soluble organic material in the sediments of the clay unit as well as the distribution and the compound-specific isotopic composition of n-alkanes have been determined. Prior to different analyses all samples were freeze-dried for 3–4 days. The dried samples were than ground using an achat mill.

In total 48 samples were analyzed for some of their bulk organic geochemical properties with Rock-Eval Pyrolysis in the laboratories of the Research Centre of Turkish Petroleum Corporation in Ankara using a Rock-Eval-6 instrument and the standard IFP 160000 provided by Institut Français du Pétrole. Hereby, standard procedures of sample preparation and Rock-Eval pyrolysis defined by Espitalié et al. (1977) have been utilized. The Total Organic Carbon (TOC) content of these 48 samples was determined using LECO.

For analysis of the TOC content and the stable carbon isotope ratio of the organic fraction (δ¹³C_org) of 89 samples from the clay unit, 1–3 mg sediment were placed in Ag capsules, in situ treated with 20% HCl at 75°C, and subsequently processed in a Carlo Erba NC 2500 elemental analyzer coupled via a ConFloIII to a Finnigan DELTAplusXL isotope ratio mass spectrometer (EA-IRMS) at GFZ Potsdam. Total nitrogen (TN) content and stable nitrogen isotope ratio (δ¹⁵N) measurements were carried out with the same analytical instrumentation (15–50 mg sediment in Sn capsules). The TOC and TN content values were used to calculate the C/N ratio. Results of the TOC and TN analyses are expressed as percent of dry weight, while those of the δ¹³C_org and δ¹⁵N measurements are expressed in the conventional δ-notation relative to the Vienna Pee Dee Belemnite (VPDB) and atmospheric nitrogen (AIR) standards, respectively. Based on repeated measurements of internal standards for the carbon and nitrogen amount (Urea, Boden 3, HEKATECH) and international reference standards for δ¹³C_org (IAEA CH-7, USGS24) and for δ¹⁵N (IAEA-N-1, -N-2), the precision of the elemental and isotopic analyses is <0.2% and <0.2‰, respectively.

Thirty-five samples from the Holocene clay have been selected for extraction by Accelerated Solvent Extraction (ASE) and separation of soluble organic matter (SOM) fractions by Medium Pressure Liquid Chromatography (MPLC) (GFZ-Potsdam) considering a balanced distribution along the bore-hole and the variation in TOC content. Numbers and depths of these samples are provided in Supplemental Table S2. The amount of extracted SOM was determined gravimetrically before separation of different fractions by MPLC. The aliphatic fraction was then analyzed by gas chromatography (GC) in order to determine the n-alkane distributions. Samples were extracted with an accelerated solvent extractor (ASE) (Dionex, Sunnyvale, USA). The extraction was done with dichloromethane:methanol (9:1) at 76 bar and 100°C. HCl-activated copper was added to remove elemental sulphur. The aliphatic hydrocarbon fractions were isolated with liquid chromatography, using a medium pressure liquid chromatography (MPLC) system (Radke et al., 1980). As quantification standard, 5α-androstane (Sigma–Aldrich, St. Louis, USA) was added to the extracts prior to MPLC.

The compounds within the aliphatic fraction were quantified using an Agilent 6890 GC-FID equipped with an injector heated from 40°C to 300°C at 700°C/min using splitless injection. For the separation of the compounds, an Ultra-1 fused silica capillary column (50 m length, 0.2 mm inner diameter, 0.33 µm film thickness) was used with the following temperature program: oven start temperature of 40°C, heating rate of 5°C/min to 310°C, and an isothermal phase of 60 min. Helium, with a constant flow rate of 1 ml/min, was used as the carrier gas.

Biomarkers were identified and quantified with a Thermo Electron GC-MS-system (GC: Trace GC Ultra; MS: DSQ). The GC was equipped with a PTV injector system (start temperature: 50°C; heating rate 10°C/s to 300°C; 10 min isothermal time; operated in splitless mode) and a BPX5 fused silica capillary column (50 m length, 0.22 mm inner diameter, 0.25 µm film thickness). The GC oven temperature was programmed from 40°C to 310°C at a heating rate of 5°C/min, followed by an isothermal phase of 60 min. Helium, operated with a constant flow rate of 1 ml/min, was used as the carrier gas. The mass spectrometer was operated in electron impact ionization mode. The temperature of the ion source was set to 230°C. The scan range was 50–600 Da at a rate of 2.5 scans/s.

Compound-specific carbon and deuterium isotope measurements were conducted for 37 samples (Supplemental Table S3). Carbon isotope ratios of the compounds were determined using an Agilent 6890N GC, equipped with an Ultra-1 fused silica capillary column (50 m length, 0.2 mm inner diameter, 0.33 µm film thickness). The oven was heated from 40° to 300°C at a rate of 3°C/min before a final isothermal time of 25 min. The GC was coupled to a Thermo Electron Delta V plus IRMS via a Combustion III interface (Thermo Fischer Scientific, Germany). The δ¹³C signal of the internal standard served as a quality control for the stability of the measurement system. In addition, a certified standard mixture of n-alkanes (C₁₅, C₂₀, and C₂₅; Chiron, Trondheim, Norway) was analyzed after every 10th sample. The linearity range (150–10,000 mV) of the measurement system was determined by measuring a dilution series of the same standard mixture.

Hydrogen isotope ratio values for the compounds were measured using GC–P–IRMS (gas chromatography–pyrolysis–isotope ratio mass spectrometry) in GFZ-Potsdam. The system consisted of a GC unit (6890N, Agilent Technology, USA) connected to a GC-C/TC III combustion device coupled via open split to a Delta V plus IRMS (Thermo Fisher Scientific, Germany). Saturated fractions were injected to the programmable temperature vaporization inlet (PTV, Agilent Technology, USA) with a septum-less head in split/splitless mode. The injector was held at a split ratio of 1:2 and an initial temperature of 230°C. With injection, the injector was heated to 300°C (held until the end of the analysis time) at 700°C min⁻¹. Alkanes were separated on a fused silica capillary column (HP Ultra-1, 50 m × 0.2 mm ID, 0.33 µm film thickness; Agilent Technology, USA). The GC conditions were: 40°C (2 min) to 300°C (held 45 min) at 4°C/min. He (1.0 ml min⁻¹), was used as carrier gas. The eluted hydrocarbons were pyrolyzed to H₂ and elemental carbon in a pyrolysis reactor at 1450°C. H₂ was transferred online to the mass spectrometer to determine hydrogen isotope ratio values. All saturated fractions were measured in triplicate. A mixture of n-alkanes (C₁₇, C₁₉, C₂₁, C₂₃, and C₂₅; Schimmelmann, Bloomington, Indiana, USA) with certified isotopic composition was used as external standard for calibration of the reference gas. In addition, the δD signal of the internal standard served as a quality control for the stability of the system.

¹⁴C ages were obtained from sedimentary organic material in the Radiocarbon Dating Laboratory of Illinois State Geological Survey, University of Illinois using the AMS ¹⁴C method. Organic carbon-rich samples from five different depths have been selected for this purpose (Table 1). A half-life of 5568 years has been used for age calculation. Ages are reported as before present (BP), where BP is defined as before 1950. Obtained ¹⁴C ages are calibrated according to Stuiver and Reimer (1993) using the CALIB Radiocarbon Calibration Program and the calibration curve INTCAL 20 (Stuiver et al., 2020).

Table 1.

Results of the AMS ¹⁴C analyses of samples from the Holocene clay unit (calibrated ages show minimum and maximum values according to 1σ and 2σ).

Nr.	Sample	Depth (m from surface)	Material	¹⁴C age (years BP)	¹⁴C age calibrated (cal. years BC)		¹⁴C age calibrated (cal. years BP)		Mean ¹⁴C age calibrated (cal. years BP)
Nr.	Sample	Depth (m from surface)	Material	¹⁴C age (years BP)	1σ (68.3%)	2σ (95.4%)	1σ (68.3%)	2σ (95.4%)	Mean ¹⁴C age calibrated (cal. years BP)
1	G 012522	2,95	Sediment	7745 ± 25	6550−6509	6642−6497	8499−8458	8591−8446	8518 ± 25
2	G 012543	3,85	Sediment	8095 ± 25	7076−7047	7084−7040	9025−8996	9033−8989	9017 ± 25
3	G 012552	4,40	Sediment	8570 ± 25	7595−7583	7601−7574	9544−9532	9550−9523	9538 ± 25
4	G 012569	5,35	Sediment	8405 ± 25	7527−7478	7541−7457	9476−9427	9490−9406	9449 ± 25
5	G 012590	7,10	Sediment	9820 ± 30	9295−9262	9313−9247	11,244−11211	11,262−11196	11,230 ± 30

Geochronology

The age of five organic carbon-rich samples from different depths was determined in order to define the age of the clay unit. Table 1 indicates the depths and obtained ¹⁴C ages of these samples. The minima and maxima of the calibrated ages according to 1 σ and 2 σ are also given in Table 1 as years before present (BP) and as years before Christ (BC).

The determined ¹⁴C ages range between 7745 ± 25 and 9820 ± 30 years BP. For the construction of the age model the median probability value which is determined considering the calibrated age ranges of each sample was taken as the mean age calibrated. The respective values for depths of 295, 385, 440, 535, and 710 cm are 8518, 9017, 9538, 9449, and 11,230 cal. years BP, respectively. The ¹⁴C age of 8405 ± 25 years at 5.35 m is less than the age of 8570 ± 25 years at 4.40 m, although it represents stratigraphically an older level. An explanation for this slight age reversal was not possible. However, this outlier was also considered by the regression analysis, so that this reversal could be taken into account. Using these ages a depth-age model has been constructed, which is shown in Figure 3. Accordingly, for the top and base of the clay unit an interval from about 7490 cal. years BP to 11,100 cal. years BP was defined, that is the deposition of the clay unit should have started at 11,100 cal. years BP and lasted at least until 7490 cal. years BP. These ages are in general accordance with ages obtained at the first borehole (Yenikapı-1), where the onset and end of the deposition of the clay unit were determined as 11,357 and 7403 cal. years BP, respectively (Yalçın et al., 2015). Hence, almost the entire Early Holocene and the first 1000 years of the Mid-Holocene are represented.

Figure 3.

Depth-age model of the clay unit in the Yenikapı-2 borehole. The error margins represent the range of 2σ and the median probability values obtained from calibration. The bar code represents the stratigraphy of the clay unit in the Yenikapı-2 borehole.

The depth-age model suggests a constant sedimentation rate of 0.161 cm/year (161 cm/1000 years). This is also in accordance with the sedimentation rate for the neighboring first borehole determined as 0.173 cm/year (Yalçın et al., 2015). The sedimentation rate of 0.161 cm/year means that the average sampling interval of 6.5 cm represents a time-resolution of approximately 40 years. Considering that along certain depths the sampling intervals are reduced up to 2–3 cm, a resolution from 12 to 19 years has been achieved.

Results

Bulk properties of the organic matter

Amount, quality, and isotopic composition of the organic material in the sediments of an aquatic environment may provide important information on several aspects of this water body, but also for a broader region around this body including climatic conditions (Leng et al., 2006).

The amount of organic material within the sediments depends both on the primary productivity in the respective aquatic environment and its catchment area as well as on the efficiency of organic matter preservation (Littke et al., 1997). The TOC contents of the profile vary significantly between 0.27 and 2.49%. Figure 4 reveals a marked increase of TOC values around 9000 cal. years BP. During the period between about 11,070 and 9000 cal. years BP TOC values were in general below and thereafter above 1%. However, this general trend is interrupted several times by the reduction of TOC values (Figure 4). The time period from about 9000 to 7720 cal. years BP is characterized by significantly higher and fluctuating TOC and TN contents (Figure 4).

Figure 4.

Changes of total organic carbon (TOC), hydrogen index (HI), nitrogen (N), and C/N ratio in the sediments of the swamp in Yenikapı-Istanbul through the Early and early Mid-Holocene. The bar codes represent the stratigraphy of the clay unit in the Yenikapı-2 borehole.

Insights into the quality of the organic matter may help to figure out, whether this fluctuation is related to changes in bioproduction or in preservation of organic matter or both. The quality of sedimentary organic material can be investigated with the help of different proxies such as the type of kerogen, the nitrogen content, the C/N ratio, and the molecular composition of n-alkanes. The kerogen type has been evaluated with the help of Hydrogen Index (HI) values (Supplemental Table S4) and the TOC-S2 diagram (Supplemental Figure S1). For the core studied, HI-values are generally low (29–81 mgHC/gTOC) indicating that the majority of the organic matter is of terrestrial origin (Figure 4 and Supplemental Figure S1). Hence, organic material in sediments of the swamp area should have been sourced to a great extent from the terrestrial plants in the catchment area. Over the course of Early Holocene and early Mid-Holocene the HI values show a fluctuating trend as also found for the TOC contents. However, between these parameters an inverse correlation does exist, that is the quality of organic material (HI values) increases when the amount of organic material decreases. This may be related to transport and accumulation of dead carbon (burned material) with negligible generative potential into the swamp area, which would result in an increase of TOC content but a decrease of HI (Tissot and Welte, 1984). It would also be possible that during certain periods the transport of terrestrial material into the sediments is reduced such that the quality of the organic material increases due to a higher relative contribution from autochthonous primary producers.

The amount of nitrogen varies between 0.03 and 0.18% and shows an overall increasing trend after 9000 cal. years BP. The pattern of the variations in nitrogen content is very similar to that of the TOC content (Figure 4 and Supplemental Table S1). This suggests that nitrogen is associated with the organic material in the sediments. The C/N ratio of the organic matter in the Holocene sequence varies between 6 and 14 (Figure 4). Considering that algal organic material is represented by values ranging between 4 and 10 while terrestrial organic matter typically exceeds values of 20 (Kaushal and Binford, 1999; Meyers, 1994, 1997; Meyers and Ishiwatari, 1993), a mixture of allochthonous and autochthonous organic material can be inferred to be present in the sediments of the swamp. On the other hand the δ¹³C_org versus C/N diagram of the samples (Supplemental Figure S2) suggests according to Lamb et al. (2006) an assignment to a mixed origin of the organic material from different sources. Although a few samples are pointing to a “marine dissolved organic carbon” origin, sources like “freshwater algae,” “freshwater particulated organic carbon (POC),” “freshwater dissolved organic carbon (DOC),” and “C₃ terrestrial plants” are clearly dominating. Furthermore, the HI values and, as will be discussed later, also the molecular composition of the n-alkanes point to an obvious origin from land plants. Consequently, the organic material in the sediments has a predominantly terrestrial origin, which was swept into a freshwater swamp and has been slightly altered there in a reducing environment.

Bulk isotopic composition of organic matter

Bulk δ¹³C_org values can provide important information on paleoenvironmental processes like primary productivity (Eglinton and Eglinton, 2008; Hollander and MacKenzie, 1991), bacterial activity (Hedges et al., 1997), anoxicity (Whiticar et al., 1986), and even vegetation changes in the watershed, if the organic material is significantly composed of terrestrial inputs (Castañeda and Schouten, 2011). Furthermore, changes in the amount of atmospheric CO₂ and climate also affect the δ¹³C_org values (Meyers and Teranes, 2001). Additionally, the type of vegetation in terms of the photosynthetic pathway used by respective plants, the so-called C₃ and C₄ plants can be distinguished based on the δ¹³C values (Castañeda and Schouten, 2011 and references therein). Whereas C₃ plants strongly fractionate atmospheric CO₂ resulting in δ¹³C values of approximately −27‰, C₄ plants produce δ¹³C values of around −13‰.

The δ¹³C_org values of the Holocene sediments in the Yenikapı-Istanbul area show a relatively low variability ranging between −26.4‰ and −24.3‰ (Supplemental Figures S2 and 5). In general a fluctuating trend between these two values can be seen. During certain periods remarkable and sudden shifts in isotopic composition are observed. Namely, from about 10,560 to 10,450, from 10,080 to 9930, and from 8340 to 8260 cal. years BP the isotopic composition gets lighter from −24.7‰ to −26.0‰, from −24.3‰ to −25.8‰, and from −24.8‰ to −26.4‰, respectively. Another shift toward heavier values occurred during the period from 10,450 to 10,080 cal. years BP (Figure 5). As these respective shifts are bigger than 1.0‰, they can be considered as shifts related to certain changes in the environment and/or climate.

Figure 5.

Changes of δ¹³C_org and δ¹⁵N through time. Periods of remarkable changes toward heavier (dark gray) and lighter (light gray) δ¹³C_org values are indicated. The bar codes represent the stratigraphy of the clay unit in the Yenikapı-2 borehole.

δ¹⁵N values of sediments can also provide information on paleoenvironmental conditions (Leng et al., 2006). However, the complexity related to the nitrogen input into a certain environment and isotopic fractionations in the respective environment makes the interpretation of the data difficult. For example, δ¹⁵N values of plants vary between −5‰ and +8‰, and of soil between 0‰ and +8‰ (Handley et al., 1999) or of human and animal sewage waste between +8‰ and +18‰ (Heaton, 1986). The bulk isotopic δ¹⁵N values of Holocene sediments in the Yenikapı-Istanbul range between 5.7‰ and 7.7‰, where some relatively sudden shifts are to observe (Figure 5). Furthermore, the δ¹⁵N values show a continuously decreasing trend since about 8560 cal. years BP. The δ¹⁵N values reflect in general an origin of the organic material from plants and were probably influenced by autochthonous productivity.

Molecular composition of the organic matter

The n-alkanes show a dominance of long-chain homologs (>20 carbon atoms) over the entire sequence of the Holocene clay unit as depicted in Supplemental Figure S3. Shorter-chain n-alkanes (<21 carbon atoms) are either almost missing or their amounts are negligible. Short chain alkanes do not display an odd over even preference and their amounts increase with increasing depth (age). In contrast, long-chain n-alkanes show a clear odd over even predominance. The most abundant n-alkanes are C₃₁, C₂₉, C₃₃, and C₂₇ in this order (Supplemental Figure S3).

As the long-chain n-alkanes originate mainly from vascular plant leave waxes (Eglinton and Hamilton, 1967), the dominant organic material in the sediments of the swamp area has to be of terrestrial origin. Furthermore, as short-chain n-alkanes in general indicate organic matter deriving from algae and bacteria (Han and Calvin, 1969), a contribution from such organisms can be either excluded or considered as very minor.

The concentrations of the long-chain n-alkanes are varying with depth, that is, with time. As shown for C₂₇, C₂₉, C₃₁, and C₃₃ the concentrations are less than 50 µg/gTOC at the time interval from about 10,230 to 9070 cal. years BP (Supplemental Figure S3). As all the other dominant n-alkanes exhibit the same trend during this period, the concentration of all of them was lowered. Therefore, during this 1160 years long period the contribution to the organic matter in the swamp area from this source was either reduced due to changes of vegetation in the watershed or because organic material from another source became dominant. However, the similarity of n-alkane distributions over the entire profile does not point to strong changes in the composition of the vegetation (Supplemental Figure S3). Hence, the decrease of n-alkane concentrations normalized to TOC is probably related to the dilution of labile organic matter with inert (dead carbon) organic material.

Distribution and quantitative composition of the SOM is also used in order to obtain proxies which can help to define environmental properties and provenance. Pristane/Phytane (Pr/Ph) Ratio, Carbon Preference Index (CPI), the submerged versus emergent aquatic plants predominance ratio (P_aq), Terrestrial-Aquatic-Ratio (TAR_HC), and Average Chain Length (ACL) are the proxies utilized for this purpose. The pristane/phytane (Pr/Ph) ratio values of the samples are <1 except one sample (1.35 m) (Supplemental Table S2). This indicates an anoxic depositional environment over the entire period, as also supported by the lithological properties (black clay) of the sequence. On the other hand as the sequence studied is still immature, it should be considered that the isoprenoids pristane and phytane can also derive from older organic material, which was swept in. The CPI values listed in Supplemental Table S2 are calculated according the formula (1). The CPI values are <10 except for one sample (2.63 m) indicating the predominance of odd-numbered n-alkanes. Compounds with such pattern derive from cuticular waxes of terrestrial higher plants (Tissot and Welte, 1984). The P_aq data have been calculated using the equation (2) after Ficken et al. (2000). The P_aq values vary around 0.10 (Supplemental Table S2). These data also confirm the predominance of terrestrial organic matter in the sediments of the swamp area in Yenikapı. In other words emerged and/or submerged aquatic plants did not significantly contribute to organic material in sediments of the swamp. The Terrestrial-Aquatic-Ratio values calculated using the equation (3) vary between 4.43 and 48.74 (Supplemental Table S2) and confirm that terrestrial higher plants were the dominant source of organic matter in the sediments. The average chain length (ACL) is calculated according the formula (4). ACL could have been used as a proxy for aridity or temperature at some locations (Rommerskirchen et al., 2003). However, a general and overall usage is still questionable (Castañeda and Schouten, 2011). In the Istanbul-Yenikapı area the ACL values were almost uniform around 30 over the entire time period (Supplemental Table S2). As other proxies indicated fluctuations in environmental conditions, the questionable use of ACL as a proxy for aridity is confirmed.

\begin{array}{l} C P I = 0, 5 x (D 16 + D 18 + D 20 + D 22 + D 25) / \\ (D 15 + D 17 + D 19 + D 21 + D 24) + \\ (D 16 + D 18 + D 20 + D 22 + D 25) / \\ (D 17 + D 19 + D 21 + D 24 + D 26) \end{array}

(1)

P a q = C_{23} + C_{25} / C_{23} + C_{25} + C_{29} + C_{31}

(2)

T A R_{H C} = C 27 + C 29 + C 31 / C 15 + C 17 + C 19

(3)

\begin{array}{l} A C L = (27 * H 18 + 29 * H 20 + 31 * H 22 + 33 * H 25) \\ / (H 18 + H 20 + H 22 + H 25) \end{array}

(4)

Carbon and hydrogen isotopic composition of n-alkanes

Using compound-specific carbon isotopes vegetation type and accordingly climatic parameters and primary productivity in aquatic environments can be reconstructed (Castañeda and Schouten, 2011 and references therein). In Yenikapı-Istanbul area the carbon isotopic composition of n-alkanes could be determined only for long-chain homologs, as only their amounts were high enough for δ¹³C measurements. Consequently, data are (almost) complete only for the C₂₇, C₂₉, and C₃₁ n-alkanes for the entire time period from about 11,070 to 7670 cal. years BP. Data for C₃₃ is also patchy, as in certain samples the amount of C₃₃ was too low to be measured. For the C₂₁, C₂₃, and C₂₅ n-alkanes the δ¹³C data are only available for late Early Holocene (Supplemental Table S3). Temporal changes of the compound-specific carbon isotopic compositions of the C₂₇, C₂₉, and C₃₁ n-alkanes are shown in Figure 6. All of them represent a very similar trend.

Figure 6.

Variation of the δ¹³C values of the C₂₇, C₂₉, and C₃₁ n-alkanes. Remarkable shifts toward lighter values are observed at about 11,000–10,800, 9400–9300, and 8250–8100 cal. years BP (light gray) and toward heavier values at about 10,800–10,200 and 9300–9000 cal. years BP (dark gray). The bar codes represent the stratigraphy of the clay unit in the Yenikapı-2 borehole.

The δ¹³C values of nC₂₇ in general are fluctuating between −31.0‰ and −34.0‰, those of nC₂₉ between −33.0‰ and −36.0‰ and those of nC₃₁ between −34.0‰ and −36.5.0‰. These ranges are typical for terrestrial C₃ plants. Shifts at about 11,000–10,800, 9400–9300, and 8250–8100 cal. years BP toward lighter values and shifts at about 10,800–10,200 and 9300–9000 cal. years BP toward heavier values exhibit sudden changes bigger than 1.5‰. Therefore, during these periods a change in certain factors such as vegetation type, climatic conditions (temperature, aridity, and atmospheric CO₂ concentrations), bioproductivity, or microbial processing are likely (Castañeda and Schouten, 2011 and references there in).

Hydrogen isotopic (δD) composition is used to assess changes in the hydrological regime in a certain region (Sachse et al., 2012). Particularly, hydrogen isotope ratio values of n-alkanes derived from leaf waxes can be used to reconstruct the hydrological variability, for example, variations in precipitation amounts (Schefuss et al., 2005). It has been shown that precipitation δD values are the main factor controlling the δD composition of plant leaf waxes (Castañeda and Schouten, 2011; Polissar and Freeman, 2010; Sachse et al., 2006). The depletion of meteoric water in deuterium with increasing amount of precipitation because of Rayleigh distillation is the main reason of that (Aichner et al., 2010; Peters et al., 2005).

As pointed out above for the carbon isotopic composition, the hydrogen isotopic composition of n-alkanes could be determined only for the C₂₇, C₂₉, C₃₁, and C₃₃ n-alkanes due to insufficient abundance of other homologs (Supplemental Table S3). Furthermore, reasonable values could be determined for samples, which represent a time period approximately from 9000 to 7800 cal. years BP (Supplemental Table S3). Temporal changes of the hydrogen isotopic composition of the C₂₇, C₂₉, C₃₁, and C₃₃ n-alkanes are shown in Figure 7. There are two distinct excursions in these values. The first one at about 9000–8820 cal. years BP is characterized by an abrupt shift from −185‰ to −225‰, indicating a remarkable depletion in deuterium. The δD values remain at this level until approximately 8150 cal. years BP and then the second excursion can be recognized. This time the δD values shift back from about −210‰ to −180‰ at 8050 cal. years BP (Figure 7), which indicates a sudden and remarkable enrichment in deuterium. Between these two excursions, during an about 700 years long period, δD values remain almost constant at about −220‰ suggesting stable conditions regarding the factors and/or processes which control the hydrogen isotopic composition.

Figure 7.

Variation of δD values of the C₂₇, C₂₉, C₃₁, and C₃₃ n-alkanes. A shift toward lighter values is observed at about 9000−8820 cal. years BP (light gray) and toward heavier values at about 8150–8050 cal. years BP (dark gray). The bar codes represent the stratigraphy of the clay unit in the Yenikapı-2 borehole.

Discussion

The results on bulk organic geochemical properties, molecular organic geochemical and the compound-specific isotopic composition of OM from the swamp in Yenikapı-Istanbul area will be discussed from environmental and paleoclimatic points of view, including comparison with similar other records in close and far regions, and with a particular focus on possible anthropogenic impacts. The aim of this discussion is to present a paleoenvironmental and paleoclimatic history of Istanbul area during the period studied.

At about 11,300 cal. years BP one of the major branches of the small river Lykos in Yenikapı-Istanbul area (Figure 1) was abandoned because it was blocked downstream and a swamp/wetland was formed on the flood-plain of the river. Lykos is one of the streams, which started to carry more water due to changing climatic conditions from cold/dry to wet/warm when the Younger Dryas was terminated at about 11,700 cal. years BP (Carlson, 2013; Dansgaard et al., 1989). Fine detrital material swept into the swamp by the Lykos River started to be deposited there. At this time the shoreline of the Marmara Sea was located several kilometres southward compared to present day situation. Because the global sea-level started to rise only after the termination of the Last Glacial Maximum (LGM), seawater has invaded the sill at entrance of the Dardanelles Strait being at −65 m not before 12,000 BP. From that time on the fresh-water Marmara Lake was gradually converted to saline sea conditions (Çağatay et al., 2000). Considering that the Neolithic settlement in Yenikapı was invaded by the rising sea not before about 6800 BP (Algan et al., 2011; Yalçın et al., 2015), one can assume, that the depositional environment was a swamp on the flood-plain of Lykos far from the sea.

After the Younger Dryas the first half of the Holocene was characterized in general by an amelioration of climate and various regions in the Eastern Mediterranean experienced a climate wetter than before and today (Bar-Matthews et al., 1997, 1999; Berger et al., 2016; Roberts et al., 2008, 2011a, 2011b). However, during this early Holocene period several climatic pulsations of wetter/drier phases have also been inferred (Berger et al., 2016). The period from about 11,070 to 10,800 cal. years BP was probably one of the cooler phases in the Istanbul region, as indicated by compound-specific δ¹³C values of terrestrial C₂₇, C₂₉, and C₃₁ n-alkanes (Figure 8). The shift toward lighter values of about 2‰ may also be related to a decreasing input of C₄ plants, as the OM in the swamp is significantly of terrestrial origin and the changes in isotopic composition reflect vegetation changes in the watershed. This is the first of three similar isotopic excursions (Figures 6 and 8) observed during the subsequent 4000 years period in this region. The bulk δ¹³C values of OM during this period also exhibit three similar shifts however at different periods (Figures 5 and 8). The difference between compound-specific and bulk δ¹³C values is also reported in some cases before and has been explained by the complexity of the processes influencing δ¹³C values (Castañeda and Schouten, 2011; Castañeda et al., 2009; Huang et al., 1999; Kristen et al., 2010).

Figure 8.

Interpretation of proxy parameter trends derived from bulk and molecular geochemical and isotopic composition of organic matter in sediments from the yenikapı-2 borehole. (1) 11,070–10,800 cal. years BP, cooler climatic conditions, and decrease of C₄ plants; (2) 10,800–10,080 cal. years BP, wetter climatic conditions, and drawdown of atmospheric ¹²CO₂; (3) 10,080–9930 cal. years BP, cooler climatic conditions, and decrease of C₄ plants; (4) 9400–9200 cal. years BP, 9.2 event, and/or Bond 6 event; (5) 9200–9000 cal. years BP, warmer climatic conditions, and increase of C₄ plants; (6) 9000–8880 cal. years BP, remarkable increase in humidity; (7) 8340–8050 cal. years BP, 8.2 event; (8) 8150–8050 cal. years BP, remarkable decrease in humidity.

The following 700 years until 10,080 cal. years BP were in general a period of a wetter climate, as indicated by the shift toward heavier values of the isotopic composition of terrestrial plants and of bulk organic matter (Figures 5, 6, and 8). This is probably accompanied by an increase in bio-productivity and accompanying drawdown of atmospheric ¹²CO₂ (Hayes, 1993). The study of the stalagmites in the Sofular Cave, which is approximately 200 km to east-northeast of Istanbul, pointed to a substantial increase in effective moisture between 11,600 and 9600 years BP (Fleitmann et al., 2009; Göktürk et al., 2011). Data from Tenaggi Philippion marsh in northern Greece to the west of the Yenikapı-İstanbul area also indicate more humid conditions after the Younger Dryas until 10,200 years BP (Berger et al., 2016; Peyron et al., 2011). Hence, the increase in humidity in the Istanbul area has also been experienced in the broader region (Figure 9). However, as indicated by bulk δ¹³C values of OM a short-termed colder period between about 10,560 and 10,450 cal. years BP, which caused a reduction of C₄-plants in the watershed, may have also occurred.

At about 10,230 cal. years BP the proportion of terrestrial components represented by C₂₇, C₂₉, C₃₁, and C₃₃ n-alkanes in the sediments of the swamp decreased suddenly and remarkably (Supplemental Figure S3). It remained low until about 9200 cal. years BP. The Total Organic Carbon (TOC) values were also relatively low in this period. However, as the amounts of the respective n-alkanes are expressed normalized to Total Organic Carbon (gTOC), the relative contribution of terrestrial plant material to the organic matter was reduced in comparison to earlier and later periods. This period of depressed proportion of terrestrial components coincides at the beginning with fluctuating bulk δ¹³C_org values during 10,450–10,080 and 10,080 to 9930 cal. years BP. Hence, the statement that in the Eastern Mediterranean region during the early Holocene period several environmental/climatic pulsations of wetter/drier phases have been experienced (Berger et al., 2016), is confirmed.

At about 9400–9200 cal. years BP a sudden and remarkable shift in the δ¹³C values of terrestrial n-alkanes and a moderate shift in the bulk δ¹³C values may point to another rapid climatic change (RCC) event, which may be related with the 9.2 event (Figure 8). The 9.2 event is one of the three bigger events determined in the Greenland ice cores, which were triggered by melt water pulses in Greenland (Bond et al., 2001, 1997; Flohr et al., 2016; Grootes et al., 1993; Mayewski et al., 1997) (Figure 8). Fleitmann et al. (2008) stated that this event caused a remarkable change of climate toward dry/cold conditions in the northern hemisphere. This global event was reflected in lower monsoon precipitation in China defined by δ¹⁸O data from stalagmites in Dongge cave (Dykoski et al., 2005). Data from Qunf cave in Oman also indicated drier conditions around 9200 years BP (Fleitmann et al., 2003, 2007) (Figure 9). In the Tenaghi Philippon marsh in Greece short-termed dryer climatic conditions at 9600–9300 years BP are reported (Berger et al., 2016; Kotthoff et al., 2008) (Figure 9). Just after this dry period an increase in woodland in this region indicated by palynomorphs of deciduous trees points to a return to warmer conditions (Peyron et al., 2011). Also in the Yenikapı-Istanbul area a sudden shift of the δ¹³C values of terrestrial n-alkanes toward heavier values from 9300 to 9000 cal. years BP suggests a return into warmer conditions and probably to an associated increase of C₄ plants (Figures 6 and 8). Expansion of alluvial fans in Central Anatolia to the north of the Taurus Mountains, which started at 9500 years BP and lasted until 9000 years BP, is explained by enhanced water recharge from the mountains to the Konya plain (Boyer et al., 2006; Kuzucuoğlu et al., 2013). This river dynamics is explained by a possible increase in seasonal temperature contrast, which produced enough snow and ice melt water (Berger et al., 2016). As mentioned before, the shift in compound-specific isotope values in Yenikapı-Istanbul area, observed at about 9400–9300 cal. years BP, may be related to the 9.2 event, if a degree of uncertainty in geochronology is taken into account. However, it should also be considered that a strong reduction in solar irradiance can also cause such a shift. The Bond Event 6, which is dated to 9350 years BP (Bond et al., 2001), can therefore be the main cause of this shift in the Yenikapı area.

Figure 9.

Comparison of the 9.2 and 8.2 events defined in the Yenikapı-2 borehole based on δ¹³C_org, δ¹³C nC₂₉, and δDnC₂₉ values with those obtained from other locations using different proxies. The upper part of the figure used for comparison is a modified version of Figure 1 from Flohr et al. (2016).

At about 9000 cal. years BP a very significant change in the δD values of the C₂₇, C₂₉, C₃₁, and C₃₃ n-alkanes has happened. A sudden excursion toward more negative values up to 40‰ is observed in a period from 8970 to 8880 cal. years BP (Figure 7). Long-chain n-alkanes (C₂₇, C₂₉, C₃₁, C₃₃) represent epicuticular waxes of vascular terrestrial plants (Eglinton and Eglinton, 2008; Sachse et al., 2012) and δD values of these compounds are governed by δD of the source water, which is used from the plants for their growth (Sachse et al., 2012; Schemmel et al., 2016). Consequently, δD data of plant waxes can be used as a proxy for precipitation reconstructions (Schemmel et al., 2016 and references therein). Furthermore, as the deuterium content of precipitation depends mainly on climate, increasing with increasing temperature, variations of compound-specific δD values would reflect variations in temperature and/or humidity (Xie et al., 2000). Consequently, this excursion which started at 8970 cal. years BP and lasted until 8880 cal. years BP, should point to a remarkable increase in humidity and temperature in the Istanbul region during this almost 100 years long period (Figure 8). The continuously increasing trend in Total Organic Carbon (TOC) content in the sediments of the swamp observed in the period from approximately 8900 cal. years BP which continued until 8250 cal. years BP (Figure 4) is probably related to increasing intensity of rain and decreasing temperatures, which may have resulted in a rise of the water level in the swamp area, in a better preservation of organic material, and in an increase of bioproductivity in and around the swamp.

The climatic conditions represented by enhanced humidity and temperature conditions remained for a long period almost without any major change as indicated by bulk δ¹³C, by compound-specific δ¹³C, and by δD values of organic material (Figures 5, 6, and 7), which exhibit only small fluctuations until approximately 8300 cal. years BP. Hence, it can be inferred that during this 600 years long period relatively stable environmental and climatic conditions were effective in the Istanbul area.

Toward the end of 9th millennium BP (approximately 7th millennium BC) in the Yenikapı-Istanbul area a major change of the environmental and climatic conditions has occurred. This remarkable change is reflected in all the respective isotopic proxies taken into account in this study. At about 8340 cal. years BP a first indication is observed in the bulk δ¹³C values and then at 8250 cal. years BP in the δ¹³C values of the C₂₇ and C₃₃ n-alkanes. A depletion of more than 1.00‰ points to a first tendency toward drier and colder conditions and to respective changes of the flora (Figures 5 and 6). As nC₂₇ represents wax from tree leafs and nC₃₃ from grasses (Zech et al., 2013), one can assume that the entire flora in the catchment was affected by this change. These excursions confirm that the dry/cold climatic conditions continued almost uninterrupted until 8100 cal. years BP. The very obvious shift (~25 ‰) of compound-specific δD values of terrestrial n-alkanes toward less negative values, which started at 8150 cal. years BP and lasted until 8050 cal. years BP (Figure 7) testify that drier climatic conditions, which were experienced before, have also resulted in a change toward less humidity in the hydrological regime of the area. A certain temporal shift between the onset of drier atmospheric conditions and decreasing humidity in the hydrological regime can be inferred. Consequently, the period from 8340 to 8050 cal. years BP was a dry/cold period, which coincides temporarily very well with the so-called 8.2 event (Alley and Agustdottir, 2005; Alley et al., 1997; Barber et al., 1999; Thomas et al., 2007). This event was triggered by the melt water outburst of Laurentide lakes in Northern Canada into the North Atlantic, which resulted in reduction of the Atlantic Meridional Overturning Circulation (AMOC) and in a subsequent increase of sea-ice in North Atlantic (Bauer et al., 2004; Renssen et al., 2001; Schemmel et al., 2016). All these phenomena led to remarkable changes in the climate of northern hemisphere in terms of a decline of winter temperatures in northern high latitude regions, and drier and cooler conditions around the Mediterranean (Mayewski et al., 2004; Rohling and Paelike, 2005; Rohling et al., 2002; Schemmel et al., 2016). Studies of Greenland ice cores showed, that the decline in δ¹⁸O values started at 8247 years BP and lasted 160.5 ± 5.5 years (Thomas et al., 2007). However, in the eastern Mediterranean regions the 8.2 event is recorded as a much longer period lasting from 8400 to 8000 years BP (Berger et al., 2016; Weninger and Clare, 2011; Weninger et al., 2006). Therefore, we believe that the isotopic excursions observed in Yenikapı-Istanbul area, which commenced at 8340 cal. years BP and lasted until 8050 cal. years BP, are related with the 8.2 event (Figure 8). Hence the Neolithic settlements in this region such as Yenikapı, Fikirtepe, Pendik (Figure 1), which are dated approximately to a period between 8500 to 7500 years BP (Kızıltan and Polat, 2013; Özdoğan, 2013) should have been affected by this event.

After the dry/cold 8.2 event, as indicated by the bulk, compound-specific δ¹³C and δD isotopic values of organic material, a return to pre-event environmental conditions occurred (Figures 5, 6 and 7). These conditions remained probably at least until 7490 cal. years BP, the date determined by extrapolation for the top of the swamp deposits in the Yenikapı-2 borehole. This date coincides partly with the termination of the Neolithic settlement, which was probably abandoned due to globally rising sea-level taking place since the LGM. The swamp, the fluvial plain of the Lykos River, and the former site of the settlement were flooded by this marine transgression, which is dated in Yenikapı to 6740–6950 cal. years BP (Algan et al., 2009, 2011). It is likely that the Neolithic people left the respective site before it was flooded.

Assuming that the Neolithic village was settled at about 8500 years BP and abandoned at about 7400 years BP, during a time period longer than 1000 years, a close relation existed between the people and this wetland. This relationship is also confirmed by several archaeological objects, such as burials, pithos graves, wooden findings, holes of wooden posts, shingles, and several hundred foot-prints of people, found in swamp deposits (Kızıltan and Polat, 2013; Yalçın et al., 2015). In order to find out, whether anthropogenic impacts can be detected with the help of organic geochemistry as it has been demonstrated at some archaeological sites (Dubois and Jacob, 2016; Heim and Schwarzbauer, 2013; Schwarzbauer et al., 2018), we looked for specific molecular organic geochemical indicators such as faecal sterols, in particular, coprostanol/cholestanol ratios (D’Anjou et al., 2012) or for strong enrichment by δ¹⁵N by human and animal waste (Kendall et al., 2007). However, such molecular and isotopic geochemical indicators could not be detected. Therefore, it is likely that the swamp has not so intensively been used by Neolithic people and/or respective indicators of impacts have been diluted by the high sedimentation rate in the swamp.

Conclusions

Gray-black clay sediments deposited in a small swamp on the flood-plain of Lykos River has been uncovered during the archaeological excavations in the Byzantine Theodosian harbor in Yenikapı Istanbul.

The depth-age model based on Carbon-14 (¹⁴C) data showed that the clay was deposited between 11,100 and 7490 cal. years BP, that is, during the Early-Mid-Holocene period.

The clay unit is in general rich in organic material, although the amounts show fluctuations through time. Until 9000 cal. years BP TOC values were in general lower and thereafter higher than 1.00%.

The origin of the organic matter was predominantly terrestrial C₃ plants as indicated by Hydrogen Index values lower than 100 mgHC/gTOC, n-alkane distributions with maxima at nC₂₉ or at nC₃₁, a predominance of long-chain n-alkanes (C₂₅–C₃₃) and δ¹³C_org values around −24‰ to −27‰.

Shifts toward drier, wetter, colder and warmer periods, and toward subsequent floral changes in terms of C₃ and C₄ plants were identified with the help of bulk and compound-specific δ¹³C_org data.

Two distinct changes of the hydrological regime were identified with the help of compound-specific δD data of epicuticular waxes of vascular terrestrial plants (C₂₇, C₂₉, C₃₁, and C₃₃). Sudden changes toward a wet and dry hydrological regimes were dated to 9000–8820 and 8150–8050 cal. years BP, respectively.

Specific molecular organic geochemical indicators such as faecal sterols or a strong enrichment of δ¹⁵N caused by human impact were not observed. Therefore, the swamp likely has not so intensively been used by Neolithic people and/or respective indicators of impacts have been diluted by the high sedimentation rate.

Yenikapı excavations take on an important task in understanding the interaction between the cultural history of Istanbul beginning from the Neolithic period and the changes observed in the environmental system.

Supplemental Material

sj-docx-1-hol-10.1177_09596836211033197 – Supplemental material for Organic geochemical characterization of Early-Mid-Holocene swamp deposits near the Neolithic settlement in Yenikapı-Istanbul: Assessment of environmental variability and anthropogenic impacts

Supplemental material, sj-docx-1-hol-10.1177_09596836211033197 for Organic geochemical characterization of Early-Mid-Holocene swamp deposits near the Neolithic settlement in Yenikapı-Istanbul: Assessment of environmental variability and anthropogenic impacts by Mehmet Namık Yalçın, Heinz Wilkes and Birgit Plessen in The Holocene

Supplemental Material

sj-docx-2-hol-10.1177_09596836211033197 – Supplemental material for Organic geochemical characterization of Early-Mid-Holocene swamp deposits near the Neolithic settlement in Yenikapı-Istanbul: Assessment of environmental variability and anthropogenic impacts

Supplemental material, sj-docx-2-hol-10.1177_09596836211033197 for Organic geochemical characterization of Early-Mid-Holocene swamp deposits near the Neolithic settlement in Yenikapı-Istanbul: Assessment of environmental variability and anthropogenic impacts by Mehmet Namık Yalçın, Heinz Wilkes and Birgit Plessen in The Holocene

Supplemental Material

sj-docx-3-hol-10.1177_09596836211033197 – Supplemental material for Organic geochemical characterization of Early-Mid-Holocene swamp deposits near the Neolithic settlement in Yenikapı-Istanbul: Assessment of environmental variability and anthropogenic impacts

Supplemental material, sj-docx-3-hol-10.1177_09596836211033197 for Organic geochemical characterization of Early-Mid-Holocene swamp deposits near the Neolithic settlement in Yenikapı-Istanbul: Assessment of environmental variability and anthropogenic impacts by Mehmet Namık Yalçın, Heinz Wilkes and Birgit Plessen in The Holocene

Supplemental Material

sj-docx-4-hol-10.1177_09596836211033197 – Supplemental material for Organic geochemical characterization of Early-Mid-Holocene swamp deposits near the Neolithic settlement in Yenikapı-Istanbul: Assessment of environmental variability and anthropogenic impacts

Supplemental material, sj-docx-4-hol-10.1177_09596836211033197 for Organic geochemical characterization of Early-Mid-Holocene swamp deposits near the Neolithic settlement in Yenikapı-Istanbul: Assessment of environmental variability and anthropogenic impacts by Mehmet Namık Yalçın, Heinz Wilkes and Birgit Plessen in The Holocene

Supplemental Material

sj-docx-5-hol-10.1177_09596836211033197 – Supplemental material for Organic geochemical characterization of Early-Mid-Holocene swamp deposits near the Neolithic settlement in Yenikapı-Istanbul: Assessment of environmental variability and anthropogenic impacts

Supplemental material, sj-docx-5-hol-10.1177_09596836211033197 for Organic geochemical characterization of Early-Mid-Holocene swamp deposits near the Neolithic settlement in Yenikapı-Istanbul: Assessment of environmental variability and anthropogenic impacts by Mehmet Namık Yalçın, Heinz Wilkes and Birgit Plessen in The Holocene

Footnotes

Acknowledgements

We are grateful to the Turkish Ministry of Culture, the Directorate of the Istanbul Archaeological Museums, and its former director, Zeynep Kızıltan, for the permission to conduct such a study in the Yenikapı excavation site. The support of the archaeologists of the museum, Mehmet Ali Polat and Sırrı Çölmekçi, is kindly acknowledged. The supports of Dr. Ayşin Konak (Kocaeli University) in the documentation and sampling of the cores, and Dr. Selman Er and Doğacan Özcan (Istanbul University) in the preparation of the figures are also acknowledged. We thank Kristin Günther, Anke Kaminsky, Cornelia Karger, Doreen Noack, Sylvia Pinkerneil (all GFZ) for skilled technical assistance. The authors thank the two anonymous reviewers for their helpful and constructive comments and suggestions.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study is supported by the Istanbul University Research Fund (Project Nr. ÖNAP-472 and ACIP-7421) and by the Alexander von Humboldt Foundation, which enabled a research visit of M. Namık Yalçın at the Deutsches GeoForschungsZentrum Potsdam (GFZ).

ORCID iD

Mehmet Namık Yalçın

Supplemental material

Supplemental material for this article is available online.

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