Holocene environmental change in southwest Turkey: a palaeoecological record of lake and catchment-related changes

Percentage, concentration and accumulation pollen data together with diatom and non-siliceous microfossil data are presented for the site of Gölhisar Gölü (37°8′N, 29°36′E; elevation 930 m), a small intramontane lake in Burdur Province, southwest Turkey. Microfossil assemblages from the longest sediment core (GHA: 813 cm) record changes in local and regional vegetation and lake productivity over the last ∼9500 years. Pollen spectra indicate that vegetation progressed from an open landscape with an increase in arboreal pollen occurring ∼8500 bp to mixed forest comprising oak, pine and juniper until around 3000 bp (Cal ∼1240 BC) when a human occupation phase becomes discernible from the pollen spectra. This occurs shortly after the deposition of a volcanic tephra layer which originated from the Minoan eruption of Santorini (Thera) and radiocarbon dated to 3330±70 yr bp (Cal ∼1600 BC). This human occupation phase is comparable to the Beyşehir Occupation phase recorded at other sites in southwest Turkey and involved forest clearance and the cultivation of fruit trees such as Olea, Juglans, Castanea and Vitis together with arable cereal growing and pastoralism. The presence of pollen types associated with the Beyşehir Occupation phase in deposits above the Santorini tephra layer confirms a Late Bronze Age/early Anatolian Dark Age date for its commencement. Since ∼3000 bp notable changes in aquatic ecology associated with tephra deposition and subsequent nutrient and sediment flux from the lake catchment are recorded. The Beyşehir Occupation phase at Gölhisar Gölü came to an end around 1300 bp (Cla AD ∼700) when pine appears to have become the dominant forest tree.     

Mechanism and geochemical implications of the Late Holocene organic carbon burial event: an example from the southwest coast of India

Carbonaceous clay found in the palaeo-deposits of Meenachil River basin was analysed for the total organic carbon, nitrogen and textural characters. Radiocarbon dating of this clay formation and the embedded carbonized wood fragments was also done. The values obtained for the organic carbon, nitrogen and C/N ratio of the carbonaceous clay exhibited a very remarkable range, suggestive of different environmental conditions of formation. It is evident from the present study that since the lignin and cellulose are the dominant components of terrestrial higher plants, allochthonous and submerged organic matter have high C/N ratio. The radio carbon dating of the sediment and wood samples suggested that the palaeo-deposits of Meenachil River basin were formed as result of many transgrassive–regressive episodes, which had started even before the formation of Vembanad Lake. The formation of carbonaceous clay, as found sandwiched in palaeo-deposits, was due to the global eustatic sea-level fluctuations and tectonism.     

A note on rare structure of fossil coralline algae from the southwest coast of India

The coralline algae (Rhodophyta) are well preserved in the sediments of the Dwarka Formation in and around Porbandar area, southwest coast of India. There are few records of the preservation of genicula in the fossil coralline algae. Three algal fragments with genicula are noted and recorded from the area.     

Heavy metal accumulation in the surficial sediments along southwest coast of India

Concentration and distribution of heavy metals (Cd, Cr, Cu, Hg, Ni, Pb and Zn) in surface sediments collected from five stations located along the southwest coast of India were investigated seasonally to assess whether there is insidious buildup of heavy metals. Spatial variation was in accordance with textural characteristics and organic matter content. The concentration of the metals in sediments of the study area followed the order: Zn > Cr > Ni > Cu > Pb > Cd > Hg. The use of geochemical tools and sediment quality guidelines to account for the magnitude of heavy metal contamination revealed high contamination in monsoon and impoverishment during post-monsoon. Estimated total metal concentrations in the present investigation were comparable with other studies; however, concentrations of Ni and Zn were higher than that of other coastal regions. Concentrations of metals in sediment largely exceed NOAA effects range:low (e.g., Cu, Cr, Hg) or effects range:median (e.g., Ni) values. This means that adverse effects for benthic organisms are highly probable.     

Multi-proxy evidence for late Holocene anthropogenic environmental changes at Bongpo marsh on the east coast of Korea

We present a multi-proxy record (pollen, microscopic charcoal, magnetic susceptibility, carbon-isotopic composition, total organic carbon [TOC], carbon/nitrogen [C/N] ratios, and particle size) of the late Holocene environmental change and human activities from Bongpo marsh on the east coast of Korea. Mutual interaction between the environment and humans during the late Holocene has not been properly investigated in Korea due to the lack of undisturbed samples with high sedimentation rates. In this study, the history of human responses to late Holocene environmental changes is clearly reconstructed using a multi-proxy paleoenvironmental approach that has not previously been applied in Korea. The evidence from Bongpo marsh indicates that 1) Bongpo marsh began to develop ca. 650 BC as a coastal lagoon was rapidly filled with organic matter, 2) agricultural disturbance around the study site remained slight until ca. AD 600, 3) full-scale intensive agriculture prevailed and the area of deforestation increased between ca. AD 600 and ca. AD 1870, and 4) the land use changed from lowland rice agriculture to upland cultivation when agricultural productivity declined after AD 1870, probably due to severe deforestation and the consequent heavy influx of clastic sediment on rice fields, as described in various historical documents.     

A quantitative analysis of relative tectonic activity classes of Kali river basin, southwest coast of India

The Kali river basin of the southwest coast of India has been investigated to examine the influence of tectonic activity through an analysis of the geomorphic indices that were computed using geographical information system (GIS). Five geomorphic indices—stream length–gradient index, asymmetry factor, hypsometric integral, valley floor width-to-height ratio, and elongation ratio—were used for identification of evidences of tectonic activity. The results obtained from these indices were combined to develop an index of relative tectonic activity classes using GIS. The average of the five measured geomorphic indices was used to evaluate the distribution of relative tectonic activity in the study area. About 18 % of the study area (～726 km²) belongs to class?1; 37 % (～1506 km²) to class?2; and 44 % (～1,762 km²) to class 3. Sub-basins found at the Western Ghat region, relative tectonic activity classes show low and medium values which indicate the higher degree of tectonic activity compared to the upland plateau regions.     

Mesoscale modeling study of the oceanographic conditions off the southwest coast of India

A high resolution model, using the Miami Isopycnic Coordinate Ocean Model (MICOM), has been implemented for the first time to study the seasonal circulation and coastal upwelling off the southwest Indian coast during 1974. This model is part of a model and data assimilation system capable of describing the ocean circulation and variability in the Indian Ocean and its predictability in response to the monsoon system. Along the southwest coast of India the dominant coastal current is the reversing West Indian Coastal Current which is well simulated and described, in addition to the weaker undercurrent of the opposite direction. Upwelling of cold water, 4‡C lower than offshore temperatures appear in April. The upwelling intensifies with the southwest monsoon and is simulated in accordance within situ observations. Upwelling appears to be strongest off Cochin and Quilon, and the upwelling of cold water is seen together with a decrease in salinity in the model simulation.     

Sea-breeze-initiated rainfall over the east coast of India during the Indian southwest monsoon

Sea-breeze-initiated convection and precipitation have been investigated along the east coast of India during the Indian southwest monsoon season. Sea-breeze circulation was observed on approximately 70–80% of days during the summer months (June–August) along the Chennai coast. Average sea-breeze wind speeds are greater at rural locations than in the urban region of Chennai. Sea-breeze circulation was shown to be the dominant mechanism initiating rainfall during the Indian southwest monsoon season. Approximately 80% of the total rainfall observed during the southwest monsoon over Chennai is directly related to convection initiated by sea-breeze circulation.     

Texture and geochemistry of the sediments of a tropical mangrove ecosystem,southwest coast of India

The textural and geochemical aspects of the sediments of a tropical mangrove ecosystem have been studied and discussed. The sediments are characterized by the abundance of silt and sand with minor amounts of clay. The mean size of the sediment ranges from 0.205 mm to 0.098 mm (fine to very fine grained sand). The sediments are very poorly sorted, negatively to very negatively skewed, and platy to extremely leptokurtic in nature. The organic carbon content of the sediments ranges from 0,33% to 4.93%, which is controlled by the particle size of the sediments. The CaCO₃ content is five times the enrichment of organic carbon. This enhanced CaCO₃ content of the mangrove sediments might be a result of the abundance of shell fragments in the sediments. The shell mining activities in the estuarine bed adjoining the Kumarakam mangroves also contribute a substantial amount of lime muds to the mangrove area, which in turn add CaCO₃ to the sediments. The relative concentrations of heavy metals are Fe > Mn > Cr > Zn > Ni > Cu. All heavy metals other than Fe show an increase in concentration compared to the other parts of the estuarine bed. Cluster analysis indicates that the contents of organic C, Fe and Mn have a marked bearing on the Cr, Zn, Ni, and Cu levels of the mangrove sediments.     

里下河地区全新世自然环境变迁

在区域地质调查项目进行过程中,以几个典型地质剖面和钻孔为基础,讨论了里下河区域全新世地层的分布规律,研究了地貌分布特征;探讨了全新世古植被、古气候与古环境变迁以及历史时期自然环境变化特征。里下河地区全新世自然环境变迁经历了4个重要的阶段:(1)10～7.5 kaBP,以湖沼发育为主,海水曾经影响到本区;(2)7.5～4.0kaBP,海水入侵本区,自然环境以潮滩、滨浅海、潟湖等为主,最大海侵甚至可到达运河以西地区,但里下河仍然有部分地区未被海水淹没;(3)4.0 kaBP～1128 AD,海水全面后退,岸线在范公堤一线曾做长时间停留,形成西冈贝壳砂堤,断续分布,海水时常影响西部地区;(4)1128 AD以来,由于黄河南泛夺淮入海,改变了里下河地区的地表水系,苏北滨海平原迅速向海推进,此后里下河地区远离海水的影响。     

Evidence of high sea level during the mid- Holocene on the southwest coast of Sri Lanka

A well-developed extensive buried coral reef at Akurala, north of Hikkaduwa, is deposited on a low plateau of decomposed crystalline rocks of Precambrian age. Radiocarbon age datings from three coral quarries in the area reveal that the branching and massive corals, in a position ofgrowth, were gradually deposited between 6, 110 ± 80 B.P. and 5,500 ± 80 B.P. in a bay or a lagoon as isolated patches, and their heights vary from 1.4m to 3.9m below mean sea level (MSL). Four radiocarbon age datings of emerged coral reef patches at Akurala and Akurala- Telwatte vary from 6,170 ± 70 B.P. to 5,350 ± 80 B.P. and at levels between 10cm and 70cm above MSL respectively. The present living corals in front of the southwest coast thrive from mean low water spring (MLWS) tidal level to 4m in depth in lagoonal reef areas. From the level of pesent living coral it is inferred that sea level was above the present level about 50cm at 6,110 ± 80 B.P. and 1m or more at 5,560 ± 80 B.P. The in situ position and condition of the materials show that they were not accumulated by catastrophic events such as storm waves.     

Geniculate coralline algae from the Neogene-Quaternary sediments in and around Porbandar,southwest coast of India

The present paper documents nine geniculate coralline algal species, namely Arthrocardia cretacica, Calliarthron antiquum, Corallina hayasaki, C. marshallensis, C. prisca, C. typica, Jania mengaudi, J. sripadaraoi and J. vetus from Neogene-Quaternary sediments of Porbandar area, Saurahtra, Gujarat. Out of nine species, six species namely Arthrocardia cretacica, Calliarthron antiquum, Corallina hayasaki, C. marshallensis, C. prisca and C. typica occur in the Dwarka Formation (lower-middle Miocene), one species Jania sripadaraoi occurs in the Adatiana Member of the Miliolite Formation (early middle-late Pleistocene) and two species namely, Jania mengaudi and J. vetus occur in the Porbandar Calcarenite Member of the Chaya Formation (late Pleistocene-late Holocene). These species indicate that the Dwarka Formation and the Adatiana Member of the Miliolite Formation were deposited in tropical marine environment with moderate to low energy conditions at depths ranging from intertidal to 60 m, and that the Porbandar Calcarenite Member of the Chaya Formation was deposited in a tropical marine environment under moderate to low energy conditions at depths ranging from 40 m to 60 m.     

Magnetic tracing of sediment dynamics of mudbanks off southwest coast of India

In this study, we utilized environmental magnetic in combination with sedimentological and hydrodynamic data to investigate the formative processes of mudbanks along southwest coast of India. We document the linkages between enrichment of silt-sized magnetic particles and formation processes of mudbanks along Alappuzha coast. A trend of increasing magnetite concentration and coarsening in magnetic grain size is observed at mudbank stations M2 and M3, while the mud-deficient station (M1) showed an opposite trend. A strong relationship between magnetic and physical grain size for all samples implies that the magnetic particle size and clastic grain size are largely adjunct. Analysis of rock magnetic and grain size data of surficial and suspended sediments from non-mudbank (M1) and two mudbank stations (M2, M3) reflect the differential sediment partitioning and transport regimes which controlled the formation of mudbanks along Alappuzha coast. Two plausible mechanisms responsible for the formation of mudbanks are identified: grain size-selective entrainment is the dominant process during pre-monsoon; weaker hydrodynamics (waves and bottom currents) favors accumulation of silt-sized (fine and coarse) magnetic and non-magnetic fractions resulting in the formation of magnetically low-enriched sediment bed of mixed grain sizes. At the onset of monsoon, wave-induced energetic bottom currents enhance the suspension of entire sediment bedload at stations M2, M3 to form fluid mud. Concurrently, mineral-density-based selective fractionation allows the settling of coarse silt-sized magnetic particles, while the fine magnetic silt-size particles accumulate forming thick fluid mud as a suspension load resulting in the formation of mudbanks. An observed increase in magnetic susceptibility and coarsening in magnetic grain size of surficial sediments at mudbank stations (M2, M3) during monsoon period supports the interpretation. Our findings are summarized in a conceptual model which can be very well applied to investigate sediment dynamics associated with mudbank formation in coastal and shelf sedimentary systems.     

Geochemistry of Cu, Co, Ni, Zn, Cd and Cr in the surficial sediments of a tropical estuary, southwest coast of India: a granulometric approach

 Geochemical characteristics of six trace metals – Cu, Co, Ni, Zn, Cd and Cr – in the bulk sediment and sand, silt and clay fractions of a tropical estuary on the southwest coast of India have been studied and discussed. In bulk sediment, the trace metal concentration is controlled mainly by the textural composition of the sample. Mud, sandy mud and sandy silt register higher concentrations of trace metals than that in sand-dominant sediments. The granulometric partitioning studies also re-affirmed the role of particle size in enriching the trace metals. The silt and clay fractions exhibit 7–8 times the enrichment of Cu and Cd compared to that in sand. The enrichment factors of Zn, Cr, Ni and Co in the silt and clay fractions, compared to that in sand, are 5–6, 4–5, 2–5 and 2–3 times, respectively. The trace metals in the sand fraction, particularly Ni and Cr, exhibit strong positive correlation with the heavy mineral content of the samples. It clearly indicates a heavy mineral pathway to the trace metals in the sand fraction. Cu and Co in silt and clay fractions exhibit a marked decrease towards the high saline zones of the estuary. This is attributed to the desorption of Cu and Co from particulate phases during estuarine mixing. Contrary to Cu and Co, the content of Zn in the clay fraction shows a marginal increase towards the estuarine mouth. This could be explained by the influx of Zn-rich contaminant discharges from Zn-smelting industries located slightly north of the estuarine mouth. The released Zn will effectively be held in the lattices of the clay mineral montmorillonite, which also exhibits a marked increase towards the estuarine mouth. The anomalously high values of Cd in some places of the Central Vembanad estuary is attributed to the local pollution. Received: 10 July 1995 · Accepted: 3 June 1996     

A multiproxy record of Holocene environmental changes in the central Kola Peninsula,northwest Russia

A sediment core from Chuna Lake (Kola Peninsula, northwest Russia) was studied for pollen, diatoms and sediment chemistry in order to infer post‐glacial environmental changes and to investigate responses of the lake ecosystem to these changes. The past pH and dissolved organic carbon (DOC) of the lake were inferred using diatom‐based transfer functions. Between 9000 and 4200 cal. yr BP, slow natural acidification and major changes in the diatom flora occurred in Chuna Lake. These correlated with changes in regional pollen, the arrival of trees in the catchment, changes in erosion, sediment organic content and DOC. During the past 4200 yr diatom‐based proxies showed no clear response to changes in vegetation and erosion, as autochthonous ecological processes became more important than external climate influences during the late Holocene. The pollen stratigraphy reflects the major climate patterns of the central Kola Peninsula during the Holocene, i.e. a climate optimum between 9000 and 5400/5000 cal. yr BP when climate was warm and dry, and gradual climate cooling and an increase in moisture during the past 5400/5000 yr. This agrees with the occurrence of the north–south humidity gradient in Fennoscandia during the Holocene. Copyright © 2002 John Wiley & Sons, Ltd.     

Seasonal variations in the sediment biogenic properties of a tropical mangrove environment,southwest coast of India

Temporal and spatial changes in the sediment properties of a mangrove ecosystem (Cochin, southwest coast India) are presented. The region was freshwater dominated during monsoon (June–September) and seawater dominated during other two seasons. The system remained eutrophic due to the high inputs of organic matter (OM) during most part of the year. The organic-rich sediments accumulated high amount of carbohydrates (22% of OM) and proteins (11% of OM) during non-monsoon months as compared to coastal environments. Principal component analysis showed that the biochemical properties are uniformly influenced by seasonal and spatial variations. Higher concentrations of sediment protein over carbohydrate indicate an efficient mineralization leading to the non-availability of aged OM in the system. The dominance of these labile components is generally indicative of the eutrophic condition of the system.     

Mid- to late Holocene environmental and climatic changes in New Caledonia, southwest tropical Pacific, inferred from the littoral plain Gouaro-Déva

Multiproxy analysis of three littoral cores from western New Caledonia supports the hypothesis that the main controlling factors of environmental changes are sea-level change, ENSO variability and extra-tropical phenomena, such as the Medieval Warm Period (MWP) marked by a tendency for La Niña-like conditions in the tropical Pacific. The record starts during the late Holocene sea-level rise when the terrestrial vegetation indicated wet and cool conditions. The site was a coastal bay definitely transformed into a freshwater swamp at around 3400 cal yr BP, after the rapid drawdown of sea level to its current level. Sediments and foraminiferal assemblages indicated subsequent episodes of freshwater infillings, emersion or very high-energy conditions, likely related to climatic changes and mostly controlled by ENSO variability. Between 2750 and 2000 cal yr BP, relatively dry and cool climate prevailed, while wetter conditions predominated between ca. 1800 and 900 cal yr BP. The Rhizophoraceae peak between ca. 1080 and 750 cal yr BP, coeval with the MWP, may indicate a global phenomenon. Microcharcoal particles present throughout the record increased after 1500 cal yr BP, suggesting an anthropogenic source. From ca. 750 cal yr BP the appearance of current type of vegetation marks the human impact.     

Brick and tile clay mining from the paddy lands of Central Kerala (southwest coast of India) and emerging environmental issues

The increasing demand for building materials has led to indiscriminate exploitation of clay-rich topsoil from wetlands including the paddy lands of Central Kerala in the southwestern coast of India. The problem is critical in areas adjoining the major developmental centers having low per capita land and natural resource availability. Loss of fertile topsoil, shrinkage of agricultural lands and consequent food security issues, erosion of naturally evolved nutrients, lowering of water table in wells adjacent to the mining sites, etc., are some of the major environmental issues arising from indiscriminate brick and tile clay mining. Although, brick and tile clay mining brings short-term economic benefits and employment opportunities to a section of people, the process in the long run creates severe damages to the environmental settings of the area. The present paper deals with a few aspects of brick and tile clay mining in the paddy lands of Central Kerala, especially around Kochi City, a fast developing urban-cum-industrial center in South India, which demands large quantities of building materials including bricks and tiles for construction of infrastructural facilities. It is estimated that 729,695 tons/year (ty^?1) of brick and tile clays are extracted from the coastal lowlands of Central Kerala, spreading to the Chalakudy (135,975 ty^?1), Periyar (483,820 ty^?1) and Muvattupuzha (109,900 ty^?1) river basins. The N, P and K loss through extraction of brick and tile clays amounts to 210 ty^?1, 96 ty^?1 and 9,352 ty^?1, respectively. As nutrient loss is an irreversible process in human time scale, its implications on agricultural productivity is a matter of serious concern. The study warrants the need for a comprehensive policy with an aim to regulate the mining activities on an environment- friendly basis in the densely populated coasts of the world, in general, and the study area in particular.     

A late Holocene record of environmental changes from the Aliki lagoon,Egion, North Peloponnesus,Greece

Aliki lagoon is a small lagoon located on the micro-tidal south coast of the Gulf of Corinth, Greece. The sediments of the lagoon recovered in three cores provide a record of late Holocene environmental change, including tectonic subsidence, tsunami layers, and change in local vegetation and sedimentation. Four periods of rapid environmental changes were identified over a 5000-yr-long record. These date from about 4700, 3000, 2500 and 2000 yr BP. Each change is linked to activity on the Egion fault, a deepening of the lagoonal bottom and a rise in relative sea level. Six tsunami events are recorded and have been caused by earthquakes on the Egion fault (three events ∼4700, ∼3000 and ∼2500 BP), Eliki fault (2350±40 yr BP) and two more distal fault ruptures. The vegetation history and pollen zones are similar to those recognised by Jahns (Vegetation Hist. Archaebot. 2 (1993) 187) on the Argive Plain, 100 km southeast of the lagoon. Five successive sedimentological configurations are established in relation to the time frame provided by the tectonic activity: (1) crevasse splay; (2) fresh to brackish water marsh; (3) and (4) brackish to hypersaline “blind” lagoon, and (5) brackish to hypersaline “blind” lagoon or brackish open lagoon.     

渤海湾西侧泥质海岸带全新世岸线的变化与海洋的影响

以渤海湾泥质海岸带为例,从形态和地层证据2个方面总结了全新世岸线变化与海洋作用对该地区海岸带发育的影响。中全新世以来千年级别的岸线变迁至少以6次停顿（形成贝壳堤和泥质岭地）和岸进的交替为特征。过去130年间10年级别的岸线变化分为4个阶段,显示了＂小冰期＂结束后随气温上升而发生的岸线自然蚀退是如何逐渐被人类活动（特别是2000年以来的围海造陆）所取代的。全新世海相沉积中发现的9个峰值期和晚全新世的7次风暴驱动事件,表明了研究区泥质海岸带增强的海洋影响。这些结果提供了一条经由地质背景认识现代泥质海岸带过程的途径。