Temporal and spatial distribution of hypoxic/seasonal anoxic zone in Amvrakikos Gulf, Western Greece

Coastal hypoxia and anoxia have become a serious environmental problem in many coastal ecosystems, and recent evidence suggests an increase in the number of systems experiencing hypoxia globally and an increased frequency and duration of hypoxia in many historically hypoxic systems. Eutrophication, low physical energy and large freshwater input are some of the most important factors, which lead to the development of hypoxia in coastal areas. The Amvrakikos Gulf, located in western Greece, is one of the most important protected areas in Greece and in Europe and past studies indicated that some regions of the Gulf experience hypoxia. Despite the importance of the Amvrakikos Gulf ecosystem, little is known about key ecological, chemical, and physical processes in the Gulf and their relationship with oxygen depletion. In the present study, authors try to answer some important questions regarding the distribution and variation of the hypoxic zone. After a year of measurements, it was concluded that according to spatial distribution of DO, the gulf can be divided into two parts, the western and eastern areas, with important differences occurring between them. Within the western area, the water column was well oxygenated during winter and spring and hypoxic conditions occurred only in summer and autumn. The eastern area was hypoxic throughout the year and anoxic conditions occurred only during autumn. In conclusion, taking into account the author’s measurements and previous studies, the seasonally hypoxic eastern area in 1987 converted into a seasonally anoxic area in 2009 and the western part of the gulf, remained seasonally hypoxic, indicating the degradation of the gulf’s environmental state within the last 20 years.     

Studies on Migratory Movements of the Prawn Penaeus kerathurus (Forskal, 1775) at Amvrakikos Gulf, Western Greece

Abstract. The prawn Penaeus kerathurus completes its life cycle in Amvrakikos Gulf. The reasons for not entering the open sea depend on the status of biotic and abiotic factors of the gulf. The migratory movements of the species in the gulf are described by a simple square model, in each corner of which, the wintering, spawning, nursery, and recruitment area exist. The wintering area is located below the 25m isobath and wintering period lasts from late December to late March. Spermatophores on females are observed throughout the year but the highest percentages between April and August. The spawning season begins late in spring and continues through the summer. The spawning area is located below the 10m isobath, mainly around 25m. The nursery area of Penaeus kerathurus is in shallow waters near river estuaries, and the temporal limits were determined to be between mid-summer and mid-autumn. Finally, the recruitment area is located near the nursery area, with recruitment taking place in autumn, while the major stock renewal is restricted to winter.     

Sedimentological response to neotectonics and sea-level change in a delta-fed,complex graben: Gulf of Amvrakikos,western Greece

The Gulf of Amvrakikos is one of several E–W grabens developed in the Middle Quaternary almost orthogonal to the tectonic grain of the external Hellenides in western Greece and is critically located at the termination of the Kefallinia transform fault linking the Hellenic subduction zone to the Adriatic-Dinaride collision lineament. The tectonic evolution of the Gulf and the response of sedimentation have been investigated based on 3.5 kHz and sparker profiles. The Holocene stratigraphy results from rising eustatic sea-level breaching the tectonic sill north of Preveza and inundating the braid plain of the Arachthos river, which then prograded across the northern Gulf following the formation of the maximum flooding surface. Older major transgressive surfaces are recognised in sparker profiles. Interpretation of these transgressions in terms of eustatic sea-level changes allows a chronology to be established and estimates to be made of neotectonic rates of subsidence. Two sets of neotectonic faults are present: reactivated NNE-trending mid-Tertiary thrusts of the Ionian zone and more active E–W trending faults. The sedimentary succession in the Gulf of Amvrakikos is the result of a complex interplay between eustatic sea level changes, the neotectonic creation of accommodation, and autocyclic delta distributary switching. The details of this process are resolved for the Holocene and the general sedimentation pattern established back to marine isotope stage (MIS) 8 (245–300 ka). In general, MIS 8 shows greater evidence of terrestrial deposition, compared with MIS 6 (130–190 ka) and especially MIS 2–4 (10–80 ka), when there was lacustrine deposition and some marine incursions at intermediate eustatic sea levels. This implies that regional subsidence has been taking place at least since MIS 8. In addition, changing sediment supply plays a role in overall sediment architecture, but is only well resolved for the Holocene, with higher rates of fluvial supply recognised in the mid Holocene.     

Plankton Distribution Patterns in a Mediterranean Dilution Basin: Amvrakikos Gulf (Ionian Sea, Greece)

Abstract. The present work describes Amvrakikos Gulf (Ionian Sea, Greece) as a dilution basin and provides information concerning the relationships between the hydrology and plankton composition and distribution.
Amvrakikos Gulf is characterized by a differentiated planktonic system which is apparently directly influenced by the input of the rivers located at the northern part of the gulf.     

Sequence Stratigraphy and Composition of Late Quaternary Shelf-Margin Deltas,Northern Gulf of Mexico

High-resolution seismic profiles and foundation borings from the northwestern Gulf of Mexico record the physical attributes and depositional histories of several late Quaternary sequences that were deposited by wave-modified, river-dominated shelf margin deltas during successive periods of lowered sea level. Each progressively younger deltaic sequence is thinner and exhibits a systematic decrease in the abundance and concentration of sand, which is attributed to a shift in the axis of trunk streams and greater structural influence through time. Our study shows that (1) contemporaneous structural deformation controlled the thickness of each sequence, the oblique directions of delta progradation, the axes of major fluvial channels, and the geometries of delta lobes at the shelf margin, (2) sedimentation was rapid in response to rapid eustatic fluctuations and structural influence, (3) boundaries of these high-frequency sequences are the correlative conformities of updip fluvial incision, and coincide with downlap surfaces at the shelf margin, (4) the downlap surfaces are not true surfaces, but zones of parallel reflections that become progressively higher and younger in the direction of progradation, (5) the downlap zones are composed of marine muds that do not contain high concentrations of shell debris that would be expected in condensed sections, (6) possible paleosols capping the two oldest sequences are regressive surfaces of subaerial exposure that were preserved during transgressions, and (7) no incised valleys or submarine canyons breach the paleoshelf margin, even though incised drainages were present updip and sea-level curves indicate several periods of rapid fall. (Published in American Association of Petroleum Geologists Bulletin 80: 505 530.) R. A. Morton and J. R. Suter AAPG Bulletin, Vol. 80, No. 4, AAPG 1996, reprinted by permission of the American Association of Petroleum Geologists whose permission is required for future use.     

Morphology and Late Quaternary sedimentation in the Gulf of Oman Basin

The morphology of the Gulf of Oman Basin, a 3,400 m deep oceanic basin between Oman and southern Pakistan and southern Iran, ranges from a convergent margin (Makran margin) along the north side, a passive type (Oman margin) along the south side, translation types along the basin's west (Zendan Fault-Oman Line) and east (Murray Ridge) sides and a narrow continental rise and a wide abyssal plain in the centre of the basin. Sediment input into the basin during the Late Quaternary has been mainly from the north as a result of the uplift of the Coast Makran Mountains in the Late Miocene-Pliocene. Today most of this detritrus is deposited on the shelf and upper continental slope and perched basins behind the fold/fault ridges on the lower slope. The presence of fans and channels on the continental rise on the north side of the basin indicate, however, that continental derived debris was, and possibly is, being transported to the deep-sea by turbidity currents via gaps in the ridges on the lower slope. In addition to land derived terrigenous sediments, the basin deposits also contain biogenic (organic matter and calcium carbonate), eolian detritus and hydrates and authigenic carbonates from the tectonic dewatering of the Makran accretionary wedge. The eolian sediment is carried into the Gulf of Oman Basin from Arabia and the Mesopotamia Valley by the northwesterly Shamal winds. This type of detritus was particularly abundant during the glacial arid periods 21,000–20,000 and 11,000 (Younger Dryas) years ago when exposure of the Persian (Arabian) Gulf increased the area of dust entrainment and shifted the position of the source of the eolian sediments closer to the basin.     

Temporal Variations of Nutrients, ­Chlorophyll a and Particulate Matter in Three Coastal Lagoons of Amvrakikos Gulf (Ionian Sea, Greece)

Abstract. The temporal variations of nutrients, chlorophyll a (chl a ), suspended particulate matter (SPM) and particulate organic carbon (POC) were measured over 12 months in three shallow coastal brackish water lagoons of the Amvrakikos Gulf, Ionian Sea. Two of the lagoons, Tsoukalio and Rodia, are interconnected but separated from Logarou by a narrow strip of land. Logarou has a better water exchange with the sea as indicated by the higher salinity and dissolved oxygen concentrations and the smaller variation of the above-mentioned parameters. Nitrate concentrations were largely the same in the three lagoons and higher than in the Amvrakikos Gulf. Phosphate concentrations in Logarou exceeded by far those of Tsoukalio/Rodia; the increased phosphate levels recorded in January caused an extended phytoplankton bloom with chl a concentrations higher than in the other two lagoons. Chl a in Tsoukalio was positively correlated with nitrate whereas in the most shallow lagoon, Logarou, it showed a positive correlation with light winds (force 4 and lower), probably caused by resuspension from the sediment. Increased phytoplankton biomass in Logarou coupled with the better water exchange may be related to the higher fish production in this lagoon.     

渤海地区晚第四纪环境演化与第四纪滨海相地下卤水的形成

由于气候变化和新构造运动,渤海曾发生多次海陆演化,从而形成了第四纪地下卤水。间冰期的海侵提供了形成地下卤水的水源,气候波动产生了海水浓缩的条件,而冰期海退过程中,陆源物质覆盖于海相沉积上,保存了地下卤水。对环境演化在“潮滩生卤”和“冰冻生卤”过程中重要作用的分析结果表明,在第四纪环境演变的过程中,两种生卤作用在地质时期卤水矿床形成中均具有重要意义,并且只要存在海水物源,就有可能形成地下卤水。     

A Survey of Estuarine Benthic, Zoo-planktonic and Phytoplanktonic Communities of Amvrakikos Gulf, Ionian Sea

Abstract. The estuarine ecosystem of the Amvrakikos Gulf, a semi-enclosed embayment of the Ionian Sea, was surveyed at 9 stations in June, 1980. Quantitative and qualitative relationships among the phytoplanktonic, zooplanktonic and benthic populations were examined and related to environmental parameters. It was found that quantitative maxima of each of the three components occurred at different stations. When stations were grouped according to a similarity index of each community, it could be shown that the stations were very similar with regard to phytoplankton and slightly less similar with regard to zooplankton. The stations differed considerably as far as the benthos is concerned. The phytoplankton also exhibited a lower species diversity (0.08-0.82 bits-indiv.^-1) than the zooplankton (1.08-2.10 bits indiv.^-1) and the benthos (0.85-5.06 bits indiv.^-1). Differences in salinity among stations showed no significant correlation with the abundance or species diversity of phytoplankton, zooplankton or benthos.     

晚第四纪朝鲜西海岸京畿湾金浦潮坪大型潮汐的演化

金浦潮坪位于京畿湾中部,在1980年开垦改造之前是坡度平缓的潮坪,西边被南北向主水道所限,该水道是汉江的主要支流水道之一,形状长直,最宽处1．5km,最深10m。树枝状的小潮流跟主水道连接。数十个岛屿分布于再生潮坪,导致岩基地形崎岖不平。而位于潮坪西部离岸的大量岛屿起到了保护潮坪不受离岸波浪侵蚀的作用。京畿湾中部的潮流在近地点高潮期达到10m,最大流速超过2．5m／s。波浪一般夏季小,台风期间除外;冬季风暴频繁之时规模巨大,一般超过2m。主潮道的悬浮沉积物浓度和盐度由于强烈的季风气候而表现出显著的季节性差异。     

Trace metals in the Pagassitikos Gulf,Greece

The concentrations of Ni, Mn, Cr, Cu, Co, Zn, Fe, Pb and organic carbon have been determined in sediments of the Pagassitikos Gulf. They vary with the ‘sand equivalent’ content, s′, characteristic of the grain size, and are related to it by the equation,

$\text{c = c}{}_1\text{·k·s′}{}^{\mathrm{d}}$

in which the constants c₁, k and d depend on the element. Consequently, since the metal concentrations in a sample are much less representative of the area from which it has been taken than its ‘sand equivalent’ content, a contour map of the latter constitutes a reliable guide to the general pattern of the elements. Superimposed on it, we detect isolated patches of moderate pollution close to the harbour of Volos and a few, slight, natural anomalies, such as increased Mn and Ni, the former in the east and the latter in the south of the Gulf.     

Continental shelf architecture and sea-level cycles: Late Quaternary high-resolution stratigraphy of the Gulf of Cádiz, Spain

 The stratal architecture of the Gulf of Cádiz continental margin (SW Spain) has been analyzed by using single-channel, very high-resolution seismic reflection profiles. An evolutionary scheme of asymmetrical depositional sequences is proposed that was governed by the Late Pleistocene–Holocene sea-level fluctuations. Stratigraphic analysis defined 14 seismic units, that are configured into two major type-1 depositional sequences related to 4th-order eustatic sea level changes (100–110 ka). Within these sequences, minor asymmetrical depositional sequences have been recognized related to 5th-order eustatic cycles (22–23 ka) superimposed and modulated by the regressive trends of 4th-order cycles. In 5th-order depositional sequences, the forced regressive and lowstand deposits are volumetrically dominant. They cause the main progradation of the margin in such a way that they form the margin structure almost entirely. Received: 6 April 1995 / Revision received: 8 March 1996     

印度扇西边缘晚第四纪沉积过程演化

印度扇沉积的开始被认为是发生于渐新世到早中新世,其时印度板块和阿拉伯板块碰撞。印度扇长1,500km,最大宽度960km,是阿拉伯海中最大的自然地理构造,东边界是印度大陆边缘/查戈斯-拉克代夫海脊（Chagos-Laccadive Ridge）,西边界是欧文-墨里海脊（Owen-Murray Ridge）,南部则是中印度海脊（Carlsberg Ridge）。印度扇主要沉积物物源来自于印度河,     

The Ecology of Benthos in the Gulf of ThermaTkos, Greece

Abstract. Benthic samples were taken at 26 stations during a two year period (1975–1977) in the Gulf of Thermaïkos, Greece. The topography and relevant physicochemical characteristics of the area are presented and discussed. Both density and biomass increase towards the northern limits in the Bay of Thessaloniki and in the Gulf of Thermaïkos, the difference between them being the degree of change in a north-south direction. Analyses of the degree of concurrence of the dominant species show the existence of a number of groups of concurrent dominant species with characteristic distributional patterns and differing areal coverage in the study area. The observed quantitative and qualitative differences in the benthos are causally related to the differing environmental conditions prevailing in the two subareas.     

Modern fan deltas in the western Gulf of Corinth,Greece

Rivers in the western Gulf of Corinth have built gravelly fan deltas into waters 100–300 m deep. Seismic profiles (3.5 kHz) and gravity cores show that sand-filled channels extend seaward of modern distributary mouths and lead to sandy depositional lobes in deeper water. Much of the fan delta slope is underlain by mud. Closely spaced gullies cut the interchannel ridges on either side of the main channels. Incised slope valleys occur on east-facing slopes, where the wave fetch is greatest, and may be formed by rip-current-induced turbidity currents.     

孟加拉湾晚第四纪冰期和间冰期古生产力演变研究

近赤道低纬度地区孟加拉湾属于大陆边缘深海环境,该区的古生产力研究对于了解低纬度地区古气候演变及其对全球气候变化的响应具有重要意义。通过对研究区４个活塞岩心δ１３Ｃ值、高生产力指示种的含量变化、浮游有孔虫与底栖有孔虫丰度、Ｕ＋Ｂ指数等方面的研究发现,研究区受冰川－气候旋回作用影响明显,古生产力波动强烈。冰期时,陆源营养物质供应充分导致生物生产力增大,因而末次冰期最盛期氧同位素第２期时生产力最高,间冰期氧同位素第１、５期时生产力较低。该区氧同位素第３期也出现高生产力的情况,可能与当时研究区气候不稳定有关。氧同位素第３期强烈的西南季风活动使研究区淡水输入增强,进一步增加了冷、暖期生物生产力的差异。     

Late Quaternary sedimentation in the Kadeok region, Korea

Analyses of high-resolution seismic-reflection data and geological samples revealed the characteristics of Quaternary sedimentation in the Kadeok region at the opening of the Nakdong River. The sediments comprise two layers, i.e., a 20- to 45-m-thick Holocene mud layer, and a coarser late-Pleistocene layer deposited in a fluvial environment. Sedimentological variations in the late-Pleistocene layer to the west and east of Kadeok Island are due to differences in channel maturity prior to the Holocene transgression. Holocene mud in the sea to the west of Kadeok Island was transported through a passway north of the island. Received: 26 October 1999 / Revision accepted: 7 February 2000     

Dispersion of bauxitic red mud in the Gulf of Corinth, Greece

Bauxitic red-mud slurry, discharged by an aluminium processing factory on the shelf of the Gulf of Corinth, Greece, is used as a tracer to examine sediment transport and dispersion processes in a tectonically active deep basin.

The Gulf of Corinth is a silled elongate basin with a maximum depth of 860 m; it is characterised by high seismicity. The red mud is discharged through a pipeline at a depth of 100 m, where it forms an extensive deposit.

Grab sampling has shown that the red mud extends over the slope and the abyssal plain up to a distance of 17 km from the mouth of the pipeline. It forms small scattered sheet-like deposits of up to 3 cm in thickness. The structures observed in the scattered patches of the red mud, which in some places are overlain by a thin veneer of grey/olive green (natural) sediments, suggest that the red mud is transported from the shelf to the abyssal plain by gravitative sediment flows. The flows are triggered by earthquakes.

Granulometric and geochemical analyses of the red-mud samples show that the red mud, during its transport from the shelf to the abyssal plain, is subjected to mixing with the surrounding sediments. A different mixing ratio is determined, however, by reference to the various trace metals (Fe, Ni, Co, Pb).     

珠江三角洲晚第四纪红树林的演化及其环境意义

广州番禺东涌剖面样品的AMS（磁谱仪）年龄及红树林孢粉分析结果表明,珠江三角洲存在晚更新世和全新世的红树林,红树林是海侵的标志之一.按照检出红树属花粉的9个剖面的分布以及5处埋藏红树林腐木的分布,可以描绘出全新世海侵的边界.根据东涌剖面的沉积旋回、样品年龄、红树林花粉含量曲线、半咸水-淡水硅藻及热性-温性硅藻含量曲线的综合分析,可将沉积环境的变迁分为4个阶段.第一阶段和第三阶段的海侵有利于红树林的发展,第二阶段不利于红树林的发展,第四阶段的晚全新世,红树林的生长频繁,显示人为因素的影响.     

Use of surface sediments in Pagassitikos Gulf, Greece, to detect anthropogenic influence

Volos city and its port are situated in the northern part of Pagassitikos Gulf, a shallow, semi-enclosed marine area in central Greece. A wastewater treatment plant (WWTP) and pipeline operate in the same area. Muddy sediments with low carbonate contents cover most of the seabed, except for the Volos embayment and the western part of the gulf where sandy carbonates prevail. Bulk organic carbon contents and the organic carbon contents of the clay fractions are high in the vicinity of Volos embayment. High element (Pb, Cu, and Zn) contents and Igeo (geoaccumulation index) values were found for the clay fractions in the northern part of Pagassitikos Gulf. This enrichment is attributed to the discharge of raw domestic and industrial effluents of Volos city and port before the WWTP was installed. The dispersal of pollutants is essentially controlled by diffusion from point sources (city, port and WWTP) and is limited to Volos Bay. Relatively high Mn levels are ascribed to diagenetic formation of manganese carbonates (authigenic phase), whereas Cr and Ni are elevated due to weathering of ultrabasic formations on land.