Operculodinium Israelianum Research Articles

Pentaplacodinium lapazense sp. nov. from Central and Southern Gulf of California, a new non-toxic gonyaulacalean resembling Protoceratium reticulatum

A new Pentaplacodinium species with six precingular plates is described from Bahía Concepción and Bahía de la Paz, Gulf of California. The non-fossil motile stage is described as Pentaplacodinium lapazense, whilst the fossil stage is described as Operculodinium lapazense. The cyst morphology is compared to topotype material of Operculodinium israelianum, which is larger, has longer processes and has a different wall structure. The motile cells display a plate formula of Po, Pt, X, 2′+*2′, 6′′, 6c, 7s, 5′′′, 1p, 1′′′′. A typical gonyaulacalean fission line and plate overlap are observed. SSU-ITS-LSU ribosomal DNA sequences demonstrate that Pentaplacodinium saltonense is its closest relative. The species is homothallic. This species occurs in relatively shallow and restricted coastal areas, and has a preference for higher sea-surface temperatures and salinities. Micro-FTIR spectra of the cysts are compared to spectra of cysts of other gonyaulacaleans and suggest very similar compositions. No yessotoxins were detected in any of the analyzed strains, hence, this species is unlikely to be responsible for the elevated yessotoxin concentration observed in shellfish on the southern and central coastal region of the Gulf of California.

Pentaplacodinium saltonense gen. et sp. nov. (Dinophyceae) and its relationship to the cyst-defined genus Operculodinium and yessotoxin-producing Protoceratium reticulatum

Strains of a dinoflagellate from the Salton Sea, previously identified as Protoceratium reticulatum and yessotoxin producing, have been reexamined morphologically and genetically and Pentaplacodinium saltonense n. gen. et sp. is erected to accommodate this species. Pentaplacodinium saltonense differs from Protoceratium reticulatum (Claparède et Lachmann 1859) Bütschli 1885 in the number of precingular plates (five vs. six), cingular displacement (two widths vs. one), and distinct cyst morphology. Incubation experiments (excystment and encystment) show that the resting cyst of Pentaplacodinium saltonense is morphologically most similar to the cyst-defined species Operculodinium israelianum (Rossignol, 1962) Wall (1967) and O. psilatum Wall (1967). Collections of comparative material from around the globe (including Protoceratium reticulatum and the genus Ceratocorys) and single cell PCR were used to clarify molecular phylogenies. Variable regions in the LSU (three new sequences), SSU (12 new sequences) and intergenic ITS 1–2 (14 new sequences) were obtained. These show that Pentaplacodinium saltonense and Protoceratium reticulatum form two distinct clades. Pentaplacodinium saltonense forms a monophyletic clade with several unidentified strains from Malaysia. LSU and SSU rDNA sequences of three species of Ceratocorys (C. armata, C. gourreti, C. horrida) from the Mediterranean and several other unidentified strains from Malaysia form a well-supported sister clade. The unique phylogenetic position of an unidentified strain from Hawaii is also documented and requires further examination. In addition, based on the V9 SSU topology (bootstrap values >80%), specimens from Elands Bay (South Africa), originally described as Gonyaulax grindleyi by Reinecke (1967), cluster with Protoceratium reticulatum. The known range of Pentaplacodinium saltonense is tropical to subtropical, and its cyst is recorded as a fossil in upper Cenozoic sediments. Protoceratium reticulatum and Pentaplacodinium saltonense seem to inhabit different niches: motile stages of these dinoflagellates have not been found in the same plankton sample.

Dinoflagellate cyst distribution in the oligotrophic environments of the Gulf of Aqaba and northern Red Sea

Abstract Oligotrophic environmental systems form a major part of the marine aquatic environments on earth. Compared to mesotrophic and eutrophic environments extremely little information is available about the relationship between the distribution of organic-walled dinoflagellate cysts and physical and biological gradients in the upper water column. Here we present the first comprehensive study of the modern geographic distribution of organic-walled dinoflagellate cysts in the oligotrophic environments of the northern Red Sea and Gulf of Aqaba. We show that sediments of both regions have characteristic dinoflagellate cyst associations consisting of both heterotrophic and phototrophic species of which the latter, including both autotrophic and mixotrophic species, form the major part of the associations in both regions. The upper water environment of the Gulf of Aqaba is characterized by slightly enhanced nutrient concentrations compared to the Red Sea, due to water column mixing in winter. Its phytoplankton composition is dominated by pico- and ultra-plankton and a slight higher amount of eukaryotes compared to northern Red Sea. Its sedimentary cyst associations are characterized by higher relative and absolute abundances of the species Brigantedinium spp., Votadinium calvum, Echinidinium spp., Lingulodinium machaerophorum, Spiniferites spp., Spiniferites bentorii, Spiniferites membranaceus and Spiniferites mirabilis. Sediments of the northern Red Sea are characterized by high relative abundances of Impagidinium aculeatum, Impagidinium sphaericum, Operculodinium israelianum, Operculodinium longispinigerum, Operculodinium centrocarpum, cysts of Pentapharsodinium dalei, and Selenopemphix nephroides. A positive relationship between the distribution of the heterotrophic species Brigantedinium spp., Echinidinium spp. and V. calvum with the occurrence of other eukaryotic groups such as e.g. diatoms is documented. The distribution of S. nephroides cannot be related to the presence of diatom occurrences and it is suggested that the distribution of food sources other than diatoms affects its distribution. We document a positive relationship between the sedimentary distribution of the phototrophic dinoflagellate species L. machaerophorum and Spiniferites species and the abundance of the cyanobacteria Synechococcus in the water column. Since Synechococcus is known to be a potential prey of Lingulodinium polyedrum and members of the Gonyaulax spinifera complex (the motile forms producing these cysts) we suggest a possible cyst distribution–prey relationship of mixotrophic dinoflagellates.

Long-term hydrological changes in the northeastern Gulf of Mexico (ODP-625B) during the Holocene and late Pleistocene inferred from organic-walled dinoflagellate cysts

Palynological analyses are used in conjunction with oxygen isotopes and Mg/Ca ratios in foraminifers in order to document the response of dinoflagellate cysts (dinocysts) assemblages to changing climate conditions in the northeastern Gulf of Mexico over the Holocene and late Pleistocene. During MIS 6, but also during the cooler phases of MIS 5, Impagidinium species and Operculodinium centrocarpum were dominating the assemblages. By contrast, during the last interglacial (LIG) and the Holocene, assemblages were mainly composed of Spiniferites taxa and characterized by high relative abundance of Spiniferites mirabilis-hyperacanthus, Operculodinium israelianum and/or Polysphaeridium zoharyi. These two periods exhibit ~1-2°C difference in temperature as inferred from Mg/Ca ratios and show significantly distinct assemblages, with higher percentages of S. mirabilis during the LIG and higher percentages of P. zoharyi during the Holocene. This likely denotes important differences in the hydrogeographical conditions (e.g. surface circulation, bathymetric configuration) between the present and last interglacial. The importance of environmental parameters other than temperature and salinity for dinocyst assemblage dynamics is furthermore illustrated.

Distribution patterns of recent organic-walled dinoflagellate cysts in relation to environmental parameters in the Mediterranean Sea

To determine the relationship between the spatial dinoflagellate cyst distribution and oceanic environmental conditions, 34 surface sediments from the Eastern and Western Mediterranean Sea have been investigated for their dinoflagellate cyst content. Multivariate ordination analyses identified sea-surface temperature, chlorophyll-a , nitrate concentration, salinity, and bottom oxygen concentration as the main factors affecting dinoflagellate cyst distribution in the region. Based on the relative abundance data, two associations can be distinguished that can be linked with major oceanographic settings. (1) An offshore eastern Mediterranean regime where surface sediments are characterized by oligotrophic, warm, saline surface water, and high oxygen bottom water concentrations (Impagidinium species, Nematosphaeropsis labyrinthus, Pyxidinopsis reticulata and Operculodinium israelianum). Based on the absolute abundance, temperature is positively related to the cyst accumulation of Operculodinium israelianum. Temperature does not form a causal factor influencing the accumulation rate of the other species in this association. Impagidinium species and Nematosphaeropsis labyrinthus show a positive relationship between cyst accumulation and nitrate availability in the upper waters. (2) Species of association 2 have highest relative abundances in the Western Mediterranean Sea, Strait of Sicily/NW Ionian Sea, and/or the distal ends of the Po/Nile/Rhône River plumes. At these stations, surface waters are characterized by (relative to the other regime) higher productivity associated with lower sea-surface temperature, salinity, and lower bottom water oxygen concentrations (Selenopemphix nephroides, Echinidinium spp., Selenopemphix quanta, Quinquecuspis concreta, Brigantedinium spp. and Lingulodinium machaerophorum). Based on both the absolute and relative abundances, Selenopemphix nephroides is suggested to be a suitable indicator to trace changes in the trophic state of the upper waters. The distribution of Lingulodinium machaerophorum is related to the presence of river-influenced surface waters, notably the Nile River. We suggest that this species might form a suitable marker to trace past variations in river discharge, notably from the Nile.

Holocene paleoenvironmental change in inner continental shelf sediments, Southeastern Mediterranean, Egypt

The palynology of marine sediments from CS Core taken on the inner continental shelf offshore Nile Delta, Southeastern Mediterranean, has been used to reconstruct the regional paleoenvironment during the past 5380 yr BP. This includes detailing the relative abundances of dinoflagellate cysts, acritarchs, prasinophytes and other algal spores, microforaminiferal linings, crustacean eggs, and fungal hyphae. The composition and ecological interpretation of the dinoflagellate cyst assemblages, acritarchs and other non-pollen palynomorphs is discussed. Concentrations of dinoflagellate cysts range from 5926 to 416 specimens per gram of sediment, and the most common taxa were Lingulodinium machaerophorum, Operculodinium centrocarpum, Operculodinium israelianum, Polysphaeridium zoharyi, Spiniferites ramosus, Spiniferites mirabilis, Echinidinium transparantum and Protoperidinum nudum. The assemblages are like those on the Tunisian Shelf, but with more protoperidinioid cysts. It is concluded that the shelf sediments were deposited under suboxic bottom water conditions. A high nutrient supply to the area during the deposition of the CS Core sediments is evidenced by the strong significant correlation ( R-values) between the nutrient-demanding species, L. machaerophorum and P. zoharyi, toxic species, total phosphorous percent (TP%) and total organic carbon percent (TOC%). These data suggest that Nile discharge from the Damietta Channel increased during the past 5830 yr BP and was accompanied by increases in fresh or brackish water algae and fungal hyphae.

Environmental significance of dinoflagellate cysts from the proximal part of the Po-river discharge plume (off southern Italy, Eastern Mediterranean)

To determine the relationship between region specific dinoflagellate cyst distribution in the Po-river discharge area and oceanic environmental conditions, surface sediments of 48 sites in the middle and distal part of the discharge plume area have been studied. Establishing such a relationship is a prerequisite to create reconstructions of the eutrophication history as well as the palaeoclimatic and palaeoceanography history of the area. Literature based information about the sedimentation rates based on 210Pb dating methods are available for 18 sites. This enables the calculation of cyst accumulation rates of individual cyst species which reflect their cyst production. Correlation of the accumulation rates of individual species with environmental parameters of the upper waters allows us to adapt and refine the ecological characteristics of a selection of cyst species. This latter is trivial since the current concepts on the ecological significance of dinoflagellate cyst have to be revised as a result of the current developments in the dinoflagellate research field. These developments have elucidated that a considerable part of the relative abundance datasets that form the basis for the present day ecological concepts of dinoflagellate cysts might have suffered from so called “closed sum effects” and have been overprinted by early diagenetic processes. The dinoflagellate cyst association reflects both upper and bottom water circulation. Based on the relative abundance data four associations can be distinguished that are characteristic for the major oceanographic settings in the region. (1) River discharge association. This association consists of Echinidinium spp., Lejeunecysta sabrina, Lingulodinium machaerophorum, Polykrikos kofoidii, Polykrikos schwarzii, cysts of Protoperidinium stellatum, Selenopemphix quanta and reworked cysts. These species have high relative abundances in sites where bottom waters are low in oxygen and upper waters are influenced by river discharge waters that are characterized by high productivity and relative low salinity. (2) Warm water association. This association consists of Spiniferites mirabilis, Spiniferites pachydermus, Spiniferites ramosus and Spiniferites spp. which have their highest relative abundances in the sites at the plume margin that are characterized by relative warm upper waters and intermediate chlorophyll- a concentrations. (3) Oxygenated bottom water group. Species of this group; Impagidinium aculeatum, Impagidinium patulum, Impagidinium sphaericum, Operculodinium centrocarpum and Operculodinium israelianum have their highest relative abundances at sites where bottom waters are formed by well ventilated Adriatic Deep Water or Eastern Mediterranean Deep Water. (4) Golfo di Taranto group consisting of round brown cysts produced by Protoperidinium species (grouped as Brigantedinium spp .). The variation in accumulation rates can be related to gradiental changes in the trophic state of the surface waters linked to river outflow. Most species show a positive relationship between cyst production and nutrient/trace element availability in upper waters. No negative correlation between cyst production and nutrient/trace element availability could be documented. Production of Brigantidinium spp., Echinidinium spp., L. sabrina, L. machaerophorum, P. kofoidii/schwarzii, Spiniferites spp., S. mirabilis and S. quanta shows the most pronounced increase with increasing nutrient/trace element availability. These species can be considered as valuable indicators for reconstructing changes in the trophic state of the upper waters within the Po-river area in palaeo-environmental studies.

A natural exposure experiment on short-term species-selective aerobic degradation of dinoflagellate cysts

Although studies have shown that organic-walled dinoflagellate cysts (dinocysts) can undergo species-selective aerobic degradation, the alteration rate of this process is not known. Here we provide data on the decay rates of dinocyst from a degradation experiment in which sediment samples of Holocene age from (a) anoxic Namibian shelf and (b) anoxic part of the eastern Mediterranean S1 sapropel have been exposed to oxic and anoxic conditions in natural environments. The two types of sediment were stored in bags composed of a dialyse membrane that allows oxygen penetration but prevents bacterial exchange. Sediment bags were placed in open containers connected to sediment traps and moored for 15 months in anoxic brines and oxic intermediate waters of the Urania and Bannock Basins areas. Within the short experimental time (15 months), exposure to oxygenated waters resulted in a 24% to 57% reduction in concentration of cysts attributable to Brigantedinium spp. and Echinidinium granulatum. Other taxa such as Spiniferites spp ., Lingulodinium machaerophorum and Echinidinium spp. appear to be less sensitive. A slight increase in cyst concentration is observed for Nematosphaeropsis labyrinthus, Echinidinium aculeatum, Operculodinium israelianum, and Impagidinium aculeatum, indicating that these cyst species are more resistant to aerobic degradation. Exposure to anoxic conditions has not lead to detectable differences between initial and exposed composition and concentration. Our study is the first to document that species-selective degradation of dinocysts in oxygenated natural environments is a rapid process that changes considerably dinocyst concentrations and assemblages.

Dinoflagellate cyst distribution along a shelf to slope transect of an oligotrophic tropical sea (Sunda Shelf, South China Sea)

From 51 surface samples collected along a shelf to slope transect of the Sunda Shelf, South China Sea, 36 taxa of organic-walled dinoflagellate cysts are identified. Oligotrophic tropical shelf assemblages on the Sunda Shelf are dominated by gonyaulacoids such as Spiniferites species, Operculodinium centrocarpum and Operculodinium israelianum. Concentrations of dinoflagellate cysts in the shelf sediments are generally low and correlate well with the content of fine-grained (clay and silt fraction) sediments. Detailed comparisons of sediment grain-size distributions to concentrations of dominant dinoflagellate taxa (Spiniferites species, O. centrocarpum and O. israelianum) in the shelf sediments indicate that these taxa behave in water like sediment particles with size range phi 5.75-6.25 (13-18 mum). In contrast, slope assemblages in fine-grained sediments are dominated by protoperidinioids. This may reflect higher nutrient availability as a result of weak winter upwelling. The concentrations of dinoflagellate cysts in the shelf sediments are mainly controlled by transport and winnowing processes and are probably not representative of surface water conditions.

Dinoflagellate cyst records and human disturbance in two neighboring estuaries, New Bedford Harbor and Apponagansett Bay, Massachusetts (USA)

The dinoflagellate cyst records in sediments from New Bedford Harbor and Apponagansett Bay demonstrate sensitivity to environmental change caused by human activity in the watersheds over the last 500 years. Changes in the species richness, as well as absolute and relative abundance of dinoflagellate cyst taxa reflect recent periods of development around the estuaries. Cyst taxa sensitive to these changes include Dubridinium spp ., Polykrikos schwartzii, Lingulodinium machaerophorum, Operculodinium israelianum and Selenopemphix quanta. The greatest changes in the dinoflagellate cyst record occur during the 20th century, when New Bedford Harbor was exposed to both toxic pollution and heavy nutrient loading from point and non-point sources. Apponagansett Bay was not subject to industrial pollution and nutrient enrichment has been lower (from non-point sources). In Apponagansett Bay there is an increase in the dinoflagellate cyst species richness while species richness first increased, then declined in New Bedford Harbor. During the same period, the total dinoflagellate cyst concentration in New Bedford Harbor fluctuated over a wide range. The decline of species richness and the large fluctuations in the total cyst abundances signal the intensified anthropogenic disturbance in the watershed, notably a high degree of eutrophication and toxic pollution.

Dinoflagellate cysts, freshwater algae and fungal spores as salinity indicators in Late Quaternary cores from Marmara and Black seas

Seismic profiles and mollusks have been used to suggest that from ∼12 500 to 7000 yr BP, the Black Sea was an isolated freshwater lake containing potable water and implying a surface salinity of <1. According to Ryan and Pitman (1999), these circumstances encouraged Neolithic settlement and farming on the shore of the Black Sea. This model conflicts with previous studies of dinoflagellate cysts and seismic profiles from the Marmara Sea. Here we investigate Ryan and Pittman’s model using palynological studies of organic-walled dinoflagellate cysts, acritarchs, freshwater algae, microforaminifera, and fungal remains as tracers of changes in surface salinity for seven cores of pleniglacial to Holocene sediments from the Marmara and Black seas. Core-top data from 16 sites along a salinity gradient from 39.5 in the Aegean Sea to ∼17 in the Black Sea show that the dinocyst species Impagidinium aculeatum, Impagidinium patulum, Operculodinium israelianum, Polysphaeridium zoharyi and Nematosphaeropsis labyrinthus are markers of Mediterranean Sea water and summer surface salinity >24, and that Spiniferites cruciformis, Spiniferites inaequalis, Peridinium ponticum, Polykrikos spp. and Quinquecuspis concreta characterize the lower salinity of the Marmara and/or Black seas. The core-top data and correlatable down-core assemblage changes in time-equivalent sapropelic and brown muds show that there is no evidence for differential aerobic decay of dinocysts in the study area. The main acritarchs are Sigmopollis psilatum, Concentricystes cf. C. rubinus and cf. Acritarch-8 of Traverse (1978), all of which are absent from the Aegean Sea and decrease in abundance with increasing salinity; the first two taxa have been reported previously as freshwater species. Fungal remains show a similar distribution pattern to the freshwater acritarchs, indicating their origin from terrestrial environments. Freshwater Chlorococcales are almost confined to the Black Sea but they have rare occurrences in the Aegean, indicating long-distance transport. Microforaminiferal linings are abundant in the Marmara Sea but are absent in deep water of the Black Sea. In the Marmara Sea, mid–late Holocene assemblages (<7 ka) are dominated by Lingulodinium machaerophorum, Operculodinium centrocarpum and halophilic Mediterranean Spiniferites spp. ( S. mirabilis, S. hyperacanthus, S. bentorii), and a diversity of heterotrophic protoperidinioid and Polykrikos species are present in both sapropels and brown lutites. In contrast, the early Holocene interval (including sapropels) has fewer halophilic Spiniferites spp. and other Mediterranean taxa ( O. israelianum, Polysphaeridium zoharyi) and more low salinity indicators ( P. ponticum, Pyxidinopsis psilata and S. cruciformis), suggesting that the overflow of Black Sea water was greater than now. The time-equivalent early Holocene unit in the Black Sea has a higher percentage of taxa found in freshwater environments (including S. cruciformis forms 1–3; Gonyaulax apiculata, fungal remains and freshwater acritarchs) but the continued presence of Spiniferites morphotypes and other taxa associated with brackish (∼7–18) to saline surface water indicates that there was some Mediterranean water present at this time. The late glacial and Pleniglacial sediments in the Marmara Sea contain a lower diversity of dinoflagellates, dominated by S. cruciformis and P. psilata, as in early Holocene sediments of the Black Sea but including the short-spine morphotypes of S. cruciformis which are not found in freshwater lakes. We conclude that although the glacial stages were marked by much lower sea-surface temperatures, there was either some periodic marine influence or the marine dinocysts were living in a brackish water environment (∼7–18) with the freshwater species being transported from glacial lakes. Overall, there is no palynological evidence that the surface salinity of the Black or Marmara seas was ever as low as a freshwater lake. This finding is consistent with models that estimate the time required to desalinate the Black Sea after closing of the Marmara–Bosphorus gateway.

Palaeoproductivity and post-depositional aerobic organic matter decay reflected by dinoflagellate cyst assemblages of the Eastern Mediterranean S1 sapropel

Abstract In the reconstruction of bioproductivity in surface waters the extent to which a proxy has been diagenetically altered is often a matter of debate. Here we investigate how organic- and calcareous-walled dinoflagellate cysts can be used for separately estimating bioproductivity and oxygen related diagenesis. This is achieved by studying the cyst content of the most recent Eastern Mediterranean sapropel S1, that is thought to have been deposited under conditions of increased primary production in surface waters and possible anoxia in the bottom waters. Based on chemical evidence, it has been shown that the visible sapropelic layer represents only the residual lower part of what was initially a much thicker sapropel, as a result of post-depositional decay of organic matter related to oxygen penetration into the sediments. The effect of aerobic organic matter decay on the cyst associations is studied through the comparison of the unaffected, lower part of the initial sapropel and the ‘oxidised’ upper part. Comparing the unaffected sapropelic sediments with pre- and post-sapropelic material gives insight into the relationship between fossil cysts assemblages and palaeoproductivity. Impagidinium aculeatum, Impagidinium patulum, Operculodinium israelianum, Polysphaeridium zoharyi and probably Impagidinium spp., Impagidinium paradoxum and Nematosphaeropsis labyrinthus are very resistant against aerobic decay and their accumulation rates appear to be primarily related to productivity in surface waters. Protoperidinium and Echinidinium species, on the other hand, are shown to be very sensitive and can be used to recognise oxygen-related decay. The calcareous-walled dinoflagellate cysts seem to be unaffected by oxic organic matter decay in Mediterranean sediments.

Synchronous palynological changes in early pleistocene sediments off new jersey and Iberia, and a possible paleoceanographic explanation

Palynomorphs record the establishment of modern conditions in the subtropical North Atlantic during the early Pleistocene. Prior to ‐1.4 Ma, muds on both the New Jersey shelf and the Iberia Abyssal Plain contained relatively few terrestrial palynomorphs, and had a dinocyst flora rich in Operculodinium israelianum and other dinocyst taxa recording warmer surface waters than at present (e.g., Tectatodinium pellitum, Lingulodinium machaerophorum, and Polysphaeridium zoharyi). Over a span of ‐250 ka, this palynological assemblage was succeeded by one rich in pollen and with a dinocyst flora similar to the “modern”; flora, i.e. rich in Operculodinium centrocarpum, Bitectatodinium tepikiense, Spiniferites spp. (predominantly S. ramosus), and Brigantedinium spp. (predominantly B. simplex). The synchronous palynological changes in such different geological settings in the eastern and western subtropical North Atlantic are attributed to global climatic deterioration and the expansion of ice sheets in the northern hemisphere. Climatic cooling increased the velocity of the Gulf Stream and other surface currents in the subtropical gyre, causing the gyre to contract and pull away from the continents. Glacioeustatically lowered sea levels also exposed a large percentage of the continental shelf areas, and together with other bathymetric highs like the Charleston Bump, deflected the gyre boundary currents (like the Gulf Stream) offshore. Consequently, surface waters of polar origin were able to penetrate between the warm waters of the gyre and the North American continent north of Cape Hatteras in the west, and Iberia in the east, around 1.4 Ma. This paleoceanographic change increased the area of “neritic”; sedimentation at mid latitudes in the North Atlantic, allowing greater terrestrial influx beyond the shelfbreak.

SYNCHRONOUS PALYNOLOGICAL CHANGES IN EARLY PLEISTOCENE SEDIMENTS OFF NEW JERSEY AND IBERIA, AND A POSSIBLE PALEOCEANOGRAPHIC EXPLANATION

Palynomorphs record the establishment of modern conditions in the subtropical North Atlantic during the early Pleistocene. Prior to ~1.4 Ma, muds on both the New Jersey shelf and the Iberia Abyssal Plain contained relatively few terrestrial palynomorphs, and had a dinocyst flora rich in Operculodinium israelianum and other dinocyst taxa recording warmer surface waters than at present (e.g., Tectatodinium pellitum, Lingulodinium machaerophorum, and Polysphaeridium zoharyi). Over a span of ~250 ka, this palynological assemblage was succeeded by one rich in pollen and with a dinocyst flora similar to the “modern” flora, i.e. rich in Operculodinium centrocarpum, Bitectatodinium tepikiense, Spiniferites spp. (predominantly S. ramosus), and Brigantedinium spp. (predominantly B. simplex). The synchronous palynological changes in such different geological settings in the eastern and western subtropical North Atlantic are attributed to global climatic deterioration and the expansion of ice sheets in the northern hemisphere. Climatic cooling increased the velocity of the Gulf Stream and other surface currents in the subtropical gyre, causing the gyre to contract and pull away from the continents. Glacioeustatically lowered sea levels also exposed a large percentage of the continental shelf areas, and together with other bathymetric highs like the Charleston Bump, deflected the gyre boundary currents (like the Gulf Stream) offshore. Consequently, surface waters of polar origin were able to penetrate between the warm waters of the gyre and the North American continent north of Cape Hatteras in the west, and Iberia in the east, around 1.4 Ma. This paleoceanographic change increased the area of “neritic” sedimentation at mid latitudes in the North Atlantic, allowing greater terrestrial influx beyond the shelfbreak.

Dinoflagellate cysts and the paleoenvironment of Late-Pliocene early-pleistocene deposits of Brittany, Northwest France

The marine Pliocene facies of the Redon clay is widely distributed in the western part of Brittany. the decrease in the abundance of Tertiary pollen towards the top of the deposits, coupled with the increase of pollen of boreal forest taxa and the development of Ericaceae and Poaceae indicates a Late-Pliocene age. The occurrence of the transgression maximum is recorded in calcareous beds which contain the highest concentration of microforaminiferal linings and dinoflagellate cysts. Hystrichokolpoma rigaudae and Melitasphaeridium choanophorum, along with Achomosphaera andalousiensis and Operculodinium israelianum make up these aseemblages. The presence of dinoflagellate cyst assemblages with estuarine and neritic affinities but with an occasional oceanic form, indicates sedimentation in coastal waters with a neritic influence. The paleotopography exerts a control on the altitudinal distribution of the Redon clays in the western part of Brittany to the west of the Rennes Basin. The Pliocene-Pleistocene dinoflagelate cyst assemblages of southern England and northwestern france show a remarkable degree of homogeneity in their composition, chiefly expressed in the apparent contradictory association of A. andalousensis and O. israelianum that suggest sedimentation in an unusual type of environment which arose in the context of climatic change and sea-level variations at that time.

Impagidinium bacatum,a new dinoflagellate cyst species from the Mediterranean Pliocene: Systematics, biostratigraphy and paleoecology

Impagidinium bacatum nov. sp. is a dinoflagellate cyst with a relatively thick and punctate wall and which has been exclusively observed in the Mediterranean Sea sediments of Early Pliocene and Late Pliocene ages (ca. 4.3–2.4 Ma). Its maximum abundance was found to occur in upper Pliocene laminites in association with other dinoflagellate cyst taxa that have a thick and ornamented cyst wall such as Achomosphaera callosa, Operculodinium israelianum and Tectatodinium pellitum. Impagidinium bacatum was probably a warm-temperate to subtropical, stenothermic species, rather tolerant toward salinity conditions.

Recent dinoflagellate cyst distribution in eastern Australia

Dinoflagellate cysts are abundant in estuarine and shallow marine sediments of eastern Australia. Some taxa, such as Protoperidinium spp., Operculodinium israelianum (Rossignol) Wall 1967, Lingulodinium sp. and Cobricosphaeridium sp. show changes in abundance with changing salinity but overall, the assemblage composition is relatively homogeneous. Other species, such as Polysphaeridium zoharyi (Rossignol) Bujak et al. 1980, Tuberculodinium vancampoae (Rossignol) Wall 1967 and Operculodinium centrocarpum (Deflandre and Cookson) Wall 1967 change in abundance with latitude. The net effect is to produce distinctly different assemblages in the north from the south.

Distribution des kystes de dinoflagellés dans les sédiments pléistocènes de la marge guinéenne de l'afrique (Equamarge I, 1983)

In sediments from core KS 03 from the Guinean margin (west coast of Africa), it is possible to distinguish two groups of dinoflagellate cysts, serving as indicators of change of temperature: a group of warm to temperate species, including Impagidinium paradoxum, Impagidinium strialatum, Impagidinium aculeatum and Impagidinium patulum, and a group of cold to temperate species, including Operculodinium centrocarpum, Nematosphaeropsis labyrinthae and Spiniferites mirabilis. The ratio of the relative abundances of the two groups indicates the ecological nature of the water masses which have migrated in the north Atlantic during the Pleistocene. The curve of the ratio of warm-temperate species to cold-temperate species shows a high similarity to the δ 18O curve from the tests of benthic foraminifers. A high percentage of Operculodinium centracarpum among the cold temperate species reveals not only the presence of subpolar water masses, but also the importance of the North Atlantic current along the west coast of Africa. The reworked and transported species from the coastal zone give evidence of the characters of the Guinean littoral environment, this being determined by the moisture and the aridity of the climate. Lingulodinium machaerophorum grows in waters rich in nutrients, with normal salinity. Polysphaeridium zoharyi prefers highly saline waters and indicate the beginning of aridity. Operculodinium israelianum is abundant in restricted environments containing high percentages of organic matter. Core KS 03 corresponds to the interval of time between 800,000 and 122,000 yr B.P. During the glacial stages, stages 20 and 18, the water masses with planktonic assemblages of transitional-subtropical character, associated with Spiniferites mirabilis, come close to the Guinean coast, as during the last glacial stage, and produce an intense aridity on the continent. At that period the influence of subpolar water masses and of the North Atlantic current, characterised by Operculodinium centrocarpum, can be perceived on the west African margin. Aridity tends to regress. At the end of stage 16, the tropical water masses remained preponderant even during glacial stages. Restricted, humid environments with Operculodinium israelianum extended along the coast. After stage 11, transitional to subtropical waters extended down again along the African coast, but the glacial stages were less cold and less arid.

The fossil floras of Kachchh- IV. Tertiary palynostratigraphy

The palynological work so far done on the various Tertiary sediments of Kachchh has been reassessed and new information added. Many genera have been redefined and new genera, viz., Intrareticulites, Retitribrevicolporites, Dermatobrevicolporites, Triangulorites, Arengapollenites, Minutitricolporites, Acanthotricolpites, Angulocolporites, Pseudonyssapollenites, Pilatricolporites, Tribrevicolporites, Triangulotricolporites, Retitetrabrevicoporites, Tripilaorites, Ligulifloraedites, Spinulotetradites, Verrudandotiaspora, Tricolporopilites, Tricolporocolumellites, Ratariacolporites, Plicatiaperturites, Palaeomalvaceaepollis, Pilapanporites, Verrupolyporites, Khariasporites, Magnamonocolpites and Hibisceaepollenites have been proposed. On the basis of relative frequency of all taxa the Matanomadh Formation (Palaeocene) has been divided into (i) Barren Zone, (ii) Dandotiaspora dilata Cenozone, (iii) Tricolpites minutus Cenozone, (iv) Couperipollis kutchensis Cenozone, and (v) Sponge spicules Zone; Naredi Formation (Lower Eocene) has been divided into (i) Lakiapollis ovatus Cenozone, and (ii) Lygodiumsporites lakiensis Cenozone. The Middle Eocene palynological assemblage has been divided into Proxapertites microreticulatus Cenozone for Harudi Formation and Cheilanthoidspora enigmata Cenozone for the Rataria bore-core. Maniyara Fort Formation (Oligocene) has been divided into (i) Operculodinium centrocarpum Cenozone, (ii) Trisyncolpites ramanujamii Cenozone, and (iii) Aplanosporites robustus Cenozone and Khari Nadi Formation (Miocene) has been classified into (i) Cordosphaeridium cantharellum Cenozone, (ii) Striatriletes susannae Cenozone, and (iii) Operculodinium israelianum Cenozone. Thus in total, there are approximately 179 spore-pollen species in Palaeocene, Lower and Middle Eocene, Oligocene and Miocene. Of them, 42 species are confined to Palaeocene, 39 species to Eocene, 25 species to Oligocene and 21 species to Miocene. The Lower Eocene has maximum number (113) of spore-pollen species. The population gradually decreases and in Miocene only three species of angiosperms are recorded. On the basis of morphological characters of spores and pollen grains the families Parkeriaceae, Amaranthaceae-Chenopodiaceae, Clusiaceae, Bombacaceae, Malvaceae, Acacieae, Caesalpiniaceae, Rhizophoraceae, Lecythidaceae, Meliaceae, Ctenolophonaceae, Polygalaceae, Alangiaceae, Apiaceae, Asteraceae, Poaceae and Arecaceae could be recognized. The palynological cenozones proposed in this paper have also been compared with other known assemblages from India.

EARLY PLEISTOCENE DINOFLAGELLATES FROM THE ROYAL SOCIETY BOREHOLE AT LUDHAM, NORFOLK

SummaryA more complete account is presented of the ‘hystrichospheres’, both indigenous and recycled, originally found by West (1961) during his palynological investigation of Early Pleistocene marine sediments penetrated by the Royal Society Borehole at Ludhatii, in Norfolk, England. The commonly encountered ‘hystrichosphere’ types of West are identified as x=Operculodinium israelianum (R.)W., y=Tectatodinium pellitum W. and z = Leptodinium mulliplexum sp. nov., while it is probable that a collection of Hystricliospliaera species comprise West's category ‘hooked‐Hystrix’. The majority of these organisms are fossilized gonyaulacid and protoceratioid dinofiagellate resting cysts (spores). These dinoflagellates form five facies‐associations in this sequence. The palaeoecological significance of their distribution is discussed with special concern to palaeoclimates and the future use of dinofiagellates in Quaternary stratigraphy.