Calcareous Dinoflagellate Research Articles

The (palaeo) environmental significance of modern calcareous dinoflagellate cysts: a review

Increased interest in the environmental applicability of calcareous dinoflagellate cysts for palaeo-environmental studies arose in the last two decades, when it was discovered that they constitute a widespread and abundant group within the calcareous phytoplankton. As primary producers they are directly influenced by environmental Parameters of the surrounding water masses, and therefore extremely suitable for detailed palaeo-environmental and -oceanographical reconstructions. During the last years, detailed investigations on their distribution in surface sediments of the South Atlantic Ocean, the Mediterranean Sea and the Arabian Sea were carried out, in order to reveal which environmental parameters influence their distribution. This, in turn, formed the base for palaeo-environmental and -oceanographical reconstructions. The compilation of the available data on calcareous dinoflagellate ecology, morphology, taxonomy and palaeo-environmental application presented here demonstrates their ample application potential as palaeo-environmental tools.

Examples for character traits and palaeoecological significance of calcareous dinoflagellates

The palaeoecological significance of calcareous dinoflagellate cysts is illustrated by various examples. Genetically fixed and ecologically triggered character traits are distinguished. A summary is given regarding intraspe-cific variability, cyst size and shape, wall thickness, size and shape of the calcitic wall crystals, paratabulation, and archeopyle morphology based on the knowledge, which has been accumulated during the last two decades. Diversity and characteristic cyst associations from different localities are compared. Information on sea level changes, water temperature, oceanographic distribution, and nutrient conditions can be gained from the investigated character traits of calcareous dinoflagellates.

Geochemistry and time-series analyses of orbitally forced Upper Cretaceous marl–limestone rhythmites (Lehrte West Syncline, northern Germany)

A cyclic marl–limestone succession of Middle–Late Campanian age has been investigated with respect to a Milankovitch-controlled origin of geochemical data. In general, the major element geochemistry of the marl–limestone rhythmites can be explained by a simple two-component mixing model with the end-members calcium carbonate and ‘average shale’-like material. Carbonate content varies from 55 to 90%. Non-carbonate components are clay minerals (illite, smectite) and biogenic silica from sponge spicules, as well as authigenically formed zeolites (strontian heulandite) and quartz. The redox potential suggests oxidizing conditions throughout the section. Trace element and stable isotopic data as well as SEM investigations show that the carbonate mud is mostly composed of low-magnesium calcitic tests of planktic coccolithophorids and calcareous dinoflagellate cysts (calcispheres). Diagenetic overprint results in a decrease of 2% δ18O and an increase in Mn of up to 250 ppm. However, the sediment seems to preserve most of its high Sr content compared to the primary low-magnesium calcite of co-occurring belemnite rostra. The periodicity of geochemical cycles is dominated by 413 ka and weak signals between 51 and 22.5 ka, attributable to orbital forcing. Accumulation rates within these cycles vary between 40 and 50 m/Ma. The resulting cyclic sedimentary sequence is the product of (a) changes in primary production of low-magnesium calcitic biogenic material in surface waters within the long eccentricity and the precession, demonstrated by the CaCO3 content and the Mg/Al, Mn/Al and Sr/Al ratios, and (b) fluctuations in climate and continental weathering, which changed the quality of supplied clay minerals (the illite/smectite ratio), demonstrated by the K/Al ratio. High carbonate productivity correlates with smectite-favouring weathering (semi-arid conditions, conspicuously dry and moist seasonal changes in warmer climates). Ti as the proxy indicator for the detrital terrigenous influx, as well as Rb, Si, Zr and Na, shows only low frequency signals, indicating nearly constant rates of supply throughout the more or less pure pelagic carbonate deposition of the long-lasting third-order Middle–Upper Campanian sedimentary cycle.

Calcareous dinoflagellates from a northwestern Pacific sediment trap and their paleoceanographic implications

Research Article| January 01, 2004 Calcareous dinoflagellates from a northwestern Pacific sediment trap and their paleoceanographic implications Yoshihiro Tanimura; Yoshihiro Tanimura 1Department of Geology, National Science Museum, Tokyo 169-0073, Japan Search for other works by this author on: GSW Google Scholar Chieko Shimada Chieko Shimada 2Doctoral Program in Earth Evolution Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8572, Japan email: tanimura@kahaku.go.jp Search for other works by this author on: GSW Google Scholar Micropaleontology (2004) 50 (4): 343–356. https://doi.org/10.2113/50.4.343 Article history received: 08 Jun 2004 accepted: 17 Nov 2004 first online: 06 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Yoshihiro Tanimura, Chieko Shimada; Calcareous dinoflagellates from a northwestern Pacific sediment trap and their paleoceanographic implications. Micropaleontology 2004;; 50 (4): 343–356. doi: https://doi.org/10.2113/50.4.343 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyMicropaleontology Search Advanced Search Abstract Year-round changes in species composition and flux of calcareous dinoflagellates at station JT (34°09.8′N, 141°59.3′E; water depth, 8942m; trap depth, 916m) are reported. A time-series of thirteen sediment-trap samples of 29 days each, between March 5, 1991 and March 2, 1992, provided materials for this study. Vegetative cysts of a calcareous dinoflagellate, Thoracosphaera heimii, were found to be overwhelmingly dominant forming >95% of the calcareous dinoflagellate associations in all trap samples. Its’ flux ranges from 910,000 shells·m−2·day−1 in May, 1991, to 76,000 shells·m−2·day−1 in September, 1991. Cysts of other calcareous dinoflagellates (Leonella granifera, Calciodinellum albatrosianum and Calciodinellum levantinum) were also found, with a maximum flux of 11,000 shells·m−2·day−1 for C. albatrosianum between December, 1991 and January, 1992. Based on physiological information, we suggest that species flux depends on water mass distribution linked to migration of the path of the subtropical Kuroshio Current. High to moderate flux of T. heimii occurred when the current took a meandering or a straight nearshore pathway. Waters southeast of the current prevailed over the trap station during this time. The most favorable environment, May, 1991, for T. heimii production seems to occur around a shallow thermocline formed above Subtropical Mode Water (STMW) in the waters southeast of the current. The species flux dropped when the current took an offshore pathway and flowed over the trap station. Surface and subsurface waters of the Kuroshio Current, especially during summer to autumn, is not productive of this species. The species flux also dropped while a “cold water mass” (i.e. lower salinity water cut off from the subarctic Oyashio Current) emerged over the trap station. Three cysts, L. granifera, C. albatrosianum and C. levantinum, show broadly similar abundance fluctuations to T. heimii. This close relationship between temporal changes in T. heimii productivity and path migrations of the Kuroshio Current, which is linked to the wind stress field over the North Pacific, should potentially provide information for paleoclimatic reconstructions. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Effect of temperature on culture growth and cyst production in the calcareous dinoflagellates Calciodinellum albatrosianum, Leonella granifera and Pernambugia tuberosa

Modern and Late Quaternary oceanic assemblages of calcareous dinoflagellate cysts are often dominated by the species Calciodinellum albatrosianum , Leonella granifera and Pernambugia tuberosa . Their distribution in surface sediments of the South and equatorial Atlantic Ocean has been found to be related to a set of environmental parameters such as temperature, nutrient concentration, stratification and salinity. However, the direct influence of single parameters on the species is as yet unknown. In order to determine the effect of temperature on culture growth and cyst production, strains of the species were investigated in a temperature gradient box under controlled laboratory conditions. Whereas culture growth was observed over a relatively broad range of 12.3–30.4°C in C. albatrosianum , 15.5–30.7°C in L. granifera , and 13.3–32.8°C in P. tuberosa , fossilisable cysts were mainly produced in a smaller range of 16.1–21.7°C in C. albatrosianum , 18.0–24.0°C in L. granifera and 22.3–27.6°C in P. tuberosa . By comparing laboratory and field data it is shown that a good correlation exists in P. tuberosa , whereas in C. albatrosianum and L. granifera higher temperatures of fossilisable cyst production were expected from the field data. As possible explanations different depths of vegetative reproduction and cyst production and seasonality in cyst production are discussed.

Changes in the pelagic fine fraction carbonate sedimentation during the Cretaceous–Paleocene transition: contribution of the separation technique to the study of Bidart section

The Bidart section (southwestern France) displays an almost complete Late Maastrichtian–Early Danian transition. As the Cretaceous–Paleocene (K/P) crisis mainly affects carbonate producers, the aim of this study is to precisely evaluate the evolution of pelagic sediments composition across the boundary. A new protocol for separation of fine carbonates into discrete size fractions was used (1) to precisely evaluate (in weight of carbonate and not only number of particles per gram of rock) the contribution of each carbonate component type (foraminifera, calcareous nannofossils and “nonbiogenic” carbonates, calcite microparticles, and calcareous macrocrystals), and (2) to measure their isotopic signature and thus constrain the origin of these carbonate particles. The Maastrichtian pelagic carbonates are mostly biogenic (70% of the bulk carbonate) but also contain “nonbiogenic” carbonates: calcite microparticles (<4 μm) and calcareous macrocrystals (>4 μm). Due to their isotopic signature, calcite microparticles cannot result from fragmentation and partial dissolution of biogenic remains, and the most likely origin appears to be early diagenetic processes and/or export from shallow-water platforms. The calcareous macrocrystals derive from an early diagenetic process. The lowermost Danian sediments are dominated by “nonbiogenic” carbonates (between 50% and 80% of the bulk carbonate). Nevertheless, two kinds of biogenic components are present: Thoracosphaera operculata and Maastrichtian-like calcareous nannofossils. Thoracosphaera operculata is an opportunistic calcareous dinoflagellate, which frequently occurs at high abundances in basal Danian sediments and is certainly in situ, this is confirmed by it showing a Danian isotopic signature. The Maastrichtian-like calcareous nannofossils are nannofossils of taxa that indisputably occur in the Maastrichtian, but which do not occur consistently in later Danian strata, they show a Maastrichtian-type isotopic signature, which strongly supports the inference that they are mainly reworked from the Maastrichtian. This study shows that “nonbiogenic” carbonates are important components of the pelagic carbonate even during periods of normal sedimentation. In the “crisis interval”, the biogenic carbonate production drops sharply, while calcite microparticles and carbonate macrocrystals remain almost unaffected and represent the major part of the carbonate in the earliest Danian sediments. Finally, the sediments return to a composition similar to that of the Maastrichtian in M. pseudobulloides foraminifera zone.

&amp;lt;i&amp;gt;Tetratropis terrina&amp;lt;/i&amp;gt; sp. nov., a new calcareous dinoflagellate cyst from the Upper Campanian &amp;lt;i&amp;gt;polyplocum&amp;lt;/i&amp;gt; zone of Lägerdorf (NW Germany)

Abstract. A new calcareous dinoflagellate cyst species, Tetratropis terrina sp. nov., with an apparent stratigraphically narrow range is described from the Upper Campanian Bostrychoceras polyplocum zone of the Lägerdorf chalk sequence (NW Germany). The electron microscopic and light microscopic analyses show that T. terrina has both a pithonelloid wall type with uniformly inclined wall crystallites and a reduced peridiniacean paratabulation pattern. The prominent morphological similarities of T. terrina to the other two Tetratropis species (T. patina and T. corbula) justify the affiliation of the new species to the genus. As a result of the extension of the morphological spectrum by the new species, the genus Tetratropis Willems, 1990 has been emended.

New calcareous dinoflagellates (Calciodinelloideae) from the Middle Coniacian to Upper Santonian chalks of Lägerdorf (northern Germany)

Abstract. Three new calcareous dinoflagellate species from the Middle Coniacian to Upper Santonian chalks of Lägerdorf (northern Germany) are formally described: Calcicarpinum macrogranulum n. sp., Pirumella fragilis n. sp. and Ruegenia quinqueangulata n. sp. The species show differing vertical distribution patterns which might result from local sea-level changes: P. fragilis and R. quinqueangulata are restricted to the possibly transgressive upper Mid-Coniacian to Lower Santonian interval and C. macrogranulum occurs consistently only in the probably regressive lower Mid-Coniacian and Middle to Upper Santonian intervals.

A PROPOSED CLASSIFICATION OF ARCHEOPYLE TYPES IN CALCAREOUS DINOFLAGELLATE CYSTS

Abstract The phylogenetic significance of archeopyles in calcareous dinoflagellates cysts has been evaluated, and a classification model is developed that focuses on the archeopyle categories and types established for organic-walled dinoflagellates by Evitt (1967, 1985). Several of Evitt's archeopyle categories are presently recognized within the calcareous dinoflagellate cysts: apical, intercalary, and combination archeopyles, which are here subdivided into eight archeopyle types and several variations. Archeopyles that cannot be assigned to a distinct type, and those with outlines that do not allow an accurate interpretation, are together placed in a separate category: miscellaneous archeopyles. The stratigraphic distribution of the different archeopyle types reveals a phylogenetic trend characterized by an increase of the number of plates involved in archeopyle formation. The first calcareous dinoflagellate cysts to appear in the late Triassic have a monoplacoid apical archeopyle. The first taxa that s...

Pithonelloid wall-type of the Late Cretaceous calcareous dinoflagellate cyst genus Tetratropis

The late Cretaceous calcareous dinoflagellate genus Tetratropis features both a pithonelloid wall-type (evenly inclined wall-components, proven here by a polarisation optical revision) and a peridinialean paratabulation strongly suggesting a dinoflagellate origin of at least part of the Pithonelloideae. This affinity with dinoflagellates sheds more light on the palaeoecology of the Pithonelloideae (commonly termed “calcispheres”), which are characteristic of the middle to Late Cretaceous. The very short-term stratigraphic occurrence of all Tetratropis species is comparable to the distribution pattern of other calcareous dinoflagellate cyst species with a distinctive paratabulation and is thought to reflect a narrow palaeoecological niche. Tetratropis species can be interpreted either as paratabulated morphotypes of otherwise atabulate Pithonelloideae formed under exceptional palaeoenvironmental conditions or as invaders from a highly specific palaeoecological niche during short-term palaeoceanographic events probably related to the initiation of the Late Cretaceous global cooling.

Different nutrient sources forcing increased productivity during eastern Mediterranean S1 sapropel formation as reflected by calcareous dinoflagellate cysts

Comparison of calcareous dinoflagellate cyst assemblages with Ba, Al, Mn, and Fe records from three sediment cores collected in the eastern Mediterranean Sea indicate that calcareous dinoflagellate cysts are generally resistant to postdepositional dissolution. Cyst association changes during and after sapropel S1 formation can therefore be closely related to variability in surface water productivity. Two groups of cysts are defined: those having highest abundances within the sapropelic and postsapropelic sediments. The temporal cyst distributions suggest increased freshwater input mainly from the Nile and a shallowing of the pycnocline as the most important processes increasing nutrient concentration in the photic zone, thus leading to increased productivity and organic carbon fluxes during sapropel formation. Furthermore, a general warming trend at the beginning of S1 formation and a slight salinity decrease are reconstructed.

Calcareous dinoflagellates from a northwestern Pacific sediment trap and their paleoceanographic implications

Year-round changes in species composition and flux of calcareous dinoflagellates at station JT (34°09.8′N, 141°59.3′E; water depth, 8942m; trap depth, 916m) are reported. A time-series of thirteen sediment-trap samples of 29 days each, between March 5, 1991 and March 2, 1992, provided materials for this study. Vegetative cysts of a calcareous dinoflagellate, Thoracosphaera heimii, were found to be overwhelmingly dominant forming >95% of the calcareous dinoflagellate associations in all trap samples. Its' flux ranges from 910,000 shells·m−2·day−1 in May, 1991, to 76,000 shells·m−2·day−1 in September, 1991. Cysts of other calcareous dinoflagellates (Leonella granifera, Calciodinellum albatrosianum and Calciodinellum levantinum) were also found, with a maximum flux of 11,000 shells·m−2·day−1 for C. albatrosianum between December, 1991 and January, 1992. Based on physiological information, we suggest that species flux depends on water mass distribution linked to migration of the path of the subtropical Kuroshio Current. High to moderate flux of T. heimii occurred when the current took a meandering or a straight nearshore pathway. Waters southeast of the current prevailed over the trap station during this time. The most favorable environment, May, 1991, for T. heimii production seems to occur around a shallow thermocline formed above Subtropical Mode Water (STMW) in the waters southeast of the current. The species flux dropped when the current took an offshore pathway and flowed over the trap station. Surface and subsurface waters of the Kuroshio Current, especially during summer to autumn, is not productive of this species. The species flux also dropped while a “cold water mass” (i.e. lower salinity water cut off from the subarctic Oyashio Current) emerged over the trap station. Three cysts, L. granifera, C. albatrosianum and C. levantinum, show broadly similar abundance fluctuations to T. heimii. This close relationship between temporal changes in T. heimii productivity and path migrations of the Kuroshio Current, which is linked to the wind stress field over the North Pacific, should potentially provide information for paleoclimatic reconstructions.

Longterm evolution of calcareous dinoflagellate associations since the Late Cretaceous.

Longterm evolution of calcareous dinoflagellate associations since the Late Cretaceous.

Calcareous dinoflagellate cysts in South and equatorial Atlantic surface sediments: diversity, distribution, ecology and potential for palaeoenvironmental reconstruction

Several marine, peridiniphycidean dinoflagellate species produce calcareous cysts during their life cycle, which are relatively resistant to chemical and physical degradation and are therefore often found in large quantities in oceanic bottom sediments. Although the use of these calcareous cysts as proxies for palaeoenvironmental and palaeoclimatic reconstructions has seen many advances over the last decade, until now only relatively patchy and regional information was available on their recent distribution patterns and ecology, especially at the species level. In this paper, comprehensive calcareous cyst diversity and distribution data have been compiled from published and unpublished work for 167 South and equatorial Atlantic Ocean surface sediments, ranging from 20°N to 50°S, and 30°E to 65°W. The main aim has been to focus on the complex, often non-linear, relationships between individual species’ distributions and the physicochemical and trophic conditions of the overlying (sub)surface waters through the use of x–y graphs of cyst abundance vs. (sub)surface water environmental parameters, and detrended correspondence analyses. Ten cyst species and the calcareous vegetative coccoid species Thoracosphaera heimii were observed in the bottom sediments, each species showing its own characteristic distribution pattern in relation to the environmental conditions of the upper water masses above them (e.g. sea surface temperature, productivity, stratification). The sensitive reactions of various species to unique combinations of environmental parameters shows that each species has its own specific ecological traits, thus rejecting the bundled use of ‘calcareous cyst accumulation’ as a general proxy for oligotrophy or stratification in future palaeoenvironmental analyses. The acquired ‘reference’ data set of this study is large and diverse enough to allow its future application in quantitative palaeoenvironmental reconstruction models, and shows that there is still an enormous reconstruction potential concealed in many fossil calcareous dinoflagellate cyst assemblages.

Calcareous dinoflagellate associations and Maastrichtian–Tertiary climatic change in a high-latitude core (ODP Hole 689B, Maud Rise, Weddell Sea)

The distribution of calcareous dinoflagellates has been analysed for the Maastrichtian–Miocene interval of Ocean Drilling Project Hole 689B (Maud Rise, Weddell Sea). The investigation thus represents a primary evaluation of the long-term evolution in high-latitude calcareous dinoflagellate assemblages during the transition from a relatively warm Late Cretaceous to a cold Neogene climate. Major assemblage changes during this interval occurred in characteristic steps: (1) an increase in relative abundance of tangentially structured species – particularly Operculodinella operculata – at the Cretaceous/Tertiary boundary; (2) a diversity decrease and several first and last appearances across the Middle–Late Eocene boundary, possibly attributed to increased climate cooling; (3) a diversity decrease associated with the dominance of Calciodinellum levantinum in the late Early Oligocene; (4) the reappearance and dominance of Pirumella edgarii in the Early Miocene, probably reflecting a warming trend; (5) monogeneric assemblages dominated by Caracomia spp. denoting strong Middle Miocene cooling. The results not only extend the biogeographic ranges of many taxa into the Antarctic region, but also indicate that the evolution of high-latitude calcareous dinoflagellate assemblages parallels the changing environmental conditions in the course of the Cenozoic climate transition. Therefore, calcareous dinoflagellates contribute to our understanding of the biotic effects associated with palaeoenvironmental changes and might possess the potential for reconstructing past conditions. The flora in the core includes one new taxon: Caracomia arctica forma spinosa Hildebrand-Habel and Streng, forma nov. Additionally, two new combinations are proposed: Fuettererella deflandrei (Kamptner, 1956) Hildebrand-Habel and Streng, comb. nov. and Fuettererella flora (Fütterer, 1990) Hildebrand-Habel and Streng, comb. nov.

Calcareous dinoflagellate cysts in surface sediments from the Mediterranean Sea: distribution patterns and influence of main environmental gradients

The distribution of calcareous dinoflagellate cysts in surface sediments from the Mediterranean Sea was quantitatively analysed. The samples contain 11 cyst species and the vegetative coccoid Thoracosphaera heimii. Cyst abundance increases towards the deeper parts of the basins and is generally higher in the eastern Mediterranean Sea. Three major distribution characteristics exist: (1) different assemblages in oceanic and neritic regions, (2) little agreement with the associations of areas studied so far like the Atlantic Ocean, and (3) a unique oceanic assemblage in the eastern Mediterranean Sea. A gradual change in cyst assemblages from the western to the eastern Mediterranean Sea was observed and statistically compared with the main environmental gradients in the upper water column. Temperature, nitrate concentration and possibly salinity appear to be the most important factors controlling cyst production. Three groups containing cysts with similar environmental preferences can be distinguished: (1) an eastern Mediterranean group related to relatively high temperature and salinity but low nitrate concentration, (2) a group of more or less consistently abundant cosmopolitan species tolerating or even preferring relatively low temperature and salinity but high nitrate concentration, and (3) a group containing species that are possibly adapted to neritic environments and have probably been transported from coastal areas into the studied regions. In contrast to other calcareous plankton, calcareous dinoflagellate cysts correlate strongly with the main environmental gradients in the Mediterranean Sea, bearing a high potential for palaeoenvironmental reconstructions.

Small acritarchs from the Upper Cretaceous: taxonomy, biological affinities and palaeoecology

A systematic study of small acritarchs (most commonly around 10 μm) from the Late Campanian (Duwi (Phosphate) Formation) and Maastrichtian (Dakhla Shale) of Egypt, based on scanning electron miscroscopy, resulted in the identification of nine genera and 27 species, among them the new genus Recticystis and 14 new species, namely Operculites bigranulatus, Bacillidinium partitum, Mecsekia acuta, M. curvispina, M. triangula, Recticystis hemispinosus, Clavaticystis septatus, C. furcatus, Odontothrix multiornatus, Filisphaeridium paucigranulosum, Cymatiosphaera parvirugosa, C. muralis, C. polyornata and C. triradiata. In addition, the following new combinations are proposed: Cymatiosphaera coronis (Habib and Knapp), Mecsekia minor (Takahashi) and Mecsekia ariakense (Takahashi). Small acritarchs are thought to include cysts of dinoflagellates because of significant morphological similarities (cyst shape, chasmic and tremic archeopyles, spinose and septate ornaments) to certain organic-walled and calcareous dinoflagellate cysts. Small size in acritarchs is regarded as an adaptation to a planktonic and possibly to an interstitial mode of life. Small acritarchs attain the highest diversity and abundance in the well agitated environment of the phosphoritic sandstones. In the pores between the sand grains they were protected from the wave action and currents which moved away most of the larger dinoflagellates. Dinoflagellates are common in the associated shales representing a more quiet marine environment. The interpretation of some small spinulose acritarchs as interstitial dinoflagellates may also be supported by the presence of spinose cysts with a chasmic archeopyle in the modern dinoflagellate Polykrikos which includes interstitial forms.

Stable isotopic indication for the cyst formation depth of Campanian/Maastrichtian calcareous dinoflagellates

δ18O and δ13C values for the calcareous dinoflagellate species Orthopithonella? globosa (Fütterer 1984) Lentin and Williams 1985 and Pirumella krasheninnikovii (Bolli 1974) Lentin and Williams 1993 from latest Campanian and earliest Maastrichtian of ODP Hole 690C (Weddell Sea, Antarctic Ocean) have been studied in order to evaluate the species' depth habitat in the water column and their applicability in paleoceanographic studies. The calcareous dinoflagellates show isotopic values comparable to probably shallow-dwelling planktic foraminifera from the same samples in δ18O, but have an offset of about −5‰ to −7‰ in δ13C. This suggests that calcareous dinoflagellate oxygen isotopes may provide information for paleoceanographic reconstructions of sea-surface water temperatures, whereas their extremely light carbon isotope values are probably due to photosynthetic processes.

NEW CALCAREOUS DINOFLAGELLATES (CALCIODINELLOIDEAE) FROM THE MEDITERRANEAN SEA1

Investigations on calcareous dinoflagellates from surface sediments from the Mediterranean Sea revealed 14 species, including one new genus and four previously undescribed species: Calciodinellum levantinum sp. nov., Calciodinellum elongatum nov. comb., Lebessphaera urania gen. nov. et sp. nov., and Scripp- siella triquetracapitata sp. nov. Furthermore, Fuettererella cf. tesserula, so far only known from the fossil record, was found. The cyst–theca relationships of C. levantinum and C. elongatum are given, based on strains established from water samples of the Mediterranean Sea and the Atlantic Ocean. This study gives an insight into the importance of the modern Mediterranean Sea as an unique region concerning calcareous cyst producing dinoflagellates.

Production of calcareous dinoflagellate cysts in response to monsoon forcing off Somalia: a sediment trap study

To study the ecology of calcareous dinoflagellates we examined the impact of the SW and NE monsoons on cyst formation using sediment trap material, collected at 1032 m water depth, off Somalia from June 1992 to February 1993. The results do not confirm the relationship between cyst production and lower nutrient concentrations, as highest cyst fluxes were recorded during late SW monsoon under the relatively nutrient-rich and less agitated conditions of mature upwelled water. Lowest cyst fluxes were found under strongly stratified, nutrient-depleted surface waters during the inter-monsoon. Although all of the studied species seem to prefer a stratified water column, an elevated concentration of nutrients appears to be necessary to maintain high cyst production. Comparison of the mean cyst flux to the sediment trap with that into the underlying surface sediments reveals a loss of 81–96%, which can be attributed to calcite dissolution. The relatively small spheres of Thoracosphaera heimii are affected more than the cysts of the other species.