Karin A F Zonneveld

Atlas of modern organic-walled dinoflagellate cyst distribution

This Atlas summarises the global distribution of extant organic-walled dinoflagellate cysts in the form of 61 maps illustrated by the relative abundance of individual cyst taxa in recent marine sediments from the Atlantic Ocean and adjacent basins, the Antarctic region (South Atlantic, southwestern Pacific and southern Indian Ocean sections), the Arabian Sea and the northwestern Pacific. This synthesis is based on the integration of literature sources together with data from 835 marine surface sediments prepared on a comparable methodology and taxonomy. The relationships between distribution patterns of cyst species and the surface-water parameters (temperature, salinity, phosphate and nitrate concentrations) are documented with graphs depicting the relative abundance of species in relation to seasonal and annual values of the above mentioned parameters at the sample sites. Two ordination techniques (detrended correspondence analysis and canonical correspondence analysis) have been carried out to statistically illustrate the relationships between species distribution and sea-surface conditions. Results have been compared with previously published records and an overview of the ecological significance of each individual species is presented. Characterisations of selected environments as well as a discussion about how additional processes such as preservation and transport could have affected the present dataset are included. This Atlas forms the basic printed version of an international database that will be freely available within the PANGAEA database: http://www.pangaea.de and on the web site www.pangea.de/projects/dino-atlas.

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.

Preservation of organic-walled dinoflagellate cysts in different oxygen regimes: a 10,000 year natural experiment

Abstract The occurrence of organic-walled dinoflagellate cysts in (fossil) sediments depends on several factors, including as the ecological preferences of the cyst-forming dinoflagellates, cyst production, transport and preservation. Although laboratory experiments have shown that several cyst species are sensitive to chemical treatment, no information about the selective preservation of dinoflagellate cyst species in natural environments has previously been presented. Here, we present data on the effects of oxygen availability in bottom sediments on a cyst assemblage from the ungraded Madeira Abyssal Plain f-turbidite of which only the upper layer has been oxidized. Based on differences in species composition between the oxidized and underlying, unoxidized layers of this turbidite, the influence of oxygen availability on the preservation of individual species has been estimated. Cyst species have been classified in ascending order of resistance to oxygen availability in sediments as: (1) highly sensitive (cysts formed by Protoperidinium species), (2) moderately sensitive (e.g. Spiniferites species), (3) moderately resistant (e.g. Impagidinium paradoxum and Nematosphaeropsis labyrinthus) and (4) resistant (e.g. Impagidinium aculeatum).

Use of selective degradation to separate preservation from productivity

The assessment of diagenetic influences on the sedimentary record is problematic despite its crucial importance for accurate environmental reconstruction and understanding of biochemical cycles. We propose a general applicable method that uses differences in degradation rates of organic components to separate degradation and productivity. We demonstrate this method on a southeastern Atlantic sediment core covering the past 145 k.y. The new method solves discrepancies between existing organic matter, silica- and carbonate-based productivity reconstructions, and emphasizes the importance of bottom- and pore-water characteristics for transformation of the sedimentary record.

New species of organic walled dinoflagellate cysts from modern sediments of the Arabian Sea (Indian Ocean)

Abstract The taxa Algidasphaeridium, spongium Zonneveld, sp. nov., Echinidinium aculeatum Zonneveld, gen. et sp. nov., Echinidinium bispiniformum Zonneveld, gen. et sp. nov., Echinidinium delicatum Zonneveld, gen. et sp. nov., Echinidinium granulatum Zonneveld, gen. et sp. nov., Echinidinium transparantum Zonneveld, gen. et sp. nov. and Stelladinium robustum Zonneveld, sp. nov. are formally described on the basis of well preserved material from sediment traps and surface sediments of the Arabian Sea (northwestern Indian Ocean). Furthermore, a new combination Echinidinium euaxum (Head) Zonneveld comb. nov. is proposed.

(Palaeo-) ecological significance, transport and preservation of organic-walled dinoflagellate cysts in the Somali Basin, NW Arabian Sea

To date, relatively little information is available about factors influencing organic-walled cyst production of tropical dinoflagellates and processes influencing the final burial of cysts in bottom sediments, such as transport and preservation. To extend this information, cyst fluxes were documented for three sediment traps from June 1992 to February 1993 at two sites in the Somali Basin (northwestern Arabian Sea) as well as the cyst association of underlying sediments. By comparing cyst associations of contemporaneously collected trap samples at different depths at one site, information about transport and processes of decay in the water column was obtained. Neither transport nor decay appears to have any detectable influence on cyst association during cyst settlement through the water column. Comparing the trap associations with the underlying sediments indicates that downslope transport appears to have influenced the cyst association on a local scale only. Species-selective decay, probably related to the presence of oxygen in bottom sediments, has influenced the cyst association most pronouncedly at the most offshore site. Relating variations in the trap associations with environmental conditions of the overlying surface waters indicates that highest production of both filled and empty cysts occurs during the SW Monsoon upwelling. Based on this correlation three groups of species can be distinguished: Species with highest fluxes during (1) the first-half of the SW Monsoon (June-August); Bitectatodinium spongium, Echinidinium granulatum, Echindinium transparantum, Echinidnium spp., cysts of Protoperidinium compressum and cysts of Protoperidinium subinerme, (2) the transition between the SW-Monsoon and inter-Monsoon; Spiniferites mirabilis and Spiniferites spp., (3) no particular season; all other species. Cyst associations of all trap samples are dominated by cyst of Protoperidinium species. Cysts with highest fluxes during the SW-Monsoon form about a third of the associations.

Geographical distributions of organic-walled dinoflagellate cysts in surficial sediments of the Benguela upwelling region and their relationship to upper ocean conditions

The organic walled cyst content of 41 surface sediment samples from the south-eastern South Atlantic Ocean have been studied to create a dataset that can be used for palaeoceanographic reconstructions. In order to obtain insight into which environmental factors influence the distribution of individual cyst species, the cyst associations have been compared with oceanographic characteristics of the overlying water masses, i.e. temperature, salinity, density and stratification gradients. The associations and relationships have been established by visual examination of the dataset and the multivariate ordination techniques, Detrended Correspondence Analysis and Canonical Correspondence Analysis. Special attention has been given to the factors of transport and preservation of the cysts. Five associations have been recognised as being characteristic of (1) areas influenced by coastal upwelling and/or river outflow, (2) open ocean, (3) Agulhas Current and southern Benguela Current, (4) Benguela Current and (5) Walvis Bay, shelf break area. The factors dominant in influencing either directly or indirectly the cyst distributions appear to be the stratification in the upper 50 m of the water column, nutrient concentration and seasonality. Variations in sea surface temperatures and salinities have only minor effect on cyst distribution.

Mechanisms forcing abrupt fluctuations of the Indian Ocean Summer Monsoon during the last deglaciation

Abstract A piston core from the Somali upwelling area has been studied at high resolution for its dinoflagellate cyst content. Variations in cyst association are inferred to reflect changes in Indian Ocean summer monsoon intensity. Several abrupt fluctuations in monsoon intensity are detected for the interval between 20 and 10 ka BP. Comparison of these fluctuations with changes in contrast between 30°N and 30°S July insolation and the δ 18 O GRIP ice-core values suggests that different mechanisms influenced monsoon intensity at different time intervals. A general trend in monsoon intensity follows variations in insolation contrast, lagging minimum contrast by 7.5 ka and maximum contrast by 4 ka. This phase lag difference can be explained by assuming the existence of an ice/snow cover over central Asia/Tibet during glacial times. Between 18.7 and 12.5 ka BP fluctuations in SW-monsoon intensity may be forced by variations in the thermohaline ocean circulation. A rapid transition. towards strong SW-monsoons at 12.5 ka BP is possibly the result of variations in atmospheric circulation and melting of the snow/ice fields in central Asia/Tibet. Variations in glacial-interglacial boundary conditions related to temperature change at northern latitudes are likely to have influenced SW-monsoon intensity between 12.5 and 10 ka BP, whereas after 10 ka BP variations in tropical land surface boundary conditions may be the dominant forcing factor. 0 1997 Elsevier Science Ltd. All rights reserved.

Shifts in the position of the north equatorial current and rapid productivity changes in the western tropical Atlantic during the last glacial

High-resolution, well-dated calcareous dinoflagellate cyst and organic carbon records from a 58 kyr sediment core (M35003-4) located southeast of the island of Grenada show that rapid and pronounced changes in cyst association and accumulation and organic carbon deposition occurred, controlled by (1) a significant southward shift in the position of the North Equatorial Current during the last glacial period and the Younger Dryas cold interval and (2) rapid changes in local productivity in marine isotopic stage 3 that are associated with variations in Orinoco River nutrient discharge and coastal upwelling strength. Prominent cyst accumulation peaks representing extremely oligotrophic and stratified thermocline conditions mimic the Greenland ice core and northern Atlantic Dansgaard/Oeschger stadials and Heinrich events. We provide new evidence for a coupled tropical/high-latitude Atlantic climate system during the last glacial period and suggest that changes in the zonality of the low-latitude winds may play an important role in modulating rapid interhemispheric climate variability.

Modem organic-walled dinoflagellate cysts in arctic marine environments and their (paleo-) environmental significance

The Arctic Ocean is one of the least known marine regions of the world. Because of its major influence on global climate and its hostile environmental conditions it is a fascinating area for paleoecological, paleoclimatic and paleoceanographic research. The composition of planktic microfossil assemblages, and both the trace-element and stable isotope compositions of hard parts, provide us with valuable information about the physical and biochemical parameters of surface waters in the high northern latitudes. Calcareous and biosiliceous microfossils that are traditionally used in Quaternary paleoenvironmental studies are of limited value in the Arctic Ocean because of their low abundances, low diversity and/or low preservation potential. The past several decades have seen considerable progress in our knowledge of the ecology and biogeography of dinoflagellates and their organic-walled cysts in the high northern latitudes, and these dinoflagellate cysts are now important proxies for reconstructing surface water conditions in the Quaternary. This arcticle gives an overview of the ecology of dinoflagellates and their cysts, the processes that transform the living communities into sediment communities, and the environmental gradients that may be reconstructed from fossil dinoflagellate cysts assemblages in the high northern latitudes.KurzfassungDer Arktische Ozean ist eine der am wenigsten untersuchten marinen Regionen des Weltozeans. Durch seinen Einfluss auf das globale Klima und die lebensfeindlichen Umweltbedingungen ist es eines der faszinierendsten Gebiete für paläoökologische, paläoklimatische und paläoozeanographische Forschung. Die Zusammensetzung der planktischen Mikrofossilvergesellschaftungen, sowie die Spurenelement- und die stabile Isotopenzusammensetzung der Hartteile, liefern wertvolle Informationen über physikalische und biochemische Parameter der Oberflächenwas-sermassen in den hohen nördlichen Breiten. Kalkige und kieselige Mikrofossilien, die traditionell in Paläoumwelt-studien des Quartärs benutzt werden, sind aufgrund von geringen Häufigkeiten, geringer Diversität und/oder geringem Fossilisationspotenzial von eingeschränkter Bedeutung. Beträchtlicher Fortschritt wurde in unseren Kenntnissen der Ökologie und Biogeographie der Dinoflagellaten und ihrer Zysten in den polaren und subpolaren Gebiete der hohen nördlichen Breiten in den vergangenen Jahrzehnten gemacht, und diese organisch-wandigen Mikrofossilien sind deshalb wichtige Proxies für die Rekonstruktion der Eigenschaften der oberflächennahen Wassermassen im Quartär. Diese Arbeit gibt einen Überblick über die Ökologie der Dinoflagellaten und ihrer Zysten, der Prozesse, die die Lebendgemeinschaften in Sedimentgemeinschaften umwandeln, und den Umweltgradienten, die mit den fossilen Dinoflagellaten-Zysten Vergesellschaftungen in den hohen nördlichen Breiten rekonstruiert werden können.