Fabienne Marret

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.

Vegetation change in equatorial West Africa: time-slices for the last 150 ka

Abstract Drawing on marine and terrestrial palynological data, vegetation maps of equatorial West Africa are presented for eleven time slices over the last 150,000 years. Long marine records are used as a basis for the regional picture and provide a chronology for the last glacial cycle. Much shorter terrestrial records help fill in the picture for the most recent periods and facilitate interpretation of regional patterns for the longer timescale. Temporal and spatial variation is revealed in relation to global patterns of climate change. Rain forest was widespread during Oxygen Isotope Stages 1 and 5, but strongly reduced during Stages 3 and 4 and especially during Stages 2 and 6 when open, grass-rich vegetation prevailed. Glacial rain forest refuges are found in the southwest of the Guinean mountains and along the eastern coast of the Gulf of Guinea. Miombo woodland of the Zambezian vegetation zone expanded during Stage 5, especially during the first half. Podocarpus forest had its largest expansion during Substages 5d (115 to 105 ka) and 5b (95 to 85 ka). The last occurrence of Podocarpus in the Guinean mountains is during Stage 5a. The distribution of mangrove swamps was extremely reduced during glacial times. During Stage 6, savanna and open dry forest covered large areas along the northern coast of the Gulf of Guinea. The southern Saharan desert reached far to the south and the Namib desert far to the north. The area of rain forest was restricted, mangrove swamps were strongly reduced, and the area of Podocarpus forest fluctuated. During Stage 5 large changes in the area of Afromontane forest, rain forest, dry open forest and savanna occurred. Rain forest was widespread and mangroves were extensive along the coast during the last interglacial (Substage 5e). Podocarpus forest area strongly extended during Substages 5d and 5b. In Substages 5c and 5a, rain forest reclaimed areas it had lost in the previous substages (5d and 5b, respectively). Mangrove swamps were less widespread in the later substages of Stage 5 than during Substage 5e. During Stage 4, the rain forest area was again strongly reduced, and recovered only slightly during the following Stage 3. Also the mangrove swamp area was reduced except along the Ivory Coast and along the northwestern coast of the Gulf of Guinea. Podocarpus forest only occurred in Angola and may be in Congo during Stage 4. Again forest was much reduced during Stage 2 and open vegetation types covered large parts of equatorial West Africa. Mangrove swamps must have been rare. At the beginning of the Holocene, mangrove swamps had recovered and reached their largest extension. Also the rain forests area increased in the early Holocene and Guinean and Congolian rain forests were probably not separated by a savanna corridor now existing in Togo and Benin.

Distribution of dinoflagellate cysts in recent marine sediments from the east Equatorial Atlantic (Gulf of Guinea)

Surface sediment samples of 46 sites from the eastern Equatorial Atlantic Ocean were analyzed for their palynological content in order to document the dinoflagellate cyst distribution in relation to oceanic parameters (sea-surface temperature, salinity and water depth). A total of 34 species were identified. The assemblages are mainly dominated by Brigantedinium spp., Spiniferites delicatus, Polykrikos kofoidii and Lingulodinium machaerophorum. Dinoflagellate cyst distribution seems to be more influenced by water depth and sea-surface salinity than sea-surface temperature. Other factors, such as the nutrient richness, seem to control the species distribution, notably that of Brigantedinium spp. and Polykrikos kofoidii. Moreover, high cyst concentration and abundant S. delicatus and P. kofoidii cysts characterize the upwelling system.

Taraxerol and Rhizophora pollen as proxies for tracking past mangrove ecosystems

Angola Basin and Cape Basin (southeast Atlantic) surface sediments and sediment cores show that maxima in the abundance of taraxerol (relative to other land-derived lipids) covary with maxima in the relative abundance of pollen from the mangrove tree genus Rhizophora and that in the surface sediments offshore maxima in the relative abundance of taraxerol occur at latitudes with abundant coastal mangrove forests. Together with the observation that Rhizophora mangle and Rhizophora racemosa leaves are extraordinarily rich in taraxerol, this strongly indicates that taraxerol can be used as a lipid biomarker for mangrove input to the SE Atlantic. The proxy-environment relations for taraxerol and Rhizophora pollen down-core show that increased taraxerol and Rhizophora pollen abundances occur during transgressions and periods with a humid climate. These environmental changes modify the coastal erosion and sedimentation patterns, enhancing the extent of the mangrove ecosystem and/or the transport of mangrove organic matter offshore. Analyses of mid-Pleistocene sediments show that interruption of the pattern of taraxerol maxima during precession minima occurs almost only during periods of low obliquity. This demonstrates the complex environmental response of the interaction between precession-related humidity cycles and obliquity-related sea-level changes on mangrove input.

Dinoflagellate cyst distribution in surface sediments of the southern Indian Ocean

We analysed 70 surface sediment samples collected in the southern Indian Ocean in order to document the distribution of dinoflagellate cyst assemblages. These organic-walled micro-organisms have a greater potential for preservation than carbonate or silicate microfossils. A total of 53 dinoflagellate cyst taxa were identified, and two new endemic species are described: Selenopemphix antarctica sp. nov. and Impagidinium variaseptum sp. nov. Dominant taxa allowed the recognition of assemblages which show a latitudinal distribution. The circum-Antarctic domain is characterized by assemblages dominated by S. Antarctica sp. nov. and accompanied by I. pallidum. The Subantarctic domain is marked by the dominance of Brigantedinium spp. accompanied by Nematosphaeropsis labyrinthus. The Subtropical domain shows high species diversity, taxa dominance varying along onshore to offshore gradient: the neritic assemblage is dominated by Brigantedinium spp., and Spiniferites spp., the outer neritic is characterized by Operculodinium centrocarpum and the oceanic assemblage is dominated by N. labyrinthus. Principal component analysis illustrates that the distribution of dinoflagellate cyst assemblages is controlled by temperature and salinity. Transfer functions based on the best analogues method are developed to reconstruct past sea-surface conditions.

Paleohydrology and paleoclimatology off Northwest Africa during the last glacial-interglacial transition and the Holocene: palynological evidences

Abstract Pollen and dinoflagellate cyst analyses of deep-sea core located off Morocco provide a continuous record of paleoclimatic and paleohydrological change off Northwestern Africa since the last glacial episode. The stratigraphy is given by isotopic analysis ( δ 18 O) of planktonic foraminifera, which shows a two-step deglaciation. Xeric conditions on the adjacent land, marked by the increase of steppe taxa ( Artemisia , Chenopodiaceae/Amaranthaceae, Ephedra ), and the development of the montane taxon, Cedrus atlantica are observed before Termination IA and during the Younger Dryas. These intervals are also marked by a high abundance of Pinus pollen grains, which indicates a strengthening of the northeastern (NE) trade winds. Variations of the surface water temperatures are shown by the fluctuations of dinoflagellate cyst assemblages which reflect a cooling of the surface waters during Termination IA and the Younger Dryas episode. Intensification of the upwelling system off Morocco resulting from enhanced trade winds occurred during these two key-periods. Quercus forests, which are an important part of the present-day vegetation of the Maghreb region, developed around 8500 yr B.P. Dinoflagellate cyst assemblages suggest that present-day oceanic conditions were established during this period.

Control of modern dinoflagellate cyst distribution in the Irish and Celtic seas by seasonal stratification dynamics

Abstract Surface sediments from seven stations located in the seasonally stratified, frontal and mixed water regions in the Celtic and Irish seas have been analysed for their dinoflagellate cyst assemblages and dinosterol content. A total of 45 dinoflagellate cyst taxa have been identified and the assemblages related to surface and sediment conditions. Sediments from the mixed water region, at 30 m water depth, are characterised by a relatively low cyst concentration (∼2300 cysts/g dry weight) and high relative abundances of Lingulodinium machaerophorum accompanied by Spiniferites membranaceus , Brigantedinium spp. and Dubridinium caperatum . Assemblages from stratified and frontal water stations are dominated by Spiniferites ramosus associated with Operculodinium centrocarpum , Brigantedinium spp., cysts of Polykrikos schwartzii and Selenopemphix quanta . Ordination techniques performed on a restricted number of 35 taxa from the assemblages differentiated the stratified and frontal assemblages based on the abundance of the less abundant species Bitectatodinium tepikiense and Spiniferites elongatus . Among the environmental parameters (sea-surface temperature and salinity, stratification index, chlorophyll concentration and sediment grain-size classes), the seasonal stratification and sedimentological context, itself a function of tidal dynamics, explain most of the variance in the environmental conditions. These results indicate that dinoflagellate cyst analyses of shelf sediment records can be used to document the planktonic signal of seasonal stratification dynamics.

Land-sea correlation by means of terrestrial and marine palynomorphs from the equatorial East Atlantic: phasing of SE trade winds and the oceanic productivity

Abstract Sporomorphs and dinoflagellate cysts from site GIK16867 in the northern Angola Basin record the vegetation history of the West African forest during the last 700 ka in relation to changes in salinity and productivity of the eastern Gulf of Guinea. During most cool and cold periods, the Afromontane forest, rather than the open grass-rich dry forest, expanded to lower altitudes partly replacing the lowland rain forest of the borderlands east of the Gulf of Guinea. Except in Stage 3, when oceanic productivity was high during a period of decreased atmospheric circulation, high oceanic productivity is correlated to strong winds. The response of marine productivity in the course of a climatic cycle, however, is earlier than that of wind vigour and makes wind-stress-induced oceanic upwelling in the area less likely. Monsoon variation is well illustrated by the pollen record of increased lowland rain forest that is paired to the dinoflagellate cyst record of decreased salinity forced by increased precipitation and run-off.

Distribution of dinoflagellate cyst assemblages in surface sediments from the northern and western shelf of Iceland

Abstract In order to provide calibration for palaeoceanographic investigations, 54 surface sediment samples from the northern and western margin of Iceland and Greenland have been analysed for their dinoflagellate cyst assemblages. Relatively high diversity was observed with a total of 28 taxa. Cysts of Pentapharsodinium dalei are dominant accompanied by Operculodinium centrocarpum and Nematosphaeropsis labyrinthus . Three groups of assemblages have been recognised based on multivariate statistical analyses and these are related to surface water masses and currents. The first association, Group I, located west of Iceland, is characterised by high abundance of O. centrocarpum and N. labyrinthus accompanied by significant occurrence of the heterotrophic taxa Brigantedinium spp., Selenopemphix quanta , cysts of Polykrikos schwartzii and cysts of Protoperidinium americanum . This region is under the influence of the Irminger Current (IC) and contains the most productive waters around Iceland. The second association, Group II, comprising high relative abundance of cysts of P. dalei accompanied by significant occurrence of O. centrocarpum and a very high concentration (up to 256 920 cysts/g), is situated in the northern Icelandic shelf, in the Polar Front realm, i.e. the marginal zone between the East Icelandic Current (EIC) and the northern branch of the IC. The third group (Group III) is in the region influenced by the East Greenland Current and the EIC and characterised by the co-dominance of cysts of P. dalei and O. centrocarpum , relatively high representation of Impagidinium pallidum and low concentrations (from 370 to 56 220 cysts/g). This investigation demonstrates that dinocyst distribution is clearly related to upper water mass physical factors. Advection of temperate species around Iceland suggests significant transport by surface currents, especially the IC; however, the apparent boundaries between the associations and decreasing percentages related to environmental gradients indicate that dispersal by surface transport is limited by the ecological requirements of the dinoflagellate cells. Bottom currents may play a role in the accumulation rate of cysts.

A forum on Neogene and quaternary dinoflagellate cysts: The edited transcript of a round table discussion held at the third workshop on Neogene and Quaternary dinoflagellates; with taxonomic appendix

Abstract An edited transcript is presented for discussions on more than 24 taxa of Neogene and Quaternary dinoflagellates, chosen either as being in some way taxonomically problematical or because they hold unusual interest concerning their morphology, (paleo)ecology, or biostratigraphy. These discussions took place at the Third Workshop on Neogene and Quaternary Dinoflagellates and are based on observations of numerous holotypes and other type materials, often with the author of the taxon in attendance. Provisional stratigraphic ranges are given for taxa discussed. A taxonomic appendix by M.J. Head deals formally with selected taxa discussed at the workshop. The important Late Cenozoic genus Filisphaera Bujak 1984 is emended to include only those specimens with a septate/microreticulate periphragm. Its type, Filisphaera filifera Bujak 1984, is also emended and the subspecies Filisphaera filifera filifera is created by autonymy and defined. Filisphaera pilosa Matsuoka & Bujak 1988 is emended and reduced i...