Organic-walled dinoflagellate cysts and environmental analysis of surface sediments from the Northwest African upwelling area

In order to examine the spatial distribution of organic-walled dinoflagellate cysts (dinocysts) in recent sediments related to environmental conditions in the water column, thirty-two surface sediment samples from the NW African upwelling region (20-32°N) were investigated. Relative abundances of the dinocyst species show distinct regional differences allowing the separation of four hydrographic regimes. (1) In the area off Cape Ghir, which is characterized by most seasonal upwelling and river discharge, Lingulodinium machaerophorum strongly dominates the associations which are additionally characterized by cysts of Gymnodinium nolleri, cysts of Polykrikos kofoidii and cysts of Polykrikos schwartzii. (2) Off Cape Yubi, a region with increasing perennial upwelling, L. machaerophorum, Brigantedinium spp., species of the genus Impagidinium and cysts of Protoperidinium stellatum occur in highest relative abundances. (3) In coastal samples between Cape Ghir and Cape Yubi, Gymnodinium catenatum, species of the genus Impagidinium, Nematosphaeropsis labyrinthus, Operculodinium centrocarpum, cysts of P. stellatum and Selenopemphix nephroides determine the species composition. (4) Off Cape Blanc, where upwelling prevails perennially, and at offshore sites, heterotrophic dinocyst species show highest relative abundances. A Redundancy Analysis reveals fluvial mud, sea surface temperature and the depth of the mixed layer in boreal spring (spring) as the most important parameters relating to the dinocyst species association. Dinocyst accumulation rates were calculated for a subset of samples using well-constrained sedimentation rates. Highest accumulation rates with up to almost 80.000 cysts cm**-2 ky**-1 were found off Cape Ghir and Cape Yubi reflecting their eutrophic upwelling filaments. A Redundancy Analysis gives evidence that primary productivity and the input of fluvial mud are mostly related to the dinocyst association. By means of accumulation rate data, quantitative cyst production of individual species can be considered independently from the rest of the association, allowing autecological interpretations. We show that a combined interpretation of relative abundances and accumulation rates of dinocysts can lead to a better understanding of the productivity conditions off NW Africa.

Planktic foraminifera analyses of surface sediments and satellite data in the Canary Islands region

The Canary Islands region occupies a key position with respect to biogeochemical cycles, with the zonal transition from oligotrophic to nutrient-rich waters and the contribution of Saharan dust to the particle flux. We present the distribution of geochemical proxies (TOC, carbonate, d15N, d13Corg, C/N-ratio) and micropaleontological parameters (diatoms, dinoflagellates, foraminifera, pteropods), in 80 surface-sediment samples in order to characterise the influence of coastally upwelled water on the domain of the subtropical gyre. Results of the surface-sediment analyses confirmed the high biomass gradient from the coast to the open ocean inferred from satellite data of surface chlorophyll or SST. The distribution of total dinoflagellate cysts, the planktic foraminifera species Globigerina bulloides, the diatom resting spore Chaetoceros spp., and TOC concentration coincided well with the areas of strong filament production off Cape Ghir and Cape Yubi. The warm-water planktic foraminifera Globigerinoides ruber (white), the diatom Nitzschia spp., and the d15N-values showed the opposite trend with high values in the open ocean. Factor analyses on the planktic foraminifera species distribution indicated three major assemblages in the Canary Islands region that represent the present surface-water conditions from the upwelling influenced region via a mixing area towards the subtropical gyre.

Dinoflagellates of sediment core GeoB1523-1

Large numbers of calcareous dinoflagellate cysts and the vegetative calcareous coccoid species Thoracosphaera heimii are generally found in sediments underlying oligotrophic and/or stratified (sub)surface water environments. It is difficult to distinguish between the relative importance of these two environmental parameters on calcareous cyst and T. heimii distribution as they usually covary, but this information is essential if we want to apply cysts properly in the reconstruction of palaeoenvironments and past surface water hydrography. In the multi-proxy core GeoB 1523-1 from the Ceará Rise region in the western equatorial Atlantic Ocean (covering the past 155 ka), periods of greatest oligotrophy are not synchronous with periods of greatest stratification (Rühlemann et al., 1996, doi:10.1016/S0025-3227(96)00048-5; Mulitza et al., 1997, doi:10.1130/0091-7613(1997)025<0335:PFAROP>2.3.CO;2; 335-338; Mulitza et al., 1998, doi:10.1016/S0012-821X(98)00012-0), giving us the unique opportunity to differentiate between the effects of both parameters on cyst accumulation. The calcareous cyst record of the core reflects prominent increases in accumulation rate of nearly all observed species only during the nutrient-enriched but more stratified isotopic (sub)stages 5.5, 5.3, 5.1 and 1. In this respect, the distribution trends in the core are more similar to those of the eastern equatorial upwelling region (GeoB 1105-4) than they are to those of the oligotrophic north-eastern Brazilian continental slope (GeoB 2204-2), even though temporal changes in bioproductivity are principally in antiphase between the eastern and western equatorial regions. We conclude that stratification of the upper water column and the presence of a well-developed thermocline are probably the more important factors controlling cyst distribution in the equatorial Atlantic, whereas the state of oligotrophy secondarily influences cyst production within a well-stratified environment.

Age model and pollen analysis from site GIK16867 in the northern Angola Basin

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.

Abundance of calcareous dinoflagellates of sediment cores from the South Atlantic Ocean

Despite the increasing interest in the South Atlantic Ocean as a key area of the heat exchange between the southern and the northern hemisphere, information about its palaeoceanographic conditions during transitions from glacial to interglacial stages, the so-called Terminations, are not well understood. Herein we attempt to increase this information by studying the calcareous dinoflagellate cysts and the shells of Thoracosphaera heimii (calcareous cysts) of five Late Quaternary South Atlantic Ocean cores. Extremely high accumulation rates of calcareous cysts at the Terminations might be due to a combined effect of increased cyst production and better preservation as result of calm, oligotrophic conditions in the upper water layers. Low relative abundance of Sphaerodinella albatrosiana compared with Sphaerodinella tuberosa in the Cape Basin may be the result of the relatively colder environmental conditions in this region compared with the equatorial Atlantic Ocean with high relative abundance of S. albatrosiana. Furthermore, the predominance of S. tuberosa during glacials and interglacials at the observed site of the western Atlantic Ocean reflects decreased salinity in the upper water layer.

Abundance of organic-walled dinoflagellate cysts of sediment core GeoB3603-2

Here, we reconstruct the varying influence of the Agulhas Current (AgC), the South Atlantic Current and the Antarctic Circumpolar Current on the Agulhas Retroflection (AgR) in the eastern South Atlantic Ocean for the last 160,000 years on the basis of the dinoflagellate cysts, pollen and spores present in a sediment core (GeoB 3603-2) from the southeastern Cape Basin offshore South Africa, where the Agulhas Current enters the Atlantic Ocean. Our analyses reveal strong orbital forcing on the heat exchange between the Indian Ocean and the South Atlantic Ocean during the Late Quaternary. Maxima in local productivity appear to be primarily related to a strengthening of the ocean circulation as a result of the high seasonal contrast during precession maxima. During precession minima, seasonal contrast was low and stratified, oligo- to mesotrophic conditions prevailed, notably when these minima coincided with the glacial terminations. The clear presence of periodicities on a sub-Milankovitch scale as well as modulations of the primary frequencies demonstrate that the Agulhas Retroflection furthermore is modulated substantially by complex interactions between the subtropical, 'precession-driven', climate and ocean circulation systems, and the southern, 'obliquity-driven', high latitudes.

Dinoflagellate cysts in western equatorial Atlantic surface sediments

In contrast to the wide range of studies carried out in temperate and high-latitude oceanic regions, only a few studies have focused on recent and Holocene organic-walled dinoflagellate cyst assemblages from the tropics. This information is, however, essential for fully understanding the ability of species to adapt to different oceanographic regimes, and ultimately their potential application to local and regional palaeoenvironmental and palaeoceanographic reconstructions. Surface sediment samples of the western equatorial Atlantic Ocean north of Brazil, an area greatly influenced by Amazon River discharge waters, were therefore analysed in detail for their organic-walled dinoflagellate cyst content. A diverse association of 43 taxa was identified, and large differences in cyst distribution were observed. The cyst thanatocoenosis in bottom sediments reflects the seasonal advection of Amazon River discharge water through the Guyana Current and the North Equatorial Countercurrent well into the North Atlantic. To establish potential links between cyst distribution and the environmental conditions of the upper water column, distribution patterns were compared with mean temperature, salinity, density and stratification gradients within the upper water column (0-100 m) over different times of the year, using correspondence analysis and canonical correspondence analysis. The analyses show that differences in these parameters only play a subordinate role in determining species distribution. Instead, nutrient availability, or related factors, dominates the distribution pattern. The only possible indicators of slightly reduced salinities are Trinovantedinium applanatum and Lingulodinium machaerophorum. Four assemblage groups of cyst taxa with similar environmental affinities related to specific water masses/currents can be distinguished and have potential for palaeoenvironmental reconstruction.

Seawater carbonate chemistry and growth, calcification of Thoracosphaera heimii in a laboratory experiment

Ocean acidification is considered a major threat to marine ecosystems and may particularly affect calcifying organisms such as corals, foraminifera and coccolithophores. Here we investigate the impact of elevated pCO2 and lowered pH on growth and calcification in the common calcareous dinoflagellate Thoracosphaera heimii. We observe a substantial reduction in growth rate, calcification and cyst stability of T. heimii under elevated pCO2. Furthermore, transcriptomic analyses reveal CO2 sensitive regulation of many genes, particularly those being associated to inorganic carbon acquisition and calcification. Stable carbon isotope fractionation for organic carbon production increased with increasing pCO2 whereas it decreased for calcification, which suggests interdependence between both processes. We also found a strong effect of pCO2 on the stable oxygen isotopic composition of calcite, in line with earlier observations concerning another T. heimii strain. The observed changes in stable oxygen and carbon isotope composition of T. heimii cysts may provide an ideal tool for reconstructing past seawater carbonate chemistry, and ultimately past pCO2. Although the function of calcification in T. heimii remains unresolved, this trait likely plays an important role in the ecological and evolutionary success of this species. Acting on calcification as well as growth, ocean acidification may therefore impose a great threat for T. heimii.

Stable carbon and oxygen isotope ratios of calcareous dinoflagellate cysts and planktic foraminifera from the Campanian/Maastrichtian section of ODP Hole 113-690C in the Weddell Sea (Table 1)

Delta18O and delta13C values for the calcareous dinoflagellate species Orthopithonella? globosa (Fütterer 1984) Lentin and Williams 1985 and Pirumella krasheninnikovii (Bolli 1974) Lentin and Williams 1993 from lates 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 sample in delta18O, but have an offset of about -5 ? to -7? in delta13C. 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.

(Appendix B Table 2) Abundance of organic-walled dinoflagellate cysts of sediment core GeoB2204-2

A palaeoceanographic reconstruction of the Late Quaternary tropical Atlantic Ocean has been made on the basis of dinoflagellate cyst associations of two sediment cores: the first core was recovered from below the highly productive waters of the equatorial divergence and the second from the oligotrophic western tropical Atlantic Ocean. Palaeoenvironmental indicators for productivity, sea surface temperature (SST) and salinity (SSS) based on selected organic-walled dinoflagellate cyst species have been established. On the basis of these palaeoenvironmental indicators, a strengthened intensity of the equatorial divergence in the eastern region during glacials and cold periods of interglacials has been reconstructed. The highest SST probably occurred around substage 5.5 and might refer to weakest upwelling intensity. In comparison, SST and SSS appear to have been generally higher in the western tropical Atlantic Ocean, with probably enhanced values during glacial intervals. Pronounced differences in accumulation rates and relative abundances of cysts formed by congruentidiacean dinoflagellates and relative abundances of oligotrophic cyst species between the eastern and the western region can be related to differences in palaeoproductivity, suggesting much higher values in the eastern area. The coherence between variation in frequency of the indicators for productivity and the boreal summer insolation and monsoon intensity in the eastern tropical Atlantic Ocean suggests an oceanographic reflection of regional intertropical, rather than boreal, dynamics.

Phytoplanktonic microfossil groups of sediments from the South and Equatorial Atlantic

Individual planktonic microfossil species, or assemblage groups of different species, are often used to, qualitatively and/or quantitatively, reconstruct past (sub)surface-water conditions of the world's oceans and seas. Until now, little information has been available on the surface sediment distribution patterns and paleoenvironmental reconstruction potential of coccolith, calcareous dinoflagellate cyst and organic-walled dinoflagellate cyst assemblages of the South and equatorial Atlantic, especially at the species level. This paper (i) summarizes the distributions of these three phytoplanktonic microfossil groups in numerous Atlantic surface sediments from 20°N-50°S and 30°E-65°W and determines their relationship with the physicochemical and trophic conditions of the overlying (sub)surface-waters, and (ii) determines the synecology of the three phytoplankton groups by carrying out statistical analyses (i.e. detrended and canonical correspondence analyses) on all groups simultaneously. Ecological relationships are additionally strengthened by statistically comparing the distribution patterns of the phytoplankton groups with those of planktonic foraminifera (Pflaumann et al. 1996; Niebler et al. 1998), as the ecological preferences of the latter are much better known. Many of the analyzed phytoplanktonic microfossil species or groups of species in the surface sediments do show restricted distributions which primarily reflect the environmental conditions of the upper water masses above them (e.g. sea-surface temperature, productivity, stratification). The acquired 'reference' data sets are large and diverse enough to allow future development of transfer functions for the reconstruction of past surface-water conditions, and show that there is still an enormous paleoenvironmental reconstruction potential concealed in many fossil coccolith and dinoflagellate cyst assemblages.

Pollen analysis of sediment profile WO1 from Wollingster See

A palynological study of a 15 m sediment core from the centre of Lake Wollingst (water depth 14,5 m) is presented. The pollen record shows 3 lateglacial thermomers, called Meiendorf, Bölling, Alleröd and the early holocene Friesland-Thermomer. The succession of forest vegetation taking place on the lake surroundings during the Holocene was typical for older moraine soils which are poor in nutrients: forest vegetation started with birch and pine, followed by hazel, oak and elm in the Boreal and by alder, lime and ash-tree in the Atlantic. Beech and hornbeam reached the area during Subboreal. However, due to the poor soils they spread out only after the Iron Age. With the deforestation during the medieval time the lake lost its character of a primeval forest lake. Lake Wollingst was oligotrophic since its origin at the end of the Pleniglacial. After medieval forest-clearing the lake has changed its quality of water particularly in connection with hemp- and flax-rotting. The modem sediments in this profile are completely disturbed. They contain reworked material, a lot of blue-green algae and remains of Bosmina longirostris indicating eutrophic conditions.

Palynological counts (dinoflagellate cysts) and foraminiferal geochemistry (d18O, d18C, Mg/Ca) of the Pliocene-Pleistocene transition in the North Atlantic

The position of the North Atlantic Current (NAC) during the intensification of Northern Hemisphere glaciation (iNHG) has been evaluated using dinoflagellate cyst assemblages and foraminiferal geochemistry from a ~260 kyr interval straddling the base of the Quaternary System from two sites: eastern North Atlantic Deep Sea Drilling Project Site 610 in the path of the present NAC and central North Atlantic Integrated Ocean Drilling Program Site U1313 in the subtropical gyre. Stable isotope and foraminiferal Mg/Ca analyses confirm cooling near the marine isotope stage (MIS) G7-G6 transition (2.74 Ma). However, a continued dominance of the dinoflagellate cyst Operculodinium centrocarpum sensu Wall and Dale (1966) indicates an active NAC in the eastern North Atlantic for a further 140 kyr. At MIS 104 (~2.60 Ma), a profound dinoflagellate cyst assemblage turnover indicates NAC shutdown in the eastern North Atlantic, implying elevated atmospheric pressure over the Arctic and a resulting shift in the westerlies that would have driven the NAC. These findings challenge recent suggestions that there was no significant southward shift of the NAC or the Arctic Front during iNHG, and reveal a fundamental climatic reorganization near the base of the Quaternary.