Description: The first online modern organic-walled dinoflagellate cyst determination key has been launched at www.marum.de/dinocystkey.html . This key is based on easily recognisable morphological features of dinoflagellate cysts that can be observed using standard transmitted light microscopy. To date, the key includes 96 cyst species that can be found in late Quaternary marine sediments. This key is free of charge to users, and will be continuously updated and improved by the authors. For each individual species of dinoflagellate cyst, the website provides information on its defining morphological characteristics and the cyst–motile stage relationship. It gives a comparison with other morphologically similar taxa, links to publications with original cyst descriptions and outlines their modern global distribution where this information is available. All species descriptions are illustrated by line drawings showing their most distinctive characteristics, and accompanied by high-quality bright-field photomicrographs. The key is compatible with all major computing platforms (including smartphones) and software.

Description: The dawn of animals remains one of the most mysterious milestones in the evolution of life. The fossil lipids 24-isopropylcholestane and 26-methylstigmastane are considered diagnostic for demosponges—arguably the oldest group of living animals. The widespread occurrence and high relative abundance of these biomarkers in Ediacaran sediments from 635–541 million years (Myr) ago have been viewed as evidence for the rise of animals to ecological importance approximately 100 Myr before their rapid Cambrian radiation. Here we show that the biosynthesis of 24-isopropylcholestane and 26-methylstigmastane precursors is common among early-branching unicellular Rhizaria—heterotrophic protists that play an important role in trophic cycling and carbon export in the modern ocean. Negating these hydrocarbons as sponge biomarkers, our study places the oldest evidence for animals closer to the Cambrian Explosion. Cambrian silica hexactine spicules that are approximately 535 Myr old now represent the oldest diagnostic sponge remains, whereas approximately 558-Myr-old Dickinsonia and Kimberella (Ediacara biota) provide the most reliable evidence for the emergence of animals. The proliferation of predatory protists may have been responsible for much of the ecological changes during the late Neoproterozoic, including the rise of algae, the establishment of complex trophic relationships and the oxygenation of shallow-water habitats required for the subsequent ascent of macroscopic animals.

Description: Continuous multiyear records of sediment-trap-gained microorganism fluxes are scarce. Such studies are important to identify and to understand the main forcings behind seasonal and multiannual evolution of microorganism flux dynamics. Here, we assess the long-term flux variations and population dynamics of diatoms, coccolithophores, calcareous and organic dinoflagellate cysts, foraminifera and pteropods in the eastern boundary upwelling ecosystem of the Canary Current. A multiannual, continuous sediment trap experiment was conducted at the mooring site CBeu (Cap Blanc eutrophic; ∼20∘ N, 18∘ W; trap depth is ca. 1300 m) off Mauritania (northwest Africa), between June 2003 and March 2008. Throughout the study, the reasonably consistent good match of fluxes of microorganisms and bulk mass reflects the seasonal occurrence of the main upwelling season and relaxation and the contribution of microorganisms to mass flux off Mauritania. A clear successional pattern of microorganisms, i.e., primary producers followed by secondary producers, is not observed. High fluxes of diatoms, coccolithophores, organic dinoflagellate cysts, and planktonic foraminifera occur simultaneously. Peaks of calcareous dinoflagellate cysts and pteropods mostly occurred during intervals of upwelling relaxation. A striking feature of the temporal variability of population occurrences is the persistent pattern of seasonal groups contributions. Species of planktonic foraminifera, diatoms, and organic dinoflagellate cysts typical of coastal upwelling, as well as cooler-water planktonic foraminifera and the coccolithophore Gephyrocapsa oceanica, are abundant at times of intense upwelling (late winter through early summer). Planktonic foraminifera and calcareous dinoflagellate cysts are dominant in warm pelagic surface waters, and all pteropod taxa are more abundant in fall and winter when the water column stratifies. Similarly, coccolithophores of the upper and lower photic zones, together with Emiliania huxleyi, and organic dinoflagellate cysts dominate the assemblage during phases of upwelling relaxation and deeper layer mixing. A significant shift in the “regular” seasonal pattern of taxa relative contribution is observed between 2004 and 2006. Benthic diatoms strongly increased after fall 2005 and dominated the diatom assemblage during the main upwelling season. Additional evidence for a change in population dynamics is the short dominance of the coccolithophore Umbilicosphaera annulus, the occurrence of the pteropod Limacina bulimoides and the strong increase in the flux of calcareous dinoflagellate cysts, abundant in warm tropical oligotrophic waters south of the study area after fall 2005. Altogether, this suggests that pulses of southern waters were transported to the sampling site via the northward Mauritania Current. Our multiannual trap experiment provides a unique opportunity to characterize temporal patterns of variability that can be extrapolated to other eastern boundary upwelling ecosystems (EBUEs), which are experiencing or might experience similar future changes in their plankton community.

Description: The Southern Ocean has the potential to regulate climate via changes in its productivity and circulation regimes. We therefore investigated the glacial/interglacial variability of bioproductivity in the upper water column and the bottom water ventilation in the Subantarctic and Antarctic zones at two sediment core locations, covering the last 150,000 years, in the eastern Atlantic sector of the Southern Ocean. We used a combined approach, and integrated information derived from two major plankton groups, diatoms and organic-walled cysts of dinoflagellates (dinocysts):- The diatom group Chaetoceros reflects high-carbon/low-silica export regimes, the abundance of Fragilariopsis kerguelensis frustules indicates low-carbon/high-silica export regimes. Changes in relative abundance of these two types of diatoms in the sedimentary record reflect past changes/shifts in productivity regimes.- The cyst-forming dinoflagellate genus Protoperidinium, the only heterotrophic dinoflagellate taxon to be found as fossil cysts in the study area, feeds predominantly on diatoms such as Chaetoceros, and thus high accumulation rates of Protoperidinium cysts in the sediment might reflect high Chaetoceros production.- Protoperidinium cysts are highly sensitive to pore water oxygen concentrations in the sediments in which they become embedded, and well preserved Protoperidinium cysts are used as an indicator for a low oxygen sedimentation environment.The direct comparison between Chaetoceros and sensitive dinocyst abundance in the sediment record thus provides information on past primary production and pore water oxygenation, which can be integrated to results derived by other proxies for export productivity (the deep-dwelling radiolarian Cycladophora davisiana), pore water oxygen (authigenic uranium) and bottom current velocity (percentage of sortable silt). Our study provides an excellent opportunity to assess the causal relationship between upper-ocean regimes (temperature, nutrient gradients, sea-ice extent) and changes in bottom water formation, and suggests higher glacial bioproductivity in both the Subantarctic and Antarctic zones synchronously to the formation of less ventilated bottom water.

Description: The Southern Ocean has the potential to regulate climate via changes in its productivity and circulation regimes. We therefore investigated the glacial/interglacial variability of bioproductivity in the upper water column and bottom water ventilation in the Subantarctic and Antarctic zones at two sediment core locations, covering the last 150,000 years, in the eastern Atlantic sector of the Southern Ocean. We used a combined approach, and integrated information derived from two major plankton groups, diatoms and organic-walled cysts of dinoflagellates (dinocysts):- The diatom group Chaetoceros reflects high-carbon/low silica export regimes, the abundance of Fragilariopsis kerguelensis frustules indicates low-carbon/high-silica regimes (Abelmann et al., 2006). Changes in relative abundance of these two types of diatoms in the sedimentary record reflect past changes/shifts in productivity regimes.- The cyst-forming dinoflagellate genus Protoperidinium, the only heterotrophic dinoflagellate to be found as fossil cysts in the study area, feeds predominantly on diatoms such as Chaetoceros (Jacobson and Anderson, 1986), and thus high accumulation rates of Protoperidinium cysts in the sediment might reflect high Chaetoceros production.- Protoperidinioid cysts are highly sensitive to pore water oxygen concentrations in the sediments in which they become embedded, and are used as proxies for a low oxygen sedimentation environment (Zonneveld et al., in press).The direct comparison between Chaetoceros and sensitive dinocyst abundance in the sediment record thus provides information on past primary production and pore water oxygenation, which can be integrated to results derived by other proxies for export productivity (the deep-dwelling radiolarian Cycladophora davisiana), pore water oxygen (authigenic Uranium) and bottom current velocity (percentage of sortable silt).Our study provides an excellent opportunity to assess the causal relationship between upper-ocean regimes (temperature, nutrient gradients, sea-ice extent) and changes in bottom water formation, and suggests higher glacial productivity in both the Subantarctic and Antarctic zones synchronously to the production of less ventilated bottom water.References: Abelmann, A., Gersonde, R., Cortese, G., Kuhn, G. and Smetacek, V., 2006. Paleoceanography 21, PA1013, doi: 10.1029/2005PA001199; Jacobson D. and Anderson, D.M., 1986. Journal of Phycology 22, 249-258; Zonneveld, K.A.F., Bockelmann, F. and Holzwarth, U., in press. Marine Geology.