Dinocyst Distribution Research Articles

Distribution of modern dinocysts and pollen in the western Mediterranean Sea (Algerian margin and Gulf of Lion)

The Mediterranean Sea is generally described as an oligotrophic area where primary productivity is limited to a few coastal environments with nutrient-enriched fluvial input. However, several studies have revealed that the hydrology of the western Mediterranean has major seasonal productive patterns linked either to significant riverine input or to seasonal upwelling cells. This study aims to: i) discuss organic microfossils (i.e. pollen and dinoflagellate cyst assemblages, as well as other non-pollen palynomorphs) from two different productive areas of the western Mediterranean Sea, and ii) examine the importance of the interconnections between marine and continental influences responsible for modern palynomorph distributions. Based on 25 samples from the Gulf of Lion (GoL) and Algerian Margin, this study key findings are: i) that GoL marine productivity is driven by the combination of discharge from the Rhône River and seasonal upwelling mechanisms, ii) that the strong productive pattern of the northern African coast is driven by water density front mixings and related upwelling. These two patterns are discussed in the light of major links that provide a better understanding of the signatures of marine and continental bio-indicators. Typical differences in vegetation across the north-south climate gradient in the western Mediterranean Basin are highlighted by the larger ratio of Euro-Siberian to Mediterranean pollen taxa in the northern sector. Synoptic maps also illustrate the complex interactions of environmental drivers determining the distributions of continental and marine palynomorphs in the western Mediterranean Sea.

Evidence for anthropogenic, climatic and oceanographic variability off southwestern Morocco during the last three millennia

In order to obtain a better knowledge of oceanic changes in the Canary Upwelling region during the Late Holocene, marine surface samples and two sediment cores retrieved off southwestern Morocco, GeoB8601–3 and GeoB4223–1, were investigated for organic-walled dinoflagellate cysts (dinocysts). The results were compared with pollen, microcharcoal particles, geochemical records, stable hydrogen and carbon isotope composition (δ 2 H and δ 13 C) of plant-waxes of the same material. The dinocyst results indicate active upwelling prior to 750 BCE and a longer upwelling season between 750 BCE and 950 CE, which is attributed to increased northeast trade winds. After 950 CE, a marked increase of Lingulodinium machaerophorum and Gymnodinium species indicates high fluvial input probably due to a combination of climate (possibly negative NAO) and anthropogenic (terrestrial erosion related to Early Arab conquest) impacts. • We present a new compilation of modern dinocyst distribution off southwestern Morocco. • We investigate Late Holocene dinocyst records from two marine sediment cores. • We employ a multiproxy approach with pollen, microcharcoal and geochemical records. • An interplay of climate and anthropogenic controls were demonstrated.

Distribution of modern dinocysts in surface sediments of southern Brittany (NW France) in relation to environmental parameters: Implications for paleoreconstructions

Dinoflagellate cyst assemblages from 15 modern surface sediment samples of the Bay of Quiberon (Southern Brittany shelf) have been examined to assess their potential as marine bio-indicators for paleoenvironmental reconstructions in a shallow coastal environment. Some discrepancies are noted in the distribution of dinocyst taxa in the study area, and particularly regarding dinocyst concentration and diversity (26 different taxa identified in total) as well as heterotrophic taxa percentages. We suggest that the proportion of heterotrophic taxa is, in an embayment of 15 m deep in average, mainly attributed to bottom water oxygenation and sediment granulometry, both acting on species-selective degradation after dinocyst deposition. More precisely, higher heterotrophic abundances are found under lower oxic conditions and in fine grain-size sediment samples, leading to caution about their use as productivity indicators in coastal environments when these parameters are not fully addressed. The comparison of the Bay of Quiberon data with surface sediment samples and top cores from previously published data makes it possible to establish a transect of the modern dinocyst distribution from inshore to offshore areas in the northern Bay of Biscay, allowing to identify different ecological groups according to the hydrological and bathymetric contexts: i) an estuarine assemblage strongly dominated by Lingulodinium machaerophorum, ii) a proximal coastal assemblage dominated by L. machaerophorum and, to a lesser extent, Spiniferites bentorii, iii) a neritic assemblage dominated by L. machaerophorum, Spiniferites ramosus and cysts of Pentapharsodinium dalei, and iv) an oceanic group dominated by Spiniferites mirabilis and Operculodinium centrocarpum.

Distribution of organic-walled dinoflagellate cysts in surface sediments of the southern Caribbean and the eastern tropical Pacific and its environmental implications

Little is known about the marine palynology of the neotropical oceans. Here, we present the first comprehensive study of organic-walled dinoflagellate cyst assemblages in 52 surface marine sediment samples from the southern Caribbean (SC) and the eastern tropical Pacific (ETP) and explain how these assemblages relate to sea-surface parameters. Multivariate analyses show that of the several environmental parameters considered, sea-surface salinity (SSS), phosphate concentrations, and nitrate concentrations best explain the relative abundances and the geographic distribution of dinoflagellate cysts in the studied area. Consistent with regional differences in marine productivity, dinoflagellate cyst concentrations were markedly different in the SC (1979 ± 1053 cysts/g) and the ETP (3105 ± 1956 cysts/g). Sediments of the SC are characterized by high relative abundances of the Spiniferites spp. group, cysts of Protoceratium reticulatum, and the presence of rare dinocyst taxa. The dinocyst assemblages from the ETP are characterized by higher relative and absolute abundances of Bitectatodinium spongium, Brigantedinium spp., and Echinidinium aculeatum. This pattern is explained by the more eutrophic nature of the ETP compared to the highly saline and oligotrophic SC. Average values of the Shannon Index (H′) from the ETP are higher compared to the SC, demonstrating that dinocysts respond to the greater climatic variability that characterizes the ETP. Brigantedinium spp. abundances are negatively correlated to H′ diversity supporting its dominant character within the dinocyst community. This work fills a gap in our knowledge on modern dinocyst distribution in neotropical oceans and provides a modern reference for interpreting down core dinocyst variations and paleocenographical reconstructions in the region.

Dinoflagellate cyst distribution in surface sediments of Ambon Bay (eastern Indonesia): Environmental conditions and harmful blooms

The present study aimed to document dinocyst ecological preferences in Ambon Bay, Eastern Indonesia, and to investigate if the bay sediments serve as a seedbank for toxic bloom events. To this end, dinocyst and geochemical analyses of surface sediment samples were performed, along with physicochemical water column parameters. Twentythree dinocyst species were identified, and high dinocyst concentrations (up to ~12,000 cysts g−1 dry sediment) were found in the inner bay. Environmental factors such as surface water temperature and salinity generally played an important role in dinocyst distribution. The concentration of Polysphaeridium zoharyi cysts showed a strong positive correlation with phosphorus. A statistically significant correlation was also found with the concentration of other autotrophic dinocysts in the sediments, and an inverse correlation was observed with the sediment C/N ratio. Cysts may serve as seedbanks for Pyrodinium bahamense blooms in the area.

Dinoflagellate cyst assemblages as indicators of environmental conditions and shipping activities in coastal areas of the Black and Caspian Seas

Pontocaspian ecosystems have deteriorated due to increasing anthropogenic pressures, including shipping activities. We studied the relationships between sedimentology, environmental and shipping variables, and the dinocyst distribution and abundance across the Pontocaspian region. Cyst diversity was characterized by the presence of 36 dinocyst morphotypes. Western Black Sea assemblages were dominated by Lingulodinium machaerophorum and Round brown cysts reaching values of 60% and 31.6% respectively. Lingulodinium machaerophorum, Impagidinium caspienense and Round brown cysts dominate the Caspian Sea assemblages with relative abundances of 80, 68 and 52%, respectively. Temperature, salinity and primary productivity are the main drivers for dinocyst distribution and species assemblages. Temperature controls the distribution and relative abundance of the potentially toxic species L. machaerophorum. Dinocysts assemblages reflect enriched-nutrient conditions in the North Caspian Sea and the Western Black Sea. Distance from the harbour correlates with dinocyst assemblages in the North and Middle Caspian Sea. This is likely to be related to the high shipping activities.

Distribution of peridiniacean dinoflagellate cysts from cores of organic rich shales of the Duwi and Dakhla formations of Egypt

The Campanian-Maastrictian black shales in Egypt comprise a significant part of the worldwide belt of organic-rich shales. These dark-colored shales stretch from the Dakhla in the Western Desert to Safaga area in the east along the Red Sea and are well known in the Middle East and North Africa. A palynological study of these shales hosted mostly in the Duwi and Dakhla formations yields a Campanian to Maastrichtian age. The extracted palynomorph assemblage from the Abu Tartur and Quseir boreholes, which is dominated by dinoflagellate cysts (dinocysts) representing a well-preserved peridinioid association (>90% of the total dinocysts), is indicative of marine origin and very high paleoproductivity. The common dinocysts are Andalusiella mauthei, Andalusiella gabonensis, Cerodinium diebelii, Senegalinium bicavatum, Senegalinium laevigatum, Palaeocystodinium golzowense and Palaeocystodinium australinum. This assemblage is comparable with the dinoflagellate cyst records of the Campanian-Maastrichtian low latitude strata in northwest Africa (Morocco and Tunisia) and southern Europe. The dinocyst distribution in the Abu Tartur and Quseir borehole sections suggests an isochronous signature during the early Maastrichtian age.

Distribution of dinoflagellate cyst assemblages in recent sediments from a southern Mediterranean lagoon (Mellah, Algeria) with emphasis on toxic species.

This is the first study on the dinoflagellate cysts in Algerian waters and in Mellah Lagoon (South Western Mediterranean), located within a protected reserve. In total, 42 species of dinocysts belonging to 7 orders, 12 families and 23 genera, were identified in the 26 superficial sediment samples from Mellah Lagoon. The distribution of dinocysts in the sediment of this lagoon is heterogeneous. Indeed, their abundance oscillates between 1 and 315cystsg-1 dry sediment (DS). Cyst morphotype assemblages were dominated by a few numbers of species: Alexandrium minutum (15.87%), Gonyaulax verior (9.81%), Protoperidinium spp. (7.74%), Alexandrium affine (7.05%), Scrippsiella trochoidea (6.67%), and Alexandrium pseudogonyaulax (6.19%). There is a positive correlation between the density of cysts and the depth (r = 0.61; p < 0.05), organic matter (r = 0.70; p < 0.05), water content (r = 0.71; p < 0.05), and the fine fraction of sediment (r = 0.74; p < 0.05). Surprisingly, although the Mellah Lagoon is almost semi-closed, it holds an important specific richness in dinocysts (42 species) higher than others observed in Mediterranean lagoons. However, cyst abundances are low compared to other lagoons in the Mediterranean Sea. Finally, the presence of dinocysts of Alexandrium catenella/tamarense, A. minutum, and Gymnodinium catenatum associated to paralytic shellfish toxins, A. pseudogonyaulax which produces goniodomin A, also Protoceratium reticulatum and Gonyaulax spinifera complex which produce yessotoxins, needs to implement a monitoring program to prevent a potential human intoxication due to the consumption of contaminated sea products by these potent neurotoxins.

Distribution of Diatoms and Dinocysts in Surface Sediments from the East Siberian and Chukchi Seas

Surface sediment samples from the East Siberian and Chukchi seas have been analyzed for the quantitative distribution, taxonomic composition, and ecological structure of diatom and dinoflagellate cyst assemblages. According to the results, the diatom and dinocyst distribution in surface sediments indicates the distribution of different water masses in the region.

Distribution of common modern dinoflagellate cyst taxa in surface sediments of the Northern Hemisphere in relation to environmental parameters: The new n=1968 database

Abstract We present a new version of the standardized Northern Hemisphere “modern” dinoflagellate cyst (“dinocyst”) database, which includes abundances of 71 taxa at 1968 sites across the Northern Hemisphere, cross-referenced with 17 environmental parameters extracted mostly from the 2013 World Ocean Atlas. Several taxa with tropical to warm temperate affinities were added to the previous database version. Dinocyst concentrations in the surface sediments reach 106 cysts g−1, with maximum values along the continental margins and minimum values offshore in distal open ocean settings. Assemblages are characterized by the co-occurrence of phototrophic (n = 41) and heterotrophic taxa (n = 30), with maximum proportions of heterotrophic taxa in high productivity regions, notably at the sea-ice edge and in upwelling regions. The main pattern of assemblage distributions includes north–south and nearshore–offshore gradients, with maximum diversity of species along the continental margins and towards the south, in warm temperate and tropical areas. Canonical correspondence analyses performed on heterotrophic and phototrophic taxa independently yield consistent results, hence suggesting similar, but not identical, ecological affinities for both taxonomic groups. For both groups, sea-surface temperature and sea-ice are the most determining parameters, but the phototrophic taxa seem more sensitive to onshore–offshore gradients marked by salinity changes. Productivity-related parameters also determine dinocyst distribution, especially primary productivity in the fall and winter, with a stronger relationship for the combined dataset of phototrophic and heterotrophic taxa.

Late Eocene Southern Ocean Cooling and Invigoration of Circulation Preconditioned Antarctica for Full‐Scale Glaciation

AbstractDuring the Eocene‐Oligocene Transition (EOT; 34–33.5 Ma), Antarctic ice sheets relatively rapidly expanded, leading to the first continent‐scale glaciation of the Cenozoic. Declining atmospheric CO2 concentrations and associated feedbacks have been invoked as underlying mechanisms, but the role of the quasi‐coeval opening of Southern Ocean gateways (Tasman Gateway and Drake Passage) and resulting changes in ocean circulation is as yet poorly understood. Definitive field evidence from EOT sedimentary successions from the Antarctic margin and the Southern Ocean is lacking, also because the few available sequences are often incomplete and poorly dated, hampering detailed paleoceanographic and paleoclimatic analysis. Here we use organic dinoflagellate cysts (dinocysts) to date and correlate critical Southern Ocean EOT successions. We demonstrate that widespread winnowed glauconite‐rich lithological units were deposited ubiquitously and simultaneously in relatively shallow‐marine environments at various Southern Ocean localities, starting in the late Eocene (~35.7 Ma). Based on organic biomarker paleothermometry and quantitative dinocyst distribution patterns, we analyze Southern Ocean paleoceanographic change across the EOT. We obtain strong indications for invigorated surface and bottom water circulation at sites affected by polar westward‐flowing wind‐driven currents, including a westward‐flowing Antarctic Countercurrent, starting at about 35.7 Ma. The mechanism for this oceanographic invigoration remains poorly understood. The circum‐Antarctic expression of the phenomenon suggests that, rather than triggered by tectonic deepening of the Tasman Gateway, progressive pre‐EOT atmospheric cooling played an important role. At localities affected by the Antarctic Countercurrent, sea surface productivity increased and simultaneously circum‐Antarctic surface waters cooled. We surmise that combined, these processes contributed to preconditioning the Antarctic continent for glaciation.

The impact of biotic and abiotic factors on the distribution of surface sediment dinoflagellate cyst assemblages on the Nanji Island in the East China Sea

The dinoflagellate cyst assemblages on the Nanji Island in the East China Sea, are documented at the first time to construct a quantitative overview of the cyst bank from 2014 to 2015. Thirty-four morphotypes from six groups are identified and quantified at eight sampling sites around the island, including a high proportion of potentially toxigenic species (14%). Autotrophic dinocysts constitute 74% of the total cyst counts, which is relatively low (two to thirty-three per millilitre sediment) compared with previous studies in adjacent areas. Scrippsiella trochoidea and Protoperidinium avellana are the most abundant autotrophic and heterotrophic species, respectively. A multivariate analysis is performed to assess associations between dinocysts and abiotic or biotic variables. Differentiation among seasons is evident in the detrended correspondence analysis (DCA) ordination plot, while a spatial pattern is not clearly revealed despite heterogeneity of the hydrodynamic conditions between sampling sites. Soluble reactive phosphate, the ratio of nitrogen to phosphorus concentrations and Karenia mikimotoi bloom are the three factors significantly (P<0.05) related to surface sediment cyst assemblage defined by the canonical correspondence analysis (CCA), highlighting the importance of nutrient regime to a dinocyst distribution in this area. Although attempts to address the origin of HAB events in recent years using seed banks have failed, knowledge can be valuable for further investigation of dinocyst dynamics and potential toxin threats on the Nanji Island.

Distribution of Modern Dinoflagellate Cyst Assemblages in Surface Sediments of San Jorge Gulf (Patagonia, Argentina)

The presence of upwelling systems and oceanic fronts makes the Southwest Atlantic Ocean a region of high primary productivity. These same conditions are present in San Jorge Gulf (SJG) along the southern Argentinian coast, where dinoflagellates and diatoms dominate primary production. The distribution of these microorganisms, including the cysts produced by some dinoflagellates during their life cycles, is controlled in marine environments by oceanographic parameters that include salinity, surface water temperature, ice cover duration, and productivity. The objective of this study is to document the modern distribution of dinoflagellate cyst assemblages in surface sediments so that the environmental preferences of each taxon can be inferred and used to reconstruct paleoenvironmental conditions. The dinoflagellate cyst (dinocyst) assemblages of 52 surface samples collected in 2014 aboard R/V Coriolis II in the SJG were described and compared to surface oceanographic conditions and grain size data. The results indicate dinocyst concentrations vary between 64 cysts g–1 and 45,848 cysts g–1 dry sediment, with Spiniferites ramosus and Operculodinium centrocarpum the dominant species, accompanied by Spiniferites mirabilis, Dubridinium sp., cysts of Polykrikos kofoidii, and cysts of Brigantedinium simplex, Brigantedinium auranteum, and Brigantedinium spp. We have defined two spatial domains based on the distribution of dinocysts in and near the SJG: northern/southern-central gulf and offshore domains. We found an increase in dinocyst concentrations along a north-south gradient in the SJG and minimum concentrations at offshore sites. In addition, multivariate analyses reveal the relationships among the relative abundances of dinocysts, fine grain size data (<63 μm; silts and clays), and primary productivity, as well as offshore upwelling, which appear to control most of the distribution of dinocysts.

Distribution of Albian dinoflagellate cyst associations along a proximal–distal transect across the Iberian margin

The analysis of Albian dinoflagellate cysts, or dinocysts, along an inshore–offshore transect across the Iberian Margin reveals the environmental influence on the assemblages composition. Two biodiversity metrics are used to analyze changes in the assemblage structure. The stress associated to environmental instability is identified as the main factor influencing the dinocyst biodiversity. The relative frequency distribution of dinocysts is analyzed to identify associations of taxa sharing similar environmental preferences. Seven dinocyst associations are identified. The environmental affinities of the seven dinocyst associations are inferred from lithological data and assemblage structure. Association 1 dominated the most proximal and unstable environments. Associations 2 and 3 characterized inner-middle neritic environments. Taxa in the Association 2 preferred stable mesotrophic conditions, whereas, taxa in the Association 3 were tolerant to variations in salinity and nutrient input. Associations 4 and 5 are indicative of open marine distal environments. Taxa in the Association 4 were tolerant to limited environmental fluctuations. Taxa in the Association 5 were restricted to stable open marine conditions. The widespread distribution of taxa in the Association 6 is interpreted as revealing their ubiquitous character. The taxon in the Association 7 is considered as cosmopolitan because its widespread distribution was conditioned to nutrients availability.

AN INTEGRATED PLANKTONIC (FORAMINIFERA, CALCAREOUS NANNOFOSSILS, DINOCYSTS) BIOSTRATIGRAPHY OF THE PALEOGENE SEDIMENTS FROM THE OIL AND GAS BEARING PROVINCES OF UKRAINE

In Ukraine, the perspective oil and gas bearing regions are located within the Carpathian-Black Sea segment of the Tethys, and the southern slopes of the East European Platform. We examined the plankton microfossil content from numerous Paleogene samples obtained from outcrop and exploration borehole sections. The interpretation of the large dataset concerning the spatial-temporal distribution of Foraminifera, Calcareous nannofossils and Dinocysts is provided. The characteristics of the stratigraphic distribution of planktonic fossil assemblages in the Paleogene sections, their cyclicity in the formations and the specifics of the zonal subdivision based on the defined correlation levels are given. As a result of an integrated study the biozonal subdivision of Paleogene sediments of Ukraine is substantiated, and an interregional correlation of various facies of the Paleogene sections with the International Stratigraphic Scheme is undertaken.

Paleoenvironmental changes and influence on Operculodinium centrocarpum during the Quaternary in the Campos Basin, southwestern Brazil

The purpose of this paper is to document the changes observed in the Quaternary dinoflagellate assemblages from 80 core samples from the Campos Basin. The Interglacial (Subzone X1), Glacial (Subzones Y5 to Y2), Last Glacial Maximum (Subzone Y1) and Post-Glacial (Zone Z) intervals were identified. High abundance of Operculodinium centrocarpum suggests the warm, high salinity and nutrient-poor water conditions dominated the upper water column of the Campos Basin. The climate and oceanic current dynamic of the continental slope of the Campos Basin appears to has been a significant controlling factor in the distribution of dinocysts, particularly of O. centrocarpum, during the Pleistocene/Holocene transition.

Comparison of qualitative and quantitative dinoflagellate cyst approaches in reconstructing glacial-interglacial climate variability at West Iberian Margin IODP ‘Shackleton’ Site U1385

Abstract Dinoflagellate cysts (dinocysts) are commonly used to reconstruct past environmental conditions at the sea surface, such as primary production, temperature and salinity. Abundances of selected dinocyst taxa are used in qualitative indices, whereas the modern analogue technique (MAT) is used for quantitative reconstructions. Qualitative indices use process-based knowledge of present-day relations between the environmental variables and the distribution of dinocysts, whereas the MAT is based on the assumption that past assemblages have modern counterparts that correspond to similar sea-surface conditions. Here we explore the potential of both approaches to reconstruct sea surface temperature (SST), production (SSP), salinity (SSS) and seasonality during the last 22 thousand years along the West Iberian Margin (WIM), at Integrated Ocean Drilling Program (IODP) Site U1385. We compare results to published paleoclimatic reconstructions. Our SST and SSS reconstructions provide the first continuous dinocyst MAT-based SST and SSS records for this area and time interval. Qualitative and quantitative dinocyst-based SST estimates from the WIM are similar and resemble previous SST estimates from dinocysts, alkenones and foraminifers from nearby sites. The surface temperature trends and millennial-scale variations largely match those from the Greenland ice core records. Quantitative MAT-based SST estimates show increased seasonality in the glacial stage resulting from strong winter cooling. Dinocyst MAT-based salinity decreases concomitantly with cooling during the Younger Dryas and Heinrich Stadial 1 (HS1), likely related to the melting of icebergs that reached the region during HS1. Our qualitative and quantitative SSP estimates show higher values in the glacial stage compared to the Holocene, which is consistent with published records and supports the usefulness of both approaches. Small differences between SST tracer records may be explained by the limited number of modern analogues from warm ocean regions in the dinocyst reference dataset for MAT, the small number of dinocysts used in the qualitative estimates, the possible effect of a parameter other than temperature that might amplify noise, and/or seasonal biases of the tracer species. In any case, the advantage of the qualitative approach is to allow reconstructions in non-analogue situations. Regression of the qualitative index versus present-day SST also allows for a quantitative reconstruction, although over a limited range of SSTs (especially towards the lower end) and with quite some uncertainty, but produces reasonable values beyond the upper limit of the MAT. The MAT reconstructs more reliable SSTs, with a much smaller error of prediction, but only up to present-day WIM values, because it is based on the assumption that past assemblages have modern counterparts that correspond to similar sea-surface conditions, which is not always valid. The advantages of the MAT approach include its quantitative nature and insights into seasonality. Hence both approaches are complementary. At Site U1385, MAT can be used for reconstructions in the colder periods (YD, HS1 and glacial stage), with a small error of prediction and the quantified index can be used to estimate SST beyond the limit of the MAT (Holocene and B-A).

Arctic sea-ice proxies: Comparisons between biogeochemical and micropalaeontological reconstructions in a sediment archive from Arctic Canada

Boxcore 99LSSL-001 from the southwest Canadian Arctic Archipelago (68.095°N, 114.186°W), studied by multiproxy approaches (sea-ice diatom biomarker IP25, phytoplankton-based biomarker brassicasterol, biogenic silica, total organic carbon, dinoflagellate cysts = dinocysts, diatoms) and their applications (sea-ice index PBIP25, modern analogue technique (MAT) transfer functions), provides a chronologically constrained (210Pb, 137Cs, two 14C dates) palaeoenvironmental archive spanning AD 1625–1999 with which to compare and evaluate proxies frequently used in sea-ice reconstructions. Whereas diatoms are rare, PBIP25, biogenic silica and qualitative dinocyst approaches show good agreement, suggesting that palaeo sea-ice histories based on biomarker and microfossil techniques are robust in this region. These combined approaches show fluctuating long open water to marginal ice zone conditions (AD 1625–1740), followed by high-amplitude oscillations between long open water and extended spring/summer sea ice (AD 1740–1870). Greater ice cover (AD 1870–1970) precedes recent reductions in seasonal sea ice (AD 1970–1999). Dinocyst-based MAT, however, produces a low-amplitude signal lacking the nuances of other proxies, with most probable sea-ice reconstructions poorly correlating with biomarker-based histories. Explanations for this disagreement may include limited spatial coverage in the modern dinocyst distribution database for MAT and the broad environmental tolerances of polar dinocysts. Overall, PBIP25 provides the most detailed palaeo sea-ice signal, although its use in a shallow polar archipelago downcore setting poses methodological challenges. This proxy comparison demonstrates the limitations of palaeo sea-ice reconstructions and emphasizes the need for calibration studies tying modern microfossil and biogeochemical proxies to directly measured oceanographic parameters, as a springboard for robust quantitative palaeo studies.

The Paleogene/Neogene boundary in continental deposits of the West Siberian Plain

This paper presents palynological and paleomagnetic characteristics of three West Siberian horizons: Zhuravka (Upper Oligocene, Chattian), Abrosimovka, and Beshcheul (Lower-Middle Miocene, Aquitanian, Burdigalian, Langhian, and Serravallian). We consider the distribution of dinocysts of the genus Pseudokomewuia in the stratotype section of the Zhuravka Horizon (Zashchitino Village) and in the section of borehole 13 (Chelyuskintsev Village), which exposes the Turtas, Abrosimovka, and Beshcheul Formations. Similar compositions and structures of dinocyst assemblages and similar palynofloras in the Turtas and Abrosimovka Horizons, as well as the sedimentation environment and cyclic structure of lacustrine deposits, suggest that the Paleogene/Neogene boundary should be localized at the base of the Beshcheul Horizon. We propose to include the Abrosimovka Horizon into the Upper Oligocene (upper Chattian). The data are correlated with the regional paleomagnetic scale. These views should be reflected in a new regional stratigraphic chart for the Paleogene-Neogene deposits of the West Siberian Plain.

An expanded modern dinoflagellate cyst dataset for the Southwest Pacific and Southern Hemisphere with environmental associations

Organic-walled dinoflagellate cyst (dinocyst) assemblages were examined in 120 sea floor sediment samples from the Southwest (SW) Pacific to highlight dinocyst distribution in the region. From these 120 samples, census counts of 40 samples were added to previously published census data from the Southern Hemisphere to form a modern dataset of 311 samples (SH-311). Cluster analysis (k-means clustering) of a 98-sample sub-set from the SW Pacific (NZ-98) reveals four distinct assemblages which coincide with modern Subantarctic surface water, the Subtropical Front and two clusters from Subtropical surface water. A similar clustering of the SH-311 dataset reveals an additional three assemblages, two associated with Polar waters colder than those sampled in the SW Pacific, and one that may be endemic to the South Atlantic Ocean. Multivariate ordination (canonical correspondence analysis and redundancy analysis) indicates that the dinocyst assemblages change most along a sea surface temperature (SST) gradient, in both the regional SW Pacific and Southern Hemisphere datasets. SST accounts for 38% to 56% of the species-environmental relationship after removal of covarying variables, and contributes 2-3 times the explainable inertia than the other environmental variables tested. Both modern datasets (SH-311 and NZ-98) are suitable as a training set for quantitative palaeotemperature transfer functions applied to Late Quaternary records, with the caveat that the modern assemblage also displays sensitivity to productivity, shoreline proximity, bottom water oxygen, and water mass; variation that may be exploited in certain situations. (c) 2013 Elsevier B.V. All rights reserved.