Subjects -> PALEONTOLOGY (Total: 46 journals)
Showing 1 - 21 of 21 Journals sorted alphabetically
Acta Palaeontologica Polonica     Open Access   (Followers: 6)
Alcheringa: An Australasian Journal of Palaeontology     Hybrid Journal   (Followers: 7)
Ameghiniana     Open Access   (Followers: 1)
Annales de Paléontologie     Full-text available via subscription   (Followers: 7)
Annals of Carnegie Museum     Full-text available via subscription   (Followers: 1)
Boreas: An International Journal of Quaternary Research     Hybrid Journal   (Followers: 12)
Comptes Rendus Palevol     Full-text available via subscription  
European Journal of Protistology     Hybrid Journal   (Followers: 6)
EvoDevo     Open Access   (Followers: 4)
Facies     Hybrid Journal   (Followers: 10)
Fossil Record     Open Access   (Followers: 5)
Geobios     Full-text available via subscription   (Followers: 6)
Historical Biology: An International Journal of Paleobiology     Hybrid Journal   (Followers: 9)
Ichnos: An International Journal for Plant and Animal Traces     Hybrid Journal  
International Journal of Speleology     Open Access   (Followers: 3)
Journal of Paleolimnology     Hybrid Journal   (Followers: 6)
Journal of Paleontology     Hybrid Journal   (Followers: 11)
Journal of Quaternary Science     Hybrid Journal   (Followers: 32)
Journal of Vertebrate Paleontology     Full-text available via subscription   (Followers: 12)
Marine Micropaleontology     Hybrid Journal   (Followers: 2)
Micropaleontology     Full-text available via subscription  
Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen     Full-text available via subscription   (Followers: 4)
Novitates Paleoentomologicae     Open Access   (Followers: 1)
Open Quaternary     Open Access   (Followers: 1)
Palaeogeography, Palaeoclimatology, Palaeoecology     Hybrid Journal   (Followers: 13)
Palaeontology     Hybrid Journal   (Followers: 18)
Palaeoworld     Hybrid Journal   (Followers: 3)
PALAIOS     Hybrid Journal   (Followers: 7)
Paläontologische Zeitschrift     Hybrid Journal   (Followers: 4)
Paleobiology     Full-text available via subscription   (Followers: 6)
PaleoBios     Open Access   (Followers: 1)
Paleoceanography and Paleoclimatology     Full-text available via subscription   (Followers: 4)
Paleontological Journal     Full-text available via subscription   (Followers: 5)
Paleontological Research     Full-text available via subscription   (Followers: 3)
Palynology     Hybrid Journal   (Followers: 2)
Papers in Palaeontology     Hybrid Journal   (Followers: 1)
Quaternaire     Open Access   (Followers: 3)
Quaternary Research     Full-text available via subscription   (Followers: 20)
Quaternary Science Reviews     Hybrid Journal   (Followers: 25)
Review of Palaeobotany and Palynology     Hybrid Journal   (Followers: 2)
Revue de Micropaleontologie     Full-text available via subscription  
Rivista Italiana di Paleontologia e Stratigrafia (Research In Paleontology and Stratigraphy)     Open Access   (Followers: 2)
Spanish Journal of Palaeontology     Open Access  
Swiss Journal of Palaeontology     Hybrid Journal   (Followers: 4)
Vertebrate Anatomy Morphology Palaeontology     Open Access   (Followers: 2)
Zitteliana     Open Access   (Followers: 4)
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Marine Micropaleontology
Journal Prestige (SJR): 0.869
Citation Impact (citeScore): 2
Number of Followers: 2  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0377-8398 - ISSN (Online) 0377-8398
Published by Elsevier Homepage  [3294 journals]
  • Survival and recovery of the foraminifer Amphistegina gibbosa and
           associated diatom endosymbionts following up to 20 months in aphotic
           conditions
    • Abstract: Publication date: Available online 28 March 2019Source: Marine MicropaleontologyAuthor(s): Benjamin J. Ross, Pamela Hallock Dormancy in the Foraminifera has been observed widely across the phylum in reaction to a variety of triggers including, in the diatom symbiont-bearing foraminifer Amphistegina gibbosa, extended periods of darkness. Resumption of activity in the host-symbiont holobiont was noted, but not fully documented, in specimens reintroduced to light following up to 12 months in darkness. Here, criteria for documenting recovery included resumption of reticulopodial activity in the host and return of pre-treatment golden-brown color characteristic of an active symbiotic diatom population. Reticulopodial activity resumed in nearly all treatment specimens (>95%) following 12 months in darkness, and in>70% of the specimens when reintroduced to light following 20 months in darkness. Image analysis using the percent of the foraminiferal surface area showing golden-brown color as a proxy for recovery of the endosymbionts showed return of such color within days for shorter treatments (7 and 12 months in darkness), but slower and less complete return in longer treatments (15 and 20 months), indicating increased susceptibility to photic damage of symbionts as the length of dormancy increased.
       
  • Deciphering latitudinal shifts in coccolith accumulation in the eastern
           tropical Pacific Ocean through the Pleistocene
    • Abstract: Publication date: Available online 27 March 2019Source: Marine MicropaleontologyAuthor(s): Gatsby-Emperatriz López-Otálvaro, José-Abel Flores, Francisco J. Sierro, Joseph J. Lalicata, David W. Lea, Alan C. Mix Middle and Late Pleistocene coccolithophore assemblages from Ocean Drilling Program (ODP) sites 1241 and 1242 in the northeastern tropical Pacific (north ETP) were analyzed to reconstruct coccolithophore-productivity and surface-water conditions over the last 925 kyr. Stratigraphic control was provided by δ18O data and geomagnetic time scales and the identification of synchronous calcareous nannofossil events, formerly described in mid and low latitudes. Changes in sea surface coccolithophore-productivity were inferred by estimates of the so-called N ratio – an independent proxy on conversion to accumulation rates – and the total coccolith-derived carbonate accumulation rate (CAR). CAR variations follow those of the N ratio but show larger amplitude changes. Fluctuations in the N ratio and total CAR values imply coccolithophore-productivity maxima during glacial times, most likely as a result of a shallower nutri-thermocline, defined as the boundary beneath the sea surface at which nutrient-rich/cool and nutrient-poor/warm waters are separated. Low interglacial values of the N ratio and CAR suggest lower coccolithophore-productivity and a deeper nutri-thermocline (deep stratification of the mixed layer). This result implies that coccolithophore-productivity-controlled CARs and dissolution were driven by the ratio between CaCO3 production and organic matter oxidation, and that effects of dissolution were enhanced when coccolith production fell. The data suggest high coccolithophore-productivity and a shallow nutri-thermocline during MIS 22 through MIS 6, likely due to the reinforcement of northeastern wind-driven advection of nutrient-rich waters, which is compatible with a La Niña-like state. The dominance of Gephyrocapsa caribbeanica during the Mid-Brunhes Event (MBE) is consistent with this eutrophic environment. Conversely, data from MIS 5 suggests a weakening of trade winds in the ETP, which would have reduced the normal upwelling of cool water and warmed SST, and which is compatible with the oligotrophic setting of an El Niño-like state. During MIS 4 through MIS 1, coccolithophore-productivity was not significantly different from MIS 5 and therefore not indicative of a prominent La Niña-like state, as previously reported for the Equatorial Cold Tongue (ECT). Comparison with coccolithophore data from Site 1240 supports a reduction of coccolithophore-productivity and nutri-thermocline deepening from the ECT to the Costa Rica margin and suggests that nutrient availability was the primary control on the distribution of the whole assemblage during the past 925 kyr.
       
  • Size patterns of the coccolith Watznaueria barnesiae in the lower
           Cretaceous: Biotic versus abiotic forcing
    • Abstract: Publication date: Available online 26 March 2019Source: Marine MicropaleontologyAuthor(s): Barbara Gollain, Emanuela Mattioli, Samer Kenjo, Annachiara Bartolini, Stéphane Reboulet Body size is a major trait allowing the assessment of the respective control of evolution vs. (palaeo)environment on unicellular micro-organisms. Size patterns can be retraced for fossilisable micro-organisms, especially for coccolithophores, over geological time spans. Here, we present coccolith size patterns of Watznaueria barnesiae, which was a dominant and ubiquitous taxon in the Mesozoic. Measurements were conducted at two sites spanning the Upper Berriasian to Lower Hauterivian, namely the Vergol-La Charce section in the epicontinental Vocontian Basin, and the ODP Leg 185 Hole 1149B located in the Nadezhda Basin, in the Pacific Ocean. The obtained results were treated using multivariate analysis in order to detect significant trends of the measured parameters. Size values of coccoliths from both sites are remarkably similar and display comparable patterns, namely a statistically significant increase in the Lower Valanginian until maximum sizes recorded in the aftermath of the Weissert event (Upper Valanginian). Although W. barnesiae coccolith-size fluctuations, in the short term, might be related to environmental changes, the observed long-term size patterns are interpreted as the result of directional selection, in which a single phenotype is favored through time. Comparison with data available in the literature shows a return to a smaller size after the Turonian.
       
  • Late Cretaceous paleobiogeography of Braarudosphaera bigelowii
    • Abstract: Publication date: Available online 25 March 2019Source: Marine MicropaleontologyAuthor(s): Maria de Lurdes Fonseca, Christopher R. Scotese, Mário Cachão The Late Cretaceous paleobiogeography of the coccolithophore Braarudosphaera bigelowii is reconstructed based on 331 stratigraphic occurrences and complemented by 307 neighboring absences.During the Cenomanian B. bigelowii was found throughout the European seaways, at the base of the North America Interior Seaway, at the paleo-Atlantic margin of South America, in the Neuquén Basin, on the southern tip of the Indian plate, and on the Kerguelen Plateau. During the Late Cretaceous, its range gradually expanded: northwards along the North Sea, into the North American Interior Seaway, eastwards through the interior European seaways, across central Russia, southeastwards into China, and along the Asian coast up to Japan. The Falkland Plateau appears to have played a pivotal role in the colonization of the eastern coast of South America, the Atlantic and Indian Ocean margins of Africa, Madagascar, India, western Antarctica, and Australia. By the end of the Maastrichtian, migration extended northwards towards the Arctic, but did not reach the northernmost regions of the North Atlantic.Because biogeographic information is scarce for the northern coast of South America, for several areas along the African margin, and for the overall Pacific coasts, it is difficult to resolve the biogeographic history in these areas. The presence of B. bigelowii could not be confirmed on the northern coast of South America or on the North Atlantic African margin. It is also not possible to ascertain whether the African margin facing the Indian Ocean was completely colonized by the end of the Cretaceous. Sparse observations suggest that the Pacific coast of North America was colonized by B. bigelowii during the Santonian. However, even though data suggests a subsequent northward colonization direction, it is not possible to accurately reconstruct the North Pacific migration paths of B. bigelowii between the Santonian and the Maastrichtian.
       
  • Sampling strategy always matters: Methodological issues on collecting
           samples in tropical transitional environments for ecological analysis
           based on recent foraminifera
    • Abstract: Publication date: April 2019Source: Marine Micropaleontology, Volume 148Author(s): Isabela Kukimodo, Décio Semensatto Sampling strategies and methodological procedures are a theme of discussion in all areas of Science, considering their potential impacts on results, interpretations, and conclusions. In the case of ecological studies based on recent foraminifera, most of papers vary on collecting single samples or replicates, on counting living and/or dead assemblages, and on the depth of the sediment layer collected. In this study we discussed the implications of the following questions, especially in the intertidal zone of a tropical estuary: (i) Do collecting a single sample or replicates affect results and interpretations' (ii) Are there differences in results and interpretations generated from counting living (stained) or dead assemblages'; and (iii) Do varying the sampling depth of sediment layers influence the results and interpretations' We defined three collection points along the mangrove margins associated to the Itapanhaú River (Bertioga, State of São Paulo, Brazil). In each point, we drilled three microcores with the depth of 20 cm, laterally distant 30 cm from each other. In each microcore sediment samples (3 mL) were extracted in the layer intervals of 0–1, 4–5, 9–10, 14–15, and 19–20 cm. Foraminifera from all the samples were compared regarding absolute abundances, species composition, diversity, evenness and, communities similarities. We observed that replicates produce better results than single samples, both for the living and dead assemblages. Pseudoreplication simulation produced divergent results. Replicates make possible the application of more accurate inferential statistical analysis because the spatial variations of the species are captured. There were significant differences in ecological indicators and respective interpretations between analyzes based on counting living and dead assemblages so that they should not be considered directly comparable to each other. Counting living foraminifera requires higher effort for collecting and picking tests to reach the statistical minimum recommended. Regarding sampling depth, the first centimeter seems to be sufficient to find the vast majority of living foraminifera, mainly to estimate species richness. However, thicker sediments result in a longer time interval integrated into the sample, so the time-scale and variables that control foraminifera may change for interpretation. Our findings are consistent with previous studies carried out in subtropical estuaries, also expanding methodological recommendations to tropical estuaries. Future studies should explore the best distances among replicates.
       
  • The biogeography and ecology of common diatom species in the northern
           North Atlantic, and their implications for paleoceanographic
           reconstructions
    • Abstract: Publication date: April 2019Source: Marine Micropaleontology, Volume 148Author(s): Mimmi Oksman, Stephen Juggins, Arto Miettinen, Andrzej Witkowski, Kaarina Weckström Sound knowledge of present-day diatom species and their environments is crucial when attempting to reconstruct past climate and environmental changes based on fossil assemblages. For the North Atlantic region, the biogeography and ecology of many diatom taxa that are used as indicator-species in paleoceanographic studies are still not well known. Using information contained in large diatom-environment calibration datasets can greatly increase our knowledge on diatom taxa and improve the accuracy of paleoenvironmental reconstructions. A diatom calibration dataset including 183 surface sediment samples from the northern North Atlantic was used to explore the distribution and ecology of 21 common Northern Hemisphere diatom taxa. We define the ecological responses of these species to April sea ice concentrations and August sea surface temperatures (aSSTs) using Huisman-Olff-Fresco (HOF)-response curves, provide distribution maps, temperature optima and ranges, and high-quality light microscope images. Based on the results, we find species clearly associated with cold, warm and temperate waters. All species have a statistically significant relationship with aSST, and 15 species with sea ice. Of these, Actinocyclus curvatulus, Fragilariopsis oceanica and Porosira glacialis are most abundant at high sea ice concentrations, whereas Coscinodiscus radiatus, Shionodiscus oestrupii, Thalassionema nitzschioides, Thalassiosira angulata, Thalassiosira nordenskioeldii and Thalassiosira pacifica are associated with low sea ice concentrations/ice-free conditions. Interestingly, some species frequently used as sea ice indicators, such as Fragilariopsis cylindrus, show similar abundances at high and low sea ice concentrations with no statistically significant relationship to sea ice.
       
  • Paleogene-early Neogene paleoenvironmental reconstruction based on
           palynological analysis of ODP Hole 959A, West Africa
    • Abstract: Publication date: April 2019Source: Marine Micropaleontology, Volume 148Author(s): Walaa K. Awad, Francisca E. Oboh-Ikuenobe Five paleoenvironmental intervals (interval 1-interval 5) are established in the late Paleogene-early Neogene of the Ocean Drilling Program (ODP) Site 959 (Hole 959A), Côte d'Ivoire-Ghana Transform Margin in the eastern Equatorial Atlantic. The intervals are based on dinoflagellate cyst and palynofacies analyses of 30 samples covering a 273.3-m interval. We observed an abundance of the Filisphaera group (Filisphaera filifera and Bitectatodinium tepikiense) which is interpreted as an Arctic migration to equatorial regions during a narrow interval in the Early Oligocene (early Rupelian). In addition, we document one hiatus within interval 3 in the Early Miocene (Aquitanian). The dominance of typically restricted marine species of the Polysphaeridium group (Homotryblium plectilum and Polysphaeridium zoharyi) at several horizons in the open-oceanic sediments of ODP Hole 959A appear to be very distinctive events. Upon integrating dinoflagellate cyst data with prior lithologic and microfossil data, we interpret these dominance events as being due to offshore transportation by turbidity currents (intervals 1 and 2), hiatus event (interval 3), or hyperstratification conditions (intervals 3 and 4). In addition, the dominance of Cribroperidinium spp. (C. giuseppei and C. tenuitabulatum) in the upper part of the section within paleoenvironmental interval 5 is suggestive of cold-water masses during a strong upwelling period in the latest Early Miocene (Burdigalian). The general abundance of amorphous organic matter alongside the dinoflagellate cyst assemblage supports an outer neritic-oceanic depositional environment for the studied site. The consistent occurrence of degraded phytoclasts in the sediments also suggests fluvial outflows to this offshore site.
       
  • Campanian carbon isotope calibrated paleofertility estimates from
           northwestern Tunisia: Inferences from calcareous nannofossils
    • Abstract: Publication date: Available online 20 March 2019Source: Marine MicropaleontologyAuthor(s): S. Farouk, S. Jain, M. Faris, Z. Elamri, F. Ahmad The δ13C calibrated Campanian (upper part of CC17/UC13 to CC23a/UC16 zones) calcareous nannofossil assemblages were analyzed to reconstruct paleofertility, paleoenvironment, and sea–level changes from the Jebil section, north–western Tunisia. Seven global–recognized δ13C events are noted: three positive [Santonian–Campanian Boundary Event (SCBE); Early–Campanian Event (ECE); Mid–Campanian Event (MCaE)] and four negative excursions (Pillula Event; Conica Event; Late–Campanian Event (LCE); Epsilon Event or the C1– Event). The nannofossil assemblage is dominated by Watznaueria barnesae (28%), Lucianorhabdus cayeuxii (8%), Micula decussata (6%), Cyclagelosphaera reinhardtii (5%) and Micula concava (4%). In spite of the dominance of W. barnesiae (range: 33–46.5%), the signal given by the nannofossil assemblage is primary. All species–based proxies (the percentage abundances of stressed/opportunistic taxa, high and low fertility taxa, cool and warm watermass taxa, and Nannoconus spp.) along with the inferred Paleotemperature Index, suggests a cooling trend for the Campanian. Data suggests that oligotrophy was a greater influencing factor than paleotemperature, for the observed changes within the nannofossil assemblage. As a result of this extreme oligotrophy, a distinct assemblage is recorded that is marked by the absence of Biscutum, reduced % abundances of Prediscosphaera (0.7%), Retecapsa (2.3%), and Zeugrhabdotus (1.8%), but with the dominance of W. barnesiae.
       
  • Intertidal and subtidal benthic foraminifera in flooded caves:
           Implications for reconstructing coastal karst aquifers and cave
           paleoenvironments
    • Abstract: Publication date: Available online 19 March 2019Source: Marine MicropaleontologyAuthor(s): Shawna N. Little, Peter J. van Hengstum Coastal karst aquifers have an upper meteoric water mass stratified from a saline groundwater mass below that increasingly mix and discharge towards the ocean. Preserved sediment in caves and sinkholes provide an opportunity to evaluate the long-term hydrodynamics in the local coastal karst aquifer (e.g., salinity, oxygenation, vertical displacement in response to sea-level forcing). Here we evaluate the response of shallow (45 μm versus>63 μm mesh sieve fractions. These modern analog results can be used to interpret subfossil benthic foraminiferal records from coastal karst aquifers, especially during early cave inundation by concomitant groundwater and sea-level rise.
       
  • Using foraminiferal test-size distribution and other methods to recognise
           Quaternary bathyal turbidites and taphonomically-modified faunas
    • Abstract: Publication date: Available online 19 March 2019Source: Marine MicropaleontologyAuthor(s): Bruce W. Hayward, Ashwaq T. Sabaa, Christopher M. Triggs The aim of this study was to develop a simple methodology using foraminifera to distinguish between sediment that has been displaced downslope (as in a turbidity current) and in-situ hemipelagic sediment. These same methods will also be useful to identify seafloor foraminiferal faunas that have suffered considerable taphonomic modification (e.g., through dissolution, winnowing, mixing), which render them unsuitable as modern analogues for paleoenvironmental reconstructions. To help develop this methodology we used Late Quaternary samples from cores containing identified turbiditic sand-mud couplets that had been deposited at lower bathyal to upper abyssal depths (1400–3000 m) off the earthquake-prone east coast of New Zealand.Comparison of the proportions of the total planktic and benthic foraminiferal tests in each of three size categories (63–125 μm, 125–250 μm,>250 μm) with those in unmodified, in-situ modern bathyal faunas from off New Zealand showed an increased proportion of larger tests in the lower sandy turbidite layers and a slight increase of smaller tests in the upper muddy layers presumably as a result of winnowing processes during deposition. A regression formula was used to estimate depositional depths based on the relative abundance of planktics in the Quaternary foraminiferal faunas (>63 μm). In all but one of our core samples, these depth estimates were considerably shallower than the cores' present depth and suggested that most sediment (both sand and mud) had been transported downslope. Modern Analogue Technique (MAT) was used to estimate depths of deposition of the core samples based on a modern benthic foraminiferal dataset (>63 μm) from around New Zealand. There was no great difference between estimates based on species % and on genus %. Some MAT depth estimates were inconsistent with those from the other foraminiferal and sedimentological proxy methods that suggested turbiditic displacement. Because of the inconsistent results and the much greater work required to acquire the species census data we exclude the MAT method from our suggested methodology. Genera were lumped into groups with similar bathymetric range and the relative abundances of these groups in each core sample were used to infer sediment provenance and mixing during downslope transport.We recommend a methodology using three elements: Test size distribution, planktic percentage, and relative abundance of bathymetric groups of benthic genera. The first two require the least amount of work and can reliably identify the majority of displaced and taphonomically-modified faunas. The third requires some taxonomic skills to identify key genera but gives more information on the provenance depth and amount of mixing in displaced turbiditic sediment.Although developed using New Zealand modern and Late Quaternary foraminiferal data, we contend that these methods should be applicable for use throughout most of the Neogene in other temperate and subtropical parts of the world's oceans. Before use elsewhere, studies in the local region may be needed to test, recalibrate and tweak the modern analogue data on local test-size distribution and planktic percentage. Our study also suggests that these methods can be useful to identify seafloor foraminiferal faunas that have suffered considerable taphonomic modification (e.g., through dissolution, winnowing, mixing), which render them unsuitable as modern analogues for paleoenvironmental reconstructions.
       
  • Reconstruction of surface water dynamics in the North Atlantic during the
           Mid-Pleistocene (~540–400 ka), as inferred from Coccolithophores and
           Planktonic Foraminifera
    • Abstract: Publication date: Available online 18 March 2019Source: Marine MicropaleontologyAuthor(s): Marta Martínez-Sánchez, José-Abel Flores, Eliana Palumbo, Montserrat Alonso-Garcia, Francisco-Javier Sierro, Filomena Ornella Amore Changes in paleoclimate and paleoproductivity patterns have been identified by analyzing the coccolithophore assemblages from the IODP Site U1314, located in the subpolar North Atlantic, together with other proxy data available during the time interval from the Marine Isotopic Stage (MIS) 14 to MIS 11 (ca. 540 to 400 ka). The comparison of this data with that of MD03–2699, located off the Iberian Margin, allowed us to study their common response to environmental changes in terms of paleoproductivity and temperature variability.Statistical analyses of the composition of coccolithophore assemblages revealed that the calcareous plankton dynamics were mainly driven by eccentricity, which controlled the alternating migration of the Polar Front (PF) and the North Atlantic Current (NAC) at glacial-interglacial timescales. The high frequency variability of paleoproductivity, over imposed onto glacial/interglacial variability at both sites, were related to NAC intensifications on a precessional timescale. The northward (southward) migration of the PF caused a strengthening (weakening) of the NAC, which created an intensification (weakening) of the Irminger Current (IC) at Site U1314 and the Portugal Current (PC) at MD03–2699. Furthermore, low-latitude processes have been shown to influence climate in the high-latitude during the late Pleistocene.During MIS 14 and 12, enhanced glacial strength affected both coccolithophores and planktonic foraminifera, indicating a southward movement of the NAC. Using the same proxies, a northward movement of the NAC is recorded during MIS 13 and 11.Alternatively, the spectral analyses performed on calcareous plankton assemblages allowed the identification of a pattern of periodic response of the plankton at the orbital and, in some cases, millennial level, as well as abrupt Heinrich-type time-scale variability during Termination V (TV). This was the most extreme event and was related to a massive iceberg discharge from high to mid-latitudes.
       
  • Life cycle association of the coccolithophore Syracosphaera gaarderae
           comb. nov. (ex Alveosphaera bimurata): Taxonomy, ecology and evolutionary
           implications
    • Abstract: Publication date: Available online 16 March 2019Source: Marine MicropaleontologyAuthor(s): Sabine Keuter, Jeremy R. Young, Miguel J. Frada The coccolithophores are an important group of marine phytoplankton bearing external calcite plates called coccoliths, and displaying complex sexual life cycles, composed of two main cell phases (haploid and diploid) that in most species can produce distinct coccolith types. Typically, diploid cells produce heterococcoliths, whereas haploid cells produce holococcoliths. An important source of evidence for the ability of coccolithophores to undergo life cycle transitions comes from observations of combination coccospheres. These combination cells bearing both hetero- and holococcoliths are interpreted as cells undertaking sexual transitions and enable linking morphologically distinct life phases, thus expanding our knowledge of coccolithophore life cycle diversity, but more widely on coccolithophore ecology and evolution. Here we report on a newly discovered life cycle in the genus Syracosphaera, linking the heterococcolithophore previously named Alveosphaera bimurata Okada & McIntyre, erroneously placed within the Calciosoleniaceae, and the holococcolithophore Poricalyptra gaarderae Borsetti & Cati, resulting in a new combination, Syracosphaera gaarderae (Borsetti & Cati) comb. nov.This life cycle association is supported by several combination coccospheres collected in the Northern Red Sea and is the first involving both the genus Poricalyptra and a Syracosphaera belonging to the lamina type subgroup. Biennial survey indicates that cells of both life cycle phases are only found during summer stratification periods and display clear depth zonation with S. gaarderae appearing in the lower photic zone and P. gaarderae in the upper photic zone. This marked vertical separation between life phases was further confirmed across other oceanic basins through bibliographic revision, confirming the prevailing view that coccolithophore life phases occupy different ecological niches.Graphical abstractUnlabelled Image
       
  • Holocene variations in North Atlantic export productivity as reflected in
           bathyal benthic foraminifera
    • Abstract: Publication date: Available online 12 March 2019Source: Marine MicropaleontologyAuthor(s): Christopher W. Smart, Ellen Thomas, Curtis M. Bracher The subpolar NE Atlantic Ocean experiences seasonal fluxes of labile organic matter (phytodetritus) which are expected to strongly influence the composition of benthic foraminiferal assemblages and benthic foraminiferal accumulation rates. We studied export production over the last 12 kyr at a sampling resolution of approximately 250–300 years through an investigation of bathyal benthic foraminiferal assemblages (>63 μm) at Ocean Drilling Program (ODP) Site 980 on the Feni Drift (55°29′N, 14°42′W, 2179 m water depth).During the last 12 kyr, faunas at Site 980 were dominated (~75%) by Cassidulina obtusa, Nonionella iridea, Bolivina difformis, Trifarina pauperata, Alabaminella weddellensis, Stainforthia fusiformis, Cassidulina laevigata and Eilohedra vitrea. The absolute and relative abundances and diversity of these and other species varied significantly. In the interval ~12–10 ka, A. weddellensis, S. fusiformis and T. pauperata had higher % abundance (named here ‘H10 species’), but this is not reflected in a higher accumulation rate, suggesting that surface productivity was low, at highly variable conditions. Species at lower % abundance during this time include B. difformis, C. laevigata, C. obtusa, E. vitrea and N. iridea (so-called ‘L10 species’). The ‘8.2 ka cold event’ was characterized by increased carbonate dissolution (reflected in decreases in the absolute abundance, benthic foraminifera accumulation rate, weight % coarse fraction, and presence of poorly preserved/fragmented benthic foraminifera). Peaks in the relative abundance of species which, in our opinion, exploited phytodetritus (‘phytodetritus species’: N. iridea, A. weddellensis, C. obtusa, and rare Epistominella exigua) occurred at 8.0 ka, 7.0 ka, 6.3–5.6 ka, 4.7 ka, 4.3–3.4 ka and 2.4 ka. These peaks generally correspond to peaks in absolute abundance (number of specimens per gram, accumulation rate), indicating increases in the seasonality of export productivity. However, the ‘phytodetritus species’ do not covary in absolute and relative abundance over the studied interval, suggesting that they have somewhat different ecological requirements.There appears to be no simple relationship between changes in the degree of seasonality of export productivity (i.e., abundance of ‘phytodetritus species’) and records of palaeoclimatic/palaeoceanographic proxies, suggesting that bentho-pelagic coupling (arrival of food on the seafloor with local surface productivity) might not have been straightforward in this region. Site 980 is located in the hydrodynamically active area of Feni Drift, and during the Holocene, currents might have winnowed and removed fine-grained organic matter, making it unavailable to benthic organisms. Alternatively, there may have been changes in remineralization and/or mid-water competition for food, so that the fraction of the organic flux that reached the seafloor may have varied. Holocene benthic foraminiferal assemblages thus reflect highly dynamic conditions in export productivity and arrival of organic matter at the seafloor.
       
  • The genetic diversity, morphology, biogeography, and taxonomic
           designations of Ammonia (Foraminifera) in the Northeast Atlantic
    • Abstract: Publication date: Available online 19 February 2019Source: Marine MicropaleontologyAuthor(s): Clare Bird, Magali Schweizer, Angela Roberts, William E.N. Austin, Karen Luise Knudsen, Katharine M. Evans, Helena L. Filipsson, Martin D.J. Sayer, Emmanuelle Geslin, Kate F. Darling The genetic diversity, morphology and biogeography of Ammonia specimens was investigated across the Northeast (NE) Atlantic margins, to enhance the regional (palaeo)ecological studies based on this genus. Living specimens were collected from 22 sampling locations ranging from Shetland to Portugal to determine the distribution of Ammonia genetic types across the NE Atlantic shelf biomes. We successfully imaged (via scanning electron microscopy, SEM) and genotyped 378 Ammonia specimens, based on the small subunit (SSU) rRNA gene, linking morphology to genetic type. Phylogenetic analyses enabled identification of seven genetic types and subtypes inhabiting the NE Atlantic margins. Where possible, we linked SSU genetic types to the established large subunit (LSU) T-type nomenclature of Hayward et al. (2004). SSU genetic types with no matching T-type LSU gene sequences in GenBank were allocated new T-numbers to bring them in line with the widely adopted T-type nomenclature. The genetic types identified in the NE Atlantic margins are T1, T2, T3, T6, and T15, with both T2 and T3 being split further into the subtypes T2A and T2B, and T3S and T3V respectively. The seven genetic types and subtypes exhibit different biogeographical distributions and/or ecological preferences, but co-occurrence of two or more genetic types is common. A shore-line transect at Dartmouth (South England) demonstrates that sampling position on shore (high, middle or low shore) influences the genetic type collected, the numbers of genetic types that co-occur, and the numbers of individuals collected. We performed morphometric analysis on the SEM images of 158 genotyped Ammonia specimens. T15 and the subtypes T3S and T3V can be morphologically distinguished. We can unequivocally assign the taxonomic names A. batava and A. falsobeccarii to T3S and T15, respectively. However, the end members of T1, T2A, T2B and T6 cannot be unambiguously distinguished, and therefore these genetic types are partially cryptic. However, we confirm that T2A can be assigned to A. aberdoveyensis, but caution must be taken in warm provinces where the presence of T2B will complicate the morphological identification of T2A. We suggest that T6 should not currently be allocated to the Pliocene species A. aomoriensis due to morphological discrepancies with the taxonomic description and to the lack of genetic information. Of significance is that these partially cryptic genetic types frequently co-occur, which has considerable implications for precise species identification and accurate data interpretation.
       
  • Paleoceanographic evolution of the Japan Sea over the last 460 kyr – A
           coccolithophore perspective
    • Abstract: Publication date: Available online 31 January 2019Source: Marine MicropaleontologyAuthor(s): Mariem Saavedra-Pellitero, Karl-Heinz Baumann, Stephen John Gallagher, Takuya Sagawa, Ryuji Tada Changes in the intensity of the influx of the Tsushima Warm Current (TWC) in the south-central part of the Japan Sea (JS), or East Sea in Korean, were reconstructed for the last 460 kyr at IODP Site U1427 using the composition and abundance of the coccolithophore assemblage. In addition, the recent distribution of coccolithophore taxa in the JS and the East China Sea was assessed using electron microscopy.Coccolithophore assemblages, dominated by Emiliania huxleyi and Gephyrocapsa species, and coccolith abundance reveal a strong relationship between sea level and ocean variability over the last five glacial/interglacial cycles, in good agreement with planktic foraminiferal data. Three different circulation modes based on calcareous nannofossil and foraminifera TWC indicators were proposed for the JS. Coccolith production was low and TWC indicators (i.e., Gephyrocapsa oceanica, Calcidiscus leptoporus s.l., and Helicosphaera carteri) absent due to the isolation of the JS during glacials in response to global sea level falls (Mode 1). In contrast, coccolith abundance and TWC indicators reach a maximum due to the most intense TWC flow through the Tsushima Strait during interglacials (Mode 3). Intermediate conditions (Mode 2) are characterized by moderate/high coccolith numbers, presence of TWC coccolith indicators, and rare TWC planktic foraminifera indicators. This mode resulted in intermittent variations in the contribution of the TWC and East China Sea coastal water due to relatively low sea level stands (ca. −90 m to −20 m). Coccoliths dominated the carbonate sequence prior to MIS 8 and were major contributors to the total carbonate of the sediment at Site U1427, suggesting high coccolithophore productivity and a bloom-type environment during MIS 11 and 9. These changes in the carbonate chemistry caused by glacio-eustacy in the JS at the northwest margin of the Pacific Ocean should be considered in future paleoceanographic and paleoclimate models.Graphical abstractUnlabelled Image
       
  • Coccolith morphological and assemblage responses to dissolution in the
           recent sediments of the East China Sea
    • Abstract: Publication date: Available online 10 September 2018Source: Marine MicropaleontologyAuthor(s): Xiaobo Jin, Chuanlian Liu, Hongrui Zhang Evaluating carbonate dissolution in deep sea sediments is of key importance in understanding the variation of the carbonate compensation depth and the ocean carbon cycle in the geological past. Since coccoliths are one of the main contributors to oceanic CaCO3, their dissolution and preservation degrees in sediments can be a useful indicator for deep sea carbonate chemistry. Varying coccolith preservation conditions have been found due to dissolution caused by organic matter degradation in the recent surface sediments of the East China Sea, which provides a good basis for the study of coccolith morphological and assemblage responses to dissolution. We measured the coccolith weight, thickness, and length of Gephyrocapsa spp. (>3 μm) using a circularly polarized light microscope. It has been found that Gephyrocapsa spp. (>3 μm) coccoliths become thinner and lighter in response to dissolution, and coccolith assemblages are also altered in poorly preserved sediments. This phenomenon was confirmed by an acidification experiment on a sediment sample, which also showed that coccoliths became thinner and lighter under increasingly acidified conditions. There is selective dissolution, i.e., Emiliania huxleyi coccoliths are most dissolution-prone, followed by Gephyrocapsa spp. (3 μm), and Helicosphaera spp.. Coccolith morphological parameters can be used to quantitatively evaluate coccolith preservation and dissolution in sediment samples. We suggest that using size-normalized weight, a mean coccolith weight loss of ~30–50% can be assigned to moderate-poor preservation for coccoliths, as reflected by the measured coccolith morphological changes in the surface sediments and in the acidification experiment.
       
 
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