Ranking of dissolution susceptibility of planktonic foraminifera at high latitudes of the South Atlantic Ocean

Surface-sediment samples from the Maurice Ewing Bank (eastern Falkland Plateau), South Atlantic Ocean, have been analyzed to rank dissolution susceptibility of cool water planktonic foraminiferal species. A dissolution index is formulated from quantitative analyses of sedimentological properties (CaCO₃ content, frequency of planktonic foraminiferal fragments, radiolarians, mineral grains, and ratio of a dissolution-tolerant to a dissolution-susceptible planktonic foraminiferal species). This index is used to assess degrees of dissolution in the samples. Quantified differences in relative abundance of species between the two dissolution regimes (less prominent and stronger dissolution) formed the basis for differentiation. The species were ranked in the following order, from most resistant to least resistant: sinistrally coiled variety ofNeogloboquadrina pachyderma (antarctic variety of this species),Globorotalia inflata, G. truncatulinoides, Globigerina bulloides andGlobigerinita glutinata (a tie), dextralN. pachyderma (subantarctic variety),Globigerinita uvula, andGlobigerina quinqueloba. Fragmentation (frequency of damaged tests) increases with increasing dissolution in tolerant species, but not in susceptible species. This may be because susceptible species are completely dissolved under intense dissolution, whereas tolerant species, although damaged, remain and increase in abundance.     

The onset of the Paleocene–Eocene Thermal Maximum (PETM) at Sites 1209 and 1210 (Shatsky Rise, Pacific Ocean) as recorded by planktonic foraminifera

High-resolution biostratigraphic and quantitative studies of subtropical Pacific planktonic foraminiferal assemblages (Ocean Drilling Program, Leg 198 Shatsky Rise, Sites 1209 and 1210) are performed to analyse the faunal changes associated with the Paleocene–Eocene Thermal Maximum (PETM) at about 55.5 Ma. At Shatsky Rise, the onset of the PETM is marked by the abrupt onset of a negative carbon isotope excursion close to the contact between carbonate-rich ooze and overlying clay-rich ooze and corresponds to a level of poor foraminiferal preservation as a result of carbonate dissolution. Lithology, planktonic foraminiferal distribution and abundances, calcareous plankton and benthic events, and the negative carbon isotope excursion allow precise correlation of the two Shatsky Rise records. Results from quantitative analyses show that Morozovella dominates the assemblages and that its maximum relative abundance is coincident with the lowest δ¹³C values, whereas subbotinids are absent in the interval of maximum abundance of Morozovella. The excursion taxa (Acarinina africana, Acarinina sibaiyaensis, and Morozovella allisonensis) first appear at the base of the event. Comparison between the absolute abundances of whole specimens and fragments of genera demonstrate that the increase in absolute abundance of Morozovella and the decrease of Subbotina are not an artifact of selective dissolution. Moreover, the shell fragmentation data reveal Subbotina to be the more dissolution-susceptible taxon. The upward decrease in abundance of Morozovella species and the concomitant increase in test size of Morozovella velascoensis are not controlled by dissolution. These changes could be attributed to the species' response to low nutrient supply in the surface waters and to concomitant changes in the physical and chemical properties of the seawater, including increased surface stratification and salinity.Comparison of the planktonic foraminiferal changes at Shatsky Rise to those from other PETM records (Sites 865 and 690) highlights significant similarities, such as the decline of Subbotina at the onset of the event, and discrepancies, including the difference in abundance of the excursion taxa. The observed planktonic foraminifera species response suggests a warm–oligotrophic scenario with a high degree of complexity in the ocean structure.     

Planktonic foraminifera of the northern Indian Ocean: Distribution and preservation in surface sediments

In the northern Indian Ocean, planktonic foraminiferal tests accumulate in a wide variety of surface-water environments and depositional settings. This variability enables us to isolate the effects that surface-water ecology and differential dissolution have on the distribution of planktonic foraminifera from 251 geographically widespread surface sediment samples.Foraminiferal abundance varies from 0 to > 10⁴ whole foraminifera in the greater than 150 μm fraction per gram dry sediment. Values < 10 characterize the three deep basins of the equatorial Indian Ocean and the western Bay of Bengal. Foraminiferal tests are most abundant on carbonate covered Ninety-East and Carlsberg Ridges. Absolute abundance patterns are mainly controlled by non-ecological processes. Variations in dissolution resistant species (RSP) with water depth reveal that the foraminiferal lysocline (FL) varies regionally. The FL is deepest (3,800 m) in the equatorial region, rises abruptly to 3,300 m in the Arabian Sea, and varies from 2,600 m to near 2,000 m moving northward in the Bay of Bengal. Deep samples with anomalously low RSP (< 30%) suggest redeposition.Systematic geographic and depth-related variation is observed for the 17 most abundant foraminiferal species. Dissolution resistant species (G. menardii, G. tumida, G. dutertrei, P. obliquiloculata) generally exhibit a rapid and continuous increase in relative abundance at and below the FL. Susceptible species (G. ruber, G. bulloides, G. glutinata, for example) exhibit a rapid and continuous decrease in relative abundance at and below the FL. Moderately susceptible species (G. conglobatus, G. aequilateralis, G. conglomerata, for example) rapidly increase in abundance at the FL and systematically decrease with depth below the FL.Principal components analysis (PCA) of faunal data from minimally dissolved (< 30% RSP) samples reveals important ecologically related species intercorrelations. The major biogeographic gradient is the negative covarying relationship between aG. bulloides-G. glutinata species pair and a grouping ofG. sacculifer, G. conglobatus, G. aequilateralis, andG. ruber. PCA of all samples demonstrates how differential dissolution alters this and other species relationships. Species groupings that incorporateG. ruber, G. menardii, andG. dutertrei are particularly affected by dissolution.Comparison of average faunal data from minimally dissolved samples in the northern Indian Ocean with similar samples from other tropical regions suggests varying environmental factors produce distinct faunas within the tropical ocean. For example,G. bulloides, G. falconensis, andG. hexagona are significantly more abundant in northern Indian Ocean surface sediments while such species asG. ruber, G. sacculifer, G. dutertrei, andP. obliquiloculata dominate in other tropical regions.     

Differential dissolution of upper Cretaceous deep-sea benthonic foraminifers from the Angola Basin,South Atlantic Ocean

Material from the Deep Sea Drilling Project (DSDP) Site 527 from the Angola Basin, South Atlantic Ocean, has been analyzed to determine whether Upper Cretaceous benthonic foraminiferal taxa are differentially sensitive to calcite dissolution, and, if so, to rank their order of susceptibility. Two regimes of dissolution, established on the basis of the degree of planktonic foraminiferal fragmentation, representing stronger and less prominent dissolution within the section studied, were used as a framework for reference. A total of 60 calcareous and eight agglutinated benthonic foraminiferal taxa were identified at the species or genus level; of these, twenty-three calcareous and five agglutinated taxa were selected for the dissolution study. Relative abundance of each of the various taxa was tested statistically, using t-test, between dissolution regimes to assess the significance of the change induced by increased dissolution.Nuttallides truempyi andNeoeponides sp. intermediate form are interpreted as resistant to dissolution.Pullenia spp.,Alabamina sp. a,Anomalina sp. a,Praebulimina sp. fusiform, andNuttallinella sp. a are susceptible to dissolution. The majority of the taxa (16 in number) are unaffected by dissolution because they show no change between dissolution regimes. Among the agglutinated taxaGaudryina pyramidata is resistant to dissolution, whereas the remaining four taxa are unaffected by dissolution. At the level of superfamilies, one calcareous superfamily (Discorbacea) is resistant, two (Orbitoidacea and Cassidulinacea) are unaffected, and two (Nodosariacea and Buliminacea) are susceptible to dissolution.     

CRETACEOUS PLANKTONIC FORAMINIFERA FROM BORNHOLM AND THEIR ZOOGEOGRAPHIC SIGNIFICANCE

Late Cretaceous formations exposed along the south coast of Bornholm Island, Denmark, contain well preserved assemblages of planktonic foraminifera, which are described and illustrated. Two taxa, Whiteinella baltica and Hedbergella bornholmensis , are described as new. The oldest assemblage, Middle to early Upper Cenomanian in age, is essentially monospecific and indicative of a restricted pelagic environment. The overlying Lower Senonian faunules are diverse, contain large populations which are associated with other pelagic microfossils, and provide a more typical example of Boreal planktonic foraminiferal associations. Taxonomically the assemblages are largely composed of species of Hedbergella, Whiteinella, Archaeoglobigerina, Globigerinelloides , and Heterohelix and double-keeled species of Globotruncana , particularly G. marginata. These species are widely distributed in space and time. Thus Bornholm assemblages have a cosmopolitan aspect, which can be identified in microfaunas from the Western Interior of North America and Alaska. Because of the lower diversity, lack of restricted stratigraphic markers, Lower Senonian correlations between Bornholm, and probably Boreal pelagic microfaunas generally, coeval Tethyan assemblages are less precise than within the Tethys.     

Calcite dissolution and the modification of planktonic foraminiferal assemblages

The results of an in situ experiment in the Panama Basin allow us to determine the way in which planktonic foraminiferal assemblages are modified by calcite dissolution. Pre-weighed planktonic foraminiferal samples of known species composition were attached to a deep-sea mooring at various water depths between 665 m and 3791 m for a period of 123 days. Weight loss due to dissolution during this period ranged from less than 5% for the shallowest samples to slightly over 30% for the deepest samples. In terms of change in foraminiferal number, this is equivalent to decreases of between 1% and 26%. Only in the samples placed at the two deepest levels (3769 m and 3791 m) was there a significant loss in the total number of foraminifera. The magnitude of change in the abundance of individual species in early related to their different susceptibilities to dissolution. Species such as Hastigerina pelagica, Globigerinella aequilateralis and Candeina nitida, which are very susceptible to dissolution, exhibited the largest decreases in frequency percentage while the more resistent species (Sphaeroidinella dehiscens, Pulleniatina obliquiloculata and Globorotalia truncatulinoides) had minimal changes. From these results a solution-susceptibility ranking for planktonic foraminifera is established that is quite similar to those derived from previous laboratory experiments and sea-floor studies.     

Benthic origin and earliest evolution of the first planktonic foraminifera after the Cretaceous/Palaeogene boundary mass extinction

There are several hypotheses on the origin and evolution of the earliest Danian planktonic foraminifera. Most experts suggest that they descended from a few opportunist planktonic foraminifera species, mainly of the genera Guembelitria and Hedbergella, which are usually considered to be survivors of the Cretaceous/Paleogene (K/Pg) boundary mass extinction. Nevertheless, early Danian specimens of Guembelitria and Hedbergella remained morphologically well separated from the associated parvularugoglobigerinids (i.e. Parvularugoglobigerina and Palaeoglobigerina), the first trochospiral planktonic foraminifera appearing after the K/Pg boundary event. The most likely alternative is a benthic origin for the parvularugoglobigerinids, which would be consistent with molecular phylogenetic studies that have suggested several episodes of benthic-planktonic transitions in the evolutionary history of planktonic foraminifera. A review of material from the El Kef section and other Tunisian sections supports the previous hypothesis that the buliminid genus Caucasina is the ancestor of the first parvularugoglobigerinids (i.e. Parvularugoglobigerina longiapertura and Palaeoglobigerina alticonusa), on the basis of similarities in test and apertural morphologies and wall texture. The intermediate morphotypes between caucasinids and parvularugoglobigerinids, which appeared approximately 3–5 kyr after the K/Pg boundary, are assigned to Pseudocaucasina antecessor gen. nov. sp. nov.     

Planktonic foraminiferal biostratigraphy and paleoenvironments at the Santonian-Campanian boundary of Northern Tunisia

The Santonian-Campanian boundary in Northern Tunisia has been studied in Oued el Khannga section, based on biostratigraphic and paleoecological analysis. The detailed biostratigraphic analysis allows us to define the stratigraphic distribution of diverse planktonic foraminifera and to establish a continuous biozonation. Sixty-six planktonic foraminiferal species belonging to 13 genera have been identified and two Tethyan planktonic foraminiferal zones have been organized, indicating the upper Santonian - lower Campanian age. These zones are: Dicarinella asymetrica (Total Range Zone) and Globotruncanita elevata/Globotruncana arca (Concurrent range zone). A major turn over event was recorded in this interval including the extinction of several species characterized by complex morphotypes with a double keel such as the genera of Dicarinella, Marginotruncana. In fact, the extinction of the index species D. asymetrica is the most important event which defines the Santonian-Campanian boundary. Many representative species of the genera Globotruncanita and Globotruncana occurred, for the first time, in the uppermost of the Santonian and thrived close to the Santonian-Campanian boundary. In addition some surviving species with a simple morphotype, which are considered like opportunistic taxa, crossed the boundary. This various responses of planktonic foraminifera and the fluctuation in diversity and in the number of species may be related to an increase in temperature and a deep outer shelf upper bathyal environment deposit.     

Foraminifera and coccolithophorid assemblage changes in the Panama Basin during the last deglaciation: Response to sea-surface productivity induced by a transient climate change

The responses of community assemblages of planktonic and benthonic foraminifera and coccolithophorids to transient climate change are explored for the uppermost 2 m of cores ODP677B (1.2°N; 83.74°W, 3461 m) and TR163-38 (1.34°S; 81.58°W, 2200 m), for the last ∼ 40 ka. Results suggest that the deglaciation interval was a time of increased productivity and a major reorganization of planktonic trophic webs. The succession in dominance between the planktonic foraminifera species Globorotalia inflata, Globigerina bulloides, and Neogloboquadrina pachyderma denote four periods of oceanographic change: (1) advection (24-20 ka), (2) strong upwelling (20-15 ka), (3) weak upwelling (14-8 ka) and (4) oligotrophy (8 ka to present). Strong upwelling for the deglaciation interval is supported by the low Florisphaera profunda/other coccolithophorids ratio and the high percentage abundance of Gephyrocapsa oceanica. Benthonic foraminifera assemblage changes are different in both cores and suggest significant regional variations in surface productivity and/or oxygen content at the seafloor, and a decoupling between surface productivity and export production to the seafloor. This decoupling is evidenced by the inverse relationship between the percentage abundance of infaunal benthonic foraminifera and the percentage abundance of N. pachyderma. The terrigenous input of the Colombian Pacific rivers, particularly the San Juan River, is suggested as a possible mechanism. Finally, the Globorotalia cultrata/Neogloboquadrina dutertrei ratio is used to reconstruct the past influence of the Costa Rica Dome-Panama Bight and cold tongue upwelling systems in the Panama Basin. A northern influence is suggested for the late Holocene (after 5 ka) and the last glacial (before 20 ka), whereas a southern influence is suggested for the 20-5 ka interval. There is a correspondence between our reconstructed northern and southern influences and previously proposed positions of the Intertropical Convergence Zone (ITCZ) after the Last Glacial Maximum (LGM).     

Planktonic foraminiferal turnover, diversity fluctuations and geochemical signals across the Eocene/Oligocene boundary in Tanzania

A major turnover in planktonic foraminifera occurred across the Eocene/Oligocene (E/O) boundary. New drill holes through the E/O boundary in southern Tanzania contain extremely well-preserved and diverse assemblages of planktonic foraminifera. Here we document a 1.2 million year record of assemblages, diversity and stable isotope fluctuations through this critical interval, which is often dissolved and/or recrystallised in carbonate-rich facies. The E/O boundary is marked by the abrupt extinction of all five remaining species of the family Hantkeninidae and a distinct size reduction in the genus Pseudohastigerina. The boundary is preceded over a short stratigraphic interval by the extinction of Turborotalia cerroazulensis, Turborotalia cocoaensis and Turborotalia cunialensis. Quantitative analysis of planktonic foraminiferal assemblages reveals significant changes in the abundance of certain species and the composition of the assemblages. We compare diversity fluctuations to the stable isotope record of Pseudohastigerina naguewichiensis and use multispecies stable isotope analyses to determine the life habitats of the most important species. A major shift in the evenness occurs at ~ 33.8 Ma associated with the extinction of the T cerroazulensis group suggesting acute ecological disturbance. We propose that the extinction of the T. cerroazulensis group at ~ 33.8 Ma was directly related to cooling of sea surface temperatures, while the extinction of Hantkeninidae was due to modifications in the thermal structure of the oceans and associated productivity changes. After the extinctions, renewed origination and diversification occurred, leading to a characteristic Oligocene planktonic foraminifer assemblage.     

Planktonic foraminiferal response to the latest Maastrichtian abrupt warm event: a case study from South Atlantic DSDP Site 525A

An abrupt global warming of 3–4°C occurred near the end of the Maastrichtian at 65.45–65.10 Ma. The environmental effects of this warm event are here documented based on stable isotopes and quantitative analysis of planktonic foraminifera at the South Atlantic DSDP Site 525A. Stable isotopes of individual species mark a rapid increase in temperature and a reduction in the vertical water mass stratification that is accompanied by a decrease in niche habitats, reduced species diversity and/or abundance, smaller species morphologies or dwarfing, and reduced photosymbiotic activity. During the warm event, the relative abundance of a large number of species decreased, including tropical–subtropical affiliated species, whereas typical mid-latitude species retained high abundances. This indicates that climate warming did not create favorable conditions for all tropical–subtropical species at mid-latitudes and did not cause a massive retreat in the local mid-latitude population. A noticeable exception is the ecological generalist Heterohelix dentata Stenestad that dominated during the cool intervals, but significantly decreased during the warm event. However, dwarfing is the most striking response to the abrupt warming and occurred in various species of different morphologies and lineages (e.g. biserial, trochospiral, keeled globotruncanids). Dwarfing is a typical reaction to environmental stress conditions and was likely the result of increased reproduction rates. Similarly, photosymbiotic activity appears to have been reduced significantly during the maximum warming, as indicated by decreased δ¹³C values. The foraminiferal response to climate change is thus multifaceted resulting in decreased species diversity, decreased species populations, increased competition due to reduced niche habitats, dwarfing and reduced photosymbiotic activity.     

Molecular evidence for an independent origin of modern triserial planktonic foraminifera from benthic ancestors

Gallitellia vivans is the only Recent representative of the triserial planktonic foraminiferal family Guembelitriidae. The origin and evolution of this interesting albeit poorly known family are enigmatic. To elucidate the phylogenetic relationships between G. vivans and other planktonic foraminifera, we sequenced the small subunit ribosomal DNA (SSU rDNA) for comparison to our extensive database of planktonic and benthic species. Our analyses suggest that G. vivans represents a separate lineage of planktonic foraminifera, which branches close to the benthic rotaliids Stainforthia and Virgulinella. Both genera resemble Gallitellia in general morphological appearance, having elongate triserial tests at least in their early ontogenic stages. The divergence time of G. vivans is estimated at ca. 18 Ma (early Miocene), suggesting an origin independent from the Cretaceous and Paleogene triserial planktonic foraminifera. Our study thus indicates that modern triserial planktonic foraminifera are not related to the Cretaceous–Paleogene triserial species, and that the sporadic occurrences in the fossil record are not the result of poor preservation, but reflect multiple transitions from benthic to planktonic mode of life.     

Phylogeny and Rates of Molecular Evolution of Planktonic Foraminifera: SSU rDNA Sequences Compared to the Fossil Record

Planktonic foraminifera are marine protists, whose calcareous shells form oceanic sediments and are widely used for stratigraphic and paleoenvironmental analyses. The fossil record of planktonic foraminifera is compared here to their molecular phylogeny inferred from ribosomal DNA sequences. Eighteen partial SSU rDNA sequences from species representing all modern planktonic families (Globigerinidae, Hastigerinidae, Globorotaliidae, Candeinidae) were obtained and compared to seven sequences representing the major groups of benthic foraminifera. The phylogenetic analyses indicate a polyphyletic origin for the planktonic foraminifera. The Candeinidae, the Globorotaliidae, and the clade Globigerinidae + Hastigerinidae seem to have originated independently, at different epochs in the evolution of foraminifera. Inference of their relationships, however, is limited by substitution rates of heterogeneity. Rates of SSU rDNA evolution vary from 4.0 × 10⁻⁹ substitutions/site/year in the Globigerinidae to less than 1.0 × 10⁻⁹ substitutions/site/year in the Globorotaliidae. These variations may be related to different levels of adaptation to the planktonic mode of life. A clock-like evolution is observed among the Globigerinidae, for which molecular and paleontological data are congruent. Phylogeny of the Globorotaliidae is clearly biased by rapid rates of substitution in two species (G. truncatulinoides and G. menardii). Our study reveals differences in absolute rates of evolution at all taxonomic levels in planktonic foraminifera and demonstrates their effect on phylogenetic reconstructions. Received: 21 January 1997 / Accepted: 17 April 1997     

Larger foraminifera and sedimentation around Fongafale Island,Funafuti Atoll,Tuvalu

Larger foraminifera are an important component of coastal sediments around Fongafale Island, Funafuti Atoll, Tuvalu, and at least 10 species are present. In the shallow lagoon, foraminifera (mainly Amphistegina lessonii, A. lobifera, Baculogypsina sphaerulata, Calcarina spengleri, Marginopora vertebralis, and Sorites marginalis) are the dominant component of sand and gravel, followed in decreasing order of abundance by calcareous red and green algae, coral, and molluscs. In deeper water, Halimeda replaces the foraminifera. Close inshore, abrasion removes Halimeda and may reduce the number of foraminiferal tests. There is some sediment movement in both onshore and offshore directions although offshore transport appears minor. On land, dissolution that preferentially removes aragonite may increase the proportion of foraminiferal tests to as much as 83% of the subsurface sediment. Sediments on the ocean side are dominated by coral and coralline red algal debris thrown up in 1972 by cyclone Bebe and later moved inshore and lagoonward.Communicated by P.K. Swart     

Sensitivity of south‐east Atlantic planktonic foraminifera to mid‐Pleistocene climate change

Abstract: The last one million years are important in terms of climate development during the so‐called Mid‐Pleistocene Transition when amplification of the glacial–interglacial cycles occurred. This study describes abundance changes in fossil planktonic foraminifera in sediments from Core T89‐40, retrieved from the Walvis Ridge in the south‐east Atlantic, across this time period. Cycles between upwelling and subtropical planktonic foraminiferal assemblages are shown to mirror changes between glacial and interglacial periods, respectively. During interglacial marine isotopic stages (MIS) 9, 11 and 31, however, anomalously high abundances of the polar left‐coiled Neogloboquadrina pachyderma occur, presumably linked to unusual seasonal upwelling waters. The planktonic foraminiferal abundance record shows 41‐ky cyclic variations in the regional oceanography linked to cycles in insolation influenced by changes in the Earth’s axial tilt (obliquity). These orbitally induced oscillations in oceanographic change occurred throughout the entire record. The most conspicuous feature of the planktonic foraminiferal record is the near absence of left‐coiled Globorotalia truncatulinoides between 960 and 610 ka (MIS 26‐15). The abrupt disappearance of this species is synchronous with the onset of the Mid‐Pleistocene Transition in MIS 26.     

Improving detection of foraminifera by cathodoluminescence

Cathodoluminescence (CL) studies of Lower–Middle Oxfordian marls and limestones, as well as clasts from the uppermost Turonian–?Early Coniacian conglomerates of the Cracow Upland (southern Poland), reveal that the CL view of foraminifers from some lithologies differs from that in transmitted light. In particular, the CL technique revealed abundant tests of planktonic species Globuligerina oxfordiana in the Middle Oxfordian glauconitic marls, which under transmitted light are either poorly visible or remain completely undetected. Bright red–orange luminescence characterizes originally hyaline aragonitic tests of G. oxfordiana, but also several calcitic benthic species, in spite of their different taxonomic position and original test structure and mineralogy. In sponge microbial boundstones, foraminifers generally do not show the CL emission, or show a weak luminescence. Similarly, Late Cretaceous foraminifera represented mostly by planktonic taxa were detected or their view was clearly improved under CL only in some clasts from the uppermost Turonian–?Early Coniacian conglomerates filling karstic cavities. In other clasts, foraminifera are clearly visible only under normal transmitted light, therefore the luminescence signature is highly spatially variable. These results indicate a strong influence of lithology and diagenesis and rather minor effects of shell structure on luminescence of microfossils. The CL technique can be a useful tool in the detection and documentation of abundance patterns of foraminifers that are poorly preserved under transmitted light.     

Paleoceanographic implications of smaller benthic and planktonic foraminifera from the Eocene Pazin Basin (Coastal Dinarides,Croatia)

Summary Smaller benthic and planktonic foraminifera from the clastic sediments of the Pazin Basin (Istria, Croatia) were studied in order to obtain more data about paleoceanographic conditions that existed in the Middle Eocene Dinaric foreland basin. The succession investigated corresponds to the Middle Eocene planktonic foraminiferal zones Globigerapsis kugleri/Morozovella aragonensis (P11), Morozovella lehneri (P12), and Globigerapsis beckmanni (P13). Benthic foraminiferal assemblages from the clastic succession are dominated by epifaunal trochospiral genera suggesting oligotrophic to mesotrophic conditions and moderately oxygenated bottom waters. Planktonic foraminiferal assemblages indicate mesotrophic to eutrophic conditions of the surface waters, with increased eutrophication in the upper part of the section. Water depth, based on the ratio between planktonic and epifaunal benthic foraminifera and on the recognized species of cosmopolitan benthic foraminifera, was estimated to have been between about 900 and 1200 m. The basin was elongated and open to marine currents on both sides allowing good circulation and ventilation of the bottom water.     

Snow cover and extreme winter warming events control flower abundance of some,but not all species in high arctic Svalbard

The High Arctic winter is expected to be altered through ongoing and future climate change. Winter precipitation and snow depth are projected to increase and melt out dates change accordingly. Also, snow cover and depth will play an important role in protecting plant canopy from increasingly more frequent extreme winter warming events. Flower production of many Arctic plants is dependent on melt out timing, since season length determines resource availability for flower preformation. We erected snow fences to increase snow depth and shorten growing season, and counted flowers of six species over 5 years, during which we experienced two extreme winter warming events. Most species were resistant to snow cover increase, but two species reduced flower abundance due to shortened growing seasons. Cassiope tetragona responded strongly with fewer flowers in deep snow regimes during years without extreme events, while Stellaria crassipes responded partly. Snow pack thickness determined whether winter warming events had an effect on flower abundance of some species. Warming events clearly reduced flower abundance in shallow but not in deep snow regimes of Cassiope tetragona, but only marginally for Dryas octopetala. However, the affected species were resilient and individuals did not experience any long term effects. In the case of short or cold summers, a subset of species suffered reduced reproductive success, which may affect future plant composition through possible cascading competition effects. Extreme winter warming events were shown to expose the canopy to cold winter air. The following summer most of the overwintering flower buds could not produce flowers. Thus reproductive success is reduced if this occurs in subsequent years. We conclude that snow depth influences flower abundance by altering season length and by protecting or exposing flower buds to cold winter air, but most species studied are resistant to changes.     

Molecular evidence for an independent origin of modern triserial planktonic foraminifera from benthic ancestors

Gallitellia vivans is the only Recent representative of the triserial planktonic foraminiferal family Guembelitriidae. The origin and evolution of this interesting albeit poorly known family are enigmatic. To elucidate the phylogenetic relationships between G. vivans and other planktonic foraminifera, we sequenced the small subunit ribosomal DNA (SSU rDNA) for comparison to our extensive database of planktonic and benthic species. Our analyses suggest that G. vivans represents a separate lineage of planktonic foraminifera, which branches close to the benthic rotaliids Stainforthia and Virgulinella. Both genera resemble Gallitellia in general morphological appearance, having elongate triserial tests at least in their early ontogenic stages. The divergence time of G. vivans is estimated at ca. 18 Ma (early Miocene), suggesting an origin independent from the Cretaceous and Paleogene triserial planktonic foraminifera. Our study thus indicates that modern triserial planktonic foraminifera are not related to the Cretaceous–Paleogene triserial species, and that the sporadic occurrences in the fossil record are not the result of poor preservation, but reflect multiple transitions from benthic to planktonic mode of life.     

南海北部HY4－901孔浮游有孔虫特征及意义

南海北部ＨＹ４－９０１孔沉积连续、粒度均匀,浮游有孔虫丰富,共鉴定１０属２６种,其中以暖水种占优势,凉水种也有相当含量。浮游有孔虫组合的研究表明,本区的溶解作用不强,不是影响ＣａＣＯ＿３分布的主要因素。全新世的气温变化,可以分为五期：１）迅速升温期,２）高温期,３）降温期,４）温暖期,５）温凉期。