2,748 research outputs found
Dispersal and biogeography of marine plankton: long-distance dispersal of the foraminifer Truncorotalia truncatulinoides
No full textSpeciation models for marine plankton commonly assume that tectonic barriers and water mass fronts act as potent isolating mechanisms. Here we present evidence indicating that tectonic and water mass barriers to dispersal are, in some cases, very weak. We identify a transient occurrence (19 k.y. duration) of the planktic foraminifer Truncorotalia truncatulinoides in the Atlantic Ocean 500 k.y. before its generally accepted first appearance anywhere outside the southwest Pacific. This finding provides strong evidence for long-distance dispersal of plankton, enabling them to opportunistically colonize normally inhospitable environments as soon as they become favorable. Our newly described appearances of T. truncatulinoides in the Atlantic are restricted to the onset of the first very severe glacial stage (marine isotope stage 100) at 2.54 Ma, ~200 k.y. after the global evolution of the species in the southwest Pacific. This ability of plankton to disperse long distances, combined with recent evidence for high gene flow throughout the extra-polar oceans, suggests that it may be very difficult, even impossible, to geographically isolate pelagic populations for extended periods of time, a key component in vicariant and allopatric speciation models. Instead, high dispersal capability favors sympatric or parapatric processes as the prevalent modes of marine speciation
Preservation of benthic foraminifera and reliability of deep-sea temperature records: Importance of sedimentation rates, lithology, and the need to examine test wall structure.
No full textPreservation of planktic foraminiferal calcite has received widespread attention in recent years, but the taphonomy of benthic foraminiferal calcite and its influence on the deep-sea palaeotemperature record have gone comparatively unreported. Numerical modeling indicates that the carbonate recrystallization histories of deep-sea sections are dominated by events in their early burial history, meaning that the degree of exchange between sediments and pore fluids during the early postburial phase holds the key to determining the palaeotemperature significance of diagenetic alteration of benthic foraminifera. Postburial sedimentation rate and lithology are likely to be important determinants of the paleoceanographic significance of this sediment–pore fluid interaction. Here we report an investigation of the impact of extreme change in sedimentation rate (a prolonged and widespread Upper Cretaceous hiatus in the North Atlantic Ocean) on the preservation and ? 18O of benthic foraminifera of Middle Cretaceous age (nannofossil zone NC10, uppermost Albian/lowermost Cenomanian, ?99 Ma ago) from multiple drill sites. At sites where this hiatus immediately overlies NC10, benthic foraminifera appear to display at least moderate preservation of the whole test. However, on closer inspection, these tests are shown to be extremely poorly preserved internally and yield ? 18O values substantially higher than those from contemporaneous better preserved benthic foraminifera at sites without an immediately overlying hiatus. These high ? 18O values are interpreted to indicate alteration close to the seafloor in cooler waters during the Late Cretaceous hiatus. Intersite differences in lithology modulate the diagenetic impact of this extreme change in sedimentation rate. Our results highlight the importance of thorough examination of benthic foraminiferal wall structures and lend support to the view that sedimentation rate and lithology are key factors controlling the paleoceanographic significance of diagenetic alteration of biogenic carbonates
Testing the Cenozoic multisite composite δ18O and δ13C curves: New monospecific Eocene records from a single locality, Demerara Rise (Ocean Drilling Program Leg 207)
No full textUntil recently, very few high-quality deep ocean sedimentary sections of Eocene age have been available. Consequently, our understanding of Eocene paleoceanography has become heavily reliant on “composite” records patched together from multiple sites in different ocean basins and generated using multiple taxa (potential sources of “local” noise in the global signal). Here we test the reliability of the early to middle Eocene composite δ18O and δ13C stratigraphies (Zachos et al., 2001) by generating new monospecific records in benthic foraminiferal calcite from a single locality, Demerara Rise, in the tropical western Atlantic (Ocean Drilling Program Leg 207). We present new stable isotope correction factors for commonly used Eocene benthic foraminiferal species. We find that interspecies isotopic offsets are constant across the isotopic range, supporting the notion that the inconstant intertaxa offsets reported elsewhere result from mixing species within genera. In general, the δ18O stratigraphy from Demerara Rise supports the validity of the Eocene δ18O composite, while revealing a temporary warming punctuating middle Eocene cooling. This warming may correspond to the so-called “Middle Eocene Climatic Optimum” previously documented in the Southern Ocean. The composite and Demerara Rise records for δ13C differ substantially. By removing the intersite and intertaxa sources of uncertainty in δ13C, we obtain a clearer picture of carbon cycling during the Eocene. Secular change in interocean δ13C gradients through the Eocene reveals that intervals of climatic warmth (especially the early Eocene) are associated with very small water mass ageing gradients
Microstructural and geochemical perspectives on planktic foraminiferal preservation: "Glassy" versus "Frosty"
No full textIn recent years it has become apparent that the “cool tropic paradox” of Paleogene and Cretaceous “greenhouse” climates arises because of the diagenetic alteration of tropical planktic foraminiferal calcite near the seafloor, yielding artificially high ? 18O values. Because the Mg/Ca compositions of foraminiferal and inorganic calcite are thought to be quite different, Mg/Ca measurements should be a sensitive way of monitoring diagenetic alteration. Here we examine the extent of diagenetic alteration of Eocene planktic foraminiferal calcite using scanning electron microscope imaging of foraminiferal test microstructures and geochemical (? 18O and Mg/Ca) analyses. We compare microstructural and geochemical characteristics between given species exhibiting two contrasting states of preservation: those that appear “frosty” under reflected light and those that appear “glassy.” Microstructural evidence reveals extensive diagenetic alteration of frosty foraminiferal tests at the micron scale, while ? 18O analyses document consistently higher ? 18O (and therefore lower paleotemperatures) in this material. Yet we find that ? 18O offsets between species in these frosty foraminiferal assemblages appear to be generally preserved, suggesting that frosty foraminifera remain valuable for generating relatively short (approximately ?1 Myr) paleoceanographic time series that do not demand absolute estimates of paleotemperature. We also find that the observed increase in Mg/Ca for planktic foraminifera exhibiting diagenetic alteration (compared to glassy taphonomies) is far smaller than would be expected from the addition of inorganic calcite based on laboratory-derived Mg2+ partition coefficients. Our findings imply that a much lower Mg2+ partition coefficient controls inorganic calcite formation in deep sea sedimentary sections, in accordance with the findings of Baker et al. (1982)
No extreme bipolar glaciation during the main Eocene calcite compensation shift
No full textMajor ice sheets were permanently established on Antarctica approximately 34 million years ago1,2,3, close to the Eocene/Oligocene boundary, at the same time as a permanent deepening of the calcite compensation depth in the world’s oceans4. Until recently, it was thought that Northern Hemisphere glaciation began much later, between 11 and 5 million years ago1,2,3,5. This view has been challenged, however, by records of ice rafting at high northern latitudes during the Eocene epoch6,7 and by estimates of global ice volume that exceed the storage capacity of Antarctica8 at the same time as a temporary deepening of the calcite compensation depth ∼41.6 million years ago9. Here we test the hypothesis that large ice sheets were present in both hemispheres ∼41.6 million years ago using marine sediment records of oxygen and carbon isotope values and of calcium carbonate content from the equatorial Atlantic Ocean. These records allow, at most, an ice budget that can easily be accommodated on Antarctica, indicating that large ice sheets were not present in the Northern Hemisphere. The records also reveal a brief interval shortly before the temporary deepening of the calcite compensation depth during which the calcite compensation depth shoaled, ocean temperatures increased and carbon isotope values decreased in the equatorial Atlantic. The nature of these changes around 41.6 million years ago implies common links, in terms of carbon cycling, with events at the Eocene/Oligocene boundary4 and with the ‘hyperthermals’ of the Early Eocene climate optimum3,10,11. Our findings help to resolve the apparent discrepancy between the geological records of Northern Hemisphere glaciation6,7,8 and model results12,13 that indicate that the threshold for continental glaciation was crossed earlier in the Southern Hemisphere than in the Northern Hemisphere
'The cracked mirror': Anne Sexton's poetics of self-representation
No full textThis thesis re-evaluates the work of the poet Anne Sexton (1928-1974), concentrating, in particular, on the indeterminacies, contradictions and aporia which it finds to be characteristic of her ostensibly frank and self-revelatory writing. The study is based on a close textual
analysis of Sexton's writing, is informed by oststructuralist theories, and is sustained by an
examination and discussion of archive collections of her previously unpublished papers. In seeking an understanding of Sexton's poetics, the thesis identifies and interrogates the strategies of denial and obfuscation apparent in her own explication of her work - principally, by scrutiny of the unpublished, and previously unresearched, drafts of a series of lectures
which she delivered in 1972. Chapters One and Two consider the origins of `confessional' or - Sexton's preferred term - 'personal' poetry and reassess her place within contemporary poetry. They suggest that
Sexton's writing is engaged in a process of negotiation and contestation, both with the boundaries and expectations of confessionalism, and with the strictures of T. S. Eliot's theory of `impersonality'. In support of these arguments, Chapter Two offer a reading of Sexton's
little-known poem, `Hurry Up Please It's Time', alongside its intertext, Eliot's The Waste Land. Chapter Three reassesses received views of the supposedly beneficial interrelationship between confessional speaker and reader. It examines Sexton's appropriation of dramatic
masks and personae and her use of metaphors of striptease and prostitution, and suggests that these are employed simultaneously to appease and to repel an intrusive audience. Similarly, Chapters Four and Five trace Sexton's problematisation of two previously-accepted tenets of confessional poetry: its status as autobiography and its truthfulness, drawing attention to the techniques employed in order to give the impression of both. Chapter Six considers Sexton's
problematic engagement with a language which is not malleable, transparent, and referential but, rather, is experienced as uncooperative and occlusive. Finally, the thesis recuperates Sexton from the common charge of narcissism, arguing that it is the writing, rather than the poet, which is self-reflexive and self-conscious. In this respect, it concludes that her work - perhaps unexpectedly - anticipates many of the tendencies of postmodernist writing
Inscription in The mystic and other poems
No full textThis edition has a gift dedication from the author's nephew to Edmund Gosse, suggesting he once owned the book. Dedicatation, "Mr. Edmund Gosse in remembrance of my Uncle Philip James Bailey Sep: 1902 F. CC."Bailey, Philip James, 1816-1902
Phillip F. O\u27Connor, 2nd Annual ODU Literary Festival
No full textPhilip F. O\u27Connor is the author of Stealing Home, a summer 1979 Book-of-the Month-Club alternate. More than 50 of his short stories are in print; including work in the late Martha Foley\u27s The Best American Short Stories 1971.\u27\u27 Mr. O\u27Connor has written two collections of short stories: Old Morals, Small Continents, Darker Times, winner of the 1971 Iowa School of Letters Award for Short Fiction, and A Season of Unnatural Causes. In 1969 he introduced the M.F A program in creative writing at Bowling Green State University, where he now teaches. Mr. O\u27Connor is a member of the board of directors of the Associated Writing Programs
An analysis of the correspondence and hagiographical works of Philip of Harvengt
No full textFor every famous author of the twelfth-century renaissance, there are numerous lesser-known writers. Despite being overshadowed by more brilliant scholars or those closer to the centre of important events, their voices add depth to the study of the intellectual history of this period. A founding member of one of the earliest Premonstratensian houses; a highly-educated and prolific author, much in demand as a hagiographer; and a vigorous defender of the clerical order, Philip of Harvengt is one such writer, and a worthy subject for study. This thesis examines two bodies of Philip’s works – his letters and his hagiographical writings – analysing the predominant and recurrent concerns and ideals expressed in them, and the means by which they are expressed.
The letters are carefully crafted works, examples of the literary labour which Philip writes is incumbent upon the cleric. The first part of this thesis approaches these letters in chapters on four themes: the role of the ecclesiastical prelate; the importance of learning; the relationship between religious orders; and Philip’s use of the motif of friendship. His hagiographical works, too, are examples of literary artistry, to move as well as to educate the audience. In the second part of the thesis, these will be discussed individually, with the first chapter analysing his vita of Oda, a nun attached to his own house, whom he portrays as a martyr. The succeeding chapters consider Philip’s rewritings of earlier vitae, and show how he managed his sources in order to produce vitae depicting their subjects according to his ideal model of sanctity.
Philip’s letters express concerns shared by contemporaries, reflecting anxieties surrounding roles and ideal forms of living in a period immediately following the first fervour of religious renewal. His hagiographies articulate ideals of sanctity, clarifying these when they are not made sufficiently explicit in earlier works, for the better edification of an audience pursuing this vita perfecta. Both letters and hagiographies are designed to exhort and instruct the reader or listener: above all, Philip is a teacher
Very large release of mostly volcanic carbon during the Palaeocene–Eocene Thermal Maximum
No full textThe Palaeocene-Eocene Thermal Maximum(1,2) (PETM) was a global warming event that occurred about 56 million years ago, and is commonly thought to have been driven primarily by the destabilization of carbon from surface sedimentary reservoirs such as methane hydrates(3). However, it remains controversial whether such reservoirs were indeed the source of the carbon that drove the warming(1,3-5). Resolving this issue is key to understanding the proximal cause of the warming, and to quantifying the roles of triggers versus feedbacks. Here we present boron isotope data-a proxy for seawater pH-that show that the ocean surface pH was persistently low during the PETM. We combine our pH data with a paired carbon isotope record in an Earth system model in order to reconstruct the unfolding carbon-cycle dynamics during the event(6,7). We find strong evidence for a much larger (more than 10,000 petagrams)-and, on average, isotopically heavier-carbon source than considered previously(8,9). This leads us to identify volcanism associated with the North Atlantic Igneous Province(10,11), rather than carbon from a surface reservoir, as the main driver of the PETM. This finding implies that climate-driven amplification of organic carbon feedbacks probably played only a minor part in driving the event. However, we find that enhanced burial of organic matter seems to have been important in eventually sequestering the released carbon and accelerating the recovery of the Earth system(12)
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