4,080 research outputs found
Population Structure and Life History Connectivity of Antarctic Silverfish (Pleuragramma antarctica) in the Southern Ocean Ecosystem
No full textAntarctic silverfish (Pleuragramma antarctica) are the most important pelagic forage fish on the Antarctic continental shelf. They have an exclusively pelagic life history, including cryopelagic eggs and early larvae. The discovery of extensive distributions of eggs and larvae under fast-ice inside Terra Nova Bay, and the revelation that the aggregates were stable between years, suggested dispersal over the continental shelf by older larvae and juveniles and a return as adults to spawning areas, consistent with observations from the Antarctic Peninsula of large-scale adult movement inshore. This life history hypothesis holds promise for understanding population structure in silverfish found around the Antarctic continental shelf. However, the hypothesis is challenged by inconsistencies concerning the distribution of spawning and feeding areas, a low-energy life strategy, and lack of phylogenetic diversification.
We review recent and past population and genetic studies in the context of published literature on the physical environment, including hydrography and a recent geological reconstruction of Antarctic Ice Sheet deglaciation. We suggest physical-biological interactions between glacial trough systems, circulation, and life history processes in shaping distributions of silverfish along and across the shelf. We discuss how these processes may result in a richly diverse population structure around the Antarctic and over time, and show how the synthesis can help account for (1) variability in spawning and feeding areas over succeeding glacial cycles, (2) connectivity without invoking active migration on large spatial scales, and (3) persistence over successive glacial cycles without further phylogenetic diversification. Based on this synthesis, we make predictions concerning population structuring and genetic signatures of paleo-climatic events, and suggest multi-disciplinary approaches to test these in future research
The World Atlas of Last Interglacial Shorelines (version 1.0)
Get PDFThis paper presents version 1.0 of the World Atlas of Last Interglacial Shorelines (WALIS), a global database of sea-level proxies and samples dated to marine isotope stage 5 (similar to 80 to 130 ka). The database includes a series of datasets compiled in the framework of a special issue published in this journal (https: //essd.copernicus.org/articles/special_issue1055.html, last access: 15 December 2022). This paper collates the individual contributions (archived in a Zenodo community at https://zenodo.org/communities/walis_database/, last access: 15 December 2022) into an open-access, standalone database (Rovere et al., 2022, https://doi.org/ 10.5281/zenodo.7348242). The release of WALIS 1.0 includes complete documentation and scripts to down-load, analyze, and visualize the data (https://alerovere.github.io/WALIS/, last access: 15 December 2022). The database contains 4545 sea-level proxies (e.g., marine terraces or fossil beach deposits), 4110 dated samples (e.g., corals dated with U-series), and 280 other time constraints (e.g., biostratigraphic constraints or tephra layers) interconnected with several tables containing accessory data and metadata. By creating a centralized database of sea-level proxy data for the Last Interglacial, the WALIS database will be a valuable resource to the broader paleoclimate community to facilitate data-model integration and intercomparisons, assessments of sea-level reconstructions between different studies and different regions, as well as comparisons between past sea-level history and other paleoclimate proxy data
Last interglacial sea levels within the Gulf of Mexico and northwestern Caribbean Sea
No full textAbstract. During the last interglacial (LIG) the volume of additional water in the world's oceans was large enough to raise global sea levels about 6–9 m higher than present levels. However, LIG sea levels vary regionally and those regional differences hold clues about the past distribution of ice sheets and local rates of subsidence and tectonic uplift. In this study, I used a standardized database template to review and summarize the existing constraints on LIG sea levels across the northern Gulf of Mexico and Caribbean shoreline of the Yucatán Peninsula. In total, I extracted 32 sea-level indicators including the insertion of 16 U-series ages on corals, 1 electron spin resonance age, 2 amino acid racemization ages, and 26 luminescence ages. Most dated sea-level indicators for the northern Gulf of Mexico are based on optically stimulated luminescence (OSL) ages of beach deposits of a mappable LIG shoreline. This shoreline extends from the Florida Panhandle through south Texas but is buried or removed by the Mississippi River across most of Louisiana. A similar feature is observed in satellite images south of the Rio Grande within the Mexican portions of the Gulf of Mexico but has yet to be dated. Elevations measured on portions of this feature close to the modern coast point to sea levels less than 1 m to ∼5 m higher than present for much of the northern Gulf of Mexico. However, a few, albeit undated, portions of the same shoreline located at more inland locations point to sea levels up to +7.2 m, attesting to up to 7 m of differential subsidence between the inland and coastal sites. Across the Yucatán Peninsula, U-series dating of corals has provided the main index points for LIG sea levels. Other carbonate coastal features such as beach ridges and eolianites have also been described but rely on corals for their dating. The maximum elevation of the LIG coral-based relative sea-level (RSL) estimates decrease from around +6 m across the Caribbean shoreline of the Yucatán Peninsula near Cancún, Mexico, to as low as −6 m to the south beneath the southern atolls of Belize, although discussion continues as to the validity of the ages for these southern corals. If these lower-elevation corals are LIG in age, their below-present elevations may be a result of vertical motion along faults dipping into the Cayman Trough. South of Belize only one purported LIG coral has been dated on the Isla de Roatán off the coast of Honduras at a likely tectonically uplifted elevation of 37.2 m. Thus the elevation of LIG sea levels within the inland siliciclastic shorelines of Guatemala and Honduras as well as the southwestern Gulf of Mexico remains poorly constrained and a potential venue for future research. The database described in this paper is available open access in spreadsheet format as Simms (2020), at this link: https://doi.org/10.5281/zenodo.4556163
Introduction: An Overview of the Reign of Alexander II
No full textBook Description: This volume explores aspects of the political, social, cultural, economic and religious development of Scotland in the reign of King Alexander II (1214-49). It constitutes the first full-length, multi-author study of the king and his reign. The nine contributors to the volume explore issues as diverse as the historiography of the reign, Anglo-Scottish relations, Church-State relations, economy and international trade, law, aristocratic symbolism, urban development and the territorial expansion of the kingdom. This book, the first major study of a reign which saw the Scottish monarchy achieve its mastery of northern mainland Britain, is of great importance to historians of medieval Scotland and the wider British Isles. The book is illustrated with 24 colour and b/w photographs and 5 maps and plans. Show More Show Les
Métricas de autor Alexander Sellamén-Garzón
No full textInforme de las métricas de autor del Dr. Alexander Sellamén-Garzón de las publicaciones indexadas en Google Académico cuyo objetivo es entregar un insumo para el fortalecimiento de las capacidades y potencialidades de los autores de la Universidad Santo Tomás en el posicionamiento y visibilidad de sus publicacionesReport of the author metrics Alexander Sellamén-Garzón of the publications indexed in Google Scholar whose objective is to provide an input for the strengthening of the capacities and potentialities of the authors of the Santo Tomás University in the positioning and visibility of their publicationshttp://unidadinvestigacion.usta.edu.c
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The Late Quaternary Evolution of the Southern California Coast: Sea-Level Change, Storms, and Subsidence
Get PDFThe highly developed and populated coast of southern California is at risk for inundation due to storms or tsunamis; coastal erosion; wildfires; earthquake-driven shaking, liquefaction, and subsidence; sea-level rise; and other hazards. Estuaries formed during periods of sea-level transgressions often record environmental changes that have affected the region over time. These records of past climate, sea level, inundation events, and other changes can provide a baseline with which to compare current changes. Past recurrence intervals of hazard events also provide an estimate for how often and at what magnitude we can expect events to recur in the future. Here we compile relative sea-level indicators from other studies on southern California estuaries to show that relative sea level in southern California has risen 0.8 ± 0.3 mm/yr over the last 4000 years, less than modern rates and predicted future rates of sea-level rise. Predicted acceleration of sea-level rise could exacerbate the effects of storm and tsunami inundation along the coast. We use a variety of biological, sedimentological, and geochemical measurements on sediment cores from Carpinteria Marsh, Carpinteria, California, to document environmental changes that have occurred along the Santa Barbara Channel over the last 10,000 years. We show evidence for at least 37 episodes of alluvial fan progradation due to large floods over the past 7 ka, clusters of which correspond to regional records of wet climate conditions. We also show evidence for one coseismic subsidence event at 1.0 ± 0.1 ka, which may correlate with records of other earthquakes in the region. Finally, the topmost sediments within the marsh record environmental changes within the historical period. Within these sediments, we use a multi-proxy approach to document the history of the marsh over the last 200 years including the appearance of European pollen species, makers of industrialization, and an overwash deposit related to the 1861-2 winter storm season in California
Métricas de autor Alexander Cotte Poveda
No full textInforme de las métricas de autor del Dr. Alexander Cotte Poveda de las publicaciones indexadas en Google Académico cuyo objetivo es entregar un insumo para el fortalecimiento de las capacidades y potencialidades de los autores de la Universidad Santo Tomás en el posicionamiento y visibilidad de sus publicacionesReport of the author metrics Alexander Cotte Poveda of the publications indexed in Google Scholar whose objective is to provide an input for the strengthening of the capacities and potentialities of the authors of the Santo Tomás University in the positioning and visibility of their publications.http://unidadinvestigacion.usta.edu.c
Odoardo Fialetti (1573-c.1638): the interrelation of Venetian art and anatomy, and his importance in England
No full textBolognese artist Odoardo Fialetti (1573 – c.1638) is a fascinating figure upon which curiously little work has been done. Though he is a rarely discussed pupil of Tintoretto, Fialetti’s oeuvre is vast (some 55 known paintings and approximately 450 prints) and incredibly diverse. His work encompasses religious subjects, portraits, books on drawing and sport, maps, and illustration for treatises on city defences, literary texts, and anatomy. His work was influential for several hundred years after his death, not only in Venice and northern Italy, but also in France where his designs were used as decoration on faïence produced at Nevers, and England, where his paintings were much admired at court. Fialetti’s close association with Sir Henry Wotton, and the careful copy of his drawing book made by Alexander Browne in the mid-seventeenth century, attest to his impact on the formation of an Italianate sensibility in the appreciation of the visual arts in Early Modern England. In the realm of science, Fialetti’s influence can be deduced from his drawings of curiously animated cadavers in detailed landscapes to those of future generations of anatomists and illustrators throughout Europe. Because of the diverse associations and projects throughout his career, the study of Fialetti is inherently interdisciplinary, encompassing the history of art, history of science and history of the Venetian book trade, as well as crossing geographical boundaries in linking Venetian art and English tastes of the late renaissance and early baroque. Through examination of his extant oeuvre, as well as discussion of lost work, I aim to recognise Fialetti’s status as an artist responding to contemporary artistic debates (disegno versus colorito), a changing cultural climate and the burgeoning importance of the printed medium
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Recording Coastal Changes observed in Beach Ridges and Prograded Beach Stratigraphy using Ground-Penetrating Radar
Get PDFBeach ridges and other prograding beach deposits are important sedimentary archives of past floods, storms, and relative sea-level changes. Accurate interpretations of beach ridges requires an understanding of their formation and preservation through time. In the following studies, I use ground-penetrating radar to observe the stratigraphy of beach ridges and prograded beach deposits. Additionally, I employ the use of elevation surveys, aerial photographs, radiocarbon dating, and optically stimulated luminescence dating to understand the timing of events preserved in the sedimentary record. In Chapter 2, I explore the formation of swash bars on the Elwha River delta after the removal of two dams on the fluvial system simulated a large sediment pulse to the system, similar to a flood or landslide. I find that mouth bars form most often after higher than average discharge events in the fluvial system, and swash bars form soon after due to wave reworking of the mouth-bar sediments. However, only 10 of 37 swash bars that formed were preserved at the time of my GPR survey, five years after dam removal. Additionally, the swash bars that did survive amalgamated with one another, forming a large barrier at the delta front, indicating that in small mountainous river settings, beach ridges may be more indicative a large sediment pulse to the system, rather than a single flood. In Chapter 3, I examine the ~600-year sedimentary record of the coastal Oxnard Plain. Progradation on the Oxnard Plain has been relatively constant on centennial (150- to 200-year) timescales, prograding at rates of 0.3 to 1.4 m a-1. However, on shorter timescales, progradation is episodic, with greater progradation occurring after high discharge events along the Santa Clara River. Extended droughts remove up to 90 m of the beach, equivalent to ~5 to ~120 years of the sedimentary record. Additionally, I image beach cusps in shore parallel GPR profiles, which previously had not been recognized in GPR profiles.Lastly, in Chapter 4 I use gravel beach ridges to reconstruct the relative sea-level (RSL) record on Joinville Island, Antarctica. I find that RSL has fallen ~5 m over the last ~3000 years, at variable rates throughout the late Holocene. I interpret that ice mass loss, similar to the scale of ice mass loss after the 2002 Larsen B Ice shelf collapse, and ice mass growth caused by glacial advance, both occurred in the Late Holocene and were recorded in my RSL reconstruction. Therefore, global- and continental-scale global isostatic adjustment models, which currently only account for ice changes on thousand-year timescales, are missing crucial centennial-timescales ice mass changes
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Sea-level records and processes operating on California shelves: Past and present
No full textContinental shelves have long been conceptualized as sediment-starved, relict landscapes shaped by past sea-level fluctuations and marked by drowned coastal features. This view, however, overlooks the dynamic nature of these environments, particularly along mid-latitude transgressed margins like the central California shelf. These environments not only archive sea-level history but also host sedimentary processes that shape and maintain geomorphic features, including subaqueous clinoforms. This dissertation investigates the interplay between relative sea-level (RSL) change and shelf morphodynamics from the Late Pleistocene to the Eocene, with a particular focus on the formation, preservation, and stratigraphic architecture of subaqueous clinoforms.The study is structured around three studies that span, Holocene, Late Pleistocene and ancient geologic contexts. Chapter 2 develops a novel methodology to reconstruct post-Last Glacial Maximum (LGM) RSL along the central California shelf. Using sediment cores, high-resolution seismic data, and modern wave data, the study develops two new sea-level indicators: the Wave Ravinement Shell Hash Burial Surface (WRSHBS) and the contact between an inner shelf sand and an offshore mud. These indicators were used to produce the earliest post-LGM RSL constraints for California, extending that record back to 13.8–15.5 cal ka BP, at which time sea level was between 86 ± 8 and 99 ± 8 m below present. Additional constraints from the contact between an inner shelf sand and an offshore mud provide RSL estimates between 37 ± 7.5 and 49 ± 7.5 m below present between ~9 and ~12 ka BP. This method allows sea-level reconstructions to be extended into a period previously lacking data along much of the globe’s mid-latitude shelves.Chapter 3 documents the progradation of a Holocene sandy subaqueous clinoform along the central California shelf, known as the Cross Hosgri Slope. Sediment cores, chirp sub-bottom profiles, and radiocarbon dating reveal that clinoform initiation began shortly after sea level stabilized following the LGM, with progradation beginning between approximately 8.3 and 7.2 cal ka BP. The clinoform is not directly sourced by fluvial input, but instead by winter swell waves that remobilize shelf sands into wave-supported sediment gravity flows. These flows deposited decimeter-scale coarsening-upward sedimentary successions characterized by ripple cross-lamination and parallel lamination, which record the waxing and waning of turbulent flow transport. This chapter presents a new facies model for sandy subaqueous clinoforms formed in isolation and demonstrates that these features can accumulate in high-energy shelf settings without river-derived sediment. This study offers new criteria for identifying sandy subaqueous clinoforms and presents tools to distinguish them from lowstand shoreline deposits, helping prevent their misinterpretation in RSL and paleogeographic reconstructions.Chapter 4 shifts to an ancient example of a shelfal clinoform: a compound delta-scale clinoform preserved in the middle Eocene Cozy Dell Formation of southern California. Measured sections, facies analysis, and detrital zircon geochronology reveal a stratigraphic architecture strikingly similar to modern compound clinoforms. The subaqueousc clinoform in the informal Nordoff sandstone of the Cozy Dell formation records a progression from distal hyperpycnite beds to proximal storm-influenced foresets, while the overlying Circle B Sandstone represents the subaerial delta front. Paleocurrent indicators suggest sediment was delivered from the southeast and redistributed along and across the shelf by wave-supported and shore-parallel currents. This sandstone member represents a rare stratigraphic link between subaerial delta deposits and their subaqueous clinoform counterparts.Collectively, these studies demonstrate that subaqueous clinoforms are underrecognized in both modern and ancient records, and are frequently misinterpreted as paleoshorelines—an error that can significantly affect sea-level and paleogeographic reconstructions. This dissertation presents new tools and facies models for identifying and interpreting clinoform deposits, emphasizing their importance as active sedimentary bodies
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