Ontogenetic constraints on foraminiferal test construction

INTRODUCTION:It is important to understand the drivers leading to adaptive phenotypic diversity within and among species. The threespine stickleback (Gasterosteus aculeatus) has become a model system for investigating the genetic and phenotypic responses during repeated colonization of fresh waters from the original marine habitat. During the freshwater colonization process there has been a recurrent and parallel reduction in the number of lateral bone plates, making it a suitable system for studying adaptability and parallel evolution. OBJECTIVE:The aim of this study was to investigate an alternative evolutionary path of lateral plate reduction, where lateral plates are reduced in size rather than number. MATERIALS AND METHODS:A total of 72 threespine stickleback individuals from freshwater (n = 54), brackish water (n = 27) and marine water (n = 9) were analysed using microcomputed tomography (μCT) to determine variation in size, thickness and structure of the lateral plates. Furthermore, whole-body bone volume, and bone volume, bone surface and porosity of lateral plate number 4 were quantified in all specimens from each environment. RESULTS:The results showed a significant difference in plate size (area and volume) among populations, where threespine stickleback from polymorphic freshwater and brackish water populations displayed lateral plates reduced in size (area and volume) compared to marine stickleback. CONCLUSIONS:Reduction of lateral plates in threespine stickleback in fresh and brackish water occurs by both plate loss and reduction in plate size (area and volume)

Investigation into the post-mortem transport of benthic foraminifera

Palaeoenvironmental reconstruction using foraminifera relies on the assumption that assemblages reflect the ecological conditions at the time of deposition. However, the distribution of taxa can be greatly affected by transport and reworking of tests. This is particularly important in high energy environments such as submarine canyon and fan systems, which are major pathways for sediment transported from the continental shelf to the abyssal plain. Traditionally, these assemblages have been abandoned as hopelessly taphonomically corrupted, but it is possible that these assemblages contain useful hydraulic information. This project aims to develop the fundamental concepts needed to extract this information, via a series of classical particle hydraulics experiments on empty tests in static water and unidirectional currents. Hyaline foraminifera have been selected for these experiments, as they are the most abundant tests found in shelf and upper-slope environments and consequently are most likely taxa to be entrained into gravity flows.Static water experiments have shown that settling velocities are significantly different between taxa, meaning that assemblages are likely to fractionate according to species during transportation. Settling velocities range from 0.01 to 0.06 ms-1 with larger specimens falling faster than smaller ones. Elphidium crispum exhibited the fastest average settling velocity of 0.03 ms-1 while Planorbulina mediterranensis fell with the lowest average settling velocity of 0.01 ms-1. The occurrence of spatial separation of taxa within a single flow is directly tested using a flume where a spatially waning turbidity current is simulated by a saline density flow. Results show that the slowly settling tests such as P. mediterranensis and Cibicides lobatulus remain suspended in the current for longer, and are thus transported further than more rapidly settling taxa such as E. cripsum and Ammonia beccarii.The experiments have shown that there are significant statistical differences in settling velocity of foraminiferal species and this does result in significantly distinct travelling distances between species in a turbidite. This information is related to the oceanic environment in the Gulf of Cadiz. The signal of fractionation is then identified in core data from Trinidad supplied by Ichron showing that useful assemblage data can be extracted to interpret the depositional environment

Investigation into the post-mortem transport of benthic foraminifera

Palaeoenvironmental reconstruction using foraminifera relies on the assumption that assemblages reflect the ecological conditions at the time of deposition. However, the distribution of taxa can be greatly affected by transport and reworking of tests. This is particularly important in high energy environments such as submarine canyon and fan systems, which are major pathways for sediment transported from the continental shelf to the abyssal plain. Traditionally, these assemblages have been abandoned as hopelessly taphonomically corrupted, but it is possible that these assemblages contain useful hydraulic information. This project aims to develop the fundamental concepts needed to extract this information, via a series of classical particle hydraulics experiments on empty tests in static water and unidirectional currents. Hyaline foraminifera have been selected for these experiments, as they are the most abundant tests found in shelf and upper-slope environments and consequently are most likely taxa to be entrained into gravity flows. Static water experiments have shown that settling velocities are significantly different between taxa, meaning that assemblages are likely to fractionate according to species during transportation. Settling velocities range from 0.01 to 0.06 ms-1 with larger specimens falling faster than smaller ones. Elphidium crispum exhibited the fastest average settling velocity of 0.03 ms-1 while Planorbulina mediterranensis fell with the lowest average settling velocity of 0.01 ms-1. The occurrence of spatial separation of taxa within a single flow is directly tested using a flume where a spatially waning turbidity current is simulated by a saline density flow. Results show that the slowly settling tests such as P. mediterranensis and Cibicides lobatulus remain suspended in the current for longer, and are thus transported further than more rapidly settling taxa such as E. cripsum and Ammonia beccarii. The experiments have shown that there are significant statistical differences in settling velocity of foraminiferal species and this does result in significantly distinct travelling distances between species in a turbidite. This information is related to the oceanic environment in the Gulf of Cadiz. The signal of fractionation is then identified in core data from Trinidad supplied by Ichron showing that useful assemblage data can be extracted to interpret the depositional environment

The past : a compass for future earth

Antarctic sea ice impacts on the ocean-atmosphere heat and gas fluxes, the formation of deep and intermediate waters, the nutrient distribution and primary productivity, the so-called &#8216;biological carbon pump&#8217;, one of the most active in the global ocean. In this study, we explore the link between sea ice dynamic, biological production and nutrient cycling during the late Holocene (the last 2,000 yrs) in the Adélie Basin, East Antarctica, from the well-dated sediments of the Ocean Drilling Program (ODP) Site U1357. This archive, composed from ~32 meters of seasonal to annual laminated diatomaceous sequences, allows reconstructions at an unprecedented time resolution (5-10 yrs). Our study combines records of diatom census counts and diatom-specific biomarkers (a ratio (D/T) of di- and tri-unsaturated Highly Branched Isoprenoid lipids (HBI)) as indicators of sea ice and biological production changes, XRF data as markers for terrigenous inputs and bulk nitrogen isotopes (d15N) and d15N on chlorins as proxies for reconstructing nitrogen cycle. The diatom and HBI records reveal five distinct periods. From 0 to 350 yrs AD, decreasing occurrences of sea ice-related diatom species (e.g. Fragilariopsis curta + F. cylindrus) together with low D/T values and increasing open ocean diatom species (large centrics, Chaetoceros Resting Spores (CRS)) document a progressive decline of sea ice presence during the year (>9 months per year) with spring melting occurring earlier in the year and autumn sea ice formation appearing later. In contrast, between 350 and 750 yrs AD, high production of open ocean diatom species and low low D/T values and sea ice related species indicate a short duration of sea ice cover (~10 months per year) is illustrated by a pronounced increase of sea ice-associated diatom species and high D/T values. Between ~1400 and 1850 yrs AD, seasonal sea ice strongly declines (<~7 months per year) as a result of early spring melting (increasing CRS production) and late autumn waxing (high occurrences of Thalassiosira antarctica). Longer growing seasons promoted a substantial development of phytoplankton communities (especially large centric diatoms) that conducted to lower D/T values. Consistent with diatom and HBI reconstructions, XRF data show higher Fe/Al and Zr/Al ratios values during inferred warmer periods and lower ratio values during inferred cooler and icier periods, thus supporting a strong impact of the sea ice seasonal cycle on glacial runoffs. The link between sea ice conditions, biological production and nutrient cycling is still being explored and we will discuss its relationship by combining all the cited records cited above with the d15N records that we are currently generated. Based on our results, we find that sea ice dynamic and associated diatom production in the Adélie Basin revealed an opposite climatic trend than that identified in the Northern Hemisphere for the last 2000 years. The 'Little Ice Age' (1400-1850 yrs AD) or the 'Dark Ages' (400-750 yrs AD) corresponded to warmer climate conditions in the Adélie Basin, while the 'Roman Warm Period' (0-350 yrs AD) or the 'Medieval Warm Period' (900-1200 yrs AD) were associated to colder conditions. We therefore emphasize that Northern and Southern Hemisphere climate evolved in anti-phase seesaw pattern during the late Holocene

Development of high-resolution 3D geological subsurface models based on airborne electromagnetic data : case studies from the Cuxhaven tunnel valley and the Lutter anticline, northern Germany

Airborne electromagnetics (AEM) is an efficient technique for geophysical investigations of the shallow subsurface and has successfully been applied in various geological settings to analyse the depositional architecture for groundwater and environmental purposes. However, interpretation of AEM data is often restricted to 1D inversion results imaged on 2D resistivity maps and vertical resistivity sections. The integration of geophysical data based on AEM surveys, with geological data is often missing and consequently this deficiency leads to uncertainties in the interpretation process. The aim of this thesis is to provide an improved methodology for the geological interpretation of AEM data and the construction of more realistic 3D subsurface models. This is achieved by the development of integrated workflows and 3D modelling approaches in the Paradigm® GOCAD software, based on the combination of different geophysical and geological datasets (airborne electromagnetic data (AEM), depth maps from the digital Geotectonic Atlas of Northwestern Germany and the German North Sea, 2D reflection seismic sections and well logs). The results of 1D AEM inversion were geostatistical analysed and interpolated in a 3D resistivity gridding procedure to create continuous 3D resistivity grids of the subsurface. Subsequently, geological interpretations have been performed by combining with, and validating against geological depth maps, borehole and reflection seismic data and high-quality topographic maps. For the research, two test sites with different geological settings were chosen. The primary aim of the first study area near Cuxhaven, northwest Germany, was to test the 3D resistivity gridding procedure for unconsolidated rock, where Neogene sediments are incised by a Pleistocene tunnel valley. The 3D resistivity grids clearly allow to distinguish between different lithologies and enabling the detection of major bounding surfaces and architectural elements. The Neogene succession is subdivided by four unconformities and consists of fine-grained shelf to marginal marine deposits. At the end of the Miocene, an incised valley was formed and filled with Pliocene delta deposits, probably indicating a paleo-course of the River Weser. The Middle Pleistocene (Elsterian) tunnel valley is up to 350 m deep, 0.8-2 km wide, and incised into the Neogene succession. The unconsolidated fill of the Late Miocene to Pliocene incised valley probably formed a preferred pathway for the Pleistocene meltwater flows, thus favouring the incision. Based on the 3D AEM resistivity models the tunnel valley fill could be imaged in high detail. It consists of a complex sedimentary succession with alternating fine- and coarse-grained Elsterian meltwater deposits, overlain by glaciolacustrine (Lauenburg Clay Complex) and marine Holsteinian interglacial deposits. The applied approaches and results show a reliable methodology, especially for future investigations of similar geological settings. The aim of the second case study was to test a method for the predictive mapping of rock types and fracture orientations in sedimentary rocks using a trend analysis of 3D resistivity pattern based on airborne electromagnetic high-resolution data. For areas with limited exposure, the airborne geophysical data approach is an important method for both, regional-scale geological mapping and local structural analysis. The method was tested in the area of the Lutter anticline structure in the northwestern Harz foreland, Germany. The developed 3D resistivity grid of this salt-cored anticline was used to map resistivity trends that are related to lateral and vertical changes in lithology, water content, anticline geometry, and the location of fractures. The 3D resistivity grid clearly allows to distinguish between rocks of Palaeozoic and Mesozoic rocks. Lineation patterns obtained from a curvature trend analysis based on the 3D resistivity grid reflect the orientation of the local fault and fracture systems. The comparison of the resistivity pattern and the trend of fractures and faults, derived from outcrop analyses, shows promising results, which imply that AEM data can allow the detection and visualization of near-surface, brittle, structural elements developed in sedimentary rocks. This opens the door to use AEM as an efficient tool for regional structural mapping.Die Aeroelektromagnetik (AEM) ist eine effiziente Methode für geophysikalische Untersuchungen im Bereich des oberflächennahen Untergrundes und wurde erfolgreich in verschiedenen geologischen Räumen getestet, um u. a. die Ablagerungsarchitektur des Untergrundes hinsichtlich grundwasserwirtschaftlicher Fragestellungen zu untersuchen. Jedoch ist die Interpretation der AEM-Daten oftmals auf 1D Inversionsergebnisse begrenzt, die anhand von 2D Widerstandskarten und Profilschnitten dargestellt werden. Die Integration der durch die Aeroelektromagnetik gewonnenen geophysikalischen Daten mit geologischen Daten fehlt oftmals und führt zu Unsicherheiten in der Interpretation. Das Ziel der vorliegenden Arbeit ist es eine verbesserte Methode für die geologische Interpretation von AEM Daten zur Erstellung von möglichst wirklichkeitsgetreuen 3D Untergrundmodellen bereitzustellen. Die Methodik basiert auf der Entwicklung integrierter Arbeitsabläufe und 3D Modellierungsansätzen mit Hilfe der Modellierungssoftware GOCAD® von Paradigm und beruht auf der Kombination verschiedener geophysikalischer und geologischer Datensätze (Aeroelektromagnetik, Karten des Geotektonischen Atlas 3D, 2D reflektionsseismische Profile und Bohrdaten). Anhand der geostatistischen Analyse und Interpolation bestehender aeroelektromagnetischer 1D Inversionsergebnisse wurden 3D Widerstandsmodelle des Untergrundes erstellt. Diese wurden anschließend durch Integration geologischer Kartenwerke, Bohrdaten, seismischer Profile und hochauflösender topographischer Karten geologisch interpretiert. Für die Untersuchungen wurden zwei Testgebiete mit unterschiedlichem geologischem Untergrund gewählt. Das Ziel des ersten Untersuchungsgebietes im Nordwesten Deutschlands, in der Nähe von Cuxhaven, lag darin die Methodik zur Entwicklung der aus Gitterzellen aufgebauten 3D Widerstandsmodelle an Lockersedimenten im Bereich einer in neogene Ablagerungen eingeschnittenen pleistozänen subglazialen Rinne zu testen. Die 3D Widerstandsmodelle ermöglichen eine genaue Unterscheidung der verschiedenen Lithologien und ermöglichen die Abgrenzung sedimentärer Architekturelemente. Die neogene Abfolge besteht aus feinkörnigen marinen Schelf- und Küstenablagerungen und gliedert sich durch vier Diskordanzen. Hinweise auf den früheren Verlauf der Weser gibt es im oberen Miozän in Form einer erosiven Rinnenstruktur, die im Pliozän mit deltaischen Sedimenten gefüllt wurde. Die im Mittelpleistozän gebildete subglaziale Rinne (Elster-Eiszeit) schneidet sich bis zu 350 m tief in die neogenen Sedimente ein und ist zwischen 0,8 bis 2 km breit. Die mit Lockersedimenten gefüllte spätmiozäne Rinnenstruktur stellte wahrscheinlich einen bevorzugten Fließweg für die pleistozänen subglazialen Schmelzwässer dar und begünstigte das erosive Einschneiden. Mit Hilfe der 3D Widerstandsmodelle konnte die Rinnenfüllung detailliert dargestellt werden. Sie besteht aus einer komplex aufgebauten sedimentären Abfolge alternierender fein- bis grobkörniger elsterzeitlicher Sedimente, die von glazilakustrinen Sedimenten des Lauenburger Ton Komplexes und marinen Sedimenten des Holstein-Interglazials überlagert werden. Die durchgeführten Untersuchungen und Ergebnisse zeigen eine zuverlässige Methode, die für zukünftige Untersuchungen ähnlicher geologischer Räume angewendet werden kann. Im zweiten Untersuchungsraum ging es um die Erprobung einer Methode zur Bestimmung vorherrschender Gesteinstypen, Störungs- und Kluftsysteme unter Anwendung von Trendanalysen dreidimensionaler Widerstandsmuster, die auf hochauflösenden aeroelektromagnetischen Befliegungsdaten basieren. In Gebieten mit begrenzter Aufschlussanzahl liefern aerogeophysikalische Messungen entscheidende gesteinsspezifische Daten zur Interpretation der regionalen und lokalen geologischen Untergrundverhältnisse. Die Methode wurde anhand eines Gebietes in Deutschland im Bereich des Harzvorlandes, dem Lutter Sattel, getestet. Anhand des erstellten dreidimensionalen Widerstandsmodells dieser auf Salztektonik zurückzuführenden Sattelstruktur konnten laterale und vertikale Änderungen in den lithologischen Einheiten, im Wassergehalt und in der Geometrie der Sattelstruktur sowie Störungszonen identifiziert und kartiert werden. Das erstellte dreidimensionale Widerstandmodell der Sattelstruktur ermöglicht eine Unterscheidung der aufgestellten paläozoischen und mesozoischen Gesteine. Am elektrischen Widerstandsmodell angewendete Kurvenanalysen zeigen Trendmuster, die mit aus Aufschlüssen bekannten Störungs- und Kluftsystemen übereinstimmen. Der Vergleich zwischen Trendmustern des Widerstandsmodells mit den lokalen, in Aufschlüssen gemessenen Störungs- und Kluftsystemen zeigt vielversprechende Ergebnisse, die darauf hinweisen, dass aeroelektromagnetische Daten zur Identifizierung von Störungssystemen oberflächennah anstehender Sedimentgesteine geeignet sind. Demnach bieten aeroelektromagnetische Daten das Potential für eine direkte strukturanalytische Anwendung

Abstracts of manuscripts submitted in 1993 for publication

This volume contains the abstracts of manuscripts submitted for publication during calendar year 1993 by the staff and students of the Woods Hole Oceanographic Institution. We identify the journal of those manuscripts which are in press or have been published. The volume is intended to be informative, but not a bibliography. The abstracts are listed by title in the Table of Contents and ar grouped into one of our five departents, Marine Policy Center, Coastal Research Center, or the student category. An author index is presented in the back to facilitate locating specific papers