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

Hydrodynamic behaviour of nummulitids

Großforaminiferen unterschiedlicher systematischer Zugehörigkeit bildeten in verschiedenen geologischen Zeiten mächtige Ablagerungen, die sich räumlich weit erstrecken. Solche Ablagerungen von Nummulites sind über einen Zeitraum von ca. 30 Millionen Jahren vom Jüngeren Paleozän bis in das Ältere Oligozän immer wieder anzutreffen. Die Interpretation der Umweltbedingungen zum Zeitpunkt dieser Ablagerungen war in den letzten 50 Jahren ein heißer Diskussionspunkt. Dies liegt teilweise in den Schwierigkeiten der Interpretation fossiler Gesteine selbst, insbesondere wenn der aktualistische Bezug durch das Fehlen rezenter vergleichbarer Organismen nicht angewendet werden kann. Ein Weg zur Klärung ist die Untersuchung der hydrodynamischen Eigenschaften von Nummuliten-Gehäusen. In den letzten 50 Jahren konnten Sedimentologen in zahlreichen Arbeiten die hydrodynamischen Eigenschaften von Sedimentkörnern erklären, insbesondere was den Transport und die Ablagerung während unterschiedlicher Wasserbewegungen (oszillatorisch oder gerichtet) sowohl im seichten als auch im tieferen Wasser betrifft. Zur selben Zeit erklärten Paläontologen die Verbreitung lebender Groß-Foraminiferen unter Verwendung komplexer statistischer Methoden. Mit diesem Datensatz ist es nun möglich, mit wenigen Kennzahlen (Parametern), die Anreicherung der fossilen Formen zu erklären. Innerhalb der Nummuliten, bei denen zahlreiche Gehäusemerkmale von Umweltbedingungen beeinflusst wurden, benötigt man nur zwei, nämlich die Gehäuseform und die Dichte, um das Abheben, die Transportweite und das Absinken zu berechnen. Zur Berechnung der beiden oben genannten Kennzahlen genügen zwei Abmessungen, nämlich der Gehäusedurchmesser und die Gehäusedicke. Nach Berechnung der hydrodynamischen Parameter wurden diese mit experimentellen Werten verglichen. Da diese Korrelation extrem signifikant ist, lassen sich die hydrodynamischen Parameter für alle Formen mit nummulitiden Gehäusen berechnen. Die Transportfähigkeit der Gehäuse konnte anhand ihrer Sinkgeschwindigkeit definiert werden: man findet Foraminiferen am häufigsten in jener Wassertiefe, wo die Wasserenergie schon zu schwach ist, um die Gehäuse abzuheben. Weil die Foraminiferen, um die Photosynthese ihrer Symbionten zu ermöglichen, so viel Licht wie möglich zu absorbieren versuchen, leben sie bevorzugt in jener kritischen Tiefe, wo einerseits das Licht noch intensiv ist, andererseits die Wasserenergie nicht zu hoch ist. Um vom Substrat nicht abgehoben zu werden, müssen die Foraminiferen Gehäuse mit bestimmten Widerstandkoeffizienten bauen. Durch die hohe Korrelation zwischen den hydrodynamischen Gehäuseparametern und der Wasserenergie, die durch die oszillatorische Wellenbewegung am Boden wirkt, lässt sich die durchschnittliche Wassertiefe, in der die Foraminiferen lebten, ermitteln. Wichtig ist jedoch, dass nicht nur die Transportfähigkeit der Gehäuse, sondern auch die Funktion von strukturellen Gehäusemerkmalen die Tiefeverteilung der einzelnen Arten charakterisieren.Larger foraminifera occurred abundantly in many Paleogene shelf carbonate platforms and were influenced by global and local factors. Ecology (e.g. temperature), geology (e.g. sea level changes) and evolution (e.g. population dynamics) affect the abundance and structure of larger foraminiferal communities. Water motion is the most important physical factor in shallow water environments directing the distribution of living individuals, and the distribution of empty shells mainly follows the input produced by water motion. The relationship between the biotic composition and the fossil association must always be taken into account for interpreting the palaeoenvironment. The shape of nummulitids and its relation with systematics on the one and water motion on the other side allows fascinating results. Concerning larger foraminifera, especially nummulitids, shape variation, size and internal structures are highly correlated with taxonomy. These parameters strongly influence the distribution of foraminiferal tests on a slope induced by water motion. Because of these correlations, estimations of palaeodepth can be based on the species distribution in the fossil environment. The calculation to obtain the hydrodynamic answer of nummulitid tests was applied to species belonging to the genera Nummulites and Assilina, as well as to some operculinids. The value of the hydrodynamic answer of a single test considers size, shape and density, and it is the combination of these variables that express the hydrodynamic behaviour of the specimen. Consequently, the diversity of forms collected within a layer is characterized by the same hydrodynamic behaviour. From a palaeoenvironmental point of view, due to sorting induced by water motion, transported tests with similar hydrodynamic behaviour are deposited in the same hydrodynamic environment. The measured and the calculated parameters allowed the definition of transport / deposition boundary and the location of accumulation areas

Growth Rate Biometric Quantification by X-ray Microtomography on Larger Benthic Foraminifera: Three-dimensional Measurements Push Nummulitids into the Fourth Dimension

This work demonstrates the potential of three-dimensional biometric quantification using microtomography on larger benthic foraminifera. We compare traditional linear and area measures used for calculating three-dimensional characters with actual 3D measurements made from volume images obtained using X-ray microtomography (microCT). Two specimens of recent larger benthic foraminifera, i.e., Palaeonummulites venosus and Operculina ammonoides, were imaged with a high-resolution microCT scanner. This method enables three-dimensional imaging and calculation of measurements like 3D distances, surfaces and volumes. The quantitative high-resolution images enabled the extraction of the lumina from the proloculus to the last complete scanned chamber and of the canal system spreading into marginal chord and septa. External surfaces and volumes were calculated on the extracted parts. These measurements allowed the calculation of porosity and microporosity to obtain the test density, which is the basis for many inferences about foraminifera, e.g., reconstructions of transport and deposition. Volume and surface measurements of the proloculus allow the calculation of sphericity deviation, which is useful for determining evolutionary trends in species based on individuals resulting from asexual reproduction (A forms). The three-dimensional data presented here show the actual growth of the foraminiferal cell and the development of the test. Measurements made on an equatorial section cannot be considered representative of a three-dimensional test, unless a correspondence between 2D data with 3D data shows significant correlation. Chamber height, septal distance, spiral growth and chamber area were measured on the equatorial section and correlated with the volume measurements from 3D images to determine the predictive value of the 1D and 2D measures for estimating the 3D morphological parameters. In particular, we show that the equatorial section area of chambers correlates significantly with the chamber volume and can be used to differentiate between nummulitid genera according to their different growth patterns. \uc2\ua9T\uc3\u9cB\uc4\ub0TAK

Chemical Controls on the Dissolution Kinetics of Calcite in Seawater

Calcium carbonate minerals are abundant on the earth’s surface. Delivery of alkalinity to the oceans is balanced by the production and burial of calcium carbonate in marine sediments, which results in a large reservoir of sedimentary calcium carbonate both in the ocean and in terrestrial rocks. Alkalinity also provides oceanic buffering capacity, which today results in about 60 times more dissolved carbon dioxide in the world oceans than is present as carbon dioxide gas in the atmosphere. Because calcium carbonate formation removes alkalinity from the oceans, calcium carbonate precipitation leads to the outgassing of carbon dioxide from the ocean into the atmosphere. Likewise, the dissolution of calcium carbonate adds alkalinity to the oceans, leading to an increased buffering capacity and a drawdown of atmospheric carbon dioxide concentration. Calcium carbonate precipitation in the form of calcite and aragonite is almost exclusively mediated by biological organisms such as corals, coccoliths, and foraminifera, which use these minerals as components in their shells. calcium carbonate is overproduced by organisms in the ocean relative to the flux of alkalinity delivered to the oceans by rivers. Thus, a significant portion of calcium carbonate must be dissolved back into seawater for the ocean alkalinity cycle to come into steady state. Because of the link between alkalinity and carbon dioxide, the ocean alkalinity cycle has a direct effect on atmospheric carbon dioxide concentration especially on timescales less than 100,000 years. How fast calcium carbonate dissolves back into seawater is thus a crucial rate in determining the response of the oceanic system to perturbations in either alkalinity or carbon dioxide input to the ocean-atmosphere system. We are testing the kinetics of this system with the large amount of carbon dioxide emitted from fossil fuel burning, about one third of which has dissolved into the surface ocean. This process is known as ocean acidification, as carbon dioxide is an acid, soaking up buffering capacity and dropping ocean pH. This carbon dioxide will eventually be neutralized through the dissolution of carbonate rich deep-sea sediments, but the process will take a long time. This thesis makes new measurements calcite dissolution in seawater, in an attempt to build an understanding of the chemical processes responsible for dissolution kinetics. I first introduce the new method, in which carbon-13 labeled calcium carbonate is dissolved in undersaturated seawater. Mass loss is directly traced by measuring the appearance of carbon-13 in seawater over time. The dissolution rate of calcite is a highly nonlinear function of calcite saturation state. Next, I show that this tracer can tell us about the balance of precipitation and dissolution at the mineral surface. I use this balance to constrain mass fluxes due to precipitation and dissolution as a function of saturation state. I also show that the enzyme Carbonic Anhydrase (CA), which rapidly equilibrates carbon dioxide and carbonic acid, greatly enhances the rate of calcite dissolution especially near equilibrium. A model of dissolution is presented in which CA is most effective in the region where dissolution proceeds via etch pit nucleation at surface defects. The dissolution behavior of biogenic carbonates is also investigated using the carbon-13 method. I cultured coccoliths, foraminifera, and soft corals in carbon-13-labeled seawater so that their skeletons incorporated the carbon-13 tracer. These skeletons were then used in dissolution experiments. I show that both magnesium and organic matter contained within the calcite lattice have large effects on the dissolution behavior of biogenic carbonates. Magnesium content generally increases dissolution rate, and it is hypothesized that highly soluble magnesium-rich phases are preferentially removed from dissolving carbonates. Organic content generally decreases dissolution rate. It is hypothesized that organic matrices within the calcite lattice promote re-precipitation reactions, due to the balance of dissolution and precipitation rates in our data, and their promotion of precipitation during biomineralization. I then analyze in 2- and 3-dimensions dissolved foraminiferal tests to locate where and how mass is being lost. It is shown that dissolution proceeds along specific layers, that are consistent with the size and location of Mg-rich carbonate spherules that are initially deposited during chamber formation. Surface topography generation of foraminiferal tests shows that sub-micron features are formed rapidly and then quickly eroded into larger pits and channels. These larger channels then propagate and cover the test surface at higher amounts of mass loss. Finally, the involvement of CA in carbonate dissolution necessitates the measurement of CA activity in the environment, especially in carbonate-rich ecosystems such as reefs, carbonate-rich sediments, and carbonate-rich marine particles. To this end, I survey a number of available techniques for measuring CA activity. In the end, it is shown that the most effective method is based on measuring the depletion of oxygen-18 from carbon-13- and oxygen-18-labeled DIC, as measured by membrane inlet mass spectrometry (MIMS). This method is promising and shows about 0.1 nM CA present in unfiltered surface seawater collected from San Pedro Basin.</p

Patterns and mechanisms of early Pliocene warmth

About five to four million years ago, in the early Pliocene epoch, Earth had a warm, temperate climate. The gradual cooling that followed led to the establishment of modern temperature patterns, possibly in response to a decrease in atmospheric CO2 concentration, of the order of 100 parts per million, towards preindustrial values. Here we synthesize the available geochemical proxy records of sea surface temperature and show that, compared with that of today, the early Pliocene climate had substantially lower meridional and zonal temperature gradients but similar maximum ocean temperatures. Using an Earth system model, we show that none of the mechanisms currently proposed to explain Pliocene warmth can simultaneously reproduce all three crucial features. We suggest that a combination of several dynamical feedbacks underestimated in the models at present, such as those related to ocean mixing and cloud albedo, may have been responsible for these climate conditions