Impact Of Dissolution Research Articles

Impact of dissolution and precipitation on pore structure in CO2 sequestration within tight sandstone reservoirs

Complex physical and chemical reactions during CO2 sequestration alter the microscopic pore structure of geological formations, impacting sequestration stability. To investigate CO2 sequestration dynamics, comprehensive physical simulation experiments were conducted under varied pressures, coupled with assessments of changes in mineral composition, ion concentrations, pore morphology, permeability, and sequestration capacity before and after experimentation. Simultaneously, a method using NMR T2 spectra changes to measure pore volume shift and estimate CO2 sequestration is introduced. It quantifies CO2 needed for mineralization of soluble minerals. However, when CO2 dissolves in crude oil, the precipitation of asphaltene compounds impairs both seepage and storage capacities. Notably, the impact of dissolution and precipitation is closely associated with storage pressure, with a particularly pronounced influence on smaller pores. As pressure levels rise, the magnitude of pore alterations progressively increases. At a pressure threshold of 25 MPa, the rate of change in small pores due to dissolution reaches a maximum of 39.14%, while precipitation results in a change rate of −58.05% for small pores. The observed formation of dissolution pores and micro-cracks during dissolution, coupled with asphaltene precipitation, provides crucial insights for establishing CO2 sequestration parameters and optimizing strategies in low permeability reservoirs.

Micro-mechanisms and modelling of the corrosion fatigue behaviour of a maraging steel

This paper addresses the uniaxial corrosion fatigue behaviour of a maraging steel in a 5 g/L NaCl solution at 25 °C. SEM detailed observations evidenced a strong coupling between localized corrosion and the cyclic loading at the early stage of pitting and fatigue crack growth. As the crack is growing, the impact of dissolution is decreasing. A predictive corrosion fatigue model was proposed based on three stages: pit nucleation and growth, pit/crack competition and crack growth. The main contributions of the corrosive environment to failure mechanisms were found highly dependent on the mechanical loading conditions: cyclic loading and loading frequency.

The Impact of Dissolution on Partnership Contracts: NHBC v Gavin Henderson Joiner and Building Contractors and ors

The Impact of Dissolution on Partnership Contracts: <i>NHBC v Gavin Henderson Joiner and Building Contractors and ors</i>

Element Desorption from and Crystal Dissolution of a Smectite by Interaction with the Bacteria Escherichia coli and/or Varied Amino Acids

Three-week experiments were completed to evaluate the interaction of the bacteria Escherichia coli and amino acids (glutamic acid, alanine, arginine, serine and leucine) on the dissolution and/or desorption rates of a smectite-type clay mineral. A systematic dominant leaching of Na confirms that the initial smectite was Na-enriched. The bacteria Escherichia coli induced leaching of a Si/Al ratio far from that released by either the amino acids or by a combination of the bacteria and amino acids. Conversely, this ratio is close to the value of the smectite itself. Therefore, the bacteria has a probable dissolution impact rather than a desorption action. This preferential action is indirectly corroborated by a low removal of Na by the bacteria. Removal impact of the bacteria on the smectite decreased when mixed with any of the amino acid. The highest releases of Si, Al, Mn and Fe characterize batches without amino acids, while most released Ca and K occurred with the amino acids. Potassium, P, Mg, Na and Ca are more released into solutions containing several amino acids, while Fe is preferentially leached by solutions with only one amino acid. This study highlights also the potential roles of amino acids in soils and other surficial geological systems. The distribution patterns of the leached rare-earth elements (REEs) confirm a clear distinction between the impact of the bacteria that produces a progressively decreasing contents of the light REEs and a flat distribution for the heavy REEs and those, more variable, of the amino acids. The impact of the amino acids influences the REE distributions, probably along complexation processes due to strong metal sorption on oxides by organic complexes.

The Impact of Mineral Dissolution on Drainage Relative Permeability and Residual Trapping in Two Carbonate Rocks

Carbon dioxide injection into deep saline aquifers is governed by a number of physico-chemical processes including mineral dissolution and precipitation, multiphase fluid flow, and capillary trapping. These processes can be coupled; however, the impact of fluid–rock reaction on the multiphase flow properties is difficult to study and is not simply correlated with variations in porosity. We observed the impact of rock mineral dissolution on multiphase flow properties in two carbonate rocks with distinct pore structures. Observations of steady-state hbox {N}_2–water relative permeability and residual trapping were obtained, along with mercury injection capillary pressure characteristics. These tests alternated with eight stages in which 0.5% of the mineral volume was uniformly dissolved into solution from the rock cores using an aqueous solution with a temperature-controlled acid. Variations in the multiphase flow properties did not relate simply to changes in porosity, but corresponded to the changes in the underlying pore structure. In the Ketton carbonate, dissolution resulted in an increase in the fraction of pore volume made up by the smallest pores and a decrease in the fraction made up by the largest pores. This resulted in an increase in the relative permeability to the nonwetting phase, a decrease in the relative permeability to the wetting phase, and a modest, but systematic decrease in residual trapping. In the Estaillades carbonate, dissolution resulted in an increase in the fraction of pore volume made up by pores in the central range of the initial pore size distribution, and a corresponding decrease in the fraction made up by both the smallest and largest pores. This resulted in a decrease in the relative permeability to both the wetting and nonwetting fluid phases and no discernible impact on the residual trapping. In summary, the impact of rock matrix dissolution will be strongly dependent on the impact of that dissolution on the underlying pore structure of the rock. However, if the variation in pore structure can be observed or estimated with modelling, then it should be possible to estimate the impacts on multiphase flow properties.

Impact of dispersants on dissolution of itraconazole from drug-loaded, surfactant-free, spray-dried nanocomposites

Dissolution of poorly soluble drugs can be improved by wet-milling their suspensions and drying the suspensions to form nanocomposites. Different classes of dispersants and their concentration can affect both nanoparticle aggregation in the suspensions and drug dissolution from the nanocomposites. In this study, we examine the impact of various classes of dispersants on nanoparticle aggregation–dissolution of itraconazole (ITZ) from spray-dried wet-milled ITZ nanosuspensions. 2.5% hydroxypropyl cellulose (HPC), 0.2% sodium dodecyl sulfate (SDS), and their combination were used as baseline dispersant formulations. Mannitol and sucrose, as model water-soluble dispersants, were added to the wet-milled ITZ suspensions with HPC. As swellable dispersants, superdisintegrants such as sodium starch glycolate (SSG), crospovidone (CP), and croscarmellose sodium (CCS) were wet-co-milled with ITZ–HPC. The wet-milled suspensions were spray-dried to prepare nanocomposites. Laser diffraction results show that wet milling with HPC–SDS and HPC with concentration at/above 4.5% led to a median drug size below ~0.20 μm due to electrosteric and steric stabilizing effects, respectively. Their nanocomposites led to immediate, fast ITZ release: >%80 dissolved in 20 min. Unlike these suspensions, other suspensions with mannitol, sucrose, and superdisintegrants along with HPC exhibited more aggregation and pseudoplasticity. Nonetheless, the addition of these dispersants resulted in faster drug release especially at higher concentrations, as quantified by the higher value of the product kn of the Korsmeyer–Peppas model, due to faster erosion/disintegration of the nanocomposite matrix. Wet co-milled superdisintegrants achieved faster drug release than mannitol and sucrose. Their dissolution impact was positively correlated with their swelling capacity (SSG > CCS > CP), which signifies a swelling-induced erosion/disintegration mechanism. Surfactant-free nanocomposites with >60% drug loading that exhibited immediate drug release were prepared with either HPC–co-milled SSG/CCS or HPC with optimal concentration.

Effect of crystallization on dissolution and biocompatibility of bioactive scaffolds

Event Abstract Back to Event Effect of crystallization on dissolution and biocompatibility of bioactive scaffolds Virginia Melli1, Elena Boccardi1, 2, Elena Canciani3, Andrea Cochis3, Elena Varoni3, Luigi De Nardo1, Stéphanie Grenier4, Lia Rimondini5, Lina Altomare1 and Louis-Philippe Lefebvre4 1 Politecnico di Milano, Dipartimento di Chimica, Materiali e Ingegneria Chimica "Giulio Natta", Italy 2 University of Erlangen-Nuremberg, Institute of Biomaterials, Germany 3 Università degli studi di Milano, Clinica Odontoiatrica A.O. San Paolo, Italy 4 National Research Council Canada, Medical Device, Canada 5 Università del Piemonte Orientale Amedeo Avogadro, Italy Introduction: Numerous approaches have been proposed to manufacture porous bioactive glass scaffolds for load bearing applications, often resulting in inadequate compressive strengths[1]. To obtain suitable mechanical properties, the consolidation of the scaffolds often requires a thermal treatment that results in a fine dispersion of crystalline phases within a glassy matrix. This study provides a better understanding of the effects of crystallization on dissolution and biocompatibility. Materials and Methods: Bioglass foams (24.5Na2O-24.5CaO-6P2O5-45SiO2 wt%) were fabricated using a powder technology process consisting of mixing powders (i.e. bioglass powder, polymeric binder and foaming agent), molding the powder blend followed by foaming, debinding and sintering[2]. Foams were characterized before and after dissolution using scanning electron microscopy, micro-computed tomography, uniaxial compression, inner gas fusion (i.e. chemical composition), weight and density measurements, ion release and x-ray diffraction. To evaluate dissolution kinetics and impact of dissolution on the structure and properties, foams were immersed in simulated body fluid (SBF) or deionized water (DW) for a period up to 28 days. To assess in vivo response, samples were implanted percutaneously in a murine model for 6 weeks. Results and Discussion: The scaffolds showed an open network of porosity (fig.1). Depending on the powder formulation and processing conditions, porosities ranging from 55 to 77% and pore sizes between 100-500 µm were obtained, as required for bone ingrowth. The material specific surface area averages 45 mm2/mm3 (measured by image analysis on µCT reconstruction) and provides large surface for cells proliferation. After sintering, crystalline structures identified as combeite and rhenanite were observed. The binder and foaming agent decomposed well and leaves low amount of residues as measured by inert gas fusion (carbon and sulfur concentration under 0.03 and 0.05% respectively). Compressive strengths varied from 5-40 MPa depending on porosity. Immersion in SBF caused immediate Na and Si ion release and the formation of a Ca-P coating within 2 days. Crystalline peaks on XRD patterns disappeared over time suggesting amorphization of the base material and solubility of the crystalline phases. Compressive strengths decreased mostly due to the dissolution of the material but foams retained structural integrity even after 28 days of immersion. Sample weight significantly decreased in the first 2 weeks and stabilized thereafter. Immersion in DW revealed that the crystalline and amorphous phases dissolve with different kinetics but produced a constant weight loss rate. Percutaneous implantation in a murine model showed good tissue ingrowth, vascularization and the absence of inflammatory response (fig.2). Fig. 1. Scanning electron micrograph of bioactive glass foam prior to dissolution, scale bar = 500 µm with embedded 2D section extracted from µCT reconstruction. Fig. 2. Percutaneous implantation in a murine model showed absence of inflammatory response, good tissue ingrowth and vascularization and after 6 weeks (coloration: blue of Toluene and Pironina G). Conclusion: Crystallization did not inhibit Bioglass foam dissolution and bioactivity was confirmed by the deposition of a Ca-P rich layer. Despite 28 days of immersion in SBF, the compressive strength of partially dissolved foams was comparable to cancellous bone values and remained higher than values reported on pristine scaffolds prepared by sol-gel foaming or replica techniques using polyurethane foam as sacrificial template. The proposed technology shows great promise for bone regeneration applications.

Determining the Gender of Nano-Fossils in the Lower Part of the Abtalkh Formation (150 M Primary)

A structural zone of Dagh Kopet as sediment (Trough) has created in the late Triassic. There are two different views of Dagh Kopet zone: A) Eurasian theory; B) Gondwana theory. The main fault zones are divided into two groups of foundation faults and overthrust. Abtalkh formation is one of the most important Late Cretaceous rock units in the Kopet Dagh sediment Basin and the geographic location of the study area is "03'43°37 north latitude and "47'35°55 the east. The calcareous nannoplanktons are the first links in the food chain and are the main producers in the seas and oceans. The calcareous Nannoplankton is found in fine sediments such as shale and marl and for study and examination; the presence of trace amounts of sample is enough. The calcareous Lannoplankton is used to identify and introduce Nannofossils of Abtalkh in the bottom of the cut, to determine biozones available at the cutting zone and comparing it with the world standard, to determine their age. In the study section, Nannofossil is in glauconitic sandstone, conglomerate, siltstone, marl, shale, limestone, clay, marl and clay marl and Chuck. Their small size makes that a very small amount of samples are sufficient for the study. The most important method for sample preparation in this study is a smear slide method. In laboratory studies and identification of Nannofossil and counting them, the optical microscope and the object lens 50* and 100* are used. To take pictures of samples, 100× objective lens and digital camera were used. In the course of this study, for the lower part of Abtalkh, Aytamir cutting was studied and 12 genera were identified. The calcareous Nannofossils were recognized and have relatively good diversity and abundance. In general, the greater thickness of the study samples had an average preservation. In some cases, the impact of dissolution was so great that the wall or part of the main sections of the species was corroded.

An experiment to assess the effects of diatom dissolution on oxygen isotope ratios.

Current studies which use the oxygen isotope composition from diatom silica (δ(18) Odiatom ) as a palaeoclimate proxy assume that the δ(18) Odiatom value reflects the isotopic composition of the water in which the diatom formed. However, diatoms dissolve post mortem, preferentially losing less silicified structures in the water column and during/after burial into sediments. The impact of dissolution on δ(18) Odiatom values and potential misinterpretation of the palaeoclimate record are evaluated. Diatom frustules covering a range of ages (6 samples from the Miocene to the Holocene), environments and species were exposed to a weak alkaline solution for 48 days at two temperatures (20 °C and 4 °C), mimicking natural dissolution post mucilage removal. Following treatment, dissolution was assessed using scanning electron microscope images and a qualitative diatom dissolution index. The diatoms were subsequently analysed for their δ(18) O values using step-wise fluorination and isotope ratio mass spectrometry. Variable levels of diatom dissolution were observed between the six samples; in all cases higher temperatures resulted in more frustule degradation. Dissolution was most evident in younger samples, probably as a result of the more porous nature of the silica. The degree of diatom dissolution does not directly equate to changes in the isotope ratios; the δ(18) Odiatom value was, however, lower after dissolution, but in only half the samples was this reduction outside the analytical error (2σ analytical error = 0.46‰). We have shown that dissolution can have a small negative impact on δ(18) Odiatom values, causing reductions of up to 0.59‰ beyond analytical error (0.46‰) at natural environmental temperatures. These findings need to be considered in palaeoenvironmental reconstructions using δ(18) Odiatom values, especially when interpreting variations in these values of <1‰.

A simulator for modeling of porosity and permeability changes in near field sedimentary host rocks for nuclear waste under climate change influences

A new simulation tool is developed to model coupled thermo-hydro-mechanical-geochemical (THM-GeoC) processes that would occur in the near field of deep geological repositories (DGRs) for nuclear wastes, and their impacts on the evolution of the rock porosity and permeability. First, a coupled thermo-hydro-mechanical-chemical (THMC) model, in which, the chemical (C) process is limited to solute transport, is developed and then implemented into COMSOL Multiphysics finite element code. Then, two types of numerical software are coupled; the first is COMSOL Multiphysics code and the second is the PHREEQC geochemical code. The coupling of the two types of software is performed by developing a special code that has been written by using MATLAB. COMSOL Multiphysics is used to solve the coupled THMC processes (the C process is limited to solute transport) and PHREEQC is used to solve the geochemical reactions resultant of the transport of chemical species. Simulation results obtained by using the THM-GeoC simulator are compared with experimental data and data from modeling reactive transport, with good agreement in the results. The developed simulator is applied to investigate the coupled effect of climate changes and water enriched with carbon dioxide gas, which would be generated from low and intermediate nuclear wastes, on the dissolution of the limestone host rock in Ontario (Canada) for nuclear wastes, and porosity and permeability changes within the near field rock. The results show that the maximum change in porosity is approximately 3.5%, with a gradual decrease to approximately zero. The zone affected by the dissolution process is mainly located on the first 10m within the host rock and does not cause a significant increase in permeability. From safety and environmental assessment perspectives, the impact of dissolution is not significant. However, parametric studies and experimental investigations need to be implemented to support the predicted results.

Impact of dissolution on the uncertainty of spent fuel analysis

One of the objectives of the French Alternative Energies and Atomic Energy Commission in the Marcoule Centre is to accurately quantify the composition of nuclear spent fuel, i.e. to determine the concentration of each isotope with suitable measurement uncertainty. These analysis results are essential for the validation of calculation codes used for the simulation of fuel behaviour in nuclear reactors and for nuclear matter accountancy. The different experimental steps are first the reception of a piece of spent fuel rod at the laboratory of dissolution studies, and then dissolution in a hot cell of a sample of the spent fuel rod received. Several steps are necessary to obtain a complete dissolution. Taking into account these process steps, and not only those of analysis for the evaluation of measurement uncertainties, is new, and is described in this paper. The uncertainty estimation incorporating the process has been developed following the approach proposed by the Guide to the Expression of Uncertainty in Measurement (GUM). The mathematical model of measurement was established by examining the dissolution process step by step. The law of propagation of uncertainty was applied to this model. A point by point examination of each step of the process permitted the identification of all sources of uncertainties considered in this propagation for each input variable. The measurement process presented involves the process and the analysis. The contents of this document show the importance of taking the process into account in order to give a more reliable uncertainty assessment to the result of a concentration or isotope ratio of two isotopes in spent fuel.

Redevelopment in California: Its Past, Present and Possible Future

DOI 10.1515/cjpp-2012-0044 Calif. J. Politics Policy 2014; 6(4): 471–506 Stewart Black* Redevelopment in California: Its Past, Present and Possible Future Abstract: On February 1 2012, in a remarkable development, California’s 400 redevelopment agencies were dissolved. This article (1) traces the agencies’ evo- lution and the wider 67-year history of redevelopment in California; makes com- parisons with other states’ use of redevelopment and tax increment finance to support redevelopment; assesses the position immediately prior to dissolution of the agencies; examines the meaning of the actions leading to dissolution; and considers the immediate impact of dissolution (Part 1). (2) Draws some conclu- sions about the recent model for redevelopment; and provides a detailed dis- cussion of how the model might be improved in the event of a future revival of redevelopment – in particular by addressing known past problems relating to clarifying policy outcomes, inter-governmental partisanship, measuring success, improving reporting and accountability, and improving responsibilities for these activities at state and local levels (Part 2). Keywords: California; redevelopment. *Corresponding author: Stewart Black, e-mail: stewart@stewartblack.com 1 Part One: Redevelopment’s Past and Present 1.1 R edevelopment in California: A Brief Summary of its Purpose, History, and Funding Redevelopment occurs where there are improvements made to land or property in localities within municipal areas. All redevelopment activity relates to the central concept of “blight” – that is, localities which have become run-down in terms of their physical and economic health, yet can be revived. The original focus of blight was dilapidation, and its association with slums. However, over the decades, in California as well as other states, the focus has shifted to addressing the problem of property which has declined in value or alternatively whose use value is significantly short of what is possible. In turn, redevelopment is based on the twin recognition that private enter- prise alone has not in the past always accomplished, and cannot always in future

Multiphase compositional modelling of CO2 injection under subcritical conditions: The impact of dissolution and phase transitions between liquid and gaseous CO2 on reservoir temperature

Modelling of CO2–H2O mixture flows in a porous media under subcritical conditions remains a challenging issue for carbon sequestration and possible leakage scenarios. Currently, there is no widely used and generally accepted numerical model that can simulate three-phase flows with both gaseous and liquid CO2-rich phases. We propose a new compositional modelling approach for sub- and supercritical three-phase flows of water, liquid CO2 and gaseous CO2. The new approach is based on the calculation of the thermodynamic potential of the mixture as a function of pressure, total enthalpy and mixture composition and storing it values as a spline table, which is then used for the hydrodynamic simulation. A three-parametric generalisation of the Peng–Robinson equation of state is used to fit the experimental data on CO2–H2O mixture properties.Using the approach developed in this paper, we assess several sample problems of CO2 injection in shallow reservoirs for the purpose of testing the model. We provide the simulation results for a simple 1D problem with a homogeneous reservoir and for a more complicated 2D problem with a highly heterogeneous reservoir using data from the 10th SPE comparative project reservoir. We analyse the temperature variations in the reservoir due to the dissolution of CO2 in water and the evaporation of liquid CO2. The interplay of these processes results in a complicated non-monotonic temperature distribution. At different distances from the CO2 injection point, the temperature can either decrease or increase with respect to the reservoir temperature before injection. The main phenomenon responsible for the considerable temperature decline around the CO2 injection point is the liquid CO2 evaporation process.

CO2 migration in saline aquifers. Part 1. Capillary trapping under slope and groundwater flow

Injection of carbon dioxide (CO2) into geological formations is widely regarded as a promising tool for reducing global atmospheric CO2 emissions. To evaluate injection scenarios, estimate reservoir capacity and assess leakage risks, an accurate understanding of the subsurface spreading and migration of the plume of mobile CO2 is essential. Here, we present a complete solution to a theoretical model for the subsurface migration of a plume of CO2 due to natural groundwater flow and aquifer slope, and subject to residual trapping. The results show that the interplay of these effects leads to non-trivial behaviour in terms of trapping efficiency. The analytical nature of the solution offers insight into the physics of CO2 migration, and allows for rapid, basin-specific capacity estimation. We use the solution to explore the parameter space via the storage efficiency, a macroscopic measure of plume migration. In a future study, we shall incorporate CO2 dissolution into the migration model and study the importance of dissolution relative to capillary trapping and the impact of dissolution on the storage efficiency.

Potential environmental impact of dissolution of raw phosphate in sea water of the Gulf of Aqaba

Dissolution of raw phosphate (apatite) in sea water of the Gulf of Aqaba was investigated through lab incubation experiments. Three types from three different sources (Al-Hasa, Al-Abyad and Esh-Shydiya) have been used for these experiments. Impact of quantity, grain size, and source (type) of raw phosphate on dissolution rate were studied. Statistical analysis shows significant differences between the results obtained from comparing each two weights; as weight of apatite increased, dissolved inorganic phosphate-phosphorus (DIP) and fluoride in sea water solution increased. The differences between the dissolution rates of raw phosphate from the three sites were not significant while the differences between the different grain size fractions were significant. Dissolution rates were inversely related to particle size. Using a worst-case scenario, a conservative estimate of the maximum increase in DIP in seawater of the Gulf of Aqaba due to the apatite particles lost to the sea during ship loading resulted in DIP concentrations of 0.03 μM per year. As the residence time of the water in the Gulf of Aqaba is about one year, the DIP concentration will not increase by more than 0.03 μM under the estimated annual quantity of exported phosphate. Fluoride will not increase by more than 0.03 mg/l under the same conditions.

The initial stage of the development of planar chromatograms

The aim of the work discussed in this paper was to re-investigate the initial stage of the retention process in TLC, namely the moment of first contact between the analyte deposited at the origin and the mobile phase employed. It was our intention to assess the impact of dissolution of the analyte by the mobile phase on the overall mobility of the analyte in the chromatographic system. To accomplish this goal parallel experiments were performed with analyte samples applied to the stationary phase and chromatographed with and without drying (i.e. with and without evaporation of the solvent used to dissolve the analyte). As test analytes we selected two compounds (5-phenylpentanol and 2-phenylbutyric acid) able to participate in lateral interactions by hydrogen bonding and another four compounds (anthracene, phenanthrene, perylene, and tetralin) totally unable to self-associate. The results obtained are presented in two different ways, i.e. as the dependence of densitometrically measured concentration profiles and of retardation factors (R F ) on the amount of analyte and on the mode of application (dry or wet) to the stationary phase layer. It was discovered that for both types of analyte (i.e. participating and not participating in lateral interactions) the process of dissolution at the origin is time-consuming and thus contributes to the overall retardation of migration of the analytes.

Carbonate dissolution and planktonic foraminiferal assemblages observed in three piston cores collected above the lysocline in the western equatorial Pacific

Planktonic foraminiferal assemblages were analyzed in three piston cores recovered from depths above the recent sedimentary lysocline (3.5 km) in the western Pacific Ocean for the purposes of (1) evaluating the effects of carbonate dissolution on fossil assemblages and (2) the impact of dissolution on paleoceanographic reconstructions for the past 300 kyr. We used the perfect test ratio (PTR) of Globorotalia menardii as an indicator of carbonate dissolution. Down-core variations of the PTR indicate that significant dissolution occurred during reglaciation steps represented by isotope stages 7–6, 5–4, and 3–2. The results of principal component analysis (PCA) based on the relative abundances of dominant species of planktonic foraminifera indicate that down-core changes in factor 1 loadings correlate with variations in PTR and with variations in the percentage of coarse fraction (>63 μm) present in the sediments. These correlations indicate that foraminiferal assemblages were apparently altered by dissolution events despite the fact that they were deposited at water depths shallower than the modern lysocline. We also estimated variations in paleo-sea surface temperature (paleo-SST) using the transfer function FP-12E. A negative correlation was found in communality as calculated from PCA and factor 1 loadings; this trend is distinct for the case of communality lower than 0.9. Thus, we conclude that estimated paleo-SST values based upon analysis of planktonic foraminifera are biased by carbonate dissolution.

Dissolution-affected coccolithophore fluxes in the central Greenland Sea (1994/1995)

Coccolithophore fluxes were investigated by sediment trap studies in the central Greenland Sea from 1994 to 1995. The trap mooring comprised traps at 300, 900, and 2100 m water depths with 19 trapping intervals (10–28 days). This site was characterised by a very strong seasonality in coccolithophore fluxes. The seasonal flux signal was most pronounced in the shallow trap with high fluxes only during two trapping intervals in September and early October 1994 (max. coccolithophore flux 12×10 6 Ind m −2 d −1). No or only very low fluxes were recorded during most of the investigated time interval. In the deeper traps high fluxes occurred over a longer time interval than in the upper traps from late August to November 1994. The dominant species (>90%) was Coccolithus pelagicus f. pelagicus. Only very few other species including Emiliania huxleyi (<7%) occasionally occurred. The coccolithophore settling assemblages of the investigated traps were strongly influenced by dissolution. The dissolution impact probably diminished diversity and sharpened seasonality in fluxes. Dissolution was prominent in near-surface waters of the East Greenland Current but not in bottom waters. However, maximum fluxes were of the same magnitude as previously reported fluxes from the nearby Norwegian Sea and higher than in the southern Greenland Sea. In contrast to the other sites, resuspension seemed to be of minor importance. Total annual coccolithophore fluxes differed significantly in the Norwegian–Greenland Seas reflecting the local oceanographic signature of coccolithophore production.

Quaternary ostracods as palaeoceanographic indicators: a case study off southern Australia

Abstract There is increasing use of ostracods in palaeoceanographic interpretation, yet few comparisons have been made with existing foraminiferal indicators. This paper examines ostracod records from two cores taken off southern Australia and compares them with foraminiferal records of abundance and dissolution. Core E55-6 from the continental margin of Victoria is located in 2346 m water depth. Core E27-30, located south of Tasmania in a water depth of 3552 m, lies to the north of the present position of the Subtropical Convergence. While benthic foraminiferal abundances parallel ostracod abundances in core E55-6, this is not the case in core E27-30. In the latter core, peaks in ostracod abundance are offset from peaks in foraminiferal abundance. This is attributed to high phytodetrital input associated with the Subtropical Convergence. An ostracod-based dissolution index is compared with foraminiferal dissolution data from both cores. The ostracod dissolution index shows greater sensitivity than foraminiferal fragmentation in water depths well above the lysocline and suggests that carbonate dissolution at these depths may be underestimated using foraminiferal indices. The impact of dissolution on ostracods can also be seen as a reduction in abundance. This is evident in both cores, although the impact is greater in the shallower core, suggesting that carbonate saturation may be a factor in the distribution of ostracods in the deep sea. Further investigation of the effects of carbonate saturation on individual ostracod taxa will enhance their utility as palaeoceanographic tools.