LABORATORY OF GEOLOGY AND GEOPHYSICS

SEDIMENTOLOGY LABORATORY

This lab specializes in sediment sampling, sample preparation and performance of a series of physical and chemical analyses of sediments recovered from marine, estuarine and freshwater environments. A brief description of the main methods follows below:

• Separation of the finer (< 63 μm) sediment fraction by wet sieving.
• Determination of the grain size distribution, ranging from 0.1 to 300 μm, is carried out using a Micromeritics SediGraph III Plus analyzer. The instrument measures the particle size distribution using the sedimentation method. Particle mass is measured directly via X-ray absorption (Webb and Orr, 1997). By measuring the rate at which particles fall under gravity, through a liquid having known properties, as described by Stokes’ law, SediGraph determines the equivalent spherical diameter of particles.
• Determination of grain size distribution in finer (< 63 μm) sediment samples is performed using the Atterberg method. The sediment fractions of 63-20, 20-5, 5-2 και < 2 μm are defined.
• Determination of inorganic carbon (occurring as carbonates) is performed using the method of Muller and Gastner (1971). This method is based on the comparison of the carbon dioxide volumes released from the chemical reactions of the examined and prototype samples with hydrochloric acid.
• Determination of inorganic phosphorus is accomplished through the sediment sample treatment with dilute hydrochloric acid solution, which causes dissolution of phosphates. Then phosphates are measured using the standard method of spectrometric determination for phosphates.
• Determination of the radioactive lead isotope ²¹⁰Po is carried out with total α-counting in collaboration with the Department of Marine Chemistry.
• Samples from gravity cores and surface sediments are subjected to a variety of preparation methods prior to their analysis for the determination of their sedimentological characteristics, geochemistry, mineralogy and geotechnical properties.

GEOCHEMISTRY AND MINERALOGY LABORATORY

The Geochemistry X-ray Laboratory Unit XRF the last 10 years, takes part in the inter-laboratory proficiency exercises from IAEA and QUASIMEME, with great results (z-scores <2, in 95% of total results). From 2017 onwards the lab is continuously certified by ISO-17025.

The lab is equipped with the X-ray instrumentation described briefly below:

• PANalytical PW-2400 wavelength dispersive X-ray fluorescence (XRF) spectrometer: the instrument is equipped with a 3 kW rhodium tube, flow-proportional xenon-sealed scintillation detectors and eight analytical crystals. For the determination of major elements, calibration curves are prepared using a large set of certified reference materials. For the determination of minor and trace elements, the PANalytical’s Pro-Trace software and standards are used. The Pro-Trace software includes a set of twenty-five pressed powder high-purity blanks, single- or multi-element interference standards and mass attenuation coefficient correction and concentration standards for forty elements ranging across the periodic table (Sc to U).
• Rigaku D/MAX-B X-ray diffractometer (XRD): X-rays are produced by a Copper target sealed tube. These diverging X-rays are incident upon a flat, vertically mounted sample and the reflected or diffracted beam converges into a diffracted beam monochromator (curved graphite crystal). Random powder mounts of bulk sediment are scanned from 2° to 40° 2θ, while identification of diffraction peaks is accomplished by comparison of the measured pattern with entries in reference databases (Moore and Reynolds, 1989).

GEOTECHNICAL LABORATORY

The lab performs a series of geotechnical analyses and tests in sediment cores. A brief description of the major activities follows below:

• High-resolution X-radiography of gravity cores using a Faxitron Cabinet X-ray System (model 43855D).

• Multi sensor core logging for the determination of properties such as P-wave velocity, magnetic susceptibility, impedance, fractional porosity and bulk density through gamma-ray attenuation.
• Vane shear testing for the estimation of undrained shear strength
• Determination of water content (moisture)
• Determination of wet bulk density (γ_w)
• Performance of one-dimensional consolidation tests
• Testing for the determination of triaxial compressive strength

SEDIMENT TRAP LABS

Time-series sediment traps are oceanographic tools that are deployed in the water to collect particles settling toward the sea floor. Traps collect tiny particles or larger accumulations called marine-snow, primarily composed of phytoplankton produced through photosynthesis and microbes. As the marine-snow sinks, it collects other particulate matter (including fecal pellets, dead and decaying animals, suspended sediments, and other organic or inorganic components, that may have been transported from the land mainly through rivers or atmosphere to the sea). The magnitude of the sinking particle flux and its temporal and spatial variations give us information of the distribution of many chemical elements and biogeochemical cycles in the ocean. Sediment traps can be also used for environmental and pollution monitoring.

Field Instruments

• 11 cylindro-conical Technicap PPS 3/3 sediment traps, with 12 receiving cups, 0.125m² collecting area and 3500m to 5000m operational depth.

Lab works

• Preparation of traps for deployment
• Ph measurement of sample supernatant
• Removal of planktonic organisms, after samples recovery, under microscope
• The subsampling was undertaken using a high precision peristaltic pump, an orbital stirrer to homogenize the sample
• Determination of biogenic Si.
• Determination of organic and inorganic C and N.
• Determination of particle fluxes
• Scanning Electron Microscopy on selected samples
• Providing subsamples for further analyses (black C, coccolithophores, biomarkers, ¹⁴C, ¹⁵N, ²¹⁰Pd, etc).

SCANNING ELECTRON MICROSCOPE

A significant part in the study of marine particles is their observation under the electron microscope. The Electron Microscopy Laboratory is a research unit of the Institute of Oceanography which maintains a Scanning Electron Microscope (SEM) (Philips XL20), and provides capabilities for microstructural and microchemical characteristics and materials properties. The SEM is equipped with an Energy Dispersive Spectrometer (EDS), which is used for both qualitative and semi-quantitative microanalysis. Analysis of the x-ray signals may be used to map the distribution and estimate the abundance of various elements in one sample. The Electron Microscopy Laboratory includes a complete specimen preparation unit equipped with Baltec SEM sample preparation devices for carbon- and gold-coating. Over the last 20 years, the Electron Microscopy Laboratory has conducted fundamental research relating to microstructure and chemical composition of particles to the fields of marine sedimentation, geological origin and processes, mineralogical composition, microfossils paleontology, anthropogenic activity and environmental impact, geo-archaeology, mineral resources, biological identification etc. Furthermore, the Electron Microscopy Laboratory provides assistance and training in electron microscopy techniques to enable research groups to achieve their research objectives, while it also collaborates with researchers and students of various research institutes and universities, industries and companies.