Improving preservation state assessment of carbonate microfossils in paleontological research using label-free stimulated Raman imaging.

In micropaleontological and paleoclimatological studies based on microfossil morphology and geochemistry, assessing the preservation state of fossils is of the highest importance, as diagenetic alteration invalidates textural features and compromises the correct interpretation of stable isotope and trace elemental analysis. In this paper, we present a novel non-invasive and label-free tomographic approach to reconstruct the three-dimensional architecture of microfossils with submicron resolution based on stimulated Raman scattering (SRS). Furthermore, this technique allows deciphering the three-dimensional (3D) distribution of the minerals within these fossils in a chemically sensitive manner. Our method, therefore, allows to identify microfossils, to chemically map their internal structure and eventually to determine their preservation state. We demonstrate the effectiveness of this method by analyzing several benthic and planktonic foraminifera, obtaining full 3D distributions of carbonate, iron oxide and porosity for each specimen. Subsequently, the preservation state of each microfossil can be assessed using these 3D compositional maps. The technique is highly sensitive, non-destructive, time-efficient and avoids the need for sample pretreatment. Therefore, its predestined application is the final check of the state of microfossils before applying subsequent geochemical analyses.

Heavy metal accumulation in surface sediments at the port of Cagliari (Sardinia, western Mediterranean): Environmental assessment using sequential extractions and benthic foraminifera.

Superficial sediments were taken at the port of Cagliari (Sardinia, Italy), which includes the oil terminal of one of the largest oil refineries in the Mediterranean. Significant trace metal concentrations were found in the whole port area. Sequential extraction of metals from the different sediment fractions (BCR method) showed a higher risk of remobilisation for Cd, which is mostly bound to the exchangeable fraction. Foraminiferal density and richness of species were variable across the study area. The living assemblages were characterized by low diversity in samples collected close to the port areas. Ammonia tepida and bolivinids, which were positively correlated with concentrations of heavy metals and organic matter content, appeared to show tolerance to the environmental disturbance. The sampling sites characterized by the highest values of biotic indices were located far from the port areas and present an epiphytic and epifaunal biocoenosis.

Environmental Quality Assessment of Bizerte Lagoon (Tunisia) Using Living Foraminifera Assemblages and a Multiproxy Approach.

This study investigated the environmental quality of the Bizerte Lagoon (Tunisia) through an integrated approach that combined environmental, biogeochemical, and living benthic foraminiferal analyses. Specifically, we analyzed the physicochemical parameters of the water and sediment. The textural, mineralogical, and geochemical characteristics of the sediment, including total organic carbon, total nitrogen, simultaneously extracted metals (SEM), acid volatile sulfides (AVS), chlorophyll a, CaCO3, and changes in bacterial populations and carbon isotopes were measured. The SEM/AVS values indicated the presence of relatively high concentrations of toxic metals in only some areas. Foraminiferal assemblages were dominated by species such as A. parkinsoniana (20-91%), Bolivina striatula (<40%), Hopkinsina atlantica (<17%), and Bolivina ordinaria (<15%) that cannot be considered typical of impacted coastal lagoons both in Mediterranean and northeast Atlantic regions. The results of this work suggest that Bizerte Lagoon is a unique setting. This lagoon is populated by typical marine species that invaded this ecosystem, attracted not only by the prevailing favorable environmental conditions but also by the abundance and quality of food. The results indicate that the metal pollution found in some areas have a negative impact on the assemblages of foraminifera. At present, however, this negative impact is not highly alarming.

Assessment of the health quality of Ria de Aveiro (Portugal): heavy metals and benthic foraminifera.

This work analyses the distribution of heavy metals in the sediments of Ria de Aveiro (Portugal) assessed by total digestion and sequential chemical extraction of the sediments. The influence of environmental parameters on the living benthic foraminiferal assemblages was studied. The most polluted parts in the Ria de Aveiro are areas where the residence time is high and cohesive sediments are deposited. Organic matter, which is an excellent scavenger for a number of metals, is in general more abundant in the finer deposits of this lagoon, which act as sinks of anthropogenic pollutants. This condition is observed in Aveiro canals and Murtosa channel where sediments with the highest concentrations of Zn, Pb, Cu, and Cr are found. The sediments of Murtosa channel are also enriched in As, Co and Hg. In Aveiro canals the enrichment of heavy metals is mostly related to the past industrial production at their margins (ceramic and metallurgy), whereas in Murtosa channel with effluent discharges of the Chemical Complex of Estarreja. Foraminiferal density and diversity reach higher values near the lagoon mouth under higher marine influence and decline in general under very low-oxygen conditions. Some species seems to be indifferent to the increasing of TOC (e.g. Haynesina germanica and Ammonia tepida) and some have an opportunistic behaviour in areas with very depressed levels of oxygen (e.g. A. tepida and Quinqueloculina seminulum) whereas other species can better tolerate sulphide/reducing conditions (e.g. H. germanica, Bolivina ordinaria, Buliminella elegantissima, Bulimina elongata/gibba and Nonionella stella) a widespread condition in this lagoon. Foraminiferal density and some species are negatively correlated with concentrations of heavy metals. A most sensitive group of species to higher concentrations of heavy metals is identified (such as B. ordinaria, B. pseudoplicata and B. elongata/gibba) and another one of more tolerant species (such as H. germanica A. tepida and Q. seminulum). Foraminifera are more tolerate higher available concentrations (AC) of Zn in any phase than higher AC of Cu adsorbed do clay minerals (F1) and associated with Fe and Mn oxides (F2) and of Pb in F2; the phase F2, probably the most mobile phase, and even phase F1 seems to be more toxic than the increasing of metals in organic matter (F3).