Phenological Changes of Blooming Diatoms Promoted by Compound Bottom-Up and Top-Down Controls

Understanding phytoplankton species-specific responses to multiple biotic and abiotic stressors is fundamental to assess phenological and structural shifts at the community level. Here, we present the case of Thalassiosira curviseriata, a winter-blooming diatom in the Bahía Blanca Estuary, Argentina, which displayed a noticeable decrease in the past decade along with conspicuous changes in phenology. We compiled interannual field data to assess compound effects of environmental variations and grazing by the invasive copepod Eurytemora americana. The two species displayed opposite trends over the period examined. The diatom decreased toward the last years, mainly during the winters, and remained relatively constant over the other seasons, while the copepod increased toward the last years, with an occurrence restricted to winter and early spring. A quantitative assessment by structural equation modeling unveiled that the observed long-term trend of T. curviseriata resulted from the synergistic effects of environmental changes driven by water temperature, salinity, and grazing. These results suggest that the shift in the abundance distribution of T. curviseriata toward higher annual ranges of temperature and salinity—as displayed by habitat association curves—constitutes a functional response to avoid seasonal overlapping with its predator in late winters. The observed changes in the timing and abundance of the blooming species resulted in conspicuous shifts in primary production pulses. Our results provide insights on mechanistic processes shaping the phenology and structure of phytoplankton blooms.     

The effect of chlorite interlayering on <Superscript>40</Superscript>Ar–<Superscript>39</Superscript>Ar biotite dating: an <Superscript>40</Superscript>Ar–<Superscript>39</Superscript>Ar laser-probe and TEM investigations of variably chloritised biotites

Biotite is one of the most common minerals dated by the ⁴⁰Ar–³⁹Ar method. It frequently shows K contents below the expected stoichiometric value, suggesting the presence of low-K impurities. The most common low-K alteration product of biotite is chlorite. Therefore, it is important to understand the effects of chlorite interlayering on ⁴⁰Ar–³⁹Ar ages in order to correctly interpret ⁴⁰Ar–³⁹Ar data. This study examines the outcome of ⁴⁰Ar–³⁹Ar dating analyses on variably chloritised biotites from Ordovician intrusive rocks. The infrared (IR) laser-probe technique and different gas extraction methods were adopted. Incremental laser-heating data on bulk samples yielded hump-shaped age profiles with meaningless young and old age steps. Both the extent of anomalous old age steps and the degree of discordance of the age spectra were much more pronounced in the more chloritised biotite samples. In contrast, in situ data on rock chips and total-fusion ages on single biotite flakes yielded ages concordant with, or younger than, the inferred emplacement ages. Transmission electron microscopy (TEM) was used to texturally characterise biotite samples at the nanometre scale. It was also used to document the complex decomposition-transformation process affecting interlayered biotite–chlorite during in-vacuo IR-laser heating to temperatures ranging from ~600 to >1,000 °C. TEM results suggest that hump-shaped age profiles result from an interplay between ³⁹Ar_K redistribution by recoil during sample irradiation and differential release of argon isotopes hosted in three main reservoirs. These reservoirs are (from least to most retentive): extended defects, chlorite and biotite. The final descending age segment is attributed to the progressive release of argon with increasing temperature from large biotite domains for which ³⁹Ar_K recoil loss was less important. ⁴⁰Ar–³⁹Ar data support previous findings, which suggest that ⁴⁰Ar–³⁹Ar ages when recoil effects are minimised, provide minimum estimates that approach the true biotite age, when the pristine domains are analysed. The most effective approach for obtaining meaningful ⁴⁰Ar–³⁹Ar ages was using individual total-fusion analyses on carefully selected, single flakes previously split along the basal cleavage by wet-grinding and corresponding to a sample mass of a few micrograms.Editorial responsibility: I Parsons     

Mid-Holocene evolution and paleoenvironments of the shoreface–offshore transition, north-eastern Argentina: New evidence based on benthic microfauna

A sedimentary record spanning 5792–5511 cal yr BP and 3188–2854 cal yr BP was recovered at 36° 45′ 43″ S–56 ° 37′ 13″ W, south-west South Atlantic. The sedimentological features and micropaleontological (benthic foraminifera and ostracoda) content were analyzed in order to reconstruct paleoenvironmental conditions. Considerable environmental fluctuations are indicated by all these proxies. Five different stages were distinguished: Stage 1 (ca. 5800–5000 cal yr BP) consists of muddy sand with abundant microfossils. In this interval, species typical for inner marine shelf environments maintained a high abundance. Stage 2 consists of plastic light greenish grey clays barren of microfossils, and probably represents fluvial input from the de la Plata River to the shelf contemporaneous of a lowering of sea level. Stage 3 is composed of brownish yellow sandy silts, and represents increasing marine conditions in the area as reflected by higher faunal diversity and typical foraminifera of inner shelf environments. Stage 4 is made of homogeneous mud, barren of microfossil, which represents a new pulse of fluvial input to the shelf in consequence of a new fall in sea level. The final part of the core (Stage 5) is a coarsening upward sequence, grading from greeny brown clayey sandy silts to coarse shelly sands and represents the modern sedimentation in the area. This interpretation strengthens the stepped model of late-Holocene sea-level fall between 5511–5792 cal yr BP and 2854–3188 cal yr BP in Buenos Aires coast, and agrees with the relative sea-level history previously proposed by some authors from western South Atlantic coasts.     

Relationship between hydrocarbons and bacterial activity in mediterranean sediments: Part 2—hydrocarbon degrading activity of bacteria from sediments

In marine sediments from the Mediterranean coast polluted by oil spills (Etang de Berre) high bacterial activity is responsible for self-purification, samples collected from these areas showing a bacterial density several orders of magnitude higher than samples from non-polluted areas (Isle des Embiez). Between 60 and 80 % of the heterotrophic bacteria in the polluted areas are hydrocarbon-degrading, compared with 0.01 % in the non-polluted area.Several strains of hydrocarbon utilisers were isolated, a mixture of strains from each biotope was taken to represent a ‘biotope population’ and their activity towards different types of hydrocarbons (n-alkanes, iso-alkanes, cycloalkanes, aromatics) was determined.With ammonia as the nitrogen source the ‘biotope population’ from the polluted area degraded hydrocarbons much more readily than the ‘biotope population’ from the non-polluted area. With nitrate as the nitrogen source the degradation was much reduced, and, for some hydrocarbons, ceased in both ‘populations’.Individual hydrocarbons encouraged the growth of individual strains in the ‘biotope population’. In natural mixtures of hydrocarbons all strains grew well and degraded aliphatics. There was a good correlation between the respiratory activity of the ‘biotope population’ and the ability of the ‘population’ to utilise hydrocarbons for growth.     

The Influence of Community Size and Location on Different Dimensions of Vulnerability: a case study of Australian coastal communities

ABSTRACT

Coastal communities are part of the Australian identity but little is known about their characteristics and their long-term prosperity prospects. Increased migration to coastal areas and increased exposure to extreme climatic events indicates a need for social and economic data to inform socio-ecological systems planning. Here, we undertake a geo-spatial analysis to develop a typology of Australian coastal communities and assess relative vulnerability to climate-driven environmental change for a range of social and economic indicators. The aim of this study is to understand how the vulnerability of Australian coastal communities varies with geographic location or community size, and in comparison to other community types. Results show that both the population size and location of a coastal community matter and that coastal communities overall are more vulnerable on some socio-economic dimensions to climate-driven environmental change than their rural equivalents. However, results also demonstrate that the smallest coastal communities are strong in some important aspects of the human, social and financial domains, putting them in a good position to deal with some changes. Scale-appropriate and context-specific social policies are needed to address identified socio-economic vulnerabilities, supported by a range of formal and informal institutional structures, such as strategies to improve education and female workforce participation, and encourage participation in volunteering to increase human and social capital.     

An approach for quantifying geomorphological impacts for EIA of transportation infrastructures: a case study in northern Spain

A methodological proposal for the assessment of impacts due to linear infrastructures such as motorways, railways, etc. is presented. The approach proposed includes a series of specific issues to be addressed for each geomorphological feature analysed—both ‘static’ and ‘dynamic’—as well as a series of steps to be followed in the process.Geomorphic characteristics potentially affected were initially identified on the basis of a conceptual activities/impacts model that helps to single out geomorphic impacts related to environmental concerns for the area. The following issues were addressed for each individual impact: nature of potential effects; indicators that can be used to measure impacts; criteria of ‘geomorphologic performance’; procedure for measurement/prediction of changes; translation of geomorphologic impacts into significant terms from the viewpoint of human concerns; possible mitigation and/or compensation measures.The procedure has been applied to a case study corresponding to a new motorway in the Basque Country, northern Spain. Geomorphological impacts considered in this analysis included: (1) consumable resources; (2) sites of geomorphological interest; (3) land units with high potential for use, high productivity or value for conservation; (4) visual landscape; (5) slope instability processes. The procedure has been designed for implementation in a Geographic Information System (GIS) environment. Details are given on the application of the method to each individual impact analysed and results are presented in both numerical and map form.Impacts assessed were initially expressed by means of heterogeneous magnitudes, depending on the geomorphological feature considered. Those geomorphological impacts were then translated into significant terms and homogeneous magnitudes. Integration was carried out on the basis of impact values thus obtained. Final integrated results were also expressed in numerical and map form.The method proposed enables comparison of alternatives as well as ‘prediction’ and assessment of impacts in terms directly related to geomorphic characteristics. It also facilitates the expression of those impacts in terms that allow integration with other types of environmental impacts.