The darkness syndrome in subsurface-shallow and deep-sea dwelling Ostracoda (Crustacea)

Biosystematics and Ecology-Series. Año 1996, Vol. 1

On the need to renew the taxonomic system of the candoninae (non-marine Ostracoda, Crustacea). Reflexions from an analysis of data using the Yule Process

http://www.geoecomar.ro/website/publicatii-revista-geo-eco-marina.htm

Spatiotemporal distribution of microbial communities in a coastal, sandy aquifer system (Doñana, SW Spain)

This is the peer reviewed version of the following article: Velasco Ayuso, S. et al. Spatiotemporal distribution of microbial communities in a coastal, sandy aquifer system (Doñana, SW Spain). Geobiology 7 (2009): 66-81, which has been published in final format at http://dx.doi.org/10.1111/j.1472-4669.2008.00183.

Environmental responses to Lateglacial climatic fluctuations recorded in the sediments of pre-Alpine Lake Mondsee (northeastern Alps)

Declakes Participants : Soumaya Belmecheri, Marc Desmet, Helmut Erlenkeuser, Bernard Fanget, Jérôme Nomade.International audienceInvestigation of the sedimentary record of pre-Alpine Lake Mondsee (Upper Austria) focused on the environmental reaction to rapid Lateglacial climatic changes. Results of this study reveal complex proxy responses that are variable in time and influenced by the long-term evolution of the lake and its catchment. A new field sampling approach facilitated continuous and precisely controlled parallel sampling at decadal to sub-annual resolution for µ-XRF element scanning, carbon geochemistry, stable isotope measurements on ostracods, pollen analyses and large-scale thin sections for microfacies analysis. The Holocene chronology is established through microscopic varve counting and supported by accelerator mass spectrometry 14C dating of terrestrial plant macrofossils, whereas the Lateglacial age model is based on δ18O wiggle matching with the Greenland NGRIP record, using the GICC05 chronology. Microfacies analysis enables the detection of subtle sedimentological changes, proving that depositional processes even in rather large lake systems are highly sensitive to climate forcing. Comparing periods of major warming at the onset of the Lateglacial and Holocene and of major cooling at the onset of the Younger Dryas reveals differences in proxy responses, reflecting threshold effects and ecosystem inertia. Temperature increase, vegetation recovery, decrease of detrital flux and intensification of biochemical calcite precipitation at the onset of the Holocene took place with only decadal leads and lags over a ca. 100 a period, whereas the spread of woodlands and the reduction of detrital flux lagged the warming at the onset of the Lateglacial Interstadial by ca. 500-750 a. Cooling at the onset of the Younger Dryas is reflected by the simultaneous reaction of δ18O and vegetation, but sedimentological changes (reduction of endogenic calcite content, increase in detrital flux) were delayed by about 150-300 a. Three short-term Lateglacial cold intervals, corresponding to Greenland isotope substages GI-1d, GI-1c2 and GI-1b, also show complex proxy responses that vary in time. Copyright © 2011 John Wiley & Sons, Ltd

Palaeoenvironmental and diagenetic reconstruction of a closed-lacustrine carbonate system - the challenging marginal setting of the Miocene Ries Crater Lake (Germany)

Chemostratigraphic studies on lacustrine sedimentary sequences provide essential insights on past cyclic climatic events, on their repetition and prediction through time. Diagenetic overprint of primary features often hinders the use of such studies for palaeoenvironmental reconstruction. Here the potential of integrated geochemical and petrographic methods is evaluated to record freshwater to saline oscillations within the ancient marginal lacustrine carbonates of the Miocene Ries Crater Lake (Germany). This area is critical because it represents the transition from shoreline to proximal domains of a hydrologically closed system, affected by recurrent emergent events, representing the boundaries of successive sedimentary cycles. Chemostratigraphy targets shifts related to subaerial exposure and/or climatic fluctuations. Methods combine facies changes with δ13C–δ18O chemostratigraphy from matrix carbonates across five closely spaced, temporally equivalent stratigraphic sections. Isotope composition of ostracod shells, gastropods and cements is provided for comparison. Cathodoluminescence and back‐scatter electron microscopy were performed to discriminate primary (syn‐)depositional, from secondary diagenetic features. Meteoric diagenesis is expressed by substantial early dissolution and dark blue luminescent sparry cements carrying negative δ13C and δ18O. Sedimentary cycles are not correlated by isotope chemostratigraphy. Both matrix δ13C and δ18O range from ca −7·5 to +4·0‰ and show clear positive covariance (R = 0·97) whose nature differs from that of previous basin‐oriented studies on the lake: negative values are here unconnected to original freshwater lacustrine conditions but reflect extensive meteoric diagenesis, while positive values probably represent primary saline lake water chemistry. Noisy geochemical curves relate to heterogeneities in (primary) porosity, resulting in selective carbonate diagenesis. This study exemplifies that ancient lacustrine carbonates, despite extensive meteoric weathering, are able to retain key information for both palaeoenvironmental reconstruction and the understanding of diagenetic processes in relation to those primary conditions. Also, it emphasizes the limitation of chemostratigraphy in fossil carbonates, and specifically in settings that are sensitive for the preservation of primary environmental signals, such as lake margins prone to meteoric diagenesis

Revision of the genus <i>Leucocythere</i> Kaufmann, 1892 (Crustacea, Ostracoda, Limnocytheridae) with the description of a new species and two new tribes

The main aim of the present contribution is to provide an unequivocal diagnosis of the genus Leucocyhtere. It appeared, however, that this could only be effected when embodied in a broader taxonomic framework. The subfamily Limnocytherinae is thus divided into four tribes: Limnocytherini, Dinarocytherini, Cytheridellini and Leucocytherini and diagnoses are provided for these taxa. The latter two are new to science while the rank of Dinarocyhterini was changed from subfamily to tribe. Three genera are lodged in the Leucocytherini: Leucocythere Kaufmann, 1892, Potamocythere Schornikov, 1986 and Ovambocythere Martens, 1989. The former, nominate, genus is characterized and its type species, L. mirabilis, is extensively redescribed. A comparative description of a limnocytheridinid with a somewhat similar appearance, Limnocythere (Limnocytherina) sanctipatricii, is offered. A second species of Leucocythere, L. algeriensis nov. sp., is described from a temporary pool in Algeria. L. baltica (Diebel) is retained as a third species in the genus. A large number of fossil records is reassessed. Most of the Asian fossils, previously assigned to Leucocythere, do not belong in this genus and a revision of their status appears urgent. Some remarks on the validity and position of Leucocytherella are also offered. L. mirabilis is a cold-stenothermic species, with a preference for oligotrophic waters and fine graine sediments. Its status in Europe can at present best be described as endangered, due to rapid degradation of suitable habitats. L. algeriensis nov. sp. and Ovambocythere milani Martens are probably both capable of producing dry resistant stages. This is thus far unique in Cytherids, but the exact taxonomic distribution of this feature remains as yet unknown. Some comments on the phylogeny and historical biogeography are presented. Leucocythere appears to be the more advanced group in the Leucocytherini, the other two genera show more plesiomorphic character states. It is here postulated that the three genera evolve by vicariance from a more widely spread ancestor: Leucocythere in Europe, Potamocythere in Asia and Ovambocythere in Africa. L. algeriensis from northern Africa is doubtlessly from Paleartic stock and its speciation from L. mirabilis must have occured fairly recently. A number of morphological peculiarities of L. mirabilis are discussed with special attention for the carapace and for those soft parts that are used for the mating process. In spite of the fact that many of the peculiarities appear maladaptive at first glance, it must be stressed that L. mirabilis thus far maintained itself very well in its environment, until recent anthropogenic pollution caused its extinction in many localities

The role of organisms in hyporheic processes : gaps in current knowledge, needs for future research and applications

Fifty years after the hyporheic zone was first defined (Orghidan, 1959), there are still gaps in the knowledge regarding the role of biodiversity in hyporheic processes. First, some methodological questions remained unanswered regarding the interactions between biodiversity and physical processes, both for the study of habitat characteristics and interactions at different scales. Furthermore, many questions remain to be addressed to help inform our understanding of invertebrate community dynamics, especially regarding the trophic niches of organisms, the functional groups present within sediment, and their temporal changes. Understanding microbial community dynamics would require investigations about their relationship with the physical characteristics of the sediment, their diversity, their relationship with metabolic pathways, their inter- actions with invertebrates, and their response to environmental stress. Another fundamental research question is that of the importance of the hyporheic zone in the global metabolism of the river, which must be explored in relation to organic matter recycling, the effects of disturbances, and the degradation of contaminants. Finally, the application of this knowledge requires the development of methods for the estimation of hydro- logical exchanges, especially for the management of sediment clogging, the optimization of self-purification, and the integration of climate change in environmental policies. The development of descriptors of hyporheic zone health and of new metrology is also crucial to include specific targets in water policies for the long-term management of the system and a clear evaluation of restoration strategies

A new species of benthic ostracod Tuberoloxoconcha: A proxy for glacioeustatic sea-level changes in the Gulf of Corinth

In 2017, sediment cores were retrieved from sites M0080, M0079, and M0078 in the Corinth basin during IODP Expedition 381. This study focuses on the Holocene and middle Pleistocene ostracod assemblages retrieved from sites M0080, in the Gulf of Alkyonides, and M0078 in the Corinth Gulf. It explores the paleoenvironmental constraints that affected the Tuberoloxoconcha species’ distribution in these two sites and investigates the stratigraphic appearance of the new species Tuberoloxoconcha aielloi in the Corinth basin during deglacial and glacial periods over the last 400,000 years. In the Gulf of Corinth, fossil assemblages dominated by T. aielloi n. sp. have identified brackish shallow water environments corresponding to deglacial and glacial phases, when the basin was likely semi-isolated from Mediterranean waters, with high fluvial input lowering the salinity of the waterbody. The study highlights the discontinuous occurrence of T. aielloi and its morphotypes, identifying cold phases during MIS 10 and MIS 7d, and warmer phases during MISs 2–3-4-5a. The variability in ornamentation potentially reflects different water chemistry in the two sites. The post-400 ky appearance of T. aielloi, coinciding with the development of the marine connection through the Rion Strait, implies a Mediterranean/Atlantic origin for the genus. This study provides insights into the environmental conditions and evolutionary history of T. aielloi species in the Corinth basin, contributing to a broader understanding of benthic species’ responses to past and future sea level changes