Search results for "Subfossil"

Environmental factors responsible for the gyrogonite formation by an endangered macroalga, Lychnothamnus barbatus, a fertility indicator of past and …

2019

Abstract Gyrogonites (calcified oospores) of charophytes are commonly used in palaeoecology. Although, the study of morphometry and gyrogonite production by extant charophytes is limited. This concerns the genus Lychnothamnus , frequent in the past but contemporarily represented only by L. barbatus , the rare and endangered species applied in assessment of water quality as a bioindicator of oligo-mesotrophic lakes. In this study two hypotheses were verified: (1) the length and width of L. barbatus gyrogonites increase with increasing depth; (2) at the deeper sites, L. barbatus produces more numerous gyrogonites compared to shallower lake areas. Gyrogonites were picked from L. barbatus thall…

Skeletal organic matrices in molluscs: origin, evolution, diagenesis

2017

8 pages; International audience; The mollusc shell comprises a small amount of organic macromolecules, mostly proteins and polysaccharides, which, all together, constitute the skeletal organic matrix (SOM). In the recent years, the study of the SOM of about two dozens of mollusc species via transcriptomics and/or proteomics has led to the identification of hundreds of shell-associated proteins. This rapidly growing set of data allows several comparisons, shedding light on similarities and differences at the primary structure level and on some peculiar evolutionary mechanisms that may have affected SOM proteins. In addition, it constitutes a prerequisite for investigating the SOM repertoires…

The seasonal water temperature cycle in the Arctic Dicksonfjord (Svalbard) during the Holocene Climate Optimum derived from subfossil Arctica islandi…

2015

Future climate change will have significant effects on ecosystems worldwide and on polar regions in particular. Hence, palaeo-environmental studies focussing on the last warmer-than-today phase (i.e. the early Holocene) in higher latitudes are of particular importance to understand climate development and its potential impact in polar systems. Molluscan bivalve shells constitute suitable bio-archives for high-resolution palaeo-environmental reconstructions. Here, we present a first reconstruction of early Holocene seasonal water temperature cycle in an Arctic fjord based on stable oxygen isotope (δ18Oshell) profiles in shells of Arctica islandica (Bivalvia) from raised beach deposits in Di…

2017

Ranking among the largest volcanic eruptions of the Common Era (CE), the ‘Millennium Eruption’ of Changbaishan produced a widely-dispersed tephra layer (known as the B-Tm ash), which represents an important tie point for palaeoenvironmental studies in East Asia. Hitherto, there has been no consensus on its age, with estimates spanning at least the tenth century CE. Here, we identify the cosmogenic radiocarbon signal of 775 CE in a subfossil larch engulfed and killed by pyroclastic currents emplaced during the initial rhyolitic phase of the explosive eruption. Combined with glaciochemical evidence from Greenland, this enables us to date the eruption to late 946 CE. This secure date rules out…

Climate controls on the Holocene development of a subarctic lake in northern Fennoscandia

2015

International audience; Climate exerts strong control over the functioning of northern freshwater ecosystems, yet their resilience and responses to climate forcing may vary. We examined postglacial development patterns in subarctic Lake Varddoaijavri to discern the impact of direct climate controls, catchment influence, and ontogenic processes on the ecological functioning of the lake over the Holocene. Subfossil diatom assemblages together with the elemental and stable isotopic (delta C-13, delta N-15) composition of sediment organic matter were used to examine climate-induced changes in the structure of the phototrophic community and transport of terrestrial organic matter from the catchm…

Reconstruction of the former charophyte community out of the fructifications identified in Albufera de València lagoon sediments

2010

Abstract Several decades ago, due to eutrophication, Albufera de Valencia lagoon lost the charophyte meadows that covered the bottom in the past but had never been studied in detail. An area close to the lagoon will be restored now to improve water quality and to recover submerged vegetation. To have information on the background of the charophytes from this area, four 80–87 cm long sediment cores were extracted from the lagoon. The subfossil charophyte fructifications (oospores and gyrogonites) were isolated and identified in two of the four cores. Moreover, sediment core fractions from the third and fourth cores were allowed to germinate under several conditions. The study of the lagoon s…

A hidden species becoming visible : biogeography and ecology of Rhynchotalona latens (Cladocera, Anomopoda, Chydoridae)

2019

A long hidden chydorid (Chydoridae, Cladocera) taxon, first found as fossil specimens and recently redefined as Rhynchotalona latens (Sarmaja-Korjonen et al., Hydrobiologia 436: 165-169, 2000) is investigated for its biogeography and ecology. Late Holocene sediment sequence from Lake Sylvilampi, NE Finnish Lapland, and R. latens spatial distribution in relation to limno-climatic attributes in Finland were examined. Principal component analyses of fossil cladoceran communities showed that R. latens is mostly affiliated with Alonella excisa-Alonopsis elongata-Alonella nana species pool. Generalized linear modeling of R. latens responses to limno-climatic variation indicated that it prefers ac…

The Balearic toad (Bufo viridis balearicus (BOETTGER, 1881)), human bronze age culture, and Mediterranean biogeography

1981

Abstract Microcomplement fixation analysis of albumin relationship shows that the Balearic green toad (Bufo viridis balearicus) is not an original, autochthonous member of the basically Miocene fauna of these western Mediterranean islands, but a quite recent newcomer. The plasma protein pattern clearly points to its close populational relationship to the Tyrrhenian islands' conspecifics. The male and female release vocalization shows the same, and this is in accordance with the external morphology too. There has been no possibility for toads to reach the Balearic Islands in Pleistocene or Holocene via land bridges, nor are they candidates for any sea drifting. Anthropogenic introduction mu…

A HYDRAULIC CONDUCTIVITY MODEL POINTS TO POST-NEOGENE SURVIVAL OF THE MEDITERRANEAN OLIVE

2004

Research on the subfossil record and paleoecology of Olea europaea suggests a new interpretation of its history and ecology with reference to the Mediterranean climate since the Neogene. New results are based on the wood anatomy of ancient and extant Olea and a model estimating hydraulic conductance established for wild forms belonging to Olea europaea subsp. europaea. These suggest that during glacial periods wild olive populations survived in protected microenvironments, particularly riparian habitats. Thereafter, the postglacial expansion of olive associated with climatic warming took place from these refuge areas. This new evidence suggests that the continued existence of Olea in Medite…

Subfossil chironomid assemblages in deep, stratified European lakes: relationships with temperature, trophic state and oxygen

2010

Summary 1. The distributions of subfossil remains of chironomid larvae in 28 large, deep and stratified lakes in Europe were examined in surface sediments along a latitudinal transect ranging from northern Sweden to southern Italy. 2. Canonical correspondence analysis (CCA) showed that summer surface water and July air temperature, as well as total phosphorus (TP) concentrations, hypolimnetic oxygen availability and conductivity were statistically significant (P < 0.05) explanatory variables explaining between 11 and 14% of the variance in the chironomid data. 3. Owing to the spatial scale covered by our study, many environmental variables were covarying. Temperature, TP concentration and o…