Fossil fish species and assemblage are relevant integrative paleo-biogeo-archives in ancient lakes

<p>In paleontological context, fish remains are frequently collected and constitute a large part of the lake macro-fossil assemblages. In the presentation, examples from continental Africa chosen in lakes of different dimension, shape and history (mainly Malawi, Chad and Turkana) will illustrate how fish fossil study potentially provides a wide range of information on the paleoenvironment (water salinity, temperature, oxygenation, seasonality, etc.) and the paleogeography (watershed connections) of the lake and its basin. It is based on the knowledge of the ecology and phylogeny of the species and through dedicated biogeochemical and sclerochronological studies of their bones and teeth that also constitute paleo-bio-archives that recorded certain environmental information. Alongside the results extracted from each dedicated study, their combination provide new information and show the gain of extracting different and independent informations from the same object or from objects from the same assemblage, and notably in the case of lake-fish assemblages. For example, the combination of the knowledge on a fish paleo-ecology in a lake with results of a biogeochemical study of their remains can evidence change in the hydrographical regime between successive lake deposits. Finally, fish study also allow an interpolation of change in paleoenvironments at different time scales and their integrative study as paleoenvironmental proxy should be more widely included in the evolution of lakes in the past. The multi-time scale and proxy study enabled on fossil fish is sensible for transfer to predict modern lake evolution.</p>

Environmental patterns of brown moss- and Sphagnum-associated microbial communities

Northern peatlands typically develop through succession from fens dominated by the moss family Amblystegiaceae to bogs dominated by the moss genus Sphagnum. How the different plants and abiotic environmental conditions provided in Amblystegiaceae and Sphagnum peat shape the respective moss associated microbial communities is unknown. Through a large-scale molecular and biogeochemical study spanning Arctic, sub-Arctic and temperate regions we assessed how the endo- and epiphytic microbial communities of natural northern peatland mosses relate to peatland type (Sphagnum and Amblystegiaceae), location, moss taxa and abiotic environmental variables. Microbial diversity and community structure were distinctly different between Amblystegiaceae and Sphagnum peatlands, and within each of these two peatland types moss taxon explained the largest part of microbial community variation. Sphagnum and Amblystegiaceae shared few (< 1% of all operational taxonomic units (OTUs)) but strikingly abundant (up to 65% of relative abundance) OTUs. This core community overlapped by one third with the Sphagnum-specific core-community. Thus, the most abundant microorganisms in Sphagnum that are also found in all the Sphagnum plants studied, are the same OTUs as those few shared with Amblystegiaceae. Finally, we could confirm that these highly abundant OTUs were endophytes in Sphagnum, but epiphytes on Amblystegiaceae. We conclude that moss taxa and abiotic environmental variables associate with particular microbial communities. While moss taxon was the most influential parameter, hydrology, pH and temperature also had significant effects on the microbial communities. A small though highly abundant core community is shared between Sphagnum and Amblystegiaceae.

Last 12 ky record of various organic geochemical proxies in the Eastern Arabian Sea

&lt;p&gt;Here we present high-resolution biogeochemical study using nitrogen/carbon isotope ratio measurement and molecular proxies from a sediment core (length = 2.9 m) collected from the center (588 mbsl; Lat: 16&lt;sup&gt;0&lt;/sup&gt;49.88&amp;#8217;N and Long: 71&lt;sup&gt;0&lt;/sup&gt; 58.55&amp;#8217; E) of the oxygen minimum zone off west coast of India. The core archives the depositional record covering 1.114 to 12.025 ky BP. The concentrations of total organic carbon (TOC) and total nitrogen (TN) range from 0.7 to 4.9 wt% and 0.068 to 0.5 wt % respectively. TOC and TN show parallel trends and the TOC/TN ratio varies within a narrow range of 8 to 11.5. The &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C values range from -20.5&amp;#8240; to -21.9&amp;#8240; (V-PDB). The TOC/TN and &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C suggest typical marine organic matter source. This observation is also further supported by the n-alkane distribution pattern where the dominance of nC&lt;sub&gt;21&lt;/sub&gt; to nC&lt;sub&gt;24&lt;/sub&gt; and the absence of odd alkane dominance over even suggest predominantly marine organic source. The &amp;#948;&lt;sup&gt;15&lt;/sup&gt;N profile shows a steady increase from 5.7&amp;#8240; at 203 cmbsf (5.5 ky BP) to 7.5&amp;#8240; at 2 cmbsf (~1ky BP) suggesting gradual increase in denitrification possibly liked to reduced ventilation in the Arabian Sea, whereas, between 5.5 to 12 ky BP, the &amp;#948;&lt;sup&gt;15&lt;/sup&gt;N values show marked fluctuations (5.2 to 7.1&amp;#8240;) possibly indicating variable level of oxygenation which in turn controlled the extent of denitrification. Possible influence of diagenesis (microbial degradation of organic matter) on the &amp;#948;&lt;sup&gt;15&lt;/sup&gt;N&amp;#160;values also need to be investigated for a better understanding of the water column processes.&lt;/p&gt;

The effect of salinity on the biogeochemistry of the coccolithophores with implications for coccolith-based isotopic proxies

Reconstruction of sea surface temperatures from the oxygen isotope composition (δ18O) of calcite biominerals synthesised in the mesopelagic zone of the oceans requires knowledge of the δ18O of seawater and constraints on the magnitude of biological 18O∕16O fractionation (the so-called vital effect). In the palaeoceanography community, seawater δ18O and salinity are unduly treated as a common parameter owing to their strong covariation both geographically and in the geological register. If the former parameter has arguably no notable influence on the biogeochemistry of marine calcifiers, salinity potentially does. However, how salinity per se and the effect of osmotic adjustment can modulate the biogeochemistry, and in turn, the expression of the vital effect in calcite biomineral such as the coccoliths remains undocumented. In this culture-based study of coccolithophores (Haptophyta) belonging to the Noelaerhabdaceae family, we kept temperature and seawater δ18O constant, and measured basic physiological parameters (growth rate and cell size), and the isotope composition (18O∕16O and 13C∕12C) of coccoliths grown under a range of salinity, between 29 and 39. Ultimately, the overarching aim of this biogeochemical study is to refine the accuracy of palaeotemperature estimates using fossil coccoliths. We found that despite significant physiological changes in the coccolithophores, varying salinity does not modulate biological fractionation of oxygen isotopes. This observation contrasts with previous in vitro manipulations of temperature and carbonate chemistry that led to substantial changes in the expression of the vital effect. As such, salinity does not affect temperature estimation from coccolith-bearing pelagic sequences deposited during periods of change in ice volume, especially at the highest latitudes, or in coastal regions. By contrast, the carbon isotope composition of the coccoliths is influenced by a growth rate mediated control of salinity with implications for deriving productivity indices from pelagic carbonate.

Structural analysis of the essential environmental factors associated with the marine meiofauna

A biogeochemical study was carried out from 2006 to 2007 in Bohai Bay, northern China, to investigate meiofauna and a number of environmental factors. A total of 18 environmental factors were selected to study their interrelations using Interpretive Structural Analysis. The results showed that these environmental factors could be divided into five levels according to their degree of impact; the results also showed clear links among these factors. The six factors designated as Level 1 included both biological and chemical factors. The other factors had indirect effects on meiofauna and affect these six factors in different ways. There was single factor, sediment grain size, in the fifth level. The structural analysis of the essential factors gave us more information than simple correlation analysis did. Both the water and sediment factors influenced the benthos community. The result is helpful in understanding the complex relationships between environmental factors, and could be used to grasp the main causes and their environmental linkages with further studies; it would be a good basis for integrative environmental management.