Shedding Light on Fish Otolith Biomineralization Using a Bioenergetic Approach

Otoliths are biocalcified bodies connected to the sensory system in the inner ears of fish. Their layered, biorhythm-following formation provides individual records of the age, the individual history and the natural environment of extinct and living fish species. Such data are critical for ecosystem and fisheries monitoring. They however often lack validation and the poor understanding of biomineralization mechanisms has led to striking examples of misinterpretations and subsequent erroneous conclusions in fish ecology and fisheries management. Here we develop and validate a numerical model of otolith biomineralization. Based on a general bioenergetic theory, it disentangles the complex interplay between metabolic and temperature effects on biomineralization. This model resolves controversial issues and explains poorly understood observations of otolith formation. It represents a unique simulation tool to improve otolith interpretation and applications, and, beyond, to address the effects of both climate change and ocean acidification on other biomineralizing organisms such as corals and bivalves

Alteration assemblages in Martian meteorites: implications for near-surface processes

The SNC (Shergotty-Nakhla-Chassigny) meteorites have recorded interactions between martian crustal fluids and the parent igneous rocks. The resultant secondary minerals – which comprise up to 1 vol.% of the meteorites – provide information about the timing and nature of hydrous activity and atmospheric processes on Mars. We suggest that the most plausible models for secondary mineral formation involve the evaporation of low temperature (25 – 150 °C) brines. This is consistent with the simple mineralogy of these assemblages – Fe-Mg-Ca carbonates, anhydrite, gypsum, halite, clays – and the chemical fractionation of Ca-to Mg-rich carbonate in ALH84001 "rosettes". Longer-lived, and higher temperature, hydrothermal systems would have caused more silicate alteration than is seen and probably more complex mineral assemblages. Experimental and phase equilibria data on carbonate compositions similar to those present in the SNCs imply low temperatures of formation with cooling taking place over a short period of time (e.g. days). The ALH84001 carbonate also probably shows the effects of partial vapourisation and dehydration related to an impact event post-dating the initial precipitation. This shock event may have led to the formation of sulphide and some magnetite in the Fe-rich outer parts of the rosettes. Radiometric dating (K-Ar, Rb-Sr) of the secondary mineral assemblages in one of the nakhlites (Lafayette) suggests that they formed between 0 and 670 Myr, and certainly long after the crystallisation of the host igneous rocks. Crystallisation of ALH84001 carbonate took place 0.5 Gyr after the parent rock. These age ranges and the other research on these assemblages suggest that environmental conditions conducive to near-surface liquid water have been present on Mars periodically over the last 1 Gyr. This fluid activity cannot have been continuous over geological time because in that case much more silicate alteration would have taken place in the meteorite parent rocks and the soluble salts would probably not have been preserved. The secondary minerals could have been precipitated from brines with seawater-like composition, high bicarbonate contents and a weakly acidic nature. The co-existence of siderite (Fe-carbonate) and clays in the nakhlites suggests that the pCO2 level in equilibrium with the parent brine may have been 50 mbar or more. The brines could have originated as flood waters which percolated through the top few hundred meters of the crust, releasing cations from the surrounding parent rocks. The high sulphur and chlorine concentrations of the martian soil have most likely resulted from aeolian redistribution of such aqueously-deposited salts and from reaction of the martian surface with volcanic acid volatiles. The volume of carbonates in meteorites provides a minimum crustal abundance and is equivalent to 50–250 mbar of CO2 being trapped in the uppermost 200–1000 m of the martian crust. Large fractionations in 18O between igneous silicate in the meteorites and the secondary minerals (30) require formation of the latter below temperatures at which silicate-carbonate equilibration could have taken place (400°C) and have been taken to suggest low temperatures (e.g. 150°C) of precipitation from a hydrous fluid

Carbon and hydrogen isotope fractionations associated with dissimilatory iron-reducing bacteria

Shewanella putrefaciens strain CN-32 and Shewanella algae strain BrY were grown in laboratory cultures at 30 °C to characterize carbon and hydrogen isotope fractionation patterns related to the growth of iron-reducing bacteria. Ferric citrate or hydrous ferric oxide (HFO) was provided as the electron acceptor and lactate or H 2 (balanced with CO 2) was used as the electron donor. Because these bacteria are not known to grow chemoautotrophically, yeast extract was provided as a carbon source when cultures were grown on H 2/CO 2. Siderite formed only when HFO was used as the electron acceptor, possibly because of chelation of ferrous iron with dissolved citrate when ferric citrate was used as the electron acceptor. Carbon isotope enrichment factors for the siderite-CO 2 system (ε sid-CO 2) ranged from 13.3‰ to 14.5‰ when lactate was used as the carbon and energy source, which were consistent with theoretical calculations of equilibrium isotope fractionation (α sid-CO 2) for the siderite-CO 2 system [Geochim. Int. 18 (1981) 85]. In experiments using H 2/CO 2 as the energy source and yeast extract as the carbon source, carbon isotope enrichment factors were relatively low (0.5‰ to 7.4‰). The potential exists that a kinetic effect related to siderite precipitation rate influenced isotope partitioning or a dynamic balance was established between carbon sinks (i.e. biomass and solid carbonate) of diverging carbon isotope composition. A more quantitative estimate of ε sid-CO 2 for biological systems that contain ambient dissolved inorganic carbon (DIC) requires a deeper understanding of carbon flow dynamics in these compartmentalized closed systems. Finally, in experiments using H 2/CO 2 as an energy source, the hydrogen isotope composition of head gas H 2 and water were analyzed for D/H ratio. The results indicate that bacterial metabolism potentially facilitates isotope exchange between water and H 2. © 2002 Elsevier Science B.V. All rights reserved.link_to_subscribed_fulltex

Lipid biomarkers, carbon isotopes, and phylogenetic characterization of bacteria in California and Nevada hot springs

Microbial mats were collected from hot springs in California (Eagleville) and Nevada (Paradise Valley and Crescent Valley) to determine bacterial community structure and pathways of carbon cycling in different geothermal environments of the western United States. Phospholipid fatty acids (PLFA) at Eagleville contained even-numbered fatty acids, with 16:0 being the most abundant (48.8%), followed by 18:1ω9c (17.2%), 16:1ω7c/t (6.3%), and 18:0 (6.2%), which are consistent with lipid profiles of cyanobacteria or other phototrophic bacteria. The PLFA profiles at Paradise Valley and Crescent Valley were dominated by similar even-numbered fatty acids; however, branched fatty acids such as iso- and anteiso- 15:0 and 17:0 were also abundant (up to 7.1% compared to 2.0% at Eagleville), suggesting greater relative abundance of heterotrophic bacteria in these springs. Analysis of neutral lipids was only performed on Eagleville and Paradise Valley springs, which revealed abundant bacterial hopanoids including the 2-methylbacteriohopane-32,33,34,35-tetrol (2-methylBHT) that is specific to cyanobacteria; however, the diversity of hopanoid compounds was significantly lower at Eagleville than at Paradise Valley. The carbon-isotope composition of individual PLFA averaged -30.7 ± 1.3%(n = 7) at Eagleville, -28.0 ± 1.8%(n = 3) at Crescent Valley, and -29.7 ± 3.1%(n = 12) at Paradise Valley. Carbon isotope fractionation between PLFA and CO2 was only available for Eagleville (-11.7%) and Paradise Valley (-21.7%), which indicated the predominance of the Calvin cycle for CO2 fixation in these hot springs. Bacterial 16S rRNA genes were extracted from environmental samples at Eagleville and Paradise Valley but not Crescent Valley. Clone libraries indicated the predominance of cyanobacteria (50-75%) at these locations, which is consistent with the lipid profiles. Phylogenetic tree of the 16S rRNA genes indicated that most of the cyanobacterial sequences are unknown and may be specific to the Nevada and California hot springs. Phototrophic green non-sulfur bacteria were also present at Eagleville (13%) and Paradise Valley (7%). The remaining sequences were related to α-, β -, and γ-Proteobacteria, Acidobacteria, Deinococcus/Thermus, Bacteroidetes, and Spirochaetes. However, not all of these sequences were present at each of the springs. Results of this study demonstrate the consistency among lipid profiles (phenotypes), carbon isotopes (biogeochemistry), and 16S rRNA genes (genotypes) of the bacterial community in these hot springs, which cumulatively suggest the importance of cyanobacteria in primary production of biomass under the environmental conditions examined.link_to_subscribed_fulltex

Deep crustal carbonate rocks exposed by meteor impact on Mars

The surface of Mars is cold, dry, oxidizing, acidic and inhospitable to life. Similar conditions may have persisted for billions of years, suggesting that the best place to search for habitable environments is the subsurface. One hint of habitable conditions at depth is the presence of atmospheric methane, which may have formed through hydrothermal processes in the crust in the presence of CO2. The observation of hydrated minerals excavated by some impact craters suggests that ancient hydrothermal systems may have existed in the subsurface, but until now, none of those deposits has been linked to carbonate minerals and CO2 -rich environments. Previous detections of carbonate minerals that could be linked to an ancient CO2 -rich surface environment have been sparse. Here we show spectral evidence for carbonate- and phyllosilicate-bearing, layered and foliated bedrock exhumed from deep (about 6km) within the martian crust by a meteor impact. The mineral assemblage, textural properties and geologic context of the deposits indicate that these rocks are probably ancient sediments that were metamorphosed during burial by younger volcanic materials from the nearby Syrtis Major volcano. We suggest that these buried layered carbonates might be only a small part of a much more extensive ancient carbonate sedimentary record that has been buried by volcanic resurfacing and impact ejecta. Our discovery may help explain the origin of other carbonates on Mars and indicates a high-priority site for future exobiological exploration. © 2010 Macmillan Publishers Limited. All rights reserved. © 2010 Macmillan Publishers Limited. All rights reserved.Link_to_subscribed_fulltex

A high-resolution Late Glacial to Holocene record of environmental change in the Mediterranean from Lake Ohrid (Macedonia/Albania)

Lake Ohrid (Macedonia/Albania) is the oldest extant lake in Europe and exhibits an outstanding degree of endemic biodiversity. Here, we provide new high-resolution stable isotope and geochemical data from a 10 m core (Co1262) through the Late Glacial to Holocene and discuss past climate and lake hydrology (TIC, δ13Ccalcite, δ18Ocalcite) as well as the terrestrial and aquatic vegetation response to climate (TOC, TOC/N, δ13Corganic, Rock Eval pyrolysis). The data identifies 3 main zones: (1) the Late Glacial–Holocene transition represented by low TIC and TOC contents, (2) the early to mid-Holocene characterised by high TOC and increasing TOC/N and (3) the Late Holocene–Present which shows a marked decrease in TIC and TOC. In general, an overall trend of increasing δ18Ocalcite from 9 ka to present suggests progressive aridification through the Holocene, consistent with previous records from Lake Ohrid and the wider Mediterranean region. Several proxies show commensurate excursions that imply the impact of short-term climate oscillations, such as the 8.2 ka event and the Little Ice Age. This is the best-dated and highest resolution archive of past Late Glacial and Holocene climate from Lake Ohrid and confirms the overriding influence of the North Atlantic in the north-eastern Mediterranean. The data presented set the context for the International Continental scientific Drilling Program Scientific Collaboration On Past Speciation Conditions in Lake Ohrid project cores recovered in spring–summer 2013, potentially dating back into the Lower Pleistocene, and will act as a recent calibration to reconstruct climate and hydrology over the entire lake history