Autoxidation of the sea ice biomarker proxy IPSO <inf>25</inf> in the near-surface oxic layers of Arctic and Antarctic sediments

© 2019 Over the last decade or so, the mono- and di-unsaturated highly branched isoprenoid (HBI) lipids IP 25 (Ice Proxy with 25 carbon atoms) and IPSO 25 (Ice Proxy for the Southern Ocean with 25 carbon atoms) have emerged as useful proxies for sea ice in the Arctic and Antarctic, respectively. A more complete understanding of their respective proxy signatures, however, requires more detailed knowledge of their stability in the water column and in sediments. In the current study, we focused on the autoxidation of IPSO 25 , first by performing laboratory-based oxidation reactions on a purified sample and characterizing products based on detailed mass spectral analysis. We then analysed for the same oxidation products in near-surface sediments retrieved from the Arctic and the Antarctic, and some suspended organic matter from the Antarctic. Our data show that IPSO 25 is susceptible to partial autoxidation within the oxic layers of Arctic and Antarctic sediments, while the same processes appear not to be so important in the water column. Although the number of primary autoxidation reactions identified in sediments was not as large as in laboratory experiments, there was evidence for their subsequent modification by biotic degradation. Quantifying the extent of degradation of IPSO 25 and IP 25 in sediments, and thus the impact of such process on the use of these biomarkers as paleo sea ice proxies, remains challenging at this stage, since most of the primary oxidation products do not accumulate, likely due to secondary biodegradation reactions. Some interesting differences in reactivity were also observed between IPSO 25 and IP 25 present in the same Arctic sediments. This suggests that factors other than environmental control may influence the IPSO 25 /IP 25 ratio (i.e. DIP 25 ) in Arctic sediments

Lipids and their oxidation products as biomarkers for carbon cycling in the northwestern Mediterranean Sea: results from a sediment trap study

Classical lipid biomarkers (sterols, fatty acids and pigments) and their photo-oxidation and autoxidation products were measured in sediment trap samples collected during the summer of 1998 at the DYFAMED time-series station in the northwestern Mediterranean Sea to investigate changes in phytoplanktonic composition and alteration of particulate organic matter (POM). The study period covered a transitional situation from bloom event to oligotrophic conditions. At the beginning of the study, the phytoplankton community appeared to be mainly composed of diatoms, prymnesiophytes, pelagophytes and dinoflagellates. During the transition to the oligotrophic period, the contribution of small cells (pico- and nanoplankton) increased. Quantification of a ``poor' of oxidation products resulting from photo-oxidation and autoxidation of phytoplanktonic sterols, monounsaturated fatty acids and chlorophyll phytyl side-chain provided very useful indications concerning the alteration state of POM during the investigated period. This ``pool,'' composed of some oxidation products which are very sensitive (but labile) indicators and of others which are less sensitive (but more refractory), allowed us to obtain a large range of diagnostic information about organic matter behaviour. Thanks to these indicators, visible light-induced and autoxidative degradative processes, which have been virtually ignored to date owing to the lack of suitable tracers, may be easily distinguished and appear to act intensively in the northwestern Mediterranean Sea. (c) 2004 Elsevier B.V All rights reserved

Seasonal monitoring of lipid degradation processes in the western English Channel links bacterial 10S-DOX enzyme activity to free fatty acid production by phytoplankton

. In a few recent studies, the action of a bacterial dioxygenase (10S-DOX) on palmitoleic acid was observed within some polar and estuarine settings. To add further mechanistic information regarding the action of this enzyme in marine settings, we measured a range of lipids (sterols, fatty acids and the chlorophyll phytyl side chain) and their biotic and abiotic degradation products in water samples collected in 2018 from two depths (5 m and 25 m) at the temperate oceanographic time series site L4, located in the western English Channel. Lipid distributions indicated a dominance of diatoms and copepods during the spring bloom, while a peak in dinoflagellate activity was evident in samples collected from late summer/autumn, both outcomes being consistent with taxonomic data reported previously for the same sampling site and interval. Monitoring of lipid oxidation products characteristic of different degradation pathways showed a relatively weak effect of photo- and autoxidation processes, with these acting mainly on the more reactive lipids (i.e. chlorophyll and polyunsaturated fatty acids). In contrast, monitoring of biotic degradation processes revealed significant quantities of 10S-hydroxyhexadec-8(E)-enoic acid in samples collected at the end of April (reaching 40% of the residual parent palmitoleic acid), attributed to the involvement of bacterial 10-dioxygenase (10S-DOX) activity during the spring bloom. We propose that this enzyme could be utilised by bacteria to detoxify free fatty acids released by wounded diatoms in the presence of copepod

Enhanced biotic degradation of terrestrial POM in an estuarine salinity gradient: interactive effects of organic matter pools and changes of bacterial communities

International audienc

Effects of Chemical Agents on Physical Properties and Structure of Primary Pulp Chamber Dentin

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)This study evaluated the effects of chemical agents on the physical properties and structure of primary pulp chamber dentin using surface roughness, microhardness tests, and scanning electron microscopy (SEM). Twenty-five primary teeth were sectioned exposing the pulp chamber and were divided into five groups (n=5): NT, no treatment; SH1, 1% sodium hypochlorite (NaOCl); SH1U, 1% NaOCl+Endo-PTC (R); SH1E, 1% NaOCl+17% EDTA; and E, 17% EDTA. After dentin treatment, the specimens were submitted to roughness, microhardness testing, and SEM analysis. Roughness and microhardness data were submitted to one-way ANOVA and Tukey's test (P0.05). Microhardness values could not be obtained in the EDTA groups (SH1E and E). The presence of intertubular dentin with opened dentin tubules was observed in the NT, SH1, and SH1U groups. SH1E showed eroded and disorganized dentin with few opened tubules and the intertubular/peritubular dentin was partially removed. Considering the physical and structural approaches and the chemical agents studied, it can be concluded that NaOCl and NaOCl associated with Endo-PTC (R) were the agents that promoted the smallest changes in surface roughness, microhardness, and structure of the pulp chamber dentin of primary teeth. Microsc. Res. Tech. 77:52-56, 2014. (c) 2013 Wiley Periodicals, Inc.7715256Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [05/58561-1

One-year seasonal survey of the chlorophyll photodegradation process in the northwestern Mediterranean Sea

Particulate samples from the water column were collected monthly from depths of 5-150 m, between May 1996 and March 1997, in the northwestern Mediterranean Sea (Ligurian Sea) as part of the DYFAMED project within the French JGOFS program. These samples were analyzed by gas chromatography-electron impact mass spectrometry for their phytol and 3-methylidene-3,7,11-trimethylhexadecan-1,2-diol (phytyldiol) content. The corresponding Chlorophyll Phytyl side chain Photodegradation Index, molar ratio of phytyldiol to phytol, was calculated and the mean amount of chlorophyll photodegraded within the euphotic zone estimated. Seasonal differences in the chlorophyll photodegradation process appear in the one-year study. The chlorophyll appeared more photodegraded in the surface water (generally more than 40% photodegraded at 5-10m) than at the deep chlorophyll maximum (DCM) (40-50m) observed in the summer stratified waters (about 20% photodegraded). This difference was attributed to the healthy state of the phytoplankton community (coincidence with the highest primary production levels) and to the lower intensity of irradiance at the DCM level. On the other hand, the bulk of the detrital chlorophyll (chlorophyll associated with phytodetritus, phaeopigments) undergoes photodegradation before it sinks out of the photic zone. However, in January (winter mixed water) the pigments exported towards the sea floor were less photodegraded. This is thought to result from a shorter period of residence of the pigments in the photic zone due to vertical convection and grazing activity of macrozooplankton (salps), which are producers of rapid sinking fecal pellets. (C) 2002 Elsevier Science Ltd. All rights reserved

Biological mechanisms underlying priming of vascular plant material in the presence of diatoms

Priming effects that stimulate increased degradation of refractory organic matter by microorganisms following fresh organic matter input is a well-known phenomenon in terrestrial environments but remains controversial in marine environments. We used a combination of chemical (gas chromatography-EI quadrupole time of flight mass spectrometry) and molecular biology (DNA stable-isotope probing [DNA-SIP]) methods to trace the fate of terrestrially derived particulate organic matter (TPOM) and the response of the marine microbial community to fresh organic matter inputs. We tested the potential for priming effects among a mixture of marine and terrestrial microbial assemblages, amended either with only 13 C-labelled TPOM ( 13 C- Avena sativa ) or with an addition of 12 C- Skeletonema costatum (a marine diatom) as a labile co-substrate within the range of diatom concentrations found in estuaries. We monitored 13 C-labelled TPOM lipid tracers (long-chain fatty acids, n -alkan-1-ols, phytol, sitosterol, β-amyrin and components of cutins) throughout a 42 d incubation experiment. Comparisons with controls carried out without diatom addition showed faster decay of phytol, n -alkan-1-ols, and components of cuticular waxes in the presence of diatoms, while fatty acids and sitosterol were unaffected. Bacteria belonging to the Bacteroidota phylum (mainly Flavobacteria and Cytophaga ) were the dominant microbes involved in priming-induced TPOM degradation in the incubation treatments. Sphingomonadales and Rhizobiales , capable of lignin and hemicellulose degradation, also contributed to the degradation of TPOM but did not seem to contribute to priming effects related to increased diatom abundance. These lab-based results demonstrate direct evidence that priming of TPOM occurred selectively via a consortium of microbes

Caractérisation de la nature des particules en suspension transportées lors des étiages du Rhône (France) - Projet CANADER

International audienceStudies conducted on the Rhône River (France) highlights that, in the current context of climate change, the frequency of lowflow situations are likely to increase throughout its basin. For these extreme periods, it is expected that the proportion of organic matter (OM) contained in suspended particles will increase. However, the fixation of several contaminants is strongly linked to OM, where its form favors their complexation/adsorption. This is confirmed by the results of the CANADER project conducted on the Rhône River and its main tributaries (Saône, Ardèche and Durance Rivers) where the concentrations in suspended solids of several contaminants (anthropogenic metals, mercury and radionuclides) tend to increase during low water periods. For several anthropogenic metals (Cr, Ni, Zn), concentrations sometimes exceed the probable effect concentration (PEC). The decrease on natural metals (from the earth's crust) coupled with the increase in methyl-mercury (suggesting bioaccumulation of concentrations in phytoplankton) shows that a significant proportion of the OM that transits at low flow is autochthonous. The first results of sterol analysis suggest that OM origins differ depending the Rhône River and its tributaries, and further work must be done to characterize the sources of these particles.Les études menées sur le Rhône soulignent que dans le contexte actuel de changement climatique les situations de faible débit et d’étiage seront probablement de plus en plus fréquentes. Pour ces périodes extrêmes, il est attendu que la proportion de matière organique (MO) contenue dans les particules en suspension augmente. Or, la fixation de certains contaminants est fortement liée à la MO car sa forme favorise la complexation/adsorption de ceux-ci. C’est ce que confirment les résultats du projet CANADER conduit sur le Rhône et ses principaux affluents (Saône, Ardèche et Durance) où les concentrations dans les matières en suspension de certains contaminants (métaux anthropiques, mercure et radionucléides) ont tendance à augmenter en période d’étiage. Pour certains métaux anthropiques (Cr, Ni, Zn), les concentrations dépassent parfois le seuil d’effet probable (PEC). Par ailleurs, la diminution des métaux naturels (issus de la croûte terrestre – Co Cs Rb et V) couplée à l’augmentation du méthylmercure (suggérant une bioaccumulation des concentrations dans le phytoplancton) montre qu’une proportion non négligeable de la MO qui transite à l’étiage est autochtone. Les premiers résultats de mesure des stérols suggèrent que l’origine de cette MO diffère selon le Rhône et ses affluents, et des travaux additionnels doivent être réalisés pour caractériser les sources de ces particules