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The MALINA oceanographic campaign was conducted during summer 2009 to investigate the carbon stocks and the processes controlling the carbon fluxes in the Mackenzie River estuary and the Beaufort Sea. During the campaign, an extensive suite of physical, chemical and biological variables were measured across seven shelf–basin transects (south–north) to capture the meridional gradient between the estuary and the open ocean. Key variables such as temperature, absolute salinity, radiance, irradiance, nutrient concentrations, chlorophyll a concentration, bacteria, phytoplankton and zooplankton abundance and taxonomy, and carbon stocks and fluxes were routinely measured onboard the Canadian research icebreaker CCGS Amundsen and from a barge in shallow coastal areas or for sampling within broken ice fields. Here, we present the results of a joint effort to compile and standardize the collected data sets that will facilitate their reuse in further studies of the changing Arctic Ocean. The data set is available at https://doi.org/10.17882/75345 (Massicotte et al., 2020).

Lipid tracers including fatty acids, hydroxyacids, n-alkanols, sterols and triterpenoids were used to determine the origin and fate of suspended particulate organic matter (POM) collected in the Rhône River (France). This seasonal survey (April 2011 to May 2013) revealed a year-round strong terrestrial higher-plant contribution to the particulate organic matter (POM), with significant algal inputs observed in March and attributed to phytoplanktonic blooms likely dominated by diatoms. Major terrigenous contributors to our samples are gymnosperms, and more precisely their roots and stems, as evidenced by the presence of high proportions of ω-hydroxydocosanoic acid (a suberin biomarker). The high amounts of coprostanol detected clearly show that the Rhône River is significantly affected by sewage waters. Specific sterol degradation products were quantified and used to assess the part of biotic and abiotic degradation of POM within the river. Higher-plant-derived organic matter appears to be mainly affected by photo-oxidation and autoxidation (free radical oxidation), while organic matter of mammal or human origin, evidenced by the presence of coprostanol, is clearly more prone to bacterial degradation. Despite the involvement of an intense autoxidation-inducing homolytic cleavage of peroxy bonds, a significant proportion of hydroperoxides is still intact in higher plant debris. These compounds could affect the degradation of terrestrial material by inducing an intense autoxidation upon its arrival at sea.

The lipid content of seven samples of sinking particles collected with sediment traps moored at ~ 100 m depth in summer and fall across the Canadian Beaufort Shelf (Arctic Ocean) was investigated. Our main goal was to quantify and characterize the biotic and abiotic degradation processes that acted on sinking material during these periods. Diatoms, which dominated the phytoplanktonic assemblage in every trap sample, appeared to be remarkably sensitive to Type II (i.e. involving singlet oxygen) photodegradation processes in summer, but seemed to be relatively unaffected by biotic degradation at the same time. Hence, the relative recalcitrance of phytodetritus towards biodegradation processes during the Arctic midnight sun period was attributed to the strong photodegradation state of heterotrophic bacteria, which likely resulted from the efficient transfer of singlet oxygen from photodegraded phytoplanktonic cells to attached bacteria. In addition, the detection in trap samples of photoproducts specific to wax ester components found in herbivorous copepods demonstrated that zooplanktonic faecal material exported out of the euphotic zone in summer were affected by Type II photodegradation processes as well. By contrast, sinking particles collected during the autumn were not influenced by any light-driven stress. Further chemical analyses showed that photodegraded sinking particles contained an important amount of intact hydroperoxides, which could then induce a strong oxidative stress in underlying sediments.

For the next decades significant climatic changes should occur in the Arctic zone. The expected destabilisation of permafrost and its consequences for hydrology and plant cover should increase the input of terrigenous carbon to coastal seas. Consequently, the relative importance of the fluxes of terrestrial and marine organic carbon to the seafloor will likely change, strongly impacting the preservation of organic carbon in Arctic marine sediments. Here, we investigated the lipid content of surface sediments collected on the Mackenzie basin in the Beaufort Sea. Particular attention was given to biotic and abiotic degradation products of sterols and monounsaturated fatty acids. By using sitosterol and campesterol degradation products as tracers of the degradation of terrestrial higher plant inputs and brassicasterol degradation products as tracers of degradation of phytoplanktonic organisms, it could be observed that autoxidation, photooxidation and biodegradation processes act much more intensively on higher plant debris than on phytoplanktonic organisms. Examination of oxidation products of monounsaturated fatty acids showed that photo- and autoxidation processes act more intensively on bacteria than on phytodetritus. Enhanced damages induced by singlet oxygen (transferred from senescent phytoplanktonic cells) in bacteria were attributed to the lack of an adapted antioxidant system in these microorganisms. The strong oxidative stress observed in the sampled sediments resulted in the production of significant amounts of epoxy acids and unusually high proportions of monounsaturated fatty acids with a trans double bond. The formation of epoxy acids was attributed to peroxygenases (enzymes playing a protective role against the deleterious effects of fatty acid hydroperoxides in vivo), while cis/trans isomerisation was probably induced by thiyl radicals produced during the reaction of thiols with hydroperoxides. Our results confirm the important role played by abiotic oxidative processes in the degradation of marine bacteria and do not support the generally expected refractory character of terrigenous material deposited in deltaic systems.

Rationale: Ferulic and p-coumaric acids are important biological and structural components of plant cell walls and possess antioxidant and antimicrobial properties. These phenolic acids are widespread in environmental samples. However, when they are present at very low concentrations or in very complex lipid extracts, their identification and quantification can be challenging., Methods: The electron ionization mass spectrometry (EI-MS) fragmentation pathways of ferulic and p-coumaric acid trimethylsilyl (TMS) derivatives were investigated. These pathways were deduced by (i) low-energy collision-induced dissociation (CID) gas chromatography (GC)/EI-MS/MS, (ii) accurate mass measurement, and (iii) 13 C labelling. These compounds were then characterized and quantified in multiple reaction monitoring (MRM) mode in total lipid extracts of deposited atmospheric particles using highly specific transitions based on the main fragmentation pathways elucidated., Results: Low-energy CID-MS/MS analyses, accurate mass measurement and 13 C labelling enabled us to elucidate EI-MS fragmentations of ferulic and p-coumaric acid TMS derivatives. Some specific fragmentations proved useful for subsequent characterization and quantification of these compounds. As an application of some of the described fragmentations, trace amounts of these phenolic acids were characterized and quantified in MRM mode in wet- and dry-deposited atmospheric particles containing low proportions of organic matter., Conclusions: EI-MS fragmentations of ferulic and p-coumaric acid TMS derivatives exhibit specific fragment ions that can be very useful for the quantification of trace amounts of both phenolic acids in environmental samples., (© 2022 John Wiley & Sons Ltd.)

Comparison of Type II photosensitized oxidation of lipids (the photodynamic effect) and photodegradation of chlorophyll (sensitizer photobleaching) in samples of particulate matter collected previously from locations representing a diverse range of latitudes reveals an enhancement of the photooxidation of lipids at the expense of chlorophyll photodegradation in the polar regions. The efficiency of the photodynamic effect appears to be particularly high in sinking particles collected under sea ice and is attributed to the rapid settling of highly aggregated sympagic algae to depths of low light transmission favouring the photodynamic effect at the expense of photobleaching of the sensitizer. Paradoxically, the low efficiency of Type II photosensitized oxidation of lipids observed in temperate and equatorial regions is associated with high solar irradiances in these regions. Type II photosensitized oxidation of lipids in senescent phytoplankton seems thus to be strongly dependent of the intensity of solar irradiance., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The aim of this paper was to study the effects of temperature and irradiance on the photodegradation state of killed phytoplankton cells. For this purpose, killed cells of the diatom Chaetoceros neogracilis RCC2022 were irradiated (photosynthetically active radiation) at 36 and 446 J · s(-1)  · m(-2) (for the same cumulative dose of irradiation energy) and at two temperatures (7°C and 17°C). Analyses of specific lipid tracers (fatty acids and sterols) revealed that low temperatures and irradiances increased photooxidative damages of monounsaturated lipids (i.e., palmitoleic acid, cholesterol and campesterol). The high efficiency of type II photosensitized degradation processes was attributed to: (i) the relative preservation of the sensitizer (chlorophyll) at low irradiances allowing a longer production of singlet oxygen and (ii) the slow diffusion rate of singlet oxygen through membranes at low temperatures inducing more damages. Conversely, high temperatures and irradiances induced (i) a rapid degradation of the photosensitizer and a loss of singlet oxygen by diffusion outside the membranes (limiting type II photosensitized oxidation), and (ii) intense autoxidation processes degrading unsaturated cell lipids and oxidation products used as photodegradation tracers. Our results may explain the paradoxical relationship observed in situ between latitude and photodegradation state of phytoplankton cells., (© 2016 Phycological Society of America.)

The effects of singlet oxygen ((1)O2) transfer to bacteria attached on phytodetritus were investigated under laboratory-controlled conditions. For this purpose, a nonaxenic culture of Emiliania huxleyi in late stationary phase was studied for bacterial viability. Our results indicated that only 9 ± 3% of attached bacteria were alive compared to 46 ± 23% for free bacteria in the E. huxleyi culture. Apparently, under conditions of low irradiance (36 W m(-2)), during the culture, the cumulative dose received (22,000 kJ m(-2)) was sufficiently important to induce an efficient (1)O2 transfer to attached bacteria during the senescence of E. huxleyi cells. At this stage, attached bacteria appeared to be dominated by pigmented bacteria (Maribacter, Roseobacter, Roseovarius), which should resist to (1)O2 stress probably due to their high contents of carotenoids. After subsequent irradiation of the culture until fully photodegradation of chlorophyll, DGGE analyses showed that the diversity of bacteria attached to E. huxleyi cells is modified by light. Photooxidative alterations of bacteria were confirmed by the increasing amounts of cis-vaccenic photoproducts (bacterial marker) per bacteria observed during irradiation time. Interestingly, preliminary chemotaxis experiments showed that Shewanella oneidensis considered here as a model of motile bacteria was attracted by phytodetritus producing or not (1)O2. This lack of repulsive effects could explain the high mortality rate of bacteria measured on E. huxleyi cells.

Autoxidation of several mono-, di-, tri- and tetra-unsaturated highly branched isoprenoid (HBI) alkenes was induced in organic solvents using a radical initiator and enhancer, and their degradation rates were compared to those of classical phytoplanktonic lipids (mono-unsaturated fatty acids, sterols and chlorophyll phytyl side-chain). Autoxidation of two HBI trienes was also investigated in senescent and highly photodegraded diatom cells, collected in the Antarctic, using Fe(2+) ions as radical inducers. Autoxidation rates of HBI alkenes were found to increase with the number of tri-substituted double bonds, as expected. Further, HBI trienes possessing one bis-allylic position (where hydrogen abstraction is highly favoured) were found to be particularly reactive towards autoxidation and degraded at similar rates compared to polyunsaturated fatty acids in diatom cells. By comparison of the autoxidation products of the most reactive tri-unsaturated HBI with the corresponding photooxidation products, some specific tracers of these two types of abiotic degradation processes were identified. The lack of reactivity of the mono-unsaturated HBI IP25 and a structurally similar di-unsaturated HBI towards autoxidative degradation supports the good preservation of these biomarkers in marine sediments.

The photooxidation of cellular monounsaturated fatty acids was investigated in senescent phytoplanktonic cells (Emiliania huxleyi) and in their attached bacteria under laboratory controlled conditions. Our results indicated that UV-visible irradiation of phytodetritus induced the photooxidation of oleic (produced by phytoplankton and bacteria) and cis-vaccenic (specifically produced by bacteria) acids. These experiments confirmed the involvement of a substantial singlet oxygen transfer from senescent phytoplanktonic cells to attached bacteria, and revealed a significant correlation between the concentration of chlorophyll, a photosensitizer, in the phytodetritus and the photodegradation state of bacteria. Hydroperoxyacids (fatty acid photoproducts) appeared to be quickly degraded to ketoacids and hydroxyacids in bacteria and in phytoplanktonic cells. This degradation involves homolytic cleavage (most likely induced by UV and/or transition metal ions) and peroxygenase activity (yielding epoxy acids).