Beschreibung: Bottom-water oxygen supply is a key factor governing the biogeochemistry and community composition of marine sediments. Whether it also determines carbon burial rates remains controversial. We investigated the effect of varying oxygen concentrations (170 to 0 μM O2) on microbial remineralization of organic matter in seafloor sediments and on community diversity of the northwestern Crimean shelf break. This study shows that 50% more organic matter is preserved in surface sediments exposed to hypoxia compared to oxic bottom waters. Hypoxic conditions inhibit bioturbation and decreased remineralization rates even within short periods of a few days. These conditions led to the accumulation of threefold more phytodetritus pigments within 40 years compared to the oxic zone. Bacterial community structure also differed between oxic, hypoxic, and anoxic zones. Functional groups relevant in the degradation of particulate organic matter, such as Flavobacteriia, Gammaproteobacteria, and Deltaproteobacteria, changed with decreasing oxygenation, and the microbial community of the hypoxic zone took longer to degrade similar amounts of deposited reactive matter. We conclude that hypoxic bottom-water conditions—even on short time scales—substantially increase the preservation potential of organic matter because of the negative effects on benthic fauna and particle mixing and by favoring anaerobic processes, including sulfurization of matter.

Beschreibung: The potential of marine dissolved organic matter (DOM) for free radical scavenging has been extensively evaluated, however, the quantitative assessment of the antioxidant potential has been recently measured for the first time. The linkage of the DOM antioxidant potential to its molecular composition has not yet been examined. Following this line, this article takes a step forward by assessing, throughout a polarity-mediated fractionation, (1) the antioxidant capacity and phenolic content and (2) the molecular characterization of DOM in a more exhaustive manner. (3) The DOM antioxidant potential and phenolic content was linked to the molecular composition of DOM, which was molecularly characterized using ultrahigh resolution Fourier transform Ion Cyclotron Resonance mass spectrometry (FT-ICR MS). Antioxidant activity and phenolic content were quantified by the free radical 2,2’-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS⋅) and the Folin-Ciocalteu methods, respectively. We considered three types of different natural DOM samples: the deep North Pacific Ocean, the oligotrophic surface of the North Pacific Ocean and porewater from the sulfidic tidal flats of the Wadden Sea. Bulk porewater and its individual polarity fractions presented the highest antioxidant activity and phenolic content. DOM from the water column samples had lower antioxidant activity and phenolic content than porewater, but exceeded what it is commonly found in macroalgae, microalgae, fruits and vegetables with cosmeceutical purposes. Our values were similar to published values for terrestrial DOM. The variations in bioactivity were dependent on polarity and molecular composition. The high resolution and high mass accuracy used to determine the molecular composition of marine DOM and the chemometric and multistatistical analyses employed have allowed to distinguish molecular categories that are related to the bioactive potential. As a future perspective, we performed cytotoxicity tests with human cells and propose marine DOM as a natural ingredient for the development of cosmeceutical products.

Beschreibung: Sinking of large organic food falls i.e. kelp, wood and whale carcasses to the oligotrophic deep-sea floor promotes the establishment of locally highly productive and diverse ecosystems, often with specifically adapted benthic communities. However, the fragmented spatial distribution and small area poses challenges for the dispersal of their microbial and faunal communities. Our study focused on the temporal dynamics and spatial distributions of sunken wood bacterial communities, which were deployed in the vicinity of different cold seeps in the Eastern Mediterranean and the Norwegian deep-seas. By combining fingerprinting of bacterial communities by ARISA and 454 sequencing with in situ and ex situ biogeochemical measurements, we show that sunken wood logs have a locally confined long-term impact (〉 3y) on the sediment geochemistry and community structure. We confirm previous hypotheses of different successional stages in wood degradation including a sulphophilic one, attracting chemosynthetic fauna from nearby seep systems. Wood experiments deployed at similar water depths (1100–1700 m), but in hydrographically different oceanic regions harbored different wood-boring bivalves, opportunistic faunal communities, and chemosynthetic species. Similarly, bacterial communities on sunken wood logs were more similar within one geographic region than between different seas. Diverse sulphate-reducing bacteria of the Deltaproteobacteria, the sulphide-oxidizing bacteria Sulfurovum as well as members of the Acidimicrobiia and Bacteroidia dominated the wood falls in the Eastern Mediterranean, while Alphaproteobacteria and Flavobacteriia colonized the Norwegian Sea wood logs. Fauna and bacterial wood-associated communities changed between 1 to 3 years of immersion, with sulphate-reducers and sulphide-oxidizers increasing in proportion, and putative cellulose degraders decreasing with time. Only 6% of all bacterial genera, comprising the core community, were found at any time on the Eastern Mediterranean sunken wooden logs. This study suggests that biogeography and succession play an important role for the composition of bacteria and fauna of wood-associated communities, and that wood can act as stepping-stones for seep biota.

Beschreibung: We hypothesized that microbial and photochemical processing of dissolved organic matter (DOM) determines its molecular formula composition in aquatic systems to a greater degree than does the original source of the DOM. To test this hypothesis, we exposed DOM from a leachate of a wetland plant (Juncus effusus) to solar radiation or incubated it in the dark for 1.25 yr. Analysis of the extracted DOM of the leachates via Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) identified 2800 molecular formulae. Of the formulae in the initial DOM, 11% were lost during microbial decomposition in the dark and 54% under solar radiation. Solar radiation also produced a large number of formulae containing N, that were preferentially degraded by microorganisms (47% loss). We compared the “recalcitrant formulae”, i.e. those not degraded in the experiment, with those of DOM from the deep North Pacific Ocean. Of the deep sea DOM formulae, 18% were present in the recalcitrant fraction of the initial DOM. An additional 18% of the formulae in marine DOM were photoproduced and recalcitrant, and 8% were produced by microbes in the experiment. Consequently, 44% of the deep sea DOM shares identical molecular formulae with the recalcitrant DOM from the experiment, most of which were produced by the combined action of sunlight and microbes. This indicates that processes in the water column may be more important than the original source in determining the composition of bulk DOM.

Beschreibung: The vast majority of freshly produced oceanic dissolved organic carbon (DOC) is derived from marine phytoplankton, then rapidly recycled by heterotrophic microbes. A small fraction of this DOC survives long enough to be routed to the interior ocean, which houses the largest and oldest DOC reservoir. DOC reactivity depends upon its intrinsic chemical composition and extrinsic environmental conditions. Therefore, recalcitrance is an emergent property of DOC that is analytically difficult to constrain. New isotopic techniques that track the flow of carbon through individual organic molecules show promise in unveiling specific biosynthetic or degradation pathways that control the metabolic turnover of DOC and its accumulation in the deep ocean. However, a multivariate approach is required to constrain current carbon fluxes so that we may better predict how the cycling of oceanic DOC will be altered with continued climate change. Ocean warming, acidification, and oxygen depletion may upset the balance between the primary production and heterotrophic reworking of DOC, thus modifying the amount and/or composition of recalcitrant DOC. Climate change and anthropogenic activities may enhance mobilization of terrestrial DOC and/or stimulate DOC production in coastal waters, but it is unclear how this would affect the flux of DOC to the open ocean. Here, we assess current knowledge on the oceanic DOC cycle and identify research gaps that must be addressed to successfully implement its use in global scale carbon models.

Beschreibung: Marine organic matter (OM) sinks from surface water to the seafloor via the biological pump. Benthic communities, which use this sedimented OM as an energy and carbon source, produce dissolved OM (DOM) in the process of degradation, enriching the sediment pore water with fresh DOM compounds. In the oligotrophic deep Arctic basin, particle flux is low but highly seasonal. We hypothesized that the molecular signal of freshly deposited, primary produced OM would be detectable in surface sediment pore water, which should differ in DOM composition from bottom water and deeper sediment pore water. The study focused on (i) the molecular composition of the DOM in sediment pore water of the deep Eurasian Arctic basins, (ii) the signal of marine vs. terrigenous DOM represented by different compounds preserved in the pore water and (iii) the relationship between Arctic Ocean ice cover and DOM composition. Composition based on mass spectrometric information, obtained via 15 T Fourier transform ion cyclotron resonance mass spectrometry, was correlated with environmental parameters with partial least square analysis. The fresh marine detrital OM signal from surface water was limited to pore water from 〈 5 cm sediment depth. The productive ice margin stations showed a higher abundance of peptide, unsaturated aliphatic and saturated fatty acid molecular formulae, indicative of recent phytodetritus deposition, than the multiyear ice-covered stations, which had a stronger aromatic signal. The study contributes to the understanding of the coupling between Arctic Ocean productivity and its depositional regime, and how it may be altered in response to sea ice retreat and increasing river runoff.

Beschreibung: A high-resolution sea surface temperature and paleoproductivity reconstruction on a sedimentary record collected at 36°S off central-south Chile (GeoB 7165-1, 36°33′S, 73°40′W, 797 m water depth, core length 750 cm) indicates that paleoceanographic conditions changed abruptly between 18 and 17 ka. Comparative analysis of several cores along the Chilean continental margin (30°–41°S) suggests that the onset and the pattern of deglacial warming was not uniform off central-south Chile due to the progressive southward migration of the Southern Westerlies and local variations in upwelling. Marine productivity augmented rather abruptly at 13–14 ka, well after the oceanographic changes. We suggest that the late deglacial increase in paleoproductivity off central-south Chile reflects the onset of an active upwelling system bringing nutrient-rich, oxygen-poor Equatorial Subsurface Water to the euphotic zone, and a relatively higher nutrient load of the Antarctic Circumpolar Current. During the Last Glacial Maximum, when the Southern Westerlies were located further north, productivity off central-south Chile, in contrast to off northern Chile, was reduced due to direct onshore-blowing winds that prevented coastal upwelling and export production.

Beschreibung: Archaea are ubiquitous and abundant microorganisms on Earth that mediate key global biogeochemical cycles. The headgroup attached to the sn‐1 position of the glycerol backbone and the ether‐linked isoprenoid lipids are among the diagnostic traits that distinguish Archaea from Bacteria and Eukarya. Over the last 30 years, numerous archaeal lipids have been purified and described in pure cultures. Coupled high‐performance liquid chromatography (HPLC) ion‐trap mass spectrometry (ITMS) now enables the detection and rapid identification of intact polar lipids in relatively small and complex samples, revealing a wide range of archaeal lipids in natural environments. Although major structural groups have been identified, the lack of a systematic evaluation of MS/MS fragmentation patterns has hindered the characterization of several atypical components that are therefore considered as unknowns. Here, we examined mass spectra resulting from lipid analysis of natural microbial communities using HPLC/electrospray ionization (ESI)‐ITMSn, and depicted the systematics in MS2 fragmentation of intact archaeal lipids. This report will be particularly useful for environmental scientists interested in a rapid and straightforward characterization of intact archaeal membrane lipids.

Beschreibung: Fluids from the diffusive hydrothermal vent Woody located at the Menez Gwen hydrothermal field were collected directly from a fissure using a Kiel pumping system (KIPS). The fluids were incubated in a biodegradation experiment with the resident microbial community at in situ temperature (55 °C). In addition to the initial fluid (T0), sub-samples were collected at three time points: 12.5 h (T1), 38 h (T2) and 180 h (Tfinal). Whole water samples were characterized by spectrophotometry and for dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) concentrations. Solid-phase extracted dissolved organic matter (SPE-DOM) was molecularly characterized using a 15 Tesla Fourier-transform ion cyclotron resonance mass spectrometer (FT-ICR-MS). Based on Mg2 + concentrations, vent fluids were diluted ca. 1:99% with seawater. SPE-DOC concentrations remained constantly low (30 μM) over the course of incubation, while DOC and TDN (1180 μM and 16 μM, respectively, at T0) decreased sharply (to 80 μM and 9 μM, respectively, at Tfinal). This biolabile DOC is likely composed of volatiles and short-chain hydrocarbons, and the reason behind their extraordinarily high concentration remains unknown. Molecular characterization of SPE-DOM in fluids and seawater identified over 3000 molecular formulae, which were separated into different groups according to their reactivity. The half-life of the more reactive groups ranged between 6–7 h, 18–21 h and 5–106 days, and represented 7.3, 2.0 and 7.5% of the total formulae present in T0, while the majority (83%) did not exhibit any significant trend during the experiment. Despite the small molecular changes in SPE-DOM, a decrease in the number of formulae and average molecular mass was observed, the latter consistent with an increase in the spectral slope over the wavelength range 275–295 nm (S275–295) during the experiment. An increase in aromatic molecular formulae during the incubation was also corroborated by a concurrent increase in the absorption coefficient at 254 nm normalized to DOC concentrations (SUVA254), an optical indicator of aromatic content. Thus both FT-ICR-MS and optical properties over the course of the incubation corroborated a decrease in molecular mass and increase in aromaticity. This study is the first to report the optical and molecular transformations of bio-labile DOM from diffusive hydrothermal systems.

Beschreibung: Hydrothermal vent fluids contain thermally modified dissolved organic matter (DOM) originally entrained from sediments and seawater. We hypothesized that in hydrothermal systems DOM molecular composition is modulated by (i) fluid contribution, (ii) thermal decomposition and pH, and (iii) aspects particular to the vent system. Hence, solid phase extracted (SPE) DOM samples collected along the Mid-Atlantic Ridge (MAR) were molecularly characterized via 15 Tesla Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The molecular character of an oceanic DOM sample was also determined before and after thermal (300 °C) decomposition at acidic and neutral pH. Multivariate statistical analysis indicated that DOM composition was strongly influenced by fluid contribution (Mg2+ concentration between 12 and 54 mM), which correlated positively with measured temperature (between 8 and 375 °C). In comparison, pH of the fluids (between 2.5 and 6.9) had a minor influence. Seafloor pressure, used as a theoretical maximum fluid temperature at the seafloor, separated the fluids collected at Menez Gwen from deeper locations, due to the higher abundance of peptide, carboxyl-rich alicyclic (CRAM) and aromatic molecular formulae at Menez Gwen. Compared with seawater DOM, thermally decomposed DOM had on average lower molecular mass, lower O/C ratios, fewer double bond equivalents, and fewer CRAM formulae but higher aromaticity - the same molecular features displayed by MAR hydrothermal fluids. The study provides evidence that thermal reworking plays a major role in shaping DOM mixtures from hydrothermal fluids along the MAR, which partly represent thermally reworked marine DOM that survived hydrothermal circulation.