Accumulation rates and composition of organic matter in sediments off Peru

Deep-sea sediment samples from three Ocean Drilling Program (ODP) Leg 112 sites on the Peru continental margin were investigated, using a number of organic geochemical and organic petrographic techniques, for amounts and compositions of the organic matter preserved. Preliminary results include mass accumulation rates of organic carbon at Site 679 and characteristics of the organic facies for sediments from Sites 679, 681, and 684. Organic-carbon contents are high, with few exceptions. Particularly high values were determined in the Pliocene interval at Site 684 (4%-7.5%) and in the early Pliocene to Quaternary section of Hole 679D (2%-9%). Older sediments at this site have distinctively lower organic-carbon contents (0.2%-2.5%). Mass accumulation rates of organic matter at Site 679 are 0.02 to 0.07 g carbon/cm**2/k.y. for late Miocene to early Pliocene sediments and higher by a factor of 5 to 10 in the Quaternary sediments. The organic matter in all samples has a predominantly marine planktonic and bacterial origin, with minor terrigenous contribution. Organic particle sizes are strikingly small, so that only a minor portion is covered by visual maceral analysis. Molecular organic-geochemical data were obtained for nonaromatic hydrocarbons, aromatic hydrocarbons (including sulfur compounds), alcohols, ketones, esters, and carboxylic acids. Among the total extractable lipids, long-chain unsaturated ketones from Prymnesiophyte algae strongly predominate among the gas chromatography (GC) amenable components. Steroids are major constituents of the ketone and free- and bound-alcohol fractions. Perylene is the most abundant aromatic hydrocarbon, whereas in the nonaromatic hydrocarbon fractions, long-chain n-alkanes from higher land plants predominate, although the total terrigenous organic matter proportion in the sediments is small.

Stable carbon and nitrogen isotope composition of organic matter in sediments of the Oman Margin

Stable isotopic compositions of carbon and nitrogen and organic carbon content of sediments ranging from the Pliocene to the Pleistocene-Holocene in age from the Oman Margin (ODP Sites 724 and 725) are reported. In general, the organic carbon content is greater than 2% at Site 724. Prior to the Pleistocene-Holocene at this site, sediments with higher content of organic matter were deposited owing to favorable preservation conditions and/or higher productivity. In the Pleistocene, lower amounts of organic matter have been preserved; this material generally has more enriched nitrogen isotopic compositions. This may indicate intensification of the Oxygen Minimum Zone and denitrification with the onset of the Pleistocene. A correlation of carbon isotope content of these sediments with oxygen isotope stages at Site 724 indicates an enrichment in 13C during glacial events. Based on the stable isotope evidence of both carbon and nitrogen, there does not appear to be major input of terrigenous-derived allochthonous material in this marine environment. The timing and extent of monsoon winds on the productivity of this region are not evident, but require further studies for collaborative interpretation of small-scale features in the isotopic and carbon content of this environment.

Carbon dioxide assimilation rate, gas and ion composition in samples, and bacterial production of organic matter within and above the Broken Spur and TAG hydrothermal fields, Mid-Atlantic Ridge

Rate of CO2 assimilation was determined above the Broken Spur and TAG active hydrothermal fields for three main ecosystems: (1) hydrothermal vents; (2) 300 m near-bottom layer of plume water; and (3) bottom sediments. In water samples from warm (40-45°C) vents assimilation rates were maximal and reached 2.82-3.76 µg C/l/day. In plume waters CO2 assimilation rates ranged from 0.38 to 0.65 µg C/l/day. In bottom sediments CO2 assimilation rates varied from 0.8 to 28.0 µg C/l/day, rising up to 56 mg C/kg/day near shrimp swarms. In the most active plume zone of the long-living TAG field bacterial production of organic matter (OM) from carbonic is up to 170 mg C/m**2/day); production of autotrophic process of bacterial chemosynthesis reaches about 90% (156 mg C/m**2/day). Thus, chemosynthetic production of OM in September-October is almost equal to that of photosynthetic production in the oceanic region. Bacterial production of OM above the Broken Spur hydrothermal field is one order lower and reaches only 20 mg C/m**2/day.

Composition of bitumen in the organic matter of Black Sea sediments from DSDP Hole 42-379B

Bituminologic analysis of sediment cores from the Black Sea (water depth up to 2000 m, drilling depth up to 625 m) has revealed all components typical for fossilized rocks, viz. hydrocarbons, resins, asphaltenes, and insoluble matter. Proportions of these components, their composition and properties do not display any dependence on depth in hole and seem to be governed by composition of organic matter and conditions and degree of its transformation at early stages of lithogenesis.

Organic and inorganic geochemistry and archaeal community composition of hypersaline sediments from Orca Basin, RV Atlantis Expedition AT18-02

Among the most extreme habitats on Earth, dark, deep, anoxic brines host unique microbial ecosystems that remain largely unexplored. As the terminal step of anaerobic degradation of organic matter, methanogenesis is a potentially significant but poorly constrained process in deep-sea hypersaline environments. We combined biogeochemical and phylogenetic analyses as well as incubation experiments to unravel the origin of methane in hypersaline sediments of Orca Basin in the northern Gulf of Mexico. Substantial concentrations of methane (up to 3.4 mM) coexisted with high concentrations of sulfate (16-43 mM) in two sediment cores retrieved from the northern and southern parts of Orca Basin. The strong depletion of 13C in methane (-77 to -89 per mill) pointed towards a biological source. While low concentrations of competitive substrates limited the significance of hydrogenotrophic and acetoclastic methanogenesis, the presence of non-competitive methylated substrates (methanol, trimethylamine, dimethyl sulfide, dimethylsulfoniopropionate) supported the potential for methane generation through methylotrophic methanogenesis. Thermodynamic calculations demonstrated that hydrogenotrophic and acetoclastic methanogenesis were unlikely to occur under in situ conditions, while methylotrophic methanogenesis from a variety of substrates was highly favorable. Likewise, carbon isotope relationships between methylated substrates and methane supported methylotrophic methanogenesis as the major source of methane. Stable isotope tracer and radiotracer experiments with 13C bicarbonate, acetate and methanol as well as 14C-labeled methylamine indicated that methylotrophic methanogenesis was the predominant methanogenic pathway. Based on 16S rRNA gene sequences, halophilic methylotrophic methanogens related to the genus Methanohalophilus dominated the benthic archaeal community in the northern basin but also occurred in the southern basin. High abundances of methanogen lipid biomarkers such as intact polar and polyunsaturated hydroxyarchaeols were detected in sediments from the northern basin, with lower abundances in the southern basin. Strong 13C-depletion of saturated and monounsaturated hydroxyarchaeol were consistent with methylotrophic methanogenesis as the major methanogenic pathway. Collectively, the availability of methylated substrates, thermodynamic calculations, experimentally determined methanogenic activity as well as lipid and gene biomarkers strongly suggested methylotrophic methanogenesis as predominant pathway of methane formation in the presence of sulfate in Orca Basin sediments.

Amount and chemical composition of the organic matter contributed by overstory and understory vegetation to forest soil.

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Relationships between flavour, lipid composition and antioxidants in organic, free-range and conventional chicken breasts from modelling

Consumers expect organic, free-range and corn-fed chicken to be nutritionally wholesome and have premium flavour characters. Interrelationships between flavour, fatty acids and antioxidants of retailed breasts were explored using simple correlations and chemometrics. Saturated fatty acid C16:0, and n-6 polyunsaturated C20:4 and C22:4 contents were correlated with lipid oxidation products (thiobarbituric acid reactive substances) and in partial least-squares regression (PLS1) with 32 high-resonance gas chromatography (flame ionization) flavour components (r2>0.90), and also linked (r2>0.80) to antioxidants (-tocopherol, glutathione and catalase). A further 10 high-resonance gas chromatography nitrogen phosphorus detector flavour components were correlated (r 2>0.85) with C18:3(n-3) content. Chicken character was correlated with C18:3(n-3), and C18:3(n-6) inversely with oily, off-flavour and lipid oxidation. Sweet, fruity and oily aromas were linked in PLS1 with 13 specific fatty acids (r2>0.6), and bland taste with total summed (six) fatty acid fractions (r2>0.81). Specific antioxidants were correlated with sweet, fruity and chicken aromas, and -tocopherol inversely with lipid oxidation. PLS2 confirmed relationships between fatty acid composition, antioxidants and the subsets of 32 and 10 flavour components. Clear relationships were thus observed between lipid and antioxidant compositions and flavour in chicken breast meat.

Local biomass control on the composition and reactivity of particulate organic matter in aquatic environments

Freshwater ecosystems have been recognized as important components of the global carbon cycle, and the flux of organic matter (OM) from freshwater to marine environments can significantly affect estuarine and coastal productivity. The focus of this study was the assessment of carbon dynamics in two aquatic environments, namely the Florida Everglades and small prairie streams in Kansas, with the aim of characterizing the biogeochemistry of OM. In the Everglades, particulate OM (POM) is mostly found as a layer of flocculent material (floc). While floc is believed to be the main energy source driving trophic dynamics in this oligotrophic wetland, not much is known about its biogeochemistry. The objective of this study was to determine the origin/sources of OM in floc using biomarkers and pigment-based chemotaxonomy to assess specific biomass contributions to this material, on a spatial (freshwater marshes vs. mangrove fringe) and seasonal (wet vs. dry) scales. It was found that floc OM is derived from the local vegetation (mainly algal components and macrophyte litter) and its composition is controlled by seasonal drivers of hydrology and local biomass productivity. Photo-reactivity experiments showed that light exposure on floc resulted in photo-dissolution of POC with the generation of significant amounts of both dissolved OM (DOM) and nutrients (N & P), potentially influencing nutrient dynamics in this ecosystem. The bio-reactivity experiments determined as the amount and rate of CO2 evolution during incubation were found to vary on seasonal and spatial scales and were highly influenced by phosphorus limitation. Not much is known on OM dynamics in small headwater streams. The objective of this study was to determine carbon dynamics in sediments from intermittent prairie streams, characterized by different vegetation cover for their watershed (C4 grasses) vs. riparian zone (C3 plants). In this study sedimentary OM was characterized using a biomarker and compound specific carbon stable isotope approach. It was found that the biomarker composition of these sediments is dominated by higher plant inputs from the riparian zone, although inputs from adjacent prairie grasses were also apparent. Conflicting to some extent with the River Continuum Concept, sediments of the upper reaches contained more degraded OM, while the lower reaches were enriched in fresh material deriving from higher plants and plankton sources as a result of hydrological regimes and particle sorting.

Stream dissolved organic matter bioavailability and composition in watersheds underlain with discontinuous permafrost

We examined the impact of permafrost on dissolved organic matter (DOM) composition in Caribou-Poker Creeks Research Watershed (CPCRW), a watershed underlain with discontinuous permafrost, in interior Alaska. We analyzed long term data from watersheds underlain with varying degrees of permafrost, sampled springs and thermokarsts, used fluorescence spectroscopy, and measured the bioavailabity of dissolved organic carbon (DOC). Permafrost driven patterns in hydrology and vegetation influenced DOM patterns in streams, with the stream draining the high permafrost watershed having higher DOC and dissolved organic nitrogen (DON) concentrations, higher DOC:- DON and greater specific ultraviolet absorbance (SUVA) than the streams draining the low and medium permafrost watersheds. Streams, springs and thermokarsts exhibited a wide range of DOC and DON concentrations (1.5–37.5 mgC/L and 0.14–1.26 mgN/L, respectively), DOC:DON (7.1–42.8) and SUVA (1.5–4.7 L mgC-1 m-1). All sites had a high proportion of humic components, a low proportion of protein components, and a low fluorescence index value (1.3–1.4), generally consistent with terrestrially derivedDOM. Principal component analysis revealed distinct groups in our fluorescence data determined by diagenetic processing and DOM source. The proportion of bioavailable DOC ranged from 2 to 35%, with the proportion of tyrosine- and tryptophan-like fluorophores in the DOM being a major predictor of DOC loss (p\0.05, R2 = 0.99). Our results indicate that the degradation of permafrost in CPCRW will result in a decrease in DOC and DON concentrations, a decline in DOC:DON, and a reduction in SUVA, possibly accompanied by

Spatial variability in Florida Bay particulate organic matter composition: combining flow cytometry with stable isotope analyses

Long-term management plans for restoration of natural flow conditions through the Everglades increase the importance of understanding potential nutrient impacts of increased freshwater delivery on Florida Bay biogeochemistry. Planktonic communities respond quickly to changes in water quality, thus spatial variability in community composition and relationships to nutrient parameters must be understood in order to evaluate future downstream impacts of modifications to Everglades hydrology. Here we present initial results combining flow cytometry analyses of phytoplankton and bacterial populations (0.1–50 μm size fraction) with measurements of δ13C and δ15N composition and dissolved inorganic nutrient concentrations to explore proxies for planktonic species assemblage compositions and nutrient cycling. Particulate organic material in the 0.1–50 μm size fraction was collected from five stations in Northeastern and Western Florida Bay to characterize spatial variability in species assemblage and stable isotopic composition. A dense bloom of the picocyanobacterium, Synechococcus elongatus, was observed at Western Florida Bay sites. Smaller Synechococcus sp. were present at Northeast sites in much lower abundance. Bacteria and detrital particles were also more abundant at Western Florida Bay stations than in the northeast region. The highest abundance of detritus occurred at Trout Creek, which receives freshwater discharge from the Everglades through Taylor Slough. In terms of nutrient availability and stable isotopic values, the S. elongatus population in the Western bay corresponded to low DIN (0.5 μM NH 4 + ; 0.2 μM NO 3 − ) concentrations and depleted δ15N signatures ranging from +0.3 to +0.8‰, suggesting that the bloom supported high productivity levels through N2-fixation. δ15N values from the Northeast bay were more enriched (+2.0 to +3.0‰), characteristic of N-recycling. δ13C values were similar for all marine Florida Bay stations, ranging from −17.6 to −14.4‰, however were more depleted at the mangrove ecotone station (−25.5 to −22.3‰). The difference in the isotopic values reflects differences in carbon sources. These findings imply that variations in resource availability and nutrient sources exert significant control over planktonic community composition, which is reflected by stable isotopic signatures.

Application of excitation emission matrix fluorescence monitoring in the assessment of spatial and seasonal drivers of dissolved organic matter composition: Sources and physical disturbance controls

The environmental dynamics of dissolved organic matter (DOM) were characterized for a shallow, subtropical, seagrass-dominated estuarine bay, namely Florida Bay, USA. Large spatial and seasonal variations in DOM quantity and quality were assessed using dissolved organic C (DOC) measurements and spectrophotometric properties including excitation emission matrix (EEM) fluorescence with parallel factor analysis (PARAFAC). Surface water samples were collected monthly for 2 years across the bay. DOM characteristics were statistically different across the bay, and the bay was spatially characterized into four basins based on chemical characteristics of DOM as determined by EEM-PARAFAC. Differences between zones were explained based on hydrology, geomorphology, and primary productivity of the local seagrass community. In addition, potential disturbance effects from a very active hurricane season were identified. Although the overall seasonal patterns of DOM variations were not significantly affected on a bay-wide scale by this disturbance, enhanced freshwater delivery and associated P and DOM inputs (both quantity and quality) were suggested as potential drivers for the appearance of algal blooms in high impact areas. The application of EEM-PARAFAC proved to be ideally suited for studies requiring high sample throughput methods to assess spatial and temporal ecological drivers and to determine disturbance-induced impacts in aquatic ecosystems.

Composition of a protein-like fluorophore of dissolved organic matter in coastal wetland and estuarine ecosystems

This study demonstrates the compositional heterogeneity of a protein-like fluorescence emission signal (T-peak; excitation/emission maximum at 280/325 nm) of dissolved organic matter (DOM) samples collected from subtropical river and estuarine environments. Natural water samples were collected from the Florida Coastal Everglades ecosystem. The samples were ultrafiltered and excitation–emission fluorescence matrices were obtained. The T-peak intensity correlated positively with N concentration of the ultrafiltered DOM solution (UDON), although, the low correlation coefficient (r2=0.140, p<0.05) suggested the coexistence of proteins with other classes of compounds in the T-peak. As such, the T-peak was unbundled on size exclusion chromatography. The elution curves showed that the T-peak was composed of two compounds with distinct molecular weights (MW) with nominal MWs of about >5×104 (T1) and ∼7.6×103 (T2) and with varying relative abundance among samples. The T1-peak intensity correlated strongly with [UDON] (r2=0.516, p<0.001), while T2-peak did not, which suggested that the T-peak is composed of a mixture of compounds with different chemical structures and ecological roles, namely proteinaceous materials and presumably phenolic moieties in humic-like substances. Natural source of the latter may include polyphenols leached from senescent plant materials, which are important precursors of humic substances. This idea is supported by the fact that polyphenols, such as gallic acid, an important constituent of hydrolysable tannins, and condensed tannins extracted from red mangrove (Rhizophora mangle) leaves exhibited the fluorescence peak in the close vicinity of the T-peak (260/346 and 275/313 nm, respectively). Based on this study the application of the T-peak as a proxy for [DON] in natural waters may have limitations in coastal zones with significant terrestrial DOM input.

Sediment and soil organic matter source assessment as revealed by the molecular distribution and carbon isotopic composition of n-alkanes

The assessment of organic matter (OM) sources in sediments and soils is a key to better understand the biogeochemical cycling of carbon in aquatic environments. While traditional molecular marker-based methods have provided such information for typical two end member (allochthonous/terrestrial vs. autochthonous/microbial)-dominated systems, more detailed, biomass-specific assessments are needed for ecosystems with complex OM inputs such as tropical and sub-tropical wetlands and estuaries where aquatic macrophytes and macroalgae may play an important role as OM sources. The aim of this study was to assess the utility of a combined approach using compound specific stable carbon isotope analysis and an n-alkane based proxy (Paq) to differentiate submerged and emergent/terrestrial vegetation OM inputs to soils/sediments from a sub-tropical wetland and estuarine system, the Florida Coastal Everglades. Results show that Paq values (0.13–0.51) for the emergent/terrestrial plants were generally lower than those for freshwater/marine submerged vegetation (0.45–1.00) and that compound specific δ13C values for the n-alkanes (C23 to C31) were distinctively different for terrestrial/emergent and freshwater/marine submerged plants. While crossplots of the Paq and n-alkane stable isotope values for the C23n-alkane suggest that OM inputs are controlled by vegetation changes along the freshwater to marine transect, further resolution regarding OM input changes along this landscape was obtained through principal component analysis (PCA), successfully grouping the study sites according to the OM source strengths. The data show the potential for this n-alkane based multi-proxy approach as a means of assessing OM inputs to complex ecosystems.

Spatial and Temporal Variability of Dissolved Organic Matter Quantity and Composition in an Oilgotrophic Subtropical Coastal Wetland

Dissolved organic matter (DOM) is an essential component of the carbon cycle and a critical driver in controlling variety of biogeochemical and ecological processes in wetlands. The quality of this DOM as it relates to composition and reactivity is directly related to its sources and may vary on temporal and spatial scales. However, large scale, long-term studies of DOM dynamics in wetlands are still scarce in the literature. Here we present a multi-year DOM characterization study for monthly surface water samples collected at 14 sampling stations along two transects within the greater Everglades, a subtropical, oligotrophic, coastal freshwater wetland-mangrove-estuarine ecosystem. In an attempt to assess quantitative and qualitative variations of DOM on both spatial and temporal scales, we determined dissolved organic carbon (DOC) values and DOM optical properties, respectively. DOM quality was assessed using, excitation emission matrix (EEM) fluorescence coupled with parallel factor analysis (PARAFAC). Variations of the PARAFAC components abundance and composition were clearly observed on spatial and seasonal scales. Dry versus wet season DOC concentrations were affected by dry-down and re-wetting processes in the freshwater marshes, while DOM compositional features were controlled by soil and higher plant versus periphyton sources respectively. Peat-soil based freshwater marsh sites could be clearly differentiated from marl-soil based sites based on EEM–PARAFAC data. Freshwater marsh DOM was enriched in higher plant and soil-derived humic-like compounds, compared to estuarine sites which were more controlled by algae- and microbial-derived inputs. DOM from fringe mangrove sites could be differentiated between tidally influenced sites and sites exposed to long inundation periods. As such coastal estuarine sites were significantly controlled by hydrology, while DOM dynamics in Florida Bay were seasonally driven by both primary productivity and hydrology. This study exemplifies the application of long term optical properties monitoring as an effective technique to investigate DOM dynamics in aquatic ecosystems. The work presented here also serves as a pre-restoration condition dataset for DOM in the context of the Comprehensive Everglades Restoration Plan (CERP).

(Table 1) Composition of organic matter from sediments of the triple junction area in the Indian Ocean

Bituminous substances in metalliferous sediments from the region of the triple junction in the Indian Ocean were studied. Specific peculiarities of their structure confirming location in "hot conditions" were revealed. Hydrocarbons are genetically connected with hydrothermal matter, and thus they could be considered as a geochemical indicator of hydrothermal processes in the ocean.