Matter In Pore Water Research Articles

Distribution pattern of dissolved organic matter in pore water of sediments from three typical areas of western Lake Taihu and its environmental implications

Abstract The migration, transformation, and accumulation of dissolved organic matter (DOM) in pore water of sediment cores play a pivotal role in lacustrine carbon cycling. In order to understand the dynamics of DOM in the sediments of large shallow eutrophic lakes, we examined the vertical profiles of DOM and the benthic fluxes of dissolved organic carbon (DOC) in sediment cores located in algae accumulated, dredged, and central areas of eutrophic Lake Taihu, China. Optical properties showed the significant influence of terrestrial inputs on the DOM components of pore water in the algae accumulated area but an abundant accumulation of autochthonous DOM in the central area. The benthic fluxes of DOC ranging from −458.2 to −139.4 mg·m−2·d−1 in the algae accumulated area displayed an opposite diffusion direction to the other two areas. The flux ranges of 9.5–31.2 mg·m−2·d−1 in the dredged area and 14.6–48.0 mg·m−2·d−1 in the central area were relatively smaller than those in the previously reported lake ecosystems with low trophic levels. Dredging engineering disturbed the pre-dredging distribution patterns of DOM in sediment cores. The deposition, accumulation, and transformation of massive algae scums in eutrophic lakes probably promoted the humification degree of sediments.

The Effects of pH, Temperature, and Humic-Like Substances on Anaerobic Carbon Degradation and Methanogenesis in Ombrotrophic and Minerotrophic Alaskan Peatlands

Methane production usually increases from the acidic sphagnum-dominated ombrotrophic peatlands to minerotrophic ones with more neutral pH and higher coverage of vascular plants. Along this ombrotrophic–minerotrophic gradient, pH, microbial communities, and properties of dissolved organic matter in porewater all vary greatly. The hydrographic change resulted from permafrost thaw and projected global warming can potentially connect the minerotrophic and ombrotrophic sites via porewater and turn acidic bogs to minerotrophic fens. It is thus very important to investigate how the anaerobic carbon degradation processes respond to changes in fundamental factors like pH, temperature, properties of dissolved organic matter, and microbial communities resulted from such hydrographic change. In this study, one ombrotrophic (pH = 3.9) and one minerotrophic peatland site were sampled in Fairbanks, Alaska in Sep 2017 and a 42-day-period anaerobic laboratory incubation was conducted to study the changes in anaerobic carbon degradation processes including primary and secondary fermentation, methanogenesis, and acetogenesis when pH, temperature, and porewater were manipulated individually and a combination of two or three of these factors. The results suggested lowering pH would inhibit many anaerobic carbon degradation processes in the minerotrophic peatland except primary fermentation. Elevating pH in the ombrotrophic site did not stimulate its methanogen community, but primary fermentation responded better with increasing pH than with increasing temperature alone. Replacing the porewater in the minerotrophic site with that from the ombrotrophic site with high aromaticity did not inhibit methanogenesis but potentially brought in highly efficient primary fermenters. Acetoclastic methanogenesis, acetogenesis, and syntrophy only exist in the minerotrophic site but not at the ombrotrophic one. Porewater from the minerotrophic site could potentially introduce acetoclastic methanogens and syntrophs to the ombrotrophic site but would not make them active unless both pH and temperature were increased. When ground water connects ombrotrophic and minerotrophic peatlands due to thawing of permafrost, secondary fermenters and acetoclastic methanogens could be introduced to acidic bogs and cooperate efficiently to degrade the stored carbon in ombrotrophic peatlands especially under elevated temperature conditions.

Halogens in Atlantis Bank gabbros, SW Indian Ridge: Implications for styles of seafloor alteration

The processes controlling halogen (F, Cl, Br, I) abundances in gabbroic ocean crust recovered from the 809-m deep Hole U1473A drilled on the Atlantis Bank during International Ocean Discovery Program (IODP) Expedition 360 were investigated. The aims were to provide new constraints on hydrothermal alteration and the abundances of halogens potentially transported to subduction zones in oceanic crust produced on a slow spreading ridge.Halogens in 51 gabbros and felsic veins have concentrations of ∼20-260 ppm F, 15-840 ppm Cl, 44-1230 ppb Br and 1-2490 ppb I. On average the gabbros retain a melt-derived magmatic F component of 58 ± 26% but are dominated by ∼96% hydrothermal Cl, Br, I and H2O. The abundances of hydrothermal Cl, Br and I are consistent with alteration at a seawater/rock ratio of <1. However, hydrothermal F is more enriched than expected and some amphiboles have high F/Cl ratios of 10-30 that provide evidence for the minor additional involvement of F-rich magmatic fluids. The abundant late-stage felsic veins that transect the gabbros and account for 1.5 vol.% of Hole U1473A lithologies are suggested as the most likely source of F-rich magmatic fluids.Downhole variations show F, Cl, Br and H2O are most abundant in amphibole- and clay-rich alteration zones at the top of the hole. The highest I concentrations of 1-2.5 ppm delineate an oxidised CO2-rich alteration zone in which seawater iodate was incorporated into carbonate and Fe-oxyhydroxide alteration. The role of iodate, which is more reactive than other halides, in generating I-rich alteration can be distinguished from alteration by I-rich sedimentary pore waters because the oxidised alteration is characterised by high I/Cl together with low Br/Cl, whereas organic matter in pore waters is enriched in both Br/Cl and I/Cl.The halogens have inferred compatibilities of F− > IO3− > OH− > Cl− ≥ Br− ∼ ≥ I− in the investigated alteration assemblage. EPMA and SHRIMP analyses indicate amphibole contains 1000-3000 ppm Cl in amphibolite facies alteration at the top of the Hole. Amphibole, chlorite and talc in greenschist facies alteration have much lower concentrations, typically in the range of 20-800 ppm Cl (median ∼100 ppm Cl), and F/Cl ratios of <4. In comparison, low temperature limonite (FeOOH.nH2O) has 160-8500 ppm Cl (median ∼840 ppm Cl). Amphibole is the dominant host of Cl and F in amphibolite facies alteration, but chlorite and limonite are important at lower grades. The samples have fairly constant Br/Cl ratios suggesting that Br excluded from the amphibole lattice is retained in minerals such as chlorite and/or non-structural sites. High I concentrations of 10's of ppm are inferred for some carbonate and limonite. Overall amphibole is a less dominant host of halogens than has been suggested previously, which has important implications for the eventual release and availability of halogens during subduction zone metamorphism.

Corrigendum: Composition of Dissolved Organic Matter in Pore Waters of Anoxic Marine Sediments Analyzed by 1H Nuclear Magnetic Resonance Spectroscopy

Corrigendum: Composition of Dissolved Organic Matter in Pore Waters of Anoxic Marine Sediments Analyzed by 1H Nuclear Magnetic Resonance Spectroscopy

Composition of Dissolved Organic Matter in Pore Waters of Anoxic Marine Sediments Analyzed by 1H Nuclear Magnetic Resonance Spectroscopy

Marine sediments are globally significant sources of dissolved organic matter (DOM) to the oceans, but the biogeochemical role of pore-water DOM in the benthic and marine carbon cycles remains unclear due to a lack of understanding about its molecular composition. To help fill this knowledge gap, we used 1H nuclear magnetic resonance (NMR) spectroscopy to examine depth variability in the composition of pore-water DOM in anoxic sediments of Santa Barbara Basin, California Borderland. Proton detected spectra were acquired on whole samples without pre-concentration to avoid preclusion of any DOM components from the analytical window. Broad unresolved resonance (operationally assigned to carboxyl-rich alicyclic molecules, or CRAM) dominated all spectra. Most of the relatively well-resolved peaks (attributed to biomolecules or their derivatives) appeared at chemical shifts similar to those previously reported for marine DOM in the literature, but at different relative intensities. DOM composition changed significantly within the top 50 cm of the sediment column, where the relative intensity of CRAM increased, and the relative intensity of resolved resonances decreased. The composition of CRAM itself also changed throughout the entire length of the 4.5-m profile, as CRAM protons became increasingly aliphatic at the expense of functionalized protons. Given that pore-water DOM is generated from sedimentary organic matter that includes pre-aged and degraded material, and that DOM could theoretically be subjected to microbial reworking in the pore waters for centuries to millennia, these data suggest that marine sediments may be sources of CRAM that are compositionally unique from CRAM generated in the upper ocean.

Quantification of dissolved organic matter in pore water of the vadose zone using a new ex-situ positive displacement extraction

Quantification of dissolved organic carbon (DOC) in pore water is vital for understanding the transport of solutes and the fate of contaminants. However, the extraction of pore water from saturated soils, and even more so, from unsaturated soils without an artificial increase in the DOC content is challenging. To this end, we have established a methodology for pore water extraction from unsaturated and saturated soils based on the displacement of the pore water from cores withdrawn from the ground by direct-push drilling machines. The displacement extraction is performed by introducing distilled water at the top of a liner filled with soil core and collecting the displaced eluent from the bottom. This positive displacement extraction (PDE) method was compared to pore water extraction by centrifugation for the analysis of DOC. Method validation was carried out with various DOC levels using different flow rates and three different soil types: sandy, sandy-clayey and clayey. The limit of detection for the suggested method was <0.22mgL−1 for all soil types, and for all studied saturation levels (>15%) under flow rates lower than 1mLmin−1. Extraction by centrifugation gave biased, unacceptable results throughout the studied DOC range (0–25mgL−1).Detailed parametric dependence by mobile – immobile modeling showed that for most soils and saturation levels collection of the first 10% of the pore water initially present in the core will introduce a bias of less 8% in DOC. For clayey soils with an exceedingly high immobile water fraction, a pedotransfer parameter estimation or comprehensive column tests should be carried out in order to estimate accurately the collectible water fraction and assure accurate prediction of the DOC level.Field studies that were carried out in a Soil Aquifer Treatment system provided 30m deep DOC profiles with <1.5m spatial resolution, a resolution that is unattainable by alternative techniques.

Experimental study on physical properties of clays with organic matter soluble and insoluble in water

Six natural clays with a predominant clay mineral of illite and two pure clay minerals (kaolinite and smectite) were mixed with organic matter to prepare 64 samples of organic clays containing different organic compounds at different contents. The organic compounds are classified into two categories (insoluble and soluble in water) for studying their effects on physical properties of organic clays investigated. When original clays are mixed with organic material insoluble in water, the particle size distributions and the particle densities of organic clays can be approximately determined pro ratio of each component. Adding humic acid into original clays causes little aggregate or disperse action on solid particles. The Atterberg limits of organic clays containing organic matter insoluble in water vary with organic content in a nonlinear fashion, and its changing rate depends on the liquid limits of original clays. On the other hand, when original clays are mixed with organic compounds soluble in water, dissolved organic matter in pore water should be taken into account for measuring their Atterberg's limits. Atterberg's limits of organic clays containing organic matter soluble in water are greatly affected by the predominant clay mineral of original clays. For the original clays with a predominant clay mineral of illite and kaolinite, liquid limit increases with the increase in organic content, but contrary changing fashion is found for smectite.

Dissolved organic matter in pore water of Arctic Ocean sediments: Environmental influence on molecular composition

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 15T 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 <5cm 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.

Impacts of crab bioturbation on the fate of polycyclic aromatic hydrocarbons in sediment from the Beitang estuary of Tianjin, China

Bioturbation by the burrowing crab Helice tiensinensis was investigated to determine its impact on polycyclic aromatic hydrocarbon (PAH)-contaminated estuarine sediments. The concentrations of 16 U.S. Environmental Protection Agency (U.S. EPA) priority PAHs in sediment and pore water from a crab bed (including surface and burrow samples) and a control area, as well as in crabs, were measured. The total concentration of the 16 U.S. EPA priority PAHs in surface sediment of the crab bed (average 2,772 ng/g dry weight) was significantly higher than in the control area (1,173 ng/g dry weight). In the crab bed, the total concentration of PAHs in burrow sediment (1,239 ng/g dry weight) was lower than in surface sediment, and a similar trend was found for most of the individual PAHs, except for indeno[1,2,3-cd]pyrene, and benzo[ghi]perylene. The enhanced PAH desorption in the burrow, which could be attributed to the increase in dissolved organic matter in pore water as well as the mechanical mixing by the crab, is expected to increase PAH flux to the sea. In addition to increased flushing to the sea, incorporation of PAHs in crab biomass and metabolism of PAHs by the crab, stimulated microbial degradation, was proposed as an ignorable factor that lowered the PAH concentration in burrow sediment, because crab bioturbation increases the abundance and activity of microorganisms through several means. Log K(OW) and log K(OC) correlated well for individual PAHs in sediment in the control area, although this correlation was poor for sediments in the crab bed. The log biota-sediment accumulation factor (BSAF) of PAHs exhibited a negative relationship with log K(OW), suggesting that the bioaccumulation of sorbed PAHs was controlled primarily by their bioavailability.

Molecular characterization of dissolved organic matter in pore water of continental shelf sediments

Dissolved organic matter (DOM) in sediment pore water is a complex molecular mixture reflecting various sources and biogeochemical processes. In order to constrain those sources and processes, molecular variations of pore water DOM in surface sediments from the NW Iberian shelf were analyzed by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and compared to river and marine water column DOM. Weighted average molecular element ratios of oxygen to carbon ((O/C) wa) and hydrogen to carbon ((H/C) wa) provided general information about DOM sources. DOM in local rivers was more oxygenated ((O/C) wa 0.52) and contained less hydrogen ((H/C) wa 1.15) than marine pore water DOM (mean (O/C) wa 0.50, mean (H/C) wa 1.26). The relative abundance of specific compound groups, such as highly oxygenated aromatic compounds or nitrogen-bearing compounds with low H/C ratios, correspond to a high concentration of lignin phenols (160 μg/g sediment dry weight) and a high TOC/TN ratio (13.3) in the sedimentary organic matter and were therefore assigned to terrestrial sources. The lower degree of unsaturation and a higher relative abundance of nitrogen-bearing compounds in the pore water DOM reflected microbial activity within the sediment. One sampling site on the shelf with a high sediment accumulation, and a humic-rich river sample showed a wide range of sulfur compounds in the DOM, accompanied by a higher abundance of lipid biomarkers for sulfate-reducing bacteria, probably indicating early diagenetic sulfurization of organic matter.

Dissolved organic matter in pore water of freshwater sediments: Effects of separation procedure on quantity, quality and functionality

Pore water was separated either with or without water extraction prior to centrifugation (7600 or 20 000 × g) in order to investigate the effects of separation procedure on the amount and properties of dissolved organic matter (DOM i.e. the material passing through a 0.45-μm filter) in three freshwater sediments. On the basis of solubility in alkaline, organic matter was concluded to compose of humic substances in two (S1 and S3) and of humin (S2) in one of the sediments. DOM in the samples was quantified by total organic carbon measurement. Specific UV-absorption (SUVA) and high performance size exclusion chromatography (HPSEC) analyses were used to characterize DOM. Sorption of pyrene was used as a measure for functionality of DOM. Both water extraction and centrifugation speed were shown to affect the properties of DOM; however, the effects were sediment dependent. Water extraction increased the amount of DOM separated from the two sediments that had humic character (S1 and S3). In most cases water extraction increased SUVA and shifted the molecular size distribution of DOM towards larger sizes. The separation procedure had also an effect on the functionality of DOM. In water extracted samples of S2 and S3 the sorption of pyrene was higher than in the corresponding samples separated without water extraction, whereas in S1 similar effect was not found. Generally, centrifugation speed had smaller effects on the properties of DOM than water extraction. The fact that the effects of separation procedure on DOM depend on the sediment characteristics complicates the comparison between samples and evaluation of functionality in field conditions.

Abundance and properties of dissolved organic matter in pore waters of a freshwater wetland

The abundances, molecular weights, molar absorptivities, and polydispersities of sediment pore water dissolved organic matter (DOM) and ferrous iron, Fe(II), were measured from three sites within a freshwater wetland (Old Woman Creek) adjacent to Lake Erie. DOM concentrations (expressed as organic carbon) increased with depth. Number‐average molecular weight, weight‐average molecular weight, and molar absorptivities (at 280 nm) also increased with depth up to 5 cm and remained relatively constant below this depth. These properties are indicative of the respective changes in the size of the DOM constituents and the number of aromatic moieties present. Moreover, a strong correlation was observed between Fe(II) and DOM, which suggests that both constituents coaccumulate in these pore fluids, It is hypothesized that reductionof iron oxides coated with organic matter releases both DOM and Fe(II). Increases in the molecular weights and molar absorptivities of the DOM constituents suggest that the “sorbed” component released by iron oxide dissolution is composed of larger and more aromatic molecules. The molecular‐weight data also suggest that much of the refractory organic carbon in the interstitial waters comprises smaller‐than‐expected polymeric molecules. Thus, the release of the sorbed organic materials during the reductive dissolution of the oxide phases in anoxic sediments coupled with the selective preservation of refractory organic components may play an important role in both the DOM‐mediated fate of pollutants and the cycling of carbon in wetlands.

The fluorescence of dissolved organic matter in porewaters of marine sediments

The fluorescence of porewaters from marine sediment cores from six different areas was measured. In most cases, fluorescence was affected primarily by the diagenesis of organic carbon first through sulfate reduction and subsequently by methane generation. Typically, fluorescence, dissolved organic carbon (DOC), absorbance, alkalinity, and ammonium ion concentrations correlate quite well, increasing in the upper sections of anoxic sediments and co-varying in deeper sections of these cores. The good correlation of DOC with fluorescence in the three cores in which DOC was measured indicates that fluorescence can be used to make a first order estimate of DOC concentration in anoxic porewaters. Data are consistent with a model in which labile organic matter in the sediments is broken down by sulfur reducing bacteria to low molecular weight monomers. These monomers are either remineralized to CO 2 or polymerize to form dissolved, fluorescent, high molecular weight molecules. The few exceptions to this model involve hydrothermally generated hydrocarbons that are formed in situ in the Guaymas Basin or are horizontally advected along the decollement in the Nankai Trench.

Bioavailability of pollutants to soil organisms via the soil solution

The hypothesis that the availability of pesticides to organisms in soil is determined solely by their concentration in the pore water was tested. The potato cyst nematode Globodera rostochiensis was exposed to the pesticides chlorpyrifos and pentachlorophenol mixed into two arable soils and one artificial soil. The nematode was also exposed to the pesticides in saline solution and in pore water isolated from these soils. Mixed in soil, chlorpyrifos was a 1000 times, and pentachlorophenol more than 100 times less toxic than if dissolved in solution. Sorption of these pesticides to dissolved organic matter in pore water decreased their toxicity only slightly. The concentrations in the soil solution, in equilibrium with soil at the soil LC 50 content, were similar to the LC 50 values determined in saline or soil solution. The use of non-adsorbing aqueous media is proposed for the toxicity testing of chemicals in the hazard assessment of soil pollution.

Jellyfish Lake, Palau: Early diagenesis of organic matter in sediments of an anoxic marine lake

Jellyfish Lake, a meromictic, marine lake in the Palau Islands, western Pacific Ocean, is accumulating organic matter‐rich sediments (46% wt/wt) below anoxic, highly sulfidic bottom water. Elemental and stable isotope (δ13C) data indicate that the sedimentary organic matter is primarily derived from vascular plant remains (65–90%) and would form a type 2 kerogen. A bacterial layer at the oxic‐anoxic interface in the water column may play an important role in the rapid recycling of algal‐derived organic matter from the highly productive surface waters.The major postdepositional change in the sedimentary organic matter is carbohydrate biodegradation, as shown by 13C NMR. Lignin and aliphatic substances are preserved in the sediments. Dissolved organic matter in pore waters is primarily composed of carbohydrates, reflecting the degradation of sedimentary carbohydrates. Rate constants for organic carbon degradation and sulfate reduction in sediments of the lake are about 10 × lower than in other anoxic sediments. This may reflect the vascular plant source and partly degraded nature of the organic matter reaching the sediments of the lake.Elemental results from sediment cores and stable isotope (δ18O, δ13C) studies of shells from the sediments indicate probable climatic or ecological fluctuations affecting the depositional environment of the lake between 80 and 110 yr ago. The high sedimentation rate and stable environment of Jellyfish Lake make it a possible environment for studies of climatic fluctuations during the Holocene.

Solid-state 13C NMR studies of dissolved organic matter in pore waters from different depositional environments

Dissolved organic matter (DOM) in pore waters from sediments of a number of different depositional environments was isolated by ultrafiltration using membranes with a nominal molecular weight cutoff of 500. This > 500 molecular weight DOM represents 70–98% of the total DOM in these pore waters. We determined the gross chemical structure of this material using both solid-state 13C nuclear magnetic resonance spectroscopy and elemental analysis. Our results show that the DOM in these pore waters appears to exist as two major types: one type dominated by carbohydrates and paraffinic structures and the second dominated by paraffinic and aromatic structures. We suggest that the dominance of one or the other structural type of DOM in the pore water depends on the relative oxidizing/reducing nature of the sediments as well as the source of the detrital organic matter. Under dominantly anaerobic conditions carbohydrates in the sediments are degraded by bacteria and accumulate in the pore water as DOM. However, little or no degradation of lignin occurs under these conditions. In contrast, sediments thought to be predominantly aerobic in character have DOM with diminished carbohydrate and enhanced aromatic character. The aromatic structures in the DOM from these sediments are thought to arise from the degradation of lignin. The large amounts of paraffinic structures in both types of DOM may be due to the degradation of unidentified paraffinic materials in algal or bacterial remains.

Dissolved organic matter in anoxic pore waters from Mangrove Lake, Bermuda

Dissolved organic matter and dissolved inorganic chemical species in anoxic pore water from Mangrove Lake, Bermuda sediments were studied to evaluate the role of pore water in the early diagenesis of organic matter. Dissolved sulphate, titration alkalinity, phosphate, and ammonia concentration versus depth profiles were typical of many nearshore clastic sediments and indicated sulphate reduction in the upper 100 cm of sediment. The dissolved organic matter in the pore water was made up predominantly of large molecules, was concentrated from large quantities of pore water by using ultrafiltration and was extensively tudied by using elemental and stable carbon isotope analysis and high-resolution, solid state 13C nuclear magnetic resonance and infrared spectroscopy. The results indicate that this material has a predominantly polysaccharide-like structure and in addition contains a large amount of oxygen-containing functional groups ( e.g., carboxyl groups). The 13C nulcear magnetic resonance spectra of the high-molecular-weight dissolved organic matter resemble those of the organic matter in the surface sediments of Mangrove Lake. We propose that this high-molecular-weight organic matter in pore waters represents the partially degraded, labile organic components of the sedimentary organic matter and that pore waters serve as a conduit for removal of these labile organic components from the sediments. The more refractory components are, thus, selectively preserved in the sediments as humic substances (primarily humin).

The Role of Dissolved Organic Matter in the Nutrition of Deep-Sea Benthos

SYNOPSIS. Deep-sea sediments contain less particulate organic matter and lower biomass than shallow-water sediments, but the dissolved organic matter in pore water varies less with depth and may provide a significant food source for deep-sea benthos. Pogonophora are a phylum of predominantly deep-sea animals, all without an internal digestive system. Experiments show that one or two species ought to be able to live by uptake of dissolved organic matter from pore water in deep-sea deposits: some other species may need local enrichment of the habitat for such uptake to be useful. Less is known about nutrition of other deep-sea animals, but dissolved organic matter may supplement a conventional diet in several groups. Chemoautotrophy, using endosymbiotic bacteria, may be important for the large vestimentiferan Pogonophora in the high-sulfide conditions of the hydrothermal vents.

Dissolved organic matter in pore water of carbonate sediments from Bermuda

Pore water samples from seven nearshore areas in Bermuda were obtained under in situ conditions and analyzed for dissolved organic carbon, dissolved carbohydrates, dissolved free amino acids and dissolved humic substances. The concentration of dissolved organic carbon is higher than in the overlying nearshore waters indicating significant diagenetic remobilization of carbon in these recently deposited carbonate sediments. Dissolved carbohydrates decrease with depth due to microbial utilization.