Carotenoid diagenesis in a marine sediment

The major carotenoids at three levels (3, 40 and 175 m below the sediment-water interface) in a core from a marine sediment (Cariaco Trench, off Venezuela) have been examined. Mass and electronic spectral data have provided evidence for the onset of a progressive reduction of carotenoids in the geological column. The time scale of the process appears to depend on the particular carotenoid. Reduction of up to two double bonds is observed for the diol, zeaxanthin, in the oldest sediment (ca. 340,000 yr B.P.) but no reduction is observed in the younger samples (ca. 5000 and ca. 56,000 yr B.P.). The diketone, canthaxanthin, shows evidence of reduction of up to two double bonds in the 56,000 yr sample and of up to five double bonds in the oldest sample. No reduction of β-carotene was observed in any of the samples.     

Early chlorin diagenesis in a recent aquatic sediment

Chlorophylls a and b, pheophytins a and b, pheophorbides a and b and pyropheophorbide a were identified in a Recent sediment (Priest Pot from Cumbria, U.K.) by laboratory preparation and structure elucidation by NMR and FAB-MS, and HPLC coelution with sedimentary extracts. Quantitative depth profiles revealed a steady decrease of the ratios of chlorophylls to pheophytins, and also a different but fairly constant a to b ratio for the pheophytins and the chlorins.     

Early diagenesis of phytyl esters in a contemporary temperate intertidal sediment

Analysis of a sediment core for hydrolysed chlorins (acidic chlorins e.g. pheophorbide a) and non-acidic chlorins, and free, bound and esterified alcohols have been performed and the results have been interpreted in terms of input and sedimentary interconversions. There is an association of the acidic chlorin input with an input of unesterified aliphatic n-alkanols (> C₂₀), and subsequent degradation of the chlorins with depth. Input of phytol to the anoxic region of the sediment is not associated with the n-alkanols:phytol in the sediment is derived largely from chlorophyll-a input to the surface layers as intact microalgae. Degradation with depth involves conversion of the chlorophyll-a to non-chlorin, colourless phytyl esters prior to incorporation of the phytol into a bound fraction. At depth this bound phytol is hydrolysed resulting in release of free phytol.     

Sterol diagenesis in Recent sediments from Buzzards Bay,Massachusetts

Sections of a 42 cm core from one area and surface sediments from two other areas of Buzzards Bay, Massachusetts were analyzed for sterols. The distribution of sterols in surface sediments appears to be influenced by benthic faunal composition or factors controlling this composition. A comparison of sterols extracted by Soxhlet-extraction with sterols extracted after subsequent saponification of the sediment showed that the former sterols decrease in concentration while the latter saponified sterols increase in concentration with depth. In both fractions, the individual sterol compositions are similar. A transformation between Soxhlet-extractable and non-Soxhlet-extractable saponified sterols appears to be occurring over the 130 yrs sampled by the core. This transformation is probably due to chemical/physical processes rather than biological processes. Comparison with fatty acid data shows that early diagenesis of sterols is slower than early diagenesis of fatty acids.     

Sources of neutral lipids in a temperate intertidal sediment

The compositions of sterol, alcohol and ketone fractions from an oxic intertidal surface sediment from Corner Inlet. Victoria, Australia, have been examined by capillary gas chromatographymass spectrometry and related to the lipids of diatoms cultured from the sediment and to lipids of the sea-grass Zostera muelleri. Of the more than thirty sterols in the sediment most appear to derive from diatoms, including the major sterol 24-methylcholesta-5.22E-dien-3β-ol. Small amounts of 24-ethylcholesterol probably derive from Zostera, with a minor diatom contribution. 5α-stanols, both fully saturated and with a side-chain double bond, represented ca. 14% of the total sterols: a significant proportion of these are probably derived from marine invertebrates. These organisms also contribute C₂₆ sterols. most of the cholesterol and possibly small amounts of Δ-sterols. The data suggest that in situ biohydrogenation of stenols was not a major process in sterol transformation in the surface oxic sediment. Alcohols ranged from C₁₂ to C₃₀ and showed an unusual abundance of unsaturated components with Δ⁹-16:1 being the major constituent. The long-chain alcohols probably originate largely from Zostera but the shorter-chain. C₁₂-C₂₀. alcohols are at least partly derived from wax esters of unknown origin. Diatoms do not contribute significant amounts of alcohols. Ketones were not major constituents of the sediment and consisted mainly of 6.10.14-trimethylpentadecan-2-one and a series of n-alkan-2-ones ranging from C₁₆ to C₃₃. The latter showed a similar distribution to that of the n-alkanes but the correspondence was not sufficient to substantiate a product-precursor relationship. Very long-chain C₃- C₃₉ unsaturated methyl and ethyl ketones, which may originate from the marine unicellular alga Emiliania huxleyi. were present in low concentration.     

Biological diagenesis: dicarboxylic acids in recent sediments

A series of even carbon numbered α, ω-dicarboxylic acids ranging from C₁₆ to C₂₄ has been identified in recent sediments from various environments and sampling localities. A lacustrine sediment did not show detectable quantities of diacids. Consideration of quantitative relationships involving the diacids leads us to propose a dual origin for these diacids: deposition by mangroves is their main source in mangal areas while in situ production by sedimentary organisms is the only important source of diacids in a non-mangal marine environment. A fresh water lagoon shows an intermediate situation between these extremes.     

Thermal alteration experiments on organic matter in recent marine sediment—II. Isoprenoids

Several isoprenoid compounds were isolated from a heat-treated marine sediment in the southern California continental shelf (from Tanner Basin) which were not present in the original sediment. Among the compounds identified were: phytol, dihydrophytol, C₁₈-isoprenoid ketone, phytanic and pristanic acids, C₁₉- and C₂₀-monoolefins, and the alkanes 2,6,10-trimethylpentadecane, pristane and phytane. The significance and possible routes leading to these compounds is discussed.     

Thermal alteration experiments on organic matter in recent marine sediment—I. Pigments

Sediment from Tanner Basin, located at the outer continental shelf off southern California, was analyzed for photosynthetic pigments and their derivatives, namely carotenes and chlorins. Samples of the sediment were also exposed to raised temperatures (65°, 100°, 150°C) for various periods of time (1 week, 1 month, 2 months). Analysis of the heat-treated sediment revealed the presence of α-ionene and 2,6-dimethylnaphthalene, thermal-degradation products of β-carotene. Chlorins were converted to nickel porphyrins of both DPEP and etio series. Possible mechanisms and geochemical significance of these transformations are presented.     

Branched-chain and cyclopropanoid acids in a recent sediment

From the recent sediments of a small productive lake in the English Lake District 10-methyl and cis-9, 10-methylene C₁₆ acids and also 10-methyl, cis-9, 10-, and cis-11, 12-methylene C₁₈ acids have been identified as constituents of the branched/cyclic acid fraction.     

Rates of trace metal and nutrient diagenesis in an intertidal creek bank

Carbon mineralization in marine sediments is a key process involved in the cycling of carbon, nutrients and trace metals. However, as marine sediments are usually diffusion dominated, the pace of element and nutrient cycling is slow, because consumption of oxidants and/or nutrients in the pore waters via microbial activity often outpaces resupply. Adding an advective flow component to such a system should change the biogeochemical dynamics considerably. Numerical simulations show that shallow coastal aquifers affected by tidal forces can establish ground water velocities of up to 7 cm h⁻¹, driving a circulation of sea water through the sediments with subsequent discharge. Although known to enhance solute exchange, the impact of advection on early diagenesis has not received much attention.To address this issue we mapped the interstitial water chemistry down to 2.5 m sediment depth along a transect on an intertidal creek bank that is subject to a periodic advective flow. Additionally a recently developed hydrogeological simulation of the creek bank was applied to calculate ages of the sampled pore waters. Sample ages obtained were used to quantify (flow path integrated) production or depletion rates for trace metals, nutrients, and sulphate.We find young sea water percolating relatively fast through sediments close to the creek showing strong signs of alteration, whereas pore waters from diffusion dominated regions are less altered. The increase in inorganic nutrients and some trace elements along the flow path requires high rates of turnover. Sulphate, molybdenum, and uranium are almost completely depleted after 200 days, while dissolved inorganic carbon (DIC), ammonia, and manganese increase. Averaged production rates for DIC appear to be three times higher when advection dominated the subsurface flow regime. Our results demonstrate that sites dominated by advection generally show signs of faster rates of diagenetic reactions.     

Early diagenesis of fatty acids in lacustrine sediments—I. Identification and distribution of fatty acids in recent sediment from a freshwater lake

Fatty acids have been isolated and quantitatively determined from a 1.5 m sediment core of Lake Suwa, a eutrophic lake in the central districts of Japan.The fatty acids identified by combined gas chromatography-mass spectrometry were straight-chain saturated (C₁₂ to C₃₄), monounsaturated with even carbon number (C₁₆ to C₂₄) and branched-chain (iso, anteiso, 10-methyloctadecanoic) acids. The concentrations of the higher molecular weight (? C₂₀) saturated fatty acids remained nearly constant throughout the core, suggesting a high degree of preservation of those acids, whereas the monounsaturated and the lower molecular weight saturated fatty acids indicated a great decrease in concentration with depth to an approximately 20cm level. It is suggested that the microbial activity in sediments causes a significant reconstruction of the fatty acid distribution during early diagenesis.     

Several unexpected marine sterols in a freshwater sediment

Some unexpected stanols, 22,23-methylene-23,24-dimethyl-5α(H)-cholestan-3β-ol (gorgostanol and the related stenol), 24,26-dimethyl-5α(H)-cholestan-3β-ol (aplystanol) and most probably 24-isopropyl-5α(H)-cholest-22-en-3β-ol, have been found in the sediment of a eutrophic pond. These compounds possess side chains which have until now been considered to belong exclusively to sterols of marine origin. The presence of these stanols in a freshwater sediment suggests that considering their side chain structures as specific marine input markers can lead to erroneous conclusions. The vertical distribution of these compounds along a 6 m core shows that they arise from organisms which still exist except for aplystanol which was found only in the sections below 5 m.     

Remobilization of Iodine in Marine Sediments During Early Diagenesis

Based on the sedimentary geochemical studies of the Antarctic Ocean and the various geochemical parameters available,this paper deals with the process of emobilization of iodine in marine sediments during early diagenesis.The results showed that the process is not always controlled completely by organic matter as was expected previously.On average the adsorption and oxide phases of iodine account respectively for 23% and 32% of the total in continental-shelf and hemipelagic surficial sediments.Chemical analysis has revealed that the upward diffusion flux and redox conditions would play an important role in the concentration of iodine in the surface sediments.And the species of iodine in the surfial sediments characteristic of high I/Corg ratios would bepredominated by the oxide and adsorption phases.As experimentally evidenced,it is the early diagenetic remoibilization of iodine associated with the oxide and adsorption phases that led to the decrease of I/Corg with increasing depth.Calculations suggested that the diffusion flux of iodine from the deep parts of te sedimentary columum upwards is on the same order of magnitude as the deposition flux of it from sea water.This may be one of the important factors leading to the depletion of iodine in sedimentary rocks.On the basis of the above discussion and calculations the author has proposed a model for the remobilization of iodine in marine sediments during early diagenesis.     

Thermal alteration experiments on organic matter in recent marine sediment—III. Aliphatic and steroidal alcohols

Recent sediments from Tanner Basin (off southern California) and Bandaras Bay (in Gulf of California) have been analyzed for normal, isoprenoid and steroidal alcohols using chromatographic (column, GLC, TLC), and spectroscopic (u.v., i.r., MS) methods, prior to and after heat-treatment (from 65 to 150°C). Normal saturated alcohols (C₁₄-C₂₄) and monounsaturated alcohols (C₂₂-C₂₄) were identified, as well as the isoprenoid alcohols, phytol and dihydrophytol.Two series of sterols (Δ⁵ and Δ⁷) were found in Tanner Basin, and Δ⁵-sterols and triterpenes, in Bandaras Bay sediment. Sterols from both sediments contained the corresponding stanols.     

Short-term morphological change and sediment dynamics in the intertidal zone of a macrotidal beach

This paper describes the morphological and sedimentological evolution of a macrotidal beach over a 20 day period under varying hydrodynamic conditions (significant breaker heights of 0·3–2 m and tidal ranges of 2–5 m). During the field campaign, an intertidal bar developed around the mid‐tide level, migrated onshore, welded to the upper beach and was then flattened under energetic wave conditions. The bar had a wave breakpoint origin and its formation was triggered by a reduction in tidal range, causing more stationary water‐level conditions, rather than an increase in wave height. Most of the onshore bar migration took place while the bar was positioned in the inner to mid‐surf zone position, such that the bar moved away from the breakpoint and exhibited ‘divergent’ behaviour. The depth of disturbance over individual tidal cycles was 10–20% of the breaker height. Such values are more typical of steep reflective beaches, than gently sloping, dissipative beaches, and are considered to reflect the maximum height of wave‐generated ripples. The grain size distribution of surficial sediments did not vary consistently across the beach profile and temporal changes in the sedimentology were mostly unrelated to the morphological response. The lack of clear links between beach morphology and sedimentology may be in part due to shortcomings in the sampling methodology, which ignored the vertical variability in the sediment size characteristics across the active layer.     

Ecology,sedimentology, and diagenesis of recent and fossil reefs

At the VIII. International Sedimentological Congress held in Heidelberg in 1971, a symposium with the above title was convened; a selection of the papers presented is assembled in this issue. In the introduction the approaches of the following studies are reviewed to show some trends and problems in reef research.     

Biogeochemistry of PCBs in interstitial waters of a coastal marine sediment

Polychlorinated biphenyls (PCBs) were measured in interstitial waters and sediments at a site in New Bedford Harbor, Massachusetts, to study partitioning processes of hydrophobic organic compounds in marine sediments. Pore water concentrations of total PCBs, expressed as Aroclor 1254, increased with depth in the sediments with a maximum concentration of 17.1 μg/L at 9–11 cm. Apparent distribution coefficients of individual chlorobiphenyls decreased with depth and were related to dissolved organic carbon levels. Results from this site suggest that most of the PCBs in interstitial waters are sorbed to organic colloids. A simple three-phase equilibrium sorption model can explain many features of the data. Changes in the composition of individual chlorobiphenyls in the sediments were also apparent. Microbial degradation appears to be responsible for large relative depletions of several chlorobiphenyls with depth in the core.     

Stereochemistry of amino acids in surface samples of a marine sediment

In two surface samples of marine sediment, the percentages of d-alanine and d-aspartic acid are significantly higher than the other d-amino acids and are similar to the range found in soils. The percentage of d-glutamic acid is also higher than the other amino acids but less than d-alanine and d-aspartic acid. These d-amino acids may come mainly from bacteria.