Terrestrial Organic Matter Sources Research Articles

PALEOHYDROGRAPHIC INFLUENCES ON PERMIAN RADIOLARIANS IN THE LAMAR LIMESTONE, GUADALUPE MOUNTAINS, WEST TEXAS, ELUCIDATED BY ORGANIC BIOMARKER AND STABLE ISOTOPE GEOCHEMISTRY

Abstract The late Guadalupian Lamar Limestone Member of the Bell Canyon Formation, Delaware Basin, west Texas, records dramatic fluctuations in radiolarian faunal composition that are interpreted to record basin-scale changes in hydrography. Samples taken across one of these intervals of fluctuation show a change from a sparse, nearly monospecific fauna dominated by Follicucullus ventricosus to a more radiolarian-rich interval dominated by spongy spumellarians of the Copicyntrinae and Spongodiscidae. Carbonate stable isotope and organic biomarker geochemical data from this same interval support a strong terrestrial-freshwater influence on the spumellarian-dominated beds. Specifically, biomarker data show lower C22/C27 ratios and n-alkane distributions indicative of terrestrial organic matter sources in the spumellarian-dominated beds. In the whole-rock carbonate fraction, δ18O and δ13C show a shift to more negative values, consistent with increased meteoric water influence in the spumellarian-dominated in...

Biogeochemistry and paleoclimate variability during the Holocene: a record from Mansar Lake, Lesser Himalaya

Investigation of biogeochemistry and amino acids on a 30-m-long core from Mansar Lake has thrown light on palaeoclimate variability during the Holocene period. The C/N ratio between 6 and 10 with some deviations and δ13C mostly between −20 and −22‰ in the shallow core, as well as a C/N ratio greater than 13 reaching from 19 to 20 and correspondingly lower δ13C of –28‰ in the deeper core suggest an aquatic source of carbon in the former and a cellulose-rich land plant source in the latter. This is supported by the abrupt increase in organic carbon content in the deeper core compared to the shallow core, which indicates a hot and wet climatic regime during the early Holocene and dry and cold during the late Holocene period. The amino acid data AA-C/C% and AA-N/N% are higher in shallow sediments compared to deeper sediments, indicating an aquatic plant source in the shallow core and greater supply of land plant sources in the deeper core. The lower percentage of the non-protein amino acids β-alanine (ALA) and γ-amino-butyric acid in the shallow core compared to the deeper core indicates different sources of organic matter in the lake basin. The higher amino acid ratio Asp/β-Ala (16.99 av.) and Glu/γ-Aba (18.18 av.) in the shallow core and lower ratios (10.32 and 12.41 av.) in the deeper core, and Asp/Glu (1.52 av.) and β-Ala/γ-Aba (1.61 av.) ratios in the former, which are potential indicators of the nature of the organic matter, are higher in the shallow core relative to the deeper core (1.33 and 1.23 av.), indicating relative biodegradation of organic matter in deeper sediments. It has been observed that the organic matter associated with the dry season is relatively less biodegraded, as evidenced from their higher ratios, and is more biodegraded in the wet season as their ratios are lower in the river sediments. In the absence of a bacterial contribution of organic matter from the soil source in this lake, since Mansar Lake is a non-drainage type, it is envisaged that the climatic variation may be responsible for biodegradation in the deeper core sediments. Therefore, the C/N ratio and δ13C values supported by amino acid data, the latter being significant in revealing primary productivity and a terrestrial source of organic matter, suggest a hot and wet climatic regime during the early Holocene (ca. 7580 bp) and a dry and cold in the late Holocene period (ca. 4050 bp).

Sources of organic carbon and depositional environment in the Bengal delta plain sediments during the Holocene period

This study investigated the sources of organic matter and sediment depositional environment within fluviatile sediments of the Ganges–Meghna (GM) delta plains. The very low contents of trace metals e.g., chromium (Cr), cobalt (Co), scandium (Sc), and vanadium (V), organic carbon content, and cerium (Ce)-anomaly data of sediments indicate the redox conditions that fall within the boundary of oxic–anoxic condition, with dominantly oxic conditions in the sediment deposition environment. The higher atomic carbon nitrogen (C/N)a ratios and depleted stable carbon isotope ratio (δ13C) values for sediments from three study areas indicated the terrestrial sources of organic matter derived from C3 plant materials, whereas the contribution of organic materials from C4 vegetation and riverine productivity is low. Some silty sand samples exhibited lower (C/N)a ratios and enriched δ13C values in Sonargaon and Faridpur areas that are attributed to the adsorption of ammonium ions on clay minerals and the contribution of organic matter from C4 plants. Total sulfur over total organic carbon (TS/TOC) ratios in sediments of the Ganges delta reflect the nonmarine environments of sediment deposition. The lower ratios of syringyl to vanillyl phenols (S/V), cinnamyl to vanillyl phenols (C/V), and acid to aldehyde in vanillyl phenols (Ad/Al)v observed in Daudkandi indicate that the lignin in sediments derived from dominant woody gymnosperm sources and is very highly degraded. By contrast, the S/V ratio, C/V ratios, and [Ad/Al]v ratios in Faridpur suggest that the lignin in sediments derived from a mixture of woody and nonwoody angiosperm plant tissue contribution that underwent high degradation as well.

Calibrating n-alkane Sphagnum proxies in sub-Arctic Scandinavia

Moss covered, high latitude wetlands hold large amounts of terrestrial organic matter (OM), which may be vulnerable to expected climate warming. Molecular analysis of fluvially transported material from these regions can distinguish between different sources of terrestrial OM. Sphagnum moss may represent one of the major sources. This study aimed to quantitatively establish a molecular proxy for identifying Sphagnum-derived OM from high latitude peatlands in the sub-Arctic coastal ocean. We collected and analyzed Sphagnum species throughout northern Sweden and Finland. Results show that the C25/(C25+C29) n-alkane ratio is most suitable for terrestrial OM source apportionment in these coastal regions since, compared to other n-alkane Sphagnum proxies, it shows (i) the least variation between species, (ii) the most constant values for different latitudinal regimes and (iii) the largest dynamic range to the higher plant end member in two-source mixing models. Application of the proxy to surface sediments and suspended particulate matter in the sub-Arctic northern Baltic Sea shows that 68–103% of the terrestrial OM fraction is derived from Sphagnum-rich peatland. We recommend that future studies on terrestrial OM fluxes into (sub-)Arctic regions should apply the C25/(C25+C29) proxy to improve insight into the contribution of Sphagnum-derived terrestrial OM from climate-vulnerable, high latitude wetlands.

Diatom and stable isotope records of late-Holocene lake ontogeny at Indrepollen, Lofoten, NW Norway: a response to glacio-isostasy and Neoglacial cooling

Borg Indrepollen is a coastal lake on the island of Vestvågøy, Lofoten, NW Norway. A sedimentary sequence spanning the last 4500 cal. yr BP was analysed for diatom, C/N and stable isotopes (δ13C and δ15 N). The record provides clear evidence of glacio-isostatic rebound in the Lofoten region. Five distinct lithostratigraphic-geochemical zones (I—V) and four major diatom zones (A—D) were identified. The early record (I—III, A—Biii; 4500—550 cal. yr BP) contains coarse sedimentary material and diatoms indicative of more marine conditions. The correlation between the isotopic data (high δ13C and low C/N) and trends in the biological data (marine/brackish flora) suggest the marine influence on the Indrepollen basin is a controlling factor of the source of organic material. The latter part of the record (IV, C; 550 cal. yr 550—226) indicates a transitional phase from marine-dominated diatom to brackish taxa and is coincident with a section of microlaminations in the core. The youngest zone (V, D; 226 cal. yr BP—present) is indicative of an isolated basin, with the deposition of fine sediments; freshwater diatom taxa dominate the biological record and δ13C are indicative of freshwater conditions. C/N suggests a shift to a terrestrial source of organic matter. The proxies show a transition from full marine conditions, when Indrepollen was a submerged fjord, to more freshwater, lacustrine conditions in the last 200 years. The record of land uplift from Borg Indrepollen mirrors changes in sedimentary records from across Northern Norway and relative sea-level curves for the region.

Sources markers in aerosols, oceanic particles and sediments

This review presents some diagnostic criteria used for identifying and quantifying terrestrial organic matter inputs to the ocean. Coupled to the isotopic composition of total organic carbon, the analysis of stable biomarkers permits to trace higher plant contributions in aerosols, dusts, sedimenting particles and dissolved phase in the water column and ultimately in recent and ancient sediments and soils. Some applications are presented, based on the analysis of n-alkyl compounds by a combination of gas chromatography and mass spectrometry (n-alkanes, n-alkanols, n-alkanoic acids and wax esters). Another approach has been developed using the analysis of macromolecular compounds present in higher plants. Abundances of the phenolic compounds from lignin, benzene carboxylic acids obtained during cupric oxide oxidation, Curie pyrolysis are used to characterise terrestrial organic matter sources and inputs. Finally due to the importance of biomass burning in continent-ocean transfers, biomarkers are presented in the polycyclic aromatic hydrocarbon class and for monosaccharide derivatives from the breakdown of cellulose.

Spatial and seasonal variations in the pelagic–benthic coupling of the southeastern Beaufort Sea revealed by sedimentary biomarkers

Photosynthetic pigments and stable isotopes from suspended particulate organic matter (POM) and surface sediment of the southeast Beaufort Sea, including the Mackenzie shelf and the Amundsen Gulf, were studied during fall 2003 and summer 2004. This multiple-biomarker approach led to an increased understanding of spatial and seasonal variation in pelagic-benthic coupling, as these 2 biomarkers reflect inherent differences in the time scales over which they integrate. Sedi- mentary pigments highlighted the importance of local water-column production as a source of phy- todetrital inputs to the sea floor. In the summer, the dominance of diatoms in the water column was reflected in the sediment by the abundance of fucoxanthin, a pigment broadly found in diatoms. In the fall, a more variable suite of sedimentary pigments reflected inputs from smaller cells such as haptophytes and prasinophytes. While stable isotope composition of the POM showed seasonal vari- ations, i.e. a more marine signature in the summer and a more terrestrial signature in the fall, sedi- mentary stable isotopes revealed geographical differences. Sediment on the Mackenzie shelf sug- gested a terrestrial source of organic matter, while in the Amundsen Gulf, sources of organic matter had a more marine origin. Finally, benthic community compositions and activity (sediment carbon demand) seemed affected by both spatial and seasonal variations in organic matter inputs to the ben- thos. This study stresses the importance of both physical factors (water depth and riverine inputs) and biological production (primary productivity and secondary production) in the determination of organic matter inputs to the benthos.

Changes in the chemistry of sedimentary organic matter within the Coorong over space and time

Like many other coastal systems across the world, the Coorong lagoonal ecosystem (South Australia) has degraded over the last 100 years; in this case as a result of extensive regulation and diversions of water across the Murray-Darling Basin following European settlement. To evaluate whether the sources of organic matter (OM) supporting its food-web have changed since the inception of water management and barrage construction, sedimentary OM was characterised in cores spanning the Coorong’s salinity gradient at depths representative of the last 100 years over which the management alterations to river and estuarine flow were most marked. Detailed 210Pb, 137Cs and Pu dating in conjunction with palaeolimnological data (Pinus pollen) allowed for the reconstruction of the timing of substantial changes observed in the composition of the OM, most of which occur during the early 1950s, concurrent with management-related variations in water flow and salinity. Negative shifts in δ13C of up to 8.3‰ in the 2–10 and <2 μm fractions after the 1950s suggest a pronounced alteration in biogeochemical cycling or in the origin of OM. Elemental ratios and δ13C values of potential sources are inconclusive as to the cause of these biogeochemical changes. However, 13C-NMR spectra of the sediments suggest that degraded phytoplankton constitutes a large proportion of today’s OM and also reveal that an OM source rich in lignin was present prior to the 1950s. The high δ13C (−18.3‰) and low C/N (7.5) signatures of the lignin-bearing sediments are inconsistent with a C3 terrestrial OM source and instead suggest that the lignin-bearing seagrass Ruppia megacarpa (δ13C of −13‰) contributed to a large degree to the sediment of the North Lagoon. R. megacarpa once was abundant in the North Lagoon but today has all but vanished from the system. Thus, only through a combination of isotopic and spectroscopic techniques was it possible to effectively decipher the changes in the composition of OM deposited throughout the Coorong over space and time. These results have important implications for research in estuarine OM dynamics in other geographic locations. Specifically, utilising complementary analytical techniques may sometimes be essential in reliably determining OM sources and processes in estuaries and lagoons.

Sources of organic matter in surface sediments of the Louisiana Continental margin: Effects of major depositional/transport pathways and Hurricane Ivan

Lignin and pigment biomarkers were analyzed in surface sediments of the Louisiana Continental margin (LCM) to distinguish differences in the degradative state of sedimentary organic matter along and between two major depositional pathways (along shore and offshore to the Mississippi Canyon) from Southwest (SW) Pass in July 2003. Barataria Bay, an inter-distributary estuary, was also assessed as a potential source of terrestrial organic matter to the LCM. Sediment signatures taken along the same pathways after Hurricane Ivan (October 2004) were compared with the pre-Ivan signature to elucidate carbon dynamics after major hurricane events. Density fractions were investigated at key stages across the LCM. Mississippi Canyon sediments are a depocenter for labile and refractory organic matter derived from river and previously deposited shelf sediments. Barataria Bay material may be a contributing source of sedimentary organic matter in shallow shelf areas bordering the bay and is thus potentially important in carbon cycling in sediments of these shallow areas; however, our results show that organic matter inputs from the bay were likely rapidly decomposed and/or diluted. Hurricane Ivan mobilized sedimentary organic carbon (SOC) offshore and homogenized terrestrial sediment parameters and gradients. As observed through pigment concentrations sediments tended to equilibrate to a more steady-state condition within months of the disturbance. Insights from density fractions show that selective degradation and aggregation/flocculation processes were also very important processes during cross-shelf transport. Zooplankton grazing, largely on diatoms and other algae, was a shelf wide phenomenon, however, grazing products dominated the marine-derived SOC in margin sediments west of the birdsfoot delta indicated by the abundance of steryl chlorin esters (SCEs).

Carbon biogeochemistry of the Betsiboka estuary (north-western Madagascar)

Madagascar’s largest estuary (Betsiboka) was sampled along the salinity gradient during the dry season to document the distribution and sources of particulate and dissolved organic carbon (POC, DOC) as well as dissolved inorganic carbon (DIC). The Betsiboka was characterized by a relatively high suspended matter load, and in line with this, low DOC/POC ratios (∼0.4–2.5). The partial pressure of CO 2 (pCO 2) was generally above atmospheric equilibrium (270–1530 ppm), but relatively low in comparison to other tropical and subtropical estuaries, resulting in low average CO 2 emission to the atmosphere (9.1 ± 14.2 mmol m −2 d −1). Despite the fact that C4 vegetation is reported to cover >80% of the catchment area, stable isotope data on DOC and POC suggest that C4 derived material comprises only ∼30% of both pools in the freshwater zone, increasing to ∼60–70% and 50–60%, respectively, in the oligohaline zone due to additional lateral inputs. Sediments from intertidal mangroves in the estuary showed low organic carbon concentrations (<1%) and δ 13C values (average −19.8‰) consistent with important inputs of riverine imported C4 material. This contribution was reflected in δ 13C signatures of bacterial phospholipid derived fatty acids (i + a15:0), suggesting the potential importance of terrestrial organic matter sources for mineralization and secondary production in coastal ecosystems.

Variability in factors causing light attenuation in Lake Victoria

Summary1. The major optical components controlling the attenuation of photosynthetic available radiation in nearshore areas of Lake Victoria (Uganda and Kenya) were examined and their impact compared. It was found that chromophoric dissolved organic matter and tripton play a dominating role in many nearshore areas, indicating that the coastal areas of Lake Victoria cannot be considered as Case I waters.2. Concentrations of chromophoric dissolved organic matter declined with distance from the coast in an exponential manner indicating dilution and degradation of terrestrial sources of organic matter rather than in situ production. The importance of tripton was found to follow a similar pattern, while the relative importance of phytoplankton biomass in overall attenuation of photosynthetic available radiation was found to increase with distance from the coast. A specific attenuation coefficient for phytoplankton biomass was determined (0.019 m2 mg Chl a−1).3. Using a light limitation approach based on carrying capacity, it was possible to map areas that are closer to being light limited. Light limitation appears to occur throughout most bays and some coastal areas receiving catchment waters. This spatial information, geographically referenced to bathymetric and catchment conditions, was utilized to understand the importance of environmental conditions in limiting phytoplankton biomass.

Elemental compositions, FT-IR spectra and thermal behavior of sedimentary fulvic and humic acids from aquatic and terrestrial environments

Studies on elemental analysis, Fourier transform infrared spectroscopy (FT-IR) and thermal decomposition (thermogravimetry, TG; and derivative thermogravimetry, DTG) of sedimentary fulvic (FA) and humic acids (HA) from marine, estuarine, lacustrine and terrestrial environments are presented. In general, H/C and N/C atomic ratios, as well as the infrared spectra, reflected the extent of the influence of algal and/or terrestrial organic matter sources on the samples, the aquatic (both, marine and freshwater) humic substances (HS) being richer in nitrogen and more saturated, than terrestrial materials. Comparison of properties of FA and HA from the same parent sediments showed that the latter are relatively richer in nitrogen and unsubstituted aliphatic chains and poorer in carboxylic groups. FT-IR spectra showed that the nitrogen present is mostly as forming part of amide groups. Concerning thermal degradation, two main steps were observed for all samples: the first, relative to the loss of moisture, being located between 40°C and 100°C and the second between 270°C and 440°C. FT-IR spectra of the samples which had been heated to 90°C, 400°C and 900°C showed that, upon heating, the carboxyl content decreases (especially for FA), the aliphaticity decreases and the aromaticity increases (especially for HA), indicating that the 270°C-470°C degradation step might be related to decarboxylation and unsaturation losses. In spite of this, both kinds of HS, were shown to be highly thermo-resistant materials retaining most of their typical original infrared spectral features, even after being heated to 400°C.

Fatty acid reactivities in sediment cores from the northern Gulf of California

Fatty acids were determined in three sediment cores from Delfin Basin, Northern Gulf of California (NGC), Mexico. Steady-state apparent degradation rate constants ( k′) were determined to assess the reactivity of the total organic carbon (TOC) pool, the total fatty acids (TFA) and selected individual fatty acids. k′ values for TFA were higher than those for TOC, indicating that fatty acids are at least 5 times more labile than the organic carbon pool. A comparison of k′ values for selected fatty acids indicates that the long-chain terrigenous fatty acids are less labile than the shorter chained fatty acids from autochthonous sources. The general order of reactivity by source was plankton>bacteria>terrestrial. There are at present essentially no inputs of terrigenous material from the Colorado River. Therefore, the lower reactivity of the terrigenous fatty acids in the Delfin Basin probably suggests that the contemporary source of terrestrial organic matter to the NGC is the eroding Colorado River Delta, which contains already degraded organic carbon. In spite of the high primary productivity in the region, k′ values for fatty acids from the NGC were low when compared with those from other marine ecosystems. These results suggest that fatty acid diagenesis during particle settling through the water column in the NGC is intense, allowing only for the deposition of relatively refractory organic matter.

Organic matter and amino acid concentrations in surface sediments of Vembanad Lake - a tropical estuary, west coast of India

The surface sediments of Vembanad Lake, a tropical estuary on the west coast of India, were analyzed for carbon (TC, TOC, TIC), nitrogen (TN), amino acids and two amino sugars. C/N ratios for the surface sediments vary from 1.0–21.8, indicating terrestrial sources of organic matter. Various biogeochemical indicators based on amino acids such as Asp/β-ala and Glu/γ-aba ratios revealed that the organic matter in the 5- to 10-cm surface sediments was fresh and had not undergone extensive degradation. However, the Gluam/Galam ratio for surface sediments of Vembanad Lake varies from 0.4–2.1, indicating the dominance of bacterial biomass in the sediments. Organic matter in the sediments was found to be highly reactive, with a reactivity index ranging from 2.4–7.4, suggesting rapid remineralization.

Carbon isotope systematics of individual hydrocarbons in hydrothermal petroleum from Middle Valley, Northeastern Pacific Ocean

Individual aliphatic hydrocarbons in samples of bulk hydrothermal petroleum from Middle Valley (ODP Site 858) were submitted to compound specific isotope analysis to trace their origins. The C isotope compositions of the n-alkanes and isoprenoid hydrocarbons [means n-alkanes: −30.1±1.01 (858A), −28.3±1.7 (858C) and −24.8±1.4 (858D)‰; isoprenoids: −26.0±2.7 (858C) and −27.9±0.4 (858D)‰, respectively] reflect mixed marine and terrestrial organic matter sources. Biphytane from thermophiles has a δ 13C value of −21.0‰.

Carbon Isotopic Evidence for Coupled Sulfate Reduction-Methane Oxidation in Amazon Fan Sediments

Carbon isotope ratios of dissolved inorganic carbon were measured on porewaters from Amazon Fan sediments collected on Ocean Drilling Program Leg 155. Values as low as −49.6‰ vs. PDB were recorded, with the lowest values coinciding with the base of the sulfate reduction zone at each site. The values indicate that on the order of 50–85% of sulfate reduction in Amazon Fan sediments takes place by methane oxidation. Estimated rates of methane oxidation range from 0.3–1.0x10 −5 moles/l/yr. The reasons for the high percentage of sulfate reduction taking place by methane oxidation are thought to be the large decrease in fan sedimentation rates in the early Holocene and the terrestrial source of organic matter in fan sediments.

Carbon isotope systematics of individual hydrocarbons in hydrothermal petroleum from Escanaba Trough, northeastern Pacific Ocean

We submitted individual aliphatic and polycyclic aromatic hydrocarbons in samples of hydrothermal petroleum from Escanaba Trough to compound specific isotope analysis to trace their origins. The carbon isotope compositions of the alkanes and polycyclic aromatic hydrocarbons (means −27.5 and −24.7‰, respectively) reflect a primarily terrestrial organic matter source.

Distribution of naphthalenes in crude oils from the Java Sea: Source and maturation effects

Amounts and distributions of C1-C3 naphthalenes and cadalene were determined by capillary gas chromatography in sixty crude oil samples from the Java Sea, southeast Asia and in a sample of Talang Akar (Oligocene) resinite supposed to be a major contributor of hydrocarbons to oils in that area. Maturity of the oils was assessed by the Methylphenanthrene Index (MPI-1). Source effects discovered by scatterplots were scrutinized by Principal Component Analysis (PCA).Based on empirical relationships with C27-C29 steranes (measured by gas chromatography-mass spectrometry), dimethylnaphthalenes in oils from the Ardjuna and Jatibarang (sub-)basins are mainly derived from terrestrial sources. Transition to a marine depositional environment in the Sunda basin, as indicated by a decrease in C29 sterane relative abundance from 70 to 30%, results in a decrease of total dimethylnaphthalene (DMN) concentrations from 20 to less than 3 mg/g oil. This is due, mainly, to a decrease in the concentration of the dominant 1,6-DMN. Thus, terrestrial Ardjuna or Jatibarang oils rich in 1,6-DMN (2–15 mg/g oil) are readily discriminated from marine Sunda oils (0.2–2 mg 1,6-DMN/g oil). Resinite of the Talang Akar type (1.4 mg 1,6-DMN/g total organic matter [TOM]) appears to be a significant contributor of 1,6-DMN to oils in the Ardjuna basin.Terrestrial affinities are inferred also for cadalene from concentration levels that are higher in terrestrial oils (1–3 mg/g oil) and Talang Akar resinite (6 mg/g TOM) than in the marine oils (0.1–1 mg/g oil). Ardjuna basin oils have the highest concentrations of cadalene, hence supporting resinite of the Talang Akar type as a possible source. However, 1,6-DMN and cadalene are likely to be derived from different terrestrial organic matter sources, because they load on different factors in PCA.Maturity levels of the oils in the range of 0.6–0.9% calculated vitrinite reflectance (Rcb), as inferred from the Trimethylnaphthalene Ratio (TNR-2), are in reasonably good agreement with MPI-1 measurements and geological constraints, e.g., highest maturities detected near the depocentre of the Ardjuna basin. The TNR-2 parameter hence proved useful for maturity assessment of Java Sea oils.