Supply Of Terrestrial Organic Matter Research Articles

Multitrophic biodiversity patterns and environmental descriptors of sub‐Arctic lakes in northern Europe

Abstract Arctic and sub‐Arctic lakes in northern Europe are increasingly threatened by climate change, which can affect their biodiversity directly by shifting thermal and hydrological regimes, and indirectly by altering landscape processes and catchment vegetation. Most previous studies of northern lake biodiversity responses to environmental changes have focused on only a single organismal group. Investigations at whole‐lake scales that integrate different habitats and trophic levels are currently rare, but highly necessary for future lake monitoring and management. We analysed spatial biodiversity patterns of 74 sub‐Arctic lakes in Norway, Sweden, Finland, and the Faroe Islands with monitoring data for at least three biological focal ecosystem components (FECs)—benthic diatoms, macrophytes, phytoplankton, littoral benthic macroinvertebrates, zooplankton, and fish—that covered both pelagic and benthic habitats and multiple trophic levels. We calculated the richnessrelative (i.e. taxon richness of a FEC in the lake divided by the total richness of that FEC in all 74 lakes) and the biodiversity metrics (i.e. taxon richness, inverse Simpson index (diversity), and taxon evenness) of individual FECs using presence–absence and abundance data, respectively. We then investigated whether the FEC richnessrelative and biodiversity metrics were correlated with lake abiotic and geospatial variables. We hypothesised that (1) individual FECs would be more diverse in a warmer and wetter climate (e.g. at lower latitudes and/or elevations), and in hydrobasins with greater forest cover that could enhance the supply of terrestrial organic matter and nutrients that stimulated lake productivity; and (2) patterns in FEC responses would be coupled among trophic levels. Results from redundancy analyses showed that the richnessrelative of phytoplankton, macrophytes, and fish decreased, but those of the intermediate trophic levels (i.e. macroinvertebrates and zooplankton) increased with decreasing latitude and/or elevation. Fish richnessrelative and diversity increased with increasing temporal variation in climate (temperature and/or precipitation), ambient nutrient concentrations (e.g. total nitrogen) in lakes, and woody vegetation (e.g. taiga forest) cover in hydrobasins, whereas taxon richness of macroinvertebrates and zooplankton decreased with increasing temporal variation in climate. The similar patterns detected for richnessrelative of fish, macrophytes, and phytoplankton could be caused by similar responses to the environmental descriptors, and/or the beneficial effects of macrophytes as habitat structure. By creating habitat, macrophytes may increase fish diversity and production, which in turn may promote higher densities and probably more diverse assemblages of phytoplankton through trophic cascades. Lakes with greater fish richnessrelative tended to have greater average richnessrelative among FECs, suggesting that fish are a potential indicator for overall lake biodiversity. Overall, the biodiversity patterns observed along the environmental gradients were trophic‐level specific, indicating that an integrated food‐web perspective may lead to a more holistic understanding of ecosystem biodiversity in future monitoring and management of high‐latitude lakes. In future, monitoring should also focus on collecting more abundance data for fish and lower trophic levels in both benthic and pelagic habitats. This may require more concentrated sampling effort on fewer lakes at smaller spatial scales, while continuing to sample lakes distributed along environmental gradients.

Depositional environmental controls on the genesis and characteristics of oil shale: Case study of the Middle Jurassic Shimengou Formation, northern Qaidam Basin, north‐west China

Two different types of oil shales (OSs) from the Middle Jurassic Shimengou Formation on the northern margin of the Qaidam Basin, north‐west China, provide a valuable opportunity to study the factors controlling the genesis of oil shales. This study presents the sedimentary characteristics of various types of oil shales from the Shimengou Formation and then discusses their possible genesis based on a comprehensive analysis on drillcores. The Shimengou Formation comprises a lower coal‐bearing member (J2sh1) and an upper shale member (J2sh2). The J2sh1 OS unit is composed of dark grey thin‐layered shales interbedded with coal seams, with total organic carbon (TOC) content of 18.8–34.1 wt.% (averagely 21.5 wt.%), and belonging to type II2 organic matter. The J2sh2 OS unit consists of dark grey to grey‐brown thick‐bedded shales and mudstone. The J2sh2 OS has a moderate abundance in organic matter, TOC contents of 6.3–11.5 wt.% (averagely 9.59 wt.%), and types I and II1 organic matters. During the deposition of the J2sh1 member, both braided river delta and freshwater–marsh facies dominate the succession, and OS developed in shallow lakes and swamps. Soon after, the depositional environment changed rapidly. Plentiful terrestrial and shallow water aquatic plants provided abundant organic matter for the sedimentation of OS and also promoted the formation of thinly‐bedded, high‐quality OS with type II2 organic matter. The frequent changes in depositional environments facilitated the formation of thin layers of oil shale. During the sedimentation of the J2sh2 member, in similar tectonic settings, the stable warm–humid climate makes the lake water deeper than before, and the oil shale was deposited mainly in a relatively deep lake. This led to a reduced supply of terrestrial organic matter, which came mainly from lake algae, leading to the formation of OS with a large, uniform thickness and the presence of types I and II2 organic matter.

The environmental conditions of MIS5 in the northern South China Sea, revealed by n-alkanes indices and alkenones from a 39 m-long sediment sequence

In order to reconstruct the environmental conditions of marine isotope stage (MIS) 5 in the coastal area of northern South China Sea, a sediment core was collected from the south coast of Hainan Island (18°16′57″N, 109°42′38″E), from which a thick marine mud unit (39 m) is found to be the deposit of MIS 5. According to the high abundance of alkenones, the thick mud sequence was deposited under marine conditions. The high TOC and n-alkanes concentrations (as normalized to TOC) suggest this was a period of high organic matter (OM) production, and the majority of OM came from terrestrial vascular plant sources. Comparatively, short chain n-alkanes (C18-22) and proportion of aquatic plant index (Paq) in the lower sub-unit appear higher than those in the middle and upper sub-units, suggesting a gradual increase in terrestrial OM supply throughout MIS 5e. The carbon preference index in long-chain n-alkanes (CPI25-33) implies high precipitation and/or temperature in this interval, whilst the average carbon length index in long-chain n-alkanes (ACL25-33) indicates a warm climate during MIS 5e.

Modern sedimentation processes in Laguna de Medina, southern Spain, derived from lake surface sediment and catchment soil samples

<p>Modern processes influencing sediment composition in the endorheic lake Laguna de Medina, southern Spain, are disentangled by analysis of 46 lake surface sediment and 32 catchment soil samples. Based on statistical analysis of the mineralogical, geochemical, elemental, and granulometric compositions of all samples, the lake surface sediments can be divided into six provinces of individual composition and depositional processes. High quartz contents and coarse grain sizes, reflecting input from ancient terraces of the Guadalete River that are exposed in the adjacent hinterland, characterize the lake sedimentation close to the northern shore. At the south-eastern shore, sedimentation is characterized by terrestrial input of the Triassic Keuper facies <em>via</em> the most important inlet, the Arroyo Fuente Bermeja, as reflected by high relative intensities of Ti, K, Al, Fe, Mg, Rb. Sediments close to the northern shore are characterized by high calcite contents, reflecting predominant sediment supply from the adjacent Cretaceous 'capas rojas', a series of Subbetic deep-water marlstones and limestones. Close to the western shore, relatively high gypsum contents presumably are due to precipitation from upwelling ground water. Anthropogenic influence is only indicated in the north-western and central eastern parts of the lake, where the surface sediments are significantly enriched in TOC and TN, reflecting enhanced primary production due to terrestrial organic matter supply from anthropogenic areas in the respective catchment. The central part of the lake is characterized by distal hemipelagic sedimentation, with high concentrations of clay and silt and a chemical and mineralogical composition that reflects a mixture of the sediment sources characterizing individual parts of the lake shores. The results of this study shed new light on the depositional processes and their potential spatial heterogeneity in small endorheic lakes. Furthermore, they will provide important information concerning the interpretation of the climate-controlled sedimentary processes through time, which are reflected in a 25.7 m long sediment record (Co1313) that was recovered in the lake centre in 2014 and 2015.</p>

The effect of river-delta system on the formation of the source rocks in the Baiyun Sag, Pearl River Mouth Basin

Source rock formation influenced by river-delta system, especially in continental margin basins, is still poorly understood. This article aimed to reveal the effect of river-delta system on the formation of the source rock by taking the Baiyun Sag of the Pearl River Mouth Basin for example. Paleo-Pearl River began to develop since the Enping Formation, providing abundant organic matter beneficial for the formation of the source rocks in the Baiyun Sag. The main controlling factor of source rock formation in the Baiyun Sag is terrestrial organic matter supply rather than the paleoproductivity or redox conditions. Low Al/Ti and P/Ti ratios suggest low marine productivity, which may be associated with a large number of terrigenous detritus input, occupying about 43.04%–94.91%. There is a positive correlation between the oleanane/C30hopane ratio and the TOC value, showing that terrigenous organic matter controls the source rock formation. The size of the delta below Pearl River estuary determines the extent of terrestrial organic matter supply. Source rocks with high organic matter abundance mainly formed in delta environment, and those in neritic environment in Enping and Zhuhai Formations also have high TOC values as a result of adequate terrestrial organic matter supply.

Effect of Native Vegetation Loss on Stream Ecosystem Processes: Dissolved Organic Matter Composition and Export in Agricultural Landscapes

Stream and river ecosystems are dependent on energetic inputs from their watersheds and thus shifts in land use from forest cover to agriculture will affect stream community composition and function. The disruption of forest-aquatic linkages alters the organic matter resources in agricultural streams. Dissolved organic matter (DOM) is the dominant form of organic matter in aquatic ecosystems, and a microbial energy source that is important for stream respiration. The concentrations and characteristics of DOM are regulated by both terrestrial (for example, terrestrial organic matter supply) and in-stream processes (for example, microbial respiration and periphyton production) that are influenced by land management. The effects of watershed land use and topographic, soil and climatic variables on DOM quantity (dissolved organic carbon concentration and load), source (terrestrial or in-stream) and quality (composition and lability) were measured in 14 streams across an agricultural land-use gradient. DOC concentration was positively correlated with watershed pasture cover and negatively correlated with watershed relief. No watershed variables were important correlates of DOC load. Stream DOM was primarily of terrestrial origin, but DOM in agricultural streams had a greater proportion of sources from in-stream sources. This may be due to reduced connection with riparian vegetation and increased in-stream primary production. We suggest that maintaining watershed tree cover greater than 52% and ensuring less than 10% of the length of riparian corridor is cleared for pasture could minimize changes to DOM composition. This is important to avoid flow-on effects for stream ecosystem processes that are mediated by DOM. Long-term DOM monitoring will be valuable for assessing the functional impacts of land-use change.

Living, dead and fossil benthic foraminifera on a river dominated shelf (northern Gulf of Cadiz) and their use for paleoenvironmental reconstruction

Same-area comparison between patterns of Recent (living) and Holocene benthic foraminiferal assemblage composition is essential to validate their utility as proxies for paleoenvironmental reconstructions. Such reconstructions have scarcely been attempted in shelf environments. In this study, we compared living (stained), dead and Holocene benthic foraminiferal assemblages from the Gulf of Cadiz continental shelf off the Guadiana River. On average, 99% of the living benthic foraminiferal species were preserved in the dead assemblage and 95% in the fossil record. Several common species were assessed as indicators for certain environmental factors, including river discharge, supply of terrestrial organic matter, heavy metal concentrations, oxygen levels, substrate properties, hydrodynamic energy levels, sea-level rise and human impact. The paleoenvironmental reconstruction depicted five stages of Holocene environmental evolution of the Guadiana shelf over the last 11,500calyr BP. The characteristics of the stages, and the transitions between them, were in particular driven by changes in sea-level, influx of terrestrial organic matter and limits of productivity.

Significant changes in land vegetation and oceanic redox across the Cretaceous/Paleogene boundary

The impact of an extraterrestrial body 65.5Ma caused the so-called Cretaceous/Paleogene (K/Pg) event that resulted in a mass extinction and rapid changes in the surface environment on Earth. Here we report changes in land vegetation and oceanic redox across the K/Pg boundary at Caravaca, southeastern Spain, using biomarkers. The results reveal that the basal 3-mm-thick layer of the K/Pg boundary clay is marked by a rapid increase in the concentration of terrestrial long-chain n-alkanes and dibenzofuran, indicating the destruction of land vegetation and an increase in the supply of terrestrial organic matter into the marine environment during the deposition of the K/Pg boundary clay. This layer also records a rapid increase in the concentration of dibenzothiophenes, which indicates a change in redox conditions from oxic to anoxic/euxinic conditions in the intermediate water over the seafloor. The low-oxygen conditions could have been caused by an increase in the influx of terrestrial organic matter into the ocean. A rapid increase in the concentration of retene and retene/cadalene occurred during the deposition of the upper part of the boundary clay 10kyr after the mass extinction, indicating the recovery of conifers, which greatly decreased at the K/Pg boundary.

Impact of recent lake eutrophication on microbial community changes as revealed by high resolution lipid biomarkers in Rotsee (Switzerland)

The effects of eutrophication on short term changes in the microbial community were investigated using high resolution lipid biomarker and trace metal data for sediments from the eutrophic Lake Rotsee (Switzerland). The lake has been strongly influenced by sewage input since the 1850s and is an ideal site for studying an anthropogenically altered ecosystem. Historical remediation measures have had direct implications for productivity and microbial biota, leading to community composition changes and abundance shifts. The higher sewage and nutrient input resulted in a productivity increase, which led predominantly to a radiation in diatoms, primary producers and methanogens between about 1918 and 1921, but also affected all microorganism groups and macrophytes between about 1958 and 1972. Bacterial biomass increased in 1933, which may have been related to the construction of a mechanical sewage treatment plant. Biomarkers also allowed tracing of fossil organic matter/biodegraded oil contamination in the lake. Stephanodiscus parvus, Cyclotella radiosa and Asterionella formosa were the dominant sources of specific diatom biomarkers. Since the 1850s, the cell density of methanogenic Archaea (Methanosaeta spp.) ranged within ca. 0.5–1.8×109cellsg−1 dry sediment and the average lipid content of Rotsee Archaea was ca. 2.2fg iGDGTs cell−1. An altered BIT index (BITCH), indicating changes in terrestrial organic matter supply to the lake, is proposed.

Organic carbon isotope values from the Late Permian Seis/Siusi succession (Dolomites, Italy): Implications for palaeoenvironmental changes

<strong class="journal-contentHeaderColor">Abstract.</strong> The Permian-Triassic boundary is marked by a globally prominent negative carbon isotope excursion traceable in marine carbonates and organic matter. In the shallow marine carbonate succession at Seis/Siusi (Dolomites, Italy), the &delta;¹³C_carb and &delta;¹³C_org signatures follow the general Permian-Triassic boundary carbon isotope trend, but the &delta;¹³C_org values are slightly less depleted in ¹³C in two episodes representing restricted lagoonal environments and in the period around the Tesero Oolite Horizon. This isotopically less depleted organic matter in the lagoons is interpreted to be most likely caused by poor oxygen ventilation and/or slightly modified salinity which may have led to restricted bioproductivity and increased hence the relative amounts of continental-sourced organic matter. In addition, elevated riverine influx and supply of terrestrial organic matter, perhaps triggered by a wet period, might be the cause for the relatively less depleted ¹³C in the organic matter around the Tesero Oolite Horizon and in overlying sediments. <br><br> doi:<a href="http://dx.doi.org/10.1002/mmng.201100008" target="_blank">10.1002/mmng.201100008</a>

Organic carbon isotope values from the Late Permian Seis/Siusi succession (Dolomites, Italy): Implications for palaeoenvironmental changes

The Permian-Triassic boundary is marked by a globally prominent negative carbon isotope excursion traceable in marine carbonates and organic matter. In the shallow marine carbonate succession at Seis/Siusi (Dolomites, Italy), the &amp;delta;&lt;sup&gt;13&lt;/sup&gt;C&lt;sub&gt;carb&lt;/sub&gt; and &amp;delta;&lt;sup&gt;13&lt;/sup&gt;C&lt;sub&gt;org&lt;/sub&gt; signatures follow the general Permian-Triassic boundary carbon isotope trend, but the &amp;delta;&lt;sup&gt;13&lt;/sup&gt;C&lt;sub&gt;org&lt;/sub&gt; values are slightly less depleted in &lt;sup&gt;13&lt;/sup&gt;C in two episodes representing restricted lagoonal environments and in the period around the Tesero Oolite Horizon. This isotopically less depleted organic matter in the lagoons is interpreted to be most likely caused by poor oxygen ventilation and/or slightly modified salinity which may have led to restricted bioproductivity and increased hence the relative amounts of continental-sourced organic matter. In addition, elevated riverine influx and supply of terrestrial organic matter, perhaps triggered by a wet period, might be the cause for the relatively less depleted &lt;sup&gt;13&lt;/sup&gt;C in the organic matter around the Tesero Oolite Horizon and in overlying sediments. &lt;br&gt;&lt;br&gt; doi:&lt;a href="http://dx.doi.org/10.1002/mmng.201100008" target="_blank"&gt;10.1002/mmng.201100008&lt;/a&gt;

Reconstruction of surface water conditions in the central region of the Okhotsk Sea during the last 180 kyrs

Core GC9A, a 6.7m long gravity core collected from the central region of the Okhotsk Sea during Cruise YK0712 on R/V Yokosuka (JAMSTEC), was used to reconstruct the changes in surface water conditions by measuring biogenic components (biogenic opal, CaCO3, total organic carbon and δ15N of sediment organic matter) of sediment samples. The age of Core GC9A was determined indirectly by graphic correlation comparing the b⁎ (psychometric yellow–blue chromaticness) values with those of well-dated Core MD01-2415, with complement to the tephra layer (K3; 50ka). The bottom age of Core GC9A was estimated to be about 180kyr; therefore it provides the history of surface water conditions from MIS 1 to MIS 6. The biogenic opal, CaCO3, and TOC contents were high during the interglacial periods as expected, indicating enhanced surface water production under warm climatic conditions. This condition resulted from sufficient nutrient supply to the surface waters by active vertical mixing, which was validated by low δ15N values of the sediment organic matter. In contrast, surface water productivity was depressed during the colder glacial periods, probably due to the expanded sea-ice distribution and limited nutrient supply. However, the glacial sediments had moderately high δ15N values, indicating enhanced nitrate utilization resulting from the limited nutrient supply caused by strong stratification of the surface water. High δ15N values were also observed during the deglaciation, which was attributed to the increased nitrate utilization during enhanced surface water productivity. However, the low δ15N values during the glacial and deglacial periods may be attributed to the increased supply of terrestrial organic matter. Diatom production was primarily responsible for surface water paleoproductivity during the interglacial periods rather than coccolithophores. However, the succession of glacial to early deglacial coccolithophore production and late deglacial to interglacial diatom production was remarkable, corresponding to the present-day seasonal phytoplankton succession. Such an advanced coccolithophore production relative to diatom production might be attributed to the degree of nutrient availability associated with surface water conditions on the basis of variations in the δ15N value. Finally, the opal and TOC contents decreased abruptly in conjunction with a gradual decrease in CaCO3 content from about 2ka, which seems to implicate a late Holocene sudden decrease in paleoproductivity in the central region of the Okhotsk Sea. According to the increase in δ15N values during this interval, nutrient availability appears to be poor, which is likely attributed to the resumed strong stratification that occurred due to the southward shift of the Aleutian Low atmospheric pressure system.

Characterization of lignin monomers in low rank coal humic acids using the derivatization/reductive cleavage method

Traditional CuO oxidation and thermochemolysis with tetramethylammonium hydroxide are the two main methods for lignin characterization in gymnosperm wood, and in soils and sediments formed from degraded gymnosperm wood, or for assessing the supply of terrestrial organic matter to marine sediments. In some cases, the overall lignin yield and the compound ratios used as plant source proxies have been found to be considerably different, depending on the method used. Thus, there is a need for finding efficient and more selective methods for lignin α- and β-aryl ether cleavage. Derivatization followed by reductive cleavage (the DFRC method) is suitable for lignocellulose material. Results from the DFRC method applied to the characterization of humic acids of a lignite (low rank coal) from the Czech Republic show that they contain intact lignin monomers with a dominance of coniferyl units, in accord with the gymnosperm origin of the lignite. It is expected that DFRC will be suitable also for tracing lignin in other sediments.

Re-assessing the nitrogen signal in continental margin sediments: New insights from the high northern latitudes

Organic and inorganic nitrogen and their isotopic signatures were studied in continental margin sediments off Spitsbergen. We present evidence that land-derived inorganic nitrogen strongly dilutes the particulate organic signal in coastal and fjord settings and accounts for up to 70% of the total nitrogen content. Spatial heterogeneity in inorganic nitrogen along the coast is less likely to be influenced by clay mineral assemblages or various substrates than by the supply of terrestrial organic matter (TOM) within eroded soil material into selected fjords and onto the shelf. The δ 15N signal of the inorganic nitrogen ( δ 15N inorg) in sediments off Spitsbergen seems to be appropriate to trace TOM supply from various climate- and ecosystem zones and elucidates the dominant transport media of terrigenous sediments to the marine realm. Moreover, we postulate that with the study of sedimentary δ 15N inorg in the Atlantic–Arctic gateway, climatically induced changes in catchment's vegetations in high northern latitudes may be reconstructed. The δ 15N org signal is primarily controlled by the availability of nitrate in the dominating ocean current systems and the corresponding degree of utilization of the nitrate pool in the euphotic zone. Not only does this new approach allow for a detailed view into the nitrogen cycle for settings with purely primary-produced organic matter supply, it also provides new insights into both the deposition of marine and terrestrial nitrogen and its ecosystem response to (paleo-) climate changes.

Climate-induced changes in sedimentary regimes for organic matter supply on the continental shelf off northern Norway

With this study, I suggest that changes in biogeochemical processes in northern Norwegian fjords during the last glacial/interglacial transition (14.3 to 6.3 ka B.P.) are predominantly climate induced. Variable strength in Atlantic water inflow, intrusion of Arctic waters and sea-ice coverage, various nutrient supply, as well as several re-advances of continental ice-sheets are recorded by both bulk organic and selected biomarkers in sediments of the Andfjord. Stable isotope (δ 13C org, δ 15N) and Rock-Eval pyrolysis data indicate a strong supply of terrestrial organic matter during stadials (e.g., Younger Dryas, Older Dryas) whereas enhanced input of marine organic matter prevailed during the interstadials (Bølling/Allerød). Profiles of selected biomarkers of marine origin show a characteristic climate-induced variation during the whole time interval, where relatively low concentrations of dinosterols and C 37 alkenones may indicate—similar to today—a minor contribution of their respective plankton groups (coccolithophorids, dinoflagellates). The prevalence of Arctic waters and seasonal sea-ice coverage during the Younger Dryas is indicated by a single maximum of 24-methylenecholesterol probably indicating the dominance of sea-ice diatoms and/or the prevalence of diatoms of Thalassiosiraceae in surface waters. The sediments of the Allerød, in contrast, show a pronounced maximum in dinosterols, indicating a better adaptation of dinoflagellates to an oceanic regime that is characterized by incipient intrusion of Atlantic water, highly variable sea surface temperatures, and well stratified water masses. The concentration of higher-molecular-weight n-alkanes, however, follows the deglacial–early Holocene trend of climate amelioration from the last deglaciation to the middle Holocene, with maxima during ice advances (stadials) and minima during the middle Holocene warm period. These new results significantly improve the understanding of climate-induced response on organic matter supply in fjords and provide a better knowledge of past variations of biogeochemical processes in high-latitude coastal environments.

Abrupt and massive influx of terrestrial biomarkers into the marine environment at the Cretaceous–Tertiary boundary, Caravaca, Spain

The mass extinction at the Cretaceous–Tertiary (K/T) boundary ca. 65 million years ago caused a major change in the nature and abundance of global life in Earth history. We present the first vertical high-resolution records of molecular distributions of n-fatty acids across the K/T boundary at Caravaca (Spain). The results reveal that the first basal thin horizon (0 to + 0.5 cm; 0 = K/T boundary) of the K/T boundary–clay layer showed as much as a ~ 35-fold increase in concentrations of terrestrial long-chain n-fatty acids (≥ C 20), representative of an eight-fold increase in mass accumulation rate, compared with the subjacent Cretaceous layers. Thereafter concentrations rapidly declined back to almost pre-boundary values within + 3 cm above the K/T boundary. The abrupt increase in supply of terrestrial organic matter into the marine environment at the K/T boundary could have been caused by an enhanced riverine flux, probably due to heavy rains associated with global warming, combined with enhanced fragments of terrestrial higher-plants withered by acid rain and/or by temporal darkness and cooling.

Source and supply of terrestrial organic matter affects aquatic microbial metabolism

Aquatic ecosystems are connected to their surrounding watersheds through inputs of terrestrial-derived dissolved organic matter (DOM). The assimilation of this allochthonous resource by recipient bacterioplankton has consequences for food webs and the biogeochemistry of aquatic ecosystems. We used laboratory batch experiments to examine how variation in the source and supply (i.e. concentration) of DOM affects the productivity, respiration and growth efficiency of heterotrophic lake bacterioplankton. We created 6 different DOM sources from soils beneath near- monotypic tree stands in a temperate deciduous-coniferous forest. We then exposed freshwater microcosms containing a natural microbial community to a 1100 µM supply gradient of each DOM source. Bacterial productivity (BP) and bacterial respiration (BR) increased linearly over the broad gradient, on average consuming 7% of the standing pool of dissolved organic carbon (DOC). Bacter- ial metabolism was also influenced by the chemical composition of the DOM source. Carbon-specific productivity declined exponentially with an increase in the carbon:phosphorus (C:P) ratio of the dif- ferent DOM sources, consistent with the predictions of ecological stoichiometry. Together, our short- term laboratory experiments quantitatively describe the metabolic responses of freshwater bacterio- plankton to variation in the supply of terrestrial-derived DOM. Furthermore, our results suggest that dissolved organic phosphorus (DOP) content, which may be linked to the identity of terrestrial vege- tation, is indicative of DOM quality and influences the productivity of freshwater bacterioplankton.

Tectono-sedimentary controls on Cretaceous black shale deposition along the opening Equatorial Atlantic Gateway (ODP Leg 159)

Abstract The Cretaceous Equatorial Atlantic Gateway between the Central and South Atlantic basins is of interest not only for palaeoceanographic and palaeoclimatic studies, but also because it provided particularly favourable conditions for the accumulation and preservation of organic-rich sediments. Deposition of carbonaceous sediments along the Côte d’Ivoire-Ghana Transform Margin (Ocean Drilling Program Leg 159) was intimately linked to the plate tectonic and palaeoceanographic evolution of this gateway. Notably, the formation of a marginal basement ridge on the southeastern border of the transform margin provided an efficient shelter of the landward Deep Ivorian Basin against erosive and potentially oxidizing currents. Different subsidence histories across the transform margin were responsible for the development of distinct depositional settings on the crest and on both sides of the basement ridge. Whereas the southern, oceanward flank of the basement ridge was characterized by rapid, continuous deepening since the latest Albian-early Cenomanian, marine sedimentation on the northern, landward flank was interrupted by a period of uplift and erosion in the late Albian, and rapid subsidence started after the early Coniacian. Organic-rich sediments occur throughout almost the entire Cretaceous section, but hydrogen-rich marine black shales were exclusively recovered from core sections above an uplift-related unconformity. These black shales formed when separation of Africa and South America was sufficient to allow permanent oceanic midwater exchange after the late Albian. Four periods of black shale accumulation are recorded, some of them are correlated with the global oceanic anoxic events: in the latest Albian-earliest Cenomanian, at the Cenomanian-Turonian boundary, during the middle Coniacian-early Campanian, and in the mid-Maastrichtian. These periods were characterized by increased carbon fluxes to the seafloor, induced by enhanced palaeoproductivity and intensified supply of terrestrial organic matter. Black shale deposition appears to be intimately linked to periods of rising or maximum eustatic sea level and to the expansion of the oxygen minimum zone, as indicated by foraminiferal biofacies. Intervals between black shale units, in contrast, indicate a shrinking oxygen minimum zone and enhanced detrital flux rates, probably related to lowering sea level. Upper Cretaceous detrital limestones with high porosities may provide excellent hydrocarbon reservoirs, although their areal extent appears to be limited. Palaeogene porcellanites, capped by Neogene pelagic marls and clays, extend over a wider area and may provide another target for hydrocarbon exploration.

Lignin geochemistry of North American coastal and continental shelf sediments

The concentrations and composition of lignin in coastal and shelf sediments at five locations along the North American continent—Georges Bank/North Atlantic shelf, northwestern Gulf of Mexico, Southern California, Norton Sound and nearshore Beaufort Sea—have been characterized using alkaline CuO oxidation. Lignin concentrations are generally highest at close proximity to the mouth of major rivers, indicating that deposition of river-borne vascular plant debris is the principal source of lignin to the offshore sediments. Arctic sediments contain the highest concentrations, presumably as a result of an abundant supply of terrestrial organic material and the prevalence of frigid temperatures and surface ice cover during much of the year. Concentrations are lowest in the Georges Bank/North Atlantic sediments, where a dynamic physical environment persists over much of the year and the supply of terrestrial organic matter to the offshore in the form of major rivers is lacking. Stable carbon isotopic compositions show that sediments containing the highest lignin concentrations also contain isotopically-lighter organic matter, consistent with a terrestrial source input. Vanillyl, syringyl and cinnamyl phenol distributions in these offshore sediments are consistent with primary contributions from gymnosperm (predominant) and angiosperm woods and secondary contributions from nonwoody tissues. These estimates may be subject to some uncertainty due to diagenetic alteration of individual lignin phenols. In contrast, p-hydroxyl phenol yields are not strongly correlated with those of the other lignin-derived phenols, suggesting generation from both lignin and non-lignin sources. Elevated acid/aldehyde ratios relative to undegraded plant tissues suggest that the lignin transported to these offshore sediments has undergone some biodegradative oxidation.

Sedimentology and Characteristics of Dispersed Organic Matter in Tertiary Niger Delta: Origin of Source Rocks in a Deltaic Environment

Organic matter in Tertiary strata of the Niger delta is mainly a mixture of types II and III kerogen as defined by pyrolysis, has a high pristane/phytane ratio (> 1%), and is composed of the macerals vitrinite and minor liptinite. The main palynofacies are structured woody material, opaque organic matter, cuticles, pollen and spores, and minor amorphous organic matter. The geochemistry, petrology, palynofacies, and distribution data indicate a predominantly terrestrial and detrital source of the organic matter irrespective of facies, formation, or age. The distribution and abundance of the organic matter are related to both the age of the strata and depositional environment. The most significant variation is the decline in mean total organic carbon (TOC) content from late Eocene (2.2% TOC) to Pliocene strata (.90% TOC) and an associated general decline in pyrolysis-defined hydrogen index (HI) and pristane/phytane ratio. The decrease in TOC and HI in younger strata reflects increased dilution of a nearly constant supply of terrestrial organic matter with the generally higher sedimentation rates of younger strata. A simple linear dilution model accounts for about 50% of the variance in measured TOC. The low pristane/phytane ratio of younger strata may reflect less-oxidizing depositional conditions. The variation in organic matter with depositional environments and environmental depth zones (defined by foraminiferal assemblages) is significant, although less important than variation due to age. The highest TOC and HI values occur in nonmarine swamp, marsh, and floodplain deposits, reflecting proximity to the organic source. Beach, barrier and offshore bar facies have lower TOC and HI values due to selective winnowing of organic matter and greater oxidation. From continental to transition marine depth zones, a marked decline in TOC and HI occurs as a result of dilution, selective transport, and oxidation of the organic matter. From transitional to bathyal depth zones, little variation is found in TOC but a general increase is found in HI, which reflects a relative increase in more hydrogen-rich autochthonous organic matter. In all facies, autochthonous organic matter comprises less than 20% of the TOC. No interpretable variation appears in maceral or palynofacies abundance with sediment type, which probably reflects the homogeneity of the organic matter. Paradoxically, no rich source rocks occur in the Tertiary succession in the Niger delta and, as conventionally measured, the strata have little or no oil-generating potential. The poor quality of the source rocks has been more than compensated for by their great volume, by the excellent migration routes provided by interbedded permeable sands, and possibly by the relatively rapid rate of maturation. Niger delta type of source rock, although an end member in terms of general source rock composition, appears to be relatively typical of Tertiary deltas.