Calcium carbonate, organic carbon, sediment description and hydrogen and oxygen index at DSDP Sites 93-603, 93-605, 93-604 and 95-603

The organic matter contents of sediments and rocks sampled during DSDP Leg 93 have been characterized by CHN and Rock-Eval analyses. Most samples from Sites 604 and 605 on the New Jersey continental slope and from Site 603 on the Hatteras outer continental rise contained less than 0.5% organic carbon. Some Neogene samples from the slope contained 1 to 2% organic carbon, and Cretaceous samples from the outer rise were as rich as 13.6% organic carbon by weight. Thin layers of black claystones of Santonian, Cenomanian, and Albian age were found interbedded in organiccarbon- lean, bioturbated, turbiditic claystones. Similar layers of turbiditic black marlstones were interspersed among Neocomian limestones and sandstones. Although the organic matter in many of the samples appeared to be detrital continental material, according to Rock-Eval and C/N values, Cenomanian black shales, in particular, contained substantial proportions of marine-derived organic matter.

Organic carbon and biomarker record from the Laptev Sea continental margin

In order to understand the processes controlling organic carbon deposition (i.e., primary productivity vs. terrigenous supply) and their paleoceanographic significance, three sediment cores (PS2471, PS2474. and PS2476) from the Laptev Sea continental margin were investigated for their content and composition of organic carbon. The characterization of organic matter indudes the determination of buk parameters (hydrogen index values and C/N ratios) and the analysis of specific biomarkers (n-alaknes, fatty acids, alkenones, and pigments). Total organic carbon (TOC) values vary between 0.3 and 2%. In general, the organic matter from the Laptev Sea continental margin is dominated by terrigenous matter throughout. However. significant amounts of marine organic carbon occur. The turbidites, according to a still preliminary stratigraphy probably deposited during glacial Oxygen Isotope Stages 2 and 4, are characterized by maximum amounts of organic carbon of terrigenous origin. Marine organic carbon appears to show enhanced relative abundances in the Termination I (?) and early Holocene time intervals, as indicated by maximum amounts of short chain n-alkanes, short-chain fatty acids, and alkenones. The increased amounts of faity acids, however, may also have a freshwater origin due to increased river discharge at that time. The occurrence of alkenones is suggested to indicate an intensification of Atlantic water inflow along the Eurasian continental margin starting at that time. Oxygen Isotope Stage l accumutation rates of total organic carhon are 0.3, 0.17, and 0.02 C/cm**2/ky in cores PS2476, PS2474, and PS2471, respectively.

Accumulation of particulate organic carbon at the Eurasian continental margin during late Quaternary times

Data on the amount and composition of organic carbon were determined in sediment cores from the Kara and Laptev Sea continental margin, representing oxygen isotope stages 1-6. The characterization of organic matter is based on hydrogen index (HI) values, n-alkanes and maceral composition, indicating the predominance of terrigenous organic matter through space and time. The variations in the amount and composition of organic carbon are mainly influenced by changes in fluvial sediment supply, Atlantic water inflow, and continental ice sheets. During oxygen isotope stage (OIS) 6, high organic carbon contents in sediments from the Laptev Sea and western East Siberian Sea continental margin were probably caused by the increased glacial erosion and further transport in the eastward-flowing boundary current along the continental margin. During OIS 5 and early OIS 3, some increased amounts of marine organic matter were preserved in sediments east of the Lomonosov Ridge, suggesting an influence of nutrient-rich Pacific waters. During OIS 2, terrigenous organic carbon supply was increased along the Barents and western Kara Sea continental margin caused by extended continental ice sheets in the Barents Sea (Svalbard to Franz Josef Land) area and increased glacial erosion. Along the Laptev Sea continental margin, on the other hand, the supply of terrigenous (organic) matter was significantly reduced due to the lack of major ice sheets and reduced river discharge. Towards the Holocene, the amount of total organic carbon (TOC) increased along the Kara and Laptev Sea continental margin, reaching average values of up to 0.5 g C/cm**2/ky. Between about 8 and 10 ka (9 and 11 Cal ka), i.e., during times when the inner shallow Kara and Laptev seas became largely flooded for the first time after the Last Glacial Maximum, maximum supply of terrigenous organic carbon occurred, which is related to an increase in coastal erosion and Siberian river discharge. During the last 8000 years, the increased amount of marine organic carbon preserved in the sediments from the Kara and Laptev Sea continental margin is interpreted as a result of the intensification of Atlantic water inflow along the Eurasian continental margin.

Organic carbon, reduced sulfur, and iron in Miocene to Holocene sediments from the Oman and Beguela upwelling systems

We examined sediments from Neogene and Quaternary sections of the Benguela and Oman upwelling systems (DSDP Site 532, ODP Sites 723 and 722) to determine environmental and geochemical factors which control and limit pyrite formation in organic-carbon-rich marine sediments. Those samples from the upwelling sites, which contained low to moderate concentrations of total organic carbon (0.7%-3%), had C/S ratios typical of normal marine sediments, i.e., around 2.8. In these sediments, TOC availability probably limited pyrite formation. Results that do not conform with accepted models were found for the sediments high in TOC (3^0-12.4%). The organic matter was of marine origin and contained considerable pyrolytic hydrocarbons, a fact that we take as a sign of low degradation, yet significant concentrations of dissolved sulfate coexisted with it (> 5 mmol/L in the case of Sites 532 and 723). Detrital iron was probably not limiting in either case, because the degree of pyritization was always less than 0.65. Therefore, controls on sulfate reduction and pyrite formation in the organic matter-rich sediments do not appear to conform simply to generally accepted diagenetic models. The data from these thermally immature, old, and organic-rich marine sediments imply that (1) the total reduced sulfur content of organic-rich marine upwelling sediments rarely exceeds an approximate boundary of 1.5% by weight, (2) the C/S ratio of these sediments is not constant and usually much higher than the empirical values proposed for marine sediments. We conclude that sedimentary pyrite formation in upwelling sediments is limited by an as yet unknown factor, and that caution is advised in using C/S ratios and C vs. S diagrams in paleoenvironmental reconstructions for organic-rich sediments.

Total organic carbon, bitumen ratio, hopane and sterane parameters of ODP Sites 128-798 and 128-799

Notable compositional changes of organic matter are observed below the silica transition zone in thermally immature sediments. The increase of bitumen ratio, and hopane and sterane isomerization parameters indicate an acceleration of the kinetics of the chemical reactions which transform the organic matter. This phenomenon is probably due to the numerous mineral and textural changes induced by the transformation of amorphous biogenic silica into crystalline authigenic silica.

The exchange of carbon, nitrogen, and phosphorus in dwarf and fringe mangroves of the oligotrophic southern Everglades

Water management has altered both the natural timing and volume of freshwater delivered to Everglades National Park. This is especially true for Taylor Slough and the C-111 basin, as hypersaline events in Florida Bay have been linked to reduced freshwater flow in this area. In light of recent efforts to restore historical flows to the eastern Everglades, an understanding of the impact of this hydrologic shift is needed in order to predict the trajectory of restoration. I conducted a study to assess the importance of season, water chemistry, and hydrologic conditions on the exchange of nutrients in dwarf and fringe mangrove wetlands along Taylor Slough. I also performed mangrove leaf decomposition studies to determine the contribution of biotic and abiotic processes to mass loss, the effect of salinity and season on degradation rates, and the importance of this litter component as a rapid source of nutrients. ^ Dwarf mangrove wetlands consistently imported total nutrients (C, N, and P) and released NO2− +NO3 −, with enhanced release during the dry season. Ammonium flux shifted from uptake to release over the study period. Dissolved phosphate activity was difficult to discern in either wetland, as concentrations were often below detection limits. Fluxes of dissolved inorganic nitrogen in the fringe wetland were positively related to DIN concentrations. The opposite was found for total nitrogen in the fringe wetland. A dynamic budget revealed a net annual export of TN to Florida Bay that was highest during the wet season. Simulated increases and decreases in freshwater flow yielded reduced exports of TN to Florida Bay as a result of changes in subsystem and water flux characteristics. Finally, abiotic processes yielded substantial nutrient and mass losses from senesced leaves with little influence of salinity. Dwarf mangrove leaf litter appeared to be a considerable source of nutrients to the water column of this highly oligotrophic wetland. To summarize, nutrient dynamics at the subsystem level were sensitive to short-term changes in hydrologic and seasonal conditions. These findings suggest that increased freshwater flow has the potential to lead to long-term, system-level changes that may reach as far as eastern Florida Bay. ^

(Table 1) Sample descriptions and results: Carbon, lipid, and kerogen analyses, at DSDP Leg 64 Holes

Pleistocene sediments in the Guaymas Basin, Gulf of California, have been intruded by sills and their organic matter thus subjected to thermal stress. Sediment samples from DSDP/IPOD Sites 477, 478, and 481, and samples of thermally unaltered materials from Sites 474 and 479 were analyzed to characterize the lipids and kerogens and to evaluate the effects of the intrusive thermal stresses. The lipids of the thermally unaltered samples are derived from microbial and terrestrial higher-plant detritus. The samples from the sill proximities contain the distillates, and those adjacent to the sills contain essentially no lipids. The pyrograms of the kerogens from the unaltered samples reflect their predominantly autochthonous microbial origin. When compared with the unaltered samples, the pyrograms of the altered kerogen samples reflect the thermal effects by a reduction in the complexity of the products. Kerogens adjacent to the sills produced little or no pyrolysis products. The effects of intrusions into unconsolidated, wet sediments resulted in in situ pyrolysis of the organic matter, as confirmed by these data.

Compilation of organic carbon distribution and sedimentology in the surface sediments on the continental margin offshore southwestern Africa

In this study we demonstrate the relevance of lateral particle transport in nepheloid layers for organic carbon (OC) accumulation and burial across high-productive continental margins. We present geochemical data from surface sediments and suspended particles in the bottom nepheloid layer (BNL) from the most productive coastal upwelling area of the modern ocean, the Benguela upwelling system offshore southwest Africa. Interpretation of depositional patterns and comparison of downslope trends in OC content, organic matter composition, and 14C age between suspended particles and surface sediments indicate that lateral particle transport is the primary mechanism controlling supply and burial of OC. We propose that effective seaward particle transport primarily along the BNL is a key process that promotes and maintains local high sedimentation rates, ultimately causing high preservation of OC in a depocenter on the upper slope offshore Namibia. As lateral transport efficiently displaces areas of enhanced OC burial from maximum production at highly productive continental margins, vertical particle flux models do not sufficiently explain the relationship between primary production and shallow-marine OC burial. On geologic time scales, the widest distribution and strongest intensity of lateral particle transport is expected during periods of rapid sea-level change. At times in the geologic past, widespread downslope lateral transport of OC thus may have been a primary driver of enhanced OC burial at deeper continental slopes and abyssal basins.

Soil organic carbon storage and soil properties for 50 soil profiles in the Lena River Delta including land form description and map

To project the future development of the soil organic carbon (SOC) storage in permafrost environments, the spatial and vertical distribution of key soil properties and their landscape controls needs to be understood. This article reports findings from the Arctic Lena River Delta where we sampled 50 soil pedons. These were classified according to the U.S.D.A. Soil Taxonomy and fall mostly into the Gelisol soil order used for permafrost-affected soils. Soil profiles have been sampled for the active layer (mean depth 58±10 cm) and the upper permafrost to one meter depth. We analyze SOC stocks and key soil properties, i.e. C%, N%, C/N, bulk density, visible ice and water content. These are compared for different landscape groupings of pedons according to geomorphology, soil and land cover and for different vertical depth increments. High vertical resolution plots are used to understand soil development. These show that SOC storage can be highly variable with depth. We recommend the treatment of permafrost-affected soils according to subdivisions into: the surface organic layer, mineral subsoil in the active layer, organic enriched cryoturbated or buried horizons and the mineral subsoil in the permafrost. The major geomorphological units of a subregion of the Lena River Delta were mapped with a land form classification using a data-fusion approach of optical satellite imagery and digital elevation data to upscale SOC storage. Landscape mean SOC storage is estimated to 19.2±2.0 kg C/m**2. Our results show that the geomorphological setting explains more soil variability than soil taxonomy classes or vegetation cover. The soils from the oldest, Pleistocene aged, unit of the delta store the highest amount of SOC per m**2 followed by the Holocene river terrace. The Pleistocene terrace affected by thermal-degradation, the recent floodplain and bare alluvial sediments store considerably less SOC in descending order.