Sedimentaology, pollen profile, and climate reconstruction on a sediment core from Trou Lake, Yukon, Canada

Beringian climate and environmental history are poorly characterized at its easternmost edge. Lake sediments from the northern Yukon Territory have recorded sedimentation, vegetation, summer temperature and precipitation changes since ~16 cal ka BP. Herb-dominated tundra persisted until ~14.7 cal ka BP with mean July air temperatures less than or equal to 5 °C colder and annual precipitation 50 to 120 mm lower than today. Temperatures rapidly increased during the Bølling/Allerød interstadial towards modern conditions, favoring establishment of Betula-Salix shrub tundra. Pollen-inferred temperature reconstructions recorded a pronounced Younger Dryas stadial in east Beringia with a temperature drop of ~1.5 °C (~2.5 to 3.0 °C below modern conditions) and low net precipitation (90 to 170 mm) but show little evidence of an early Holocene thermal maximum in the pollen record. Sustained low net precipitation and increased evaporation during early Holocene warming suggest a moisture-limited spread of vegetation and an obscured summer temperature maximum. Northern Yukon Holocene moisture availability increased in response to a retreating Laurentide Ice Sheet, postglacial sea level rise, and decreasing summer insolation that in turn led to establishment of Alnus-Betula shrub tundra from ~5 cal ka BP until present, and conversion of a continental climate into a coastal-maritime climate near the Beaufort Sea.

Organofacies reconstruction and lipid geochemistry of sediments from the Galicia margin

Samples of Lower to middle Cretaceous rocks from ODP Sites 638, 640, and 641, drilled on the Galicia continental margin in the northeast Atlantic, have been investigated by organic geochemical methods (i.e., organic carbon determination, Rock-Eval pyrolysis, kerogen microscopy, gas chromatography, and gas chromatography/mass spectrometry) to define the Organofacies types and the depositional environments of these sediments. The results of this study fit well into the general picture drawn for the depositional history of the organic matter in Cretaceous organic-carbon-rich sediments in the North Atlantic from previous DSDP investigations. During the Valanginian to Albian, terrigenous organic carbon dominated the organic matter deposited on the Galicia continental margin. Cyclic changes in total organic carbon content were probably controlled by climatic-triggered changes in the supply of terrigenous organic matter from the nearby continent. A drastic change in depositional environment must have occurred near the Cenomanian/Turonian boundary. The preservation of large amounts of marine organic carbon in these sediments was probably caused by anoxic deep-water conditions during that time, rather than high productivity. All of the primary organic matter of the sediment samples investigated is thermally immature, as indicated by very low vitrinite reflectance values.

Lignin, phenols, and some chemical elements in aerosols and bottom sediments from the Tropical North Atlantic

A study of composition of biomarkers (lignin and phenols) in aerosols and bottom sediments from the Tropical North Atlantic was carried out. It was shown that organic matter of aerosols was mostly composed of products of terrestrial plants (arboreal fibers, pollen, and spores). Biomarker composition in the aerosols and in the bottom sediments was practically similar, which proved delivery of terrigenous organic matter to the ocean via the atmosphere.

Organic geochemistry of lower Cretaceous sediments at DSDP Hole 77-535

At Site 535, the four lithologic units of Cretaceous age are controlled by two types of sedimentologic facies: (1) the massive light-colored limestones or marly limestones in which the total organic carbon (TOC) content is low and the organic matter more or less oxidized and (2) laminated dark facies in which the TOC content is higher and associated with a well-preserved organic matter of Type II origin. Very little typical Type III organic matter occurs in the whole series from late Berriasian to Aptian and Cenomanian. Fluctuations from oxidizing to reducing environments of deposition are proposed to account for the variations in properties of the Type II organic matter between the different facies. Dark laminated layers are good but immature potential source rocks: petroleum potential is often higher than 2 kg HC/t of rock.

Migration of C1 to C8 volatile organic compounds in sediments at DSDP Hole 75-530A

The distribution of C1 to C8 hydrocarbons in sediment samples from DSDP Leg 75, Hole 530A, indicates that significant amounts of methane and ethane have migrated from organic-rich to organic-lean shales in close proximity. Most compounds larger than ethane are not migrating out of black shales, where they occur in high concentrations. These results lead to a general model for assessing migration. In addition, three shale types are identified on the basis of organic carbon and pyrolysis products and patterns.

Lithology and organic geochemistry at DSDP Hole 76-534

The organic facies of Early and middle Cretaceous sediments drilled at DSDP Site 534 is dominated by terrestrially derived plant remains and charcoal. Marine organic matter is mixed with the terrestrial components, but through much of this period was diluted by the terrestrial material. The supply of terrestrial organic matter was high here because of the nearness of the shore and high runoff promoted by a humid temperate coastal climate. Reducing conditions favored preservation of both marine and terrestrial organic matter, the terrestrial materials having reached the site mostly in turbidity currents or in the slow-moving, near-bottom nepheloid layer. An increase in the abundance of terrestrial organic matter occurred when the sea level dropped in the Valanginian and again in the Aptian-Albian, because rivers dumped more terrigenous elastics into the Basin and marine productivity was lower at these times than when sea level was high. A model is proposed to explain the predominance of reducing conditions in the Valanginian-Aptian, of oxidizing conditions in the late Aptian, and of reducing conditions in the Albian-Cenomanian. The model involves influx of oxygen-poor subsurface waters from the Pacific at times of high or rising sea level (Valanginian-Aptian, and Albian- Cenomanian) and restriction of that influx at times of low sea level (late Aptian). In the absence of a supply of oxygenpoor deep water, the bottom waters of the North Atlantic became oxidizing in the late Aptian, probably in response to development of a Mediterranean type of circulation. The influx of nutrients from the Pacific led to an increase in productivity through time, accounting for an increase in the proportion of marine organic matter from the Valanginian into the Aptian and from the Albian to the Cenomanian. Conditions were dominantly oxidizing through the Middle Jurassic into the Berriasian, with temporary exceptions when bottom waters became reducing, as in the Callovian. Mostly terrestrial and some marine organic matter accumulated during the Callovian reducing episode. When Jurassic bottom waters were oxidizing, only terrestrial organic matter was buried in the sediments, in very small amounts.

Calcium carbonate, organic carbon, d13C and C/N composition of ODP Sites 186-1150 and 186-1151

Past changes in sea-surface productivity in the Oyashio Current are evaluated on the basis of abundances of biological constituents in sediments from Leg 186 sites. Organic carbon contents at Sites 1150 and 1151 are moderate (0.5 to 1.5 wt%) and have an algal origin as indicated by low C/N ratios (<10) and by carbon isotopic compositions ranging from -23.4 to -21.3. A decreasing trend in organic carbon contents, carbon isotope ratios, and C/N ratios occurs with depth at both sites, probably as a consequence of diagenetic degradation of organic matter. Mass accumulation rates (MARs) determined for organic carbon and carbonates at Sites 1150 and 1151 show an abrupt increase between ~5 and 7 Ma. Similar results have been reported for sites in the Indian Ocean and the Pacific Ocean for the same time interval. As it has been previously suggested, the observed increase in MAR for both carbonate and organic carbon at Leg 186 sites probably resulted from augmented nutrient supply either from continental sources or from a more vigorous ocean circulation.

Organic matter in sediments of ODP Site 131-808

Microscopic studies reveal a predominance of terrestrial organic matter in sediments of Site 808. Terrestrial vitrinite and inertinite are more abundant (73% to 100%) than marine organic matter (alginite, 0% to 27%), which increases from open oceanic deposits of the Shikoku Basin sediments to sediments of the outer trench wedge. The abundance of terrestrial organic matter is also reflected through carbon isotope values of -23 per mil to -25.9 per mil. Mass accumulation rates of organic carbon are low in hemipelagic sediments of the Shikoku Basin (<0.2 g/cm**2/k.y.) but increase significantly in sediments of the Nankai Trench (0.2 to 1.7 g/cm**2/k.y.). Although the organic mass accumulation is high in sediments of the Nankai Trench, a comparison of sedimentation rates and total organic carbon suggests relative dilution of organic carbon through turbidite flows. Calculated marine paleoproductivity of organic carbon is low in sediments of the open ocean (Shikoku Basin) and increases closer to the shore (Nankai Trench). Thermal evolution of organic matter is obtained from vitrinite reflectance measurements. Two populations of vitrinites have been observed between 600 and 1234 mbsf. Reflectance values change with increasing depth and temperature in both groups of vitrinite (0.3% to 0.68% in group 1; 0.6% to 1% in group 2).

Geochemistry of carbon at DSDP Hole 61-462

Seven quartered sections of Pliocene to Mesozoic (Cenomanian) cores from the Nauru Basin contain primarily marine organic matter admixed with detectable amounts of terrigenous organic matter. The mixture is immature with respect to organic genesis. Chemical properties of this organic matter are compared with properties of other deep-ocean cores from DSDP sites in the central Pacific.

Geochemical and biogeochemical parameters of bottom sediments from the area of the Spitsbergen (Svalbard) Archipelago

Quantitative characteristics for rates of diagenetic processes in the upper (0-30 cm) layer of sedimentary deposits in the area of the Spitsbergen (Svalbard) Archipelago (78°-80°N) were obtained by lithologo-geochemical, radioisotope (35S, 14C), and stable isotope (d34S, d13C) studies. It was proved that rates of diagenetic processes in polar deposits at 123-395 m depth affected by the East Spitsbergen ''warm'' current are mostly determined by bioproductivity and are commensurate with rates of processes in shelf deposits of temperate latitudes. High contents of migratory methane (up to 263 ml/dm**3) and isotopically-light organic carbon (Corg, d13C = -30 per mil PDB) were found in the 1 m layer of shelf deposits (at 123 m sea depth) with low bacterial in situ production of methane. It was shown that methane is not utilized in the deposits by the methanotrophic bacterial community and it may be supplied to the water mass and, probably, to the atmosphere.

Biomarkers in surface sediments from the Ob and Yenisei estuaries and the southern Kara Sea

Organic-geochemical bulk parameter (Total organic carbon contents, C/N ratios and d13Corg values), biogenic opal and biomarkers (n-alkanes, fatty acids, sterols and amino acids) were determined in surface sediments from the Ob and Yenisei estuaries and the adjacent southern Kara Sea. Maximum TOC contents were determined in both estuaries, reaching up to 3 %. Relatively high C/N ratios around 10, light d13Corg values of -26.5 per mil (Yenisei) and -28 to -28.7 per mil (Ob), and maximum concentrations of long-chain n-alkanes of up to about 10 µg/g Sed clearly show the predominance of terrigenous organic matter in the sediments from the estuaries. Towards the open Kara Sea, all p arameters indicate a decrease in terrigenous organic carbon. Brassicasterol as well as the short-chain n-alkanes parallel this trend, suggesting that these biomarkers are probably also related to a terrigenous (fresh-water phytoplankton) source. Amino acid spectra show characteristic trends from the Yenisei Estuary to the open Kara Sea revealing increasing state of degradation. Sedimentary organic matter in the Yenisei Estuary is relatively less degraded compared to the Ob Estuary and the open Kara Sea.