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1.
Diploptene: an indicator of terrigenous organic carbon in Washington coastal sediments 总被引：1，自引：0，他引：1
The pentacyclic triterpene 17 beta(H),21 beta(H)-hop-22(29)-ene (diploptene) occurs in sediments throughout the Columbia River drainage basin and off the southern coast of Washington state in concentrations comparable to long-chain plantwax n-alkanes. The same relationship is evident for diploptene and long-chain n-alkanes in soils from the Willamette Valley. Microorganisms indigenous to soils and soil erosion are indicated as the biological source and physical process, respectively, for diploptene in coastal sediments. Similarity between the stable carbon isotopic composition (delta 13CPDB) of diploptene isolated from soil in the Willamette Valley (-31.2 +/- 0.3%) and from sediments deposited throughout the Washington coastal environment (-31.2 +/- 0.5%) supports this argument. Values of delta for diploptene in river sediments are variable and 8-17% lighter, indicating that an additional biological source such as methane-oxidizing bacteria makes a significant contribution to the diploptene record in river sediments. Selective biodegradation resulting from a difference in the physicochemical association within eroded particles can explain the absence of the more-13C-depleted form of diploptene in Washington coastal sediments, but this mechanism remains unproven. 相似文献
2.
Polycyclic aromatic (PAH) and aliphatic hydrocarbon compositions, organic carbon, nitrogen and lignin contents were determined in whole, unfractionated sediment from the Washington continental shelf and in discrete sediment fractions separated by particle size and density. At least 20 to 25% of perylene and PAH derived from pyrolytic processes and 50% of the retene measured in whole sediment are contained within organic C- and lignin-rich panicles of density ≤ 1.9 g/cc. These particles, which include primarily vascular plant remains and bits of charcoal, comprise less than 1% of the total sediment weight. In contrast, a series of methylated phenanthrene homologs, possibly of fossil origin, are concentrated in some component of the more dense, lithic matrix of the sediment. Equilibrium models of PAH sorption/desorption from aqueous phase onto small particles of high surface area do not appear applicable to the behavior of the major PAH types identified in this aquatic environment. 相似文献
3.
Fredrick G. Prahl Joseph T Bennett Roy Carpenter 《Geochimica et cosmochimica acta》1980,44(12):1967-1976
Aliphatic hydrocarbon compositions were quantitatively characterized in plankton, sediment trap-collected particulate materials and sediments from Dabob Bay using high resolution glass capillary gas chromatography. The average net accumulation of individual hydrocarbons measured in a 1-yr series of sediment traps was compared with the net accumulation of corresponding compounds measured in three depth intervals of 210Pb-dated bottom sediments. Systematic and rapid decreases in the net accumulation of individual hydrocarbons were observed from the sediment traps to the sediments. Most pronounced decreases were measured for planktonically derived hydrocarbon constituents (e.g. pristane and two unsaturated compounds) which are rapidly remineralized at or near the sediment-water interface. Consequently, the amount of each compound measured in deposited sediments is not necessarily a quantitative indication of its initial flux to the sediments. The n-alkanes (C25,27,29,31). characteristic of terrestrial plant waxes, are the predominant hydrocarbons measured by 4–6 cm depth in these sediments and show reasonably constant net accumulation below this interval.Significant diagenetic alteration of the bulk organic matter contained in the average sediment trap particulate material is also noted through comparison with bottom sediments on the basis of organic C/N and δ13C measurements. Organic matter elementally similar to marine plankton is preferentially remineralized upon deposition of the sedimentary particulates. The residual organic matter remaining and buried in the bottom sediments closely resembles terrestrial organic matter. 相似文献
4.
Using both the photosynthetically active chlorophylla (chla) content of the organic carbon fraction of suspended particulate matter (chla/POC) and the percentage of photosynthetically, active chla in fluorometrically measured chla plus pheophytina (% chla), we determined that under specified hydrodynamic conditions, neap-spring tidal differentiation in particle dynamics could
be observed in the Columbia River estuary. During summer time neap tides, when river discharge was moderate, bottom chla/POC remained relatively unchanged from riverine chla/POC over the full 0–30 psu salinity range, suggesting a benign trapping environment. During summertime spring tides, bottom
chla/POC decreased at mid range salinities indicating resuspension of chla-poor POC during flood-ebb transitions. Bottom % chla during neap tides tended to average higher than that during spring tides, suggesting that neap particles were more recently
hydrodynamically trapped than those on the spring tides. Such differentiation supported the possibility of operation of a
particle conveyor belt process, a process in which low-amplitude neap tides favor selective particle trapping in estuarine
turbidity maxima (ETM)., while high-amplitude spring tides favor particle resuspension from the ETM. Untrapped river-derived
particles at the surface would continue through the estuary to the coastal ocean on the neap tide; during spring tide some
particles eroded from the ETM would combine with unsettled riverine particles in transit toward the ocean. Because in tensified
biogeochemical activity is associated with ETM, these neap-spring differences may be critical to maintenance and renewal of
populations and processes in the estuary. Very high river discharge (15, 000 m3 s−1) tended to overwhelm neap-spring differences, and significant oceanic input during very low river discharge (5,000 m3 s−1) tended to do the same in the estuarine channel most exposed to ocean input. During heavy springtime phytoplankton blooms,
development of a thick bottom fluff layer rich in chla also appeared to negate neapspring differentiation because spring tides apparently acted to resuspend the same rich bottom
material that was laid down during neap tides. When photosynthetic assimilation numbers [μgC (μgchl,a)−1h−1] were measured across, the full salinity range, no neap-spring differences and no river discharge effects occurred, indicating
that within our suite of measurements the compositional distinction of suspended particulate material was mainly a function
of chla/POC, and to a lesser extent % chla. Even though these measurements suggest the existence of a conveyor belt process, proof of actual operation of this phenomenon
requires scalar flux measurements of chla properties in and out of the ETM on both neap and spring tides. 相似文献
5.
M. Merck A. Karle S. Martinez F. Arqueros K. H. Becker M. Bott-Bodenhausen R. Eckmann E. Faleiro J. Fernandez P. Fernandez V. Fonseca V. Haustein G. Heinzelmann I. Holl F. Just F. Krennrich M. Kühn E. Lorenz H. Meyer N. Müller R. Plaga J. Prahl M. Probst M. Rozanska M. Samorski H. Sander K. Sauerland C. Sesea W. Stamm 《Astroparticle Physics》1996,5(3-4):379-392
A precise knowledge of the angular resolution of scintillator arrays used to observe extended air showers (EAS) is of key importance in the search for VHE/UHE γ point sources. Four independent methods have been used to determine the mean resolution for which a value of ΔΘ63 of 0.8°(1.0°) at a proton threshold of 50 (40) TeV has been found for the HEGRA EAS-array. 相似文献
6.
The sources and distributions of polycyclic aromatic hydrocarbons (PAH) and aliphatic hydrocarbons are characterized in seventeen sediments from a highly river-influenced sedimentary environment off the southwestern coast of Washington. The major hydrocarbons are land-derived, introduced as preformed compounds and display long-term stability in sediment cores. A series of PAH of anthropogenic origin and two naturally derived compounds, retene and perylene, dominate the PAH composition in these sediments. Plantwax n-alkanes are the major aliphatic hydrocarbon constituents. Aliphatic hydrocarbons of marine origin, pristane and a series of four acyclic, multibranched C25 polyolefins, are also observed in many sediments. The concentrations of these marine-derived hydrocarbons decrease to negligible levels rapidly with sediment depth from the sea-sediment interface, suggesting degradation.In general, the major land-derived hydrocarbons are concentrated in the midshelf silt deposit which extends northwestward along the continental shelf from the Columbia River mouth. A quantitatively more minor, natural series of phenanthrene homologs, also of terrestrial origin, is preferentially advected further offshore and deposited in continental slope sediments. These distributions are consistent with recognized particle associations for these compounds and sediment dispersal processes in this coastal environment. Sediment core records suggest the present pattern of dispersal has persisted for at least the past century and possibly since the Late Pleistocene. 相似文献
7.
Lydie Herfort Tawnya D. Peterson Fredrick G. Prahl Lee Ann McCue Joseph A. Needoba Byron C. Crump G. Curtis Roegner Victoria Campbell Peter Zuber 《Estuaries and Coasts》2012,35(3):878-891
The localized impact of blooms of the mixotrophic ciliate Myrionecta rubra in the Columbia River estuary during 2007–2010 was evaluated with biogeochemical, light microscopy, physiological, and molecular data. M. rubra affected surrounding estuarine nutrient cycles, as indicated by high and low concentrations of organic nutrients and inorganic nitrogen, respectively, associated with red waters. M. rubra blooms also altered the energy transfer pattern in patches of the estuarine water that contain the ciliate by creating areas characterized by high primary production and elevated levels of fresh autochthonous particulate organic matter, therefore shifting the trophic status in emergent red water areas of the estuary from net heterotrophy towards autotrophy. The pelagic estuarine bacterial community structure was unaffected by M. rubra abundance, but red waters of the ciliate do offer a possible link between autotrophic and heterotrophic processes since they were associated with elevated dissolved organic matter and showed a tendency for enhanced microbial secondary production. Taken together, these findings suggest that M. rubra red waters are biogeochemical hotspots of the Columbia River estuary. 相似文献
8.
Fredrick G. Prahl Jean-François Rontani Margaret A. Sparrow 《Geochimica et cosmochimica acta》2006,70(11):2856-2867
Our specimen of the cultured Emiliania huxleyi strain (CCMP1742, also known as NEPCC55a) that provides the benchmark for -based paleothermometry has started producing, for reasons yet unclear, major amounts of three new alkenones identified as ω15,22-C35 methyl ketone, ω15,22-C36 ethyl ketone and ω16,23-C36 methyl ketone. Comparison of these structures with those established now by the same OsO4 derivatization method applied to the di-unsaturated C37, C38 and C39 alkenones typically found in this organism provides insight into the possible pathway for their biosynthesis. Isothermal batch culture experiments also show the content and composition of these new compounds change systematically and quite significantly in cells when subjected to environmental conditions such as nutrient depletion, variation in light availability and prolonged darkness. Alkenones of similarly unusual short-chain length are evident in suspended particulate materials from present day surface waters in the Ligurian Sea (Mediterranean) and in two different Holocene time horizons (Unit I and Unit II deposits) in Black Sea sediments. However, the positions of the double bonds are different from those that we now report in our culture, implying a different biosynthetic sequence. These alkenones are most likely derived from another, as yet unknown, haptophyte species. If this other organism accounts for all documented occurrences of these compounds in natural samples, then either it has a capacity for growth over a remarkably wide salinity range or surface water salinity in the early Holocene Black Sea may not have been as low as is currently believed. 相似文献
9.
S.E. Walinsky F.G. Prahl A.C. Mix B.P. Finney J.M. Jaeger G.P. Rosen 《Continental Shelf Research》2009
Total organic carbon (TOC) and biogenic silica (opal) content, elemental (C/N) and isotopic (δ13C, δ15N) composition of organic matter and the content of lipid biomarkers derived from both marine and terrestrial sources constrain relative contributions from marine productivity and continental erosion to surface sediments throughout coastal SE Alaska (54°N to 61°N). TOC and opal content are very high (up to 8% and 33% by weight, respectively) in fjords and inlets south of Icy Strait (∼58°N) and uniformly low at offshore sites to the south, and at both offshore and inland sites to the north (averaging 0.6±0.3% and 2.3±1.8%, respectively). TOC and opal mass accumulation rates (MARs, based on bulk density and 210Pb-derived sediment MAR) suggest dilution with terrigenous, inorganic detrital materials accounts for the low concentrations of both biogenic phases in sediments from the glacial tidewater fjords of Muir and Yakutat Bays but not elsewhere. C/N, δ13C, and δ15N indicate a dominant marine origin for organic matter deposited at most sites. This conclusion implicates elevated primary productivity in inland waters to the south with diatoms, based on opal results, being the dominant contributor. A very significant terrestrial organic fraction (25–50%) is contained in sediments deposited on the continental shelf to the north of 58°N. Hydrocarbon biomarkers indicate the terrestrial fraction in sediments from this region is represented by old organic matter (kerogen) likely contained within riverborne particles eroding from now heavily glaciated adjacent landscapes. In sediment to the south, the terrestrial fraction is traced to modern soil organic matter eroded from the now non-glaciated, heavily forested adjacent landscape. Our study provides a framework to guide future investigations of short- (anthropogenic) to long- (Holocene) term environmental and/or climate change in this region through down-core, stratigraphic analysis. 相似文献
10.
Hermann Held Friedrich-Wilhelm Gerstengarbe Tobias Pardowitz Joaquim G. Pinto Uwe Ulbrich Kai Born Markus G. Donat Melanie K. Karremann Gregor C. Leckebusch Patrick Ludwig Katrin M. Nissen Hermann Österle Boris F. Prahl Peter C. Werner Daniel J. Befort Olaf Burghoff 《Climatic change》2013,121(2):195-207
We present projections of winter storm-induced insured losses in the German residential building sector for the 21st century. With this aim, two structurally most independent downscaling methods and one hybrid downscaling method are applied to a 3-member ensemble of ECHAM5/MPI-OM1 A1B scenario simulations. One method uses dynamical downscaling of intense winter storm events in the global model, and a transfer function to relate regional wind speeds to losses. The second method is based on a reshuffling of present day weather situations and sequences taking into account the change of their frequencies according to the linear temperature trends of the global runs. The third method uses statistical-dynamical downscaling, considering frequency changes of the occurrence of storm-prone weather patterns, and translation into loss by using empirical statistical distributions. The A1B scenario ensemble was downscaled by all three methods until 2070, and by the (statistical-) dynamical methods until 2100. Furthermore, all methods assume a constant statistical relationship between meteorology and insured losses and no developments other than climate change, such as in constructions or claims management. The study utilizes data provided by the German Insurance Association encompassing 24 years and with district-scale resolution. Compared to 1971–2000, the downscaling methods indicate an increase of 10-year return values (i.e. loss ratios per return period) of 6–35 % for 2011–2040, of 20–30 % for 2041–2070, and of 40–55 % for 2071–2100, respectively. Convolving various sources of uncertainty in one confidence statement (data-, loss model-, storm realization-, and Pareto fit-uncertainty), the return-level confidence interval for a return period of 15 years expands by more than a factor of two. Finally, we suggest how practitioners can deal with alternative scenarios or possible natural excursions of observed losses. 相似文献