Showing papers by "Philip A. Meyers published in 2006"

A multiple proxy and model study of Cretaceous upper ocean temperatures and atmospheric CO2 concentrations

Abstract: foraminiferal d 18 O and Mg/Ca suggests that the ratio of magnesium to calcium in the Turonian-Coniacian ocean may have been lower than in the Albian-Cenomanian ocean, perhaps coincident with an ocean 87 Sr/ 86 Sr minimum. The carbon isotopic compositions of distinct marine algal biomarkers were measured in the same sediment samples. The d 13 C values of phytane, combined with foraminiferal d 13 C and inferred temperatures, were used to estimate atmospheric carbon dioxide concentrations through this interval. Estimates of atmospheric CO2 concentrations range between 600 and 2400 ppmv. Within the uncertainty in the various proxies, there is only a weak overall correspondence between higher (lower) tropical temperatures and more (less) atmospheric CO2. The GENESIS climate model underpredicts tropical Atlantic temperatures inferred from ODP Leg 207 foraminiferal d 18 O and Mg/Ca when we specify approximate CO2 concentrations estimated from the biomarker isotopes in the same samples. Possible errors in the temperature and CO2 estimates and possible deficiencies in the model are discussed. The potential for and effects of substantially higher atmospheric methane during Cretaceous anoxic events, perhaps derived from high fluxes from the oxygen minimum zone, are considered in light of recent work that shows a quadratic relation between increased methane flux and atmospheric CH4 concentrations. With 50 ppm CH4, GENESIS sea surface temperatures approximate the minimum upper ocean temperatures inferred from proxy data when CO2 concentrations specified to the model are near those inferred using the phytane d 13 C proxy. However, atmospheric CO2 concentrations of 3500 ppm or more are still required in the model in order to reproduce inferred maximum temperatures.

An Overview of Sediment Organic Matter Records of Human Eutrophication in the Laurentian Great Lakes Region

Abstract: The isotopic and molecular compositions of organic matter buried in lake sediments provide information that helps to reconstruct past environmental conditions and to assess impacts of humans on local ecosystems. This overview of sedimentary records from the North American Great Lakes region describes examples of applications of organic geochemistry to paleolimnological reconstructions. These lakes experienced a succession of human-induced environmental changes that started after completion of the Erie Canal in 1825. Agricultural deforestation in the mid-nineteenth century released soil nutrients that increased algal productivity and caused an associated increase in algal biomarkers in sediment records. Eutrophication that accompanied magnified delivery of municipal nutrients to the lakes in the 1960s and 1970s created excursions to less negative δ13C values in sediment organic matter. Increased organic carbon mass accumulation rates mirror the isotopic evidence of eutrophication in the Great Lakes.

IUPAC-NIST Solubility Data Series. 81. Hydrocarbons with Water and Seawater—Revised and Updated Part 12. C5–C26 Hydrocarbons with Seawater

Abstract: The mutual solubility of C5–C26 hydrocarbons with seawater is exhaustively and critically reviewed. Reports of experimental determination of solubility in 46 chemically distinct binary systems that appeared in the primary literature prior to end of 2002 are compiled. For 15 of these systems sufficient data are available to allow critical evaluation. All data are expressed as mass percent and mole fraction as well as the originally reported units.

29. geochemistry of organic carbon in south atlantic sediments from deep sea drilling project leg 75

Abstract: CHN analyses of sediments and rocks sampled during DSDP Leg 75 in the South Atlantic have provided concentrations of organic carbon and atomic C/N ratios of organic matter from two sites. High values of organic carbon were measured in sediments deposited during Neogene and Cretaceous times at Site 530 in the Angola Basin; sediments deposited at other times contain less than 0.5% organic carbon. Development of the Benguela Current and associated upwelling-supported biological productivity is recorded in late Miocene to Holocene sediments which contain 1 to 7% organic carbon. These sediments include debris flows and turbidites composed of predominantly biogenic materials originally deposited on the Walvis Ridge and on the African continental margin. Organic-carbon-rich black shales containing up to 17% organic carbon occur in late Albian to Coniacian turbidite sequences. These Cretaceous black shale layers are commonly several centimeters thick and are separated by bioturbated fine-grained organic-carbon-poor turbidites which are usually much thicker. At Site 532 on the Walvis Ridge, biogenic sediments deposited between late Miocene and Holocene times contain 1 to 9% organic carbon. Fluctuations in the intensity of high biological productivity associated with the Benguela Current are preserved in alternating light and dark layers of sediments. C/N ratios of organic matter in sediments from both sites are typical of marine sources.

10. data report: multiproxy geochemical characterization of oae-related black shales at site 1276, newfoundland basin

Abstract: During Ocean Drilling Program Leg 210, a greatly expanded sedimentary sequence of continuous Cretaceous black shales was recovered at Site 1276. This section corresponds to the Hatteras Formation, which has been documented widely in the North Atlantic Ocean. The cored sequence extends from the lowermost Albian, or possibly uppermost Aptian, to the Cenomanian/Turonian boundary and is characterized by numerous gravity-flow deposits and sporadic, finely laminated black shales. The sequence also includes several sedimentary intervals with high total organic carbon (TOC) contents, in several instances of probable marine origin that may record oceanic anoxic events (OAE). These layers might correspond to the Cenomanian–Turonian OAE 2; the midCenomanian event; and OAE 1b, 1c, and 1d in the Albian. In addition, another interval with geochemical characteristics similar to OAE-type layers was recognized in the Albian, although it does not correspond to any of the known OAEs. This study investigates the origin of the organic matter contained within these black shale intervals using TOC and CaCO3 contents, Corg/Ntot ratios, organic carbon and nitrogen isotopes, trace metal composition, and rock-eval analyses. Most of these black shale intervals, especially OAE 2 and 1b, are characterized by low δ15N values (<0‰) commonly observed in mid-Cretaceous black shales, which seem to reflect the presence of an altered nitrogen cycle with rates of nitrogen fixation significantly higher than in the modern ocean. 1Arnaboldi, M., and Meyers, P.A., 2006. Data report: multiproxy geochemical characterization of OAErelated black shales at Site 1276, Newfoundland Basin. In Tucholke, B.E., Sibuet, J.-C., and Klaus, A. (Eds.), Proc. ODP, Sci. Results, 210: College Station, TX (Ocean Drilling Program), 1–16. doi:10.2973/odp.proc.sr.210.102.2006 2Marine Geology and Geochemistry Program, Department of Geological Sciences, The University of Michigan, 1100 North University Avenue, Ann Arbor MI 48109-1063, USA. Correspondence author: marna@umich.edu Initial receipt: 21 November 2005 Acceptance: 5 May 2006 Web publication: 21 November 2006 Ms 210SR-102 M. ARNABOLDI AND P.A. MEYERS DATA REPORT: MULTIPROXY GEOCHEMICAL CHARACTERIZATION 2

40. sources, preservation, and maturation of organic matter in pliocene and quaternary sediments of the gulf of california: a synthesis of organic geochemical studies from deep sea drilling project leg 64

Abstract: This synthesis of organic geochemical studies from Leg 64 was designed to answer fundamental questions about the source, deposition, preservation, and alteration of organic matter in the Gulf of California. The answers to these questions help to determine the extent and degree of influence not only of paleoenvironmental factors, but also of geothermal processes; understanding both these features was among the main objectives of drilling on this leg. The organic matter is mostly marine, and was deposited as pelagic sediment. Deep in the Guaymas Basin at Sites 477, 478, and 481, turbidites containing terrigenous organic matter are abundant. Total organic carbon (TOC) is most abundant at Sites 479 and 480 in the oxygen-minimum zone on the continental margin. Deeper-water sites contain much less organic matter, and generally their organic contents decrease with depth downhole in response to diagenetic processes. There are local exceptions to this general rule, for instance (1) deep in Hole 476, where there are some fossil(?) lagoonal deposits, rich in organic matter, (2) deep in Hole 478, where laminated sediments rich in organic matter represent a period of stagnation of bottom water in the Guaymas Basin, and (3) 15-20 meters sub-bottom throughout the Gulf, probably in response to some basinwide productivity event in the Holocene transgression. Despite high heat flow, most of the sediments drilled are immature, except close to sills and in Guaymas Basin Hole 477, where the heat flow reaches 20 HFU. Thermogenic methane is widespread as a minor component of gases near the spreading center in the Guaymas Basin, and is a major component of gas deep in Hole 477. Small amounts of light (gasoline-range) hydrocarbons are being generated within the deeper parts of the drilled section in the Guaymas Basin, close to sills throughout the Gulf, and on the Guaymas margin (Site 479). Migration of these light hydrocarbons is most apparent near sills.

11. data report: organic carbon, total nitrogen, carbonate carbon, and carbonate oxygen isotopic compositions of albian to santonian black shales from sites 1257-1261 on the demerara rise

Abstract: Organic carbon, total nitrogen, carbonate carbon, and carbonate oxygen isotopic compositions were measured for 95 samples selected from the black shale sequences drilled during Ocean Drilling Program Leg 207 on the Demerara Rise. Most samples have organic δ13C values smaller than –27‰, with the exception of several samples that have values between –24.9‰ and –23.9‰ that may correspond to oceanic anoxic events. Bulk δ15N values range between –4.2‰ and +4.4‰ and become smaller as organic carbon concentrations increase. Comparison of the δ15N values of nondecarbonated samples to their decarbonated analogs reveals no systematic effect of the acid treatment used in the decarbonation.

39. geolipid comparison of biogenic sediments from deep sea drilling project holes 530b, angola basin, and 532, walvis ridge

Abstract: Distributions of free and bound n-alkanes, n-alkanoic acids, and n-alkanols were determined in order to compare the character of organic matter contained in organic-carbon-rich sediments from two sites sampled by the hydraulic piston corer. Two diatomaceous debris-flow samples of Pleistocene age were obtained from Hole 53OB in the Angola Basin. A sample of bioturbated Pleistocene diatomaceous clay and another of bioturbated late Miocene nannofossil clay were collected from Hole 532 on the Walvis Ridge. Geolipid distributions of all samples contain large terrigenous contributions and lesser amounts of marine components. Similarities in organic matter contents of Hole 53OB and Hole 532 sediments suggest that a common depositional setting, probably on the Walvis Ridge, was the original source of these sediments through Quaternary, and possibly late Neogene, times and that downslope relocation of these biogenic deposits has frequently occurred.

22. geolipids of late cenozoic sediments from the western flank of the east pacific rise, deep sea drilling project leg 92

Abstract: Low concentrations of organic carbon in slowly accumulating sediments from Sites 597, 600, and 601 reflect a history of low marine productivity in the subtropical South Pacific since late Oligocene times. The distributions of n-alkanes, n-alkanoic acids, and n-alkanols provide evidence of the microbial alteration of sediment organic matter. Landderived hydrocarbons, possibly from eolian transport, dominate n-alkane distributions in these samples.