Concentrations and isotopic compositions of low molecular weight hydrocarbons in hydrothermal fluids from ODP Field, Middle Valley, northern Juan de Fuca Ridge

The presence of sedimentary organic matter blanketing midocean ridge crests has a potentially strong impact on metal transport in hydrothermal vent fluids. To constrain the role of organic matter in metal mobility during hydrothermal sediment alteration, we reacted organic-rich diatomaceous ooze from Guaymas Basin, Gulf of California, and organic-poor hemipelagic mud from Middle Valley, northern Juan de Fuca Ridge, with seawater and a Na-Ca-K-Cl fluid of seawater chlorinity, at 275° to 400°C, 350 to 500 bars, and initial fluid: sediment mass ratios ranging from 1.6 to 9.8. Reaction of these fluids with both sediment types released CO2 and high concentrations of ore-forming metals (Fe, Mn, Zn, Pb) to solution. Relatively low concentrations of Cu were observed in solution and likely reflect the reducing conditions that resulted from the presence of sedimentary organic matter. Both the concentrations of CO2 and dissolved metals were lower in fluids reacted with Middle Valley sediment compared with aqueous concentrations in fluids reacted with Guaymas Basin sediment. During alteration of both sediment types, metal concentrations varied strongly as a function of temperature, increasing by up to an order of magnitude over the 75°C range of each experiment. Major element fluid chemistry and observed alteration assemblages suggest that during hydrothermal alteration of organic-lean sediment from Middle Valley a feldspar-quartz-illite mineral assemblage buffered in situ pH. In contrast, data from the experimental alteration of organic-rich Guaymas Basin sediment suggest that a calcite-plagioclase-quartz assemblage regulated in situ pH. Fluid speciation calculations suggest that in situ pH during Guaymas Basin sediment alteration was lower than during alteration of Middle Valley sediment and accounts for the substantially greater metal mobility at a given temperature and pressure during the former experiment. Comparison of our results with the results of basalt alteration experiments indicate that except for Cu, hydrothermal sediment alteration results in equal or greater concentrations of ore-forming metals at a given temperature and pressure. Accordingly, the presence of ore-forming metals in fluids currently venting from sediment-covered hydrothermal systems at concentrations substantially lower than in fluids from bare-rock systems may reflect chemical reequilibration during subsurface cooling within the sediment pile.

(Table 1) Sea surface temperature reconstruction for eastern equatorial Pacific surface sediment samples

Significant uncertainties persist in the reconstruction of past sea surface temperatures in the eastern equatorial Pacific, especially regarding the amplitude of the glacial cooling and the details of the post-glacial warming. Here we present the first regional calibration of alkenone unsaturation in surface sediments versus mean annual sea surface temperatures (maSST). Based on 81 new and 48 previously published data points, it is shown that open ocean samples conform to established global regressions of Uk'37 versus maSST and that there is no systematic bias from seasonality in the production or export of alkenones, or from surface ocean nutrient concentrations or salinity. The flattening of the regression at the highest maSSTs is found to be statistically insignificant. For the near-coastal Peru upwelling zone between 11-15°S and 76-79°W, however, we corroborate earlier observations that Uk'37 SST estimates significantly over-estimate maSSTs at many sites. We posit that this is caused either by uncertainties in the determination of maSSTs in this highly dynamic environment, or by biasing of the alkenone paleothermometer toward El Niño events as postulated by Rein et al. (2005).

Geochemistry of Fe-Mn crusts at seamounts in the Northwest Pacific

Hydrogenetic ferromanganese crusts were dredged from four seamounts in the western Pacific, OSM7, OSM2, Lomilik, and Lemkein, aligned in a NW-SE direction parallel to Pacific Plate movement. The crusts consist of four well-defined layers with distinct textural and geochemical properties. The topmost layer 1 is relatively enriched in Mn, Co, Ni, and Mo compared to the underlying layer 2, which is relatively enriched in Al, Ti, K, and Rb and Cu, Zn, and excess Ba. Textural and geochemical properties of layer 2 suggest growth conditions under high biogenic and detrital flux. Such conditions are met in the equatorial Pacific (i.e., between the Intertropical Convergence Zone (ITCZ) and equatorial high-productivity zone). Layer 2 likely formed when each seamount was beneath the equatorial Pacific along its back track path. On the other hand, layer 1 probably started to grow after seamounts moved northwest from the ITCZ. This interpretation is consistent with the thickness of layer 1 across the four crusts, which increases to the northwest. Ages of the layer 1-layer 2 boundary in each crust, a potential proxy for northern margin of the ITCZ, also increase to the northwest at 17, 11, 8, and 5 Ma for OSM7, OSM2, Lomilik, and Lemkein, respectively. Assuming Pacific Plate motion of 0.3°/Myr, the seamounts were located at 12°N, 11°N, 9°N, and 8°N at the time of boundary formation. This result suggests that the north edge of the ITCZ has shifted south since the middle Miocene in the western Pacific, which agrees with information from the eastern Pacific.

Rules of the District court of the United States for the Northern district of Indiana, effective June 1, 1941.

Mode of access: Internet.

Birds of the southwest Pacific, a field guide to the birds of the area between Samoa, New Caledonia, and Micronesia,

Mode of access: Internet.

The Canadian railway act 1903 : (annotated) /

90694DLA.

Ocean harvest; the story of commercial fishing in Pacific coast waters.

Mode of access: Internet.

Hawaiian and Pacific foods; a cook book of culinary customs and recipes adapted for the American hostess,

"References": p. 271-275.

Standard tee rail construction for steam rail road and industrial railway track and switch work.

"Catalogue no. 21."

Raveneau de Lussan, buccaneer of the Spanish Main and early French filibuster of the Pacific;

Mode of access: Internet.

Vikings of the Pacific; the adventures of the explorers who came from the West, eastward; Bering, the Dane; the outlaw hunters of Russia; Benyowsky, the Polish pirate; Cook and Vancouver, the English navigators; Gray of Boston, the discoverer of the Columbia; Drake, Ledyard, and other soldiers of fortune on the west coast of America.

"The contents of this volume appeared serially in Leslie's monthly, Outing, and Harper's magazine." - Foreword.

Pacific charter; our destiny in Asia.

"First edition."

In the arbitration proceedings between the employes of Indianapolis traction and terminal company by and through their committee and Indianapolis traction and terminal company before the Public service commission of Indiana, acting as a voluntary board of arbitration ...

Argument of W.H. Latta, counsel for the respondent, testimony, etc.

Letters from leading engineers and naval architects as to the practicability of constructing and operating a ship railway.

Mode of access: Internet.

Report to the President by the Emergency Board appointed March 15, 1949 by Executive order 10045 pursuant to Section 10 of the Railway Labor Act, as amended : to investigate and report in respect to a dispute involving the Wabash Railroad Co. and the Ann Arbor Railroad Co., carriers, and certain of their employees, represented by the Brotherhood of Locomotive Engineers, Brotherhood of Locomotive Firemen and Enginemen, Order of Railway Conductors, and Brotherhood of Railroad Trainmen : (NMB case A-3028) : St. Louis, Mo., April 6, 1949.

Signed: Roger I. McDonough, chairman, Curtis G. Shake, member, John W. Yeager, member.