Mixed terrigenous—Carbonate sedimentation in the Hispaniola—Caicos turbidite basin

Sedimentation in the 9500 km², 4100 m deep Hispaniòla—Caicos Basin is dominated by turbidity currents. Carbonate turbidites originate from the Bahama Islands, Great Inagua and Caicos at the north end of the basin. Mixed carbonate—non-carbonate flows come from Hispaniola and perhaps Cuba. Most flows originate on insular slopes rather than in shallow water. The relatively low CaCO₃ content of hemipelagic sequences throughout the entire basin reveals that the influence of non-carbonate Hispaniola—Cuba sources is widespread.The basin was sampled with closely spaced piston cores. Sand-layer isopach and frequency maps reveal four or five major basin entry points for turbidity currents. Flow size is proportional to the size of source areas. Average volumes of flows originating from Hispaniola—Cuba, the largest source, are 10⁹ m³. This compares to an average flow volume of 10⁶ m³ for flows derived from the smallest source area, the Southeastern Caicos Bank. Measures of turbidity-current activity, such as thickness and frequency, change in a regular fashion away from each entry point. Average lutite thickness (combining hemipelagic and turbiditic lutite) are greatest near the basin entry points. On the abyssal plain occupying the south half of the basin, Bouma turbidite sedimentary structure sequences tend to be complete. However, on the Caicos Fan, the sedimentary structure sequences in turbidites are characterized by missing or repeated units. Six radiocarbon dates of two widespread presumed pelagic units in the basin yielded younger dates in stratigraphically older positions. The reversed dates are assumed to reflect storm erosion of older sediment on adjacent insular shelves.Consideration of a north—south reflection seismic profile over the basin indicates that the present sediment regimen has pertained through much of the Neogene. The coherence, convergence and termination of reflections in the seismic section are consistent with and tend to confirm conclusions based on the core study regarding the greater extent and volume of sediment deposits derived from the Hispaniola source area.     

The structure, mass and interactions of the hydrothermal plumes at 26°N on the Mid-Atlantic Ridge

Water-column surveys by combined nephelometer/CTD (NCTD) tows contributed to the 1985 discovery of the first black smokers on the Mid-Atlantic Ridge. Subsequent regional water-column mapping has helped define the extent, mass and interactions of the suspended particulate matter phase (SPM) of the hydrothermal plumes emanating from the known and other nearby sources. The results of 29 NCTD cast/tows, covering 25–30 km² of ridge segment, indicate the presence of as many as two additional sources based on SPM concentration gradients and plume-top doming over source areas. Plume doming, documented here for the first time from field observations, conforms strikingly with laboratory experiments and can serve as a marker for source field location. A comparison of the plumes' SPM with potential temperature and salinity distributions indicates close correlation in water-column anomaly patterns for each, confirming modification of the regional potential temperature and salinity structure by hydrothermal plumes, which is expressed by wide separation and sloping of isotherms and isohalines.     

Evaluation and comparison of spatial interpolators II

The performance of several variations on ordinary kriging and inverse distance estimators is evaluated. Mean squared errors (MSE) were calculated for estimates made on multiple resamplings from five exhaustive data bases representing two distinctly different types of estimation problem. Ordinary kriging, when performed with variograms estimated from the sample data, was more robust than inverse-distance methods to the type of estimation problem, and to the choice of estimation parameters such as number of neighbors.Notice: Although the research described in this article has been funded in part by the United States Environmental Protection Agency through Cooperative Agreement CR818526 to the Harry Reid Center for Environmental Studies, University of Nevada-Las Vegas, it has not been subjected to Agency review. Therefore it does not necessarily reflect the views of the Agency. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.     

DNAPL — Stop the Madness

"The EPA decided that showing the presence of DNAPL would prove that cleanup to non-detect was improbable, and that a new end point could be selected."
"The only thing that really matters is the total mass of from the natural attenuation."