Eric H. DeCarlo

Calcareous nannofossil biostratigraphic dating of a ferromanganese crust from Schumann Seamount

Abstract Calcareous nannofossil biostratigraphy was employed to determine the age and growth rates of the different layers within ferromanganese crusts from Schumann Seamount, 200 miles north of the island of Kauai, Hawaii. This work is part of a study to reconstruct the paleoceanographic history of crusts using various geochemical indicators. The methods are based on the identification of coccolith imprints, not actual coccolith remains. Age constraints on the time span of a particular horizon are defined either (1) by the presence of a species which was extant for only a limited geological time interval or (2) by the presence of two organisms whose time ranges overlapped. Age resolution is optimized by short time ranges or narrow overlaps. In the crust studied there was considerable inter-horizon variability in the preservation of coccolith imprints, in imprint abundance and in species diversity. Some of the crust layers examined were narrowly constrained temporally (1–4 Myr), while others were less so (> 10 Myr). Our results indicate that the minimum age for the interval at 27 mm depth is at least Eocene. This is the maximum age many believe any crust can be. The position of this interval, however, is only about one half of the way through the crust. While the data support previous estimates of average crust growth rates (0.5 mm/Myr), the actual apparent growth rate appears to have varied by an order of magnitude (0.1 to 2 mm/Myr).

The Geochemistry of Lake Joyce, McMurdo Dry Valleys, Antarctica

Lake Joyce is one of the least studied lakes of the McMurdo Dry Valleys. Similar to other lakes in this region, Lake Joyce is a closed-basin, permanently ice-covered, meromictic lake. We present here a detailed investigation of major ions, nutrients, and dissolved trace elements for Lake Joyce. Specifically, we investigate the role of iron and manganese oxides and hydrous oxides in trace metal cycling.Lake Joyce is characterized by fresh, oxic waters overlying an anoxic brine, primarily Na–Cl. Surface waters have a maximum nitrate concentration of 26 μM with a molar dissolved inorganic nitrogen to phosphorus ratio of 477. The supply of nitrogen is attributed to atmospheric deposition, possibly from polar stratospheric clouds. Dissolved phosphorus is scavenged by hydrous iron oxides. The pH is highest (10.15) just beneath the 7-m thick ice cover and decreases to a minimum of 7.29 in the redox transition zone. Dissolved Al exceeds 8 μM in surface waters, and appears to be controlled by equilibrium with gibbsite. In contrast, concentrations of other trace elements in surface waters are quite low (e.g., 5.4 nM Cu, 0.19 nM Co, 3 O 4 ). Co tracks the Mn profile closely, suggesting Co(III) is bound in the lattice of Mn oxides, whereas the Ce profile is similar, yet the Ce anomaly suggests oxidative scavenging of Ce. Release of Cu, Ni, Cd and trivalent REE appears to be controlled by pH-induced desorption from Fe and Mn oxides, although Cu (and perhaps Ni) may be scavenged by organic matter in surface waters.

Hillslope soil erosion estimated from aerosol concentrations, North Halawa Valley, Oahu, Hawaii

Concentrations of aerosolic quartz and137Cs were used to estimate rates of hillslope soil erosion during 1990–1991 in the North Halawa Valley on the island of Oahu, Hawaii. Fluvial transport of quartz was estimated to be 6.1 Mg in 1990 and 14.9 Mg in 1991. Fluvial transport of137Cs from North Halawa Valley was estimated to be 1.29 × 109 pCi in 1991. Results were used with quartz contents,137Cs activities, and bulk densities of hillslope soils to compute rates of basinwide hillslope soil erosion ranging from 0.1 to 0.3 mm yr−1. These rates are within the range of previous estimates of denudation computed for drainage basins on Oahu. The aerosol-concentration approach, therefore, is a useful method for assessing basinwide soil erosion.

Using sediment ‘fingerprints’ to assess sediment-budget errors, North Halawa Valley, Oahu, Hawaii, 1991–92

Reliable estimates of sediment-budget errors are important for interpreting sediment-budget results. Sediment-budget errors are commonly considered equal to sediment-budget imbalances, which may underestimate actual sediment-budget errors if they include compensating positive and negative errors. We modified the sediment ‘fingerprinting’ approach to qualitatively evaluate compensating errors in an annual (1991) fine (<63 μm) sediment budget for the North Halawa Valley, a mountainous, forested drainage basin on the island of Oahu, Hawaii, during construction of a major highway. We measured concentrations of aeolian quartz and 137Cs in sediment sources and fluvial sediments, and combined concentrations of these aerosols with the sediment budget to construct aerosol budgets. Aerosol concentrations were independent of the sediment budget, hence aerosol budgets were less likely than sediment budgets to include compensating errors. Differences between sediment-budget and aerosol-budget imbalances therefore provide a measure of compensating errors in the sediment budget. The sediment-budget imbalance equalled 25 per cent of the fluvial fine-sediment load. Aerosol-budget imbalances were equal to 19 per cent of the fluvial 137Cs load and 34 per cent of the fluvial quartz load. The reasonably close agreement between sediment- and aerosol-budget imbalances indicates that compensating errors in the sediment budget were not large and that the sediment-budget imbalance is a reliable measure of sediment-budget error. We attribute at least one-third of the 1991 fluvial fine-sediment load to highway construction. Continued monitoring indicated that highway construction produced 90 per cent of the fluvial fine-sediment load during 1992. Erosion of channel margins and attrition of coarse particles provided most of the fine sediment produced by natural processes. Hillslope processes contributed relatively minor amounts of sediment.

Recovery of Metals from Process Streams of Deep-Sea Ferromanganese Nodules by Adsorptive Bubble Techniques

Abstract A method for the separation of Cu, Co, Ni, and Zn with varying degrees of selectivity from chemically treated deep-sea ferromanganese nodules is described. Quantitative removal of these species is achieved primarily by precipitate flotation of insoluble sulfides. Recovery of residual metal values of Cu, Co, Ni, and Zn in process rejects of the nodules is also possible. The quantitative removal of Pb and V, which are the most abundant toxic elements in nodules and tailings, is achieved simultaneously. Cationic and anionic surfactants are employed for collection depending on zeta potentials of the flocs generated upon addition of Na2S to sample solutions. Separations are more selective and efficient at lower pH than previously reported for flotation of metals from nodules as insoluble hydroxides. Modifications resulting in slight improvements over previously employed high temperature sulfation processes are also described.

Methodologies for Surveying and Assessing Deep-Water Munitions Disposal Sites

The Hawaii Undersea Military Munitions Assessment (HUMMA) was designed to develop methodologies for surveying and assessing a historic deep-water munitions sea disposal site to determine the potential impact of the ocean environment on seadisposed munitions and of sea-disposed munitions on the ocean environment and those that use it. HUMMA is the most comprehensive deep-water investigation conducted in the United States to look at both chemical and conventional munitions. Recognizingthateachsea-disposedmunitionssiteposesuniquelogisticalandenvironmental challenges, the HUMMA approach emphasizes adaptability. Here, we describe the techniques used to determine the spatial extent and distribution of munitions, evaluate theintegrity of munitions casings,andsamplesediments andseawaternearmunitions present at water depths ranging from 330 to 550 m. We discuss integration and management of the diverse and voluminous datasets that the program produced. Notable results from HUMMA include demonstrating that reconnaissance-style mapping effectively locates distinctive trails of disposed munitions in sandy environments and that visual observations, in combination with acoustic data, constrain the poorly documented historical disposal process. Based on our findings, we conclude with several suggested future avenues of research for evaluating sea-disposed munitions sites.