Temporal variation of228Ra in the near-surface Gulf of Mexico

The Mn-fiber technique for extracting radium from seawater has proved useful for studying the marine geochemistry of²²⁸Ra. In the Gulf of Mexico, this technique was used to measure the surface and near-surface distribution of²²⁶Ra and²²⁸Ra. The observed surface distribution of²²⁸Ra, and particularly the radium activity ratio (228/226) can be explained by known circulation patterns, or, when local surface currents are not well understood, may provide insight into their general characteristics.The radium activity ratio has increased from 0.5 in 1968 to 0.7 in 1973 in the surface Gulf of Mexico. This observed increase cannot be attributed to known anthropogenic or natural source perturbations within the Caribbean Sea-Gulf of Mexico system. Possible causes include a change in the residence time for near-surface water, or variations in the relative dominance of the two sources for water entering the eastern Caribbean; the North Equatorial Current and the Guiana Current.The temporal distribution of²²⁸Ra is unstable and naturally variable over a time period less than or equal to five years in the Gulf of Mexico and by extrapolation, the Caribbean Sea. Therefore, its usefulness in calculations of eddy diffusion coefficients for these regions is greatly diminished.     

Carbonatization and mobility of Ti,Y, and Zr in Ascot Formation metabasalts,SE Quebec

The middle Ordovician Ascot Formation of southeastern Quebec consists of greenschist facies metamorphosed silicic to mafic pyroclastic rocks and lava flows and associated metasediments. Chemical analyses of lavas reveal a preponderance of metarhyolites and metabasalts, together with some porphyritic rocks with intermediate SiO₂ contents. The metabasalts exhibit wide ranges in concentrations of TiO₂ (0.25–2.0 wt.°), Y (9–46 ppm), and Zr (5–135 ppm). The extent of the ranges, and unusual interelement ratios, suggest that the concentrations of these normally immobile elements have been affected by secondary processes.There is a strong correlation between trace-element concentrations and the degree of carbonatization of the metabasalts. Low carbonate rocks are severely depleted in Ti, Y, and Zr whereas high carbonate rocks are depleted in Y and Zr and enriched in Ti. The differing movement of Ti can be explained in terms of variable chemical potential due to the various carbonatization reactions affecting titaniferous phases. Overall mobility of these generally immobile/rd elements is attributed to high CO₂ levels in the fluid phase during metamorphism.Extrapolation of the two alteration trends to a common origin enables one to infer primary concentrations of the trace-elements. Primary inter-element ratios arrived at in this way are compatible with an island-arc origin for the Ascot Formation although TiO₂ concentrations are a little high (1.5 wt/%).     

Radium isotopes in sub-Arctic waters

Measurements of the²²⁸Ra/²²⁶Ra activity ratio in the waters of the Greenland, Norwegian and Labrador Seas and Baffin Bay reveal strong horizontal gradients in the surface waters. The coastal waters are dominated by²²⁸Ra injection from nearshore sediments. There is an inverse correlation between the²²⁸Ra/²²⁶Ra activity ratio and salinity in the 30–36‰ salinity range. Vertical profiles indicate that the²²⁸Ra/²²⁶Ra activity ratio is also strongly coupled toσ_θ except for some regions where²²⁸Ra is being injected into higher density water as these isopycnals intersect coastal areas. We use these measurements in the area of formation of North Atlantic Deep Water to estimate that this water mass forms with a²²⁸Ra/²²⁶Ra activity ratio of 0.10.     

226Ra behavior in the Pee Dee River-Winyah Bay estuary

Concentrations of dissolved²²⁶Ra in Winyah Bay, South Carolina, and in the adjacent Atlantic Ocean are augmented by the desorption of radium from sediments in the low-salinity area of the estuary and diffusion from bottom sediments. Desorption of²²⁶Ra is reflected by lower concentrations in suspended sediments from higher-salinity regions of the estuary. Bottom sediments from the high-salinity region have lower²²⁶Ra/²³⁰Th activity ratios than those from the low-salinity end.The shape of the dissolved²²⁶Ra vs. salinity profile is influenced by the river discharge. During average-discharge conditions, desorption of²²⁶Ra from suspended and bottom sediments increases the dissolved²²⁶Ra concentrations by a factor of 3.5 as the water passes through Winyah Bay. High river discharge produces an initial increase of dissolved²²⁶Ra by a factor of 2 to 3 and apparently reflects only desorption from suspended sediments. By driving the salt wedge down the estuary and reducing the zone of contact of salt water with bottom sediments, the high-flow conditions sharply reduce the flux of²²⁶Ra from bottom sediments.     

Nontidal circulation and mixing processes in the lower Potomac estuary

An analysis of the vertical structure of nontidal longitudinal currents and salinity in a reach of the lower Potomac River Estuary suggests that values for vertical eddy viscosity and eddy diffusivity scale with water depth H, tidal current amplitude U and bulk Richardson number according to conventional empirical formulas. However, the constant which relates the vertical eddy coefficients under conditions of neutral stability to UH is found to be an order of magnitude less than that expected for tidal conditions. Analyses also suggest that the degree of enhancement of longitudinal dispersion by the shear effect associated with the nontidal currents is a strong function of bulk Richardson number.     

Growth rates of manganese nodules in Oneida Lake,New York

²²⁶Ra is used to document the growth histories of six manganese nodules from Oneida Lake, New York. Detailed sectioning and analysis reveal that there are discontinuous gradients in²²⁶Ra content in these samples. These gradients result from periods of rapid growth (>1 mm/100 years) separated by periods of no growth of erosion. Although the²²⁶Ra “age” of the nodules approximates the age of Oneida Lake, the nodules are not sediment-covered because they occur only in areas of the lake where fine-grained sediments are not accumulating.     

Late Wisconsinan glaciation models of northern Maine and adjacent Canada

Surficial stratigraphic units of Aroostook County, Maine, have been mapped and formal stratigraphic names for these units are proposed. Evidence exists for at least two distinct glacial phases which are represented by three tills. Two of these tills were deposited penecontemporaneously either as the result of coalescing ice sheets or as the result of the thermal regime existing within a single ice sheet. The oldest till is named the St. Francis and is correlated with the Chaudière Till of southeastern Quebec. The other tills are named the Mars Hill and Van Buren tills, respectively, and are correlated with the Lennoxville till of southeastern Quebec. Interbedded stratified sediments associated with the St. Francis till are correlated with the Gayhurst Formation. Stratified sediments associated with Van Buren and Mars Hill tills are correlated with post Lennoxville sediments of Quebec. Granite-gneiss erratics of Canadian Shield provenance in the Van Buren till indicate advance of the Laurentide ice into northern Maine during late Wisconsinan time. Moraines in southern Aroostook County with associated outwash and eskers record general recession from coastal Maine. Recession occurred after the formation of the Pineo Ridge moraine in Maine and the St. Antonin-Highland Front moraine complex in Quebec. The Caribou-Winterville moraine complex in northern Maine marks the boundary between the penecontemporaneously deposited Van Buren and Mars Hill surface tills and is correlated with the Grand Falls moraine at Grand Falls, New Brunswick.     

Toxicity of No. 2 fuel oil to coon stripe shrimp

Bioassay of a No. 2 fuel oil dispersion with shrimp in a continuous flow system using measured waterborne oil as the indicator of oil concentrations reveals a treatment more definable than those previously described in terms of volume ratios and produces lower lethal concentrations. Shrimp 96-h LC₅₀ was 0.8 mg/l in this study as compared to values from 1.5 to 50 mg/l reported for other methods. Mean concentrations in tests do not give significant differences in concentration with respect to day of the test or spatial distribution in the exposure tanks.