Phytoplankton ecology of a barrier island estuary: Great South Bay,New York

The phytoplankton ecology of Great South Bay, New York, was studied over a 1-year period. The study area, a large barrier island estuary (coastal lagoon with estuarine circulation), was characterized by high levels of inorganic nutrients, high turbidity and a shallow euphotic zone (<2 m). Net annual primary production by phytoplankton was high—450 g C m^?2 year^?1—and accounted for approximately 85% of the total ecosystem primary production. Chlorophyll a-specific productivity was dependent on mean photic zone light intensity in areas of the bay <1 m in depth from September 1979 through June 1980; 65–95% of the total light extinction in those areas was attibutable to suspended solids. Nitrogenous nutrient concentration did not limit phytoplankton productivity. Diatom and dinoflagellate cell densities varied greatly over time, while cryptomonad and chlorophyte species were abundant throughtout the year. Chlorophytes of 2–4 μm (‘small forms’) were numerically dominant, and contributed approximately half of the total phytoplankton biomass. Dilution of bay water by intruding ocean water appeared to control the spatial distribution of chlorophyll a on the south side of the bay; in other areas, growth appeared to exceed the rate of dilution by flushing. Waters entrained in eelgrass beds were significantly higher in salinity and mean photic zone light intensity, and had lower phytoplankton standing stock and depth-integrated primary production than control areas; waters in the sediment plume of active clamdigging boats were statistically similar to control areas with respect to water quality and phytoplankton community characteristics.     

Whistler wave propagation in magnetospheric ducts (in the equatorial region)

An analytical theory of whistler wave propagation in axially symmetric field-aligned density ducts is developed. Both enhancements and rarefactions of the density (crests and troughs) are considered. Simple equations giving the dependence of the number of modes n upon the angular frequency ω are derived. From these results it follows that in density crests n decreases when ω approaches ω_c/2 for ω < ω_c/2. The limiting frequency of the wave trapping is calculated. An analytical investigation of wave attenuation in a density crest due to wave leakage is presented. An analysis of the whistler modes in density troughs for ω < ω_c/2, ω > ω_c/2, and ω → ω_c/2 shows that the number of modes is of the same order of magnitude in these three cases.     

Fluid inclusions in high-grade gneisses of the Kapuskasing structural zone,Ontario: metamorphic fluids and uplift/erosion path

Fluid inclusions in quartz grains from five samples of high-grade rocks (two paragneisses, an amphibolite, a mafic gneiss and a tonalite dike) from the 2.7 Ga Kapuskasing structural zone (KSZ), Ontario, were examined with petrographic, microthermometric and laser Raman techniques. Three types of fluid inclusions were observed: CO₂-rich, H₂O-rich and mixed CO₂-H₂O. CO₂-rich fluid inclusions are pseudosecondary or secondary in nature and are generally pure CO₂; a few contain varying amounts of CH₄·H₂O-rich fluid inclusions are secondary in nature, contain variable amounts of dissolved salts, and generally contain daughter crystals. Mixed CO₂-H₂O fluid inclusions occur where trails of H₂O-rich inclusions intersect trails of CO₂-rich inclusions. Isochores for high density (p=1.03 g/cm³) pseudosecondary, pure CO₂ inclusions intersect the lower pressure portion of the estimated P-T field for high-grade metamorphism, implying that pure CO₂ was the peak metamorphic fluid. The variable CH₄ content of CO₂ inclusions within graphite-bearing samples suggests that CH₄ was introduced locally after the formation of the CO₂ inclusions; however the origin of the CH₄ remains problematic. An aqueous fluid clearly penetrated the gneisses after the peak metamorphism (during uplift/erosion), forming secondary inclusions and contributing to the minor retrogressive hydration observed in these rocks. The presence of the pseudosecondary, high-density CO₂ inclusions in quartz crystals in the KSZ rocks constrains the uplift/ erosion path for the KSZ to one of simultaneous decrease in pressure and temperature.     

The residence time of thorium in surface sea water and its implications regarding the rate of reactive pollutants

The activity ratio of²²⁸Th/²²⁸Ra in the open surface ocean averages 0.21. This suggests that thorium is removed from surface water in about 0.7 yr. As plant matter is cycled within the surface sea on a similar time scale, the suggestion is made that highly reactive compounds are inadvertently removed by plants in their quest for the critical nutrients nitrate and phosphate. Combined with the coefficient for horizontal eddy diffusivity obtained from the distribution of²²⁸Ra in surface sea water this result provides a basis for the prediction of the distribution of “reactive” pollutants released to the surface sea from coastal areas.     

210Pb and210Po during the destruction of stratification in the Dead Sea

The progressive weakening and final disappearance (in 1979) of the long-term meromictic structure of the Dead Sea are clearly reflected in the depth profiles of²¹⁰Pb and²¹⁰Po. In 1977/78, prior to overturn, dissolved²¹⁰Pb (35–50 dpm kg^?1) predominated over particulate²¹⁰Pb (1–2 dpm kg^?1) in the oxic upper waters, whereas the reverse was true in the anoxic deep waters (16–20 dpm kg^?1 particulate vs. 2–5 dpm kg^?1 dissolved). The exact extent of the disequilibrium between²¹⁰Pb and²²⁶Ra is hard to evaluate in the upper oxic layers, because the progressive deepenings resulted in mixing with deep waters. By contrast, one can estimate the residence time of dissolved²¹⁰Pb in the unperturbed anoxic deepest layers, because these remained isolated, at about 3 years. Following the overturn of 1979, dissolved²¹⁰Pb exceeded particulate²¹⁰Pb at all depths. The²¹⁰Po profiles of the stratified lake resembled in shape those of its grandparent²¹⁰Pb, but with distinct characteristics of their own in the oxic upper waters where particulate²¹⁰Po (8–12 dpm kg^?1) was greatly in excess over particulate²¹⁰Pb, while dissolved²¹⁰Po (25–40 dpm kg^?1) was slightly deficient. Immediately following the overturn, dissolved and particulate²¹⁰Po were similar (about 15 dpm kg^?1), at all depths. The destruction of the lake's meromictic structure was accompanied by a reduction of its²¹⁰Pb inventory, while that of²¹⁰Po was almost unaffected. Thus, at overturn a transient state was created with the inventory of²¹⁰Po exceeding that of²¹⁰Pb.