Green line observations of the March 1970 coronal enhancements

Monochromatic observations of a double coronal enhancement were obtained on 3 March and 17 March 1970. These data are used, along with the assumption of cylindrical symmetry, to calculate the emittance of the Fexiv 5303 Å lines as a function of height. These estimates are then used to find the electron density and the density of ions in the ² P _3/2 level of the ground state as a function of height above the limb.     

Analytic short period lunar and solar perturbations of artificial satellites

The short period luni-solar theory of Kozai is generalized for arbitrary obliquity of the ecliptic and inclination of the moon's orbit to the ecliptic. Analytic first order lunar perturbations to the elements are derived. The theory is illustrated by an application to the communication satellite Intelsat 3F3.Presently at the Department of Environmental Sciences, University of Tel Aviv, Ramat Aviv, Israel.     

Characterization of grass shrimp (Palaemonetes pugio) embryo toxicity tests using the water soluble fraction of number 2 fuel oil

Toxicity test procedures using grass shrimp Palaemonetes pugio exposed to water soluble fraction (WSF) of Number 2 fuel oil were modified to improve test utility and efficiency. The original test procedure, a 12-day embryo exposure period in glass tubes, was compared with modified 4-day and 12-day tests in plastic tissue culture plates. Comparison of LC₅₀ values, coefficients of variation and time to hatch indicated no significant change in test sensitivity due to the plastic containers. Sensitivity was slightly reduced by shortening the test to a 4-day exposure period initiated 9 days after oviposition. This exposure period encompassed sensitive life stages of the developing organism. Using the 4-day exposure in plastic plates, variability due to different broods and preparations of WSF was characterized.     

Radiative heating and the buoyant rise of magnetic flux tubes in the solar interior

We study the effect of radiative heating on the evolution of thin magnetic flux tubes in the solar interior and on the eruption of magnetic flux loops to the surface. Magnetic flux tubes experience radiative heating because (1) the mean temperature gradient in the lower convection zone and the overshoot region deviates substantially from that of radiative equilibrium, and hence there is a non-zero divergence of radiative heat flux; and (2) the magnetic pressure of the flux tube causes a small change of the thermodynamic properties within the tube relative to the surrounding field-free fluid, resulting in an additional divergence of radiative heat flux. Our calculations show that the former constitutes the dominant source of radiative heating experienced by the flux tube.In the overshoot region, the radiative heating is found to cause a quasi-static rising of the toroidal flux tubes with an upward drift velocity 10^-3|| cm s^-1, where _e – _ad < 0 describes the subadiabaticity in the overshoot layer. The upward drift velocity does not depend sensitively on the field strength of the flux tubes. Thus in order to store toroidal flux tubes in the overshoot region for a period comparable to the length of the solar cycle, the magnitude of the subadiabaticity (< 0) in the overshoot region must be as large as 3 × 10^–4. We discuss the possibilities for increasing the magnitude of and for reducing the rate of radiative heating of the flux tubes in the overshoot region.Using numerical simulations we study the formation of -shaped emerging loops from toroidal flux tubes in the overshoot region as a result of radiative heating. The initial toroidal tube is assumed to be non-uniform in its thermodynamic properties along the tube and lies at varying depths beneath the base of the convection zone. The tube is initially in a state of neutral buoyancy with the internal density of the tube plasma equal to the local external density. We find from our numerical simulations that such a toroidal tube rises quasi-statically due to radiative heating. The top portion of the nonuniform tube first enters the convection zone and may be brought to an unstable configuration which eventually leads to the eruption of an anchored flux loop to the surface. Assuming reasonable initial parameters, our numerical calculations yield fairly short rise times (2–4 months) for the development of the emerging flux loops. This suggests that radiative heating is an effective way of causing the eruption of magnetic flux loops, leading to the formation of active regions at the surface.The National Solar Observatory is one of the National Optical Astronomy Observatories by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.     

Cellular iron contents of plankton during the Southern Ocean Iron Experiment (SOFeX)

Iron (Fe) availability limits phytoplankton biomass and production in large regions of the Southern Ocean and influences community composition and size structure, which may affect C export and other system-level functions. To improve our understanding of Fe partitioning within communities and the response of different components to fertilization, we assessed the cellular Fe contents of individual diatoms, autotrophic flagellates, and heterotrophic flagellates during the recent Southern Ocean Fe Experiment using synchrotron-based X-ray fluorescence (SXRF). Dual ⁵⁵Fe/¹⁴C radioisotope incubations were also conducted to estimate Fe:C ratios in size-fractionated plankton. Cellular Fe quotas determined by the two techniques were in close agreement when low amounts of ⁵⁵Fe (0.2 nM) were added, but ⁵⁵Fe additions of 2 nM resulted in 2–3-fold higher quotas. SXRF assessments of cellular Fe quotas (normalized to C) were generally in good agreement with prior bulk analyses of natural assemblages, but revealed compositional differences among protistan taxa not previously detected. Mean Fe:C ratios for diatoms, autotrophic flagellates, and heterotrophic flagellates from unfertilized waters were 6.0, 8.7, and 14.1 μmol mol C⁻¹, respectively. Smaller cells had higher Fe:C ratios than larger cells. Fertilization enhanced Fe quotas in all cell types, with mean Fe:C ratios increasing approximately 4-fold (from about 10 to about 40 μmol mol C⁻¹) after two Fe additions. This study provides some of the first measurements of Fe quotas in phytoplankton cells from natural communities and the first measurements of Fe quotas in natural protozoa.     

Succession in Gulf of Mexico Cold Seep Vestimentiferan Aggregations: The Importance of Spatial Variability

Abstract. The slow rate of change in hydrocarbon seep communities on the upper ­Louisiana slope prevents the use of direct observation in studying successional trends. We used a chronosequence consisting of three presumed stages – juvenile, adult and senescent – to test a previous model which proposed that sulfide availability and vestimentiferan growth and physiological health decline over the lifespan of a vestimenti­feran aggregation. We replicated the chronosequence at two sites to simultaneously ­explore the influence of spatial heterogeneity on the characteristics of these communities. We determined environmental sulfide concentrations and vestimentiferan growth and condition in at least two vestimentiferan aggregations representative of each stage at each of these two sites. Hydrogen sulfide concentrations were highly variable both above and below the sediment's surface, and sulfide was present in high concentrations to sediment depths of 70  cm. Vestimentiferan growth and condition varied significantly on multiple spatial scales from sites separated by tens of kilometers, to aggregations separated by tens to hundreds of meters within a site, to individual vestimentiferans ­separated by tens of centimeters within an aggregation. The striking variability in both environmental sulfide and vestimentiferan growth and condition within individual ­aggregations suggests a crucial role for microhabitat variability in the persistence of vestimentiferan aggregations at these sites. Few significant successional trends in ­environmental sulfide or vestimentiferan growth and condition were found over the three stages tested.     

Life in the Slow Lane: Growth and Longevity of Cold-seep Vestimentiferans

Abstract. Yearly, in situ growth of two species of cold-seep vestimentiferan tubeworms was measured using a combination of banding and video analysis. A total of 53 animals from 15 different aggregations were included in the study, which was conducted over a Cyear period. The most common species, Lamellibrachia sp., grows very slowly (averaging 0.77 cm. a^-1) and yet commonly reaches lengths over 2 m. Based on conservative calculations we conclude that individuals in mature aggregations are a minimum of 100 a old and are likely to be much older. Smaller numbers of a second species of vestimentiferan (related to escarpids) were also monitored over this period. We consider it likely that the individuals of the second species banded for this study were already on the plateau of their growth curve, and that the very low average growth rates recorded here would lead to an overestimate of the ages of the individuals used in this study. However, life history considerations combined with the extremely low measured growth rates of this species suggest it is also long-lived.     

Variability of physico-chemical conditions in 9°50′N EPR diffuse flow vent habitats

The physico-chemical characteristics of habitats have been considered to be one of the prime determinants of animal distribution within hydrothermal vent sites. However, the relative importance of abiotic to biotic influences is still debated. The primary aim of this study is twofold. The first is to determine and compare the ranges of physico-chemical conditions that characterize mussel-dominated and tubeworm-dominated communities at different sites within the vent field of the 9°50′N segment on the East Pacific Rise. The second is to better understand the processes that determine the variability of physico-chemical conditions in these habitats. In situ chemical and temperature measurements confirmed the high variability on small spatial and temporal scales within single aggregations of animals. The correlation of temperature and sulfide or pH revealed substantial differences between similar habitat-types at different sites, which cannot be attributed to changes in the extent of fluid dilution in the subseafloor. Further investigation of habitat variability within individual sites highlighted specific chemical features for the four sites studied, emphasizing the importance of an extensive in situ chemical analyses survey before using temperature as a proxy for chemical conditions. At Tica and Biovent, the fluid source characteristics were shown to vary only slightly within the sites, among aggregations discretely distributed over several meters distance. The variability of the total sulfide concentration and chemical speciation with temperature in the various habitats at each of these sites, can be reasonably simulated from the conservative mixing model of a single source fluid with seawater. The small variation of the empirical trends between different types of faunal assemblages at Tica suggests that changes in the fluid chemistry are not a prime determinant of the temporal succession of mussels and tubeworms. The findings of very similar sulfide–temperature relationships in two sites of different age and faunal compositions, Biovent and Tica, further support this idea. The two other sites, Mussel Bed and Riftia Field, differ both in the animal communities present and their chemistries show significant discrepancies from the predictions of the conservative mixing model. At Riftia Field, elevated iron concentrations and relatively low sulfide levels were correlated to unusually low pH, which could not be fully explained by conservative mixing of a typical diffuse vent fluid with seawater. The increased acidity results in a dramatic reduction in the anionic form, HS⁻. This is the form preferentially assimilated by the tubeworms and could explain the decline of the tubeworms at this site. At Mussel Bed the relationship between the sulfide concentration and temperature varied substantially among the aggregations surveyed and may reflect the influence of associated free-living microbial communities on the chemistry of mussel habitats. This study emphasizes the complex interplay of diffuse fluid formation in subsurface, chemical reactivity in the mixing zone, and biological activity in controlling of characteristics of vent habitats.     

Patterns of growth in cold-seep vestimenferans including Seepiophila jonesi: a second species of long-lived tubeworm

Seepiophila jonesi is a vestimentiferan tubeworm (Siboglinidae: Polychaeta) inhabiting the cold seeps of the upper slope of the Gulf of Mexico. It commonly co‐occurs with Lamellibrachia luymesi, which is among the most long‐lived non‐clonal animals known. The growth pattern of S. jonesi is best described by a model including a size‐specific probability of growth and an average growth rate that does not vary with individual size. This model, based on growth data from in situ staining and collection approximately 1 year later, predicts that S. jonesi is very slow growing and may attain ages comparable with L. luymesi. The efficacy of this model in describing L. luymesi growth rate was assessed, but the previously employed model of declining growth rate with individual size provided the better fit to the empirical data. Comparisons of both S. jonesi and L. luymesi growth rates among sites and among aggregations within a site indicate that there is some degree of habitat variability contributing to differences in growth rates. However, position of the anterior end of the worm within an aggregation did not have a significant effect on growth rate in comparisons among groups of L. luymesi from different distances from the center of an aggregation. The evolution of longevity in these species of vestimentiferans was favored by the relative stability of the seep habitat and sulfide sources, in contrast to the hydrothermal vent environment inhabited by relatively short‐lived and fast‐growing vestimentiferan species.