Comparison of spawning seasons,age, growth rates,and food of two sympatric species of searobins,Prionotus carolinus and Prionotus evolans,from Long Island Sound

Prionotus carolinus and Prionotus evolans were collected from many locations within Long Island Sound in 1971–1973, and in 1976–1977. Data from earlier collections in Block Island Sound (1943–1945) were also included. A total of 1751 specimens, 960 P. carolinus and 791 P. evolans was examined within these two time periods. Both species entered the Sound in April and spawned during June and July. P. evolans appeared to spawn slightly earlier in summer than P. carolinus. Adults began to leave the Sound after spawning and were usually absent after November. Young-of-the-year were taken regularly from August to November and, occasionally in water over 20 m deep, into February when the bottom water temperature was 1.4°C. At the end of the first growing seasons both species exhibited large variations in standard lengths. Back-calculations from scale annuli measurements indicated that linear growth rates during the juvenile years were similar in both species. However, P. evolans was considerably heavier than P. carolinus. During adulthood P. evolans was not only longer and heavier than P. carolinus, but lived longer. Growth rates are described by the following equations: P. carolinus L_t+1=9.60+0.68 (L_t), and p. evolans L_t+1=7.70+0.80 (L_t). Both species were opportunistic feeders, and crustaceans were clearly the dominant group of prey. Young-of-the-year, between 3–6 cm, ate copepods. As they grew they ate larger prey, such as Neomysis americana, Diastylis quadrispinosus, various species of amphipods of small sizes, and juvenile Crangon septemspinosus. Older fish ate larger sizes of these same prey, a number of species of crabs, juvenile Homarus americanus, and Squilla empusa. Occasionally they ate polychaetes, molluscs, and juvenile fish. Partitioning of the resources of Long Island Sound by these two species appeared to be by prey size. P. evolans ate prey that, on the average, were slightly larger than those eaten by P. carolinus. Furthermore, P. evolans ate a greater amount of nektonic species than P. carolinus, which appeared to prefer benthonic invertebrates.     

The use of assumed displacement fields in finite-element analysis to calculate the gravity effect of crustal deformation

An expression is derived which relates a displacement field u defined on a continuum to the change in gravity (Δg_D) brought about by deformation:

Full-size image (1K)

-

Full-size image (1K)

where GG is the gravitational constant; ρ_R is the pre-deformation density function; V_R is the volume occupied by the continuum before deformation; T_D is a transformation which represents the one-to-one mapping of V_R onto the volume V_A occupied by the continuum after deformation: A₁ = R₁ + U₁(R₁, R₂, R₃)T_D: A₂ = R₂ + U₂ (R₁, R₂, R₃)A₃ = R₃ + U₃ ( R₁, R₂, R₃) where A₁, a₂, A₃, are the Cartesian coordinates of a point in V_A; R₁, R₂, R₃ are the Cartesian coordinates of a point in V_R; U₁, U₂, U₃, are the components of u; and α is the distance from the field point (x, y, z) to a general point in V_A or V_R. The derivation is based on the principle of conservation of mass as stated in continuum mechanics. The formulation of the finite-element procedure for problems in linear elasticity typically involves the selection of an assumed function for u within each element. Unknown constants which characterize the function are determined in terms of nodal displacements. The integral in the first equation above may therefore be evaluated for each element, and the results summed to obtain Δg_D. Convergence to the exact solution for Δg_D depends on the convergence of the finite-element solution for u. The procedure is demonstrated for axisymmetric, torsion-free deformation of a solid of revolution in which the elements are tori of triangular cross-section. These results may be useful in the analysis of gravity change associated with tectonic deformation of the earth's crust.     

A sediment trap intercomparison study in the Santa Barbara Basin

Four sediment traps of radically different design were deployed in the Santa Barbara Basin for approximately 45 days. The measured fluxes ranged from 370 to 774 g m^?2 yr^?1 for the different designs. These values lie within flux measurements previously determined for the basin. Compared to the 25-year record (920 g m^?2 yr^?1), however, all fluxes determined in this experiment are somewhat low. Because this experiment was conducted during a general period of high storm activity and runoff, measurement of greater than average flux was expected. It is probable that the higher flux recorded by the sediments results from a significant input of detritus into the basin by near bottom transport.The chemical composition of trapped material was nearly identical in all four trap designs. The deep cone design, however, had a significantly lower Mn content. Since this trap was the only one in which reducing conditions were produced in the sample container, reduction and mobilization of manganese after collection is believed to have occurred.In spite of the very different designs tested, the factor of two agreement in flux determination and the compositional similarity of the material collected is encouraging for future attempts to directly measure the flux of particulates in the ocean.     

Climatological and hydrographic influences on nearshore food webs off the southeastern United States: bacterioplankton dynamics

Bacterioplankton productivity, numbers, and cell specific activity were studied in nearshore waters of the southeastern U.S. continental shelf during seasons of maximum freshwater discharge. In April 1984, coastal waters were stratified from normal spring discharge and typical northeastward wind stress. In April 1985, shelf waters were vertically homogeneous due to below normal runoff and southwestward wind stress. In 1984, nearshore bacterial productivity ranged from 7.0 to 14.7 × 10⁶ cells l⁻¹ h⁻¹ and midshelf rates were 40–50% less. In 1985, nearshore productivity ranged from 0.9 to 2.4 × 10⁶ cells 1⁻¹ h⁻¹, and productivity was extremely patchy over the entire shelf. The cell-specific activity (thymidine incorporation per cell) suggests that although productivity was high in 1984, only a fraction of the bacterioplankton was actively growing or incorporating thymidine (0.9–2.9 × 10⁻²¹ mol cell⁻¹ h⁻¹). In 1985, a higher percentage of cells appeared to be active and incorporating thymidine (5–13 × 10⁻²¹mol cell⁻¹h⁻¹) even though productivity was low. Hydrographic conditions along the southeastern coastline may have had a significant impact on the overall community structure and carbon flow through the microbial food web. When coastal waters were stratified in 1984, bacterial biomass was a significant percentage (35–320%) of the phytoplankton biomass. During vertically homogeneous conditions of 1985, bacterial production and biomass were a small percentage (2–13%) of the phytoplankton production and biomass across the shelf. The interannual variation in the microbial food web was attributed to the interannual variability of the southeastern U.S. hydrology due to changes in freshwater discharge and wind direction and intensity. The ecological implications of these results extend to the potential impact of seasonal microbial food webs on nearshore allochothonous and autochothonous organics before removal from the southeastern U.S. coastline.     

Solar flare activity: Evidence for large-scale changes in the past

An analysis of radar and photographic meteor data and of spacecraft meteoroid penetration data indicates that there probably has not been a large increase in meteoroid impact rates in the last 10⁴ yr. The solar flare tracks observed in the glass linings of meteoroid impact pits on lunar rock 15205 are therefore reanalyzed assuming a meteoroid flux that is constant in time. Based on this assumption, the data suggest that the production rate of Fe-group solar flare tracks may have varied by as much as a factor of 50 on a time scale of about 10⁴ yr. No independently obtained data are known to require conflict with this interpretation. Confidence in this conclusion is somewhat qualified by the experimental and analytical uncertainties involved, but the conclusion nevertheless remains the present “best” explanation for the observed data trends.     

Gravity field of Mars from Mariner 9 tracking data

Further reduction of Doppler tracking data from Mariner 9 confirms our earlier conclusion that the gravity field of Mars is considerably rougher than the fields of either the Earth or the Moon. The largest positive gravity anomaly uncovered is in the Tharsis region which is also topographically high and geologically unusual. The best determined coefficients of the harmonic expansion of the gravitational potential are: J₂ = (1.96 ± 10.01) × 10^?3 ; C₂₂ = ?(5.1 ± 0.2) × 10^?5; and S₂₂ = (3.4 ± 0.2) × 10^?5. The other coefficients have not been well determined on an individual basis, but the ensemble yields a useful model for the gravity field for all longitudes in the vicinity of 23° South latitude which corresponds to the periapse position for the orbiter.The value obtained for the inverse mass of Mars (3 098 720 ± 70 M⊙^?1) is in good agreement with prior determinations from Mariner flyby trajectories. The direction found for the rotational pole of Mars, referred to the mean equinox and equator of 1950.0, is characterized by α = 317°.3 ± 0°.2, δ = 52°.7 ± 0°.2. This result is in excellent agreement with Sinclair's recent value, determined from earth-based observations of Mars' satellites, but differs by about 0°.5 from the previously accepted value. Other important physical constants that have either been refined or confirmed by the Mariner 9 data include: (i) the dynamical flattening, f = (5.24 ± 0.02) × 10^?3; (ii) the maximum principal moment of inertia, C = (0.375 ± 0.006) MR²; and (iii) the period of precession of Mars' pole, P ? (1.73 ± 0.03) × 10⁵ yr, corresponding to a rate of 7.4 sec of arc per yr.     

Extensive degradation and fractionation of organic matter during subsurface weathering

Organic carbon, sulphur, ¹³C_org, iron, manganese and calcium have been measured across a subsurface-weathering front in Pliocene sediments in southern Sicily. The results show an almost quantitative removal of C_org and sulphur and an increase in iron and manganese oxides over the weathering front, accompanied with a significant shift of the ¹³C_org to lower values. These data are among the first to support the rapid, extensive weathering of sedimentary organic matter and sulphur, a basic assumption made in global biogeochemical models on a Phanerozoic timescale.     

Evaluation of210Pb dating in lake sediments using stable Pb,Ambrosia pollen,and137Cs

We used sediment chronology data from fourteen published studies of lake cores across much of North America and Scandinavia in order to make a large scale comparison of the different dating techniques. The uncertainty of²¹⁰Pb derived dates was determined using common sediment event markers: the stable Pb rise, the¹³⁷Cs rise, and theAmbrosia pollen rise. For all data combined, the 95% confidence intervals for the stable Pb rise and theAmbrosia rise, were approximately 30 years. These 95% confidence intervals are slightly higher than those derived by First-Order Error analysis performed by others on²¹⁰Pb derived dates. When comparing the concordance of two²¹⁰Pb models (CRS and CIC) against markers of known history, we found that the CRS model dates (constant rate of supply) had consistently better agreement than the CIC model dates (constant initial concentration). Major discrepancies between¹³⁷Cs and²¹⁰Pb were common, but were consistently more severe in sediments of soft water lakes pointing to an inability of sediments with low mineral content to immobilize Cs.This is the ninth of a series of papers to be published by this journal following the 20 ^th anniversary of the first application of²¹⁰Pb dating of lake sediments, Dr. P. G. Appleby is guest editing this series.