Variation in sunscreen compounds (mycosporine‐like amino acids) for marine species along a gradient of ultraviolet radiation transmission within doubtful sound,New Zealand

We examined the response of four species of New Zealand marine algae (Ecklonia radiata, Apophlaea lyallii, Rhodymenia spp., Ulva lactuca) and a sea urchin (Evechinus chloroticus) to spatial variation in ultraviolet radiation (UV‐R) by examining the concentration of UV‐R absorbing compounds known as mycosporine‐like amino acids (MAAs). The purpose was to understand how, and the degree to which, local marine species could potentially respond to any future increases in incident UV‐R in the New Zealand marine environment. The research was undertaken in Doubtful Sound, where we observed a gradient of water column UV‐R transmission along the 40 km length of the fiord. We examined spatial differences in MAAs along the UV‐B gradient in the macrophytes and temporal changes in MAAs in sea urchin gonads. Among the algae, thallus MAA concentrations (nmol mg^–1 protein) ranged from 12.5 to 87.8 in E. radiata, from 433.1 to 1446.4 in A. lyallii, 12.7 to 103.4 in Rhodymenia spp., but were not detected in U. lactuca. For E. chloroticus, gonadal MAA concentrations ranged from 83.9 to 224.3 nmol mg^–1 protein spatially, and over the year from 1.85 to 14.12 nmol mg^–1 dry weight (DW) depending on site and gametogenic cycle. Laboratory manipulations indicated that concentrations of MAAs in E. chloroticus gonads and eggs are influenced by diet. MAA concentration could be correlated with UV‐B intensities in two of the algal species. E. chloroticus MAA concentrations could also be correlated with UV‐B transmission, which we concluded was a reflection of the greater ingestion and accumulation of MAA‐rich macrophytes at those sites where higher ambient UV‐R induced greater MAA concentrations to occur in the algae. Given this, we suggest that one response of marine species to increases in UV‐B would be an increase in the synthesis and/or accumulation of MAAs for photoautotrophs and a dietary accumulation of those MAAs in E. chloroticus, an important herbivore in this system.     

Geochemical Stratigraphy of Submarine Lavas (3-5 Ma) from the Flamengos Valley, Santiago, Southern Cape Verde Islands

New high-precision Pb–Sr–Nd isotope, major and traceelement and mineral chemistry data are presented for the submarinestage of ocean island volcanism on Santiago, one of the southernislands of the Cape Verde archipelago. Pillow basalts and hyaloclastitesin the Flamengos Valley are divided into three petrographicand compositional groups; the Flamengos Formation lavas (4·6Ma) dominate the sequence, with the younger Low Si and Coastalgroups (2·8 Ma) found near the shoreline. Olivine andclinopyroxene compositions and isotopic data for minerals andtheir host melts indicate disequilibrium between some crystalsand the melt. Intra-sample disequilibrium suggests homogenisationof liquids but eruption before complete equilibration betweencrystals and melt preserves the heterogeneity. Pressures ofcrystallization for clinopyroxene (0·4–1·1GPa) indicate stalling and crystallization of the magmas overa range of depths in the lithosphere. Major element compositionsindicate melting of a carbonated eclogite source. Sr–Nd–Pbisotope data suggest the involvement of FOZO-like and EM1-likecomponents in the mantle source, which are simultaneously availableat all depths in the melting column. The Flamengos Valley lavasdisplay large compositional variations, often between stratigraphicallyadjacent flows; these frequent abrupt changes of magma compositionsuggest stalling and crystallization of discrete magma batcheson transport through the lithosphere. KEY WORDS: Cape Verde; crystal–melt disequilibrium; submarine volcanism; source heterogeneity; Pb–Sr–Nd isotopes     

Regulation of bacterial sulfate reduction and hydrogen sulfide fluxes in the central namibian coastal upwelling zone

The coastal upwelling system off central Namibia is one of the most productive regions of the oceans and is characterized by frequently occurring shelf anoxia with severe effects for the benthic life and fisheries. We present data on water column dissolved oxygen, sulfide, nitrate and nitrite, pore water profiles for dissolved sulfide and sulfate,³⁵S-sulfate reduction rates, as well as bacterial counts of large sulfur bacteria from 20 stations across the continental shelf and slope. The stations covered two transects and included the inner shelf with its anoxic and extremely oxygen-depleted bottom waters, the oxygen minimum zone on the continental slope, and the lower continental slope below the oxygen minimum zone. High concentrations of dissolved sulfide, up to 22 mM, in the near-surface sediments of the inner shelf result from extremely high rates of bacterial sulfate reduction and the low capacity to oxidize and trap sulfide. The inner shelf break marks the seaward border of sulfidic bottom waters, and separates two different regimes of bacterial sulfate reduction. In the sulfidic bottom waters on the shelf, up to 55% of sulfide oxidation is mediated by the large nitrate-storing sulfur bacteria, Thiomargarita spp. The filamentous relatives Beggiatoa spp. occupy low-O₂ bottom waters on the outer shelf. Sulfide oxidation on the slope is apparently not mediated by the large sulfur bacteria. The data demonstrate the importance of large sulfur bacteria, which live close to the sediment-water interface and reduce the hydrogen sulfide flux to the water column. Modeling of pore water sulfide concentration profiles indicates that sulfide produced by bacterial sulfate reduction in the uppermost 16 cm of sediment is sufficient to account for the total flux of hydrogen sulfide to the water column. However, the total pool of hydrogen sulfide in the water column is too large to be explained by steady state diffusion across the sediment-water interface. Episodic advection of hydrogen sulfide, possibly triggered by methane eruptions, may contribute to hydrogen sulfide in the water column.     

Rolling torus structures in astronomy

Ken Barker puts forward an idea that may have a place in astrophysical modelling.
Torus structures that roll and orbit the centre of mass can produce a family of nested, almost elliptical orbits. These orbits, with the centre of mass at one focus, have a range of eccentricities and are inclined to the principal plane of the torus. Individual orbiting particles have an "anti-collision feature" from the nature of the rolling torus. In turn, because the torus can be regarded as a family of nested elliptical orbits, it rolls without needing any additional force. The system is acted upon only by central gravitational attraction and has low dissipation and a long lifetime.     

Radioelements,radiogenic helium and age relationships for groundwaters from the granites at Stripa,Sweden

The solution of radioelements and radiogenic ⁴He by groundwaters in fractured rocks is dependent upon the radioelement distribution in the rock matrix and the extent of the rock-water interface. The ${}^{234}\text{U}{}^{238}\text{U}$ activity ratio and the dissolved U, Rn and He contents of such groundwaters respond to changes in the flow regime with time. Although ${}^{234}\text{U}{}^{238}\text{U}$ activity ratios change with groundwater residence time as a consequence of ²³⁴Th-recoil induced solution of ²³⁴U, the activity ratio is strongly influenced by the U distribution within fractures, by the extent of the rock-water interface and by the amount of ²³⁸U in solution. A model for the quantitative evaluation of these effects is presented.Groundwaters from depths up to 880 m in the Stripa granite have variable dissolved uranium contents and ${}^{234}\text{U}{}^{238}\text{U}$ activity ratios. The uranium geochemistry is primarily determined by variations in flow path rather than by groundwater age.Dissolved radiogenic ⁴He in the groundwaters increases with their depth of origin, and is dependent upon the U content of the granite and upon its fracture porosity. It increases with groundwater residence time but movement of ⁴He by diffusion and transport processes make the actual groundwater age indeterminate.     

Geochemical modelling of basalts from DSDP Leg 65, East Pacific Rise,Gulf of California

Major and rare earth element (REE) data for basalts from Holes 483, 483B, and 485A of DSDP Leg 65, East Pacific Rise, mouth of the Gulf of California, support a simple fractional crystallization model for the genesis of rocks from this suite. The petrography and mineral chemistry (presented in detail elsewhere) provide no evidence for magma mixing, but rather a simple multistage cooling process. Based on its lowest TiO₂ content (0.88%), $\text{FeO}{}^1\text{MgO}$ ratio (0.95 with total Fe as FeO), and Mg# (100 $\text{Mg}\text{Mg + Fe}\text{″ = 70}$), sample 483-17-2-(78–83) has been selected as the most primitive primary magma of the samples analyzed. This is supported by the REE data which show this sample has the lowest total REE content, a $\text{La}\text{Sm}{}_{\mathrm{cn}}$ (chondrite-normalized) = 0.36, and $\text{Eu}\text{Sm}{}_{\mathrm{cn}}$ = 1.05. Because other samples analyzed have higher SiO₂, lower Mg#, and a negative Eu anomaly ($\text{Eu}\text{Sm}{}_{\mathrm{cn}}$ as low as 0.89), they are most likely derivative magmas. Wright-Doherty and trace element modelling support fractional crystallization of 14.1% plagioclase (An₈₈), 6.7% olivine (Fo₈₆), and 4.7% clinopyroxene (Wo₄₁En₄₉Fs₁₀) from 483-17-2-(78–83) to form the least differentiated sample with Mg# = 63. The $\text{La}\text{Sm}{}_{\mathrm{cn}}$ of this derivative magma is almost identical to the parent magma (0.35 to 0.36), but the other samples have higher $\text{La}\text{Sm}{}_{\mathrm{cn}}$ (0.45 to 0.51), more total REE, and lower Mg# (60 to 56). Both Wright-Doherty and trace element modelling indicate that the primary magma chosen cannot produce these more evolved samples. For the major elements, the TiO₂ and P₂O₅ are too low in the calculated versus the observed (1.38 to 1.90; 0.11 to 0.17, respectively, for example). Rayleigh fractionation calculates a lower $\text{La}\text{Sm}{}_{\mathrm{cn}}$ and requires about 60% crystal removal versus 40% for the Wright-Doherty. These more evolved samples must be derived from a parent magma different from the one selected here and, unfortunately, not sampled in this study. A magma formed by a smaller degree of partial melting with slightly more residual clinopyroxene left in the mantle than for sample 483-17-2-(78–83) is required.     

Leaching of quartz from precambrian hypabyssal rhyolite porphyry,Llano County,Texas

A Precambrian hypabyssal rhyolite porphyry in central Texas has retained its original texture, although alkali feldspar phenocrysts have inverted and unmixed from zoned, single-phase high-temperature feldspar to zoned microperthite with an intermediate microcline host.Blue quartz phenocrysts owe their color to dispersion by zircon inclusions. Neutron activation analysis reveals substitution of tetravalent cations for silicon in the quartz.In two outcrops, quartz and albite have been completely leached from the rock and K-feldspar added, leaving the texture intact. The leaching was most likely accomplished by residual brine from an overlying Lower Cretaceous evaporite deposit subsequently removed by erosion.     

Nocturnal swimming ofScolecolepides viridis (Polychaeta: Spionidae)

AdultScolecolepides viridis were collected by nocturnal plankton tows in the Lafayette River, Norfolk, Virginia. All adults (40–70 mm) were filled with ripe gametes. Swimming individuals were collected only at night on ebb tides. Large (36–60 setigers) post-metamorphic worms were also collected in the plankton. The occurrence of down estuary adult movement is used to explain paradoxical information concerning this species within estuary distribution and early development.     

A theoretical model of the stable sulfur isotope distribution in marine sediments

A diffusion-diagenesis model of the sulfur cycle is developed to calculate theoretical distributions of stable sulfur isotopes in marine sediments. The model describes the depth variation in δ³⁴S of dissolved sulfate and H₂S. and of pyrite. The effects of sulfate reduction, sulfate and H₂S diffusion. and of sedimentation are considered as well as the bacterial isotope fractionation and the degree of pyrite formation. Under open system conditions of sulfur diagenesis the isotopic difference, ΔSO^2?₄ — H₂S, tends to increase with depth being smaller than the bacterial fractionation factor near the sediment surface and larger in deeper layers. The two isotopes in SO^2?₄ or in H₂S do not diffuse in the same proportion as they occur in the porewater. This explains why sulfur, which is incorporated from seawater sulfate by diffusion and precipitation as pyrite, can be enriched in ³²S relative to the seawater sulfate. The model calculations demonstrate the importance of taking the whole dynamic sulfur cycle into account before drawing conclusions about sulfur diagenesis from the stable isotope distribution.