Diatoms grow faster using ammonium in rapidly flushed eutrophic Dokai Bay,Japan

The importance of the nitrogen source for phytoplankton growth in a highly eutrophic embayment, Dokai Bay, was investigated. The DIN concentration often exceeded 100 μM of which 40–70% was NH₄ ⁺. During two incubation experiments, the natural assemblage of mainly diatoms took up NH₄ ⁺ instead of NO₃ ⁻. The growth of two Skeletonema species isolated in Dokai Bay were significantly faster on NH₄ ⁺ (1.86 and 1.27 div. d⁻¹ respectively) than on NO₃ ⁻ (1.55 and 1.04 div. d⁻¹ respectively). Our results indicated that these diatoms could grow faster by using NH₄ ⁺ compared to NO₃ ⁻ in this eutrophic bay.     

Sodic(–calcic) alteration in Fe-oxide–Cu–Au districts: an origin via unmixing of magmatic H2O–CO2–NaCl ± CaCl2–KCl fluids

Iron-oxide–Cu–Au deposits, particularly those formed in deeper level (plutonic) environments, are commonly characterized by regional scale sodic(–calcic) alteration, which typically formed pre- or syn-Cu–Au mineralization. The sodic(–calcic) assemblages include albite, scapolite, pyroxene, actinolite, apatite, titanite, epidote and calcite. The consistent presence of coexisting hypersaline aqueous and CO₂-rich fluids in minerals from sodic(–calcic) alteration and associated Fe-oxide–Cu–Au deposits is the result of unmixing of H₂O–CO₂–NaCl ± CaCl₂–KCl magmatic fluids. Experimental evidence indicates that the Na/(Na + K) ratio of fluids in equilibrium with two alkali feldspars in CO₃ ²⁻-bearing parent fluids would be significantly higher than in unmixed chloride-bearing aqueous fluids. Therefore, fluid unmixing caused by decreases in temperature and/or pressure, will result in albitization of wall rocks, as is observed in most deeper level Fe-oxide–Cu–Au deposits. This alteration style may be succeeded by K-feldspathization with decreasing temperature because of the increase in equilibrium Na/(Na + K) in chloride-bearing fluids buffered by alkali feldspars. Received: 26 May 1999 / Accepted: 8 June 2000     

Dynamic response of tipping core buildings

When subjected to major earthquakes, core-stiffened buildings may begin to tip. That is, the overturning moment on the core's footing becomes so large that the footing breaks contact with the ground and begins to rock. A method is described for including the effects of tipping in the analysis of multistorey core-braced structures. Curves are presented which summarize the maximum response to both pulse and earthquake excitations; these data are elucidated via a typical design example. By comparison to fixed-base behaviour, tipping greatly reduces the base shear and moment. This makes possible a more economical design. However, attention must be devoted to avoiding potential soil-mechanics problems associated with the wobbling behaviour of the tipping core.     

Partitioning of Ru, Rh, Pd, Re, Ir, and Au between Cr-bearing spinel, olivine, pyroxene and silicate melts

A series of high temperature experiments was undertaken to study partitioning of several highly siderophile elements (HSE; Ru, Rh, Pd, Re, Os, Ir, Pt and Au) between Cr-rich spinel, olivine, pyroxene and silicate melt. Runs were carried out on a Hawaiian ankaramite, a synthetic eucrite basalt, and a DiAn eutectic melt, at one bar, 19 kbar, and 20 kbar, respectively, in the temperature range of 1200 to 1300°C, at oxygen fugacities between the nickel-nickel oxide (NNO) and hematite-magnetite (HM) oxygen buffers. High oxygen fugacities were used to suppress the formation of HSE-rich “nuggets” in the silicate melts. The resulting oxide and silicate crystals (<100 μm) were analyzed using both SIMS and LA-ICP-MS, with a spatial resolution of 15 to 50 μm. Rhenium, Au and Pd were all found to be incompatible in Cr-rich spinel (D_Re^sp/melt = 0.0012-0.21, D_Au^sp/melt = 0.076, D_Pd^sp/melt = 0.14), whereas Rh, Ru and Ir were all found to be highly compatible (D_Rh^sp/melt = 41-530, D_Ru^sp/melt = 76-1143, D_Ir^sp/melt = 5-22000). Rhenium, Pd, Au and Ru were all found to be incompatible in olivine (D_Re^oliv/melt = 0.017-0.073, D_Pd^oliv/melt = 0.12, D_Au^oliv/melt = 0.12, D_Ru^oliv/melt = 0.23), Re is incompatible in orthopyroxene and clinopyroxene (D_Re^opx/melt = 0.013, D_Re^cpx/melt = 0.18-0.21), and Pt is compatible in clinopyroxene (D_Pt^cpx/melt = 1.5). The results are compared to and combined with previous work on HSE partitioning among spinel-structured oxides, and applied to some natural magmatic suites to demonstrate consistency.     

Compression studies of gibbsite and its high-pressure polymorph

Various X-ray diffraction methods have been applied to study the compression behavior of gibbsite, Al(OH)₃, in diamond cells at room temperature. A phase transformation was found to take place above 3 GPa where gibbsite started to convert to its high-pressure polymorph. The high-pressure (HP) phase is quenchable and coexists with gibbsite at the ambient conditions after being unloaded. This HP phase was identified as nordstrandite based on the diffraction patterns obtained at room pressure by angle dispersive and energy dispersive methods. On the basis of this structural interpretation, the bulk modulus of the two polymorphs, i.e., gibbsite and nordstrandite, could be determined as 85 ± 5 and 70 ± 5 GPa, respectively, by fitting a Birch-Murnaghan equation to the compression data, assuming their K_o ^′ as 4. Molar volume cross-over occurs at 2 GPa, above which the molar volume of nordstrandite is smaller than that of gibbsite. The differences in the molar volume and structure between the two polymorphs are not significant, which accounts for the irreversibility of the phase transition. In gibbsite, the axial compressibility behaves as c/c _o > a/a _o > b/b _o. This is due to the fact that the dioctahedral sheets along the c-axis are held by the relatively weak hydrogen bonding, which results in the greater compressibility along this direction. In nord- strandite, the axial compressibility is b/b _o > c/c _o > a/a _o, which can also be interpreted as resulting from the the existence of hydrogen bonds along the b-axis. Received: 28 September 1998 / Revised, accepted: 22 December 1998     

The bedrock topography of the botany basin,New South Wales

The bedrock topography of the Botany Basin has been determined from seismic‐sparker records made in Botany Bay and Bate Bay, and from seismic‐refraction and gravity measurements on the Kurnell Peninsula. Supplementary information has been obtained from boreholes both on land and in the sea.

The Cooks and Georges Rivers formerly constituted the main drainage of the Basin and flowed generally southeastwards (beneath the present Kurnell Peninsula) and joined the Port Hacking River east of Cronulla. The depth of the bedrock channel of the former Georges River is 75–80 m b.s.l. at Taren Point, 90–95 m beneath the Kurnell Peninsula and 110–115 m at its junction with the Port Hacking River channel. The bedrock channel of the former Cooks River is about 30 m b.s.l. at Kyeemagh, its present entrance to Botany Bay, and it joined the Georges River at a location now 90 m b.s.l. beneath the Kurnell Peninsula.

A second drainage system existed in the north and east of Botany Bay and generated the present mouth beneath which the bedrock is now 110 m b.s.l. This channel followed a southeasterly course parallel to the present northern shore of Botany Bay and was separated from that of the ‘Cooks and Georges Rivers’ by a bedrock ridge which extended from beneath Sydney Airport to the northern extremity of the Kurnell Peninsula. Over much of its length this divide had a depth of about 30 m b.s.l.

The formation of the Kurnell Peninsula tombolo led to the diversion of the ‘Cooks/Georges River’ through the mouth of Botany Bay and subsequently led to the development of the bay. This change in the drainage system occurred when the sea was less than 30 m below the present sea level.     

The effects of a copper-based antifouling paint on mortality and enzymatic activity of a non-target marine organism

Antifouling paints are used on a wide range of underwater structures in order to protect them from the development of fouling organisms. The leaching of the toxic substances from the matrix of the paint causes toxic effects not only to the fouling organisms but also on other "non-target" biota. The present study addresses the impact of the antifouling paint Flexgard VI-II on brine shrimp nauplii selected as convenient test organisms. The surface to volume (S/V) concept developed by Persoone and Castritsi-Catharios (1989) was used to determine S/V-LC50s for the test biota exposed to PVC test panels of 400-1000 mm2 surface coated with the antifouling paint in test vessels containing 20 ml seawater. Total ATPase and Mg2+-ATPase were also analyzed for coated surface areas inducing less than 50% mortality in the brine shrimp nauplii. The calculated S/V-LC50 (24 h) was 24.6 mm2/ml, which shows the high toxic character of the antifouling paint. Decreased enzymatic activities were noted in the brine shrimp nauplii exposed to test panels of 50 and 100 mm2 in 20 ml seawater. The present study indicates that the "surface to volume" concept is an interesting methodology that can be applied with both lethal and sublethal effect criteria for the determination of toxic stress from leaches of painted surfaces.