The effect of metal complexation on hydrogen sulfide transport across the sea-air interface

Hydrogen sulfide dissolved in surface seawater is distributed into free forms which include the volatile neutral H₂S and its conjugate anions, and also into a set of involatile metal complexes. Calculation of the sulfide fraction capable of supporting sea-air flux is sensitive to large uncertainties in complexation equilibrium relationships, both for the sulfides themselves, and for organic ligands competing with them to coordinate dissolved copper. Saturation can be achieved relative to the troposphere if metal interactions are minimized, or if strong sulfide binders are titrated.     

Restoration of an impounded salt marsh in New England

The restoration of a 20 ha tidal marsh, impounded for 32, yr, in Stonington, Connecticut was studied to document vegetation change 10 yr after the reintroduction of tidal flushing. These data were then compared to a 1976 survey of the same marsh when it was in its freshest state and dominanted byTypha angustifolia. Currently,T. angustifolia remains vigorous only along the upland borders and in the upper reaches of the valley marsh. Live coverage ofT. angustifolia has declined from 74% to 16% and surviving stands are mostly stunted and depauperate. Other brackish species have also been adversely effected, except forPhragmites australis which has increased. In contrast, the salt marsh speciesSpartina alterniflora has dramatically expanded, from <1% to 45% cover over the last decade. Locally, high marsh species have also become established, covering another 20% of the marsh.     

The formation of circular littoral cones from tube-fed pāhoehoe: Mauna Loa,Hawai'i

Pyroclastic cones along the southwest coast of Mauna Loa volcano, Hawai'i, have a common structure: (a) an early formed circular outer rim 200–400 m in diameter composed mostly of scoria and lapilli, and (b) one or more later-formed inner rims composed almost exclusively of dense spatter. The spatter activity locally fed short lava flows that ponded within the outer rims. Based on various lines of evidence, these cones are littoral in origin: relationships between the cones and associated flows; the degassed nature of the pyroclasts; and (although not unequivocal) the position of the cones relative to known eruptive vent locations on Mauna Loa. Additional support for the littoral interpretation comes from their similarity to (smaller) littoral cones that have been observed forming during the ongoing Kilauea eruption. The structure of these Mauna Loa cones, however, contrasts with that of standard Hawaiian littoral cones in that there is (or once was) a complete circle of pyroclastic deposits. Furthermore, they are large even though associated with tubefed phoehoe flows instead of 'a'. The following origin is proposed: An initial flow of tube-fed phoehoe into the ocean built a lava delta with a base of hyaloclastite. Collapse of an inland portion of the active tube into the underlying wet hyaloclastites or a water-filled void allowed sufficient mixing of water and liquid lava to generate strong explosions. These explosions broke through the top of the flow and built up the outer scoria/lapilli rims on the solid carapace of the lava delta. Eventually, the supply of water diminished, the explosions declined in intensity to spattering, and the initial rim was filled with spatter and lava.     

Submillimetre continuum observations of pre-protostellar cores

Results are outlined of a JCMT submillimetre continuum survey of Myers cores that have no known infrared associations - the so-called starless cores. Detailed parameters are calculated, such as temperature, mass, luminosity and radial density dependence. On the basis of lifetime and luminosity arguments, the cores are found to be pre-protostellar in nature, undergoing the ambipolar diffusion phase prior to protostellar collapse. The cores do not follow the r^–2 density dependence predicted by the standard model, but are consistent with a recent model of magnetic support of cloud cores.     

STRUCTURE AND ROTATION OF THE SOLAR INTERIOR: INITIAL RESULTS FROM THE MDI MEDIUM-L PROGRAM

The medium-l program of the Michelson Doppler Imager instrument on board SOHO provides continuous observations of oscillation modes of angular degree, l, from 0 to 300. The data for the program are partly processed on board because only about 3% of MDI observations can be transmitted continuously to the ground. The on-board data processing, the main component of which is Gaussian-weighted binning, has been optimized to reduce the negative influence of spatial aliasing of the high-degree oscillation modes. The data processing is completed in a data analysis pipeline at the SOI Stanford Support Center to determine the mean multiplet frequencies and splitting coefficients. The initial results show that the noise in the medium-l oscillation power spectrum is substantially lower than in ground-based measurements. This enables us to detect lower amplitude modes and, thus, to extend the range of measured mode frequencies. This is important for inferring the Sun's internal structure and rotation. The MDI observations also reveal the asymmetry of oscillation spectral lines. The line asymmetries agree with the theory of mode excitation by acoustic sources localized in the upper convective boundary layer. The sound-speed profile inferred from the mean frequencies gives evidence for a sharp variation at the edge of the energy-generating core. The results also confirm the previous finding by the GONG (Gough et al., 1996) that, in a thin layer just beneath the convection zone, helium appears to be less abundant than predicted by theory. Inverting the multiplet frequency splittings from MDI, we detect significant rotational shear in this thin layer. This layer is likely to be the place where the solar dynamo operates. In order to understand how the Sun works, it is extremely important to observe the evolution of this transition layer throughout the 11-year activity cycle.     

Determination of the Geopotential Scale Factor from TOPEX/POSEIDON Satellite Altimetry

The geopotential scale factor R _o = GM/W _o (the GM geocentric gravitational constant adopted) and/or geoidal potential Wo have been determined on the basis of the first year's (Oct 92 – Dec 93) ERS-1/TOPEX/POSEIDON altimeter data and of the POCM 4B sea surface topography model: R _o °=(6 363 672.58°±0.05) m, W _o °=(62 636 855.8°±0.05)m ² s ^–2 . The 2°–°3 cm uncertainty in the altimeter calibration limits the actual accuracy of the solution. Monitoring dW _o /dt has been projected.