Opal-associated particulate phosphorus: Implications for the marine P cycle

Previous attempts to evaluate ocean P mass balance and residence time have utilized sequential extraction techniques to isolate and analyze P associated with Fe and Mn oxides and oxyhydroxides, authigenic minerals, detrital, and organic phases. However, in many oceanographic settings, diatoms are the primary producers, and the traditional sequential extraction protocol does not result in complete dissolution of diatom frustules and may not liberate all of the opal intrinsic P associated with the frustules themselves. By adding an opal dissolution step to the end of the extraction protocol, additional P was liberated from the sediments, suggesting that there is an opal-associated P fraction that likely contributes to total reactive P concentrations. In opal-rich sediments, the opal-associated P fraction averages as much as 50-60% of extractable P, and total reactive P concentrations are often more than double when the opal-associated P fraction is included. The presence of opal-intrinsic P potentially has significant implications for ocean P mass balance and residence time of P in the oceans. For example, P burial has possibly been underestimated in settings dominated by diatoms. Additionally, consideration of a significant sedimentary opal-P component suggests that the residence time of P in the oceans may be even shorter than currently suspected.     

Performance and Early Results from the Golf Instrument Flown on the Soho Mission

GOLF in-flight commissioning and calibration was carried out during the first four months, most of which represented the cruise phase of SOHO towards its final L1 orbit. The initial performance of GOLF is shown to be within the design specification, for the entire instrument as well as for the separate sub-systems. Malfunctioning of the polarising mechanisms after 3 to 4 months operation has led to the adoption of an unplanned operating sequence in which these mechanisms are no longer used. This mode, which measures only the blue wing of the solar sodium lines, detracts little from the detection and frequency measurements of global oscillations, but does make more difficult the absolute velocity calibration, which is currently of the order of 20%. Data continuity in the new mode is extremely high and the instrument is producing exceptionally noise-free p-mode spectra. The data set is particularly well suited to the study of effects due to the excitation mechanism of the modes, leading to temporal variations in their amplitudes. The g modes have not yet been detected in this limited data set. In the present mode of operation, there are no indications of any degradation which would limit the use of GOLF for up to 6 years or more.     

Using a regional frequency analysis approach for calculating the Standardized Precipitation Index: an operational approach based on the two-parameter gamma distribution

Theoretical and Applied Climatology - The Standardized Precipitation Index (SPI) is a worldwide used probability-based drought index. Considering that the two-parameter gamma distribution (gam) is...     

Assessing landslide volume using two generic models: application to landslides in Whatcom County,Washington, USA

Landslides - Geomorphological analysis of landslide processes in mountainous terrains with difficult access has benefited from virtual representation of topography through the use of...     

Periodicities in the occurrence rate of solar proton events

Power spectral analyses of the time series of solar proton events during the past three solar cycles reveal a periodicity around 154 days. This feature is prominent in all of the cycles combined, cycles 19 and 21 individually but is only weak in cycle 20. These results are consistent with the presence of similar periodicities between 152 and 155 days in the occurrence rate of major solar flares, the sunspot blocking function (P _s ), the 10.7 cm radio flux (F _10.7) and the sunspot number (R _z ). This suggests that the circa 154-days periodicity may be a fundamental characteristic of the Sun. Periods around 50–52 days are also found in the combined data set and in the three individual cycles in general agreement with the detection of this periodicity in major flares in cycle 19 and inP _s ,F _10.7, andR _z in cycle 21. The cause of the 155 day period remains unknown. The spectra contain lines (or show power at frequencies) consistent with a model in which the periodicity is caused by differential rotation of active zones and a model in which it is related to beat frequencies between solar oscillations, as proposed by Wolff.     

Tidally-induced melting events as the origin of south-pole activity on Enceladus

The intense activity at the south pole of Enceladus hints at an internal water reservoir. However, there is no direct evidence of liquid water at present and its long-term stability in the interior remains problematic. By modeling heat production and transfer in the ice shell in a spherical geometry, we show that tidal heating naturally leads to a concentration of convective hot upwellings in the south polar region, favoring the preservation of liquid water at depth. We show that large volumes of water are produced within the ice shell at the south pole during periods of elevated orbital eccentricity (3–5 times the present-day value). Strong lateral variations in the melt production and crystallization rates result in stress concentration in the south polar region, thus providing an explanation for the tectonic activity observed today. We predict that an internal ocean may be sustained over the long term as the consequence of repeated periods with elevated orbital eccentricity, leading to episodic melting and resurfacing events.     

New gravity maps of the Eastern Alps and significance for the crustal structures

The deep seismic profile Transalp crosses, from north to south, Germany, Austria and Italy. The gravity measurements for each country were made by national agencies with different reference systems and data reduction methods. Within the frame of the Transalp-project a comprehensive database of the Eastern Alps was compiled covering an area of 3.5° by 4° in longitude and latitude (275 by 445 km), respectively. To increase the data coverage in the south Alpine area two gravity surveys were carried out, resulting in 469 areally distributed new stations, of which 215 have been measured with the intent to improve the geoid in the area of the planned Brenner Basistunnel (BBT). The resulting gravity database is the best in terms of resolution and data quality presently available for the Eastern Alps. Here the free air, Bouguer and isostatic gravity fields are critically discussed. The spatial density of existing gravity stations in the three countries is discussed. On the Italian side of the Alps the spatial density is rather sparse compared to the Austrian side. The Bouguer-gravity field varies between − 190 * 10^− 5 m/s² and + 25 * 10^− 5 m/s², with the minimum located along the Alpine high topographic chain, but with a small offset (a few tens of km) to the greatest topographic elevation, showing that the Airy-type local isostatic equilibrium does not fully apply here. The maximum of the Bouguer anomaly has an elongated shape of 100 by 50 km located between the towns of Verona and Vicenza and covers the Venetian Tertiary Volcanic Province (VTVP), a feature not directly related to the plate collision in the Eastern Alps. The gravity high is only partly explainable by high-density magmatic rocks and requires also a deeper source, like a shallowing of the Moho. The isostatic residual anomalies (Airy model) are in the range ± 50 * 10^− 5 m/s², with the greatest positive anomaly corresponding to the location of the VTVP, indicating here under-compensation of masses. At last a discussion of a 2D density model based on reflection seismic data and receiver functions is made.     

Micro- and macro-dispersive fluxes in canopy flows

Resolving every detail of the three-dimensional canopy morphology and its underlying topography remains untenable when modeling high Reynolds number geophysical flows. How to represent the effects of such a complex morphological variability and any concomittant topographic variability into one-dimensional bulk flow representation remains a fundamental challenge to be confronted in canopy turbulence research. Theoretically, planar averaging to the scale of interest should be applied to the time-averaged mean momentum balance; however, such averaging gives rise to covariance or dispersive terms produced by spatial correlations of time-averaged quantities that remain ‘unclosed’ or require parameterization. When the averaging scale is commensurate with few canopy heights, these covariances can be labeled as ‘micro-dispersive’ stresses. When averaging is intended to eliminate low-wavenumber topographic variations, we refer to these covariances as ‘macro-dispersive’ terms. Two flume experiments were used to explore the magnitude and sign of both micro- and macro-dispersive fluxes relative to their conventional Reynolds stresses counterparts: a rod-canopy with variable roughness density and a dense rod canopy situated on gentle hilly terrain. When compared to the conventional momentum flux, the micro-dispersive fluxes in the lowest layers of sparse canopies can be significant (∼50%). For dense canopies, the dispersive terms remain negligible when compared to the conventional momentum fluxes throughout. For the macro-dispersive fluxes, model calculations suggest that these terms can be neglected relative to the Reynolds stresses for a deep canopy situated on a narrow hill. For the region in which topographic variations can interact with the pressure, both model calculations and flume experiments suggest that the macro-dispersive fluxes cannot be neglected, and their value can be 20% of the typical Reynolds stresses.     

Monitoring the 2004 andesitic block-lava extrusion at Volcán de Colima,México from seismic activity and SO2 emission

The 2004 andesitic block-lava extrusion at Volcán de Colima, México was accompanied and followed by numerous seismic signals associated with rockfalls, pyroclastic flows and explosive events. We analyze temporal variations in the number of rockfalls and explosions, the seismic signal duration of rockfalls and the energy of the explosion and compare this with both the rate of magma discharge and SO₂ emission. Characteristics of seismic signals and SO₂ emission are compared with those observed during the 1998–1999 Volcán de Colima block-lava extrusion. For both eruptions, the explosive activity was low during the lava extrusion and increased after its termination. The variation in the daily number and the total duration of rockfall seismic signals gives a good reflection of the development of the lava emission process. An increase in magmatic degassing (SO₂ flux) was observed some days before the onset of lava extrusion. The degassing strongly decreased some days before the peak in the rate of the 1998–1999 lava emission but reached its peak together with the peak in the rate of the 2004 lava emission. These features of seismic activity and SO₂ emission demonstrate that they are good tools for monitoring the extrusion process.