Chemical weathering of a marine terrace chronosequence, Santa Cruz, California I: Interpreting rates and controls based on soil concentration-depth profiles

The spatial and temporal changes in element and mineral concentrations in regolith profiles in a chronosequence developed on marine terraces along coastal California are interpreted in terms of chemical weathering rates and processes. In regoliths up to 15 m deep and 226 kyrs old, quartz-normalized mass transfer coefficients indicate non-stoichiometric preferential release of Sr > Ca > Na from plagioclase along with lesser amounts of K, Rb and Ba derived from K-feldspar. Smectite weathering results in the loss of Mg and concurrent incorporation of Al and Fe into secondary kaolinite and Fe-oxides in shallow argillic horizons. Elemental losses from weathering of the Santa Cruz terraces fall within the range of those for other marine terraces along the Pacific Coast of North America.Residual amounts of plagioclase and K-feldspar decrease with terrace depth and increasing age. The gradient of the weathering profile b_s is defined by the ratio of the weathering rate, R to the velocity at which the profile penetrates into the protolith. A spreadsheet calculator further refines profile geometries, demonstrating that the non-linear regions at low residual feldspar concentrations at shallow depth are dominated by exponential changes in mineral surface-to-volume ratios and at high residual feldspar concentrations, at greater depth, by the approach to thermodynamic saturation. These parameters are of secondary importance to the fluid flux q_h, which in thermodynamically saturated pore water, controls the weathering velocity and mineral losses from the profiles. Long-term fluid fluxes required to reproduce the feldspar weathering profiles are in agreement with contemporary values based on solute Cl balances (q_h = 0.025-0.17 m yr⁻¹).During saturation-controlled and solute-limited weathering, the greater loss of plagioclase relative to K-feldspar is dependent on the large difference in their respective solubilities instead of the small difference between their respective reaction kinetics. The steady-state weathering rate under such conditions is defined as

     

A late Pleistocene long pollen record from Lake Urmia, NW Iran

A palynological study based on two 100-m long cores from Lake Urmia in northwestern Iran provides a vegetation record spanning 200 ka, the longest pollen record for the continental interior of the Near East. During both penultimate and last glaciations, a steppe of Artemisia and Poaceae dominated the upland vegetation with a high proportion of Chenopodiaceae in both upland and lowland saline ecosystems. While Juniperus and deciduous Quercus trees were extremely rare and restricted to some refugia, Hippophaë rhamnoides constituted an important phanerophyte, particularly during the late last glacial period. A pronounced expansion in Ephedra shrub-steppe occurred at the end of the penultimate late-glacial period but was followed by extreme aridity that favoured an Artemisia steppe. Very high lake levels, registered by both pollen and sedimentary markers, occurred during the middle of the last glaciation and late part of the penultimate glaciation. The late-glacial to early Holocene transition is represented by a succession of Hippophaë, Ephedra, Betula, Pistacia and finally Juniperus and Quercus. The last interglacial period (Eemian), slightly warmer and moister than the Holocene, was followed by two interstadial phases similar in pattern to those recorded in the marine isotope record and southern European pollen sequences.     

Geologic factors controlling groundwater chemistry in the coastal aquifer system of Douala/Cameroon: implication for groundwater system functioning

Douala city, located in the littoral province of Cameroon, receives abundant rainfall quantities due to its geographical position in the Gulf of Guinea and bears considerable surface water and groundwater resources. Due to socioeconomic development and rapid demographic growth in the city and its consequences of unplanned urbanization and improper sanitation system, these water resources are poorly protected and managed. Streams in the Wouri watershed receive large amounts of wastewater discharge, and hundreds of boreholes have been drilled into the aquifer system without any management plan. A detailed hydrodynamic and hydrogeochemistry study in Douala town and its environs was conducted to get a better insight into the groundwater system functioning in order to provide information for the sustainable management and protection of the groundwater resource. Two field campaigns were carried out with 187 samples collected and analyzed for major ions, stable isotopes (¹⁸O, ²H), and tritium ³H. The results of the sampling have shown that the weathering of silicate minerals is the dominant geochemical process affecting groundwater chemistry in this system. However, acid rainfall in the humid climate has also caused carbonate mineral dissolution, amorphous silica deposition, and ion exchange reactions to occur in aquifers in the region. The various water types identified were categorized into four major clusters C1 to C4, based on the major ion composition and the local hydrogeological conditions. Environmental isotope data reveal that modern-to-submodern waters occur in the phreatic Quaternary/Mio-Pliocene and Oligocene/Upper Eocene aquifers, respectively. These results corroborate with the conceptual model built where modern groundwater types indicated silicate mineral weathering and calcite dissolution (C1 and C2), whereas submodern groundwater mostly showed silica deposition, ion exchange, and, to a lesser extent, carbonate mineral dissolution (C3 and C4). This improved understanding of the aquifer system functioning is essential to provide a reasonable basis for effective control measures and sustainable water management.     

High feeding rates on large particles by Neocalanus flemingeri and N. plumchrus,and consequences for phytoplankton community structure in the subarctic Pacific Ocean

The open subarctic Pacific Ocean is a high nitrate low chlorophyll (HNLC) system characterized by low concentrations of phytoplankton, a community dominated by small cells, and iron-limited growth of, especially, the larger phytoplankton. In such systems the main energy and material flow is through the microbial web, with large copepods considered primarily to be grazers on the larger microzooplankton occupying the top of this web. Consistent with this is the recognition that much of the nutrition of the dominant copepods in this system, Neocalanus flemingeri, N. plumchrus and N. cristatus, is derived from microzooplankton. Also, these copepods consume only a small fraction of the total phytoplankton production. In this paper, we show that the contribution made by N. flemingeri and N. plumchrus to establishing and maintaining the community structure of this ecosystem should be re-evaluated. Our experiments indicate these grazers have high clearance rates on large particles, including both large phytoplankton and microzooplankton, and this selective removal contributes to establishment and maintenance of the observed foodweb structure in the Gulf of Alaska. These high feeding rates combined with large populations of these two Neocalanus species concentrated in the upper layer of the ocean, result in population-based feeding rates approximately equal to the growth rates of large phytoplankton under iron-limited conditions. We conclude that N. flemingeri and N. plumchrus populations (a) directly prevent the accumulation of large phytoplankton cells by selectively feeding on them at high rates, and (b) indirectly stimulate the accumulation of the smaller phytoplankton by consumption of their major grazers, the microzooplankton.     

Topographic monitoring of a middle estuary mudflat, Humber estuary, UK--anthropogenic impacts and natural variation

Annual topographic surveys were carried out at the Saltend mudflat (Humber estuary, UK) between 1998 and 2006. These surveys formed part of an ongoing monitoring programme to examine the potential effects on the mudflat topography of the construction and operation of a waste water treatment works (WwTW) development by Yorkshire Water. Of particular concern was the potential disruption to the sedimentological regime within the special protection area (SPA) and candidate special area of conservation (cSAC) which could affect the invertebrate communities and ornithological functioning of the site. In addition to the development of the WwTW located to the extreme north-west of the site, a port extension removing 10ha of the Saltend intertidal mudflat (outside the SPA but immediately south east of the WwTW) also occurred between 1999 and 2006. Minimal change was noted across the site following the construction and operation of the WwTW between 1998 and 2000. However, the construction of the bund in closer proximity to the SPA and cSAC masked any potential impact the WwTW could have had across the site after 2000. Profiles and contour mapping indicate that significant mudflat accretion occurred in the immediate area of the bund, with a general increase recorded across the western section of the site since 2000. In contrast the alternations to channel planform and subsequent rapid accretion of the mudflat to the east of the jetty, being a significant distance from the developments, are attributed to natural cyclical changes.     

Phase curves of nine Trojan asteroids over a wide range of phase angles

We have observed well-sampled phase curves for nine Trojan asteroids in B-, V-, and I-bands. These were constructed from 778 magnitudes taken with the 1.3-m telescope on Cerro Tololo as operated by a service observer for the SMARTS consortium. Over our typical phase range of 0.2-10°, we find our phase curves to be adequately described by a linear model, for slopes of 0.04-0.09 mag/° with average uncertainty less than 0.02 mag/°. (The one exception, 51378 (2001 AT33), has a formally negative slope of −0.02 ± 0.01 mag/°.) These slopes are too steep for the opposition surge mechanism to be shadow-hiding (SH), so we conclude that the dominant surge mechanism must be coherent backscattering (CB). In a detailed comparison of surface properties (including surge slope, B-R color, and albedo), we find that the Trojans have surface properties similar to the P and C class asteroids prominent in the outer main belt, yet they have significantly different surge properties (at a confidence level of 99.90%). This provides an imperfect argument against the traditional idea that the Trojans were formed around Jupiter’s orbit. We also find no overlap in Trojan properties with either the main belt asteroids or with the small icy bodies in the outer Solar System. Importantly, we find that the Trojans are indistinguishable from other small bodies in the outer Solar System that have lost their surface ices (such as the gray Centaurs, gray Scattered Disk Objects, and dead comets). Thus, we find strong support for the idea that the Trojans originally formed as icy bodies in the outer Solar System, were captured into their current orbits during the migration of the gas giant planets, and subsequently lost all their surface ices.     

Population trends in the Slavonian grebe <Emphasis Type="Italic">Podiceps auritus</Emphasis> (L.) and Chironomidae (Diptera) at a Scottish loch

Loch Ruthven holds the largest British population of the rare water-bird Podiceps auritus, the Slavonian or horned grebe. The breeding success of this bird has fluctuated annually since records began in 1970. To investigate whether these trends are linked to the abundance of chironomid midges, which are an important food-source for the grebe chicks, we analysed a sediment core from the lake, which was sliced at 2.5-mm intervals and provided near-annual sampling resolution. We also analysed diatoms and algal pigments in the lake sediments and inferred changes in total phosphorus from the diatom assemblage to determine whether changes in lake productivity have influenced the abundance of chironomids. Trends in grebe productivity, chironomid abundance and algal assemblages were compared against climate data to determine whether climate, specifically, the North Atlantic Oscillation, was the ultimate driver of the trends we recorded. Our results show that grebe breeding success is positively correlated with chironomid abundance and chironomid abundance is positively correlated with diatom-inferred total phosphorus. Lake productivity and chironomid abundance began to rise early in the twentieth century and continued to rise on a steeper trajectory from the mid-twentieth century to the present. Since the mid-1960s, chironomid abundance began to fluctuate erratically and since 1970 was in phase with grebe productivity, with the grebe trends most plausibly lagging by 1 year. These trends appear to correlate with inter-annual fluctuations in diatom-inferred total phosphorus. No correlation was found between grebe productivity or chironomid abundance and climate variables, suggesting that the size of the chironomid population and breeding success of Podiceps auritus at Loch Ruthven is resource-linked.     

Mars high resolution gravity fields from MRO, Mars seasonal gravity, and other dynamical parameters

With 2 years of tracking data collection from the MRO spacecraft, there is noticeable improvement in the high frequency portion of the spherical harmonic Mars gravity field. The new JPL Mars gravity fields, MRO110B and MRO110B2, show resolution near degree 90. Additional years of MGS and Mars Odyssey tracking data result in improvement for the seasonal gravity changes which compares well to global circulation models and Odyssey neutron data and Mars rotation and precession (). Once atmospheric dust is accounted for in the spacecraft solar pressure model, solutions for Mars solar tide are consistent between data sets and show slightly larger values (k₂ = 0.164 ± 0.009, after correction for atmospheric tide) compared to previous results, further constraining core models. An additional 4 years of Mars range data improves the Mars ephemeris, determines 21 asteroid masses and bounds solar mass loss (dGM_Sun/dt < 1.6 × 10⁻¹³ GM_Sun year⁻¹).     

Litho- and biofacies analysis of postglacial marine mud using CT-Scanning

Marine silty clay deposited during the Late-Wisconsinian postglacial marine transgression of eastern Québec (Goldthwait Sea) is ubiquitous in the sedimentary column of intertidal zones of the St-Lawrence Estuary. This mud is very compact and limits the penetration of organisms composing the modern Macoma balthica community. In order to describe the characteristics of intertidal sediments containing Goldthwait Sea mud, axial tomography (CT-Scan) is used. CT-Scan is a non-destructive method that can be used to describe sediment characteristics (grain size, mineralogy, primary and secondary sedimentary structures, fabric, shape and roundness, bedding contact), and to obtain high resolution, 3D representations of structures within sediment cores. Based on differences in the densities of analysed materials, the different lithologies, lithofacies, and organisms within the core can be discriminated, and a quantification of the volume occupied by the different components of the material can be made. Here, CT-Scan images provide information on the distribution, orientation and interweaving of thanatocœnosis shell beds that alternate with massive or faintly laminated postglacial marine mud beds, as well as on ichnofacies characteristics. In addition, we show 3D images of bioturbation structures within the recent sediment layer, which is distinguished from the underlying Goldthwait Sea mud. When coupled with conventional sedimentary (grain size statistics) and radiochronological (¹⁴C) analyses, these data provide information which is valuable for identifying depositional processes within sedimentary environments.